FE simulation of the SPR process to predict joint characteristics : innovation report

Self-pierce riveting (SPR) is the core joining technology used by Jaguar Land Rover (JLR) to join aluminium & mixed material body in white (BIW). Currently, the application of this process has a serious constraint to the business due to the high investment and intensive labour required by physically testing joint feasibility. This is a critical issue especially where different stacks need to be joined by one SPR gun. In this case, the selection of a common rivet/die combination which suits different material stacks requires labour intensive work that in some cases can create long delays during a vehicle development and commissioning. In this context, the development of a simulation technique, based on Finite Element Analysis (FEA), could allow virtual assessment of the manufacturing feasibility of a joint. This will enable significant business benefits including: saving time, costs and materials requirement for the experimental trials. Three major challenges need to be addressed: short CPU time, accuracy and robustness in order for its application in a manufacturing environment. To achieve these objectives, detailed numerical methods capable of reproducing the key factors affecting the experimental process like tooling, boundary conditions and material plastic deformation are developed. For the first time, a thermo-mechanical finite element model for simulation of the SPR process has been proposed. This allowed consideration of the increase in temperature due to friction and plastic deformation generated during the rivet insertion. The effect of thermal softening and strain hardening were characterized for the development of the substrate material model and their influence on the numerical simulation was assessed. This study has been validated via production line data and a significantly high level of correlation between simulation and experimental data for over 1000 joints representative of a vehicle platform has been achieved. The application of the developed simulation technique will enable several business benefits such as significant reduction of engineering time and costs in contrast to the experimental procedure. These advantages allow a smooth implementation of the SPR process in a JLR production line by providing engineering recommendations rapidly and consistently. All these features, combined with accuracy and robustness have enabled the application of the developed tool into JLR business