Work Hardening Distribution and Iron Loss of Electrical Steel after Punching Process

The iron loss of the electrical steel sheet increases dramatically due to the plastic strain and work hardening after punching process. This effect also reduces the overall efficiency of the motor, and the iron loss effect of electrical steel sheet in the punching process is difficult to predict and control. So, in this research will discuss the iron loss in punching process. In order to find out the reason of the iron loss in punching process, this research will discuss the slot of stator, the parameter of punching process and the quality of cutting edge. To discuss the effect of punching process, work hardening distribution and estimated iron loss is used to be a standard of comparison. In the experiment of the slot of stator, three slots with different fillet radius was discussed. The fillet radius of upper part has 0.254mm, 1mm and 2mm. The fillet radius of bottom part has cusp angle, 0.254mm and 0.4mm. The results show that the hardening area and the iron loss in the fillet area will reduce when increasing the fillet radius. When the fillet radius exceeds 1mm, the iron loss will increase due to the fillet area increase. The best design of slot can reduce 16% of iron loss. In the experiment of the parameter of punching process, the hardening area and the iron loss can be reduced by raising the punching speed, punching with vibration mode and large amplitude or raising blank holder and counter punch pressure. In these four parameters, adjusting punching mode makes biggest effect on reducing iron loss. When using vibration mode and amplitude 80μm can reduce 30% of iron loss. In part of the quality of cutting edge, the work hardening will be severe when measuring in deeper depth, and relates to the part of cutting edge. Adjusting the parameter of punching process can change the distribution of cutting edge.