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Design and Finite Element Analysis DESIGN AND FINITE ELEMENT ANALYSIS OF THE BROACHING TOOLS. A Thesis Presented to The Faculty ofthe Fritz J. and Dolores H. Russ College ofEngineering and Technology Ohio University In Partial Fulfillment ofthe Requirement for the Degree Master ofScience By Sham Kumar Rajam August 1997 Acknowledgments 111 The author wishes to thank his advisor Dr. Bhavin Mehta for his valuable support and suggestions during the course of this research. The author thanks Dr. Jay Gunasekara for providing useful tips and guiding through the right direction. The author also extends his thanks to Dr. John Deno and Prof. Ralph Sims for their constant encouragement and sincere advise without which, none of this was possible. Finally author thanks his family and close friends specifically Brenda Chamberlain for the unconditonal moral support they provided during the crucial phases. IV TABLE OF CONTENTS Acknowledgments iii Table of Contents iv List of Tables vi List of Figures vii CHAPTER Page I. Introduction ,.., 1.1 Literature Review -' 1.2 Objective 4 II. Broaching Process and Types of Broaches 6 2.1 Types ofBroaching 6 2.1.1 Internal Broaching 6 2.1.2 External Broaching 9 2.2 Broaching Machines 11 2.2.1 Vertical Broaching Machines 11 2.2.2 Horizontal Broaching Machines 12 III Design of Broaches 14 3.1 Cutting Elements ofBroach tools 14 3.1.1 Pitch 14 3.1.2 Chip Space 16 3.1.3 Face Angle 17 3.1.4 Land and Back offAngle 17 3.1.5 Cut per tooth 18 3.1.6 Pull End 19 3.1.7 Follower End 20 3.1.8 Pilots 20 3.2 Design ofBroaching tools Using Associative modeling 21 3.2.1 Associative Modeling 21 3.2.2 Variational Design 22 3.2.3 Parametric Design 22 3.2.4 Feature based modeling 23 3.2.5 Profiles 23 3.2.6 Constraints 24 3.3 Development ofBroach models 27 v IV Finite Element Analysis 31 4.1 Introduction to Finite Element Analysis 31 4.2 Development ofBroach finite element models 33 4.2.1 Mapped Meshing 34 4.2.2 Model Description 35 4.3 Material Property 36 4.4 Boundary Conditions 37 4.4.1 Constraints 40 4.4.2 Forces Applied 41 V Analysis Results 46 5.1 Results 46 5.2 Results ofBroach tooth under varying land width 52 VI Conclusions and Recommendation 56 6.1 Conclusions 56 6.2 Recommendations 58 References 59 Appendix 62 VI List ofTables Page Table 5.1.1 (a) Stresses in Round hole Broach 47 Table 5.1.1 (b) Displacements in Round hole Broach 47 Table 5.1.2 (a) Stresses in Octagonal hole Broach 48 Table 5.1.2 (b) Displacements in Octagonal hole Broach 48 Table 5.1.3 (a) Stresses in Flat Broach 48 Table 5.1.3 (b) Displacements in Flat Broach 48 Table 5.1.2 Comparison ofMaximum stresses for the three cases 52 VII LIST OF FIGURES Page Figure 1.1 Internal Round Broach Terminology. 2 Figure 3.1 Broach Tooth Form Details. 15 Figure 4.1 Boundary Conditions on Flat Broach. 38 Figure 4.2 Boundary Conditions on Octagonal Broach. 39 Figure 5.1 Von-Mises Stress for the required force for the Round Hole Broach. 49 Figure 5.2 Von-Mises Stress for the required force for the Flat Broach. 50 Figure 5.3 Von-Mises Stress for the required force for the Octagonal Hole Broach. 51 Figure 5.4 Von - Mises Stress for the baseline model. 53 Figure 5.5 Von-Mises Stress for the iteration 1 model. 54 Figure 5.6 Von-Mises Stress for the iteration 2 model. 55 CHAPTERl INTRODUCTION Broaching is a machining process in which a cutting tool, having multiple transverse cutting edges, is pushed or pulled through a hole or surface to remove metal by axial method. Broaching has wide range of applications and several advantages over the other machining processes. Its ability to do roughing and finishing operation in one pass is an ample proofofits rapidity and efficiency. Close tolerances, smooth surface finish and higher accuracies are the added advantages ofthis process. Broaching, ifproperly used, is a highly productive, precise and extremely versatile process. It is capable ofproduction rates as much as 25 times faster than any traditional metal removing methods. The interesting aspect of broaching is that the feed is built directly into the broach (cutting tool) and has the machine provide only one function -speed, for metal removal, unlike in the other processes such as milling, planing, etc., where the speed and feed are the metal removing functions that machine tool is required to provide. A broach is usually a tapered round or flat bar upon which teeth are cut so as to pro­ duce a desired contour in a workpiece in a single pass ofthe tool. A typical broach is shown in figure 1.1. A broach has three cutting sections: roughing, semi-finishing, and finishing teeth. The broach tapers from the first roughing tooth to the first finishing tooth, the outside diameter of each tooth being slightly larger than the tooth that precedes it. Usually the finishing teeth are all ofsame diameter. 2 PULL END SHANK LENGTH LENGTH TO FIRST TOOTH ROOT DIAMETER OVERAll LENGTH ROUGHING TEETH CUTTING TEETH FINISHING TEETH _i~_ REAR PI LOT FOLLOWER Figure 1.1 Internal Round Broach Terminology. 1.1 Literature Review Research done at Ohio University: Chad Richards, [10] a former student of the Industrial and Systems Engineering department at Ohio University, developed a knowledge based system that designs the round hole broaches. The codification of the knowledge base system was done using procedural based programming. Most of the broaching tools have procedure based design rules. The knowledge based system was developed USIng Microsoft Quick basic programming. Chad Richards [10] used the results from the knowledge based system to model a 2-dimension profile of the tool. The aim of his research was to reduce the time required to design and fabricate them. Another student, Yean-Jenq Huang [11], also a former student of the same department designed a methodology for the optimal integrated broaching manufacturing process. This methodology was based on the three manufacturing evaluation criteria which were: • The maximum production rate was used to design the broach design parameters that can maximize the number ofproducts produced in a unit time interval. • The minimum cost criteria which cites the production of the piece of the part at the least cost corresponding to the broach design parameters. • The maximum profit rate criteria to determine the broach design parameters which can maximize the profit rate in a given interval oftime. 4 Huang [11] also examined the behavior of a single flat broach tooth using finite element analysis application. His objective was to find an efficient and economical operation in addition to a new design method that would result in the lowering of the costs associated with broaching and thus increasing the productivity. Not much research has been done in the area ofthe broach tool design. The broach tools are usually designed and manufactured by the companies using the empirical rules and are done by experienced personneL Broaching, though a versatile process, is not being used as much as the other metal cutting operations and the reason being the high expenses involved in the manufacturing of these tools. Any damage to the tool results in the loss of the tool, workpiece and the production time. Proper care should be taken by checking the tool frequently and by knowing the strength of the tool. By estimating the force it can withstand and the stress distribution in the teeth, the behavior of the broach during the cutting performance can be assessed and care can be taken in increasing its life cycle. 1.2 Research Objectives • To lower the cost of design process by reducing the time required to design and fabricate broach tools. • To predict the strength characteristics of the broaching tools in the preliminary stage for the tool engineer. • To provide a guideline for the future research aimed at the performance improvement ofdifferent kinds ofbroaching tools. 5 The first objective was materialized by the parametric design of the broach, where the design intent of the broach tool geometry is captured. A geometrical relationship is developed on the broach tool geometry which is very flexible and can be altered for most of the tools with very little user intervention. This was achieved using the software called I/EMS [12], a design and modeling product from Intergraph corporation. The second objective was to evaluate the stress characteristic of the broach tool subjected to the cutting conditions. This would be useful for the tool engineer to keep a check on the tool's strength characteristics during every stage of the tools life and also on improving its characteristics during the wear out period. This was achieved by meshing and performing analysis using the Finite Element Modeler package called IIFEM [13]. The model built from the parametric design was utilized to make a finite element model and analysis was performed to predict the stress and deflection in the tool. 6 CHAPTER II BROACHING PROCESS AND TYPES OF BROACHES 2.1 Types ofBroaching Broaches can be generally classified depending on [3] • Type ofoperation: Internal broaching or External broaching • Method ofoperation: Pushup or down, Pull up or down. • Construction: Solid, built-up, progressive, circular, inserted-tooth, rotary cut, overlapping tooth. • Function: Keyway, square hole, round hole, serration, spline, combination round and spline, helical tooth, special contour and so on. 2.1.1 Internal Broaching: In Internal Broaching there is a pilot hole through which the broach is pushed or pulled.
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