GB534089A - Improvements in or relating to hydraulic presses - Google Patents

Abstract

534,089. Cupping. ERNST, W. Oct. 18, 1939, No. 28177. Convention date, March 27. [Class 83 (iv)] A hydraulic drawing-press has a fluid operated press ram associated with hydraulic clamping means for the work piece, a control valve being responsive to initiation of the working stroke to cause fluid to be trapped in the clamping motor and being also responsive to initiation of the retraction stroke to be moved so as to release fluid from the clamping motor. The base 10 connected by tie rods to the top member 11 carries a drawing die 14 with a cavity 15 into which the blank 16 is drawn by the die plunger 41. A reservoir 19 in the member 11 surrounds the main cylinder 20 having a piston 23 secured to the platen 36 which carries the plunger 41. The opposite ends of the main cylinder are connected by lines 26, 27 to a fourway valve 28 to which fluid is supplied by a pump 30. A line 31 leads from the valve back to the reservoir. The platen is formed with clamping cylinders 37 actuating plungers 38 secured to a clamping member 44. The cylinders 37 are supplied through tubular members 48 extending into cylinders 52. From each of the cylinders 52 one line extends through a check valve 54 opening towards the cylinder to the tank and another line extends to a pressure gauge 59, safety valve 56, and relief valve 57, the former operating at a higher pressure if the relief valve fails to act. The valves may be set to give different clamping pressures at different parts of the blank periphery. A line 61 from each clamping cylinder leads through a check valve 62 and common line 63 to a valve 70 the opposite ends of which are connected to the supply lines of the main cylinder 20. The platen 36 is bored to receive rods 82 secured to the clamping platen 44, and fitted with screwed rods 86 and nuts 84. The workpiece is stripped when the rods 86 meet the member 11 on the return of the main plunger. In operation the valve 28 is shifted by the lever 87 so that fluid is admitted to the line 26 to lower the main plunger. At the same time pressure in the lines 26, 77 causes the valve 72 to move to the right. When the clamping platen 44 engages the work it is arrested but continued movement of the main platen moves the punch into the work. The plungers 38, after stopping of the clamping platen move into the cylinders 37 and these plungers are of greater sectional area than the members 48 so that pressure builds up in the cylinders 52 until excess fluid escapes through relief valves 57, this build up of pressure being sufficient to engage the clamping platen firmly with the blank while drawing is completed. When the operation is complete the valve 28 is shifted to admit pressure fluid to the lower end of cylinder 20 to withdraw the main platen upwardly. At the same time the pressure in lines 27, 78 causes valve 72 to move to the left whereby fluid displaced by the rise of the tubular plungers 48 may pass through valve 62 and line 63 to the tank. In a modification, Fig. 2, the pressure fluid is supplied from a variable delivery reversible pump 101 controlled by a servomotor 102 whose piston is controlled by a valve member 104 connected through linkage to a rocker arm 113 coacting with a control rod 117 and solenoid 125. A pilot pump 126 delivers fluid to the servomotor and a byepass valve 140 is connected to the upper end of the main cylinder. In operation the pumps 101, 126 are started, preferably by energizing the solenoid 125 or by shifting the control rod 117 downwardly. This causes servomotor valve 104 to actuate the pump control to deliver pressure fluid to line 26 and move the main plunger downwards. At a pre-determined point a control device 147 de-energizes solenoid 125 to reverse the pump, 101 and withdraw the main plunger. At the same time pressure in the line 146 shifts valve 90 to the right, Fig. 2, thus permitting escape of fluid from the cylinders 52, 37 so that the clamping platen is also withdrawn. At the end of the upward return stroke. the platen 36 is stopped by a part 121 of the platen which engages a collar on control rod 117 and thus neutralizes the pump 101.