Reduction of friction stir welding setup loadability, process forces and weld seam width by tool scaling

Abstract

Friction stir welding is an increasingly used method to join similar and dissimilar materials with excellent mechanical weld seam properties. However, in certain cases, friction stir welding is restricted by high mechanical loads as a result of high forces and torques during the welding process. This relates in particular stiffness-reduced machine concepts which may cause path deviations, massive vibrations and insufficient tool plunging. Against this background, this investigation demonstrates a method to reduce forces and torques by tool scaling. Due to the stepwise diameter reduction of shoulder and probe and a simultaneous adjustment of the process parameters, a significant force and spindle torque reduction was achieved. Furthermore, it could be shown that tool scaling does not affect the mechanical strength properties. The experimental investigations were carried out with EN AW 5754 H11 with a sheet thickness of 8 mm. The weld seams were performed on a robotized friction stir welding setup (KUKA KR500) with a maximum axial force of 10 kN. Based on a 26-mm shoulder and a 10-mm pin diameter, it could be demonstrated that the general weldability of 8 mm EN AW 5754 H11 is restricted (incomplete tool plunge) by the maximum axial force of the robotized friction stir welding setup (10 kN). Due to the stepwise reduction of the shoulder and probe diameter from 26 mm to 20.8 mm and 10 mm to 8 mm, respectively, a general weldability and weld seams without irregularities could be achieved by the equal robotized friction stir welding setup. Furthermore, it could be shown that an axial force and spindle torque reduction from 10 kN to 4 kN and 29 Nm to 10 Nm, respectively, was obtained due to further reduction of the tool diameters.