Analytical model for straight hemming based on minimum energy method

An analytical model for straight hemming was developed based on minimum energy method to study the effect of flanging die comer radius on hemming qualities. In order to calculate plastic strain and strain energy more exactly, the neutral layer of specimen comer after hemming is assumed to be a half ellipse with its major semi-axis unknown. Isotropic hardening rule is adopted to describe bending and reverse bending processes neglecting Bauschinger effect. The model takes into account the material property parameters in order to satisfy a wide application range of different materials. Specimen profile, creepage/ growing （roll-in/roll-out） and maximum equivalent strain are predicted, which are greatly influenced by the flanging die comer radius. Experimental facilities were designed and hemming experiments were undertaken. The predicted results of the present analytical model were compared to experimental data as well as finite element （FE） simulation results. It was confirmed that they are in good agreement, and the model can be used to evaluate whether the material used as an outer panel for hemming is appropriate and to optimize process parameters when the material used for hemming is changed.