| 主权项 |
1. A method of manufacturing a rotor core having a cylindrical boss section formed with an axial hole extending in an axial direction, a disc section radially extending from one end of the boss section, and a plurality of claw sections provided at equal intervals along an outer periphery of the disk section so as to extend in the axial direction toward the other end of the boss section, comprising:
a preliminary shaping step of shaping a billet to have a part of the axial hole on a side of the boss section as a boss section-side hole, the boss section, and preliminary shape portions of the claw sections, the billet being disposed on a lower mold formed with an annular groove with a column-shaped projection located at a center of the annular groove, and pressed by an upper mold so that the billet is formed with the disk section at an upper surface thereof, and simultaneously formed with the boss section side-hole and the boss section; a flush/punch through step of ejecting burrs occurred during the preliminary shaping step and shaping a remaining part of the axial hole on a side of the disk section as a disk section-side hole; an ironing step of bending the preliminary shape portions of the claw sections to form claw bent portions and claw tip portions, and taper-shaping the claw tip portions; and a sizing step of performing finish shaping to achieve necessary thickness and flatness of the boss section, wherein, the billet is formed with the boss section-side hole by plastic deformation in the preliminary shaping step, and the remaining part of the axial hole of the billet disposed on a die is punched through using a center hole punch having a diameter smaller than an inner diameter of the boss section-side hole to form the disk section-side hole in the flush/punch through step, so that the axial hole is constituted of the boss section-side hole, the disk section-side hole and a step portion between the boss section-side hole and the disk section-side hole. |
