die maintenance handbook introduction

Die MaintenanceHandbook

David A. Smith

Society of Manufacturing EngineersDearborn, Michigan

Die Maintenance Handbook

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Copyright © 2001 Society of Manufacturing Engineers

987654321

All rights reserved, including those of translation. This book, or partsthereof, may not be reproduced by any means, including photocopying,recording or microfilming, or by any information storage and retrievalsystem, without permission in writing of the copyright owners.

No liability is assumed by the publisher with respect to use of informa-tion contained herein. While every precaution has been taken in thepreparation of this book, the publisher assumes no responsibility forerrors or omissions. Publication of any data in this book does not consti-tute a recommendation or endorsement of any patent, proprietary right,or product that may be involved.

Library of Congress Catalog Card Number: 2001094396International Standard Book Number: 0-87263-525-2

Additional copies may be obtained by contacting:Society of Manufacturing EngineersCustomer ServiceOne SME Drive, P.O. Box 930Dearborn, Michigan 481211-800-733-4763www.sme.org

SME staff who participated in producing this book:

Cheryl Zupan, Staff EditorRosemary Csizmadia, Production SupervisorKathye Quirk, Graphic Designer/Cover DesignFrances Kania, Administrative CoordinatorJon Newberg, Production Editor

Printed in the United States of America

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Dedication

I would like to dedicate this book to the many people that madeit possible, especially my wife Marlyn Smith who helped with theformatting and proofreading of the original training manuals thatwere used to produce this work. I would also like to thank mem-bers of the production and editorial departments at SME who wentthe extra mile to give this work polish and continuity. Those indi-viduals include Cheryl Zupan, Bob King, Rosemary Csizmadia,Kathye Quirk, Jon Newberg, and Frances Kania.

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Table of Contents

Preface ..................................................................................... xiiiContributors ............................................................................ xvii1 An Overview of Basic Die Operations ................................... 1

Cutting, Punching, and Perforating ........................................ 1Bending and Forming............................................................. 2Bending and Straightening .................................................... 3Stretching ............................................................................... 4Drawing ................................................................................... 6Squeezing or Coining Operations .......................................... 6Analytical Tools ....................................................................... 8

2 Troubleshooting Punching and Cutting Operations ........... 11Understanding the Sequence of Operations ....................... 11Effect of Die Clearance ......................................................... 15Cutting Forces ...................................................................... 21

3 Designing Large EDM Die Sections for Repairability ......... 27Application of EDM Technology ........................................... 27Throwaway versus Repairable Die Sections ........................ 28Die Section Location and Retention ..................................... 29Punch and Die-steel Design ................................................. 30Conclusion ............................................................................ 32

4 Die-shaving Operations ........................................................ 33Purpose ................................................................................ 33Punch-to-die Clearance ........................................................ 34Size of Shave Punch versus Part Hole Size ......................... 34Multiple Shaving Operations ................................................ 34Application of the Hollow-ground Concept .......................... 36


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5 Solving Punch Head Breakage Problems ........................... 39Punch Head Breakage ......................................................... 39Safety of Personnel ............................................................... 45Function of the Punch Backing Plate ................................... 46Ironworker- and Bulldozer-style Punches ............................ 47

6 The Cost of Punch and Die Maintenance ............................ 49Record Causal Factors ......................................................... 49The Real Cost of Die Damage .............................................. 51The Value of Good Workmanship ........................................ 51

7 Good Maintenance Practice ................................................. 53Good Grinding Practice ........................................................ 53Stress-relieving Cutting Tools ............................................... 63Shimming Die Components ................................................. 65Ball-lock Punches and Die Buttons ...................................... 69

8 Compound Dies .................................................................... 73Compound Blank and Piercing Dies .................................... 73

9 Pressure Pad and Stripper Selection .................................. 79Positive or Tunnel Strippers .................................................. 79Pressure Systems for Pads and Strippers ........................... 81Elastomer Strippers .............................................................. 86Stripping Forces ................................................................... 87

10 Anti-slug Pulling Methods .................................................. 89Resolving Slug-pulling Problems ....................................... 89Overview of Methods .......................................................... 97

11 Cutting Force and Snap-through Reduction ................... 101Types of Punch Shear ...................................................... 101Punching Thick Carbon Steel .......................................... 102Importance of Timing ....................................................... 104Press Reverse-load Capacity ........................................... 105Die Timing Improvement .................................................. 106Providing Angular Shear on the Die ................................. 108Summary .......................................................................... 110

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12 Bending of Metals .............................................................111Bend Allowances .............................................................. 113Press-brake Operations.................................................... 115Wipe-bending Die Operations .......................................... 117Rotary-action Die-bending Operations ............................ 119Control of Bend Angle by Adjusting Pad Pressure .......... 122

13 Forming Flanges and Hems ............................................. 129Flanging Operations ......................................................... 129Flange Types .................................................................... 129Minimum Bend Radii ........................................................ 132Stock Thickness Variation ................................................ 133Hemming Operations ....................................................... 136Pressures .......................................................................... 137

14 Drawing and Stretching of Metals ................................... 141Deep Drawing of a Cylindrical Cup .................................. 141Stretch Forming ................................................................ 148Bending and Straightening .............................................. 149Drawing and Bending ....................................................... 150

15 Stamping Analysis Techniques ........................................157Computerized Analysis Techniques ................................. 158Circle Grid Analysis .......................................................... 159

16 Die Maintenance Documentation and Tracking .............. 167Die Maintenance Team ..................................................... 167A Systematic Die Maintenance System ........................... 168The Request for Maintenance Form................................. 175Case Study ....................................................................... 176Continuous Improvement ................................................. 180

17 Effective Die Maintenance Program Strategy ................. 183Understanding the Die Maintenance Facility ................... 183Addressing Production-scheduling Problems ................. 184Planning Die Maintenance ............................................... 185Tracking the Cost of Maintenance and Downtime ........... 186

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Continuous Improvement ................................................. 186Spare Parts Inventory ....................................................... 190Calculating Costs ............................................................. 193Pareto Charting ................................................................. 200Dealing with an Outside Vendor ....................................... 203Used Dies ......................................................................... 204Good Engineering Practice .............................................. 205

18 Metallic Springs as Die-pressure Devices ...................... 211Types of Metal Springs ..................................................... 211Materials Used to Make Metal Springs ............................ 215Selecting Springs ............................................................. 216Considerations When Repairing Dies .............................. 220Analysis of Spring Failures ............................................... 222Winding Springs In-house ................................................ 225Conclusion ........................................................................ 225

19 Gas and Hydraulic Die-pressure Systems ...................... 227Pneumatic Cylinders ........................................................ 227Nitrogen Die-pressure Systems ....................................... 231Nitrogen Manifold Systems .............................................. 235Self-contained Nitrogen Cylinders ................................... 237Hydraulic Die-pressure Systems ...................................... 243

20 Press Selection and Maintenance ................................... 247Press Terminology ............................................................ 247Types of Presses .............................................................. 250Overload Protection .......................................................... 259Mechanical Press Drives .................................................. 260Speed Reduction and Torque Capacity ........................... 268Mechanical versus Hydraulic Presses ............................. 268Upgrading Existing Presses ............................................. 275Die Cushions .................................................................... 275Centering the Load in the Press ....................................... 278

21 Troubleshooting Large Panel Stamping Dies .................. 283Die Bolting ........................................................................ 283Nitrogen Pressure Systems.............................................. 286

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A Systematic Approach to Die Tryout .............................. 286Draw Beads ...................................................................... 291Double-action Press Operations ...................................... 295Dirt Problems .................................................................... 295Forming Ribs and Embossments ..................................... 297Knockout Bars .................................................................. 299

22 Waveform Signature Analysis .......................................... 301Stress-strain Curves ......................................................... 301Case Study: Webster Industries ....................................... 302Diagnosing Hydraulic Overload Problems ...................... 307Press-tonnage Curves ...................................................... 311Detecting Waveform Changes ......................................... 315Die- and Press-protection Systems.................................. 317Conclusion ........................................................................ 320

23 Repairing Damaged Die Steels and Castings ................. 323Making the Repair Decision ............................................. 323Mechanical Repair Techniques ........................................ 325Electrical Welding Repairs ................................................ 333

24 Die Materials and Treatments .......................................... 339Characteristics of Tool and Die Steels .............................. 340Choosing Tool Steels ........................................................ 340Heat Treatment of Die Steels ............................................ 353Tool Steel Production Methods ........................................ 358Die Surface Coatings and Treatments ............................. 360Wrought Low-carbon Steels and Cast Irons .................... 363Nonferrous and Nonmetallic Die Materials ...................... 365

Appendix A: Generic Die Standards ...................................... 371Design-and-build Process .................................................. 371Production and Safety ........................................................ 372Quotes ................................................................................ 373Completion ......................................................................... 373Cancellations and Damages .............................................. 374Designing Strong Die Sections .......................................... 375Screws, Dowels, and Keys ................................................. 377

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Die Shoes, Subplates, and Parallels .................................. 379Die Springs ......................................................................... 380Strip Starting Stops ............................................................ 382Commercial Perishable Details .......................................... 383Pads and Strippers ............................................................. 384General Tool Steel Details .................................................. 385Guide Pin, Bushing, Heel Block, Keeper, and Wear Plates 386Scrap Discharge ................................................................. 387Stock Sensors .................................................................... 388General Good Practice ....................................................... 388OSHA and Additional Die Identification ............................. 389

Appendix B: Case Study—Phoenix Specialty Manufacturing Company ......................... 391

Order Entry ......................................................................... 391Machine Shop Capabilities ................................................ 392Plant Culture ....................................................................... 394Spare Parts Storage ........................................................... 394Ergonomics ........................................................................ 395Aluminum Die Sets ............................................................. 396Bench Die Build Up ............................................................ 398Quick Die Change Capabilities .......................................... 399An Eye to the Future ........................................................... 400Conclusion .......................................................................... 400

Index ........................................................................................ 403

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Preface

Developing a popular book on the topic of die repair has been achallenging task. The goal of every shop should be to minimize diemaintenance expenditures through good die design. To do this, eachof the metal forming, pressworking processes need to be under-stood from a simple, yet analytical, point of view. Thus, this refer-ence work on die maintenance deals with metal-forming processesin an elementary way, before looking at the bigger picture of costcontainment using damage avoidance and robust die designs.

CHOOSING THE CONTENT OF THIS BOOK

A goal of this reference work is to produce a handbook that willmake solving stamping-process problems understandable by new-comers to the trade. At the same time, it is intended to serve theexperienced journeyman with reference information for solvingdifficult problems. An essential theme is that die maintenance is acost that needs to be minimized. Too often, die maintenance istreated as unavoidable and unacceptable, with its very real costslumped in with other overhead. Success in any critical mechani-cal repair or defect correction necessitates that required tasks oc-cur correctly and in the proper sequence. This takes both skilland the ability to document results for future reference.

Those who have spent most of a lifetime in the tool and dietrade hope for the day when educators will quit teaching thathourly employees in industry have chosen a second-rate alterna-tive to completing a college degree. In reality, many journeymenalso hold two-year, technical degrees. Some go on to complete ad-vanced degrees in engineering and business management. Yes,


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these skilled workers will continue to hold engineering and topmanagement positions in the future.

Most community colleges and trade schools do a good job ofteaching the basic principles of computer numerical control (CNC)machining, industrial welding, hydraulics, pneumatics, and elec-tronic technology. However, schools lack hands-on training in thebasic theories of die making and metal-forming processes. Hands-on experience needs to occur in a die building and/or repair facil-ity under the guidance of skilled workers.

Apprentices or trainees are not a source of low-cost labor. Diebuilders and the manufacturers who depend on pressworking tool-ing in their processes have a duty and an obvious, personal staketo provide the best training to all in the trade, without regard toexperience level. Anything less deprives both the craftsperson andemployer of the critical skills that are essential to remain innova-tive and competitive in a world market.

BOOK ORGANIZATION

An essential die-repair skill is the ability to modify existing tool-ing to correct design mistakes and problems that can affect partquality and proper tool operation. A good understanding of metal-forming processes in pressworking tooling is necessary to main-tain and correct die problems.

This book begins with an overview of basic die operations andcontinues with the anatomy of how these processes work. Trouble-shooting, or using insight into the process, is an essential factorin problem solving. Formability theory and practice begin withhaving basic knowledge of bending and stretching metals throughcomplex, forming states. Essential, analytical methods that areneeded to solve problems are also covered. Here, the informationis in a simple format, yet it is comprehensive enough to be techni-cally correct from a tool-engineering perspective.

The appropriate use of electronic instrumentation for processprotection and optimization is essential in modern pressworking.This ties in with pressworking safety—both of the process andespecially of the pressroom personnel.

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Preface

Troubleshooting of large dies, including casting repair, is basedon the experience of co-workers and the author with large, sheet-metal-forming dies. The reader will find that much of the infor-mation here is either hard to find, or that it has never been put inprint. Topics include solving dirt problems in automotive, outer-skin-panel, forming operations, as well as repair methods forbroken cast-iron die shoes. This unique text is meant to aid thosefaced with these repair and troubleshooting problems. Toolengineering, including problem solving, is not a black art. It is adiscipline based mainly on mechanical engineering and materialscience.

The material science behind die materials, heat treatment, andtool coatings is objective and based on expert review. Objectiveinformation is a problem area because of large amounts of con-flicting information and negative comparisons prevalent today intrade advertising.

This book offers detailed procedures for establishing a die main-tenance program. Problem tracking and cost control to start orimprove a system are explained. Examples of die standards aregeneric and recast subject to applicable law and good engineeringpractice.

It is hoped that the individuals, organizations, and firms whohave contributed to this work will recognize the benefits gainedfrom cooperation and mutual assistance that extend far beyondany financial recompense. By donating time, talent, and designexamples, contributors have provided a wealth of practical designand troubleshooting information. Their help has made this workpossible.

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Contributors

Taylan Altan, Ph.D.Professor and DirectorERC/NSMOhio State UniversityColumbus, Ohio

Gary AminSupervisorDie Design and StandardsFord Motor CompanyDearborn, Mich.

Jim AustinDirector of ContinuousImprovement

Michigan Seat CompanyJackson, Mich.

James Barrett, Jr., Ph.D.PresidentLink SystemsNashville, Tenn.

John BatesPresident and CEOHeidtman Steel Products, Inc.Toledo, Ohio

Lisa BissonEditorEagle PublicationsNovi, Mich.

Rollin BondarPresidentMPD Welding, Inc.Orion, Mich.

Arthur BrownPublisherEagle PublicationsNovi, Mich.

Douglas BurkeForms ConsultantSuperior Business SolutionsKalamazoo, Mich.

Bill ChristiansenSenior Process EngineerJostens, Inc.Princeton, Ill.

Daniel N. FalconeVice PresidentToledo Transducers, Inc.Holland, Ohio

The author wishes to acknowledge the following individuals fortheir contributions to this book:


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Kevin M. FesslerElectrical MaintenanceConsultant

Centerville, Ind.

Chuck FitchDirector of FluorescentOperations

Cooper IndustriesAmericus, Ga.

Jeff FredlinePresidentFredline & AssociatesOkemos, Mich.

Henry H. GehlmannBlanking Area Manager(retired)Ford Motor CompanyWoodhaven, Mich.

Leo GoepfrichTool and Die Manager(retired)Ford Motor CompanyChicago Heights, Ill.

Bob GreenEngineering & FacilitiesManager

Cooper IndustriesAmericus, Ga.

Roger P. HarrisonDirector of TrainingRockford Systems, Inc.Rockford, Ill.

Bill HaysDistrict MaintenanceSupervisor

Governor’s Office ofTechnology

Frankfort, Ky.

John HeffelfingerManufacturing ManagerNorlen, Inc.Schofield, Wisc.

James HicksProfessor of ChemistryCumberland CollegeWilliamsburg, Ky.

Robert HurstPresidentPhoenix SpecialtyManufacturing Company, Inc.

Bamberg, S.C.

Casimir S. JaniszewskiPresident and CEOSuperior Die Set CorporationOak Creek, Wisc.

Stuart P. Keeler, Ph.D.PresidentKeeltech TechnologiesGrosse Ile, Mich.

Karl A. KeyesPresidentFeinblanking Ltd.Fairfield, Ohio

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Gregory A. KrepsTooling EngineerCapital Die, Tool andMachine Company

Columbus, Ohio

James L. LehnerApplications ManagerHMS Products CompanyTroy, Mich.

Ernie LevinePresident and CEOAdmiral Tooland Manufacturing

Chicago, Ill.

Cecil LewisCorporate Vice PresidentMidway Products Group, Inc.Monroe, Mich.

Albert A. ManduzziSupervisor (retired)Die Design and StandardsFord Motor CompanyDearborn, Mich.

John McCurdyPresident (retired)W. C. McCurdy CompanyOxford, Mich.

Bradley K. MettertField Engineering ManagerToledo Transducers, Inc.Holland, Ohio

Carl MeyerPresidentProgressive Tool CompanyWaterloo, Iowa

Harry J. MickaManufacturing EngineerLA-Z-BOY Chair CompanyDayton, Tenn.

Richard MickaVice Presidentof Administration

LA-Z-BOY Chair CompanyMonroe, Mich.

Arnold MiedemaPresidentGreen Meadows EngineeringHudsonville, Mich.

Ernest E. MorganConsultingStructural Engineer

Henderson, Ky.

Eugene J. NarbutDie Room Unit LeaderAuto Alliance InternationalFlat Rock, Mich.

Al NicholsArea LeaderStamping EngineeringAuto Alliance InternationalFlat Rock, Mich.

Mark NicholsCorporate Safety DirectorLA-Z-BOY Chair Co.Maplewood, Minn.

Michael F. Ollie, Jr.PresidentHenry & Wright CorporationFairforest, S.C.

Contributors


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Pat OntropApplications EngineerMinster Machine CompanyMinster, Ohio

Dick PeoplesMetallurgistHeidtman Steel Products, Inc.Toledo, Ohio

Jim PientaProduction ManagerJostens, Inc.Princeton, Ill.

Gerald A. PoolConsultantRoyal Oak, Mich.

Ronald E. PraterPresident, Koppy CorporationOrion, Mich.

Frank RandallEngineering Manager(retired)Zippo Manufacturing CompanyBradford, Pa.

Anthony RanteDirector of EngineeringFitzpatrick CompanyElmhurst, Ill.

Jim RickettsProduction ManagerLA-Z-BOY Chair Co.Dayton, Tenn.

Mike RileyMechanical Engineer, P.E.Consultant & WriterPinson, Ala.

Brad SauerIndustrial EngineerLA-Z-BOY Chair Co.Monroe, Mich.

Daniel A. SchochMechanical Engineer, P.E.Minster Machine CompanyMinster, Ohio

Mike SearsonMachine Shop SupervisorPhoenix SpecialtyManufacturing Company, Inc.

Bamberg, S.C.

Aniese SeedPresident (retired)Toledo Transducers, Inc.Holland, Ohio

Kenneth L. SmedbergPresidentSmedberg MachineCorporation

Chicago, Ill.

Andrew D. SmithMechanical Engineer, T. R. WLivonia, Mich.

Gary D. SmothermanInternational Representative(retired)U. A. W.Detroit, Mich.

Fredric SpurckPresidentWebster Industries, Inc.Tiffin, Ohio

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Robert StadlerTool EngineerRanger Tool & DieGrand Rapids, Mich.

Allan SteinbockVice PresidentSuperbolt, Inc.Carnegie, Pa.

Robert StorerPresidentToledo Transducers, Inc.Holland, Ohio

Leslie SuthersManagerManufacturing ServicesNorlen, Inc.Schofield, Wisc.

Thomas A. SuthersPresidentNorlen, Inc.Schofield, Wisc.

Nick TarkanyDirectorResearch & TechnicalEducation

Dayton Progress Corp.Dayton, Ohio

Ed TarneyDirectorCPM DevelopmentCrucible Materials CorporationCamillus, N.Y.

Jack ThompsonPresidentPenda CorporationPortage, Wisc.

Contributors

Ed TremblayVice President, Engineeringand Manufacturing

P/A IndustriesBloomfield, Conn.

Robert VanceConsulting Marine EngineerGlasgow, Ky.

Bob WahlsChief EngineerMichigan Seat CompanyJackson, Mich.

Keith WeaverPress EngineerCapital Die, Tooland Machine Company

Columbus, Ohio

Joe WiseMaintenance SupervisorH. J. Heinz CompanyFreemont, Ohio

Wayne WittakerVice President of OperationsUnisorb MachineryInstallation Systems

Jackson, Mich.

Greg YirgaMetal Department ManagerLA-Z-BOY Chair Co.Dayton, Tenn.

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