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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) has been successfully used to fabricate skin stiffened compression panels. The “Refill” Friction Spot Welding (RFSW) process also shows promise for fabrication of such panels. Spot welds can be made using the “fixed position refill” method in a lap weld configuration where a spot of plasticized metal is developed at the location of pin penetration into the work piece. This paper presents the preliminary findings of the structural performance of a RFSW skin stiffened compression panel. The panel was fabricated with 2024 aluminum sheet and a single T-shaped stiffener. Spot welds were made between the skin and the stiffener to form the panel. The study revealed that RFSW can be successfully used to fabricate skin stiffened panels. The compressive strength of the test specimen was found to be within 10% of that predicted for a riveted skin stiffened panel of identical dimensions.

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.

Friction Stir Spot Welding (FSSW) has a strong potential to find applications in both the automotive and aerospace industries. At the present time, research efforts are taking place to gain a better understanding of the process, to explore different tool configurations, and to optimize the set of process parameters. In this regard, gaining an understanding of how the material flows under a given set of processing parameters is of particular importance for tool design and to validate numerical models aimed at simulating the process. In this paper, the results corresponding to an experimental study performed using markers are presented to provide insight about the material flow during the plunge phase of the fixed-position refill FSSW process.

Friction Stir Welding (FSW) of skin stiffened structures is being developed as a rivet replacement technology in the aerospace industry. Preliminary research was done on compressive strength and deformation characteristics of FSW aluminum skin stiffened panels. 7075-T6 aluminum sheets were bent to form stiffeners and friction stir welded to 7075-T6 aluminum sheets to fabricate two FSW panels. Another stiffened panel of similar dimensions was made by using traditional riveting. The compression test results and the failure modes of the panels are presented in this paper. The tests revealed that the FSW panels failed at approximately 17% higher load than the riveted panel. The failure loads of the FSW test panels were within 3 to 10% of the predicted load obtained by using two existing theoretical methods, and the failure load of the rivet panel was within 11 to 20% of the predicted load.

Friction Stir Spot Welding (FSSW), originally developed by GKSS (Germany), has a strong potential to find applications in the automotive and aerospace industries. At the present time, research efforts are taking place to gain a better understanding of the process, to explore different tool configurations, and to optimize the set of process parameters. In this regard, having reliable numerical models capable to simulate FSSW can be useful to reduce the number of physical experiments required in those studies. In this paper, a simplified isothermal three-dimensional Finite Element model of the initial plunge phase of the FSSW process is presented. The model, based on a solid mechanics approach, was developed using the commercial software ABAQUS/Explicit. The results of the simulations are compared against experimental information corresponding to similar tool geometry, sequence of operations, and process parameters.

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.