Abstract
Targeted magnetic flux guidance in the rotor cross section of rotational electrical machines is crucial for the machine’s efficiency. Cutouts in the electrical steel sheets are integrated in the rotor sheets for magnetic flux guidance. These cutouts create thin structures in the rotor sheets which limit the maximum achievable rotational speed under centrifugal forces and the maximum energy density of the rotating electrical machine. In this paper, embossing-induced residual stress, employing the magneto-mechanical Villari effect, is studied as an innovative and alternative flux barrier design with negligible mechanical material deterioration. The overall objective is to replace cutouts by embossings, increasing the mechanical strength of the rotor. The identification of suitable embossing geometries, distributions and methodologies for the local introduction of residual stress is a major challenge. This paper examines finely distributed pyramidal embossings and their effect on the magnetic material behavior. The study is based on simulation and measurements of specimen with a single line of twenty embossing points performed with different punch forces. The magnetic material behavior is analyzed using neutron grating interferometry and a single sheet tester. Numerical examinations using finite element analysis and microhardness measurements provide a more detailed understanding of the interaction of residual stress distribution and magnetic material properties. The results reveal that residual stress induced by embossing affects magnetic material properties. Process parameters can be applied to adjust the magnetic material deterioration and the effect of magnetic flux guidance.
Highlights
The development toward electromobility and the connected demand for energy-efficient electrical machines requires further progress and alternatives in the processing and construction of rotating electrical machines
This effect can be evaluated by calculating the standard deviation of the residual stress distribution over the full simulated volume
We examined the influence of pyramidal embossings on the mechanical and magnetic material properties of electrical steel
Summary
The development toward electromobility and the connected demand for energy-efficient electrical machines requires further progress and alternatives in the processing and construction of rotating electrical machines. Permanent magnet synchronous machines (PMSM) [1] and synchronous reluctance machines (SynRM) [2] are gaining significance in this field Both electrical machine topologies require an optimal. Cutouts in the rotor sheets are used for magnetic flux guidance and for stray flux suppression to increase the magnetic coupling between rotor and stator [4] These cutouts reduce the mechanical strength of the rotor construction limiting the maximum angular velocity of electrical machines [5]. Pinned magnetic domains lead to decreased magnetic permeability in the mechanically modified material volume These areas act as magnetic flux barriers, suppressing the magnetic flux in undesired directions with negligible mechanical weakening of the rotor construction. Microhardness tests in conjunction with local and global magnetic measurements validate the simulation results
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