Friction welding of lightweight motor shafts for electric vehicles

The reduction in weight of an electric vehicle (EV) is essential for the improvement of driving performance and reducing cost. In particularly, lightening the weight of motor shaft used for EV contributes to not only total weight reduction but also decrease in shaft inertia, which determines responsiveness of the induction motors. The motor shaft has complicated figures at both shaft ends in order to connect to bearings or a drive shaft. Therefore, these shafts with complicated structures have been made of single solid shaft by cutting using machine tools. Therefore, the shaft weight for the high-power motor used by EV is heavy, and the cost is high. In order to reduce both shaft weight and manufacturing cost, a hollow shaft structure was developed. It was assembled from a pipe and solid parts by ultraprecision friction welding. The hollow shafts that agree with the quality required for EV motor shaft (up to 0.10 mm or less) successfully produced by changing welding condition or work cramping method. In addition, strict inspection on weld defect was conducted by microscopic observation in weld zone. These hollow shafts without any weld defect were usable for practical applications.