Method of manufacturing a large- or medium-sized wheel disk and a product manufactured thereby

A method of manufacturing a large- or medium-sized wheel disk comprising:

• a first step of forming a blank of a flat plate as a material by ironing to a first-stage product having a cylindrical rising portion of an axially non-constant thickness using a punch and a die, the punch having a convex-concave side surface formed in a form of a wave having at least one convex portion and at least one concave portion connected to each other via an inclined surface inclined relative to an axial direction of the punch, the first-stage product including a thick portion located at a tip portion of the rising portion and a thickness-reduced portion which is a remaining portion of the rising portion excluding the thick portion, and
• a second step conducted after the first step, of diametrically enlarging an entirety of the rising portion of the first-stage product to form a conical rising portion thereby forming the first-stage product to a second-stage product,
• a third step, the third step being conducted after the second step, of forming a tip portion of the second-stage product to a final disk configuration thereby forming the second-stage product to the third-stage product, wherein
• the wheel disk includes a conical portion and a disk flange, the conical portion being thinned by ironing and having the non-constant thickness, and the wheel disk includes a surface made by ironing at a portion of the conical portion of the wheel disk, and
• during the first step, the thickness-reduced portion of the rising portion is ironed.