Structural optimization study of stationary shoulder friction stir welding head with non-rigid support

To enhance the quality and efficiency of repairing aluminum alloy freight car bodies in railways, a friction stir head structure suitable for welding and repairing aluminum alloy freight car bodies was designed while employing stationary shoulder friction stir welding (SSFSW) technology. By analyzing the relationship between the structure of the friction stir welding head and the heat generation mechanism, a nearly stationary-shoulder friction stir head structure was proposed. Through the analytical heat generation model of the stationary shoulder stir pin, the functional relationship between the heat dissipation, stir pin dimensions, and process parameters was determined, and the geometric shape of the stir pin and the size of the stationary shoulder end cap were designed. Simulation and experimental results indicate that using this designed stir pin structure for welding repair, the temperature field of the weld seam is uniformly distributed along the thickness direction of the welded piece, which is conducive to forming good weld joints and seams. Practical field applications have shown that the designed structure can ensure heat generation while solving the problems of insufficient upsetting force and local stress concentration during non-rigid support processes, significantly improving the welding success rate. The tensile strength of the weld seam and other indicators also achieved satisfactory results. The design method used has certain referential value and can provide insights for similar research endeavors.