Forging die and upset forging method

An upset-forging method comprising:

• imparting a back-pressure to an upper pin provided in an upper punch and to a lower pin provided in a lower punch by supplying hydraulic oil to hydraulic cylinders;
• contacting under pressure a lower surface of said upper punch to an upper surface of a molding die under a state where a tip portion of said upper pin is protruded from the lower surface of said upper punch and a tip portion of the lower pin is protruded from an upper surface of the lower punch thereby to close a cavity;
• subsequently pressing a raw material into said cavity using the upper and lower pins so that the raw material flows into said cavity, simultaneously pressing the raw material at a portion between the upper punch and the lower punch so that said cavity is filled up with the raw material until a time just before the raw material has completely filled said cavity;
• and
• thereafter, further pressing said raw material using the upper and lower punches under a state that said back-pressures on the upper and lower pins are removed by switching a solenoid valve provided between the hydraulic cylinders and an oil tank to a communicating position so that the hydraulic oil is discharged from the hydraulic cylinders to the hydraulic oil tank thereby to mold the raw material in a final shape.

An upset-forging method comprising:

• tightly closing a cavity by contacting, under pressure, a lower surface of an upper punch to an upper surface of a molding die;
• imparting a back-pressure to an upper pin provided in the upper punch and to a lower pin provided in a lower punch by supplying a hydraulic oil to hydraulic cylinders for applying a back-pressure to the upper and lower pins, so that a tip portion of said upper pin is protruded from a lower surface of the upper punch and a tip portion of the lower pin is protruded from an upper surface of the lower punch and a raw material in the cavity is then pressed by means of the tip portions so that said raw material flows into the cavity, and simultaneously pressing the raw material at a portion between the upper punch and the lower punch whereby said cavity is filled up with the raw material until a time just before the raw material has completely filled said cavity;
• and
• thereafter, further pressing said raw material using the upper and lower punches under a state that the back-pressures on the upper and lower pins are removed by switching a solenoid valve provided between the hydraulic cylinders and an oil tank to a communicating position so that the hydraulic oil is discharged from the hydraulic cylinders to the hydraulic oil tank thereby to mold the raw material in a final shape.