Sheet Metal Forming Processes and Die Design

By Vukota Boljanovic

Written by an engineer with decades of practical manufacturing experience, this new edition has been thoroughly revised and is a complete modern guide to sheet metal forming processes and die design – still the most commonly used methodology for the mass-production manufacture of aircraft, automobiles, and complex high-precision parts. Included are the “hows” and “whys” of product analysis, as well as the techniques for blanking, punching, bending, deep drawing, stretching, material economy, strip design, movement of metal during stamping, and tooling. Its focus is on simple, applicable engineering methods rather than complex numerical techniques.   
 

• Language: English
• Publisher: Industrial Press, Inc.
• Release date: Apr 1, 2014
• ISBN: 9780831191870

Book preview

SHEET METAL FORMING

PROCESSES AND DIE DESIGN

Second Edition

SHEET METAL FORMING

PROCESSES AND DIE DESIGN

Second Edition

VUKOTA BOLJANOVIC, Ph.D.

Industrial Press

COPYRIGHT

A full catalog record for this book is available from the Library of Congress.

ISBN 978-0-8311-9187-0

Industrial Press, Inc.

32 Haviland Street, Unit 2C

South Norwalk, CT 06854

Sponsoring Editor: John Carleo

Developmental Editor: Robert Weinstein

Interior Text and Cover Design: Janet Romano

Copyright© 2014 by Industrial Press Inc., Printed in the United States of America. All rights reserved.

This book, or any parts thereof, may not be reproduced, stored in a retrieval system, or transmitted in any form without the written permission of the publisher.

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DEDICATION

To my granddaughter Milla Liv Broadwater

and

to my grandson Alexandar Boljanovic

TABLE OF CONTENTS

Cover

Title Page

Copyright

Dedication

Preface to the Second Edition

Preface to the First Edition

List of Tables

Introduction

PREFACE TO THE SECOND EDITION

The science, engineering, and technology of sheet metal forming processes and die design continue to advance rapidly on a global scale and with major impact on the economies of all nations. In preparing this second edition, my goal throughout has been to provide an expanded and more comprehensive treatment of the sheet metal forming processes, while placing forming processes and die design in the broader context of the techniques of press-working sheet metal.

As in the first edition, this text presents topics with a balanced coverage of relevant fundamentals and realworld practices to help the reader develop an understanding of the often complex plastic deformation process. The book is now a more complete text for academics as well as for practicing designers and manufacturing and industrial engineers.

This new edition has essentially the same introductory nature, format, and organization as the first edition. However, enhancements and extensions of several of the chapters in the First Edition have been included, and one new chapter on a topic of great importance to the modern manufacturing industry has been added.

What Is New in this Edition

A careful page-by page comparison with the first edition will show that hundred of changes have been made to improve the clarity and readability of the numerous topics covered.

•Chapter 1 (concerning the structure of metals) has been rewritten and sections on atomic structure and bonding between atoms and molecules have been added.

•Chapter 2 (concerning mechanical behavior of metals) has new sections on hardness and the effect of temperature on material properties.

•Chapter 4 (concerning blanking and punching) has new examples on blanking clearance and force.

•Chapter 5 (concerning bending) has a rewritten section on bending force as well as new examples.

•Chapter 6 (concerning deep drawing) has a rewritten section on blank calculation for rotational symmetrical shells and new methods for blanking calculation.

•Chapter 7 (concerning various forming processes) has a rewritten section on flexible die forming, while new sections discussing the Guerin process, Verson-Wheelon process, Marform process, and hydroforming process have been added.

•All of the illustrations in the book have been redrawn for improved graphic impact and clarity, and numerous new illustrations have been added.

•A new Chapter 14 (on the topic of quick die-change systems and die design) has been added, as has an Appendix 4 on the topic of technical specifications of helical and Belleville springs.

•The glossary and bibliography at the end of the book have been thoroughly updated.

I would like to thank my colleagues and readers of the book for their helpful suggestions regarding improvements to the second edition, and my family and personal friends who indirectly contributed to this book through their love and friendship during the last few years.

Vukota Boljanovic

PREFACE TO THE FIRST EDITION

A very large variety of sheet-metal forming processes is used in modern sheet-metal press-working shop practice. Many of these deformation processes, used in making aircraft, automobiles, and other products, use complex equipment that is derived from the latest discoveries in science and technology. With the ever-increasing knowledge of science and technology, future deformation processes promise to be even more complex to satisfy the demand for more productivity, lower cost, and greater precision. However, for all their advantages, the more sophisticated deformation processes of today have not replaced the need for basic sheet-metal forming processes and dies.

This book draws on the author’s 30-plus years of experience as an engineer and provides a complete guide to modern sheet-metal forming processes and die design — still the most commonly used manufacturing methodology for the mass production of complex, high-precision parts. Much more practical than theoretical, the book covers the hows and whys of product analysis, and the mechanisms of blanking, punching, bending, deep drawing, stretching, material economy, strip design, movement of metal during stamping, and tooling design. Readers will find numerous illustrations, tables, and charts to aid in die design and manufacturing processes; Formulas and calculations needed for various die operations and performance evaluation are included; and designations, characteristics, and typical applications of various carbon and alloy steels for different die components are evaluated.

The book concentrates on simple, practical engineering methods rather than complex numerical techniques to provide the practicing engineer, student, technician, and die maker with usable approaches to sheet-metal forming processes and die design.

The first part of the book deals with the structures of metals and the fundamental aspects of the mechanical behavior of metals. Knowledge of structures is necessary to controlling and predicting the behavior and performance of metals in sheet-metal forming processes.

The second part of the book covers all aspects of forming sheet metal. It presents the fundamental sheet-metal forming operations of shearing, blanking and punching, bending, stretching, and deep drawing. Mechanics of various drawing processes indicate ways in which the deformation, loads, and process limits can be calculated for press forming and deep drawing operations. The book includes various drawing processes (nosing, expanding, dimpling, spinning and flexible die forming) mostly used in the aircraft and aerospace industry.

Dies are very important to the overall mass production picture, so they are discussed in the last section of the book, which presents a complete picture of the knowledge and skills needs for the effective design of dies for sheet-metal forming processes described. Special attention is given to:

•Formulas and calculations needed for various die parts.

•Rules of thumb and innovative approaches to the subject.

•Properties and typical applications of selected tool and die materials for various die parts.

Although the book provides many examples of calculations, illustrations, and tables to aid in sheet-metal forming processes, die design, and die manufacturing, it should be evident that it is not possible to present all the data, tables, statistics, and other information needed to design complicated dies and other tools for sheet-metal forming in one text. However, the book endeavors to provide most of the information needed by a die designer in practical situations.

The author owes much to many people. No book can be written in a vacuum. I am grateful to my wife, who understands my need for long periods of isolation. I also wish to express my deepest appreciation and thanks for the competent work of Em Turner Chitty, who labored countless hours at editing and proofreading. Finally, I wish to thank my English language teacher from The University of Tennessee, Anwar F. Accawi, who encouraged me to begin writing this book.

Vukota Boljanovic

Knoxville, Tennessee

LIST OF TABLES

INTRODUCTION

I.1Basic Characteristics of Sheet Metal Forming Processes

I.2Categories of Sheet Metal Forming Processes

I.3Characteristics of Sheet Metal Parts and Their Technological Properties

I.1 BASIC CHARACTERISTICS OF SHEET METAL FORMING PROCESSES

Sheet metal parts are usually made by forming material under cold conditions. (In many cases, however, sheet-metal parts are formed under hot conditions because the material, when heated, has a lower resistance to deformation—i.e., it is more easily deformed).

Strips or blanks are very often used as initial materials and are formed on presses using appropriate tools. The shape of a part generally corresponds to the shape of the tool.

Sheet-metal forming processes are used for both serial and mass production. Their characteristics include high productivity, highly efficient use of material, easy servicing of machines, the ability to employ workers with relatively lower basic skills, and other advantageous economic aspects. Parts made from sheet metal have many attractive qualities: good accuracy of dimension, adequate strength, light weight, and a broad range of possible dimensions, from the miniature parts used in electronics to the large components of airplane structures.

I.2 CATEGORIES OF SHEET METAL FORMING PROCESSES

All sheet-metal forming processes can be divided into two groups:

1.Cutting processes: shearing, blanking, punching, notching, cutoff, shaving, trimming, parting, slotting and perforation, and lancing.

2.Plastic deformation processes: bending, twisting, curling, deep drawing, spinning, stretch flanging, shrink flanging, hole flanging, necking, bulging, ribbing, hemming, and seaming.

a) The First Group of Processes

Cutting processes involve cutting material by subjecting it to shear stresses usually between punch and die or between the blades of a shear. The punch and die may be any shape, and the cutting contour may be open or closed.

Shearing. Shearing involves the cutting of flat material forms from sheet, plate, or strip. The process may be classified by the type of blade or cutter used, whether straight or rotary.

Blanking. Blanking involves cutting the material to a closed contour by subjecting it to shear stresses between punch and die. In this process, the slug is usually the work part and the remainder is scrap.

Punching. Punching is the cutting operation by which various shaped holes are sheared in blanks. In punching, the sheared slug is discarded, and the material that surrounds the punch is the component produced.

Notching. Notching is cutting the edge of the blank to form a notch in the shape of a portion of the punch. If the material is cut around a closed contour to free the sheet metal for drawing or forming, this operation is called semi-notching.

Cutoff. Cutoff is a shearing operation in which the shearing action must be along a line. A cutoff is made by one or more single line cuts.

Shaving. Shaving is a cutting operation that improves the quality and accuracy of blanked parts by removing a thin strip of metal along the edges. Only about 100 microns (0.004 inches) of material are removed by shaving.

Trimming. For many types of drawing and forming parts, excess metal must be allowed; the workpiece can then be held during the operation that shapes the metal into the form of the part. The cutting off of this excess metal after drawing or forming operations is known as trimming.

Parting. Parting is the cutting of a sheet metal strip by die cutting edges on two opposite sides. During parting, some amount of scrap is produced. This might be required when the blank outline is not a regular shape and cannot perfectly nest on the strip.

Lancing. Lancing is an operation in which a single line cut is made partway across the work material. No material is removed, so there is no scrap

b) The Second Group of Processes

Involves partial or complete plastic deformation of the work material.

Bending. Bending consists of uniformly straining flat sheets or strips of metal around a linear axis. Metal on the outside of the bend is stressed in tension beyond the elastic limit. Metal on the inside of the bend is compressed.

Twisting. Twisting is the process of straining flat strips of metal around a longitudinal axis.

Curling. Curling is a forming operation that is used to strengthen the edge of sheet metal. The edges of the drawn part are formed into a roll or curl for providing a smooth rounded edge.

Deep Drawing. Deep drawing is a sheet metal forming process in which a sheet metal blank is radially drawn into a cylindrical or box-shape forming die by the mechanical action of a punch. It is thus a shape transformation process with material retention. Drawing may be performed with or without a reduction in the thickness of the material.

Spinning. Spinning is a process of forming the workpiece from a circular blank or from a length of tubing. All parts produced by spinning are symmetrical about the central axis.

Stretch flanging. During the forming of the flange, the periphery is subjected to tension. Stretched flanges are susceptible to splitting and thinning. Cracking or tearing of the metal is the most common defect in