Carbon composite process improves surface finish by eliminating lacquer

Automotive and motorsport technology specialist, Prodrive, has developed an answer to the problem of lacquer deterioration on visible carbon composite parts.

Normally, a smooth, high gloss finish is achieved by spraying a lacquer coat over the finished surface, but stone chips can cause the lacquer to delaminate from the carbon substrate.

Gary White, Prodrive's composites engineering manager, said: "It's highly unsatisfactory if a large panel, like a diffuser, has to be replaced after a few thousand miles due to cosmetic deterioration when the part is, functionally, still serviceable.
"We now have a finish which is so good that we can dispense with the lacquer entirely. [This gives] multiple benefits; piece part cost reduction, better durability in service and improved consistency of appearance."

Prodrive analysed the fundamental steps required to produce a carbon composite part and identified the key parameters that affect surface finish. One of the key areas is very precise control of the interface between the composite and the mould. As each of the composite layers are added to the mould, there is a possibility of air bubble entrapment which hinders both adhesion between plies and seating of the outermost layer against the mould surface. The Prodrive process achieves outstanding results by carefully developed values of pressure, temperature and duration during the curing cycle inside the autoclave.

White added: "We have established a set of process conditions that give the best possible consolidation of the outer layer against the mould surface. We also pay particular attention to the mould surface finish and have developed an appropriate prepreg specification with our supplier."

Other composite manufacturers can benefit from the improved process but where prior tooling exists, a level of refurbishment must be expected, to bring the surface up to the necessary standard. Significant production quantities can be handled; currently Prodrive's biggest application is approximately 400 parts per month. Cell based manufacture with predominantly manual operation means the process can be scaled up as required to suit the volume demanded.
As well as the automotive sector, Prodrive's customer base for composites includes aerospace, telecoms and yachting applications.

White concludes: "The end product doesn't cost any more, but often has more functionality and helps our customers to be more competitive."

Author
J Cunningham

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