Patent ID: 7296454

Claim:
An upsetting method using an extruder equipped with an extrusion nozzle having an extrusion opening at a tip end portion of the extrusion nozzle and a closed-die having a cavity, the closed-die being divided into a plurality of closed-die divided members, the upsetting method, comprising: a clamping step of forming the closed-die by combining the plurality of closed-die divided members so that the tip end portion of the extrusion nozzle is arranged in the cavity with an extruded raw material extruded from the extrusion opening of the extrusion nozzle of the extruder and clamping the extruded raw material with clamping portions provided at the plurality of closed-die divided members; and a diameter expansion step of extruding the extruded raw material from the extrusion opening of the extrusion nozzle with the extruder and expanding an exposed portion of the extruded raw material exposed between the extrusion opening of the extrusion nozzle and the clamping portions of the plurality of divided members while filling the cavity with a material of the exposed portion by moving the plurality of closed-die divided members in a forward direction with respect to an extrusion direction of the extruded raw material relative to the extrusion opening of the extrusion nozzle at a speed slower than an extrusion speed with the extruded raw material clamped by and between the clamping portions of the plurality of divided members.