Bending Angle and Its Time Dependence in Hat Forming of Carbon Fiber Reinforced Thermoplastics

Abstract

To improve the shape accuracy of formed carbon fiber reinforced thermoplastics (CFRTP), the bending angle of hat-formed CFRTP and its changes with time have been investigated. Two types of CFRTP with different resins (Nylon 6 or polycarbonate) as the matrix were hat-formed in a die temperature range of 35 °C to 160 °C. The bending angle at the corner of formed products and its shape transition during heat treatment at 140 °C were measured. In the case of Nylon 6 as the matrix resin, spring-in due to anisotropic thermal shrinkage occurs depending on die temperature conditions, and then continues owing to the progress of resin crystallization. In the case of polycarbonate as the matrix resin, bending angle is not affected by die temperature conditions because the resin does not crystallize during cooling. However, spring-back of the bending angle occurs with time because of the recovery from the elongated strain in the bending process.