Vehicle wheel disc and manufacturing method of vehicle wheel disc

A manufacturing method of a vehicle wheel disc, the manufacturing method comprising:

• a thinning step of performing a thinning process that is a spinning process or a flow forming process on a flat plate-shaped metal disc material, at a hat-outer-peripheral-portion-corresponding portion that is to be the hat outer peripheral portion later, to form a first intermediate shaped body including a truncated conical portion in which a substantially entire region of a side surface is formed by the hat-outer-peripheral-portion-corresponding portion having a smaller plate thickness than a portion other than the hat-outer-peripheral-portion-corresponding portion and which protrudes outward in a disc axial direction;
• a first drawing step of performing, on the first intermediate shaped body, a first drawing process of further pulling a portion of the first intermediate shaped body, inward of the hat-outer-peripheral-portion-corresponding portion in the disc radial direction, toward an outside in the disc axial direction, to form a second intermediate shaped body including a truncated conical portion in which a base end-side portion of a side surface is formed by the hat-outer-peripheral-portion-corresponding portion having the smaller plate thickness than the portion other than the hat-outer-peripheral-portion-corresponding portion and which protrudes outward in the disc axial direction;
• a second drawing step of performing, on the second intermediate shaped body, a second drawing process of pressing a portion of the second intermediate shaped body, inward of the hat-outer-peripheral-portion-corresponding portion in the disc radial direction, toward an inside in the disc axial direction, to form a third intermediate shaped body including a hub-mounted-part-corresponding part that is to be the hub-mounted part later and a hat-shaped-part-corresponding part that is to be the hat-shaped part later;
• and a finishing step of performing a finishing process including one or more predetermined processes on the third intermediate shaped body to form the vehicle wheel disc.