Die cushion device and press machine including the same

Abstract

To provide a die cushion device which is excellent in reactivity and can efficiently apply sufficiently high energizing pressure, and to provide a press machine including the same.SOLUTION: The present invention includes a cushion pad disposed on a lower side of a press unit, a support column attached to a lower surface of the cushion pad, a hydraulic cylinder attached to an intermediate portion of the support column and configured to apply an intermediate biasing pressure to the cushion pad, a biasing mechanism attached to a lower end portion of the support column and configured to apply a lower end biasing pressure to the cushion pad, a servo motor configured to drive the biasing mechanism, and an output control unit attached to the hydraulic cylinder. In the die cushion device, the output control unit controls the intermediate biasing pressure to a first intermediate biasing pressure or a second intermediate biasing pressure smaller than the first intermediate biasing pressure, the first intermediate biasing pressure is applied by the hydraulic cylinder when the cushion pad is moved downward, and the second intermediate biasing pressure is applied by the hydraulic cylinder when the cushion pad is not moved downward.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a die cushion device and a press machine equipped with the same, and more specifically to a die cushion device that applies an upward biasing pressure in advance so as to counteract a downward processing pressure applied by a press unit during pressing, and a press machine equipped with the same. [Background technology]

[0002] In a press machine, a die cushion device is provided below a press section that performs press working on a workpiece. The die cushion device is a device that applies an upward biasing pressure in advance to counter the downward processing pressure applied by the press unit during pressing, thereby preventing wrinkles from occurring in the workpiece during press processing.

[0003] One known example of such a die cushion device includes a plurality of small pads that receive the pressing force of the slide via cushion pins, a large pad that supports the plurality of small pads, and a biasing force generating means that raises and lowers the large pad while generating an upward biasing force in response to the pressing force. The small and large pads form a die cushion pad that is provided in an internal space within a bed on which the die cushion device is provided. The small pads rise and lower within small spaces that are partitioned by ribs provided on the bed, and the large pad rises and lowers within the internal space below the ribs (see, for example, Patent Document 1).

[0004] Also known is a die cushion device that includes a cushion pad, a support column attached to the underside of the cushion pad, an air cylinder attached to the support column and urging the cushion pad upward, an upward urging device attached to the support column and urging the cushion pad upward, and a drive source for driving the upward urging device, wherein the air cylinder exerts cushion pressure from the support column against the weight of the upper movable part, and the upward urging device exerts the remaining cushion pressure, an oil chamber filled with oil is provided between the cushion pad and the support column, the upward urging device is a rack and pinion mechanism including a rack rod connected to the lower end of the support column and a pinion shaft meshed with the rack rod, and the drive source is a servo motor (see, for example, Patent Document 2).

[0005] The die cushion device also includes a first hydraulic cylinder that supports the cushion pad and generates a die cushion force on the cushion pad when the slide of the press machine descends; a first hydraulic circuit that drives the first hydraulic cylinder; a first pressure command generator that outputs a first pressure command indicating a die cushion pressure corresponding to the die cushion force; a first pressure detector that detects the pressure in a lower chamber of the first hydraulic cylinder; and a first controller that controls the first hydraulic circuit based on the first pressure command and the pressure detected by the first pressure detector so that the pressure applied to the first hydraulic cylinder becomes a pressure corresponding to the first pressure command. The first hydraulic circuit includes a die cushion pressure generation line connected to the lower chamber of the first hydraulic cylinder and a first system pressure A known die cushion device includes a hydraulic closed circuit including a system pressure line connected to a first accumulator that accumulates pressure in hydraulic fluid, a pilot-driven logic valve having an A port connected to the die cushion pressure generation line and a B port connected to the system pressure line, and a pressure generator that generates a pilot pressure that acts on the pilot port of the logic valve, wherein a first controller controls the pilot pressure based on a first pressure command and a pressure detected by a first pressure detector, and controls the pressure in a lower chamber of a first hydraulic cylinder, which is the pressure on the A port side of the hydraulic fluid that flows from the A port to the B port of the logic valve, to a pressure that corresponds to the first pressure command (see, for example, Patent Document 3). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 4704047 [Patent Document 2] Patent No. 5020216 [Patent Document 3] Japanese Patent Publication No. 2022-102104 Summary of the Invention [Problem to be solved by the invention]

[0007] In recent years, there has been a demand for faster and larger presses to accommodate the variety of workpieces, which has led to a demand for die cushion devices that are superior in responsiveness during pressing and that have a high biasing pressure capable of withstanding high processing pressure. However, although conventional die cushion devices including the die cushion devices described in Patent Documents 1 to 3 can exert a certain amount of biasing pressure, they cannot be said to be able to apply a sufficiently high biasing pressure. In particular, the die cushion device described in Patent Document 3 has difficulty in increasing speed, and cannot be said to have excellent reactivity.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a die cushion device that has excellent responsiveness during pressing and is capable of efficiently applying a sufficiently high biasing pressure, and a press machine including the same. [Means for solving the problem]

[0009] The inventors have conducted extensive research to solve the above problems, and have found that the above problems can be solved by providing a biasing mechanism and a hydraulic cylinder to enable efficient application of sufficient biasing pressure, by providing an output control unit for the hydraulic cylinder, and by using a servo motor as the drive source for the biasing mechanism to improve responsiveness, thereby completing the present invention.

[0010] The present invention provides a die cushion device for applying an upward biasing pressure against a downward processing pressure applied by a press unit during pressing, the die cushion device including: a cushion pad disposed below the press unit; a support pillar attached to the underside of the cushion pad; a hydraulic cylinder attached to an intermediate portion of the support pillar and for applying an intermediate biasing pressure to the cushion pad; a biasing mechanism attached to a lower end of the support pillar and for applying a lower-end biasing pressure to the cushion pad; a servo motor for driving the biasing mechanism; and an output control unit attached to the hydraulic cylinder, wherein the output control unit controls the intermediate biasing pressure to a first intermediate biasing pressure or a second intermediate biasing pressure that is smaller than the first intermediate biasing pressure. When the cushion pad is moving downward, the first intermediate biasing pressure is applied by the hydraulic cylinder, and when the cushion pad is not moving downward, the second intermediate biasing pressure is applied by the hydraulic cylinder.

[0011] In the die cushion device of the present invention, it is preferable that the output control unit has at least a servo pump and a control unit that controls the output of the servo pump, and that the control unit controls the output of the servo pump to switch between at least a high output at which a first intermediate biasing pressure is applied and a low output at which a second intermediate biasing pressure is applied.

[0012] In the die cushion device of the present invention, it is preferable that the output control unit further includes an outflow path through which oil in the hydraulic cylinder flows out, an inflow path through which oil flows into the hydraulic cylinder, a relief valve provided in the outflow path, and a pilot line through which the servo pump applies pressure to the relief valve, wherein the servo pump is provided in the inflow path, and when the control unit sets the output of the servo pump to high, a first pressure equivalent to a first intermediate energizing pressure is applied to the relief valve via the pilot line, and when there is an excess pressure exceeding the first intermediate energizing pressure in the processing pressure handled by the hydraulic cylinder, the relief valve opens to allow some of the oil to flow out from the hydraulic cylinder to the outside, thereby eliminating the excess pressure, and when the control unit sets the output of the servo pump to low, a second pressure equivalent to a second intermediate energizing pressure is applied to the oil in a direction that causes the oil to flow into the hydraulic cylinder.

[0013] In the die cushion device of the present invention, it is preferable that the output control unit further includes an oil tank for storing the oil flowing out from the hydraulic cylinder and the oil to be flowed into the hydraulic cylinder, that the inflow path is provided with a check valve closer to the hydraulic cylinder than the servo pump and a filter closer to the oil tank than the servo pump, and that the outflow path is provided with a filter closer to the oil tank than the relief valve.

[0014] In the die cushion device of the present invention, the second intermediate biasing pressure is preferably a pressure that is sufficient to support at least the total mass of the cushion pad, the support pillar, the hydraulic cylinder, and the movable parts of the biasing mechanism.

[0015] In the die cushion device of the present invention, the second intermediate biasing pressure is preferably 0.025 to 0.07 times the magnitude of the first intermediate biasing pressure.

[0016] The present invention is a press machine including a press section and the above-described die cushion device. [Effects of the Invention]

[0017] The die cushion device of the present invention employs a servo motor as the drive source for the biasing mechanism, thereby achieving excellent responsiveness. That is, when the cushion pad is pressed down by the downward processing pressure during pressing, the cushion pad can be quickly pushed up by the biasing pressure (hereinafter referred to as "responsiveness"). This enables the die cushion device to accommodate higher speeds in press processing.

[0018] In addition, the die cushion device includes a hydraulic cylinder for applying an intermediate biasing pressure and a biasing mechanism for applying a lower end biasing pressure, and therefore is capable of applying a sufficiently high biasing pressure. That is, the biasing pressure that counteracts the processing pressure is the sum of the intermediate biasing pressure and the lower end biasing pressure, so it is possible to apply a sufficiently high biasing pressure. Alternatively, if a high biasing pressure is not required, the load on the servo motor can be reduced, and the device can be made more compact.

[0019] Furthermore, in the hydraulic cylinder, the output control unit applies a first intermediate biasing pressure when the cushion pad is moving downward (when pressing), and applies a second intermediate biasing pressure that is smaller than the first intermediate biasing pressure at times other than when the cushion pad is moving downward, thereby making it possible to reduce energy loss. Specifically, by setting the second intermediate biasing pressure to 0.025 to 0.07 times the magnitude of the first intermediate biasing pressure, it is possible to sufficiently reduce energy loss. As a result, it is possible to apply the biasing pressure efficiently.

[0020] Here, since no processing pressure is applied except when the cushion pad is moving downward, it is sufficient for the second intermediate biasing pressure to be a pressure that is at least sufficient to support the total mass of the cushion pad, the support pillar, the hydraulic cylinder, and the movable parts of the biasing mechanism. This allows energy loss to be significantly reduced, making it possible to apply biasing pressure more efficiently.

[0021] In the die cushion device of the present invention, the output control unit includes a control unit, and therefore, the output of the servo pump can be quickly switched. Furthermore, because a servo pump, which is a pump driven by a servo motor, is used, it has excellent responsiveness to control commands, and the output based on that is accurate, making it possible to quantify the output value. As a result, the first intermediate biasing pressure and the second intermediate biasing pressure can be accurately set to necessary and sufficient levels, thereby reliably reducing energy loss. Furthermore, the servo pump can also improve the reaction of the hydraulic cylinder itself as much as possible.

[0022] In the die cushion device of the present invention, if the output control unit has a relief valve, when the processing pressure handled by the hydraulic cylinder contains excess pressure that exceeds the first intermediate biasing pressure, the relief valve opens to allow some of the oil to flow out from the hydraulic cylinder to the outside, thereby eliminating the excess pressure. This eliminates the excess pressure, so that the hydraulic cylinder can reliably exert the first intermediate biasing pressure that counteracts the processing pressure it is responsible for. It is also possible to mitigate the propagation of excessive processing pressure due to an overload that occurs the moment the cushion pad starts to descend.

[0023] On the other hand, when the cushion pad is not moving downward, the servo pump applies the second pressure to the oil, so that the hydraulic cylinder is filled with oil and a second intermediate biasing pressure is applied.

[0024] In the die cushion device of the present invention, if the output control unit further includes an oil tank, a circuit is formed by the output control unit and the oil tank, allowing oil to circulate. In addition, by providing a check valve on the hydraulic cylinder side of the inlet passage rather than the servo pump, the servo pump can cause oil to flow into the hydraulic cylinder via the inlet passage, preventing oil flowing out of the hydraulic cylinder from entering the inlet passage. In other words, the oil flowing out of the hydraulic cylinder can be reliably directed to the outflow path where the relief valve is located.

[0025] The press machine of the present invention is equipped with the die cushion device described above, and therefore has excellent responsiveness during pressing, enabling press working to be performed at high speed. Furthermore, since a sufficiently high biasing pressure can be applied efficiently, the press machine itself can be made larger (the load can be increased). As a result, it becomes possible to efficiently perform press working on a variety of workpieces. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 1 is a schematic diagram illustrating an outline of a die cushion device according to this embodiment. [Figure 2] FIG. 2 is a schematic diagram for explaining the output control unit of the die cushion device shown in FIG. [Figure 3] FIG. 3 is a schematic diagram showing an outline of the press machine according to this embodiment. [Figure 4] FIG. 4 is an explanatory diagram for explaining the operation of the press machine shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings as necessary. In the drawings, the same elements are denoted by the same reference numerals, and redundant explanations will be omitted. Furthermore, unless otherwise specified, the positional relationships such as up, down, left, and right will be based on the positional relationships shown in the drawings. Furthermore, the dimensional ratios of the drawings are not limited to those shown in the drawings.

[0028] The die cushion device according to the present invention is disposed below the press unit and applies an upward biasing pressure to the press unit in advance via a cushion pad to counteract the downward processing pressure applied by the press unit during pressing. Here, in this specification, the term "processing pressure" refers to the pressure applied to the cushion pad based on the downward load during pressing, and the term "urging pressure" refers to the pressure that urges the cushion pad upward against the processing pressure. In addition, the biasing pressure applied by the hydraulic cylinder is referred to as the "intermediate biasing pressure," and further, the intermediate biasing pressure applied when the cushion pad is moving downward is referred to as the "first intermediate biasing pressure," and the intermediate biasing pressure applied when the cushion pad is not moving downward is referred to as the "second intermediate biasing pressure." The biasing pressure exerted by the biasing mechanism is referred to as the "lower end biasing pressure." Furthermore, the "processing pressure provided by the hydraulic cylinder" is the pressure obtained by subtracting the lower end biasing pressure from the processing pressure provided by the press unit. Furthermore, "when pressing" and "when the cushion pad moves downward" are synonymous, and both refer to the timing at which the pressing section exerts processing pressure.

[0029] First, an embodiment of a die cushion device according to the present invention will be described. FIG. 1 is a schematic diagram illustrating an outline of a die cushion device according to this embodiment. As shown in FIG. 1, the die cushion device 100 includes a cushion pad 3 arranged below the press section 5 (see FIG. 3), a support pillar 11 attached to the underside of the cushion pad 3, a hydraulic cylinder 2 attached to the middle section of the support pillar 11, an output control unit 20 attached to the hydraulic cylinder 2, a biasing mechanism 1 attached to the lower end of the support pillar 11, a servo motor 13 for driving the biasing mechanism 1, a reducer 14 attached to the servo motor 13, and a housing 15 that houses at least the biasing mechanism 1 and the servo motor 13. Therefore, in the die cushion device 100, the hydraulic cylinder 2 and the biasing mechanism 1 are arranged in series in the vertical direction along the support pillar 11.

[0030] In the die cushion device 100, an upward intermediate biasing pressure is applied to the cushion pad 3 by the hydraulic cylinder 2 via the support pillar 11, and an upward lower end biasing pressure is applied to the cushion pad 3 by the biasing mechanism 1 via the support pillar 11. Therefore, the biasing pressure that can be applied by the die cushion device 100 is the sum of the intermediate biasing pressure and the lower-end biasing pressure. In other words, the processing pressure is dispersed into a pressure that opposes the lower-end biasing pressure (the processing pressure that is provided by the biasing mechanism 1) and a pressure that opposes the intermediate biasing pressure (the processing pressure that is provided by the hydraulic cylinder 2).

[0031] As described above, the die cushion device 100 is provided with the hydraulic cylinder 2 capable of applying a high biasing pressure in addition to the biasing mechanism 1, and is therefore able to apply a more sufficiently high biasing pressure. This makes it possible to accommodate larger press machines. On the other hand, if the press machine is not enlarged, the biasing pressure borne by the biasing mechanism 1 is reduced, which reduces the burden on the servo motor 13. Furthermore, by making the biasing mechanism 1 smaller, the die cushion device 100 itself can be made more compact. Furthermore, the energy load and noise can be reduced, and the life of the biasing mechanism 1 can be extended.

[0032] The cushion pad 3 is box-shaped with an open bottom, and is located at the top of the die cushion device 100. The cushion pad 3 has an upper surface that abuts against the cushion pins 51 of the press unit 5, and is movable up and down in conjunction with the up and down movement of the slide 56 of the press unit 5 (see FIG. 4). The cushion pad 3 has an oil chamber 4 at approximately the center of its lower surface, and a support pillar 11 is attached to the oil chamber 4.

[0033] In the cushion pad 3, the oil chamber 4 is box-shaped with an opening at approximately the center of the bottom wall, and the internal space is filled with oil. A support 11 is attached to the opening of the bottom wall, thereby sealing the space filled with oil and the opening. Therefore, the processing pressure during pressing is transmitted to the support 11 via the oil in the oil chamber 4.

[0034] In the die cushion device 100, by providing the oil chamber 4, the downward processing pressure during pressing is transmitted via oil, and therefore the processing pressure can be transmitted to the support columns 11 accurately. In addition, the oil in the oil chamber 4 also functions as a buffer material, which can mitigate the propagation of excessive processing pressure due to the overload that occurs the moment the cushion pad 3 begins to accelerate due to the processing pressure during pressing.

[0035] The support pillar 11 is a cylindrical rod, and its upper end is attached to the oil chamber 4. At this time, the shape of the upper end of the support pillar 11 is a spherical seat, so even if the cushion pad 3 is tilted due to an eccentric arrangement of the mold, etc., it is possible to transmit the processing pressure in the length direction of the first support pillar 11.

[0036] The support pillar 11 has a hydraulic cylinder 2 attached to its middle portion. The hydraulic cylinder 2 is a so-called power cylinder that is driven to expand and contract by hydraulic pressure, and has a cylinder portion 2a and a rod portion 2b attached and fixed to a support 11. The support 11 acts as a piston that slides the rod portion 2b along the inner wall of the cylinder portion 2a.

[0037] In the hydraulic cylinder 2, the area below the rod portion 2b in the cylinder portion 2a is filled with oil. Then, when the output control section 20, which will be described later, applies pressure to the oil, the pressure is transmitted to the hydraulic cylinder 2, and an intermediate biasing pressure is exerted in the direction of pushing up the rod section 2b.

[0038] The hydraulic cylinder 2 is attached and fixed to the upper surface of the upper wall of a housing 15, which will be described later, with fasteners such as bolts. By attaching the hydraulic cylinder 2 to the upper wall of the housing 15 in this way, a separate member for supporting the hydraulic cylinder 2 is not required. Furthermore, by utilizing the space above the housing 15 to place the hydraulic cylinder 2, the die cushion device 100 can be made compact.

[0039] In the hydraulic cylinder 2, the intermediate biasing pressure is variable. That is, the hydraulic cylinder 2 can change the intermediate biasing pressure to an intermediate biasing pressure applied when the cushion pad 3 moves downward (hereinafter referred to as the "first intermediate biasing pressure"), or an intermediate biasing pressure applied at times other than when the cushion pad 3 moves downward (hereinafter referred to as the "second intermediate biasing pressure").

[0040] Here, the second intermediate biasing pressure is smaller than the first intermediate biasing pressure. In the die cushion device 100, a high intermediate biasing pressure is not necessarily required except when the cushion pad 3 is moving downward, and therefore, by reducing the second intermediate biasing pressure, energy loss is reduced.

[0041] Specifically, the second intermediate biasing pressure is preferably a pressure that is at least sufficient to support the entire mass of the cushion pad 3, the support 11, the hydraulic cylinder 2, and the rack lever 1a, which is the movable part of the biasing mechanism 1. As a result, there is almost no load on the servo motor 13 except when the cushion pad 3 is moving downward, so that the load on the servo motor 13 can be reduced and energy loss can be significantly reduced.

[0042] The second intermediate biasing pressure is preferably 0.025 to 0.07 times the first intermediate biasing pressure. In this case, the first intermediate biasing pressure is sufficiently large relative to the processing pressure that the hydraulic cylinder is responsible for when the cushion pad 3 moves downward, and the second intermediate biasing pressure is sufficiently small when the cushion pad 3 is not moving downward, so that the intermediate biasing pressure can be applied efficiently.

[0043] In the die cushion device 100, the intermediate biasing pressure of the hydraulic cylinder 2 is controlled by the output control unit 20. FIG. 2 is a schematic diagram for explaining the output control unit of the die cushion device shown in FIG. As shown in FIG. 2, the output control unit 20 includes a mainstream passage 21 connected to the hydraulic cylinder 2, an outlet passage 21a connected to the mainstream passage 21 and allowing oil to flow out of the hydraulic cylinder 2, a relief valve 22 provided in the outlet passage 21a, an inlet passage 21b connected to the mainstream passage 21 and allowing oil to flow into the hydraulic cylinder 2, a check valve 26 and a servo pump 23 provided in the inlet passage 21b, a control unit 24 that controls the output of the servo pump 23, a pilot line 25 for applying pressure from the servo pump 23 to the relief valve 22, and an oil tank 27 in which oil is stored.

[0044] In the output control unit 20, a main passage 21 connected to the hydraulic cylinder 2 branches into an outflow passage 21a and an inflow passage 21b, and a check valve 26 is provided in the inflow passage 21b on the hydraulic cylinder side of the servo pump to prevent outflowing oil from flowing into the inflow passage 21b. Therefore, oil in the hydraulic cylinder 2 flows from the main passage 21 through the outflow passage 21a and out to the oil tank 27, and oil in the oil tank 27 flows from the inflow passage 21b through the main passage 21 and into the hydraulic cylinder 2.

[0045] In the output control section 20, a relief valve 22 is provided in the outflow path 21a. The relief valve 22 is a valve that opens when the pressure exceeds a set value. In the die cushion device 100, the set value is the value of the first pressure that corresponds to the first intermediate biasing pressure applied by the servo pump 23 via the pilot line 25. The relief valve 22 opens when the processing pressure that the hydraulic cylinder 2 is responsible for exceeds the first intermediate biasing pressure.

[0046] The servo pump 23 is a pump driven by a servo motor. By employing the servo pump 23, the output control section 20 can accurately output the first intermediate biasing pressure and the second intermediate biasing pressure that are necessary and sufficient for the hydraulic cylinder 2. In addition, it is also possible to digitize the output value. This makes it possible to control the processing pressure, biasing pressure, etc. by calculation. Moreover, by setting a reasonable value, energy loss can be reliably reduced. Furthermore, the servo pump 23 has excellent responsiveness to control commands from the control unit 24, and therefore the responsiveness of the hydraulic cylinder itself can be improved as much as possible.

[0047] The output of the servo pump 23 is controlled by a control unit 24 . The control unit 24 is a general one, and includes a CPU, a RAM, a ROM, and a memory. In the control unit 24, the CPU performs various calculation processes in accordance with the programs read from the ROM, and controls the output, operation, etc. of the servo pump 23.

[0048] The control unit 24 controls the output of the servo pump 23 to switch between at least a high output (first pressure) at which a first intermediate biasing pressure is applied, and a low output (second pressure) at which a second intermediate biasing pressure is applied. This allows the hydraulic cylinder 2 to exert the first intermediate biasing pressure at an appropriate time, and to exert the second intermediate biasing pressure at an appropriate time.

[0049] The oil tank 27 is a tank that stores oil that flows out of the hydraulic cylinder and oil that flows into the hydraulic cylinder. Therefore, by having the oil tank 27, the output control section 20 forms a circuit with the hydraulic cylinder 2, making it possible to circulate oil.

[0050] In the output control unit 20, a filter F is provided in the inflow path 21b closer to the oil tank 27 than the servo pump 23, and a filter F is provided in the outflow path 21a closer to the oil tank 27 than the relief valve 22. This makes it possible to prevent impurities from being mixed into the circuit and also to remove impurities that have been mixed in.

[0051] Here, the control of the hydraulic cylinder 2 in the output control unit 20 will be described. First, during pressing by the press unit, the moment a processing pressure is applied, the servo pump 23 applies a high-output first pressure to the relief valve 22 via the pilot line 25 based on a command from the control unit 24. As a result, the hydraulic cylinder 2 exerts a first intermediate biasing pressure based on the first pressure.

[0052] Then, when the processing pressure increases instantaneously, the processing pressure handled by the hydraulic cylinder 2 becomes greater than the first intermediate biasing pressure, and the rod portion 2b of the hydraulic cylinder 2 moves downward together with the cushion pad 3 by the amount of excess pressure exceeding the first intermediate biasing pressure. As a result, the oil in the hydraulic cylinder 2 is pushed out into the main passage 21 and flows through the outflow passage 21a. That is, because there is excess pressure exceeding the first intermediate biasing pressure, the relief valve 22 opens and some of the oil flows from the outflow passage 21a through the filter F to the oil tank 27. This eliminates the excess pressure. Therefore, when the cushion pad moves downward, the first intermediate biasing pressure is maintained at a constant value. It is also possible to mitigate the propagation of excessive processing pressure due to an overload that occurs the moment the cushion pad starts to descend. In addition, since the check valve 26 is provided in the inflow passage 21b on the hydraulic cylinder 2 side of the servo pump 23, the oil flowing through the main passage 21 does not flow into the inflow passage 21b.

[0053] When the cushion pad 3 reaches the bottom dead center, the processing pressure is released, and the servo pump 23 applies a second pressure, which is a low output, to the oil based on a command from the control unit 24. As a result, the hydraulic cylinder 2 exerts a second intermediate biasing pressure based on the second pressure.

[0054] Then, the second intermediate biasing pressure naturally becomes larger than the released processing pressure, and the rod portion 2b of the hydraulic cylinder 2 moves downward together with the cushion pad 3. Then, the oil in the oil tank 27 flows through the inflow passage 21b via the filter F and flows into the hydraulic cylinder 2 from the main passage 21. Therefore, the second intermediate biasing pressure is maintained at a constant value except when the cushion pad is moving downward. In addition, since the outflow passage 21a is provided with a relief valve 22, the oil flowing through the inflow passage 21b does not flow into the outflow passage 21a. In this way, the hydraulic cylinder 2 returns to its original state.

[0055] Returning to FIG. 1, the support column 11 has a biasing mechanism 1 attached to its lower end. As the biasing mechanism 1, a linear motion mechanism is preferably used because the cushion pad 3 moves up and down, and specifically, a ball screw, a rack and pinion mechanism, a belt drive mechanism, a slider crank mechanism, etc. can be used. Among these, it is preferable to use a rack and pinion mechanism as the biasing mechanism 1. In this case, the biasing mechanism 1 (rack and pinion mechanism) can handle a larger load (processing pressure) than other biasing mechanisms 1, and is superior in terms of high-speed operation.

[0056] In the die cushion device 100, a rack and pinion device is used as the biasing mechanism 12. In the die cushion device 100, the rack and pinion mechanism includes a rack rod 1a and a pinion shaft 1b that meshes with the rack rod 1a. The rack rod 1a is connected to the lower end of the support 11 so as to be integral with it, and moves up and down together with the support 11. The pinion shaft 1b is meshed with the rack shaft 1a and is connected to a servo motor 13.

[0057] The servo motor 13 drives the biasing mechanism 1, whereby the lower end biasing pressure is transmitted to the cushion pad 3 via the support 11. Furthermore, a reducer 14 may be attached to the servo motor 13. In this case, it becomes possible to appropriately convert the rotation speed or rotation torque of the servo motor 13. Furthermore, by using the reducer 14 and appropriately selecting the reduction ratio, the motor shaft torque can be reduced.

[0058] The biasing mechanism 1 employs the servo motor 13 as a drive source, and therefore has excellent responsiveness. Furthermore, by making the reaction of the operation of the hydraulic cylinder 2 follow the reaction of the servo motor 13 of the biasing mechanism 1 as much as possible, the die cushion device 100 as a whole can have excellent reaction properties. As a result, the die cushion device 100 can accommodate higher speeds in press working.

[0059] The housing 15 accommodates at least the biasing mechanism 1 and the servo motor 13 . Since the servo motor 13 is generally huge, the housing 15 has an area substantially equal to that of the cushion pad 3 when viewed from above. In the die cushion device 100, by providing the housing 15, it is possible to reduce the noise generated by the servo motor 13 and ensure safety. Furthermore, by disposing the hydraulic cylinder 2 on the upper surface of the upper wall of the housing 15, it can also function as a base for the hydraulic cylinder 2.

[0060] In the die cushion device 100, the cushion pad 3 moves up and down in accordance with the upward and downward movement of the slide 56 of the press unit 5. That is, in the die cushion device 100, before pressing, the cushion pad 3 is located at the top dead center. At this time, the cushion pad 3 is constantly subjected to the second intermediate biasing pressure and the lower end biasing pressure. During pressing, the processing pressure momentarily exceeds the first intermediate biasing pressure, so that the cushion pad 3 is pressed downward. Then, when the processing pressure is released after pressing, the cushion pad 3 returns to the original position of the top dead center due to the second intermediate biasing pressure. The details of the movement of the die cushion device 100 will be described later together with the press machine.

[0061] As described above, the die cushion device 100 can apply a sufficiently high biasing pressure to the cushion pad 3, and therefore can also accommodate an increase in processing pressure. In other words, it can accommodate an increase in the size of a press machine. Furthermore, as described above, the die cushion device 100 has excellent responsiveness during pressing, so the cushion pad 3 returns quickly and can accommodate higher speeds in press working.

[0062] Next, an embodiment of a press machine according to the present invention will be described. FIG. 3 is a schematic diagram showing an outline of the press machine according to this embodiment. 3, the press machine 101 includes a press section 5 and the above-described die cushion device 100. The press section 5 is usually installed on the ground, and the die cushion device 100 is installed underground in a place called a pit.

[0063] In the press machine 101, the press section 5 includes at least a bolster 53 fixed to the ground, a lower die 55a installed on the upper surface of the bolster 53, an upper die 55b having a shape corresponding to the lower die 55a, a slide 56 on which the upper die 55b is supported, a cushion pin 51 provided on the upper surface of the cushion pad 3 and protruding upward through a hole provided in the bolster, and a blank holder 52 provided at the upper end of the cushion pin 51. The workpiece W is placed on the upper surfaces of the lower die 55b and the blank holder 52.

[0064] In the press machine 101, the slide 5 can be moved up and down by a known driving mechanism (not shown) such as a crank mechanism, a link mechanism, or a knuckle mechanism. Further, in the press machine 101, a known conveying device (not shown) such as a feeder or a robot for carrying in or out the workpiece W is arranged in the press machine 101 or in the vicinity of the press machine 101.

[0065] FIG. 4 is an explanatory diagram for explaining the operation of the press machine shown in FIG. First, the workpiece W is placed so that the center of the workpiece W is on the lower die 55a and the periphery of the workpiece W to be deformed is on the blank holder 52. As shown in FIG. 4, a first state 101A of the press machine (upper left of the drawing in FIG. 4) is a state before press working. At this time, the slide 56 is positioned at the top dead center within the range in which the slide 56 moves up and down, and the cushion pad 3 is positioned at the top dead center within the range in which the cushion pad 3 moves up and down with the second intermediate biasing pressure and the lower end biasing pressure being applied.

[0066] In the press working, the slide 56 and the upper die 55b are lowered. In a second state 101B of the press machine (upper right in FIG. 4), the press machine is in the process of pressing, and the upper die 55b is in contact with the workpiece W. Note that the processing pressure has not yet been generated. The cushion pad 3 is constantly maintained in a state in which the second intermediate biasing pressure and the lower end biasing pressure are applied.

[0067] Next, a processing pressure (load) is applied to the workpiece W, and the workpiece W is sandwiched between the lower die 55a and the upper die 55b, thereby forming the workpiece W into a predetermined shape. The time when the processing pressure is applied to the workpiece W is the pressing time. At this time, the output of the servo pump 23 of the output control unit 20 is switched from low output to high output. During pressing, the cushion pins 51 are pressed downward as the workpiece W is deformed. In addition, the processing pressure is transmitted to the cushion pad 3 via the cushion pin 51, and since the instantaneous processing pressure is greater than the sum of the first intermediate biasing pressure and the lower end biasing pressure, the cushion pad 3 is also pressed down.

[0068] The third state 101C of the press machine (bottom right of the page in Figure 4) is a state in which the slide 56 has reached the bottom dead center within the range in which the slide 56 moves up and down, and the cushion pad 3 has also reached the bottom dead center within the range in which it moves up and down. At this time, the output of the servo pump 23 of the output control unit 20 is switched from high output to low output.

[0069] Then, the slide 56 and the upper die 55b are raised. At this time, the slide 56 returns to the top dead center within the range in which the slide 56 moves up and down, and since the processing pressure has been released, the cushion pad 3 returns to the top dead center within the range in which the cushion pad 3 moves up and down due to the second intermediate biasing pressure and the lower end biasing pressure. The fourth state 101D of the press machine (bottom left of the paper in Figure 4) is a state in which the slide 56 after press processing has reached the top dead center within the range of its vertical movement, and the cushion pad 3 has also reached the top dead center within the range of its vertical movement.

[0070] Then, the workpiece W machined into a desired shape is removed by a transfer device (not shown) or the like after the upper die 55b has been retracted. In this cycle, press working is continuously performed on the workpiece W.

[0071] The press machine 101 is equipped with the die cushion device 100 described above, and therefore can quickly perform the reaction of returning the cushion pad 3 to the top dead center. As a result, it is possible to speed up the press working. Furthermore, since the die cushion device 100 described above is provided, a sufficiently high biasing pressure can be applied, so the press machine itself can be made larger (the load can be increased). Furthermore, it becomes possible to efficiently perform press working on a variety of workpieces.

[0072] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments.

[0073] In the die cushion device 100 according to this embodiment, the biasing mechanism 1 is provided approximately in the center of the lower surface of the cushion pad 3, but if the mold is disposed eccentrically, the biasing mechanism 1 may be shifted from the center.

[0074] In the die cushion device 100 according to this embodiment, the intermediate biasing pressure applied by the hydraulic cylinder 2 is variable in two stages: a first intermediate biasing pressure and a second intermediate biasing pressure. However, it may also have another intermediate biasing pressure, making it variable in three or more stages.

[0075] In the die cushion device 100 according to this embodiment, the output control unit 20 includes the main passage 21, but this is not essential. That is, the outflow passage 21a and the inflow passage 21b may be directly connected to the hydraulic cylinder 2, respectively. Furthermore, if it is possible to supply oil to the hydraulic cylinder 2 and to recover oil from the hydraulic cylinder 2, the oil tank 27 is not essential.

[0076] In the die cushion device 100 according to this embodiment, the biasing mechanism 1 has a housing 15 that houses the biasing mechanism 1 and the servo motor 13, but this is not essential. In this case, the hydraulic cylinder 2 is supported and fixed to a frame or the like.

[0077] In the die cushion device 100 according to this embodiment, the servo motor 13 may be controlled by a separate control unit so that the lower end biasing pressure can be varied.

[0078] In the die cushion device 100 according to this embodiment, the second intermediate biasing pressure and the lower end biasing pressure are always applied and maintained except when the cushion pad 3 is moving downward. However, it is also possible to maintain the state in which only the second intermediate biasing pressure is applied.

[0079] In the press machine according to this embodiment, one die cushion device 100 is attached to one press section 5, but multiple die cushion devices 100 may be attached to one press section 5. [Industrial Applicability]

[0080] The die cushion device according to the present invention can be used as a device for applying an upward biasing pressure in advance to counter the downward processing pressure applied by the press unit during pressing. The die cushion device has excellent responsiveness during pressing and can efficiently apply a sufficiently high biasing pressure. The press machine according to the present invention can be used as a machine for pressing a workpiece into a desired shape. According to this press machine, the press machine itself can be made larger, and the press working speed can be increased. [Explanation of symbols]

[0081] 1...Biasing mechanism 100 Die cushion device 101 Press Machine 11...post 13. Servo motor 14...Reducer 15. Enclosure 1a···Rack 1b Pinion shaft 2. Hydraulic cylinder 20 Output control section 21... Mainstream passage 21a...Outflow channel 21b...Inflow channel 22 Relief valve 23 Servo pump 24 Control section 25 Pilot Line 26. Check valve 27 Oil tank 2a Cylinder section 2b Rod section 3. Cushion pad 4...Oil room 5. Press Department 51···Cushion pin 52 Blank holder 53 Bolster 55a...Lower mold 55b···Upper mold 56 Slide F···Filter W...Work

Claims

1. A die cushion device for applying an upward biasing pressure against a downward processing pressure applied by a press unit during pressing, a cushion pad disposed below the press unit; a support column attached to the underside of the cushion pad; a hydraulic cylinder attached to an intermediate portion of the support pillar for applying an intermediate biasing pressure to the cushion pad; a biasing mechanism attached to a lower end of the support pillar and configured to apply a lower end biasing pressure to the cushion pad; a servo motor for driving the biasing mechanism; an output control unit attached to the hydraulic cylinder; Equipped with the output control unit controls the intermediate biasing pressure to a first intermediate biasing pressure or a second intermediate biasing pressure that is smaller than the first intermediate biasing pressure, When the cushion pad moves downward, the first intermediate biasing pressure is applied by the hydraulic cylinder, the second intermediate biasing pressure is applied by the hydraulic cylinder except when the cushion pad is moving downward.

2. The output control unit includes at least A servo pump, a control unit for controlling the output of the servo pump; and 2. The die cushion device according to claim 1, wherein the control unit controls the output of the servo pump to switch between at least a high output at which the first intermediate biasing pressure is applied and a low output at which the second intermediate biasing pressure is applied.

3. The output control unit an outflow path for outflowing oil from the hydraulic cylinder; an inlet passage for allowing oil to flow into the hydraulic cylinder; a relief valve provided in the outflow path; a pilot line for the servo pump to apply pressure to the relief valve; and The servo pump is provided in the inlet passage, When the control unit sets the output of the servo pump to the high output, a first pressure equivalent to the first intermediate energizing pressure is applied to the relief valve via the pilot line, and when the machining pressure applied to the oil has an excess pressure exceeding the first intermediate energizing pressure, the relief valve opens to allow a portion of the oil to flow out from the hydraulic cylinder, thereby eliminating the excess pressure, 3. The die cushion device according to claim 2, wherein, when the control unit sets the output of the servo pump to the low output, a second pressure corresponding to the second intermediate biasing pressure is applied to the oil in a direction that causes the oil to flow into the hydraulic cylinder.

4. The output control unit further includes an oil tank for storing oil flowing out of the hydraulic cylinder and oil to be flowed into the hydraulic cylinder, a check valve is provided in the inflow path closer to the hydraulic cylinder than the servo pump, and a filter is provided in the inflow path closer to the oil tank than the servo pump, 4. The die cushion device according to claim 3, wherein a filter is provided in the outflow path on the oil tank side of the relief valve.

5. 2. The die cushion device according to claim 1, wherein the second intermediate biasing pressure is a pressure sufficient to support the entire mass of the cushion pad, the support column, the hydraulic cylinder, and a driving portion of the biasing mechanism.

6. 2. The die cushion device according to claim 1, wherein the second intermediate biasing pressure is 0.025 to 0.07 times the magnitude of the first intermediate biasing pressure.

7. The press unit; A press machine comprising: the die cushion device according to any one of claims 1 to 6.

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