Patent ID: 8800335

Claim:
A method of manufacturing a flange through a ring rolling process using a ring rolling machine which includes a main roll for pressing a circumferential outer surface of a blank, a pressure roll for pressing a circumferential inner surface of the blank, and a pair of axial rolls for pressing upper and lower surfaces of the blank, the method comprising: expanding by ring rolling an inner diameter and outer diameter of the blank using the ring rolling machine; transferring the pressure roll vertically so that a protrusion provided on a circumferential outer surface of the pressure roll comes into contact with the circumferential inner surface of the blank; and forming by ring rolling a depression in the circumferential inner surface of the blank using the protrusion of the pressure roll, wherein in said forming the depression, as a thickness of the blank changes from S 1 to S 2 , a cross-sectional area A 1 of the protrusion and a cross-sectional area A 2 of the depression satisfy Equation (a), where Equation (a) is S 1 >S 2 (1+A 1 /A 2 ).