Hydraulic cushioning system for press, having shut-off valve for disconnection of pressure-pin cylinders from power supply upon contact of movable die with workpiece

A hydraulic cushioning apparatus for a press having a movable die, comprising a pressure pin associated with a workpiece, a hydraulic cylinder linked with said pressure pin, a cushioning device linked with said hydraulic cylinder, a hydraulic power supply for supplying a pressurized fluid at a preset pressure level to said hydraulic cylinder, and fluid passage means for hydraulically connecting said hydraulic power supply and said hydraulic cylinder, said apparatus comprising:

• a check valve disposed in said fluid passage means, said check valve permitting a flow of said pressurized fluid from said hydraulic power supply to said hydraulic cylinder;
• a shut-off valve disposed in said fluid passage means, in series connection with said check valve, and having an open position and a closed position for connection and disconnection of said hydraulic power supply to and from said hydraulic cylinder, respectively;
• and
• control means connected to said shut-off valve, for controlling said shut-off valve such that said shut-off valve is operated from said open position to said closed position to inhibit a flow of the fluid from said hydraulic power supply into said hydraulic cylinder before said movable die comes into pressing contact with said workpiece, and is held in said closed position for at least a period until a fluid pressure in said hydraulic cylinder rises to said preset pressure level, thereby preventing an increase in the fluid pressure in said hydraulic cylinder above said preset level due to a flow of the fluid into said hydraulic cylinder when said fluid pressure is lower than said preset level.

A hydraulic cushioning apparatus for a press having a movable die, comprising a pressure pin associated with a workpiece, a hydraulic cylinder linked with said pressure pin, a cushioning device linked with said hydraulic cylinder, a hydraulic power supply including a reservoir and a hydraulic pressure source for supplying a pressurized fluid of a preset pressure level to said hydraulic cylinder, and fluid passage means for hydraulically connecting said hydraulic power supply and said hydraulic cylinder, said fluid passage means including a first fluid passage which connects said hydraulic pressure source and said hydraulic cylinder, and a second fluid passage which connects said first fluid passage to said reservoir, said apparatus comprising:

• a first shut-off valve disposed in said first fluid passage means and having an open position and a closed position for connection and disconnection of said hydraulic power supply to and from said hydraulic cylinders, respectively;
• a second shut-off valve disposed in said second fluid passage;
• and
• control means connected to said first and second shut-off valve, for controlling said first shut-off valve such that said first shut-off valve is operated from said open position to said closed position before said movable die comes into pressing contact with said workpiece, and held in said closed position for at least a period until a pressure of said fluid in said hydraulic cylinders rises to said preset pressure level, and for controlling said second shut-off valve such that said second shut-off valve is opened after said movable die has started an upward stroke from a lower stroke and during each pressing cycle in which said movable die is reciprocated between an end of said upward stroke and an end of said lower stroke, said control means holding said second shut-off valve open for a period which expires before said first shut-off valve is operated to said closed position.