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An integrated approach to Cost-effective Process Planning and Equipment Selection in cold, warm and hot Forming
Dissertation
Presented in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in the Graduate School of The Ohio State University
By
Ravikiran Duggirala, B.E. (Hons.), M.S.
The Ohio State University 1995
Dissertation Committee: Approved by
Dr. Rajiv Shivpuri Dr. Taylan Altan Rajiv Shivpuri Dr. Kosuke Ishii Advisor Department of Industrial and Systems Engineering ÜMI Number; 9526019
Copyright 1995 by DÜGGIRALA, RAVIKIRAN All rights reserved.
OMI Microform 9526019 Copyright 1995, by UMI Company. All rights reserved.
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UMI 300 North Zeeb Road Ann Arbor, MI 48103 Copyright by Ravikiran Duggirala 1995 In Memorium To my beloved and great brother, Shyam (1962-1994) To my Wife, Parents, and Family AN INTEGRATED APPROACH TO COST-EFFECTIVE PROCESS PLANNING AND EQUIPMENT SELECTION IN COLD, WARM AND HOT FORMING By Ravikiran Duggirala, Ph. D. The Ohio State University, 1995 Professor Rajiv Shivpuri, Adviser
In response to customer request for forged parts, the supplier needs to determine the cost-effective process and the equipment to meet required quantity, shape and properties ensuring the production of defect-free parts. Experts layout a sequence of forming operations to transform a simple billet to a finished forging. These forming operations can be performed in different temperature regimes such as cold, warm or hot of a given material and on several equipment. The choice and design of the individual forming operations influences the need for intermediate operations such as heat treatment, coating, heating, etc. and the selection of forming equipment. It is extremely difficult and nearly impossible to evaluate all possible combinations of processes and equipment to produce a cost-effective forging, manually. In this dissertation, a cost-effectiveness evaluation model and a solution method has been developed to address the above problem. A discriminating cost model (DCM) has been developed to measure cost-effectiveness, and a
iv modified form of 'generate and evaluate' search methodology applied to find cost-effective solutions to produce formed parts. A prototype computer system 'CEPESS' (Cost-Effective Process and Equipment Selection System) has been developed incorporating the developed evaluation model and solution method. The research focussed on steels for materials, presses and headers for forming equipment and processes which are cold, warm and hot combinations of the forming operations: open fonvard extrusion, closed forward extrusion, backward extrusion, upset and dimple. The capabilities of the CEPESS was verified by running different example scenarios. The validation of the system was accomplished by application of CEPESS to the current process of making 'outer races'. Forming trials and experiments were conducted to verify the feasibility and cost-effectiveness of the process and equipment changes recommended by the system. The system has been built using 'ICAD' and 'Lisp' with features to enable sensitivity evaluation. The methodology developed in this research is an element of concurrent engineering where forming process planning and equipment selection have been considered concurrently with costs. The developed methodologies and system can be extended to include machining operations utilized subsequent to forming operations. ACKNOWLEDGEMENTS
This dissertation is the culmination of a pursuit which involved the time and efforts of many people, whom I wish to acknowledge. To Dr. Rajiv Shivpuri, my advisor, my sincere appreciation and gratitude for his guidance, counsel and insight. To Dr. Taylan Altan for supporting my work at Ohio State University and the ERG, and being a source of inspiration for new ideas and innovation. I extend my gratitude to Dr. Ishii and Dr. Miller for providing guidance and suggestions. I wish to thank Dr. Aly Badawy, my mentor, who stood beside me in good faith through thick and thin with continued encouragement and guidance. I also thank him and General Motors Corporation for providing me with a fellowship and support to pursue my academic goals. Thanks to Mr. Dave Hitz, my supervisor, for his encouragement and support in completing my work. I thank my colleagues and personnel at work who have provided me with assistance to assimilate knowledge, run experiments, and build software modules. My thanks to Dr. Uday Korde for his valuable suggestions and support. Finally, I wish to thank my wonderful wife, Kalpana, for her unfailing support, love, and endurance throughout this seemingly never-ending pursuit of my dreams. I am grateful to my parents, brothers, parents-in-law, and relatives who also provided inspiration and encouragement throughout this period.
vi Unto God, my ultimate gratitude, for his grace and guidance that he has showered on me throughout my life and pray for his continued support.
VII VITA
September 28th, 1961 ...... Born - Madras, India 1983 ...... B.E. (Hons.), Mechanical Engineering College of Engineering, Guindy, Madras, India. 1985 ...... M.S. Mechanical Engineering, Ohio University, Athens, Ohio. 1985-present ...... Senior Process Engineer, Saginaw Division, General Motors Corp. Saginaw, Michigan.
FIELDS OF STUDY
Major: Industrial and Systems Engineering
Manufacturing Engineering, Artificial Intelligence, and Mechanical Metallurgy
VIII TABLE OF CONTENTS
ABSTRACT...... iv ACKNOWLEDGEMENTS...... vi VITA...... vii TABLE OF CONTENTS...... ix LIST OF FIGURES...... xiv LIST OF TABLES...... xviii 1. INTRODUCTION...... 1 1.1 Global competition in manufacturing ...... 1 1.2 Overview of forming processes, materials and equipment ...... 2 1.3 Organization of the dissertation ...... 5
2. PROBLEM STATEMENT...... 8 2.1 Need for cost-effective process and equipment selection ...... 8 2.2 Problem definition ...... 17 2.3 Research Objective...... 18 2.4 Current approaches to process selection ...... 19 2.4.1 Costing and process selection methods ...... 19 2.4.2 Limitations of process planning and costing systems in metal forming ...... 27
ix 2.5 Approach ...... 28 2.5.1 Literature review...... 28 2.5.2 Selection of part family ...... 28 2.5.3 Knowledge acquisition ...... 29 2.5.4 Develop structure for knowledge ...... 30 2.5.5 Develop a cost-effectiveness evaluation method ...... 30 2.5.6 Develop a computer system ...... 31 2.5.7 Generate cost-effective process and equipment selection scenarios ...... 31 2.5.8 Perform forming process trials ...... 31 2.5.9 Run forming process simulations ...... 31 2.5.10 Perform simple upset tests ...... 32 2.5.11 Perform forming equipment trials ...... 32 2.5.12 Verification of system and approach...... 32
3. DISCRIMINATING COST MODEL...... 34 3.1 Introduction to knowledge engineering ...... 34 3.2 Knowledge acquisition process used ...... 39 3.3 Development of the Discriminating Cost Model ...... 44
4. STATE-SPACE SEARCH APPROACH TO COST-EFFECTIVE PROCESS AND EQUIPMENT SELECTION...... 57 4.1 Definition of search space of problem domain ...... 57 4.2 Problem solution methods...... 61 4.2.1 Operation Evaluation ...... 65
X 4.2.2 Equipment selection ...... 69 4.2.3 Cost-effective process selection ...... 72 4.3 Organization of knowledge structure ...... 73 4.3.1 Operations Knowledge ...... 77 4.3.2 Evaluation procedures and methods ...... 83
5. COST-EFFECTIVE PROCESS AND EQUIPMENT SELECTION SYSTEM...... 85 5.1 Objectives...... 85 5.2 System description ...... 86 5.3System Implementation ...... 89 5.4Verification of the capabilities of the system ...... 89
6. FORMABILITY LIMITS EVALUATION EXPERIMENT...... 105 6.1 Objective...... 105 6.2Typical failures in foming operations of an 'outer race' ...... 105 6.3Simple upset tests ...... I l l 6.4 Results of the upset tests ...... 112
7. SYSTEM VALIDATION - 1 PROCESS SELECTION FOR OUTER RACE BLANK’...... 118 7.1 Objectives of system validation on process change ...... 118 7.2 Selection of part family for experiment ...... 120 7.3Process modification experiment ...... 121 7.3.1 Forming process trials set-up and execution ...... 124
xi 7.3.2 Finite element method based process simulations ...... 130 7.3.3 Results of forming trials and system response evaluation ...... 140
8. SYSTEM VALIDATION - II •EQUIPMENT SELECTION FOR OUTER RACE BLANK'...... 148 8.1 Objectives of system validation on equipment selection ...... 148 8.2 Selection of part family for system validation on equipment selection ...... 148 8.3 Equipment change trials set-up and execution ...... 152 8.4 Results of forming trials and system response evaluation ...... 153
9. CONCLUSIONS AND FUTURE WORK ...... 156 9.1 Conclusions from forming trials and system application ...... 156 9.2 Benefits ...... 158 9.3 Contributions ...... 160 9.4 Future work ...... 160 9.5Technology transfer ...... 161
APPENDICES A - Overview of metal forming processes and equipment ...... 162 A. 1.1 Cold forming ...... 163 A. 1.2 Hot forming ...... 164 A. 1.3 Warm forming ...... 165 A. 1.4 Forming operations and tooling ...... 165
xii A. 1.5 Intermediate forming process operations ...... 168 A. 1.6 Forming materials ...... 172 A. 1.7 Forming equipment ...... 172 A.I.6 Forming Sequences ...... 173 A. 1.9 Process and equipment interactions ...... 174 B - Literature Review of cold forming technology ...... 181 C - Constraints evaluation for different forming operations ...... 186 D - Additional case studies depicting the discriminating capabilities of DCM ...... 193
LIST OF REFERENCES...... 201
XIII LIST OF FIGURES
Figure 1. a. Sheet Forming b. Bulk or massive deformation [Lange, 1985] ...... 3 Figure 2. Flow chart of typical operations in the production of hot forgings [Byrer, 1985] ...... 6 Figure 3. Example layout of equipment in a cold forming plant ...... 7 Figure 4. Current forged part development process ...... 9 Figure 5. Traditional engineering process ...... 10 Figure 6. Forged parts for constant velocity joint (CVJ) [ Fujikawa et. al.. 1992]] 12 Figure 7. Production process for a tripot housing [Fujikawa et. al., 1992] 13 Figure 8. Process comparison (cold tripot manufacturing)[Fujikawa et. al.,1992] 14 Figure 9. Process comparison (hot tripot manufacturing) [Fujikawa et. al., 1992] 14 Figure 10. Process comparison (warm tripot manufacturing)[Fujikawa et. al.. 1992] 15 Figure 11. Flow of Design Compatibility Analysis [Ishii, et., al., 1989] ...... 21 Figure 12. Schematic of the Pugh Selection Method ...... 22 Figure 13. Cost versus selection criteria tradeoff curves ...... 23 Figure 14. Advantages of the IBIS approach to process cost evaluation ...... 24 Figure 15. Disadvantages of the IBIS approach to process cost evaluation. 25 Figure 16. Key elements of the Technical Cost Model ...... 26 Figure 17. Forming sequence for an outer race ...... 33
XIV Figure 18. Stages in the knowledge acquisition and system development process [Hayes-Roth, et. al., 1983] ...... 36 Figure 19. Methods of knowledge representation [Gevarter, 1987] ...... 37 Figure 20. Inference strategies [Gevarter, 1987] ...... 38 Figure 21. Knowledge acquisition process [Hayes-Roth et. al., 1983] ...... 38 Figure 22. Key cost elements of the discriminating cost model (DCM) ...... 50 Figure 23. State space representation of problem ...... 58 Figure 24. Forge part example to apply DCM ...... 59 Figure 25. Solution method for problem ...... 67 Figure 26. Forming sequence for example part ...... 68 Figure 27. Range of equipment available to form the example part ...... 71 Figure 28. Calculations for forming sequence options for example part ..... 74 Figure 29. Evaluation of alternate sequences for example part ...... 75 Figure 30. Cost evaluation of different processes for example part ...... 76 Figure 31. Knowledge and data structure for the discriminating cost model ...... 77 Figure 32. Overview of CE-PESS system structure ...... 95 Figure 33. Evaluation of node in state space ...... 96 Figure 34. Example sequence used for system verification ...... 97 Figure 35. Example system screen showing some case study 1 results ..... 98 Figure 36. Case study 1 : Selected example sequence ...... 99 Figure 37. Case study 2;Billet diameter changed from 1 to 1.25" ...... 100 Figure 38. Case study 3: Increase billet length to 2.5" ...... 101 Figure 39. Case study 4: Decrease extruded diameter tolerance to 0.002" 102 Figure 40. Case study 5; Increase extruded length and dia tolerance to 0.06" and check savings with cost of added turning operation ($0.01/part) ...... 103 Figure 41. Case study 6; Add 1000 ton warm former with machine cost of $1 per part 104 Figure 42. Case study 7: Change material from AISI 8620 to AIS11050 .....104 Figure 43. Schematics of typical cracks in cold forgings (internal cracks are identified by shaded regions [Kim, 1994] ...... 108 Figure 44. Criterion for prevention of central bursting or chevrons [ ] ...... 109
XV Figure 45. Cracks observed during a pierce upset test [Kim, 1994] ...... 110 Figure 46. Criteria for cracking in dimple operations [Kim, 1994] ...... 110 Figure 47. Specimens before and after upset ...... 114 Figure 48. Process employed to prepare the specimens ...... 115 Figure 49. Samples of a backward extrude test ...... 117 Figure 50. State space representation of alternatives for an outer race ...... 119 Figure 51. Sequence for a dimple outer race blank without tooling artifacts 120 Figure 52. Process sequence recommended by CEPESS ...... 125 Figure 53. Process modification options (Samples A and B) tried out ...... 128 Figure 54. Schematic of tooling layout for warm dimple operation ...... 129 Figure 55. Finite element models of punch, die and upset part used in the warm form simulation ...... 131 Figure 56. Material flow at end of forming operation ...... 132 Figure 57. Temperature profiles in punch at the end of forming operation 133 Figure 58. Temperature profiles in the die at the end of forming operation 134 Figure 59. Temperature profiles in the part at the end of forming operation 135 Figure 60. Principal stresses on punch at end of simulation ...... 136 Figure 61. Principal stresses on die at end of simulation ...... 137 Figure 62. Effective stresses in part at end of simulation ...... 138 Figure 63. Load-stroke curve for the dimple forming process ...... 139 Figure 64. Grain flow in dimple outer race of sample A ...... 142 Figure 65. Grain flow in dimple outer race of sample B ...... 143 Figure 66. Grain flow in dimple outer race of current process ...... 144 Figure 67. Grain flow in finish formed outer race of sample A ...... 145 Figure 68. Grain flow in finish formed outer race of sample B ...... 146 Figure 69. Grain flow in finish formed outer race of current process ...... 147 Figure 70. Forming sequence for consideration of cold header/press ...... 150 Figure 71. Output of CEPESS for equipment selection problem ...... 151 Figure 72. Schematic illustration of a cold forming sequence of a gear blank [Altan, 1983] 176 xvi Figure 73. Hot forge sequence for gear blanks produced on a hot former [Byrer, 1985] 177 Figure 74. Relationships between process and machine variables in hot forming processes conducted in presses [Altan, 1970] ...... 178 Figure 75. Breakeven points of quantity versus cost for cold, hot and machined parts [Ishi, 1989] ...... 180 Figure 76. Best plans for example in case study D1 ...... 196 Figure 77. Three best plans shown for case study D1 ...... 197 Figure 78. Best plan showing effect of increase in weight of the part ...... 198 Figure 79. Effect of decrease in order quantity of parts ...... 199 Figure 80. Four best plans for case study D3 ...... 200
XVII LIST OF TABLES
Table 1. Sources of information of cost estimating [Salvendy, 1982] ...... 43 Table 2. Materia! cost table used ...... 46 Table 3. Typical costs laid out by forging process sequence ...... 48 Table 4. Typical consideration of other cost factors ...... 49 Table 5. Forming operation costs table ...... 51 Table 6. Lubrication costs table ...... 53 Table 7. Shear costs table ...... 53 Table 8. Sawing costs ...... 53 Table 9. Material database table...... 82 Table 10. Results of upset tests ...... 117 Table 11. Specifications of equipment used for process experiment ...... 126 Table 12. Specifications of equipment used for process experiment ...... 155 Table 13. Comparison of process selection models and DCM ...... 157 Table 14. Classification of forming processes [Altan, 1983] ...... 166 Table 15. Important process variables in forging ...... 179 Table 16. Important machine characteristics in forging ...... 179
XVIII CHAPTER I
INTRODUCTION
1.1 Global competition in manufacturing
Fierce competition in the international market has forced companies to re examine their part production strategies. Cost, quality, and time-to-market have become a priority for survival in the industry. The same holds true for the metal forming industry. Metal forming, has traditionally been practiced more as an art than science. Years of experience in forming practices have produced generic empirical guidelines and rules. However, much of the explicit forming knowledge is captured in the minds of the experts within an organization. Until recently such knowledge was transferred from the experts to others more by way of apprenticeships. In the last few decades, metal forming has seen a significant trend toward scientific analysis and research. However, only in the past decade have these methods seen more effective and successful application. The recent trend toward scientific approaches to metal forming practice has elicited the need for a culture change within the organizations. Global competition has further influenced this change. The expansion of previously localized markets to a global arena has caused economic pressure to be applied to the manufacturing organizations. This in turn has served as a causal factor stimulating a thorough investigation of current forming practices and research into developing a more cost-effective and responsive manufacturing process. 1 2 Concurrent engineering, simultaneous engineering, lean manufacturing, agile manufacturing and life cycle design are some of the latest technologies to address the changing issues of manufacturing. Materials, processes, tools, equipment and even formed parts for the manufacturing industry can be purchased from different sources around the world. These sources differ in their economic environments and therefore cause a more agressive competition at the global level. Therefore, the manufacturing and forming industry need to re-evaluate their processes to enable them to compete in the developing global scenario. In the past few years, productivity gains have been made to narrow the gaps in economies. However, such gains alone are not sufficient to bridge the gap. A better understanding of the current processes and procedures available to produce parts and the development of appropriate tools and methods to enable cost-effective production of formed parts is proposed to address this emerging global competition.
1.2 Overview of forming processes, materials and equipment
Forming processes refer to a group of manufacturing methods by which the given shape of a workpiece or billet is converted to another shape without change in the mass or composition of the material of the workpiece. In industrial practice related to metal forming, a distinction is made between the two groups of bulk or massive forming and sheet forming as shown in figure 1. Examples of bulk metal forming processes are rolling, forging, drawing, and extrusion. In this research metal forming process will refer to bulk metal forming processes. A common way of classifying bulk metal forming processes is as cold, warm and hot forming depending upon the temperature range of forming operations for a given material.
Deep drawing Bending Extruding Upsetting Forging
Figure 1. a. Sheet Forming b. Bulk or massive deformation [Lange, 1985]
The manufacture of forged products is fundamentally a process of forming metal, under impact or pressure, to economically produce a desired shape with improved mechanical properties. There are several types of basic operations utilized for transformation of geometry and shape such as extrusions, upset, drawing, etc.. Also, several additional operations are required, such as heat treat, lubrication, heating, and material handling to enable the basic operations. The particular forging method and equipment used in a given instance is dependent on factors such as the quantity of parts to be produced, the characteristics of the material, and the configuration to be forged. A detailed overview of forming technology is presented in appendix A to provide a background for the problem under consideration in this research. The pros and 4 cons of different types of operations, and the interactions of forming operations with equipment and other factors are also included in appendix A. Large or small, a forge plant and its organization reflect the basic operations into which the manufacturing steps are divided, as shown for a hot forming process in figure 2. Forging stock is acquired as bar stock and inspected. The bars are then cut by shearing or sawing and heated typically in induction heating equipment. The stock at the forging temperature is manually or automatically fed into the forming press. The press operations sometimes produce flash which is trimmed subsequently. The parts are then cleaned, heat treated (normalized), inspected, packed and shipped to the customer. In the case of hot formers used instead of presses, heating and shearing is performed on-line at the forming machine and the operations, in general, do not produce any flash. Figure 3 shows an example layout of a cold forging plant and its equipment. Cold forming operations are characterized by the need for phoscoating and annealing equipment and the absence of part heating equipment. Cold forming is also performed on vertical presses as well as horizontal machines such as cold headers which run at higher number of strokes per minute in comparison to presses. Cold headers also allow the use of coil stock as opposed to bars and shearing on-line. The coil stock may also be purchased in the annealed condition. For a given organization, specific processes are more cost-effective than others depending upon equipment already available and local practices. Therefore, there is a need for a system that would enable determining the cost-effective choice for a given organization, equipment scenario and part requirements. 1.3 Organization of the dissertation
The following chapters describe the work done in this research. Chapter 2 defines the problem, describes some of the efforts made to address the problem, research objectives and the approach taken to determine a solution. Chapter 3 describes the development of the model for determining cost- effectiveness in forming process and equipment selection. Chapter 4 describes the solution method developed to determine the cost-effective process plan and equipment selection from the large number of alternatives. Chapter 5 describes the computer system built based on the developed cost-effectiveness evaluation model and the modified 'generate and test' search method of solution. Example sessions run to verify the capabilities of the system are also illustrated in this chapter. Chapter 6 describes a simple test procedure used to determine formability limits of a material for upset operations for use by the developed system. The developed system was validated by application to the current process of producing outer races at Saginaw Division of General Motors. The application of the system recommended a process change for the outer race part family and an equipment selection change for the smallest of the outer races. Actual experiments were carried out to verify the system recommendations. Chapter 7 describes the experiment conducted to validate the cost-effective process change recommended and chapter 8 describes the system validation experiment of the recommended change in equipment selection. Chapter 9 provides the conclusions and suggestions of future work. VU-
V : SLOCKi
INSPECTION
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HEATING fOR FORGING : - T OF "PESSIQN OIE
fOCK Af FOPGING TEVPFPAr,
i DIES HtATEO
f l a s h in g s
FORGED PARTS
Ci.LAN:p,G HEAT'.TREATING/FI.NiSHINC' INSPECTION -COUNTING', PACKING SHIPPING:
Figure 2. Flow chart of typical operations in the production of hot forgings [Byrer, 1985] gSOOl^ $500l\)
^5001^ $5001^ PHOSCOATER-1
^ P ^ ^0001^ 500H H ^OOOÜ) O 500H S $000Ü) 0 i ANNEALPf O 500M A ANNPAI FR T $000C^ E 500M 500M I ANNFAI FR" $50000
$50000 fOODI^ ■AMMEALER s H .ANNEALER E A ^OODI^ |OODM) R BAR BAR BAR D MILL MILL MILL
LEGEND
OH- Oold header, M- Mechanical press, H- Hydraulic Press, DM- Drawing press
PROOESS FLOW;
BAR DRAW -> SHEAR -> ANNEAL -> PHOSOOAT ~> PRESS
Figure 3. Example layout of equipment in a cold forming plant. CHAPTER II
PROBLEM STATEMENT
2.1 Need for cost-effective process and equipment selection
In the conventional process, given the product geometry information, significant amount of time and effort are required to produce forged parts (figure 4). The design and machining process sequence are studied and a minimum machining envelope geometry of the part is produced. The generated envelope is then transformed into a forging geometry based on forming process capability. Upon generation of the forged part geometry, forming experts study the part and requirements and select a forming process based on past experience and practice as shown in figure 5. Further, it is required to determine if this process selected would form a defect-free part and meet the requirements marked on the forged part print. This verification is typically performed by trial and error. Tooling has to be manufactured, die design laid out, process equipment selected and physical parts made. The selection of equipment typically is also performed based on practice and experience. However, there are several alternate competitive forming processes and equipment that can be utilized to produce the given part which influences cost.
8 FORGED PART DEVELOPMENT PROCESS
CURRENT PART DRAWING
TASK TIME/LEAD TIME FORGED PART DESIGN 2 hrs /1 week (MANUAL) MANUAL LAYOUT OF PROCESS 2 weeks / 4 weeks SEQUENCE MANUAL SELECTION OF PRESS AND 4 weeks / 8 weeks MATERIAL & TOOL/DIE DESIGN PROCESS VERIFICATION BY >1 month / 2 months ACTUAL TRIALS $$$$ FAIL _ ----- MANUAL COST ESTIMATION AND 2 weeks / 6 weeks TOOL DRAWING PRODUCTION MANUAL DIE DESIGN NO & CMM DATA SET UP FOR PRODUCTION
Figure 4. Current forged part development process 10 Figure 6 shows some of the components of a constant velocity joint. The process (cold forming) for producing one of the components, namely, the tripot housing is shown in figure 7. It may be observed that the forming process includes forming and intermediate operations. However, recently suppliers of these forgings are investigating the improved economics of warm forming and combinations of warm and cold forming operations and in some cases are forced to warm form the components due to the increased demand for the use of high- carbon steels. The outcome of such process re-design should produce lower costs.
Modify
SPECIFICATION Extrapolate RELEASE Previous BUILD TEST Design
Figure 5. Traditional engineering process
Figures 8 thru 10 show alternate forming sequences for tripot housings. The fundamental set of operations required for shape transformation from billet to tripot housing are forward extrude, upset, backward extrude, and draw wipe. In the cold forming sequence, there are two forward extrusions, whereas the warm and hot forging process requires only one step to extrude the stem. In the case of hot forging, both the upset and extrude operations are possible in one step. 11 In cold forming, a spherodize annealing is typically required for treating billet or wire. Furthermore, after a certain amount of cold forming (the limit for low carbon steels is normally an effective strain (logarithmic forming ratio) of * = 1.6) an intermediate annealing has to be carried out. Prior to a cold forming operation, a chemical surface treatment has to be performed, which creates a lubrication layer, consisting of a phosphate and soap (alternatively molykote) coating. In the cold forming process laid out for the tripots (figure 8), one has to anneal and phoscoat three times, whereas the hot and warm form operations, require only one time before final wipe or cold calibrating. This affects not only the cost for additional operations but adds the need for material handling to and fro from forming equipment to coating and annealing facilities. The number of required passes and the energy costs for the thermal and chemical intermediate treatments (annealing, pickling, bonderizing, soaping) are high. Cold forging dies have to be prestressed due to the high inner forming pressures. Cold- working tool steels and high-speed steels are used for the dies and punches. In some cases, cemented carbide tools have been applied advantageously. In the case of cold forming three presses may be required, whereas the warm and hot forming process may be performed in two. The tonnages for the different processes vary and therefore different sizes of equipment will be required. The press forces in warm and hot forming are smaller and permit use of smaller machines. 12
susinn ïvun snait n ne r race Ball c a ge C u te r race
Tripod type jj- Zeopa type (closed)
■ciaer siiae •Qusinng witn snatt
Tripod type Tripod type (open) (tulip)
Hcusino' with Shaft Spider Slide Spider fixed
Figure 6. Forged parts for constant velocity joint (CVJ) [ Fujikawa et. al., 1992]] 13
Spheroidizing Cold Forging Cold Forging Shot Blast Lubiication Cut Annealing 1 SI Operation 2nd Operation
Low Temp Cold Forging Spheroidizing Shot Blast Lubrication Shot Blast Annealing 3rd Operation Annealing
Profile Supersonic Magnetic Cold Sizing Measurement Inspection Detection Detection
Mateiial 1st 2nd 3rd 4th
Figure 7. Production process for a tripot housing [Fujikawa et. al., 1992] 14
061
W
P r m F o f t * KN 1500
1500
ErMTsnr n«Qutrtm«nt for AnniaUng in d 0.02 KWh 0.50 KWh 0.50 KWh PHOS-CocUng ( (•pftorodtzsd annoeling) (toflinneoling) (nomttttzfng)
/Cs aivnaUng Q picUtng, PHOS-ootttng, hibrteatfno
Figure 8. Process comparison (cold tripot manufacturing)[Fujikawa et. al.,1992]
Cold caiibraung jTESrëm iTgsriw--^)
A I > 8kg 1150'C
2800 1400 1
250 (15001
Enargy Raqiriramtnt iKW h
annaaUnQ (normaltztng) A picUing. PHOS-coating, hJbdcaling Q
Figure 9. Process comparison (hot tripot manufacturing) [Fujikawa et. al.,1992] 15
Cold cilibratlng ^ 061
1.4 kg 760-020‘C
PfW# Fore# KN
0.56 KWh
annMling (normaitdng) <-j pJcWing, PHOS Figure 10. Process comparison (warm tripot manufacturing)[Fujikawa et. al.,1992] Next, consider the process of hot forging (figure 9) combined by cold sizing to produce the tripots. In hot forming, control of tolerances and run-out are difficult. The larger range of tolerances on part dimensions requires proper pairing of the tripods with appropriate roller diameters to meet smooth performance requirements of the joint. A reasonable tool-life in hot forging is achieved only with low stroking rates (250 per hour); so although smaller machines may be required one may require more of them. Edge decarborization and scale formation are additional technical problems of this processing method. The required number of forming steps are however, less. Figure 10 shows a more economical manufacturing process which is a combination of warm forming followed by cold sizing for the tripots. Some of the key issues of warm forming include selection of appropriate lubrication, die-life and attaining tight tolerances similar to those obtained in cold forming. One of 16 the prime areas for warm form application is in producing precision parts in high volumes made of steel grades, that cannot be easily cold formed. Warm form operations may also reduce the amount of material on the final forging especially in the case of extrusions as the extrusion angles are larger in cold forging. In the warm form/cold size process for tripots, operations of full forward extrusion (including reduction), head upsetting, additional centering, backward cup extrusion and shape forming can be performed warm without prior treatment in one pass. During the final sizing operation, ironing has to be performed cold to achieve better surface quality and greater size accuracy. From economical considerations, the most important advantages of warm extrusion of tripots, as compared to cold extrusion, lie in lower process costs (energy and intermediate treatment) with about the same amount of starting material as well as in the process-specific longer production time (3 passes, intermediate treatment). As compared to hot forging, the dominant advantages lie in low material and energy costs, also reduced amount of material required and reduced rework and investment costs. However, for successful warm forming, there are several issues to be considered. The major problem areas are achieving part geometry requirements without neglecting the effect of temperature and normalizing treatments. Dies have to be well lubricated and cooled to reduce die wear and failure. Hot forging die materials are typically H11 thru HIS. Warm form die materials are M2 and D2. Different surface and heat treatments and tool-life influence the economics of dies for cold, warm and hot forming operations. From the above discussion, it can be seen that for the same shape transformation operations, there are several alternative process routes and equipment selection and it is necessary to determine the cost-effective route for 17 a given organization for a given part and quantity. As the final operations for all three processes is cold forming, the part requirements of finish and tolerances are met. In addition to process selection, the supplier has to select the right equipment (presses, heaters, lubrication coaters, etc.) for the process and evaluate use of existing equipment versus purchase of new or additional equipment. The different kinds of forming machines and the characteristics required of the equipment for cold and warm forming machines have been described [Schmoeckel, 1992]. Selection of equipment depends on equipment characteristics, tonnage capacity, throughput, number of forming stations available, load distribution characteristics, size, knock-out length and force, automation of loading and transfer of parts from station to station and so on. 2.2 Problem definition Given an ordered set of forming operations 'Fj' in sequence to change shape, and part requirements 'R' = {r-|,r 2 ,r3 rp} where 'Fj' are operations such as upset, open forward extrude, etc.. and ri,r 2 ,... are part requirements such as quantity, surface finish, etc.. The objective function is to minimize cost of: C= Cfy F|j + cnfjj Nfy + cafy A'y + ce^ + CPp Pp + CP^ Om + CPq where, 18 Fjj are a feasible set of operations satisfying set of operations constraints Cjj and j = cold, warm or hot N^jj are non-forming operations required for Fjj to satisfy constraints Cjj A^ij are additional forming operations required for Fjj to satisfy constraints Cjj E% are the least cost set of equipment that meet the equipment requirement constraints of (Fjj ^ Afjj) C^jj cost of forming operation Fjj CPp cost penalty for trying out a new process Pp CPm cost penalty for additional machining operation 0 ^ CPq cost penalty for quality C®k cost of equipment E|< C®fjj cost of additional forming operations, Afjj C^fjj cost of non forming operations, Nfjj meeting requirements 'R' and satisfying the set of constraints and requirements for Fjj, Nfjj, Afjj, and machines {M} 2.3 Research Objective Develop an evaluation model and solution method for performing cost- effective forming process planning and equipment selection 19 2.4 Current approaches to process selection The following sections describe some of the key methods that have been used to address the issues of the problem statement. 2.4.1 Costing and process selection methods There are several cost modeling systems described in literature and available commercially. [Dieter, 1983] provides a good description of the technical cost model. An excellent review of work done in economic evaluation of processes and materials is provided by Ishi et. al. [1990]. Busch and Field [1989] have developed engineering based models of the cost of producing semi finished and finished components by a variety of processing technologies. Some cost estimating systems have been built at GM and Chrysler in co ordination with IBIS consultants of Massachusetts based on the Technical cost model and the multi-attribute utility analysis [Nallicheri, 1990]. These systems however, focus on a single area such as injection moulding or forming and are essentially costing systems. The Analytic Cost Estimator (ACE), developed originally for the U.S. Army, is a full-function estimating program designed by senior program managers for companies performing development and production of electro-mechanical systems. This program, however, is based on U.S. Government Industry standards. Of the recent recent costing systems, ABC or activity based costing approach [Cooper, 1988] is notable. This is a commercial system marketed by Strategic Cost Systems, Inc., Waltham, Massachusetts to overcome the drawbacks of traditional costing systems. 2 0 The literature survey shows that most expert systems and other methods have involved some costing of metal forming processes but primarily focussed on process planning. However a combined effort of verifying process plan and determining cost-effectiveness in all combinations of process and equipment selection has not been performed. Most work has been made primarily in two areas; process selection methods and cost models. The key approaches are: DESIGN COMPATIBILITY ANALYSIS(DCA): The fundamental strategy of DCA is as shown in figure 11. The user enters the constraints, specifications, requirements of the part and the proposed machine choice. The expert system then infers some physical characteristics, attribute data or a-data, about the proposed design. The expert system evaluates the compatibility of the design and generates the Match Index (a measure of the compatibility of the entire design), a justification of the measure, and suggestions for improvements [Ishii, 1989]. PUGH CONCEPT SELECTION METHOD: In this method an analysis matrix is filled out by experts about selection criteria versus different concepts or process/design selections. One selection is used as a datum and the others are judged relatively on the different criteria (figure 12). A scoring and refining technique selects the relatively better concept. However, the relativity is not explicitly quantified and interactions of different selection criteria cannot be captured. 21 User & Process Candidate Requirements, Machine Constraints Attribute Compatibility Knowledge Base Knowledge Base Inference Matching Compatibility Data Mapping Match Coefficients, Reasons, Suggestions Weighted Match Index Average and Match Range Range Figure 11. Flow of Design Compatibility Analysis [Ishii et. al., 1989] 2 2 TSM PUGH ANALYSIS MATRIX Date. Concepts Criteria Criteria Evaluation 1 : D 1 ' . i ■ i I i ! ! 1 i 1 i 1 N 1 1 + 1 1 1 1 1 1 1 j|MWWHHHÉiÉri 1 Totoi Score i 1 : ! 1 1 ! 1 s 1 - , 1 1 1 1 Oetermine Criteria Generate Compare & Enhance Sdect3to4 Concept Select ' Criteria Baseline - Score "Weak" "Best" Evaluation Alternatives Datum Alternatives Concept Concept Alternatives Alternatives Document ' Iterate Selections & Procedure Eliminatiaiis Figure 12. Schematic of the Pugh Selection Method [GM Training manual] 23 MULTI-ATTRIBUTE UTILITY ANALYSIS (MAUA) PROCESS 1. ATTRIBUTE EVALUATION 2. INTERVIEW EVALUATION 3. INTERVIEWING 4. ANALYSIS OF THE DATA A n ttx n V a k n Annbut» V ttu o Cost-Perlormance Tradeoff for Cost (X )S t-Performance Tradeoff for Sensfitve Case Intermediate Case 9S 90 4S a S I 3 AWtout»V«K» (Numbtn on graph lioM (o uttliy) ‘'ost-Performance Tradeoff for Breakup of Cost by Factor for tire Performance Sensitive Case Camstraft Figure 13. Cost versus selection criteria tradeoff curves [Nallicheri, 1990] 24 ADVANTAGES OF IBIS 1. EASY TO USE ON LOTUS 2. PROVIDES COMMON GROUND FOR RELATIVE COMPARISONS 3. ENSURES THAT ALL COSTS ARE ACCOUNTED FOR 4. VERY FLEXIBLE 5. ACCOUNTS FOR BOTH PRODUCT AND PROCESS DRIVERS 6. GOOD ROUGH CUT DECISION MAKING TOOL 7. GOOD FOR "WHAT IF" AND SENSITIVITY ANALYSIS 8. GOOD FOR ESTIMATING NEW PROCESS TECHNOLOGIES 9. TAKES BURDEN OFF FINANCIAL 10. CAN USE TO DETERMINE COST DRIVERS. THEN REDUCE 11. BETTER USED FOR COMPARING SINGLE PART ALTERNATIVES (NOT LARGE ASSEMBLIES) Figure 14. Advantages of the IBIS approach to process cost evaluation 25 DISADVANTAGES OF IBIS 1. REQUIRES KNOWLEDGE OF BOTH PRODUCT AND PROCESS 2. FLEXIBILITY YIELDS LESS USER FRIENDLINESS (NOT MENU DRIVEN) 3. SIZE OF MODEL IS CUMBERSOME FOR LARGE ASSEMBLIES 4. TOOL AND MACHINE COST ESTIMATES ARE GENERALLY LOW (CAN BE OVERRIDDEN) 5. CAN BE MISLEAD IF YOU USE ALL INTERNAL DEFAULTS 6. DOES NOT FORCE YOU TO REVIEW EXISTING DEFAULTS 7. PEOPLE RUN WITH NUMBERS, W /0 FINANCIAL BLESSING 8. ASSUMES ALL MANUFACTURERS USE SAME PROCESS 9. EASY TO MAKE MISTAKES IF INVALID INFO IS USED (GARBAGE IN. GARBAGE OUT) 10. ONLY A CALCULATOR, ONCE DEFAULTS ARE OVERRIDDEN Figure 15. Disadvantages of the IBIS approach to process cost evaluation. 26 TECHNICAL COST MODEL KEY ELEMENTS VARIABLE COST ELEMENTS: 1. MATERIAL 2. DIRECT LABOR. AND 3. ENERGY FIXED COST ELEMENTS 1. MAIN MACHINE COST 2. AUXILIARY EQUIPMENT COST 3. TOOLING COST 4. BUILDING COST 5. OVERHEAD LABOR COST 6. MAINTENANCE COST 7. COST OF CAPITAL Figure 16. Key elements of the Technical Cost Model [Nallicheri, 1990] 27 MULTI-ATTRIBUTE UTILITY ANALYSIS (MAUA): The process is briefly described in figure 13 and detailed in reference [Nallicheri, 1990]. The figure shows cost versus selection criteria tradeoff curves, which are generated based on expert input. The final analysis is performed using a costing method, in this case, the Technical cost model [Busch and Field, 1989]. This method relies on heuristics. The advantages and disadvantages of this method are listed in figures 14 and 15. TECHNICAL COST MODEL KEY ELEMENTS: The elements of this particular costing model is detailed in [Busch and Field, 1989]. The key elements are listed in figure 16. ACTIVITY BASED COSTING (ABC): ABC analyzes product costs by the specific activities which are performed in order to produce the products [Cooper, 1988]. Production activities are categorized into four groups: unit, batch, product sustaining and process sustaining levels with an optional administrative level. Once the activities are identified and categorized, second stage drivers are determined and assigned. 2.4.2 Limitations of existing process planning and costing systems in metal forming • Process selection models rely on heuristics • Simultaneous evaluation of part requirement, operation feasibility with costs and equipment not performed 28 • Sensitivity not provided for change in costs, equipment, materials and part requirements • Cost models vary with organization and methods • Cost models do not necessarily discriminate between processes and equipment selection. 2.5 Approach The approach adopted in this research is described in the following sections. 2.5.1 Literature review A survey of existing systems used for process design and planning in metal forming was performed and is included in Appendix B. In addition a study of current process and equipment selection methods used was presented earlier in this chapter. 2.5.2 Selection of part family In order to develop an approach to accomplish the research objectives, preliminary investigations were focussed on a part family. The selected part family would have several forming operations as part of the forming sequence and be formable by different combinations of cold, warm and hot forming. The 'outer race' of a constant velocity joint (figure 6) is produced by a multi-stage forming process consisting of forming operations of forward extrusion, upset, dimple, backward extrude and draw wipe as shown in figure 17. 29 Currently, this part is being produced by several combinations of cold, warm and hot forming operations by different organizations. The selection of the above part family provided a scope for investigating alternate sets of forming sequences and operations (cold, warm and hot) as well as equipment choices these sequences could be performed in (presses and cold headers) with sufficient data on costs to evaluate the options. This part family also encounters different kinds of defects. Material substitutions are also being evaluated such as AISI 1050 steel versus AISI 8620. Also it was possible to conduct physical tests on this part family as there was access to equipment and materials at Saginaw Division. Although the sequence shown is cold forming, alternate temperature ranges for forming some of the operations was considered. 2.5.3 Knowledge acquisition Extensive consultation with industry experts was conducted to better understand the underlying issues of material, process and equipment selection. A particular organization, Saginaw Division of General Motors was selected. The key areas within the organization that have input into the above selection process were determined and experts selected from the identfied areas. In addition, the current scenario of equipment, capacities, and layout of processes within that particular organization was studied as the selection process considered the current state of operations within the selected organization. The typical specifications for the selected forged part was determined and the process to ensure these requirements are met were investigated. Issues of tooling and tool-life were also studied. Alternate materials being considered for the part and related issues of material selection were also be determined. 30 Material handling, process times and costs were studied. Equipment currently available in the organization were studied and equipment selection criteria gathered from experts. Alternate equipment for performing the operations required for the selected part were determined. Methods for knowledge engineering were applied and some innovative methods were developed to enable more effective knowledge gathering. Investigations were conducted to understand the different methods of producing the selected part in different organizations. 2.5.4 Develop structure for knowledge A structure was developed to assimilate the knowledge gathered in a formal manner to be used for the selection process. This structure comprised of formats for knowledge gathering, databases, rules, heuristics, parametrics, tables, functions etc. 2.5.5 Develop a cost-effectiveness evaluation method • Performed a literature review of cost-effective process and equipment selection methods • Defined a formal description of problem • Determined methodology to solve above problem • Evaluated developed methodology 31 2.5.6 Develop a computer system • Implemented the developed methodology in a computer system • Established a framework for the system • Determined functional flow of the system • Gathered all knowledge and structure to perform the functions • Selected appropriate programming tools • Developed a prototype system 2.5.7 Generate cost-effective process and equipment selection scenarios Utilized the system and evaluated current process for producing the outer races. Generated possible alternate scenarios of process and choice of equipment that provide better cost-effectiveness. 2.5.8 Perform forming process trials Set up a procedure and performed the trials of the generated cost- effective process for forming the part. 2.5.9 Run forming process simulations Performed process simulations to verify the modified process sequence recommended by the system using the finite element method. 32 2.5.10 Perform simple upset tests Developed a procedure and ran simple upset tests to evaluate formability limits in a plant type environment. 2.5.11 Perform forming equipment trials Set-up a procedure and performed the trials of forming a part from the selected part family on a cost-effective alternate choice of equipment. 2.5.12 Verification of system and approach Verified the results of the forging trials with the generated selections of the computer system to verify the process and equipment selection methodology. 33 1 1 1 1 ! i 1 i 1 i N ! r " “ »i i Ll Extrude Upset Upset Backward Draw Wipe (Size) Extrude Figure 17. Forming sequence for an outer race CHAPTER III DISCRIMINATING COST MODEL 3.1 Introduction to knowledge engineering An "Expert System" is a computing system capable of representing and reasoning about some knowledge-rich domain, such as diagnosis, design or analysis, with a view to solving problems and giving advice. The process of constructing an expert system is often called knowledge engineering. Knowledge engineering requires the knowledge engineer (KE) to gather the appropriate knowledge, select the proper representation, and build a prototype system. The five stage development process proposed by [Hayes-Roth et al, 1983], for developing a system is shown in figure 18. The first stage identifies the problem characterisitics and produces a set of requirements (finding experts, a clear problem statement). Stage two searches for and defines the concepts to represent the domain knowledge. Stage three designs the structure of the knowledge. In stage four, the implementation formalizes the rules and implements the prototype system. The fifth and final stage requires the testing and validation of the system and the rules that organize the knowledge. The knowledge sources, as commonly found in any domain, are literature (reference manuals, periodicals, books), databases, the KE's own experience, 34 35 and interviews with domain experts. In instances where the KE is well versed in the domain, the KE actually takes on both the role of the domain expert and the knowledge engineer. Once the information is gathered, an appropriate knowledge representation must be found. Additionally, an inference method or combination of inference methods must be chosen to drive the reasoning process. [Gevarter,1987] provides an array of knowledge representations as shown in figure 19 and inference strategies (figure 20) to aid the knowledge engineer. Knowledge acquisition is often said to be the bottleneck in applying knowledge-based systems [Forsythe et. al.,1987]. Experts have difficulty in verbalizing their reasoning process well enough for computerized representations. Although various techniques for knowledge acquisition are available for use by the KE, the quality of the final product is in large part dependent upon the KE's ability to act as a mediator between the expert and the computer representation. Knowledge acquisition techniques and common pitfalls Ishi, et al have detailed knowledge acquistion techniques in chapter V of reference [Ishi et. al., 1989]. A knowlege acquisition process is shown in figure 21. A brief account of some of the key methods are described in the following section. Three basic approaches to knowledge acquisition exist: • Interviewing domain experts to capture reasoning process used by experts to solve the problem • Learning by interaction, where the computer system obtains knowledge from the user (or even the KE) through question and answer sessions. 36 Learning by induction, where knowledge is generated from data and examples from actual experience. fWonmADora RaStiign Concepts Rites IDEHHFCATOH C0NCEFTUAUZAÎ10H FORIUUZAHON UIPLEUEHTATIOH 1E5HHG Figure 18. Stages in the knowledge acquisition and system development process [Hayes-Roth et. al., 1983] 37 With Inheritance — Frames Hr No Inheritance — Objects — Parameter Values Object Description - — Logic Rules ^— Multiple Worlds Knowledge Representation Certainties r Ungrouped — Rules — Grouped — Examples Actions -Logic — Messages -Procedures Figure 19. Methods of knowledge representation [Gevarter, 1987] 38 -Backward Chaining -Forward Chaining ViewDoints (Contexts) -Hypothetical Reasoning Truth Maintenance -Object-Oriented -E Hypothesize and Test -Blackboard -Logic -Induction -Demons Inference -Meta-Control Engine -Uncertainty Management — Rules -Examples Pattern Matching — Logic — Messages Math Calculations Feature Integration Linking Figure 20. Inference strategies [Gevarter, 1987] Data, Problems, Questions Formalized, Structured Knowledge DOMAIN KNOWLEDGE EXPERT ENGINEER Knowledge, Concepts, Solutions KNOWLEDGE BASE Figure 21. Knowledge acquisition process [Hayes-Roth et. al., 1983] 39 Some pitfalls and suggestions for the knowledge acquisition process are described [Forsythe et al,1987]. Out of them, the problems related to the interview process which were of interest to our research were: o treating the expert as some kind of a database versus a person • twin dangers of over and under directedness of questions asked • fear of silence when questions need to be asked and failing to listen • difficulty asking the right questions • interviewing without a record and appropriate documentation There could also be conceptual problems such as: • Treating interview methodoiogy as unproblematic and not have a formal process for knowledge elicitation • Blaming the expert for lack of co-operation or understanding « Reducing abstract knowledge into something qualitative or quantitative. The knowledge engineering method used for building expert systems, is the method in which domain knowledge of economics of forging process and equipment selection has been studied. Paying attention to the pitfalls of knowledge elicitation discussed above and the difficult task of accessing domain experts, especially in forming, due to the nature of the business, a knowledge acquisition process has been determined and applied in generating the discriminating cost model. 3.2 Knowledge acquisition process used Initially, the current procedure for costing out a process and equipment selection to make a forged part was studied in a forging organization. Some of 40 the key elements of cost estimating are described [Salvendy,1982] and table 1 shows sources of information for cost estimating. In the organization studied, the following were the sources identified as those that contributed to put a cost estimate for a forged part together. • Cost estimating « Industrial engineering Plant engineering Forming experts Purchasing Accounting Estimating Plant personnel responsible for individual operations and equipment Personnel were identified from the key functional areas listed above within the organization. Group meetings were organized with the experts and the objective of the meeting clearly defined. In the current employment scenario, people are very sensitive to knowledge extraction and new technologies such as computers and expert systems especially in the areas of manufacturing and metal forming. Lack of job security for the aging workforce to which segment most of the experts belong to, immensely affects knowledge engineering. Therefore, it was important to be sensitive to these issues. The experts were informed first that the study being done was not toward replacement of the current cost estimating procedure. The current procedure would yet be used to provide a cost estimate. It was clearly pointed out that the reason for developing this new cost model was to help in discriminating different selections of forming process and equipment. It also helps to point out how this new model would help them in their current job function. So it was pointed out 41 that a model such as the one proposed for development would enable them to make better judgement and evaluate different scenarios more effectively and quickly. The system would also relieve some of their time in evaluating different scenarios to be used for more critical problem solving and creative sequence design. The first step, in summary, is to get the buy in of the experts toward the endeavour. Next the group was divided into sub-groups, each focussed on a specific area of expertise required for cost estimating. Interviews were arranged with each sub-group to address the details of the specific area. Then a preliminary model was built and reviewed by all the experts to verify it reflecting the primary discriminating cost drivers and selection parameters. After approval on the model elements at the highest level, the mechanisms for determining the values for these elements were determined and refined. This process resulted in the "final model". During the process of knowledge acquisition, it was also important to guide the experts to think in terms of the objective of the model. Experts have their own reasoning mechanisms which they may not necessarily be aware of or voice them. Therefore, it is critical to assist the experts in thinking in terms of a structured model form, at the same time not overguiding them onto a track as desired by the KE. Another major effort in gaining the co-operation from experts was to obtain management support. Therefore, a sound business case of the advantages and benefits of such a system was prepared. The limitations were also clearly presented so that the management would feel comfortable to make an honest opinion. Once management approves support for the project, the 42 scheduling and the interviews themselves seem to run in a relatively productive manner with less tension. The KE's were selected with some background in the areas the interviews were being conducted. Experts are generally very busy and have little time to spare. Therefore it is critical that it is not required of the experts to teach the KE's about the basics of the area under discussion. This could cause the experts to be exasperated and lose respect for the knowledge acquisition activity and not be committed to it. Another point made to the experts was that a discriminating cost model would enable them to effectively communicate to the management why their practical concerns are valid as the current cost estimation methods are not concerned with factors at the detailed level. Finally, a good communication channel was established to keep all the people involved with the project up to date on progress and directions. This encourages team effort and prevents skepticism from developing due to lack of awareness of developments and surprises. Separate set of interviews were conducted to determine knowledge with respect to the forming operations, process and equipment selection. Also, the cost drivers for the different equipment were determined. The important forming system components and their characteristics are easily found in the literature. More effort was required trying to pinpoint the complex relationships and compatibilities between the forging system components. The parameters used for equipment, forming operation, and intermediate operation selection were determined and defined by the experts. Interviewing experts remained the dominant approach to knowledge acquisition. Process and operation constraints are discussed extensively in literature. Equipment selection parameters and methods have been captured in the work of 43 [Ishi et al,1989]. The methodology of Design Compatibility Analysis (DCA) used in their work was modified for application in this research and some of the knowledge about equipment selection was collected from this reference. Knowledge gathered from experts or other intrinsic equipment selection detail such as for example, a retrofit knockout mechanism for greater knockout length on a particular die station on a particular machine were added to the list. Table 1. Sources of information of cost estimating [Salvendy, 1982] Design Information Required for Estimating Sources Operation Labor time, wages, fringes Industrial engineering, methods and standards, personnel Material shape and policy cost Engineering, industrial Material losses Estimating Variable overhead rates Accounting Product Bill of materials, drawings Engineering Special tests, packaging, shipping Engineering Quantity and rate of production Marketing, sbeduling Operation estimates Cost estimating Project Fixed costs of equipment Industrial engineering Life periods Industrial engineering Direct operating costs, cash flows Accounting, estimating Indirect costs, working capital Accounting Operation and product estimates Estimating Project design specifications and drawings Engineering System Operation, product, and project estimatesCost estimating Budgets, wages Public authority Fiscal money available Public authority Reimbursable and nonreimbursable costs Public authority Taxation, sources, amounts Public authority Eminent domain, legal requirements Legal officer 44 3.3 Development of the Discriminating Cost Model Studying the current procedure for cost estimating, at the highest level, the standard hours for different operations Involved In the process of making a forging, a variable cost and the total cost are compiled as shown In tables 3 and 4. Other factors used are equipment costs. Investment capital, tooling costs, shipping racks, labor, material and freight, burdens, and amortization. However, a closer analysis of these accounting methods revealed the following: • the cost estimate did not distinguish between extrusion and upset tooling, as the cost for tooling Is a lump cost for tooling (distinguished only In terms of cold, warm or hot) • did not distinguish a 500 ton press from a 1000 ton press as the costs are allocated as the cost for the operation of an equipment In a given department. For example, the cost for operating any press In the "High Bay (Dept. 97) was the same. Irrespective of the size of the press . did not distinguish between a 2 lb part and a 2.25 lb part In the processes of phoscoating, annealing as the cost was based on a typical annealing time cycle. • did not distinguish between different composition of steels In process operations such as annealing, phoscoating, etc. and was reflected only In material cost If there was a significant difference In alloy content. • costed differently depending on plant, which side of the aisle the equipment was on (department), and other factors which should have no Influence due to the accounting system based on 'standard hours' of a department with given overheads and different labor rates. 45 • the cost data contained burden and other costs such as electricity for divisional offices, janitors for cleaning, etc.. This drove the need for a more fundamental cost model that would be common to forming organizations and local costing methods, and yet discriminate the costs for different choice of operations, process and equipment. The noise caused by the existing costing methods which cloud the information required to discriminate between the choices of process and equipment has to be reduced. Also direct costing of several alternatives requires considerable time and effort and is in some cases impractical. Costing methods have been described earlier. Therefore a model was investigated that would provide for the following: • at the highest level identity parameters/cost drivers that clearly reflect variations and differences in operations, processes, and equipment • provide for a mechanism for individual organizations to input information into these parameters based on their local costing methods, so that the model at the highest level is independent of organizations (open architecture) • provide for modification of parameters as well as mechanisms if needed by individual organizations to tailor the model to their needs (modular) Utilizing this approach, for the forming process, a discriminating cost model was arrived at as shown in figure 22. ELEMENTS OF DOM The elements of the model were determined as described in the following sections. 46 1. Cost of Material: The interviews with the purchasing department determined that the following factors contributed to the cost of the material used for the part; • composition or specification of the material « weight of material for the part • the physical form in which the material is ordered (bar, coil, etc.) • the heat treated form in which the material is ordered (annealed, spheroidized anneal, etc.) • the process used to make the input material (hot rolled, cold rolled, cold drawn, strand cast, etc.) o the supplier The above information could be provided as a table for the different materials per unit weight as shown in table 2. Table 2. Material cost table used AISI NAME COMPOSITION FORM HEAT TREAT MFG.PROCESS SUPPLIER DIA RANGE PRICE/LB 8620 bar annealed cold rolled ACME 1-3" 0.28 8620 coll annealed cold rolled ACME .5-1.5" 0.24 1050 bar annealed hot rolled ACME 1-3" 0.22 2. Cost of a forming operation A thorough study of the costs related to a forming operation determined that it was the tooling cost that varied depending on the operation being performed on a given piece of equipment. For example, there is a difference in the cost on the same press 'X' to run a cold upset operation versus a hot 47 extrude. The forming operation consumes tools at a different rate based on the type of operation. Also, the tools used for the different operations are manufactured by different processes and using different materials thereby causing further difference in cost. Therefore the differentiating factor due to a forming operation in terms of economics was the cost of tooling itself. This cost may be represented as a function or a table. A particular organization may have specific materials and manufacturing methods used for tooling for different types of forming operations. Therefore, a table is created of tooling costs for a given forming machine, forming operation, part size, material, and temperature range. The cost of equipment in process operations includes machine operating costs, labor, investment costs distributed over quantity of part, and overheads. Example of costs associated with an operation are shown in table 5. 3. Cost of non forming operations Annealing: In the annealing process a certain weight of material is fed onto a belt at a certain speed. The parts are then heated in different zones to the prescribed temperature for a certain length of time. The atmosphere is controlled by metered amounts of inflow of the appropriate gases. Therefore the cost of annealing is described as a function of the weight of the part, the temperature the part is heated to, the time for which the heat is applied, the machine, the composition of the material, and the atmosphere. The energy costs required to perform the above process and the equipment operating costs are taken into account in the function. 48 Table 3. Typical costs laid out by forging process sequence DEPT. STD. VAR. t o t a l OPER # OPER. DESCRIPTION HRS. COST COST PURCH 1005 (5 .3 8 1 6 LBS) «1.39 «1.51 PURCH 1050 (5 .3 8 1 6 LBS) DRN S ll 10 DRAW 4-74 0.00015 «0.05 «0.13 20 WASH IIML 4 33 0 .0 0 0 7 0 «0.01 40.02 27H R7I-PPA ni ANK 10 bllLAR 4 U3 0.00100 «0.07 50.16 4 0 a n n e a l 4-73 0.00026 «0.03 «0.08 50 PHOSPHATE COAT 4-73 0.00059 «0.08 «0.19 60 IJP SLI & EXTRUDE 4-36 0.00106 «0.16 «0.39 4-93 0.00034 «0.01 «0.01 80 a n n e a l 4-79 0.0 0 0 3 9 «0.05 50.13 30 PHOSPHATE COAT 4-79 0.0 0 0 6 3 «0.08 «0.20 100 DIMPLE 4-96 0.00111 «0.10 «0.41 4 39 0.0 0 0 3 4 «0.01 «0.01 120 ANNEAL 4-79 0 .0 0 0 4 5 «0.00 «0.14 130 PHOSPHATE COAT 4-79 0.00067 «0.09 «0.21 140 BACKWARD EXT & FIN FORM 4-96 0.0 0 1 1 5 «0.17 «0.43 4-99 0 .0 0 0 3 4 «0.01 ♦ 0.01 150 NORMALIZE & BLAST TOTAIS PAGF 1 0 .0 0 9 1 8 «2.43 «4.05 1 49 Table 4. Typical consideration of other cost factors III.. Caoitot £guipm*nt • $1.400 OH THIS CR 91,040 M iic. Câoiial Sub»To(al Caoital 51,400 91.040 Sagmow Tooling S 300 OH THIS CR 9280 Nan*Alll«d Tooting Allied Tooling Sub'Total Tooling 5300 9280 Mise. Operations 560 OH THIS CR 900 Shipping flacka Sub-Total Goarations 560 900 Grand Total ($1.000) 51.780 $1.380 Lead Time (Weeks) 1 From Project Aoprovai 1 From Customer P.O. Labor: 1993 Model Year Compare to Pan K Current Total Oper. Cost: Material: 1993 Model Year Prod. Design Change (Y or N): Exchange Rate: Cost Center Burden Rates: 1993 Model Year Costed in Plant: • 32^ Floor Space Available lY or N): . . . I A c e Comoared To 1. . B 1 D O UT RACE Material & Freignt 53.93 1 55.12 151.1911 53.96 54.78 (9 0 .8 2 ) Labor 5 1.38 $1.44. 150.061 1 51.24 51.23 9 0 .0 0 Variable Burden 53.91 $4.33 1 1$0.4211 53.28 53.11 5 0.1 7 Sub-Total Var. Cost 59.211 510.89 1 (51.6811 58.48 5 9 .1 3 (5 0 .8 6 ) 5 2 .2 4 jOeer.. Ins., Tax Cost 50.75 $0.79 1 l$0.04ll $0.85 5 0 .5 7 5 0.0 8 Other Fixed Costs 5 5 .3 0 1 $5.99 i l$0.63li $4.68 5 4 .4 8 5 0 .1 0 Ooeraimo Costs 5 1 5 .3 2 1 317.57 1 '$2.3511 $13.70 514.17 1 150.47) 52.54 Bus. Plan Red. (Mat.) 1 Bus. Plan Red. (Other) I j j N ew Eq uip . Oaor. 52.74 1 5 2 .7 4 5 2 .7 4 9 2 .7 4 5 0.04 1 Operation Am on. (4 Yrs.) 5 0 .3 2 1 50.32 1 50.32 5 0 .3 2 50.01 O ther 1 1 i Total Ooeratino Costs 518.38 I il7.S7 1 30.71 ! i10.70l 514.17 1 52.58 52,59 iNaw Tools Amon (3 Yrs.l 1 32.12 1 52.121 52.12 1 1 5 2 .1 2 50.04 {STD.HOURS 1 0.07830 I 0.08701 1 -0.00865 1 0.06981 1 0.07408 I -0.00487 50 COST DRIVERS OF DISCRIMINATING COST MODEL 1. Cost of material- - f (spec, weight, form, process, heat treat, supplier) 2. Cost of forming operation - f (tooling cost, machine, temp) 3. Cost of non forming operations Anneal - f(weight, temp, time,machine,material) Heating - f(weight,temp,machine/material/shape) Phoscoat - f(surface area/vol,material,weight) Graphite coat - f(surface area,volume,material,weight) Shear - f(length, diameter, material) Saw - f(length, diameter, material) 4. Cost of trying new process/operation - penalty cost 5. Cost of material handling/transportation/lb of material To annealers, coaters, presses, etc. 6. Cost of additional material on part due to process 7. Cost penalty for adding machining operations 8. Cost of quality 9. Other costs Figure 22. Key cost elements of the discriminating cost model (DCM) 51 Table 5. Forming operation costs table OPERATIONCOLD i/VARM HOT =ORMING MACHINE QUANTITY COST AUTOMATION TOOL TOOL TOOL COST/SHIFT RANGE /PC upset X m1 1000-5000 no 0.08 upset X mi 1000-5000 no 0.18 back ext X m3 3000-6000 yes 0.34 Cost by machine Energy consumed = efficiency * mass * specific heat of material * temperature increase * time Cost = Energy consumed * Energy cost + Machine operation cost/pc where Machine operation cost/pc includes labor, maintenance, and cost of operation such as atmosphere, etc. costed by shift and divided by pieces produced per shift Heating: Heating of the workpiece may be done by several methods such as induction, gas-fired etc. However the basic function of these machines is to increase the temperature of the material by a certain amount in a certain amount of time. The costs for heating irrespective of equipment type may be expressed as a function of weight, diameter, material, temperature increase, machine, and shape. The energy required to heat the part may be determined by the temperature increase, specific heat of the material, mass of the part, and the efficiency of the heating equipment. Cost by machine Energy consumed = efficiency of machine * mass * specific heat of material * temperature increase * time 52 Cost = Energy consumed * energy cost + Machine operation cost/shift Phoscoat: There are different kinds of phoscoaters which are commonly used for cold forming. These equipment require energy, chemicals replenished at regular intervals, transportation of parts, and so on. The cost of this operation may be expressed as a function of the surface area/volume of material, equipment, and weight. The weight is a parameter as it determines the amount of material that can be loaded in the baskets used for coating. Graphite coat: Although the process of coating graphite (used for warm forming) is different from the phoscoaters, these equipment also consume energy, and materials and process by weight and shape. Therefore the same function used for phoscoat may be used to represent the coating costs. The costs for graphite and phoscoating are shown in table 6. Shear: Shearing is carried out on different types of shearing equipment. The principle cost elements for the shearing operation was determined as a function of machine, length of cut, type of material (coil or bar), temperature (cold, warm, or hot), diameter of cut, material and if performed on a forming machine or a separate shearing machine. Example costs are shown in table 7. Saw: Sawing cost depends on machine, length of cut, diameter of cut, material and material loss due to sawing and some sample costs are shown in table 8. 53 Table 6. Lubrication costs table WEIGHT SURFACE AREA MATERIALCOATING VIACHINE OPERATION COST lbs RANGE sq inch TYPE COST/SHIFT fPIECE 1-5 12-40 aisi8620 phoscoat 1000.00 - 5-10 50-100 aisi1050 synthetic-c 700.00 - 1-5 12-40 aisi8620 graphite 500.00 - 5-10 50-100 aisHOSO synthetic-w 400.00 - Table 7. Shear costs table DIAMETER LENGTH/DIA MATERIAL TEMPER MACHINE TOOL COST RANGE RANGE ATURE COST/PIECE 1-3" 1.2-3 aisiS620 cold acmel 0.04 1-3" 1.5-4 aisi8620 warm acme2 0.06 1-3" 1.5-3 aisi1050 cold acmel 0.05 Table 8. Sawing costs DIA RANGE LENGTH/DIA MATERIAL MACHINE M/cCOST MATERIAL /SHIFT waste 3-5" 1-5 aisl8620 acmes 400 2% 5-8" 1-5 aisi8620 acme? 400 4% 3-5" 1-5 aisilOSO acmes 400 2% 54 Material handling: Material handling may be expressed as a function of number of parts, weight, size and shape and distance of travel. COST= Cost of fork lift truck operation (truck + driver)/shift Washers: The cost is a function of machine, part weight, material, and type of cleaning operation. 4. Cost of trying new process/operation Besides the cost of forming and intermediate operations there are other costs incurred in a forming process. Most forming organizations are specialists in a certain area of forming such as cold, warm or hot forging or extrusions and so on. In such cases, there is significant apprehension of trying out new processes not performed in a given organization before. Therefore, although an alternate process route would be economical there is a cost penalty for trying out operations and processes a given organization is not familiar with. This includes increased number of tooling iterations, consultation and research costs, etc.. This can be included as a penalty cost to influence the process evaluation. Penalty cost = input by user as a function of tooling design iterations, tooling costs, equipment costs, analysis, etc. distributed over the quantity. 5. Cost of additional material on part due to process In cold extrusions, the die angles are selected to be between 30-40 degrees for typical reduction ratios for steels to prevent chevrons. However, in warm and hot forging the extrusion angles can be much higher. This changes the forged part geometry in that some additional material added in the taper of the extrusion angle is reduced. Therefore, this additional material cost has to be 55 accounted for. This may be represented by a percentage of weight of the part subjected to a given operation. For example, for cold extrusions 10% of material extruded may be added, in warm 5% and hot 8%. In hot forging, a higher diametric tolerance and poor surface finish increases material to be added for an extrusion although the extrusion angles are higher. This could also be expressed as a function of the extruded diameter. In a similar manner, additional material has to be accounted for by appropriate percentages for the other forming operations. Another approach is to consider a standard table of typical extrusion angles in cold, warm and hot forming. These angles are used to calculate the amount of material to be added to the extruded diameter, given the input diameter and the extrusion ratio. The material dictated by tolerances and surface finish is next added to this amount which when multiplied by cost of the material produces the additional cost. Most of the other operations may simply require a calculation based on the tolerances. 6. Cost penalty for adding machining operations In evaluating alternate processes for making a part, one may wish to evaluate the economics of adding another turning operation to machine the stem from an extrusion and expand the tolerances on the stem diameter to +/- 0.030". In that case, previously infeasible processes such as hot forging will be included in the evaluation and if found cheaper may be the process to go with. Therefore by providing this penalty cost parameter, such additional scenario investigations are possible. This also enables considering outsourcing to smaller manufacturing shops from large organizations, which has become more commonplace due to increased global competition. In addition, one may also 56 investigate alternate machining operations by changing the surface finish requirements. Machining cost is entered by user as a function of operation and quantity. 7. Cost of quality Different processes have an intrinsic effect of quality. However, quality is difficult to quantify and define and varies from organization to organization. If a cost for quality data is available with appropriate defining parameters such as range of tolerances, cold formed surface finish, etc., then such data can be incorporated so quality is taken into account during evaluation of operations. The above model attempts to capture the top level cost drivers that can discriminate between forming, intemediate and non-forming operations and for other typical costs incurred during layout of different processes. Individual organizations may enter the functions, tables, and data required to use the above model reflecting their locally used costing mechanisms. In addition, they may include or modify the cost drivers themselves, if found appropriate. In the United states, forming using massive equipment, high capital investment for automated mass production lines may be more cost-effective. However, in the third world countries where labor is cheap and capital is scarce, alternate processes involving smaller equipment, less net shape, may be more economical. This model can be extended to reflect cost scenarios in different countries to help in process planning especially in global ventures. CHAPTER IV STATE-SPACE SEARCH APPROACH TO COST-EFFECTIVE PROCESS AND EQUIPMENT SELECTION 4.1 Definition of search space of problem domain Artificial intelligence (Al) is defined as the study of how to make computers do things at which, at the moment, people do better [Rich, 1989]. The current problem under investigation in this research as defined in chapter 2 falls in the problem class of Al. There are several ways of formally representing problems and different ways of solving them. In this research, based upon the class of problem being solved, the state-space approach is used. In order to provide a formal description of a problem, it is necessary to do the following; Define a state space that contains all the possible configurations of the relevant objects (and perhaps some impossible ones). It is, of course, possible to define this space without explicitly enumerating all of the states it contains. 1. Specify one or more states within that space that describe possible situations from which the problem-solving process may start. These states are called the initial states. 2. Specify one or more states that would be acceptable as solutions to the problem. These states are called goal states. 3. Specify a set of rules that describe the actions (operators) available. 57 58 The problem can then be solved by using the rules, in combination with an appropriate control strategy, to move through the problem space until a path from the initial state to a goal state is found. Al techniques typically comprise of search, use of knowledge, and abstraction. OPERATION COLD FORM WARM FORM HOTFORM “W 9.0 ■oQ8 S "cfig,- OPEN FORWARD EXTRUDE ] = l UPSET [5^ Mn BACK EXTRUDE M1...Mn are machine choices Possible combined operation Figure 23. State space representation of problem Figure 23 shows the state-space representation of the problem under investigation. The problem under consideration is complex, and therefore a three dimensional representation has been used to describe the state-space as complete as possible. Consider the part shown in figure 24 which can be made using the sequence of operations of forward extrude, upset and backward 59 extrude. Each of the operations can be performed cold, warm or hot. Therefore the combination of the operations in the sequence is equal to 3", where 'n' is the number of operations. For a three operation sequence, there are 27 combination of operations. Tolerances 2.0 On dia +/- 0.012 On length +/- 0.010 On thickness +/- 0.010 0.9 Quantity - 3000/day Figure 24. Forge part example to apply DCM Given there are'm' machines, the combinations expand to (3m)n. This Is because each operation choice may be performed in any of the'm' machines available within an organization. The choice of machines is more complex than just described. For example, if a machine 'MT is chosen for the cold extrude operation, in considering the next operation cold upset, the same machine Ml may be chosen if it has at least two stations with sufficient capacity available. Furthermore, if the backward extrude operation is also done cold, and the press Ml is capable of performing all three operations then M1 becomes a selection for all three operations. This kind of combination influences the cost, as the cost 60 for all three operations would relate to cost of one machine but two or three die stations depending on how many operations are being performed on the press. This also emphasizes the need that machines chosen earlier in the search need to be reconsidered as every operation in the sequence is explored. This complexity has not been represented in the search space. Another addition to the search space is due to the possibility of combining operations. For example, if the extrude and upset operations were performed hot, the two operations may be accomplished in one blow if the ratios are appropriate. Thus in the 'hot' branch of the search space two operation nodes have to be combined. As it is more common to find two sequential operations (as designed for cold forming) combined in warm or hot forming, the combinations permitted for operations is limited to two in this research. The maximum number of combinations possible are n/2. Therefore the search space then further expands to ( 3 m ) n + n /2 or ( 3 m )1 This addition is shown by the example of the circled set of operations. The search space described for the combination of two operations is further complicated and needs to be adressed. For example, consider that the cold open forward extrusion laid out for the part involves a reduction of 60 %. As the limit for open cold forward extrusion is 38%, the system has to recommend or include an additional extrusion operation. Therefore, the extrusion as designed has to be performed in two stages. This addition of another forming operation, also expands the choice of equipment for this operation. This process further expands the search space. These additional alternatives are not included in the figure, as the figure could get very busy. The splitting of individual forming operations if not feasible in one stage is limited to two in this research. The 61 maximum number of such splits would then be n/2. The search space then would expand to (3m)1 -5n+n/2 or (3m)2n. From the above description of the search space, it is evident that the problem is extremely complex and an efficient solution method is essential to reduce the combinatorial explosion and the computational intensity. Sufficient knowledge is also required to be able to determine solutions. 4.2 Problem solution methods There are several basic problem solving methods of A. I and are discussed in [Rich, 1969]. Some of the key general-purpose search strategies fall under the category of weak problem solving methods and a brief description is provided below: General search strategy for searching through problem spaces are: • Explore the problem graph • Avoid cycles « Avoid dead ends • Restrict search with evaluation For 'OR' Graphs, search methods are: • Generate and Test • Hill Climbing • Breadth-first-search • Best-first-search For 'AND-OR' Graphs, search methods are: • Problem reduction • Constraint satisfaction 62 • Means-ends analysis The search space for the problem under consideration is a complex form of 'OR' graph and the search strategies of 'OR' graphs are applicable. Therefore, a brief description of these strategies is reviewed in the following section. Generate and Test: Strategy: • Generate a possible solution o Test against goal • If goal, then stop, else repeat Comments • Very simple • May take a long time • It is a depth-first strategy • Requires backtracking for failures Hill Climbing: (Similar to generate and test except a heuristic function used for evaluation) Strategy (Stack + Evaluation) Generate possible solution Test against goal If goal, then stop, else Generate new solutions from old If goal, then stop, else choose closest to goal o Repeat process with closest as old Comments 63 • Low cost advantages over generate and test provided one has a reasonable evaluation function • A local method • May get stuck with no successors (reaching local min or max or reach plateau) o May have to incorporate lookahead Breadth-first search: Strateov (Queue) • Generate all possible solutions of length N o Test each against goal • If goal, then stop, else • Increase N and repeat Comments • Will find solution (if it exists) o Requires a lot of memory • Requires a lot of work Best-first search: Strateov: Use heuristic function = g (cost) + h (heuristic) Put start state on Open list If Open is empty, then fail Move Best from Open to Closed Check Best for goal state Foreach New in successor (Best) 64 • Point from New to Best o Compute g by adding cost • Check Open for New o Check Closed for New • else add New to Open Comments • Use of 'g' can help compute shortest, cheapest or fastest path » Use of 'h' appropriately will help find optimal solution Representation Information in Nodes • Problem state • Evaluation functions • Ancestors and successors The problem space under consideration in this research is not a simple OR or AND-OR graph and therefore the solution method is a combination of some of the search methods described above. Here, a modified form of 'breadth-first-search' using heuristics is used to find the cost-effective solution in the state-space. All possible solution paths are generated and evaluated to prevent losing the optimal goal state. Pruning of the search space is effected using heuristics, constraint satisfaction and means-ends analysis. For example, once a path has been successfully explored upto the goal state and a cost is determined, then cost during the exploration of other paths is constantly compared with the least cost to goal state. In this manner, costlier paths are not evaluated any further as exploring these paths further will only provide a costlier solution even if feasible. Also, nodes that do not satisfy constraints trigger failure handling mechanisms which attempt to satisfy the constraints by redesigning the operation. If these mechanisms fail, the search is terminated. 65 Figure 25 shows the solution structure to reach the goal state of the cost- effective selection of process and equipment. The incorporated search algorithm is modified based on the conflict resolution strategies within 'ICAD'. In order to illustrate the solution method let us consider the part shown in figure 24. The part may be divided into two zones, namely, the stem and the bowl. In a typical forged part print, the inputs would be the tolerances on diameters and lengths and surface finish of the above zones, material specification, and sometimes required hardness and grain flow. Along with this information the supplier needs to know the quantity being ordered to schedule production over equipment available or investigate investment options for additional equipment. 4.2.1 Operation Evaluation The sequence of operations required to form the part geometry is selected by a forming engineer to be an open forward extrude to form the stem, an upset to the final diameter of the bowl and subsequent backward extrusion of the upset head to form the final shape of the bowl as shown in figure 26. Each of the forming operations, extrude, upset, and backward extrude can be performed cold, warm or hot as discussed earlier. Let us consider the first operation, open forward extrude at room temperature. The first check to be made is to determine if the operation being considered produces a zone that is not further processed. In this case, the forward extrusion produces the stem which is not formed in subsequent operations. Therefore, we need to determine if the operation under consideration is capable of producing the tolerances and surface finish produced in the stem in the final part. It may be seen that for 6 6 tolerances of less than 0.01" the cold and warm extrusion are feasible operations. However, hot extrusion is not capable of such close tolerances and therefore need not be considered as an alternate operation. The next step is to perform all calculations required for further processing. Knowing the material and thereby the average flow stress, the load for open forward extrusion can be calculated. Consider steel A whose flow stress at room temperature is represented as o = 120 s 012 ^si. Given that the open forward extrusion reduction in area is 19%, the load is 78 tons. The effective strain of the reduction being performed is also determined as In (1/(100-19)) or 0.21. Other calculations may be stresses etc. Now considering cold forward extrusion, we next need to verify that for the given dimensions, the operation is feasible. The extrusion requires that the diameter of the billet is reduced from 1 inch to 0.9 inch. This corresponds to a reduction in area of 19% which is within the constraint that to perform an open forward extrusion the reduction in area must be less than 40%. Given that the incoming material is annealed, the strain calculated for this operation is compared with the maximum strain before cracking. If the strain is below the limit then another feasibility check is approved. Another check for feasibility is that the length to diameter ratio of the billet must be less than 2.5 to prevent buckling. In our case, the length to diameter ratio is 2.3 and so the open forward cold extrusion is feasible. In open forward extrusions, typical defects are chevrons. Given the reduction ratio, the selection of the right die angle will provide defect free parts. Considering warm extrusion, the constraints of the operation are also met and therefore becomes a feasible alternate. 67 quantity, matorial. toleranca. swtacaflnlih INPUTS (orming sequence, billet size, part shape OPERATION _G Q U 1 GENERATE ENTIRE OPEN FORWARD STATE SPACE OF EXTRUDE COLD. WARM. HOT S'» UPSET COMBINATIONS OF ABOVE SEQUENCE BACK EXTRUDE ‘ CHECK FORTOLERANCES AND SUAFACEnnSHnEQURBIEHTS IF NOT NET AND THESE AREAS ARE NOTWORKED SUBSEQUENTLY DELETE THE CURRENT NODE FROU EVALUATIOH AT EACH NODE ‘ PERFORM ALL CALCULATIONS REQUIRED (LOADS. STRAINS. ETC4 PERFORM FOLLOWING ‘ CHECK OPERATION FEASœOITY. IF FAILS. USE FAILURE HANDUNO HECHAMSUS EVALUATION ‘ DETERMINE NONfORUUIQ OPERATIONS REQUIRED (COATING; HEAT TREAT. E TC j ‘ DETERUHE ANY UATERiALHANDllHaOPERATIOHS REQUIRED ‘ GENERATE SET OF FEAStBLEEQUPUENTINHERE OPERATIONS UPTO CURRENT STATE CAM BE PERFORMED ‘ COST A U . THE ABOVE OPTIONS UPTO CURRENT NODE ‘ DETERUNE LEAST COST OPTION USE EFFiaENTSEARCHUETHOOS BEYOND GENERATE AND EVALUATE CONTINUE SEARCH ‘ IF A PATH UPTO ACERTAIN NODE COSTS GREATER THAN A PATH UNTIL GOAL STATE THAT HAS REACHED THE GOAL STATE. STOP EXPANDING THAT PATH IS REACHED 'CEPESS* FUNCTIONAL FLOW CHART Figure 25. Solution method for problem 68 Open Forward Head Upset Back Extrude Bowl Extrusion Figure 26. Forming sequence for example part In the above calculation, we found that the operation was feasible. Now consider that the length to diameter ratio was 3.5. Then the feasibility would be violated. However, there are remedies that may be applied based on expert knowledge. For example, a closed forward extrusion would prevent the buckling due to the higher I/d ratio. Now if the reduction was higher than 40% a remedy would be to include an additional open forward extrusion. This would imply that the desire is to perform open extrusions only. Another option may be to convert the open extrusion to a closed extrusion as higher reductions are then possible. Therefore, there has to be failure handling mechanisms as described to overcome the infeasibility of the operations. In the process of establishing feasibility of a given operation, other intermediate operations (non forming) that influence feasibility have to be selected. If the material has been work-hardened during forming and the strain added due to the extrusion would cause fracture, then an annealing operation 69 has to be added, if the extrusion is being performed cold, then a phoscoating lubrication operation is required. If the extrusion were warm, a graphite coating may be applied. These are examples of additional operations required before the operation under consideration becomes entirely feasible. In addition to the determination of additional forming and intermediate operations, there are material handling operations to be considered. The parts have to be transferred from press to heaters, annealers, coater, and so on. As a part of confirming feasibility of an operation all associated material handling operations have to be identified. Another complex dimension to the solution of operations is the combination of operations. This is possible between an upset and extrusion, forward and backward extrusion, and so on. These operations become feasible depending on the combination of operations. Consider, for example, that the load required in a warm form operation for upset is greater than the extrusion required in the first operation. Then the extrusion and upset can be performed at the same time, as the extrusion will be complete before the load can be increased to upset the head. This combination of operations adds further complexity. In a similar manner, the other options of warm and hot forming of all the operations in the given sequence have to be considered. 4.2.2 Equipment selection At each state in the search space, for every forming operation, a machine has to be selected. In order to illustrate the solution method to select machine for a forming operation, consider the list of machines in a given organization as 70 shown in figure 27. Considering the first cold forward extrude operation alone, the following characteristics of a forming machine are required; peak load capacity of more than 100 tons energy of more than 200 Ib-in knockout length of more than 3 inches requires at least one die station to perform the operation able to form required quantity of 9000/day given a machine is available 2 shifts or 16 hours • machine accuracy and stiffness should enable tooling installed in it to hold tolerances of +/- 0.006 inches on part These operation driven requirements are then compared with the capabilities of the equipment that are available. There may be certain equipment which is more conducive to a certain type of process such as a hydraulic press for an extrusion operation. In this research, as we are strictly optimizing based on cost, we seek any equipment that satisfies requirements of process. It is however not difficult to add qualitative information and allow the user to select a threshold limit for acceptance or consideration of machine for a given operation. By comparing of the requirements with equipment capability, we find the machines that are capable of performing the extrusion. Machine selection is determined in a similar manner for the warm and hot extrusion, if they are states yet to be considered after the initial screening methods. In the case of warm and hot forging other parameters such as temperatures which influence strain rate, die chilling, etc. which in turn influence the load and energy requirement have to be considered. 71 M l-100 ton Mechanical M2-100 ton Hydraulic M3- 500 ton Hydraulic coet 6 9000/day = $1.00 #stations -1 strokes/min- 30 #5tations-1 k.0. length - 6" strokes/min-10 //stations-1 k.0. length - 6" strokes/min-12 k.0. length - 8" M5-1000 ton MechanicalM4- 500 ton Mechanical M5-1000 ton MechanicalM4- cost @ 9000/day M6-1000 ton cold header (1“) = $0.9 k.0. length - 9“ #stations - 3 #stations-4 strokes/min- 20 strokes/min- 24 »st@ 9000/day k.o. length - 8" k.o. length - 6" = $0.8 Figure 27. Range of equipment available to form the example part Consider the next operation of upset of the head from 1" to 1.8" diameter. The strain after this operation is 1.386. The average flow stress for the material for this strain is 125 ksi, considering cold forming. The corresponding tonnage is 318 tons. At this point we once again generate the requirements for the equipment. However, there is one difference. We also consider the possibility of including the previous forming operation Into the machines available as long as there has been no intermediate operation needed between the previous and current forming operation. There is no intermediate operation required between the cold extrude and cold upset operations and therefore all the equipment that can be used to form these two operations separately as well as those that can 72 perform the two operations in the same machine are considered. Of the candidate machines, the machine that meets requirement and is cheapest is chosen. In the case of warm or hot upset, after cold extrude, the machine has to be selected for individual operations as the temperature range of forming cannot be, in general, changed in the same machine. However, two or more warm operations can be performed on the same machine. The constraint is that for the selection of a machine for more than one operation the temperature range of forming has to be the same (cold, warm or hot). In warm and hot forming, billet heating operations may be performed at the machine itself, i.e. the machine comes with a heating arrangement. This is noted in further cost-evaluation. In a similar manner, shearing operations are performed in some machines before forming in all the forming ranges of cold, warm and hot. If a machine does not provide for this additional intermediate operations such as sawing, shearing and heating have to be selected. 4.2.3 Cost-effective process selection Having described the solution procedure for the evaluation of operations and equipment selection, the procedure for determining cost-effectiveness is described in this section. The cost-effectiveness is determined in two parts; cheapest equipment, and cheapest process. For the problem under consideration, let us lay out the options and determine the method to evaluate cost-effectiveness. As the tolerances specified on the stem as well as the bowl of the part are below 0.02", hot forging operations are not feasible. Therefore we are left with cold and warm combinations only, which are 2^, or 8. 73 The calculations of loads, strains and feasible equipment for the variations of cold and warm operations are shown in figure 28. Given, these conditions the operations and equipment required for the eight different scenarios are shown in figure 29. The costs for the individual operations and equipment determined by the DCM method are then applied to the eight different process sequences and equipment selections. From figure 30 it can be seen that the warm forming process (8) performed on machine 4 is the cost-effective process to meet requirement of quantity, shape and tolerances. The above discussion represents a specific case and it must be understood that during evaluation there are several alternatives and the solution is not algorithmic. The search technique used could be further enhanced in its efficiency. Consider the case where the goal state has been reached following some path in the search space (process 1) and the cost is '$3.7T. Then, if in the process of evaluating another path (process 3) the cost upto that state (upto upset) is greater than '3.7T then that path may be deleted from further search as it will not lead to a cheaper solution. This is an efficient way of pruning the search space. 4.3 Organization of knowledge structure In order to perform the above solution procedure, the knowledge and data have to be captured in an appropriate manner. Figure 31 shows the structure of the knowledge and databases required for the discriminating cost model to perform the search and arrive at the cost-effective process and equipment selection. The knowledge sources needed may be categorized as follows: • Process sequences • Process Operations 74 Equipment Materials Costs 1.6 1.8 1.8 1C 2C Flow stress -1 0 0 ksi Flow stress-1 2 5 ksi Flow stress -1 3 2 ksi Strain - 0.21 Strain-1.38 Strain - 2.31 Load - 78 tons Load - 318 tons Load - 204 tons Feasible presses Feasible presses Feasible presses -m1,m2,m3,m4,m5,m6 -m3,m4,m5,m6 -m3,m4,m5,m6 Op. Combo presses low cost press - combo m4 low cost press - ml -m4,m5,mB low cost press - combo m6 1^ Flow stress - 35 ksi Flow stress - 35 ksi Flow stress-4 0 ksi Load - 27 tons Load - 89 tons Load - 62 tons Feasible presses Feasible presses Feasible presses -mlm2,m3,m4,m5 -m1,m2,m3,m4,m5 -m1,m2,m3,m4,m5 Op. Combo presses Op. Combo presses low cost press - m l -m4,m5,m3 -m4,m5 low cost press - combo m4 low cost press - combo m4 Figure 28. Calculations for forming sequence options for example part 75 ALTERNATE SEQUENCES OF OPERATIONS " le g e n d S- Shear 1. CFE->CU->CBE A- Anneal PC- Phoscoat 2. CFE->CU->WBE FE- forward extrude 3. CFE->WU->CBE GC- Graphite coat H- induction heat 4. CFE->WU->WBE BE- back extrude 5. WFE->CU->CBE U - upset C- cold forming 6. WFE->CU->WBE W- warm forming 7. WFE->WU->CBE H- hot forming M- Machine 8. WFE->WU->WBE VJ-Transport ______ PCM4T cMQi M6 PCU4T cMar M6 PCU4T cMlJ Ml wM4i M4 cM3j MS PCU4T cM1_fM1 l/G C U H wMtBwMM M4 EwMXf M1 1(PCX 2T XM4)4JcMi ( H XG Cy(^Ty0vi% (^ 7. (S_ G 9 ^ EwMM M4 X J w M X P C V if '^ ^ 8 . CS "G0Y4f" :wMM M4 U) wI\McM/ Figure 29. Evaluation of alternate sequences for example part 76 Some cost data to evaluate the processing options per part Machine Cpfvation* Shear >$0.1 Pc lie Rft Phoscoat- $0.4 Anneal-$0.45 M l 0.1 0.08 0.12 Heating-$0.30 M2 0.09 0.08 0.10 Graphite coat - $0.25 Transport-$0.05 M3 0.12 0.10 0.14 M4 0.11 0.10 0.12 M5 0.11 0.10 0.12 MS 0.1 0.09 0.11 Machine___ ------^ leralKHB^ c EW Uw___ 3w Ph llh Rh 1.18 0 22 M l 0.2 1 M l 0.3 0.38 ).32 M2 0.19 3.18 (.20 M2 0.29 0.28 0.30 M3 0.22 3.20 C.24 M3 0.32 0.30 0.34 M4 0.21 3.20 ( .22 M4 0.31 0.30 0.32 M5 0.21 3.20 ( .22 M5 0.31 0.30 0.32 PROCESS 1 : $3.71 PROCESS 2 ; $3.46 PROCESS 3 : $4.97 PROCESS 4 : $3.32 PROCESS 5 : $4.52 PROCESS 6 : $5.17 PROCESS 7 : $4.03 PROCESS 8 : $2.38 Figure 30. Cost evaluation of different processes for example part 77 EQUIPMENT MATERIALS COSTS PROCESS SEQUENCE LUBRICATION PROCESS DISCRIMINATING OPERATIONS COST MODEL (DCM) HEAT TREAT - minimize cost 3LUG PREPARATION VIATERIAL HANDLING SEARCH TECHNIQUE cost-effective process and equipment CONCURRENT ENGINEERING SYSTEM MODEL FOR FORMING Figure 31. Knowledge and data structure for the discriminating cost model 4.3.1 Operations Knowledge Process operations may further be categorized as forming, part lubrication, heat treat, slug preparation, material handling, and heating. The following sections describe the knowledge required In the above areas to enable cost-effective process selection as deschbed in the earlier section. 78 Forming Operations The feasibility of a forming operation is determined by constraints. The key forming operations being considered in this research are open forward extrusion, closed forward extrusion, backward extrusion, pierce upset (dimple) and simple upset. Each of the above operations are characterized by typical feasibility constraints. For example, in a open forward extrusion the constraining phenomenon are fracture, upset before extrude, buckling, and flash. These constraints vary depending on the temperature range of the forming operation. The knowledge about the operations can be categorized as follows: • Geometry transformation due to a given operation • Methods to calculate strain, strain rate, flow stress, loads, and pressures for a given operation • Operation feasibility constraints • Fracture and failure preventing criterion during a given operation • Remedies and responses when operation feasibility is violated (failure handling mechanisms) These are detailed for the five operations considered in this research in Appendix C. This knowledge base of operations can be similarly extended further to include other forming operations. As part of the solution procedure an effort is made to remedy failure to meet operation constraints or provide suggestions. Therefore additional knowledge of 'failure handling mechanisms' have to be determined and captured. At the same time, the limitations of these mechanisms have to be determined along with a mechanism to trigger these when an operation is infeasible. 79 Lubrication Different operations at different temperature ranges use different pre- lubrication mechanisms on the part. This lubrication selection is primarily used for costing purposes in this research. So, we need to determine the knowledge of typical lubrication used in different forming operations based on temperature and pressure and the corresponding friction factors. For example, in cold extrusion, the typical lubricant application made on the part is a phoscoat providing a friction factor of 0.08. In warm extrusions of steel a graphite coat is used and may have a friction factor of 0.25 at 1300 degrees F. Several sources are available in literature [Altan et al., 1983] to provide information on this topic. A database of typical lubrication chosen for a given forming operation, temperature and pressures, and corresponding friction factors is created. Heat Treatment In forming processes, heat treatment is performed on the workpiece to improve its formability, refine grain size and microstructure, and reduce flow stress. The typical heat treatment procedures are annealing in cold forming, normalizing in warm and hot forming and tempering for a stress relieve. Annealing in cold forming improves formability of the material by removing the effect of cold working. The knowledge required in the heat treatment area is to determine the type of treatment to be made to the part, and related aspects of 'how* and 'when'. Also would require a function or table that represents the reduction in hardness, effect on formability with respect to the operation performed, so that the state of the material after a heat treatment process can be determined based on the condition of the material before heat treatment. There also needs to be a link established between the failure handling mechanisms 80 that elicit a heat treatment operation. For example, an annealing operation in organization 'A' performed on material A IS I8620 with initial hardness of RB 93 is reduced to a hardness of RB 86 providing a formability of a strain limit in upset of 1.3. When an upset operation fails due to the strain exceeding the formability limit, a failure handling mechanism to anneal the material is triggered. Such knowledge is captured. Heating Heating is required in warm and hot forming operations. The knowledge required is in terms of the different types of heating equipment and what are the parts typically well suited for a certain type of heating source. Some of the details have been covered in an earlier chapter. A default selection of heating equipment for a given operation may be provided or a least cost selection of heating equipment made available. Slug preparation Slug preparation operations are typically shearing (cold, warm and hot), and sawing. A table of the accuracies and tolerances that can be held by the above slug preparation methods for a given material and geometry (diameter and length) would assist in determining the selection of a particular method for a given forming operation. For example, cold forming may require that the slugs be within +/-0.005", and a bad shear end may not be acceptable. Therefore, the slug may have to be cold sheared versus warm or hot. If the tolerances on the roundness and ends is tight, it might require sawn billets. A knowledge base that matches requirement of the slug for a given forming operation to the type of slug preparation method is developed. 81 Material Handling A database of material handling methods and corresponding class of parts needs to be established. In this research, material handling is limited to the transportation of material from one operation to another by fork lift trucks. Other material handling operations that may be included are automation of feeding and extracting parts from a given operation. Materials The flow stress data of different materials as a function of temperature, strain and strain rate will be required and is available in literature [Altan et al., 1983] and from data determined by industry. Also, the formability limits and fracture causing phenomenon have to be determined to provide information for operation feasibility evaluation. A material database that relates the composition of a steel with its flow stress data and formability data is created (table 9). Costs A knowledge base of the cost drivers of process operations, materials and equipment in conjunction with a database of cost values would serve as tools to capture the costs required for economic evaluation of alternate processes and equipment. The knowledge of costs primarily consists of the cost drivers and methods for evaluating these drivers for a given operation, equipment choice, and so on as described in the earlier chapter on DOM. 82 Table 9. Material database table. MSICOMPOSITION HEAT TREATMENT FLOW STRESS DATA SPECIFIC HEAT K r , m n T A Equipment The knowledge of equipment in this research was gathered primarily for forming equipment. The key elements of this knowledge are equipment selection parameters and costs associated with the use of a given equipment. Typical data entities for an equipment database are: 1. Total tonnage capacity 2. Number of die stations 3. Type (mechanical, hydraulic, screw, etc.) 4. Number of points of support of ram 5. Number of strokes/minute 6. Stroke length 7. Knock-out stroke 8. Knock-out tonnage 9. Workpiece heating available at equipment ? 10. Workpiece shearing available at equipment (cold, warm or hot)? 11. Maximum die size in station? 12. Total energy available 13. Automated feed and transfer or not. 83 13. Automated feed and transfer or not. 14. Efficiency In addition to the above database, there needs to be a knowledge base that determines the equipment most suited for a certain type of forming operation. Some representations used in the study of [Ishii, et al., 1989] are shown in figure 11. Other equipment related knowledge are cost data associated with a certain operation performed on a given equipment. Such data is captured as tables or functions. 4.3.2 Evaluation procedures and methods In order to perform the operation feasibility evaluation, certain parameters have to be determined such as: 1. Load for operation 2. Strain upto current state 3. Tolerance 4. Surface finish 5. Punch pressures 6. Flow stress 7. Strain rate 8. length to diameter ratios 9. Reduction ratios, etc.. In order to determine loads for a forming operation, the strain and strain rate due to the operation is determined and the current state of strain and strain rate in the given material calculated. Based on the strain, strain rate and 84 temperature, the average flow stress is calculated. The load Is then a function of the flow stress and friction conditions. The load estimation methods have been detailed in [Raghupathi, 1989] and the methods used for some operations is included in appendix C. In addition, a table of tolerances and surface finishes obtained by different forming operations based on the values of incoming material is needed and is available in literature [Bralla, 1986]. Average forming pressures on the punch may also be calculated to check for limits on tooling, etc. CHAPTER V COST-EFFECTIVE PROCESS AND EQUIPMENT SELECTION SYSTEM (CEPESS) The developed methodology and cost model can be more effectively used if incorporated into a computer system owing to the computational intensity of obtaining the solution of the large combinatorially expanding problem space. Therefore, a prototype system, Cost-Effective Process and Equipment Selection System (CEPESS) was developed. The design and implementation of the system is described in this chapter. Also, example sessions are shown to verify the capabilities of the system. 5.1 Objectives The objectives were as follows: • Develop a prototype computer system based on the 'discriminating cost model' and incorporating the search method of solving the complex problem domain. • Define a structure for the system, and integrate knowledge and function for a specific set of operations, materials and equipment • Apply the system to a process selection and an equipment selection scenario and verify the methodology and the system. 85 8 6 5.2 System description In line with the objectives described, the computer system was built with a focus on a specific subset of the problem domain which includes the following: Forming operations: Open fonvard extrude, Closed forward extrude. Backward extrude. Open upset. Dimple or Pierce Upset operation. Temperatures: Cold, warm, and hot Materials: Steels - AISI 8620 and AIS11050 Lubrication: Phoscoating, Graphite coating, sprays at forming equipment Heat treatment: Annealing, Normalizing Heating: Induction heating Slug preparation: Shearing, Sawing (specified by user) Material Handling: Transport by trucks Costs: Data available as tables and functions Equipment: Mechanical presses. Hydraulic presses. Cold headers Figure 32 depicts an overview of the proposed system design. The inputs to the computer program are: • number of parts to be made • geometry of the workpiece in its progression from billet to part (forming sequence) is represented by zones which represent characteristic features of the different operations. • The tolerances required on these zones in the final part • The surface finishes required on these zones in the final part 87 • The material of the part (this research was limited to steels, but it no means implies that this model cannot be used for other materials) . dimensions of the initial billet and form (sheared or sawn) These inputs are then processed by the computer system which posesses the knowledge and function as shown in figure 32. The knowledge structure required for the system was described in the last chapter. The knowledge has been captured in the form of rules, databases and analytical methods.. The databases in the system are Forming Machines, Materials, Operation Limits, and Costs. Rules, calculations and knowledge of operations are captured as an object class. For example, the operations forward extrusion, backward extrusion and upset belong as objects of the 'forming class'. The operations forward extrusion and upset can be further classified as 'open' and 'closed'. The system function is provided by generating the search space based on the given input and evaluating each node until the desired goal state of the cost- effective choice of equipment and process is made. Figure 33 shows some of the typical evaluation that occurs at a given node during search. As a first step, the tolerances and suface finishes of the different zones in the final part are reviewed, and the search space is pruned of all the nodes that cannot provide these requirements. This is accomplished by determining the operations that provide the final shape of the zone of a part and verifying if it has the capability to meet part tolerance and surface requirement. For example, if the requirement on the stem of a part is a tolerance of +/-0.010", and the zone 'stem' is formed by the operation forward extrude with no subsequent operation working on this zone, then all hot forward extrusions can be deleted as they cannot meet requirement. 8 8 At a given node, the data representing the current state of search is reviewed (pre-operation data). At the node, critical parameters for the operation are calculated. These parameters are then checked against the constraints for feasibility of the operation at the node. If they satisfy the constraints, the operation is performed. If not, then the failure handling mechanisms are activated and appropriate action or suggestion provided. In the process of meeting constraints, additional forming and non-forming operations are selected. Based on the parameters of the operation, all equipment that can feasibly perform the operation are identified. If the node happens to be a non-iniital level node, then another set of equipment that can perform all the operations in the process upto the current node are identified (combo selection). The equipment selections are costed and the cheapest selection made. Once the operation is performed the current state of the process data is updated in terms of the surface finish and tolerances of all zones, parameters of costs, and equipment selection data. The calculations and checks are illustrated for fonvard extrude, backward extrude and upset in appendix C. The solution method as described in figure 33 is executed until the goal state is reached. The output of the system is the following: • Cost-effective process sequence: includes all forming operations, additional forming operations, and intermediate operations • Cost-effective equipment selection: forming equipment and the forming operations performed on them There are provisions that are also provided to produce a list of upto 5 process and equipment selections in the order of their cost-effectiveness. This feature enables management to make an appropriate selection which may be guided by other reasons than strictly cost. 89 5.3 System Implementation The system implementation was determined based on the needs of the organization. There are several computer systems (hardware and software) that can be utilized for the build of the computer system. However, each organization has committed itself to a specific environment of hardware and software for the sake of consistency, economics, maintenance and so on. Therefore the prototype system was built using the tools available at the organization where this study was conducted. The knowledge-based shell used to capture the data and knowledge was the I CAD system. The user-interfaces were also implemented on the ICAD system. There are other design and tool development systems that have been built in the organization in ICAD which encouraged the use of ICAD for interfacing with these systems at a later stage. 5.4 Verification of the capabilities of the system The system implementation was tested out on the example part and forming sequence shown in figure 34. The same equipment scenario as shown In figure 27 was used. Seven case studies are presented that describe the system response to different changes in input parameters, equipment and cost scenarios, verifying the capabilities and function of the system. A specific input was modified and the system response evaluated against expected results to verify the function of the system built. 90 Figure 35 shows a sample screen of the system. The system screen shows the forming sequence plan in the left upper box; the plans generated by the system in upper right box; the process parameters evaluated, checked and plan assembled in the lower left box; and the input for the forward-open-extrude operation in the sequence in the lower right box. The plans shown do not include the variations of machine selection as well as the selection of intermediate operations such as annealing, phoscoating, transport, etc. This is because the figure would get very crowded and difficult to fit in a page. However, the evaluations are performed but are hidden from display. In order to determine the cause for failure of operations in the plans, information is obtained by simply clicking on the "operation infeasible" statement in the generated plans. CASE STUDY 1 : Cost-effective process for Input sequence in figure 34. The requirements of the part in figure 34 were input as shown in figure 36. The diameter and length tolerances for the stem and cup were specified as +/- 0.01" which allow cold and warm form operations. However, hot forging operations are not feasible as they do not meet the tolerance requirements. Out of the various combinations possible, the best plan chosen is shown as the cost- effective solution in figure 36. The plan consists of shearing; transport and graphite coat; transport and heat; and transport to machine 'M4' and perform operations 10, 20 and 30 which are forward open-extrude warm, simple upset warm and backward extrude warm respectively. The system also clearly indicates that hot operations are infeasible as shown in figure 36. If the user clicks on the infeasible operations in the 'Select-Plans' output, the system responds with the reason as "tolerances and surface finish requirements not met". 91 The cost-effective process determined is shown in figure 36 with a cost of $1.23. CASE STUDY 2: Impact of increased open forward extrusion ratio A single parameter was changed from the inputs in the last case study to verify system response. The initial billet diameter was changed from 1" to 1.25". This change increases the reduction from 19% to 48% and therefore open forward extrusion is not possible. The system recognizes this condition and upon failure to perform the open extrusion requested by the user, triggers the 'failure handling mechanism' associated with this condition. The solution implemented in the failure handling mechanism for open forward extrude is to split the extrusion into two stages and the reductions in each of the split extrusions iteratively determined until both extrusions meet the criterion for feasible open forward extrusion. Figure 37 shows the split of the extrusion into two indicated by operations 10 and 11. Once again the hot operations are not feasible due to the tolerance and surface finish requirements input. CASE STUDY 3: Buckling constraints verification In this study, the initial input of case 1 was modified. Here, the billet length was increased from 2" to 2.5". The objective was to test the system response to buckling constraints. The constraints built into the system were that buckling in cold forming occurs if length to diameter ratio was greater than 2.5, buckling in warm forming occurs if the above ratio was greater than 2.3 and in hot forming if the ratio is greater than 2. As expected, the system considered only the cold form operation as the length to diameter ratio for this case study was 2.5. The more economical warm 92 forming operations recommended by the system in case 1 and case 2 were discarded and the cold forming sequence of operations proved to be the only cost-effective choice that met the requirements. The part cost, however, increased from $1.23 to $1.80 due to the addition of phoscoating and annealing operations required for cold forming. CASE STUDY 4: Effect of tight tolerance specifications In this study, the extruded diameter tolerance was reduced to 0.002". This would impose upon the system that only cold extrusions are feasible to meet the tolerance requirement. Accordingly, the system responded with the cold forming sequence as the cost-effective choice that met requirement with a part cost of $1.80 (figure 39) Under 'select-plans' in figure 39, the machines considered are also displayed. This is shown to indicate that machine selection is performed simultaneously with operation selection. CASE STUDY 5: Investigation of adding machining after forming When considering cost-effectiveness of forming processes one also has to consider subsequent machining operations. The system has been built with the forging supplier in mind, i.e., given a forge part print, how does the supplier of forgings determine the cost-effective process. However, the supplier could interact with the customer to investigate some forming-machining interactions in cost-effectiveness. In order to illustrate this, case study 5 was performed. Considering the part to be made in figure 34, if the supplier were to investigate turning the stem diameter as he has found a cheap machining source, the following procedure could be utilized to address this issue. The 93 tolerances and surface finish specified on the stem are opened up so that the previously blocked out hot forming processes are also now considered. As shown in figure 40, the warm form sequence is still the cost-effective option as the tolerances on the bowl do not allow hot forming for the backward extrusion. Now, if we added the turning cost (assumed at $0.01/part) the net process cost would be higher ($1.23 + $0.01 ). However, if the tolerances and surface finish requirements are relaxed on the bowl too and the hot forming operations turn out to be cheaper then the cost for turning may be added and the net process cost computed and cost-effectiveness evaluated. It must however, be noted that the cost of heating to hot forming temperatures is higher than for warm forming and therefore, warm forming may yet be the cost-effective option. CASE STUDY 6: Investigation of adding equipment In the past case studies the warm form sequence has been the lowest cost at $1.23. It may also be noted that the machine selected for the warm form operations is M4, which is a 500 ton mechanical press. In this case study, we evaluate the option of utilizing another piece of equipment that has become available. For example, if a warm former were available with a machine cost of $0.3/part for the given production volume as opposed to M4, whose cost for the same quantity is $0.37/part, the cost-effective scenario change due to the addition of equipment is evaluated. In this case, the cheaper warm former (M7) is appropriately chosen by the system for the warm form sequence and part cost reduces to $1.16 from $1.23. 94 CASE STUDY 7: Investigation of change in material In this case study, the effect of changing the material was investigated. The material specified for the part was changed from AISI8620 to AISI1050. This changes the flow stress data and the maximum strain to failure (formability). As this change may not significantly affect the selection in warm and hot forming, as strain to failure is not a key issue, the tolerances were tightened to force evaluation of cold forming operations. As expected, the strain limit was exceeded after extrusion and upset and the system chose warm forming subsequent to cold extrusion as the cost-effective choice. This is because the lower formability of the higher carbon steel forces annealing more times in cold forming all the operations. This leads to additional costs for annealing, phoscoating and machine change after each anneal. The extrusion had to be formed cold on cold header M6 (cheapest cold forming equipment in our database), due to the tolerance requirement on the stem. The upset and backward extrude are performed warm on the same machine M4 subsequently as the cost-effective choice. As there is a combination of cold and warm forming, the part cost increases to $1.99. This case study shows that the cost-effective choice is considered at every step in the sequence and the appropriate intermediate operations and equipment selected. 95 INPUTS QUANTITY MATERIAL TOLERANCE BILLET SIZE SURFACE FINISH PART SHAPE FORMING SEQUENCE & SENSlTIVm TOGGLE CEPESS COST-EFFECnVE PROCESS SELECTION SYSTEM KNOWLEDGE FUNCTION FORMING EQUIPMENT FORMING OPERATION SELECTION (COLD/WARM/HOT) FORMING OPERATIONS NON-FORMING OPERATION SELECTION PROCESS SEQUENCES HEAT-TREAT OPERATIONS OPERATION FEASIBILITY EVALUATION MATERIALS EQUIPMENT SELECTION HEATING OPERATIONS OPERATION EQUIPMENT CONSTRAINTS COATING OPERATIONS CHECK SLUG PREPARATION OPERATIONS PART REQUIREMENT EVALUATION COSTS COST EFFECTIVENESS EVALUATION MATERIAL HANDLING OUTPUT COST EFFECTIVE SEQUENCE OF OPERATIONS COST EFFECTIVE EQUIPMENT SELECTION Figure 32. Overview of CE-PESS system structure 96 OPERATION NAME: FORWARD OPEN EXTRUSION INPUT - PRE-OPERATION DATA: - INITIAL RADIUS AND LENGTH, DIE ANGLES IF KNOWN - MATERIAL CONDITION : SURFACE FINISH, TOLERANCES, STRAINS, DAMAGE, HARDNESS, ETC. - TOLERANCES HELD ON THESE RADII AND LENGTHS - REQUIREMENTS FROM THE OPERATION: - SURFACE FINISH, TOLERANCES, HARDNESS (FUNCTION OF STRAIN), ETC. - FINAL RADIUS AND LENGTH (SHAPE) OPERATION KNOWLEDGE-BASE - OPERATING PARAMETERS (CALCULATED FROM INPUT DATA): - TONNAGE - STRAINS AND DAMAGE - DIE ANGLES IF NOT SPECIFIED - OPERATION CONSTRAINTS: - FRACTURE CONSTRAINT: » FUNCTION OF REDUCTION RATIO, DIE ANGLE, MATERIAL IN COLD FORMING ONLY » REMEDY: INSERT NON-FORMING OPERATION, ANNEALING PRIOR TO THIS OPERATION - UPSET CONSTRAINT: » FUNCTION OF EXTRUSION RATIO, MATERIAL, DIE ANGLE » REMEDY: ADD AN EXTRUDE OPERATION AND ESTABUSH REQUIRED REDUCTION RATIOS - BUCKING CONSTRAINT: » FUNCTION OF LENGTH TO DIAMETER RATIO » REMEDY: CHANGE TO A CLOSED DIE OPERATION - FLASH CONSTRAINT: » FUNCTION OF TEMPERATURE, FORMING PRESSURE, ETC. » REMEDY: REDUCE EXTRUSION RATIO BY ADDING ANOTHER EXTRUSION OPERATION RESULTS OF THE OPERATION » ADDITIONAL OPERATION REQUIRED IDENTIFIED » SURFACE FINISH, TOLERANCES, STRAINS, DAMAGE, ETC. » TRANSFER PARAMETERS REQUIRED FOR COSTING » TRANSFER PARAMETERS TO EVALUATE ALL POSSIBLE EQUIPMENT USABLE Figure 33. Evaluation of node in state space The scenarios shown here represent only a fraction of the capabilities of this tool. Given that the cost data input reflect reality, the output of the system would be highly reliable. The system build has more complex features built into 97 it. It should be noted that a lot of detailed programming and implementation was required to be able to consider every possible alternative process and equipment. For example, in equipment evaluation, one has to consider not only performing one operation in a given equipment but also look at the possibility of accomodating two or more operations in the given equipment as long as there are sufficient stations, tonnage capacity, and knock-out length available. The above description has been made to reflect the complexity of the system implementation to facilitate all such detailed evaluations. The above case studies depict the expected outcomes of the changes made thus validating the system. Three additional cases are included in Appendix D which depict other cost sensitive discriminating characteristics of DCM. 1.0 25 1.5 0.25 a U_ 7T«" 2.0 1.5 0.S25 Material: 0.9 AISI 8620 Open Forward Extrusion Head Upset Back Extrude Bowl Figure 34. Example sequence used for system verification 98 I # .i V:' ;'': i iy ' : Y 'Op2Q : Si rÿ! e-dpset -iim; ■ ■ 4'4':y:%4J ;i it' . ' i ^<^3î:Btda)ard-Cm-£xt^^Kfe-(^at Is lnfeœ iblfc ■■i'; 4'4'f'?'f|î2Œ;5ijçil^^ ' ' .'ininir-*'-- V u 4 4 1 Id ;,EDf H i * t f lile -fiir R ; N r jAdd befot'e Add a f t e r iF a n B ii CoarEst'rs !;',{l 4 '';'^4^(îâ:8:Sitçle4jfSetr{ql£t4'" ■'4^ v i t 4 ■ ^itj^O plïB ockuar^C tîS tf^ itftrOTd'ClDsédi'&trude^ ,;{l 4 A t :/v'^!^M:&Kldm rd-CÿAtri^ Oferntiœi Itjjg: ;*r i ; \ 'Op30:Bndujord-cai-Extrimk-Hiil l i infeasible 4|444'4r^QiS j:Sii|il^üps^'!ifflni': ; 4/; r i \ ’^'^'-Oplipncinard-Os-Ei'.trisig-Coid- ', ■ ,,jW tw d Qÿ ùtrude, %'v. i"'' 14'tt 4i 4 A : ' 41 W d :telflwrdtnnr£xtriife 4to^ : i ■ 'i^QiBii^iHJpetrHot Is Infeflîiblé , . Edit Cpsratics» RISI-S620 m m i m c m a iw -m -w m p .Æ im : f.O M .O M 0.0 IH-Ip O.5 mCMOW-P.Mt: IBBBI M lAmimi >>i Hi UtBaMr:sanKîaoskfflîiH5:TOBBîaa;:’cpi^ (|*Cp20:SI»i£-®5EmiO' '{(m gœ iim m Dm m W j. lESS! S B 9 HBI : (QwnKMnHÇifflwai;^ j PreTOpefations: ; iS M n g i't a t : Traispôrtf jS fe w i^ fif e iir te d iWs-cûMimrmmRT 'qp3P:mcBmwi*7m-cmyNiw m oHm E-m e hiu»)i hfBif^'iÿerfltim'SeqiÆncg^tâaterr dC ’■ • ,4- ■ •';>:[,''d4 CndUISECSr SUIBGIQWIEFODATDIG'BUtSFCRI E ü i msPOM ‘ Oçlll:rO(tllIugHMi: dperrterta'Fetitire:^-; " :,; /; : v, ; ;D% (W ;(0Mi:Gm GEm :'#:swu4m i-c«u)1] .([7EffiSICBT;nUD:iEAISrat*(^0:&A(ll^^ nu IQim: perifèdOiœetefr4: : ', .4' 4 pPt mun ('()p2Q:SMI£«P5n-«fflA ((PE«- — ^ c s ; pliil.'sâi; '; : : ' ‘■- •■.ïCaaa.üap Figure 35. Example system screen showing some case study 1 results 99 Input: Cost-effective solution Num ber of parts: 3000/day Length of billet: 2" ::PRE;OPS:;:SHBRDIG:'# Diam eter of billet: 1" ::OP::a!'OplO:fORIIARb-OPEf(-E!{IRlIDFii\f-:"" Diameter tolerance: 0.01” Length tolerance: 0.01” Surface finish: 200 micron System Response: All hot operations fail due to tolerances not met Process plans generated: ï::OP:ÿKOp30-:BACKilARDT&tKXÎRUbtliARi^ EEr-PEAlE ^ - O p 10 : Foroord'-Open'Extriide.'^old. I r--^0p20:Sipiple-ilpseKoid \ . '{\ Op30: BockwardrCon-Extrude-CoId 1 \\ V'Op30:Backuard-Can-Extrude-Harn - \ \ ' 0p30 :BdctaiiardM)atî-Extriide-Hgt Is Infeasible 1 \ ’^OpZBiSinpleHjpset-Hont \ \ ^r--0p30:BQ[kword-GQn=-B(trudE4:old \ ’V^0p3(I‘:Backuar:drCan?-Extrùde-Harn I \ \ >0p304B(!çkward-enn^Extrude-Hot Is Infeasible 1 1 'OpZO:SipipLerUpset-Hatl£ Infeasible I 'OplO:rorward-Oper^S.truderHarrr ' I ^--OpZO :Si[']ple-UpsefrCold I \\ "^r--Op30:Baclai|ard-Caii-Extrude-CdId • \ \ \^Op30:BackwardrCan-Extrude-Harn \ \ ''Op30iBdckwnrd-eonrEX:trude-Hot Is Infeasible . \ 'OpZOïSinpleÿpseHlorn' \ '^^■OpIO'BoEkijaritGnrrrEx.trudE^Cold \ ■ \ \AnQn~» bnrl/iJrtrfL-/'niT.i^ô4:rtf#^ni.t!firm \ Op30:Rickimd-6on=^ 'OpI 0: ForM ord^pen^rud^afe IK InfeasihtE Figure 36. Case study 1 : Selected example sequence 100 Number of parts: 3000/day Cost-effective solution Length of billet: 2 " Diam eter of billet: 1.25" 'Plan Cost = 1.23 Diameter tolerance: 0.01" PRE-OPS: SHEARIIIG TRAHSPORT GRA.PHITE-COATIHG TRAtlSPORT HEAT IRA.tlSPORT Length Tolerance: 0.01" OP: /i)plO:FOR|[ARD-OPEll-EXTRUDE-llARtl\“ Surface finish: 200 micron System Response: Forward extrude cold split into OP:SlrOpZD ::sitlRLBUP5Er4iARll\“:’ : two extrusions due to maximum extrusion ratio for open extmde PRE#^, exceeded 0P:/Ë0p38:mkliARlWl-ËXTRÊBlëll^P Hot forward extrusion, upset TËHÏHEt^%ü#p: and backward extrude are not feasible due to tolerances not met Process plans generated: ECECPPLAllSr ^"~-OplO: Foruard-Open-Extrude-Cold "^-■'Op 11 : Foiiiard-Open-Bitrude-Cold ' r^^-OpZU : SiFiple-Upset-Col d \ ^;--Op30 : Bockword-Ccin-Extrude-Col d i V ' i \ N^Op30:Backuard~Can-Extriide-Wnni 11 \ \ "''0p30 : Backuard-Con-Extrude-Hot Is , Infeasihls 11 \ ^Op20 : SinplerUpsetHlorn I I '^^-'0p30,:Backuard-Can-ExtriiderCold \ \ ''^Op30:Backijard-Can-Extrude-Hnrn ■ I I' I ''■0p30:Bockiiiard-CQii-Extrud&-Hot Is InfeosiblE ' M 'OpZO: Sifiple-Upset-Bot Is Infeasible 'Op i 0 : Forward-Open-BitruderHarn I r^^OpZOiSinpleriJpset-Coid J I l\ V>__ \C'Op30 . A—.'Ift. : Backtmd-CanrExtruderrCold n ■ 'I’-. 2l />_ _ r ± I ■ /\ 1 I I \ \ \'0p30: Bockwird-Ccin-ExtriideHlQri'i I \ \ ^Op3D: BockworcHMBtrtide-Hot Is Infeasible I \ ^Op20:5iFipleHlpse#lw i %--Op30 : Backuord-Can-Extrode-Col d ' I \ '''^Op3d: B a ckw d # n ^# I \ ''Op30iBQ[ktmWdn#truder^ Is Infeasible . : ’■0p20:SinpIerUpSEt-Hotl£. Infeasible - 'OpjOlFori'iord-Open-B'triide-Hot Is Infeasible Figure 37. Case study 2:Billet diameter changed from 1 to 1.25" 101 Input: Cost-effective process Num ber of parts; 3000/day Length of billet: 2.5" Diam eter of billet: 1" j'P ln n C o s t = 1.80 Extruded dia. tolerance:0.05" PRE-OPS: SHEARIIIG TRA.NSPORT PHOS-COATIHG TRAHSPORT Length Tolerance: 0.01" - : OP : \ "Op 10 : FORHARD-OPEH-EXTRUDE-COLD\" Surface finish: 200 micron 'ittA.CHIHE: System Response: : PRE-OPS: Forward open extrude hot and , :0P: \ ”0p2Q:SIl!PLE-UPSET-C0LD\“ warm fail due to buckling limits .iltACHINE; \"tl6i." exceeded : PRE-OPS: TRAHSPORT ANNEALED TRA.NSPORT Hot upset and backward extrude : OP : " Op30 : BAtKliA.RD-tA[|-EXTRUDE-COLD\ " are not feasible due to :HACHINE: tolerances not met Process plans generated: Figure 38. Case study 3; Increase billet length to 2.5" 1 0 2 Input: Cost-effective solution Num ber of parts: 3000/day Length of billet: 2" Finn Cost = 1.80 Diameter of billet: 1" PRE-OPS: SHEARIIIG TRA.HSPORT PHOS-COATIHG TRAHSPORT Extrude Dia. tolerance:0.002" OP : j ” Op I OjFORIlARD-OPEH-EXTRUDEiCQLDi:______Length Tolerance: 0.01" HÂ.CHIHÊ: \"H 6 \“ Surface finish: 200 micron PRE-OPS: System Response: .OP: \ '‘0p20:SIliPLE-UPSET-C0LD\" .. Forward extrude warm and hot, HA.CHIHE: and hot simple upset not PRE-OPS: TRAHSPORT AHHEA.LED TRA.HSPORT possible due to tolerances not OP : \"0p3G : BACKHA.RD-CA.tl-EXTRUDE-COLD\ “ ‘ met HA.CHIHE; \"H 6 \" . Process plans generated SELECT-PLANS...... -OplO:Foruari±-Open-Ext.rutli--r. V\ I l \ Is Infeasible ' ' i 1 \ vtfli I ll % \ '111 Ts Infeasible ■ I I * . •'Op3D : Bnckioard-Cnn-Extriide-Mnri'i . . j ; I I Vk -112 Is Infeasible 1 - TI A ••''I* M I I m \ Ml Is Infeasible : -.I. I T . Wop30:Backi.iard-Cnn-Ex triide-Hot Is Infeasible \ | i -II I . 'iMZ Is Infeasible ^ \ ' ; '.'I -Ml: Is Infeasible I I Op20 : Sinple-Upset-Harn , ... : ' I I T"——OpSU: Bockuard-Can-Exirude-Cold , ; \ \ TC'112 Is -Infeasible \ VM6 ■ \ ill Is Infeasible '0p30 : Bockuard-CanrEx trude-rHar n 4ft VOM2ViiG Is Infeasible Vhy : 'Ml Is Infeasible %,'iOp30:Bockuard-Cnn-Exiriide-Uot Is Infeasible t e lopZOrSinple-LlpsetrHoir Is Infeasible I m5 ' ■■ Ii P (nfr ■ I 'Ml loplOrForward—Open"-Extriirle-Mur I'» r< ihie lop 10 rForward-Opert-"Extrude-Ho t Is , ,lrif easibI e Figure 39. Case study 4: Decrease extruded diameter tolerance to 0.002" 103 Input; Cost-effective solution Number of parts: 3000/day Length of billet: 2" Plnn Cost = 1.23 Diam eter of billet: 1" PR|H)iPS::' SHâRIHG: TRWisPORft TRAHSpORL iHEftf TRAHSPORT OP! ÿ Op10 : F O R i # :0PB |:EX TR æ Ë -ttW tT ^ J.»: t Diameter tolerance: 0.09" WA:\!("II4\'-: J:' Length Tolerance: 0.09" PRE^OPS:: Surface finish: lOOOmicron OPiTBOpZOiSIMPLETUPSil^imtr:::.::'^ System Response Hot upset and backward extrude not feasible due to tolerances ■ÛP:-\''0p3û:BACkllÀRD--CAIlÆpRUDEcHARIlV":: -T'T not met TËRIliE::'KTl4V'^ Process plans generated | gELECT-PLAHS kTT—-O p IQ: For iiord-OpenHEx tr i iilp-Cii 1 ri I ' f - ~ ' O p 20:Sii'iple-Upset-Cold l\ '^"':::^Op30 : Bnckuord-Con-Extriide-Cal d l\ •’\ '--\''0p3D:Bnckuard-Can-E}f trude-Mari't- h \ \ ' Op30:Bnckuard-ConrExtrude-Hot Is Infensible; l \ \ 0p20:Sinple-Upset-Unrn h i, \ '^--Op 30:Backiinid-Con-Extriide-Cold- 1 ', ^''O p 3G:Bncki)ard^Can-Extrude-Hnrm : I ' \ '>Op30:.Bnckuard-Can-Ex:lriide-Hot I s I I I f e a s i b l e ■ I \ Op20: S i n p 1e-Upset-Hot I I ' ^ ~ - 0p3D:BackwQrd-Can-Extrude-Cold. '' I \ ' ' ' 0p30:Backtiord-Con-Extriide-Horn 1 V T0p3G:Backunrd-Cnn-Extrade-Hot Is Infensible . I 'OpIOiForwardrOpen-Extriide^Harn , i ' r ' ' ^ 0p2G: S in p l e -U p s e t-C o Id I "^^rz^OpOG : B n c k w o r d -C a n -E x triid e -C o ld -' - - I ' ^Op30 : Bnckuord-ConTExtrude-Horn I \ > 'O p 3G:BncknardTCan-Extriide-Hot Is Infeosibie I \ 'Op20:Sinple-Upset-Harn I \ \x;--:bp 30:Bockwnrd-Can-Extriide-Cold I \ \ ' - 0p3G:Backunrd-Cnn-Extriide-Harn I \ ''P p 3G:Batkiiiard-Can-Extriide-Hot Is In feasible I Op2G:Sinpld-llpset-Hot I ' ^ T ^ 0p3Q : Backword Con-ExtrudeTCol d I ' ' : '0p3G:BackuafdrGanrExtrnde-:Warn \ ' Op3G:Backward^Con-Exti iide-Hot Is, Infensible ' 'Op IG : Faruaf d-O pen-Extf nde-Hot S ~ - - 0p2GrSinpié-UpsétrCüld -Op30 : Backwof d-Con-Extrude-Col d ' . ''•''■'■Op30:Bqckuard-Can-Extrude-Harn- \ \ 'OpOO : Bnckward-Can-Ex trLide-Hot Is In feasible \ "'0020:Sinple-Upset-Harn \ -'^'^OpSGrBdckwnfdrCnii-Extrnde-tpl.d \ ' ■T>pp30;Bdckuard-Çan-Extfnde-Hnrn \ >O p30;Bnckijard--Can-Extrude-Hot Is Infensible; Op2G:Sinple-Upset-Uot • Bdcknard-Cari-Ek trijde-Cni d '''O p 30:Bqckward-Coii-Extrnde-Hnrti '' Op3,G!Bdckwàrd-Cnn-Extriide-Hôt; Is in fen sible Figure 40. Case study 5: Increase extruded length and dia. tolerance to 0.06" and check savings with cost of added turning operation ($0.01/part) 104 Input: Cost-effective solution Number of parts: 5000/day Length of billet: 2" Diam eter of billet:1" "Plan Cost = 1.16 Diameter tolerance: 0.01" : PRE-OPS: SHEARING TRAIISPORF GRAPHITE-COATING TRANSPORT HEA.T Length Tolerance: 0.01" : OP : '/O p 10 : FORIIARD-OPEH-EXTRUDE-HARtl\ " Surface finish: 200 micron illACHIlE: System Response: Hot operations are not feasible :0P: '<"Op20:SIHPLE-UPSEr-ilARli\" due to tolerances not met ;NACHI|iE(0l7^^//^::f'g::/ :0P: \"Op30:BACKllARD-CA,N-EXTRUDE-HA,RH\" itiA.CHIlE; \" ti7 \" - , Figure 41. Case study 6:Add 1000 ton warm former with machine cost of $0.3/part Input: Cost-effective solution Number of parts: 3000/day Length of billet: 2" Diam eter of billet: 1" “Plnn'Cost'= 1.99 ...... Extrude Dia. tolerance:0.002" : PRE-OPS: SHEA.RING 'TRANSPORT PHOS-COATIHG TRANSPORT Length Tolerance:0.01" Surface finish: 200 micron : OP : ■ \ " Opl 0 : F0RNARD-0PE1I-EXTRUDE-C0LD\ " ■ System Response: fitlA.CHINE: \"N 6 \" Forward extrude and simple upset : PRE-OPS: GRAPHITE-COATING TRANSPORT HEAT TRANSPORT hot not feasible as tolerances not met :0P: :\''Op20:SIllPLE-UPSEr-NARI1\" ' ;:liA.CHIlEl \ ’’H4\" !:PRE-OPS: . , ' : OP : S ” Op3Q : BACK1IARD-CAN-EXTRUDE-NARH\ " Figure 42. Case study 7: Change material from AISl 8620 to AIS11050 CHAPTER VI FORMABILITY LIMITS EVALUATION EXPERIMENT 6.1 Objective In the process of establishing feasibility of a given or chosen forming operation, the formability limits of the material needs to be determined. It is the objective to determine a simple suitable method of determining formability limits in upset operations. It should be noted here that a quick estimate of the formability limit during a given forming operation is desired, and it is not the goal to study material behavior under all conditions of stress, strain etc. 6.2 Typical failures in forming operations of an 'outer race* In the part family chosen for study, the outer race, the set of forming operations and common failures in these operations observed in practice were determined. Next, the necessary criteria and parameters required to prevent such defects need to be gathered or determined. Some of the typical defects in cold forming processes are shown in figure 43. In the current cold forming process of the outer race, the operations are forward extrude, upset, dimple, backward extrude and draw wipe (figure 17). 105 106 In forward extrusion, defects primarily occur in the cold extrusion process. Chevron cracks are typical internal cracks, observed in the forward rod extrusion (figure 43e). Tensile stresses at the center of the workpeice, in the axial direction, due to inhomogeneous deformation across the cross section causes the chevron cracks. Another type of internal defect is observed during simultaneous rod extrusion in opposite directions (figure 43f). The metal flow in opposite directions, generates tensile stresses at the separation point of the metal flow, where ductile fracture initiates. Surface cracks are also observed in forward rod extrusion under poor lubrication conditions between the die and workpiece (figure 43g). Chevrons are avoided by determining the right extrusion die angle for a given reduction ratio for a given material and avoiding very light reductions. Figure 44 shows the criteria to be used to prevent such failures. Surface cracks may be avoided by using appropriate lubrication. However, some limitations occur when processes are laid out to extrude on previously extruded material which reduces the amount of lubrication available on the workpiece for the subsequent extrusion. There are empirical guidelines available in industries to prevent such cracks by selecting appropriate reductions and number of extrusions over previously extruded lengths. In the upset operations, the primary defects are surface tensile cracks in cold forming because of significant tensile hoop stresses generated during deformation and shear banding in hot forging of some thermally sensitive materials. Internal cracks are also observed in the heading process (figure 43c). These internal cracks, normally microcracks, are caused by severe deformation at the center of the billet, where separation of material flow occurs. Catastrophic separation of the workpiece is aso reported in the heading process where both 107 ends are restricted (figure 43d). Residual stresses generated by the severe deformation may act as a driving force for the catastrophic rupture. Therefore, it is necessary to know the amount of deformation that the given material can be subjected to without causing cracks in order to design a feasible cold upset operation or suggest the requirement of an intermediate operation, such as annealing for steel, to reduce the amount of prior strain-hardening. Shear banding studies have been performed extensively in literature [Kuhn, 1986] and [Semiatin, 1990]. Defects in the dimple operation are typically laps, which are controlled by the choice of the appropriate dimple angles and depth of dimple. Other defects in the dimple (pierce upsetting) are cracks due to high strains from tool contact on surface of part as shown in figure 43j. Cracks in the radial direction are also reported in the pierce upsetting (dimple) process as shown during a pierce upset test in figure 45. These cracks are dependent on the height reduction ratio and the thickness of the wall sections (figure 46). Pierce upset tests have been described in Kim, [1994]. In the cold dimple operation, the formability limit is controlled by the amount of cold work before cracking. In warm and hot forging, the issue of cracks in the material is absent. Circumferential cracks occur in the cold backward extrusion operations. Maximum work hardening of metal limits the amount of backward extrusion. The reduction ratios, wall thickness, and bottom thickness are selection parameters to prevent fracture of the workpiece during backward extrusion. These parameters have been empirically determined and are available in literature. In the draw wipe operation, the typical mode of failure is by tensile 108 CZOCZI ■ ■ (a) Upsetting (b) Heading (c) Heading (d) Heading, both ends restricted m (e) Forward extrusion (f) Simultaneous# (g) Forward extrusion rod extrusion I I rÉ a ü g a i I (h) Single cup (i) Double cup backward extrusion extrusion (j) Pierce upsetting Figure 43. Schematics of typical cracks in cold forgings (internal cracks are identified by shaded regions [Kim, 1994] 109 Safe Zone Non-Slrain-«ardening Max. Friction No Friction Moderate Strain- Hardening g «005 Max. Fnction No Friction Central Bursting High-Strain- Hardenmg 8 = 0 * Max Fnction No Friction 10 20 30 40 50 60 70 80 90 Die Semicone Angle, degrees Figure 44. Criterion for prevention of central bursting or chevrons[A!tan, 1973] 1 1 0 I I I I I 1 M 1 I 1 M ' I ‘.a) Initiai billet (b) Cracks at the (c) Cracks at the inner surface outer surface Figure 45. Cracks observed during a pierce upset test [Kim, 1994] Max. Min. Average # o f Standara Testing material R%* R%* R% specimens dev. (Gn) AISI1045 as-annealed 58.5 55.6 56.8 6 0.9 A IS I1045 as-received 53.2 50.9 52.5 4 0.9 R%=(H-Hf)/H X 100; H: initial specimen height, Hp bottom thickness of the deformedj specimen. i Figure 46. Criteria for cracking in dimple operations [Kim, 1994] 111 rupture. This occurs in cold, warm and hot forming wipe operations. The reduction provided by the wipe operation, the bottom and wall thicknesses are critical paramters to be controlled to prevent fracture. In the draw wipe operation the wall could be failed by tensile rupture as in a tensile test. From the above discussion it may be seen that the criteria of the typical failures in operations under investigation are fairly well understood. However, one of the critical parameters that is required is the formability limit to which the working of material in the cold condition can be subjected to. The objective here is to show how formability limits of the material required for the evaluation system may be determined by a simple procedure to relate to the phenomenon of surface cracking in upsets. Similar tests may be designed to determine the limits of the material due to the other forming operations. Some of such tests have been discussed in detail elsewhere in literature. 6.3 Simple upset tests 'Upset tests' have been used in several forms in determining the flow stress data for a material and to establish fracture criterion [Kim, 1994, Altan,1983]. In a manufacturing organization, it is difficult and expensive to perform detailed tests and experiments to determine formability limits. Also variations during production can change the characteristics of incoming or processed material. The material's formability has to be evaluated right away without much loss in time or money. So a simple form of the upset test was carried out to determine a useful 'practical' formability limit. Cylindrical specimens of 1" diameter and 1.5" length (25 each) were machined from two steels, AISI 8620 and AISI 8720 from sheared bars of 1.945" 112 and 2.125" respectively. This was done to fit the test specimens in the 600 ton hydraulic press. The diameter of the specimens at the largest reduction (to a height of 0.25") was assumed to be 2.5". Given that the average flow stress of AISI 8620 at room temperature is lOOksi, the corresponding tonnage would be 500 tons. The corresponding height after upset was calculated and the load required for providing such a reduction determined for the above materials. Spacers were then made up of AISI 4320 steel (hardened) of different heights to control the reduction in height on the hydraulic press. Two flat platens were used to upset the specimens. The specimens were reduced to different heights until surface cracks were observed. No lubricant was used. The hardness of the specimens at the beginning and end of the test was measured. The next batch of specimens were also machined as before. However, these were annealed using the recommended annealing process. The annealed specimens were once again checked for hardness and reduced in height. These specimens however did not crack in spite of significant reduction in height. Figure 47 shows the specimens (unannealed and annealed) before and after upset of the two steels. Figure 48 shows the process employed to prepare the specimens. 6.4 Results of the upset tests The specimens of AISI 8620 required higher strains (higher reduction in height) than those made of AISI 8720 before surface cracks were found. These specimens were not annealed and had hardnesses as shown in the table 10. The annealed specimens (of both steels) were reduced significantly (to a height 113 of 0.2" or a strain of 2) and did not display any surface cracks. Therefore there appears to be a correlation of the initial hardness, composition and microstructure of the material to strain before fracture. The occurrence of actual cracks on the outer race parts was used as the datum to correlate the strain at fracture of test specimens to that on the actual parts. The strain that the outer race exhibits cracks is 1.1 (2ln(112.5/65.15)). It should be noted that the upset part is not entirely cylindrical and the strain calculated is the maximum strain at the outside diameter of the part. The material of this particular outer race is AISI 8720. The strain of poorly annealed specimens (hardness HB 93) before fracture was In (1.5/0.42) or 1.3. It was found that fracture occurs in the actual parts and the ratio of the strain in the part to the strain obtained from the upset test was 1.2. Next considering the material AISI 8620, the unannealed specimens did not fracture until a height of 0.35 or a strain of 1.5. The corresponding strain on the parts that fail in upset with this material is 1.35 (2ln (3.85/1.945)). The batch of annealed specimens were run next. These were reduced to a height of 0.2" or a strain of 2.0 without failure for both steels. At this point the limit of the press was reached and as none of the parts being produced involved strains higher than 1.35, further testing was stopped. This indicates the need to establish a procedure to determine formability limits based on the variations that can occur in material, and processes such as annealing on a day to day basis in the plants. In the above tests, it was found that parts did not show any cracking upto a strain of 2.0 if the annealed hardness was below HRS 90. 114 a. unannealed AISI 8720 AISI 8620 b. annealed AISI 8720 AISI 8620 II Figure 47. Specimens before and after upset 115 SAMPLE A SAMPLE B BAR BAR LUBRICATE (OIL) LUBRICATE (OIL) (d r a w ) (d r a w ) SHEAR SHEAR MACHINE & MACHINE & GRIND GRIND (a n n e a l ) (PHOSCOAT & SOAP (PHOSCOAT & SOAP ) UPSETUPSET Figure 48. Process employed to prepare the specimens The simple upset test can thus be used to determine the formability limit of a given material processed in a given organization and used with a factor of safety in process evaluation. A table of hardness versus fracture strain for a given material can be generated and used in a given organization based on material used and processing conditions within that organization. In the organization studied, the hardness range after anneal for AISI 8720 varied from 116 88HRB to 96HRB depending on steel supplied and annealing process. For the operations being performed, and given a factor of safety, one can determine the hardness range of annealed material acceptable for the given operation at that plant to prevent fracture. It should be noted that when fracture occurs on actual parts, it may be random or sporadic and therefore a safe range of hardness with a factor of safety, in this case, has to be determined for upset operation. Similar tests and limits can be derived for other forming operations. Figure 49 shows a backward extrude test. This test may be similarly modified for use in determining the formability limits in backward extrusion. 117 Table 10. Results of upset tests SPECIMEN MATERIAL HARDNESS STRAIN TO FRACTURE ANNEALED AISI 8620 RB 85-88 NO FRACTURE UPTO 2.0 ANNEALED AISI 8720 RB 87-89 NO FRACTURE UPTO 2.0 UNANNEALED AISI 8620 RB 93 FRACTURE AT 1.5 UNANNEALED AISI 8720 RB 94-104 FRACTURE AT 1.3 sheared upset annealed & extruded lubricated Initial billet, intermediate workpieces, and final cup Figure 49. Samples of a backward extrude test. CHAPTER Vîl SYSTEM VALIDATION - PROCESS SELECTION FOR OUTER RACE BLANK* 7.1 Objectives of system validation on process change The validation of the developed approach and system was accomplished by application to the current production process of forming 'outer races' at the chosen organization. The current equipment and process scenario was input to the system. The system processed the information and recommended a cost- effective process and equipment selection for the production of outer races at this organization. This recommended process change was carried out by actual experimentation. The objective of the process modification experiment is to evaluate a most promising alternate for the current forming sequence of operations upto the dimple operation for the 'outer races' and to verify that the more cost-effective alternate also meets the requirements of the final formed part after backward extrude and draw wipe. There were a few issues that warranted running the experiment in addition to generate a formal cost request to verify the feasibility and cost-effectiveness of the recommended process. Some of the key issues were to verify that the requirements of tolerances, surface finish, grain flow and microstructure of the final formed part was met in spite of the process change. 118 119 This was required to ensure that any process parameter interactions which might affect the above requirements were not ignored in the study. OPERATION SEQUENCE I COLD FORM WARM FORM HOT FORM “b P P - O OPEN FORWARD EXTRUDE "b.9 UPSET DIMPLE BACK EXTRUDE & DRAW WIPE M1...Mn are machine choices Figure 50. State space representation of alternatives for an outer race. 120 Extrude Billet Extrude Dimple closed open Upset 1.6' 1.5" 1.5" 1.25" ihoscoat 1.56" 1.25" C^ne'aj^ phoscoat Tolerances required on stem +/- 0.003" phoscoat on dimple outside dia +/- 0.015" on dimple height +/- 0.015" Figure 51. Sequence for a dimple outer race blank without tooling artifacts 7.2 Selection of part family for experiment An experimental plan was developed to apply the research approach to a current production process on a given part to investigate forming operation alternatives and determine the cost-effectiveness. The outer race in a halfshaft assembly is formed as shown in figure 12. The search space for the sequence 121 of operations for the outer race is shown in figure 50. However, in order to meet the requirements of tolerances, and surface finish on the grooves in the final part, and to attain a near-net shape to reduce machining, the last two operations, namely, backward extrude and draw wipe will have to be performed at room temperature. The vertically shaded area indicates the options that need not be considered for options as they have to be performed cold owing to the final forge part tolerance and netshape requirement. The forged blank upto the dimple operation could be performed at several temperature ranges. However, the tolerance requirements of under 0.02" on the diameter and lengths on the dimple part eliminates the hot form operations as shown by the horizontal shaded regions. Therefore, there are yet eight different alternatives that need to be evaluated. The current process sequence upto the dimple stage is shown without the artifacts of die angles, fillets, radii, etc. in figure 51. 7.3 Process modification experiment In the current process sequence, hot rolled steel is cold drawn to reduce the tolerances on the diameter and to better control the weight in the subsequent shearing operation. After the cold drawn bars are sheared to the right size and weight, the billets are annealed in a belt furnace. The annealed billets are then processed through a phoscoating operation and delivered to a 1500 ton Verson press where they are open forward extruded and upset. Owing to the significant amount of cold work and deformation through the upset operations, the parts are once again annealed and phoscoated prior to the dimple operation. After the dimple operation, the parts are. again annealed and coated to perform the 122 backward extrude and draw wipe operations as significant amount of deformation and cold work is imparted to the material. The above process was reviewed closely, and the developed system run to analyze the scenario. The tolerances specified on the dimple part requires the extrusion of the stem to be cold and the head to be either cold or warm as hot forming operations would not meet the tolerance and surface finish requirements. The current scenario of machines available were a 1500 ton, 2- point, 4-station Verson Mechanical press, a 1000 ton, single point, single station. Verson Mechanical Press, and a 600 ton, single point, single station. Clearing Mechanical press to run the production quantities required for the part. As there was no induction heater available, the cost of induction heating the workpiece was factored in for investment of installing heating equipment over the quantity of the part. The cost-effective scenario recommended by CEPESS (figure 52) comprised of the following: 1. Draw 2. Shear 3. Anneal 4. Phoscoat 5. Open forward extrude (2 reductions), upset head in Verson 1500 ton Press 6. Graphite Coat 7. Induction heat 8. Warm form dimple in 500 ton Clearing 9. Phoscoat 10. Backward Extrude and Draw wipe 123 The issues identified with the recommended process in the objectives, warranted the need for actual experimental trials. The effect of the warm form operation on the tolerance of the stem and bowl needs to be determined. It should however, be noted that the warm form dimple does not warm work the stem and the dies containing the stem during the dimple of the upset head was corrected for the appropriate increase due to thermal expansion based on the temperature of the stem. Furthermore, the effect of the warm form dimple part on the surface finish after cold backward extrude and draw wipe operations needs to be determined. From this it may be verified if cold working a warm formed surface produces acceptable cold formed surface finish values. Also, the tolerance increase on the bowl due to warm forming may affect finish part and needs to be verified. It was also noted that any scale produced in warm forming is removed during the pickling operation of the subsequent phoscoat operation before cold backward extrude and draw wipe. These issues have to be proved physically for the plant manufacturing personnel to accept the change. The final product performance characteristics such as yield, fatigue strength, etc. also have to be verified and approved by product design. There needs to be a check on the influence of the new process on the microstructure, grain flow and grain size of the final formed part by the metallurgy department. Therefore, the parts after machining need to be tested to validate that they meet the test requirements of parts in production today by the cold forming process. The dies and tooling were redesigned for a warm forming operation. The process required to heat the workpiece head alone were determined for experimentation with some thought given to production requirements. The costs associated with warm form tooling versus cold form tooling, as well as the investment costs for the induction heating system were determined to evaluate 124 the cost-effectiveness. Also, the costs for a graphite coating system versus a phoscoating system was evaluated. Taking the above issues into consideration the process recommended was tried out. 7.3.1 Forming process trials set-up and execution As the operations upto the forming of the upset head is the same in the modified process as in the current process, the primary experimentation was carried out from the dimple operation onward upto product testing. First, the equipment to be used for the experiment had to be selected and lined-up for trials. An induction heater built by the organization was utilized for heating the workpiece. Owing to the size of the heater coil, a particular size of the outer race family was chosen. The heater settings were set to heat the workpiece head to a temperature of 1200 degrees F. This temperature was determined after running finite element simulations to determine the temperature rise in the part due to deformation. This temperature has to be held below the recrystallization temperature. A 1000 ton Clearing press which was available (as others were running production parts) for experiment was used for the warm form dimple operation. 1500 ton Versons were used to run the cold form operations of extrude, upset, bacward extrude and draw wipe. A Fitch phoscoater was used for phoscoating, a graphite coater was used for coating the billets for warm forming, and a Holcroft annealer used for heat treatment of the material. The specifications of the forming, heating and annealing machines are shown in table 11. 125 Billet Extrude Extrude DimpleUpset closed open 1.6 3" 1.5' 1.5' Jieat 1.25' .shear 1.56' 1.25' ( draw^) phoscoat anneal 1 - ihoscoat cold cold cold warm Figure 52. Process sequence recommended by CEPESS 126 Table 11. Specifications of equipment used for process experiment Presses Parameter Verson Clearing Stroke length 24" 24" T onnage capacity 1500 Ton 1000 Ton Strokes/minute 24 24 No. of stations 4 1 Annealer: Holcroft Zone 1 Temperature: 1450 degrees F Zone 2 Temperature: 1425 degrees F Zone 3 Temperature: 1200 degrees F Atmosphere: 22000 CFH of nitrogen Belt Speed: 10 feet/hr Heaters: Welduction Frequency: 9638 Hz Power: 100-150 kw Coil diameter: 3.5" diameter Number of turns: 8 Phoscoater: Fitch Process sequence: Cold water rinse->Sulfuric acid pickle~>Hot water rinse ->Clean—>Zinc Phosphate->Cold water rinse- >Neutralize ->Soap->Cold water rinse->Tumble dry Graphite coater: MCinnes Process sequence: Caustic wash->Heat->Graphite tumble 127 Next, the part was selected. Hot rolled bars of AISI 8620 steel were cold drawn, and sheared to produce 500 pieces. The five hundred pieces were separated into two lots of 250. It was decided to run one set which eliminated the annealing operation both before and after warm form dimple, and another where only the anneal after the warm form dimple was eliminated as shown in figure 54. The pieces were separated into well tagged gons to ensure that they were not mixed up throughout the tests. The two gons of 250 billets each were then processed through the annealers and phoscoaters. The coated billets were then run through the Verson press and the upset blanks made as in the current cold forming process. One set of upset blanks were annealed (set A) and the other 250 pieces (set B) were not. Both sets of cold formed upset blanks were then washed and coated with graphite. The coated blanks were fed one by one into the induction heater. A pyrometer was used to measure the temperature of the head to ensure that it had reached a temperature of 1250 degrees F. It was assumed that there could be a 50 degree drop in moving the part to the press by the operator. Once the head reached the required temperature, the operators placed the part into the warm form die and cycled the press to form the part. A schematic of the warm form dimple punch and die set-up in the press is shown in figure 54. One set of the dimpled parts (set A), were annealed and phoscoated. The other set of dimpled parts (set B) were not annealed but phoscoated. Next, both sets were backward extruded and draw wiped cold in the Verson 1500 ton press. Both sets of parts made were found to be dimensionally acceptable when checked using production gages. As the parts were to final print, they were 128 CURRENT PROCESS AND MODIFICATIONS OP.10 OP. SO OP. 60 OP. 40 OP. 80 SHEAR PHOSCOAT& FORWARD ANNEAL ANNEAL TO LENGTH LUBE EXTRUDE OP. 140 OP. 90 OP. 100 OP. 120 OP. 130 BACKWARD PHOSCOAT DIMPLE ANNEAL PHOSCOAT EXTRUDE SAMPLEA SAMPLE B (PLT23 0NLY) OP. 150 WASH OP 120 DELETE OP 80+120 OP 90/GR ^ REPLACE g» OP90/GR IND. HEAT ADD IND. HEAT Figure 53. Process modification options (Samples A and B) tried out 129 --j i ü Figure 54. Schematic of tooling layout for warm dimple operation 130 further processed through machining and heat treatment. Metallurgical analyses were carried out on some of the parts from the two sets A and B. The samples analyzed were those after the dimple operation, after the final forming operation and after final machining and heat treatment. The analyses and reports are discussed in the following sections. A few samples were then processed through product testing. The tests performed and the associated results are discussed in the following sections. 7.3.2 Finite element method based process simulations In the warm form dimple operation, certain issues were required to be adressed before the experiment. The temperature rise in the workpiece head due to forming was to be determined to select the temperature the part had to be heated to. In addition, it was required to determine the temperatures on the punch to check for the necessity for additional die and punch cooling at the press. Also, the punches and dies could be checked for stresses to evaluate tool-life and design. The dimple operation under study is a warm form operation and therefore, the strain history of the part upto the upset operation is not critical. Therefore, the metal flow simulation of the warm form operation alone was run using the FEM code 'ANTARES*. The finite element models of the punch, die and part used in the trial is shown in figure 55. Figure 56 shows the punch, die and part at the end of forming. Figures 57 thru 59 show the temperature profiles in the punch, die and part at the end of forming where the temperature of the workpiece was 1300 degrees F and the punch and die at 100 degrees F.. Figures 60 and 61 show the maximum principal stresses in the punch and die 131 !!'»' H I I I I I I' . I|"k Iiilj IJ-.I , . i ...... i ..« % rp NiMhnr Figure 55. Finite element models of punch, die and upset part used in the warm form simulation. 132 DigplaU I Miff f PostScript 1 Help _{ i- .J X = S i‘ » :L L»^i,j!iTrLJ ,lim it,,ntt- r„ki~u_,«- , . •.lo.n,-.-'.,.'iMtn'I,,1:11"M"-:.,_"'Li Figure 56. Material flow at end of forming operation 133 527.8508 489.3274 470.8040 442.2806 413.7572 385.2339 356.7105 328.1871 299.6637 271.1404 242.6170 214.0936 185.5702 157.0468 128.5234 100.0000 TEMPERATURE CONTOUR STEP NUMBER = 12 Figure 57. Temperature profiles in punch at the end of forming operation 134 697.9181 6S8.0S69 618.1957 578.3346 538.4733 498.6121 458.7509 418.8896 379.0284 339.1672 299.3060 259.4448 219.5836 179.7224 139.8612 100.0000 TEMPERATURE CONTOUR STEP NUMBER = 12 Figure 58. Temperature profiles in the die at the end of forming operation 135 1391.4305 1336.0702 1280.7098 1225.3495 1169.9891 1114.6288 1059.2684 1003.9080 948.5477 893.1873 837.8270 782.4666 727.1063 B 671.7459 616.3856 561.0252 TEMPERATURE CONTOUR STEP NUMBER = 12 Figure 59. Temperature profiles in the part at the end of forming operation 136 101.4678 90.5148 79.5618 68.6088 57.6558 46.7028 35.7498 24.7969 13.8439 2.8909 8.0621 19.0151 29.9681 40.9210 w 51.8740 62.8270 MAXIMUM PRINCIPAL STRESS CONTOUR STEP NUMBER = 12 Figure 60. Principal stresses on punch at end of simulation 137 113.7158 SS.1552 84.5947 ' 70.0341 55.4736 40.9131 26.3525 11.7920 -2.7CT6 17.3291 3 1 .8 ^ 7 46.4502 61.0107 -75.5713 -90.1318 -104.6924 MAXIMUM PRINCIPAL STRESS CONTOUR STEP NUMBER = 12 Figure 61. Principal stresses on die at end of simulation 138 36.9095 3S.S88S 111 34.2675 1 r 32.9485 31.6255 30.3045 28.9835 27.6625 26.3415 25.0205 23.6995 22.3785 21.0575 19.7365 18.4156 17.0946 FLOW STRESS CONTOUR STEP NUMBER = 12 Figure 62. Effective stresses in part at end of simulation 139 594*0 497*8, 0*2189 1*257 S tro k e Legend Load (FEA) Figure 63. Load-stroke curve for the dimple forming process 140 respectively at the end of forming. Figure 62 shows the effective stresses in the part at the end of forming Figure 63 shows the load stroke curve for the operation. From the above results, it may be seen that the stresses on the punch are within the limits for a M2 type tool steel. The temperatures of the surface of the punches and dies increase as high as 600 degrees F and therefore will require that there be appropriate cooling provided to improve tool-life. There is also a maxmimum 150 degree F increase in the part due to work of deformation. Therefore, in order to prevent grain growth and recrystallization, the upset part must be heated to 1200 degrees F so that after the part is deformed the highest temperatures are below 1350-1400 degrees F. Simulation of the process was used to determine the above operating parameters and to check for issues of die-life, die cooling and press tonnage capacity requirements. 7.3.3 Results of forming trials and system response evaluation The 500 parts made by the two process options discussed earlier were found to be dimensionally acceptable and comparable to the current production parts. A metallurgical evaluation of the parts was conducted. Figures 64 thru 66 show the grain flow in the sample A, sample B and current part after the dimple operation. Figures 67 thru 69 show the grain flow in the final forge part of the sample A, sample B and current part respectively. The metallurgists did not notice any distinct difference in the grain flow or microstructure, and the hardness and surface finish values of the parts were also within the specifications for the part. Therefore, the parts made through the two process options of the dimple, sample A and sampe B, were acceptable, with the process 141 eliminating two annealing operations being the more cost-effective choice. The samples made were machined and heat treated to final product specifications. The parts were then assembled for product testing. The product tests performed were: • Ultimate torsion test • Low cycle torsional fatigue • High cycle torsional fatigue The summary of the tests were that the magnaglo and X-ray showed no cracking other than that expected from the product test. The grain flow and microstructure appeared to be typical. The product tests were conducted in the organization to their specifications. In conclusion, the process change recommended by the developed system 'CEPESS' was validated by actual experiment. The experiments positively identified the cost-effectiveness as well as the capability of the recommended process modification to meet final formed part requirement. The parts made met requirements and the cost study showed the potential savings in pursuing the modified sequence compared to the current process. The above study also showed how the developed system could be applied to actual practice. 142 m Figure 64. Grain flow in dimple outer race of sample A 143 < f : !u 1-:; SA-iU Figure 65. Grain flow in dimple outer race of sample B 144 Figure 66. Grain flow in dimple outer race of current process 145 Figure 67. Grain flow in finish formed outer race of sample A 146 Figure 68. Grain flow in finish formed outer race of sample B 147 3 C l l t H • • -4 J V." • 9 -V l_‘ Figure 69. Grain flow in finish formed outer race of current process CHAPTER VHI SYSTEM VALIDATION-EQUiPMENT SELECTION FOR OUTER RACE BLANK 8.1 Objectives of system validation on equipment selection In the previous chapter, a process modification was applied to the forming process for making outer races. Apart from process modifications, equipment selection changes also provide cost savings and effectiveness. Therefore, in this chapter, the objective is to apply the system on a current production part and investigate possible forming equipment selection change that would improve cost-effectiveness and add to the validation of the sytem. 8.2 Selection of part family for system validation on equipment selection As discussed earlier the outer races are currently cold formed on Verson Presses. In the part family of outer races, the parts range from 3 lb to 6 lb in weight and from 2" to 5" in diameter of the bowl. Traditionally, in the field of metal forming, there is a tendency to do what has been followed for several years. Therefore, as outer races were traditionally formed on Verson mechanical presses, there has not been a conscientious effort in evaluating other equipment for some of the smaller parts that belong to the part family which may not require the 1500 ton presses. Cold headers are another class of 148 149 cold forming machines that provide certain potential alternatives to slower running mechanical presses provided certain constraints are satisfied. Therefore, it was decided to pick the smallest outer race and determine if the selection of the Verson to perform the forward extrude, upset and dimple of the part is cost-effective compared to other equipment available for the same volume of parts using the current cold forming process. Figure 70 shows the forming sequence laid out for the smallest outer race blank considering the options of running on a cold header or a press. The forming sequence shown in figure 70 was input into CEPESS. Note that the number of forming operations being considered here are four. The current production process involves an anneal and phoscoat before and after the dimple operation and forming upto the upset on one 1500 ton Verson press and performing the dimple operation on another Verson press. On this smaller part, as cold headers were also being evaluated, coil stock also becomes a choice. Coil stock can be obtained spheroidized annealed with considerably more formability than rolled bar stock. Therefore the material input was changed to AISI8620M with a higher formability limit. The input entered into the system CEPESS was processed and the output is shown in figure 71. The cost-effective plan selected was a cold form sequence with extrusion, two upsets and the final dimple performed on the 1000 ton cold header (M6). As there was no need for annealing before forming and as the coil stock costs less, the part cost was lower at $1.08. The option of performing this sequence in a press would have involved higher costs due to use of bar stock, additional anneal and use of a slower running mechanical press. 150 Billet Extrude Upset Dimple Upset closed 1.5' 4.6' 1.5' 2.6 5.5" .shear phoscoat (dravv^ phoscoat anneal Tolerances required phoscoat on stem +/- 0.003" on dimple outside dia +/- 0.015' on dimple height +/- 0.015" Figure 70. Forming sequence for consideration of cold header/press 151 SELECT-PLANS ! —Opi0 : Forward-Closed-Extrude-Cold f. -Op20 : Cone-Upset-Cüld ' \ -Op3 0 : Cone-Upset -Col d ' \ \ "T"—Op40 : Dinpl e-Coi d r \ - M 5 \ ‘ M6 M6 M6 OK! Save ? ' "Plan Cost = 1.08 : PRE-ORS; SHEARING PHOS-COATING TRANSPORT ■ ; OP : \ '■ Op 10 : FORNARD-CL OSED-EX TRUDE-COL D \ " : MACHINE: \ "M 6\ " :PRE-OPS: NONE : OP : OpZO : CONE-UPSET-COL D \ " : MACHINE:; \ ’M6\ ’ ': PRE-OPS ; I NONE :0P: \ Op^O:CONE-UPSET-COLD\ : MACHINE: \"M6\" >: PRE-OPS:, NOME :0P: \ ’Op40:DIMPLE-COLD\' i:M A C H IN E : Figure 71. Output of CEPESS for equipment selection problem 152 8.3 Equipment change trials set-up and execution The equipment which had capacities available to form parts at a rate of 9,000/day were first identified. The identified machines and the specifications are shown in table 12. In this investigation, the focus was to maintain the cold forming process, but evaluate alternate equipment. Cold headers and mechanical presses become the most viable equipment for such operations and production rate of parts required. In the case of cold headers, they are rated based on the diameter of wire stock that they can handle. For example, a 1" header would handle coil stock upto 1 inch in diameter. On further investigation with the purchasing department it was found that coil stock is cheaper than bar stock and may also be purchased in the spheroidized annealed condition. This would eliminate the need for an annealing operation and provide higher formability compared to the sub-critical anneal performed in-house. Larger outer races would certainly need larger diameter stock to start with, and therefore would not be suitable for a header operation (maximum size for coil stock is 1.5" diameter). Cold headers also run at significantly higher strokes per minute (60-100) in comparison to the presses (15-25). Therefore, the smallest outer race was chosen for the equipment selection investigation. The amount of strains that the part is subjected to is less for the smaller outer race which would enable forming the part upto the dimple stage on the same header (5-station) using the spherodized annealed coil. In this manner, significant savings in eliminating two annealing operations, a phoscoat, material handling, and reducing number of equipment from two to one, was anticipated. This would however, be limited to the smallest outer race. 153 There was a limitation on the energy that could be provided by the header. Although there were five stations to accomodate the operations, the energy was not sufficient. Therefore, it was proposed to run the header in a mode where it would form parts every alternate stroke. This would reduce the number of active strokes/min by half but enable the machine to recover sufficient energy from the flywheel during the idle stroke. However, the number of strokes/minute for the header (60 strokes/min) would still be higher than that on a mechanical press (20 strokes/min) even at half the rate (30 strokes/min). A progression was laid out for the cold header, on the smallest outer race and the design tried out. At the same time a formal cost request was submitted to determine the savings from such an equipment selection change with some process modification. The tooling design had to be modified for use in the header. The header is a horizontal machine, with different sizes of punch and die pots, and constraints dicatated by the finger transfer mechanism and the high rate of production. 8.4 Results of forming trials and system response evaluation The spheroidized annealed coil stock was ordered at a slight premium compared to the unannealed coil stock. This was then processed through the cold header. As the shearing is performed on the machine, the shearing costs are lower as it does not require a separate machine, labor and handling costs. The billets for the outer races made on presses have to be made on separate shearing machines. Also, the coating of coil stock is cheaper than parts as the volume handled through the coating system is higher for coil stock than separate pieces. These variations in costs are reflected in the cost model. As the strains 154 to fracture calculated for the smallest part thru the dimple operation was found to be less than the fracture limit, the dimple operation could also be performed before an anneal is required. The parts made on the National 1500 ton cold header were to requirement and indicated the feasibility of this cost-effective alternative for the smaller parts. The system was used to evaluate alternate equipment for a given part (smallest outer race) and come up with a recommended cost-effective equipment selection. Actual trials needed to be run to address the issues of tooling, energy requirements of the header, and production related issues. Once again, it is required to physically implement the change for acceptance by the manufacturing personnel. Thus the system was validated for both cost-effective process selection and equipment selection as discussed in chapters 7 and 8. 155 Table 12. Specifications of equipment used for process experiment Presses Parameter Verson National Cold former Stroke length 24" 24" Tonnage capacity 1500 Ton 1000 Ton Strokes/minute 24 62 No. of stations 4 5 Shearing off-line on-line Phoscoater: Fitch Process sequence: Cold water rinse->Sulfuric acid pickle->Hot water rinse ->Clean—>Zinc Phosphate->Cold water rinse- >Neutralize ______—>Soap->Cold water rinse—>Tumble dry ______CHAPTER IX CONCLUSIONS AND FUTURE WORK 9.1 Conclusions from forming trials and system application The discriminating cost model serves as a powerful tool in evaluating cost-effectiveness and economics of equipment and process selection in metal forming process. The search method of solution of problem space has proved to be an effective technique. The system enables putting forward process and equipment changes that even experts would not be able to come up with due to the large domain of knowledge and altenatives to be evaluated. Provided the knowledge, the approach has proved to be effective in reducing cost. The comparison of the different process selection models is presented in table 13. The different features used to compare the models are: 1. Reliance on heuristics. 2. Capability of the model to clearly discriminate between two selection choices both within a parameter as well as between parameters. For example, the model should discriminate between phoscoat and graphite coat as a form of lubrication and at the same time reflect the difference in costs for lubrication operations versus say cost for a forming operation. The ratio of the difference in such costs should be well reflected by the model. 156 157 3. Sensitivity capability, or the capability of the model to react to changes in costs of different parameters and reflect effects of such changes in process and equipment selection. 4. Data acquisition methods required to feed the model with appropriate data. 5. Flexibility of the model in being adapted from organization to organization. 6. Capability to provide an absolute estimate of cost for part production by a given process 7. Robustness, or the capability of the model to discriminate even if the cost estimates of the drivers are in error within 10-15%. Table 13. Comparison of process selection models and DCM FEATURE OCA FUGM cosTMnoffatxu RK-YGM HIGH HIGH LITTLEIHDOBIATE HEURISTICS DISCRIMINATION GOOD OK MERB.Y BOCD CAPABILITY ABSOLUTE PHMARY FOCUS seieiTiviTY MDOBWE LOW VEHYLnTLE GOOD CAPABILfTY DATA ACQUISITION DIFFICULT DIFFICULT MODBVTE IMDOBIAIE FORIMETHOD FLEXIBHITY LOW-MEDIUMLOW VERYLTTTLE GCCD O F M O DEL 1 1 ABSOLUTECOST NO ND YES SOME WITH EXTENSION ! ESTIMATE 1 ' ! : ROBUSTNESS LOW UTTLE MODERATE M D C eW E I 158 Based on the above comparisons, DCM proves to be a more appropriate model especially in this problem domain. Some of the difficulties and shortcomings of this model are: • System relies on representative data for cost drivers (garbage in, garbage out) Bias of experts in knowledge and data supplied Interviewing experts Expansion of methodology to areas with very sensitive costs is difficult Representation and handling of complex operations Cannot easily handle make vs buy decisions Not a costing system but DCM drivers can be extended to provide a cost estimate • Need integration with current design systems 9.2 Benefits • The approach enables evaluation of an exhaustive set of alternatives in process and equipment selection, which is not practical if done manually. • The approach captures knowledge and data in a formal manner that would be available even as experts leave the organizations due to attrition and retirement. • The application of the developed method would reduce cost of producing formed parts. • The approach also enables effective scheduling of the forming equipment by allocating the right parts to the right equipment. 159 . The application of this approach improves productivity and lead time as unnecessary intermediate operations may be eliminated. • The application of this approach would provide reduction in investment costs, as only the cost-effective choice of equipment would be selected. • The approach makes significant inroads into facilitating concurrent engineering. • This approach enables one to evaluate subsequent processing options on a part such as machining, heat treatment, etc. • The search methodology has been applied in a domain of forming. However, this solution method may be extended to consider additional operations in the chain of producing a part, such as machining operations and heat treatment, provided the appropriate knowledge and operations interactions are captured. • The approach provides a powerful tool of sensitivity analysis such as: 1. changing product requirement (tolerances, surface finish, quantity) 2. changing material 3. changing equipment availability scenario 4. Adding or deleting an operation 5. Changing cost elements 6. Investigating additional machining operations • The system could be used as a training tool for young engineers or others new to the field • A framework for a system that attempts to evaluate design, material and manufacturing process simultaneously can be built based on this approach 1 6 0 • The system's knowledge can be easily enhanced or modified and provide non-monotonic reasoning capability 9.3 Contributions • A discriminating cost model for cost-effective evaluation of alternate processes and equipment selection. The same methodology can be applied to other forgings to realize similar gains of this research. • Management decision making tool. Currently, the costing methods sometimes cloud the cost-effectiveness of alternate process and equipment selection. This would be alleviated. Also, engineers who are resilient to change, would not consider alternatives that are unfamiliar to them. A tool such as the one developed would provide sufficient information to a Manager to evaluate and provide direction in forming process development. • A search methodology as a solution method for a complex problem domain as the one discussed in this dissertation. 9.4 Future work • The system has been built currently as a prototype with knowledge of extrusion, upset, dimple and backward extrude operations. However, other operations need to be included. • In the case of hot forming, some operations are combined. Knowledge of when such combinations are more effective need to be captured. 161 • Mechanisms to capture some complex interactions of operations need to be developed. For example, when a extrude and upset operation are laid out starting from a bar, the choice of the bar diameter is dependent on both the operations. An optimization scheme using finite element simulations and genetic algorithms was developed to address this scenario. Such optimization schemes linked to the system may be one such mechanism to handle these complex interactions. • Methodologies to capture and implement interactions of forming operations with design features on the front end, and machining operations at post-forming would enable the larger picture of total concurrent engineering. 9.5 Technology Transfer The developed approach is powerful in its application and may be transferred in a couple of ways; • The system can collect cost information from individual organizations to fit into the DCM structure and thus be portable from one organization to another. » The solution method (search) can be extended to include not only forming and intermediate operations but also machining, heat treatment and other manufacturing operations as well as different design choices. • The system has been built on an ICAO shell and can be used where this tool is available. The ICAD shell may be replaced with other knowledge- based shells as found appropriate. APPENDIX A OVERVIEW OF METAL FORMING PROCESSES AND EQUIPMENT 1 6 2 163 Metal forming processes may be classified primarily as cold, warm and hot forming. The following sections describe the various forming regimes, forming and other operations and the associated equipment required for the manufacture of forged parts . The pros and cons of different processes and their interactions are also described in some detail. A.1.1 Cold forming Cold forging is a process to transform a simple geometry billet into a more complex product geometry by force between a punch and dies at ambient temperature. In practice, cold forming temperatures may extend to 400°C (750°F). However, for example, low carbon steels exhibit blue brittleness at a temperature range between 200^0 to 400^0 (400°F to 750°F) and hence may not be conducive for forming at that range. Cold forming provides advantages of: high production rates reduced energy costs as no heating of workpiece is involved close dimensional control excellent surface finish of formed parts improved grain flow providing strength to product forming to net shape providing material savings and minimizing post machining operations • chip formation improved by cold working In cold forming, the process development and tools costs are relatively high as it involves close tolerances, high forming pressures and loads and limited flash. Also, requirements of large minimum lot sizes, limitations in 164 geometries and size of products, and difficulties in producing products from brittle materials are other major limitations of the cold forging process. A.1.2 Hot forming Hot forging is the process of transforming a heated billet (for steel between 1900-2300 op) which has a simple cross-section to a complex shaped forging different from the original dimensions of the billet. Usually the forging process involves a sequence of operations to transform the simple billet geometry to the required part shape. Hot forming is performed by heating the workpiece to a temperature greater than the recrystallization temperature of the workpiece material. Hot forming is done using both open and closed-die configurations, as well as flash producing and flashless processes. Hot forming provides the advantages of: • processing any steel grade and hard to cold form materials • more complex shapes • economic production of small batches • high rate of production • larger parts • lower tonnages allow smaller equipment for the same part Hot forming is limited by scale and poor surface finish, larger tolerances, lower tool-life due to higher die wear at higher temperatures, flash, additional heating requirements for billet and cooling. 165 A.1.3 Warm forming Warm forming Is the process of transformation of workpiece geometry at temperatures closer but below the recrystallization point of the material. For steels, the warm forming range is above the blue brittleness range but below the recrystallization point ( 400°C to 800°C or 1100°F to 1350°F). Forming metals at temperatures below the normal hot-working range offers certain potential advantages over either hot or cold forging such as: good formability of difficult to cold form materials tolerances and surface finish closer to those attained in cold forming lower tonnages than required for cold forming Better lubrication than hot forming, thereby better tool-life ability to form complex shapes that rival those produced by hot forging less energy required for heating workpiece than hot forming economical production quantities between those of hot and cold forging Although warm forming attempts to be the best of both worlds of cold and hot forging, there are some limitations such as more complex tooling and process controls, additional die cooling, and lower tool-life. A.1.4 Forming operations and tooling There are several types of forming operations that are used in transforming the shape of a workpiece in cold, warm and hot working ranges as listed in the classification of forming processes in table 14. These operations are detailed extensively elsewhere in literature. The primary objective of these 166 Table 14. Classification of forming processes [Altan, 1983]. Forging Rolling Extrusion Drawing Closed-die forging Sheet rolling Nonlubricated hot Drawing with flash Shape rolling extrusion Drawing with Closed-die forging Tuhe rolling Lubricated direct hot rolls without flash Ring rolling extrusion Ironing Coining Rotary tube Hydrostatic extrusion Tube sinking Electro-upsetting piercing Forward extrusion Gear rolling forging Roll forging Backward extrusion Cross rolling forging Surface rolling Hobbing Shear forming Isothermal forging (flow turning) Nosing Tube reducing Open-die forging Orbital forging P/M forging Radial forging Upsetting operations is to transform shape. The feasibility of providing such a shape change is dependent on the workpiece material, lubrication, temperature of workpiece and dies, tool geometries and the rate of forming. For a part to be formed successfully without any internal or external defects, certain design rules and guidelines must be followed for each forming operation [Badawy, 1983]. Considering, for example, the forward extrusion operation, the limits on the percent reduction in area are as follows: 30-35% reduction in area in case of open die extrusion 70-75% reduction in area in case of trapped extrusion % reduction = (billet cross-sectional area-extrusion cross-sectional area)*100 billet cross sectional area 167 In the case of open die extrusion, the limitation is due to the tendency of the part to upset before extrusion, and in the case of closed die extrusion, the forming pressures increase tremendously. However, it should be noted that if the fonvard extrusion operation were performed warm or hot the above feasibility limits are different and higher reductions are possible. The warm or hot extrusion process is performed with the tools heated and the billet temperatures above the recrystallization temperature of the material extruded which reduces the flow stress of the material resulting in lower punch pressures and higher obtainable deformation strains without failure. Similar rules exist for the other forming operations such as upset, backward extrusion, draw wipe, etc. which vary also with material and temperature regime (cold, warm or hot). Dies are used to provide the shapes necessary to contain the part being produced by the deformation process operations. The forming operations being performed on the part, the temperatures of forming and the forming equipment being used drive the tooling design. The key tooling variables include: design and geometry surface finish stiffness mechanical and thermal properties under conditions of use life material heat treatment manufacturing method Forming operations and die design directly influence the change in shape from billet to part. The design of the operation and dies is an art as well as a science, requiring significant levels of creativity and analysis. The requirements 1 6 8 of the formed part such as surface finish, hardness, tolerances, etc. are met by appropriate selection of operations and die design. Die design involves selection of die materials, surface coating or treatment, heat treatment, and building of a die-set to provide appropriate strength to withstand stresses from the forming operations and provide ease of change and installation of tooling in the forming equipment. A.1.5 Intermediate forming process operations The forming operations discussed earlier contribute to shape change of the incoming billet or preform. However, other auxiliary operations are required to enable successful forming operations. A brief overview is presented in the following section on the different intermediate operations that are part of the forming process. Stock preparation The incoming material is typically in the form of bars, billets or wire. The bars and wire have to be cut to the prescribed weight and length before forming. Forge shops may use one of several alternative methods for cutting stock, depending on size and hardness of the material and required surface condition of the cut ends. Carbon and low-alloy stock up to 6 inch square having a hardness no higher than 250HB usually may be sheared quickly and efficiently at room temperature, with the exception that some materials are inherently unsuited to cold shearing regardless of their hardness. When stock hardness is too high and for materials that are not suited for cold shearing, the bar may be heated to increase its plasticity and may be sheared hot. Sometimes shearing is 169 performed on the forming equipment itself and may be performed cold, warm or hot depending on the forming operation being performed cold, warm or hot. If shearing is not suitable, bars, billets and blooms may be cut into multiples with power hacksaws, automatic circular sawing machines, band saws, or abrasive wheel cutoff machines. In certain applications, burrs left from the sawing operation are removed from either or both ends of the cut stock to ensure a forging with less likelihood of defects. A special radius machine may be used to form a constant radius on the end of the mult, but small quantities are usually deburred on a grinding wheel or disc. In sawing one loses some material and the operation is slow, although one gets a better cut. Sawing is reliable and is widely used for cheaper low- carbon steel slugs, particularly where the length of the slug is smaller than the diameter. The equipment and method of slug preparation influences economics depending on size, material, and quantity. Peeling is another operation besides sawing or shearing that is used to prepare the billet by removing material from the bar by machining to reduce the tolerance on the diameter and remove surface defects and imperfections. Surface Treatment The significance of surface treatment as a way of preparing workpieces for metal forming operations and influence friction conditions are discussed in detail in [Altan, 1983]. The surface treatment process consists of surface preparation and cleaning, application of a lubricant carrier and finally the lubricant itself. Typically in cold forming, phoscoating operations are used where a zinc phosphate/stearate soap lubricant is applied, in warm forming synthetic lubricants and graphite coatings in acqueous emulsions are common. 170 and in hot forging water base lubricants are common. Lubricants in hot and warm forming are discussed in detail in [Lange, 1985]. The surface treatment operations and their economics are influenced by material, quantity, forming operation, temperature of forming (cold, warm or hot), form of application (coating process or spray/swab/flood) and surface treatment equipment. Surface Cleaning Cleaning operations are performed to remove dirt and scale and to provide a better surface for forming operations. Scale may be produced during forging operations at high temperatures as in hot forging or due to heat treatment where the materials acquire a thin coating of hard, abrasive oxide. The typical cleaning operations are blast cleaning, tumbling, pickling, caustic etch and use of industrial cleaners in washers. The choice of cleaning operations influences the economics of the forming process. In addition, forming operations require the parts to be at a certain level of cleanliness. Cleaning methods are discussed in some detail in reference [Lange, 1985]. Heating The heating of a metal workpiece reduces the flow stress and thus leads to a corresponding decrease in the force and work for deformation. The heat energy supplied to the workpiece, however, far exceeds the deformation work, and thus hot forging offers no advantage from the point of view of energy efficiency. Hot upsetting sometimes may require about 17 times as much energy as cold upsetting [Altan, 1983]. The typical methods used to heat a workpiece to forging temperature are heating in furnaces, by induction and conduction. 171 Details on heating are provided in reference [Altan, 1983]. The economics of these heating methods depend on part, shape, size, material, equipment and forming operation. In some cases, parts are partially heated and certain heating methods then become more attractive than others. Heat Treatment In general, heat treatment involves specific controlled thermal cycles of heating and cooling to improve one or more of the properties of the forged part. The primary objectives of such treatment may be to relieve internal stresses (as in tempering and stress relieving), control distortion, optimize the depth of hardening, refine grain size (by normalizing), change the microstructure to improve machinability, or develop the final specification for mechanical or physical properties. Details of heat treatment methods and processes are described elsewhere in literature [Lange, 1985]. However, with respect to the forming processes, the heat treatment methods are applied to improve formability, reduce distortion, and relieve stresses. The typical processes used in forming are annealing, normalizing, tempering, and stress relieve. Cold working is relieved by annealing in order to enable further forming. Hot worked materials are normalized to provide some grain refinement. Forgings are stress- relieved to prevent defects in subsequent machining operations. Depending on the forming process and operations required to transform shape certain heat treatment operations become necessary to refine the material. Spheroidize anneal is performed to modify the microstructure to improve formability. Material Handling 172 During the forming process, the initial billet is transported from one operation to another and therefore incurs costs. The parts have to be collected in gons, and transported to the different equipment where the forming and non forming operations are performed. Typically, the mode of transportation is through fork lift trucks. In some cases, the parts may be shipped to alternate sources or other plants to perform some of the intermediate operations and have to be costed accordingly. A. 1.6 Forming materials The materials used for making forged parts are steels (unalloyed, low-alloyed, high-alloyed), non-ferrous light metals (aluminum and magnesium and their alloys), nonferrous heavy metals (copper and its alloys, nickel, cobalt, molybdenum, and tungsten and their alloys), titanium and its alloys, beryllium, and other special metals. The selection of forging materials is made considering factors of product performance requirements, formability, availability, machinability, hardenability and heat treatment applicable, and cost. Also, the material is available in different forms. The incoming material may be hot rolled, cold rolled, annealed, cold drawn, etc. and may be available in bar, coil, or billet. Typically coil stock is cheaper than bar, but is available only in smaller diameters. A. 1.7 Forming equipment Forging machines can be classified into three types: • Load-restricted machines (hydraulic presses) 173 • Stroke-restricted machines (crank and eccentric mechanical presses) • Energy-restricted machines (hammers and screw presses) The significant characteristics of these machines comprise all machine design and performance data that are pertinent to the machine's economic use, including characteristics of load and energy, time-related characteristics, and characteristics of accuracy. The different types of machines are extensively described elsewhere in literature. A.1.8 Forming Sequences Beyond simple shaped geometries, a sequence of forming operations are required to transform the billet geometry into the part shape. Also netshape and flashless forming processes require control of material flow which is possible only through a sequence of operations. These forming sequences are determined primarily be trial and error, previous experience and creativity of the designers. Figures 72 and 73 show a cold form sequence and a hot form sequence used to make gear blanks. Some of the key parameters that drive the sequence design are: guarantee shape transformation should provide parts defect free should require minimum number of operations should determine the feasibility of individually laid out operation should minimize intermediate operations should utilize equipment effectively should balance loads in equipment selected should be transferable utilizing the transfer mechanisms on equipment 174 A.1.9 Process and equipment interactions In a practical sense, each forming process is associated with at least one type of forming machine. The introduction of a new process invariably depends on the cost-effectiveness and production rate of the machine associated with that process. The behavior and characteristics of the forming machine influence; • The flow stress and workability of the deforming material • The temperatures in the material and in the tools, especially in hot forming • The load and energy requirements for a given product geometry and material • The "as formed" tolerances of the parts • The production rate The process variables listed in table 15 and the machine variables listed in table 16 are tightly coupled. An increase or decrease in the value of one or more of the variables has an impact upon the other variables. In hot forging for example, the slide velocity of the machine affects the strain rate and the contact time. As the slide velocity increases, the rate of deformation (strain rate) increases and the contact time is decreased (neglecting dwell times). As the contact time is decreased, less heat transfer from the workpiece to the die occurs. For more on the formability of materials see [Semiatin, 1984]. Correct selection of the forming machine, then, plays an important and economic role. A machine requiring high costs (such as utility consumption per part, maintenance, number of operators) should be correctly used for production that can justify the use of a high cost machine. Secondly, business opportunities may be lost by not having production time available for a machine because it is producing parts which should be made on a more appropriate machine. 175 In addition, the type of forging process influences other process variables. Coining, for example, demands very high loads to the end of the stroke whereas extrusion processes generally demand near peak loading over the entire stroke. The principal process and equipment variables and their interactions in hot forging unders presses are shown schematically in figure 74. For a given material and forming operation a certain variation of load with stroke is required. For a given part geometry, the absolute load values will vary with the flow stress of the material as well as with friction conditions. In the forming operation, the equipment must supply the maximum load required during the stroke as well as the energy required by the process. Within a given type of press, for example, mechanical presses, the deflection and accuracy are different as discussed in earlier sections. Therefore variations within the different classification of equipment also affect the capability for a given process. Detailed accounts of equipment and process interactions are provided in references [Altan, 1983, Ishi, 1989, Altan, 1973]. In order to obtain the benefits of forging though, the manufacturer must produce enough parts to surpass the breakeven decision point. Due to the relatively high capital equipment costs of forming machines and dies, a large volume of parts must be produced to distribute the fixed costs and overhead (figure 75). Costs vary substantially among the different forging processes. The die costs and machine costs in cold forging may be two to four times that of hot forging. The higher production rate capabilities of cold forging, in the range of an order of magnitude, often justify the expenses. Furthermore cold forging operates with automatic equipment while hot forging operates manually. Lower part volumes, though, necessitate lower initial capital outlays. The planned 176 production volumes are often the reason behind the process and equipment choices, at least from the economic point of view. Materials influence the limits of different processes to process them as well as parameters such as stresses and loads which in turn influence equipment selection. z Figure 72. Schematic illustration of a cold forming sequence of a gear blank [Altan. 1983] 177 PIERCE FINISH FORM PREFORM UPSET SHEAR Figure 73. Hot forge sequence for gear blanks produced on a hot former [Byrer, 1985] 178 Process Variables Equipment Variables Strain Rate Slide Velocity Forging Material Die Temp. Friction, ^ Temperature Contact Time Lubrication Forging Geometry Stiffness Machine Load Machine Energy Variations in Strokes stock (wt. and per min. temp.) (idle) Required Strokes Load, per min. Energy (load) Figure 74. Relationships between process and machine variables in hot forming processes conducted in presses [Altan, 1970] 179 Table 15. Important process variables in forging Material Choice. Die Temperature. Part Tolerances. Required Load and Energy. Part Geometry. Friction Conditions, Lubrication. Flow Stress. Strain. Strain Rate. Table 16. Important machine characteristics in forging • Load and Energy * Available Energy. * Available Load. * Efficiency Factor. • Time-related. * Number of Strokes per Minute. * Contact Time Under Pressure. * Velocity Under Pressure. • Accuracy. * Clearances in the Gibs. * Parallelism of Upper and Lower Beds. * Flatness of Upper and Lower Beds. * Perpendicularity of Slide Motion. * Tilting of the Ram * Deflection of the Ram and Frame. * Stiffness of the Press. 1 8 0 Cost Per Part $ machined parts hot forged parts cold forged parts machine | hot forge | cold forge No. of Planned Parts (Volum e) Figure 75. Breakeven points of quantity versus cost for cold, hot and machined parts [Ishi, 1989] APPENDIX B LITERATURE REVIEW 181 1 8 2 A brief review is presented of different process selection methods in manufacturing with emphasis on metal forming. The objective of this review is to present the current state of art systems, methods and models available, their functions, their capabilities and their limitations. Existing systems for process design and planning in metal forming A comprehensive review of expert systems for process planning of cold forging has been recently presented [Osakada,1993]. In the 1960s pioneering research work in computer-aided process planning (CAPP) and tool design of forming processes was initiated by Niebel and Barker, et al [Osakada, 1993]. These systems addressed design and detailing simple blanked and pierced components. In the 1970s several efforts were made at computer aided process planning for hot forging primarily the work of [Altan and Akgerman, 1972] and [Biswas and Knight, 1974]. Application of the principles of Group Technology (GT) was emphasized for CAD, CAM and CAPP for hot forging. The early systems for hot forging included: programs for axisymmetric components computer aids for producing dies cost and forming load estimation [Knight, 1982] programs to assist in preform design CAD/CAM for different parts such as compressor blades, gears, etc [Kuhlman, 1984] and [Yin, 1982] Some efforts at process planning for cold forming were made [Badawy, 1985]. Noack reported the initial attempt to write computer programs for 183 determining the operating process and production costs for manufacturing geometrically similar steel workpieces [Osakada, 1993]. Lengyel proposed a computer-aided method of optimization for alternative cold forming processes [45 of 1]. However these systems lacked the technical knowledge of cold forming processes. Design guidelines were formal, written rules of thumb, or narrow experiences of one or several human designers. Consequently, results were inadequate, except in special cases. The advent of the 80s saw several AI and expert systems built. AI opened new areas for computers, granting a variety of application options and breakthrough in complex problematics of conventional programming tools. Early work using this technology was carried out by Golker [Osakada, 1993] who proposed a method for shape classification and geometric representation of forged products with a four digit code, of which the first digit describes the material and the last three describe the shape and some volumetric elements. Systematic design was carried out for the process of hot upset forgings and horizontal forging machines based on this method [Knight, 1982 and 1984]. Tang, et al. developed an expert system called Automatic Forging Design (AFD), to automate the design of rib-web type forging geometries [Tang, et., al., 1985]. Vemuri, et al. developed a prototype expert system called Blocker Initial Design (BID) that modifies the geometric values of a rib-web cross-section with stored rules to come up with an initial blocker or preform design for design of preforming or blocker dies in forging with flash [Vemuri, 1986]. At the same time Finite element methods for metal flow simulation were applied [Oh, 1981]. Some efforts were made to incorporate FEM simulation into intelligent knowledge based systems [Hartley, 1986]. In addition, a feasibility study on an integrated modeling system using the Upper Bound Elemental 184 Technique (UBET) was carried out by Bramley, et al. [Osakada, 1993]. FEM simulations were used to establish limits of deformation for use in CAPP of hot and cold forging. Badawy, et al at Battelle labs developed a computer-aided process planning system, FORMNG, that recognizes automatically the geometric characteristics of a rotationally symmetric solid product and to establish the necessary process of forming operations required to cold or warm forge the product [Badawy, 1985]. This work was extended by others with the introduction of AI techniques for knowledge representation and problem solving of cold forging process design. FORMEX verifies the feasibility of individual operations that can be built into a composite to represent a forming sequence. Kim et al, [Kim, 1992] improved this with interactive graphics and dimensioning. A parallel effort to the above was conducted [Bariani and Knight, et., al., 1987] which included functions for process generation and analysis based on the 'generate, test, and rectify' strategy with a post processor for determining machine setting conditions, and so on. At the current time, the system is capable of generating feasible processes for cold forging of solid and hollow rotationally symmetric products. It also tests the processes for suitability on the basis of load-peak distribution in the differrent forming stages and the effective strain accumulated in the blanks and the finished product. [Mahmood, et., al., 1987] built a system 'COFEX' (cold froming expert) which provides forging part drawing with tolerances after a possible sequence is selected for a forged part. Contact tooling is also designed. A press selection and costing module assists in the selection of the forming equipment and provides some cost information. [Kuhn, et., al., 1986] developed a system for preform design using AI techniques. [Lange, 1989] developed another approach 185 to designing forming sequences for cold forging. Yang and Osakada have made some efforts in applying neural networks to be trained using FEM simulations for forming process generation for cold forming [Osakada, 1991]. [Fujikawa, et., al., 1992] developed a system for diagnosing defects in hot forging by a combination of probability theories and knowledge-based approach. The factors considered toward their influence on defect formation include tool design, process conditions, lubrication, part shape, etc. Remedies for problems are provided by knowledge derived from experts and FEM simulation studies. APPENDIX C CONSTRAINTS EVALUATIONS FOR DIFFERENT FORMING OPERATIONS 1 8 6 187 The following sections describe the procedures and methods used to verify feasibility of operations and evaluation of critical parameters of forming operations used to evaluate constraints and selection criteria for equipment and other operations. lA. Cold Forward Extrusion (open and closed) Evaluations 1. Calculation of reduction, R = (Dj2-Do2)/Dj2 * 100 2. Calculation of effective strain, e = In (1/1-R) 3. Calculation of flow stress, a = 'K' and 'n' values are chosen from the material database corresponding to the strain. 4. Calculation of approximate load = Aq a 5. Punch pressure = a Constraints 1. Buckling Ratio = Length/Diameter <= 2.3 (8.0 in closed extrusion) Failure handling mechanism: Tell user to change billet size 2. Punch pressure < 275 ksi (limit of typical cold forming tool materials) 3. Upset before extrude (primarily for open extrusion) This phenomenon was studied and assumed that when there is a 10% increase in the area of the initial diameter of the extrusion then upset would have occurred. This would imply that the load required to upset the workpiece becomes less than that required for the extrusion ratio. Ks'^ <=1.1 where s' corresponds to 10 % upset Upon solution, the allowable open extrusion reduction % before upset was 43%. 1 8 8 General guideline is: Open : 30% Failure handling mechanisms: split the extrusion into two 4. Fracture: strain s <= 0.8 sf (from fracture limit table for a given material) Failure handling mechanism: Add anneal unless annealed already 5. Chevron: (Typically for the first extrusion) Reduction >= 15 % for any steel (as the die angles are very limited for this reduction to prevent chevrons) Failure handling mechanism: Tell user to change billet size or extrusion ratio. IB. Warm forward extrude (1100 oF to 1400 oF) and Hot forward extrude (1900 oF to 2300 oF): Evaluations 1. Calculation of reduction, R = (Dj2-Do^)/Dj2 * 100 2. Calculation of effective strain, s = In (1/1-R) 3. Calculation of flow stress, a = Ce'^ The strain rate is determined as Vavg/Lo where Vavg is assumed to be 15'Vsec for an initial guess in warm and 30"/sec hot, which is modified later depending upon machine. 'C and'm' values are selected from the material database based on temperature and strain 4. Calculation of approximate load = Aq a 5. Punch pressure = a Constraints 1. Buckling Ratio = Length/Diameter <= 2.25 for warm and 2 for hot 189 (n/a in closed extrusion) Failure handling mechanism: Tell user to change billet size 2. Punch pressure < 200 ksi (limit of typical cold forming tool materials) 3. Upset before extrude (primarily for open extrusion) This phenomenon was studied and assumed that when there is a 10% increase in the area of the initial diameter of the extrusion then upset would have occurred. This would imply that the load required to upset the workpiece becomes less than that required for the extrusion ratio. <=1.1 G'n, where s' corresponds to 10 % upset Upon solution, the allowable open extrusion reduction % before upset was 75% Failure handling mechanisms: split the extrusion into two II.A Cold simple upset Evaluations 1. Calculation of reduction, R = {Dq^-D-^)IDq^ * 100 2. Calculation of effective strain, s = In (1/1-R) = In (Hj/Ho) 3. Calculation of flow stress, a = Ks" 'K' and 'n' values are chosen from the material database corresponding to the strain. 4. Calculation of approximate load = Aq a 5. Punch pressure = c Constraints 1. Buckling Ratio = Length/Diameter <= 2.3 (n/a in closed extrusion) Failure handling mechanism: Tell user to change billet size 190 2. Punch pressure < 275 ksi (limit of typical cold forming tool materials) 3. Fracture: strain s <= 0.8 ef (from table for a given material) Failure handling mechanism: Add anneal unless annealed already II.B. Warm and Hot upset: Evaluations 1. Calculation of reduction, R = (Do2-Dj2)/Do^ *100 2. Calculation of effective strain, s = In (1/1-R)= In (Hj/Ho) 3. Calculation of flow stress, a = Cs"^ The strain rate is determined as Vavg/Lo where Vavg is assumed to be 15"/sec for an initial guess in warm and 30"/sec hot, which is modified later depending upon machine. 'C and'm' values are selected from the material database based on temperature and strain 4. Calculation of approximate load = Aq a 5. Punch pressure = a Constraints 1. Buckling Ratio = Length/Diameter <= 2.25 warm, and 2 hot (n/a in closed extrusion) Failure handling mechanism: Tell user to change billet size 2. Punch pressure < 200 ksi (limit of typical cold forming tool materials) 191 III.A. Cold backward extrude Evaluations 1. Calculation of reduction, R = {Dq^-D-^)IDq^ * 100 2. Calculation of effective strain, e = In R 3. Calculation of flow stress, a = Ks^ "K" and 'n' values are chosen from the material database corresponding to the strain. 4. Calculation of approximate load = Aq a 5. Punch pressure = a Constraints 1. Buckling Ratio = Length/Diameter <= 2.3 (n/a in closed extrusion) Failure handling mechanism: Tell user to change billet size 2. Punch pressure < 275 ksi (limit of typical cold forming tool materials) 3. Necking failure : (wall thickness/bottom thickness) < 1 Failure handling mechanism: Inform user to increase bottom thickness or reduce wall thickness 4. Fracture: strain s <= 0.8 ef (from fracture limit table for a given material) Failure handling mechanism: Add anneal unless annealed already 5. Bottom thickness limit: > 0.06" and > 0.2*punch diameter Failure handling mechanism: Increase bottom thickness> 0.06" 6. Minimum wall thickness: >0.2" Failure handling mechanism: Increase min. wall thickness> 0.2" 7. Minimum reduction: 30% Failure handling mechanism: Inform user to increase reduction 8. Minimum Extruded length: < 3*Punch diameter 192 Failure handling mechanism: Inform user to alter extruded length III.B. Warm and Hot backward extrude: Evaluations 1. Calculation of reduction, R = * 100 2. Calculation of effective strain, s = In R 3. Calculation of flow stress, a = Cs*^ The strain rate is determined as Vavg/Lo where Vavg is assumed to be 15"/sec for an initial guess for warm and 30'Vsec for hot which is modified later depending upon machine. 'C and'm' values are selected from the material database based on temperature and strain 4. Calculation of approximate load = Aq o 5. Punch pressure = a Constraints 1. Buckling Ratio = Length/Diameter <= 2.25 warm, 2 hot (n/a in closed extrusion) Failure handling mechanism: Tell user to change billet size 2. Punch pressure < 200 ksi (limit of typical cold forming tool materials) 3. Necking failure : (wall thickness/bottom thickness) < 1 Failure handling mechanism: Inform user to increase bottom thickness or reduce wall thickness 4. Bottom thickness limit: >0.1" warm and 0.15" hot Failure handling mechanism: Increase bottom thickness 6. Minimum wall thickness: >0.2" Failure handling mechanism: Increase min. wall thickness> 0.2" APPENDIX D ADDITIONAL CASE STUDIES DEPICTING THE DISCRIMINATING CAPABILITIES OF DCM 193 194 In the following sections three additional case studies are described to depict the discriminating capabilities of DCM. CASE STUDY D1 : Effect of alternate machine selection on costs In this case study the cost differential due to a different selection of equipment for the same set of operations which was determined by DCM is described. The same input sequence provided in the example in figure 34 with slightly different material cost was considered for this study. The best sequence and plan cost is shown in figure 76. For the same inputs three additional best plans were requested in ascending order of costs. The system response is shown in figure 77. On closer examination of the resulting three best plans, one can note that the process sequence and operations are identical. However, there is a different selection of equipment in each of the three best plans. The cost for the machines M4 and M8 were made identical in the knowledge database of the system CEPESS. Therefore, the best plans 1 and 2 show the same cost of $1.34. However, machine M5 (1000 ton machine vs 500 ton of M4 or M8) is more expensive than M4 or M8 by $0.15 and therefore the plan cost is $1.49. Thus DCM is able to represent this difference in costs due to different selection of equipment. In the traditional cost systems, costs for equipment are accounted by department and all forming machines in the forming deparment may be allocated the same costs. 195 CASE STUDY 02: Effect of increased part weight on costs In this case study, the effect of weight of the part on the cost was investigated. If the part geometry were changed to induce a weight change, this may lead to alternate process selection and may not accurately track the impact of the weight change on costs and the sensitivity of DCM to such a change. Therefore, the weight was increased by increasing the density of steel fictitiously from 0.28 to 0.6. This change forced the same best process selection as in the previous case study. However, the cost of heavier material, cost of heating a higher weight (as energy required is calculated based on mass), are factored into the overall cost by DCM. The resulting plan cost was $1.48 (figure 78). This shows another notable discriminating feature of DCM. In conventional cost systems, heating costs are accounted by an amount that is insensitive to slight changes in weight of the parts. CASE STUDY D3: Impact of order quantity on costs In this case study, the impact of part quantity ordered was investigated. The data in the costs database contains different costs for operations performed on different order quantities. The ranges used were (0-1000) and (3000-10000). The order quantity in the above case studies was 9000/day. However, when the order quantity was reduced to 500/day, the cost of the best plan rose from $1.34 to $1.87 as shown in figure 79. This was due to the increased tooling cost for small order quantities which was reflected in the costs for forming operations in the database. On requesting four best plans for the lower order quantity, the 196 plan costs also vary based on the machine selected as shown in figure 80. Note that the best process has not changed, which is warm forming. From the above case studies, the capability of DCM in discriminating subtle influences of various parameters on costs which are not captured by traditional costing systems and selection methods is apparent. SELECT-PLANS , —-Op 10 : For wnr d-Open-Ex t r ude-Hor n '^■“~-Op20 : Sinple-Upset-Harr'i - -Op30 : Bockiiiard-Con-Ex trude-Horn In fo rm a d o n P r i n t ! Sovel ■ Pi on Cost = 1.34 : PRE-OPS: SHEARING TRAHSPORT GRAPHITE-COATING TRANSPORT HEAT TRANSPORT :0P: 'OplO:FORHARD-OPEN-EXTRUDE-HARH' ‘ : MACHINE; ' "N4\ " : PRE-OPS: NONE :0P: "0p20: SIMPLE-UPSET-HARM-. ■ : MACHINE: ' ,"M4\ " : PRE-OPS: NONE : OP : \ " 0p30 : BACKHARO-CAN-EXTRUOE-HARM', - : MACHINE: Figure 76. Best plans for example in case study D1 197 i flu Y e i No ïpfannatijctti OK! PrinU Stive!' P l a n C o s t =1.3-1 PRE-OPS: SHEARING IRANSPORT GRAPHIIE-COAr[NG IRAHSPORI HEAT IRANSptiRT OP: '.■OplO:FORHARO-OPEN-EXTRUDE-HAKM\" HA CHINE: -Ht', PRE-OPS: NOME , " • OP : ‘ \~'0p20 : St MPI E-MPSFT-NARM\ " MACHINE: ' 'M-t' PRE-OPS: NOME OP: -0p30:BACKHARD-CAN-EXTRUDE-NARH- ' MACHINE: ' -M-t . ' P l a n C o s t =1.31 PRE-OPS: SHEARING TRANSPORT GRAPHITE-COATING TRANSPORT HEAT rRAMSPi'RI OP: \ "Op In :FORMARO-OPEN-E%TRlIDE-NARM' ' MACHINE: \"M 8' PRE-OPS: NONE OP: '" Op20:SIMPIE-UPSET-MARM\" M A C H IN E : ' PRE-OPS: NONE OP: '. "0p30 : BACKl'lARD-CAN-EXTRUDE-MARM'. ' MACHINE: '\-M 8\ ' Plon Cost = 1.(9 PRE-OPS: SHEARING TRANSPORT GRAPHITE-COATING TRANSPORT HEAT TRANSPORT! OP: V”QpI0:F.OR!!ARD-OPEN-E: Figure 77. Three best plans shown for case study D1. 198 S J ^ E C T - F L ^ M a i n H e n u llpdnte! Accept! ;Validnte! Y e s Mu /ce-peS3/'pldiis/fi;irga>plci.;do~ Inform ation OK! Print! Cave! "Plan Cost =1.48 : PRE-OPS: SHEARING TRANSPORT GRAPHITE-COATING TRANSPORT HEAT TRANSPORT : O P : \ "Op 10 :FORHARD-OPEN-EXTRUDE-HARM\ ' . . .' . /■ /:t1ACHINE: \-H4\ ' ■' : PRE-OPS: NONE :0P: \ Op20:SINPLE-UPSET-HARN\' : MACHINE: \-M 4\" : PRE-OPS; NONE : OP: \ ''Op3QYQACKl(ARD -CAN-EXTRUDE-llARM\ " : MACHINE; ”M4\" ______ Figure 78. Best plan showing effect of increase in weight of the part. 199 SELECT-PLANS "^-Op 10: Forward-Open-Extriide-Harr'i —-Op20 : Sifiple-Upset-Uarn \ -Op30:OackMard-Can-ExtrurJerUnrM ' M8 ■ ■HO Infortnalion .OKI Print! Save! Plon Cost = 1.87 PRE-OPS: SHEARING TRANSPORT GRAPHETE-COArTNG TRANSPORT HEAT TRANSPORT OP: \ "OplOiFORHARD-OPEN-EXTRUDE-NARM'- " MACHINE: \ "M8>\" PRE-OPS: NONE OP; \"O p20: SIMPLE-UPSET-HARM'-." MACHINE; \"M 8\" PRE-OPS; NONE OP: \ "0p30:BACKHARD-CAN-EXTRUDE-NARM\" MACHINE: \"M 8v‘‘ Figure 79. Effect of decrease in order quantity of parts. 2 0 0 SELECT-PLAHS Op 10 1'For w nrcj-O pen-Extr Lide-Hiii III V—— -OpZO:Sinple-Upset-Uarn , V . v"-:7-~Op30 ; Backwcu d-.Cun-Ex tr tide-Hur i=i \ \ 'T- - US rn farm u riott OK! Print! Suvi^l •"Plan Cost = 1.37 “:PHE-OPS: SriEARItK; fRAMSPOHr CNAPHf rE-COA t Ùi(, I RAHSPURt lliA l fKAnSPOHT . :0P: 'OpJO:EORPARD-OPEt{-ESrRUDE-t-lAW1...... : M A C H IN E : \ " M 8 \ : PRE-OPS: NONE .OP: '. 'Op20;SIHPLE-nPSEl-HARtt', ' -tlACHINE: - - ' PRE-OPS: NONE :0P: ' Op30:BACKNARD-CAN-EX rRUDE-HARM .- :N A C H IN E : ' 'M8\' ^ ;plnn Cost = 1.97 - .:”pRE-OPS;;.SHEARINC fRANSPORI GRAPHITE-COATItfC' IRANSPORl HhAl IK A N SP O R l :0P: 'OplO:FORHARD-OPEN-EXrRUUE-MARN : MACHINE: \ "MÜ " : PRE-OPS: NONE : OP : \ ■ O p 20 : SIMPLE-UPSET HARM'' “ ; M A C H IN E : ' M4 • " : PRE-OPS: NONE :0P: ' •Op30;BACKNARD-CAN-EXrRUDE-WARM'- : MACHINE: ' "M4'." “Plan Cost = 2.32 : PRE-OPS: SHEARING IRAdSPORT GRAPHI TE-COA Ï IMG ' I P.ANbPOPi MÜ1 I R/ NSPORT. : OP; \'O p 10:FORWARD-OPEN-EXIRUOE-HARM- “ ' : M A C H IN E ; \ ' M5 \ ' : PRE-OPS: NONE :0P; Op20:SIMPLE-UPSEr-NARH\ " ; MACHINE: ' M5'\ ' : PRE-OPS: NONE :0P: \ 'Op30:BACKNARD-CA.N-E% TRUDE-NARM “ : M A C H IN E : \ 'H 5 \" 'Plon Cost - 2.61 , !; PRE-OPS: SHEARING TRANSPORT GRAPHITE-rCOATING TRAtiSPORfHEA 1 TRANSPORT :0P: ' Op 10 : FORHARD-OPEN-E%TRUDE-NARM \ : M A C H IN E : \'MI\" : PRE-OPS: TRANSPORT : OP: \'b p 2 0 :SIftf»LE-UPSET-HARM\" : MACHINE: \ 'M8\' Figure 80. 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