In-line strategies and methods to reduce balancing efforts within rotor production for electric drives

The manufacturing of electric drives is still time- and cost-intensive. In order to reduce processing time balancing is identified as one of the processes with a high potential for innovation. In contrast to most research efforts, the presented paper follows the approach of concentrating on the impact of process steps prior to rotor assembly and the actual balancing operation. Within current production processes, weighing is almost exclusively performed as an end-of-line. However, the production of drives with permanent magnets integrated into the lamination stack (IPM-Drives) already deliver prefabricated single modules. Those modules can be evaluated separately regarding their imbalance and then can be combined in a manner to achieve a minimum imbalance without additional weighing. In order to assemble rotor and shaft, a new joining operation is subsequent to the pre-balancing operation. For this, the shaft has special carrier geometries and is pressed in axial direction into the lamination stack. Thus, a joining by forming operation is performed. The combination of both process steps could increase the efficiency of production process. The paper describes methods to improve the production process for rotors focusing on a selective balancing step and an innovative joining operation. Therefore strategies to evaluate the imbalance of single lamination stacks prior to their assembly operation are presented. A procedure to calculate ideal rotor assemblies with minimum imbalance will be introduced. Depending on the rotor topology, restrictions regarding free rotation will be considered. The developed concept will be experimentally validated. Based on obtained results, a reduction of imbalance up to 30 % may be possible. To proof the applicability of the selective balancing and the joining operation, joining test were carried out and analyzed regarding the radial runout.