Numerical Investigation on the Effects of Process Parameters on the Pre-Holed Self-Piercing Riveted Joint Quality

Although the self-piercing riveting (SPR) process is widely used in the automotive industry, it faces challenges in achieving mechanical interlock when joining high-strength steel. In this paper, the pre-holed self-piercing riveting (PH-SPR) process is adopted to join high-strength steel to aluminum alloy. This paper aims to investigate SPR joinability and select suitable rivets and dies for different steel–aluminum combinations. A 2D axisymmetric numerical model is developed using LS-DYNA commercial software to simulate the PH-SPR process with varying process parameters (e.g., rivet hardness, geometric dimensions of rivet and die, hole size, and material and thickness of sheet). The accuracy of the FE model is verified by comparing the forming quality parameters between the experimental test and the simulation result. The results show that (i) the rivet with strength of 0.9 GPa is suitable for the bottom sheet with yield stress of 89 MPa, and the rivet with strength of 1.34 GPa is appropriate for the bottom sheet with yield stress greater than 165 MPa. (ii) The increasing rivet diameter, rivet length, and hole size can improve forming quality, and the decreasing die depth and top sheet thickness can enhance the undercut. (iii) The undercut of the joint with 1.2 mm top sheet increases with the increase in yield stress of the bottom sheet, while a decreasing tendency is found for the joint with 1.6 mm top sheet. (iv) The minimum rivet length required for a successful joining increases with the increase in thickness ratio, while the opposite trend is observed for maximum rivet length.