Sheet metal working machine and method thereof

Abstract

A sheet metal working machine (100) comprises a working tool (51, 151, 61) for carrying out machining on a workpiece (200) and a hydraulic drive system (1) for separately and independently driving the working tool (51, 151, 61) and comprising at least one hydraulic cylinder (2, 102, 202) provided with a piston (21, 121, 221) defining in the hydraulic cylinder (2, 102, 202) a thrust chamber (22, 122, 222) and a return chamber (23, 123, 223) and associated with the working tool (51, 151, 61); a reversible hydraulic pump (3), connected to a hydraulic fluid tank (4) and to the thrust chamber (22, 122, 222) to send fluid at a supply pressure (pm) or to suck fluid and move the piston (21, 121, 221) and allow the working tool (51, 151, 61) to interact with, or disengage and move away from, the workpiece (200); a hydraulic accumulator (5) connectable to the return chamber (23, 123, 223); valve means (10) configured and controlled to connect the return chamber (23) selectively to the accumulator (5) in a non-operating configuration (K0) and in a second operating configuration (K2) or to the pump (3) in a first operating configuration (K1) or to the tank (4) in a third operating configuration (K3).

Description

[0001] Sheet metal working machine and method thereof

[0002] The invention relates to sheet metal working machines and, in particular, it relates to a sheet metal working machine provided with a hydraulic drive system adapted to drive a plurality of working tools in a separate and independent manner, for example punching tools and / or cutting tools.

[0003] Sheet metal working machines are known which are provided with a multi-press or multitool punching apparatus and / or a single punching apparatus and / or a cutting or shearing apparatus, which can therefore perform a plurality of punching and cutting operations simultaneously and / or in sequence on the sheets to be worked.

[0004] The known multi-tool punching apparatuses comprise a plurality of punching tools or punches arranged adjacent and placed side by side on one or more rows, for example to form a parallel-row matrix structure, and driven linearly by respective presses, constituted by linear actuators, typically hydraulic cylinders, in a separate and independent way to interact with the workpiece.

[0005] The multi-press punching apparatuses comprise all the tools necessary to execute in sequence the workings required on the workpiece. In this way, it is not necessary to perform tool change operations during the production cycle, thus allowing to eliminate both stops for tool replacement (thus increasing the productivity of the machine) and automatic devices for setting up and replacing the tools (simplifying the structure of the machine).

[0006] Known cutting apparatuses or shearing units generally comprise two blades orthogonal to each other, independently movable along respective axes to perform cuts on the sheet. The blades or shears are driven by respective linear actuators, typically by hydraulic cylinders of adequate dimensions.

[0007] In combined machines, also called punching- shearing machines, which include a cutting apparatus and a multi-press punching apparatus, the latter are often integrated into a single structure.

[0008] In order to correctly perform the punching and / or cutting workings it is necessary to check the position, the displacement, or stroke, and the speed along a respective working axis of each tool, since these parameters depend on and are a function of the thickness and type of material of the workpiece and / or type of machining to be performed.

[0009] To drive and precisely control the movement of the punching and / or cutting tools, the known machines are provided with hydraulic drive systems capable of supplying and therefore driving in a separate and independent manner the hydraulic cylinders to which pistons are connected to and move the respective tools, so as to produce a single machining process or a plurality of machining processes on the workpiece in the same operating step. Known hydraulic drive systems generally comprise one or more hydraulic pumps driven by an electric motor, which supply with a high pressure hydraulic fluid (oil) (up to 300 bar) a supply circuit connected to each hydraulic cylinder by means of suitable by-pass and pressure regulation valves. By means of the aforementioned valves, it is therefore possible to select the hydraulic cylinder, that is the tool to be driven, the direction of movement of the piston of the cylinder, i.e. a working stroke or a return stroke of the piston / tool and the supply pressure of the hydraulic cylinder, i.e. the punching force that the tool exerts on the workpiece. The high pressure (up to 300 bar) with which the hydraulic pump feeds the supply circuit is calculated to ensure that one or more hydraulic cylinders of the punching apparatus exert maximum punching force on the workpieces.

[0010] However, in the usual machining processes only a small part (about 20%) of the machining processes performed on the workpieces requires the application of the maximum punching or cutting force, that is the maximum supply pressure for the hydraulic cylinders, the normally required supply pressure being much smaller (60-100 bar).

[0011] A disadvantage of the machines provided with the aforementioned hydraulic drive systems therefore lies in the high power consumption (necessary for pumping the oil in the high pressure supply circuit) and in the overall low power efficiency (in most workings the oil pressure must in fact be reduced).

[0012] Another disadvantage lies in the fact that due to the high supply pressure and thermal dissipations due to the pressure reduction in the hydraulic cylinder control valves, the oil heats up and must therefore be appropriately cooled by cooling means, which make the machine more complex and expensive.

[0013] Sheet metal working machines are also known in which the punching apparatus provides that each hydraulic cylinder is powered and controlled by a respective hydraulic pump through a closed supply circuit and without valves. The hydraulic pump is of the reversible type that is operable in the two rotation directions so as to move the cylinder piston, and therefore the tool, in the working stroke or in the return stroke by sending the pressurized oil respectively to an upper thrust chamber or to a lower return chamber. The hydraulic pump is in particular driven by an electronically controlled electric motor (typically by inverter) so as to change the rotation direction and automatically vary the supply pressure of the hydraulic cylinder according to the needs of use (punching force), thus allowing to contain energy consumption and to increase the overall efficiency of the punching apparatus. In the case of machines provided with multi-press punching apparatus having a plurality of punches and relative hydraulic cylinders arranged adjacent and side by side to form a parallel row matrix structure, this solution is, however, very expensive and cumbersome since for a separate and independent operation of the punches, a pump with relative electric motor and power supply circuit is necessary for each of the hydraulic cylinders.

[0014] An object of the present invention is to improve known machines and methods for machining sheet metal and in particular the machines provided with a plurality of working tools to be driven in a separate and independent manner, for example punching tools and / or cutting tools.

[0015] Another object is to provide a machine having low power consumption and high power efficiency.

[0016] A further object is to provide a machine which allows the working tools to perform in an optimal manner the machining processes, for example punching and cutting, in particular capable of driving and controlling the position, displacement and speed of each tool along a respective working axis in a precise and accurate way.

[0017] A first aspect of the invention provides a sheet metal working machine according to claim 1.

[0018] A second aspect of the invention provides a method for driving working tools in a sheet metal working machine according to claim 13.

[0019] The invention can be understood more fully and implemented with reference to the attached drawings, which illustrate some exemplary and non-limiting versions of the implementation thereof, in which:

[0020] - figure 1 is a schematic and partial view of a sheet metal working machine according to the invention, in particular a punching machine provided with a hydraulic drive system configured to drive a plurality of hydraulic cylinders of a multi-press punching apparatus in a non-operating step of the working tools;

[0021] - figure 2 is a schematic view like that of figure 1 which illustrates the machine and the hydraulic drive system in an approaching step to a workpiece with a working tool moved by a respective hydraulic cylinder.

[0022] - figure 3 is a schematic view like that of figure 2 illustrating the machine and the hydraulic drive system in a working step of the working tool which abuts against and is pushed against the workpiece by the hydraulic cylinder to perform the machining;

[0023] - figure 4 is a schematic view, like figure 2, illustrating the machine and the hydraulic drive system in a further working step of the working tool which abuts against the workpiece to perform the machining with a higher thrust force.

[0024] - figure 5 is a schematic view like that of figure 2 illustrating the machine and the hydraulic drive system in a disengagement step of the working tool detached and moved away from the workpiece;

[0025] - figure 6 is a schematic view of another embodiment of the machine of the invention, in particular of the combined punching and cutting type, wherein the hydraulic drive system is configured to drive a plurality of hydraulic operating cylinders of a multi -press punching apparatus, of a single punching apparatus and of a cutting apparatus.

[0026] Referring to figures 1 to 5, a machine 100 according to the invention suitable for the machining of metal sheets and comprising at least one working tool 51, 151, 61 for performing the machining on a workpiece 200 and a hydraulic drive system 1 suitable for driving the working tool 51, 151, 61 is schematically and partially illustrated.

[0027] The hydraulic drive system 1 comprises at least one hydraulic cylinder or jack 2, 102, 202 provided with a piston 21, 121, 221 defining inside the hydraulic cylinder 2, 102, 202 a thrust chamber 22, 122, 222 and a return chamber 23, 123, 223 and associated with the working tool 51, 151, 61 to move it along a respective working axis XI, X2, X3.

[0028] More precisely, the piston 21, 121, 221 comprises a main body slidable inside the respective hydraulic cylinder 2, 102, 202 to form the two variable volume chambers and a stem 24, 124, 224 which protrudes from the hydraulic cylinder 2, 102, 202 and is connected to the relative working tool 51, 151, 61 by means of connection means, of the known type and not illustrated in the figures.

[0029] The piston 21, 121, 221 of the hydraulic cylinder 2, 102, 202 comprises a first wall 21a, 121a, 221a facing the thrust chamber 22, 122, 222 and a second annular wall 21b, 121b, 221b facing the return chamber 23, 123, 223, a first surface or area Sila of the first wall 21a, 121a, 221a being larger than a second surface or area Siib of the second wall 21b, 121b, 221b, since to the latter the stem 24, 124, 224 is fixed which has a respective cross-section St. The second surface Siib of the second wall 21b, 121b, 221b and the cross-sectional area St of the stem 24 are equal to the first surface Siia of the first wall 21a, 121a, 221a. In particular, the first surface Siia is for example double the second surface Siib of the second wall 21b, 121b, 221b.

[0030] The machine 100 preferably comprises a plurality of working tools 51, 151, 61 and the hydraulic drive system 1 comprises a plurality of hydraulic cylinders or jacks 2, 102, 202 each of which is separately and independently operable and associated with a respective working tool 51, 151, 61 and provided with a respective piston 21, 121, 221 adapted to define inside the hydraulic cylinder 2, 102, 202 a thrust chamber 22, 122, 222 and a return chamber 23, 123, 223 and associated with the corresponding working tool 51, 151, 61 to move the latter along a respective working axis XI, X2, X3.

[0031] In the embodiment illustrated in figures 1 to 5 and described below, the machine 100 is, for example, a punching machine of the multi-press type, provided with a multi-press punching apparatus 50 comprising a plurality of punching working tools or punching tools 51 associated with respective hydraulic cylinders 2 and operable separately and independently from the hydraulic drive system 1.

[0032] The punching tools 51 of the multi-press punching apparatus 50, of the known type, only some of which illustrated in the figures for ease of representation, are for example arranged on several rows side by side so as to form a matrix structure of punching tools 51.

[0033] The hydraulic drive system 1 further comprises at least one reversible hydraulic pump 3 connected to a hydraulic fluid tank 4, in particular oil, and to the thrust chambers 22, 122, 222 and configured to send fluid at a supply pressure pminto at least one thrust chamber 22, 122, 222 during a driving step or to suck fluid from at least one thrust chamber 22, 122, 222 in a return step so as to move the piston 21, 121, 221 respectively along a working direction L, and allow the working tool 51, 151, 61 to interact with the workpiece 200 in a driving step C, D (fig. 2-4), or along a return direction R, and allow to disengage and move away the working tool 51, 151, 61 from the workpiece 200 in a disengagement step E (fig. 5).

[0034] In the working steps C and D, the pump 3 sucks the fluid from the tank 4 and sends it under pressure to one or more hydraulic cylinders 2, 102, 202 and in the disengagement step E, the pump 3 returns the fluid sucked from one or more hydraulic cylinders 2, 102, 202 back into the tank 4.

[0035] The fluid tank 4, in particular at atmospheric pressure, is connected to one mouth of the pump 3 via a drain duct 16, the other mouth of the pump 3 is connected to the hydraulic cylinders 2, 102, 202 via a supply circuit 15 formed by a plurality of supply ducts.

[0036] The hydraulic drive system 1 further comprises a hydraulic accumulator 5, of the known type and not described in detail, connectable to the return chambers 23, 123, 223 of the hydraulic cylinders 2, 102, 202 to supply fluid at a defined preload pressure pace, and valve means 10 interposed between the return chambers 23, 123, 223 of the hydraulic cylinders 2, 102, 202 and the hydraulic accumulator 5, the pump 3 and the tank 4. The valve means 10 are configured and controlled to connect the return chambers 23 selectively to the accumulator 5 in a non-operating configuration K0 and in a second operating configuration K2 or to the pump 3 in a first operating configuration KI or to the tank 4 in a third operating configuration K3.

[0037] The hydraulic drive system 1 also includes a plurality of valves 7, in particular inserted in the supply circuit 15, each of which is associated with a respective hydraulic cylinder 2, 102, 202, interposed between the pump 3 and the thrust chamber 22, 122, 222 of the hydraulic cylinder 2, 102, 202 and which can be opened to put the first pump 3 in flow connection with the thrust chamber 22, 122, 222 so as to drive the hydraulic cylinder 2, 102, 202 and the relevant working tool 51, 151, 61 in the working direction.

[0038] The valve means 10 are configured to connect the return chamber 2 selectively: to the accumulator 5 in the non-operating configuration K0 in which at least one working tool 51, 151, 61 is in a non-operating step A, spaced apart from the workpiece 200 and the pump 3 is not activated; to the pump 3 in the first operating configuration KI in which the at least one working tool 51, 151, 61 is in an approaching step B, moved by the respective hydraulic cylinder 2, 102, 202 towards the workpiece 200, when the pump 3 is activated and the supply pressure pmis higher than a first operating pressure pi; to the accumulator 5 in the second operating configuration K2 in which the at least one working tool 51, 151, 61 is in a working step C, pushed by the respective hydraulic cylinder 2, 102, 202 so as to interact with the workpiece 200 when the supply pressure pmof the pump 3 is higher than a second operating pressure p2, being higher than the first operating pressure pi; to the tank 4 in the third operating configuration K3 in which the at least one working tool 51, 151, 61 is in a further working step D, further pushed by the respective hydraulic cylinder 2, 102, 202 to interact with the workpiece 200 if and when the supply pressure pmof the pump 3 is higher than a third operating pressure ps being higher than the second operating pressure pi; to the accumulator 5 in the non-operating configuration K0 in which the at least one working tool 51, 151, 61 is in a disengagement step E and is disengaged and moved away from the workpiece 200 when the supply pressure pmof the pump 3 is lower than the first operating pressure pi.

[0039] As better explained in the following description, the first operating pressure pi is a function of the preload pressure pacc and the surfaces Sna, Sub of the walls 21a, 21b of the piston 21, 121, 221 according to the formula: pi = Pace • Sub / Sna [eq. 1]

[0040] The valve means 10 comprise, for example, a first control valve 11, a second control valve 12 and a third control valve 13, each of which, for example, of the three-way two-position type and provided with a respective inlet port Al l, A12, A130 and two respective outlet ports Pl l, Ti l, P12, T12, P13, T13. Each control valve 11, 12, 13 is controlled to switch between the two rest operating Rl l, R12, R13 and activation Wi l, W12, W13 positions hydraulically or electrically or pneumatically.

[0041] For example, in the embodiment illustrated in the figures, the control valves 11, 12, 13 are hydraulically controlled by the supply pressure pmat the outlet of the pump 3 by means of a control circuit 17 in flow connection with the supply circuit 15.

[0042] Alternatively, the control valves 11, 12, 13 can be controlled by electric or pneumatic actuators controlled by a control unit 10 of the machine 1 based on the supply pressure pmdetected in the supply circuit 15 by a pressure sensor 19.

[0043] The first control valve 11 comprises a first inlet port Al l connected to the return chambers 23 of the hydraulic cylinders 2 and connected to a first outlet port Pl 1, in a first rest position Rl l, and to a further first outlet port T11, in a first activation position Wi l. The first outlet port Pl 1 of the first control valve 11 is connected to a third inlet port A13 of the third control valve 13, and the further first outlet port Ti l of the first control valve 11 is connected to a second inlet port A12 of the second control valve 12. The second inlet port A12 of the second control valve 12 is connected in a second rest position R12 to a second further outlet port T12 which is connected to the pump 3 and in a second activation position W12 is connected to a second outlet port P12 connected to the third inlet port A13 of the third control valve 13.

[0044] The third inlet port A13 of the third control valve 13 is connected in a third rest position R13 to a third outlet port P13 which is connected to the accumulator 5 and in a third activation position W13 is connected to a further third outlet port T13 which is connected to the tank 4.

[0045] In the non-operating configuration KO of the valve means 10 the first, second and third control valves 11, 12, 13 are respectively in the first, second and third rest position Rl l, R12, R13.

[0046] In the first operating configuration KI of the valve means 10 the first control valve 11 is in the first activation position Wil and the second and third control valves 12, 13 are respectively in the second and third rest positions R12, R13.

[0047] In the second operating configuration K2 of the valve means 10 the first control valve 11 and the second control valve 12 are respectively in the first activation position Wi l and in the second activation position W 12 and the third control valve 13 is in the third rest position R13.

[0048] In the third operating configuration K3 of the valve means 10 the first, second and third control valves 11, 12, 13 are respectively in the first, second and third rest positions Rl l, R12, R13.

[0049] The hydraulic drive system 1 also comprises an electric motor 6 controlled by the control unit 10 of the machine 100 and arranged to drive the pump 3 in both rotation directions and in such a way that it delivers a defined flow rate of fluid at a set supply pressure pmin the thrust chamber 22, 122, 222 of the hydraulic cylinder 2, 102, 202 during the driving step to move the piston 21, 121 , 221 in the working direction L or suck fluid from the thrust chamber 22, 122, 222 during the return step to move the piston 21, 121, 221 in the return direction R. More precisely, the control unit 10 regulates the operation of the electric motor 6, in particular by varying the torque, speed and acceleration of the motor shaft that drives the pump 3 according to the operating conditions, such as the number of working tools 51, 151, 61 (i.e. hydraulic cylinders) to be driven, and the force to be exerted on the workpiece 200 (i.e. supply pressure pman of the fluid to the hydraulic cylinders). For this purpose the hydraulic drive system 1 may comprise a plurality of pressure sensors 19 inserted in the supply circuit 15, each of which is associated with a respective hydraulic cylinder 2, 102, 202 and capable of measuring a pressure of the fluid in the thrust chamber 22, 122, 222. The pressure sensors 19 are connected to the control unit 10 to send to it signals relating to the sensed pressures.

[0050] The operation of the sheet metal working machines 100 of the invention provided with the hydraulic drive system 1 provides for moving the tool or the working tools 51, 151, 61 necessary to perform the required machining processes on the workpiece 200. For example, in the embodiment of the machine 1 illustrated in figures 1 to 5, the hydraulic drive system 1 is controlled to move one of the plurality of punching tools 51 of the multi -press punching apparatus 50 by driving the respective first hydraulic cylinder 2.

[0051] The latter is driven by opening the corresponding activation valve 7 and driving the pump 3 in a first rotation direction, so as to send pressurized fluid into the thrust chamber 22 of the hydraulic cylinder 2. More precisely, the electric motor 6 is controlled by the control unit 10 so as to rotate the pump 3 in the first rotation direction at a defined speed and torque so that it delivers a set fluid flow rate at a supply pressure pmwhich determines the thrust force Fs(in this case, punching) to be exerted on the piston 22 and is linked to the resisting force FR that the latter opposes to movement along the working direction L.

[0052] In this initial step in which the working tool 51 is in the non-operating step A, spaced apart from the workpiece 200, the valve means 10 are arranged in the non-operating configuration KO in which they connect the return chamber 23 of the hydraulic cylinder 2 to the accumulator 5 which provides fluid at the preload pressure pace More precisely, in the nonoperating configuration KO of the valve means 10 the first, second and third control valves 11, 12, 13 are arranged respectively in the first, second and third rest positions Rl l, R12, R13.

[0053] To move the piston 21 in the working direction L it is necessary that the thrust force Fsexerted on the first wall 21a of the piston 21 by the supply pressure pmis higher than a resistive force FR exerted on the second wall 21b of the piston 21 by the preload pressure Pace guaranteed by the accumulator 5, i.e.:

[0054] Fs = Pm • S21a > FR = Pace ’ Sllb [eq. 2] where:

[0055] S2ia: first surface or area of the first wall 21a of the piston 21;

[0056] S2it>: second surface or area of the second wall 21b of the piston 21.

[0057] When the piston 21 begins to move in the working direction L and therefore the supply pressure pmis higher, for example by a defined value, for example equal to 1 Mpa than the first operating pressure pi equal to pacc• S2ib / Sila, that is when:

[0058] Pm pi=Pace ’ S21b / §21a [eq. 3] the valve means 10 are switched into the first operating configuration KI to connect the return chamber 23 of the hydraulic cylinder 2 to the pump 3. In this way, the pressure of the fluid in both the thrust chamber 22 and the return chamber 23 is equal to the supply pressure pm, and the fluid in the return chamber 23 is transferred to the thrust chamber 22. Since the first surface S2ia of the first wall 21a of the piston 21 is larger than the second surface S2ib of the second wall 21b of the piston 21, being, for example, twice as large with a minimum supply pressure pm, just slightly higher than the first operating pressure pi defined above, and without increasing the flow rate of the pump 3, that is, keeping the driving torque of the motor 6 unchanged and therefore the energy consumption unchanged, the piston 21 is moved in the working direction L at a speed higher than the initial one and equal to about double. In this way, the time necessary to move the piston 21 and then the working tool 51 in an approaching step B in which the latter is approached to the workpiece 200, decreases and substantially halves with respect to the time necessary to move the piston 21, thus keeping the return chamber 23 in connection with the accumulator 5.

[0059] In the first operating configuration KI of the valve means 10 the first control valve 11 is arranged in the first activation position Wi l while the second and third control valves 12, 13 are arranged respectively in the second and third rest positions R12, R13.

[0060] When the working tool 51 abuts against the workpiece 100, the resisting force FR exerted on the piston 21 increases and consequently the supply pressure pmof the fluid in the thrust chamber 22 increases.

[0061] When the supply pressure pmis higher than a second operating pressure p2 higher than the first operating pressure pi, the valve means 10 are switched into the second operating configuration K2 so as to connect the return chamber 23 to the accumulator 5 and solicit the working tool 51 to interact with the workpiece 200 in a working step C. The thrust force Fs exerted by the piston 21 in this working step C is given by the following formula:

[0062] FS = pm• S21a - Pace ’ S21a [eq. 4]

[0063] In the second operating configuration K2 of the valve means 10 the first control valve 11 and the second control valve 12 are arranged respectively in the first activation position Wi l and in the second activation position W12 and the third control valve 13 is arranged in the third rest position R13.

[0064] It should be noted that the preload pressure pace of the fluid in the return chamber 23 of the hydraulic cylinder 2 gives greater rigidity to the latter and to the supply circuit 15, i.e. the entire hydraulic drive system 1, which is thus more responsive and precise in the movements of the piston 21 and therefore of the working tool 51 during machining of the workpiece 200. In the event that the resisting force FR necessary to perform the machining on the workpiece 200 increases and a thrust force Fs of a value higher than a defined limit force is therefore necessary, that is, if the supply pressure pmis higher than a third operating pressure ps, higher than the second operating pressure p2, the valve means 10 are switched to the third operating configuration K3 so as to connect the return chamber 23 to the tank 4 to further push the working tool 51 against the workpiece 200 in a further working step D.

[0065] The thrust force Fsexerted by the piston 21 in this further working step D is given by the following formula:

[0066] Fs= pm• S2ia [eq. 5]

[0067] In the third operating configuration K3 of the valve means 10 the first, second and third control valves 11, 12, 13 are arranged respectively in the first, second and third rest positions R11, R12, R13.

[0068] Once the machining on the workpiece 200 has been completed, for example when the workpiece is punched, the resisting force FR drastically decreases and with it the thrust force Fs and therefore the supply pressure pm. When the supply pressure pmis lower than the first operating pressure pi, the valve means 10 are switched in the non-operating configuration KO to connect the return chamber 23 of the hydraulic cylinder 2 to the accumulator 5 which supplies fluid at the preload pressure pace necessary to push the piston 21 along the return direction R to disengage and move the working tool 51 away from the workpiece 200 in the disengagement step E. At the same time the pump 3 is driven by the motor 6 in the second rotation direction, opposite to the first rotation direction, to suck fluid from the thrust chamber 22 and convey it into the tank 4 via the drain duct 16.

[0069] This reduces the fluid pressure in the thrust chamber 22 (to a value close to the atmospheric pressure in the tank 4), allowing the fluid contained in the return chamber 23 at the preload pressure pacc (provided by the hydraulic accumulator 5) to push the piston 21 in the return direction R.

[0070] It should be noted that the use of the hydraulic accumulator 5 to move pistons 21 in the return direction simplifies the hydraulic drive system 1 and makes it more economical, as it avoids the use of additional valves to convey the fluid delivered by pump 3 to the return chambers 23. Moreover, the energy consumption of the electric motor 6 and the pump 3, which is essentially driven to connect the thrust chambers 22 to the tank 15, is minimal and lower than that which would be required for the pump 3 to move the pistons 21 in the return direction L.

[0071] The hydraulic drive system 1 is also able to simultaneously move several tools of the plurality of punching tools 51 of the multi-press punching apparatus 50 by driving the respective hydraulic cylinders 2, the operation being the same as that described below for the single punching tool 51 of the multi -press punching apparatus 50.

[0072] Figure 6 illustrates another embodiment of the machine 100 of the invention, of the so-called combined punching and cutting type, comprising a multi-press punching apparatus 50, a single punching apparatus 150 and a cutting apparatus 60. In this embodiment, the hydraulic drive system 1 is arranged to separately and independently drive a plurality of punching working tools or punching tools 51 of the multi -press punching apparatus 50, a single punching working tool or single punching tool 151 of the single punching apparatus 150, and one or more cutting working tools or cutting tools 61 of the cutting apparatus 60.

[0073] The punching tools 51 of the multi-press punching apparatus 50, of the known type, only one of which illustrated in the figures for ease of representation, are for example arranged on several rows side by side so as to form a matrix structure of punching tools 51. Each punching tool 51 is driven along a respective first working axis XI by a respective first hydraulic cylinder 2 of the hydraulic drive system 1 provided with a first piston 21 defining inside the first hydraulic cylinder 2 a first thrust chamber 22 and a first return chamber 23. The first piston 21 is connected via a first stem 24 to the punching tool 51.

[0074] The hydraulic drive system 1 further comprises a second hydraulic cylinder 102 for driving a single punching tool 151 of the single punching apparatus 150. The second hydraulic cylinder 102 is provided with a respective second piston 121 that forms a second thrust chamber 122 and a second return chamber 123 inside the second hydraulic cylinder 102 and is associated via a second stem 124 with the corresponding single punching tool 151 to move it along a respective second working axis X2.

[0075] The cutting apparatus 60 or shear unit, of a known type, comprises, for example, two cutting tools or blades 61 orthogonal to each other, movable independently along their respective axes to perform cuts on the sheet metal, a single cutting tool 61 being illustrated for simplicity of representation in figure 6.

[0076] The hydraulic drive system 1 therefore comprises at least one pair of third hydraulic cylinders 202 (only one of which is shown) arranged to drive the two cutting tools 61 of the cutting apparatus 60. Each third hydraulic cylinder 202 is provided with a respective third piston 221 which forms a third thrust chamber 222 and a third return chamber 223 inside the third hydraulic cylinder 202 and is associated with the corresponding cutting tool 61 by means of a third stem 224 to move it along a respective third working axis X3.

[0077] The hydraulic drive system 1 of this embodiment of the machine 100 of the invention further comprises a further pump 33, also of the reversible type, for example driven by a respective motor 36. The electric motors 6, 36 are commanded by the control unit 10.

[0078] The multi-press punching apparatus 50, the single punching apparatus 150 and the cutting apparatus 60 can work in sequence on the same workpiece 200 or on two or more workpieces 200 simultaneously.

[0079] The hydraulic drive system 1 is also capable of simultaneously moving multiple tools of the plurality of punching tools 51 of the multi-press punching apparatus 50 by driving the respective first hydraulic cylinders 2, or of driving the single punching tool 151 of the single punching apparatus 150 by driving the second hydraulic cylinder 102 or even of operating at least one cutting tool 61 of the cutting apparatus 60 by driving the respective third hydraulic cylinder 202, the operation being the same as the one described below for the single punching tool 51 of the multi-press punching apparatus 50.

[0080] Thanks to the hydraulic power supply system 1 of the sheet metal working machine 100 of the invention, it is therefore possible to drive precisely and accurately, individually and independently, one or more working tools 51, 151, 61 to perform one or more machining operations at the same time on the workpiece 200, thus allowing for a reduction in energy consumption, in particular the energy required to operate the pump 3.

[0081] By activating the activation valves 7, one or more hydraulic cylinders 2, 102, 202 can be selected to be driven to move the respective working tools, and in particular at least one of a single punching tool 151 of a single punching apparatus 150, one or more cutting tools 61 of a cutting apparatus 60 and at least one of a plurality of punching tools 51 of a multi-press punching apparatus 50.

[0082] By adjusting the rotation speed of the pump 3, by acting on the electric motor 6 controlled by the control unit 10, and by switching the valve means 10 it is possible to adjust the flow rate and the supply pressure pmof the fluid in the thrust chambers 22, 122, 222 of the hydraulic cylinders 2, 102, 202 and to control the position, displacement and speed of the pistons 21, 121, 221 and of the respective working tools along the operating axes XI, X2, X3.

[0083] In particular, the valve means 10 switched in the first operating configuration KI, when the supply pressure pmis higher than the first operating pressure pi, connect the return chambers 23 of the hydraulic cylinders 2 to the pump 3 and allow to have the same pressure (supply pressure pm) in both the push 22 and return chambers 23 and to the fluid present in the return chamber 23 to be transferred to the thrust chamber 22. Since the first surface S2 la of the first wall 21a of the piston 21 is higher than the second surface Siib of the second wall 21b of the piston 21, for example double, with a minimum supply pressure pmjust higher than the first operating pressure pi and without increasing the flow rate of the pump 3, i.e. keeping the driving torque of the motor 6 unchanged and therefore the energy consumption unchanged, the piston 21 is moved in the working direction L at a speed higher than the initial one and equal to about twice the latter. In this way, the time required to move the piston 21 and thus the working tool 51 in the approaching step to the workpiece 200 substantially decreases.

[0084] The valve means 10 switched into the third operating configuration K3, in which they connect the return chambers 23 of the hydraulic cylinders 2 to the tank 4 at atmospheric pressure, also allow the thrust force Fsto be increased while maintaining the supply pressure pmsubstantially constant, without increasing the power of the engine 6, i.e. energy consumption. The thrust force Fsactually exerted by the piston 21, 121, 221 in the working direction L is in fact equal to Fs= pm• Sila.

[0085] The hydraulic accumulator 5, in cooperation with the valve means 10 arranged in the nonoperating configuration K0, also allows to move the pistons 21, 121, 221 in the return direction R, thus simplifying and making the hydraulic drive system 1 more economical, since the use of dedicated valves to direct the fluid delivered by the pump 3 to the return chambers 23, 123, 223 is avoided, and the energy consumption of the electric motor 6 and the pump 3 is reduced, as the latter does not need to supply pressurized fluid to move the aforementioned pistons 21, 121, 221 in the return direction R.

[0086] Finally, the precision and responsiveness, i.e. the ability to react to the commands and adjustments (flow rate and / or pressure variations of the fluid in the cylinders) of the hydraulic cylinders 2, 102, 202 and of the entire hydraulic drive system 1 of the invention, is ensured by the rigidity of the latter obtained, as already highlighted, by connecting the return chambers 23, 123, 223 of the hydraulic cylinders 2, 102, 202 to the hydraulic accumulator 5 which maintains the fluid at a defined preload pressure pace, in particular by arranging the valve means 10 in the second working configuration K2 during the machining of the workpiece 200.

[0087] Thanks to the hydraulic drive system 1 the machine 100 of the invention is therefore more efficient in power consumption than the known sheet metal working machines.

[0088] It should also be noted that the use of the hydraulic drive system 1 which comprises a limited number of valves 11, 12, 13 and a normal hydraulic accumulator 5 is simple and economical and with reduced and compact dimensions and space requirements.

[0089] The method according to the invention for separately and independently driving at least one working tool 51, 151, 61 of a sheet metal working machine 100, provided with the hydraulic drive system 1 described above and illustrated in figures 1 to 5, comprises the following steps: driving the pump 3 in a first rotation direction to send pressurized fluid into a thrust chamber 22, 122, 222 of the hydraulic cylinder 2, 102, 202 associated with the at least one working tool 51, 151, 61, the return chamber 23, 123, 223 of the hydraulic cylinder 2, 102, 202 being connected by valve means 10 arranged in a non-operating configuration K0 to the hydraulic accumulator 5 which provides fluid at the preload pressure pacc, in particular in a non-operating step A of the working tool 51, 151, 61 in which it is spaced apart from the workpiece 200; switching the valve means 10 into a first operating configuration KI when the supply pressure pmof the fluid in the thrust chamber 22, 122, 222 is higher than a first operating pressure pi so as to connect the return chamber 23, 123, 223 to the pump 3 and move the working tool 51, 151, 61 closer to the workpiece 200 in an approaching step B; switching the valve means 10 to a second operating configuration K2 when the supply pressure pmof the fluid in the thrust chamber 22, 122, 222 is higher than a second operating pressure p2, higher than the first operating pressure pi, so as to connect the return chamber 23, 123, 223 to the accumulator 5 and push the working tool 51, 151, 61 to interact with the workpiece 200 in a working step C; switching the valve means 10 into a third operating configuration K3 if and when the supply pressure pmof the fluid in the thrust chamber 22, 122, 222 is higher than a third operating pressure ps, higher than the second operating pressure p2, so as to connect the return chamber 23, 123, 223 to the tank 4 and further push the working tool 51, 151, 61 to interact with the workpiece 200 in a further working step (D); switching the valve means 10 to the non-operating configuration K0 when the supply pressure pmof the fluid in the thrust chamber 22, 122, 222 is lower than the first operating pressure pi so as to connect the return chamber 23, 123, 223 to the accumulator 5 and driving the pump 3 in a second rotation direction, opposite to the first rotation direction, to suck fluid from the thrust chamber 22, 122, 222 in order to disengage and move the working tool 51, 151, 61 away from the workpiece 200 in a disengagement step E.

[0090] The first operating pressure pi is a function of the preload pressure pace and of the surfaces S2ia, S2ib of the walls 21a, 21b of the piston 2, 122, 222 according to the formula: pi = Pace • S21b / S21a [eq. 1] where:

[0091] S2ia: is the first surface of a first wall 21a, 121a, 221a of the piston 21, 121, 221 of the hydraulic cylinder 2, 102, 202 defining the thrust chamber 22, 122, 222;

[0092] S2ib: is the second surface of a second annular wall 21b, 121b, 221b of the piston 21, 121, 221 of the hydraulic cylinder 2, 102, 202 defining the return chamber 23, 123, 223 and smaller than the first surface Sila.

[0093] The method also comprises, before driving the pump 3 in a first rotation direction, selecting the at least one working tool 51, 151, 61, in particular among a plurality of working tools 51, 151, 61 of said machine 100, by opening an activation valve 7 associated with the respective hydraulic cylinder 2, 102, 202 so as to place the pump 3 and the thrust chamber 22, 122, 222 in flow connection in order to operate the hydraulic cylinder 2, 102, 202.

Claims

CLAIMS1. Sheet metal working machine (100) comprising at least one working tool (51, 151, 61) for performing machining operations on a workpiece (200) and a hydraulic drive system (1) suitable for separately and independently driving said at least one working tool (51, 151, 61) and comprising:- at least one hydraulic cylinder (2, 102, 202) provided with a piston (21, 121, 221) defining inside said hydraulic cylinder (2, 102, 202) a thrust chamber (22, 122, 222) and a return chamber (23, 123, 223) and associated with the working tool (51, 151, 61) to move it along a respective working axis (XI, X2, X3);- at least one reversible hydraulic pump (3), connected to a hydraulic fluid tank (4) and to the thrust chamber (22, 122, 222) of the hydraulic cylinder (2, 102, 202) and configured to send fluid at a supply pressure (pm) into said thrust chamber (22, 122, 222) in a driving step or to suck fluid from said thrust chamber (22, 122, 222) in a return step and to move the piston (21, 121, 221) respectively along a working direction (L) and allow the working tool (51, 151, 61) to interact with the workpiece (200) or along a return direction to disengage and move the working tool (51, 151, 61) away from the workpiece (200);- a hydraulic accumulator (5) connectable to the return chamber (23, 123, 223) of said at least one hydraulic cylinder (2, 102, 202) to supply fluid at a defined preload pressure (p acc), characterized in that it comprises valve means (10) interposed between the return chamber (23) of the hydraulic cylinder (2, 102, 202) and said hydraulic accumulator (5), said pump (3) and said tank (4), said valve means (10) being configured and controlled to connect said return chamber (23, 123, 223) selectively:- to said accumulator (5) in a non-operating configuration (K0) in which said working tool (51, 151, 61) is in a non-operating step (A), spaced apart from said workpiece (200) and said pump (3) is not activated;- to said pump (3) in a first operating configuration (KI) in which said working tool (51, 151, 61) is in an approaching step (B), moved by the respective hydraulic cylinder (2, 102, 202) towards said workpiece (200), when said pump (3) is activated and the supply pressure (pm) is higher than a first operating pressure (pi);- to said accumulator (5) in a second operating configuration (K2) in which said working tool (51, 151, 61) is in a working step (C), pushed by the respective hydraulic cylinder (2, 102, 202) so as to interact with said workpiece (200) when thesupply pressure (pm) is higher than a second operating pressure (pi), higher than the first operating pressure (pi);- to the tank (4) in a third operating configuration (K3) in which said working tool (51, 151, 61) is in a further working step (D), further pushed by the respective hydraulic cylinder (2, 102, 202) to interact with said workpiece (200) if and when said supply pressure (pm) is higher than a third operating pressure (ps), higher than the second operating pressure (pi);- to said accumulator (5) in a non-operating configuration (KO) in which said working tool (51, 151, 61) is in a disengagement step (E) and is disengaged and moved away from the workpiece (200) when the supply pressure (pm) is lower than the first operating pressure (pi).

2. Machine (100) according to claim 1, wherein said valve means (10) comprise a first control valve (11), a second control valve (12) and a third control valve (13), each of which is of the three-way, two-position type and provided with a respective inlet port (Al l, A12, A130) and two respective outlet ports (Pl l, Ti l, P12, T12, P13, T13), in particular each control valve (11, 12, 13) being hydraulically or electrically or pneumatically controlled in switching between a respective rest position (Rl l, R12, R13) and a respective activation position (Wi l, W12, W13).

3. Machine (100) according to claim 2, wherein said first control valve (11) comprises a first inlet port (Al l) connected to said return chamber (23, 123, 223) and connected to a first outlet port (Pl l), in a first rest position (Rl l), and to a further first outlet port (Ti l), in a first activation position (Wi l), said first outlet port (Pl l) being connected to a third inlet port (A 13) of said third control valve (13) and said further first outlet port (Ti l) being connected to a second inlet port (A12) of said second control valve (12), the second inlet port (A 12) of said second control valve (12) being connected, in a second rest position (R12), to a second further outlet port (T12) which is connected to said pump (3) and being connected, in a second activation position (W12), to a second outlet port (P12) connected to the third inlet port (A13) of said third control valve (13), the third inlet port (A13) of said third control valve (13) being connected in a third rest position (R13) to a third outlet port (P13) which is connected to said accumulator (5) and being connected, in a third activation position (W13), to a further third outlet port (T13) connected to said tank (4).

4. Machine (100) according to claim 3, wherein: in said non-operating configuration (K0) of said valve means (10) said first, secondand third control valves (11, 12, 13) are respectively arranged in the first, second and third rest positions (Rl l, R12, R13);- in said first operating configuration (KI) of said valve means (10) said first control valve (11) is arranged in the first activation position (W 11) and said second and third control valves (12, 13) are arranged respectively in the second and third rest position (R12, R13);- in said second operating configuration (K2) of said valve means (10) said first control valve (11) and said second control valve (12) are arranged respectively in the first activation position (Wi l) and in the second activation position (W12) and said third control valve (13) is arranged in the third rest position (R13);- in said third operating configuration (K3) of said valve means (10) said first, second and third control valves (11, 12, 13) are arranged respectively in the first, second and third rest position (Rl l, R12, R13).

5. Machine (100) according to one of the preceding claims, wherein said piston (21, 121, 221) of said at least one hydraulic cylinder (2, 102, 202) comprises a first wall (21a, 121a, 221a) defining said thrust chamber (22, 122, 222) and a second annular wall (21b, 121b, 221b) defining said return chamber (23, 123, 223), a first surface (Sila) of said first wall (21a, 121a, 221a) being larger, in particular double, than a second surface (Siib) of said second wall (21b, 121b, 221b).

6. Machine (100) according to claim 5, wherein said first operating pressure (pi) is a function of said preload pressure (pace) and of said surfaces (Sila, Siib) of said walls (21a, 21b) of the piston (21, 121, 221) according to the formula:Pl = Pace • S21b / S21a [eq. 1]7. Machine (100) according to one of the preceding claims, comprising a plurality of working tools (51, 151, 61), said hydraulic drive system (1) comprising a plurality of hydraulic cylinders (2, 102, 202) each of which is separately and independently operable and associated with a respective working tool (51, 151, 61) and provided with a respective piston (21, 121, 221) defining within the corresponding hydraulic cylinder (2, 102, 202) a thrust chamber (22, 122, 222) and a return chamber (23, 123, 223) and coupled to the working tool (51, 151, 61) for moving it along a respective working axis (XI, X2, X3), said thrust chambers (22, 122, 222) being connected to said at least one pump (3), said return chambers (23, 123, 223) being connected to said valve means (10).

8. Machine (100) according to one of the preceding claims, wherein said hydraulic drive system (1) comprises at least one activation valve (7) associated with the respectivehydraulic cylinder (2, 102, 202), interposed between the pump (3) and the thrust chamber (22, 122, 222) of the respective hydraulic cylinder (2, 102, 202) and operable to bring the pump (3) and the thrust chamber (22, 122, 222) into flow connection so as to operate the hydraulic cylinder (2, 102, 202), in particular said activation valve (7) being controlled by a control unit (10) of said machine (100).

9. Machine (100) according to one of the preceding claims, wherein said hydraulic drive system (1) comprises at least one electric motor (6) controlled by a control unit (10) of said machine (100) and arranged to drive said pump (3) in both rotation directions and in such a way that it delivers a defined flow rate of fluid at a set supply pressure (pm) in the driving step.

10. Machine (100) according to one of the preceding claims, wherein said hydraulic drive system (1) comprises a plurality of reversible type hydraulic pumps (3, 33) connected to said hydraulic fluid tank (4) and to the thrust chamber (22, 122, 222) of said at least one hydraulic cylinder (2, 102, 202).

11. Machine (100) according to one of the preceding claims, wherein said fluid tank (4) is at atmospheric pressure.

12. Machine (100) according to one of the preceding claims, comprising a plurality of working tools (51, 151, 61) belonging to at least one of a multi -press punching apparatus (50), single punching apparatus (150), cutting apparatus (60), said hydraulic drive system (1) being arranged to separately and independently drive at least one of a single punching working tool (151) of said single punching apparatus (150), cutting working tool (61) of said cutting apparatus (60) and punching working tool (51) of said multipress punching apparatus (50).

13. Method for separately and independently driving at least one working tool (51, 151, 61) of a sheet metal working machine (100) according to one of the preceding claims, comprising the steps of:- driving the pump (3) in a first rotation direction to send fluid under pressure into a thrust chamber (22, 122, 222) of the hydraulic cylinder (2, 102, 202) associated with the at least one working tool (51, 151, 61), the return chamber (23, 123, 223) of said hydraulic cylinder (2, 102, 202) being connected by means of valve means (10) arranged in a non-operating configuration (K0) to the accumulator (5) which supplies fluid at the preload pressure (pace), in particular in a non-operating step (A) of said working tool (51, 151, 61) in which the latter is spaced apart from a workpiece (200) to be machined;- switching said valve means (10) to a first operating configuration (KI) when the supply pressure (pm) of the fluid in the thrust chamber (22, 122, 222) is higher than a first operating pressure (pi) so as to connect said return chamber (23, 123, 223) to said pump (3) and move the working tool (51, 151, 61) closer to the workpiece (200) in an approaching step (B);- switching said valve means (10) into a second operating configuration (K2) when the supply pressure (pm) of the fluid in the thrust chamber (22, 122, 222) is higher than a second operating pressure (pi), higher than said first operating pressure (pi), so as to connect said return chamber (23, 123, 223) to the accumulator (5) and push the working tool (51, 151, 61) to interact with the workpiece (200) in a working step (C);- switching said valve means (10) into a third operating configuration (K3) if and when the supply pressure (pm) of the fluid in the thrust chamber (22, 122, 222) is higher than a third operating pressure (ps), higher than said second operating pressure (pi), so as to connect said return chamber (23, 123, 223) to the tank (4) and further push the working tool (51, 151, 61) to interact with the workpiece (200) in a further working step (D);- switching said valve means (10) into the non-operating configuration (K0) when the supply pressure (pm) of the fluid in the thrust chamber (22, 122, 222) is lower than said first operating pressure (pi) so as to connect said return chamber (23, 123, 223) to the accumulator (5) and driving the pump (3) in a second rotation direction, opposite to the first rotation direction, to suck fluid from the thrust chamber (22, 122, 222) in order to disengage and move the working tool (51, 151, 61) away from the workpiece (200) in a disengagement step (E).

14. Method according to claim 13, wherein said first operating pressure (pi) is a function of said preload pressure (pacc) and of surfaces (Sila, Siib) of walls (21a, 21b) of the piston (2, 122, 222) according to the formula:Pl = Pace • S21b / S21a [eq. 1] where:S2ia: is a first surface of a first wall (21a, 121a, 221a) of the piston (21, 121, 221) of the hydraulic cylinder (2, 102, 202) defining the thrust chamber (22, 122, 222);S2ib: is a second surface of a second annular wall (21b, 121b, 221b) of the piston (21, 121, 221) of the hydraulic cylinder (2, 102, 202) defining the return chamber (23, 123, 223) and smaller than the first surface (Sila).

15. Method according to claim 13 or 14, comprising before said driving said pump (3) in afirst rotation direction, selecting said at least one working tool (51, 151, 61) by opening an activation valve (7) associated with the respective hydraulic cylinder (2, 102, 202) to bring the pump (3) and the thrust chamber (22, 122, 222) into flow connection so as to operate the hydraulic cylinder (2, 102, 202).

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