Resin Transfer Moulding

259 Pages·1997·10.447 MB·English

by  Kevin Potter (auth.)

Resin Transfer Moulding
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Resin Transfer
Moulding
Kevin Potter
Department of Aerospace Engineering
University of Bristol
UK
CHAPMAN &. HALL
London· Weinheim . New York· Tokyo· Melbourne· Madras
Published by Chapman & Hall, 2-6 Boundary Row, Loudon SEt 8HN, UK
Chapman & Hall, 2-6 Boundary Row, London SEI 8HN, UK
Chapman & Hall GmbH, Pappelallee 3, 69469 Weinheim, Gernlany
Chapman & Hall USA, 115 Fifth Avenue, New York, NY 10003, USA
Chapman & Hall Japan, ITP-Japan, Kyowa Building, 3F, 2-2-1 Hirakawacho, Chiyoda
ku, Tokyo 102, Japan
Chapman & Hall Australia, 102 Dodds Street, South Melbourne, Victoria 3205, Australia
Chapman & Hall India, R. Seshadri, 32 Second Main Road, CIT East, Madras 600 035,
India
First edition 1997
© 1997 Kevin Potter
Softcover reprint of the hardcover 1s t edition 1997
Typeset in 10/12 Times by Florencetype Ltd, Stoodleigh, Devon
ISBN-13: 978-94-010-6497-2 e-ISBN-13: 978-94-009-0021-9
DOl: 10.1 007/978-94-009-0021-9
Apart from any fair dealing for the purposes of research or private study, or
criticism or review, as permitted under the UK Copyright Designs and Patents
Act, 1988, this publication may not be reproduced, stored, or transmitted, in
any form or by any means, without the prior permission in writing of the
publishers, or in the case of reprographic reproduction only in accordance with
the terms of the licences issued by the Copyright Licensing Agency in the UK,
or in accordance with the terms of licences issued by the appropriate
Reproduction Rights Organization outside the UK. Enquiries concerning
reproduction outside the terms stated here should be sent to the publishers at
the London address printed on this page.
The publisher makes no representation, express or implied, with regard to
the accuracy of the information contained in this book and cannot accept any
legal responsibility or liability for any errors or omissions that may be made.
A catalogue record for this book is available from the British Library
Library of Congress Catalog Card Number: 96-72035
.~ Printed on permanent acid-free text paper, manufactured in accordance with
ANSI/NISO Z39.48-1992 and ANSIINISO Z39.48-1984 (Permanence of Paper).
Contents
Preface Vll
Introduction IX
1 RTM theory 1
1.1 The basics of flow in RTM processes 2
1.2 RTM theory 5
References 26
2 Materials for RTM 28
2.1 Reinforcements 28
2.2 Resins for RTM 38
2.3 Binders 44
2.4 Core materials for RTM 48
References 49
3 Reinforcement manipulation and preforming 52
3.1 Introduction 52
3.2 Deformation modes of composite reinforcements 55
3.3 Steps in the preforming process for bound
reinforcements 62
3.4 Preforming equipment 66
3.5 Preforming tools 69
References 73
4 RTM mould tool design 74
4.1 Introduction 74
4.2 Tooling materials 75
4.3 Requirements for the design of RTM tools 96
References 144
5 Production engineering requirements 146
5.1 Working environment 146
5.2 Specific requirements 147
VI II C__O_ N_ T_E_N_T__S _____________________~
L _______________________
6 Component design for RTM 152
6.1 Specific design features 158
References 166
7 Flexible tool RTM 167
7.1 Materials 167
7.2 Materials handling 169
7.3 Tooling design for large area RTM 171
Reference 179
8 Thick section RTM 180
Reference 183
9 Known applications of RTM processing 184
9.1 Aerospace and defence 184
9.2 Automotive uses 185
9.3 Construction 185
9.4 Electrical and electronic 185
9.5 Industrial and mechanical 186
9.6 Marine 186
9.7 Sports equipment 186
9.8 Transportation 187
10 Tronbleshooting RTM processing problems 188
Reference 199
11 Suggestions for good practice in the design and development
of RTM components 200
12 Costing 204
12.1 Top down costing 204
12.2 Outline costing 205
12.3 Production costing 208
Reference 210
13 Quality controVassurance 211
13.1 Documentation requirements 212
13.2 Process control and process monitoring 214
13.3 Specimen documents 218
14 Case study 231
14.1 Introduction 231
14.2 Preform design and tooling 233
14.3 Mould tool design 235
Appendix A brief word about patents 239
Reference 240
Index 241
Preface
The science and technology of composite materials has generated a large
number of processes by which components can be manufactured. These
range from the contact moulding approach of rolling resin into the rein
forcement on simple tools to the use of capital-intensive automatic tow
placement machinery. All of these processes have a single aim in common;
the cost-effective meeting of the design requirements for the part to be
made. To meet this aim the strengths and weaknesses of the manufac
turing route must be reflected accurately in the design of the part.
There is a tendency to treat design and manufacture as two boxes
which, while they overlap, can be handled separately. For processes that
have a large experience base that can be called upon there may be some
justification for this belief, although maximum effectiveness will always
arise from a concerted design and manufacture approach. For emerging
processes there is a danger that carrying over design practices from other
processes will be, at best, non-optimal.
In order to utilize a concerted design and manufacture approach it is
essential that access is available to sources of information to guide both
design and manufacture. In the case of resin transfer moulding (RTM) a
great deal of information is available in the academic literature. Perhaps
the majority of this information is concerned with details of the scientific
underpinnings of the process and less is available on the apparently more
mundane aspects. It is often these less imPlediately exciting issues that
have the greatest influence on matters such as detailed design and, vitally,
production costs.
This work aims to provide an adequate understanding of the basic sci
ence of RTM and to provide much needed information on the technolog
ical aspects of the process. The aim throughout is to equip both designers
of components and those entrusted with their manufacture with the tools
to make the best of the opportunities that RTM presents to them.
Lastly, the word advanced will be found throughout the text. This is a
difficult word as it seems to mean very different things to different people.
I LI ____________
viii P_R_E_F_A_C_E_ __________- --'
In this work it can be taken as a shorthand way of saying any or all of
the following: highly loaded; complex in geometry; intended for use in
safety critical applications; of high moulded quality and free of defects;
optimally cost-effective and so on.
Introduction
It must be stressed at this early point that RTM is not a single manu
facturing process that can be dealt with in a monolithic manner. RTM is
better thought of as a philosophy of manufacturing in which the resin
and fibres are held apart until the last possible moment. In this it can be
contrasted with those manufacturing methods where the resin and fibre
are combined prior to use.
In many ways the development of an aerospace or, more broadly,
advanced composites industry was permitted by the development of
pre impregnated reinforcements (prepreg). This development permitted
real structures and components to be designed and manufactured that
could reflect the properties of high-performance fibres. A variety of indi
vidual processes, such as autoclave moulding, vacuum bag moulding,
compression moulding, expanding bladder moulding, and silicone rubber
expansion moulding were developed that utilized the new form of semi
finished material known as prepreg. As people became comfortable and
experienced with the new material form, a design and manufacturing data
base grew up such that the strengths and limitations of the materials and
processes were reflected in design philosophies and detailed designs.
These design philosophies and detailed design features have become the
norm for advanced composite products. They largely reflect the capabil
ities of the dominant aerospace manufacturing route, autoclave moulding.
Despite the similarities between the various processes it is unusual to
refer to prepreg moulding. Each process has its own literature and the
commonalities between them are sometimes lost. By contrast, RTM has
as many different processes under the RTM umbrella as there are prepreg
processes; but it is more or less commonplace to speak of RTM rather
than, for'example, rigid tool RTM with semi-rigid preforms.
All the process variants have common features. Unresinated fibres are
held within a tool cavity and a differential pressure is applied to a supply
of resin such that the resin flows into the reinforcement completely
wetting it out. The tool may be essentially rigid, semi-rigid, or contain
IL-___________________
L-_x_ _~ 1 I_N_T_R_O__D _U_ C_T_ IO_ _N_ _________________~
flexible elements. Any consolidation pressure required to give the
required reinforcement volume fraction (Vf%) may be applied by
mechanical clamps, from a tooling frame or press, or by the use of an
internal vacuum or external applied pressure in non-rigid tooling.
Reinforcements may be of any fibre, and the use of all forms has been
reported, from unidirectional (UD) through woven or knitted cloths to
needled and random mats and fully three-dimensional reinforcement
preforms. Volume fractions from below 20% to above 60% have been
reported. The reinforcement may be laid onto the mould by hand, formed
to shape by the mould closure, assembled by a wide variety of preforming
techniques or may utilize specially woven or braided constructions. The
resin can be of a very wide range of chemistries and formulations, so long
as the basic process requirements are met. Cure times can be from a few
minutes to many hours. Resin injection machines can be of a very wide
variety of types and production line design can be just as varied.
The focus he're will be on those RTM techniques that are intended to
produce components to high-quality standards for structural applications.
Thus material combinations such as random glass mats and polyester
resins will not be discussed in any depth. Concentration will be on the
materials that can produce advanced structural components and the
processes for their conversion into such products.
The age of RTM as a manufacturing process is, despite its apparently
recent origins, much greater than that of any prepreg-based system. RTM
can be traced back to the Marco process of the 1930s,[1] and in the 1960s
work was done on the pressure injection of a high-performance matrix
into an organized fibrous preform. [2] The fact that the matrix was
aluminium does not detract from the fact that the process was clearly a
variant of the RTM methodology.
The use of an RTM approach for the manufacture of advanced polymer
matrix composites is more recent. Even so RTM was used to manufac
ture radomes in high- and low-temperature matrices as early as the mid
1970s.[3] Later in the 1970s RTM was used for other components such
as aeroengine compressor blades.[4] Most of these early applications were
driven by the need for high levels of geometrical accuracy and this is still
a major driving force behinq many RTM component developments. By
1980 many groups were attempting to devise manufacturing methods that
could step beyond the cost and geometrical complexity limitations
imposed by the baseline aerospace manufacturing processes.
At that time RTM was fairly well developed as a niche process in the
general engineering composites area, and some of the early advanced
RTM work was carried out at the top end of the general products area
rather than in aerospace. This sort of work is exemplified by the devel
opment by British Petroleum of high-speed flywheel system components
by RTM.[5, 6] The materials used were glass fibre cloths and polyester