Joining of Laminated Core and Shaft of an Electric Machine Rotor by Electromagnetic Forming

In the mobility industry and especially in case of electrically powered vehicles the implementation of lightweight powertrain components with high efficiency and minimum in-stallation space is of utmost importance. One approach to realize a particularly compact and light design is using a central motor, which is aligned with a planetary gearbox via coaxial (partly) hollow rotor shafts positioned one within the other to operate the left and right-hand wheels of the car. To enable further weight reduction, aluminium alloys might be considered for the hollow shafts instead of the conventionally used steel. When the electrical machine is assembled, the shafts must be firmly connected to the rotor core, which is typically made of laminated electrical steel core. Electromagnetic forming is a promising technology for joining tubular aluminium components with similar or dissimilar materials. In this paper, the suitability for the described joining task is investigated. For this purpose, an inductor specifically suitable for expanding a round tube into a non-rotationally symmetric cross section shape is suggested and the corresponding joining process is developed using coupled electromagnetic and structural mechanical simulation. Experimental validation is carried out using a technology demonstrator.