A model to account for magnetic permeability changes resulting from edge damage caused by laser cutting in a high performance cobalt-iron alloy

Laser cutting is the mainstay of electrical machine stator core manufacture for prototyping and for high value, small and medium batch sizes. However, it can introduce localized damage into electrical steels, with reduction in magnetic permeability and increase in core loss in regions adjacent to the edge. These phenomena have been studied in Silicon-iron alloys, but there is little published data on Cobalt-iron. This paper presents experimental measurements on magnetic edge damage effect in Cobalt-iron alloys due to laser cutting. The paper then uses magnetic measurements for an increasing number of cuts in test samples to develop a model that represents the deterioration of magnetic permeability with distance from the cut edge, including cumulative damage effects from multiple cuts. The model is suitable for incorporation into finite-element models, either as a continuous function of position or to generate individual magnetization curves for discrete layers in finite-element mesh. The paper concludes by using the model to generate a series of magnetization curves which include the damage effect and in turn uses these to predict the net magnetic behavior of a series of rectangular strips. Good agreement is obtained between these predictions and measurements of samples from the same batch of Cobalt-iron.