Hemming method

Abstract

To address a conventional problem of having to increase a plate thickness or provide a protective resin at an end surface without carrying out hemming in order to prevent wrinkles from being generated in a sheet metal due to forming large curve R after hemming.SOLUTION: A nick 13 is linearly formed in a part to be RF-curved. Then, an edge of a sheet metal is hemmed to form a hemmed part 12a. Then, a corner part is former bv carrying out R-curving on the basis of a R-curve center 14. As the nick 13 is formed in advance, no wrinkle is generated in the hemmed part of the corner part even if R-curving is carried out.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a hemming process for folding the edge of sheet metal to perform hemming, and particularly to an improvement in the hemming process for the R-bending portion forming the corner portion.

Background Art

[0002] The hemming process folds the edge of sheet metal to perform hemming, and is carried out as the finish of the end face of a thin sheet material. There are Patent Documents 1 to 4 as prior arts that disclose hemming processes and hemming processing apparatuses.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

[0004] As described in paragraph 0003 of Patent Document 3, the treatment of corners is a problem in sheet metal hemming.

[0005] Recently, metal office products have increasingly incorporated gentle curves into their design from a design perspective. This has led to a greater emphasis on increasing the bending radius (R) in sheet metal processing. Here, R corresponds to the bending radius, and the larger the bending R, the gentler the curve. A challenge in this process was the treatment of the edges when the sheet metal was thinned. Specifically, when a large bending radius was applied after hemming, wrinkles would form in the sheet metal. Therefore, protective resin was sometimes applied to the edges instead of hemming. If hemming was not performed, the sheet metal thickness was increased. In any case, hemming could not be used when applying a large bending radius to thin sheet metal.

[0006] Patent Document 1 is an invention relating to a roller used for hemming, and there is no particular description of corners or bending radii in that document.

[0007] Patent Document 2 is an invention relating to a pre-pressing roller, and there is no particular description of corners or bending radii in that document.

[0008] Patent Document 3 states that, generally, when processing the corner portion of a hem flange, bending the corner portion toward the edge of the inner panel inevitably results in excess material, and this excess material causes numerous wrinkles. It describes that conventionally, to solve this problem, material removal from the corner portion was performed. However, it points out that although this method can prevent the occurrence of wrinkles in the corner portion, special consideration is required separately, such as filling the gap between the corner portion and the inner panel that results from not performing the main bending with a sealant or paint (paragraphs 003 to 005). To solve this problem, the invention of cited document 3 states that when pre-bending the corner portion of a hem flange, a localized pressure is applied to only a part of the corner portion in the initial stage to deform it, thereby concentrating the occurrence and growth of wrinkles caused by excess material in the corner portion in this area (paragraph 0020).

[0009] The invention described in Patent Document 3 improves the appearance by concentrating wrinkles caused by excess material at the corners in this area, but it does not eliminate the wrinkles.

[0010] Patent Document 4 discloses a hemming apparatus that processes a workpiece placed on an anvil while pressing a pressure roller attached to a robot against it. According to paragraph 0043 and Figure 9 of the same document, a wave-shaped wrinkle is formed.

[0011] The inventions described in Patent Documents 1 to 4 cannot solve the problem of treating the end face when the sheet metal is thinned, namely, the problem that wrinkles occur in the sheet metal when a large bending radius is applied after hemming.

[0012] This invention was made to solve the above-mentioned problems, and aims to provide a hemming method that can reduce wrinkles that occur at the corners when bending is performed after hemming. [Means for solving the problem]

[0013] The hemming method according to this invention is: The first step involves preparing a sheet metal and making cuts in the curved sections of the sheet metal where hemming will be performed, specifically in the sections where R-bending will be performed to form the corners. A second step involves hemming the edge of the sheet metal at the bent portion, The method comprises a third step of performing R-bending on the portion to be bent as described above.

[0014] The length of the cut in the first step corresponds to the size of the R-bend. For example, when forming a 90-degree corner bend, the length should be approximately the same as the length of the 90-degree arc. It may be slightly longer, or slightly shorter to prevent wrinkles. The same applies to other angles such as 60 degrees and 45 degrees. The width of the cut may be short; for example, when cutting with a laser, the beam width is approximately 0.2 mm. [Effects of the Invention]

[0015] By providing a cut at a predetermined position in the first step, when bending is performed after hemming, wrinkles generated at the corner portion can be reduced.

Brief Description of the Drawings

[0016] [Figure 1] It is an explanatory diagram of a hemming method according to an embodiment of the invention. It shows a state where a cut is made in the sheet metal developed in the first step. [Figure 2] It is an explanatory diagram of a hemming method according to an embodiment of the invention. It shows a state where the end portion of the sheet metal is bent for hemming in the second step, and the position of the R-bending process at the corner portion. [Figure 3] It is an explanatory diagram of a hemming method according to an embodiment of the invention. It shows a state where the R-bending process is performed in the third step. [Figure 4] A perspective view (photo) of an article (an example) manufactured by the hemming method according to an embodiment of the invention is shown. [Figure 5] An enlarged view (photo) of the corner portion of FIG. 4 is shown. [Figure 6] A further enlarged view (schematic plan view, photo) of the corner portion of FIG. 5 is shown.

Embodiments for Carrying Out the Invention

[0017] Hereinafter, an explanation of a hemming method according to an embodiment of the invention will be added.

[0018] <First Step> Prepare a sheet metal material 1, and as shown in Figure 1, make a straight cut (slit) 13 in the R-bend portion a using a fiber laser. The length of the slit corresponds to the size of the R-bend, specifically the length of the R-bend portion a (described later). An example of the sheet metal material is a 0.8 mm thick metal plate made of, for example, SPCC (cold-rolled steel sheet). For the sake of explanation, only the component constituting one corner is shown in the figure, but it is not limited to this. A component of an appropriate size can be used depending on the required size and the number of corners.

[0019] The edge of the sheet metal 1 is a bent portion 12 where hemming is performed. The hemming bend (fold line) 11 is indicated by a dotted line. The arrow indicates the direction of the hemming bend. The symbol b represents the size of the bent portion 12. For example, the length of b is approximately 6 mm or 9 mm, but is not limited to this.

[0020] In the example shown in the figure, the cut 13 is straight, just like the hemming bend (fold line) 11. The cut 13 is located on the extension of the hemming bend (fold line) 11 (the two are approximately on the same straight line).

[0021] In the third step described below, the corner section is subjected to R-bending. Figure 2 shows the R-bending center 14. The R-bending center 14 intersects with the cut 13 at approximately the midpoint of the cut 13.

[0022] As an example of the length of symbol a and the bending radius R, when the radius R of corner section 2 is 30 mm, the length of cut 13 is approximately 55 mm. The cutting width of the fiber laser is the same as the width of cut 13. The cutting width is approximately 0.5 mm or less. In actual measurements, the cutting width (laser diameter) was approximately 0.2 mm. In this example, cut 13 is made slightly longer than the length of corner section 2 (when bending 90 degrees with R30, the length of the 90-degree arc is approximately 47 mm), but it is not limited to this. It may be approximately the same as the length of corner section 2, or shorter, as long as wrinkles do not occur in corner section 2.

[0023] <Second process> The hemming bend portion 12 of the sheet metal 1 is folded back at the hemming bend point (fold line) 11 to perform hemming. Figure 2 shows the state after hemming. A hemmed portion 12a is formed at the edge.

[0024] <3rd process> The corner portion 2 is formed by performing R-bending based on the R-bending center 14 in Figure 2. Figure 3 shows the corner portion 2 after the third step. According to the embodiment of the invention, no wrinkles occur in the portion indicated by reference numeral c.

[0025] <4th process> For the finishing touches, the area including corner section 2 is buffed. Note that step 4 can be omitted.

[0026] Figures 4 to 6 show examples of articles actually manufactured using the hemming method according to an embodiment of the invention. As can be seen from these photographs, no wrinkles are observed at the corners. In the enlarged photograph of Figure 6, some cuts 13 are visible.

[0027] According to the embodiment of the invention, when bending is performed after hemming, it is possible to reduce the wrinkles that occur at the corners.

[0028] By eliminating the need to apply protective resin to the end faces instead of hemming, we were able to reduce the number of parts, labor hours, and costs through integrated manufacturing.

[0029] This eliminated the need to increase the sheet metal thickness to reduce wrinkles, resulting in weight reduction and cost savings through the use of thinner sheets. [Explanation of Symbols]

[0030] 1 Sheet metal 11. Hemming bends (fold lines) 12. Hemmed bend at the edge of the metal plate 12a Hemmed portion 13 Slits 14 R bending center 2. Corner section that has been hemmed and then R-bent. a. Hemming bend length b. Length of the bent portion c. Hemmed corner section

Claims

1. The first step involves preparing a sheet metal and making cuts along the bending lines, which are the bending points for hemming, in the R-bends that form the corners of the sheet metal where hemming is to be performed. A second step involves hemming the edge of the sheet metal at the bent portion, A hemming method comprising a third step of performing R-bending on the portion to be bent as described above.

2. The hemming method according to claim 1, characterized in that the length of the cut in the first step corresponds to the size of the R bend.

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