Application of Non-Uniform Stretch Flanging Theory to Edge-Crack-Prevention Product Design

In order to quickly obtain an appropriate (semi-)product shape that prevents edge fracture in stretch flanging, the non-uniform stretch flanging theory proposed by Nagai was applied to the prediction of strain distribution observed in sheet metal forming of a product with a flat top and a concave wall. The strains calculated by the finite difference method along the flange edge are comparable to those obtained by finite element analysis. Furthermore, flange height h, corner radius R, and shape angle θ were selected as significant factors on circumferential strain ε_c along the flange edge. The investigation on the effect of those factors shows that ε_c increases as R decreases, h increases, and as θ increases. A further increase in θ, however, reduces the increasing rate of ε_c.