Numerical simulation and experimental validation of self-piercing riveting (SPR) of 6xxx aluminium alloys for automotive applications

Abstract

Two-dimensional axisymmetric models of the self-piercing riveting (SPR) process consisting of punch, blank holder, die, rivet, upper blank and lower blank were built using the finite element software package simufact.forming™. Three different joint configurations were modelled. An optical measurement system was used for capturing the actual geometries of both the die and the rivet which were then introduced into the simulation model. The stiffness of the riveting pliers was modelled as numerical spring. A combined model of Coulomb friction and shear friction was applied. Both friction coefficients were determined by inverse modelling. The deformation behaviour of the 6xxx aluminium alloy blanks to be joined was described with flow curves extrapolated from results of uniaxial tensile tests. In order to validate the results of the simulations self-piercing riveting experiments using 6xxx aluminium alloy blanks and coated steel rivets were conducted. Force-displacement curves of the punch were captured during the riveting process. Characteristic geometrical features of cross-sections of these joints including horizontal undercut of the rivet, bottom thickness of the lower blank and rivet head overlap were investigated using optical microscopy. The cross-sections of the self-piercing riveting joints obtained from simulations and experiments showed very good geometrical agreement, and just slight differences were observed between the force-displacement curves.