Three-dimensional simulation of hemming with the explicit FE-method

This paper is dedicated to three-dimensional simulation of hemming of an automotive hood. The results from the simulations are compared with measurements on hoods manufactured in the production line, both with and without adhesives, in order to check the validity of the FE-model. Both the ordinary serial version as well as the massively parallel processing (MPP)-version of the code LS-DYNA have been applied in the simulations, in order to verify that the two versions are giving the same results, and thereby ensuring that the MPP-version can be used for this type of simulations. Four different types of under-integrated shell elements, three of them based on the Mindlin shell theory and one based on a degenerated solid element, have been used in order to determine which of them is showing the best agreement with test results. Furthermore, results from a transversely anisotropic material model are compared to results from a model with full anisotropy in order to study if anisotropy is a crucial issue in these simulations. One simulation was performed of the case with adhesives between the parts. The effects on the roll-in of the adhesives were in this simulation modelled as a smaller friction coefficient in the contacts between the two parts. Finally, the effect on roll-in from the preceding stamping is studied in an FE-model with pre-strained outer and inner parts.