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

Abstract

A step bending method includes step bending for forming a step bent portion (Wd) on a flat plate-shaped workpiece (W) with a step bending roller die (K), and a correction processing for correcting warpage of the step bent portion (Wd) after the step bending, wherein the step bent portion (WR3) protruding from a flat plate portion (WR1) is formed by the step bending, and the correction processing is a processing in which the step bent portion (Wd) is pressed downward with a roller die (K34) while a lower surface of the flat plate portion (WR1) is supported and the step bent portion (Wd) is unsupported from below due to a space (Va) formed below the step bent portion (Wd).

Description

TECHNICAL FIELD

[0001] The present invention relates to a step bending method and a warpage correction method in step bending.BACKGROUND ART

[0002] Patent Literature 1 describes a technique for performing linear or curved step bending on a workpiece by sandwiching the workpiece between an upper die and a lower die equipped with stepped rollers and moving the workpiece relative to the upper and lower dies. Step bending is a process of forming a level difference in sheet metal and is also referred to as offset processing.CITATION LISTPATENT LITERATURE

[0003] Patent Literature 1: Japanese Patent Publication No. 6250079SUMMARY OF INVENTIONTECHNICAL PROBLEM

[0004] In the step bending with the stepped rollers as described in Patent Literature 1, warpage occurs in the workpiece to a certain extent. This warpage increases as the step bending height in step bending becomes larger. Therefore, for example, problems may arise such as the warped workpiece coming into contact with members on the processing machine side during subsequent punching, making processing difficult, or correction being required in a process separate from step bending. Therefore, in step bending using stepped rollers, a step bending method and a warpage correction method in step bending that make problems caused by warpage less likely to occur are desired.TECHNICAL SOLUTION

[0005] A step bending method according to one aspect of the present invention includes the following steps. Namely, it includes step bending for forming a step bent portion on a flat plate-shaped workpiece with a step bending roller die; and correction processing for correcting warpage of the step bent portion after the step bending, wherein the step bent portion protruding from a flat plate portion of the workpiece is formed by the step bending, and the correction processing is processing in which the step bent portion is pressed downward with a roller die while a lower surface of the flat plate portion is supported and the step bent portion is unsupported from below due to a space formed below the step bent portion.

[0006] A warpage correction method in step bending according to another aspect of the present invention includes the following steps. Namely, it includes a performing correction processing on a step-bent workpiece having a flat plate portion and a step bent portion protruding from the flat plate portion, in which the step bent portion is pressed downward with a roller die while a lower surface of the flat plate portion is supported and the step portion is unsupported from below due to a space formed below the step bent portion.EFFECT OF THE INVENTION

[0007] According to the step bending method and the warpage correction method in step bending according to aspects of the present invention, problems caused by warpage are less likely to occur in step bending using stepped rollers.BRIEF DESCRIPTION OF DRAWINGS

[0008] FIG. 1 is a partial cross-sectional view showing a state in which step bending is performed on a workpiece W with a step bending roller die K equipped with stepped rollers in a step bending method according to an embodiment of the present invention. FIG. 2 is a front view showing a first correction die K34 used in correction processing in the step bending of the present invention. FIG. 3 is a front view showing a second correction die K56. FIG. 4A is a plan view showing a workpiece W on which the step bending has been performed. FIG. 4B is a cross-sectional view taken along line S4B-S4B in FIG. 4A. FIG. 4C is a cross-sectional view taken along line S4C-S4C in FIG. 4A showing warpage of the workpiece W on which step bending has been performed. FIG. 5A is a first diagram for explaining a 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. FIG. 6 is a diagram for explaining a warpage correction method using the second correction die K56. FIG. 7A is a table showing a first processing procedure using the first correction die K34. FIG. 7B is a warpage distribution diagram of the workpiece W that has been step bent according to the first processing procedure. FIG. 7C is a warpage distribution diagram of the workpiece W in step bending that does not include correction processing. FIG. 8A is a table showing a second processing procedure using the second correction die K56. FIG. 8B is a warpage distribution diagram of the workpiece W that has been step bent according to the second processing procedure. FIG. 9A is a table showing a third processing procedure using the first correction die K34. FIG. 9B is a table showing a fourth processing procedure using the second correction die K56. FIG. 10 is a partially cross-sectioned front view showing a third correction die K78 which is a modified example of the first correction die K34. FIG. 11 is a block diagram of a punch press that performs the step bending method according to the embodiment of the present invention. DESCRIPTION OF EMBODIMENTS

[0009] A step bending method according to an embodiment of the present invention performs a step bending on a flat plate-shaped workpiece with a step bending roller die K (see FIG. 1) (hereinafter also simply referred to as step bending die K), and thereafter, performs a warpage correction processing using either a first correction die K34 (see FIG. 2) or a second correction die K56 (see FIG. 3), which are roller dies.

[0010] The step bending die K, the first correction die K34, and the second correction die K56 have an upper die and a lower die. The upper die and the lower die are detachably mounted on an upper turret and a lower turret of a punch press, respectively, and under the control of a control unit 7 (see FIG. 11) of the punch press, vertical movement of the upper die and synchronized rotation around holder axes CL1V to CL6V (see FIGs. 1 to 3) extending in the vertical direction are performed by a die drive unit 71 (see FIG. 11). The upper turret and the lower turret are equipped with an auto-index device (hereinafter referred to as AI device) that rotates the mounted dies around their axes, and 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 synchronized 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 correction die K34, and the second correction die K56 will be described with reference to FIGs. 1 to 3.

[0011] FIG. 1 is a partial cross-sectional view showing a state in which step bending is performed on a workpiece W with a step bending die K equipped with stepped rollers in the step bending method according to the present embodiment. FIG. 2 is a front view showing the first correction die K34 used in correction processing in the step bending of the present invention. FIG. 3 is a front view showing the second correction die K56.(Step Bending Die K: See FIG. 1)

[0012] The step bending die K comprises a lower die K1 and an upper die K2. The lower die K1 has a substantially disk shape and is detachably mounted via a mounting base 82 on the lower turret (not shown) of the punch press. The upper die K2 has an elongated substantially cylindrical shape, and the upper portion in FIG. 1 is detachably mounted on the upper turret (not shown) of the punch press.

[0013] When the step 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. Further, the step bending die K is controlled by the AI drive unit 711 of the control unit 7 of the punch press to synchronously rotate around the concentric holder axes CL1V and CL2V in a posture in which a roller axis CL1 and a roller axis CL2 extending in the horizontal direction are parallel.

[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 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 end portions of a single shaft member and are portions that protrude and are exposed on the outside.

[0015] The holder K11 rotatably supports the pair of shaft portions 123, whereby the stepped roller K12 is rotatable 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 upward from 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 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 end portions of a single shaft member and are portions that protrude and are exposed on the outside.

[0017] The holder K21 rotatably supports the pair of shaft portions 223, whereby the stepped roller K22 is rotatable 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 from the lower end of the holder K21.

[0018] In this example, the axial width of the large diameter portions 121 and 221 is approximately half the axial width of the small diameter portions 122 and 222, but this ratio is not limited.(First Correction Die K34: See FIG. 2)

[0019] The first correction die K34 is a roller die comprising a lower die K3 and an upper die K4. The lower die K3 has a substantially disk shape and is detachably mounted via a mounting base 82 on the lower turret (not shown) of the punch press. The upper die K4 has an elongated substantially cylindrical shape, and the upper portion in FIG. 2 is detachably mounted on the upper turret (not shown) of the punch press.

[0020] When the first correction die K34 is mounted on the turret of the punch press, it is indexed to a position where a holder axis CL3V of the lower die K3 extending in the vertical direction and a holder axis CL4V of the upper die K4 are concentric. Further, the first correction die K34 is controlled by the AI drive unit 711 of the control unit 7 of the punch press to synchronously rotate around the concentric holder axes CL3V and CL4V in a posture in which a roller axis CL3 and a roller axis CL4 extending in the horizontal direction are parallel.

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

[0022] The holder K31 rotatably supports the pair of shaft portions 323, whereby the non-stepped roller K32 is rotatable around the roller axis CL3. At the upper part of the non-stepped roller K32, the peripheral surface of the roller 321 protrudes upward from 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 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 end portions of a single shaft member and are portions that protrude and are exposed on the outside.

[0024] The holder K41 rotatably supports the pair of shaft portions 423, whereby the stepped roller K42 is rotatable around the roller axis CL4. At the lower part of the stepped roller K42, the peripheral surfaces of the lower portions of the large diameter portion 421 and the small diameter portion 422 protrude downward from 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.(Second Correction Die K56: See FIG. 3)

[0026] The second correction die K56 is a roller die comprising a lower die K5 and an upper die K6. The lower die K5 has a substantially disk shape and is detachably mounted via a mounting base 82 on the lower turret (not shown) of the punch press. The upper die K6 has an elongated substantially cylindrical shape, and the upper portion in FIG. 3 is detachably mounted on the upper turret (not shown) of the punch press.

[0027] When the second correction die K56 is mounted on the turret of the punch press, it is indexed to a position where a holder axis CL5V of the lower die K5 extending in the vertical direction and a holder axis CL6V of the upper die K6 are concentric. Further, the second correction die K56 is controlled by the AI drive unit 711 of the control unit 7 of the punch press to synchronously rotate around the concentric holder axes CL5V and CL6V in a posture in which a roller axis CL5 and a roller axis CL6 extending in the horizontal direction are parallel.

[0028] The lower die K5 has a holder K51 and a non-stepped roller K52. The non-stepped roller K52 has a cylindrical roller 521 having a constant outer diameter, and a pair of shaft portions 523 extending outward on the roller axis CL5. The pair of shaft portions 523 are both end portions of a single shaft member and are portions that protrude and are exposed on the outside.

[0029] The holder K51 rotatably supports the pair of shaft portions 523, whereby the non-stepped roller K52 is rotatable around the roller axis CL5. At the upper part of the non-stepped roller K52, the peripheral surface of the roller 521 protrudes upward from 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 at the central portion in the axial direction, a pair of small diameter portions 622 (622a, 622b) formed on both axial sides connected to 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 CL6. The pair of shaft portions 623 are both end portions of a single shaft member and are portions that protrude and are exposed on the outside.

[0031] The holder K61 rotatably supports the pair of shaft portions 623, whereby the center roller K62 is rotatable around the roller axis CL6. At the lower part of the center roller K62, the peripheral surface of the large diameter portion 621 protrudes downward from the lower end of the holder K61.

[0032] In this example, the axial width of the large diameter portion 621 is approximately one-third of the overall axial length of the center roller K62, but this ratio is not limited.

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

[0034] In step bending, a flat metal plate workpiece W placed on the table of the punch press is clamped at one edge portion by upper and lower clamp jaws 811 and 812 of a plurality of clampers 81 (see FIG. 5A) provided in the punch press. The gripping operation of the workpiece W by the clamper 81 is performed by a clamper drive unit 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 X and Y axes that are orthogonal to each other. 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 a carriage drive unit 73 (see FIG. 11) according to instructions from the control unit 7. Thereby, processing can be performed at arbitrary positions on the workpiece W by each die mounted on the turret.

[0035] FIG. 4A is a plan view showing a workpiece W on which step bending has been performed, and FIG. 4B is a cross-sectional view taken along line S4B-S4B in FIG. 4A. FIG. 4C is a cross-sectional view taken along line S4C-S4C in FIG. 4A showing warpage of the workpiece W on which step bending has been performed.

[0036] Step bending using the step bending die K is the same as conventional methods. First, the upper die K2 is moved upward relative to the lower die K1 to separate them, the workpiece W is moved to a position where the portion to be step bent coincides with the holder axis CL1V (CL2V), and the rotational posture of the lower die K1 and the upper die K2 is set to a posture corresponding to the step bending direction. Then, the upper die K2 is lowered toward the lower die K1 by the operation of a striker (not shown) driven by the die drive unit 71 (see arrow DR1 in FIG. 1). As a result, a step portion Wd1 is formed in the workpiece W by the clamping action of the misalignment of the stepped rollers K12 and K22. Thereafter, as shown in FIG. 4A, the control unit 7 moves the step bending die K along the shape of the step portion Wd1 while the AI drive unit 711 controls the rotational posture around the holder axis CL1V according to the direction in which the step portion Wd1 is formed (see arrow DR2).

[0037] FIGs. 4A and 4B show an example in which step bending is performed on a rectangular workpiece W by rotating the step bending die K around the perimeter to form a step bent portion Wd having a rectangular shape in plan view with a step bending height Hd. Hereinafter, the plan view regions of the workpiece W subjected to step bending are classified and referred to as follows. That is, the flat plate portion at the peripheral edge that has not been step bent is referred to as a first region WR1, the raised portion inclined by step bending is referred to as a second region WR2, and the flat plate-shaped step bent portion lifted by step bending is referred to as a third region WR3. The second region WR2 corresponds to the step portion Wd1.

[0038] When step bending is performed on a flat plate-shaped workpiece W with the 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. For example, the third region WR3 warps in a curved surface shape with a concave center. In this case, when one of the left and right portions of the first region WR1 in FIG. 4C is maintained horizontal, the third region WR3 via the second region is not horizontal in cross-sectional shape and is in a state of being curved and inclined upward.

[0039] This warpage can be effectively reduced by performing correction processing on the step bent portion Wd with 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 operations of the die drive unit 71 and the carriage drive unit 73 under the control of the control unit 7.(Correction A) (First Correction Die K34: See FIGs. 5A and 5B)

[0040] 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 a 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] In the first correction die K34, the radius difference Rd4 (see FIG. 2) between the large diameter portion 421 and the small diameter portion 422 is set equal to or slightly smaller than the radius difference Rd2 (see FIG. 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 correction 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 extending in the vertical direction are concentric. Next, the clamper 81 is moved while gripping the workpiece W to position the holder axis CL3V at a position where correction of the step portion Wd1 of the workpiece W is to be started (for example, position PM1 in FIG. 4A). The first correction die K34 is positioned at a rotational position around the concentric holder axes CL3V and CL4V such that the roller axis CL1 and the roller axis CL2 are parallel and in a posture corresponding to the step portion Wd1 to be corrected (a posture perpendicular to the extending direction of the step portion Wd1) .

[0043] As shown in FIG. 5A, after raising the upper die K4 to separate it from the lower die K3, the workpiece W that has been kept gripped by the clamper 81 since step bending is inserted and positioned. For positioning, for example, as shown in FIG. 5A, position J1, which is the edge on the small diameter portion 422 side of the large diameter portion 421, is made to correspond to position J2 at the boundary between the first region WR1 and the second region WR2 in the workpiece W. The workpiece W is held in a substantially horizontal posture in the first region WR1 by gripping by the clamper 81, and in this state, the third region WR3 is warped so as to go upward as it moves away from the clamper 81.

[0044] Next, as shown in FIG. 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 a portion P1 on the second region WR2 side in the first region WR1 against the roller 321 with force F1, and the small diameter portion 422 presses a portion P2 of the third region WR3 downward with force F2.

[0045] Here, the radius difference Rd4 is set equal to or slightly smaller than the radius difference Rd2, and a space Va is formed as a gap between the third region WR3 pressed downward by the small diameter portion 422 and the non-stepped roller 321 of the lower die K3. 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 unsupported from below, that is, 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 extending direction of the step portion Wd1, and controls the rotational posture around the holder axes CL3V and CL4V so that the roller axes CL3 and CL4 are always perpendicular to the tangent line at the current position of the step portion Wd1.

[0047] In this way, the non-stepped roller K32 of the lower die K3 and the stepped roller K42 of the upper die K4 rotate around the roller axes CL3 and CL4 while correcting the warpage of the track-shaped step portion Wd1, making one rotation or multiple rotations, and the correction processing is completed.(Correction B) (Second Correction Die K56: See FIG. 6)

[0048] 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 operations of the die drive unit 71 and the carriage drive unit 73 under the control of the control unit 7.

[0049] As in the case of the first correction die K34, after raising the upper die K6 to separate it from the lower die K5, the workpiece W that has been subjected to step bending and gripped by the clamper 81 is inserted and positioned. Specifically, the large diameter portion 621 of the center roller K62 of the upper die K6 is positioned near the edge on the second region WR2 side in the third region WR3 of the workpiece W.

[0050] Next, the upper die K6 is lowered to a predetermined position (see arrow DR6), and a portion P4 near the edge on the second region WR2 side in the third region WR3 is pressed downward with force F3 by the large diameter portion 621 of the center roller K62. As a result, a portion P3 on the second region WR2 side of the first region WR1 comes into contact with the non-stepped roller K52 of the lower die K5 and is supported from below. Further, since a space Vb is formed as a gap between the portion P4 of the third region WR3 and the roller 521 of the non-stepped roller K52 of the lower die K5, the third region WR3 of the workpiece W is easily deformed downward (see arrow DR7) by being pressed downward by the large diameter portion 621 in a state where it is unsupported from below, that is, it is corrected.

[0051] The descending position of the upper die K6 is preset according to the material, plate thickness, step bending height Hd, etc. of the workpiece W so that optimal correction is 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 extending direction of the step portion Wd1, and controls the rotational posture around the holder axes CL5V and CL6V so that the roller axes CL5 and CL6 are perpendicular to the tangent line at the current position of the step portion Wd1.(Examples of Correction Processing Procedures)

[0053] Next, examples of processing procedures for step bending including either of the above-mentioned correction A or correction B will be described. The procedure of processing operations performed by the punch press, including this processing procedure, is 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 performs it based thereon.(Example of Processing Procedure Including Correction A)

[0054] A first processing procedure, which is an example of applying correction A using the first correction die K34 to 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 FIGs. 7A to 7C. FIG. 7A is a table showing the first processing procedure using the first correction die K34. FIG. 7B is a warpage distribution diagram of the workpiece W that has been step bent according to the first processing procedure. FIG. 7C is a warpage distribution diagram of the workpiece W in step bending that does not include correction processing.

[0055] The first processing procedure performs four processes in order of processing number. Processing numbers 1 to 3 are three step bending operations using the step bending die K, and by limiting the step bending height Hd lifted in one processing to less than the plate thickness and performing multiple step bending operations, 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, three (three rotations) step bending operations are performed. After the step bending operations of processing numbers 1 to 3, correction A of processing number 4 is performed.

[0056] The specifications of the workpiece W used for the processing in the first processing procedure are as follows. These specifications are hereinafter referred to as specification α.(Specification α)

[0057] Material: SGCC (hot-dip galvanized steel sheet) External dimensions: 200 mm × 100 mm Plate thickness: 0.5 mm Plan view shape of step bent portion Wd to be formed: 150 mm × 60 mm R25 The step bending including correction processing was performed on this workpiece W according to the first processing procedure so that the final step bending height would be approximately 1.0 mm.

[0058] The step bending height was measured by performing step bending on the workpiece W and placing the processed workpiece W on the stage of a three-dimensional measuring instrument. The three-dimensional measuring instrument used was a 3D scanner type three-dimensional measuring instrument VL-500 (manufactured by KEYENCE CORPORATION).

[0059] The step bending height Hd after step bending is the average value of measurements at, for example, three points on the edge on the second region WR2 side in the third region WR3.

[0060] As shown in FIG. 7A, in the step bending operations of processing numbers 1 to 3, the step bending height Hd after processing was 0.3 mm, 0.7 mm, and 1.2 mm, respectively. After the step bending of processing number 3, as a result of performing the correction A processing of processing number 4 (see FIG. 5B), the step bending height Hd could be made 1.0 mm. In this way, it became clear that a step bent portion Wd with a step bending height Hd of approximately twice the plate thickness can be formed on the workpiece W by the first processing procedure in which correction A is performed continuously after step bending.

[0061] Next, the correction of warpage by the first processing procedure will be described with reference to FIGs. 7B and 7C. FIG. 7C is a warpage distribution diagram in a state before performing processing number 4 in the first processing procedure. In the workpiece W shown in FIG. 7C, significant warpage has occurred, and the distribution of the warpage is shown by three distribution regions M2 to M4 according to the degree of warpage. In FIGs. 7B and 7C, a stage contact portion LNp when the workpiece W is placed on the stage of the measuring instrument is shown by a chain line.

[0062] As shown in FIG. 7C, in the state without correction processing, significant warpage occurred in a wide area indicated by distribution regions M2 to M4, with a maximum of 7.7 mm in distribution region M4. In contrast, when the correction processing of correction A of processing number 4 was performed, it became a small area indicated by distribution region M1 in FIG. 7B, and the warpage was reduced to a maximum of 2.8 mm.

[0063] As described above, the step bending according to the present embodiment has a procedure of continuously performing correction processing using the first correction die K34 after step bending by the step bending die K. Thereby, a step bent portion Wd with a step bending height Hd approximately twice the plate thickness can be formed with small warpage. Further, since step bending and correction processing can be performed in the same process while being gripped by the clamper 81, the trouble of re-gripping and repositioning the workpiece by the clamper 81 becomes unnecessary, and production efficiency is improved.(Example of Correction Processing Using Second Correction Die K56)

[0064] A second processing procedure, which is an example of applying correction processing to a workpiece W on which a step bent portion Wd has been formed by the step bending die K using the second correction 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 correction die K56. FIG. 8B is a warpage distribution diagram of the workpiece W that has been step bent according to the second processing procedure.

[0065] The second processing procedure differs from the first processing procedure in that the correction processing of processing number 4 is correction B performed with the second correction die K56 instead of the first correction die K34. That is, processing numbers 1 to 3 are step bending operations using the step bending die K, and by limiting the step bending height Hd lifted in one processing to less than the plate thickness and performing multiple step bending operations, 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, three (three rotations) step bending operations are performed. After the step bending operations of processing numbers 1 to 3, correction B is performed as processing number 4. The specifications of the workpiece W are the above-mentioned specification α, and step bending including correction processing was performed on the workpiece W so that the final step bending height would be approximately 1.0 mm. The measuring method and measuring instrument for the step bending height are also the same as in the first processing procedure.

[0066] As shown in FIG. 8A, in the step bending operations of processing numbers 1 to 3, the step bending height after processing was 0.3 mm, 0.7 mm, and 1.2 mm, respectively. After the step bending of processing number 3, as a result of performing the correction B processing using the second correction die K56 of processing number 4 (see FIG. 8B), the step bending height Hd could be made 1.1 mm. In this way, it became clear that a step bent portion Wd with a step bending height Hd of approximately twice the plate thickness can be formed on the workpiece W by the second processing procedure in which correction B is performed continuously after step bending. Further, as shown in FIG. 8B, the warpage could be reduced to a maximum of 3.0 mm in a small range indicated by distribution region M5.(Other Examples of Correction Processing)

[0067] As described above, by continuously performing correction processing using the first correction die K34 or the second correction die K56 after step bending in which the step portion Wd1 is traced once or multiple times, a step bent portion Wd with a step bending height Hd approximately twice the plate thickness can be formed with small warpage. Therefore, the results of performing processing in which a set of combined processing of step bending and subsequent correction processing is repeated as a third processing procedure and a 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.(Third and Fourth Processing Procedures)

[0068] The specifications of the workpiece W are the above-mentioned specification α. As shown in FIG. 9A, in the third processing procedure, after processing numbers 1 to 4 which is the first processing procedure, processing of processing numbers 5 to 8 including correction A is implemented, and in the fourth processing procedure, after processing numbers 1 to 4 which is the second processing procedure, processing of processing numbers 5 to 8 including correction B is implemented.

[0069] In the third and fourth processing procedures, processing numbers 5 to 8 continuously execute a processing set that performs step bending and correction processing once each in this order twice. As a result, step bending is performed five times (five rotations) and correction processing is performed three times (three rotations) as a whole. In the third processing procedure, the step bending height Hd is suppressed by 0.2 mm, 0.1 mm, and 0.1 mm, respectively, by correction A of processing numbers 4, 6, and 8, and in the fourth processing procedure, the step bending height Hd is suppressed by 0.1 mm each by correction B of processing numbers 4, 6, and 8. In both the third and fourth processing procedures, a step bent portion Wd with a final step bending height Hd of 2.1 mm is obtained.

[0070] That is, by the third and fourth processing procedures, a final step bending height Hd of 2.1 mm, which is a large value of four times or more the plate thickness, can be obtained respectively. Thus, according to the step bending method according to the present embodiment, a step bent portion Wd with a high step bending height Hd can be obtained.

[0071] One aspect of the present invention is not limited to the configurations and procedures described above, and may be modified within a range that does not depart from the gist of the present invention.

[0072] Instead of the first correction die K34 and the second correction die K56, a third correction die K78 as a modified example shown in FIG. 10 may be used. FIG. 10 is a partially cross-sectioned front view showing the third correction die K78, which is a modified example of the first correction die K34. In FIG. 10, the holders are not shown and only the rollers are described.

[0073] The lower die K7 has a non-stepped roller K72. The non-stepped roller K72 has a cylindrical roller 721 having a constant outer diameter, and a pair of shaft portions 723 extending on the roller axis CL7. The pair of shaft portions 723 are both end portions of a single shaft member and are portions that protrude and are exposed on the outside.

[0074] The upper die K8 has a center roller K82, and ringshaped first collar 822 and second collar 823. The center roller K82 has a large diameter portion 821 having a maximum outer diameter formed in a flange shape at the central position in the axial direction. Small diameter portions 825 and 826 are formed on both sides in the axial direction connected to the large diameter portion 821. A first collar 822, which is a ring having a first thickness t822, is interchangeably mounted on one small diameter portion 825 by being externally fitted, and a second collar 823, which is a ring having a second thickness t823, is interchangeably mounted on the other small diameter portion 826 by being externally fitted. The outer diameter difference between the large diameter portion 821 and the first collar 822 is a level difference d3, and the outer diameter difference between the large diameter portion 821 and the second collar 823 is a level difference d4.

[0075] The third correction die K78 can be applied to the first and third processing procedures in the same manner as the first correction die K34 by selectively making the first collar 822 and the second collar 823 correspond to the step bending height Hd. Further, the large diameter portion 821 can be regarded as the large diameter portion 621 in the upper die K6 of the second correction die K56 and applied to the second and fourth processing procedures. That is, the third correction die K78 has the functions of two types of dies, the first correction die K34 and the second correction die K56.

[0076] The shape of the step bent portion Wd to be formed on the workpiece W is not limited to a track shape closed in top view, and can be freely set. The step bent portion Wd may be linear including a curved portion.

[0077] As described in detail above, the step bending method according to the present embodiment includes step bending for forming a step bent portion Wd on a flat plate-shaped workpiece W with a step bending roller die K, and correction processing for correcting warpage of the step bent portion Wd after the step bending, wherein a step bent portion WR3 protruding from a flat plate portion WR1 of the workpiece W is formed by the step bending, and the correction processing is processing in which the step bent portion Wd is pressed downward with a roller die K34 while the lower surface of the flat plate portion WR1 is supported and the step portion Wd is unsupported from below due to a space Va formed below the step bent portion Wd.

[0078] According to this step bending method, by forming the space Va below the step bent portion Wd, the step bent portion Wd easily bends downward, and the warpage of the step bent portion Wd is favorably corrected.

[0079] Further, in this step bending method, the workpiece W may be gripped by a clamper 81, the step bent portion Wd may be formed by a step bending roller die K, and the correction processing may be performed while maintaining gripping of the workpiece W by the clamper 81.

[0080] Thereby, since re-gripping of the workpiece W by the clamper 81 and the like is unnecessary, the correction processing can be performed efficiently.

[0081] Further, when a set of step bending and correction processing performed after the step bending is defined as a processing set, one or more processing sets may be performed.

[0082] Thereby, the step bending height Hd can be increased.

[0083] Further, the step bending may perform step bending at the same step bending position multiple times with the step bending roller die K.

[0084] Thereby, the step bending height Hd can be further increased.

[0085] Further, a warpage correction method in step bending according to an embodiment of the present invention performs correction processing on a step-bent workpiece W having a flat plate portion WR1 and a step bent portion Wd protruding from the flat plate portion WR1, in which the step bent portion Wd is pressed downward with a roller die K34 while the lower surface of the flat plate portion WR1 is supported and the step portion Wd is unsupported from below due to a space Va formed below the step bent portion Wd.

[0086] In this warpage correction method, by forming the space Va below the step bent portion Wd, the step bent portion Wd easily bends downward and is favorably corrected.

[0087] Further, in this warpage correction method, the workpiece W may be gripped by a clamper 81, the step bent portion Wd may be formed by a step bending roller die K, and the correction processing may be performed while maintaining gripping of the workpiece W by the clamper 81.

[0088] Thereby, since re-gripping of the workpiece W by the clamper 81 and the like is unnecessary, the correction processing can be performed efficiently.

[0089] Further, when a set of step bending and correction processing performed after the step bending is defined as a processing set, multiple processing sets may be performed.

[0090] Thereby, the step bending height Hd can be increased.REFERENCE SIGNS LIST

[0091] 7 control unit 701 CPU (central processing unit) 702 storage unit 71 die drive unit 711 AI drive unit 72 clamper drive unit 73 carriage drive unit 81 clamper 811, 812 clamp jaw 82 mounting base CL1 to CL8 roller axis CL1V to CL6V holder axis d3, d4 level difference F1 to F3 force Hd step bending height J1, J2 position K step bending die (step bending roller die) K1 lower die K11 holder K12 stepped roller 121 large diameter portion 122 small diameter portion 123 shaft portion K2 upper die K21 holder K22 stepped roller 221 large diameter portion 222 small diameter portion 223 shaft portion K34 first correction die (roller die) K3 lower die K31 holder K32 non-stepped roller 321 roller 323 shaft portion K4 upper die K41 holder K42 stepped roller 421 large diameter portion 422 small diameter portion 423 shaft portion K56 second correction die (roller die) K5 lower die K51 holder K52 non-stepped roller 521 roller 523 shaft portion K6 upper die K61 holder K62 center roller 621 large diameter portion 622, 622a, 622b small diameter portion 623 shaft portion K78 third correction die K7 lower die K72 non-stepped roller 721 roller 723 shaft portion K8 upper die K82 center roller 821 large diameter portion 822 first collar 823 second collar 825, 826 small diameter portion M1 to M5 distribution region LNp stage contact portion PM1 position P1 to P4 portion Rd2, Rd4 radius difference t822 first thickness t823 second thickness Va, Vb space W workpiece Wd step bent portion Wd1 step portion WR1 first region (flat plate portion) WR2 second region (raised portion) WR3 third region (step bent portion)

Claims

1. A step bending method comprising: a step bending for forming a step bent portion on a flat plate-shaped workpiece with a step bending roller die; and a correction processing for correcting warpage of the step bent portion after the step bending, wherein the step bent portion protruding from a flat plate portion of the workpiece is formed by the step bending, and the correction processing is a processing in which the step bent portion is pressed downward with a roller die while a lower surface of the flat plate portion is supported and the step bent portion is unsupported from below due to a space formed below the step bent portion.

2. The step bending method according to claim 1, wherein in the step bending, the workpiece is gripped by a clamper and the step bent portion is formed by the step bending roller die, and the correction processing is performed while maintaining gripping of the workpiece by the clamper.

3. The step bending method according to claim 2, wherein one or more processing sets are performed, each processing set comprising the step bending and the correction processing performed after the step bending.

4. The step bending method according to claim 3, wherein the step bending performs step bending at the same step bending position multiple times with the step bending roller die.

5. A warpage correction method in step bending, comprising: performing a correction processing on a step-bent workpiece having a flat plate portion and a step bent portion protruding from the flat plate portion, in which the step bent portion is pressed downward with a roller die while a lower surface of the flat plate portion is supported and the step portion is unsupported from below due to a space formed below the step bent portion.

6. The warpage correction method in step bending according to claim 5, wherein the workpiece is gripped by a clamper, the step bent portion is formed by a step bending roller die, and the correction processing is performed while maintaining gripping of the workpiece by the clamper.

7. The warpage correction method in step bending according to claim 6, wherein multiple processing sets are performed, each processing set comprising the step bending and the correction processing performed after the step bending.

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