Deformation mechanics and failure mode in stretch and shrink flanging by double-sided incremental forming

Incremental sheet metal flanging is efficient and cost-effective in prototyping and low-volume production. However, how the sheet metal fails and how the overall formability is enhanced during incremental sheet flanging are still not well understood. This study attempts to provide an updated level of understanding for the deformation mechanics in fabricating a clover hole-flange with complex in-plane curvatures by double-sided incremental forming. Compared with traditional flanging methods, higher formability has been achieved for both stretch flanging and shrink flanging on a single part. Additionally, numerical simulation is conducted complementarily to reveal the strain evolution, based on which failure modes and reasons are analyzed. Moreover, DMV (Donell–Mushtari–Vlasov) equations are employed to analytically study the shrink flanging process. The investigations lead to the conclusions that meridional tension has positive effect in improving the formability during shrink flanging, while an adverse effect is found in the formability during stretch flanging.