Single point incremental forming of multi-matrix continuously-reinforced composites: a feasibility study

Fibre-reinforced plastics offer remarkable strength-to-weight ratios, making them an excellent choice for lightweight engineering solutions. However, the forming of precursor materials such as preforms or prepregs poses substantial challenges, with defects such as delaminations or fibre misalignments occurring frequently. One approach to de-risk composite parts manufacturing are Multi-Matrix Continuously-Reinforced Composites (MMCRCs), pre-structured with formable and non-formable matrix materials connected by continuous fibre reinforcement. Regions with a matrix of covalent adaptable networks (CANs, aka vitrimers) can be locally formed to the desired shape, while unformable regions with a conventional thermoset matrix restrict undesirable deformations. As targeted local forming operations are required, incremental sheet forming is proposed as a flexible forming process that does not involve expensive moulds. To evaluate the feasibility of incrementally forming MMCRCs, a simple corner geometry is formed using single point incremental forming (SPIF) in this study. The prepared sample with a formable hinge region is attached to a metal dummy sheet with a vacuum bag and heated to forming temperature. Using a specifically developed toolpath strategy, the layup is deformed in a robotic SPIF setup. Albeit revealing challenges in the simultaneous forming of metal and MMCRC sheets, results prove that the proposed approach is promising in allowing the manufacture of high-quality composite parts in decoupled production and forming processes.