Post-Forming Limits of Carbon Fibre Reinforced Thermoplastic Tubular Structures in a Rotary Draw Bending Process

Abstract

This paper presents the post-forming limits of polyamide 6 carbon (CF/PA6) thermoplastic tubes to facilitate design and process optimisation of bent tubular CF/PA6 part manufacturing. Straight CF/PA6 tubes can be post-formed using rotary draw bending at elevated temperature to achieve desired curvatures. Forming limits of the tubes are predicted based on their winding angles, tube geometry, and bending radius, presented as the relation between tube winding angle and bending ratio. Additionally, the corresponding principal shear strain limits are derived from the winding angle limits and tube axial strains. Three sets of CF/PA6 tubes with the configurations of [±30°]4, [±45°]4, and [±60°]4 are heated to 220 °C and post-formed to a bending angle of 90° with a bending ratio of 2. Micro computed tomography imaging is performed to analyse tube geometry after forming to identify forming and failure modes for tubes beyond the forming limits.