Numerical modelling of friction stir welding of pipes: Effect of tool shoulder on mechanical property and metallurgical characterization

One of the challenges during FSW of pipe is establishing sufficient contact between the tool shoulder and the pipes to be welded. With improper contact, the torque requirement increases, which thereby increases the power consumption. The present work focuses on the demonstration of a 3D thermo-mechanical model showing the influence of tool shoulder diameter on temperature rise, plastic strain development, spindle torque, material flow occurrence, and power consumption. The model showed a good correlation with experimentally observed temperature and maximum spindle torque for different rotational speeds. It was observed from the developed model that, an increase in the shoulder diameter increases the contact area and spread of maximum temperature resulting in a wider HAZ zone. Hence, optimization of the tool shoulder diameter was necessary, and it has been addressed considering its effect on contact area, heat generation, material flow, and spindle torque. The material flow behaviour has also been studied, and it was found that a larger shoulder diameter does not produce sufficient material stirring. The welded sample has been investigated by tensile strength and microstructure analysis. The optimum tool shoulder diameter of 16 mm resulted in joint strength efficiency of 90%.