Controlled Rivet Deformation During Self-piercing Riveting Through a Tailored Strength Distribution Within the Rivet Material

The use of stainless steel with high strain hardening as material for self-piercing rivets is a promising approach to shorten the manufacturing process. Due to the corrosion resistance of the material and the achieved high strength within the forming process, the heat treatment and the coating can be omitted. As the strength within the rivet material is achieved by cold forming, the strength distribution within the rivet remains intact after the manufacturing process. The aim of the contribution presented is the exploitation of the potential of this strength distribution to improve the performance of the self-piercing rivets. Therefore, the scope of the examination is on the analysis of the influence of the local strength on the deformation behaviour of the rivet during joining. While it is unfeasible to manufacture rivets with any desired strength distribution, numerical simulation offers an efficient opportunity to study the effects of varying local strengths. By using a definable true strain distribution within the rivet as presetting for the simulation, different strength distributions can be modelled. Through the simulation of the joining process, the deformation behaviour of the rivet can be examined. Based on the insights of this analysis, a strength distribution is created that supports the joining of challenging material combinations consisting of high strength steel and aluminium. Finally, the approach is verified by experimental joining tests.