Alternative Magnetflussführung in Elektromotoren: Reproduzierbar eingebrachte Eigenspannungen zur gezielten Magnetflussführung in nicht-kornorientiertem Elektroblech

Non-oriented electrical steel is a core component in the construction of rotating electrical machines for the targeted guidance and amplification of the magnetic flux. A strong magnetic coupling between rotor and stator flux is crucial for the maximization of the efficiency and power density of the electric drives. For this purpose, flux barriers are inserted into permanent magnet excited synchronous machines and synchronous reluctance machines in order to suppress leakage flux and to ensure targeted guidance of the magnetic flux. The flux barriers are typically implemented through cutouts in the rotor cross-section. The resulting filigree structures of the electrical steel lead to a mechanical weakening of the rotor and thus to lower achievable speeds and power densities. In this work an alternative approach for guiding the magnetic flux based on the Villari effect is presented. Locally changed magnetic material properties are achieved through increased residual stresses in the embossed material areas. The relationship between residual mechanical stresses introduced by the forming process and the reduced magnetic permeability of the electrical steel sheet is investigated using homogeneously embossed samples. Higher forming forces associated with increased mechanical stresses lead to a greater reduction in magnetic permeability. The functionality of these alternative magnetic flux barriers is shown using circular embossed patterns. In addition to showing the influence of varying stamping parameters on the magnetic properties of the electrical steel sheet, the reproducibility of the changed magnetic properties due to residual stresses caused by the forming process is demonstrated.