Laser Cutting and Mechanical Cutting of Electrical Steels and its Effect on the Magnetic Properties

It is well established that laser cutting or mechanical cutting of nonoriented electrical steel causes structural changes at the cutting edge, which finally affect the magnetic properties. During mechanical cutting, plastic deformation appears in the zone near the cutting edge. On the contrary, laser cutting induces thermal stress due to temperature gradients within the material during processing, which finally also results in deterioration of the magnetic properties. The knowledge of the type of the deterioration mechanism and the degree of the deterioration of magnetic property deterioration mechanisms is important for designing electrical machines in terms of magnetic field and loss calculations. In this paper, the effect of cutting on the magnetic flux distribution for mechanical cutting as well as solid state laser cutting is calculated and analyzed space-resolved using the data obtained from investigations by neutron grating interferometry. In addition, the resulting changes of magnetization behavior, i.e., the character of the B versus H curve, were studied. It will be demonstrated that the deterioration of the magnetic properties depends on the geometry of the parts at cutting. It is shown that the nature of the resulting spatial distribution of the magnetic flux is different for mechanical cutting and cutting by laser. By mechanical cutting, a drop of the magnetic flux in the region at the cutting edge appears. Through cutting by laser, the observed decrease of the magnetic flux B is observed over the total width of the strip. The decrease of B at cutting of small parts by laser is remarkably different at the cutting edges, which are opposite to each other. Finally, the observed magnetic behavior is correlated to the different character of the induced residual stresses by mechanical cutting and cutting by laser.