Method of forging outer joint member of constant velocity universal joint

A method of forging an outer joint member of a constant velocity universal joint from a pre-processing material including a shaft portion and a cylindrical portion formed at one end of the shaft portion,

• the constant velocity universal joint comprising:
• an outer joint member having a spherical inner peripheral surface in which at least eight track grooves are formed;
• an inner joint member having a spherical outer peripheral surface in which at least eight track grooves are formed so as to be paired with the track grooves of the outer joint member as a plurality of pairs of track grooves;
• at least eight balls, which are interposed between the track grooves of the outer joint member and the track grooves of the inner joint member, and are configured to transmit torque;
• and
• a cage, which is interposed between the spherical inner peripheral surface of the outer joint member and the spherical outer peripheral surface of the inner joint member, and is configured to hold the balls, wherein
• the track grooves of the outer joint member and the track grooves of the inner joint member each have an arc-shaped ball raceway center line having a curvature center that is prevented from being offset in an axial direction with respect to a joint center,
• for each of the track grooves of the outer joint member and each of the track grooves of the inner joint member, a plane including the arc-shaped ball raceway center line and the joint center is inclined in a circumferential direction with respect to a joint axial line,
• each pair of the plurality of pairs of track grooves includes one track groove inclined in one direction and another track groove inclined in an opposite direction,
• the method comprising performing ironing by press-fitting the cylindrical portion of the pre-processing material into a hole of a die in a state in which a punch set that is radially expandable and contractable is fitted to an inner peripheral surface of the cylindrical portion,
• the punch set comprising:
• at least a plurality of punches;
• and
• a punch base configured to guide the punches so as to enable advancing and retreating,
• wherein each of the punches is a single element having a pair of forming surfaces for forming an adjacent pair of the at least eight track grooves of the outer joint member.