The energy efficiency of electric machines can be improved by optimizing their manufacturing process. During the manufacturing of ferromagnetic cores, silicon steel sheets are cut and stacked. This process introduces large stresses near cutting edges. The steel near cutting edges is in a plastically deformed stress state without external mechanical load. The magnetic properties of the steel in this stress state are investigated using a custom magnetomechanical measurement setup, stress strain measurements, electrical resistance measurements, and transmission electron microscopic (TEM) measurements. Analysis of the core energy losses is done by means of the loss separation technique. The silicon steel used in this paper is non-grain oriented (NGO) steel grade M270-35A. Three differently cut sets of M270-35A are investigated, which differ in the direction they are cut with respect to the rolling direction. The effect of sample deformation was measured—both before and after mechanical load release—on the magnetization curve and total core energy losses. It is known that the magnetic properties dramatically degrade with increasing sample deformation under mechanical load. In this paper, it was found that when the mechanical load is released, the magnetic properties degrade even further. Loss separation analysis has shown that the hysteresis loss is the main contributor to the additional core losses due to sample deformation. Releasing the mechanical load increased the hysteresis loss up to 270% at 10.4% pre-release strain. At this level of strain, the relative magnetic permeability decreased up to 45% after mechanical load release. Manufacturing processes that introduce plastic deformation are detrimental to the local magnetic material properties.

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When optimizing the design of electrical machines, it is recommended to take into account the effect of the manufacturing processes on the core losses and magnetic properties of the electrical steel. This paper demonstrates a methodology for incorporating the effects of interlocking, a process frequently applied to fix a stack of laminations, on the magnetic properties of the machine core. The methodology requires magnetic measurements on several sets of Epstein strips. The proposed methodology is demonstrated on NO27, a low loss grade of electrical steel. A validation is done to show the transferability from Epstein strips to a realistic stator core geometry. The results show that the proposed methodology succeeds accurately in predicting the degrading impact of interlocking on the magnetic properties of electrical steel laminations. Additionally, the effect of magnetic anisotropy on the degrading impact of interlocking is investigated.