Power Loss Models in Punched Non-Oriented Electrical Steel Rings

The stresses and strains generated during punching of electrical steel laminations degenerate the magnetic properties in the region near the cut edge. The existing work has tended to focus on strips, with estimates of the damaged width ranging from less than 1 up to 10 mm. In this paper, ring samples, which are more representative of motor laminations, are considered. Increasing the diameter of the samples and, therefore, increasing the proportion damaged by the punching allowed the creation of mathematical models to describe and analyze the power loss and estimate the extent of the damaged region. Five samples each measuring five laminates high with a constant outer diameter of 200 mm and various inner diameters (150, 160, 170, 180, and 190 mm) were stamped from coils of M250-35A and M330-35A of a non-oriented electrical steel. A simple model was initially proposed, where power loss is proportional to the ratio of the undamaged to the total width and the square of the flux density passing through that region. An average width for the damaged region was calculated at 0.31 mm for the two materials.