01 October 2010
01 October 2010
Prodrive has developed an answer to the problem of lacquer deterioration on visible carbon composite components – eliminate the lacquer completely.
As well as increasing cosmetic durability and reducing cost, Prodrive say that the new process delivers an exceptional surface finish that is thought to be at least equivalent to the best lacquered finishes.
Until now, the demand for a smooth, high gloss finish on composite parts has necessitated spraying a lacquer coat over the finished surface. Unfortunately, any surface chips (e.g. stone chips) can cause the lacquer to delaminate from the carbon substrate, leading to unsightly white blotches.
“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,” comments Gary White, Prodrive’s composites engineering manager. “We now have a finish which is so good that we can dispense with the lacquer entirely so we have multiple benefits: piece part cost reduction, better durability in service and improved consistency of appearance.”
The long term quality of finish on composite parts is of great importance both to discerning buyers of premium road cars and to prominent motorsport teams wishing to project a professional image, but achieving this has not been easy.
“In twenty years of working with composite parts, I’ve never seen such a consistent, high gloss surface finish produced without lacquer,” advises White, “we call it AA finish quality because it sets a new standard of excellence.”
To achieve the exceptional finish, Prodrive analysed the fundamental process steps required to produce a carbon composite part and identified the parameters that affect surface finish. One of the key areas is very precise control of the interface between the component and the mould. As each of the composite layers (the plies) is 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. Prodrive achieves their finish by the use of carefully developed values of pressure, temperature and duration for this phase of the manufacturing process.
“We have established a set of process conditions that give the best possible consolidation of the outer layer against the mould surface,” says White. “We also pay particular attention to the mould surface finish and have developed an appropriate ‘prepreg’ specification with our supplier.” [prepreg = a curable mix of fibres and resin]
The first production application of the Prodrive Process is the supply of various panels and assemblies for a new European supercar. When the company’s engineers approached Prodrive, they assumed that a lacquered finish would be essential.
White takes up the story, “all their quality processes were based on a lacquered finish. The issues you control with an unlacquered surface are completely different. For instance, spray finishes can suffer from runs and fish eyes; non-sprayed finishes can suffer from pin holes. We wrote new quality standards for them to reflect this, and they were delighted; they not only received top quality parts from us but developed their supplier quality standards for the future.”