JP2011177725A - Forming method of frame structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a forming method for forming a frame structure from a high tension steel sheet and forming it into a desired shape even when the curvature of the bent part is large. <P>SOLUTION: The formability of the steel sheet is raised by forming a weak parts 30 (slit or the like) on a planar steel sheet 10' and the bent parts 14, 15 are formed by bending the steel sheet 10' in the weak parts 30, and then the frame structure is reinforced by welding the weak parts 30 of the bent parts 14, 15. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for forming a frame structure by bending a steel plate, and particularly to a method for forming a frame structure using a high-tensile steel plate.

  As a frame structure used for a frame member of an automobile, for example, as shown in Patent Document 1, a member obtained by bending a steel plate into a hat shape by pressing may be used.

Japanese Patent Laid-Open No. 2004-174551

  If the frame structure as described above is formed of a high-strength steel plate (tensile strength of 400 MPa or more) or an ultra-high strength steel plate (tensile strength of 900 MPa or more) excellent in strength and rigidity, the steel plate is thinned while maintaining the strength and rigidity. Therefore, it is possible to reduce the weight of the frame structure and improve the fuel efficiency of the automobile.

  However, high-strength steel sheets have high hardness, so that formability is poor, and cracks may occur in the bent portions, or the angle of the bent portions may spread due to springback after press forming. For this reason, when forming a frame structure using a high-strength steel plate, it is dealt with by performing bending by pressing several times or by loosening the bent part (increasing the radius of curvature). Is the actual situation. Dividing the press work into a plurality of times is not preferable because the number of steps increases. Moreover, since the rigidity of a frame structure will fall when a bending part is made loose, it will be necessary to increase the thickness of a steel plate and to raise rigidity, and will cause the increase in a weight.

  The problem to be solved by the present invention is to provide a forming method capable of accurately forming into a desired shape without increasing man-hours and weight even when the frame structure is formed of a high-tensile steel plate. is there.

  In order to solve the above-mentioned problems, the present invention is a method for forming a frame structure by bending a steel sheet, and forming a fragile part in the steel sheet, and forming the steel sheet by pressing. Provided is a frame structure forming method that is performed in order through a bending step of bending at the fragile portion and a welding step of reinforcing the fragile portion by welding.

  As described above, in the frame structure forming method of the present invention, the fragile portion (slit or the like) is formed in the steel plate prior to the bending step. Since the weak part has a lower strength and rigidity than other regions and can be easily bent, the formability of the bent part can be improved by bending the steel plate at the weak part. As a result, it is possible to prevent cracking at the bent portion, and to reduce the spring back after the bending and accurately form the bent portion at a desired angle. In general, since the frame structure is required to have high strength and high rigidity, the formation of the fragile portion in the steel sheet in the manufacturing process is contrary to the characteristics required for the frame structure. When forming a frame structure with a hard material, dare to form a fragile part on a steel plate and then bend it, and then weld and strengthen the fragile part to enhance formability while giving high strength and high rigidity. Can do.

  As described above, according to the method for forming a frame structure of the present invention, even when formed with a high-tensile steel plate, the desired shape can be obtained without dividing the press work into multiple times or gradual curvature of the bent portion. Can be molded accurately.

It is a perspective view of a frame structure. It is a top view of the steel plate in which the weak part was formed. It is sectional drawing in the XX line of FIG. It is sectional drawing which shows the state which joined the upper steel plate and the lower steel plate. It is an expanded sectional view of the bending part of an upper steel plate. It is sectional drawing of the steel plate which shows the other example of a weak part.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  A frame structure 1 shown in FIG. 1 is, for example, a hollow columnar part used as a frame part (side member or the like) of an automobile, and is formed by welding a steel plate 10 having a cross-sectional hat shape and a flat plate-like steel plate 20. The In the following, for the sake of convenience, the flat steel plate 20 is arranged in the horizontal direction, and the direction perpendicular to the flat steel plate 20 will be described as the vertical direction. The steel plate 10 having a cross-sectional hat shape is referred to as the “upper steel plate 10”. 20 is referred to as “lower steel plate 20”.

  The upper steel plate 10 and the lower steel plate 20 are formed of, for example, a high-tensile steel plate having a tensile strength of 400 MPa or more, particularly an ultra-high-tensile steel plate having a tensile strength of 900 MPa or more.

  The upper steel plate 10 includes a U-shaped portion 11 that opens downward, and flange portions 12 and 13 that protrude from the lower end of the U-shaped portion 11 to both sides in the horizontal direction. Of the upper steel plate 10, the bent portions 14 on both edges of the top surface of the U-shaped portion 11 and the bent portion 15 at the boundary between the U-shaped portion 11 and the flange portion 12 include the bent portions 14, 15. A welded portion W is formed along the extending direction, and in this embodiment, the welded portion W is formed over the entire length in the longitudinal direction of the upper steel plate 10. The flange portions 12 and 13 of the upper steel plate 10 and the lower steel plate 20 are joined by an arbitrary welding method (for example, direct spot welding, indirect spot welding, series spot welding, etc.). Are integrated.

  Next, a procedure for forming the upper steel plate 10 having a hat-shaped cross section will be described. This process is performed by the molding method according to an embodiment of the present invention, and specifically, is performed through a weak part forming process, a bending process, a structure joining process, and a weak part welding process.

(1) Fragile part formation process First, as shown in FIG. 2, the weak part 30 is formed on bending plan part 14 ', 15' of flat steel plate 10 '. For example, as shown in FIG. 3, the fragile portion 30 is a slit having a very small width that penetrates the steel plate 10 ′ in the thickness direction and extends in the extending direction of the portions 14 ′ and 15 ′ to be bent (vertical direction in FIG. 2). Can be configured. In this case, the flat plate shape is maintained without completely dividing the steel plate 10 ′ by forming the fragile portions 30 (slits) in the region excluding both end portions of the planned bending portions 14 ′ and 15 ′ of the steel plate 10 ′. Therefore, the subsequent bending process can be performed without hindrance. In this embodiment, since the weak part 30 is further formed in the area | region except the center part of bending plan part 14 ', 15', the flat plate shape of steel plate 10 'can be maintained more reliably. In addition, this weak part formation process may be performed after the blanking process (the process of cutting out steel plate 10 'of a predetermined magnitude | size from a coil-shaped steel plate), and may be performed simultaneously with a blanking process.

(2) Bending process The steel plate 10 'having the cross-sectional hat shape is formed by bending the steel plate 10' on which the fragile portion 30 is formed along the planned fold portions 14 'and 15', that is, along the fragile portion 30 by pressing or the like. Form. As described above, since the formability of the bent portions 14 and 15 is improved by bending the steel plate 10 'with the weakened portion 30 having low strength and rigidity, the occurrence of cracks and springback in the bent portions 14 and 15 is suppressed. The bending portions 14 and 15 can be accurately formed by the press working. Thereby, the design which makes the curvature radius in the bending parts 14 and 15 small becomes possible, and since the rigidity of the frame structure 1 can be improved, the upper steel plate 10 can be made thin and weight reduction can be achieved. Further, in this bending step, even if a crack occurs in the bent portions 14 and 15, a crack can be generated on the bent portions 14 and 15 starting from the fragile portion 30. Can easily repair cracks.

(3) Structure joining step The flange portions 12 and 13 of the upper steel plate 10 thus formed into a hat shape are fixed to predetermined positions on the lower steel plate 20 by welding (see P portion in FIG. 4). At this time, the bent portions 14 and 15 of the upper steel plate 10 are allowed to be slightly deformed because the fragile portion 30 is formed, and the bending angle can be finely adjusted. Thereby, for example, as shown by a chain line in FIG. 4, even when the shape of the upper steel plate 10 is slightly different from the predetermined shape (the shape shown by the solid line in FIG. 4), the angle of the bent portions 14 and 15 is changed. By changing the shape of the upper steel plate 10, the upper steel plate 10 can be accurately joined to a predetermined position.

(4) Weak zone welding step As described above, after the upper steel plate 10 and the lower steel plate 20 are joined to form the shape of the hollow columnar frame structure 1, the bent portion 14 of the upper steel plate 10, By welding 15 fragile portions 30 to form welded portions W, the fragile portions 30 are reinforced. Specifically, for example, the slit is filled by arc welding to restore the state before slit formation (see FIG. 5). In this embodiment, welding is performed from the outside of the frame structure 1, and the welded portion W is provided over the entire length in the longitudinal direction of the bent portions 14 and 15 (see FIG. 1). At this time, as shown in FIGS. 5A and 5B, if the thickness of the bent portions 14 and 15 is increased at the welded portion W, the strength and rigidity of the frame structure 1 can be further increased. Thus, the frame structure 1 is completed. Although heat distortion occurs in the upper steel plate 10 due to heating in this welding process, since the upper steel plate 10 is joined to the lower steel plate 20 and the shape of the frame structure 1 has already been determined, Deformation of the frame structure 1 due to thermal strain can be suppressed.

  The present invention is not limited to the above embodiment. For example, in the above embodiment, the case where the weakened portion 30 formed in the steel plate 10 ′ is configured by a slit (see FIG. 3) is not limited to this, but, for example, a notch (see FIG. 6A) or Fragile part by stepped part (see FIG. 6 (b)), V-shaped groove (see FIG. 6 (c)), or a concave groove (see FIG. 6 (d)) having a rectangular section 30 can also be configured. In these cases, the bent portions 14 and 15 are reinforced (not shown) by closing the notch with the welded portion W or increasing the thickness of the locally thin portion such as a stepped portion, V-shaped groove, or recessed groove. In addition, in the case of the weak part 30 shown to FIG.6 (b)-(d), since steel plate 10 'is connected without parting by the weak part 30, it is not necessarily bend | folded part 14', like above-mentioned embodiment. It is not necessary to form the fragile portion 30 in the region excluding both end portions of 15 ′, and the fragile portion 30 can also be formed over the entire length of the planned folding portions 14 ′ and 15 ′ of the steel plate 10 ′.

  Moreover, in said embodiment, although the welding part W is formed over the full length direction of the upper steel plate 10, it is not restricted to this, For example, as shown in FIG. 2, the weak part 30 is formed in a part of longitudinal direction. When doing, you may form the welding part W only in the formation part of this weak part 30. FIG.

  Moreover, although the case where the weak part 30 and the welding part W are formed in both the bending parts 14 and 15 of the hat-shaped steel plate 10 is shown in the above embodiment, the weak part and the welding part are not necessarily provided in all the bending parts. There is no need to form. For example, since the bent portion 14 on the top surface side is more likely to crack than the bent portion 15 on the flange portion side, the weakened portion and the welded portion may be formed only on the bent portion 14 on the top surface side.

1 Frame structure 10 Upper steel plate (hat shape)
11 U-shaped part 12, 13 Flange part 14, 15 Bent part 14 ', 15' Planned part 20 Lower steel plate (flat plate)
30 Weak zone W Weld zone

Claims (1)

A method for forming a frame structure by bending a steel plate,
A frame structure forming method that is performed through a fragile portion forming step of forming a fragile portion on a steel plate, a bending step of bending the steel plate at the fragile portion by pressing, and a welding step of reinforcing the fragile portion by welding.

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