Effects of laser cut on the performance of permanent magnet assisted synchronous reluctance machines

It is well established that various electrical machine manufacturing steps induce stresses which affect the magnetic properties of electrical steel laminations. Some of these stresses, such as those associated with cutting of the laminations, result in irreversible changes. In fact, punching and laser cutting, are frequently identified as the most severe cause of magnetic degradation [1]. Recent studies show that punching and laser cutting exhibit different deterioration mechanisms due to the nature of internal stresses they induce [2]. Namely, punching causes plastic deformation near the cut edge, whereas laser induces thermal stresses during cutting. In [2-3], the experimental characterization of the spatial distribution (i.e., edge-to-edge) of the magnetic degradation from the two cutting processes revealed that for punching a significant drop in permeability occurs near the cut edge. Whereas, in the case of laser cutting the damage seems to extend further from the edge due to the temperature gradient during processing, resulting in a substantial permeability reduction over the total sample width. The intensity of degradation was strongly influenced by the geometry of the sample, i.e., the strip width and thickness. Therefore, it is important to understand and model such complex phenomena in order to predict their influence on the performance of electrical machines. Discrepancies between predictions and measurements are frequently observed and reported in the literature. For instance, for the case of iron loss these are reported as “built-factors”. Such an approach neglects to reflect the link between the machine design geometrical details and the degree of electrical steel degradation [1]. The quantification of the effects of the magnetic degradation of electrical steel laminations on the machine's flux or back-EMF has received little attention in the literature (to date).