Refinement of the Thermal Press Curing Process for Advanced Composites

Abstract

Thermal press curing (TPC) is an alternative process to autoclaving for consolidating and curing thermoset and thermoplastic prepreg composite parts by pressing them between a heated “curing mold” and a customized rubber-faced “base mold” that are engineered to provide uniform temperature and pressure conditions. A study was performed with a kayak paddle part made from eight plies of woven carbon/epoxy prepreg material and formed by double diaphragm forming (DDF). The study expounds on the narrow body of TPC knowledge around three main objectives: (1) to experimentally compare TPC cured parts to a benchmark autoclave process using a realistic part shape with fine geometrical details, (2) to evaluate the necessity of vacuum bagging of TPC cured parts, and (3) to characterize the robustness/sensitivities of pressure application during the TPC process by varying both the total pressure applied to the base mold and the location the hydraulic press ram applied pressure to the base mold. Maximum temperature and pressure variations around the target levels over the entire clamped tool surface were measured as 5.0 °C and 5.5%, respectively, both of which were well within the manufacturer's recommendations. The TPC part had fewer defects, was generally thinner, and had a higher fiber volume fraction than a comparable autoclaved part. Little difference was observed between the TPC parts made with and without vacuum bagging. Parts with too little pressure (90%) resulted in more thickness variation and defects than too much pressure (110%). Finally, TPC parts exhibit some thickness variation, as expected, when ram force is applied off the center of pressure (COP).