Manufacturing method for cylindrical portion

1. A manufacturing method of forming a workpiece from a metal plate, the workpiece including a cylindrical portion in a cylindrical shape protruding in a plate thickness direction of a metal plate and a tooth profile, the cylindrical portion and the tooth profile being formed integrally with the metal plate, the manufacturing method comprising:

plastically forming the cylindrical portion integrally with the metal plate; and

plastically forming the tooth profile after the plastically forming of the cylindrical portion is completed,

wherein the plastically forming of the cylindrical portion uses a manufacturing device including:

a first metal mold provided with an inner circumferential surface that comes in contact with an outer circumferential surface of the cylindrical portion to be formed;

a second metal mold coming in contact with a protruding tip of the cylindrical portion to be formed; and

a third metal mold disposed on an opposite side of the second metal mold with the metal plate therebetween, the third metal mold coming into press contact with the workpiece toward a side of the second metal mold,

wherein, in the plastically forming of the cylindrical portion, the third metal mold is displaced toward the side of the second metal mold and a portion of the metal plate undergoes plastic flow toward the inner circumferential surface, such that the portion of the metal plate that underwent the plastic flow comes into press contact with the inner circumferential surface, and

wherein, in the plastically forming of the tooth profile, the tooth profile is plastically formed on an outer side in a radial direction of the cylindrical portion in the metal plate.

2. The manufacturing method according to claim 1 , further comprising:

performing punching after the plastically forming of the cylindrical portion and before the plastically forming of the tooth profile,

wherein the punching uses the manufacturing device including:

the first metal mold;

the third metal mold; and

a tubular metal mold having an inner diameter substantially identical to the diameter of the third metal mold,

wherein, in the punching, the third metal mold is displaced toward the tubular metal mold and penetrates the protruding tip of the cylindrical portion to provide a through-hole in the protruding tip of the cylindrical portion.

3. The manufacturing method according to claim 1 , wherein

a diameter of the third metal mold is smaller than a diameter of the second metal mold, and

the second metal mold includes a cylindrical projecting portion projecting from an end surface of the second metal mold toward the third metal mold, the cylindrical projecting portion being provided at a position that is opposed to the third metal mold, and having a diameter substantially corresponding to the diameter of the third metal mold.

4. A manufacturing method of forming a workpiece from a metal plate, the workpiece including a cylindrical portion in a cylindrical shape protruding in a plate thickness direction of a metal plate and a tooth profile, the cylindrical portion and the tooth profile being formed integrally with the metal plate, the manufacturing method comprising:

plastically forming an intermediate workpiece including a protruding portion integrally formed with the metal plate;

plastically forming the cylindrical portion, after the plastically forming of the intermediate workpiece; and

plastically forming the tooth profile, after the plastically forming of the cylindrical portion is completed,

wherein, in the plastically forming of the intermediate workpiece, a portion of the metal plate is pressed to undergo plastic flow, so that the protruding portion protrudes from the metal plate in a first direction of the plate thickness direction of the metal plate,

wherein the plastically forming of the cylindrical portion uses a manufacturing device including:

a first metal mold provided with an inner circumferential surface that comes in contact with an outer circumferential surface of the cylindrical portion to be formed;

a second metal mold coming in contact with a protruding tip of the cylindrical portion to be formed; and

a third metal mold disposed on an opposite side of the second metal mold with the intermediate workpiece therebetween, the third metal mold coming into press contact with the workpiece toward a side of the second metal mold,

wherein, in the plastically forming of the cylindrical portion, the third metal mold is displaced in the first direction toward the side of the second metal mold and a portion of the protruding portion undergoes plastic flow toward the inner circumferential surface, such that the portion of the protruding portion that underwent the plastic flow comes into press contact with the inner circumferential surface, and

wherein, in the plastically forming of the tooth profile, the tooth profile is plastically formed on an outer side in a radial direction of the cylindrical portion in the metal plate.

5. The manufacturing method according to claim 4 ,

wherein the plastically forming of the intermediate workpiece uses the manufacturing device including:

a first die coming in contact with a protruding tip of the protruding portion to be formed;

a second die provided with an inner circumferential surface that comes in contact with an outer circumferential surface of the protruding portion to be formed;

a movable punch disposed on an opposite side of the first die with the metal plate therebetween, the movable punch coming into press contact with the metal plate in the first direction toward a side of the first die,

wherein a diameter of the movable punch being greater than a diameter of the first die, and a diameter of the third metal mold is smaller than a diameter of the second metal mold.

6. The manufacturing method according to claim 5 , wherein the movable punch includes a tapered portion at an end of an outer circumferential portion of the movable punch, the tapered portion having a truncated cone shape so as to slope and come closer to the first die as the truncated cone shape approaches the central axis of the movable punch.