Visualization of metal flow in friction stir spot welding with particle image velocimetry

The flow visualization for friction stir spot welding (FSSW) was realized with a translucent organic material and the Particle Image Velocimetry (PIV) was adopted to analyze the flow behavior in the vicinity of welding tool. The simulated welding tests were performed with an apparatus at a rotating speed of 150RPM. The welding tools which are five times larger than the actual welding tools such as right screw, left screw and non-threaded cylindrical tool were adopted for the present study. The PIV analysis was performed with a translucent organic material containing some percent of small particles which are highlighted by a slit light. The videotaped images were then analyzed to evaluate flow velocity which varies depending on the location around the welding tool. The right and left screws created peculiar flows with vertical component such as downward and upward flows, respectively when the tool rotates in anti-clockwise direction while non-threaded tool mainly created rotational flow around the tool. The PIV analysis revealed that the particles flow relatively slowly inside the stir zone than in the outer zone around it, representing heterogeneity of flow during FSSW.