The present disclosure provides a method for forging a gear capable of preventing burrs from being formed at an edge of the surface opposite to a direction in which a material in external teeth of the material is pushed. A first exemplary aspect is a method for moving the second punch along a tooth profile groove of the guide die to stack the material and the second punch in this order; and pushing the material and the second punch into a tooth profile groove of the tooth profile die in a stacked state to pass them therethrough, in which a tooth pressing part of the second punch covers at least an edge of a region where external teeth are formed on a surface of the material on the first punch side.

The present invention provides a ring gear and a gear reduction device. The ring gear includes a one-piece annular body made from powder metallurgy material, and a first ring gear part and a second ring gear part formed on a surface of the annular body. The first ring gear part and the second ring gear part are arranged along an axial direction of the annular body. The ring gear has a density that is less than 92% of its theoretical density and in the range of 6.0 to 8.0 grams per cubic centimeter. The present invention further provides a mold for manufacturing the ring gear. The ring gear of the present invention includes two ring gears integrally formed at once, and the two ring gears have improved concentricity.

A method for forging a gear according to the present disclosure includes pushing a material into a molding space of a teeth profile die from one side of the teeth profile die for molding external teeth by a punch, and after the pushing, discharging a gear having the external teeth formed thereon from another side of the teeth profile die by the punch. The method further includes providing a material outer diameter constraint die for constraining an outer diameter of a previous material before the material is pushed into the molding space of the teeth profile die on the one side of the teeth profile die, and setting an inner diameter size of the material outer diameter constraint die to be smaller than a large diameter size of the gear set in the teeth profile die.

The present invention provides a ring gear and a gear reduction device. The ring gear includes a one-piece annular body made from powder metallurgy material, and a first ring gear part and a second ring gear part formed on a surface of the annular body. The first ring gear part and the second ring gear part are arranged along an axial direction of the annular body. The ring gear has a density less than 92% of its theoretical density and a mass of 6.0 to 8.0 grams per cubic millimeter. The present invention further provides a mold for manufacturing the ring gear. The ring gear of the present invention includes two ring gears integrally formed at once, and the two ring gears have improved concentricity.

In the context of a forming method for producing a helical toothing of a cylindrical workpiece by extrusion, a relative movement of a forming tool and of a workpiece blank carried out in a peripheral direction of the forming tool and of the workpiece blank is superimposed on an axial forming movement of the forming tool and of the workpiece blank. Due to a forming relative movement of the forming tool and of the workpiece blank resulting from the mutual superimposition of the axial forming movement and the forming movement in the peripheral direction, the helical toothing of the workpiece is produced on the workpiece blank, in that the forming tool engages, with a shaping helical toothing, in the workpiece blank during the resulting forming relative movement. A forming machine is designed to carry out the aforementioned method.