The Effects of the Punching Process Upon the Magnetic Properties of Steel Laminations

Abstract

The punching process used to stamp out iron laminations Causes a deterioration in the magnetic properties of the lamination material. This investigation is concerned with an experimental examination of the deterioration and finding the magnitude of the change in material properties due to punching. The punching effect is considered in terms of the ratio of total surface area of the lamination to the punched area, the material thickness and the punching tool clearance. Annular laminations of various sizes are punched out of sheet material and their magnetic properties measured under static and dynamic conditions. The material is then annealed and the tests repeated. A particular feature of the investigation is the equipment used for the dynamic tests. This consists of an electronic hysteresigraph, which maintains the rate of change of flux density constant for each hysteresis loop, used in conjunction with a specially designed test rig and an on-line digital computer. A metallurgical analysis of the material is made so as to obtain the optimum temperature for annealing and also to assist in determining the extent of the plastic deformation. The deformation of the punched edge is also examined in terms of its micro-hardness and the Kerr optical method is used to investigate the reduction in permeability in the region of the punched edge.