Influence Of Blanking Process Parameters On The Quality Of Non-oriented Silicon Steel Parts

Cold-rolled non-oriented silicon steel with excellent magnetic properties is widely used for all kinds of motor cores. In order to obtain the motor core, the original silicon steel coil material must be processed through slitting, blanking, folding and riveting. Unreasonable blanking process parameters may cause various defects in blanking part. In addition, the residual stress produced on shear edge due to the punching process would deteriorate the magnetic properties of non-oriented silicon steel and reduce the motor efficiency. Therefore, this paper mainly studied the influence of blanking process parameters on the quality of the commonly used non-oriented silicon steel parts. We analyzed the mechanism of blanking defects from the aspects of macroscopic and microscopic and explored the appropriate blanking process parameters.The impacts of die clearance, blanking speed and die condition on the quality of silicon steel parts were studied through laboratory blanking experiment, mass blanking in enterprise and finite element simulation.The burr height, springback, ovality, flatness and cross section were analyzed from the aspect of macroscopic. For the material with 0.5 mm in thickness, the burr height and springback of parts are minimum when the die clearance is between 7% and 9% of the thickness. For the material with 0.35 mm in thickness, the burr height is minimum when the die clearance is between 6% and 12% but the springback is minimum when the die clearance is between 12% and 16%. The die clearance has a great impact on the quality of parts' cross section and flatness. However, the blanking speed has little influence on the quality of parts' cross section.Microstructure, residual stress, microhardness and magnetic domain structure were analyzed to study the influence of blanking process on the micro-quality of blanking parts. The grain distortion caused by the punching process can be seen within the area of 20-80?m from the sheared edge. The width of residual stress affected zone by punching was about 0.5 mm and the width of strain hardening zone was about 0.3 mm. Magnetic domain structure of 50WW470 was observed by the Bitter method. The sample exhibited complicated domain patterns, and the widths of the magnetic domains varied between 3 ?m and 8 ?m. After annealing treatment, the sample had an orderly distribution of domain structure and the widths of the domains decreased to 1-3 ?m. It demonstrated that the magnetic performance of parts would be improved by stress relief annealing.