Bending Method

The present disclosure relates to a bending method.

A press brake for bending a workpiece by applying pressure to the workpiece using a tool is known. As one bending method using the press brake, “FR bending” is known as a processing method in which a workpiece is bent at a desired bending angle by intermittently repeating minute bending while feeding the workpiece.

Patent Literature 1 discloses a method of correcting processing data while bending a workpiece. In the method of Patent Literature 1, correction data is calculated based on an error between an actual bending angle obtained up to a predetermined process and a target bending angle. When the correction data is calculated, bending is started from the next process, and bending after the next process is performed according to the correction data.

Patent Literature 2 discloses a press brake having an upper table for holding a punch and a lower table for holding a die, and a workpiece is clamped and bent by the punch and the die. When performing a certain process, the press brake measures a shape of the workpiece based on displacement data received by a two-dimensional laser displacement sensor. A stroke for lowering the punch toward the die is corrected so that the difference between a measured shape of the workpiece and a predetermined target shape of the workpiece becomes small. When the stroke is corrected, bending is started from the next process, and bending after the next process is performed with a corrected stroke.

However, according to the methods disclosed in Patent Literature 1 and 2, the correction does not have an effect on the processing positions in which the bending is performed before the correction, resulting in a bending state with the error remaining. From the viewpoint of product quality, it is desirable that there are less variations in the bending state at respective processing positions.

An aspect of some embodiments includes a series of processes of repeating bending of a workpiece by applying pressure to the workpiece with an upper tool attached to an upper table and a lower tool attached to a lower table of a press brake from a first process to an N-th process (where N is a natural number) while feeding the workpiece at a predetermined pitch so as to bend the workpiece at N processing positions, thereby bending the workpiece at a desired bending angle, the series of processes including: a measuring process of measuring a bending angle of the workpiece at completion of an M-th process (where M is a natural number less than N); and a calculation process of correcting a table output for applying pressure to the workpiece based on a measurement value of the bending angle of the workpiece measured in the measuring process and a target value of the bending angle of the workpiece at completion of the M-th process, wherein, in a case where the table output is corrected, the bending is restarted from a previous process which is the M-th process or a process before the M-th process based on the corrected table output.

According to the aspect of some embodiments, since bending is restarted from the previous process, pressure is again applied to the workpiece based on the corrected table output even at the processing position in which bending has already been performed. Through again applying pressure to the workpiece, deviation from the target value generated in the bending performed before correction is corrected and a desired bending state can be obtained even at the processing position related to the previous process. Further, pressure is applied to the workpiece based on the corrected table output in the processes subsequent to the M-th process, a desired bending state can be obtained even at processing positions related to the subsequent processes.

According to the aspect of some embodiments, variations in the bending state at each processing position can be suppressed. Thus, the product quality can be improved.

A bending method according to an embodiment will be described below with reference to the drawings.

is a flowchart illustrating a procedure of a bending method according to the present embodiment.is a perspective view illustrating a press brake which performs bending. In the following description, a left-right direction X, a front-rear direction Y, and an up-down direction Z are used to define the press brake. The left-right direction X and the front-rear direction Y correspond to two directions orthogonal to each other in a horizontal direction, and the up-down direction Z corresponds to a vertical direction. However, these directions are only used for convenience in explaining the press brakein the present embodiment.

A bending method according to the present embodiment includes a series of processes of repeating bending of a workpiece W by applying pressure to the workpiece W with an upper toolattached to an upper tableand a lower toolattached to a lower tableof the press brakefrom a first process to an N-th process (where N is a natural number) while feeding the workpiece W at a predetermined pitch, so as to bend the workpiece W at N processing positions, thereby bending the workpiece W at a desired bending angle. The series of processes includes: a measuring process of measuring a bending angle of the workpiece W at completion of an M-th (where M is a natural number less than N) process; and a calculation process of correcting a table output for applying pressure to the workpiece W based on a measurement value of the bending angle of the workpiece W measured in the measuring process and a target value of the bending angle of the workpiece W at completion of the M-th process. In a case where the table output is corrected, the bending is restarted from a previous process which is the M-th process or a process before the M-th process based on the corrected table output.

Hereinafter, configuration of the press brakewill be described. The press brakeis a processing machine which bends the workpiece W by applying pressure to the workpiece W using the upper toolwhich is a tool such as a punch and the lower toolwhich is a tool such as a die.

The press brakeincludes the lower table, the upper table, left and right lifting mechanismsL,R, left and right crowning mechanismsL,R, a control device, and an operation panel.

The press brakeincludes left and right side framesL,R arranged at a distance in the left-right direction X. The upper tableextends in the left-right direction X and is supported by front upper portions of the side framesL,R. The upper tableis configured to be movable in the up-down direction Z. The lower tableextends in the left-right direction X and is supported by front lower portions of the side framesL andR.

An upper tool holder for detachably holding the upper toolis provided on a lower side of the upper table. A holder groove for inserting a base of the upper toolis formed in the upper tool holder in the left-right direction X. The upper tool holder has a clamp mechanism for fixing the upper toolto the upper table.

A lower tool holder for detachably holding the lower toolis provided on an upper side of the lower table. A holder groove for inserting a base of the lower toolis formed in the lower tool holder in the left-right direction X. The lower tool holder has a clamp mechanism for fixing the lower toolto the lower table.

The left and right lifting mechanismsL andR are provided on left and right upper portions of the side framesL,R, respectively. The left and right lifting mechanismsL,R are mechanisms for moving the upper tablein the up-down direction Z, and are, for example, hydraulic cylinders. However, a combination of an electric motor and a reduction gear may be used for the left and right lifting mechanismsL,R. The left and right lifting mechanismsL,R can be independently controlled. The left and right stroke positions of the upper tablecan be independently controlled by the left and right lifting mechanismsL,R. The stroke position is a relative position (a depth value, D value) from an upper end of the lower tableto a lower end of the upper table, and is one of parameters corresponding to the table output for applying pressure to the workpiece W.

A front plateand a rear plateare provided on a front side and a rear side of the lower table, respectively. The front plateand the rear plateare integrally attached to the lower tablethrough left and right pivot shaftsL,R penetrating in the front-rear direction Y.

The left and right crowning mechanismsL,R are provided at left and right positions of the lower tablewith respect to a center position in the left-right direction X.

The respective left and right crowning mechanismsL,R are fixed to the front plateand the rear plate. By operating the left and right crowning mechanismsL andR, a part of the lower tablecan be bent upward or downward.

The left and right crowning mechanismsL,R can be independently controlled. The left and right crowning mechanismsL,R can adjust crowning output. The crowning output indicates how much the lower tableis to be curved and which position of the lower tableis to be curved, and is one of the parameters corresponding to the table output for applying pressure to the workpiece W.

The control deviceincludes, for example, a computer such as a numerical control (NC) device. The computer mainly includes a hardware processor such as a central processing unit (CPU), a memory, and various interfaces. The memory and various interfaces are connected to the hardware processor via a bus. A predetermined computer program is installed in the computer. When the hardware processor executes the computer program, the computer executes the functions provided in the control device.

The control devicecontrols the operation of the press brake. Specifically, the control devicecontrols the left and right lifting mechanismsL andR, and the left and right crowning mechanismsL andR. The control devicecontrols the left and right lifting mechanismsL andR based on left and right D values to lower the upper tableand apply pressure to the workpiece W. The control devicecontrols the left and right crowning mechanismsL andR based on the crowning output, so that pressure can be applied to the workpiece W with the lower tablepartially curved.

The operation panelhas, for example, a display unit such as a liquid crystal display and an input unit such as a touch panel. The operation panel, controlled by the control device, displays various setting screens and operation screens, and outputs information input from an operator to the control device.

In bending using the press brakeconfigured in such a manner, the operator places the workpiece W in a shape of a plate on the lower toolattached to the lower table. At this point, the operator positions the workpiece W by abutting the workpiece W against a back gauge (not illustrated) positioned at a predetermined position behind the lower table. Then, the control devicelowers the upper tabletoward the lower tablein response to an instruction from the operator. As a result, pressure is applied to the workpiece W between the upper tooland the lower tool, and the workpiece W is bent in a desired bending state.

Hereinafter, a bending method which is one of features of the present embodiment will be described. The bending method in the present embodiment is suitable for FR bending using the press brake. FR bending is a bending method in which the workpiece W is bent at a desired bending angle by repeating bending from a first process to an N-th process while feeding the workpiece W at a predetermined pitch so as to bend the workpiece W at N processing positions.

is an explanatory diagram illustrating a bending angle and processing positions of the workpiece W. A bending angle at of the workpiece W is an internal angle of the workpiece W curved due to a bending effect at each processing position.illustrates an example in which the bending angle at of the workpiece W is 90 degrees. For example, when “N” is 20, the bending is repeated from the first process to the twentieth process, and the workpiece W is bent atprocessing positions from Pto P. When the bending angle at of the workpiece W is 90 degrees, the bending state of the workpiece W obtained in each process (each processing position) is ideally 4.5 degrees.

Referring to, in step S, the bending is performed from the first process to the M-th process.is an explanatory diagram illustrating the first process of the bending. In the drawing, a left side corresponds to a rear side in the front-rear direction Y of the press brake, and a right side corresponds to a front side in the front-rear direction Y of the press brake. Directions of the workpiece W placed on the lower toolcan be defined with reference to the press brake. A back gauge side of the press brakeis a rear side of the workpiece W, and an operator side is a front side of the workpiece W. In the first process, pressure is applied at a first processing position Pby the upper tooland the lower tool, and bending is performed to the first processing position P.

is a diagram illustrating a bending angle when a third process is completed. When the first process is completed, the operator feeds the workpiece W at a predetermined pitch and positions the workpiece W so that a second processing position Pis positioned between the upper tooland the lower tool. Then, in a second process, bending is performed at the second processing position P. Such processes are performed up to the M-th process. “M” is a natural number less than N, and the M-th process is the third process in the present embodiment.

When the third process is completed, the operator temporarily stops operation of the press brake. Then, in step S, a bending angle αof the workpiece W is measured when the third process is completed (a measuring process). The bending angle αcan be measured manually by the operator using an angle sensor. Alternatively, the control devicemay operate the angle sensor mounted on the press braketo automatically measure the bending angle αin response to a predetermined operation on the operation panelperformed by the operator. When the operator manually measures a bending angle, the operator inputs a measurement value of the bending angle αto the operation panel, and the control devicecan acquire information of the value. When the control deviceautomatically measures the bending angle α, the control devicecan directly acquire a measurement value of the bending angle αfrom the angle sensor.

However, the bending angle of the workpiece W is not only measured when the third process is completed, but may be measured when the second process is completed, or when a fourth process or a processe after the fourth process is completed. Note that the bending angle of the workpiece W is preferably measured in a range of 165 degrees or more and 175 degrees or less. For this reason, among the first to twentieth processes, a process in which the bending angle at completion of the process is 165 degrees or more and 175 degrees or less is set as the M-th process.

The bending angle may be measured intentionally by the operator when the M-th process is completed, but is not limited thereto. For example, the operator operates the operation paneland sets, in the control device, the M-th process for which a bending angle is measured. The control devicemay use the completion of the M-th process as a trigger to urge the operator to measure a bending angle or to automatically measure a bending angle. Alternatively, the control devicestores a target value of a bending angle of the workpiece W at completion of each process, whereby the control devicedetermines whether or not the target value of the bending angle falls within a range of 165 degrees or more and 175 degrees or less when each process is completed. Then, the control devicemay urge the operator to measure the bending angle or automatically measure the bending angle, using, as a trigger, completion of a process in which the target value of the bending angle is 165 degrees or more and 175 degrees or less.

In step S, the operator determines whether correction is necessary. When bending of 90 degrees is performed through all 20 processes, the target value of the bending angle αof the workpiece W at completion of the third process is 166.5 degrees. If the difference between the measurement value of the bending angle αand the target value (166.5 degrees) of the bending angle αof the workpiece W at completion of the third process is equal to or greater than a predetermined threshold value, the operator determines that correction is necessary. On the other hand, if the difference between the measurement value of the bending angle αand the target value (166.5 degrees) of the bending angle αof the workpiece W at completion of the third process is smaller than a predetermined threshold value, the operator determines that correction is unnecessary. Whether or not correction is necessary may be determined by the operator or the control device.

If correction is necessary, proceed to a step S. On the other hand, if correction is not necessary, bending is performed from the fourth process to the twentieth process in step S.

In step S, the control deviceperforms a correction calculation based on the bending angle α(calculation process).is a diagram illustrating an operation screen displayed on an operation panel in accordance with the correction calculation. The operation paneldisplays items of a first display item, second and third display itemsand, fourth to seventh display items,,,, and first to third operation items,,.

The first display itemindicates a target value of the bending angle αof the workpiece W at completion of the third process. The second display itemindicates the current number of processes, that is, the number of times of bending up to the current process (for example, “3 times”), and the third display itemindicates the total number of processes, that is, the total number of times of bending (for example, “20 times”).

The fourth to seventh display items,,andindicate measurement values of the bending angle α. When the bending angle αis measured at one representative point such as a center of the workpiece W in the left-right direction, and a measurement value of this representative point is treated as the bending angle αof the workpiece W as a whole, the measurement value of the bending angle αis indicated as the fourth display item. On the other hand, when the bending angle αis measured at a plurality of positions, for example, at three positions of a left side, a center, and a right side of the workpiece W, measurement values of the bending angle αat the left side, the center, and the right side are indicated as the fifth to seventh display items,, and, respectively.

The first and second operation items,are operation items for selecting a correction mode of the table output between overall correction and longitudinal correction. The overall correction is a method of uniformly correcting the table output between the left and right ends of the workpiece W based on the measurement value of the bending angle αmeasured at the representative point. The longitudinal correction is a method of correcting the table output based on the measurement values of the bending angle αat the left side, the center, and the right side of the workpiece W so that the bending angle between the left and right ends of the workpiece W becomes uniform. The overall correction can be selected by operating the first operation itemand the longitudinal correction can be selected by operating the second operation item. The third operation itemis an operation item for executing the correction calculation.

After confirming the display itemsto, the operator selects the overall correction or the longitudinal correction through the first and second operation itemsand, and then operates the third operation item. Thus, the control deviceexecutes correction calculation corresponding to the selected correction mode.

First, a description will be given of a case where the first operation itemcorresponding to the overall correction is selected. The control devicecalculates an accumulated error in a case where the bending is continued from a first process to a twentieth process, based on an error between the measurement value of the bending angle αof the workpiece W at completion of the third process and the target value of the bending angle αof the workpiece W at completion of the third process. The control devicethen calculates a bending correction amount β that cancels out the accumulated error. The bending correction amount β is calculated by, for example, Formula 1.

Bending correction amount β=(α33)×()  [Formula 1]

In Formula 1, “3t” is the target value of the bending angle αof the workpiece W at completion of the third process and “α3m” is the measurement value of the bending angle αof the workpiece W at completion of the third process. “RNW” is the total number of processes and “RNM” is the current number of processes.

For example, when the measurement value of the bending angle αof the workpiece W is 170 degrees and the target value of the bending angle αof the workpiece W is 166.5 degrees, the bending correction amount β is −23.33 degrees ((166.5 degrees−170 degrees)×(20/3)).

When the bending correction amount β is specified, the control devicecalculates a corrected table output based on the bending correction amount β. When the overall correction is selected, the control devicecorrects the D value as the table output. However, the control devicemay correct the crowning output or may correct the D value and the crowning output.

Assuming that the bending angle αis uniform between the left and right ends of the workpiece W, the control devicecalculates corrected left and right D values based on the bending correction amount β. As illustrated in, the control deviceindicates the left and right D values as the eighth and ninth display itemsand. According to this calculation method, the corrected left and right D values can be automatically calculated from the measurement value of the bending angle αwithout the operator calculating left and right bending correction amounts β and β′ and then inputting the left and right bending correction amounts β and β′ to the 10 and 11 display itemsand, respectively.

However, the operator may calculate the left and right bending correction amounts β and β′ and input the left and right bending correction amounts β and β′ as the tenth and eleventh display itemsand, respectively, using the operation panel. In this case, the control devicecalculates the corrected left and right D values based on the input left and right bending correction amounts β and β′.

On the other hand, when the longitudinal correction is selected, the control devicecalculates the bending correction amount β for each of left end, center, and right end measurement points. Then, the control devicecalculates a corrected table output based on the bending correction amount β at each of the measurement points so that the bending angle between the left and right ends of the workpiece W becomes uniform.

When the longitudinal correction is selected, the control devicecorrects both D value and the crowning output as the table output. However, the control devicemay correct only one of the D values or the crowning output.

As illustrated in, when the correction calculation is completed, the operator restarts operation of the press brakeby operating the operation panelto restart the bending from the first process (step). However, using completion of the correction calculation as a trigger, the control devicemay restart the operation of the press brakeand control the press brakeso that the bending is automatically restarted from the first process.