Inversion friction stir welding for fabricating hollow structures
By Yoshiaki Morisada (Joining and Welding Research Institute, Osaka University), Hidetoshi Fujii (Joining and Welding Research Institute, Osaka University)

Hollow structures cannot be easily fabricated by conventional FSW because a back-plate is indispensable for supporting the work-piece during the process. Although a bobbin tool has been developed for fabricating hollow structures, the no-tilt angle of the tool limits the optimal welding conditions. Under these circumstances, a novel FSW technique without the back-plate, named Inversion FSW (IV-FSW), was invented by our research group. The rotating tool is pulled up to the bottom surface of the work-piece, and the top surface of the weld area is covered with a small stationary part. Therefore, the tilt angle can be implemented. It was revealed that the tilt angle for the IV-FSW increased the optimal process window compared to that of the bobbin tool.