Production engineering technology

PRODUCTION ENGINEERING TECHNOLOGY

Other Mechanical and Production Engineering titlesfrom Macmillan

INTRODUCTION TO ENGINEERING MATERIALS: V. B.John

MANAGEMENT OF PRODUCTION, Third Edition: J. D. RadJord and

D. B. Richardson

THE MANAGEMENT OF MANUFACTURING SYSTEMS: J. D. RadJord

and D. B. Richardson

MECHANICAL ENGINEERING DESIGN, Second Edition: G. D. Redford

MECHANICAL TECHNOLOGY, Second Edition: G. D. RedJord, J. G.

Rimmer and D. Titherington

STRENGTH OF MATERIALS, Third Edition: G. H. Ryder

AN INTRODUCTION TO PRODUCTION AND INVENTORY CONTROL:

R. N. van Hees and W. Monhemius

Production

Engineering Technology

J. D. Radford, B.SC. (ENG.), M.I.MECH.E., F.LPROD.E.

D. B. Richardson, M.PHIL., D.LC., F.I.MECH.E., F.LPROD.E.,

A.M.B.I.l\f.

Brighton Polytechnic

THIRD EDITION

M

MACMILLAN

© J. D. Radford and D. B. Richardson, 1969, 1974, 1980

All rights reserved. No part of this publication

may be reproduced or transmitted, in any form

or by any means, without permission.

First edition 1969

Second edition 1974

Reprinted 1976 (with corrections), 1978

Third edition 1980

Reprinted 1982, 1983, 1984

Published by

Higher and Further Education Division

MACMILLAN PUBLISHERS L TD

London and Basingstoke

Companies and representatives

throughout the world

British Library Cataloguing in Publication Data

Radford. John Dennis

Production engineering technology. - 3rd ed.

1 Production engineering

I. Tide 11. Richardson. Donald Brian

621. 7 TS176

ISBN 978-0-333-29398-0 ISBN 978-1-349-16435-6 (eBook)

DOI 10.1007/978-1-349-16435-6

Contents

Preface to the Third Edition Vi

Introduction

2 Manufacturing Properties of Metals 4

3 Basic Plasticity 1 I

4 Hot Forging and Rolling 38

5 Extrusion, Tube-making and Cold Drawing 65

6 Sheet Metal Forming and Cold Forging 87

7 Cutting Tool Geometry and Tool Materials 125

8 Metal Cutting 136

9 Milling and Broaching 165

10 Economics of Metal Removal 178

11 Abrasive Machining 191

12 Recently Developed Techniques ofMetal Working 211

13 Fabrication by Welding, Brazing or Adhesion 224

14 Casting and Sintering of Metals 242

15 Polymer Processing 273

16 Control of Machine Tools 289

17 Metrology 308

Appendix 1 356

Appendix 2 362

Appenr:ix 3 364

Examination Questions 367

ReJerences 373

Index 377

Preface to the Third Edition

The main object in writing this book is to provide a concise treatment of

production engineering technology for Degree and Higher National

Diploma students.

Although the many aspects of the subject have been separately covered

in much greater detail in various books and papers, the authors believe

that this is the first time that an attempt has been made to contain the

necessary work at this level in one volume.

The third edition has enabled us to include new material and to bring

cutting too1 nomenclature into line with BS I296. The chapter 'Polymer

Processing' has been contributed by our colleague, Mr R. S. G. Elkin,

M.I.Mech.E., M.R.Ae.S.

'Ve should like to thank those who, by their suggestions and advice, have

assisted in the preparation ofthe book, and also Miss Grace Vine, who typed

the manuscript.

J. D. RADFORD

D. B. RICHARDSON

I Introduction

The shaping of materials before they are incorporated into a product

usually occurs in a number of stages. Specific examples of the shaping

processes used to produce five different parts are illustrated in Fig. LI (a)

and an outline of the main groups of shaping processes is shown in

Fig. LI (b). It will be seen that some parts which have been cast, sintered

,. WASHER , PR/MARY FORM/NG : FAC~O%:~~,":/NG

0---:---0-----0---0--0--;.

Cast 5t",,' : Hof roll Hol roll Hot roll Cold roll: Piwrcw

Inflol I hloom slah strip strip ,and hlank

I

2. CAR DYNAMO YOKE

PRIMARY FORMING

F'ACTORY BLANKI NG

i AND FORMING :

} __ ~' __ { I

" f---" I

MACHINING

Casl 51",,/ ,Hot roll Hol roll Hot roll : Crop hur Ist« 2nd! Wttld Borrt Fue""nd

Ingot I hloom 6illet 6ur, I"nd I

I "

drill. tup

J. SPUR GEAR

PRIMARY FORM/NG MACHINING

I Cast St",,1 I Hof roll Hot roll Hotroll Crop Drop for!J"IDrill,horrt G"n"rul"

Ingot : hloom hill"t hur har gtt<1rhlan*:'uc". turn footh profil"

4. GAS COOkER HANDLE

I CASrlNG

Cust aluminium' Pr"ssur"

ingot 'di"cast

S. TELEPHONE EARP/ECE

,MOULDING

0+0

Th"rmoplasti~

gra"ul"s

Inirtct ion

mou/ding

MACHINING

Drill Polis!>

Fig. 1.1 (a) Typical shaping process

2 PRODUCTION ENGINEERING TECHNOLOGY

RAW MArERIAL

ASSEM8LY OF PRODucr

Fig. 1.1 (b) Main subdivisions in metal shaping

" .... ---------------------------------"',

I

J

I

J

I

J

I

I

Informafion

availabl, SALES

Pr.v;ous d,s;gns t

Com~ditors Function

I1ulgns target cost

Maierial prop.rlies .stimatltd soles

Forming fechniqu.s t

MacMning t'chnique ~ OE S IG N

Casling tltchni'luu t

Shop.

Maulding lechni'lults malerial

to/~ronr:es

Sin/cring fechni'lUltS performance

t

Finishing techniques PROOUCr ION J ENGINEERING

t Proccss

Specified

'>---------,

I More I : inforllKltion. :

•

I changu l /'--------'

t-------', I

-I Special ~ - ... 1 H \ materials J J

\ " I ' ______ • J ,)-.... -----, ~ ,More \ •

I informat ion, :

: chang/ls I , , )-------.' I

, J

"--Ne-;"- -'\ ; .J '.c:;~ques ~ ..... "" I . I I ~~ql.JIpmcn ,I

'"------'"

Fig. 1.2 Stages in specification 01' process

INTRODucnON 3

or moulded can be incorporated directly into assemblies without further

processes, although usually machining is required. Primary forming

operations produce a range of products such as forgings, bar, plate and

strip, which is either machined or further formed in the factory. Some

factory formed parts, however, still have to be machined before they are

assembled.

Within the broad groupings shown in Fig. LI (b) lie a very large

number of different processes. Some have origins which can be traced

back to ancient tim es, while others are in a very early stage of develop￾ment. Some are basic techniques which demand considerable experience

and skill from those who perform them, while at the other end of the

scale there are highly sophisticated processes, often· automatically

controlled.

The material specified for a part will of course influence the choice of

process. Most materials can be shaped by a range of processes, some by a

very limited range and others by a range wide enough to embrace most

of the known processes. In any particular instance however, there is an

optimum sequence of shaping processes. The main factors influencing this

choice are the desired shape and size, the dimensional tolerances, the

surface finish and thc quantity required. The choice must not only be

made on the grounds of technical suitability: cost is an important and

frequently a paramount consideration. A diagram showing the interaction

of factors affecting the choice of process for factory made parts is shown

in Fig. 1.2.

Not only must the production engineer know a great deal about methods

of materials shaping, but this knowledge must be shared by the designer.

New shaping processes are being introduced and existing ones are being

developed at such a rapid rate that no book of this type can claim to be

completely up to date, nor can any engineer have knowledge in real

depth other than in selected fields. A qualitative and partly quantitative

account of as many shaping processes as possible has been included so that

students entering industry will be able to see current practice as an

integrated whole.

2 Manufacturing Properties of

Metals

2.1 METAL FORMING PROCESSES

Methods of plastic deformation are used extensively to force metal into

a required shape. The processes used are diverse in scale, varying from

forging and rolling of ingots weighing several tons to drawing of wire less

than 0'025 mm (0'001 in) in diameter. Most large-scale deformation

processes are performed hot, so that a minimum of force is needed and the

consequent recrystallization refines the metallic structure. Cold working

ENG INEERING

Bloel(

hor

PRooucrs

MACHINING ol>d/or A S SEMB LY

BILur (C"st)

Sp.ciol

s8ctlOl>

& tuh.

Fig.2.1 Major meta! forming processes: cold operations shown in double frame

4

MANUFACTURING PROPERTIES OF METALS 5

is used when smooth surface finish and high dimensional accuracy are

required. Although a growing number of components is manufactured

completely from aseries of deformation processes, metal forming is

primarily used to produce such material as bar and sheet which is subse￾quently machined or pressed into its final shape. Achart showing the

major metal-forming processes can be seen in Fig. 2. I.

2.2 YIELDING

To achieve permanent deformation, metal must be stressed beyond its

elastic limit. A typical relationship between true stress and logarithmic

strain for steel is shown in Fig. 2.2 and the initial yield stress is shown by

point A.

StrllS$

Cf

o

z

A Ini/iol yillld s/r,ss

B Yi/lld s/rll$$ of/,r

stroining fo €,

Z rroc/vrll

Log $/roin E:

Fig. 2.2 Stress/strain curve for steel

Due to the considerable changes in shape occurring when metal is

formed the logarithmic, true or natural strain jdl/l is preferred to the

conventional strain (l - lo)/lo. The relations hip between conventional

and logarithmic strains is considered in Chapter 3.2.

The stress system in most metal forming operations is a complex one;

hence a knowledge of the stress at which the metal fails in simple tension

or compression is of little direct use. The analysis of three-dimensional

stresses involves the consideration of three direct stresses and six pairs of

shear stresses. In the simple treatment used in this book the stresses are

resolved whenever possible into a system containing only three principal

stresses. To determine the combination of direct stresses wh ich produces

yielding some generally applicable criterion is needed. Two criteria of

yielding are commonly used, one proposed by Tresca and the other by

von Mises; both are discussed in the next chapter.

2.3 FRACTURE

When metals are deformed below their recrystallization temperature

they will work harden due to progressive deformation of the metallic

6 PRODUCTION ENGINEERING TECHNOLOGY

structure making further deformation more difficult. This effect can be

observed from the inclination of the stress/strain curve shown in Fig. 2.2.

Apart from increasing the yield stress of a material, work hardening

reduces its ductility and makes fracture more likely.

Most deforming operations are compressive; this enables the metal to

withstand considerably larger strains before fracture than would be

possible with tensile deformation. In fact, brittle materials such as cast

iron, can be extruded like ductile ones if differential hydrostatic extrusion

is used (see Section 6.5.6).

2.4 EFFECT OF TEMPERATURE IN METAL WORKING

Most large-scale processes of ingot and billet reduction and forming are

performed at temperatures well above those at which recrystallization

occurs. Hot working greatly reduces the yield strength during deformation,

but to produce a satisfactory surface finish the product often has to be

finished either by descaling and cold working, or by machining. Due to

recrystallization, hot working is normally characterized by an absence of

strain hardening; however, since the rate of recrystallization is tempera￾ture dependent, the working temperature should be sufficiently above the

minimum necessary for recrystallization. The rate of straining is also

important, for ifit is too fast there will be insufficient time for the annealing

effect of recrystallization; in fact, when hot worked metal is rapidly

strained and then quickly cooled, it will strain harden. On the other hand

if the rate of deformation is too slow there will be an undesirable weakening

caused by grain growth.

2.5 CONCEPT OF RIGID-PLASTIC MATERIAL

It is convenient in metal working to consider that the material behaves

in a rigid-plastic manner (Fig. 2.3). This concept neglects elastic strains

as they are very sm all compared with the total plastic strain which occurs

in metal working. The metal is there￾fore considered rigid up to the stress

at which it yields; after yielding it

is assumed that no additional stress is

needed to increase strain, i.e. no work

hardening occurs. This assumption of

o Log struin €

Fig. 2.3 Stressfstrain relationship

for rigid-plastic material

plastic behaviour is reasonable for hot

working processes and it is a fair

approximation for cold working when

the material has already undergone

MANUFACTURING PROPERTIES OF METALS

considerable work hardening and the slope of the stress/strain curve has

flattened, (zone XV, Fig. 2.2).

2.6 EFFECT OF FRICTION BETWEEN WORK AND TOOL

7

In most cold working processes, the coefficient of friction between the

plastically deforming material and its constraints is low and Coulomb

friction applies. i.e. the frictional force is proportional to the normal force.

However, in hot working, the coefficient of friction is high and the yield

stress of the material is lower than that for cold working. In consequence

the shear flow stress is often reached at the surface of the material and a

thin layer of metal adheres to the container or tool. Under these conditions

the frictional force is independent of the normal force but depends on the

shear flow stress of the metal being formed (see Section 3.10.4).

2.7 EFFECT OF STRAI N RATE

The effect of rapid deformation on yield is as yet imperfectly understood.

Strain rate effects in manufacture are inseparable from those due to

temperature; in machining and high velocity forming processes there is

little heat transfer due to conduction, and the increase in yield stress due to

high strain rate is at least partly balanced by thermal softening.

With steel the net effect of strain rate and temperature appears to

produce a large increase in the initial yield stress, but at high strains the

dynamic increase in yield stress is much less. The resulting stress/strain

curve thus indicates a lower rate of strain hardening and approaches that of

a rigid plastic material.

Unfortunately, the strain rate and temperature dependence of metals

makes accurate quantification of cutting forces from material data

impossible.

2.8 HIGH VELOCITY DEFORMATION

Considerable development has occurred in high velocity processes for

forming and blanking. Deformation speeds are in the order of6-300 ms- 1

(20-1000 ft/s) , compared with conventional speeds ofup to 2 ms-1 (6 ft/s).

The main areas of development have been (a) billet forming, (b) blanking

and cropping and (c) sheet forming.

The yield stress of steel falls appreciably when preheated above 300°C,

thus permitting lower capacity, less expensive forming equipment to be

8 PRODUCTION ENGINEERING TECHNOLOGY

used. However, at very high strain rates the preheat temperatures have to

be substantially increased to achieve a similar reduction in yield point.

Almost all of the work in high velocity forming reappears as heat in the

workpiece and the resultant temperature rise can cause deterioration in

metals with a narrow range of working temperatures, such as some of the

high strength alloys. Other changes in material properties when subject to

rapid deformation will be discussed when the processes are themselves

described in later chapters.

2.9 CALCULATION OF DEFORMING LOADS

In the design of machines and tools it is important that the forces

necessary to produce a given deformation are known. Most formulae used

are derived from a consideration of stresses, work done or metal flow.

Where these formulae do not agree with experimental results they often

provide a basis for more accurate semi-empirical expressions.

In the uniaxial tensile test, deformation can be assumed to be homo￾geneous until necking commences. In homogeneous deformation each

element keeps its geometrical form: plane sechons remain plane and

rectangular elements remain rectangular. For homogeneous deformation

the applied load F is easily obtained from the expression F = A . Y where

Ais the cross-sectional area and Y is the yield stress. The load required to

produce plastic ßow will vary as deformation proceeds, as both A and Y

will change in value. Apart from the work necessary to produce homo￾geneous deformation, work is also needed to overcome friction and per￾form redundant work. Friction occurs between the ßowing metal and a

constraint: this constraint will be the die in wire drawing and extrusion,

the rolls in rolling, the dies in forging, or the cutting tool in machining.

Fig. 2.4 Changes in direction of

metal How in drawing

Fig. 2.5 Homogeneous deformation

(compressive)