Validation of Bending Simulation Models Based on Yield Strength Influences of Electrical Steel Sheets on Stator Core Radius

Abstract

Against the background of rising electro mobility concepts for vehicles, corresponding demands on electric machines with regard to their efficiency and power density remarkably influence stator production of such machines in terms of required power output. Here, fundamental parameters that must be considered when designing stators are magnetic properties of the stator core and the electric properties of the winding. Furthermore, the performance of stators is influenced by geometrical properties such as copper filling of the stator grooves and the inner radius of the stator core. In order to increase copper fill factors within the stator body, several stator production technologies have recently been developed and investigated, e.g. hairpin, flyer winding and insertion technology. In addition to those technologies, the so called flatpack bending process constitutes a new process for stator production in which the pre-bent winding is first inserted into a flat, comb like shaped stator core. This assembly is subsequently rounded in a multi-stage rotary draw bending process, obtaining high copper filling ratios. However, the main challenge for this bending and subsequent springback procedure arises from the roundness deviations occurring along current process chains. For this reason, a simulation model has been created in the framework of a collaborative research project between SEG Automotive and the Institute for Metal Forming Technology, Stuttgart, aiming to better understand and to improve this stator flatpack bending process. For an extensive validation of this model, various parameters need to be examined and their influence to be evaluated. In this study, simulations were performed using this numerical model, in which levels of yield strength of the material to be formed were varied in order to calculate their influences on the outer radius. For validation objectives of simulation results, bending experiments were subsequently conducted, so samples obtained were evaluated using 3D scan technology. As a result, only a maximum difference of 0.3 mm of bent stator core was observed by comparing the numerically calculated results and the results measured during the experiments.