Die cushion system for press machine

Abstract

The present invention relates to a die cushion system for press machine where elevation of a lower press die is controlled in relation to the elevation of an upper press slide in a press machine, the die cushion system for press machine comprising: a hydraulic cylinder supporting and driving a press die; a proportional flow control valve supplying working fluid to a lower port of the hydraulic cylinder to raise it and receiving the working fluid within the hydraulic cylinder for discharging it while the hydraulic cylinder is being lowered; a constant pressure supplying means supplying pressured fluid to an upper port of the hydraulic cylinder to lower the hydraulic cylinder; and a controller controlling operation of the proportional flow control valve to adjust lowering and raising of the press die according to the position of the press slide through a slide position detector and a die cushion position detector, and during the lowering process of the press slide, the controller enabling the press die to exert multi-level reacting force onto the press slide. Accordingly, response speed of the die cushion in relation to the press slide is enhanced to exert forming pressure of various patterns so that elastic restoration and residual stress due to a plastic deformaton of a subject of press forming can be minimized.

1 . A die cushion system for press machine comprising:
 a hydraulic cylinder supporting and driving a press die disposed at a lower side in relation to a press slide driven to be raised and lowered at an upper side;   a proportional flow control valve receiving working fluid from a tank via a first pump and supplying it to a lower port of the hydraulic cylinder to raise the hydraulic cylinder, and receiving the working fluid within the hydraulic cylinder from the lower port and discharging it to the tank while the hydraulic cylinder is being lowered;   a constant pressure supplying means receiving pressured fluid from the tank via a second pump and supplying it to an upper port of the hydraulic cylinder to lower the hydraulic cylinder with the pressured fluid;   a slide position detector for detecting position of the press slide;   a die cushion position detector for detecting position of the press die; and   a controller controlling operation of the proportional flow control valve to adjust lowering and raising of the press die according to the position of the press slide through the slide position detector and the die cushion position detector, and during the lowering process of the press slide, the controller controlling the operation of the proportional flow control valve so that the press die can exert multi-level reacting force onto the press slide.   
     
     
         2 . The die cushion system for press machine according to  claim 1  wherein the multi-level reacting force is controlled to generate an initial load at the time the press slide is lowered and starts contacting the press die, a maximum load greater than the initial load and a final load smaller than the initial load. 
     
     
         3 . The die cushion system for press machine according to  claim 2  wherein a first interim load smaller than the initial load is generated between the initial load and the maximum load, and a second interim load smaller than the final load is generated between the maximum load and the final load. 
     
     
         4 . The die cushion system for press machine according to  claim 3  wherein at least one of the first interim load and the second interim load is 0 (zero) load. 
     
     
         5 . The die cushion system for press machine according to  claim 4  wherein the press slide and the press die are separated from each other during the 0 (zero) load. 
     
     
         6 . The die cushion system for press machine according to  claim 1  wherein the controller controls the operation of the proportional flow control valve for the press die to be lowered at a speed lower than that of the press slide so as to relieve contacting impact at the time the press slide is lowered and start to contact the press die.