Patent ID: 7221072

Claim:
A method of fabricating a helical core, comprising: a stamping step of blanking a pair steel plate cores in two rows from an electrical steel sheet to form a pair of bases confronting each other in a width direction and teeth protruding from each of the bases to alternately cross with each other; providing at least one ejector concavity to the teeth so as to facilitate separation of the steel plate cores blanked in two rows from the electrical steel sheet; and a winding step of helically stacking the steel plate core from a bottom layer to a top layer to configure a multi-layer structure, wherein the stamping step includes forming each of the teeth to include a tip having a bottom surface facing the base of the steel plate core, and wherein the step of providing the at least one ejector concavity includes forming the at least one ejector concavity having a curved recess in the bottom surface of each of the tips.