Material Flow by Tools for Friction Stir Spot Welding

［Abstract］In the Kinki University Research Institute of Fundamental Technology for Next Generation (KURING), studies were carried out on tools for friction stir spot welding as part of a MEXT-supported program for strategic research foundations at private universities between 2009 and 2013. From this study, some useful results were obtained. The size of stir zones produced decreases in friction stir spot welds when the thread on the cylindrical probe tool is worn. However, the effects of thread wear are limited since the production of stir zones can be controlled by the conditions of welding. The mechanical properties of friction stir spot welds made using three-flat tools are excellent since the bonded width and Y values are increased by the material flow in which the arc parts of the triangular vertex region in the cross-section of the probe press the surrounding material. The mechanical properties of friction stir spot welds are increased when the dimensions of the tip of a three-flat tool are enlarged proportionally. However, at the welding conditions of high speed, there is a limit to the extent that an expansion of the tool size can improve the mechanical properties of friction stir spot welds