Influence of Cutting Tool Wear on Core Losses and Magnetizing Demand of Electrical Steel Sheets

In this paper, the influence of cutting tool wear on the core losses and magnetizing demand of electrical steel sheets and the possible effects in electrical machine production are illustrated. Test strips with dimensions of 7.5 mm × 300 mm are punched with a sharp industrial cutting tool from four different electrical steel sheet types. Afterwards a total of 200 000 punch strokes are performed by using 8 tons of one type of electrical steel sheet. Every 10 000 strokes the punching process is interrupted and measurement test strips are punched by the four different types of electrical steel sheets in rolling direction and transverse to rolling direction. Measurements of the magnetic properties are carried out with a single sheet tester at 50 Hz with a defined sinusoidal waveform of the magnetic polarization. For displaying a trend over constant polarization an averaging over the results of the four electrical steel sheets is done as well as a moving average of the measurement points. The magnetizing demand of test strips shows a continuous increasing up to the last punched test strips. It is shown that the cutting tool reaches a level of wear at about 75 000 punch strokes. From there specific core losses almost have a constant deviation.