Abstract
Non-oriented electrical steel sheets are applied as a core material in rotors and stators of electric machines in order to guide and magnify their magnetic flux density. Their contouring is often realized in a blanking process step, which results in plastic deformation of the cut edges and thus deteriorates the magnetic properties of the base material. This work evaluates the influence of the material’s grain size on its iron losses after the blanking process. Samples for the single sheet test were blanked at different cutting clearances (15 µm–70 µm) from sheets with identical chemical composition (3.2 wt.% Si) but varying average grain size (28 µm–210 µm) and thickness (0.25 mm and 0.5 mm). Additionally, in situ measurements of blanking force and punch travel were carried out. Results show that blanking-related iron losses either increase for 0.25 mm thick sheets or decrease for 0.5 mm thick sheets with increasing grain size. Although this is partly in contradiction to previous research, it can be explained by the interplay of dislocation annihilation and transgranular fracturing. The paper thus contributes to a deeper understanding of the blanking process of coarse-grained, thin electrical steel sheets.
Highlights
Soft magnetic cores of high permeability are used in electric drives in order to amplify magnetic flux densities
139 (±82) 5 × 60 mm blanking work and iron losses are correlated to the average grain size in the mid
For 0.25 mm thick thicknesses, as well as the corresponding relative cutting clearance in percent of the sheet sheets blanked with 6% cutting clearance, the blanking work is clearly decreasing with thickness
Summary
Soft magnetic cores of high permeability are used in electric drives in order to amplify magnetic flux densities. These magnetic cores mostly consist of stacked, insulated sheets of non-oriented electrical steel with alloying contents of silicon (up to 3.2%) and aluminum (1%) and sheet thicknesses between 0.1–0.5 mm. Plastic deformation of the cut edges introduces dislocations surrounded by microstress, which effectively hinders domain wall motion and domain rotation. As a consequence, this leads to lower permeability, larger coercivity and larger hysteresis losses. Stresses in electrical steel affect the magnetic properties as a result of the inverse magnetostrictive effect [5]
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