Wheel disc manufacturing method and wheel disc

A manufacturing method for a wheel disc including an annular flange portion provided in an outer periphery so as to extend inwardly in a vehicle width direction generally in parallel with a wheel axial direction,

• the flange portion including a plurality of base portions provided in a plurality of ranges different from each other in a wheel circumferential direction and having a uniform basic length in the wheel axial direction, and
• a plurality of window portions each provided between the base portions adjacent to each other in the wheel circumferential direction and having a length, in the wheel axial direction,
• shorter than the basic length,
• the manufacturing method comprising:
• forming the flange portion such that an outer edge of a disc material in which the flange portion has not been formed is bent inwardly in the vehicle width direction over a whole circumferential region so as to be generally in parallel with the wheel axial direction,
• the disc material including a hub attachment portion with a hub hole and a hub attachment surface,
• the hub attachment portion having a disc shape that extends continuously around the hub hole and that is configured to extend around a wheel shaft, wherein:
• in the forming of the flange portion,
• the flange portion is formed such that,
• in a state where the disc material is coaxially put on an inner mold having a cylindrical outer surface with a first outside radius,
• the inner mold and an outer mold, which has a cylindrical inner surface with a first inside radius larger than the first outside radius and is placed above the inner mold coaxially with the inner mold, are brought close relative to each other in the wheel axial direction by one stroke so that the outer edge of the disc material is bent downward;
• and
• the cylindrical inner surface of the outer mold is provided with recessed portions hollowed outwardly in a wheel radial direction,
• the recessed portions being located at positions aligned with the window portions in the wheel circumferential direction and formed in a range from a middle position to a bottom end in the wheel axial direction.