Stepped bending method and warp correction method in stepped bending

Abstract

To provide a stepped bending method capable of making difficult the occurrence of inconvenience caused by warp in stepped bending by a stepped roller.SOLUTION: This stepped bending method includes stepped bending for forming a stepped bent part Wd on a flat plate-like workpiece W by a stepped roller mold K, and correction for correcting the stepped bent part Wd after the stepped bending. A stepped bent part WR3 protruding with respect to a flat plate-like part WR1 is formed by stepped bending, and the correction is performed by pressing down the stepped bent part Wd by a roller mold K34 in a state where the bottom surface of the flat plate-like part WR1 is supported and the lower part of the stepped bent part Wd is not supported by forming a space Va.SELECTED DRAWING: Figure 5B

Description

[Technical field]

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

[0002] Patent Document 1 describes a technique for performing stepped bending on a workpiece in a straight or curved shape by clamping 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 processing. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6250079 Summary of the Invention [Problem to be solved by the invention]

[0004] In step bending using stepped rollers as described in Patent Document 1, the workpiece is warped to some extent. The warp becomes larger as the step bending height in the step bending is increased, so that, for example, the warped workpiece may come into contact with a member on the processing machine side in the subsequent punching process, making processing difficult, or may require correction in a process other than the step bending. Therefore, a step bending method and a warp correction method in step bending using stepped rollers that make it difficult to cause problems due to warp are desired. [Means for solving the problem]

[0005] In order to solve the above problems, one aspect of the step bending method of the present invention has the following configuration: That is, the step bending method includes 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 the step bent portion after the step bending process, in which the step bent portion protruding from the flat portion is formed by the step bending process, and the correction 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.

[0006] One aspect of the warpage correction method in the step bending method of the present invention has the following configuration: That is, the warpage correction method in step bending performs a correction process on a step-bent workpiece having a flat portion and a step bent portion protruding from the flat portion by pressing the step bent portion downward with a roller die while supporting the lower surface of the flat portion and leaving a space below the step bent portion unsupported. Effect of the Invention

[0007] According to one aspect of the step bending method and the method for correcting warpage in step bending of the present invention, defects caused by warpage are less likely to occur in step bending using stepped rollers. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a partial cross-sectional view showing a state in which a step bending is performed on a workpiece W by a step bending roller die K equipped with a stepped roller in one embodiment of the step bending method of the present invention. [Diagram 2] FIG. 2 is a front view showing a first corrective die K34 used in the corrective process in the step bending process of the present invention. [Diagram 3] FIG. 3 is a front view showing the second corrective die K56. [Figure 4A] FIG. 4A is a plan view showing the workpiece W that has been subjected to stepped bending. [Figure 4B] FIG. 4B is a cross-sectional view taken along the line S4B-S4B in FIG. 4A. [Figure 4C] FIG. 4C is a cross-sectional view taken along the line S4C-S4C in FIG. 4A, showing warpage of the workpiece W after step bending. [Figure 5A] FIG. 5A is a first diagram for explaining a warpage correction method using a first correction die K34. [Figure 5B] FIG. 5B is a second diagram for explaining the warpage correction method using the first correction die K34. [Figure 6] FIG. 6 is a diagram for explaining a warpage correction method using the second correction die K56. [Figure 7A] FIG. 7A is a table showing a first processing procedure using the first corrective die K34. [Figure 7B] FIG. 7B is a warpage distribution diagram of the workpiece W that has been step-bent in the first processing procedure. [Figure 7C] FIG. 7C is a diagram showing the warpage distribution of the workpiece W in step bending without straightening. [Figure 8A] FIG. 8A is a table showing a second processing procedure using the second corrective die K56. [Figure 8B] FIG. 8B is a warpage distribution diagram of the workpiece W stepped in the second processing procedure. [Figure 9A] FIG. 9A is a table showing a third processing procedure using the first corrective die K34. [Figure 9B] FIG. 9B is a table showing a fourth processing procedure using the second corrective die K56. [Figure 10] FIG. 10 is a partially sectional front view showing a third corrective die K78 which is a modified example of the first corrective die K34. [Figure 11] FIG. 11 is a block diagram of a punch press for carrying out one embodiment of the step bending method of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] In one aspect of the step bending method of the present invention, a metal plate 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 warp correction is performed using either a first straightening die K34 (see Figure 2) or a second straightening die K56 (see Figure 3), which are roller dies.

[0010] The stepped bending die K, the first straightening die K34, and the second straightening die K56 each have an upper die and a lower die. The upper die and the lower die are detachably attached to the upper turret and the lower turret of the punch press, respectively, and under the control of the control unit 7 (see FIG. 11) of the punch press, the upper die is moved up and down and rotated synchronously around the holder axis lines CL1V to CL6V (see FIGS. 1 to 3) extending in the up and down direction by the die driving unit 71 (see FIG. 11). The upper turret and the lower turret are equipped with an auto-indexing device (hereinafter, AI device) that rotates the attached die around its axis line, and the die driving unit 71 has an AI driving 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 axis lines CL1V to CL6V is performed by driving the AI ​​device under the control of the AI ​​driving unit 711. First, the configurations of the step bending die K, the first corrective die K34, and the second corrective die K56 will be described with reference to Figs.

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

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

[0013] When the stepped bending die K is attached to 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 a posture in which the roller axis CL1 and roller axis CL2 extending in the horizontal direction are parallel to each other.

[0014] The lower die 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 in the axial direction of the stepped roller K12, 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 part 121 and the small diameter part 122 protrude upward beyond the upper end of the holder K11.

[0016] The upper die 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 in the axial direction of the stepped roller K22, 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 the pair of shafts 223, which allows the stepped roller K22 to rotate around the roller axis CL2. In the lower part of the stepped roller K22, the peripheral surfaces of the large diameter part 221 and the small diameter part 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, although this ratio is not limited.

[0019] (First correction mold K34: see Figure 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 substantially 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 substantially elongated and cylindrical, and the upper portion in FIG. 2 is detachably mounted to an upper turret (not shown) of the punch press.

[0020] The first straightening die K34, when attached to the turret of the punch press, 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 straightening 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 a posture where the roller axis CL3 and roller axis CL4, which extend in the horizontal direction, are parallel to each other.

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

[0022] The holder K31 rotatably supports a pair of shafts 323, which allows the flapless roller K32 to rotate about a roller axis CL3. At the upper part of the flapless roller K32, the peripheral surface of the roller 321 protrudes upward beyond the upper end of the holder K31.

[0023] The upper die 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 in the axial direction of the stepped roller K42, 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, although this ratio is not limited.

[0026] (Second correction mold K56: see Figure 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 substantially 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 substantially long and cylindrical, and the upper portion in FIG. 3 is detachably mounted to an upper turret (not shown) of the punch press.

[0027] The second straightening die K56, when attached to the turret of the punch press, 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 straightening 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 a posture where the roller axis CL5 and the roller axis CL6, which extend in the horizontal direction, are parallel to each other.

[0028] The lower die K5 has a holder K51 and a flapless roller K52. The flapless roller K52 has a cylindrical roller 521 having 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, and are portions that protrude and are exposed to the outside.

[0029] The holder K51 rotatably supports a pair of shafts 523, which allows the flapless roller K52 to rotate about a roller axis CL5. At the upper part of the flapless roller K52, the peripheral surface of the roller 521 protrudes upward beyond the upper end of the holder K51.

[0030] The upper die 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 to the outside.

[0031] The holder K61 rotatably supports the pair of shafts 623, thereby allowing the center roller K62 to rotate about a roller axis CL6. In the lower part of the center roller K62, the peripheral surface of the large diameter part 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.

[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 the step bending process, one edge of the workpiece W, which is a metal plate placed on the table of the punch press, is clamped by upper and lower clamp jaws 811, 812 of a plurality of clampers 81 (see FIG. 5A) provided on the punch press. The operation of the clamper 81 to grip the workpiece W is executed by the clamper driving unit 72 (see FIG. 11) under the control of the control unit 7. The clamper 81 is supported so as to move along the X-axis and Y-axis, which are set horizontally and perpendicular to each other, by a carriage (not shown). The carriage moves the workpiece W to a predetermined position on the XY plane between the lower turret and the upper turret by the operation of the carriage driving unit 73 (see FIG. 11) under the command of the control unit 7. This allows machining to be performed at any position on the workpiece W by each die attached to the turret.

[0035] Fig. 4A is a plan view showing the workpiece W after the stepped bending process, 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 the warpage of the workpiece W after the stepped bending process.

[0036] The step bending process using the step bending die K is the same as the conventional process. First, the upper die K2 is moved upward and separated from the lower die K1, the workpiece W is moved to a position where the part to be stepped is aligned with the holder axis CL1V (CL2V), and the rotation posture of the lower die K1 and the upper die K2 is set to a posture according to the step bending direction. Then, the upper die K2 is lowered toward the lower die K1 by the action of a striker (not shown) driven by the die driving unit 71 (see arrow DR1 in FIG. 1). As a result, a step portion Wd1 is formed in the workpiece W by the misaligned clamping action of the stepped rollers K12 and K22. After that, the control unit 7 moves the step bending die K along the shape of the step portion Wd1 while the AI ​​driving unit 711 controls the rotation posture around the holder axis CL1V according to the direction in which the step portion Wd1 is formed (see arrow DR2), as shown in FIG. 4A.

[0037] 4A and 4B show an example in which a rectangular workpiece W is subjected to step bending by rotating a step bending die K to form a step bent portion Wd having a rectangular shape in a plan view and a step bend height Hd. Hereinafter, the planar view regions of the workpiece W that has been subjected to step bending will be named and classified as follows. That is, the flat portion of the periphery that is not step bent is referred to as the first region WR1, the raised portion that is inclined by the step bending is referred to as the second region WR2, and the flat step bent portion that is raised by the step bending 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 processing using a step bending die K, warping may occur in a direction intersecting with the extending surface of the workpiece W before step bending processing, as shown in Fig. 4C. For example, the third region WR3 is curved into a curved shape with a concave center. In this case, if one of the left and right parts of the first region WR1 in Fig. 4C is kept horizontal, the third region WR3 that has passed 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 die K34 and the second correction die K56. First, the correction operation of the first correction die K34 will be described with reference to Figs. 5A and 5B. The correction operation of the first correction die K34 is performed by the operation of the die driver 71 and the carriage driver 73 under the control of the controller 7.

[0040] (Correction A) (First correction mold K34: see Figures 5A and 5B) First, correction A, which is a correction operation using the first correction die K34, will be described. Fig. 5A is a first diagram for explaining the warpage correction method using the first correction die K34. Fig. 5B is a second diagram for explaining the warpage correction method using the first correction die 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 straightening 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 holding the workpiece W, and positioned at a position where the holder axis CL3V starts straightening the step Wd1 of the workpiece W (for example, position PM1 in FIG. 4A). The first straightening die K34 is positioned at a rotation position around the concentric holder axis CL3V and holder axis CL4V where the roller axis CL1 and roller axis CL2 are parallel to each other and in a posture corresponding to the step Wd1 to be straightened (a posture 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 held by the clamper 81 is inserted and positioned after the step bending process. For example, as shown in Fig. 5A, the positioning is performed so that the position J1 which is the edge of the large diameter portion 421 on the small diameter portion 422 side corresponds to the position J2 of 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 substantially horizontal position 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 die K4 is lowered (see arrow DR4), the first region WR1 is clamped by the large diameter portion 421 and the roller 321, and a 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 stepless roller 321 of the lower die K3 and the lower side of the third region WR3 pressed downward by the small diameter portion 422. Therefore, the third region WR3 of the work 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., it 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 about the holder axes CL3V, CL4V so that the roller axes CL3, CL4 are always perpendicular to the tangent to the step portion Wd1 at its current position.

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

[0048] (Correction B) (Second correction mold K56: see Figure 6) Next, correction B, which is a correction operation using the second correction die K56, will be described. Fig. 6 is a diagram for explaining a warpage correction method using the second correction die K56. The correction operation of the second correction die K56 is performed by the operation of the die driver 71 and the carriage driver 73 under the control of the controller 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 the portion P4 near the edge of the third region WR3 on the second region WR2 side downward with a force F3. As a result, the portion P3 on the second region WR2 side of the first region WR1 abuts against the stepless roller K52 of the lower die K5 and is supported from below. In addition, since a space Vb is formed as a gap between the portion P4 of the third region WR3 and the roller 521 of the stepless roller K52 of the lower die K5, the third region WR3 of the work W is easily deformed downward (see arrow DR7) by being pressed downward by the large diameter portion 621 in a state where it is not supported from below, i.e., is corrected.

[0051] The position to which the upper die K6 descends is preset according to the material, plate 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 extending to the step portion Wd1, and controls the rotational posture about the holder axes CL5V, CL6V so that the roller axes CL5, CL6 are perpendicular to the tangent to the step portion Wd1 at its current position.

[0053] (Example of correction processing procedure) Next, a description will be given of an example of a processing procedure for step 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 storage 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 storage unit 702, and executes 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 by the first correcting die K34 on a workpiece W in which a step bent portion Wd is 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 step-bent by the first processing procedure. Fig. 7C is a warpage distribution diagram of the workpiece W step-bending not including correction.

[0055] In the first processing procedure, four processes are performed in the order of 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 one process is suppressed to less than the plate thickness, and step bending is performed multiple times to finally form a step bent portion Wd with a step bending height Hd equal to or greater than the plate thickness. In this example, step bending is performed three times (three rounds). After the step bending processes of process numbers 1 to 3, straightening A of process number 4 is performed.

[0056] The specifications of the workpiece W used in the machining in the first machining procedure are as follows. These specifications are hereinafter referred to as specifications α. (Specification α) Material: SGCC (hot-dip galvanized steel sheet) External dimensions: 200mm x 100mm Plate thickness: 0.5mm Planar shape of the bent part Wd to be formed: 150mm x 60mm R25 This workpiece W was subjected to step bending including straightening by the first processing procedure so that the final step bending height was about 1.0 mm.

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

[0058] As shown in Fig. 7A, the step bending heights Hd after processing in the step bending processes of process numbers 1 to 3 were 0.3 mm, 0.7 mm, and 1.2 mm, respectively. As a result of performing the straightening A process of process number 4 (see Fig. 5B) after the step bending process of process number 3, the step bending height Hd could be reduced to 1.0 mm. In this way, it was revealed that the first processing procedure in which straightening A is performed continuously after the 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, the correction of warpage by the first processing procedure will be described with reference to Fig. 7B and Fig. 7C. Fig. 7C is a warpage distribution diagram in the state before performing processing number 4 in the first processing procedure. In the workpiece W shown in Fig. 7C, significant warpage occurs, and the distribution of the warpage is shown by three distribution regions M2 to M4 according to the degree of warpage. In Fig. 7B and Fig. 7C, the stage grounding 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 Fig. 7C, without straightening processing, significant warpage occurred in a wide area shown by distribution areas M2 to M4, and the maximum warpage was 7.7 mm in distribution area M4. In contrast, when straightening processing of processing number 4, straightening A, was performed, the warpage was reduced to a maximum of 2.8 mm in a small area shown by distribution area M1 in Fig. 7B.

[0061] As described above, one aspect of the step bending process of the present invention has a procedure of performing the step bending process using the step bending die K, followed by the straightening process using the first straightening die K34. This allows a step bent portion Wd with a step bend height Hd approximately twice the plate thickness to be formed with small warpage. In addition, since the step bending process and the straightening process can be performed in the same process while the workpiece is held by the clamper 81, the time and effort of re-holding and re-positioning the workpiece by the clamper 81 is not required, improving production efficiency.

[0062] (Example of straightening process using the second straightening die K56) A second processing procedure, which is an example in which a workpiece W in which a step-bent portion Wd is formed by a step-bending die K is subjected to a correction process by a second corrective die K56, will be described with reference to Figs. 8A and 8B. 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.

[0063] In the second processing procedure, the correction process of processing number 4 is performed by the second correction die K56 instead of the first correction die K34, as correction B, in comparison with the first processing procedure. That is, processing numbers 1 to 3 are step bending processes using the step bending die K, and the step bending height Hd raised in one processing is suppressed to less than the plate thickness, and by performing step bending processes multiple times, a step bending part 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 processing numbers 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 about 1.0 mm. The method and device for measuring the step bending height are also the same as those in the first processing procedure.

[0064] As shown in FIG. 8A, the step bending heights after the step bending processes of process numbers 1 to 3 were 0.3 mm, 0.7 mm, and 1.2 mm, respectively. After the step bending process of process number 3, the straightening B process (see FIG. 8B) using the second straightening die K56 of process number 4 was performed, and as a result, the step bending height Hd was reduced to 1.1 mm. Thus, it was revealed that the second processing procedure in which straightening B is performed continuously after the step bending process can form a step bending portion Wd of about twice the plate thickness of the workpiece W. In addition, as shown in FIG. 8B, the warpage was reduced to a maximum of 3.0 mm in a small range indicated by the distribution region M5.

[0065] (Other examples of straightening) As described above, by performing the step bending process of tracing the step portion Wd1 once or multiple times, and then performing the correction process using the first correction die K34 or the second correction die K56, the step bent portion Wd with a step bend height Hd of about twice the plate thickness can be formed with small warpage. Therefore, the results of performing the process of repeating a combination of step bending and the subsequent correction process as the third processing procedure and the fourth processing procedure for the first correction die K34 and the second correction die K56, respectively, will be 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 processing steps) The specification of the workpiece W is the above-mentioned specification α. ​​As shown in Fig. 9A, in the third machining procedure, after the machining numbers 1 to 4 which are the first machining procedure, the machining numbers 5 to 8 including the correction A are performed, and in the fourth machining procedure, after the machining numbers 1 to 4 which are the second machining procedure, the machining numbers 5 to 8 including the correction B are performed.

[0067] In the third and fourth processing procedures, the processing numbers 5 to 8 are each performed twice in succession, with the step bending and straightening being performed once each in that order. As a result, the step bending is performed five times (five laps) and the straightening is performed three times (three laps) in total. In the third processing procedure, the straightening A of the processing numbers 4, 6, and 8 reduces the step bending height Hd by 0.2 mm, 0.1 mm, and 0.1 mm, respectively, and in the fourth processing procedure, the straightening B of the 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 provide a final step bending height Hd of 2.1 mm, which is a large value that is more than four times the plate thickness. Thus, according to one aspect of the step bending method of the present invention, a step bending portion Wd with a large step bending height Hd is obtained.

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

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

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

[0072] The upper die K8 has a center roller K82, and a ring-shaped first collar 822 and a second collar 823. The center roller K82 has a large diameter portion 821 formed in a flange shape at the center position in the axial direction and having the maximum outer diameter. Small diameter portions 825, 826 are formed to be connected to both sides of the large diameter portion 821 in the axial direction. The first collar 822, which is a ring with a first thickness t822, is attached to one small diameter portion 825 in an exchangeable manner by extrapolation, and the second collar 823, which is a ring with a second thickness t823, is attached to the other small diameter portion 826 in an exchangeable manner by extrapolation. 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 processing procedures in the same manner as the first corrective die K34 by selectively making the first collar 822 and the second collar 823 correspond to the step bending height Hd. Also, the large diameter portion 821 can be regarded as the large diameter portion 621 in the upper die K6 of the second corrective die K56 and applied to the second and fourth processing procedures. That is, 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 bent portion Wd formed in the workpiece W is not limited to a closed track shape when viewed from above, and can be freely set. The stepped bent portion Wd may be a straight line shape including a curved portion.

[0074] As described in detail above, one aspect of the step bending method of the present invention includes step bending in which a step bent portion Wd is formed on a flat workpiece W using a step bending roller die K, and correction processing in which the step bent portion Wd is corrected after the step bending processing, in which a step bent portion WR3 protruding from the flat portion WR1 is formed by the step bending processing, and the correction processing is performed by pressing the step bent portion Wd downward with the roller die K34 while the underside of the flat portion WR1 is supported and a space Va is formed below the step bent portion Wd to leave it unsupported.

[0075] In this embodiment, a space Va is formed below the stepped bent portion Wd, so that the stepped bent portion Wd can be easily bent downward and satisfactorily corrected.

[0076] In addition, in this embodiment, the workpiece W may be held by the clamper 81, the stepped bent portion Wd may be formed by the stepped bending roller die K, and the straightening process may be performed while the workpiece W is still being held by the clamper 81.

[0077] This eliminates the need for the clamper 81 to re-grasp the workpiece W, making it possible to efficiently carry out the straightening process.

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

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

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

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

[0082] In addition, one aspect of the warp correction method in the stepped bending method of the present invention is to perform correction processing on a stepped bent workpiece W having a flat portion WR1 and a stepped bent portion Wd protruding from the flat portion WR1, while supporting the underside of the flat portion WR1 and forming a space Va below the stepped bent portion Wd so that the stepped bent portion Wd is unsupported, and pressing the stepped bent portion Wd downward with a roller die K34.

[0083] In this embodiment, a space Va is formed below the stepped bent portion Wd, so that the stepped bent portion Wd can be easily bent downward and satisfactorily corrected.

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

[0085] This eliminates the need for the clamper 81 to re-grasp the workpiece W, making it possible to efficiently carry out the straightening process.

[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. [Explanation of symbols]

[0088] 7 Control section 701 CPU (Central Processing Unit) 702 Storage section 71 Mold drive unit 711 AI Drive Unit 72 Clamper drive unit 73 Carriage drive unit 81 Clamper 811,812 Clamp jaw 82 Mounting base CL1~CL8 Roller axis CL1V~CL6V Holder axis d3,d4 steps F1~F3 Power Hd Step bending height J1,J2 position K-step bending die (step bending roller die) K1 lower mold K11 Holder K12 stepped roller 121 Large diameter section 122 Small diameter section 123 Shaft K2 Upper mold K21 Holder K22 stepped roller 221 Large diameter section 222 Small diameter section 223 Shaft K34 First straightening die (roller die) K3 lower mold K31 Holder K32 Stepless roller 321 Lola 323 Shaft K4 Upper mold K41 Holder K42 stepped roller 421 Large diameter section 422 Small diameter section 423 Shaft K56 Second straightening die (roller die) K5 lower mold K51 Holder K52 Stepless roller 521 Lola 523 Shaft K6 upper mold K61 Holder K62 Center Roller 621 Large diameter section 622,622a,622b Small diameter part 623 Shaft K78 3rd correction mold K7 lower mold K72 Stepless roller 721 Lola 723 Shaft K8 Upper mold K82 Center roller 821 Large diameter section 822 1st Color 823 2nd Color 825,826 Small diameter section M1~M5 distribution area LNp stage grounding part PM1 position P1~P4 parts Rd2,Rd4 radius difference T822 1st Thickness T823 second thickness Va,Vb space W work Wd Step bending section Wd1 Step WR1 1st area (flat plate part) WR2 2nd area (start-up area) WR3 Third area (step bend)

Claims

1. A step bending process in which a step bent portion is formed on a flat workpiece using a step bending roller die; A correction process for correcting the step bent portion after the step bending process, The step bending process forms the step bent portion protruding from the flat plate portion, The correction process is a step bending method in which the lower surface of the flat plate portion is supported and the step bent portion is pressed downward by a roller die while a space is formed below the step bent portion and the step bent portion is left unsupported.

2. In the step bending process, the workpiece is held by a clamper and the step bent portion is formed by a step bending roller die; 2. The step bending method according to claim 1, wherein the correction is performed while the clamper continues to grip the workpiece.

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

4. The step bending method according to claim 3, wherein the step bending is performed by performing step bending at 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 subjected to stepped bending processing, which has a flat portion and a stepped bent portion protruding from the flat portion, is subjected to correction processing in which the stepped bent portion is pressed downward by a roller die while the underside of the flat portion is supported and a space is formed below the stepped bent portion, leaving it unsupported.

6. 6. A method for correcting warpage in stepped bending according to claim 5, further comprising the steps of: holding the workpiece with a clamper; forming the stepped bent portion with a stepped bending roller die; and performing the correction process while maintaining the workpiece held by the clamper.

7. 7. The method for straightening warpage in stepped bending according to claim 6, wherein when the step bending and the straightening performed after the step bending are grouped into a set of processes, a plurality of sets of processes are performed.

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