The expansion machine is to expand the copper wire together to facilitate the turning operation of the back process. The device uses 16 expansion claws, and the device can expand 16 sets of copper wires at a time. When the expansion claw is stuck and the copper wire is pulled outward, the stator moves downward at the same time to compensate for the change in the size of the copper wire end from the iron core end due to the outward expansion.

The order of expansion is: starting from the outer two layers in turn, the two layers are expanded together, and the inner two layers of copper wire are not expanded.