Abstract: A grooved nut including a cylindrical shaft portion having a screw hole at the center, a head portion whose outer periphery is polygonal and which is provided at one end portion of the shaft portion, and a peripheral groove provided at a boundary part between the head portion and the shaft portion, in which the peripheral groove is formed by a plasticizing process.

Abstract: An apparatus for full-enclosed die forging for forging a material into a workpiece having concavities on its opposite end surfaces including a first die provided on a stationary frame. A second die is provided on a movable frame which moves toward and away from the stationary frame to come into and out of contact with the first die. A first punch on the stationary frame and a second punch on the movable frame plunge into a cavity formed by the closed pair of these dies from the opposite sides. The first die is movable in a forging direction in a die housing provided on the stationary frame and is forced to the second die by a first spring member in the die housing. A plurality of die engaging members are housed in the die housing, and are disposed at the surrounding of the first die and are biased into the die housing.

Abstract: The invention provides an apparatus for full enclosed die forging having a stationary die, a movable die toward and away from the stationary die and punches which plunge into a work in the closed dies to form tools. After the stationary die in the die housing and the movable die on the ram are closed, the closed pair of dies is moved in a forging direction into the inside of the die housing. In the die housing is equipped an annular engaging member which is movable in the forging direction and shrinkable toward the closed pair of dies in the die housing. The annular engaging member is thrusted into the inside of the die housing along with the closed pair of dies by thrusting means. Shrinking means is provided for shrinking the annular engaging member toward the closed pair of dies in the die housing as the annular engaging member is thrusted into the die housing so that the annular engaging member engages with the closed pair of dies and clamp them tightly.

Abstract: The invention provides a multi-stage forging apparatus for forging a work in transportation through a plurality of forging stations each provided with a die and a punch so that the work is progressively refined, in which the position of the work is changed during the forging procedure. A work, for example, consisting of a shank and a ring-shaped head can be produced. The forging apparatus includes a position change station having a rotation unit instead of a die. The rotation unit contains a pair of rotation bodies with gears. The gears are engaged with racks rotated synchronously with the movement of a crank shaft. When an intermediate work consisting of a shank and a ball-like head is driven into a space between the rotation bodies, the rotation bodies are rotated so as to shift the intermediate work to a vertical position where the shank extends perpendicularly to the driving direction of a punch, and the vertically positioned intermediate work is pushed out of the rotation unit by a knockout pin.