Soochow University
Assembly Line
Joining Aluminum With Friction-Based Self-Pierce Riveting
High-strength aluminum is a key material for reducing weight in auto body applications. However, the material’s low ductility at room temperature can cause cracking issues with conventional mechanical fastening methods. Paper “Crack-Free Joining of High-Strength AA7055 Sheets by Friction Based Self-Piercing Riveting with the Aid of Numerical Design”
A new process—friction self-pierce riveting—promises to solve that problem. The process combines the mechanical joining mechanism of self-pierce riveting with the solid-state joining mechanism of friction-stir spot welding.
Under heat effects from friction and plastic work, the strength and ductility of the joined materials, as well as the force required for joining, are very different from that of self-pierce riveting (SPR). Mechanical performance and fatigue life of the joint are also improved, because of the increased local hardness of the aluminum due to grain refinement and the formation of solid-state joining.
To achieve a high-strength joint with this technique, the rivet, die and process parameters must be optimized to match the materials. For instance, to facilitate mechanical interlocking, the rivet should have an appropriate tip angle and adequate strength relative to the base materials. Similarly, the flaring of the rivet is influenced by the depth of the die cavity and the depth of rivet penetration. On the other hand, the plunging speed and depth, as well as the rotation speed of the rivet, will influence how much frictional heat is generated to soften the materials.