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.