Materials Information for CAD/CAM

171 Pages·1991·4.198 MB·English

by  Philip Sargent (Auth.)

Materials Information
for CAD/CAM
Philip Sargent
University of Cambridge,
Cambridge, UK
U T T E R W O R TH
E I N E M A N N
Butterworth-Heinemann Ltd
Linacre House, Jordan Hill, Oxford OX2 8DP
fç$ PART OF REED INTERNATIONAL BOOKS
OXFORD LONDON BOSTON
MUNICH NEW DELHI SINGAPORE SYDNEY
TOKYO TORONTO WELLINGTON
First published 1991
© Butterworth-Heinemann Ltd 1991
All rights reserved. No part of this publication
may be reproduced in any material form (including
photocopying or storing in any medium by electronic
means and whether or not transiently or incidentally
to some other use of this publication) without the
written permission of the copyright holder except in
accordance with the provisions of the Copyright,
Designs and Patents Act 1988 or under the terms of a
licence issued by the Copyright Licensing Agency Ltd,
90 Tottenham Court Road, London, England W1P 9HE.
Applications for the copyright holder's written permission
to reproduce any part of this publication should be addressed
to the publishers.
British Library Cataloguing in Publication Data
Sargent, Philip
Materials information for CAD/CAM.
I. Title
670.285
Library of Congress Cataloguing in Publication Data
A catalogue record for this book is available
from the Library of Congress
Printed and bound in Great Britain by
Redwood Press Limited, Melksham, Wiltshire
Preface
This book is intended for anyone who is planning the
construction, use or management of any kind of engineering
materials property information system.
Readers are expected to have a basic familiarity with
engineering materials at a level similar to that of a first-year
student in general engineering. Only general knowledge of
databases, programming and other software is assumed though
the greater experience the reader has in these areas, the more
useful this book will be. The book is intended to demonstrate to
materials experts which types of software expertise they need to
acquire and to convince software experts, in terms they can
appreciate, how materials databases are perhaps somewhat
different from those they are familiar with.
The book addresses the problem of designing databases,
decision support aids, expert systems and communication
systems that can be integrated with manual and software-
supported tasks in design and manufacture, in CAD and CAM.
The tasks covered are those of materials selection, materials
modelling and materials process simulation: anything that
involves access to materials identification or property
information.
I would like to thank the following people for making comments
and suggestions on early drafts of parts of this book (though they
may not have realised it at the time): Roger Bamkin, John
Rumble, Jane Vvedensky, Arthur Fairfull, Steve Roberts,
Norman Swindells and Mike Ashby, and my innumerable
colleagues at Cambridge University Engineering Department and
the Engineering Design Research Center at Carnegie Mellon
University, but especially to Hugh Shercliff, David Cebon, Chris
vin Preface
Turner and Claire Barlow at the former and Paul Fussell,
Eswaran Subrahmanian, Peter Piela and Rob Coyne at the latter.
Adrian Demaid, Adrian Hopgood and John Zucker of the Open
University and David Williams of Loughborough University of
Technology have contributed much to my appreciation of
knowledge-based tools and their place in distributed,
manufacturing environments.
I wish to thank Mary Downs, Diane Rishel and Reid Greene
who permitted me to participate in their project developing
concept hierarchies of materials information at Alcoa Technical
Center. Many thanks also to Bridget Buckley of Butterworth
Heinemann for her painstaking and rapid editing.
Of course I would like to thank my wife Margot for putting
up with the the absence of her husband while this book has been
written.
I would like to apologise for the inadequacy of the list of
references at the end of the book. In a fast-developing subject
such as this, most current work appears first as unpublished
working papers, as presentations at workshops and standards
committee meetings, by conversation, by electronic mail and on
bulletin boards. Unreferenced assertions in the text often come
from these sources which have not been listed since few readers
will have access to them. Where appropriate, my published
academic papers give more detailed references and technical
depth.
Throughout the book I have used 'he', 'him' and 'his' to
refer to an engineer. I hope very much that as time goes on this
description will become less appropriate as a description of the
typical engineer.
This is a short book, there is far more to say now and will be
more in the future. My best wishes go to those who will write
succeeding and, I hope, better volumes on this important subject.
This book was written and typeset using Microsoft Word 4.0
and MacDraw Π on an Apple Macintosh SE/30.
Philip Sargent
[email protected]
Cambridge, 13 June 1991
Chapter 1
Introduction and reader's guide
This is a book about the use of materials information in
engineering design and manufacture, and how computerized
CAD/CAM systems change the ways in which this information has
been, and should be, effectively used.
The importance of new materials to future industrial
competitiveness is widely appreciated but the problems of
assimilating and using effectively the materials we already have
are much less well known. These are the problems of managing
the process of measuring, abstracting and using materials
information and are the subject of this book. As will be shown,
there are difficult and complex technical issues to be solved
which require combinations of expertise in fundamental materials
engineering and materials physics, engineering design practice,
and several diverse software technologies.
Materials are a common thread running through much of
routine, innovative and creative engineering design, never quite
appearing important enough to devote a great deal of attention to,
but also never unimportant enough to completely ignore. This
lack of immediate impact has led designers of computer aided
design software systems to assume that materials information is
all more or less available: in databases, from handbooks, at low
cost, in simple representations and in stable, standard form.
None of this is true.
It is a fact that despite extensive efforts to make materials
property data available by providing access to materials
databases, it is not an exaggeration to say that in general,
practising designers make absolutely no use of these resources
because they do not match their needs.
Nevertheless, the volume and complexity of information on
engineering materials, their processing, properties and
2 Materials Information for CAD/CAM
identification, is such that there is no alternative to increasing
computerization. Materials selection, materials databases and
materials models of behaviour are all enabling technologies that
must be developed if computerized engineering techniques are to
fulfil their true promise. It is the challenge of producing
appropriate, correct and useful databases, models, knowledge-
based systems and integrated CAD/CAM concurrent engineering
design environments that this book addresses.
Materials and design
The processes of materials selection and other uses of materials
information form only a small part of the entire design and
manufacturing process, but it is an unavoidable part and its study
displays in microcosm problems of breadth, completeness and
complexity which are more general in their implications.
If a materials information system is to be useful, it must (a)
relate to real world materials using the names and designation
systems currently in use, and (b) hold appropriate data on all
possible candidate materials. The problem is not just one of
breadth, but of size too. The number of engineering materials is
such (estimated at 80,000 or so) that in most cases no single
organization can reformulate all the information necessary into
some simple, universal form (the approach taken by expert
systems projects), but must be able to use incoherently and
diversely created databases in a sensible way, complete with their
inconsistent and conflicting naming schemes and categorizations.
Materials information is most important to mechanical,
electro-mechanical and production engineering and design. These
are the activities central to manufacturing, automotive and
aerospace industries, and the examples in the book are taken from
these three sectors.
Design and manufacture
Materials information has been causing trouble for years.
Misunderstandings between engineers, materials scientists,
physicists, database managers, programmers and knowledge
engineers have led to an high degree of wasted, and repeatedly
wasted, effort. Much of the problem stems quite simply from the
multifarious nature of materials information: raw data,
Introduction 3
experimental results, reference data, scientific data, standards,
legal requirements and specifications etc. which do not form a
single, connected theme.
Materials information is crucially important to industry and
will be seen to be so over the next 10 years as companies
computerize their data holdings. There are large publicly funded
development programmes underway under the direction of the
Commission of the European Communities (CEC) in Europe
[Krö85, Krö87c, Swi90], the National Institute for Standards and
Technology (NIST) and the Materials Property Data Network
(MPDN) in the USA [Wes82, Gra86, Kau89, Rum89], and the
Versailles Agreement on Materials and Standards (VAMAS)
world-wide [Krö87b, Krö88, Eri90]. Also several CAD companies
are extending their design-bases into areas which need materials
data [Srdc89]. Large high-technology companies see their own
proprietary materials information as 'the crown jewels' in their
future competitiveness but also wish to cut unnecessary costs by
trading valuable but non-critical materials information [Bam89].
The importance of materials-related problems in product
development is seen to be increasing and the current focus on
manufacturability and life-cycle issues in design means that
increasingly these are problems with existing, rather than with
new, materials. Hence there is a growing interest in the correct
use of materials information as well as in developing new
materials.
A number of international engineering conferences and
workshops were held throughout the 1980s on the
computerization of materials property data and among the
relatively small number of engineers involved there is complete
agreement that a world-wide attitude is the only feasible approach
[Krö87a, Kau88]. Not a single nation, or continent, is sufficiently
self-contained in its needs for materials that it could attempt to
force a single approach to handling materials information. This
lends a special character to systems which are likely to succeed
since they must be developed by consensus and with the attitude
that it is the developers' responsibility to ensure that users can
make several diverse systems work together.
There are already probably several thousand materials
databases (loosely speaking) in Europe alone, set up entirely
independently of each other in companies, universities and
research institutes. They have grown up without reference to
4 Materials Information for CAD/CAM
developments outside their own immediate interests, which
include useful new ideas in computer science, human-computer
interface studies, materials modelling, knowledge-based systems
and database engineering. The VAMAS task group for materials
databases estimates that the number of large databases will
increase by a factor of 10 within the next decade.
Unfortunately a general feature of materials databases is that
they are rarely used effectively by design engineers. It is the
more detailed production engineering aspects which have been
most appreciated: the most heavily used of the eleven databases
which participated in the European Commission's five-year
Materials Databank Demonstrator Programme was INFOS, a
database of the machining properties of alloys [Swi90]. It is true
that engineers are not generally interested in materials science, but
those managers responsible for keeping their engineers within the
law, given recent developments in both European and American
product liability, certainly are. There is thus great scope for, and
a great need for, effective materials data and knowledge systems.
This book is intended to supply the technical bases from
which future appropriate materials information systems can be
developed which will fit well into their global role.
How this book is organized
The early part of this book is intended to be read through from
the beginning. The last few chapters contain more specialized
material that could be skimmed at first reading but which may be
useful for reference in the future. The final chapter draws
conclusions and attempts to predict the future.
Basics
The book begins by considering the problem of materials
selection which is assumed by many to be the only use of
materials information in engineering design. The chapter sets this
small core problem of selection in its wider context and
introduces through concrete examples some of the fundamental
problems of materials designations and the use of property
information. This is followed by a chapter which reviews
techniques for representing materials information in ways that are
appropriate and useful, given the practical problems previously
outlined.
Introduction 5
Specialist themes
The next four chapters are largely independent of each other and
can be read separately. They cover the transfer or exchange of
materials information, management science decision techniques
applied to materials selection, a comprehensive review of data
quality, and a commentary on knowledge-based systems in
materials engineering.
Data interchange is subtly important in ways that might not be
expected, so this chapter should be studied by anyone
contemplating setting up a materials database. It discusses
technical and organizational issues in transferring materials
information from one organization to another. This builds on the
earlier chapters by explaining the consequences for interchange of
representing materials information in the ways described
beforehand, and the need for interchange based on the uses to
which information is put, in the engineering design context
previously outlined.
The chapter on decision techniques will be of use to anyone
attempting to systematize their organization's use of materials
data in its internal procedures, and will be of interest to anyone
who uses databases which purport to rank materials according to
their fitness for some purpose. It could be required reading for
anyone attempting to construct decision support systems using
materials information.
Issues of quality in materials information are universal, they
apply to all kinds of computerized or manual repositories and
design or maintenance methods. The chapter on quality reviews
techniques and metrics for both ensuring and measuring the
quality and appropriateness of information.
Knowledge-based systems, especially object-oriented expert
systems, are sometimes viewed as a panacea for hard problems
involving complex information representation and manipulation.
This chapter shows that they are affected by the same
considerations of quality, maintainability, need for knowledge
transfer and fitness ranking as are other types of software. They
do add, however, the capability to present significantly more
case-based information from extensive historical or experiential
records and the capability to present information only implicit in
the facts they contain. More important, they perform these
functions without overwhelming users with unwanted detail.
6 Materials Information for CAD/CAM
Advice and predictions
Finally there is a concluding chapter which discusses the
prospects for integrated computer-aided engineering design
environments and advises on procedures for setting up materials
information systems.
The book finishes with a glossary o fterms and acronyms, a
list of references and an index.