| Cores are manufactured by cutting silicon steel sheets into a specified shape, then laminating and clamping the cut sheets. Punching and cutting process induce stress in silicon steel and consequently magnetic properties near the cutting edge are partially deteriorated. This not only increases energy loss, but also affects the motor’s safety and service life. Therefore, it is important to measure the residual stress near the cutting edge and minimize the deterioration of magnetic properties by means of proper process and heat treatment.In this thesis, the crack initiation and propagation during punching process of silicon steel were deeply studied by ABAQUS. And the rules for the impact of die wear and clearance on punching section quality and residual stress were discussed. The impact laws provided some reference for choosing reasonable clearance.The residual stress near the cutting edge of silicon steel 50WW470 was investigated by nanoindentation method. And the Suresh theoretical model was used to calculate the residual stress with constant displacement. Comparing the results from the X-ray diffraction method, the results showed that it was feasible to estimate the residual stress of silicon steel by nanoindentation method. Besides, laser cutting and Wire Electric Discharge Machining(WEDM) were also studied. We compared the characteristics of the cutting edges of non-oriented silicon steel sheets cut by punching, laser cutting and WEDM. We systematically analyzed the impact laws of three kinds of cutting ways on the microstructure and residual stress of silicon steel.Finally, based on nanaoindentation experiment and FEM, the effects of residual stresses, the depth, friction and other factors on the indentation load displacement cures and indentation morphology were systematically studied. It suggested estimating the nanoindentation process by FEM was feasible and provided useful guidance for the nanoindentation experiment. |
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