Patent GB-928545-A (GB)
Title: Control of hydraulic forging presses
IPC: B21J9/12
Filed: 1961-06-30
Abstract: 928,545. Forging. SCHLOEMANN A.G. June 30, 1961 [July 21, 1960], No. 23690/61. Class 83 (4). [Also in Group XXIX] A process for controlling an hydraulic forging press having valves controlled according to the position and direction of movement of the upper die of the press comprises generating impulses which are dependent on the position and direction of movement of the upper die and are used to produce switching signals to be fed to a control means for the valves to effect control of the movement of the upper die. The press has a bed 4 supporting a lower die 5 and a transom 2 which carries the upper die 5 and is lowered by supplying hydraulic fluid to a ram 9 through one or other of valves 46, 47 and is raised by supplying hydraulic fluid through a valve 48 to retracting cylinders 6; the valve 46 controls a supply of fluid at low pressure for filling the cylinder of ram 9 and the valve 47 controls a supply of high pressure fluid. The transom 2 is connected by a rod 13 and rack-and-pinion mechanism 14, 15 to an impulse generator 17 which feeds a negative or positive impulse, depending on the direction of movement of the die, for each millimetre of movement of the die to an indicator 19 connected to a control difference counter 31 also connected to an impulse generator 27 having an automatic or manuallyoperable control for producing negative or positive impulses which are compared with those from the generator 17 by an indicator difference counter 25 and shown on an indicator 26a. The control difference counter 31 is connected to control means 37 for the valves 46, 47, 48 and exhaust valves 50, 54, and a pair of decade switches 33, 34 are connected to the control difference counter 31 and are adjustable to set the desired upper limit of the stroke of the die 3 and the position at which the valves 46, 47 are operated to switch over from filling liquid to pressure liquid. A counter 53 and indicator 26b are provided to show the amount the die overruns its lower limit position due to inertia and other causes and the impulse generator 27 enables the upper and lower limits of the stroke of the press and the position of the die at which the filling liquid and pressure liquid changes over to be adjusted to compensate for the overrun. In operation, the impulse generator 27 is actuated to give a number of impulses to the counters 25 and 31 corresponding to the desired finished size of the workpiece, and the decade switches 33, 34 are adjusted to determine the upper limit position of the upper die and the position at which the valves 46, 47 are actuated to change over the filling and pressure liquids. With valves 48 and 54 open, the die 3 is moved towards its upper position until the generator 17 has supplied a number of impulses to the difference counter 31 corresponding to the upper limit of the die. The counter 31 then actuates the control means 37 so that valves 48 and 54 are closed and valves 46 and 50 opened to enable filling liquid to act on the ram 9 and move the die 3 downwardly until the counter 31 detects from the impulses supplied by the generator 17 that the position of the die has been reached for the change over from filling to pressure liquid and operates the control means which in turn changes over the valves 46, 47. When the impulse generator 17 indicates that the lower limit of the stroke, corresponding to the desired size of the workpiece, has been reached, the control means is operated to actuate the valves 47, 48, 50, 54 to raise the die. However, because of the inertia and other causes, the die will overrun the lower limit position and the impulse generator 17 sends impulses to the counter 53 and indicator 26b to show the extent of the overrun so that the impulse generator 27 can be operated au O- matically or manually to compensate for the overun by supplying impulses to the counter 31 which has the effect of raising the positions at which the valves are actuated to reverse the stroke of the die and change over from filling to pressure liquid. A selector valve 50 is provided to change over the operation of the machine from coarse forging, in which both filling and pressure liquids are used, to fine forging, in which only pressure liquid is used.