Numerical modeling of thermal field during friction stir welding using tool with polygonal pin profile

Abstract

Friction stir welding produces better joint strength comparing with other conventional fusion welding techniques as the complete metal joining operation is executed in solid state itself. Even though the quality of weld is comparatively good, this joining technique has its own disadvantages. Improper material flow along the weld line may result in weld defects. Usage of polygonal pin geometry in tool pin rather than using conventional cylindrical pin geometry enhances flow of plasticized metal under the tool shoulder in the stir zone. Major problem associated with polygonal shaped tool pin is poor tool life. Yield strength of material under the tool shoulder creates opposing force for the movement of tool pin, which is submerged inside the workpiece for the entire joining process. Uneven stress distribution along the outer surface of the polygonal tool pin shape leads to premature tool failure. As the strength of material is a temperature dependent property, the heat input during the process has to be optimised with respect to the geometrical shape of the tool pin to improve tool life without compromising the weld quality a lot. In this paper, the variation in thermal field based on the geometrical shape of the tool pin was analysed using MATLAB based on the moving coordinate system. Rosenthal equation was used to estimate variation the peak temperature and temperature distribution with respect to pin shape in the view of optimising thermal environment towards better weld quality.