INSTRUMENTED THERMOFORMING OF ADVANCED THERMOPLASTIC COMPOSITES .2. DYNAMICS OF DOUBLE CURVATURE PART FORMATION AND STRUCTURE DEVELOPMENT FROM PEEK CARBON-FIBER PREPREG TAPES

Poly(ether ether ketone) (PEEK) carbon fiber prepreg tapes (APC-2) have been thermoformed into a hemispherical double curvature part under a variety of processing conditions. Conventional matched die molding using aluminum molds (at 200-degrees-C) were not successful in thermoforming acceptable parts. Parts with severe wrinkling and folding were obtained. A novel three-piece (steel) mold with built-in sheet clamping arrangement was, therefore, designed and fabricated. This mold was used at 400-degrees-C temperature to thermoform parts from preheated preconsolidated laminates. More interestingly, using the above conditions, 8- and 16-ply unconsolidated laminates could be directly thermoformed into parts that were microstructurally sound and exhibited good shape conformity. Results suggest a cycle time of 15 min, with scope for further reduction, if mold cooling is employed. Notwithstanding the simplicity of the thermoforming process, such a short cycle time compares quite favorably with cycle times of several hours for conventional thermosetting resin based composites.