Effect of Tool Thermal Expansion and Durability in Friction Stir Spot Welding 2007-01-1699

Experiments were carried out to study the effect of thermal expansion of the tool during Friction Stir Spot Welding (FSSW) of large commercial automotive grade aluminum sheets. The objective of this study was to evaluate the tool “growth” using both experimental and numerical techniques and to see its effect on the weld quality (measured in terms of static strength). Two hundred friction stir spot welds were made over 25 Al sheets (A6022-T4) with a specific time interval between each sheet, thereby trying to simulate the welding conditions/sequence on a production line. An Infrared (IR) camera was used to monitor the temperature gradient on the tool during the welds. In addition, finite element analysis was run to predict the thermal expansion of the tool based on the temperature boundary conditions obtained from the IR camera during the experiment. The cross-sections of the spot welds showed an increase in plunge depth of 0.14 mm between the first and the last weld which agreed well with the simulation results. The static strength of the spot welds measured in lap shear configuration increased by approximately 20% from start till the time the tool attained steady state. In addition, a separate tool durability study showed that even after welding 25,000 spots using a single tool, the tool wear did not affect the weld quality