Experimental and numerical investigation on the effect of rotational speed on exit-hole-free friction stir spot welding with consumable pin

The present work investigates the effect of rotational speed on joint quality during Friction Stir Spot Welding (FSSW) using a consumable pin, where a consumable pin is used with a rigid tool shoulder for welding AA6061-T6 sheets to produce an exit-hole-free FSSW joint. Joint quality was analysed using lap shear test, macrostructure, microstructure and microhardness analysis at five rotational speeds, viz. 360, 462, 557, 900 and 1200 revolutions per minute (RPM). The joint strength increased with increase in rotational speed from 360 RPM to 900 RPM and then decreased with further increase in rotational speed. A 1.7 times increase in joint strength was observed for FSSW at 900 RPM with reference to 360 RPM. As expected, both energy input and temperature increased with rotational speed. The energy input increased by only 27.5% as the rotational speed was increased from 360 to 900 RPM. Finite element (FE) simulations were conducted for validation and study using commercial FE software, DEFORM-3D, to predict temperature distribution, force, torque and material flow. Lap shear test simulations matched with experimental results within reasonable (∼7%) accuracy except for very low rotation cases. However, failure load provided better matching with experimental results when Cockcroft-Latham damage model was used instead of Freudenthal damage model.