Composite raw
materials
Composites offer the designer many different
options in terms of materials selection,processing
methods, processing costs and physical properties for the
completed part, with the key engineering advantage being
the ability to add strength in the areas of highest
stress, which in turn allows the designer to be very
selective in the placement of materials and orientation
of fibre along load paths.
A wide range of materials and processing methods
are now available to designers, from traditional wet
lay-up methods right through to complicated pressure and
bladder type moulding applications. However, early
developments of composite parts usually followed one of
two standard routes:
1. Wetlay-up, which allowed for simple
processing methods and cheap tooling costs and generally
produced a relatively dense laminate utilising little or
no lightweight core.
2. Filament winding, which was usually
constrained to tube or pressure vessel manufacture, and
sometimes required high cost tooling and also generally
resulted in the manufacture of a solid wall without the
use of core.
However, over time, these techniques and
moulding methods have significantly developed, spurred on
by some crucial changes in the composite raw materials
available — polyesters and phenolic resins have evolved
and epoxy resins became more widely available. As a
result, component manufacturing methods started to
polarise in to different industries, with various
manufacturing disciplines specialising in particular
areas.
For example, until about 10 years ago, as a
general rule aerospace used Epoxy, Phenolic and some
Bismaliemide resins for autoclave or press moulded
applications, while the Marine industry utilised wet
lay-up methods in open moulded tools. RTM and resinfusion
applications have also developed along a separate route,
but have also helped to increase the use of composites
and led to further increasing demands for composite raw
materials.
Current Status...The aerospace industry
continues to dominate the long term development of these
materials, but one of the most dramatic developments in
the use of composite materials has been the huge
in-crease in automotive and particularly autosport
applications.
Manufacturers are also looking to shorten the
time-to-market and cut down the development material
requirements and resulting costs — this has helped to
drive improvements in material processing capabilities
and has also led to the development of significant
processing technology improvements.
In Practice, the use of composites in the rapid
product development process of cars allows the design
engineers to produce parts with a higher power to weight
ratio giving improved performance in speed handling
characteristics and fuel economy.
The reduction in mass on the vehicle also
putsless strain on the moving parts, allowing other
efficiencies to be made in the design of other partssuch
as the brakes and suspension components. In the last 10
years in particular there has been a growing demand for
more involved moulding methods, which require moulded
parts to be ready to paint and fit with little or no
surface preparation.
Traditionally, a common problem with composite
parts was that they usually would require edge trimming
and some kind of surface preparation if a gel-coat had
not been used. The increase in limited edition requests
and the desire to be able to produce a number of bespoke
vehicles for either customer sale or racing purposes
points the designer to carbon fibre composites as a
practical and efficient manufacturing
solution.
Thus keeping design and tooling to a minimum,
and allowing relatively easy changes much later in the
design stage compared with traditional metal pressing
techniques.
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