When punching, the outer edge and inner hole precision of the punched parts are reduced and the reason for the change in size is:

1. The positions of positioning pins, stopper pins, etc. have changed or are too worn.
2. The operator's negligence caused the material to shift left and right when feeding.
3. The dimensional accuracy of the strip is low. If it is too narrow or too wide, it is difficult to feed the material, making it difficult to deliver it to the designated location. The strip will shift forward and backward in the guide plate, and the inner hole of the punched workpiece will have a large deviation from the front and rear position of the outer shape.