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The same setup can be used for tack welding and full friction stir welding.

A small friction-stir- welding tool has been developed for use in tack welding of aluminum-alloy workpieces. It is necessary to tack-weld the workpieces in order to hold them together during friction stir welding because (1) in operation, a full-size friction-stir-welding tool exerts a large force that tends to separate the workpieces and (2) clamping the workpieces is not sufficient to resist this force.

This Friction-Stir-Welding Tool is designed specifically for tack welding of 0.32-in. (8.1-mm)-thick pieces of aluminum-lithium alloy 2195. Different values of pin-tool extension and shoulder diameter might be needed for optimum tack welding of different alloys or different thicknesses.
It is possible to tack the pieces together by gas tungsten arc welding, but the process can be awkward and time-consuming and can cause sufficient damage to necessitate rework. Friction stir tack welding does not entail these disadvantages. In addition, friction stir tack welding can be accomplished by use of the same automated equipment (except for the welding tool) used in subsequent full friction stir welding.

The tool for friction stir tack welding (see figure) resembles the tool for full friction stir welding, but has a narrower shoulder and a shorter pin. The shorter pin generates a smaller workpiece-separating force so that clamping suffices to keep the workpieces together. This tool produces a continuous or intermittent partial-penetration tack weld. The tack weld is subsequently consumed by action of the larger tool used in full friction stir welding tool.

This work was done by Gerald W. Bjorkman, Johnny W. Dingler, and Zachary Loftus of Lockheed Martin Corp. for Marshall Space Flight Center. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Manufacturing category. MFS-31392.

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