JP2024058788A - Hemming method - Google Patents

Abstract

[Problem] When a large bend radius was processed after hemming, wrinkles would appear in the sheet metal. To avoid this, the only options were to increase the sheet thickness, or to not hemming and instead apply protective resin to the end surface. [Solution] A straight cut 13 is made in the part where R bending will be performed. Next, the edge of the sheet metal is hemmed to form the hemmed part 12a. Next, a corner is formed by performing R bending based on the R bending center 14. By making the cut 13 in advance, no wrinkles will appear in the hemmed part of the corner even when R bending is performed. [Selected drawing] Figure 2

Description

The present invention relates to a hemming method in which the edge of a metal sheet is folded back to remove the edging, and in particular to improvements in hemming for R-bend sections that form corners.

Hemming is a process in which the edge of a metal sheet is folded back to remove the edge, and is performed to finish the end surface of a thin plate material. Prior art that discloses hemming methods and hemming devices includes Patent Documents 1 to 4.

JP 2021-70030 A "Method for forming metal sheets, and rollers and devices used therein" This paper discloses a roller-type hemming process that uses a roller to roll, and has a different shape from conventional rollers with cylindrical surfaces. The degree of freedom in bending is large, and robots that can change the posture (orientation) of the rotation axis in a complex manner are not necessarily required. JP 2022-15443 A, "Roll hemming method and roll hemming device" Discloses that by providing a leading pressure roller near the bending roller, quality defects such as surface sagging, where the outer surface of the outer panel is slightly bent toward the inner panel at the outer edge of the outer panel, are reduced. Patent Publication No. 3451592: "Hemming method and apparatus" In a hemming method in which a hem flange provided on the edge of an outer panel is pre-bent toward the edge of an inner panel, and then a pressure is applied to this pre-bent hem flange to perform the final bending, thereby folding back the hem flange of the outer panel to clamp the edge of the inner panel. When processing the corner of the hem flange, pressure is applied locally to only a portion of the corner to deform it at the beginning of the pre-bending, and wrinkles caused by excess material accompanying the subsequent bending of the corner are concentrated and grow in this portion. Patent Publication No. 5285463 "Hemming device" The hemming device is equipped with a support arm that rotatably supports the pressure roller at its tip, a motor that is journaled at the base end of the support arm and rotates the support arm around the base end, and a support head that fixes the motor to the robot, and the pressing force of the pressure roller is controlled by the rotational torque of the motor. This provides a hemming device that has a simple configuration, good tracking, and is compact with a small number of parts.

As described in paragraph 0003 of Patent Document 3, corner processing becomes an issue when hemming sheet metal.

Recently, metal office products are increasingly incorporating gentle curves into their design. This has led to the bend radius being made larger in sheet metal processing. Here, R corresponds to the bend radius, and the larger the bend radius, the gentler the curve. One issue with this is how to deal with the edges when the sheet metal is made thinner. Specifically, if a large bend radius is created after hemming, wrinkles form in the sheet metal. For this reason, instead of hemming, protective resin is inserted into the edges. If hemming is not performed, the thickness of the sheet metal is increased. In any case, hemming cannot be used when a large bend radius is created on a thin sheet metal.

Patent document 1 is an invention related to rollers used in hemming, and does not specifically mention corners or bend radius.

Patent document 2 is an invention related to a leading pressure roller, and there is no specific mention in the document of corners or bend radius.

Patent Document 3 states that, in general, when processing the corners of a hem flange, bending the corners toward the edge of the inner panel inevitably results in excess material, which causes numerous wrinkles, and states that in order to solve this problem, the corners have traditionally been trimmed. However, it points out that while this method can prevent wrinkles from forming at the corners, it requires special care to fill the gaps between the corners and the inner panel that occur when the main bending is not performed with a sealant or paint (paragraphs 003 to 005). To solve this problem, the invention of Cited Document 3 claims that when pre-bending the corners of the hem flange, pressure is applied locally to only a portion of the corner to deform it at the beginning, so that wrinkles caused by the excess material at the corners are concentrated and grow in this area (paragraph 0020).

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

Patent document 4 discloses a hemming device that processes a workpiece placed on an anvil while pressing a pressure roller attached to a robot against the workpiece. According to paragraph 0043 and Figure 9 of the same document, wavy wrinkles are generated.

The inventions in Patent Documents 1 to 4 do not solve the problem of processing the end faces when the sheet is thinned, that is, the problem of wrinkles appearing in the sheet metal when a large bending radius is processed after hemming.

This invention was made to solve the above problem, and aims to provide a hemming method that can reduce wrinkles that occur at corners when bending is performed after hemming.

The hemming method according to the present invention comprises the steps of:
A first step of preparing a sheet metal and cutting a portion of the sheet metal where a R-bending process is to be performed to form a corner portion among bending portions where a hemming process is to be performed;
A second step of hemming the edge of the metal plate at the bent portion;
and a third step of performing R-bending on the portion to be R-bended.

The length of the cut in the first step corresponds to the size of the R bend. For example, when forming a 90-degree bent corner, the length should be approximately the same as the length of the 90-degree arc. It may be slightly longer than this, or slightly shorter as long as wrinkles do not form. The same applies to other angles such as 60 degrees or 45 degrees. The width of the cut may be short; for example, when cutting with a laser, the beam width is about 0.2 mm.

By providing a cut at a specified position in the first step, this invention was able to reduce wrinkles that would occur at the corners when bending was performed after hemming.

1 is an explanatory diagram of a hemming method according to an embodiment of the present invention, showing a state in which a cut is made in the sheet metal developed in a first step. 1 is an explanatory diagram of a hemming method according to an embodiment of the present invention, showing a state in which an end of a metal plate is bent and hemmed in a second step, and a position of a round bend processing of a corner portion. 1 is an explanatory diagram of a hemming method according to an embodiment of the present invention, showing a state where R-bending is performed in a third step. FIG. 1 is a perspective view (photograph) of an article (one example) manufactured by a hemming method according to an embodiment of the present invention. An enlarged view (photograph) of the corner portion of FIG. 4 is shown. 6 shows a further enlarged view (schematic plan view, photograph) of the corner portion of FIG. 5 .

The hemming method according to the embodiment of the invention is explained below.

<First process>
A sheet metal material 1 is prepared, and as shown in Fig. 1, a fiber laser is used to make a linear cut (slit) 13 in the portion a where the R-bending is to be performed. The length of the slit corresponds to the size of the R-bending, specifically, the length of the portion a where the R-bending is to be performed (described later). An example of the sheet metal material is a metal plate with a thickness of 0.8 mm, and the material is, for example, SPCC (cold rolled steel plate). For convenience of explanation, only a member constituting one corner is shown in the figure, but this is not limited to this. A member of an appropriate size can be used depending on the required size and number of corners.

The edge of the metal sheet 1 is the bent portion 12 where hemming is performed. The hemming bending location (bending line) 11 is shown by a dotted line. The arrow indicates the direction of hemming bending. The symbol b is the size of the bent portion 12. For example, the length of b is about 6 mm or 9 mm, but is not limited to this.

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

The corners are rounded in the third step, which will be described later. Figure 2 shows the rounded bend center 14. The rounded bend center 14 intersects with the cut 13 at approximately the midpoint of the cut 13.

As an example of the length of the symbol a and the bending radius R, when the radius R of the corner portion 2 is 30 mm, the length of the slit 13 is about 55 mm. The cutting width of the fiber laser is the same as the width of the slit 13. The cutting width is about 0.5 mm or less. When actually measured, the cutting width (laser diameter) was about 0.2 mm. In this example, the slit 13 is slightly longer than the length of the corner portion 2 (when bending 90 degrees with R30, the length of the 90-degree arc is about 47 mm), but this is not limited. It may be approximately the same as the length of the corner portion 2, or shorter than that as long as wrinkles do not occur in the corner portion 2.

<Second step>
The hemming process is performed by folding back the hemmed portion 12 of the metal sheet 1 at the hemming bending location (folding line) 11. Fig. 2 shows the state after the hemming process. A hemmed portion 12a is formed by folding back the edge.

<Third step>
The corner portion 2 is formed by performing R-bending based on the R-bending center 14 in Fig. 2. Fig. 3 shows the corner portion 2 after the third process. According to the embodiment of the invention, no wrinkles are generated in the portion indicated by the symbol c.

<Fourth step>
For finishing, the portion including the corner portion 2 is buffed. The fourth step may be omitted.

An example of an article actually manufactured using the hemming method according to the embodiment of the invention is shown in Figures 4 to 6. As can be seen from these photographs, no wrinkles are observed in the corners. In the enlarged photograph of Figure 6, some cuts 13 can be seen.

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

It is no longer necessary to apply protective resin to the end faces instead of hemming, and the number of parts, labor, and costs have been reduced by integral processing.

It is no longer necessary to increase the thickness of the sheet metal to reduce wrinkles, and the use of thinner plates has made it possible to reduce weight and costs.

1 Metal plate 11 Hemming bending part (bending line)
12 Hemmed portion of edge of metal plate 12a Hemmed portion 13 Slit
14 R-bend center 2 Corner part that has been R-bended after hemming a Hemming bend length b Length of bent part c Hemming part of corner part

Claims (2)

A first step of preparing a sheet metal and cutting a portion of the sheet metal where a R-bending process is to be performed to form a corner portion among bending portions where a hemming process is to be performed;
A second step of hemming the edge of the metal plate at the bent portion;
and a third step of performing R-bending on the portion to be R-bended. 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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