Effect of Cooling Rate on the Mechanical Strength of Carbon Fiber-Reinforced Thermoplastic Sheets in Press Forming

The purpose of this study is to elucidate the effect of the cooling rate of the carbon fiber-reinforced thermoplastic (CFRTP) sheets on the mechanical property in the press forming within 1 min cycle time. In order to pay attention only to the compression stage after the deformation stage in press forming, a flat sheet of dimensions 200 mm × 100 mm × 3 mm was produced. It was fabricated by stacking 15 CFRTP sheets of 0.2-mm-thick plain woven fabric impregnated with PA6, preheating them to 280 °C and pressing them at 5 MPa using a die cooled from near the melting temperature of PA6 with various cooling rates. Cooling rate of −26 °C/s with pressure holding time (defined in this study as the period that the pressure sensor detects high pressure) of 7 s and that of −4.4 °C/s with pressure holding time of 18 s gave a flexural strength of 536 and 733 MPa, respectively. It was found that the cooling rate during pressure holding is related to the mechanical property of press-formed CFRTP part.