JPH08174075A - Plate bending with press-brake and press-brake - Google Patents

Abstract

PURPOSE: To bend a product to the same angle as a test piece by controlling a brake press so that an objective load is operated and final bending load is tuned to the objective load. CONSTITUTION: A test piece, which has the same plate thickness and material as that of a product W, is bent to the desired angle by upper/lower dies 11, 13. The max load from bending start up to completion at air vent and the load at completion are detected by a detecting means 19. Based on the max load and completion load, a basic load ratio is operated. Bending of the product is executed. The max load at air vent at this time is detected by the detecting means 19. Based on the basic load ratio and the max load at bending of the product W, the objective load is operated. A press brake 1 is controlled by NC device 17, etc., so that the final bending load is set to the target load. By this method, a number of test pieces can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of bending a plate material by a press brake and a press brake, and more specifically, when a test bending is performed by using a test piece having the same material and plate thickness as the product. The basic load ratio is calculated based on the maximum load at the air bend and the load at the end of bending, and at the end of the bending of the product based on the maximum load detected at the air bend of the product and the above basic load ratio. The present invention relates to a method of bending a plate material for controlling the press brake so that the final bending load becomes the target load, and a press brake used in the method.

[0002]

2. Description of the Related Art A press brake has a structure including an upper table having an upper die and a lower table having a lower die. One of the table and the lower table is fixed to a frame, and the other table is fixed. Is configured as a movable table that moves up and down.

When a plate material is bent by a press brake, there is a spring back in the air bend area, a spring back in the bottoming area, and a spring in (sometimes called spring go). In some cases, trial bending is generally performed.

[0004]

When trial bending is performed with a press brake, a large number of test pieces having the same material, plate thickness and bending length as the bent product are prepared until the required bending accuracy is obtained. Trial bending is performed. Even with the same material and plate thickness, the required pressing force is different when the bending length is different, and the correction amount due to the distortion of the frame is different. There is a problem that is necessary.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the conventional problems as described above, and the invention described in the first item is to bend a plate material by upper and lower molds provided in a press brake. The step (a) of bending a test piece having the same plate thickness and the same material as the bent product at a desired angle by the upper and lower molds, and from the start of bending the test piece to the end of bending. Based on the (b) step of detecting the maximum load (FA) at the time of air bend and the load (FB) at the end of bending in the process of reaching, and the above-mentioned maximum load (FA) and load at the end of bending (FB) Calculate the load ratio (H) (c)
Process, product bending process (d) process, and product maximum bending load during air bending (F)
Step (e) of detecting A ′) and the basic load ratio (H)
And (f) step of calculating the target load (FB ') based on the maximum load (FA') during air bending during product bending, and the final bending load of the product is the target load (F).
There is a plate material bending method including a step (g) of controlling the press brake so as to be B ′).

The invention according to claim 2 is a method of bending a plate material by means of upper and lower molds provided in a press brake, wherein a test piece having the same plate thickness and the same material as the bent product is used for the upper and lower molds. In the step (a) of bending the test piece to a desired angle and the step of bending the test piece, the relationship between the amount of protrusion of the upper mold with respect to the lower mold or the elapsed time from the start of bending and the bending load is detected ( The rate of change (FC) of the bending load in the elastic deformation region of the test piece is calculated based on the step b), the plunge amount or the bending time and the bending load (c).
A basic ratio (HA) based on a step, a step (d) of detecting a load (FB) at the end of bending of the test piece, and the change rate (FC) and a load (FB) at the end of bending. (E) step for calculating the following, and (f) step for bending the product,
The step (g) of calculating the change rate (FC ') of the bending load in the elastic deformation region of the product during the bending process of the product, the change rate (FC') of the bending load of the product and the basic ratio (HA).
A plate material comprising a step (h) of calculating a target load (FB ') based on the above and a step (i) of controlling the press brake so that the final bending load of the product becomes the target load (FB'). This is a bending method.

The invention according to the third aspect is a press brake for bending a plate material by means of upper and lower molds, a table drive device for vertically moving a movable table in the press brake, and a bending process of the plate material. The basic load ratio (H) is calculated based on the load detection means for detecting the load at the time point, the maximum load (FA) at the time of air bending during bending of the test piece, and the load (FB) at the end of bending. The first calculation means, the maximum load (FA ') during air bending detected during bending of the product, and the basic load ratio (H)
Second calculation means for calculating a target load (FB ') based on the above, and control means for controlling the table drive device so that the final bending load of the product becomes the target load (FB').
It is a press brake equipped with.

The invention according to the fourth aspect is a press brake for bending a plate material by means of upper and lower molds, a table drive device for vertically moving a movable table in the press brake, and a plate material when bending the plate material. Load detecting means for detecting the load, position detecting means for detecting the amount of protrusion of the upper die relative to the lower die during bending of the plate material, or timing means for measuring the elapsed time from the start of bending the plate material, and the test piece. Calculating means for calculating the change rate (FC) of the bending load in the elastic deformation region of the test piece based on the amount of plunge detected during the bending process or the measured elapsed time and the detected bending load; Based on the detected load (FB) at the end of bending and the change rate (FC), the basic ratio (H
A) second calculation means for calculating A) and the rate of change in bending load (FC ') in the elastic deformation region of the product based on the amount of plunge detected during bending of the product or the measured elapsed time and the detected bending load And a fourth calculation means for calculating the target load (FB ') based on the rate of change (FC') of the bending load of the product and the basic ratio (HA), and the final bending of the product. And a control means for controlling the table drive device so that the load becomes the target load (FB ').

[0009]

According to the first aspect of the present invention, the method of bending the plate material by the upper and lower molds provided in the press brake is used. The maximum load (FA) at the air bend and the load (FB) at the end of bending (FB) in the process of bending the test piece to a desired angle (a) and in the process from the start of bending the test piece to the end of bending The step (b) of detecting, the step (c) of calculating the basic load ratio (H) based on the maximum load (FA) and the load at the end of bending (FB), and the bending of the product (d). ) Step, detecting the maximum load (FA ') during air bending during product bending (e) step, the basic load ratio (H) and maximum during air bending during product bending Target load (FB ') based on load (FA') And calculation to step (f), the final bending load of the product to control the press brake so that the target load (FB ') and step (g) is a bending method become more plate material.

In the invention described in the first item, the basic load ratio between the maximum load at the time of air bending and the load at the end of bending when bending a test piece having the same plate thickness and material as the product is performed. When bending the product, calculate the maximum load during air bending when bending the product, calculate the target load based on this maximum load and the basic load ratio, and finish bending the product. Since the press brake is controlled so that the load at the time becomes the above target load, even if the bending length of the test piece and the bending length of the product are different, make the product the same angle as the test piece. It can be bent.

Therefore, when the bending angle is the same for the same material and plate thickness, the target load at the end of bending is calculated based on the same basic load ratio even if the bending length is different. It is only necessary to control the press brake, and the test piece is only necessary to obtain the basic load ratio.
It is not necessary to prepare the same test piece as the product, and the number of test pieces can be reduced.

The invention according to claim 2 is a method for bending a plate material by means of upper and lower molds provided in a press brake, wherein a test piece having the same plate thickness and the same material as the bent product is used for the upper and lower molds. In the step (a) of bending the test piece to a desired angle and the step of bending the test piece, the relationship between the amount of protrusion of the upper mold with respect to the lower mold or the elapsed time from the start of bending and the bending load is detected ( The rate of change (FC) of the bending load in the elastic deformation region of the test piece is calculated based on the step b), the plunge amount or the bending time and the bending load (c).
A basic ratio (HA) based on a step, a step (d) of detecting a load (FB) at the end of bending of the test piece, and the change rate (FC) and a load (FB) at the end of bending. (E) step for calculating the following, and (f) step for bending the product,
The step (g) of calculating the change rate (FC ') of the bending load in the elastic deformation region of the product during the bending process of the product, the change rate (FC') of the bending load of the product and the basic ratio (HA).
A plate material comprising a step (h) of calculating a target load (FB ') based on the above and a step (i) of controlling the press brake so that the final bending load of the product becomes the target load (FB'). Is a bending method.

According to the second aspect of the present invention, when a test piece having the same material and plate thickness as the product is bent, the rate of change of the bending load in the elastic deformation region of the test piece and the load at the end of bending The basic ratio of the product is calculated, and when bending the product, calculate the rate of change of the bending load in the elastic deformation area of the product, and based on this rate of change and the basic ratio, the target load at the end of bending the product. Is calculated and the press brake is controlled so that the load at the end of bending of the product becomes the above-mentioned target load.Therefore, when the bending length of the test piece and the bending length of the product are different, Also, the product can be bent into the same corner as the test piece.

Therefore, the test piece is only necessary for obtaining the basic ratio, and it is not necessary to prepare the same test piece as the product, and the number of test pieces can be reduced.

The invention according to the third aspect is a press brake for bending a plate material by means of upper and lower molds, a table drive device for vertically moving a movable table in the press brake, and a bending process of the plate material. The basic load ratio (H) is calculated based on the load detection means for detecting the load at the time point, the maximum load (FA) at the time of air bending during bending of the test piece, and the load (FB) at the end of bending. The first calculation means, the maximum load (FA ') during air bending detected during bending of the product, and the basic load ratio (H)
Second calculation means for calculating a target load (FB ') based on the above, and control means for controlling the table drive device so that the final bending load of the product becomes the target load (FB').
It is a press brake equipped with.

In the invention described in the third item, it is possible to detect the maximum load at the time of air bending and the load at the end of bending when bending the test piece of the same material and plate thickness as the product. In addition, the basic load ratio can be calculated based on the maximum load and the load at the end of bending. During product bending, the target load can be calculated by detecting the maximum load during air bending during product bending, and the table drive device is controlled so that the final bending load of the product becomes the above target load. Is what you can do.

That is, in the invention described in the third aspect, the invention described in the first aspect can be implemented and the same operational effect can be obtained.

According to the fourth aspect of the present invention, in a press brake for bending a plate material by means of upper and lower molds, a table drive device for vertically moving a movable table in the press brake, and a plate material when bending the plate material are used. Load detecting means for detecting the load, position detecting means for detecting the amount of protrusion of the upper die relative to the lower die during bending of the plate material, or timing means for measuring the elapsed time from the start of bending the plate material, and the test piece. Calculating means for calculating the change rate (FC) of the bending load in the elastic deformation region of the test piece based on the amount of plunge detected during the bending process or the measured elapsed time and the detected bending load; Based on the detected load (FB) at the end of bending and the change rate (FC), the basic ratio (H
A) second calculation means for calculating A), and the change rate (FC ') of the bending load in the elastic deformation region of the product based on the amount of plunge detected during bending of the product or the measured elapsed time and the detected bending load. And a fourth calculation means for calculating the target load (FB ') based on the rate of change (FC') of the bending load of the product and the basic ratio (HA), and the final bending of the product. And a control means for controlling the table drive device so that the load becomes the target load (FB ').

In the invention described in the fourth item, when a test piece having the same material and plate thickness as the product is bent, the rate of change of the bending load in the elastic deformation region of the test piece is calculated. In addition, the basic ratio can be calculated based on the load at the end of bending and the change rate.

Further, at the time of bending the product, the rate of change of the bending load in the elastic deformation region of the product can be calculated, and the target at the end of the bending of the product can be calculated based on this rate of change and the basic ratio. The load can be calculated, and the table drive device can be controlled so that the load at the end of bending the product becomes the target load.

That is, in the invention described in the fourth aspect, the invention described in the second aspect can be implemented, and the same effect as the invention described in the second aspect can be obtained.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, an upper table 5 is mounted on an upper portion of a frame 3 of a press brake 1, and a lower table 7 is mounted on a lower portion of the frame 3. An upper die 11 is attached to the upper table 5 via an appropriate fixture 9, and a lower die 13 for bending the plate W in cooperation with the upper die 11 is attached to the lower table 7. I am doing it.

One of the upper table 5 and the lower table 7 (the upper table 5 in this embodiment) is fixed to the frame 3, and the other table (the lower table 7 in this embodiment) is vertically movable. It is configured as a movable table. Either of the upper and lower tables 5 and 7 may be a movable table.

A table drive device 15 is provided for moving the movable table 7 up and down, and an NC device 17 as a control means for controlling the table drive device 15 is provided. Then, the table drive device 1
5 is provided with load detecting means 19 for detecting a load when the plate W is bent.

The table driving device 15 is constructed such that the movable table 7 is moved up and down by a piston rod provided in a hydraulic cylinder, or a ball screw or ball nut which is moved up and down by a screw structure which is rotationally driven by a motor such as a servomotor. The movable table 7 can be moved up and down by means of the above (hereinafter, the latter configuration is referred to as a screw drive mechanism).

When a hydraulic cylinder is used as the table drive device 15, a pressure sensor for detecting the pressure of the hydraulic cylinder can be used as the load detecting means 19. When the screw drive mechanism is used, the load detection means 19
A sensor (for example, a current sensor, a power sensor, or a torque detector) that detects the load of the motor can be used as the above.

As the load detecting means 19, regardless of the structure of the table driving device 15, the piezoelectric element 19A is interposed between the upper mold 11 and the lower mold 13 to attach the piezoelectric element 19A.
Alternatively, the load applied to the lower mold 13 may be detected. Further, it is also possible to adopt a configuration in which the strain of the upper and lower molds 11, 13 is detected by a strain detector.

That is, various detectors can be used as the load detecting means 19. The detection value (detection signal) of the load detection means 19 is the NC device 1
It is entered in 7.

A plate material W is formed by the upper mold 11 and the lower mold 13.
Position detecting means 21 is provided to detect the amount of protrusion of the upper mold 11 with respect to the lower mold 13 when the bending process is performed.

In this embodiment, the position detecting means 21 is, for example, a magnes cable or the like, and the frame 3 is provided with a detecting head 21H facing the linear scale 21S attached to the movable table 7. I am doing it.

However, the position detecting means 21 is not limited to the above-mentioned structure, but may be any structure that can detect the vertical movement position of the movable table 7, and various structures can be adopted. Is. The detection signal (detection value) of the position detecting means 21 is input to the NC device 17.

In the above structure, the plate material W is bent by the upper mold 11 and the lower mold 13, and the amount of protrusion D of the upper mold 11 into the lower mold 13 or the elapsed time T from the start of the bending of the plate material W. Is plotted on the horizontal axis and the bending load at that time is plotted on the vertical axis, and a graph as shown in FIG. 2 is obtained.

To measure the amount of protrusion D of the upper die 11 with respect to the lower die 13 or the elapsed time T from the start of bending of the plate material W, the movable table 7 is raised by the drive of the table drive device 15 and the upper die 13 is placed. The detection is started when the lower end of the upper die 11 comes into contact with the plate material W.
The load detection means 19 detects, for example, a change point at which the load detecting means 19 changes from an unloaded state to a loaded state (for example, in the case of pressure detection, a point at which the pressure rapidly rises). Can be detected), or one of the upper and lower molds 11 and 13 is in an insulated state, and a point where the upper mold 11 abuts the plate W and a weak current is conducted can be detected. Is.

Therefore, as described above, the position detecting means 21 starts from the time when it is detected that the upper die 11 has come into contact with the plate material W.
2 or the measured value of the clock signal of the clock 23 as the time measuring means provided in the NC device 17 and the detected value of the load detecting means 19 at that time are graphed to obtain the graph shown in FIG. The load curve 25 is obtained.

In FIG. 2, a region A of the load curve 25 is an elastic deformation region where the plate W is elastically deformed, and a region B is an air bend region where the plate W is subjected to air bending. The area C is a bottoming area in which the plate W is subjected to bottoming.

Here, when the material of the plate material W, the plate thickness and the bending angle are the same, the basic load ratio H (H = H = H = H = H) in the air bend region B and the load FB at the end of bending. FB / FA) and the bending load change rate FC (FC = ΔF / ΔD or ΔF / in the elastic deformation region A)
It has been found that the basic ratio HA by ΔT) and the load FB at the end of bending is constant.

Therefore, when the bending line length is different even if the material, plate thickness and bending angle of the plate material W are the same, the bending load F naturally differs due to the difference in the bending line length.
After obtaining the basic load ratio H or the basic ratio HA, a target load at the end of bending of the product is calculated in the product bending process, and the press brake is controlled so that this target load is obtained. In order to obtain the load curve 25, the product can be bent so that the bending angle is the same as the bending angle of the test piece that has been previously bent.

Now, referring to FIG. 3, in step S1, the bending work is started using a test piece having the same material and plate thickness as the product to be bent. Then, in step S2, the maximum load FA of the bending load F in the air bend region is measured (detected).

Next, in step S3, it is determined whether or not the detected load has changed from rising to falling. If it is rising, the process returns to step S2, and if it has decreased, the process proceeds to step S4.

In step S4, it is determined whether or not the bending of the test piece is completed. If NO, the bending is continued, and if YES, step S5
Move to

In step S4, it is determined whether or not the bending process is completed by detecting the bending angle by the bending angle detector provided in the press brake during the bending process of the test piece, or by checking the upper and lower metal parts. The test piece is removed from between the molds, the bending angle is detected, and when the bending angle is within the allowable value, it is determined that the bending process is completed.

In step S5, the load FB when the bending angle is detected in step S4 is detected.

The maximum load FA and the load F when bending is completed
B is detected by the load detecting means 19, and based on the detected maximum load FA and the load at the time of completion of bending, the first calculating means provided in the NC device 17 has a basic load ratio H (H = FB / FA) is calculated (step S6).

At the same time when the bending of the test piece is started, the amount of protrusion D of the upper mold 11 with respect to the lower mold 13 is detected by the position detecting means 21 and the NC device 17 is started.
The load curve 25 by the test piece can be obtained by starting the time measurement by the clock 23 provided in the above, detecting the load F by the load detecting means 19, and plotting the relationship between the respective detected values into a graph. .

As described above, after the basic load ratio H is calculated based on the bending process of the test piece, the process shifts from step S7 to the bending process of the product, and in step S8, the product of the same material and plate thickness as the test sample is used. Start the bending process.

Then, in step S9, the maximum load FA 'of the air bend area A during the bending process of the product is performed.
To detect. In step S10, it is determined whether or not the detected load has changed from an increase to a decrease. If NO, the process returns to step S9, and if YES, the process moves to step S11.

In step S11, the target load FB '(FB' = FA '× H) at the end of bending of the product is based on the basic load ratio H calculated in step S6 and the maximum load FA' detected in step S9. ) Is calculated.

This target load FB 'is calculated by the NC device 1
Is performed by the second computing means provided in 7.
Based on this calculation result, the NC device 17 controls the press brake, that is, the table drive device 15 so that the final bending load of the product becomes the target load FB '(step S12).

Therefore, the load at the end of bending the product is FB ', and the ratio (FB' / FA ') between this load FB' and the maximum load AF 'detected in step S9 is equal to the basic load ratio H. Becomes Therefore, the bending angle of the product is substantially equal to the bending angle of the test piece that is bent to obtain the load curve 25.

Therefore, according to the present embodiment, even if the bending length of the product varies, if the material, plate thickness and bending angle are the same, the test piece calculates the basic load ratio H. Therefore, only the necessary test pieces are required, and the number of test pieces can be reduced. In other words,
The number of trials and bendings can be reduced (for example, only once), and the work efficiency can be improved.

In the above description, the basic load ratio H is calculated from the maximum load FA during air bending during bending of the test piece and the load FB upon completion of bending, and the air bend of the product during bending of the product is calculated. Maximum load F
The case has been described in which the target load FB 'at the end of bending of the product is calculated based on A'and the basic load ratio H, and the control is performed so as to be such.

However, as shown in steps S21 to S30 in FIG. 4, when the test piece is bent (step S21), the rate of change FC of the load in the elastic deformation region FC
(FC = ΔF / ΔT or ΔF / ΔD) is calculated (step S22), and the load FB at the end of bending of the test piece is detected (steps S23 and S24).

Then, the basic ratio HA (HA = FB / FC) is calculated based on the change rate FC and the load FB at the end of bending (step S25).

After that, the product is bent (steps S26 and S27), the change rate FC 'of the load in the elastic deformation region of the product is calculated (step S28), and this change rate FC' and the basic ratio HA are calculated. A target load FB ′ (FB ′ = FC ′ × HA) at the end of bending of the product is calculated based on the above (step S29), and the table drive device is set so that the load at the end of bending of the product becomes FB ′. Also by the method of controlling 15 (step S30), the product can be bent at the same bending angle as the test piece, and the same operational effects as described above can be obtained.

[0055]

As can be understood from the above description of the embodiments, the invention described in the first item is the air when a test piece of the same plate thickness and material as the product is bent. The basic load ratio between the maximum load at the bend and the load at the end of bending is calculated, and when the product is bent, the maximum load at the time of air bend when the product is bent is detected. The target load is calculated based on the load ratio, and the press brake is controlled so that the load at the end of bending of the product becomes the above target load. Therefore, the bending length of the test piece and the bending length of the product are controlled. Even if they are different, the basic load ratio is the same, and the product can be bent into the same corner as the test piece.

Therefore, when the bending angle is the same for the same material and plate thickness, the target load at the end of bending is calculated based on the same basic load ratio even if the bending length is different. Since it is only necessary to control the press brake, the test piece is only necessary for obtaining the basic load ratio, and it is not necessary to prepare the same test piece as the product,
The number of test pieces can be reduced.

According to the second aspect of the present invention, when a test piece having the same material and plate thickness as the product is bent, the rate of change in bending load in the elastic deformation region of the test piece and the load at the end of bending And the bending ratio of the product in the elastic deformation region of the product during the bending process of the product, and the target at the end of bending of the product based on this change ratio and the basic ratio. Since the load is calculated and the press brake is controlled so that the load at the end of bending of the product becomes the above target load, there is a case where the bending length of the test piece and the bending length of the product are different. However, the basic ratio is the same, and the product can be bent into the same corner as the test piece.

Therefore, the test pieces are only necessary for obtaining the basic ratio, and it is not necessary to prepare the same test pieces as the product, and the number of test pieces can be reduced.

In the invention described in the third item, the maximum load at the time of air bending and the load at the end of bending can be detected when bending a test piece having the same material and plate thickness as the product. The basic load ratio can be calculated based on the maximum load and the load at the end of bending. In addition, when bending the product, the target load can be calculated by detecting the maximum load during air bending during product bending.
Moreover, the table drive device can be controlled so that the final bending load of the product becomes the target load.

That is, in the invention described in the third item, the invention described in the first item can be implemented and the same operational effect can be obtained.

In the invention described in item 4, when the test piece having the same material and the same plate thickness as the product is bent, the rate of change of the bending load in the elastic deformation region of the test piece can be calculated. In addition, the basic ratio can be calculated based on the load at the end of bending and the rate of change.

When the product is bent, the rate of change of the bending load in the product elastic deformation region can be calculated. Based on this rate of change and the basic ratio, the target load at the end of bending of the product can be calculated. Can be calculated, and the table drive device can be controlled so that the load at the end of bending the product becomes the target load.

That is, in the invention described in the fourth aspect, the invention described in the second aspect can be implemented, and the same effect as the invention described in the second aspect can be obtained.

[Brief description of drawings]

FIG. 1 is a conceptual explanatory diagram of a press brake according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a load curve showing the relationship between the amount of protrusion of the upper die with respect to the lower die and the bending load.

FIG. 3 is an explanatory diagram of a flowchart for performing bending work.

FIG. 4 is an explanatory diagram of a flowchart for performing a bending process.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Press brake 11 Upper mold 13 Lower mold 15 Table drive device 17 NC device 19 Load detection means 21 Position detection means 23 Clock

Claims (4)

[Claims] 1. A method for bending a plate material using a press brake, comprising: a method for bending a plate material by means of upper and lower molds provided for the press brake; The process of bending a test piece of the same thickness and material as the bent product to the desired angle by the upper and lower molds. (B) Maximum load during air-handing in the process from the start of bending the test piece to the end of bending. (FA) and the step of detecting the load (FB) at the end of bending, (c) the maximum load (FA) and the load at the end of bending (FB)
Based on the above, the step of calculating the basic load ratio (H), (d) the step of bending the product, (e) the maximum load (FA ') during air bending during the bending of the product is detected. Step (f) Target load (FB ') based on the basic load ratio (H) and the maximum load (FA') during bending of the product
(G) A step of controlling the press brake so that the final bending load of the product becomes the target load (FB '). 2. A method for bending a plate material by means of a press brake, which comprises a step of bending a plate material by means of upper and lower molds provided for the press brake, and comprising the following steps: (a) folding Bending the test piece of the same thickness and material as the bent product to the desired angle by the upper and lower dies, (b) In the step of bending the test piece, the amount of protrusion of the upper die relative to the lower die or the start of bending A step of detecting the relationship between the elapsed time from time and the bending load, (c) calculating the rate of change (FC) of the bending load in the elastic deformation region of the test piece based on the plunge amount or the bending time and the bending load. And (d) detecting the load (FB) at the end of bending of the test piece, (e) the change rate (FC) and the load (F) at the end of bending
B) and the step of calculating the basic ratio (HA), (f) the step of bending the product, (g) the rate of change of the bending load in the elastic deformation region of the product during the bending of the product ( FC '), (h) a target load (FB') is calculated based on the bending load change rate (FC ') of the product and the basic ratio (HA), (i) the final product A step of controlling the press brake so that the bending load becomes the target load (FB '). 3. In a press brake for bending a plate material by means of upper and lower molds, a table drive device for vertically moving a movable table in the press brake,
Basic load ratio based on the load detection means for detecting the load during bending of the plate material, the maximum load (FA) during air bending during the bending of the test piece, and the load (FB) at the end of bending A first calculation means for calculating (H), and a target load (FB ') based on the maximum load (FA') during air bending detected during bending of the product and the basic load ratio (H). A press brake comprising: a second calculation means for controlling the table drive device so that the final bending load of the product becomes the target load (FB '). 4. In a press brake for bending a plate material by means of upper and lower molds, a table drive device for vertically moving a movable table in the press brake,
Load detecting means for detecting the load during bending of the plate material, position detecting means for detecting the amount of protrusion of the upper die with respect to the lower die during bending of the plate material, or measuring the elapsed time from the start of bending the plate material A first calculation for calculating the change rate (FC) of the bending load in the elastic deformation region of the test piece based on the timing means, the plunge amount detected during bending of the test piece or the measured elapsed time and the detected bending load. Means, a second calculating means for calculating the basic ratio (HA) based on the detected load (FB) at the end of bending of the test piece and the change rate (FC), and detected during bending of the product. Third calculating means for calculating the change rate (FC ') of the bending load in the elastic deformation region of the product based on the amount of plunge or the measured elapsed time and the detected bending load, and the change rate of the bending load (F) of the product
C ') and the basic ratio (HA) based on the target load (F
B ') fourth calculating means, and control means for controlling the table drive device so that the final bending load of the product becomes the target load (FB'). brake.