Bend forming method for metal plate

Abstract

A bend forming method for a metal plate 1 includes: a first step for pressing a central part 3 of the metal plate 1; a second step for sandwiching an end part 4 of the metal plate 1 while adjusting a clearance of a die 10 by means of a movable mechanism 13 and forming a corner part 2 having a prescribed bending angle between the end part 4 and the central part 3; and a third step for pushing the corner part 2 so as to shorten the length of the metal plate 1 and sharpening the corner part.

Description

Method for bending a metal plate

[0001] The present disclosure relates to a method for bending a metal plate.

[0002] In the method for bending a metal plate, it is required to sharpen the corners from the viewpoints of dimensional constraints and designability of the product. In addition, in the case of a product that requires strength and rigidity in addition to designability, especially in the case of a box-shaped product, it is necessary to sharpen the corners with a high-strength and thick metal plate in order to increase the volume efficiency. However, when targeting a high-strength and thick metal plate, if it is bent using a mold with a small radius of curvature, deformation may concentrate at the corners and cracks may occur. Also, there are methods to suppress cracking by reducing the plate thickness only at the corners and reducing the tensile deformation occurring outside the corners, or by heating the corners to reduce the strength of the metal plate. However, since the plate thickness and material strength of the corners are reduced, there is a risk of impairing the strength and rigidity of the product.

[0003] Patent Document 1 discloses a press body having sharp corners. In the press body, the outer bending radius of the corners is defined to be less than or equal to the thickness of the metal plate, thereby making the corners sharp. Also, for crack suppression, bending is performed by pressing the end face of the side wall portion (in a state where the tip of the end of the metal plate abuts against the mold), so that the metal plate does not extend and a reduction in plate thickness is suppressed. Further, for springback suppression, it is disclosed that press working is performed in a heated state.

[0004] Japanese Patent Application Laid-Open No. 2014-221493

[0005] Patent Document 1 suppresses the reduction in the thickness of a metal sheet by preventing elongation of the metal sheet from the viewpoint of suppressing cracking of the metal sheet. However, the inside of the corner is already sharpened in the first step, and only the outside of the corner is sharpened in the second step. In such processing, there is a risk of cracking in the first step, especially in the case of high-strength materials with low ductility. Furthermore, when press-forming a high-strength, thick metal sheet in an unheated state, a large springback occurs, so it is necessary to suppress the springback. In addition to this, due to variations in the properties and dimensions of the metal sheet, contact with the mold and springback may not occur as expected during press forming, resulting in variations in the outcome. Therefore, in the bending forming method of a metal sheet, there is room for improvement from the viewpoint of sharpening the corners while considering not only cracking and springback, but also variations in the springback and thickness of the metal sheet.

[0006] This disclosure addresses the challenge of sharpening the corners of a metal sheet without reducing its thickness, while suppressing cracking and springback, in a method for bending a metal sheet.

[0007] This disclosure provides a method for bending a metal sheet, comprising: a first step of pressing down on the central part of the metal sheet; a second step of sandwiching the ends of the metal sheet while adjusting the clearance of the mold with a movable mechanism, thereby forming a corner portion with a predetermined bending angle between the ends and the central part; and a third step of pressing and sharpening the corner portion so that the length of the metal sheet is shortened.

[0008] This method allows for the prevention of material escaping to the center by pressing down on the center in the first step, and also prevents the metal plate from shifting by fixing the position of the center. In the second step, springback can be suppressed by clamping the edges, and the metal plate can be securely held regardless of the magnitude of the springback. Since the amount of springback varies greatly depending on the type and thickness of the material, it is effective to be able to adjust the clearance with a movable mechanism. In the third step, the corners are pressed in so that the length of the metal plate is shortened while the center and edges are pressed down, so that the excess material generated by the wire length compression of the metal plate flows into the corners without escaping to the center and edges. Therefore, sufficient material can be supplied to the corners, and cracking at the corners can be suppressed. In addition, since the center and edges are pressed down, out-of-plane deformation such as wrinkles in the metal plate due to the wire length compression can be suppressed. Thus, the corners of the metal plate can be sharpened without reducing their thickness while suppressing cracking and springback. Furthermore, this method is particularly effective for metal plates made of materials with a tensile strength of 590 MPa or higher (for example, ultra-high-strength steel plates).

[0009] In the first step, the central portion may be processed to create a recess. Alternatively, the central portion may be recessed before the first step.

[0010] These methods can suppress the central bulge that is a problem with springback in metal sheets. Specifically, in the bending process of metal sheets, there is a risk of springback occurring, where the central part deforms and bulges as the corners are formed. However, by creating a concave shape in the opposite direction to this springback deformation, the springback that causes the central part to bulge can be canceled out.

[0011] In the third step, the tip of the end may be abutted against the mold.

[0012] This method prevents the length of the metal plate from increasing, thus preventing a decrease in the thickness of the metal plate and further suppressing cracking of the metal plate.

[0013] The movable mechanism may include a cam slide mechanism.

[0014] This method allows for the concrete realization of a movable mechanism with a simple configuration. In particular, since presses used for bending metal sheets are generally machines that move up and down, the cam slide mechanism can convert this up and down movement into left and right movement, allowing it to grip the end of the sheet after bending.

[0015] The predetermined bending angle may be 90°.

[0016] According to this method, 90° bends are in high demand and useful in the bending process of metal sheets.

[0017] The amount X of indentation of the corner in the third step may be determined using the radius R of the corner before indentation by the following formula: (Formula) X ≥ R(4 - π) / 2

[0018] This method allows the length of the corner after the third step to be less than or equal to the length of the corner before the third step. Therefore, excess material can be generated as the wire length is compressed. However, excessive wire length compression that causes folding on the inside of the corner should be avoided.

[0019] In the third step, the outer surface of the corner may be flattened by crushing.

[0020] This method allows for the application of compressive force to the outer surface of the corner to counteract the tensile force acting on it, thereby further suppressing cracking at the corner. Here, flattening the outer surface of the corner means applying a process that gives the corner a flat outer surface, as if it had been chamfered.

[0021] In the third step, the central portion adjacent to the corner portion may be crushed in a striated manner.

[0022] This method allows for the formation of groove-like structures that suppress the outflow of excess material from the corners to the center, thereby further suppressing cracking at the corners. Here, crushing the central section adjacent to the corners in a groove-like manner means applying a process that creates groove-like structures through crushing.

[0023] According to this disclosure, a method for bending a metal sheet can be used to sharpen the corners of the metal sheet without reducing their thickness, while suppressing cracking and springback.

[0024] A perspective view showing a metal sheet processed by the metal sheet bending method according to the first embodiment. A front view showing the pre-forming process of the metal sheet. A front view showing the first step of the metal sheet bending method according to the first embodiment. A front view showing the second step of the metal sheet bending method according to the first embodiment. A front view showing the third step of the metal sheet bending method according to the first embodiment. A schematic diagram showing the amount of indentation at the corner in the third step. A contour plot showing the analysis results of the maximum principal strain at the corner generated by the metal sheet bending method according to the first embodiment. A contour plot showing the analysis results of the maximum principal strain at the corner generated by a general metal sheet bending method. A front view showing a modified example of the metal sheet pre-forming process. A front view showing the third step of the metal sheet bending method according to the second embodiment. A contour plot showing the analysis results of the maximum principal strain at the corner generated by the metal sheet bending method according to the second embodiment. A front view showing the third step of the metal sheet bending method according to the third embodiment.

[0025] Embodiments of this disclosure will be described below with reference to the attached drawings.

[0026] (First Embodiment) Figure 1 shows the final shape of the metal plate 1 processed by the metal plate bending method according to the first embodiment.

[0027] The metal plate 1 has a channel shape and sharpened corners 2. In the illustrated example, rounded corners 2 are schematically shown, but the sharpness of the corners 2 is not limited to that shown.

[0028] The metal plate 1 has a central portion 3 extending horizontally and ends 4 extending vertically from both ends of the central portion 3 via corner portions 2. The angle between the central portion 3 and the ends 4 (i.e., the bending angle of the corner portions 2) is, for example, 90°. However, the bending angle can be any angle greater than 90°, taking into consideration the processability of the press machine.

[0029] The material of the metal plate 1 can be any metal. In this embodiment, the metal plate 1 is made of a difficult-to-process material with high tensile strength (for example, 590 MPa or more), such as an ultra-high-strength steel plate. Even with a metal plate 1 made of such a difficult-to-process material, the bending method of the metal plate 1 in this embodiment makes it possible to sharpen the corners 2 while suppressing cracking and springback.

[0030] In this embodiment, preforming is performed before the main forming. However, preforming can be omitted if necessary. That is, it is also possible to include preforming in the main process and complete all processes in a single bending process.

[0031] Figure 2 is a front view showing the preforming process of the metal plate 1.

[0032] Before preforming, the metal plate 1 is a flat plate extending horizontally (upper part of Figure 2). Preforming gives the metal plate 1 a roughly channel shape (lower part of Figure 2). However, unlike the final shape of the metal plate 1 shown in Figure 1, the angle between the central part 3 and the end part 4 (i.e., the bending angle of the corner part 2) is greater than 90°. Also, the central part 3 is not flat horizontally but has a concave shape. Due to this concave shape, the length of the central part 3 is longer than that of the final shape in Figure 1. Furthermore, the corner part 2 is not sharpened and has a larger radius of curvature than that of the final shape in Figure 1.

[0033] In this embodiment, the preformed metal sheet 1 (lower diagram in Figure 2) is processed into the final shape of the metal sheet 1 (see Figure 1) through the first to third steps described later.

[0034] Figures 3 to 5 are front views showing the first to third steps of the bending method for the metal plate 1 according to this embodiment.

[0035] In the bending method for the metal sheet 1 of this embodiment, a die 10 for press working is used. The die 10 has an upper die 11 positioned on the upper side, a lower die 12 positioned on the lower side, and a movable mechanism 13 positioned between the upper die 11 and the lower die 12.

[0036] The upper mold 11 has a first pressing portion 11a positioned in the horizontal center and second pressing portions 11b positioned on both horizontal sides of the first pressing portion 11a. The first pressing portion 11a is the part that presses the central portion 3 of the metal plate 1. The second pressing portion 11b is the part that presses the remaining central portion 3 and corner portions 2 that are not pressed by the first pressing portion 11a. The first pressing portion 11a is suspended via a spring member 11c and protrudes downward from the second pressing portion 11b.

[0037] The lower mold 12 consists of two sections: an upper section 12a and a lower section 12b. The upper section 12a protrudes upward from the horizontal center of the lower section 12b and has a shape complementary to the final metal plate 1 (see Figure 1). The final metal plate 1 is formed by pressing the metal plate 1 against the top and side surfaces of the upper section 12a. The lower section 12b is configured so that the tip of the end 4 of the metal plate 1 abuts against it. That is, the vertical length of the side surface of the upper section 12a is approximately equal to the length of the end 4 of the metal plate 1. This length can be changed as needed.

[0038] The movable mechanism 13 has a cam slide mechanism. The movable mechanism 13 has a cam driver 13a that moves vertically and a cam slider 13b that moves horizontally. The cam driver 13a and the cam slider 13b are configured to push against each other via an inclined surface. Therefore, when the cam driver 13a moves downward, the cam slider 13b moves horizontally inward, that is, toward the upper part 12a of the lower die 12. By moving in this way, the cam slider 13b presses the end 4 of the metal plate 1 against the upper part 12a of the lower die 12. The horizontal clearance between the cam slider 13b and the upper part 12a (the clamping force on the end 4 of the metal plate 1) can be adjusted by the amount the cam driver 13a moves downward.

[0039] In the first step shown in Figure 3, the first pressing part 11a presses down on the central part 3 of the metal plate 1. Specifically, as the upper die 11 descends toward the lower die 12, the first pressing part 11a presses the metal plate 1 before the second pressing part 11b. The first pressing part 11a presses only the horizontal central portion (only the recessed portion of the central part 3), not the entire central part 3. In other words, the area near the corners 2 of the central part 3 is not pressed, and the recessed shape of the central part 3 formed by pre-forming is maintained even after the first step.

[0040] In the second step shown in Figure 4, the end portion 4 of the metal plate 1 is clamped between the end portion 4 and the central portion 3 while adjusting the clearance of the mold 10 using the movable mechanism 13, forming a corner portion 2 with a predetermined bending angle (90° in this embodiment) between the end portion 4 and the central portion 3. Specifically, the cam driver 13a descends and the cam slider 13b moves horizontally inward. This clamps the end portion 4 of the metal plate 1 between the cam slider 13b and the upper portion 12a with a suitable clearance. This clearance is appropriately set to suppress springback depending on the material of the metal plate 1. In this step, the corner portion 2 is not yet sharpened and has a larger radius of curvature compared to the final shape shown in Figure 1.

[0041] In the third step shown in Figure 5, the corner 2 is pressed and sharpened by the second pressing part 11b. Specifically, after the second step, the upper die 11 performs further processing, the spring member 11c (see Figure 4) compresses, and the second pressing part 11b presses the metal plate 1. The second pressing part 11b presses not only the corner 2 but also the central part 3 in the area near the corner 2, sharpening the corner 2 while flattening the central part 3. At this time, the length of the metal plate 1 shortens as the central part 3 is flattened (the indentation is eliminated), i.e., the wire length is compressed. In this step, the tip of the end 4 abuts against the lower part 12b of the lower die 12, so the metal plate 1 does not stretch. As the wire length of the metal plate 1 is compressed, deformation occurs in which the thickness increases (hereafter referred to as excess material is created), but the excess material does not flow into the central part 3 and end 4 which have already been pressed in the first and second steps, and the excess material flows into the corner 2. Therefore, the thickness of corner 2 will increase.

[0042] Figure 6 is a schematic diagram showing the amount of indentation of the corner 2 in the third step.

[0043] After the second step and before the third step, the corner 2 has a radius of curvature R, a bending angle of 90°, and a line length of πR / 2 (see the dashed line). In the third step, the corner 2 is pushed in by a distance X in the vertical direction (the pushing-in amount X). After the third step, the corner 2 is sharpened, and the horizontal length is R, and the vertical length is R−X (see the solid line). In order to make the length of the corner 2 after the third step not exceed the length of the corner 2 before the third step (compress the line length), the equation πR / 2≧R + R−X holds. That is, it can be expressed as X≧R(4−π) / 2. In this embodiment, the pushing-in amount X is set to R(4−π) / 2. However, the pushing-in amount X can be changed as necessary.

[0044] FIG. 7 is a contour diagram showing the analysis result of the maximum principal strain of the corner 2 generated by the bending method of the metal plate 1 according to this embodiment.

[0045] As shown in FIG. 7, the principal strain of the corner 2 becomes large on the outer surface, and the maximum value is 0.261.

[0046] FIG. 8 is a contour diagram showing the analysis result of the maximum principal strain of the corner 2 generated by a general bending method of the metal plate 1, different from this embodiment. That is, FIG. 8 shows the result of simply bending without any contrivance like this embodiment in order to achieve the same sharpness as FIG. 7.

[0047] As shown in FIG. 8, the principal strain of the corner 2 becomes large on the outer surface, and the maximum value is 0.527.

[0048] Comparing the two results, it was confirmed that the bending method of the metal plate 1 of this embodiment can reduce the maximum principal strain, and thus has the effect of suppressing cracks.

[0049] According to the bending method of the metal plate 1 of this embodiment, the following operational effects are achieved.

[0050] In the first step, by pressing down on the central part 3, it is possible to prevent the material (excess material) from escaping to the central part 3, and to fix the position of the central part 3, thereby preventing the metal plate 1 from shifting. In the second step, by clamping the end part 4, springback can be suppressed, and the metal plate 1 can be securely held regardless of the magnitude of the springback. Since the amount of springback varies greatly depending on the type of material and thickness, it is effective to be able to adjust the clearance with the movable mechanism 13. In the third step, while pressing down on the central part 3 and the end part 4, the corner part 2 is pushed in so that the length of the metal plate 1 is shortened, so that the excess material generated due to the wire length compression of the metal plate 1 does not escape to the central part 3 and the end part 4, but flows into the corner part. Therefore, sufficient material can be supplied to the corner part 2, and cracking of the corner part 2 can be suppressed. In addition, since the central part 3 and the end part 4 are pressed down, it is possible to suppress out-of-plane deformation such as wrinkles in the metal plate 1 due to the wire length compression. Thus, while suppressing cracking and springback, the corner part 2 of the metal plate 1 can be sharpened without reducing its thickness.

[0051] Furthermore, since the metal plate 1, with its central portion 3 indented by pre-forming, is bent, the bulging of the central portion 3, which is a problem due to the springback of the metal plate 1, can be suppressed. Specifically, in the bending of the metal plate 1, there is a risk of springback occurring, in which the central portion 3 deforms to bulge as the corner portion 2 is formed. However, by indenting the central portion 3 in the opposite direction to this springback deformation, the springback that causes the central portion 3 to bulge can be canceled out.

[0052] Furthermore, since the end portion 4 of the metal plate 1 is configured to abut against the lower portion 12b, it is possible to prevent the length of the metal plate 1 from extending. Therefore, it is possible to prevent a decrease in the thickness of the metal plate 1 and further suppress cracking of the metal plate 1.

[0053] Furthermore, the movable mechanism 13 can be concretely realized with a simple configuration such as a cam slide mechanism. In particular, since a press machine that bends a metal plate 1 is generally a machine that moves up and down, the cam slide mechanism can convert this up and down movement into left and right movement, and can grip the end portion 4 after bending. Note that the movable mechanism 13 is not particularly limited to a cam slide mechanism and may take any other form.

[0054] Furthermore, although a 90° bend is used in this embodiment, a 90° bend is in high demand and useful in the bending process of the metal sheet 1.

[0055] Furthermore, by defining the indentation amount X as described above, the length of corner 2 before the third process can be made less than or equal to the length of corner 2 after the third process. Therefore, excess material can be generated as the wire length is compressed. However, excessive wire length compression that causes folding on the inside of corner 2 should be avoided.

[0056] In the above embodiment, an example was described in which the central portion 3 was made concave during pre-forming, but this is not the only example. For example, as shown in Figure 9, the central portion 3 may be made flat during pre-forming. In this case, in the first step, the central portion 3 may be processed to be concave when the first pressing portion 11a presses it (see Figure 3).

[0057] (Second Embodiment) The bending method for the metal plate 1 in the second embodiment shown in Figure 10 differs from the first embodiment in the way the corner portion 2 is pressed in the third step. Except for this part, it is substantially the same as the first embodiment. Therefore, explanations of the parts shown in the first embodiment may be omitted.

[0058] In this embodiment, a projection 11d is provided on the horizontal outer edge of the second pressing portion 11b of the mold 10, projecting downward. The projection 11d is configured to flatten the outer surface of the corner portion 2. Here, flattening the outer surface of the corner portion 2 means that the corner portion 2 is processed to have a flat outer surface, as if it had been chamfered. In the illustrated example, the outer surface of the corner portion 2 is flattened to become a flat surface inclined at 45° from the vertical direction. The cam slider 13b is also configured to avoid interference with the projection 11d. Note that the projection 11d is not limited to the one shown, and any configuration that can flatten the outer surface of the corner portion 2 can be adopted. For example, a projection of a similar shape may be provided on the cam slider 13b instead of the second pressing portion 11b.

[0059] Figure 11 is a contour plot showing the analysis results of the maximum principal strain at the corner 2 generated by the bending method of the metal plate 1 according to this embodiment.

[0060] As shown in Figure 11, the principal strain at the corner 2 is greater on the outer surface, with a maximum value of 0.251. This is smaller than the maximum principal strain of 0.261 shown in Figure 7 and the maximum principal strain of 0.527 shown in Figure 8, which were described in the first embodiment. Therefore, it was confirmed that the bending method for the metal plate 1 of this embodiment can reduce the maximum principal strain and thus suppress cracking.

[0061] According to the bending method for the metal plate 1 of this embodiment, a compressive force can be applied to the outer surface of the corner 2 in such a way that it counteracts the tensile force received by the outer surface of the corner 2, thereby further suppressing cracking of the corner 2.

[0062] (Third Embodiment) The bending method for the metal plate 1 in the third embodiment shown in Figure 12 differs from the first and second embodiments in the way the corners 2 and central portion 3 are pressed in the third step. Except for this part, it is substantially the same as the first and second embodiments. Therefore, explanations of the parts shown in the first and second embodiments may be omitted.

[0063] In this embodiment, the lower surface of the second pressing portion 11b of the mold 10 is provided with a striated (extending in the depth direction as shown in the figure) protrusion 11e having a downwardly convex shape on the horizontally outward side. Here, the protrusion 11e is configured to sandwich the central portion 3 between itself and the upper portion 12a. As a result, in the third step, the central portion 3 adjacent to the corner portion 2 is crushed in a striated shape. Here, crushing the central portion 3 adjacent to the corner portion 2 in a striated shape means performing a process that forms striated grooves by crushing. In the illustrated example, the protrusion 11e is aligned horizontally with the horizontal outer edge of the upper portion 12a (see dashed line AL).

[0064] According to the bending method for the metal plate 1 of this embodiment, groove-like lines can be formed to suppress the outflow of excess material from the corners 2 to the central part 3, thereby further suppressing cracking of the corners 2.

[0065] Although specific embodiments and variations of the present disclosure have been described above, the present disclosure is not limited to the above forms and can be implemented with various modifications within the scope of this invention. For example, a combination of the contents of individual embodiments may be used as one embodiment of the present invention.

[0066] This disclosure may include the following embodiments: (Embodiment 1) A method for bending a metal sheet, comprising: a first step of pressing down on the central part of a metal sheet; a second step of sandwiching the end of the metal sheet while adjusting the clearance of the mold with a movable mechanism to form a corner of a predetermined bending angle between the end and the central part; and a third step of pressing the corner to sharpen it so that the length of the metal sheet is shortened. (Embodiment 2) The method for bending a metal sheet according to Embodiment 1, wherein in the first step, the central part is processed to be concave. (Embodiment 3) The method for bending a metal sheet according to Embodiment 1, wherein the central part is concave before the first step. (Embodiment 4) The method for bending a metal sheet according to any one of Embodiments 1 to 3, wherein in the third step, the tip of the end is abutted against the mold. (Embodiment 5) The method for bending a metal sheet according to any one of Embodiments 1 to 4, wherein the movable mechanism has a cam slide mechanism. (Aspect 6) The method for bending a metal sheet according to any one of aspects 1 to 5, wherein the predetermined bending angle is 90°. (Aspect 7) The method for bending a metal sheet according to aspect 6, wherein the amount X of indentation of the corner in the third step is determined by the following formula using the radius R of the corner before indentation: X ≥ R(4-π) / 2. (Aspect 8) The method for bending a metal sheet according to any one of aspects 1 to 7, wherein in the third step, the outer surface of the corner is flattened. (Aspect 9) The method for bending a metal sheet according to any one of aspects 1 to 8, wherein in the third step, the central portion adjacent to the corner is flattened in a slit-like manner.

[0067] This application is based on a Japanese patent application, Japanese Patent Application No. 2025-7884, filed on January 20, 2025. Japanese Patent Application No. 2025-7884 is incorporated herein by reference.

[0068] 1 Metal plate 2 Corner 3 Center 4 End 10 Mold 11 Upper mold 11a First pressing part 11b Second pressing part 11c Spring member 11d Projection part 11e Convex part 12 Lower mold 12a Upper section 12b Lower section 13 Movable mechanism 13a Cam driver 13b Cam slider

Claims

1. A method for bending a metal sheet, comprising: a first step of pressing down on the central part of the metal sheet; a second step of sandwiching the end of the metal sheet while adjusting the clearance of the mold with a movable mechanism, thereby forming a corner portion with a predetermined bending angle between the end and the central part; and a third step of pressing and sharpening the corner portion so that the length of the metal sheet is shortened.

2. The method for bending a metal plate according to claim 1, wherein the first step involves processing the central portion to create a recess.

3. The method for bending a metal plate according to claim 1, wherein the central portion is pre-indented before the first step.

4. The method for bending a metal sheet according to any one of claims 1 to 3, wherein in the third step, the tip of the end is abutted against the mold.

5. The method for bending a metal plate according to any one of claims 1 to 3, wherein the movable mechanism has a cam slide mechanism.

6. The method for bending a metal sheet according to any one of claims 1 to 3, wherein the predetermined bending angle is 90°.

7. The amount X of indentation of the corner in the third step is determined by the following formula using the radius R of the corner before indentation: X ≥ R(4 - π) / 2. The method for bending a metal plate according to claim 6.

8. The method for bending a metal plate according to any one of claims 1 to 3, wherein in the third step, the outer surface of the corner is flattened by pressing.

9. The method for bending a metal plate according to any one of claims 1 to 3, wherein in the third step, the central portion adjacent to the corner portion is crushed in a slit-like manner.

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