Method of producing a stator iron core

A method of production of an iron core for a rotary electric machine comprising the steps of:

• forming an iron core blank of the comb shape having a plurality of teeth spaced apart from one another a predetermined distance and extending widthwise at one side of the iron core blank, said iron core blank being formed by blanking from steel strip in such a manner that two iron core blanks can be formed in one operation with the teeth of the two blanks being in staggered relationship;
• forming a plurality of projections on said iron core blank, said projections each having a straight portion and being located on one surface of the iron core blank with said straight portion being perpendicular to said one surface, so that when said blank is spirally wound the projections are disposed equidistantly from one another circumferentially on each of the convolutions of the spirally wound iron core blank, while a plurality of recesses are formed on the other surface of said blank in positions corresponding to the projections on said one surface, said recesses each having a plurality of bulges in positions symmetrical in rotation with respect to the center of the recess;
• winding said iron core blank with said projections and recesses into a spiral form by applying a winding force on said straight portion of each of said projections while subjecting the blank to plastic deformation, and superposing convolutions of the spirally wound blank one above another by inserting the projections in the recesses of the adjacent convolution while forming a clearance between the adjacent convolutions of the spirally wound iron core blank;
• and
• joining the convolutions of the spirally wound iron core blank together by electric resistance welding at the joints of said projections and said recesses of the adjacent convolutions.