COMPUTER MODELING OF FLOW LINES AND FLAW MIGRATION --- IN
BULK DEFORMATION PROCESSES 1 I
A Thesis Presented to The Faculty of the College of Engineering and Technology Ohio University
In Partial Fulfillment of the Requirements for the Degree Master of Science
NITIN V. HATTANGADY ,* - -"- November, 1987 ACKNOWLEDGEMENTS
I take this opportunity to express my sincere gratitude to Dr. J.S. Gunasekera for the valuable guidance and assistance during the course of this project and my stay at Ohio University.
I would also like to thank Dr. Shesh Srivatsa (GE- AEBG, Cincinnati, Ohio), Dr. Sulekh C. Jain (GE-AEBG, Cincinnati, Ohio), Dr. H.L. Gegel (WPAFB-MLLM, Dayton, Ohio) and Dr. J.M. Alexander (Stocker Visiting Professor, Ohio University) for their participation and suggestions during this project.
September 1987 NITIN V. HATTANGADY TABLE .OF CONTENTS
1 . INTRODUCTION ......
2 . PREFERRED ORIENTATION AND MECHANICAL FIBERING ..... 6 METAL INGOT STRUCTURE ...... 7 EFFECT OF MECHANICAL WORKING ON THE METAL STRUCTURE ...... 10 DIRECTIONALITY OF THE MECHANICAL
PROPERTIES DUE TO METAL WORKING ...... 25
3 . PROGRAM STRUCTURE AND DESCRIPTION ...... 30 IMPLEMENTATION OF FLOW LINES IN ALPID 2.0 .... 31 DESCRIPTION : PROGRAM FLINES ...... 35 POST PROCESSOR FLPLOT ...... 40
4 . VALIDATION OF THE SOFTWARE ...... 52 FLOW LINE PLOTS FROM EXTRUSION SIMULATION ..... 53
5 . CONCLUSIONS ...... 62
6 . REFERENCES ...... 64
7 . APPENDIX A (USER'S MANUAL) ...... 66
8 . APPENDIX B (SAMPLE RUN) ...... 76
9 . APPENDIX C ...... 106
10 . APPENDIX D ...... 109 11. APPENDIX E : LISTING OF SAMPLE DATA FILES ...... 110 12. APPENDIX I?: ULTRASONIC NON-DESTRUCTIVE TESTING IN THE FORGING INDUSTRY ...... 115 --LIST OF FIGURES
1. Macrostructure of cast steel containing 0.8 %
carbon ...... 9
2. Typical development of grain flow by plastic
deformation of metals, (a) As consolidated, (b)
As wrought, (c) Wrought and re-crystallized ...... 11
Macrostructure of deformed metal after forging ......
4. Comparison of grain structures of forging, bar
stock and casting ...... 14
5. Deformation in compression of idealized
equiaxed grains in a workpiece, such as is done in forging or rolling of metals. (a) Before,
and (b) After plastic deformation ...... 17
6. Deformation of single crystals. (a) Slip in
tension. As deformation progresses, the slip planes tend to align themselves in the direction of pulling. (b) Slip in compression. The slip planes tend to align themselves parallel to the plattens ...... 18
7. A1ignment of Manganese Sulphide inclusions (thin dark elongated regions) in AISI 1215
steel leading to mechanical fibering. Magnification 100x ...... 22
8. Schematic illustration of the deformation of soft and hard inclusions, and their effect on
void formation in plastic deformation of metals ..... 24
9. Anisotropy in wrought metals, (a) development of
ductility anisotropy, (b) nature of anisotropy ...... 27
10. Effect of forging reduction on longitudinal and transverse reduction in area ...... 28
11. Flow chart fo the FLINES ALPID version ...... 38
12. Flow chart for the post processor FLPLOT ...... 44
13. Flow lines in the extrusion of cast billets - step 0 ...... 53
14. Flow lines in the extrusion of cast billets - step 40 ...... 54
15. Flow lines in the extrusion of cast billets - step 60 ...... 55
16. Flow lines in the extrusion of cast billets - step 110 ...... 56
17. Display of maximum strain directions in cast billets (step 110) ...... 57
18. Flow lines in the extrusion of extruded billets -v- .step 0 ...... 58 19. Flow lines in the extrusion of extruded billets .step 40 ...... 59
20 . Flow lines in the extrusion of extruded billets .step 60 ...... 60
21. Flow lines in the extrusion of extruded billets .step 110 ...... 61 Chapter 1
INTRODUCTION
One of the most important goals of any manufacturing organization is to produce defect free parts. Defect avoidance is critical for rotating parts such as an engine disk, and the ability to detect flaws having the characteristic of a flat bottom hole by ultrasonic inspection is absolutely essential. The ability to find such a flaw by ultrasonic inspection when a forged part is ensonified is determined by the Flow Line Theorem [5], which states that most defects will lie along flow lines and the sonic beam must be normal to the flow lines to maximize the ability to detect ideal flat bottom flaws. An empirical criterion says that the limit of detection is when the sonic beam makes an angle of 25 degrees with respect to the flow line normal [5].
New complex materials, with structural and high temperature applications in future aircraft systems, are being developed to meet specific needs. The processing of these expensive materials entails the use of special, expensive and complex metal forming operations in order to achieve the desired properties in the product. The application also imposes a requirement of using defect free parts. As a result of mechanical working, a certain degree of directional ity is introduced into the microstructure in 2 which the second phases and inclusions are oriented para1 lel to the direction of greatest deformation. When viewed at low magnification, this appears as flow lines or fiber structure. Flaws in a final forged component often originate and can be detected in the original billet. Hence, predicting the metal flow, orientations of the flow lines formed and/or the ability to model the migration of flaws would be an important capability in any metal forming simulation program. The location and the orientation of the flaws determines the directional properties of the formed part and hence, tracking the movement of the flaws would help in deciding whether the billet should be subjected to further processing.
Thepreforned billets used in the forging industryare generally extruded and in some cases cast into the desired shape. Extruded billets have a fiber structure with the flow lines in the direction of applied force due to the extrusion operation. A further deformation operation would result in re-orientation of the existing flow lines. Cast billets, on the other hand, have an initial homogeneous structure and any metal forming operation results in a breakdown of the dendritic structure. The grains get elongated in the direction of greatest deformation, i.e., the direction of maximum principal strain to form a fibrous structure.
The objective of this project was to develop a 3 computer program, linked with ALPID (Analysis of Large
Plastic Incremental Deformation) [8,9], to predict the orientations of flow lines and to serve as a tool to improve the efficacy of the ultrasonic non-destructive testing technique used in the forging industry.
A computer program, FLINES, with graphics capability has been developed and incorporated into the rigid plastic finite element program ALPID to predict the orientation of the flow lines and track the path of user specified material points at randomly oriented flaws. The module
FLINES, developed in FORTRAN 77, provides two options viz., tracking user specified material points on flow lines of known orientations (as in extruded billets) or placing circles on the billet cross section and track their deformation (as in the case of cast billets). This program has been interfaced with the ALPID program version 2.0. A post processor, FLPLOT, with the capability of displaying the orientation of the flow lines before and after deformation, has been developed. The post processorhas the capabilty of displaying the gradual distortion of the finite element mesh placed on the initial billet geometry, if the nodes are being tracked. Additional features include tracing the path of a single point within the billet geometry through the entire metal forming process, and display of the magnitude and direction of the principal strain and the material rotations (in case of cast 4 billets). The post processor provides graphics display of the results on Tektronix 4000/4100 series terminals and compatibles and Intergraph Interact/Interpro32 workstations. An important feature of the post processor is the creation/update of the global flow lines data base which can be used to carry over the data through re- meshings and view the movement of the flow lines and migration of user specified material points during the entire simulation. The validation of the software has been carried out by simulating extrusion of a round to round section as an example problem. Extrusion has been used as the example problem because flow lines in extruded products are always oriented parallel to the direction of extrusion and hence the results would be self-validating. The software developed has been used successfully to predict flow line orientations formed in a complex forging. The experimental validation of the orientation predictions was carried out, the results of which cannot be published here due to proprietary reasons.
The information provided by the program can be used to devise an effective and efficient scan plan to detect defects. Also, the grain flow can be studied and if necessary, the preform and/or the final forged envelope can be modified in order to obtain the desired grain flow. The software is also capable of providing information on the strain distribution by providing a display of the distorted 5 mesh placed on the initial billet geometry. This information is useful to identify visually, the regions for metallurgical study. Chapter 2
PREFERRED ORIENTATION AND MECHANICAL FIBERING
Mechanical working of metals/al loys by forming processes like forging, rolling, extrusion introduces a pronounced degree of directionality into the micro and macro-structure of the metal/alloy. The orientation of the crystal lattice about a particular direction is known as preferred orientation or texture [6]. The grains get elongated and the inclusions, segregations and second phases get oriented along the principal direction of working resulting in the formation of flow lines or fiber texture.
Most applications in the metal forming industry involving forging and extrusion use extruded billets, wherein the forming operation begins with a billet with known flow line orientations. The flow lines in the billet get re-oriented by the forming process and the final shape and orientation depends on the geometry of the product and process parameters likelubrication etc. In cases where cast billets are used, the forming operation begins with an initial workpiece which is nearly homogenous. Depending on thetype ofthe formingoperation, the flow lines formed in a cast billet may or may not have the same orientation as the flow lines formed on using the extruded billet. For example, extrusion of cast as we11 as extruded billets will 7 produce flow lines in the product oriented in the direction of extrusion. This can also be visualized from the fact that a circular cross sectional area in the initial billet geometry, in a 4:l round to round reduction by extrusion, would deforminto an elliptical section due to the area reduction and the velocity profile. The resulting section wouldhave a width half the original diameter and length 4 times the original diameter (approximately) in axisymmetric extrusion. The flow line orientations in a forged product wherein the initial workpiece is an extruded billet would be different from the flow line orientations in the forged part with cast billet as the initial workpiece.
This chapter deals with the cast ingot macrostructure, preferred orientation, mechanical f ibering and the effect of mechanical working on the mechanical properties of the metal/alloy.
Metal Ingot Structure :
The crystals which form in the process of solidification of a metal may have many different structures (dendritic, lame1 lar, needle type or acicular etc.) depending on the rate of cooling, and the type and amount of admixtures or impurities in the melt. Perfect crystals of proper external shape can be obtained only under controlled cooling conditions and when the metal has a very high purity. In the great majority of cases, 8 branched or tree-like crystals are obtained which are called dendrites [3]. More often, dendritic structure is revealed only after special etching of microsections (Fig.
1). Etching reveals not only the structure of crystallites but the boundaries between them as well. Mechanical working of a cast billet results in the breakdown of the dendritic structure and formation of the fiber texture or flow lines [3].
In general, castings are characterized by porosity and segregation of alloying elements on a small scale [l2]. Because al'loying elements have a higher solubility in liquid state than in the solid state, they concentrate in the melt during freezing. Therefore, the alloy content is slightly higher in the interdendritic regions, which contain the last region to freeze, than at the axes of the dendrites. The severity of the concentration gradients depends on freezing time, subsequent thermal treatments and the diffusivity of the alloys. Indigenous inclusions also precipitate in the interdendritic regions. Because of 1 iberation of gas, difficulty is frequently encountered in supplying liquid metal to all parts of the interdendritic areas. Porosity is a natural consequence. Even small metal working reductions tend to close and weld voids, and the thermal treatments reduce alloy segregation compared with that of castings. By reducing porosity, the first small amounts of working improves both strength and Fig. 1 Macrostructure of cast steel containing 0.8 % carbon [3] 10 ductility. Heavier reductions develop anisotropy or directional variations in properties.
Effect -of -Mechanical Workinq --on the Metal Structure :
The initial breakdown of the cast ingots or its subsequent working - for example, by forging, results in thepreferred a 1 ignment of the segregations, secondphases, inclusions and the crystalline grains themselves in the direction of greatest deformation (or metal flow), as shown in Fig.2 . The directional pattern of the crystals following working is known as the grain flow pattern [lo]. An example of the grain flow pattern in an actual forging is shown in Fig. 3.
Fiber grain flow is one of the most important properties to be checked in finished forgings. The fiber flow is determined by the extent of hot working and the amount of plastic flow during the fabrication of the forging [ll]. The correct grain flow in a forging determines the maximum strength to a forged part. Proper grain flow in dense forgings increases the strength of the part, improves machinability and reduces warpage during heat-treatment [ll]. Flow lines are easily shown by macro- etching a ground and polished section of a forging. The fibrous structure of forged parts is usually attributed to segregations of inclusions which may be composed of carbides, phosphides, sulphides or other metallic or non- 4 OIRECTION OF METAL FLOW IN PLASTIC OEFORMATIOW -
SECONO ,PHASE
SECONO PHASE
Fig. 2 Typical development of grain flow by plastic deformation of metals, (a) As consolidated : grains, segregation and second phases are randomly oriented, (b) As wrought : grains, segregations and second phases are elongated in the direction of plastic deformation, (c) Wrought and re- crystallized : grains are randomly oriented, segregations and second phases are oriented in the direction of plastic deformation [lo]. Fig. 3 Macrostructure of deformed metal after forging [3] metal 1ic inclusions. While subsequent heat-treatment can change the grain micro-structure of the parent metal/alloy, the arrangement of the inclusions is fixed by the forging process and cannot be changed by heat-treatment (as shown in Fig. 2 ). Thus, the fibrous structure is retained regardless of the heat-treatment. Properly developed grain flow closely follows the outline of the component. In contrast, bar stock and plate have grain flow in only one direction and changes in contour require that flow linesbe cut, exposing grain ends and rendering the material more liable to fatigue and more sensitive to stress corrosion.
A number of factors affect the grain flow in forgings. Location of the parting line has a critical bearing on the grain flow and the directional properties of the forged piece. Objectionable flow patterns may be created if the flow path is not smooth [lo]. In the forging of some parts, the die sequence as well as the designs of the dies themselves may be altered in order to control the grain flow pattern [lo]. Forging and lubrication techniques can also be used for control 1ing grain flow. Fig. 4 shows the grain structures of forging, machined bar stock and casting. Maximum strength is not obtained in the product machined from bar stock because the grain flow is in one direction and is interrupted by machining. Also, maximum strength is not obtained because the fibers are not interlocked. GRAIN
FORGING BAR STOCK CAST l NG True grain flow Grain flow broken No grain flow by machining
Fig. 4 Comparison of grain structures fo forging, bar stock and casting [lo] 15 To a degree, grain flow or fibering produces directional characteristics in properties such as strength, ductility and resistance to impact and fatigue [lo]. In forging, this directionality is used to provide a unique and important advantage. This is achieved by orienting grain flow within the component so that it lies in the direction requiring maximum strength. This variation of properties with orientation with respect to some system of axes is known as anisotropy.
Two general types of anisotropy are found in metals
[21 : (1) Crystal lographic anisotropy results from the preferred orientation of grains produced by severe deformation. Most crystalline materials contain grains with lattice orientations that are not random but instead are clustered to some degree about a particular orientation. Bodies in which the grains are oriented non-randomly are said to have
a preferred orientation or texture [6]. The mechanical and thermal history of a specimen determines the nature of the texture that is developed. Preferred orientations have an important effect on the properties of commercial products. A fine grained metal specimen in which the grains have random lattice orientations will possess identical properties in all directions (provided that there are no elongated inclusions, segregations or boundaries), but a specimen with a preferred orientation will have directional 16 or anisotropic properties which may or may not be desireable depending on the intended use of the material. A metal which has undergone a severe amount of deformation, as in rolling or wire drawing, will develop a preferred orientation, or texture, in which certain crystallographic planes tend to orient themselves in a preferred manner with respect to the direction of the maximum strain. Plastic flow also produces a preferred change of shape of grains. The progress of re-orientation is gradual; the orientation change proceeds as plastic flow continues, until a texture is reached that is stable against indefinitely continued flow of a given type. The texture is also influenced by the temperature of the specimen during deformation - especially if the temperature is high enough to permit re- crystal 1ization to occur during deformation. The symmetry of the preferred orientation generally tends to match the symmetry of the principal strains [6].
If a piece of metal with uniform equiaxed grains
(spherical, as shown in Fig.5 ) is subjected to plastic deformation either by compressing it, as shown, or by subjecting it to tension in the horizontal direction, the grains become elongated in one direction and contracted in the other. As a result, the material has become anisotropic. As shown in Fig.6 , when a metal crystal is subjected to tension, the sliding blocks rotate towards the direction of pulling. Thus, slip planes tend to align with Fig. 5 Deformation in compression of idealized equiaxed grains in a workpiece, such as is done in forging or rolling of metals. (a)Before,and (b) After plastic deformation [2]. Fig. 6 Deformation of single crystals. (a) Slip in tension. As deformation progresses, the slip planes tend to align themselves in the direction of pulling, (b) Slip in compression. The slip planes tend to align themselves parallel to the plattens [2]. 19 the direction of deformation. Likewise, for a polycrystal line aggregate, with grains in various orientations, all slip directions tend to align themselves with the direction of pulling. Under compression, the slip planes tend to align themselves in a direction perpendicular to the direction of compression (Fig. 6b). In deformation processes more complex then simple tension or compression, slip planes tend to align themselves in the general direction of deformation. Since the individual grains in a polycrystal 1 ine aggregate cannot rotate freely, lattice bending and fragmentation will occur.
A number of theories have been proposed to explain the texture formation in mechanically worked metals and alloys
and have been reviewed by Barret and Massalski [6] and Hsun
Hu, Cline and Goodman [7]. It is not the intent of the author to delve into these theories dealing with deformation textures in metals and the interested reader is referred to the above references.
The preferred orientation resulting from plastic deformation is strongly dependent on the slip and twinning systems available and the principal strains, but it is not generally affected by processing variables such as die angle in case of drawing and roll diameter, roll speed and reduction per pass in case of rolling. The most important mechanical variables are the geometry of flow and the amount of deformation (reduction). Thus the same deformation texture is produced whether a rod is made by rolling or drawing [I].
A preferred orientation can be detected with X-rays after about a 20 to 30 percent reduction incross-sectional area. At this stage of reduction, there is appreciable scatter in the orientation of the individual crystals about the ideal orientation. The scatter decreases with increasing reduction, until at about 80 to 90 percent reduction, the preferred orientation is essentially complete.
The re-crystallization of a cold worked metal generally produces a preferred orientation which is different from and stronger than that existing in the deformed metal. This is called an annealing texture, or re-crystal 1 ization texture. Since the existence of a re- crystallization texture depends on a preferential orientation of the re-crystallized grains, the resulting texture is strongly dependent on the texture produced by the deformation. Other important variables which affect the annealing texture are the composition, the initial grain size and the grain orientation of the alloy, and the annealing temperature and time. Generally, the factors which favour the formation of fine re-crystallized grain size also favour the formation of a random orientation of the re-crystallized grains. Moderate cold reductions and low annealing temperatures are beneficial. 2 1 Sometimes the formation of a strong texture in a finished part is beneficial. An example in which anisotropy is very important and is much desired is the steel sheet used for electrical transformer cores. A high permeability in the direction of the applied magnetic field is wanted, and may be obtained by rolling and annealing treatments designed to orient as many grains as possible with their easily magnetized directions in one direction in the sheet. On the other hand, unequal mechanical properties caused by a specific texture in a sheet may cause difficulties or waste in certain deep drawing operations.
(2) Mechanical anisotropy (or mechanical fibering) is due to the preferred alignment of structural discontinuities such as inclusions, voids, segregations and second phases in the direction of working. This appears as flow lines or fiber structure on an etched macrograph. The alignment of Manganese Sulphide inclusions in steel after rolling is shown in Fig. 7. This type of anisotropy is important in forgings or plates. If the spherical grains in -~ig.5 were coated with impurities, these impurities would a1ign themselves general ly in the horizontal direction after deformation. As a result of a mechanical working operation, second phase particles will tend to assume a shape and distribution which roughly corresponds to the deformation of the body as a whole. Second phase particles Fig. 7 Alignment of Manganese Sulphide inclusions (thin dark elongated regions) in AISI 1215 steel leading to mechanical fibering. Magnification lOOx [2]. 23 which are originally spheroidal will be distorted in the principal working direction into an ellipsoidal shape if they are softer and more ductile than the matrix. If the inclusions or particles are brittle, they will be broken into fragments which will be oriented para1 lel to the working direction, while if the particles are harder and stronger than the matrix, they will essentially be undeformed, as shown in Fig. 8 . The orientation of second phase particles during hot or cold working and the preferred fragmentation of the grains during cold working are responsible for the fibrous structure which is typical of wrought products. The existence of a fiber structure is characteristic of all forgings and plates and is not to be considered as a defect.
The principal direction of working is defined as the longitudinal direction. This is the long axis of a bar or the rolling direction in a sheet or a plate. Two transverse directions must be considered. The short- transverse direction is the minimum dimension of the product, for example, the thickness of a plate. The long- transverse direction is perpendicular to both the longitudinal and the short-transverse directions. In a round or a square, both the transverse directions are equivalent, while in a sheet, the properties in the short- transverse direction cannot be measured. To achieve an
optimum balance between ductil ity in the longitudinal and Before deformation - Strong direction + of deformed metal
After deformation . '. Void Voids
Soft inclusion Hard inc:aion Hard inciueion 6
Fig. 8 Schematic illustration of the deformation of soft and hard inclusions, their effect on void formation in plastic deformation of metals [2]. 25 transverse directions of a forging, it is often necessary to limit the amount of deformation to 50 to 70 percent reduction in cross-section.
Directional* --of the Mechanical Properties -due -to Metal--
Working :
It is frequently found that the tensile properties of the wrought metal products are not the same in all directions. The dependence of properties on orientation is called anisotropy. While engineering materials such as steel, cast iron and aluminium may appear to be isotropic when viewed on a gross scale, it is readily apparent when they are viewed through a microscope that they are anything but homogeneous and isotropic. Most engineering materials are made up of more than one phase, with different mechanical properties, such that on a micro scale they are heterogeneous. Further, even a sing1 e-phase metal will usual ly exhibit chemical segregation resulting in varying mechanical properties from point to point. Metals are made up of an aggregate of crystal grains having different properties in different crystal lographic directions. The equations of strength of materials are valid, in general, because for a specimen of any macroscopic volume, the materials are statistically homogeneous and isotropic. However, when metals/al loys are severely deformed in a particular direction, as in rolling or forging, the mechanical properties may be anisotropic on a macro scale
The mechanisms affecting the influence of deformation on mechanical properties are known qualitatively but not quantitatively [12]. Grain flow or fibering produces directional properties in characteristics like ductility, strength and resistance to impact and fatigue. In forging, this directionality is used to orient the grain flow in the direction requiring maximum strength. The variation in yield strength and tensile strength is not particularly important.
In the case of heat treated wrought steels, these strength properties are independent of the direction of testing. The important anisotropies are in ductility, notched bar strength and fatigue. The variation of these properties with increasing degree of working is shown in
Fig. 9 [lo]. The effect of forging reduction on longitudinal and transverse reduction of area of SAE 4340 steel is shown in Fig. 10 [I]. The forging ratio is the ratio of the original to the final cross sectional area of the forging. It is usually found that the optimum properties are obtained with a forging ratio of 2 to 3:l. The resistance to stress corrosion cracking can be highly directional, for example, in high-strength aluminium alloys. The maximum load bearing capacity in a forging is realized when the component is loaded along the fiber, or INCREASING IMPACT STRENGTH INCREASING TENSILE REDUCTION OF AREA. TRANSVERSE DUCTILITY - FATIGUE - -a "2 & (D I-'------3 Prn PO0 rtw rt F: El 4 4 (0 0 (D r'd rt LC 0 MOI-'-'?I m r r- 9 raceP P-F: Y rnOO\D 0 rtF: rt r-9 4 PS' o r.rt w rt Y'C P P nplP rro o r-LC -mrn 0 rt Y 0 w '4 Fig. 10 Effect of forging reduction on longitudinal and transverse reduction of area [I] 29 the grain flow direction [lo]. Measures of ductility like reduction of area are most affected. In general, the reduction of area is lowest in the short-transverse direction, intermediate in the long-transverse direction, and highest in the longitudinal direction. Transverse properties are particularly important in thick-walled tubes like guns and pressure vessels, which are subjected to high internal pressures. Chapter 3
STRUCTURE DESCRIPTION
Implementation -of --Flow Lines -in ALPID -2.0 :
The implementation of flow lines logic into ALPID does not take into account the presence of flow lines or defects in the workpiece before the metal forming operation. Hence, the material is modelled as homogeneous and isotropic. The program does not attempt to predict the microstructural behaviour of the material. A1so, defects, if any, are assumed to have the same flow behaviour as the metal alloy. For cases where in the material flow behaviour is different in the defect zone, the material properties for that zone will have to be specified as required by ALPID 2.0 (refer ALPID 2.0 User's manual) .
The flow lines logic has been incorporated into ALPID 2.0 as separate subroutines, which do not alter the results of ALPID. The program caters to two different tyhes of billets used in forging, viz., cast billets and extruded billets. Cast billets have an initial homogeneous structure and forging or any other metal forming operation results in breakdown of the dendritic structure. The grains are elongated in the direction of deformation to form a fibrous structure. The objective in this case is to identify the orientation of the flow lines. Since the flow lines are oriented generally in the principal direction of working and the fiber structure results from the elongation of grains, the orientation of flow lines in this case can be shown by placing circles (rings of circular cross- section, in axisymmetric cases) on the billet cross- section, defined by discrete points and tracking their migration through the forming process. After plastic deformation, the major axis of the ellipse thus formed would represent the maximum strain direction and hence the orientation of the flow line. In the computer program, for
this option, 16 points are generated to define a circle on the initial billet geometry, each circle being treated as a flow line for post-processing with connectivity specified
in a data file FLCON.DAT generated by the program. The maximum principal strain is calculated by measuring the
length of the longest diagonal. Since the circle is defined by discrete points, this is a source of error,
which has been reduced by using 16 points to define each circle. The accumulated strain values in each circle can be displayed by the post-processor. Arrows are placed representing the magnitude and direction of the maximum principal strain.
In case of extruded billets, due to previous history of plastic deformation, the homogeneous grain structure is already destroyed and flow lines exist parallel to the 32 direction of extrusion. Hence, in this case, the user specifies the co-ordinates of the points assumed to lie on flow lines of known orientations and their connectivity (to be used later during post-processing of the results) in separate data files. The program tracks these user specified material points and with successive updates of the data base, the user has the facility to view the initial and final orientation of the flow lines or the orientation for any other combination of output time steps. Effectively, the program displays the gradual distortion of the flow lines already formed due to extrusion.
The program FLINES has three working versions, viz., the FLINES ALPID version which is interfaced with the fortran code of ALPID, the FLINES Batch mode version in which the program is executed independently by accessing the binary output file of the ALPID simulation and the FLINES REVFL version in which the reverse flow lines calculations are carried out. The use of the FLINES Batch mode version is to be encouraged since this would result in considerable savings as regards to the CPU time. This is due to the fact that FLINES is executed only for the required number of steps before re-meshing, thus avoiding redundant calculations for extra steps which is the case in
ALPID. In the use of the Batch mode version of Flines, the user has to particularly ensure that all the points to be tracked are within the billet geometry. This is because 33
some of the calculations that are performed by ALPID to position the points that come in contact with the dies cannot be carried out in this version. In cases where points on the billet surface are to be tracked, the FLINES ALPID verion would have to be used. The REVFL (REVerse
Flow Lines calculations program) option is useful to map a critical region in the product geometry to the initial billet geometry. Thus, only this region can be subjected to a more severe non-destructive testing. This version can be run only after a complete ALPID simulation has been carried out.
The output from the program FLINES consists of a user specified printed output data file in which the initial and final positions of the points being tracked are printed and a flow lines data base for access by the post processor, FLPLOT .
The input data file for the cast billet case differs from that of the extruded billet case only for the initial run. This is because the circles being placed on the billet cross-section are defined by discrete points and each of the points is tracked individually during the
subsequent runs. A utility program, FLREAD, extracts data from the flow lines data base obtained on running ALPID and
writes a new data file POINT.DAT which can be used as input for subsequent FLINES ALPID runs. 34
The program FLINES has three other features incorporated into the post processor, FLPLOT, in addition to the display of flow lines and the maximum principal strain directions. The program has the capability to display the path of user specified material points through the deformation process, view the gradual distortion of the finite element mesh placed on the initial billet geometry (this option can be used when all nodes are specified as points to be tracked) and also view the material rotations due to deformation. The post-processor, FLPLOT, has been interfaced with Intergraph Interact/Interpro32 workstations and Tektronix 4000 and 4100 series terminals.
A number of error checks have been incorporated into the program and effort has been made to make the program user-friendly and bug-free.
The preparation of input data files for FLINES is quite simple and is explained in Appendix A (user's manual) of thisreport. The data is read in free format duringthe execution of the program. A listing of some sample data files required for the execution of the program is provided in Appendix E along with a typical flow lines printed output data file generated by the program. Appendix F describes the ultrasonic non-destructive testing process used in the forging industry. DESCRIPTION :
Program Name : FLINES
The program FLINES, which has been incorporated as a special subroutine in the metal forming simulation package ALPID (Analysis of Large Plastic Incremental Deformations)
version 2.0, uses the finite element technique to track the path of user specified material points. The user has to specify the flow lines option (for cast or extruded billets) and the co-ordinates of the points to be tracked in a data file POINT.DAT. In case of cast billets, the user specifies the co-ordinates of the center and the radius of the circle to be placed on the billet. The program then generates the points to define the circle and
outputs the connectivity in the data file FLCON.DAT, to be used later. The user has to ensure that the approximate location of each of the point that would be generated is within the billet geometry. In case of extruded billets, the user can specify points on the billet surface to be tracked. Two variables in addition to the co-ordinates define the position of the point on the billet.
The subroutine FLINES reads in the co-ordinates of the points to be tracked from the data file POINT.DAT, receives
the nodal velocities and the time step values from ALPID, calculates the shape functions, interpolates to obtain the value of the velocity at the point being tracked, and updates the position. The element within which the point being tracked lies, is determined by subroutine AREA using the area logic as explained below :
For the point P to be within an element El the sum of the
areas Al, A2, A3, A4 of the triangles formed by joining the four nodes to point P, must be equal to the areas of the
element E. After determining the element in which the
point P being tracked lies, the local co-ordinates S and T are calculated using the interpolation functions, the
complete derivation of which is given in Appendix C.-
For the special case of an element with parallel
sides, the interpolation equations reduce from a quadratic to a linear form. Hence, a separate subroutine FLLIN calculates the values of the local co-ordinates in this case. The derivation of the equations involved is given in
Appendix D. 3 7
The program output, stored in a user specified file (Flow lines printed output file), lists the initial and the final position of the points being tracked in a tabular form at the end of every time step. If the point to be tracked does not lie within the specified billet geometry, the program outputs an error message listing its number in the file POINT-DAT and value of the corresponding co- ordinates. The program output also consists of a user specified flow lines data base which is to be accessed by the post processor, FLPLOT, for graphics display.
The flow chart for the ALPID version of FLINES is shown in Fig. 11. Similar calculations take place in the other versions. FLOWCHART FOR FLINES (ALPID VERSION)
INPUT?
uCAST GENERATE POINTS AND BILLET CONNECTIVITY FlLE EXTRUDED I I BILLET bi I EXTRACT DATA FROM ALPlD 1 BINARY OUTPUT FlLE I TAKE NEXT POINT TAKE NEXT PMHT
NO EOMETRY
Fig. 11 Flow chart for the FLINES Batch version VELOCITY AND DISPLACEMENT
UPDATE FLOW LINES OATA BASE AND PRINTED OUTPUT OATA FILE
Fig. 11 Flow chart for the FLINES Batch version (contd.) POST PROCESSOR : FLPLOT
The post processor FLPLOT displays graphically the flow line orientations, the path of the points being tracked as well as the gradual distortion of the finite element mesh from start till end of the computer simulation. Additional features added are the placement of vectors representing the magnitude and direction of the maximum principal strain and material rotations due to deformation. The graphics display can be obtained on Tektronix 4000/4100 series and compatible terminals or on Intergraph Interact/Interpro32 workstations.
An important feature in the use of the post processor is the creation/update of the global flow lines data base. Generally, for complete forging simulation of a fairly complex geometry, re-meshing may have to carried out at least 4-5 times. In such a case, the user can create a new global flow lines database at the endofthe first run and keep updating it successively after each re-meshing by specifying the global data base, the flow lines data base generated by running ALPID and the step number, N, after which re-meshing will be performed. The global flow lines data base is then updated to include the data of step 1 through step N (except during creation of new global flow lines data base after first ALPID run, when data from step
0 through step N is included). 41
FLPLOT has 5 graphics display options. They are :
1. Display of Flow Lines : In cases where an extruded billet is used as the workpiece, the orientation of the flow lines is already established due to the extrusion operation and is parallel to the direction of the applied force during extrusion. A subsequent metal forming operation would result in re-orientation of the existing flow lines. In this case, the user can specify a number of points assumed to lie on the flow line/s, in the known direction, in file POINT.DAT, track their movement and view the new orientation of the flow line by specifying the connectivities for the points on the flow line in a data file. In addition, the user can define a closed shape/curve representing a randomly oriented flaw in the initial billet geometry or a critical region which permits inclusions or flaws of very small dimensions and needs to be inspected more closely. The user can treat the region as a flow 1ine for display purpose, and observe the final location and orientation of the region after deformation using the above method.
2. Point Tracking (tracing the path of individual points) : The path of a material point can be graphically displayed from its initial position in the undeformed billet geometry to its final position at the end of the forging simulation which may be after several re-meshings. These material points could be the points used to define a flow line or 42 just additional points specified representing randomly oriented flaws. For this the user needs to specify the initial ALPID data base file, the final ALPID data base file and the corresponding step numbers in the global flow
1ines data base.
3. Display of the distortion of the mesh placed on the initial billet geometry : In some cases it might be useful to observe the gradual distortion of the finite element mesh placed on the initial billet geometry. This would give a rough idea to the designer as to the amount of strain which the material has been subjected to, during the deformation process. FLPLOT provides for this display option and the user can view the distorted finite element mesh, as the simulation progresses. The user has to specify the number of elements and their respective connectiv ities in a separate data file.
4. Display of maximum strain directions : This option can be used only for cast billets where circles are placed on the initial billet cross-section. Selection of this option places arrows representing the magnitude and direction of the maximum principal strain. The information regarding the magnitude and direction of the maximum principal strain can also be output into a user specified data file. The output using this option could be then utilized to position the ultrasonic transducer during the non-destructive testing of the workpiece, since the orientation of the flaws is generally in the direction of maximum principal strain. Insome axisymmetric cases, the straininthe direction may be larger than the strains in either the r
or the z directions. In such cases the post-processor places a '*I on the point (center of the circle) to indicate the same.
5. Display of material rotations ( initial and final
orientations ) : This option is presently available only for the cast billet simulation case. The post processor displays the initial and final orientations or the orientations for any combination of output steps, of the center line of the circles placed on the initial billet geometry. The rotation values (in degrees) can also be output into a user specified data file).
The flow chart for the post processor is shown in Fig.
12. The post processor, FLPLOT, has been made very user- friendly and interactive. Hence, no further explanation of
the program is presented. A sample run of the post processor along with the graphics output is presented in
Appendix B of this thesis report. FLOWCHART FOR POST-PROCESSOR FLPLOT
CREATE NEW GLOBAL FLOW LINES DATA BASE
UPDATE GLOBAL DATA BASE^ -? Y NPUT DATA FOR WORKPIEC OUTLINE PLOTTING 9 CNPUT DATA FOR PLOTTING STEP^ 1 \L GRAPHICS DISPLAY OPTION , 1. DISPLAY OF FLOW LINES 2. POINT TRACKING 3. DISPLAY OF INITIAL MESH DISTORTION 4. DISPLAY OF MAXIMUM STRAIN DIRECTIONS 1 5. DISPLAY OF MATERIAL ROTATIONS 1
Fig. 12 Flow chart for post processor, FLPLOT *I I READ FLOW LINE 1
PLOT SUPER-IMPOSING OPTION 8 ' 1 , SUPERIMPOSE PLOTS 2. SEPARATE PLOTS
CAST BILLET
<
Y RE-ARRANGE DATA FOR THE PLOTTING ROUTINES
Fig. 12 Flow chart for post processor, FLPLOT (contd.) 3 1 READ POINT TRACKING I IDISPLAY DATA 1 PLOTTING ROUTINES
Fig. 12 Flow chart for post processor, FLPLOT (contd.) YREAD ELEMENT CONNECTIVITY DATA
Fig. 12 Flow chart.for post processor, FLPLOT (contd.) (>+CHECK EXTRUDED
.BILLET I READ FLOW LINE 1 I CONNECTIVITY DATA 1
SIMULATION TYPE OPTION 11. PLANE STRAIN 2. AXISYMMETRIC
c.L I CALCULATE STRAIN IN EACH I I ELLIPTICAL SECTION I
RE-ARRANGE DATA FOR THE
Fig. 12 Flow chart for post processor, FLPLOT (contd.) 1 OAST ' . ,BlULT I READ FLOW LINE I I CONNECTIVITY DATA 1 I \1, 1 CALCULATE MATERIAL ROTATIONS]
v I RE-ARRANGE DATA FOR THE I sPLOTTING ROUTINES
Fig. 12 Flow chart for post processor, FLPLOT (contd.) 4 I OUTPUT DEVICE OPTION , 1 1. INTERGRAPH/INTERPRO 32 2. TEKTRONIX COMPATIBLES
1 . 4006/4014 [ READ TITLES AND SCALES] 2. 4100 SERIES
DEFINE SCALES AND TITLES. 1 WRITE INTO DESIGN FILE] I ~ . ~PARAMETER REVIEW OPTION] +DRAW THE PLOTS
Fig. 12 Flow chart for post processor, FLPLOT (contd.) sDELETE SCRATCH FILES
Fig. 12 Flow chart for post processor, FLPLOT (contd.) Chapter 4
VALIDATION --OF THE SOFTWARE
The validation of the software was carried out by performing an extrusion simulation. Extruded billets always have flow lines parallel to the direction of extrusion and hence the results would be self-validating.
The ALPID run for a 14 degree conical die was completed with 2 re-meshings. ALPID does not take into account the initial billet structure and hence the same results were usedto analyze flow line formationina cast aswell asan extruded billets. As shown in the figures, the flow line orientations after the extrusion operation are, as expected, parallel to the direction of extrusion. SCALE IOISTAMCE BETWEEM TWO CONSECUTIVE OOTS) I X-AXIS - . SO0 INCHES Y-AXIS - 0. 12soeee Incncs FLOW LINES IN EXTRUSION OF CAST BILLETS P 0 + + + + + + + + I M I T
T -- + + + + + + + + R A C K I N -- + + + + + t + + G
+ + + + + + + +
+ + + + + + +
800 + + + + + + + 'LRAOIUS :: ; + + + + + + n -- + + + + + + v n I J s G, t SUPER TECHNOLOGY INTL. INC OECEMBER. 1906 VERSION 2. 8 • XMAX- 4. 580888 INCHES YMAX- 4. SBBBBB INCHES XMIN- -8. 5880888 INCHES IN -9. ~~88080 IMCHES HIT
Fig. 13 Flow lines in extrusion of cast billets - step 0 SCALE (OISTANCE BETWEEN TWO CONSECUTIVE DOTS) I X-AXIS - a. 1250006 INCHES Y-AXIS - 9. 12SOQIO INCHES FLOW LINES IN THE EXTRUSION Of A CAST 81 LLET + + + + + + + +
+ + + + + + 1RAOIUS -- I;\+ + + + + + + +
M + + + + + + + ' + v -- W f J s G, t SUPER TECHNOLOGY INTL. INC. OECEMBER, 1986 VERSION 2. 8 XMAX- 4. 588886 INCHES YMAK- 4. 566666 INCHES XMIN- -8. 58668d6 INCHES I -9. S866090 INCHES
IT Fig. 14 Flow lines in extrusion of cast billets - step 40 SCALE IOISTANCE BETWEEN TWO CONSECUTIVE 0015) : X-AXIS - e. 1~~8888 INCHES Y-AXIS 0 9. 12Sb880 INCHES FLOW LINES IN THE EXTRUSION OF A CAST 81 LLET P + 0 + + + + + + + + I N T T -- + + + + + + + + R A C K I n -- + + + + + + + + C + + + + + + + + + + + + + QOO + + + + + + + RAOIUS : 0 00 +!L 900 + + + + + + + N -- + + + + + + + + v H / J S G -, l- SUPER TECHNOLOGY INTL. INC. OECEMBER. 1386 VERSION 2. B XHAX- 4. 588888 INCHES YMAX- 4. 500808 INCHES IN-B. SBBBB88 INCHES IMIN- -8. 5888888 INCHES HIT Fig. 15 Flow lines in extrusion of cast billets - step 60 SCALE (DISTANCE BETWEEN TWO CONSECUTIVE OOTSI I X-AXIS - 4. ~tseooo IncnEs Y-AXIS - 4. 12SQeOQ INCnfS HIT Fig. 16 Flow lines in extrusion of cast billets - step 110 SCALE (OISTANCC BCTWtCM TWO COYSECUTIVC 0011) 8 X-AXIS - 0.12s00a0 INcncs Y-AXIS - 0. aaIncncs DISPLAY OF MAXIMUM STRAIN DIRECTIONS .. +....+....+....+....+....+....+ RAOIUS XMAS- 4. sreeeo xncnfs YMAX- 4. soeeeo IMC~CS XI- -e. seaeoee xncnes YMI~- -a. seoraeo ~wcnts HIT Fig. 17 Display of maximum strain directions in cast billets (step 110) SCALE (OISTANCE BETWEEN TWO CONSECUTIVE 001s) : X-AXIS - 0. 12Sb@Oe INCNES Y-AXIS - e. 12seeee Incncs EXTRUSION SIMULATION FOR FLOW LINES VALIDATION t + + + + + + + t n E I + + + + + + + +: + + + + t + + + + + + + + + n -- + + + + + + + v n I J 8 G, SUPER TECHNOLOGY INTL. INC. OECEMBER. 1986 VERSION 2 a XMAX- 4. 5Qeeee INCHES YNAX- 4. SBB800 INCHES XMIN- -0. seeeeee INCHES YMIN- -8. seeeeae INCHES HIT Fig. 18 Flow lines in extrusion of extruded billets - step 0 SCALE (OISTANCE BETWEEN TWO ConsEcurIvr OOTS) I X-AXIS - e. 12seoee IncnEs Y-AXIS - Q. 125988b INCHES EXTRUSION SIMULATION FOR FLOW LINES VAL1 OATION + + + + + + + + iT H E I + + + + + + + ", + + + t + + + I RAOIUS + + + + + + + N + + v -- + + + + + + H / 1 s G, k SUPER TEC~NOLOCYINTL. INC. OECEMBER. 1906 VERSION 2. e XNAX- 4. 5QQebO INCHES YMAX- 4. seebee INCHES X~IN- -e. seeeeee r~cn~s YMIN- -e. seeeeeb INCHES T (CR) TO CONTINUE , Fig. 19 Flow lines in extrusion of extruded billets - step 40 SCALE (OISTANCC EElWEEN TWO CONSECUTIVE 00151 I X-AXIS - 8. 1258191 INCHES I-AXIS - e. 12soeee rncncs EXTRUSION SIMULATION FOR FLOW LINES VALIDATION :\t + + +. + + + + + 1 LRAOIUS L' J SUPER TECHNOLOGY INTL. INC. OECEMBER. 1986 VERSION 2. B YMAX- 4. saaeee INCHES IN-9. SB'd'JBQB INCHES HIT Fig. 20 Flow lines in extrusion of extruded billets - step 60 SCALE (DISTANCE OETWCEN TWO CONSECUTIVE DOlS 3 I X-AXIS - a. 1258Q80 INCHES Y-AXIS a. 1258088 INCHES XMAX- 4. 588888 INCHES ?MAX- 4. 588888 INCHES XMIN- -8. 5888888 INCHES YPlIN- -8. 5888888 INCHES hIT Fig. 21 Flow lines in extrusion of extruded billets - step 11 Chapter 5 CONCLUSIONS The software developed can effectively predict the flow line orientations which could be utilized to devise an efficient scan plan to detect defects and/or modify the preform/forged shape geometries in order to obtain the desired flow line orientations and directional properties in the product. The software can also be used to identify the test sample regions for metallurgical examinations and model the migration of flaws during the process. The software developed has been successfully used to predict the orientations of the flow lines formed in a complex forging. The results of this simulation being proprietary, cannot be published here. The logic for the cast billet simulation is valid for the cases where the principal strain direction does not change for the circle placed. Hence, accuracy of the results would be improved if the diameter of the circle to be placed is smaller. This would ensure that the deformed shape remains an ellipse even if the metal flow direction changes. The experimental validation of the results of the program for cast billets is yet to be carried out by us and is suggested as scope for further work. The assumption of a homogeneous structure and isotropic properties is not really valid in the case of mechanically worked metals/al loys. It is suggested here that the predicted results would match the actual values more closely if the anisotropy, of the metal/alloy, which is now neglected, is also taken into account during the metal flow simulation. References 1. George E. Dieter, 'Mechanical Metal lurgy', McGraw-Hill Series in Materials Science and Engineering, Second Edition, 1976. 2. Serope Kalpakj ian, 'Manufacturing Processes for Engineering Materials', Addison-Wesley Publishing Co., 1985. 3. Y Lakhtin, 'Engineering Physical Metallurgy', Mir Pub1 ishers, Moscow, 1977. 4. B. Banks, G.E. Oldfield, H. Rawding, 'Ultrasonic Flaw Detection in Metals - Theory and Practice', Prentice Hall Inc., 1962. 5. H.L. Gegel, AFWAL-MLLM, Dayton, Ohio, Private communication. 6. C.S. Barret, T.B. Massalski, 'Structure of Metals - Crystal lographic Methods, Principles and Data', Material Science and Engineering Series, McGraw Hill Book Co., 1966. 7. Conference Proceedings - 'Recrystal1 ization, Grain Growth and Textures', papers presented at a seminar of the American Society for Metals, October 16-17, 1965. 8. ALPID System User's Manual Version 2.0, Battelle Columbus Labs., November, 1985. 65 9. Technical Report AFML-TR-79-4105, 'Rigid Plastic Finite Element Analysis of Plastic Deformation in Metal -Forming Processest, August 1979. 10. Forging Handbook, ed. T.G. Bryer, Forging Industry Association, American Society for Metals, 1985. 11. Norman E. Woldman, 'Metal Process Engineering', Rheinhold Publishing Corporation, 1948. 12. T. Altan, F.W. Boulger, J.R. Becker, N. Ackgerman, H.J. Henning, 'Forging Equipment, Materials and Practices', Battelle Columbus Laboratories, Metalworking Division, Sponsored by Air Force Materials Laboratory, WPAFB, Dayton, Ohio, October 1973. Appendix A USER'S MANUAL INTRODUCTION : Inclusions are very important in void formation and in the formability of metals and alloys. Inclusions can be various impurities or second phase particles such as oxides, carbides and sulphides. Inclusions or flaws in a forged part often originate and can be detected in the initial billet. A metal forming operation, which results in gross deformation being imparted to the work piece, produces flow lines in the work piece. Flow lines indicate the path of material flow and the oriented grain structure of the second phases and inclusions after the metal forming operation and are visible on the etched cross sections of the deformed work piece. The prediction of the material flow path or point tracking is of particular interest to the metal forming industry. The parts that are forged or extruded are subjected to a non-destructive mode of testing, general ly ultrasonic testing. Best results for this mode of non- destructive testing are obtained when the sonic beam is directed perpendicular to the flow lines developed in the deformed work piece. A computer program, FLINES, has been developed to 67 predict flow line orientations in formed products. The user's manual describes the use of this software. The format for preparation of the various data files required for the execution of the program and the post processor is given along with some sample input and output data files. A sample runofthepostprocessor is also included. 68 PROGRAM INPUT The program FLINES requires the number and co- ordinates of the points being tracked to be specified in a data file POINT.DAT in the following format. The first line in the data file specifies whether an extruded or a cast billet is being used for the forming operation and is known as the flow lines simulation option. In case of an extruded billet, the user has to specify the co-ordinates of the points to be tracked along with the associated boundary conditions (whether the given point is touching any die). In case of cast billets, the user has to specify the co-ordinates ofthe center and the radius ofthe circle to be placed on the billet cross-section. Care should be taken to ensure that the entire circle is within the billet geometry. The program generates 16 points to define each circle and outputs a connectivity file FLCON.DAT. The program cannot track any point that does not lie within the billet geometry and prints out an error message in the output file. The file POINT.DAT for the cast billet case differs from the one for the extruded billet case only for the initial run. This is because each circle being tracked is represented by 16 discrete points, each tracked individually. Hence, for continuing run, the user has to select the value of NFLOPT as 1 and use the program FLREAD 69 to obtain a new input data file POINT.DAT from the flow lines data base. The program FLREAD can be used to obtain a new input data file POINT.DAT from the flow lines data base generated from the ALPID run. The user has to specify the flow lines data base from which the data has to be extracted and the step number of the ALPID run after which re-meshing has been carried out. This output data file can be used as the flow lines input file for a continuing run. NOTE : The value of the input/output parameter NINOUT(3) should always be set to 1 when the FLINES ALPID version is used. --NOTE : The connectivity forthe elements in themeshhas to be specified in the f 01lowing anti-clockwise order during ALPID execution (see figure below). POST PROCESSOR FLPLOT The post processor FLPLOT is a user friendly graphics module to display the orientation of the flow lines, the distortion of the finite element mesh, the path of a point through the entire simulation, the direction and magnitude of the maximum principal strain and material rotations on a Tektronix 4000/4100 series and compatible terminals or a Intergraph Interact/Interpro32 work stations. The initial part of the post processor involves the creation/update of the global flow lines data base. The global flow lines data base stores the data for the entire ALPID simulation and carries over the data through re- meshings. The global flow lines data base is to be created only once after the initial ALPID simulation and has to be updated after subsequent re-meshings. Hence a graphics display of the flow lines developed for the entire simulation can be obtained. The post processor is also capable of displaying the gradual distortion of the initial mesh placed on the billet successively and through re-meshings. For this, a data file containing the connectivities of the points being tracked has to be specified. The interactive input to the program during the execution of the post processor is simple and does not entail further clarifications. A sample run for the post 71 processor is included in this report. A number of checks have been incorporated into the program to eliminate the possibil ity of erroneous input. FORMAT -FOR CONNECTIVITY --FILE FOR DISPLAY ---OF FLOW LINES This file specifies the connectivity of the points representing the flow lines in the billet. A data file is to be prepared by the user when running FLINES for the extruded billet case. In case of cast billets, a data file FLCON.DAT is generated by the program giving the connectivity of the points generated for each circle placed on the billet. A maximum of 75 points can be used to represent a flow line. A maximum of 125 flow lines can be tracked and the user has to specify their respective connectivities for graphics display in this data file. FORMAT FOR CONNECTIVITY --FILE FOR DISPLAY -OF DISTORTED MESH This data file is essential for obtaining a display of the distortion of the finite element mesh placed on the initial billet geometry. This display is useful in visual identification of the regions for metallurgical examination. In this data file, the user specifies the number of elements for which the data has to be read(a maximum of 2000 elements can be displayed) and their respective connectivities. 74 FORMAT OF THE DATA FILE TO SPECIFY DISPLAY DATA OF FLOW ___ -- I--_.------I_------LINES This data file specifies the display data for flow lines. The software has been written to a1low a display of only 30 flow lines atatime. This feature has been set to retain the clarity of the figure. The user specifies the number of flow lines to be displayed and their numbers in the flow line connectivity file. In case of cast billet simulation, the user is not prompted for this file and all the circles placed on the initial billet geometry are plotted. 75 ----FORMAT -OF --THE ---DATA ---FILE --TO ----SPECIFY DISPLAY DATA --FOR POINTS This data file specifies the display data for points. The software has been written to allow a display of only 60 points at a time. This feature has been set to retain the clarity of the figure. The user specifies the number of points to be displayed and their numbers in thef ile POINT.DAT. Appendix B SAMPLE RUN A sample run of the post processor, FLPLOT, is presented in this chapter. This sample run was conducted with file NVHTHE3.TP3 as the ALPID binary output file, NVHCGR3.DAT as the flow lines data base file and NVHCCON.DAT as the flow line connectivity file. f LPLOT fttttftftttttttttffttttttttttttfttttttft%ttttttttt 6 t t f mmn t t ------f t t ilc POST-MSSOR FOR PROGlUEI ' FLOW LINES t t ...... t t t t VERSION : 2.0 OATED : DECEMBER, 1906 t ilc t t DEVELOPED BY : NITIN V. HATTANGADY t t t t DEVELOPED AT : SUPER TECH. INTL. INC. t t t t PROGRAM MGR. : OR. JAY S. GUNASEKERA f t X t t t t t%tttt%tttttttttttfttttttttttttittttttttttt#t**ttt HIT (CR) TO CONTINUE : 1 FLPLOT 00 YOU WANT TO UPOATEICREATE THE GLOBAL FLOW LINES DATA BASE (YIN) 7 : YU FLPLOT ftfftttttftfffftt3ffttttftItftttfttftffttttt t f f THIS PROGRAM CREATES/UPOATES THE DATA t # BASE TO BE USED BY THE POST-PROCESSOR f t FLPLOT FOR VIEWING THE FLOW LINES IN t t THE DEFORMED BILLET GEOMETRY. d t t tttttttttXtttttfttttttttttttttt*tttttttttt* ENTER THE NAME OF THE GLOBAL FLOW LINES DATA BASE TO BE CREATED/UPOATED ENTER THE NAME OF THE FLOW LINES DATA BASE TO BE INCLUDED IN DEMO. OAT ttf f t NClJ GlWAL TiUW LINES DATA BASE DEMO. DAT CREAm tttff I 81 FLPLOT OETAILS OF FLOW LINES OATA BASE : NUMBER OF NODES : 336 NUMBER OF STEPS : 8 (NUMBER OF STEPS INCLUDES STEP 0 FOR THIS RUN) ENTER STEP NUMBER AFTER WHICH RE-MESHING WILL BE CARRIED OUT (PLEASE NOTE THAT A VALUE OF 7 AS ANSWER WOULD RESULT IN THE DATA FOR STEP 2 THROUGH STEP 7 BEING ADDED TO THE DATA BASE EXCEPT FOR THE FIRST UPDATE (CREATION OF OATA BASE), WHEN DATA FOR STEP 1 THROUGH STEP 7 WILL BE AOOED TD THE DATA BASE 00 YOU WANT TO UPOATE/CREATE THE GLOBAL FLOW LINES DATA IASE (Y/N) ? : N PLEASE WAIT WRITING COMMUNICATION FILES. #.. . ENTER SELECTION FOR TYPE OF PROCESSING CONDITION 1. ISOTHERMAL FORMING 2. FORMING WITH HEAT TRANSFER 3. NON-ISOTHERMAL FORMING 84 FLPLOT ENTRY OF DATA FOR PLOTTING THE WORKPIECE OUTLINE le INPUT OF INITIAL STEP DATA : - ...... ENTER ALPID DATA BASE FILENAME (TAPE 3 FILE) )))))) 51 SOLUTION STEPS WERE RECORDED IN THE FILL TITLED : FLOW LINES VALIDATION WITH 14 OEG. CONICAL DIE THEYARESTEPS: 8 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 20 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 40 49 50 ENTER INITIAL STEP NUMBER ,,,,,, 2- INPUT OF FINAL STEP DATA : - ...... ENTER ALP10 DATA BASE FILENAME (TAPE 3 FILE l H)))) FLPLOT 51 SOLUTION STEPS WERE RECORDED IN THE FILE TITLED : FLOW LINES VALIDATION WITH 14 DEG. CONICAL DIE THEY ARE STEPS: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 ENTER FINAL STEP NUMBER 1 GENERATING MTk . . . . . FLPLOT ENTER NAME OF THE GLOBAL FLOW LINES ,,,,,, DATA EASE FLPLOT DETAILS OF GLOBAL FLOW LINES DATA BASE : GLOBAL FLOW LINES DATA BASE : OEMO. OAT NUMBER OF POINTS BEING TRACKED : 336 NUMBER OF STEPS 8 ENTER INITIAL STEP FOR PLOTTING DETAILS OF GLOBAL FLOW LINES OATA BASE : ...... GLBBAL FLOW LINES OATA BASE : OEMO. OAT NUMBER OF POINTS BEING TRACKED : 336 NUMBER OF STEPS 8 INITIAL STEP FOR PLOTTING 1 ENTER,,,,,, FINAL STEP FOR PLOTTING GRAPHICS OISPLAY OPTION : ...... 5 2. POINT TRACKING : TRACING THE PATH OF INDIYIDUAL POINTS 3. OISPLAY OF DISTORTION OF THE INITIAL MESH PLACED ON THE BILLET 4. DISPLAY OF MAXIMUM STRAIN DIRECTIONS 5. DISPLAY OF MATERIAL ROTATION ( INITIAL AN0 FINAL ORIENTATIONS 1 ENTER CHOICE ACCORDINGLY ))))) 1 92 FLPLOT ENTER,,,,,, NAME OF FILE CONTAINING CONNECTIYITIES FOR THE FLOW LINES [FLCON. MTI ENTER OUTPUT DEVICE OPTION : 3. QUIT EXECUTION OF POST PROCESSOR TEKTRONIX TERMINAL TYPE OPTION : 2. 4100 SERIES COMPATIBLES ENTER CHOICE ACCORDINGLY ))))) I] I DEFINITION Of AXES SCALES ...... : PLEASE NOTE THAT THE VALUES WITHIN PARANTHESES REPRESENT DEFAULT YALKS ENTER X-AXIS MINIMUM [ 0.00001 : a ENTER X-AXIS MAXIMUM r 10.00001 : a FLPLOT OEFINITION OF AXES SCALES : ...... PLEASE NOTE THAT THE VALUES WITHIN PARANTHESES REPRESENT DEFAULT VALUES ENTER Y-AXIS MINIMUI [ OaOOOOl : ENTER Y-AXIS MAXNUM [ 30a 00001 : DEFINITION OF AXES AND PLOT TITLES : PLEASE NOTE THAT THE VALUES IN PARANTHESES REPRESENT OEF AULT Y ALUES ENTER TITLE FOR X-AXIS [RADIUS I (MAXIMUM OF 12 CHARACTERS) ENTER TITLE FOR Y-AXIS [HEIGHT I (MAXIMUM OF 12 CHARACTERS) ENTER UNITS FOR X-AXIS SCALE INCHES I (NOT EXCEEDING 12 CHARACTERS 1 (FOR EX : INCHES,MIN, SECONDS ETC. ENTER UNITS FOR Y-AXIS SCALE [ INCHES I (NOT EXCEEDING 12 CHARACTERS l (FOR EX : INCHES,MIN, SECONDS ETC. 1 ENTER TITLE FOR THE PLOT ( NOT EXCEEDING 50 CHARACTERS l [FLOV LINES IN EXTRUSION OF CAST BILLETS I PARAMETER REVIEW : -----I---- FOLLOWING ARE THE DETAILS ENTERED FOR THE PLOT : 1. X-AXIS MINIMUM : -0a5000000 2. X-AXIS MAXIMUM : 4.500000 3. Y-AXIS MINIMUM : -0.5000800 4. Y-AXIS MAXIMUM : 4.500000 5. X-AXIS TITLE : RAOIUS 6. Y-AXIS TITLE : HEIGHT 7. X-AXIS UNITS : INCHES 8. Y-AXIS UNITS INCHES 9. TITLE FOR PLOT : FLOW LINES IN EXTRUSION OF CAST BILLETS ENTER CHOICE TO CHANGE PARAMETER OR (CR> TO QUIT PARAMETER REVIEW >>>>> I FLPLOT PLEASE ENSURE THAT THE TERMINAL IS IN THE TEKTRONIX MODE NOW HIT (CR) TO Y IEV PLOTS I SCALE (OISTANCE BETWEEN TWO CONSECUTIVE OOTS) : X-AXIS - 8. 1258888 INCHES Y-AXIS - 8. 12SBBBB INCHES FLOW LINES IN EXTRUSION OF CAST BILLETS 1 + + + + + + + + T + + + + + + + + R I A C K I n -- + + + + + + + + C + + + + + + + H E I + + i t + + +: 000 + + + + + + 600 + RAOIUS !\0 00 000 + + + + + + + n -- + + + + + + + + v H I J s G 7 I- SUPER TECHNOLOGY INTL. INC. OECERBER. 1986 VERSION 2. 8 XUAX- 4. 588888 INCHES YWAX- 4. 5bQbBB INCHES XUIN- -e. seeeeee INC~ES YRIN- -8. sebeeee INCHES HIT 1 -- + + + + + + + + R A C K I + + + + + + + + G + + + + + + + + + + + + + 000 N: 400 + + + + + + +'!+ 0 00 LRAOIUS 0 00 + + + + t + + N + + + + + + + + v -- n / J S G, t SUPER TECHNOLOGY INTL. INC. OECEMBER. 1986 VERSION 2. 8 XMAX- 4. 588888 INCHES *MAX- 4. See888 INCHES XRIN- -e. seeeeee INCHES I -0. seeeeee INCHES HIT 00 YOU WANT RE-RUN THIS PROGRAM TO GET ANOTHER PLOT U/N) : GRAPHICS DISPLAY OPTION : ...... 1. DISPLAY OF FLOW LINES 2. POINT TRACKING : TRACING THE PATH OF INDIVIDUAL POINTS 3. OISPLAY OF DISTORTION OF THE INITIAL MESH PLACED ON THE BILLET 4I'.I. 5. DISPLAY OF MATERIAL ROTATION ( INITIAL AND FINAL ORIENTATIONS 1 ENTER CHOICE ACCOROINGLY )) ))) 1 SCALE (OISTANCE BETWEEN TWO CONSECUTIVE 00151 : X-AXIS - 8. 1258898 INCHES Y-AXIS - a. ~zseeee I HCHES DISPLAY OF MAXIMUM STRAIN DIRECTICNS !lt + + t + + + + + I RAOIUS N -- + + + + t v + + + H / J S G, + SUPER TECHNOLOGY INTL. INC. OECEPlBER. 1986 VERSION 2. 0 XUAX- 4. 588888 INCHES YUAX- 4. 588888 INCHES XMIN- -8. 5008888 INCHES - YUIN- -8. 5888888 INCHES HIT Appendix D Appendix E INPUT DATA FILE POINT. DAT FOR EXTRUDED BILLET CASE -7- -- 1 100 0.71107602 0.93576008 1.06347227 1.16658962 1.20290923 1.20926166 1.20173919 1.17406154 1.10608900 1.06941187 1.03672004 1.00337458 0.96351725 0.92626452 0.85806340 0.81744230 0.78084016 0.74767494 0.71003783 0.68005627 0.62803668 0.59682697 0.56321132 0.51779234 0.46768066 0.43583906 0.42901078 0.41032726 1.50495493 1.84057415 2.16868210 2.31337380 2.34068441 2.33547378 2.29423666 2.24635363 2.19059229 2.13646293 2.07206702 2.03422022 1.96159828 1.88686514 1.81083310 1.72760010 1.65318751 1.57597899 1.50657463 1.44020295 1.38117290 ----SAMPLE INPVT DATA FILE POINT DAT FOR CAST --BILLET CASE P--Sam le Flow Lines Printed Output --Data File Appendix F ULTRASONIC TESTING Ultrasonic inspection techniques are more widely used for inspecting forgings than any other single non- destructive testing method. Ultrasonic techniques are especially appropriate for inspecting wrought metal. Different techniques are used to evaluate different parameters in the test material. Sound waves in the ultrasonic range tend to travel in straight lines rather than diffuse in all directions, as they do in the audible range, when passing through a metal. A defect in the path of the sonic beam will cause a reflection of some of the energy, thus depleting some of the energy transmitted. This casts an accoustic shadow, which can be monitored by a detector placed opposite the energy source. If the accoustic energy is introduced as a very short burst, then the reflected energy coming back to the originating transducer can also be used to show the size and location of the defect. The transducer must be coupled to the material under test by some liquid medium, because air is too compressible. There are three distinctively different methods of ultrasonic testing [12], viz., the pulse-echo method, the through transmission method and the resonance method. 116 In the pulse-echo or back reflection method, a pulsed ultrasonic beam is transmitted through the couplant into the material to be tested. The beam is reflected at the opposite face and the echo is picked up by a transducer. A defect will also reflect back an echo. The time interval that elapses between the initial pulse and the other reflected echoes is measured with a cathode ray oscilloscope. In the echo pattern, a defect can be recognized by the relative position and amplitude of its echo. The resolution of this technique depends on the duration of the ultrasonic pulses. The shorter the durationofthepulse,thethinnerthematerialthatcanbe tested. The through transmission method requires two transducers. One transducer is used as a transmitter and the other is used as a receiver. As in pulse-echo testing, short pulses of ultrasonic energy are transmitted into the material. The transducers are aligned so as to allow the receiving transducer to receive the ultrasonic energy which passes through the material. In the resonance method, a tunable, variable frequency, continuous wave oscillator is used to drive a transducer. Resonance occurs whenever the thickness of the specimen is equal to an integral number of half-wave lengths of the ultrasonic wave. This method is used for thickness measurement and detection of internal corrosion and delaminations. The sensitivity of ultrasonic inspection improves as a material is forged because of grain refinement, better surface conditions and reduction in dimensions. The choice of ultrasonic frequency to be employed depends on the attenuation characteristics, and size of the forging; higher frequencies give better detail but have poored penetrating power [12]. Forging or any other forming operation causes grain flow and develops fiber patterns which should be considered in planning ultrasonic testing procedures. The deformation causes inclusions, sulphides and stringers of deoxidation products to be aligned along the flow lines in the principal direction of working. To detect such flaws, the ultrasonic beam should be transmitted at right angles to the fiber direction [12]. The type of defects which can usually be located by ultrasonic inspection are non metal 1 ic inclusions, unwelded pipe, cavities and interior bursts, cracks and tears, surface defects etc. Fig. I shows a schematic of the transmission and pulse echo methods used in sonic inspection. ELECTRICAL GENERATOR ELECTRICAL ELECTRICAL GENERATOR\ /INDICATOR G G I TRANSMI?TER TRANSMITTER TRANSDUCER ACOUSTIC COUPLANT ELECTRICAL INOICATOR Fig. I Schematic of transmission method (left) and pulse-echo method (right) used in sonic inspection of forgings.