Currently, when moulding carbon fibre composites in an autoclave, it is common practice to also make the tools from carbon fibre prepregs. This ensures that there are no significant differences in the thermal expansion of the tool and the component being moulded that might introduce unwanted distortion. However, this also means that the tooling tends to be relatively expensive.
Working in partnership with moulders KS Composites, Composites Evolution has developed a new tooling prepreg system based on a hybrid combination of carbon and flax reinforcements. Currently, a standard all-carbon tool might consist of a number of heavier weight bulking plies sandwiched between lower weight outer surface plies. In the new hybrid tooling system, several of the carbon bulking plies are replaced with more cost-effective flax. It is possible to do this because the thermal expansion properties of flax fibres are sufficiently similar to those of carbon. The result is a hybrid carbon-flax tool in which the material costs are reduced by up to 15% in comparison to an all-carbon tool. Secondary benefits include a reduction in tool weight of up to 15% (flax fibres being less dense than carbon fibres) and a reduced environmental impact due to the use of sustainable flax.
In trials performed by KS Composites, the hybrid carbon-flax tooling material has successfully completed over 400 thermal cycles. Furthermore, a mould tool manufactured from the system is now used in routine production.
Both carbon and flax reinforced epoxy tooling prepregs are now available from Composites Evolution as part of its Evopreg EPT range of tooling materials.
Gareth Davies, Composites Evolution's commercial manager, commented: "Yet again, we're pleased to be offering our customers new material options that challenge conventional practices and provide them with real benefits. In a similar manner to our fire-resistant PFA prepregs, we're bringing bio-based materials to the market that provide real technical and commercial advantages in addition to their sustainability credentials.”
