Apple project bears fruit

Lightweight structural automotive components could be volume-produced from thermoplastic composites following the success of a Warwick University project.

Components made using the technique could also be easily recycled and researchers believe car makers could start adopting the process on new models within the next year.

The Apple project (Advanced polymeric composite panels with low environmental impact) is part of the DTI-backed Foresight Vehicle programme and is a collaboration between Warwick’s Advanced Technology Centre and Midlands-based BI Composites and Security Composites.

Warwick senior research fellow Dr Mark Pharaoh, who leads the team, said the project built on two earlier programmes to investigate structural properties and impact characteristics of lightweight thermoplastic composites for vehicles, the latter involving Ford and MG Rover. The earlier projects used glass mat thermoplastics, in which reinforcement is provided by a mat of short glass fibres running in random directions.

Apple has concentrated on composites with reinforcement running continuously in one direction only or two directions at right angles. It used three proprietary products that use a polymer (polypropylene or thermoplastic polyester) woven into a fabric or tape with glass or carbon-fibre reinforcement. When heated, the component melts and coats the fibre reinforcement. While melted the material can be stamped or vacuum-formed – avoiding labour-intensive laying-up.

Stamp forming could be used initially to make relatively small, complex components in volumes up to 100,000 annually, with a good surface finish. Security Composites uses this to make non-metallic protective toe-caps for boots.

Membrane forming is suitable for bigger but less complex components at a rate of up to 50,000 annually. The technique is a modification of vacuum-forming in which the composite is placed between two silicone membranes. The silicone is vacuum-formed to the required shape and drags the composite fibres with it.

Pharaoh said it has yet to be shown if this process can produce the required surface finish for an external panel. But he added that the first application for membrane formed components is likely to be for vehicle undertrays or door liners, where aesthetics are not important because the panel is hidden.

At the end of its life a component can be heated to melt the polymer, shredded into lumps of about 10-15mm and reused in an injection-moulding process. The material will still contain relatively long randomly oriented glass fibres.

A number of car makers have shown interest, and it is hoped the process will be adopted for a new model programme within the next 12 months. The fact that the materials melt if heated is not a problem in service: BI Composites has made a Plytron bonnet for a future MG Rover model.