Process development for self-pierce riveting with solid formable rivet of boron steel in multi-material design

Mechanical joining techniques are important joining processes for the implementation of lightweight structures in automotive engineering and other branches of industry. However, existing processes such as self-pierce riveting with semi-tubular rivet (SPR-ST) or solid rivet (SPR-S) reach their limits in certain applications, e.g. joining press-hardened boron steel sheets in multi-material constructions of automotive bodies. A new method to join these materials reliably and with high quality is the self-pierce riveting with solid formable rivet (SPR-SF).This paper shows different problems during the mechanical joining of press-hardened steel 22MnB5 by conventional SPR-S and illustrates the numerical as well as the experimental development of the new rivet concept: the solid formable rivet. On the basis of validated simulation models for conventional SPR-S numerical sensitivity analyses are carried out to investigate the correlations between the rivet properties (geometry parameters, material) and important quality characteristics of the joint like interlock, punching force and upsetting force for the new SPR-SF joining process. With the knowledge of these studies, specific rivet geometries are determined and prototypes manufactured for joining the material combination EN AW-6016 T4 (t = 1.5 mm) into 22MnB5 (t = 1.2 mm) in good quality. So, the application potential of the new SPR-SF is shown.