Step bending processing method and warpage correction method in step bending processing

Abstract

The step bending processing method includes: a step bending processing for forming a step bent portion (Wd) with a step bending roller mold (K) with respect to a flat plate-shaped workpiece (W); and a correction processing for correcting warpage in the step bent portion (Wd) after the step bending processing. A step bent portion (WR3) protruding from a flat plate part (WR1) is formed by the step bending processing. In the correction processing, the step bent portion (Wd) is pressed downward by a roller mold (K34), in a state in which the lower surface of the flat plate part (WR1) is supported, and the lower part of the step bent portion (Wd) forms a space (Va) and is not supported.

Description

Step bending method and warpage correction method in step bending

[0001] The present invention relates to a step bending method and a method for correcting warpage in step bending.

[0002] Patent Document 1 describes a technique for bending a workpiece into a linear or curved stepped shape by sandwiching the workpiece between upper and lower dies equipped with stepped rollers and moving the workpiece relative to the upper and lower dies. Step bending is a process for forming steps in sheet metal, and is also called offset bending.

[0003] Patent No. 6250079

[0004] In stepped bending using stepped rollers as described in Patent Document 1, the workpiece undergoes some degree of warping. This warping increases as the step bending height increases in the stepped bending process. Therefore, for example, problems may occur in which the warped workpiece comes into contact with components on the processing machine during the subsequent punching process, making processing difficult, or in which correction is required in a process separate from the stepped bending process. Therefore, a stepped bending method and a method for correcting warping in stepped bending that are less likely to cause problems due to warping in stepped bending using stepped rollers are desired.

[0005] A step bending method according to one aspect of the present invention comprises the following steps: a step bending process for forming a step bent portion in a flat workpiece using a step bending roller die, and a correction process for correcting warpage of the step bent portion after the step bending process, in which the step bending process forms the step bent portion that protrudes relative to the flat portion of the workpiece, and the correction process is performed by pressing the step bent portion downward with the roller die while supporting the underside of the flat portion and leaving a space below the step bent portion unsupported.

[0006] According to another aspect of the present invention, there is provided a method for correcting warpage in a step bending process, which comprises the following steps: a step-bent workpiece having a flat portion and a step-bent portion protruding from the flat portion is subjected to a correction process in which the step-bent portion is pressed downward by a roller die while the lower surface of the flat portion is supported and a space is formed below the step-bent portion to leave it unsupported.

[0007] According to the stepped bending method and the method for correcting warpage in stepped bending according to the aspects of the present invention, defects caused by warpage are less likely to occur in stepped bending using stepped rollers.

[0008] FIG. 1 is a partial cross-sectional view showing a state in which a step bending is performed on a workpiece W using a step bending roller die K equipped with a stepped roller in a step bending method according to an embodiment of the present invention. FIG. 2 is a front view showing a first correcting die K34 used in the correcting process in the step bending process of the present invention. FIG. 3 is a front view showing a second correcting die K56. FIG. 4A is a plan view showing a workpiece W that has undergone step bending. FIG. 4B is a cross-sectional view taken at the S4B-S4B position in FIG. 4A. FIG. 4C is a cross-sectional view taken at the S4C-S4C position in FIG. 4A showing the warpage of a workpiece W that has undergone step bending. FIG. 5A is a first diagram for explaining a warpage correction method using the first correcting die K34. FIG. 5B is a second diagram for explaining a warpage correction method using the first correcting die K34. FIG. 6 is a diagram for explaining a warpage correction method using the second correcting die K56. FIG. 7A is a table showing a first processing procedure using the first correcting die K34. FIG. 7B is a warpage distribution diagram of the workpiece W step-bent by the first processing procedure. FIG. 7C is a warpage distribution diagram of the workpiece W step-bent without correction. FIG. 8A is a table showing the second processing procedure using the second corrective die K56. FIG. 8B is a warpage distribution diagram of the workpiece W step-bent by the second processing procedure. FIG. 9A is a table showing the third processing procedure using the first corrective die K34. FIG. 9B is a table showing the fourth processing procedure using the second corrective die K56. FIG. 10 is a partially cross-sectional front view showing the third corrective die K78, which is a modified example of the first corrective die K34. FIG. 11 is a block diagram of a punch press that performs the step-bending method according to an embodiment of the present invention.

[0009] In the step bending method according to an embodiment of the present invention, a flat workpiece is subjected to step bending using a step bending roller die K (see Figure 1) (hereinafter also referred to simply as the step bending die K), and then warpage correction is performed using either a first correction die K34 (see Figure 2) or a second correction die K56 (see Figure 3), which are roller dies.

[0010] The step bending die K, the first straightening die K34, and the second straightening die K56 each include an upper die and a lower die. The upper die and the lower die are detachably mounted on the upper and lower turrets of the punch press, respectively. Under the control of the punch press control unit 7 (see FIG. 11), the upper die is moved up and down and synchronously rotated around holder axes CL1V to CL6V (see FIGS. 1 to 3) extending in the vertical direction by a die drive unit 71 (see FIG. 11). The upper and lower turrets are equipped with auto-indexing devices (hereinafter referred to as AI devices) that rotate the mounted dies around their axes. The die drive unit 71 has an AI drive unit 711 (see FIG. 11) that controls the operation of the AI ​​device. That is, the synchronous rotation of the upper die and the lower die around the holder axes CL1V to CL6V is performed by driving the AI ​​device under the control of the AI ​​drive unit 711. First, the configurations of the step bending die K, the first correcting die K34, and the second correcting die K56 will be described with reference to FIGS.

[0011] Fig. 1 is a partial cross-sectional view showing a state in which a step bending die K equipped with a stepped roller is used to perform step bending on a workpiece W in a step bending method according to this embodiment. Fig. 2 is a front view showing a first correcting die K34 used in warpage correction in the step bending of the present invention. Fig. 3 is a front view showing a second correcting die K56.

[0012] (Step bending die K: see Figure 1) The step bending die K comprises a lower die K1 and an upper die K2. The lower die K1 is roughly disk-shaped and is detachably mounted to a lower turret (not shown) of the punch press via a mounting base 82. The upper die K2 is long and roughly cylindrical, and the upper portion in Figure 1 is detachably mounted to an upper turret (not shown) of the punch press.

[0013] When the stepped bending die K is mounted on the turret of the punch press, it is indexed to a position where a holder axis CL1V extending in the vertical direction in the lower die K1 and a holder axis CL2V extending in the vertical direction in the upper die K2 are concentric. The stepped bending die K is controlled by the AI ​​drive unit 711 of the control unit 7 of the punch press so as to rotate synchronously around the concentric holder axis CL1V and holder axis CL2V in an attitude where the roller axis CL1 and roller axis CL2 extending in the horizontal direction are parallel to each other.

[0014] The lower mold K1 has a holder K11 and a stepped roller K12. The stepped roller K12 has a large diameter portion 121 and a small diameter portion 122 connected in the axial direction, and a pair of shaft portions 123 extending outward on the roller axis line CL1. The large diameter portion 121 is formed on one end side of the stepped roller K12 in the axial direction, and the small diameter portion 122 is formed on the other end side connected to the large diameter portion 121. The pair of shaft portions 123 are both ends of a single shaft member and are portions that protrude and are exposed to the outside.

[0015] The holder K11 rotatably supports a pair of shafts 123, which allows the stepped roller K12 to rotate around the roller axis CL1. At the upper part of the stepped roller K12, the peripheral surfaces of the large diameter portion 121 and the small diameter portion 122 protrude above the upper end of the holder K11.

[0016] The upper mold K2 has a holder K21 and a stepped roller K22. The stepped roller K22 has a large diameter portion 221 and a small diameter portion 222 connected in the axial direction, and a pair of shaft portions 223 extending outward on the roller axis line CL2. The large diameter portion 221 is formed on one end side of the stepped roller K22 in the axial direction, and the small diameter portion 222 is formed on the other end side connected to the large diameter portion 221. The pair of shaft portions 223 are both ends of a single shaft member and are portions that protrude and are exposed to the outside.

[0017] The holder K21 rotatably supports a pair of shafts 223, which allows the stepped roller K22 to rotate around the roller axis CL2. At the lower part of the stepped roller K22, the peripheral surfaces of the large diameter portion 221 and the small diameter portion 222 protrude downward beyond the lower end of the holder K21.

[0018] In this example, the axial width of the large diameter portions 121, 221 is approximately half the axial width of the small diameter portions 122, 222, but this ratio is not limited thereto.

[0019] (First corrective die K34: see FIG. 2) The first corrective die K34 is a roller die including a lower die K3 and an upper die K4. The lower die K3 is generally disk-shaped and is detachably mounted to a lower turret (not shown) of the punch press via a mounting base 82. The upper die K4 is generally long and cylindrical, and the upper portion in FIG. 2 is detachably mounted to an upper turret (not shown) of the punch press.

[0020] When the first correcting die K34 is mounted on the turret of the punch press, it is indexed to a position where the holder axis CL3V of the lower die K3 and the holder axis CL4V of the upper die K4, which extend in the vertical direction, are concentric. The first correcting die K34 is controlled by the AI ​​drive unit 711 of the control unit 7 of the punch press so as to rotate synchronously around the concentric holder axis CL3V and holder axis CL4V in an attitude where the roller axis CL3 and roller axis CL4, which extend in the horizontal direction, are parallel to each other.

[0021] The lower mold K3 has a holder K31 and a flapless roller K32. The flapless roller K32 has a cylindrical roller 321 with a constant outer diameter and a pair of shaft portions 323 extending outward on the roller axis line CL3. The pair of shaft portions 323 are both ends of a single shaft member that protrude and are exposed to the outside.

[0022] The holder K31 rotatably supports a pair of shafts 323, which allows the flatless roller K32 to rotate around the roller axis CL3. At the top of the flatless roller K32, the peripheral surface of the roller 321 protrudes above the upper end of the holder K31.

[0023] The upper mold K4 has a holder K41 and a stepped roller K42. The stepped roller K42 has a large diameter portion 421 and a small diameter portion 422 connected in the axial direction, and a pair of shaft portions 423 extending outward on the roller axis line CL4. The large diameter portion 421 is formed on one end side of the stepped roller K42 in the axial direction, and the small diameter portion 422 is formed on the other end side connected to the large diameter portion 421. The pair of shaft portions 423 are both ends of a single shaft member and are portions that protrude and are exposed to the outside.

[0024] The holder K41 rotatably supports the pair of shafts 423, which allows the stepped roller K42 to rotate around the roller axis CL4. In the lower part of the stepped roller K42, the peripheral surfaces of the lower parts of the large diameter part 421 and the small diameter part 422 protrude downward beyond the lower end of the holder K41.

[0025] In this example, the axial width of the large diameter portion 421 is approximately half the axial width of the small diameter portion 422, but this ratio is not limited thereto.

[0026] (Second corrective die K56: see FIG. 3) The second corrective die K56 is a roller die including a lower die K5 and an upper die K6. The lower die K5 is generally disk-shaped and is detachably mounted to a lower turret (not shown) of the punch press via a mounting base 82. The upper die K6 is generally long and cylindrical, and the upper portion in FIG. 3 is detachably mounted to an upper turret (not shown) of the punch press.

[0027] When the second correcting die K56 is mounted on the turret of the punch press, it is indexed to a position where the holder axis CL5V of the lower die K5 and the holder axis CL6V of the upper die K6, which extend in the vertical direction, are concentric. The second correcting die K56 is controlled by the AI ​​drive unit 711 of the control unit 7 of the punch press so as to rotate synchronously around the concentric holder axis CL5V and holder axis CL6V in an attitude where the roller axis CL5 and the roller axis CL6, which extend in the horizontal direction, are parallel to each other.

[0028] The lower mold K5 has a holder K51 and a flapless roller K52. The flapless roller K52 has a cylindrical roller 521 with a constant outer diameter and a pair of shaft portions 523 extending outward on a roller axis line CL5. The pair of shaft portions 523 are both ends of a single shaft member that protrude and are exposed to the outside.

[0029] The holder K51 rotatably supports a pair of shafts 523, which allows the flatless roller K52 to rotate around the roller axis CL5. At the top of the flatless roller K52, the peripheral surface of the roller 521 protrudes above the upper end of the holder K51.

[0030] The upper mold K6 has a holder K61 and a center roller K62. The center roller K62 has a large diameter portion 621 formed in the center in the axial direction, a pair of small diameter portions 622 (622a, 622b) formed on both axial sides of the large diameter portion 621 and having a smaller diameter than the large diameter portion 621, and a pair of shaft portions 623 extending outward on the roller axis line CL6. The pair of shaft portions 623 are both ends of a single shaft member and are portions that protrude and are exposed outward.

[0031] The holder K61 rotatably supports a pair of shafts 623, which allows the center roller K62 to rotate around the roller axis CL6. At the bottom of the center roller K62, the peripheral surface of the large diameter portion 621 protrudes downward beyond the lower end of the holder K61.

[0032] In this example, the axial width of the large diameter portion 621 is approximately 1 / 3 of the overall axial length of the center roller K62, but this ratio is not limited thereto.

[0033] The lower die K3 of the first corrective die K34 and the lower die K5 of the second corrective die K56 may be the same.

[0034] In stepped bending, a workpiece W, a flat metal plate, placed on the table of a punch press has one edge clamped between upper and lower clamp jaws 811, 812 of multiple clampers 81 (see FIG. 5A) provided on the punch press. The clamper 81 grips the workpiece W by a clamper driver 72 (see FIG. 11) under the control of the control unit 7. The clamper 81 is supported by a carriage (not shown) so as to move along horizontally set, mutually perpendicular X- and Y-axes. In response to a command from the control unit 7, the carriage driver 73 (see FIG. 11) moves the carriage to a predetermined position on the XY plane between the lower and upper turrets. This allows machining of any position on the workpiece W using each die attached to the turret.

[0035] Fig. 4A is a plan view showing the workpiece W that has been subjected to stepped bending, Fig. 4B is a cross-sectional view taken along the line S4B-S4B in Fig. 4A, and Fig. 4C is a cross-sectional view taken along the line 4C-4C in Fig. 4A showing warpage of the workpiece W that has been subjected to stepped bending.

[0036] Step bending using the step bending die K is similar to conventional bending. First, the upper die K2 is moved upward and separated from the lower die K1. The workpiece W is then moved to a position where the portion to be stepped is aligned with the holder axis CL1V (CL2V). The rotational posture of the lower die K1 and the upper die K2 corresponds to the step bending direction. Then, the die driver 71 drives a striker (not shown) to lower the upper die K2 toward the lower die K1 (see arrow DR1 in FIG. 1 ). This forms a step Wd1 in the workpiece W due to the offset clamping action of the stepped rollers K12 and K22. Then, as shown in FIG. 4A , the control unit 7 controls the AI ​​driver 711 to control the rotational posture around the holder axis CL1V in accordance with the direction in which the step Wd1 is to be formed, and moves the step bending die K along the shape of the step Wd1 (see arrow DR2).

[0037] 4A and 4B show an example in which a rectangular workpiece W is subjected to step bending processing in which a step bending die K is rotated to form a step bent portion Wd that is rectangular in plan view and has a step bend height Hd. Hereinafter, the planar view regions of the workpiece W that has been subjected to step bending processing will be designated and classified as follows: the flat portion of the periphery that is not bent in a step is referred to as the first region WR1, the raised portion that is inclined by the step bending processing is referred to as the second region WR2, and the flat step bent portion that is raised by the step bending processing is referred to as the third region WR3. The second region WR2 corresponds to the step portion Wd1.

[0038] When a flat workpiece W is subjected to step bending using a step bending die K, warpage may occur in a direction intersecting the extending surface of the workpiece W before step bending, as shown in Fig. 4C. For example, the third region WR3 may be warped into a curved shape with a concave central portion. In this case, if one of the left and right portions of the first region WR1 in Fig. 4C is maintained horizontal, the third region WR3 after passing through the second region will not be horizontal in cross section but will be curved and inclined upward.

[0039] This warpage can be effectively reduced by performing correction processing on the stepped bent portion Wd using the first correction mold K34 and the second correction mold K56. First, the correction operation of the first correction mold K34 will be described with reference to Figures 5A and 5B. The correction operation of the first correction mold K34 is performed by the operation of the mold driver 71 and the carriage driver 73 under the control of the controller 7.

[0040] (Correction A) (First correction mold K34: see Figs. 5A and 5B) First, correction A, which is a correction operation using the first correction mold K34, will be described. Fig. 5A is a first diagram for describing the warpage correction method using the first correction mold K34. Fig. 5B is a second diagram for describing the warpage correction method using the first correction mold K34.

[0041] The first corrective die K34 has a radius difference Rd4 (see Figure 2) between the large diameter portion 421 and the small diameter portion 422 equal to or slightly smaller than the radius difference Rd2 (see Figure 1) between the large diameter portion 221 and the small diameter portion 222 of the upper die K2 in the step bending die K.

[0042] First, in the punch press, the first correcting die K34 is indexed to a position where the holder axis CL3V of the lower die K3 and the holder axis CL4V of the upper die K4, which extend in the vertical direction, are concentric. Next, the clamper 81 is moved while gripping the workpiece W, and the holder axis CL3V is positioned at a position where the holder axis CL3V starts correcting the step Wd1 of the workpiece W (for example, position PM1 in FIG. 4A ). The first correcting die K34 is positioned at a rotational position around the concentric holder axis CL3V and holder axis CL4V where the roller axis CL1 and roller axis CL2 are parallel and correspond to the step Wd1 to be corrected (a position perpendicular to the extending direction of the step Wd1).

[0043] As shown in Fig. 5A, the upper die K4 is raised and separated from the lower die K3, and then the workpiece W, still held by the clamper 81, is inserted and positioned after the step bending process. For example, as shown in Fig. 5A, the position J1, which is the edge of the large diameter portion 421 on the side of the small diameter portion 422, corresponds to the position J2 at the boundary between the first region WR1 and the second region WR2 in the workpiece W. The first region WR1 of the workpiece W is held in a generally horizontal position by being held by the clamper 81, and in this state, the third region WR3 warps upward as it moves away from the clamper 81.

[0044] 5B , the upper mold K4 is lowered (see arrow DR4), the first region WR1 is sandwiched between the large diameter portion 421 and the roller 321, and the portion P2 of the third region WR3 close to the second region WR2 is pressed downward by the small diameter portion 422. That is, the large diameter portion 421 presses the portion P1 of the first region WR1 on the second region WR2 side against the roller 321 with force F1, and the small diameter portion 422 presses the portion P2 of the third region WR3 downward with force F2.

[0045] Here, the radius difference Rd4 is set to be equal to or slightly smaller than the radius difference Rd2, and a space Va is formed as a gap between the third region WR3, which is pressed downward by the small diameter portion 422, and the stepless roller 321 of the lower mold K3 below the third region WR3. Therefore, the third region WR3 of the workpiece W is easily deformed downward (see arrow DR5) by being pressed downward by the small diameter portion 422 in a state where it is not supported from below, i.e., is corrected.

[0046] The control unit 7 of the punch press moves the position of the first correction die K34 on the XY plane along the extension direction of the step portion Wd1, and controls the rotational posture around the holder axes CL3V, CL4V so that the roller axes CL3, CL4 are always perpendicular to the tangent line of the step portion Wd1 at its current position.

[0047] In this way, the stepless roller K32 of the lower mold K3 and the stepped roller K42 of the upper mold K4 rotate around the roller axes CL3 and CL4, making one or more revolutions while correcting the warp of the track-shaped step portion Wd1, thereby completing the correction process.

[0048] (Correction B) (Second correction mold K56: see FIG. 6) Next, correction B, which is a correction operation using the second correction mold K56, will be described. FIG. 6 is a diagram for explaining a warpage correction method using the second correction mold K56. The correction operation of the second correction mold K56 is performed by the operation of the mold driving unit 71 and the carriage driving unit 73 under the control of the control unit 7.

[0049] As in the case of the first corrective die K34, the upper die K6 is raised and separated from the lower die K5, and then the workpiece W that has been subjected to the stepped bending process and held by the clamper 81 is inserted and positioned. More specifically, the large diameter portion 621 of the center roller K62 of the upper die K6 is positioned near the edge of the third region WR3 of the workpiece W on the second region WR2 side.

[0050] Next, the upper die K6 is lowered to a predetermined position (see arrow DR6), and the large-diameter portion 621 of the center roller K62 presses downward with force F3 a portion P4 of the third region WR3 near the edge thereof on the second region WR2 side. As a result, the portion P3 of the first region WR1 on the second region WR2 side abuts against the flapless roller K52 of the lower die K5 and is supported from below. Furthermore, because a space Vb is formed as a gap between the portion P4 of the third region WR3 and the roller 521 of the flapless roller K52 of the lower die K5, the third region WR3 of the workpiece W is easily deformed downward (see arrow DR7), i.e., corrected, by being pressed downward by the large-diameter portion 621 while not being supported from below.

[0051] The position to which the upper die K6 descends is set in advance according to the material, thickness, step bending height Hd, etc. of the workpiece W so that optimal correction can be performed.

[0052] The control unit 7 of the punch press moves the position of the second correction die K56 on the XY plane along the direction of extension of the step portion Wd1, and controls the rotational posture around the holder axes CL5V, CL6V so that the roller axes CL5, CL6 are perpendicular to the tangent at the current position of the step portion Wd1.

[0053] (Example of Correction Processing Procedure) Next, a description will be given of an example of a processing procedure for stepped bending including either of the above-mentioned correction A and correction B. Processing operation procedures performed by the punch press, including this processing procedure, are stored in advance in a memory unit 702 (see FIG. 11 ) provided in the control unit 7, and a CPU 701 (see FIG. 11 ), which is a central processing unit provided in the control unit 7, selects the processing to be performed next from the processing operation procedures stored in the memory unit 702 and performs it based on that selection.

[0054] (Example of processing procedure including correction A) A first processing procedure, which is an example of performing correction A using the first correcting die K34 on a workpiece W in which a step bent portion Wd has been formed by the step bending die K, will be described with reference to Figs. 7A to 7C. Fig. 7A is a table showing the first processing procedure using the first correcting die K34. Fig. 7B is a warpage distribution diagram of the workpiece W subjected to step bending processing using the first processing procedure. Fig. 7C is a warpage distribution diagram of the workpiece W subjected to step bending processing without correction processing.

[0055] In the first processing procedure, four processes are performed in the order of the process numbers. Process numbers 1 to 3 are three step bending processes using a step bending die K, in which the step bending height Hd raised in each process is kept below the plate thickness, and by performing step bending processes multiple times, a step bent portion Wd with a step bending height Hd equal to or greater than the plate thickness is finally formed. In this example, step bending is performed three times (three laps). After the step bending processes of process numbers 1 to 3, correction A of process number 4 is performed.

[0056] The specifications of the workpiece W used in the processing performed in the first processing procedure are as follows. These specifications are hereinafter referred to as specification α. ​​(Specification α) Material: SGCC (hot-dip galvanized steel sheet) External dimensions: 200 mm x 100 mm Sheet thickness: 0.5 mm Planar shape of the formed stepped bent portion Wd: 150 mm x 60 mm R25 Step bending including correction processing was performed on this workpiece W using the first processing procedure so that the final stepped bend height would be approximately 1.0 mm.

[0057] The step bending height Hd was measured by subjecting the workpiece W to step bending and placing the processed workpiece W on the stage of a three-dimensional measuring device. The three-dimensional measuring device used was a 3D scanner type three-dimensional measuring device VL-500 (manufactured by Keyence Corporation). The step bending height Hd after step bending is the average value obtained by measuring, for example, three points on the edge of the third region WR3 on the second region WR2 side.

[0058] As shown in Figure 7A, the step bending heights Hd after processing for process numbers 1 to 3 were 0.3 mm, 0.7 mm, and 1.2 mm, respectively. As a result of performing correction A process for process number 4 (see Figure 5B) after step bending process number 3, the step bending height Hd was reduced to 1.0 mm. Thus, it was revealed that the first processing procedure, in which correction A is performed continuously after step bending process, can form a step bent portion Wd in the workpiece W with a step bending height Hd approximately twice the plate thickness of the workpiece W.

[0059] Next, warpage correction by the first processing procedure will be described with reference to Figures 7B and 7C. Figure 7C is a warpage distribution diagram of the state before processing number 4 in the first processing procedure is performed. The workpiece W shown in Figure 7C has significant warpage, and the distribution of the warpage is shown by three distribution regions M2 to M4 according to the degree of warpage. In Figures 7B and 7C, the stage contact portion LNp when the workpiece W is placed on the stage of the measuring instrument is shown by a dashed line.

[0060] As shown in Figure 7C, without correction processing, significant warpage occurred in a wide area shown as distribution areas M2 to M4, with the maximum warpage being 7.7 mm in distribution area M4. In contrast, when correction processing of processing number 4, correction A, was performed, the warpage was reduced to a small area shown as distribution area M1 in Figure 7B, and the maximum warpage was reduced to 2.8 mm.

[0061] As described above, the step bending according to this embodiment involves a procedure in which step bending using the step bending die K is followed immediately by correction using the first correction die K34. This allows a step bent portion Wd with a step bend height Hd approximately twice the plate thickness to be formed with little warpage. Furthermore, because step bending and correction can be performed in the same process while the workpiece is still held by the clamper 81, there is no need to re-hold or reposition the workpiece using the clamper 81, improving production efficiency.

[0062] (Example of correction processing using second corrective die K56) A second processing procedure, which is an example of corrective processing using the second corrective die K56 on a workpiece W on which a step bent portion Wd has been formed by the step bending die K, will be described with reference to Figures 8A and 8B. Figure 8A is a table showing the second processing procedure using the second corrective die K56. Figure 8B is a warpage distribution diagram of the workpiece W step-bent by the second processing procedure.

[0063] In the second processing procedure, in comparison with the first processing procedure, correction B for processing number 4 is performed using the second correction die K56 instead of the first correction die K34. That is, processing numbers 1 to 3 are step bending processes using a step bending die K, in which the step bending height Hd raised in one processing is suppressed to less than the plate thickness, and by performing step bending multiple times, a step bent portion Wd with a step bending height Hd equal to or greater than the plate thickness is finally formed. In this example, step bending is performed three times (three laps). After step bending processes 1 to 3, correction B is performed as processing number 4. The specifications of the workpiece W are the above-mentioned specifications α, and step bending including correction was performed on the workpiece W so that the final step bending height was approximately 1.0 mm. The method and measuring instrument for measuring the step bending height are also the same as those in the first processing procedure.

[0064] As shown in Figure 8A, the step bending heights after processing for process numbers 1 to 3 were 0.3 mm, 0.7 mm, and 1.2 mm, respectively. After the step bending process for process number 3, correction B (see Figure 8B) was performed using the second correction mold K56 for process number 4, resulting in a step bending height Hd of 1.1 mm. Thus, it was revealed that the second processing procedure, which performs correction B consecutively after step bending, can form a step bending portion Wd in the workpiece W with a step bending height Hd approximately twice its plate thickness. Furthermore, as shown in Figure 8B, warpage was reduced to a maximum of 3.0 mm within the narrow range indicated by the distribution region M5.

[0065] (Other Correction Examples) As described above, by performing step bending that traces the step portion Wd1 once or multiple times, and then subsequently performing correction using the first correction die K34 or the second correction die K56, a step bent portion Wd with a step bend height Hd approximately twice the plate thickness can be formed with small warpage. Therefore, the results of repeating a combination of step bending and subsequent correction as a third processing procedure 2 and a fourth processing procedure for the first correction die K34 and the second correction die K56, respectively, are described with reference to FIGS. 9A and 9B . FIG. 9A is a table showing the third processing procedure using the first correction die K34. FIG. 9B is a table showing the fourth processing procedure using the second correction die K56.

[0066] (Third and Fourth Machining Procedures) The specifications of the workpiece W are the above-mentioned specifications α. As shown in Fig. 9A, in the third machining procedure, machining numbers 1 to 4, which are the first machining procedure, are followed by machining numbers 5 to 8, which include correction A, and in the fourth machining procedure, machining numbers 1 to 4, which are the second machining procedure, are followed by machining numbers 5 to 8, which include correction B.

[0067] In the third and fourth processing procedures, for processing numbers 5 to 8, a processing set in which step bending and straightening are performed once each in that order is performed twice in succession. As a result, step bending is performed five times (five laps) and straightening is performed three times (three laps) in total. In the third processing procedure, straightening A for processing numbers 4, 6, and 8 reduces the step bending height Hd by 0.2 mm, 0.1 mm, and 0.1 mm, respectively. In the fourth processing procedure, straightening B for processing numbers 4, 6, and 8 reduces the step bending height Hd by 0.1 mm, respectively. In both the third and fourth processing procedures, a step bending portion Wd with a step bending height Hd of 2.1 mm is finally obtained.

[0068] That is, the third and fourth processing procedures each achieve a final step bend height Hd of 2.1 mm, which is a large value that is four times or more the plate thickness. In this way, the step bending method according to this embodiment achieves a step bent portion Wd with a large step bend height Hd.

[0069] One aspect of the present invention is not limited to the above-described configuration and procedure, and may be modified within the scope of the gist of the present invention.

[0070] A third corrective mold K78 as a modified example shown in Fig. 10 may be used instead of the first corrective mold K34 and the second corrective mold K56. Fig. 10 is a partially cross-sectional front view showing the third corrective mold K78, which is a modified example of the first corrective mold K34. In Fig. 10, holders are not shown, and only rollers are described.

[0071] The lower mold K7 has a flapless roller K72. The flapless roller K72 has a cylindrical roller 721 with a constant outer diameter and a pair of shaft portions 723 extending along the roller axis CL7. The pair of shaft portions 723 are both ends of a single shaft member that protrude and are exposed to the outside.

[0072] The upper mold K8 has a center roller K82 and ring-shaped first and second collars 822 and 823. The center roller K82 has a large-diameter portion 821 with a maximum outer diameter formed in a flange-like shape at the axial center. Small-diameter portions 825 and 826 are formed on both axial sides of the large-diameter portion 821. A first collar 822, which is a ring having a first thickness t822, is attached to one small-diameter portion 825 in an exchangeable manner by being fitted over the other small-diameter portion 826. A second collar 823, which is a ring having a second thickness t823, is attached to the other small-diameter portion 826 in an exchangeable manner by being fitted over the other small-diameter portion 826. The difference in outer diameter between the large-diameter portion 821 and the first collar 822 is a step d3, and the difference in outer diameter between the large-diameter portion 821 and the second collar 823 is a step d4.

[0073] The third corrective die K78 can be applied to the first and third machining procedures in the same manner as the first corrective die K34 by selectively configuring the first collar 822 and the second collar 823 to correspond to the stepped bending height Hd. Furthermore, the large diameter portion 821 can be regarded as the large diameter portion 621 of the upper die K6 of the second corrective die K56 and applied to the second and fourth machining procedures. In other words, the third corrective die K78 has the functions of two types of dies: the first corrective die K34 and the second corrective die K56. The shape of the stepped bending portion Wd formed in the workpiece W is not limited to a closed track shape in top view and can be freely set. The stepped bending portion Wd may also be a straight line including a curved portion.

[0074] As described above in detail, the step bending method according to this embodiment includes step bending, which forms a step bent portion Wd on a flat workpiece W using a step bending roller die K, and correction processing, which corrects the warping of the step bent portion Wd after the step bending processing.The step bending processing forms a step bent portion WR3 that protrudes relative to the flat portion WR1 of the workpiece W, and the correction processing is performed by pressing the step bent portion Wd downward with the roller die K34, while supporting the underside of the flat portion WR1 and forming a space Va below the step bent portion Wd so that it is not supported.

[0075] According to this step bending method, the space Va is formed below the step bent portion Wd, so that the step bent portion Wd can be easily bent downward, and the warp of the step bent portion Wd can be corrected well.

[0076] In addition, in this stepped bending processing method, the workpiece W can be held by a clamper 81, the stepped bending portion Wd can be formed by a stepped bending roller die K, and the correction processing can be performed while maintaining the clamper 81 holding the workpiece W.

[0077] This eliminates the need to re-grasp the workpiece W using the clamper 81, allowing for efficient correction processing.

[0078] Furthermore, when a step bending process and a straightening process performed after the step bending process are set as a processing set, the processing set may be performed one or more times.

[0079] This allows the step height Hd to be increased.

[0080] Furthermore, the stepped bending may be performed multiple times at the same stepped bending position using the stepped bending roller die K.

[0081] This allows the step height Hd to be increased.

[0082] Furthermore, the warpage correction method in the stepped bending processing method according to an embodiment of the present invention involves performing correction processing on a stepped bent workpiece W having a flat plate portion WR1 and a stepped bent portion Wd protruding from the flat plate portion WR1, by supporting the underside of the flat plate portion WR1 and forming a space Va below the stepped bent portion Wd so that the stepped bent portion Wd is not supported, and then pressing the stepped bent portion Wd downward with a roller die K34.

[0083] In this warp correction method, the space Va is formed below the stepped bent portion Wd, so that the stepped bent portion Wd can be easily bent downward and corrected well.

[0084] In addition, in this warp correction method, the workpiece W may be held by a clamper 81, the stepped bent portion Wd may be formed by a stepped bending roller die K, and the correction processing may be performed while the workpiece W is still being held by the clamper 81.

[0085] This eliminates the need to re-grasp the workpiece W using the clamper 81, allowing for efficient correction processing.

[0086] Furthermore, when a step bending process and a straightening process performed after the step bending process are defined as a processing set, a plurality of processing sets may be executed.

[0087] This allows the step height Hd to be increased.

[0088] 7 Control unit 701 CPU (Central Processing Unit) 702 Memory unit 71 Die drive unit 711 AI drive unit 72 Clamp drive unit 73 Carriage drive unit 81 Clamp 811, 812 Clamp jaw 82 Mounting base CL1 to CL8 Roller axis CL1V to CL6V Holder axis d3, d4 Step F1 to F3 Force Hd Step height J1, J2 Position K Step bending die (step bending roller die) K1 Lower die K11 Holder K12 Step roller 121 Large diameter portion 122 Small diameter portion 123 Shaft portion K2 Upper die K21 Holder K22 Step roller 221 Large diameter portion 222 Small diameter portion 223 Shaft portion K34 First correction die (roller die) K3 Lower die K31 Holder K32 Stepless roller 321 Roller 323 Shaft K4 Upper die K41 Holder K42 Stepped roller 421 Large diameter portion 422 Small diameter portion 423 Shaft K56 Second correction die (roller die) K5 Lower die K51 Holder K52 Stepless roller 521 Roller 523 Shaft K6 Upper die K61 Holder K62 Center roller 621 Large diameter portion 622, 622a, 622b Small diameter portion 623 Shaft K78 Third correction die K7 Lower die K72 Stepless roller 721 Roller 723 Shaft K8 Upper die K82 Center roller 821 Large diameter portion 822 First collar 823 Second collar 825, 826 Small diameter section M1 to M5 Distribution area LNp Stage ground contact section PM1 Position P1 to P4 Section Rd2, Rd4 Radius difference t822 First thickness t823 Second thickness Va, Vb Space W Workpiece Wd Stepped bent section Wd1 Step section WR1 First section (flat section) WR2 Second section (raised section) WR3 Third section (stepped bent section)

Claims

1. A step bending method comprising: a step bending process for forming a step bent portion on a flat workpiece using a step bending roller die; and a straightening process for straightening warping of the step bent portion after the step bending process, wherein the step bending process forms the step bent portion that protrudes from the flat portion of the workpiece, and the straightening process is performed by pressing the step bent portion downward with a roller die while supporting the underside of the flat portion and leaving a space below the step bent portion unsupported.

2. A step bending method as claimed in claim 1, wherein in the step bending, the workpiece is held by a clamper and the step bent portion is formed by a step bending roller die, and the correction process is carried out while the workpiece is still being held by the clamper.

3. The step bending method according to claim 2, wherein when the step bending and the straightening performed after the step bending are grouped together, one or more step groups are performed.

4. The step bending method according to claim 3, wherein the step bending is performed by step bending the same step bending position a plurality of times using the step bending roller die.

5. A method for correcting warpage in stepped bending, in which a workpiece that has been bent in a stepped manner and has a flat portion and a stepped bent portion protruding from the flat portion is subjected to correction processing in which the underside of the flat portion is supported and a space is formed below the stepped bent portion, leaving it unsupported, and the stepped bent portion is pressed downwardly with a roller die.

6. A method for correcting warpage in stepped bending as described in claim 5, in which the workpiece is held by a clamper, the stepped bent portion is formed by a stepped bending roller die, and the correction process is carried out while maintaining the clamper holding the workpiece.

7. A method for straightening warpage in stepped bending according to claim 6, wherein when the stepped bending and the straightening performed after the stepped bending are grouped together, a plurality of groups are executed.

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