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Technology ofMetal Forming

Processes

Technology ofMetal Forming

Processes

Surender KumarSurender Kumar

KopyK

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Technology of Metal Forming Processes

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Technology of MetalForming Processes

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New Delhi-1100012008

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TECHNOLOGY OF METAL FORMING PROCESSESSurender Kumar

© 2008 by PHI Learning Private Limited, New Delhi. All rights reserved. No part of this book maybe reproduced in any form, by mimeograph or any other means, without permission in writing fromthe publisher.

ISBN-978-81-203-3425-0

The export rights of this book are vested solely with the publisher.

Published by Asoke K. Ghosh, PHI Learning Private Limited, M-97, Connaught Circus,New Delhi-110001 and Printed by Raj Press, New Delhi-110012.

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itabPreface ....................................................................................................................................... xiii

Nomenclature ...............................................................................................................................xv

1. INTRODUCTION ...................................................................................... 1–191.1 Conceptual Framework 11.2 Cold, Hot and Warm Forming 21.3 Metalworking and Types of Stresses 41.4 Temperature in Metalworking 41.5 Workability and Crack Formation 61.6 Experiments in Metalworking 61.7 Bulk Deformation Processes 81.8 Sheet Metalworking Processes 16Exercises 19

2. STATE OF STRESS ................................................................................. 20–362.1 Introduction 202.2 Components of Stresses 222.3 Principal Stresses 232.4 Stress Invariants 252.5 Mean Stress and Stress Deviator 262.6 Maximum and Octahedral Shear Stresses 282.7 Mohr’s Representation of the State of Stress 302.8 Differential Equations of Equilibrium 32Exercises 34

3. STRAIN AND STRAIN RATES ............................................................. 37–433.1 Introduction 373.2 Strain Rates and Velocities 37

Contents

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3.3 Principal Strain Rates and Their Axes 403.4 Incompressibility 413.5 Infinitesimal Strains and Displacements 42Exercises 42

4. STRESS–STRAIN AND STRESS–STRAIN RATE LAWS ................. 44–554.1 Introduction 444.2 The Load–Extension Diagram in Simple Tension 444.3 True Stress–Strain Diagram 454.4 Some Important Deviations 474.5 Idealization of Stress–Strain Diagrams 484.6 Empirical Equation for Stress–Strain Curve 494.7 Elastic Stress–Strain Laws 494.8 The Prandtl–Reuss Equation 504.9 The Levy–Mises Equations 514.10 The Levy–Lode Variables 514.11 Von-Mises Stress–Strain Rate Law 53Exercises 54

5. YIELD CRITERIA AND FLOW RULES ............................................. 56–645.1 Introduction 565.2 Tresca Yield Criterion 565.3 Von-Mises Yield Criterion 575.4 Geometrical Representation of the Yield Criteria 585.5 Yield Criteria for Plane Stress 605.6 Experimental Evidence for the Yield Criteria 61Exercises 63

6. FRICTION IN METALWORKING ....................................................... 65–726.1 Introduction 656.2 Mechanics of Friction 666.3 Discussion 70Exercises 72

7. LUBRICATION MECHANISM AND METALWORKINGLUBRICANTS.......................................................................................... 73–937.1 Introduction 737.2 Principle of Lubrication 737.3 Lubrication Mechanism 757.4 Lubricant Needs of the Industry 767.5 Components of Lubricants 767.6 Cost and Final Selection 777.7 Classification of Lubricants 78

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7.8 Lubricants Used in Forming Processes 797.8.1 Extrusion Lubricants 797.8.2 Wire Drawing Lubricants 807.8.3 Sheet Metal Lubricants 827.8.4 Rolling Lubricants 847.8.5 Forging Lubricants 85

7.9 General Properties of Lubricants 877.10 Chemical Characteristic Values 897.11 Solid Lubricants 90

7.11.1 Categories of Solid Lubricants 917.11.2 An Ideal Solid Lubricant 92

Exercises 92

8. DRAWING AND EXTRUSION OF CYLINDRICAL BODIES ........ 94–1108.1 Introduction 948.2 Free-body Equilibrium Approach 948.3 Optimal Cone Angle and Dead Zone Formation 1038.4 Hydrodynamic Wire Drawing 1058.5 Hydrostatic Extrusion 1068.6 Defects and Irregularities 107Exercises 107

9. DRAWING AND EXTRUSION IN PLANE STRAIN ....................... 111–1199.1 Introduction 1119.2 Drawing and Extrusion of a Strip 1119.3 Tube Drawing with a Mandrel 1139.4 Maximum Reduction 1149.5 Drawing without Friction 1159.6 The Constant B for Various Drawing Processes 117Exercises 117

10. DEEP DRAWING................................................................................. 120–13310.1 Introduction 12010.2 General Considerations 12110.3 Approximate Analysis of Load 12410.4 Analysis of Strain 12710.5 Formability 13010.6 Defects and Irregularities 131Exercises 133

11. STRIP ROLLING ................................................................................ 134–14811.1 Introduction 13411.2 Pressure Distribution 134

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11.3 Position of the Neutral Section 14011.4 Evaluation of Roll Force, Roll Torque and Mill Horsepower 14011.5 Limiting Thickness and Limiting Reduction 14111.6 Elementary Assessment of Roll Load 14211.7 Strip Biting by Rolls 14411.8 Determination of Forward Slip 145Exercises 145

12. FORGING ............................................................................................. 149–16412.1 Introduction 14912.2 Slow Speed Forging 15012.3 Very High Speed Forging 15612.4 Overall Forging Reduction 160Exercises 161

13. BENDING AND FORMING ............................................................... 165–17113.1 Introduction 16513.2 Stretch Forming 16513.3 Bending 16613.4 Spinning 168Exercises 171

14. SLIP LINE FIELD TECHNIQUE ...................................................... 172–18414.1 Introduction 17214.2 Stress Equations 17214.3 Velocity Equations 17514.4 Geometry of the Slip Line Field 17614.5 Boundary Conditions 17714.6 Some Simple Examples 179

14.6.1 State of Uniform Stress 17914.6.2 Centred Fan 17914.6.3 Plane Indenting Die 17914.6.4 Machining 180

Exercises 182

15. LOAD BOUNDING TECHNIQUE .................................................... 185–20915.1 Introduction 18515.2 Upper-Bound Theorem 18615.3 Examples 186

15.3.1 Strip Forging without Barreling 18615.3.2 Solid Square Plate without Barreling 18915.3.3 Solid Circular Disc without Barreling 19015.3.4 Forging of Polygonal Disc with Barreling 193

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15.3.5 Polygonal Disc with Bulging of Sides 19815.3.6 Hollow Circular Disc without Barreling 204

Exercises 207

16. LUBRICATED METALWORKING PROCESSES.......................... 210–24716.1 Introduction 21016.2 Lubricated Forging Process 210

16.2.1 Basic Assumptions 21216.2.2 Analysis 21216.2.3 Parametric Analysis 217

16.3 Lubricated Direct Extrusion 22016.3.1 Description and Assumptions 22116.3.2 Analysis 22316.3.3 Parametric Analysis 227

16.4 Lubricated Strip Drawing 23116.4.1 Description and Assumptions 23116.4.2 Analysis 23216.4.3 Parametric Analysis 235

16.5 Lubricated Strip Drawing with Newtonian Lubrication 24016.6 Avenues Open on Research on Metalworking Lubrication 246Exercises 247

17. COLD PROCESSING OF POLYMERS ............................................ 248–26417.1 Introduction 24817.2 Cold Formability of Polymers 24817.3 Interfacial Friction 24917.4 Yield Criteria 25017.5 Analysis for Pressure Distribution 251

17.5.1 Initial Feeding Phase 25217.5.2 Rolling Phase 256

17.6 Roll Force 25917.7 Roll Torque 26017.8 Experimental Evidence 26017.9 Parametric Analysis 261

17.9.1 Pressure Distribution at Roll Workpiece Interface 26217.9.2 Effective Coefficient of Friction 26317.9.3 Roll Force and Roll Torque 263

Exercises 264

18. PROCESSING OF METAL POWDER PREFORMS ...................... 265–29118.1 Introduction 26518.2 Interfacial Friction 26518.3 Yield Criterion 267

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18.4 Basic Assumptions 26718.5 Axisymmetric Condition 26718.6 Plane Strain Condition 26918.7 Experimental Verification 27118.8 Results and Discussion 27118.9 Deformation Through Conical Dies 276

18.9.1 Theoretical Analysis 27618.9.2 Parametric Analysis 282

Exercises 290

19. HIGH ENERGY RATE FORMING .................................................. 292–30319.1 Introduction 29219.2 High Energy Rate Forming Processes 29219.3 Comparison of HERF and Conventional Methods 29619.4 Types of Explosives 29719.5 Explosive Forming Technique for Stand-Off Operations 29819.6 Design of Explosive Forming Facilities 299Exercises 303

20. ADVANCES IN MATERIAL PROCESSING ................................... 304–32420.1 Introduction 30420.2 Mechanical Working 305

20.2.1 Processes Involving Progressive Deformation 30520.2.2 High Energy Rate Forming 30820.2.3 Composite Forming 31020.2.4 Other Processes 317

20.3 Machining Techniques 32120.3.1 Stretched Machining 32120.3.2 Hot Machining 32120.3.3 Cryogenic Machining 32120.3.4 Dynamic Cutting 32120.3.5 Oscillatory Machining 32220.3.6 Magnetic Machining 32220.3.7 Ballistic Machining 322

20.4 Modern Techniques Used in Instrumentation 32220.5 Tooling Requirements 323Exercises 324

21. COMPUTER APPLICATION IN METALWORKING ................... 325–33421.1 Introduction 32521.2 CAD/CAM Applications 32621.3 Development of Expert System for Sintered Forged Products 329

21.3.1 Main Components of an Expert System 329

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21.3.2 Basic Configuration Needed for an Expert Shell 33121.3.3 Steps in Development 33121.3.4 Knowledge-based System Approach for Forging

Sintered Components 332Exercises 333

Appendix A Comparison of Various Methods of Analysis of Forming Load ........................................................................ 335–339

Appendix B Derivation of Reynolds Equation for Power Law Fluids .............................................................................. 340–343

Appendix C Useful Tables .......................................................................... 344–345

Appendix D Stress–Strain Curves for Various Materials .................................. 346

References/Bibliography ............................................................................... 347–353

Index ............................................................................................................... 355–358

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itabMaterial Forming Technology is an interdisciplinary subject, encompassing the study of such

topics as the behaviour and properties of metals, applied mechanics, metallurgy, heat transferetc., and including the more practical and industrial aspects of the subject. In the past, theapproach to the teaching of this subject was in general largely descriptive in nature, whereby onlyqualitative discussions of the processes and equipment were imparted to the students.

The current postgraduate and undergraduate syllabi for students of mechanical engineering,production engineering, and metallurgical engineering accommodate this subject matter in suchorder as to give them a better understanding of the engineering problems by presenting rationalsolutions which help in assimilating scientific principles.

This book is an attempt to present the subject of material forming technology by maintaininga proper balance between the theory and its applications. It is designed to serve as a textbook forthe above engineering disciplines both at undergraduate and postgraduate levels. Besides, thebook would be useful to practising engineers and researchers in the field of metal forming.

The first seven chapters are devoted to basic concepts and provide the students with a soundbackground in plasticity, in addition to highlighting the importance of friction and lubrication inmetal forming processes. Only that portion of theory of plasticity is covered, which is relevant tothe subsequent treatment of the subject matter of metalworking, because the book is not meantfor the study of the theory of plasticity.

The remaining chapters cover specific forming processes and new and powerful techniques(load bounding and slip line field) for solving engineering problems in metal forming. Theimportant factors in the study of individual processes such as force, power requirements,formability and machinability are briefly discussed. The analytical methods for the treatment ofmetal forming processes include the free-body equilibrium approach and energy methods.Friction characteristics at the interface are according to the constant shear factor, Coulomb’sfriction law and the composite friction. The analysis is restricted only to plastic materials. In thefinal chapter, the application of computer-aided analysis to the metalworking processes has beendemonstrated, which is the demand in this competitive scenario.

Preface

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Because of the extensive information available in the field and desirability of exposing thestudent to other sources of knowledge, the references provided at the end of the book aresomewhat more comprehensive than ordinarily found in a book of this nature.

I am indebted to many individuals for the help rendered on many fronts. This book has beenan outcome of my extensive experience in teaching and guiding research in the field oftechnology. I wish to express my gratitude to all the distinguished authorities in the field whoseworks have inspired me in the preparation of my subject matter.

Finally, I would like to thank my family members for their patience, encouragement andcooperation during preparation of this manuscript.

Although great care has been taken to eliminate errors and misprints, it is inevitable thatsome will still be found. The author will appreciate being informed about these, and alsowelcome any comments and suggestions that the readers may wish to offer.

Surender Kumar

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Nomenclature

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Unless otherwise specified the following symbols have been used in the book:

A areaA0 dimensionless area (A0 = Ar/A)Ar real area of contact (Ar = AA0)ai acceleration fieldB coefficient, B = b/h; B = m/tan a2b breadth or diameter of forging, width of rolled stripD diameterd depthE modulus of elasticitye strain, engineering strain

e ij strain rate components

f feed rateG torsion modulus, modulus of rigidityg acceleration due to gravityh thicknessh0 initial blank thicknessI1, I2, I3 stress invariantsJ * upper bound energy consumptionJ1, J2, J3 invariants (stress deviator, strain rate)K yield stress in pure shearl lengthm constant, friction factor (0 < m < 1)n normal unit vector, neutral point in rolling, strain hardening exponent,

number of sides of polygonal disc

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O origin of co-ordinate systemP roll force, die loadp pressurep dimensionless die load, relative average pressure

R reductionR0 roll radiusr inner radius of bend, radius, radial distancer, q, z cylindrical co-ordinater, q, j spherical co-ordinateS surface of velocity discontinuitySij components of stress deviatorSt surface on which the stress vector Ti is prescribedT torquet timeUi velocityui displacementV volume, velocityv velocityW work, work done per unit volume

W powerx, y, z axes of a co-ordinate system

Greek Symbols

a angle, die angle, bend angle, Mandrel anglea i directional cosinesa2 angle of contact in rolling (plastic zone)b barreling parameterg shearing strainh coefficient of viscosity, efficiencyDv velocity discontinuity, velocity differencee true straine0 effective strain

e true strainq angular positionm coefficient of frictionv Poisson’s ratiom, n Lode’s parametersr density

xvi Nomenclature

Technology Of Metal FormingProcesses

Publisher : PHI Learning ISBN : 9788120334250 Author : Surender Kumar

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