Development of the friction stir welding process has just literally turned a corner. In a radical adaptation of the process FSW has been used to perform right angled inside corner joints.
The process now opens the door to specialist fabricators using T, L, and V sections, external and internal angle joints and even round sections. The technique uses much of the recently developed stationary shoulder friction stir welding technology (SSFSW). It has been adapted to penetrate 6mm into an inside corner joint in an aluminium alloy.
In SSFSW, a pin rotates through a non-rotating shoulder which slides along the joint. This technique originally evolved as a means of welding high temperature low conductivity materials and it became clear during development that it could be adapted to corner welding. During corner welding the shoulder is profiled to match the joint being welded.
Recently Nippon Light Metal approached TWI to apply the SSFSW concept to their particular application of internal corner welding. Nippon Light Metal was granted a patent on the technique in January 2009 in Japan. However TWI continues to hold the rights to use it outside the Far East and can publicise homegrown results with the agreement of NLM.
Since the internal angular join is an abrupt one it is by definition a stress concentrator. So Jonathan Martin's next task is to devise a way of forming a fillet in the capping bead.