An optimization procedure for the friction stir welding FEM model of corner fillet joints

Friction stir welding (FSW) is an energy efficient and environmentally "friendly" (no fumes, noise, or sparks) welding process, during which the sheets are welded together in a solid-state joining process. FSW is mature for simple configurations but a significant lack of knowledge is found when dealing with different designs such as T-sections, box sections and corner welds. Although the latter joint morphology has traditionally been considered unfeasible for the process, it seems to have a great potential to be used also for T-joint configurations, a recurrent design pattern in transport applications. A specific tool has been developed and a set of experimental welds has been produced with it. In this paper, experimentally measured and numerically calculated thermal histories were compared and a response surface approach was applied in order to model the behavior of the error functions taken into account. Once the conflicting trend of the selected indicators was observed, a constrained minimization approach was developed. The numerical results, obtained utilizing the numerical parameters from the optimization procedure, showed a very good matching with the experimental evidence. According to the obtained results, the proposed model is able to represent a useful design tool for the process.