Method and device for controlling, checking or optimizing pressure of cushion pin cylinders of press by discharging fluid or initial pressure

A device for determining an optimum condition relating to a hydraulic pressure of a plurality of hydraulic cylinders in a cushioning apparatus for a press having an upper die and a lower die which cooperate to perform a pressing action on a blank during a downward movement of the upper die, and a pressure member which cooperates with said upper die to hold said blank during said pressing action, said cushioning apparatus including (a) force generating means for generating a blank-holding force (b) a cushion platen disposed below said lower die and biased toward said lower die by said blank-holding force, (c) said plurality of hydraulic cylinders disposed on said cushion platen and having fluid chambers communicating with each other, and (d) a plurality of cushion pins associated at lower ends thereof with said hydraulic cylinders, respectively, and supporting at upper ends thereof said pressure member, and wherein said blank is held by said upper die and said pressure member during said pressing action, by said blank-holding force which is generated by said force generating means and which is transmitted to said pressure member through said cushion platen, hydraulic cylinders and said cushion pins such that said blank-holding force is substantially evenly distributed on all of said cushion pins by said hydraulic cylinders, said device comprising:

• detecting means for detecting a hydraulic pressure in said hydraulic cylinders;
• initial pressure changing means for changing an initial value of said hydraulic pressure prior to said pressing action, in a plurality of steps at a predetermined rate of change, so that pressing actions in a plurality of pressing cycles are effected at different initial values of said hydraulic pressure;
• calculating means for calculating an amount of change of an in-process value of said hydraulic pressure detected by said detecting means during one of said pressing cycles with respect to an in-process value of said hydraulic pressure detected by said detecting means during a preceding one of said pressing cycles, said amount of change arising from a difference between the initial values established by said initial pressure changing means in said one and preceding pressing cycles;
• judging means for judging whether said amount of change of said in-process value calculated by said calculating means is larger than a predetermined value;
• and
• determining means for determining an optimum condition relating to said hydraulic cylinders, on the basis of an optimum range of said initial value of said hydraulic pressure in which said amount of change of said in-process value is not larger than said predetermined value.

A method of checking an optimum condition relating to a hydraulic pressure of a plurality of hydraulic cylinders in a cushioning apparatus for a press having an upper die and a lower die which cooperate to perform a pressing action on a blank during a downward movement of the upper die, and a pressure member which cooperates with said upper die to hold said blank during said pressing actions said cushioning apparatus including (a) force generating means for generating a blank-holding force, (b) a cushion platen disposed below said lower die and biased toward said lower die by said blank-holding force, (c) said plurality of hydraulic cylinders disposed on said cushion platen and having fluid chambers communicating with each other, and (d) a plurality of cushion pins associated at lower ends thereof with said hydraulic cylinders, respectively, and supporting at upper ends thereof said pressure member, and wherein said blank is held by said upper die and said pressure member during said pressing action, by said blank-holding force which is generated by said force generating means and which is transmitted to said pressure member through said cushion platen, hydraulic cylinders and said cushion pins such that said blank-holding force is substantially evenly distributed on all of said cushion pins by said hydraulic cylinders, said method comprising the steps of:

• lowering said upper die to a predetermined blank-holding position for abutting contact with said pressure member;
• detecting a plurality of values of a hydraulic pressure of a working fluid in a hydraulic circuit including said hydraulic cylinders, at a predetermined time interval while said upper die is held in said predetermined position and while an amount of said working fluid in said hydraulic circuit is changed;
• and
• determining an optimum range of the hydraulic pressure in which said hydraulic pressure is substantially constant irrespective of a change in said amount of the fluid in said hydraulic circuit as a function of time.