Wheel disc manufacturing method and wheel disc

A manufacturing method for a wheel disc that has an annular flange at an outer periphery of the wheel disc, the annular flange extending inwardly in a vehicle width direction generally parallel to a wheel axial direction, the annular flange including a plurality of base portions and a plurality of window portions that alternate with each other around a circumference of the annular flange, each of the base portions having a uniform basic length in the wheel axial direction extending from a bottom of the annular flange to an outermost edge of the annular flange, and each of the window portions having a length in the wheel axial direction extending from the bottom of the annular flange to the outermost edge of the annular flange that is shorter than the basic length, so that the outermost edge of the annular flange has a plurality of recesses corresponding to the window portions, the manufacturing method comprising:

• forming the annular flange by bending an outer edge of a disc material in which the annular flange has not been formed inwardly in the vehicle width direction over an entirety of a circumference of the disc material so that the annular flange is generally parallel to the wheel axial direction, wherein:
• in the forming of the annular flange, (i) the disc material is coaxially placed on an inner mold having a cylindrical outer surface with a first outside radius, (ii) an outer mold having a cylindrical inner surface with a first inside radius larger than the first outside radius is placed above the inner mold coaxially with the inner mold, and (iii) the inner and outer molds 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,
• the cylindrical inner surface of the outer mold is provided with a plurality of recessed portions corresponding in number to the plurality of window portions, each of the recessed portions having a second outside radius larger than the first outside radius, the recessed portions being formed at locations corresponding to locations of the window portions in a wheel circumferential direction and extending in the wheel axial direction from a location between top and bottom ends of the outer mold to the bottom end of the outer mold, and
• the recessed portions are aligned with the window portions when the inner and outer molds are brought close relative to each other in the wheel axial direction by the one stroke so that the outer edge of the disc material is bent downward.