US2286798A - Hydraulic circuit for press brakes - Google Patents

Description

June 16, 1 942. P. E. FLOWERS 2,286,798 HYDRAULIL) CIRCUIT FOR PRESS BRAKES v Filed May 16, 1940 2 sneets sheet 1 Paul. E. FLowsRs. t E p un) w /M June 16, 1942. p FLOWERS 2,286,798

HYDRAULIC CIRCUIT FOR PRESS BRAKES Filed May 16, 1940 2 Shets-Sheet 2 F=TOTAL PRESSING FORCE NECESSARY FOR v GIVEN WORKPIECE I {FPRESSING FORCE N LEFT END OF PLATEN f2=PRESSlNG FORCE 0N RIGHT END OF PLATEN I B F s F )f rows 70 so :4 gross I 0 Id i A #70 rates 30 2 O /\J/ "T00 5 1o f 20? o i/ J 0 I0 20 30 4O 5O 8O I00 LENGTH OF PLATEN IN uvcnes Jmmmu am. E.FLQWER6,

M li,

Patented June 16, 1942 Paul E. Flowers, Mount The Hydraulic Devel mington, Del.,

Gilead, Ohio, assignor to opment Com, Inc., Wila corporation of Delaware Application May 16, 1940, Serial .No. 335,596 6 Claims. (Cl. 100-71) The present invention relates" to presses, and

in particular to presses having a plurality of spaced pressing plungers connected with one and the same platen. Such machines, which are particularly useful for forming long extended parts, such as airplane wings, and which include the so-called press brakes, shear brakes, and bending brakes, have heretofore been operated mechanically to assure a uniform movement of the ends of the'platenas far as possible. Nevertheless, with the said known presses, an asynchronous movement of the spaced pressing plungers has often been encountered with the result that one .end of the platen is moving ahead of the opposite end, thereby causing a cocking of the platen and great wear of the plungers, in addition to spoiling the workpiece.

Moreover, the said mechanical presses are relatively complicated in construction and expensive in manufacture.

Accordingly, it is an object of the present invention to provide a machine which would overa come the above identifled drawbacks.

It is a further object ofthe invention to provide a multi-plunger press of the above character in which synchronous movement of the spaced plungers connected with the ends of a pressing platen, bending beam,.or-shear is assured by hydraulic means.

Another object is to provide a machine, as set forth in the preceding paragraph in which the ing on the individual plungers in correspondence to the location of the workpiece ,with respect to the ends of the platen.

The press brake, illustrated in the drawings,- comprises a plurality of cylinders I, 2, each having two chambers 3, 4 5, 6, respectively separated from each other by a partition I, 8. 'Reciprocably mounted in the cylinder chamber 3 is a doubleacting .piston 9 having connected thereto a plunger l0 passing through a. closelyfitting bore ll into the cylinder chamber 4. Any convenient means may be provided for preventing leakage from the chamber iibelow the piston 9 into the chamber 4. Reciprocably mounted in the chamber I is adouble-acting piston having connected therewith a ram l9, which in its turn is connected with one end of the platen I 4.

The piston I2 is connected with the plunger III in any convenient manner, but so that the effective area on the upper and lower surfaces of the piston I2 is the same. It will be noted that in contra-distinction thereto, the piston 9 has a larger upper surface or advance area and a smaller lower surface or retraction area.

Similarly to the cylinder I, the cylinder 2 comprises two pistons l5 and I6 arranged in tandem total force necessary for performing a working operation on a given workpiecewill remain the same, irrespective of the location of the workpiece with respect to the ends of the press platen, bending beam, or shear.

A still further object of the invention consists in providing a press ,with' spaced multi-cylinder and connected with each otherby means of the plunger l'l, while the piston I6 is connected by a ram 18 of the same diameter as the plunger l'l with the other end of the platen. Each of the pistons l2 and I6 is preferably provided with a collar I9, 20, respectively, for abutment with the lower. surface of .the partitions 1, 8, respectively.

Supported by theupper ends of the cylinders I l and 2 is a fluid reservoir or surge tank 2| com-.

,prisingsurge valves 22 and 23 extending respecpiston assemblies operatively connected with one and the same platen, beam or shear, in which the pressing, bending or shearing forces exerted by each cylinder piston assembly automatically adjust themselves in correspondence to the loca-. I

tion of the workpiece with respect to the ends of the. platen or the cylinder piston assemblies operatively connected therewith.

These and other objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawings, in which:

. valves, which in themselves do tively into'thecylinders I and 2. .The surge valve 22 is connected with a main cylinder relief and pump by-pass valve 24, while the surge'valve 23 is hydraulically connected with a similar relief and pump by-pass valve 25. The purpose of the said surge valves and relief and pump by-pass of the present inventlon, is to sure in the main cylinder chambers 3 and 5' above the pistons 9 and I5 at the beginning of the retraction stroke, while the surge valves enable fluid to flow from the fluid reservoir or surge tank Figure 1 is a diagrammatic illustration of a press brake according to the present invention, while Figure 2 shows agraph illustrating the automatic distribution of the individual forcesactinto the upper portion of the main cylinder chambers 3 and 5 at the first portion of the downward, stroke of pistons 9 and I5. I

. For a more v detailed descriptionof the surge valves referred to, reference may be had to United States Patent 2,193,248 to Walter Ernst.

The main cylinder relief and pump by-pass not form a part I release the presstep with the other through control valve 44,

means of conduits 29 and 3|lwith the lower part of the cylinder chamber 3. Branching off from the conduit 30 is a conduit 3| having connections to the surge tank 2| and the main cylinder relief and pump by-pass valve 24, while another branched conduit 32 is adapted to communicate with the surge tank 2| by means of the check valve 33.

Similarly, nected with theupper and lower cylinder chamber 5.

The upper portion of the cylinder chamber '4 communicates with a conduit 34 containing a check valve 35 and leading to the upper portion of the cylinder chamber 3. Similarly, the upper portion of the cylinder chamber 5 may communicate with the upper portion of the cylinder chamber 6 by means of the conduit 35 and the check valve 31 arranged in the said conduit 38.

The connections 34, 35 between the cylinder chambers 3 and 4, and the connections 36, 31, serve to insure that the upper portions of the chambers 4 and 8 above the pistons l2 and I8, are always completely fllled with fluid, and that the pressure is the same as in the main pressure cylinder chambers 3 and 5. This also serves to correct any tendency for one side to get out of leakage past the the conduits 21 and'29 are conportion of the pistons.

The upper portion of the cylinder chamber 4, furthermore communicates with a conduit 38 communicating by means of a conduit 39 with the lower portion of the cylinder chamber 8, whereas the upper portion of the cylinder chamber 8 communicates by means of conduits 48 and 4| with the lower portion of the cylinder chamber 4.

Between the conduits 38 and 48-.are arranged two oppositely opening check valves 42 and 43 adapted to establish communication between the conduits 38 and 40 on one hand, and a tonnage control valve 44 arranged in a conduit 45 leadin to the surge tank 2|. The tonnage control valve 44 is adjusted so as to actuate an electric contact at the attainment of apredetermined pressure, thereby causing a reversing movement of the variable delivery pump 28 and initiating the retraction stroke of the pistons 9 and I5.

For a more detailed description of the tonnage reference may be had to United States patent application #214,772 to Ernst, filed June 20, 1938.

Although the operating-circuit is shown as a closed circuit, it might equally as well be an open ci cuit with a pump delivering in one direction only, and with the control of the upward and downward movement of the pistons effected by means of an operating valve.

Operation Assuming that the position of the press, as shown in Figure 1, corresponds to the end of the retraction stroke and that it is now desired to perform another working stroke, the variable delivery pump 28 is started in any convenient manner, for instance, by energizing an electric motor connected with the pump 28. Fluid pres- 5 are connected through sure will then be delivered by the pump 28 through the conduits 21. and 26 into the. upper portions of the cylinder chambers 3 and 5, while the lower portions of the cylinder chambers 3 and conduits 30 and 29 with the suction side of the variable delivery pump 28. Supposing that the'pistons 9 and I5 move down- *wardly by gravity, fluid pressure delivered by the pump 28 through the conduits 21 and 26 is supplemented by fluid pressure from the surge tank 2| through the surge valves 22 and 23.

Due to the fluid pressure in the chambers 3 and 5, the check valves 35 and 3| open, thereby allowing pressure fluid to flow from the chambers 3 and 5 respectively, into the upper portions of the chambers 4 and 8. While the pistons 9 and I5 move downwardly, the pistons l2 and I6 connected with the plungers l0 and I1 respectively, likewise move downwardly. During this operation, fluid expelled from the chamber 4 below the piston |2 escapes through the conduits 4| and 40 into the upper portion of the cylinder chamber 6 above the piston l8, whereas fluid expelled from the lower portion of the cylinder chamber 8 below the piston l6 escapes through conduits 39 and 38 into the upper chamber 4 above the piston l2. In this way, the increasing spaces above the pistons l2 and I6 are continuously filled with fluid. As soon as the pistons 9 and I5 have moved downwardly to such an extent that the platen l4 engages the work-piece, pressure builds up in the chambers 3 and 5 above the pistons 9 and I5, and will cause closure of the surge valves 22 and 23.

The conduit means 34 and 35 convey the pressure prevailing in the upper portion of the chamber 3 above the piston 9 into the upper portion of the chamber 4 above the piston l2. Similarly, the conduit means 35 and 31 convey the pressure prevailing in the upper portion of the cylinder chamber 5 above the piston |5 to the upper portion of the cylinder chamber 8 above the piston l8. These pressures will also prevail in the conduits 38 and .40 leadingto the tonnage control valve 44, by means oi the check-valves 42 and 43 respectively.

Assuming now that the workpiece 48 has been placed, as shown in the drawings, that is, more adjacent the ram I8 than adjacent the ram l3, it

sistance will prevail at the other end of the platen l4 adjacent the ram l3. Consequently, the platen end adjacent the ram |3 will tend to advance more rapidly than the platen end adjacent the ram l8. This is, however, prevented by the fact that the platen end adjacent the ram |3 can ad vance only when fluid below the piston I2 is adapted to escape into the upper portion of the cylinder chamber 6 above the piston l8. Consequently, the piston l2 and the platen end adjacent thereto cannot advance more rapidlyvthan the piston l8 and the platen end adjacent to the piston l8. In this way, synchronous movement of both platen ends is assured.

As soon as the working stroke has'been finished,

l2 from the chamber 4 above the piston I2 is conveyed through the conduits 38 and 39 into the lower portion of the cylinder chamber 6 below the piston It. In a similar manner, fluid expelled from the chamber 6 above the piston it passes through conduits l and GI into the chain her 4 below the piston I2. When the pistons 9 and I have finished their retraction stroke, the press comes to a standstill, by any convenient means, or, if desired, may start a new working 7 operation.

In connection with the operation of the press,

accordingto the present invention, attention may 1 be directed to the feature that the total pressing force necessary for carrying out a working operation on a given workpiece remains the same irrespective of the location of the workpiece with regard to the ends of the press platen l4. To more clearly elucidate this feature, three characteristic positions of the workpiece 48 with respect to the ends of the press platen it may be considered.

(a) Assume that the length of the platen is 100 inches and that the total force F for carrying out the pressing operation is 80 tons. Assume, furthermore, that the workpiece I6 is pressed so that the distance of its right end from the right platen end is the same as the distance between the left end of the workpiece it and the left platen end. Provided that the material is the same throughout the workpiece, it will be obvious that on each of the pistons 9 and is a pressing force of 40 tons will be exerted. This situation is illustrated in Figure 2 and marked by the point A on the line L; it will be noticed that the distance between the point A and the line F-F indicating the force f1 acting upon the piston 9 equals the distance between the point A and the abscissa. indicating the iorce is acting upon the piston it,

(b) Suppose now that it would be possible to press the workpiece so that its center is just below the right end of the platen it, that is, 100

inches away from the left platen end. As soon as the right platen end engages the workpiece the piston IE will, at least for a fraction of a second,

he stopped and in this instance the piston 9 will likewise be stopped, since it can move only when pressure fluid, as previously explained, may escape from-below the piston it into the upper portion of the cylinder chamber 6 above the piston it. However, a halt of the piston S'is possible only when the pressure below the piston |2 equals the .pressure above the pistons. This is actually the case in the present instance, and the whole pressing force must be exerted "on the piston it. In

other words, while no pressing force is exerted on piston 9, the pressing force on piston I 5 equals- 80 tons. This position is illustrated by point B at the intersection of the line L with the line F-F.

(c) If the situation be now reverse that is, when the workpiece ispressed at the 1 it end of the platen l4, the pressing force is upon the piston IE will become zero, whereas the pressing force on the piston 8 will be 80 tons.- This p'ositibn'is indicated by point C located at the intersection of line L or the abscissa.

gradually and progressively changes during the working operation. f

It will be understood that! desire to comprehend within my invention such modifications as come within the scope of the claims and the invention. r

Having thus; fully described my invention,

what I claim as new and desire to secure by Letters Patent, is:

1'. In combination, a plurality of spaced cylinder piston assemblies connectedwith a common platen or beam adapted to act on a workpiece, each or said cylinder pistonassemblies comprising a plurality of double-acting pistonsin tandem arrangement, a pressure fluid source adapted to supply pressure fluid to said cylinder piston assemblies, and conduit means connecting 7 one side of one piston of each cylinder piston assembly with the opposite side of a corresponding piston of another cylinder piston assembly. 7 2. In combination, a plurality of spaced cylinders,' each cylinder comprising two cylinder chambers, a plurality of spaced double-acting pistons, two pistons being reciprocably' mounted in each cylinder but in separate cylinder chamhers, valve means responsive to a difl'erencein pressure in two adjacent cylinder chambers during the advancingmovement of said pistons for hydraulically interconnecting said adjacent chambers, common means mechanically interconnecting all pistons, a fluid source adapted to supply pressure fluid to said cylinders for reciprocating said pistons, and conduit means con-v necting the advancing side of a piston in one cylinder and the retracting side of a corresponding piston in another cylinder for eifecting syn-- chronous movement of all pistons,

3. In combination, a plurality of spaced hydraulic motors, each motor comprising two double-acting pistons arranged in tandem and connected with a common platen or beam, a fluid source adapted to convey fluid pressure selectively to one or the other side of one piston The automatic adjustment of. the pressing forces acting upon the individual pistons in accordance with the location 01' the workpiece is 'also ofparticular importance in connection with of each hydraulic motor for actuating the same, and conduit means hydraulically interconnecting a pair of the other pistons in such a manner that each side or one piston of said pair is hydraulically connected to the opposite side of the other piston of said pair, whereby to cause synchronous movement of all pistons.

4. In combination, a plurality of spaced cylinder pairs, the cylinders of each cylinder pair being adapted hydraulically to be interconnected,

a plurality of spaced pistons reciprocably mounted in each cylinder pair and operatively connectedwith each other, common means mechanically interconnecting all pistons and adapted to act on a workpiece, means responsive to a difference in pressure on corresponding sides of the pistons of each cylinder pair to establish hydraulic connectionbetween the cylinders of each cylinder pair, a fluid source common to and directly connected with one cylinder of each cylinder pair andadapted to supply pressure fluid thereto for reciprocating a piston in said cylinder, and means hydraulically connecting the other cylinders to assure synchronous movement of all pistons.

5. In combination, a plurality of spaced verti-- cally reciprocable primary pistons, said primary pistons having a larger advancing area and a smaller retracting area, a plurality of spaced vertically reciprocable secondary pistons, said secshear brakes where the position oi the counterondary pistons having equal piston areas on each 3 forces exerted by'the workpiececontinuously.

side thereof and being arranged in tandem with said primary pistons so as to be reciprocable thereby, means mechanicallyinterconnecting all secondary pistons and adapted to act on a workpiece, first conduit means hydraulically connecting the upper side of one secondary piston with the lower side of another-secondary piston, and second conduit means separate from said first conduit means for connecting the lower side of said first mentioned secondary piston with the upper side of said last mentioned secondary piston.

6. A hydraulic press comprising a plurality of vertically arranged and spaced primary cylinders, a plurality of spaced secondary cylinders, each primary cylinder being in alignment with adapted tosupply pressure and superposed upon a secondary cylinder, a plurality of double-acting piston pairs with the pistons of each piston pair in tandem arrangement, each piston pair having one piston reciprocably mounted in one primary cylinder and the other piston reciprocably mounted in the adjacent secondary cylinder, a fluid source fluid to said primary cylinders for-reciprocating said piston pairs, a platen connected'with said piston pairs, and means adapted to allow equalization of the pressure prevailing in the upper portion of one secondary cylinder with the pressure prevailing in the lower portion of another secondary cylinder,

Pauli E. FLOWERS.

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