Hydraulic press

Abstract

A hydraulic press, in particular for deep-drawing or curving metal discs, comprises a hydraulic syringe cylinder for moving an upper die and a pump group. The pump group comprises an electro-hydrostatic pump having a pump shaft controllable for introducing / di scharging a command fluid into / from the hydraulic cylinder. The syringe section is substantially equal to the annular section of the rod-side piston so that the volume of the command fluid entering into the syringe during the descent movement of the piston is substantially equal to the volume of the command fluid exiting from the front cylinder chamber.

Description

HYDRAULIC PRESSDESCRIPTION

[0001] The present invention relates to a hydraulic press , in particular of the type suitable for deep-drawing or curving metal discs , for example for pressuri zed tanks and apparatuses .

[0002] As is known, presses for deep-drawing or curving are generally operated by mechanical systems or hydraulic systems .

[0003] Mechanical presses are designed to mold pieces wherein the diameter thereof does not normally exceed 1500 mm and having thicknesses of up to 10 mm.

[0004] Hydraulic presses have a very wide dimensional range both in terms of the diameter of the discs and in terms of thickness .

[0005] The maximum diameter of those discs that are currently on the market is 10 , 000 mm with a thickness of up to 100 mm for intermediate diameters .

[0006] Such presses are normally combined with manipulators that move the disc during the pressing cycle such that progressive deformation of the entire surface of the disc is possible to obtain a finished shape with a regular radius that represents a dome of a sphere .

[0007] The forming process requires pressure / force control of the press cylinder, combined with position control formore accurate processing .

[0008] All of the hydraulic power plants currently on the market for this type of press consist of a main central tank, a quick cylinder filling tank, pump groups , hydraulic blocks and proportional valves for position and force control .

[0009] These systems have an ef ficiency that generally does not exceed 65-70% even when applying pumps with a variable flow rate .

[0010] The ef fect of oil lamination through the proportional valves also produces very signi ficant overheating .

[0011] The obj ect of the present invention is to propose a hydraulic press which has a higher ef ficiency than the hydraulic presses mentioned above and which is capable of performing very accurate machining of metal discs .

[0012] Such obj ect is achieved with a hydraulic press according to claim 1 . The dependent claims describe preferred or advantageous embodiments of the hydraulic press .

[0013] The idea behind the present invention is to use an electro-hydrostatic pump, the delivery and return of which are directly connected to the chambers of a central hydraulic syringe cylinder which has the purpose of controlling the approach and return speed, with a volumeconstraint between the syringe and the lower ( front ) chamber of the cylinder, without the application of proportional valves .

[0014] The hydraulic command is in fact comparable to an electrical axis command insofar as a drive controls a brushless motor directly keyed into the pump shaft without any intermediate coupling j oints .

[0015] By controlling the motor, the flow rate and speed and also the pressure delivered to the cylinder may be varied automatically . Closed-loop control allows for accurate positioning of the rod under any pressure condition without oil lamination, as would occur in a traditional hydraulic press .

[0016] The features and advantages of the hydraulic press according to the invention shall be made readily apparent from the following description of preferred embodiment examples thereof , provided purely by way of non-limiting examples , with reference to the accompanying figures , wherein :

[0017] - Fig . 1 schematically illustrates the components of the hydraulic circuit of the press according to the invention;

[0018] - Fig . 2-5 show, with arrows indicating the direction of the flow of the command fluid, the hydraulic circuit of the press in as many steps of the pressingcycle .

[0019] In said drawings , the hydraulic circuit of the hydraulic press according to the invention has been schematically indicated with the numeral 1 .

[0020] The hydraulic press comprises a lower die and an upper die - not shown, wherebetween a metal piece to be subj ected to processing, for example deep-drawing or curving, is arranged .

[0021] The hydraulic press is provided with a hydraulic cylinder 10 for moving the upper die . The cylinder is driven by a command fluid, such as oi l .

[0022] The hydraulic cylinder 10 has a piston 12 provided with a rod 14 at the end of which the upper die is connected . The piston 12 divides the inner cylinder chamber into a front cylinder chamber 18 , crossed by the rod 14 , and a rear cylinder chamber 16 .

[0023] The front cylinder chamber 18 communicates with the outside through a front chamber port 18a ; the rear cylinder chamber 16 communicates with the outside through a rear chamber port 16a .

[0024] The hydraulic cylinder 10 is a syringe cyl inder . The syringe cylinder, in comparison to a traditional cylinder, has the piston 12 and the rod 14 which are crossed by an axial cavity 20 , parallel to the axis of the cylinder and closed at the distal end of the rod 14 .A bar 22 , known as a syringe , is inserted into the axial cavity 20 in a fluid-tight manner, wherein a syringe supply duct 24 , in fluid communication with the outside , is obtained by means of a syringe supply / discharge port 26 .

[0025] For example , the syringe 22 is rigidly connected to the sleeve of the cylinder 10 . The syringe 22 then extends from the rear head 10a of the cylinder, passes through the rear chamber 16 of the cyl inder, and is coaxially inserted into the rod 14 .

[0026] The piston 12 and the rod 14 thereof slide on the syringe 22 . The distal end 22a of the syringe 22 and the distal end 14a of the rod delimit a syringe chamber 28 which may be supplied through the syringe supply duct 24 .

[0027] According to one aspect of the invention, the cross section of the syringe 22 is substantially equal to the annular section of the piston 12 on the rod side, such that the volume of the command fluid entering the syringe 22 during the descent movement of the piston 12 is substantially equal to the volume of the command fluid exiting the front chamber 18 of the cylinder 10 .

[0028] The hydraulic press comprises a pump group 30 which controls the hydraulic cylinder 10 described above .

[0029] The pump group comprises an electro-hydrostatic pump32 having a pump shaft .

[0030] The pump shaft is controllable so as to drive the electro-hydrostatic pump 32 to introduce / discharge the command fluid into / from the hydraulic cylinder 10 . The electro-hydrostatic pump 32 has a first port 32 a connected to the front cylinder chamber 18 and a second port 32b connected to the rear cylinder chamber 16 .

[0031] Such first and second ports 32a, 32b constitute a delivery port or a return port for the command fluid depending upon the direction of rotation of the pump shaft .

[0032] Further, the second port 32b of the electrohydrostatic pump 32 is fluidically connected to the syringe supply / discharge port 26 .

[0033] In one embodiment , the pump group 30 comprises a pump motor 34 , for example a brushless motor, and a motor control unit 36 configured to control the pump motor 34 .

[0034] In one advantageous embodiment , the pump motor 34 is directly keyed to the pump shaft , i . e . , without the interposition of intermediate connection j oints .

[0035] The control unit 36 is configured to control the pump motor 34 so as to adj ust the flow rate , speed, and pressure of the command fluid .

[0036] More precisely, the hydraulic press comprises a closed-loop control circuit configured to adj ust the flow rate , speed, and pressure of the command fluid on thebasis of detecting the position of the rod .

[0037] In one embodiment , the second port 32b of the electro-hydrostatic pump 32 is connected to the rear chamber 16 of the hydraulic cylinder 10 by means of a hydraulic circuit 40 comprising controllable valve means 42 for directing the command fluid from the second port 32b alternatively towards the syringe supply / discharge port 26 , the rear chamber inlet port 16a, or both .

[0038] For example , these valve means 42 comprise a first solenoid valve 44 that intercepts the portion of the hydraulic circuit between the electro-hydrostatic pump 32e and the rear chamber ports 16a and the syringe supply / discharge ports 26 , a second solenoid valve 45 that intercepts the portion of the hydraulic circuit between the front chamber port 18a and the electrohydrostatic pump 32 , and non-return valves 46a, 46b .

[0039] In one embodiment , the hydraulic press further comprises a compensation tank 50 fluidically connected to the rear chamber 16 of the hydraulic cylinder .

[0040] Such compensation tank does not have , as in the presses according to the prior art , the task of supplying the chambers of the hydraulic cylinder, but serves only to prevent the formation of cavitation phenomena within the rear chamber, in particular during the quick piston push-down step, as will be described below .

[0041] In one embodiment , the compensation tank 50 is connected to the rear chamber 16 of the hydraulic cylinder by means of controllable tank valve means 52 for introducing by gravity a compensation volume of command fluid into the rear chamber during the piston push-down step and for recovering said compensation volume of command fluid from the rear chamber during the piston decompression and / or ascent steps .

[0042] For example , the tank valve means 52 comprise a fill valve 53 driven by a tank pump 54 through a third solenoid valve 55 .

[0043] As mentioned above , in one embodiment , the hydraulic press comprises a control unit 36 configured to drive the pump group 30 in order to perform the movement of the piston - and thus of the upper die connected to the rod thereof - so as to implement a pressing cycle .

[0044] In particular, the control unit 36 drives the pump 32 to carry out , from an initial completely raised piston position :

[0045] - a quick piston push-down step, wherein the electro-hydrostatic pump is driven to aspirate the command fluid from the front chamber of the hydraulic cylinder and to introduce it into the syringe ( Fig . 2 ) ;

[0046] - a compression step, wherein the electrohydrostatic pump is driven to aspirate the command fluidfrom the front chamber of the hydraulic cylinder and to introduce it into the rear chamber of the hydraulic cylinder and into the syringe chamber 28 (Fig. 3) ;

[0047] - a decompression step, wherein the electrohydrostatic pump is driven to aspirate the command fluid from the rear chamber of the hydraulic cylinder and from the syringe chamber and to introduce it into the front chamber of the hydraulic cylinder (Fig. 4) ;

[0048] - a quick piston return step, wherein the electrohydrostatic pump is driven to aspirate the command fluid from the rear chamber of the hydraulic cylinder and from the syringe and to introduce it into the front chamber of the hydraulic cylinder (Fig. 5) .

[0049] Furthermore, in some preferred embodiments, the control unit is configured to control the tank valve means 52 so that:

[0050] - during the quick piston push-down step (Fig. 2) , the tank valve means 52 are open to allow the command fluid to pass from the compensation tank to the rear cylinder chamber;

[0051] - during the compression step (Fig. 3) , the tank valve means 52 are closed;

[0052] - during the piston decompression and quick return steps (Fig. 4 and 5) , the tank valve means 52 are open so as to allow the command fluid to pass from the rearcylinder chamber to the compensation tank.

[0053] The operation of the hydraulic circuit components, in one possible embodiment thereof, in the various steps of the pressing cycle will now be described.

[0054] Step 1: Quick push-down ( Fig . 2)

[0055] The electro-hydrostatic pump pushes oil into the syringe supply duct 24 through the first solenoid valve 44; the second solenoid valve 45 opens to supply the pump with oil exiting from the annular chamber; the rear chamber 16 of the cylinder is filled by the pre-filling valve 53 driven by the tank pump 54 through the third solenoid valve 55.

[0056] Step 2 Work / Compression (Fig. 3)

[0057] The operating logic is akin to that of the previous step. Furthermore, the tank pump 54, through the third solenoid valve 55 in the de-energized state, keeps a support accumulator 56 supplied, which, (through a nonreturn valve 57) contributes to powering the electrohydrostatic pump 32 in the event that it does not receive sufficient oil from the annular cylinder chamber 18, namely the front chamber.

[0058] Step 3 Decompression (Fig. 4)

[0059] The first solenoid valve 44 opens the rear chamber 16 of the cylinder towards the electro-hydrostatic pump 32, which controls the decompression thereof. When apredetermined pressure , for example less than 20 bar, is reached, the third solenoid valve 55 drives the prefilling valve 53 so as to place the rear chamber 16 in communication with the compensation tank 50 .

[0060] Step 4 Quick return ( Fig . 5 )

[0061] The electro-hydrostatic pump 32 reverses the direction of rotation and, by means of the first solenoid valve 44 , sends oil from the syringe chamber 28 towards the front chamber 18 , with the second solenoid valve 45 open; the oil present within the rear chamber 16 returns to the compensation tank 50 by means of the pre- filling valve 53 driven by the third solenoid valve 55 .

[0062] The combination of the electro-hydrostatic pump and the syringe cylinder described above allows for a number of advantages to be obtained, both in terms of the ef ficiency and precision of the pressing cycle , and in environmental terms . In particular :

[0063] - the possibility of operating within an ambient temperature range and of the command fluid greater than a plant that uses proportional valves , without losing position and pressure control ;

[0064] - uni form and controlled speed in the quick positioning movements of the piston, both descending and ascending ( in traditional systems the piston descends by gravity thereby not ensuring uni form speed for thecompleted stroke ) ;

[0065] - the possibility of managing acceleration and deceleration ramps with direct command and without any delay;

[0066] - the possibility of varying the positioning and working speeds of the piston ( and therefore of the upper die ) by acting upon the pump motor so as to obtain signi ficant energy savings when it is not necessary to use the press on a machine at maximum productivity;

[0067] - the possibility of interpolating with a closed loop the electrical absorption with the positioning in order to obtain an optimal pressing cycle using only the energy that is actually required . For example , the pump speed may be adj usted according to the position of the piston within the cylinder thereby optimi zing the electrical consumption;

[0068] - optimi zation of the cycle during pressing which allows for calibration of the thinning of the sheet metal thereby preventing an ef fect of pressing an upper die against a lower die ;

[0069] - much more ef fective piston return reversal cycle insofar as the reversal is implemented directly by means of the pump with minimal system inertia;

[0070] - el ectronic management of the pump motor which leads to an improvement in cycle time ef ficiency with areduction in the overall time ;

[0071] - the possibility of setting a slow cycle with a single button in order to proportionally reduce energy consumption when high cycles per minute are not required ( a normal hydraulic circuit would require substantial modi fications to the controls of several components in order to reduce speeds without , however, achieving the same energy savings ) ;

[0072] - the possibility of performing an in-depth analysis of the pressing cycle as the resistance to forming varies , and the possibility of digiti zing the steps according to the di f ferent qualities of the sheet metal ;

[0073] - the possibility of creating a signi ficantly resi zed hydraulic power plant that is moved on board the press , with consequent compacting of the layout of the plant and a substantial reduction in the hydraulic connections and hydraulic components present within the circuit ;

[0074] It should be noted that the electro-hydrostatic pump only functions during the movement of the cylinder and does not require a drive circuit for the operation thereof insofar as it has almost instantaneous activation through the pump motor .

[0075] As a result of the above , the number of maintenance interventions ( leaks , gasket replacements , etc . ) isreduced .

[0076] The smaller number of components reduces oil contamination caused by slag from the normal wear thereof and consequently promotes an extension to the li fe cycle of the hydraulic oil which has a two to four times greater replacement interval than with a traditional plant .

[0077] The main tank, which is normally applicable in a traditional hydraulic press , is eliminated .

[0078] A single compensation ( or pre- filling) tank may be provided, for example limited to 130 liters , thereby resulting in a reduction in the costs of disposing the spent oil when it is necessary to replace it .

[0079] Noise is reduced insofar as the electro-hydrostatic pump is decidedly less noisy than traditional pumps .

[0080] The energy consumption for each pressing cycle is signi ficantly reduced when compared to a traditional plant .

[0081] It is possible to obtain an accumulation of energy during the decompression step and a subsequent release thereof during the movement and press ing step .

[0082] To the embodiments of the hydraulic press according to the invention, in order to meet contingent needs , a person skilled in the art may make a number of changes , adaptations , and substitutions of elements with otherfunctionally equivalent ones without departing from the scope of the following claims . Each of the features described as belonging to a possible embodiment may be obtained independently of the other described embodiments .

Claims

CLAIMS1 . A hydraulic press , in particular for deep-drawing or curving metal discs , comprising :- a lower die and an upper die ; a hydraulic cylinder for moving the upper die , the hydraulic cylinder having a piston provided with a rod at the end of which the upper die is connected, the piston defining a front cylinder chamber crossed by the rod and a rear cylinder chamber ; a pump group comprising an electro-hydrostatic pump having a pump shaft controllable for introducing / discharging a command fluid into / from the hydraulic cylinder, the electro-hydrostatic pump having a first port connected to the front cylinder chamber and a second port connected to the rear cylinder chamber, said first and second ports being a delivery port or a return port for the command fluid according to the rotation direction of the pump shaft , wherein the hydraulic cylinder is a syringe cylinder, the syringe having a syringe inlet port fluidically connected to the second port of the electro-hydrostatic pump, and wherein the syringe section is substantially equal to the annular section of the rod-side piston, so that the volume of the command fluid entering into the syringe during the descent movement of the piston issubstantially equal to the volume of the command fluid exiting from the front cylinder chamber .2 . Hydraulic press according to claim 1 , wherein the pump group comprises a pump motor directly keyed onto the pump shaft and a motor control unit configured to control the pump motor .

3. Hydraulic press according to claim 2 , wherein the control unit is configured to control the pump motor so as to regulate the flow rate , speed and pressure of the command fluid .4 . Hydraulic press according to claim 3 , comprising a closed-loop control circuit configured to regulate the flow rate , speed and pressure of the command fluid based on a detection of the rod position .5 . Hydraulic press according to any one of the preceding claims , wherein the second port of the electrohydrostatic pump is connected to the rear chamber of the hydraulic cylinder by means of a hydraulic circuit comprising controllable valve means for directing the command fluid from the second port alternatively towards the syringe inlet port , the rear chamber inlet port , or both .

6. Hydraulic press according to any one of the preceding claims , further comprising a compensation tank fluidically connected to the rear chamber of thehydraulic cylinder through tank valve means controllable to introduce , by gravity, a compensation volume of command fluid into the rear chamber when pushing down the piston and recover said compensation volume of command fluid from the rear chamber when decompressing and / or pushing up the piston .7 . Hydraulic press according to any one of the preceding claims , comprising a control unit configured to drive the pump group to carry out , from an initial completely raised-piston position :- a quick piston push-down step, wherein the electrohydrostatic pump is driven to aspirate the command fluid from the front chamber of the hydraulic cylinder and introduce it into the syringe ; a compression step, wherein the electro-hydrostatic pump is driven to aspirate the command fluid from the front chamber of the hydraulic cylinder and introduce it into the rear chamber of the hydraulic cyl inder ;- a decompression step, wherein the electro-hydrostatic pump is driven to aspirate the command fluid from the rear chamber of the hydraulic cylinder and introduce it into the front chamber of the hydraul ic cylinder ; a quick piston return step, where the electrohydrostatic pump is driven to aspirate the command fluid from the front chamber of the hydraulic cylinder andintroduce it into the front chamber of the hydraulic cylinder .8 . Hydraulic press according to claims 6 and 7 , wherein the control unit is configured to control the tank valve means so that :- during the quick piston push-down step, the tank valve means are open so as to allow the command fluid to pass from the compensation tank to the rear cyl inder chamber ;- during the compression step, the tank valve means are closed;- during the decompression and quick piston return steps , the tank valve means are open so as to allow the command fluid to pass from the rear cylinder chamber to the compensation tank .

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