Improving Production Performance of Refill Friction Stir Spot Welding

Refill friction stir spot welding (RFSSW) is a solid-state, spot joining technique that produces ostensibly flush surfaces. While historically weld properties have been reported to be superior to other spot joining technologies, the process has been hampered by long cycle times and unquantified tool life. Weld cycle times for aluminum alloys have ranged between two and ten seconds depending on alloy and thickness. Recent collaborations within the Center for Friction Stir Processing at Brigham Young University have demonstrated cycle times as low as 250ms, with both static and dynamic mechanical properties that exceed the performance of resistance spot welding. Tool life of both coated steel and tungsten carbide tooling was evaluated to determine the influence of material selection on both the frequency of tool changes and cleaning as well as the overall cost per spot associated with the tooling. Various dissimilar and similar alloy combinations (6xxx, 7xxx and 2xxx series aluminums) were evaluated ranging in forms from medium grade precipitation hardened sheet to high strength extrusions in two and three sheet stack-ups. Assembly of flat sections as well as extruded stringers and curved skins are presented to showcase the process flexibility, productivity, and manufacturing readiness.