Table Of ContentCAD/CAM IN PRACTICE
A Manager's Guide to Understanding
and Using CAD/CAM
CAD/CAM
IN PRACTICE
A Manager's Guide to Understanding
and Using CAD/CAM
A J Medland and Piers Burnett
&
Kogan
Page
Authors' Note
We have throughout used the personal pronouns 'he', 'him' and 'his' to
refer to individuals such as 'the designer' or 'the manager'; this does not
mean that we unthinkingly assume that all such people are likely to be
male, and certainly not that we believe such a state of affairs to be desir-
able. It merely reflects the fact that we feel the convolutions of usage that
are required to produce a text that is totally non-sexist often represent a
cure that is worse than the original disease.
A Note on the Figures
Except where otherwise noted in the captions which accompany them, all
the figures in the book were produced on one of the CAD systems cur-
rently in use in the Department of Engineering and Management Systems
at Brunei University. We would like to thank Computervision who helped
by making the other figures available to us, or by creating them to our
specifications.
First published in 1986 by Kogan Page Ltd
120 Pentonville Road, London N1 9JN
Copyright © 1986 A J Medland and Piers Burnett
Softcover reprint of the hardcover 1s t edition 1986
All rights reserved
British Library Cataloguing in Publication Data
Med1and, A.J.
CAD/CAM in practice: a manager's guide to
understanding and using CAD/CAM
1. CAD/CAM systems
I. Title II. Burnett, Piers
670.42'7 TS155.6
ISBN-13: 978-94-011-7122-9 e-ISBN-13: 978-94-011-7120-5
DOl: 10.1007/978-94-011-7120-5
Contents
Introduction 9
Chapter 1: CAD - What is it All About? 11
Concepts and descriptions 12
The design process 13
The origins of CAD 15
Automated drafting: creating a model 17
Representations and simulations 21
Analytical programs: simulating performance 27
Summary: CAD defined 29
Chapter 2: CAM - An Introduction 31
Design and manufacture: two processes or one? 31
Numerical control: the basis of CAM 36
Computer-assisted part programming 38
Direct numerical control 42
Computer numerical control 44
The future of numerical control 44
Flexible manufacturing systems 46
Computer-integrated manufacturing 47
Group technology 48
Summary: from CAD/CAM to CADAM 51
Chapter 3: The Elements of a CAD System 53
From mainframe to mini 53
Enter the micro - distributing 'intelligence' 56
Memory and storage devices 61
Machine communicates with man: the graphics display 66
Stroke-writing display systems 67
Raster display systems 69
Man communicates with machine: menus and input
arrangements 72
Light pen input 73
Cursor steering input devices 74
Graphics tablet input 77
Choosing an input system 78
Plotters and other hard copy devices 80
Chapter 4: Principal Types of CAD System 85
Two-dimensional modellers 85
Wire-frame modellers 88
Surface modellers 95
Solid modelling I: boundary representation 99
Solid modelling II: constructive solid geometry 100
Summary: making a choice of modelling system 102
Chapter 5: The Software - What CAD Can Do 105
Basic drafting 106
Macros 108
Parametrics 108
Graphic conventions 111
'Drafting' with primitive solids 112
Transformations 113
Taking things apart - sectioning 117
Putting things together - segmentation and assembly 119
Moving things about - simulated operations 120
Automatic dimensioning 121
Testing things - analytical programs 125
Chapter 6: A Look Ahead 129
Towards standardization? 129
Horses for courses: tailor-made CAD 130
Extending CAM - computer-aided everything 131
Building-in more knowledge - expert systems 132
Trends (and limitations) in hardware development 136
New roles for CAD 138
Near relations: computer graphics and simulators 140
Chapter 7: Justifying CAD/CAM 143
The fallacy of productivity 143
Not-so-simple arithmetic 144
Saving waste - consistency of information 147
Saving time - availability of information 149
Saving trouble - analysis of information 151
Doing what could not be done before 152
Chapter 8: Identifying the Needs of a Company 153
Who should conduct the feasibility study? 153
Geometrical information - the vital commodity 156
Where does the information originate? 158
How is information stored, communicated and used? 160
The place of CAD/CAM in the information structure 162
Setting identifiable goals 163
Chapter 9: Choosing a System and Persuading the Company to Buy It 165
'Turnkey' systems 165
Assembled systems 167
Sources of information 168
The politics of CAD 169
Making a shortlist 171
Benchmarking 174
The 'best' system? 175
Ready, get set ... 178
Chapter 10: Buying and Installing a System 181
Implementation: the role of the CAD manager 182
Planning the installation: physical factors 183
Planning the installation: psychological and organizational
factors 187
Selling CAD to the users 189
Training 190
The first six months 192
Appendix I: Glossary of terms and acronyms used in CAD / CAM 197
Appendix II: Checklist for potential purchasers of CAD systems 211
Appendix III: Suppliers of turnkey CAD systems in the UK and USA 217
Select bibliography 223
Index 225
Introduction
Little more than a decade ago computer-aided design and manufacture
(CAD/CAM) was a very esoteric field indeed, not one that was of much
practical concern to a manager or industrialist unless his business was on
the scale of, say, a major automobile manufacturer or in a field of high
technology such as aerospace. Like so much else, this situation was revo-
lutionized by the invention of the silicon chip, the arrival of the micro-
processor and the dramatic fall in the cost of computer hardware. Today,
CAD/CAM has spread down the market, and down the price scale, to the
point at which it is both a feasible and an affordable technology for a wide
range of small- and medium-sized companies in areas as various as architec-
ture and general engineering, plastic moulding and consumer electronics.
But the explosion - there is no other word for it - in the variety and
capabilities of CAD/CAM systems, and their spectacular climb to the
top of the hi-tech hit parade, has placed the potential purchaser and user
of the new technology in a difficult position. On the one hand he is
assured, not least by the manufacturers of CAD/CAM equipment, that a
failure to invest in it will leave his company stranded in the industrial
Stone Age. But, on the other hand, if he tries to discover exactly what
CAD/CAM is all about, and to determine why and how it could be
applied to his particular business, he will quickly find himself deluged
with a flood of technicalities, swamped by whole alphabets of acronyms
and floundering in a morass of competing claims and conflicting advice.
Between the high-level technical works produced by and for those
actually engaged in researching and producing CAD/CAM systems
(which will tell the average manager rather more than he either wants or
needs to know about the technicalities of the subject) and the glossy
manufacturers' literature (which may tell him rather less than he would
like to know about the relative merits and demerits of the various systems
on offer and their relevance to his problems) there is an almost total void.
It is that space which this book is designed to fill. Our intention, in short,
is to provide a guide, written in plain language, for the prospective user of
CAD/CAM who wants to take a careful and considered look at the
implications and the options before committing his money, his staff and
his business's future prospects.
9
10 CAD/CAM in Practice
In the first part of the book we have set out to provide a layman's guide
to CAD/CAM - a clear, non-technical summary of its underlying princi-
ples and present state of development. This is a prerequisite, since there
is, even among practitioners, considerable lack of clarity about the pre-
cise meaning of many of the terms employed, the real advantages and dis-
advantages of different kinds of system and, above all, the way in which
the technology is best employed. As some companies which plunged
recklessly ahead have already discovered, it is all too easy to be seduced
into purchasing a very expensive collection of 'space age' technology,
only to find out, too late, that you have bought the wrong kind of system,
that you are using it in the wrong way or, in some instances, that you have
no genuine use for it at all.
The second half ofthe book tackles the question of how CAD/CAM is
best deployed, how it can fit into a company's existing operations, and
how far those operations have to be rethought and reorganized to ensure
that the full potential of CAD/CAM is realized. This last point is a vital
one. It is fatally easy to assume that CAD/CAM is merely a modern sub-
stitute for traditional methods, or a useful adjunct to them, whereas the
fact is that, properly used, CAD/CAM requires a radical rethinking of
the entire sequence of operations that takes a product from drawing
board to market place.
It would, of course, be foolhardy to pretend that anyone book can
provide a manager with all the information he needs to go out and buy
and install a CAD/CAM system to his best advantage. What we have
provided, we hope, is a text that will clarify the issues and problems
involved so that the reader knows what questions to ask, what difficulties
to anticipate and what sort of further information and advice he requires,
as well as where it may be obtained.
Chapter 1
CAD - What is it All About?
With the advent of the cheap, mass-produced silicon chip in the early
1970s the rising tide of information technology which had been steadily
seeping into industry for the previous 20 years suddenly became a surging
flood. One of the consequences of the dramatic growth in the availability
and application of computers which followed has been the opening up of
a 'generation gap' separating those who ride the fast-moving waves of
'hi-tech' from those whose feet remain planted upon the terra firma of
the pre-silicon age.
In the case of CAD/CAM, those who develop, manufacture, sell or
apply the technology - the 'insiders', as it were - are by definition on the
'hi-tech' side of this gap; but many of their potential customers are 'out-
siders' who find themselves stranded on the other side, baffled and
bewildered by unfamiliar ideas and impenetrable jargon. Insiders are full
of enthusiasm for the new technology and the visions of the future which
it opens up. Among themselves they will talk with relish of the pros and
cons of solid modellers, the use of parametrics or the algorithms needed
to handle B-spline curves. But they find difficulty in communicating with
outsiders, for whom such monologues might as well be conducted in
Sanskrit for all the meaning they convey.
Experience suggests that outsiders are seeking answers to questions
which, from the insider's point of view, seem almost embarrassingly
naive and elementary. First and foremost, they would like to be told
'what CAD/CAM is all about' - and to be told it in plain language. This
is not a demand which insiders find easy to fulfil: partly, no doubt,
because they have difficulty in imagining what it is like to be ignorant of
ideas which they themselves have long taken for granted, and partly, it
must be said, because they, like many other 'experts', cherish their mono-
poly of expertise.
In our opinion, however, the outsiders have a point! Apart from any-
thing else, a grasp of the basic principles involved in CAD/CAM is the
indispensable foundation without which no one can be expected to
understand the technology or to appreciate the ways in which it might be
applied to their problems. We have, therefore, set out to provide in these
first two chapters the sort of explanation which outsiders seem to stand
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