Effect of Setting Velocity on Self-Piercing Riveting Process and Joint Behaviour for Automotive Applications

The increased application of lightweight materials, such as aluminium has initiated many investigations into new joining techniques for aluminium alloys. As a result, Self-piercing riveting (SPR) was introduced into the automotive industry as the major production process to join aluminium sheet body structures. Although both hydraulic and servo types of SPR equipment are used by the industry, the servo type is most commonly used in a volume production environment. This type uses stored rotational inertia to set the rivet. The initial rotational velocity of the mass dictates the setting force and hence the tool is described as velocity-controlled. A study was therefore conducted to examine the effect of setting velocity on the process including tooling and joint performance. It was found that the setting velocity would have a significant effect on tooling life. Over 80kN force could be introduced into the tooling depending on selection of the setting velocity. The results also suggested that the joint quality and strength are affected by the setting velocity. An increase in the setting velocity would lead to a decrease in the head height and an increase in the interlock. Too low velocity may cause the rivet head to protrude; too high velocity may result in breakthrough failure. Both cases would lead to corrosion concerns. The examination also indicated that the higher the setting velocity the higher the shear strength of the joints.