Filling Friction Stir Welding In-Process Exit Holes in Copper Squirrel Cage Rotors for Electric Motors

The automotive industry is developing designs and manufacturing processes for new generations of electric motors intended for use in hybrid and electric vehicles. This paper focuses on the in-process exit hole at the end of the friction stir welding (FSW) path where the tool is withdrawn along the Z-axis and this leaves an impression in the material at the point of extraction. Despite the interest in the FSW technology of solid-state welding to join copper end rings to copper spokes in the fabrication of copper rotors, one of the concerns about the circular tool path is the exit hole produced. Several processes were considered and some of them evaluated for mass production application. The exit hole mitigation was explored using the friction plug welding process for refilling the hole made in copper end rings with consumable tool plugs. The influences of the tool plug’s taper geometry and plunging process parameters for two different method variations were investigated. The microstructure of the plug boundary was difficult to control. The weld characteristics were sufficient for this application but large defects at the interface could result in the separation of the plug at higher speeds due to thermo-mechanical stresses in the end rings during motor operation. Finally, this work puts forth a major welding process for induction copper rotors.