Quantifying Effects of Cutting and Welding on Magnetic Properties of Electrical Steels

The magnetic properties, namely the iron losses and the relative permeability, of SiFe electrical steel laminations after guillotine shearing and cutting by means of fiber and CO₂ lasers are studied. The magnetic measurements are conducted on the Epstein frame for lamination strips with 1, 2, and 3 additional cutting edges along their length, in order to increase the cutting effect and the characterization data. The quantified effects of manufacturing (cutting and welding) are presented for three different material grades: M270-50A, M400-50A, and a nonoriented electrical steel of gauge 0.2 mm called NO20. Usage of the Epstein frame method allows any electrical steel company to reproduce the measurements for any specific grade. Data presented in normalized values facilitate utilization of the presented results and comparison between materials. An original model that incorporates the cutting effect considering homogenously damaged areas is developed and implemented in a finite-element method-based motor design software. Its originality is that it includes dependence on the geometry, included in the material magnetic properties. Simulations made for an industrial low voltage induction motor indicate a more than 15% increase in the iron losses compared with a model that does not consider the mechanical cutting effect. In the case of laser cutting, this increase reaches 30% to 50%, depending on laser settings. These relatively large increases of iron losses justify the implementation of the effect of cutting in industrial finite-element design tools, using a method that does not increase the simulation time.