Improving weld quality with optimized bobbin tools : an innovative approach to friction stir welding of aluminium

Friction stir welding (FSW) has gained significant attention as a viable method for joining aluminum alloys due to its ability to produce high-quality welds. In recent years, bobbin tools have emerged as an innovative tool geometry for FSW of aluminum. Because of their unique tool design and weld setup, there is no backing plate needed and weak points such as root defects cannot form. The creation of strong and high-quality joints in similar aluminum structures is a challenging task for welding processes. In this regard, the current study aims at investigating the effect of shape-optimized bobbin tools on the welding quality of the joints. For this purpose, a simulation of the critical run-in process was performed in an initial step. Thus, the contact conditions between the tool and the work-piece could be analyzed, and a qualitative impression was gained of the welding behavior of this welding set-up. Subsequently, the tool was shape-optimized by imposing ideal contact conditions. The optimized and non-optimized tools were then used to perform FSW on similar aluminum joints made of AA5754. The resulting joints were analyzed for their mechanical and microstructural properties, and it was found that the optimized tool led to a different microstructure and tensile strength than the non-optimized tool. Therefore, this study provides a new and effective approach to improve the weld quality of similar aluminum joints by optimizing the geometry of bobbin tools through simulation.