To prevent a core from being pushed back by pressurized hydraulic fluid from a high load accompanying casting pressure of molten metal during casting and pressurizing in a core driving cylinder of a die casting machine.
A boosting cylinder 2a communicating to a head side cylinder chamber 22 of an operation cylinder 1 at a boosting chamber 31 side and a control hydraulic circuit are provided. When a load and a rated pressure Pp of a hydraulic pump 25 are balanced during insertion and setting of a core 41, a check valve 21 is closed, then, a sequence valve 34 is opened to make the boosting cylinder 2a depart and to increase pressure of the head side chamber 22. A boost ratio of the boosting cylinder 2a is set to a pressure higher than a pressure in the head side cylinder 22 generated by casting pressure, and a discharge amount of the boosting cylinder 2a is set to a value equivalent to hydraulic fluid compression amount of the head side cylinder chamber 22. The compression amount is automatically corrected by departure of the boosting cylinder 2a.
KITAMURA HIROSHI
KOMATSU SATOSHI