Development of bending limit strain and stress curves of bendability prediction for assembling automotive body panels

panels. However, the Forming Limit Curve (FLC) inappropriately induces to predict the bendability in hemming process as it has a different failure mechanism and deformed sheet metals can undergo greater bending than predicted by the FLC. In this work, the newly developed Bending Limit Curve (BLC) based on strain and stress were experimentally and numerically proposed for bendability prediction tools of hemming process in assembling automotive body panels. For the experimental procedures, the BLC based on strain of dual phase steel grade DP590 with a thickness of 1.0 mm was experimentally determined by simulative tests. Firstly, the various steel sample geometries were pre-stretched using the modified Marciniak in-plane stretch-forming tests for realistic reflection with the stamping processes before hemming process. Afterwards, to establish the BLC, the pre-stretched samples were experimentally conducted on a three-point bending test. Moreover, the influence of different bending radius of 0.4 and 2.0 mm on BLC was investigated both of BLCs and Bending Limit Stress Curves (BLSCs). The obtained BLSCs were plastically calculated by using the experimental BLC data corresponding with punch plate radii, which were coupled with anisotropic yield criteria namely, Hill’48 and Yld2000-2d and the Swift hardening model. It was found that the developed BLC exhibited greater strain level than the FLC. Obviously, the higher punch radius established lower strain and stress level of BLC and BLSC, respectively. The experimental BLSCs have the similar trend of their curves which used same yield criterion. In conclusion, the BLCs and BLSCs were completely accomplished to realistically predict the bending and hemming process. The calculated BLSCs are not sensitive with non-linear strain paths which establishes before hemming process.