Improvement of hem quality by optimizing flanging and pre-hemming operations using computer aided die design

Flanging and hemming of straight edge-flat surface (plane strain) aluminum killed-draw quality steel was investigated restricting the study to the radius flat hem with an inner sheet. The major process parameters in straight edge hemming were determined and relations between them and some forming defects were established. Among these parameters were flanging die corner radius, pre-hem path, pre-hem stroke and final hemming force. Possible process and tool design modifications, which may lead to quality improvements in hemming were tested experimentally and using FEM. The commercial finite element program DEFORM was used to simulate the flanging and hemming operations including springback, and the predictions were compared with limited experimental results. Results of the experiments and simulations were summarized in the form of trend-lines for the use of process and die designers.