Bending work method

Abstract

To shape, with a bending work, a flange part prevented from cracking and having stable surface texture.SOLUTION: In a bending work method for a plate-like workpiece 1, when applying a bending work to a concave peripheral edge part 2 of a peripheral edge part of the plate-like workpiece 1 to form a flange part 3 extending to one of front and rear sides of the plate-like workpiece 1, a corner part 5b being one of corner parts 5a, 5b of front and rear sides provided in the peripheral edge part 2 and located on a large diameter side of the flange part 3 is crushed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a bending method, and more particularly to a technique for bending a concave peripheral portion of a plate-shaped workpiece. [Background technology]

[0002] In recent years, automobile suspension structures such as lower arms and intermediate beams have been made of sheet metal to reduce costs. In this case, a single metal plate is subjected to sheet metal processing such as predetermined drilling and bending to manufacture a sheet metal structure of a desired shape.

[0003] One example of the sheet metal processing is a method called burring, which involves drilling a metal plate to form a pilot hole, and then forcing a punch with an outer diameter larger than the pilot hole into the pilot hole, causing bending deformation of the peripheral edge of the pilot hole in the direction of the punch, thereby forming a flange that extends in the direction of the punch (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-61977 [Patent Document 2] Patent Publication No. 2021-94580 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, when forming a flange around a pilot hole by burring, the inner peripheral surface of the pilot hole is stretched circumferentially to form the leading edge of the flange. Therefore, the leading edge of the flange, particularly the larger-diameter portion of the leading edge, of the plate-shaped workpiece after burring is likely to have residual tensile stress in a direction (circumferential direction) and magnitude that could lead to cracking. Furthermore, pilot holes for burring are typically formed by punching, so the inner peripheral surface of the pilot hole is often rough. Therefore, these factors combined can lead to cracks (also called hairline cracks) on the leading edge of the flange when the flange is formed by burring. Even if visible cracks are not formed during burring, microscopic cracks are likely to occur. Therefore, if this type of flange portion is provided for the purpose of fitting and holding a specified part on its inner circumference, when the part is assembled by fitting, the flange portion will expand in diameter by the amount of fitting and its tip will be stretched in the circumferential direction, which will increase residual tensile stress and may easily cause cracks in a subsequent durability test.

[0006] The above-mentioned problem is not limited to forming a flange portion around a hole, but can also occur when forming a flange portion by bending the concave peripheral edge of a plate-shaped workpiece to be sheet metal processed.

[0007] In view of the above circumstances, the technical problem to be solved in this specification is to make it possible to form a flange portion by bending that prevents cracking and has stable surface properties, thereby improving the strength of an article that includes a flange portion. [Means for solving the problem]

[0008] The above-mentioned problems are solved by a method for bending a plate-shaped workpiece according to the present invention. That is, this bending method is a bending method for forming a flange extending on one of the front and back sides of a plate-shaped workpiece by bending a concave peripheral portion of the plate-shaped workpiece, and is characterized in that, when forming the flange, of the corners on both the front and back sides of the peripheral portion, the corner on the larger diameter side of the flange is crushed.

[0009] In the bending method according to the present invention, when forming a flange portion by bending a concave peripheral portion of a plate-shaped workpiece, the corners on both the front and back sides of the peripheral portion that form the larger diameter side of the flange are crushed during the formation of the flange portion. When forming a flange portion by bending a concave peripheral portion of a plate-shaped workpiece, the larger diameter side of the tip of the flange is stretched more in the circumferential direction. In light of this, by crushing the corners on both the front and back sides of the peripheral portion that form the larger diameter side of the flange during the formation of the flange, the corners can be compressed, thereby reducing or eliminating the tensile stress (residual tensile stress) that occurs in the circumferential direction. Alternatively, under certain conditions, it is also possible to change the direction of the residual stress from tension to compression. This makes it possible to minimize the occurrence of cracks during bending or subsequent handling. Furthermore, when the edge of the peripheral portion is formed by a specific press process, such as punching, the edge often has a rough surface that is prone to cracking. In response to this, the edge can be smoothed by crushing a portion (corner) of the edge of the peripheral portion, which forms the leading edge of the flange. This removes minute cracks that could be the starting point for cracks and stabilizes the surface texture of the edge, thereby minimizing the occurrence of cracks during bending or subsequent handling.

[0010] In the method for bending a plate-shaped workpiece according to the present invention, the peripheral edge may constitute the inner peripheral surface of a hole formed in the plate-shaped workpiece. In this case, when forming the flange by expanding the hole with a punch while the main body of the plate-shaped workpiece is held down with a die, the die may be provided with an inclined crushing surface, and the corners of the hole being expanded with the punch may be pressed against the crushing surface to crush the corners.

[0011] In this case, when the peripheral edge constitutes the inner peripheral surface of a hole formed in a plate-shaped workpiece, the hole can be expanded with a punch to form a flange. In this process, a die that holds the body of the plate-shaped workpiece is provided with an inclined crushing surface. By pressing the corners against the crushing surface while the hole is being expanded with the punch, the corners can be crushed before the inner peripheral surface of the hole is fully expanded in the circumferential direction. This allows the residual tensile stress generated in the corners to be alleviated or eliminated before it reaches its maximum, more effectively preventing cracks. Furthermore, since the corners can be crushed during bending, the flange formation and the forming (crushing) for crack prevention can be performed in a single process, which is advantageous in terms of work efficiency. [Effects of the Invention]

[0012] As described above, according to the method for bending a plate-shaped workpiece of the present invention, it is possible to form a flange portion on a plate-shaped workpiece by bending the workpiece, the flange portion having a stable surface texture and preventing cracking. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view of a main part illustrating an outline of a method for bending a plate-shaped workpiece according to an embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged view of part A in FIG. [Figure 3] 2 is a cross-sectional view of a main part showing a state immediately after starting bending by expanding the hole portion with a punch from the state shown in FIG. 1. FIG. [Figure 4]3 is a cross-sectional view of a main part showing a state immediately after the hole is further expanded from the state shown in FIG. 2 and the corner is pressed against the inclined surface. FIG. [Figure 5] FIG. 10 is a cross-sectional view of a main part showing a state in which molding of the flange portion is completed. [Figure 6] 1A is a diagram conceptually showing the residual stress distribution in the flange portion after bending according to the prior art, and FIG. 1B is a diagram conceptually showing the residual stress distribution in the flange portion after bending according to the present invention. [Figure 7] FIG. 10 is a cross-sectional view showing an outline of a main part of a bending device according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, the details of a method for bending a plate-shaped workpiece according to one embodiment of the present invention will be described with reference to the drawings. Note that the up-down direction in the following description is merely for convenience, and the actual bending mode is not limited by the following embodiment.

[0015] This method of bending a plate-shaped workpiece involves bending the peripheral portion 2 of the plate-shaped workpiece 1 to form a flange portion 3.In this embodiment, we will explain the example of forming the peripheral portion 2 into the flange portion 3 by expanding the peripheral portion 2 of a hole portion 4 provided in the plate-shaped workpiece 1.

[0016] 1 shows an overview of a bending apparatus 10 according to this embodiment. The bending apparatus 10 includes a punch 11 and a die 12 into whose inner periphery the punch 11 can be inserted.

[0017] Here, the outer diameter of the punch 11 is set to an appropriate size depending on the inner diameter of the hole 4 and the height of the flange 3 (the protrusion dimension from the plate-shaped workpiece body 1a to either the front or back side). Here, it is assumed that both the hole 4 and the punch 11 are perfectly circular, but the shape of the punch 11 may be changed depending on the shape of the hole 4. For example, if the hole 4 is elongated, it is preferable that the punch 11 also have an elongated hole shape similar to that of the hole 4.

[0018] The die 12 has a crushing surface 13 for crushing the corner 5b on one side (the side from which the flange portion 3 protrudes) of the front or back of the plate-like workpiece 1. Here, the crushing surface 13 is inclined, and is disposed at an appropriate position, size, and orientation relative to the die 12 so that the crushing of the corner 5b by the crushing surface 13 begins during the forming of the flange portion 3 accompanied by the expansion of the hole portion 4 by the punch 11 (between the start and end of forming), as will be described later.

[0019] Next, an example of a method for bending the plate-shaped workpiece 1 using the bending device 10 having the above-described configuration will be described mainly with reference to FIGS.

[0020] First, the plate-shaped workpiece 1 is placed between the punch 11 and the die 12, and the plate-shaped workpiece 1 is positioned so that the central axis of the hole 4 coincides with the central axis of the punch 11 (see FIG. 1). Here, the inner peripheral surface (end surface 4a) of the hole 4 formed in the plate-shaped workpiece 1 exhibits a surface texture that becomes rougher toward the front in the punching direction (press direction), as shown in FIG. 2. Thereafter, the punch 11 is brought close to the die 12 and pressed into the hole 4, thereby starting the expanding operation of the hole 4 (see FIG. 3). As a result, the peripheral edge 2 of the hole 4 is gradually pressed and bent in the pressing direction as the punch 11 is pressed in.

[0021] Then, by further expanding the hole 4 and bending the peripheral edge 2, the corner 5b on the bending side (i.e., the corner 5b on the side that will ultimately become the larger diameter side of the flange 3) of the corners 5a, 5b on the front and back of the peripheral edge 2 is pressed against the crushing surface 13 arranged at a predetermined position of the die 12 (see FIG. 4). This causes the crushing surface 13 to start crushing the corner 5b.

[0022] In this way, the operation of expanding hole 4 and the operation of crushing corner 5b are carried out in parallel, and when peripheral edge 2 of hole 4 has been formed into the predetermined shape, that is, when the formation of flange 3 is complete, the operation of crushing corner 5b is also completed. In this case, a forming surface (here, inclined forming surface 3a) having a shape similar to crushing surface 13 is formed on the outer periphery of the tip of flange 3 (see Figure 5).

[0023] As described above, according to the bending method for a plate-shaped workpiece of this embodiment, when forming the flange portion 3, the corner 5b on the larger-diameter side of the flange portion 3, out of the corners 5a, 5b on both the front and rear sides of the peripheral edge 2 of the hole 4, is crushed. This puts the corner 5b in a compressed state, thereby reducing or eliminating the tensile stress (residual tensile stress) that occurs in the circumferential direction. That is, when the flange portion 3 is formed by expanding the hole 4 with the punch 11 without crushing the corner 5b, the residual tensile stress tends to be greater toward the outer diameter side of the end face 4a of the flange portion 3, which is stretched more in the circumferential direction (see FIG. 6( a)). In contrast, according to the bending method of this embodiment, when forming the flange portion 3, the corner 5b on the larger-diameter side of the flange portion 3, where the residual tensile stress tends to be higher, is crushed. This compresses the corner 5b and its surroundings, thereby reducing or eliminating the residual tensile stress that occurs inside (see FIG. 6( b)). Alternatively, depending on the conditions, it is possible to change the direction of the residual stress generated in the corner 5b and its surrounding area from tension to compression. As a result of the above-described actions, the bending method according to this embodiment can minimize the occurrence of cracks during bending or subsequent handling. Furthermore, when the end surface 4a of the peripheral portion 2 (hole 4) is formed by a predetermined press process, such as punching, the end surface 4a often has a rough surface texture that makes it prone to cracks. In contrast, by crushing a portion (corner 5b) of the end surface 4a of the hole 4, which forms the tip end surface of the flange portion 3, the end surface 4a can be smoothed. This removes minute cracks that could be the starting point for cracks and stabilizes the surface texture of the end surface 4a, thereby minimizing the occurrence of cracks during bending or subsequent handling.

[0024] Furthermore, in this embodiment, the crushing operation of the corner portion 5b by the crushing surface 13 is started (and completed) between the start and completion of the expanding operation of the hole portion 4, in other words, between the start and completion of the molding of the flange portion 3, so that the molding of the flange portion 3 and the molding (crushing) to prevent cracking can be performed in one process, making it possible to carry out both operations extremely efficiently.

[0025] Although one embodiment of the present invention has been described above, the method for bending a plate-shaped workpiece according to the present invention can also adopt configurations other than those described above within the scope of the gist of the method.

[0026] For example, in the above embodiment, the stepped crushing surface 13 is integrally provided on the inner periphery of the die 12, but of course this is not limited to this. For example, as shown in Fig. 7, in consideration of ease of manufacture, the die 12 may have a divided structure consisting of an upper split mold 12a and a lower split mold 12b, and the crushing surface 13 may be provided on the lower end of the inner periphery of the upper split mold 12a.

[0027] In the above embodiment, the corner 5b is crushed by the inclined crushing surface 13 over an area of ​​about half of the end face 4a of the peripheral edge 2 (hole 4), but of course this is not limited to this. As long as the residual tensile stress state can be alleviated (or eliminated), or as long as the direction of the residual stress can be changed from tension to compression, the crushing area and crushing shape (shape of the crushing surface 13) can be any shape.

[0028] In the above embodiment, the hole 4 is expanded by the punch 11 to form the flange 3 at the peripheral edge 2 of the hole 4, extending substantially perpendicular to the surface of the plate-like workpiece 1. However, the manner in which the flange 3 is formed is not limited to this. For example, although not shown in the drawings, the present invention may be applied when forming the flange 3 so that it extends at an acute angle (such as 45° to 60°) relative to the surface of the plate-like workpiece 1.

[0029] Furthermore, in the above explanation, an example has been given of forming a flange portion 3 at the peripheral edge 2 of a hole 4 by expanding the hole 4 provided in a plate-shaped workpiece 1 with a punch 11, but it is of course possible to apply the present invention to bending flange portions 3 in other forms. That is, although not shown in the drawings, it is also possible to apply the present invention to a case where a peripheral edge portion (outer peripheral edge) that is concave in a plan view among the outer peripheral edges of a plate-shaped workpiece such as a lower arm is bent to one side to form a flange portion. [Explanation of symbols]

[0030] 1 Plate-shaped workpiece 1a Plate-shaped workpiece body 2 Periphery 3 Flange 3a Molding surface 4 Hole 4a End face 5a,5b corner 10 Bending equipment 11 Punch 12 Die 13 Crushing surface

Claims

[Claim 1] A bending method for forming a flange portion extending on one side of a front or rear surface of a plate-shaped workpiece by bending a concave peripheral portion of the plate-shaped workpiece, A bending method for a plate-shaped workpiece, characterized in that when forming the flange portion, the corner on both the front and back sides of the peripheral portion that is on the larger diameter side of the flange portion is crushed.

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