The low strength and large protrusion of the traditional dieless clinched joint hindered its application. To improve the mechanical properties of the dieless clinched joint, a novel dieless clinching process considering the limitation of the blank holder was proposed. The finite element model of the dieless clinching process was established by DEFORM-2D, the influences of the blank holder spring stiffness, the blank holder limit height, and the punch diameter on the mechanical interlock of the joint were analyzed, and the influence laws of blank holder spring stiffness and blank holder limit height on material flow and mechanical interlock were obtained. Then, the influence of these three die parameters and their interaction on the joint interlock were analyzed using the response surface method. The results show that the blank holder displacement plays a key role in the formation of mechanical interlock in the dieless clinching process. Reasonable limit height and spring stiffness of the blank holder can control the flow direction of materials, so as to improve the mechanical interlock and the strength of dieless clinched joints. It provides a new idea for improving the dieless clinching process.

The use of lightweight sheets such as carbon fiber reinforced composites (CFRP), magnesium alloys, and aluminum alloys is of great significance to realize the lightweight of automobiles. However, the differences between the sheets make the joining processes of dissimilar sheets a great challenge. A pre-holed screw-drilling riveting (PH-SDR) process is proposed based on a study of existing joining processes, the rivet with threads is riveted into the sheets by rotating, and the effective joining between the sheets is achieved by embedding the sheets into the rivet threads. The joint strength of the PH-SDR and self-piercing riveting (SPR) was compared through the lap-shear test. It was found that in the case of 1 mm Al6061-T6 + 2 mm AZ31B, the strength of the PH-SDR joint was 3.09 kN, which is 30.9% higher than the SPR of 2.36 kN. In the case of 2 mm CFRP + 2 mm Al6061-T6, when the spindle speed was 600 rpm, the strength of 5.43 kN and the energy absorption of 20.3 J were obtained for the PH-SDR joint, which is 51.2% and 89.7% higher than the optimal SPR joint. The results show that the proposed PH-SDR process provides a feasible solution for the joining of dissimilar lightweight sheets.