Effect of die misalignment on the joining quality of Al/steel self-piercing riveting structure

Self-piercing riveting (SPR) is one of the advanced mechanical joining techniques, and it has been widely used in automobile industry. In this paper, the effect of die misalignment on the cross-section parameters and mechanical properties of SPR joints were respectively studied through numerical simulation and experiment, and the mechanical properties degradation mechanism of the misaligned riveted joint were analyzed. A three-dimensional explicit finite element model (FEM) of SPR joint was developed by ABAQUS, and the section observation was performed to evaluate the accuracy of FEM. The riveting process and the strain of SPR joints with different misalignment distance was analyzed, and the quasi-static shear test was carried out. The results revealed that the rivet leg near the die edge was thickened due to limitations in deformation space, and a cavity was formed at the outer edge of the rivet leg near the die center, during the riveting process. It resulted in different cross-section parameters and mechanical properties of SPR joints. Specifically, the interlock distance decreased as the misalignment distance increased. The bottom thickness of the side near the die edge increased with increasing misalignment distance, while that near the die center decreased slightly as the misalignment distance increased. In addition, the maximum shear load decreased nonlinearly with increasing misalignment distance, and the movement of die along the loading end had a significantly greater impact on the maximum shear load than the movement along the fixed end. This was mainly because the interlock distance of SPR joints was asymmetrically and nonlinearly reduced due to the die misalignment.