Friction stir welding of aluminum using a tapered shoulder tool

Since the time when friction stir welding (FSW) was invented by The Welding Institute (TWI) advancements in welding tool design have allowed the process to be operated at higher travel speeds, in thicker sections, and with more reliable quality. A new feature has been developed, referred to as the tapered shoulder, which allows FSW to be operated more easily and with simpler equipment. The tapered shoulder consists of a scrolled shoulder that is not generally flat but is tapered outward, i.e. convex, from the outside diameter to the pin. This scrolled cone can be embedded beneath the surface of the plate to any depth, with the width of the crown of the weld being variable depending on the depth of penetration. This tool design, patented by Concurrent Technologies Corporation (CTC), has implications for conventional welds, for welds in material with complex curvature, for thick-section pipe, and for self-reacting or "bobbin" welds using tools that have a fixed geometry. This paper describes the welding tool design and its use in different welding applications.