Center hole forming method and forging device

3:

• A forging device, comprising:
• a first die having a die hole for shank extruding;
• a second die arranged in a large diameter side of the die hole and configured to apply a load to an object to draw a shaft from the object, the object being inserted in the die hole;
• a die drive section configured to drive the second die;
• a counter punch arranged in a small diameter side of the die hole and configured to be pressed against a first axial end surface of the object to form a center hole in the first axial end surface;
• a counter punch drive section configured to drive the counter punch;
• and
• a controller configured to control the die drive section and the counter punch drive section, wherein
• the controller is configured to control the die drive section and the counter punch drive section to apply a load toward the first axial end surface to a second axial end surface of the object by the second die,
• the controller is configured to control the die drive section and the counter punch drive section to form, after the shaft is drawn from the object, the center hole in the first axial end surface by the counter punch in a state that the load is applied to the second axial end surface, and
• a diameter of the first axial end surface is smaller than a diameter of the second axial end surface.

5:

• The forging device according to claim 4, wherein
• the movement control mechanism is configured to be switchable between a movement prohibition state and a movement permission state,
• in the movement prohibition state, once the counter punch reaches the specified position, the counter punch is prohibited from moving beyond the specified position toward the object, and
• in the movement permission state, even after the counter punch reaches the specified position, the counter punch is permitted to move beyond the specified position toward the object.

7:

• The forging device according to claim 3, further comprising:
• a movement control mechanism including a first moving block and a second moving block, the first moving block and the second moving block being provided in the first die, wherein
• the counter punch includes a small diameter part and a large diameter part, a diameter of the small diameter part being equal to or smaller than a diameter of an opening of the die hole, the opening being opposite the counter punch, a diameter of the large diameter part being larger than the diameter of the small diameter part,
• the first moving block is movable in a direction that is perpendicular to an axial direction of the counter punch,
• the second moving block is movable in the axial direction,
• the second moving block is configured to move in conjunction with movement of the second die,
• the first moving block is configured to move in conjunction with movement of the second moving block, and
• the first moving block is located in contact with an end surface of the large diameter part in the axial direction when the counter punch is located at the specified position in a state that the first die and the second die collide with each other.

8:

• The forging device according to claim 7, wherein
• a first inclined surface is formed at an end of the first moving block,
• a second inclined surface is formed at an end of the second moving block, and
• the first inclined surface and the second inclined surface are in contact with each other.

9:

• The forging device according to claim 7, wherein
• the movement control mechanism includes a rod and a spring,
• the rod is connected to the first moving block and penetrates the first die,
• the spring is arranged between a tip of the rod and an outer surface of the first die, and
• the spring is configured to be compressed and extended in conjunction with movement of the first moving block.

10:

• The forging device according to claim 8, wherein
• the movement control mechanism includes a rod and a spring,
• the rod is connected to the first moving block and penetrates the first die,
• the spring is arranged between a tip of the rod and an outer surface of the first die, and
• the spring is configured to be compressed and extended in conjunction with movement of the first moving block.