PURPOSE: To deeply draw a sink by reducing a frictional resistance between a punch and a blank, by forcing a pair of punches into a die by adding a hydraulic pressure from the bottom of the punch.
CONSTITUTION: A blank 7 is mounted on a die 1 and clamped with a blank holder 6. A working oil is forced into a space between the bottom of punches 5a, 5b and the blank 7 by driving a pump 9 to add a hydraulic pressure P. Hereby, the blank 7 expands in cavities 3a, 3b of the die 1 and at the same time, the drawing of the flange part of the blank 7 clamped between the die 1 and the blank holder 6 begins. At this time, while increasing the hydraulic pressure P, the punches 5a, 5b are forced to press with a prescribed force F1 against a prescribed force F2 of blank supporting plates 11a, 11b. When the forming is advanced, the oil contained in the space between the bottom of the punch and the blank 7 is exhausted through a relief valve 13. By this method, the materials flow smoothly to the central side wall, and the sink is drawn deeply.
SAKAI YOSHIHITO
MUTOO TOMOYOSHI
