Probing Load Bearing Capacity of Circular and Non-Circular Tool Pins in Friction Stir Welding

The tool pin in friction stir welding experiences fluctuating stresses due to combined bending and torsion because of the linear and rotational motions. Because of the typical small length to diameter ratio (< 10), the bending stress as well as the shear stress due to both bending and torsion will contribute to the magnitude of the fluctuating stresses experienced by the pin. Here we propose a methodology to estimate the maximum shear stress and the extent of fluctuating stresses on tool pins with circular, triangular and square cross-sections using a three-dimensional heat transfer and material flow model and solid mechanics based principles. The computed values of peak temperature, thermal cycle, torque and traverse force are validated with the corresponding measured results. The tool pin with circular cross-section is shown to experience the lowest magnitude and variation of the maximum shear stress for a given welding condition.