Die cushion device

There is provided a die cushion device that includes a cushion pad, a hydraulic cylinder configured to lift the cushion pad, and a hydraulic closed circuit connected to a die cushion pressure creation chamber of the hydraulic cylinder. The hydraulic closed circuit includes a pilot drive type logic valve that is operable as a main relief valve at the time of the die cushion operation, and a pilot relief valve configured to create pilot pressure for controlling the logic valve. Hydraulic oil is filled in the hydraulic closed circuit, in a pressurized manner, and the hydraulic oil in the hydraulic closed circuit is pressurized by only die cushion force applied from the cushion pad through the hydraulic cylinder, in one cycle period of the cushion pad.

CROSS-REFERENCE TO RELATED APPLICATIONS

The subject application claims priority to Japanese Patent Application No. 2014-120394 filed Jun. 11, 2014, the subject matter of which is incorporated herein by reference in entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a die cushion device, and more particularly, to an inexpensive and functionally efficient die cushion device.

Description of the Related Art

Heretofore, there is proposed a die cushion device configured to create die cushion pressure by using a balance piston type relief valve (Japanese Patent Application Laid-Open No. 2001-079694, hereinafter referred to as PTL 1).

The die cushion device described in PTL 1 includes, as a device that creates hydraulic pressure to be supplied to a cushion cylinder, a first hydraulic creation mechanism that creates low hydraulic pressure, and a second hydraulic creation mechanism that creates high hydraulic pressure. In the die cushion device, the first hydraulic creation mechanism first applies low hydraulic pressure to a cushion cylinder after molding for each molding cycle to extend the cushion cylinder, and while the cushion cylinder is positioned near a top dead center, the second hydraulic creation mechanism applies high hydraulic pressure to the cushion cylinder to increase the cushion pressure in advance. In addition, when die cushion is operated, hydraulic oil in the cushion cylinder is returned to a sealed oil tank through a pilot check valve to which pilot pressure (high hydraulic pressure) is applied and a pilot relief valve to which compressed air is applied.

Here, the first hydraulic creation mechanism is composed of the sealed oil tank, a compressed air supply source that supplies compressed air at low pressure to the sealed oil tank, and the like, and the second hydraulic creation mechanism is composed of a hydraulic pump and an electric motor, which are continuously operated during operation of a press machine.

SUMMARY OF THE INVENTION

In the die cushion device described in PTL 1, when the first hydraulic creation mechanism (sealed oil tank) applies low hydraulic pressure to the cushion cylinder to extend the cushion cylinder, compressed air (0.5 MPa, for example) is supplied to the sealed oil tank from the compressed air supply source, and the hydraulic pump and the electric motor constituting the second hydraulic creation mechanism are continuously operated during operation of the press machine. In addition, high hydraulic pressure (20 to 30 MPa, for example) created by the second hydraulic creation mechanism is accumulated in an accumulator to be applied to the cushion cylinder while the cushion cylinder is positioned near the top dead center.

That is, since the die cushion device described in PTL 1 requires a compressed air supply source for creating low hydraulic pressure and a hydraulic pump and an electric motor for creating high hydraulic pressure, there is a problem in which the device becomes complicated and expensive. In addition, there is a problem of requiring power costs (running costs) of driving the compressed air supply source and the electric motor for each cycle of die cushion operation.

The present invention has been made in light of the above-mentioned circumstances, and an object of the present invention is to provide an inexpensive and functionally efficient die cushion device that does not require a device consuming electric power such as a hydraulic pump.

In order to achieve the object above, a die cushion device in accordance with one aspect of the present invention includes: a cushion pad; a fluid-pressure cylinder configured to lift the cushion pad; and a fluid-pressure closed circuit that includes a die cushion pressure creation line connected to a die cushion pressure creation chamber of the fluid-pressure cylinder, a system pressure line to which an accumulator is connected, the accumulator being configured to accumulate hydraulic fluid at low system pressure capable of knockout operation, a pilot drive type logic valve that is provided between the die cushion pressure creation line and the system pressure line, and that is operable as a main relief valve at a time of die cushion operation, and a pilot relief valve that is provided between the die cushion pressure creation line and the system pressure line, and that creates pilot pressure for controlling the logic valve. In the die cushion device, hydraulic fluid is filled in the fluid-pressure closed circuit in a pressurized manner, and a fluid-pressure pump configured to pressurize and feed the hydraulic fluid is not provided, so that it is possible to pressurize the hydraulic fluid in the fluid-pressure closed circuit in one cycle period of the cushion pad, including the die cushion operation and the knockout operation, by using only die cushion force applied from the cushion pad through the fluid-pressure cylinder.

In accordance with the one aspect of the present invention, there is provided a fluid-pressure closed circuit including a pilot drive type (balance piston type) relief valve of combination of the logic valve and the pilot relief valve. In the fluid-pressure closed circuit, hydraulic fluid is filled in a pressurized manner, and the hydraulic fluid in the fluid-pressure closed circuit is pressurized in one cycle period of the cushion pad, including the die cushion operation and the knockout operation, by using only die cushion force applied from the cushion pad through the fluid-pressure cylinder, so that a fluid-pressure pump is not provided. At the time of the die cushion operation, the logic valve operates as a main relief valve to create die cushion pressure corresponding to the pilot pressure created by the pilot relief valve. In addition, rising (uplift) operation including the knockout operation of the cushion pad is performed by using hydraulic fluid at system pressure accumulated in the accumulator. In this manner, the hydraulic fluid is pressurized in one cycle period of the cushion pad by only die cushion force applied from the cushion pad through the fluid-pressure cylinder. As a result, no fluid-pressure pump is provided in the fluid-pressure closed circuit so that it is possible to save power costs.

In a die cushion device in accordance with another aspect of the present invention, there is provided a first solenoid valve that switches pressure to act on a pilot port of the logic valve to any one of the pilot pressure and the system pressure during one cycle period of the cushion pad. When the first solenoid valve switches so that the pilot pressure acts on the pilot port of the logic valve, it is possible to create die cushion pressure corresponding to the pilot pressure in the die cushion pressure creation line. In addition, when the first solenoid valve switches so that the system pressure acts on the pilot port of the logic valve, it is possible to reduce die cushion pressure created in the die cushion pressure creation line to the system pressure.

In a die cushion device in accordance with yet another aspect of the present invention, it is preferable that the first solenoid valve is a poppet type solenoid valve. This is because there is no leak of hydraulic fluid in the poppet type solenoid valve.

In a die cushion device in accordance with yet another aspect of the present invention, it is preferable to provide a second solenoid valve between the die cushion pressure creation line and the system pressure line. The second solenoid valve is controlled to enable locking operation and rising operation of the cushion pad at the bottom dead center.

In a die cushion device in accordance with yet another aspect of the present invention, it is preferable that the second solenoid valve is a poppet type solenoid valve. This is because there is no leak of hydraulic fluid in the poppet type solenoid valve.

In a die cushion device in accordance with yet another aspect of the present invention, there is provided a controller configured to control the first solenoid valve and the second solenoid valve. The controller controls the first solenoid valve so that the pilot pressure is applied to a pilot port of the logic valve during a descending period of the cushion pad, and controls the second solenoid valve so that the second solenoid valve is opened during a rising period of the cushion pad. Since the controller performs only a simple control of the first and second solenoid valves (since no special control device is required), a part of a controller, such as a programmable logic controller (PLC), of a press machine, and the like, is available for the controller to become inexpensive.

In a die cushion device in accordance with yet another aspect of the present invention, the first solenoid valve is controlled so as to apply the pilot pressure to the pilot port of the logic valve during a descending (lifting down) period of the cushion pad to enable die cushion pressure corresponding to the pilot pressure to be created in the die cushion pressure creation line, as well as to enable die cushion force to be created in the fluid-pressure cylinder during a descending period of the cushion pad. In addition, the second solenoid valve is opened at an appropriate timing after the die cushion operation to enable hydraulic fluid at the system pressure accumulated in the accumulator to be supplied to the fluid-pressure cylinder through the die cushion pressure creation line. As a result, it is possible to raise the cushion pad to a standby position.

In a die cushion device in accordance with yet another aspect of the present invention, it is preferable to provide a plurality of second solenoid valves in a line between the die cushion pressure creation line and the system pressure line in parallel, and preferable that the controller individually controls opening and closing of the plurality of the second solenoid valves during a rising period of the cushion pad to control a rising speed of the cushion pad. That is, the number of the plurality of second solenoid valves to be opened or closed is varied so that it is possible to vary a flow rate of hydraulic fluid to be supplied to the die cushion pressure creation line from the accumulator in a stepwise manner. As a result, it is possible to control the rising speed of the cushion pad.

In a die cushion device in accordance with yet another aspect of the present invention, it is preferable that the second solenoid valve is a proportional solenoid valve, and that the controller controls opening of the proportional solenoid valve during a rising period of the cushion pad to control a rising speed of the cushion pad. That is, the opening of the proportional solenoid valve is continuously varied so that it is possible to continuously vary the flow rate of hydraulic fluid to be supplied to the die cushion pressure creation line from the accumulator. As a result, it is possible to control the rising speed of the cushion pad.

In a die cushion device in accordance with yet another aspect of the present invention, it is preferable to provide a die cushion position detector configured to detect a position of the cushion pad, and preferable that the controller controls the second solenoid valve in accordance with a detection signal of a position of the cushion pad, detected by the die cushion position detector during a rising period of the cushion pad. That is, the second solenoid valve is controlled in accordance with the detection signal of a position of the cushion pad so that it is possible to vary the rising speed of the cushion pad as well as possible to stop the cushion pad at a desired standby position.

In a die cushion device in accordance with yet another aspect of the present invention, it is preferable to provide a die cushion pressure command unit that instructs die cushion pressure, a die cushion speed detector that detects a speed of the cushion pad, a solenoid proportion pilot relief valve serving as the pilot relief valve, and a die cushion pressure controller that controls the solenoid proportion pilot relief valve in accordance with a die cushion pressure command value commanded by the die cushion pressure command unit and a detection signal of a speed of the cushion pad, detected by the die cushion speed detector to control the die cushion pressure. Accordingly, it is possible to keep the die cushion pressure constant as well as possible to vary the die cushion pressure in accordance with a desired pattern.

In a die cushion device in accordance with yet another aspect of the present invention, it is preferable to provide a cooling device that cools the system pressure line, or the accumulator. Since the die cushion pressure is created by throttling a liquid current, energy consumed in the die cushion operation is converted into heat to raise temperature of the hydraulic fluid. Thus, it is preferable to provide the cooling device to reduce a rise in temperature of the hydraulic fluid.

In a die cushion device in accordance with yet another aspect of the present invention, it is preferable to mount a throttle valve, or a throttle valve and a coupler for feeding fluid and filling system pressure in the die cushion pressure creation line, the system pressure line, and a pilot pressure creation line in which the pilot relief valve is provided. This is because when hydraulic fluid is filled in a fluid-pressure closed circuit in a pressurized manner by an external feeding fluid device, the valve or the valve and the coupler serve as a filler port and an exhaust port for the hydraulic fluid.

In a die cushion device in accordance with yet another aspect of the present invention, there is accompanied a feeding fluid device that includes a tank that stores the hydraulic fluid, a discharge port through which the hydraulic fluid is fed into the fluid-pressure closed circuit, a return port through which the hydraulic fluid is returned form the fluid-pressure closed circuit, the return port being connected to the tank, and a fluid-pressure pump that supplies the hydraulic fluid from the tank to the fluid-pressure closed circuit through the discharge port. In the feeding fluid device, the fluid-pressure pump is driven only when the hydraulic fluid is filled in the fluid-pressure closed circuit in a pressurized manner. The feeding fluid device above is an external device that is attached to and detached from the die cushion device, and that is connected to be used only when the hydraulic fluid is filled in the fluid-pressure closed circuit in a pressurized manner. The feeding fluid device is not required to be accompanied for each of die cushion devices, but one feeding fluid device may be prepared for a plurality of controlled die cushion devices.

In a die cushion device in accordance with yet another aspect of the present invention, it is preferable to accompany the feeding fluid device with an extension hose that is to be connected to at least one of the discharge port and the return port, and preferable that a coupler is provided at each of both ends of the extension hose. As a result, if the discharge port and the return port of the feeding fluid device cannot be directly connected to the fluid-pressure closed circuit, it is possible to be connected to the fluid-pressure closed circuit through the extension hose.

In accordance with the present invention, the hydraulic fluid is filled in the fluid-pressure closed circuit in a pressurized manner, and no fluid-pressure pump for pressurizing and feeding the hydraulic fluid is provided. As a result, it is possible to achieve a simple and inexpensive die cushion device as well as possible to save power costs required for the die cushion operation.

DETAILED DESCRIPTION OF THE EMBODIMENTS

With reference to accompanying drawings, embodiments of a die cushion device in accordance with the present invention will be described in detail.

(Configuration of the Die Cushion Device)

FIG. 1is a constitution diagram illustrating an embodiment of a die cushion device in accordance with the present invention. InFIG. 1, a press machine10is illustrated with two-dot chain lines and a die cushion device100is illustrated with solid lines.

The press machine10illustrated inFIG. 1includes a frame that is composed of a bed11, a column12, and a crown13, and a slide14that is movably guided in a vertical direction by a guide section15provided in the column12. The slide14is moved in the vertical direction inFIG. 1by a servo motor (not illustrated), or a crank mechanism including crankshaft16to which rotational driving force is transmitted by a flywheel (not illustrated).

It is preferable that the press machine10is provided on its bed11side with a slide position detector17that detects a position of the slide14, or that the crankshaft16is provided with a crankshaft encoder18that detects an angle of the crankshaft16.

An upper mold20is mounted in the slide14, and a lower mold22is mounted on a bolster19of the bed11.

A blank holder (blank holding plate)102is arranged in a space between the upper mold20and the lower mold22so that a lower side thereof is supported by a cushion pad110through a plurality of cushion pins104and a material30is set on (brought into contact with) an upper side thereof.

(Structure of the Die Cushion Device)

The die cushion device100includes the blank holder102, the cushion pad110that supports the blank holder102through the plurality of cushion pins104, a hydraulic cylinder (fluid-pressure cylinder)120that supports the cushion pad110to allow the cushion pad110to apply die cushion force, and a hydraulic closed circuit (fluid-pressure closed circuit)150that is connected to a die cushion pressure creation chamber120aof the hydraulic cylinder120.

The hydraulic cylinder120and the hydraulic closed circuit150serve as a cushion pad lifting unit that allows the cushion pad110to perform lifting operation, as well as serve as a die cushion force creation unit that allows the cushion pad110to apply die cushion force.

In addition, the hydraulic cylinder120is provided with a die cushion position detector124that detects a position of a piston rod of the hydraulic cylinder120in an extending direction thereof as a position of the cushion pad110in a lifting direction thereof. The die cushion position detector124may be provided in a space between the bed11and the cushion pad110.

Next, a configuration of the hydraulic closed circuit150that drives the hydraulic cylinder120will be described.

The hydraulic closed circuit150includes: a die cushion pressure creation line152that is connected to the die cushion pressure creation chamber120aof the hydraulic cylinder120; a system pressure line156to which an accumulator154that accumulates hydraulic oil (operating oil, hydraulic fluid, operating fluid) at low system pressure is connected; a pilot drive type logic valve158that is provided in a line between the die cushion pressure creation line152and the system pressure line156, and that is operable as a main relief valve at the time of die cushion operation; and a pilot relief valve160that is provided in a line between the die cushion pressure creation line152and the system pressure line156, and that creates pilot pressure for controlling the logic valve158. At this time, it is preferable that the logic valve158and the pilot relief valve160are a direct drive type in which there is little leak (no leak).

System pressure in the system pressure line156, to which the accumulator154is connected, is required to be equal to or more than a pressure that is at least capable of raising the cushion pad110, capable of knockout operation for a product, and capable of moving the cushion pad to its standby position. It is preferable that the system pressure is set at a pressure within a range of 1 to 10 MPa, for example.

In addition, the hydraulic closed circuit150includes a first solenoid valve164that switches pressure to act on a pilot port of the logic valve158to any one of the pilot pressure created in the pilot pressure creation line162and the system pressure created in the system pressure line156. In the pilot pressure creation line162, throttle valves (variable throttle valves)166and168are provided to regulate a flow rate. In the present example, the throttle valve168is fully opened.

Further, in a line between the die cushion pressure creation line152and the system pressure line156, a throttle valve170and a second solenoid valve172, and a throttle valve174and a second solenoid valve176, are provided in parallel. The second solenoid valves172and176are individually controlled so as to be turned on and off. It is preferable that the second solenoid valves are a poppet type solenoid valve in which there is little leak (no leak) when turned off (fully closed).

The accumulator154is provided with a cooling device178so that it is possible to cool the accumulator154(hydraulic oil) by the cooling device178. The cooling device178may be provided so as to cool the system pressure line156.

In addition, the die cushion pressure creation line152, the system pressure line156, and the pilot pressure creation line162, include throttle valves (needle valves)180,182, and184, for feeding fluid and filling system pressure, and couplers186,188, and190, respectively.

Further, the die cushion pressure creation line152and the pilot pressure creation line162include a die cushion pressure detector192that detects die cushion pressure and a pilot pressure detector194that detects pilot pressure, respectively.

InFIG. 1, a reference numeral196designates a silencer, and a reference numeral198designates a relief valve serving as a safety valve.

Next, an oiling device will be described.

FIG. 2is a constitution diagram illustrating an embodiment of the oiling device.

The oiling device200is used when fluid is fed and system pressure is filled, or when system pressure is reduced (at the time of setup preparation), but is not used at the time of a cyclic function (normal function) of the die cushion device100.

Thus, the oiling device200is not required to be accompanied for each of die cushion devices100, but one feeding fluid device is to be prepared for a plurality of controlled die cushion devices100. In addition, a user is not required to possess the oiling device, but a service department at a service site may possess the oiling device.

As illustrated inFIG. 2, the oiling device200includes a tank202that stores hydraulic oil, a hydraulic pump (fluid-pressure pump)206that is driven by an induction motor204, a relief valve208that serves as a safety valve, couplers210and212, a check valve214, and filters216and218.

The two couplers210and212of the oiling device200are connected to any two of the three respective couplers186,188, and190, provided in die cushion pressure creation line152, the system pressure line156, and the pilot pressure creation line162, in the hydraulic closed circuit150, respectively.

In a case where the couplers210and212of the oiling device200cannot be connected to any two of the three respective couplers186,188, and190, of the hydraulic closed circuit150, the couplers210and212are connected to any two of them through one extension hose230or two extension hoses230and240illustrated inFIG. 3.

The extension hose230(240) is provided at its both ends with respective couplers232(242) and234(244), so that the coupler210or212in the oiling device and the coupler186,188, or190in hydraulic closed circuit can be connected through the couplers.

When a switch220is turned on, the induction motor204of the oiling device200is driven by AC current (alternating-current) from an AC (alternating-current) power source222to operate the hydraulic pump206. Accordingly, it is possible to feed hydraulic oil in the tank202to the hydraulic closed circuit150of the die cushion device100through the filters216and218, the check valve214, and the coupler210(or the coupler210and the extension hose230), as well as possible to return the hydraulic oil to the tank202from the hydraulic closed circuit150through the coupler212(or the coupler212and the extension hose230).

In addition, the oiling device200is provided in its lower surface with casters224to be easily movable.

(Preparation and Setup (Filling Hydraulic Oil into the Hydraulic Closed Circuit in a Pressurized Manner))

When the die cushion device100of the present example is used, it is required to perform preparation and setup operation of filling hydraulic oil into the hydraulic closed circuit150in a pressurized manner.

With reference toFIG. 4, a specific example of the preparation and setup operation will be described.

First, the coupler210in a discharge port of the oiling device200is connected to the coupler232at one end of the extension hose230, and the coupler234at another end of the extension hose230is connected to the coupler186in a connection port in the die cushion pressure creation line152in the hydraulic closed circuit150. In addition, the coupler212in a return port of the oiling device200is connected to the coupler242at one end of the extension hose240, and the coupler244at another end of the extension hose240is connected to the coupler188in a connection port in the system pressure line156in the hydraulic closed circuit150.

Subsequently, in a state where each of the pilot relief valve160and the relief valve198is set at a minimum pressure by fully opening the throttle valve166,168,170,174,180,182, and184, and by turning on the first solenoid valve164and the second solenoid valves172and176, the switch220of the oiling device200is turned on to drive the hydraulic pump206by the induction motor204.

Accordingly, the hydraulic oil in the hydraulic closed circuit150and the oiling device200(tank202) is circulated to gradually remove air and contaminants in the hydraulic closed circuit150. In addition, the throttle valve182on a return side is throttled to adjust set pressure in the relief valve208of the oiling device200(so that a certain pressure is applied), and after pressure in the hydraulic closed circuit150is accumulated, the throttle valve182is opened to circulate the hydraulic oil. As a result, a ratio of air included in the circulating hydraulic oil is increased to improve air-bleeding efficiency. Further, after the hydraulic oil is sufficiently circulated in the connection above, the connection is changed so that the coupler244at another end of the extension hose240is connected to a coupler190in a connection port in the pilot pressure creation line162in the hydraulic closed circuit150to perform the same processing. It is preferable to repeat the processing above multiple times.

Finally, the throttle valve184on the return side is closed to adjust set pressure in the relief valve208of the oiling device200to the system pressure, and when the pressure in the hydraulic closed circuit150is accumulated to the system pressure, the throttle valve180on a forward side is closed, and then the switch220is turned off to stop the hydraulic pump206.

After that, setting of each of all of the pilot relief valve160, the relief valve198, and the throttle valves166,168,170, and174in the hydraulic closed circuit150is returned to a predetermined value to finish feeding fluid in the hydraulic closed circuit150, that is, filling hydraulic oil at system pressure is finished. After feeding fluid (filling system pressure), the couplers234and244at another ends of the extension hoses230and240are separated from the couplers186and188in the hydraulic closed circuit150, respectively.

Next, die cushion pressure control by the logic valve158and the pilot relief valve160will be described.

InFIG. 1, in a state where hydraulic oil is filled in the hydraulic closed circuit150in a pressurized manner, the press machine10is operated so that when the slide14descends to allow the upper mold20attached to the slide14to impact (collide) the material30on the blank holder102, the cushion pad110after the impact descends in synchronization with the slide14. Then, power of the slide14creates pressure in the die cushion pressure creation chamber120aof the hydraulic cylinder120through the upper mold20, the material30, the blank holder102, the cushion pin104, and the cushion pad110. The pressure (die cushion pressure) is controlled by the logic valve158and the pilot relief valve160.

FIG. 5is an enlarged view of the logic valve158illustrated inFIG. 1. InFIG. 5, the logic valve158is provided with an A port and a B port to which the die cushion pressure creation line152and the system pressure line156are connected, respectively so that the die cushion pressure and the system pressure are applied to the A port and the B port, respectively. In addition, the logic valve158is provided with a pilot port (X port) to which the pilot pressure or the system pressure is to be applied by turning on and off the first solenoid valve164.

Hereinafter, area, pressure, and spring force of each of the ports of the logic valve158are designated by reference characters below.

AA: pressurized area on an A port side

AB: pressurized area on a B port side

AX: pressurized area on an X port side

PA: A port pressure (die cushion pressure)

F: spring force

In a case where Expression 1 shown below is satisfied, depressing force toward the X port side is applied to a poppet158aof the logic valve158to open the valve, and in a case where Expression 2 is satisfied, depressing force toward the A port side is applied to the poppet158aof the logic valve158to close the valve.
AA×PA+AB×PB>AX×PX+FExpression 1
AA×PA+AB×PB<AX×PX+FExpression 2

In Expression 1 and Expression 2, since AA, AB, AX, PB, and F are constant, the logic valve158is opened and closed in accordance with balance between the die cushion pressure (A port pressure) PAand the pilot pressure (X port pressure) PX.

Since the pilot pressure PXis adjustable by means of pressure setting in the pilot relief valve160, the logic valve158can adjust the die cushion pressure in accordance with the pilot pressure (relief pressure) set in the pilot relief valve160.

FIG. 6is a block diagram illustrating an embodiment of a controller130applied to the die cushion device100.

The controller130illustrated inFIG. 6controls turning on and off of the first solenoid valve164and the second solenoid valves172and176of the hydraulic closed circuit150illustrated inFIG. 1. The controller130controls turning on and off of relays134,136, and138in response to a signal of a position of the slide14detected by the slide position detector17and a signal of a die cushion speed change position detected by a die cushion speed change position detector126, and outputs a driving current to the first solenoid valve164and the second solenoid valves172and176through the relays134,136, and138, whose turning on and off is controlled. As a result, the controller130individually controls turning on and off of the first solenoid valve164and the second solenoid valves172and176. The die cushion speed change position detector126detects a die cushion position (die cushion speed change position) at which a rising speed of the cushion pad110is changed, while the cushion pad110is rising. It is possible to use a proximity switch, a limit switch or the like that can be provided so that a desired die cushion speed change position is detected.

The controller130of the present example performs a simple control in which turning on and off of the first solenoid valve164and the second solenoid valves172and176are individually controlled, so that no special control device is required, and a part of a controller of the press machine10(programmable logic controller (PLC)) is available for the turning on and off of the first solenoid valve164and the second solenoid valves172and176. Thus, cost of the die cushion device100does not increase.

Specific timing of controlling turning on and off of the first solenoid valve164and the second solenoid valves172and176by the controller130will be described later. The controller130may control turning on and off of the first solenoid valve164and the second solenoid valves172and176in response to an angle of the crankshaft16detected by the crankshaft encoder18.

(Cyclic Function (Normal Mechanism) of the Die Cushion Device)

Next, each function in one cycle in a case where the die cushion device100illustrated inFIG. 1is used will be described.

Portion (a) inFIG. 7is a waveform chart illustrating a slide position of the slide14in one cycle period (0.0 to 9.0 seconds) of pressing. Each of portions (b) to (d) inFIG. 7is a timing chart illustrating timing of controlling turning on and off of the first solenoid valve164and the second solenoid valves172and176. Each of portions (e) and (f) inFIG. 7is a waveform chart illustrating a position (die cushion position) of the cushion pad110and die cushion pressure in one cycle.

In addition,FIG. 8Ais a waveform chart illustrating a slide position and a die cushion position in one cycle period of pressing, andFIG. 8Bis a waveform chart illustrating die cushion pressure in the one cycle period.

(1) Standby Process

The controller130turns on each of the first solenoid valve164and the second solenoid valve172, and turns off the second solenoid valve176, at least when the slide14is positioned at the top dead center, so that the die cushion pressure creation line152and the system pressure line156have the same pressure. Accordingly, the system pressure acts in the die cushion pressure creation chamber120aof the hydraulic cylinder120so that the hydraulic cylinder120rises and the cushion pad110is brought into contact with an upper limit stopper111of the bed11to stop (stand by) (the upper limit stopper111receives reaction force against rising force acting on the hydraulic cylinder120).

(2) Impact and Die Cushion Force Acting Process

Before the slide14of the press machine10impacts the cushion pad110through the upper mold20, the material30, the blank holder102, and the cushion pin104after starting descending (a position near a half of a stroke on a descending side (a crank angle of approximately 90 degrees)), the controller130turns off the first solenoid valve164and the second solenoid valve172(refer to portions (b) and (c) inFIG. 7). In that state, when the slide14impacts the cushion pad110, die cushion pressure in proportion to die cushion force is created in the die cushion pressure creation chamber120aof the hydraulic cylinder120by means of synergism of the logic valve158, the throttle valve166(throttle valve168), and the pilot relief valve160(refer to portion (f) inFIG. 7andFIG. 8B). That is, a hydraulic flow (a flow rate of hydraulic oil flowing per unit time) occurs because the die cushion pressure applied from the die cushion pressure creation line152to the system pressure line156is applied through the throttle valve166, the throttle valve168, the pilot relief valve160, in order. Accordingly, the pilot pressure less than the die cushion pressure is created between the throttle valve166and the throttle valve168(the pilot pressure creation line162). As a result, pressure acts on the poppet of the logic valve158to keep balance of force as follows: the die cushion pressure acts mainly on pressurized area of a die cushion pressure acting side; the system pressure acts on pressurized area of a system pressure acting side; the pilot pressure acts on pressurized area of a pilot pressure acting side (pressurized area of an X port side) through the first solenoid valve164; spring force acts on the poppet inside the logic valve; and fluid force acts on the logic valve158in a direction interfering with a flow of the hydraulic oil from the die cushion pressure creation line152to the system pressure line156(closing the valve). Thus, a poppet position (opening) of the logic valve158is held in accordance with speed of the slide14(held almost constant if the speed is constant), and the die cushion pressure is created during a series of actions.

Reduction in surge pressure, and steadiness (constancy) of pressure with respect to change in slide speed, at the time of the impact (at the time of starting a die cushion action) are feasible by a method that is not shown in the present example.

If the die cushion pressure detector192and a pressure gauge are provided in the die cushion pressure creation line152to check the die cushion pressure, operation of a user becomes easier.

In addition, a solenoid proportion pilot relief valve is used as the pilot relief valve160, so that it is possible to remotely set the die cushion force (or the die cushion pressure) by using a setting controller or the like.

Further, the solenoid proportion pilot relief valve is used as the pilot relief valve160, so that it is also possible to control the die cushion pressure in a constant manner or in a variable manner.

FIG. 9is a block diagram illustrating a die cushion pressure control unit that controls die cushion pressure by using a solenoid proportion pilot relief valve, and a solenoid proportion pilot relief valve308is used as the pilot relief valve160.

As illustrated inFIG. 9, a die cushion pressure control unit300includes a die cushion pressure command unit302, a die cushion pressure controller304, the solenoid proportion pilot relief valve308provided instead of the pilot relief valve160illustrated inFIG. 1, a die cushion speed detector191, and a die cushion pressure detector192provided in the die cushion pressure creation line152. The die cushion speed detector191detects a speed (die cushion speed) of the cushion pad110that almost coincides with a slide speed calculated by an encoder provided in the crankshaft16to detect a crank angle and a crank angular speed after the impact. The die cushion speed detector191may detect the die cushion speed by differentiating a die cushion position detected by the die cushion position detector124.

The die cushion pressure command unit302creates a command value showing die cushion pressure that varies stepwise or continuously, on the basis of constant die cushion pressure, a die cushion position of the cushion pad110detected by the die cushion position detector124, or the like, for example, and outputs the created command value to the die cushion pressure controller304.

Other inputs to the die cushion pressure controller304include a speed detection signal (die cushion speed detection value) of the cushion pad110detected by the die cushion speed detector191, and a detection value of die cushion pressure that is created in the die cushion pressure creation line152, detected by die cushion pressure detector192. The die cushion pressure controller304creates a control signal of remotely operating setting of pressure of the solenoid proportion pilot relief valve308on the basis of die cushion pressure command value, the detection value of die cushion speed, and the detection value of die cushion pressure, through control algorithm calculation in which the detection value of die cushion pressure follows the die cushion pressure command value. Then, the die cushion pressure controller304outputs the created control signal to the solenoid proportion pilot relief valve308through an amplifier306. The die cushion speed is used to compensate a response lag of the solenoid proportion pilot relief valve308with respect to the pressure command. In the present embodiment, although the detection value of die cushion speed (a speed detection value of the cushion pad) and the detection value of die cushion pressure are used together, only the speed detection value of the cushion pad may be used for controlling compensation because it is most effective to use the speed detection value of the cushion pad for controlling compensation.

Accordingly, it is possible to allow the die cushion pressure created in the die cushion pressure creation line152to follow a command value of die cushion pressure outputted from the die cushion pressure command unit302, as well as possible to control the die cushion pressure at a constant pressure regardless of a speed of the slide14at the time of the die cushion operation, and to vary the die cushion pressure in accordance with a position of the slide14.

(3) Removing Pressure Process

The controller130turns on the first solenoid valve164when the slide14of the press machine10descends to reach the bottom dead center or slightly in front of the bottom dead center (near the bottom dead center) (refer to portion (b) inFIG. 7). Accordingly, the poppet of the logic valve158moves in an opening direction (because the pilot pressure acting in a direction of closing the poppet (in pressurized area on a pilot pressure acting side) is released into the system pressure line156) so that the die cushion pressure is removed.

The die cushion pressure at this time decreases to a pressure (pressure A illustrated inFIG. 8B) equal to or close to a sum total of the system pressure that acts in the system pressure line156, and that rises as compared with the pressure in a standby state because the hydraulic cylinder120descends to push away oil from the die cushion pressure creation chamber120aso that the amount of the oil is accumulated in the accumulator154, and of cracking pressure corresponding to spring force of the logic valve158. When removal of the pressure is finished, the poppet of the logic valve158is closed.

(4) Locking Process

After the removing pressure process, when the slide14of the press machine10rises from the bottom dead center, the die cushion pressure decreases to a pressure (pressure B illustrated inFIG. 8B) that is created by means of gravity acting on total mass of movable parts, such as the blank holder102, the cushion pin104, the cushion pad110, and a piston rod of the hydraulic cylinder120, from the pressure (pressure A) equal to the sum total of the system pressure and the cracking pressure. At this time (during a process in which the pressure decreases to the pressure B from the pressure A), hydraulic oil for a compressed volume in the die cushion pressure creation chamber120aof the hydraulic cylinder120is released so that the cushion pad110slightly rises. After that (after slightly rising), the die cushion pressure creation line152and the system pressure line156are shut off by the logic valve158and the second solenoid valves172and176, so that the cushion pad110is locked near the bottom dead center.

At this time, it is preferable that a direct drive type in which there is little leak (no leak) is used as the pilot relief valve160, and poppet type solenoid valves164′,172′, and176′, in which there is little leak (no leak) are used for the first solenoid valve164and the second solenoid valves172and176, respectively, as illustrated inFIG. 10. In a case where a balance piston type (pilot operation type) is used as the pilot relief valve160, as illustrated inFIG. 10, there is also a method in which a check valve161is provided in a direction shown inFIG. 10to prevent a leak.

In the locking process, when the slide14reaches a position near a half of a stroke on a rising side (a crank angle of approximately 270 degrees) after locking for a predetermined period, the controller130simultaneously turns on the second solenoid valves172and176(refer to portions (c) and (d) inFIG. 7). Accordingly, the cushion pad110rapidly rises (refer to portion (e) inFIG. 7). In the rising process (knockout process), the controller130turns off one of second solenoid valves (the second solenoid valve176in the present example). Accordingly, the cushion pad110slowly rises (slow down), and finally reaches the upper limit stopper111to stop. During the rising process, the second solenoid valve176is turned off when the die cushion speed change position detector126detects a die cushion speed change position.

FIG. 11is an enlarged view of a main section (the rising process of the cushion pad110) of the waveform chart shown inFIG. 8Bto illustrate the die cushion pressure.

When gaps (openings) created by the throttle valves170and174occur between the system pressure line156on which the system pressure (pressure C) acts and the die cushion pressure creation line152on which the pressure B acts during locking, a hydraulic flow (a flow of hydraulic oil) from the system pressure line156to the die cushion pressure creation line152occurs in accordance with a throttled condition of the gaps (openings) and a differential pressure (pressure (C−B): pressure C>pressure B). As a result, in a process of pressurizing the die cushion pressure creation chamber120aof the hydraulic cylinder120, positioned near the bottom dead center of the press, at the time (a time of 6.4 seconds) when pressure reaches pressure B′ more than the pressure B (refer toFIG. 11), the hydraulic cylinder120starts rising.

As volume of the die cushion pressure creation chamber120aincreases with rising of the hydraulic cylinder120, pressure in the die cushion pressure creation chamber120adecreases. The hydraulic cylinder120reaches a steady speed Vc (Vc1in a rapid rising process, and Vc2in a slow rising process) after exceeding an acceleration range with starting rising of the hydraulic cylinder120, and the steady speed Vc is determined so that driving pressure of the hydraulic cylinder120(pressure B″ illustrated inFIG. 11(B″1in the rapid rising process, and B″2in the slow rising process)) reached the steady speed Vc acting on the die cushion pressure creation chamber120ais balanced with a property I determined by resistance force depending on the steady speed Vc, and a property II in which a flow rate in proportion to the steady speed Vc is determined by a differential pressure (the pressure C-pressure B″) between pressure in the system pressure line156and that in the die cushion pressure creation line152, and an opening of a gap. In order to increase the steady speed Vc, the pressure B″ is required to increase, and as the pressure B″ increases, a flow rate of fluid flowing through a gap between the lines, in proportion to the steady speed Vc, decreases. Thus, the steady speed Vc at the time when the cushion pad110rises is determined so that the two properties I and II are balanced with each other.

In the beginning of the rising, both of the second solenoid valves172and176are turned on to perform a rapid rising of the cushion pad110in accordance with both openings of the throttle valves170and174, and in the rising process, only the second solenoid valve172is turned on to perform a slow rising of the cushion pad110in accordance with the opening of the throttle valve170.

In the rising process, a device that changes an opening by switching the two second solenoid valves172and176is only an example of the speed change device that varies a rising speed of the cushion pad110. For the speed change device in a broad sense, any device that can change an opening between the system pressure line156and the die cushion pressure creation line152in a rising stroke of the hydraulic cylinder120is available. For example, more solenoid valves (second solenoid valves) may be provided in parallel to stepwise vary openings of the second solenoid valves, or a proportional solenoid valve may be used for the second solenoid valve to steplessly (continuously) change an opening.

In order that the controller130determines timing of changing openings of the second solenoid valves172and176, it is possible to use a position detection signal of the die cushion position detector124capable of detecting a position of a full stroke of the cushion pad110, and possible to use a detection signal of a proximity switch or a limit switch, capable of being fixed at any position in the stroke, or capable of being provided in a variable and adjustable manner.

That is, detection of a slide position (or a crank angle) of the press machine is not an absolute requirement for controlling the die cushion, but it is required to detect at least timing of controlling turning on and off of the first solenoid valve164and the second solenoid valves172and176. For example, if there are provided a limit switch (LS1) for detecting the top dead center of the slide14, a limit switch (LS2) for detecting a position near a half of the stroke on the descending side (a crank angle of approximately 90 degrees) of the slide14, a limit switch (LS3) for detecting a bottom dead center (crank angle 180 degrees) of the slide14, and a limit switch (LS4) for detecting a position near a half of the stroke on the rising side (a crank angle of approximately 270 degrees) of the slide14, it is possible to control turning on and off of the first solenoid valve164and the second solenoid valves172and176on the basis of detection signals of the limit switches (LS1to LS4).

In addition, in the rising process, if all openings between the system pressure line156and the die cushion pressure creation line152are shut off, it is also possible to stop the cushion pad110in the middle of the stroke for a purpose of feeding a product by a robot, and the like.

Further, if a proportional solenoid valve (a valve capable of proportionally adjusting an opening, including a servo valve) is used as the second solenoid valve to feed back a position detection signal from the die cushion position detector124to the controller130, it is also possible that the controller130(based on closed loop control) performs position control to stop the cushion pad110at any stroke position. As a result, it is possible to allow the cushion pad110to stand by at any stroke position and start die cushion force operation from the any stroke position.

As described above, since the die cushion device100does not use devices consuming electric power, such as a hydraulic pump, it is possible to achieve low cost and energy saving. In addition, the die cushion device100is made functional by including high response die cushion pressure control, a locking mechanism at the bottom dead center, and a speed change mechanism at the time of knockout (slow down mechanism having no shock at an upper limit of rising).

At the time of the die cushion operation, when hydraulic oil at the die cushion pressure is released into the system pressure by the logic valve158, the hydraulic oil generates heat due to squeezing action of the hydraulic oil applied by the logic valve158.

In the present example, as illustrated inFIG. 1, there is provided the cooling device178that blows air on the accumulator154with a large surface area to cool the accumulator154(hydraulic oil). The cooling device178is an air-cooled cooling device using a fan, but is not limited to the air-cooled cooling device. Thus, a water-cooled cooling device that cools hydraulic oil by circulating cooling water may be provided. If the die cushion device100is less used, it is possible to cool hydraulic oil by only natural heat dissipation without providing a cooling device. As a result, a more inexpensive device can be achieved.

In addition, there is described the present embodiment in which oil is used as hydraulic fluid of the die cushion device, but the hydraulic fluid is not limited to oil. Thus, water or another liquid may be used. That is, there is described a configuration of the embodiment of the present application, in which a hydraulic cylinder and a hydraulic closed circuit are used, but the configuration is not limited to the above. Thus, it is needless to say that a fluid-pressure cylinder and a fluid-pressure closed circuit in which water or another liquid is used are applicable to the present invention. In addition, the die cushion device in accordance with the present invention is applicable to not only a crank press but also to any type of press machine, primarily a mechanical press.

Further, the hydraulic cylinder may be provided not only at one place in the cushion pad as described in the embodiment above, but also at two places of the front and rear of the cushion pad or at four places of the front and rear, and the right and left, of the cushion pad, for example.

Furthermore, the present invention is not limited the examples above, and therefore it is needless to say that various modifications and variations are possible within a range without departing from the essence of the present invention.