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
