Design of continuous Friction Stir Extrusion machines for metal chip recycling: Issues and difficulties

Friction Stir Extrusion is an innovative direct-recycling technology developed for metal machining chips. During the process, a rotating die is plunged into a cylindrical chamber containing the material to be recycled. The stirring action of the die prompts solid bonding phenomena allowing the back extrusion of a full dense rod. One of the main weakness of this technology is the discontinuity of the process itself that limits the extrudates volume to the capacity of the chamber. In order to overcome that limitation, a dedicated extrusion fixture has to be developed, keeping into account the concurrent needs of a continuous machine. The geometry of the die has to ensure proper pressure in the extrusion channel to prompt the extrusion while allowing the continuous loading of fresh charge. Furthermore, the chips entering the chamber have to find proper conditions for the solid bonding to happen. In this study, the design challenges of a continuous Friction Stir Extrusion machine are described and analyzed, giving an insight on the possible solutions using both experimental, numerical analysis, and keeping into account the sensor equipment necessary to monitor the process.