Shoulderless Friction Stir Welding : a low-force solid state keyhole joining technique for deep welding of labile structures

Abstract

This paper reports on the possibility of performing Friction Stir Welding (FSW) without the usual immanent shoulder to enable FS processing to deep welding of narrow and labile structures and applications where backing is not possible. Requirements and prerequisites, advantages and limitations for Shoulderless Friction Stir Welding (SLFSW) are discussed and an industrial application of the joining technology is presented. For leaving the shoulder out, its central functions in FSW have to be transferred to the pin. The resulting tool design of SLFSW is comparably small and slim and so reduces contact area and effective lever and in turn forces and heat input during processing. SLFSW allows welding paths almost at the edge of components and enables a complete and gap-free joining while a deformation of overhanging structures can be avoided. Compared to standard FSW processes, force reductions of about 80–85 % and power reductions of about 75-80 % were found in this study for a 6.5 mm deep weld opening up additional potential for integration with other spindle processes like milling. The locally very limited process impact of SLFSW resulted in comparably low distortion with a part precision reached of +/- 0.05 mm.