Electrically-heated ceramic composite tooling for out-of-autoclave manufacturing of large composite structures

This paper describes the development of electrically-heated ceramic composite tooling, aimed primarily at the manufacture of large composites structures, for aerospace or for wind energy. The tooling is designed to operate at temperatures up to 300°C, but has the potential to be used at temperatures up to 500°C and above. The ceramic material is an alumi-nosilicate material, reinforced by continuous fibres and thermoplastic polymer, and laid up with embedded electrical heaters. The ceramic and reinforcing layers are laid up by hand at room temperature, on a standard pattern and cured initially to 60°C, followed by a free-standing post-cure, in stages to approximately 400°C. Special-purpose gel-coats and surface sealing layers are employed to ensure a smooth, vacuum-tight surface. The tooling is lightweight, strong and durable, and has a low coefficient of thermal expansion. Electrical heating power per square metre of tool surface is typically between 5.0 and 15.0 KW/sq.m. Examples are given of the use of the tooling to manufacture 12.6 metre long glass-fibre/epoxy and glass-fibre/PBT wind turbine blades (250KW machine). Aerospace carbon-fibre epoxy prepregs are also processed on the tooling successfully. In all cases, the materials need to be processed between 180°C and slightly above 200°C. The integrally-heated ceramic composite tooling provides a more cost-effective tooling system for processing thermoplastic or thermoset composites at these temperatures than standard metal tooling.