Patent ID: 7694408

Claim:
A method of manufacturing a cylindrical yoke of a rotary electric machine wherein a cutout steel plate, having one end formed with a plurality of concave portions and the other end formed with a plurality of protrusions, has a cylindrically rolled shape with the protrusions being inserted into the concave portions, respectively, to mechanically joint the both ends of the steel plate, the method comprising: providing a cutout steel plate having one end formed with a plurality of concave portions, each of which has a bottom wall and axially spaced sidewalls extending from both ends of the bottom walls and circumferentially extending in substantial parallel to each other, and the other end formed with a plurality of protrusions, each of which has sidewalls extending from the other end of the steel plate and circumferentially extending in substantial parallel to the sidewalls of each concave portion and having a width and a circumferential depth substantially equal to or slightly less than a width and a circumferential depth, respectively, of each concave portion, wherein the sidewalls of each concave portion have indents axially facing with each other to mate with each protrusion; rolling the cutout steel plate into a cylindrical shape until a distal end of each protrusion faces the inlet of each concave portion; inserting the protrusions into the concave portions, respectively, in a circumferential direction until the distal end of each protrusion is brought into contact with the bottom wall of each concave portion and both ends of the steel plate are brought into contact with each other; and conducting punch-caulking press on each protrusion at near-wall areas on both sides thereof in close proximity to the indents of each concave portion to form localized expanding portions at the near-wall areas on both sides of each protrusion while causing the localized expanding portions to flow axially outward to be fitted into the indents of each concave portion, respectively, such that the distal end of each protrusion and the bottom wall of each concave portion are brought into abutting engagement with each other with no clearance.