Numerical Analysis of the Influence of a Movable Die on Joint Formation in Versatile Self-Piercing Riveting

Self-piercing riveting (SPR) is a well-established joining technique in lightweight construction, as it enables the joining of different materials without requiring pre-drilling. However, the necessary adaptation of the rivet-die combination to the respective material and thickness combinations requires a large number of specific tool sets, which significantly limits the process's flexibility. To overcome these limitations, the versatile self-piercing riveting (V-SPR) was developed, which features enhanced punch actuation in combination with a multi-range-capable rivet . In this context, the concept of a movable die was introduced, which enables an extended process window and adaptable joint formation. Kappe et al. presented initial studies demonstrating the potential of this approach . However, a detailed numerical understanding of the underlying mechanisms remains lacking. This paper presents a numerical analysis of V-SPR with a movable die using a finite element (FE) model. The model includes deformable rivets, sheet metal materials and a kinematically controlled die with adjustable movement. A parameter study was conducted to analyse the influence of die movement on the material flow of the rivet and sheets, as well as joint formation. The simulations were validated using selected experimental data. The goal is to compare the joint geometries achieved with fixed and moving dies and expand the process windows of VSPR. The results demonstrate that the movable-die concept significantly enhances the material flow of both the sheets and the rivet, resulting in a noticeably larger and more reliable interlock than what is achievable with V-SPR using a fixed die. The numerical analyses support the observations reported by Kappe et al. and extend them by providing a quantitative description of how die displacement influences the resulting interlock size. Moreover, the ability to precisely control the die movement makes it possible to join challenging sheet-metal combinations that are difficult to process with conventional setups, particularly in cases involving thicker sheet materials.