Method of manufacturing flange structure

A method of manufacturing a flange structure including a first shaft portion, a second shaft portion, and a flange provided between the first shaft portion and the second shaft portion, the method comprising:

• forming a primary product by extending a columnar material in an axial direction by cold or warm forging such that the first shaft portion is formed at the first axial end of the material and the second shaft portion is formed at a second axial end of the material, the primary product forming step including:
• forming the first shaft portion on the first axial end of the material by pushing the material in a first die hole of a first shaft portion die with a first shaft portion punch the first shaft portion die including the first die hole and a first shaft hole that is adapted to form the first shaft portion on the first axial end of the material;
• ejecting the material having the first shaft portion from the first die hole of the first shaft portion die with a knock out pin;
• inverting an orientation of the material having the first shaft portion ejected from the first die hole of the first shaft portion die;
• and
• forming the second shaft portion on the second axial end of the material by pushing the material in a second die hole of a second shaft portion die with a second shaft portion punch, the second shaft portion die including the second die hole and a second shaft hole that is adapted to form the second shaft portion on the second axial end of the material;
• forming a secondary product by making a middle portion of the primary product overhang outwardly by cold or warm forging such that a first overhang having a thickness greater than a thickness of the flange is formed;
• forming a tertiary product by squeezing the first overhang by cold or warm forging such that a second overhang having an outline greater than an outline of the flange is formed, at least a part of an outer circumference of the first overhang being kept free from a constraint by a tertiary product die and a tertiary product punch while the second overhang is being formed;
• and
• defining an outer edge of the flange by cutting off an excessive portion of the second overhang, the excessive portion protruding outwardly from the outline of the flange.