Development of friction stir welding method using a tilted spherical tool

The feasibility of friction stir welding (FSW) with a simple spherical tool, which has neither a shoulder nor a probe, was studied. The spherical tool allows for localised welding with narrow weld widths and extended tool life but tends to generate flashes and weld thinning. The material flow around the spherical tool during FSW of the aluminium alloys was observed in detail, and the flash generation behaviour was discussed. As a result, a new FSW method in which a spherical tool tilted to the retreating side (RS) was developed, and by expanding the flow path of the leading surface on the RS, the flow of hot material was controlled to reduce flash and smooth the weld surface.