Sheet metal bending method and press brake

Abstract

The present invention provides a sheet metal bending method that can reduce deviations in the bending angle at the ends of the bent line in the width direction. [Solution] In the first bending process, the upper table 1, which is in a non-inclined reference state, is lowered to the lower table and the sheet metal W is bent to a predetermined angle along the bending line (a). In the second bending process, the upper table 1, which is in an inclined state with an upward and right inclination, is lowered to the lower table and the sheet metal W is further bent along the bending line (b). In the third bending process, the upper table 1, which is in an inclined state with an upward and left inclination, is lowered to the lower table and the sheet metal W is further bent along the bending line (c).

Description

Technical Field

[0001] The present invention relates to a method for bending sheet metal and a press brake.

Background Art

[0002] A press brake lowers an upper table on which a punch is mounted to a lower table on which a die is mounted, and bends a sheet metal sandwiched between the punch and the die at a predetermined angle along a bending line having a predetermined width set for the sheet metal.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When bending a sheet metal at a predetermined angle by a press brake, the actual bending angle at one or both ends in the width direction of the bending line may deviate from the predetermined angle. There is a demand for the emergence of a method for bending sheet metal and a press brake that can reduce the deviation of the bending angle at the end in the width direction of the bending line when bending the sheet metal at a predetermined angle.

Means for Solving the Problems

[0005] A first aspect of one or more embodiments includes a first bending step in which an upper table on which a punch is mounted is set to a non-inclined reference state, the upper table is lowered to a lower table on which a die is mounted, and the sheet metal sandwiched between the punch and the die is bent at a predetermined angle along a bend line having a predetermined width set on the sheet metal, and the width direction of the bend line of the lower end surface of the upper table, which is the width direction of the bend line of the first bending step, where the bending angle of the sheet metal by the first bending step deviates from the predetermined angle. The present invention provides a method for bending sheet metal, comprising: a second bending step in which the upper table is tilted such that the lower end of the first end of the first end of the sheet metal is positioned downward and the lower end of the second end of the sheet metal is positioned upward, and the upper table is lowered to the lower table to bend the sheet metal along the bending line; and a third bending step in which the upper table is tilted in the opposite direction to the tilt in the second bending step, and the upper table is lowered to the lower table to bend the sheet metal along the bending line, performed in succession.

[0006] A second aspect of one or more embodiments comprises an upper table on which a punch is mounted, a lower table on which a die is mounted, a table lifting mechanism having a tilting function to tilt the upper table with respect to the width direction of the upper table and raising and lowering the upper table, and a control device that controls the tilting and raising and lowering of the upper table by the table lifting mechanism, wherein the control device sets the upper table to a non-tilted reference state, lowers the upper table to the lower table, and bends the sheet metal sandwiched between the punch and the die at a predetermined bend line having a predetermined width set on the sheet metal. The present invention provides a press brake that controls the table lifting mechanism to bend the sheet metal at an angle, tilting the upper table such that, of the first and second ends in the width direction of the upper table, the lower end on the end in the width direction of the bend line where the bending angle when the sheet metal is bent with the upper table in the reference state deviates from the predetermined angle is positioned downwards, and the lower end on the opposite end in the width direction of the bend line is positioned upwards, and then lowering the upper table to the lower table to further bend the sheet metal along the bend line. [Effects of the Invention]

[0007] According to one or more embodiments of the sheet metal bending method and press brake, it is possible to reduce the deviation of the bending angle at the widthwise end of the bend when the sheet metal is bent to a predetermined angle. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 shows the overall configuration of a press brake according to one or more embodiments. [Figure 2] Figure 2 is a perspective view showing an example of a box-bent product. [Figure 3] Figure 3 shows an example of bending sheet metal using two lug dies. [Figure 4]Figure 4 shows the relationship between the position of the bend line and the bending angle when sheet metal is bent using two lug dies and when sheet metal is bent using a punch with a standard shape that does not have lugs. [Figure 5] Figure 5 shows the first to third bending steps in sheet metal bending using two lug dies. [Figure 6] Figure 6 is a perspective view showing an example of a product made by bending sheet metal into an L-shape. [Figure 7A] Figure 7A shows the state in which the bent sheet metal has been unloaded more than necessary when moving from the first bending process shown in Figure 5 to the second bending process. [Figure 7B] Figure 7B shows the state when the bent sheet metal is unloaded to the extent that the springback is not completely removed, as it moves from the first bending process shown in Figure 5 to the second bending process. [Figure 8] Figure 8 shows the relationship between the position of the bend line and the bending angle when sheet metal is bent using two lug dies in only the first bending process shown in Figure 5, and when it is bent in the first to third bending processes shown in Figure 5. [Figure 9] Figure 9 shows the first and second bending processes in sheet metal bending using a die with an ear portion protruding to the left and a punch without an ear portion. [Figure 10] Figure 10 shows the first and second bending processes in sheet metal bending using a punch without ears and an ear die with ears protruding to the right. [Figure 11A] Figure 11A is a side view showing a gooseneck punch. [Figure 11B] Figure 11B is a side view showing a straight sword punch. [Figure 12A] Figure 12A shows the relationship between the bending load and the amount of deflection at the end of the bent line when sheet metal is bent with a gooseneck punch that has an ear die and a gooseneck punch without an ear die. [Figure 12B] Figure 12B shows the relationship between the bending load and the amount of deflection at the end of the bend when sheet metal is bent with a straight punch that has an ear die and a straight punch that does not have an ear die. [Figure 13] FIG. 13 is a schematic diagram showing the deflection range L at the end of the bending line, the inclination angle θ, the deflection amount δ, the D-axis distance H, and the D-axis inclination amount Δ. [Figure 14A] FIG. 14A is a partial flowchart showing the operation of a press brake according to one or more embodiments of bending a sheet metal to a target bending angle. [Figure 14B] FIG. 14B is a partial flowchart following FIG. 14A showing the operation of a press brake according to one or more embodiments of bending a sheet metal to a target bending angle. [Figure 15] FIG. 15 is a diagram showing an example of a preferable arrangement position of an angle sensor used in the first to third bending steps shown in FIG. 5.

MODE FOR CARRYING OUT THE INVENTION

[0009] Hereinafter, a method for bending a sheet metal and a press brake according to one or more embodiments will be described with reference to the accompanying drawings.

[0010] FIG. 1 shows the overall configuration of a press brake 100 according to one or more embodiments. As shown in FIG. 1, the press brake 100 includes an NC (Numerical Control) device 10 that functions as a control device for controlling the press brake 100. A machining program database 50 is connected to the NC device 10 via a network. The press brake 100 includes an upper table 1, a lower table 3, and left and right side plates 5L and 5R. An upper die holder 2 is attached to the upper table 1, and a lower die holder 4 is attached to the lower table 3.

[0011] The upper table 1 is configured to move up and down by hydraulic cylinders 6L and 6R provided on the left and right. A servo motor may be used instead of the hydraulic cylinders 6L and 6R. The hydraulic cylinders 6L and 6R or the servo motor shall be referred to as the table lifting mechanism 6. The NC device 10 controls the table lifting mechanism 6 so as to lower the upper table 1 closer to the lower table 3 or raise it away from the lower table 3.

[0012] The NC device 10 can individually control the amount of lifting and lowering of the upper table 1 by the hydraulic cylinder 6L and the hydraulic cylinder 6R. The vertical direction in which the upper table 1 moves up and down by the hydraulic cylinders 6L and 6R is referred to as the D axis. The D axis on which the hydraulic cylinder 6L raises and lowers the upper table 1 is referred to as the D axis D1, and the D axis on which the hydraulic cylinder 6R raises and lowers the upper table 1 is referred to as the D axis D2. The distance between the D axis D1 and the D axis D2 is defined as the D axis distance.

[0013] If the NC device 10 makes the amount of lifting and lowering of the upper table 1 common between the hydraulic cylinder 6L and the hydraulic cylinder 6R, the upper table 1 can be lifted and lowered while maintaining the lower end surface of the upper table 1 in a state substantially parallel to the horizontal plane. If the NC device 10 makes the amount of lifting and lowering of the upper table 1 different between the hydraulic cylinder 6L and the hydraulic cylinder 6R, the upper table 1 can be lifted and lowered with the lower end surface of the upper table 1 inclined with respect to the horizontal plane. That is, the table lifting mechanism 6 has an inclination function of inclining the upper table 1 with respect to the width direction (left - right direction) of the upper table 1. The NC device 10 can incline the upper table 1 upward to the right so that when viewed from the front of the upper table 1, the left end (the first lower end) of the lower end surface is below and the right end (the second lower end) of the lower end surface is above, or incline it upward to the left so that the left end of the lower end surface is above and the right end of the lower end surface is below.

[0014] The upper mold holder 2 is fitted with the upper mold, which is the punch Tp, and the lower mold holder 4 is fitted with the lower mold, which is the die Td. Figure 1 shows a modular type in which the upper mold holder 2 is integrally attached along the entire length of the lower end of the upper table 1, but it may also be an intermediate plate type in which multiple intermediate plates for which the punch Tp is attached are attached in the longitudinal direction of the lower end of the upper table 1. The intermediate plates are also upper mold holders.

[0015] Mounting a punch Tp on the upper table 1 means mounting the punch Tp on the upper die holder 2 or the intermediate plate. Mounting a die Td on the lower table 3 means mounting the die Td on the lower die holder 4. Two or more punches Tp may be mounted side by side on the upper table 1, and two or more dies Td may be mounted side by side on the lower table 3.

[0016] A back gauge 40 is positioned on the underside of the lower table 3. The back gauge 40 includes abutments 42a and 42b that move left and right along the back gauge carriage 41. Here, there are two abutments, 42a and 42b, but the number of abutments is not limited to two. The abutments 42a and 42b are configured to move up and down and front and back.

[0017] Before the operator places the sheet metal W to be processed on the die Td and bends it by sandwiching it between the punch Tp and the die Td, the abutments 42a and 42b move to positions corresponding to the die Td. The operator places the sheet metal W on the die Td so that its rear end abuts against the abutments 42a and 42b. In other words, the abutments 42a and 42b act to determine the front-to-back position of the sheet metal W when it is placed on the die Td.

[0018] An operating pendant 7 is attached to the left side of the press brake 100 via an arm 7a, and has a display unit 71 and an operating unit 72 including a plurality of operating buttons. The operating pendant 7 is connected to the NC device 10. The NC device 10 is connected to a foot switch 8 which has an open foot switch 81 for raising the upper table 1 and a close foot switch 82 for lowering the upper table 1.

[0019] When a sheet metal W is bent to a predetermined angle by the press brake 100 configured as described above, the actual bending angle at one or both ends of the bend in the width direction may deviate from the predetermined angle. Figures 2 to 4 illustrate typical examples of when the actual bending angle at the ends of the bend in the width direction deviates from the predetermined angle.

[0020] Figure 2 shows a box-bent product 200 made by bending sheet metal W with a press brake 100. The box-bent product 200 has sides 202-205 bent at a right angle to the bottom surface 201, and inner bent surfaces 206-209 formed by bending the upper ends of sides 202-205 inward at a right angle. Suppose that sheet metal W is bent to form, for example, side 204, with only sides 202 and 203 and inner bent surfaces 206 and 207 formed. In this case, if one or more punches Tp with a standard shape are used to bend the sheet metal W at the bend line which is the boundary between the bottom surface 201 and side 204, the inner bent surfaces 206 and 207 will interfere with the punches Tp, making it impossible to bend the sheet metal W.

[0021] Therefore, as shown in Figure 3, ear molds Tp1 and Tp2 are used instead of a standard-shaped punch Tp. Ear mold Tp1 is the first punch, and ear mold Tp2 is the second punch. An ear mold is a mold (punch) that has an ear protruding from one side in the width direction of the bend line. When viewed from the front, ear molds Tp1 and Tp2 have ears EL and ER protruding in opposite directions, to the left and to the right, respectively. Figure 3 shows an example of bending a sheet metal W along a bend line using two punches Tp, which are ear molds Tp1 and Tp2. If the bend line is longer, a standard-shaped punch Tp without an ear may be placed between ear mold Tp1 and ear mold Tp2. In Figure 3, the upper mold holder 2 is not shown.

[0022] As shown in Figure 3, when sheet metal W is bent by sandwiching it between the ear dies Tp1 and Tp2 and the die Td, the sheet metal W is subjected to forces as indicated by the arrows. At this time, the ears EL and ER flex, so the force applied to the part of the bent line where the ears EL and ER or their vicinity are in contact is weaker than the force applied to the central part of the bent line. As a result, as shown in Figure 4, the actual bending angle is close to the target bending angle at the central part P3 of the bent line, but deviates significantly from the target bending angle at the left end P1 (first end) and the right end P2 (second end). In Figure 4, the target bending angle is 90.5 degrees and the length of the bent line is 400 mm. The center of the 400 mm bent line is defined as bending line position 0 mm, the left end as bending line position -200 mm, and the right end as bending line position 200 mm.

[0023] Typically, when using ear dies Tp1 and Tp2, the bending angle deviates significantly from the target bending angle at both ends of the bend. Furthermore, depending on various conditions, even when using a punch Tp with a standard shape, the bending angle may deviate from the target bending angle at both ends of the bend. In Figure 3, if the side surface 202 and inner bending surface 206 are not formed, and only the side surface 203 and inner bending surface 207 are formed, then the sheet metal W can be bent by combining ear die Tp1 with ear portion EL and a punch Tp with a standard shape without ear portion. In this case, the bending angle deviates significantly from the target bending angle only at the left end P1 of the bend in Figure 4.

[0024] To reduce the deviation of the bending angle from the target bending angle when the sheet metal W is bent to a predetermined angle along a bending line having a predetermined width set on the sheet metal W, the press brake 100 performs a sheet metal bending method according to one or more of the following embodiments.

[0025] Figure 5, similar to Figure 3, shows an example of bending sheet metal W using ear dies Tp1 and Tp2 as punch Tp. In Figure 5, the sheet metal W is bent into an L-shape along the bending line 301 as shown in Figure 6 to produce product 300. The target bending angle is, for example, 90 degrees. The length of the bending line 301 is 400 mm. In Figure 5, the upper die holder 2 is also omitted from the illustration.

[0026] As shown in Figure 5(a), the NC device 10 controls the table lifting mechanism 6 to bend the sheet metal W to a predetermined angle along the bending line 301 by lowering the upper table 1 to a non-tilted reference state as the first bending process. The non-tilted reference state of the upper table 1 is a state in which the lower end surface of the upper table 1 is approximately parallel to the horizontal plane. As explained in Figure 4, in the state in which the sheet metal W has been bent in the first bending process, the bending angle at the left end P1 and right end P2 in the width direction of the bending line 301 deviates from the predetermined angle which is the target bending angle.

[0027] As shown in Figure 5(b), the NC device 10 controls the table lifting mechanism 6 to tilt the upper table 1 upwards and to the right, so that, when viewed from the front, the left end 11 of the lower end surface of the upper table 1 is positioned downwards and the right end 12 is positioned upwards, as a second bending process. With the upper table 1 tilted upwards and to the right, the NC device 10 controls the table lifting mechanism 6 to lower the upper table 1 to the lower table 3 and further bend the sheet metal W along the bending line 301. In the second bending process, the pressing force applied to the die Td via the sheet metal W by the ear dies Tp1 and Tp2 is relatively strong at the ear portion EL of the ear die Tp1 and its vicinity, and weak at the ear portion ER of the ear die Tp2 and its vicinity.

[0028] Next, as shown in Figure 5(c), the NC device 10 controls the table lifting mechanism 6 to tilt the upper table 1 to an upper-left inclination, opposite to the inclination in the second bending process, so that the left end 11 of the upper table 1 is positioned upward and the right end 12 is positioned downward, as the third bending process. With the upper-left inclination, the NC device 10 controls the table lifting mechanism 6 to lower the upper table 1 to the lower table 3 and further bend the sheet metal W along the bending line 301. In the third bending process, the pressing force applied to the die Td via the sheet metal W by the ear dies Tp1 and Tp2 is relatively weak at the ear portion EL of the ear die Tp1 and its vicinity, and strong at the ear portion ER of the ear die Tp2 and its vicinity.

[0029] The order of the second bending process shown in Figure 5(b) and the third bending process shown in Figure 5(c) may be reversed.

[0030] The second and third bending processes are bending angle correction processes that correct the bending angle in the deflection range, which will be described later. The deflection range refers to the region where the bending angle on the bending line does not reach a predetermined target bending angle due to the deflection of the punch Tp (especially the ends of the ear dies Tp1 and Tp2), and the sheet metal W on the bending line is deflected. Multiple deflection ranges may exist on the bending line. Once the deflection ranges are identified, the bending line is divided into two or more regions, each containing at least one deflection range and a region other than the deflection range (a third region). Typically, a first deflection range is set on one end of the bending line, and a second deflection range is set on the other end. The bending angle correction process is performed on the first and second deflection ranges. In Figure 4, the left end P1 and the right end P2 correspond to the deflection ranges, and the central part P3 corresponds to the third region.

[0031] In Figure 5, when transitioning from the first bending process shown in (a) to the second bending process shown in (b), and when transitioning from the second bending process to the third bending process shown in (c), the NC device 10 slightly raises the upper table 1 to unload the sheet metal W. In Figures 7A and 7B, the dashed line shows the position of the sheet metal W in the first bending process, and the solid line shows the position of the sheet metal W in the unloaded state between the first and second bending processes. Figure 7A shows a state where the load has been unloaded more than necessary. If the load is unloaded too much, the bent sheet metal W will tilt, and the position of the bend line 301 of the sheet metal W in the first bending process may shift not only vertically but also horizontally in the second bending process.

[0032] Figure 7B shows the bent sheet metal W after being unloaded to the extent that the springback is not completely relieved. When the bent sheet metal W is unloaded to the extent that the springback is not completely relieved, the force that causes the bent sheet metal W to open fixes its position in the front-rear direction, and the bent sheet metal W does not tilt. The same applies when transitioning from the second bending process to the third bending process.

[0033] When transitioning from the second bending process to the third bending process, if the load on the sheet metal W is not removed or is not removed sufficiently, the sheet metal W may be overpressed, causing it to bend beyond the target bending angle. It is advisable to raise the upper table 1 to remove the load to the extent that the springback of the bent sheet metal W is not completely removed, and to avoid excessive pressure when transitioning from the second bending process to the third bending process.

[0034] In Figure 8, the dashed line shows the bending angle at the bending line position when the sheet metal W is bent in the first bending process. When the sheet metal W is bent in the first bending process, the bending angle at both ends in the width direction of the bending line 301, corresponding to the left end P1 and right end P2 in Figure 4, deviates significantly from the target bending angle of 90 degrees. The solid line shows the bending angle at the bending line position when the sheet metal W is bent in the first to third bending processes. At both ends in the width direction of the bending line 301, the bending angle approaches the target bending angle of 90 degrees.

[0035] When the sheet metal W shown by the dashed line is bent in the first bending process, the bending angle is ±1.83 degrees relative to the target bending angle. When the sheet metal W shown by the solid line is bent in the first to third bending processes, the bending angle is ±0.95 degrees relative to the target bending angle. The accuracy of the alignment of the bent line 301 in the width direction has improved by approximately 48%. In this way, by performing the sheet metal bending method according to one or more embodiments, the deviation of the bending angle at both ends of the bent line 301 in the width direction can be reduced.

[0036] As described above, even when using a punch Tp with a standard shape, the bending angle at both ends in the width direction of the bent line may deviate from the target bending angle. In this case as well, the NC device 10 can reduce the deviation in the bending angle at both ends by executing a bending method consisting of the first to third bending steps shown in Figure 5.

[0037] Figure 9 shows an example of bending a sheet metal W using a die Tp1 with an ear portion EL and a punch Tp without an ear portion. The sheet metal W shown in Figure 9 has a pre-bent side surface 203 and an inner bent surface 207.

[0038] As shown in Figure 9(a), the NC device 10 controls the table lifting mechanism 6 to bend the sheet metal W along the bend line at a predetermined angle, starting with the upper table 1 in a non-inclined reference state as the first bending process, and lowering the upper table 1 to the lower table 3. As shown in Figure 9(b), the NC device 10 controls the table lifting mechanism 6 to incline the upper table 1 to the upper right, so that, when viewed from the front, the left end 11 of the lower end surface of the upper table 1 is positioned downwards and the right end 12 is positioned upwards. The NC device 10 controls the table lifting mechanism 6 to further bend the sheet metal W along the bend line by lowering the upper table 1 to the lower table 3. This reduces the deviation in the bending angle at the widthwise end (in this case, the left end) of the bend line of the sheet metal W.

[0039] Figure 10 shows an example of bending a sheet metal W using a punch Tp without an ear portion and an ear die Tp2 having an ear portion ER. The sheet metal W shown in Figure 10 has a pre-bent side surface 202 and an inner bent surface 206.

[0040] As shown in Figure 10(a), the NC device 10 controls the table lifting mechanism 6 to bend the sheet metal W along the bend line to a predetermined angle, starting with the upper table 1 in a non-inclined reference state as the first bending process, and lowering the upper table 1 to the lower table 3. As shown in Figure 10(b), the NC device 10 controls the table lifting mechanism 6 to incline the upper table 1 to the upper left so that the left end 11 of the upper table 1 is positioned upward and the right end 12 is positioned downward as the second bending process. The NC device 10 controls the table lifting mechanism 6 to lower the upper table 1 to the lower table 3 and further bend the sheet metal W along the bend line. This reduces the deviation in the bending angle at the end of the bend line in the width direction of the sheet metal W (in this case, the right end).

[0041] In Figure 5(b) and Figure 9(b), the difference in distance between the vertical position of the lower end surface of the upper table 1 on the D-axis D1 and the vertical position of the lower end surface of the upper table 1 on the D-axis D2 is referred to as the D-axis inclination amount. Similarly, in Figure 5(c) and Figure 10(b), the difference in distance between the vertical position of the lower end surface of the upper table 1 on the D-axis D1 and the vertical position of the lower end surface of the upper table 1 on the D-axis D2 is also referred to as the D-axis inclination amount.

[0042] Assume that the left end of the leftmost end P1, which corresponds to the deflection range shown in Figure 4, and the right end of the rightmost end P2, which corresponds to the deflection range, deflect by a deflection amount δ. If the deflection constant is c, the bending load is Bf [kN], the mold pressure resistance is At [kN / m], and the bending length, which is the length of the bend, is B [mm], then the deflection amount δ [mm] can be expressed by equation (1). δ = c × {(1000 × Bf) / B} / At =(1000×c×Bf) / (At×B) …(1)

[0043] Figure 11A shows a gooseneck punch TpG, an example of punches Tp with various shapes, and Figure 11B shows another example, a straight-bladed punch TpS. The ear dies Tp1 and Tp2 are the gooseneck punch TpG, the straight-bladed punch TpS, or punches Tp with other shapes. As shown by the solid lines in Figures 12A and 12B, when sheet metal W is bent with the gooseneck punch TpG and straight-bladed punch TpS, which are the ear dies Tp1 and Tp2, the amount of deflection δ at the end of the bent line has characteristics corresponding to the bending load Bf. Note that the die pressure resistance At and the bending length B are predetermined values. As shown by the dashed lines in Figures 12A and 12B, when sheet metal W is bent with the gooseneck punch TpG and straight-bladed punch TpS, which do not have ears, the amount of deflection δ at the end of the bent line is smaller compared to when using the ear dies Tp1 and Tp2.

[0044] Let the length of the bending line at the left end P1 or right end P2 shown in Figure 4 be the deflection range L [mm], the inclination angle of the deflected left end P1 or right end P2 be θ, the distance between the D axes be H [mm], and the D axis inclination amount be Δ [mm]. The deflection range L, inclination angle θ, deflection amount δ, distance between D axes H, and D axis inclination amount Δ can be expressed as shown in the schematic diagram in Figure 13.

[0045] The inclination angle θ of the upper table 1 corresponds to the amount of inclination of the sheet metal W due to the amount of deflection δ in the deflection range L at the end of the bend, and is expressed by equation (2). As shown in Figure 13, tanθ in equation (2) can also be expressed by equation (3). tanθ = δ / L …(2) tanθ = Δ / H …(3)

[0046] From equations (1) to (3), the D-axis tilt Δ is expressed by equation (4). Δ = H × tanθ =H × δ / L =H × {(1000 × c × Bf) / (At × B)} / L =(1000×H×c×Bf) / (At×B×L) …(4)

[0047] The NC device 10 should control the hydraulic cylinders 6L and 6R so that the upper table 1 tilts by a D-axis tilt amount Δ calculated by equation (4) in each of the second and third bending processes shown in Figures 5(b) and (c), the second bending process shown in Figure 9(b), and the second bending process shown in Figure 10(b).

[0048] By the way, when bending sheet metal W with a press brake 100, it is difficult to bend the sheet metal W to the target bending angle in a single bending process. Also, if the sheet metal W is bent to an angle narrower than the target bending angle, it cannot be returned to the target bending angle. Therefore, it is common practice for the press brake 100 to bend the sheet metal W to an angle wider than the target bending angle in the first bending process, and then gradually approach the target bending angle in subsequent bending processes until the sheet metal W is finally bent to the target bending angle.

[0049] The same applies to bending processes including the first to third bending processes shown in Figure 5, bending processes including the first and second bending processes shown in Figure 9, and bending processes including the first and second bending processes shown in Figure 10. Using the flowcharts shown in Figures 14A and 14B, the operation of the press brake 100 that bends the sheet metal W to the target bending angle will be explained using the bending process shown in Figure 5 as an example.

[0050] In Figure 14A, when the press brake 100 starts operating, in step S1, the processing program is read from the processing program database 50. The processing program is configured to bend the sheet metal W sequentially in the first to third bending processes. In step S2, the NC device 10 bends the sheet metal W to an angle slightly wider than the target bending angle in the first bending process.

[0051] As shown in Figure 15, the press brake 100 measures the bending angle of the sheet metal W at multiple angle measurement positions SC, SL, and SR. The angle measurement positions SC, SL, and SR correspond to the central part P3 (third region), the left end P1 (deflection range), and the right end P2 (deflection range), respectively. Preferably, angle measurement position SC is at the center of central part P3, angle measurement position SL is at the left end of left end P1, and angle measurement position SR is at the right end of right end P2. The bending angles at angle measurement positions SC, SL, and SR may be measured by multiple angle sensors, or by shifting the position of one angle sensor in the left-right direction. If angle measurement position SL is the first angle measurement position, then angle measurement position SC is the second angle measurement position, and angle measurement position SR is the third angle measurement position. If angle measurement position SR is the first angle measurement position, then angle measurement position SC is the second angle measurement position, and angle measurement position SL is the third angle measurement position.

[0052] In step S3, the NC device 10 obtains the measurement result of the bending angle of the central part P3 measured by the angle sensor located at the angle measurement position SC. In step S4, the NC device 10 determines whether or not the central part P3 is at the target bending angle. If the central part P3 is not at the target bending angle (NO), in step S5, the NC device 10 finely adjusts the amount of descent to slightly lower the upper table 1 and repeats steps S3 to S5.

[0053] If the central part P3 is at the target bending angle in step S4 (YES), the NC device 10 unloads the sheet metal W in step S6 to the extent that the springback is not completely removed. Subsequently, in step S7, the NC device 10 tilts the upper table 1 to the upper right as shown in Figure 5(b) in the second bending process, bending the sheet metal W to an angle slightly wider than the target bending angle.

[0054] In step S8, the NC device 10 acquires the measurement result of the bending angle of the left end P1 measured by the angle sensor located at the angle measurement position SL. Preferably, in step S8, the NC device 10 acquires both the measurement result of the bending angle of the left end P1 measured by the angle sensor located at the angle measurement position SL and the measurement result of the bending angle of the central part P3 measured by the angle sensor located at the angle measurement position SC.

[0055] In step S9, the NC device 10 determines whether the left end P1 is at the target bending angle. If the left end P1 is not at the target bending angle (NO), the NC device 10 fine-tunes the D-axis tilt amount Δ and the lowering amount of the upper table 1 in step S10 and repeats steps S8 to S10. If the NC device 10 obtains both the bending angle measurement result of the left end P1 from the angle sensor located at angle measurement position SL and the bending angle measurement result of the central part P3 from the angle sensor located at angle measurement position SC, it is preferable to adjust the D-axis tilt amount Δ and the lowering amount of the upper table 1 to balance the angles of both. By adjusting the D-axis tilt amount Δ and the lowering amount of the upper table 1 in this way, the second bending process can be executed while taking into account the region on the bending line where the bending angle should be maintained.

[0056] If the left end P1 is at the target bending angle in step S9 (YES), the NC device 10 unloads the sheet metal W in step S11 to the extent that the springback is not completely removed. Subsequently, in step S12 shown in Figure 14B, the NC device 10 tilts the upper table 1 to an upper-left inclined position as shown in Figure 5(c) in the third bending process, bending the sheet metal W to an angle slightly wider than the target bending angle.

[0057] In step S13, the NC device 10 acquires the measurement result of the bending angle of the right end P2 measured by the angle sensor located at angle measurement position SR. Preferably, in step S13, the NC device 10 acquires both the measurement result of the bending angle of the right end P2 measured by the angle sensor located at angle measurement position SR and the measurement result of the bending angle of the central part P3 measured by the angle sensor located at angle measurement position SC.

[0058] In step S14, the NC device 10 determines whether the right end P2 is at the target bending angle. If the right end P2 is not at the target bending angle (NO), the NC device 10 fine-tunes the D-axis tilt amount Δ and the lowering amount of the upper table 1 in step S15 and repeats steps S13 to S15. If the NC device 10 obtains both the bending angle measurement result of the right end P2 from the angle sensor located at angle measurement position SR and the bending angle measurement result of the central part P3 from the angle sensor located at angle measurement position SC, it is preferable to adjust the D-axis tilt amount Δ and the lowering amount of the upper table 1 to balance the angles of both. By adjusting the D-axis tilt amount Δ and the lowering amount of the upper table 1 in this way, the third bending process can be executed while taking into account the region on the bending line where the bending angle should be maintained.

[0059] If the rightmost end P2 is at the target bending angle in step S14 (YES), the NC device 10 raises the upper table 1 in step S16 to complete the bending process of the sheet metal W.

[0060] The present invention is not limited to the one or more embodiments described above, and can be modified in various ways without departing from the spirit of the invention. [Explanation of Symbols]

[0061] 1 Upper table 2 Upper mold holder 3 Lower table 4. Lower mold holder 5L,5R side plate 6L, 6R Hydraulic Cylinders 7 Operation Pendant 7a Arm 8 Footswitches 10 NC device 11 Left end 12 Right end 40 Back Gauge 41 Back Gauge Carriage 42a, 42b Nose 50 Processing Program Database 71 Display section 72 Operation section 81 Open Foot Switch 82 Foot switch for closing 100 Press Brake 200 box-bent products 300 products EL, ER ear area P1 left end P2 Right end P3 central part SC,SL,SR Angle measurement position Td Die Tp Punch Tp1,Tp2 Ear mold TpG Gooseneck Punch TpS Straight Sword Punch W Sheet Metal

Claims

1. A first bending step involves setting the upper table on which the punch is mounted to a non-tilted standard position, lowering the upper table to the lower table on which the die is mounted, and bending the sheet metal sandwiched between the punch and the die to a predetermined angle along a bending line having a predetermined width set on the sheet metal. A second bending step is performed in which the upper table is tilted such that, of the first and second lower ends in the width direction of the bending line in which the bending angle of the sheet metal in the first bending step deviates from the predetermined angle, the lower end on the first end side is positioned downward and the lower end on the second end side is positioned upward, and the upper table is lowered to the lower table to bend the sheet metal along the bending line. A third bending step is performed in which the upper table is tilted to the opposite position to the tilted position in the second bending step, the upper table is lowered to the lower table, and the sheet metal is bent along the bending line. A method for bending sheet metal, which involves continuously performing the bending process.

2. A first deflection range on the first end side and a second deflection range on the second end side are set on the bending line such that when the sheet metal is bent in the first bending process, the bending angle deviates from the predetermined angle and deflects. The second and third bending steps are steps to correct the bending angles in the first and second deflection ranges, respectively. The method for bending sheet metal according to claim 1.

3. In the second bending step, the amount of inclination of the upper table and the amount of descent of the upper table are adjusted based on the measurement result of the bending angle in the first deflection range measured by an angle sensor located at a first angle measurement position corresponding to the first deflection range, and the measurement result of the bending angle in a third region of the bent line other than the first and second deflection ranges measured by an angle sensor located at a second angle measurement position corresponding to the third region. In the third bending step, the amount of inclination of the upper table and the amount of descent of the upper table are adjusted based on the measurement result of the bending angle in the second deflection range measured by an angle sensor located at a third angle measurement position corresponding to the second deflection range, and the measurement result of the bending angle in the third region of the bent line measured by an angle sensor located at the second angle measurement position. The method for bending sheet metal according to claim 2.

4. Two or more punches are mounted on the upper table, In the two or more punches, of the first and second punches located at both ends of the bending line in the width direction, the first punch is a mortise die having an ear portion that protrudes in the opposite direction to the second punch in the width direction of the bending line, and the second punch is a mortise die having an ear portion that protrudes in the opposite direction to the first punch in the width direction of the bending line. The second bending step involves inclining the upper table so that, of the first and second lower ends of the upper table, the lower end on the side where the ear portion of the first punch protrudes is lower than the lower end on the side where the ear portion is not provided. The third bending step involves tilting the upper table so that, of the first and second lower ends of the upper table, the lower end on the side where the ear portion of the second punch protrudes is lower than the lower end on the side where the ear portion is not provided. A method for bending sheet metal according to any one of claims 1 to 3.

5. The upper table for attaching the punch, The lower table on which the die is mounted, The upper table has a tilting function that tilts the upper table with respect to its width, and a table lifting mechanism that raises and lowers the upper table. A control device that controls the tilting and raising / lowering of the upper table by the table lifting mechanism, Equipped with, The control device is The upper table is set to a non-tilted reference state, and the upper table is lowered to the lower table, and the table lifting mechanism is controlled to bend the sheet metal sandwiched between the punch and the die to a predetermined angle along a bend line having a predetermined width set on the sheet metal. The upper table is tilted such that, of the first and second ends in the width direction of the upper table, the lower end of either end in the width direction of the bend line, where the bending angle when the sheet metal is bent with the upper table in the reference state deviates from the predetermined angle, is positioned downwards, and the lower end of the opposite end in the width direction of the bend line is positioned upwards. The upper table is then lowered to the lower table, and the table lifting mechanism is controlled to further bend the sheet metal along the bend line. Press brake.

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