Numerical simulation of the roll hemming process

This study focuses on the finite element simulation of the roll hemming process of an Al–Mg alloy, an alternative to classical hemming in which the flanged length is progressively bent over the inner part by a cylindrical roller along a given trajectory. In a first step, a simplified geometry is considered: planar convex samples are flanged and then bent in two steps along a curved line with a roller. Special emphasis is given to the influence of constitutive models on numerical predictions. The mechanical behaviour of the material is investigated with uniaxial tension and simple shear tests and material parameters are determined by inverse optimization. Three different constitutive models are dealt with isotropic yield surface with either isotropic or mixed hardening and Hill’s 1948 anisotropic yield surface with isotropic hardening. The influence that the constitutive models have on roll-in and load applied on the roller is then presented. Furthermore, the final geometry of the part obtained during roll hemming is compared to the one obtained during classical hemming.