Method of manufacturing outside joint member

A method of manufacturing an outside joint member, the outside joint member including a cup portion in a bottomed tubular shape and a shaft portion that is a shaft-like portion extending from a bottom portion of the cup portion and that has a spline shaft having an outer peripheral surface on which spline teeth are formed, the manufacturing method comprising:

• forging a forming material to form a shape of the cup portion and a shape of the spline shaft on the shaft portion simultaneously using a forging die,
• wherein the forging die includes a first die, a second die housed in the first die, and a third die disposed on an entrance side with respect to the first die and the second die, in which the first die, the second die, and the third die are disposed coaxially with each other,
• wherein the first die includes a first housing portion and a second housing portion provided on an entrance side of the first housing portion, the first housing portion including a first cylindrical inner peripheral surface with an inside diameter that is larger than an outside diameter of the forming material at which the shaft portion is formed, the second housing portion including a second cylindrical inner peripheral surface with an inside diameter that is larger than the inside diameter of the first cylindrical inner peripheral surface, the second die being housed inside the second housing portion,
• wherein the third die includes a third cylindrical inner peripheral surface with an inside diameter corresponding to an outside diameter of the cup portion,
• wherein the second die includes a spline shaping portion and a regulation portion, the spline shaping portion having an inner peripheral surface shape corresponding to an outer shape of the spline shaft and configured to shape the spline teeth at a portion at which the spline shaft is to be formed in the forging, and the regulation portion being provided on an entrance side with respect to the spline shaping portion and having a regulation surface that regulates displacement of the forming material in a radial direction,
• wherein the spline shaping portion includes spline shaping teeth and distal end teeth, the spline shaping teeth corresponding to a plurality of tooth grooves provided in the spline shaft, and the distal end teeth being provided continuously with the spline shaping teeth on the entrance side of the spline shaping portion, the distal end teeth becoming narrower toward the entrance side of the spline shaping portion,
• wherein each of the spline shaping teeth includes a shaping tooth top surface corresponding to a bottom surface of each of the tooth grooves of the spline shaft and a pair of shaping tooth side surfaces corresponding to side surfaces of each of the tooth grooves of the spline shaft, and
• wherein each of the distal end teeth includes a distal end tooth top surface and a pair of distal end tooth side surfaces, the distal end tooth top surface being provided continuously with the shaping tooth top surface on the entrance side of the spline shaping portion and becoming smaller in height toward the entrance side of the spline shaping portion, and the pair of distal end tooth side surfaces being provided continuously with the pair of shaping tooth side surfaces on the entrance side of the spline shaping portion and becoming smaller in width in a circumferential direction toward the entrance side of the spline shaping portion.