PURPOSE: To wholly remove residual billets in the die and to prevent a poor press-fit by forming both side faces of the front end of the bridge part in the extrusion direction into an inclined face part having a restricted tilt angle and by restricting the front end width of the both inclined face part.
CONSTITUTION: The tilt angle θ of the inclined face parts 12, 12 of the both front end sides in the extrusion direction of the bridge part 9 of the bridge type extrusion working die 6 equipped with plural bridge part 9 supporting the core 10 on the male die 7 is made to be in the range of 20W30°. At this case, when it is under 20°, the intensity of the front end part of the bridge part becomes difficult to keep, and if it exceeds 30°, the billet is not pulled out sufficiently. Further, the width (l) of the front end face is set in the range of 0.5W4mm. At this case, when the width (l) is under 0.5mm, the crack is apt to generate during the extrusion working and if it exceeds over 4mm, the billet is possible to remain.
MIYATE YUKIHIRO
IIZUKA KOICHI
OKUBO KUNIO
MORITA TADAAKI
