Scaling effects during friction stir welding of aluminum alloys with reduced tool aspect ratios

Friction stir welding (FSW) is a solid-state welding technique providing a number of unique advantages such as the weldability of various similar and dissimilar material combinations, the absence of process gases and filler materials, and high mechanical joint strengths. The operation principle is based on a rotating tool consisting of shoulder and probe. Due to friction-induced heat input, generated by the tool, the work pieces can be firmly bonded by dynamical deformation across the interface. However, the general application for this method is restricted by properties such as accessibility, high demands on the clamping technique, and in particular comparatively high process forces in the range of several kN. Process forces arise during the interaction between welding tool and the joining material and are decisively influenced by the dimensioning of shoulder and probe. In this study, a decrease of the process force could be achieved by tool scaling, which means the stepwise reduction of the shoulder and probe diameter. Furthermore, a method is developed to adapt the welding conditions for scaled FSW-tools. The study was carried out with a robotised FSW setup on 2-mm thick EN AW 6060 T66 sheets. The results show a decrease in process force of up to 60% and a spindle torque reduction of up to 80%.