The reason of burr for electric motor laminations

At present, the iron core blanking of large electric motors at home and abroad is mainly made of 0.5mn wafer 0.35mm thin electrical silicon sheet.Generally speaking, the reasons of big burr in the punching process are mainly caused by the following aspects.

(1) the die clearance is too large, too small or uneven
The cross - section quality and surface basin quality all have great influence on these three conditions.It can be seen from the analysis of blanking deformation process that if the gap between punch and die is too small.The cracks near the edge of the punch are staggered some distance from the normal clearance range.When the silicon steel sheet is finally separated, the fracture layer will appear a burr layer.Due to the extrusion effect of the concave die edge, a second bright zone is formed on the cutting surface, and there are extrusion burrs or jagged edges on the upper part, which are inverted tapered.If the clearance is too large, the shear cracks near the punch edge stagger a certain distance to the inside than the normal clearance range.When the material is deeply drawn, the inclination of the cutting surface increases. In this way, the silicon steel sheet is easy to be pulled into the original, thus forming an elongated burr.In addition, uneven clearance distribution of die can also cause large burrs on the blanking plate locally, that is, extrusion burrs on the small clearance and elongated burrs on the large clearance.
(2) blunt edge of punching die working part
When the edge of punching die is rounded due to long-term grinding, it can not play a good role in material separation.At this time, the entire section because of tearing and irregular, will produce a larger burr.Especially in blanking when the punch edge and punching when the concave die edge becomes blunt burr is more serious.