Influence of irregular rivet-die offsets on the integrity and on the load-bearing capacity of self-piercing-riveted aluminum alloy joints

Self-piercing riveting (SPR) has established as key technology for cost-efficient mechanical joining of components in the serial production of lightweight car bodies. The SPR process is basically quite stable and reliable; however, irregular process conditions that affect the interlock between the rivet and the joined components cannot be completely avoided. Such conditions may reduce the load-bearing capacity of the joints. Therefore, this experimental study investigates the influence of irregular offsets between the rivet and the die on the quality/integrity and on the load-bearing capacity of SPR lap joints of commercial 1.5 mm-thick EN AW-6016-T4 aluminum alloy sheets. A steel die and semi-tubular high-strength steel rivets of different hardness were used in the experiments. Characteristic cross-section features and the quasi-static shear-tensile strength of the joints were assessed. The rivet-die offset and the hardness of the rivet were both identified to influence the deformation behavior of the rivet and the symmetry of the joint. However, the influence on the shear-tensile strength was negligible, as the horizontal undercut of the rivet and, thus, the interlock between the rivet and the sheets were still sufficient even for notably asymmetric joints. If the undercut is sufficient, the rivet-die offset can be regarded as uncritical with respect to the load-bearing capacity of lap joints.