To prevent formation of voids, volatiles are removed before applying consolidation pressure.
A double-vacuum-bag process has been devised as a superior alternative to a single-vacuum-bag process used heretofore in making laminated fiber-reinforced resin-matrix composite-material structural components. This process is applicable to broad classes of high-performance matrix resins — including polyimides and phenolics — that emit volatile compounds (solvents and volatile by-products of resin-curing chemical reactions) during processing. The superiority of the double-vacuum-bag process lies in enhanced management of the volatile compounds. Proper management of volatiles is necessary for making composite material components of high quality: if not removed and otherwise properly managed, volatiles can accumulate in interior pockets as resins cure, thereby forming undesired voids in the finished products.
Single-vacuum-bag processing in an oven is one of the most cost-effective techniques for making fiber-reinforced resin matrix composites in cases in which resins undergoing curing do not emit volatiles. However, this technique is often ineffective in cases in which volatiles are emitted. In order to produce a void-free composite laminate, it is imperative to remove the volatiles before commencing forced consolidation. A single-vacuum-bag assembly inherently hinders the removal of volatiles because the vacuum-induced compaction interferes with the vacuum-induced outgassing. The present double- vacuum-bag process eliminates this interference while still providing for vacuum-induced compaction.