Out-of-autoclave (OOA) processing of composites inevitably results in laminate fibre volume fractions being limited by the maximum ～1000 mbar pressure given the power-law compressibility characteristics of the reinforcement. The lower fibre volume fraction produces a higher resin volume fraction which becomes resin-rich volumes (RRV). Textile reinforcements with clustered fibres and consequent RRV generally have low strength but high in-plane permeability, whereas the opposite is true for uniformly distributed fibres. The inevitable increase in resin content of OOA composites compromises composite performance, and results directly in parasitic weight and higher fuel consumption in transport applications. Retention of autoclave processing is recommended for highest performance when compression press moulding in not appropriate (for example, for complex 3D components). The traditional autoclave heats not only the component to be cured but also parasitic air and the vessel insulation. Subject to minor modifications to the pressure vessel, electrically-heated tooling and cool air pressurisation could be implemented, This approach would need to balance insulation of the heated tool surface (and any heater blanket on the counter-face) against the quenching effect during introduction of the pressurised cool air. Further to the potential for significant reductions in energy consumption, the laminate on the heated tool could be taken to the end of the dwell period before loading the autoclave leading to significant reductions in cycle times. Components could be cured simultaneously at different temperatures provided there are sufficient power and control circuits in the autoclave. While autoclave processing has usually involved vacuum-bagged pre-impregnated (or wetlaid) reinforcements, there is scope for using the pressure vessel to cure vacuum-infused composites. Lewin et al and Wilkinson et al have undertaken preliminary experiments towards optimisation of the process methodology for high-quality resin-infused laminates cured in the autoclave.
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