Defects in double-sided incremental forming of woven fabric prepreg: Experimental and numerical analysis

Forming processes of fiber-reinforced polymers have been widely investigated for decades, driven by the need for lightweight, high-performance components in industries such as aerospace and automotive. However, the traditional forming techniques for composites often depend on the use of dies, which can be expensive and timeconsuming to produce, resulting in increased overall manufacturing costs and extended production timelines, particularly for small batch production and prototype manufacturing. In this study, a die-less forming method, namely double-sided incremental forming (DSIF), was firstly investigated for the forming of woven fabric prepregs. Key manufacturing parameters, including the auxiliary dummy sheets (material, thickness, and combinations) and tool diameters as well as their influence on forming quality, were systematically investigated. The mechanisms underlying the formation of macroscopic defects, such as wrinkling and fabric breakage, were analyzed through both experimental and numerical approaches. Results showed that dummy sheet selection and tool diameter significantly impact the prepreg forming quality in DSIF and defect-free parts can be obtained through optimized parameters. Specially, the combination of a hard upper dummy sheet and soft lower dummy sheet helped mitigate deformation discrepancies between the sheets and reduced prepreg wrinkling, while larger tool diameters minimized yarn failure by alleviating the high local contact pressures on the prepreg. The study can provide insights for future research and highlights the potential of DSIF for industrial applications, enabling more efficient small-batch production and prototype manufacturing of complex composite parts.