Influence 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 mechanical and laser cutting are studied. Mechanical cutting with guillotine shears and cutting by means of fiber and CO2 lasers are considered. The magnetic measurements are conducted on the Epstein frame for frequencies of 50, 100 and 200 Hz. The specimens also include Epstein strips with 1, 2 and 3 additional cutting edges along their length, in order to increase the cutting effect and the characterization data. Mechanical cutting results in more than 20% iron loss increase and more than 40% relative permeability reduction at 1 T for 0.5 mm gauge, for a strip width of 10 mm compared with the reference of 30 mm, while corresponding values for laser cutting are 40% and 60%. It is also noted that different steel grades of the same raw material show lower magnetic deterioration with thinner lamination thickness. The influence of welding is also investigated by means of Epstein measurements. Experiments show an iron loss increase of up to 50% with a corresponding 62% reduction in the permeability compared to similar non-welded laminations. A model that incorporates the cutting effect with geometry dependency is developed and implemented in a FEM-based motor design software. Simulations made for an industrial low voltage induction motor indicate a more than 15% increase in the iron losses compared to 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.