Vehicle wheel disk and a manufacturing method thereof

A manufacturing method of a vehicle wheel disk for manufacturing a wheel disk for a vehicle from a disk material,

• wherein the wheel disk comprises:
• a hat including a hat top, a radially outer hat portion and a radially inner hat portion;
• a disk flange;
• a first disk position (D1) located outer than the hat top in a radial direction of the disk and inner than the disk flange in the radial direction of the disk;
• a second disk position (D2) located at a boundary between the radially outer hat portion and the disk flange;
• a third disk position (D3) located at an inner end of the disk flange in an axial direction of the disk;
• and
• a fourth disk position (D4) located inner than the second disk position (D2) in the axial direction of the disk and outer than the third disk position (D3) in the axial direction of the disk,
• the disk flange extending straight in the axial direction of the disk in a cross section taken along a radially extending plane of the disk,
• wherein before the disk material is formed to the wheel disk, the disk material includes:
• a first material position (M1),
• a second material position (M2),
• a third material position (M3), and
• a fourth material position (M4) which are brought to the first disk position (D1), the second disk position (D2), the third disk position (D3) and the fourth disk position (D4), respectively, after the disk material has been formed to the wheel disk,
• the method comprising:
• a first step for ironing a portion or an entirety of a disk material portion from M1 to M2 to a cylindrical portion having a thickness smaller than a thickness of the disk material portion before ironing;
• and
• a second step for changing a diameter of at least one of a disk material portion between M2 and M3 and a disk material portion at M1 so that the disk material portion between M2 and M3 becomes larger in diameter than the disk material portion at M1.