Solid-state stamp forming of UD CF/PA6: Forming window and defect evolution

Abstract

Solid-state stamp forming offers a route to retain fibre and ply support in unidirectional carbon-fibre-reinforced thermoplastics (UD CFRTPs), but insufficient matrix softening increases forming resistance and defect formation. This study investigates the solid-state forming window of cross-ply UD carbon fibre/polyamide 6 (CF/PA6) through finite-element analysis, dome-forming experiments and X-ray computed tomography (CT). Blank shape and ply blocking were examined as controlled comparisons, while temperature was treated as the principal process variable. The simulations predicted progressively less wrinkling with increasing temperature, whereas the experiments showed that overall forming quality did not improve monotonically as the laminate softened. At 180 °C, high forming resistance resulted in extensive surface cracking and severe local deformation. Among the temperatures tested, the 195 and 205 °C conditions provided the most favourable surface response, whereas at 215 °C and in the 260 °C melt-state reference, fibre waviness, inter-ply movement and shape instability became more pronounced as fibre and ply support decreased. CT further showed that the cleaner surface of the 195 °C component did not correspond to better internal quality, with more pronounced delamination in the examined CT sections than in the 205 °C component. The numerical model reproduced the global component dimensions with differences of 1.62–9.91% and captured the principal wrinkle regions. These results show that the useful solid-state forming window is governed by competing temperature-dependent mechanisms: excessive forming resistance at the lower-temperature side and insufficient fibre and ply support at the higher-temperature side.