Neutron grating interferometry investigation of punching-related local magnetic property deteriorations in electrical steels

摘要

Mechanical residual stress induced by manufacturing influences the magnetic behavior of non-grain oriented electrical steels, which are used for producing rotors and stators of electrical machines. The impairment occurs mainly along the cutting line of stator and rotor laminations. A locally resolved assessment of the magnetic material behavior of punched electrical steels is possible by using the neutron grating interferometry. In addition to this in situ measurement method, additional ex-situ measurements allow correlating local domain wall mobility and global magnetic polarization. Four different non-grain oriented electrical steels are investigated in this paper. This includes two sheet thicknesses of 0.35 mm and 0.65 mm both available having silicon contents of 2.30 wt-% as well as 2.74 wt-%. The specimens are produced by wire cutting and by punching using different process parameters, i.e., two relative cutting clearances of 5% and 10% plus a sharp and worn cutting edge wear state. The cutting method's influence on the four different electrical steel's magnetic behavior is discussed with respect to the local polarization distributions at varying magnetic field strengths next to the cutting lines. This novel approach for the first time allows an in situ investigation of altered magnetic properties with respect to the punching induced residual stress along the cutting line. Not only the maximum deterioration of the polarization next to the cutting line but also the extent of the magnetic property deterioration is pointed out. The effect of punching parameter variations is further verified using global magnetic measurements. The knowledge about the local polarization distribution next to the cutting line is critical for an improved development and design of electrical machines.