Experimental investigation on forming defects in flat surface–convex edge hemming: roll, recoil and warp

Forming defects, roll and warp, in hemming of mild steel sheets with flat surface–convex edge geometry are experimentally investigated. The objectives in this study were to develop fundamental knowledge of the effects of process parameters on the final hem quality (defects including roll-in/out, recoil and warp without wrinkling and hem-out) and to develop improved process and tool design rules for flanging and hemming based on experimental findings. The experiments were designed using half a fractional factorial array with four 2-level factors replicated three times. All main effects were determined as well as non-alias 2-level interactions. Results of the experiments were summarized for the use of process and die designers.