Finite Element Simulation of Tunnel Defect in Friction Stir Welding of Pure Copper: Effect of Tool Geometry

The current work describes the development of a numerical model to accurately predict the occurrence of various defects during FSW of pure copper using thermomechanical responses. The developed numerical model examines the effect of varying tool dimensions on thermomechanical responses and defect formation. The tool traverse and rotation speed are kept constant at 30 mm/min and 1200 rpm. The shoulder diameter is varied between 14 and 28 mm. The 14 mm tool produces an imperfect weld with surface and sub-surface tunnel defects, whereas the 18 mm tool eliminates the surface tunnel defect. An increase of the shoulder diameter to 28 mm further reduces the extent of sub-surface tunnel defect. The increase in the shoulder diameter eliminates the surface tunnel and reduces the height of the sub-surface tunnel by about 50%. Significant material velocity, strain rate, and temperature on the retreating side (RS) produces the sub-surface tunnel defect on the advancing side (AS). The model can predict the initiation and advancement of the tunnel defect along the welding length. The velocity profile indicates that the material is equally distributed between the AS and RS behind the tool at the conclusion of the dwell stage. Alternatively, the material deposition becomes unequal between the AS and RS as the tool starts traversing. The tool–workpiece interface observes less stress and alternatively high strain, strain rate, and velocity distribution compared to the rest of the workpiece.