Cushion pin pressure equalizing device, die cushion device with cushion pin pressure equalizing function and cushion pin pressure equalizing method

A die cushion device with a cushion pin pressure equalizing function, comprising:

• a plurality of cushion pins inserted through a bolster of a press machine;
• a cushion pad configured to support a blank holder via the plurality of cushion pins;
• a hydraulic cylinder configured to support the cushion pad and generate a die cushion load to be applied to the cushion pad;
• a first hydraulic device configured to supply first working fluid to an ascending-side pressurizing chamber of the hydraulic cylinder or discharge the first working fluid from the ascending-side pressurizing chamber;
• a first pressure detector configured to detect a first pressure in the ascending-side pressurizing chamber of the hydraulic cylinder;
• a first controller configured to control the first hydraulic device based on the first pressure detected by the first pressure detector so that the die cushion load generated by the hydraulic cylinder becomes a set target die cushion load;
• a hydraulic cylinder group provided on the cushion pad in which lower ends of the cushion pins that are inserted through the bolster are brought into abutment with piston rods of the hydraulic cylinder group, and ascending-side pressurizing chambers of the hydraulic cylinder group are in communication with each other;
• a second hydraulic device configured to supply second working fluid to the ascending-side pressurizing chambers of the hydraulic cylinder group or discharge the second working fluid from the ascending-side pressurizing chambers;
• a second pressure detector configured to detect a second pressure in the ascending-side pressurizing chambers of the hydraulic cylinder group;
• an initial pressure setting unit configured to set an initial pressure in the ascending-side pressurizing chambers of the hydraulic cylinder group;
• and
• a second controller configured to control the second hydraulic device based on the initial pressure set by the initial pressure setting unit and the second pressure detected by the second pressure detector so that the second pressure in the ascending-side pressurizing chambers of the hydraulic cylinder group becomes the initial pressure before the die cushion load starts to be applied, and
• wherein the initial pressure setting unit sets the initial pressure based on (1) a total volume of the ascending-side pressurizing chambers of the hydraulic cylinder group and a pipe line, (2) a minimum volume change amount of the ascending-side pressurizing chambers of the hydraulic cylinder group when a variation in height of the plurality of cushion pins is absorbed, and (3) a volume elastic modulus of the second working fluid so that the second working fluid has a third pressure corresponding to a lowest die cushion load of the set target die cushion load when the total volume of the second working fluid having the initial pressure is compressed by the minimum volume change amount.

A cushion pin pressure equalizing method for a die cushion device including a plurality of cushion pins inserted through a bolster of a press machine, a cushion pad configured to support a blank holder via the plurality of cushion pins, a die cushion load generator configured to generate a die cushion load to be applied to the cushion pad, and a die cushion controller configured to control the die cushion load generator so that the die cushion load generated by the die cushion load generator becomes a set target die cushion load, the cushion pin pressure equalizing method comprising:

• preparing a hydraulic cylinder group provided on the cushion pad in which lower ends of the cushion pins that are inserted through the bolster are brought into abutment with piston rods of the hydraulic cylinder group, and ascending-side pressurizing chambers of the hydraulic cylinder group are in communication with each other;
• setting an initial pressure for the ascending-side pressurizing chambers of the hydraulic cylinder group;
• and
• controlling a first pressure of a working fluid sealed in the ascending-side pressurizing chambers of the hydraulic cylinder group so that the first pressure in the ascending-side pressurizing chambers of the hydraulic cylinder group becomes the set initial pressure while the cushion pad is waiting in one operation cycle of the press machine,
• wherein, in the setting of the initial pressure, the initial pressure is set based on (1) a total volume of the ascending-side pressurizing chambers of the hydraulic cylinder group and a pipe line, (2) a minimum volume change amount of the ascending-side pressurizing chambers of the hydraulic cylinder group when a variation in height of the plurality of cushion pins is absorbed, and (3) a volume elastic modulus of the working fluid so that the working fluid has a second pressure corresponding to a lowest die cushion load of the set target die cushion load when the total volume of the working fluid having the initial pressure is compressed by the volume change amount.