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Friction Stir Spot Welding (FSSW) is a relatively new solid state joining technology that has the potential to be a replacement for single point joining processes like Resistance Spot Welding and rivet technology in certain applications. Since the material flow around the pin plays an important role in determining the quality of the weld, understanding how the material moves is important to optimize process parameters and to validate the results of numerical simulations of the process. In this paper, an experimental study aimed at visualizing the material flow during the plunge phase of refill FSSW of an aluminum alloy is presented. Different marker materials were placed at a certain depth from the plate surface and metallographic samples in three mutually perpendicular directions were prepared and examined to identify the final location of the marker material after the plunge of the pin.

Friction Stir Welding (FSW) is being developed as a rivet and resistance spot welding replacement technology for aerospace and aircraft structures. While the FSW process is at a high Technology Readiness Level (TRL) and is being implemented on selected DOD and NASA hardware components, it has not seen extensive application due to limitations in the understanding of the design constraints and fixturing issues associated with a producible design. This paper describes the preferred FSW joint types and designs for beam structures which facilitate production implementation. The effects of fixturing and tooling on the FSW process development needs and resultant joint properties are discussed along with examples of fixturing and tooling approaches for fabrication of aluminum stiffened beam assemblies.

The Friction Spot Welding (FSSW) process as invented by GKSS in Germany has shown potential for application in several industrial fields as a solid state joining technology. This study evaluates this “refill” method of friction spot welding in aluminum sheet. Efforts to date have concentrated on simple flat lap joints. Process and tool development studies have been performed and have focused on understanding and managing material flow in order to minimize flash, ensure full consolidation and produce a nearly flush surface. The metallurgical and mechanical properties as a function of tool geometry and processing parameters are discussed and the lap shear strength is shown in this preliminary work to compare favorably to riveting and resistance spot welding.