JPH08281337A - Method for vibration forming for press brake and press brake - Google Patents

Abstract

PURPOSE: To reduce a spring back of a blank without an excessive driving source when a press forming by a press brake. CONSTITUTION: A piping enabling a supply of pressurized oil to a correction cylinder 7 for correcting a slack at a center part is connected between an oil pump 12 and a relief valve 13. By arranging a pressure control valve 15 to this piping, the driving of the correcting cylinder 7 is made possible to control, independently of a hydraulic system driving a ram 3 mounted on a hydraulic cylinder 1. At the time of bending, a pressure command signal is outputted to the pressure control valve 15 from a numerical controller 17, an oil pressure to be applied to the correction cylinder 7 is varied in a vibration state, and a table 6 connected to a piston 9 is driven vertically in a vibration state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vibration forming method capable of preventing springback during bending in a press brake and a press brake suitable for carrying out this method.

[0002]

2. Description of the Related Art As is well known, press brakes are press machines in which the width of rams and bolsters is designed to be narrow and long in order to perform bending work with complicated cross-sectional shape on the material of long products.
It is used for forming structural columns and beams of various structures. The processing part of this type of press brake consists of a lower mold (or die) and an upper mold (or punch) that abuts the lower mold with a material and bends it according to the lower mold. Generally, the lower die is fixed, and the upper die is stroked by a hydraulic cylinder or the like.

By the way, in the bending process of the material by this type of press brake, it is necessary to consider the spring back of the material. For this reason, for example, in the process of bending a material by 90 degrees, a tool whose angle of the mold is set to 90 degrees or less in consideration of spring back is used, or it is originally necessary for the bending process at the stroke end of the upper mold, that is, the abutting end. Processing is performed so that springback is less likely to occur by applying a pressing force that is larger than the force. There is also known a device in which a lower die is provided with a stroke operation for bending in order to reduce springback.

However, since the amount of springback varies depending on the thickness and bending radius of the material or the material even at the same bending angle, when forming the angle of the mold in anticipation of springback, for example, the same 90 degree bending Even so, it is not versatile and it is necessary to prepare different molds for each material. Further, when a large pressing force is applied at the end of the stroke of the upper mold, a hydraulic cylinder or the like having a large capacity is required as a drive source. That is, the cost of the device is increased in any case.

In order to solve the problems associated with the springback in such a press brake, Japanese Patent Laid-Open No. 54-
The method described in Japanese Patent Publication No. l39873 has been proposed. In this method, the middle of a cylinder rod that is operated by a stroke is formed in a joint portion having an uneven joint surface, and one surface of this joint portion is rotated by a motor so that the tip end of the cylinder rod, that is, the punch side is It is intended to reduce the springback by causing a low frequency vibration during stroke operation and repeatedly applying a load to the material being processed.

Although this method can reduce the springback, the mechanical structure becomes complicated when the existing press is modified to make such improvement.
In addition, since the amplitude of the applied vibration is single and the compressed air of the air cylinder of the drive source is a compressed fluid, it is necessary to prevent the low frequency vibration formed by the uneven joint surface from being absorbed on the cylinder side. It requires a large source of compressed air.

A method disclosed in Japanese Patent Publication No. 4-31764 is also a means for improving the problems caused by springback in a press brake and improving the method disclosed in Japanese Patent Laid-Open No. 54-13987. Is proposed. This method inserts a servo valve in the hydraulic circuit of the hydraulic cylinder that strokes the mold,
When the stroke of the hydraulic cylinder is operating, the servo valve is controlled to open and close near the end of the bump to give an arbitrary oscillatory change to the stroke speed, which slows the operation of the mold to reduce springback. is there.

[0008]

However, even though the method described in Japanese Patent Publication No. 4-31764 can reduce the spring back, (1) the stroke speed of the hydraulic cylinder is controlled by controlling the flow rate by the servo valve. It is difficult to improve the responsiveness because it changes the speed of the mold in an oscillating manner, and it takes more machining time than normal operation, and (2) the stroke speed is slowed by the servo valve. This means that high-pressure fluid is wasted, resulting in a very large energy loss, which naturally lowers the power efficiency and (3) causes the oil temperature to rise, resulting in poor stability of hydraulic control. In addition, there is a problem that a shadow machine that accelerates the deterioration of hydraulic oil may be considered.

The present invention solves the above-mentioned problems of the prior art, eliminates the need for an excessive drive source, improves energy efficiency, and reduces the number of spring packs. The purpose is to provide.

[0010]

In order to achieve the above object, a vibration forming method for a press brake according to the present invention sandwiches a material with a pair of molds and presses one of the molds to drive the material. A method of forming a press brake having a correction cylinder for correcting a drooping that occurs in a ram or table of a press brake when a hydraulic cylinder that gives a bend is actuated, wherein the hydraulic pressure for driving the correction cylinder is driven by the hydraulic cylinder. It is characterized in that it is controlled independently from the hydraulic control system that is operated, and is oscillated by a pressure command signal that is arbitrarily set.

In the vibration forming method for the press brake according to the present invention, the deflection amount may be measured, and the pressure command signal may be fed back based on the measured value to control the hydraulic pressure for driving the correction cylinder. .

In order to achieve the above object, the press brake according to the present invention presses a material between a pair of molds and presses one of the molds to bend the material when the hydraulic cylinder is actuated. In a press brake that has a correction cylinder to correct the drooping that occurs in the ram and table of the brake, connect the piping that supplies and discharges pressure oil to the correction cylinder.
It is connected between a relief valve and a hydraulic source in a hydraulic control system for driving the hydraulic cylinder, and the pipe is equipped with a pressure control valve that operates at a pressure equal to or lower than the operating pressure of the relief valve, and drives the correction cylinder. The configuration is provided with a numerical control device capable of oscillatingly varying the hydraulic pressure by a pressure command signal that is set arbitrarily.

In the press brake according to the present invention, the numerical control device may be configured to automatically calculate the pressure command signal according to the type of material to be formed, the bending width of the material, and the plate thickness.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. 1 is a block diagram showing a hydraulic circuit configuration of an embodiment of a press brake according to the present invention, and FIG. 2 is a diagram showing an example of a correction pressure command signal used for carrying out the vibration forming method according to the present invention in the apparatus of FIG. Is.

First, the structure will be described. In the figure, reference numeral 1 is a hydraulic cylinder, and a punch 4 serving as an upper mold is attached to the lower end of a ram 3 connected to a piston 2. In the figure, reference numeral 5 denotes a die serving as a lower die, which is mounted on a table 6 which can be vertically moved so as to face the punch 4. Reference numeral 7 in the drawing is a correction cylinder, which is fixed on the pedestal 8 and the rod end of the piston 9 is brought into contact with the lower surface of the table 6 so that the table 6 can be driven up and down together with the die 5. In addition, reference numeral 10 in the drawing is a material. Although not clearly shown in FIG. 1, an appropriate number of correction cylinders 7 may be provided along the longitudinal direction of the punch 4 and the die 5 (direction perpendicular to the paper surface of the drawing).

An oil pump 12 is provided in the upper chamber and the lower chamber of the hydraulic cylinder 1 via a servo valve 11 for switching the supply and discharge of pressure oil.
Is connected to the pressure oil pipe from which the ascending / descending direction of the piston 2 can be switched and the ascending / descending speed can be varied. A relief valve 13 is provided in the pipe between the servo valve 11 and the oil pump 12 so that pressure oil can be returned to the tank 14, and a high response pressure control valve 15 is provided between the oil pump 12 and the relief valve 13. A pipe that enables the supply of pressure oil to the lower chamber of the correction cylinder 7 is connected via the so that the correction cylinder 7 can be driven at high speed. The pressure control valve 15 is, for example, a high response proportional pressure reducing valve having a discharge side pressure as a pilot pressure, and operates at an operating pressure of the relief valve 13 or less. Reference numeral 16 in the figure denotes a motor for driving the oil pump 12.

Reference numeral 17 in the drawing is a numerical controller, which is a position detector 18 for the ram 3, a deflection amount detector 19 (for example, a strain gauge) on the table 6, and a pressure detector 20 for the correction cylinder 7.
Receiving the detection signal from the servo valve 11 and the relief valve 13
Also, an operation control signal is sent to the solenoid of the pressure control valve 15 to control these operations. As the position detector 18, the deflection amount detector 19, and the pressure detector 20, various known sensors may be adopted.

Next, an embodiment of a vibration forming method for a press brake according to the present invention will be described. Even in the device of FIG.
The basic press working operation is similar to that of the conventional press brake, in which the material 10 is positioned between the punch 4 and the die 5, which are molds, and the ram 3 is lowered by the operation of the hydraulic cylinder 1 to move the punch 4 into the material. Die 5 with the upper surface of 10 abutting
Then, the material 10 is bent while controlling the hydraulic pressure of the hydraulic fluid supplied to the hydraulic cylinder 1 by the servo valve 11 until the raw material 10 is bent.

In the present invention, the position at the moment when the punch contacts the work is calculated by the numerical controller 17, and the pressure command is issued to the pressure control valve 15 from any position from the contact position to the bottom dead center. When the pressure command is issued, the pressure control valve 15 keeps the same pressure as the main circuit pressure until the pressure in the correction cylinder 7 reaches the command value, and at the moment when the command value is exceeded, the circuit is closed and the pressure oil is discharged from the drain. To do. When the pressure in the correction cylinder 7 falls below the command value, the main circuit is connected again. Such an operation is repeated, and as a result, the pressure in the correction cylinder 7 is maintained as the command value. Therefore, if this pressure command is issued oscillatingly, the pressure in the correction cylinder 7 also becomes oscillating and the table 6 is oscillatingly displaced.

At this time, since the central portion of the die 5 and the table 6 in the longitudinal direction hangs downward and is easily deformed into an arch shape (drip phenomenon), the deflection amount is detected by the deflection amount detector 1
9, the solenoid of the pressure control valve 15 is turned on / off by the operation control signal from the numerical control device 17, the pressure in the lower chamber of the correction cylinder 7 is increased, and the die 9 is pushed up together with the table 6 by the piston 9. Who is eliminated (for the operation of the correction cylinder for eliminating the drool, see, for example, Japanese Patent Publication No. 5-500111).

In a normal bending process using a press brake, the position of the ram 3 is detected by the position detector 18, and the ram 3 is decelerated and stopped at the bottom dead center at the final stage of processing. Since the oil pump 12 is generally a metering pump, most of the pressure oil is relieved from the relief valve 13 and returns to the tank 14 near the bottom dead center of the ram 3. Most of the pressure energy of the oil that is relieved in the tank 14 becomes heat and wasteful work is performed. Therefore, in the present invention, the pressure oil to be relieved during this bending is effectively used. That is, the pressure control valve 15 is arranged in the hydraulic system so as to control independently of the hydraulic circuit for driving the ram 3, and the drive circuit for the correction cylinder 7 is configured. The correction pressure command signal as shown in FIG. 2 is output to the solenoid of the pressure control valve 15, and thereby the hydraulic pressure applied to the correction cylinder 7 is oscillated to be varied, and the table 6 connected to the piston 9 is oscillatedly moved up and down. To do. As the pressure command signal from the numerical controller 17, for example, the one shown in the example of FIG. 2 can be considered, and the variable (P1 ...
..: Amplitude, t1 ...: Cycle) can be changed to arbitrarily and easily form and apply an optimum vibration waveform. Then, vibration displacement is applied to the die 5 during bending, and bending is performed in that state.

When the internal pressure of the correction cylinder 7 exceeds a predetermined value at the final stage of bending, the pressure control valve 15 having this pressure as the pilot pressure is turned off, and the oil returns to the drain. When such vibration forming is performed, the punch 4 is formed near the bottom dead center of the ram 3, that is, at the end of the punch 4 hitting the die 5.
As a result, the bending process can be performed without applying the excessive pressing force and the spring back of the material 10 hardly occurs as in the conventional method described above. However, in the method of the present invention, unlike the method disclosed in Japanese Patent Publication No. 4-31764,
Since the stroke speed of the ram 3 does not fluctuate oscillatingly, the processing time does not become long. Further, since the fluid energy of the pressure oil that is discarded in the normal bending process is effectively used, there is sufficient fluid energy to drive the correction cylinder 7, and the high response pressure control valve 15 drives the correction cylinder at high speed. This can improve the energy efficiency of the hydraulic system. In addition, Japanese Patent Publication No. 4-3176
In the method disclosed in Japanese Patent Laid-Open No. 4 publication, the response (frequency response characteristic) of the servo valve itself can be generally several tens Hz or more, but since the weight of the ram is heavy, the response of the system is usually several H.
z, the maximum is about 15 Hz. In the pressure control by the correction cylinder of the method of the present invention, the response of the pressure control valve itself is several tens Hz and is equivalent to that of the servo valve, but since the correction cylinder capacity is smaller than the pump flow rate, the system response is 15 A response of about 35 Hz is possible.

As described above, the number of correction cylinders is one.
The number of the correction cylinder 7 is not limited to one, and the correction cylinder 7 is installed not only on the lower side of the table 6 but also on the ram 3 side, or on the ram 3 and the table 6.
It may be installed on both sides of. Although the apparatus of FIG. 1 has a configuration in which the ram 3 descends, it may have a configuration in which the table 6 side is raised to perform bending, or a configuration in which the punch 3 is fixed and the die 5 is raised and lowered by the hydraulic cylinder 1. Further, although a plunger type is often used as the correction cylinder 7, the method of the present invention can be applied in the same manner as the piston type.

If a suitable numerical control device 17 is adopted, the detection signals of the position detector 18 of the ram 3, the deflection amount detector 19 of the table 6 and the pressure detector 20 of the correction cylinder 7 are sent to the numerical control device 17. The feedback control for the pressure command signal and the feedback control for the table displacement can also be performed by performing the calculation with, and it is also possible to perform vibration molding at an arbitrary position of the stroke of the ram 3 by the detection signal from the position detector 18. Furthermore, even with a general numerical control device, it is possible to store and newly enter processing conditions such as material type, bending width, plate thickness, etc., so pressure commands and vibration forming time according to the processing target can be set. It is possible to calculate and process automatically. Further, since the pressure in the correction cylinder 7 and the amount of deflection of the table 6 are constantly detected by the respective detectors, the relationship between the processing conditions and these detected amounts is calculated by the numerical controller 17 to be a function, and numerical control is performed. It is also possible to record it in the storage device of the device and build a processing database to enable more automated bending.

[0025]

As described above, the vibration forming method in the press brake according to the present invention allows the pressure of the correction cylinder to be arbitrarily and oscillatingly controlled near the end of the bending, that is, the stroke end of the hydraulic cylinder, so that the mold is made. Since the pressure of the correction cylinder is controlled optimally for the drooping phenomenon in which the die is drooped while giving the repeated displacement, there is an effect that it becomes possible to realize the press working in which the springback and the drooling phenomenon hardly occur.

As described above, in the press brake according to the present invention, the pressure control valve is arranged so that the pressure brake can be controlled independently of the hydraulic system for driving the hydraulic cylinder. Nearly the bottom dead center of the piston of the cylinder, the energy of the pressure oil that was wasted in the past was mostly wasted and can be effectively used, and the correction cylinder drive source does not need to be excessive and energy efficiency is improved. There is an effect that it becomes possible to do. Further, since it is possible to bend a thick plate material even if the pressurizing ability is smaller than that of the conventional one, there is an effect that the efficiency of the device configuration and the size of the mechanical structure can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing a hydraulic circuit configuration of an embodiment of a press brake according to the present invention.

2 is a diagram showing an example of a corrected pressure command signal used for carrying out the vibration forming method according to the present invention in the apparatus of FIG.

[Explanation of symbols]

 1 Hydraulic Cylinder 2 Piston 3 Ram 4 Punch 5 Die 6 Table 7 Compensation Cylinder 8 Frame 9 Piston 10 Material 11 Servo Valve 12 Oil Pump 13 Relief Valve 14 Tank 15 High Response Pressure Control Valve 16 Motor 17 Numerical Control Device 18 Position Detector 19 Deflection amount detector 20 Pressure detector

Claims (4)

[Claims] 1. A method for compensating for drooling which occurs in a ram or table of a press brake when a hydraulic cylinder that sandwiches a material between a pair of molds and presses one mold to bend the material is operated. A molding method in a press brake having a correction cylinder, wherein the hydraulic pressure for driving the correction cylinder is controlled independently from a hydraulic control system for driving the hydraulic cylinder, and is oscillated by an arbitrarily set pressure command signal. A vibration forming method in a press brake, comprising: 2. The vibration forming method for a press brake according to claim 1, wherein the deflection amount is measured, and the pressure command signal is fed back based on the measured value to control the hydraulic pressure for driving the correction cylinder. 3. A method for compensating for drooling which occurs in a ram or table of a press brake when a material is sandwiched between a pair of molds and one of the molds is driven under pressure to bend the material. In a press brake having a correction cylinder, a pipe for supplying / discharging pressure oil to / from the correction cylinder is connected between a relief valve and a hydraulic source in a hydraulic control system for driving the hydraulic cylinder, and the pipe is provided with the relief. A press brake comprising a pressure control valve that operates at a pressure equal to or lower than an operating pressure of the valve, and a numerical control device that is capable of oscillatingly varying the hydraulic pressure that drives the correction cylinder by a pressure command signal that is arbitrarily set. 4. The press according to claim 3, wherein the numerical control device automatically calculates the pressure command signal according to the type of material to be molded, the bending width of the material, and the plate thickness. brake.