Out-of-Autoclave and Out-of-Oven Composite Tooling for Curing Thin-ply Composite Structures

Deployable composite booms (DCB) are manufactured with thin-ply composite prepreg that is vacuum bagged and oven-cured on composite tooling. The current state-of-the-art (SOA) composite tool used to achieve this has a carbon foam core (CFOAM®) and fiber reinforced polymer composite tool surface. CFOAM is synthesized from coal precursor and upon pyrolysis yields a porous, lightweight, high-heat resistant structural carbon foam. Advantages to the carbon-based composite tool technology are that it significantly reduces the overall tool weight, has high-stiffness, and low coefficient thermal expansion (CTE).

DCB’s have lengths that often exceed conventional autoclave capacity. This is not a constraint to tool manufacturing whereby the tools are built in sections and subsequently assembled prior to layup and cure of the thin-ply composite prepreg. Producers typically resort to lower cost ovens for curing the DCB prepreg. Nonetheless the ever-increasing demands on DCB length has significantly resulted in increased capital costs of curing oven technology that is hard to justify especially for limited production units.

Touchstone has designed OOA-OOO tooling that overcomes these processing constraints. More specifically, the carbon foam core was replaced with graphite foam. Like carbon foam, the graphite is synthesized from coal precursor and maintains the desirable attributes of carbon-based foam core tooling technology. The principal advantage of graphite foam being high thermal conductivity and reduction of thermal gradients. Included in the design is a power supply and programmable logic controller that operates up to eight heaters independently to 450 °F. Analytical results used to facilitate design and verification of the technology will be presented. Results will also be presented for a 13 (ft) prototype tool for product validation by 1) demonstration of successful thin-ply prepreg curing trials, 2) process control, i.e. achieves peak temperature at prescribed heating rates through process, and 3) maintains prescribed temperature uniformity along the tool surface.