JP6832208B2 - Manufacturing method of pipe material - Google Patents

Description

The present invention relates to a method for producing a pipe material.

For example, some automobile parts have a closed cross-sectional shape in a direction intersecting the longitudinal direction. Examples of automobile parts having a closed cross-sectional shape include members that form a part of a vehicle body skeleton and members of a suspension device.

For example, the front side member, which is a member constituting the vehicle body skeleton, is composed of a closed cross-sectional shape member obtained by welding a flat plate-shaped member to a hat-shaped member formed so that the cross section has a hat shape. Since the hat-shaped member itself does not have a closed cross-sectional shape, it can be press-molded into a relatively complicated shape. For example, even a shape bent along the longitudinal direction can be molded relatively easily. Therefore, when one part is manufactured by joining two members such as a front side member and a center pillar, it is possible to manufacture an automobile part having a relatively complicated shape.

On the other hand, the suspension device is configured by mutually combining parts having a closed cross-sectional shape having various sizes and shapes. As the parts constituting the suspension device, a pipe material bent along the longitudinal direction is often used. Such a pipe material is generally manufactured by bending a welded pipe such as a UO pipe or an electric sewing pipe. However, the welded pipe may buckle due to the bending process, and the buckled welded pipe cannot be used as a part. Therefore, as described in Patent Document 1, an attempt is made to manufacture a bent welded pipe by U-molding a metal plate to obtain an intermediate molded product and further O-molding the intermediate molded product, and to apply this to an automobile part. Has been made.

International Publication No. 2016/043280

When molding a bent welded pipe from a metal plate as described in Patent Document 1, there is a demand for molding so that the welded portion of the welded pipe is inside the bent portion of the part. This is because the welded portion may have weaker tensile strength and fatigue strength than other portions, and therefore, it is more difficult to break the welded portion when the welded portion is arranged at a portion exposed to compressive deformation rather than tensile deformation. However, it has become clear that when the welded portion of the welded pipe is molded so as to be inside the bent portion of the part, the pipe end portion buckles during molding, causing a problem that the desired closed cross-sectional shape cannot be formed.

When observing the buckled part, it was found that the buckling occurred on the tube end side. Therefore, the inventors speculated that the cause of buckling was as follows. Buckling occurs when the corner portion that becomes the end of the pipe hits the mold and the corner portion is bent (buckled) when the intermediate molded product is O-molded. During O forming, deformation (extension flange deformation) occurs in which the line length of the cross section of the bent portion is shortened. For this reason, the time when the center of the bent portion comes into contact with the mold and the time when it is abutted are delayed from the part where the pipe ends. At this time, if the part that becomes the end of the pipe is bent, it will buckle greatly. That is, since the intermediate molded product is deformed as shown in FIG. 8 during O-molding, buckling is likely to occur at the end of the pipe.
The present invention has been made in view of the above circumstances, and an object of the present invention is to apply a method for manufacturing a pipe material in which buckling does not occur at an end portion in the longitudinal direction.

[1] The cross-sectional shape is U-shaped, the line connecting the U-shaped bisectors is curved, and the inside of the arc of the line connecting the bisectors is inside the U-shaped bent portion. Adjacent to both ends of the curved portion and the curved portion, the cross-sectional shape is U-shaped, the line connecting the U-shaped bisectors is a straight line, or the line connecting the U-shaped bisectors is said. A first molding step of press-molding a metal plate into an intermediate molded product provided with an extension portion that is a curved line with the outside of the U-shaped bent portion inside.
A second molding step of bringing the U-shaped open ends of the intermediate molded product close to each other,
The pipe making process of joining the open ends and
Equipped with a,
Manufacturing method of the after pipe process, you cut off the extension tube.
[2] The method for producing a pipe material according to claim 1, wherein the length L on one side of the extension portion of the intermediate molded product satisfies the formula (1).
L> (R + 1.25 × θ- (14 × H / t-26)) / (-0.4)… (1)
L, H, R, θ, and t in the formula (1) are as follows.
L: Length of a straight line or curved line connecting the U-shaped bisectors in the extension portion (unit: mm)
H: Height (unit: mm) of the pipe material in a cross section orthogonal to the line connecting the U-shaped bisectors.
R: Radius of curvature inside the curved portion of the pipe material (difference between the radius of curvature of the line connecting the U-shaped bisection points of the curved portion and the H) (unit: mm)
θ: Scissors angle of the curved portion (angle formed by normals of the cross section of the end of the curved portion) (unit: °)
t: Thickness of the metal plate (unit: mm)
[3] The production of the pipe material according to [1] or [2], which comprises a step of adjusting the contour shape of the U-shaped opening end of the intermediate molded product between the first molding step and the second molding step. Method .
[ 4 ] The method for manufacturing a pipe material according to any one of [1] to [3 ], wherein the pipe material is a pipe material for automobile parts.

In the present invention, an intermediate molded product having a U cross-sectional shape having extension portions on both sides in the longitudinal direction of the curved portion is manufactured, and this is molded into a closed cross-sectional shape in the second molding step. The extension portion is adjacent to both ends of the curved portion and has a U-shaped cross section. The line connecting the U-shaped bisectors of the extension portion is a straight line or a curved line with the outside of the U-shaped bent portion as the inside.
Such an extension portion is provided in order to suppress a change in the line length of the cross section on the pipe end side in the longitudinal direction. This is because the line length of the cross section of the extension portion is less likely to change than the line length of the cross section of the curved portion. By providing the extension portion, it becomes difficult for the portion to be molded at the pipe end to locally hit the mold at the initial stage of the second molding step. As a result, as shown in FIG. 9, the change in the line length of the cross section in the longitudinal direction becomes gradual, and the buckling caused by the local contact of the pipe end portion with the mold can be suppressed.
By providing the extension part, the parts on the pipe end side are butted against each other over a certain length, so the timing of the butting of the curved part in the center of the longitudinal direction is larger than the butting timing of the pipe end. Even if there is a slight delay, the part on the pipe end side will not buckle.
Further, when the extension portion is not a straight portion and is bent in the direction opposite to the bending portion, the portion to be the pipe end portion is less likely to hit the mold locally, so that buckling is less likely to occur.
As described above, in the method for producing a pipe material of the present invention, when an intermediate molded product having a curved portion is produced, extension portions are formed on both sides in the longitudinal direction of the curved portion, and then the intermediate molded product is processed and closed. The pipe material has a cross-sectional shape. By providing the extension portion, as described above, the second upper mold comes into contact with the opening end in a wide range at the initial stage of the second molding step, and buckling of the opening end is less likely to occur. As a result, according to the method for producing a pipe material of the present invention, when manufacturing a pipe material in which the joint portion is arranged inside the bending direction of the curved portion, buckling is less likely to occur at both ends in the longitudinal direction of the intermediate molded product, and the bending portion is curved. The occurrence of wrinkles in the part can be suppressed.

Further, according to the method for manufacturing a pipe material of the present embodiment, buckling at both ends in the longitudinal direction of the intermediate molded product is caused by setting the length L on one side of the extension portion of the intermediate molded product within the range satisfying the formula (1). The occurrence can be reliably suppressed and the occurrence of wrinkles in the curved portion can be prevented.

Further, by performing a step of adjusting the contour shape of the U-shaped opening end of the intermediate molded product between the first molding step and the second molding step, the opening ends are appropriately connected to each other when the second molding step is performed. It can be butted and wrinkles can be prevented.
Further, by cutting and removing the extension portion after the pipe making step, it is possible to form a desired part shape.

The perspective view which shows an example of the trailing arm used for the torsion beam type suspension apparatus. The process chart which shows the examination example of the manufacturing process of the pipe material which becomes the raw pipe of a trailing arm. The perspective view which shows a part of the pipe material manufactured by the manufacturing process shown in FIG. The perspective view explaining the 1st molding process at the time of manufacturing a pipe material. The perspective view explaining the 2nd molding process at the time of manufacturing a pipe material. It is a figure which shows the pipe material manufactured through the 1st molding process and the 2nd molding process, (a) is a perspective view, (b) (c) are cross-sections X ₁ and X _{2 of (a), respectively.} The figure which shows the cross-sectional shape in. The side view of the intermediate molded product after the first molding process. The schematic diagram explaining the relationship between the shape of the opening end of an intermediate molded article, and buckling. The schematic diagram explaining the relationship between the shape of the opening end of an intermediate molded article, and buckling. The process drawing explaining the manufacturing method of the pipe material which is an embodiment of this invention. The schematic diagram explaining the parameter of formula (1).

FIG. 1 shows a perspective view of a trailing arm 1 used in a torsion beam type suspension device as an example of an automobile part. The trailing arm 1 shown in FIG. 1 is made of a hollow tubular member formed in a substantially S shape. The trailing arm 1 has a rectangular closed cross-sectional shape at one end 1b in the longitudinal direction, and a circular closed cross section at the other end 1c in the longitudinal direction. Two curved portions 1d and 1e are provided between one end portion 1b in the longitudinal direction and the other end portion 1c in the longitudinal direction. The cross-sectional shape of the curved portion 1d is a rectangular closed cross-sectional shape similar to the cross-sectional shape of one end portion 1b in the longitudinal direction. On the other hand, the cross-sectional shape of the curved portion 1e is a circular closed cross-sectional shape similar to the cross-sectional shape of the other end portion 1c in the longitudinal direction. The cross-sectional shape between the curved portion 1d and the curved portion 1e gradually changes from a circular shape to a rectangular shape.

Conventionally, for the trailing arm 1 shown in FIG. 1, for example, a hollow tubular metal tube is prepared, curved portions 1d and 1e are provided on the metal tube by bending, and the cross-sectional shape of one end side of the metal tube is rectangular. Manufactured by molding into. However, when the metal pipe is bent, wrinkles may occur in or near the curved portions 1d and 1e. Therefore, the present inventors have studied the production of a tube material having a closed cross-sectional shape having a curved portion by press-molding a metal plate.

FIG. 2 shows an example of studying the manufacturing process of the pipe material 1a which is the raw pipe of the trailing arm 1. First, 1 g of the metal plate shown in FIG. 2 (a) is prepared. Next, as shown in FIG. 2B, as the first molding step, the metal plate 1g is formed by press molding to provide a bent portion 1h along the longitudinal direction of the metal plate at the center in the width direction of the metal plate 1g. It is molded into a U shape to make an intermediate molded product 1 m. Further, the intermediate molded product 1 m is provided with a curved portion 1n over the entire length in the longitudinal direction during press molding. Further, in the intermediate molded product 1 m, an open end 1i, which is an end portion in the width direction of the metal plate 1 g before processing, is formed. Further, the curved portion 1n is curved so that the opening end 1i is located inside the curved shape.

Next, as a second molding step, as shown in FIG. 2C, bending is performed so that the open ends 1i of the intermediate molded product 1 m are brought close to each other. Next, as a pipe making step, the pipe material 1a is obtained by joining the open ends 1i to each other and providing the joint portion 1f.

FIG. 3 is a partial perspective view of the pipe material 1a. As shown in FIG. 3, the pipe material 1a is provided with a joint portion 1f along the longitudinal direction of the pipe material 1a on the upper portion thereof. As described above, the joint portion 1f is formed by joining the open ends 1i of the intermediate molded product 1 m to each other. Examples of the joining method include welding. As shown in FIG. 3, the joint portion 1f is arranged inside the curved shape of the curved portion 1n.

The present inventors have attempted to manufacture the pipe material 1a by the manufacturing method shown in FIG. However, it was found that the method shown in FIG. 2 may cause buckling at both ends of the pipe material 1a in the longitudinal direction. Hereinafter, problems in the method for manufacturing the pipe material 1a shown in FIG. 2 will be described.

FIG. 4 is a perspective view of the first molding step when the pipe material 1a is manufactured. In the first molding step, 1 g of a metal plate to be blank is arranged between the first upper mold 2 and the wrinkle pressing pad 3 and the first lower mold 4. Next, by bringing the first upper mold 2 and the wrinkle pressing pad 3 and the first lower mold 4 closer to each other, molding processing is performed while forming a bent portion 1h on the metal plate 1g, as shown in FIG. 2B. Intermediate molded product 1 m. Both ends in the width direction of the metal plate 1 g before processing become open ends 1i. Since the intermediate molded product 1m is provided with the bent portion 1h, the cross-sectional shape in the direction orthogonal to the longitudinal direction thereof is substantially U-shaped, and the intermediate molded product 1m is curved over the entire longitudinal direction. The direction of curvature is defined by the direction of the line connecting the U-shaped bisectors (hereinafter referred to as the bisector) in the intermediate molded product 1 m. The bisector of the intermediate molded product 1 m manufactured in the process shown in FIG. 4 is bent so that the opening end 1i side is inside the curve.

Next, FIG. 5 shows a perspective view of a second molding step when the pipe material 1a is manufactured. In the second molding step, as shown in FIG. 5, the intermediate molded product 1 m is arranged between the second upper mold 5 and the second lower mold 6. Next, by bringing the second upper mold 5 and the second lower mold 6 closer to each other, the intermediate molded product 1 m is formed into a pipe material 1a.

FIG. 6A shows the manufactured pipe material 1a. Further, FIGS. 6 (b) and 6 (c) show the cross-sectional shapes of the cross- _{sections X 1} and X _{2 of FIG. 6 (a), respectively.} As shown in FIG. 6 (a) and 6 (b), the cross-sectional shape in the cross section X ₁ in the longitudinal center of the tube 1a, has a circular cross-sectional shape of interest. However, as shown in FIG. 6 (a) and FIG. 6 (c), the cross-sectional shape in the cross section X ₂ in the longitudinal ends of the tube 1a is not circular, the distorted shape circular part buckles It has become. In particular, the abutting portion between the open ends is greatly distorted.

The cause of buckling at the longitudinal end of the pipe material 1a is that when the opening ends 1i are butted against each other in the second molding step, the both ends k1 of the opening end 1i hit the second upper mold 5. This is because the opening ends 1i were butted while being bent and deformed and buckled.

FIG. 7 shows a side view of the intermediate molded product 1 m before the second molding step. Further, FIG. 7 shows the position of the opening end 1i after the second molding step by a chain double-dashed line. When the length of the opening end 1i before the second molding step is q1, the length q2 of the opening end 1i after the second molding step is longer than the length q1 before molding. That is, the opening end 1i is pulled along the longitudinal direction by the second molding step, and the tensile stress is concentrated on the central portion of the opening end 1i in the longitudinal direction. When tensile stress is concentrated in the central portion of the opening end 1i and the material in this portion is stretched, the material is shrunk by the amount stretched in the longitudinal direction in the circumferential direction orthogonal to the longitudinal direction of the opening end 1i. On the other hand, the longitudinal end portion of the intermediate molded product is hardly deformed as compared with the longitudinal central portion. Therefore, the end portion in the longitudinal direction does not shrink and deform in the circumferential direction. FIG. 8 illustrates this situation.

As shown in FIG. 8, in the intermediate molded product being processed in the second molding step, the material shrinks in the circumferential direction at the central portion in the longitudinal direction, while the shape of the material does not change significantly at the end portion in the longitudinal direction.
Therefore, the height difference of the opening end 1i during the second molding step is widened, and the angle of the tip of the longitudinal end portion k1 of the opening end 1i is reduced from ψ1 to ψ2. As a result, when the second upper mold first contacts the intermediate molded product, it easily hits only the longitudinal end portion k1 of the opening end 1i. In FIG. 8, the contact range of the second upper die is shown by a two-dot chain line circle. As a result, the corner portion of the longitudinal end portion k1 is likely to buckle, and buckling is likely to occur at the longitudinal end portion of the pipe material.

Therefore, as shown in FIG. 9, the inventors prevent the second upper mold from contacting only the longitudinal end k1 of the opening end 1i by keeping both ends in the longitudinal direction of the intermediate molded product away from the curved portion. I tried to do it. As shown in FIG. 9, the amount of shrinkage of the material in the central portion in the longitudinal direction of the intermediate molded product being processed in the second molding step is not significantly different from that in the case of FIG. 8, but the length of the intermediate molded product. By lengthening and moving the positions of both ends k1 in the longitudinal direction away from the curved portion, the height difference of the opening end 1i during the second molding process becomes smaller, and the change in the angle of the tip of the end k1 in the longitudinal direction changes from ψ3. It will be a slight change to ψ4. Therefore, the contact range of the second upper die is expanded to the range indicated by the ellipse of the alternate long and short dash line in FIG. 9, and the contact range is clearly wider than that in the case of FIG. As described above, by expanding the contact range of the second upper mold in the intermediate molded product, the tip of the longitudinal end portion k1 is less likely to buckle, and the longitudinal end portion of the pipe material is less likely to buckle.

Hereinafter, embodiments of the present invention will be described.
The method for manufacturing a pipe material for an automobile part of the present embodiment is a first molding step of press-molding a metal plate to obtain a U-shaped intermediate molded product, and a closed cross-sectional shape by bringing the open ends of the intermediate molded product into contact with each other. It is composed of a second molding process for molding and a pipe making process for joining the open ends to each other. The intermediate molded product molded in the first molding step has a curved portion and linear or curved extension portions at both ends in the longitudinal direction of the curved portion. By providing extension portions at both ends in the longitudinal direction of the intermediate molded product, it becomes possible to suppress the occurrence of buckling in the intermediate molded product. Hereinafter, this embodiment will be described with reference to the drawings.

First, as shown in FIG. 10A, the metal plate 11 is prepared. The material of the metal plate 11 is not particularly limited, and examples thereof include steel, pure aluminum, aluminum alloy, copper, and copper alloy. However, a steel plate or an aluminum alloy plate is preferable for use as an automobile part. Further, the thickness of the metal plate 11 is preferably 4 mm or less, for example. The metal plate 11 shown in FIG. 10A preferably has a sufficient length for obtaining an intermediate molded product having a curved portion and an extending portion. Further, the plan view shape of the metal plate 11 may be a simple rectangle, but it may be formed into a predetermined shape in advance in order to omit the trim step described later.

Next, as shown in FIG. 10B, in the first molding step, the metal plate 11 is press-molded using the first upper die, the first lower die, and the wrinkle pressing pad (not shown) to perform intermediate molding. Product 12 is manufactured. More specifically, the metal plate 11 is formed into a U shape by providing a bent portion 11a along the longitudinal direction of the metal plate at the center in the width direction of the metal plate 11 to obtain an intermediate molded product 12. Further, the intermediate molded product 12 is provided with a curved portion 12a at the central portion in the longitudinal direction during press molding. Further, linear extension portions 12b are provided on both sides of the curved portion 12a in the longitudinal direction. The length L of the extension portion 12b will be described later. Further, an open end 12c is formed in the intermediate molded product 12. The open end 12c is the end portion in the width direction of the metal plate 11 before processing. The open end 12c extends along the longitudinal direction of the intermediate molded product 12.

The cross-sectional shape of the intermediate molded product 12 is U-shaped over the entire longitudinal direction. That is, the cross-sectional shapes of the curved portion 12a and the extending portion 12b are U-shaped. There is a bent portion 11a at a portion corresponding to the bottom portion of the U shape, and an opening end 12c at the upper portion of the U shape. In the curved portion 12a, the line 12f connecting the U-shaped bisectors is curved toward the inside of the bent portion 11a. That is, the inside of the arc formed by the line 12f connecting the U-shaped bisectors is the inside of the bent portion 11a. Further, in the extension portion 12b, the line 12f connecting the U-shaped bisectors is a straight line. The extension portion 12b is not limited to a straight line, and may be curved in a direction opposite to the bending direction of the curved portion 12a. The line 12f connecting the U-shaped bisectors in this case curves toward the outside of the U-shape.

Further, the extension portions 12b must be provided on both sides of the curved portion 12a in the longitudinal direction. If the extension portion 12b is provided only on one side of the curved portion 12a, buckling will occur at the end portion of the curved portion 12a on the side where the extension portion 12b is not provided, which is not preferable.

The cross-sectional shape of the bent portion 11a is a semicircular shape in the example shown in FIG. 10B, but it is not limited to the arc shape, and may be an elliptical shape or a shape having a corner portion. Other shapes may be used. Further, two extension portions 12b are formed on both sides of the curved portion 12a in the longitudinal direction, but the lengths of the extension portions 12b may be the same or different as long as the conditions described later are satisfied. There may be. Further, both of the extension portions 12b shown in FIG. 10B are linear, but the present invention is not limited to this, and even if one or both extension portions are curved to the opposite side to the curved portion 12a. Good.

After the first molding step, a trim step for adjusting the contour shape of the opening end 12c may be performed. Since the intermediate molded product 12 after the first molding step has undergone bending and drawing, the amount of deformation as a whole is relatively large, and the contour shape of the opening end 12c may be disturbed. If the next second molding step is performed while the contour shape of the opening end 12c is disturbed, the opening ends 12c cannot be properly abutted against each other over the entire length of the intermediate molded product 12, and the opening ends 12c are between the opening ends 12c. A gap may be formed, or the opening ends 12c may partially overlap each other. By performing the trim step as necessary and adjusting the contour shape of the opening ends 12c, the opening ends 12c can be appropriately butted against each other in the second molding step. Moreover, the trim step may be omitted. For example, the trim step can be omitted by molding the shape of the metal plate into a predetermined shape in advance or by performing the first molding step in anticipation of the amount of deformation of the metal plate 11 in the first molding step.

Next, as shown in FIG. 10C, in the second molding step, the second upper mold and the second lower mold (not shown) are used, and the intermediate molded product 12 is used over the entire length in the longitudinal direction of the intermediate molded product. Bending is performed to bring the open ends 12c closer to each other. Since there are extension portions 12b on both sides of the curved portion 12a in the longitudinal direction, the position of the longitudinal end portion of the opening end 12c is separated from the curved portion 12a, whereby in the second molding step, the longitudinal direction of the opening end 12c of the intermediate molded product The angle change at the tip of the end is reduced. Therefore, the second upper die comes into contact with not only the longitudinal end of the opening end but also the opening end near the center, and buckling of the opening end is less likely to occur.

The length L of the extension portion 12b is not particularly limited, but a more preferable length of the extension portion 12b can be expressed by the following formula (1). The following equation (1) was experimentally obtained, and it has been confirmed that buckling can be prevented more reliably by satisfying the equation (1).

L> (R + 1.25 × θ- (14 × H / t-26)) / (-0.4)… (1)

In the formula (1), L is the length of the straight line 12f or the curved line 12f connecting the U-shaped bisection points in the extension portion 12b (unit: mm), and H is the longitudinal direction of the pipe member 13. It is the height in the orthogonal direction (unit: mm), and R is the radius of curvature inside the curved portion 12a of the pipe material 13 (the radius of curvature of the line 12f connecting the U-shaped bisection points of the curved portion 12a and the above H). (Difference from) (unit: mm), θ is the sandwiching angle of the curved portion 12a (angle formed by the normals of the cross section of the curved portion 12a) (unit: °), and t is the metal. The plate thickness of the plate 11 (unit: mm). FIG. 11 shows L, H, R, and θ, respectively.

Next, as a pipe making step, the open ends 12c are joined to each other to provide a joint portion 12d. In this way, the pipe material 13 is manufactured.

Further, as shown in FIG. 10D, the extension portion 12b may be cut and removed from the pipe material 13 after the pipe making step. As shown in FIG. 10D, the two extension portions 12b on both sides of the curved portion 12a may be cut and removed, or one extension portion 12b may be left and the other extension portion 12b may be cut and removed. .. The cutting and removal of the extension portion 12b may be appropriately selected according to the shape of the target automobile part.

The extension portion 12b in the present embodiment is provided in order to suppress a change in the line length of the cross section on the pipe end side in the longitudinal direction. This is because, as described above, the line length of the cross section of the extension portion 12b is less likely to change than the line length of the cross section of the curved portion 12a. By providing the extension portion 12b, it becomes difficult for the portion to be molded at the pipe end to locally hit the mold at the initial stage of the second molding step. As a result, as shown in FIG. 9, the change in the line length of the cross section in the longitudinal direction becomes gradual, and the buckling caused by the local contact of the pipe end portion with the mold can be suppressed.
Further, by providing the extension portion 12b, the portions on the pipe end side are butted against each other over a certain length, so that the timing of the butting of the curved portion in the center in the longitudinal direction is the butting of the pipe end. Even if it is slightly behind the timing, the part on the pipe end side does not buckle.
Further, when the extension portion 12b is not a straight portion and is bent in the direction opposite to the bending portion, the portion to be the pipe end portion is less likely to hit the mold locally, so that buckling is less likely to occur.

In the method for manufacturing a pipe material of the present embodiment, when the intermediate molded product 12 having the curved portion 12a is manufactured, extension portions 12b are formed on both sides in the longitudinal direction of the curved portion 12a, and then the intermediate molded product 12 is processed. The tube material 13 has a closed cross-sectional shape. By providing the extension portion 12b, as described above, in the initial stage of the second molding step, the second upper mold comes into contact with not only the longitudinal end portion of the opening end but also a wide area including the longitudinal end portion. Therefore, buckling of the open end is less likely to occur. As a result, according to the method for producing the pipe material of the present embodiment, buckling is less likely to occur at both ends in the longitudinal direction of the intermediate molded product 12, and the occurrence of wrinkles at the curved portion can be suppressed.

Further, according to the method for manufacturing a pipe material of the present embodiment, by setting the length L on one side of the extension portion 12b of the intermediate molded product 12 to a range satisfying the formula (1), the length L at both ends in the longitudinal direction of the intermediate molded product 12 The occurrence of buckling can be reliably suppressed, and the occurrence of wrinkles in the curved portion can be prevented.

Further, by performing a trim step for adjusting the contour shape of the U-shaped opening end 12c of the intermediate molded product 12 between the first molding step and the second molding step, the opening end 12c is performed when the second molding step is performed. It is possible to properly match each other and prevent the occurrence of wrinkles.
Further, by cutting and removing the extension portion 12b after the pipe making step, it is possible to form a desired part shape.

The method for manufacturing a pipe material of the present embodiment can be applied to, for example, a method for manufacturing a pipe material for an automobile part, for example, a method for manufacturing a trailing arm used in a torsion beam type suspension device, and molding a metal plate. Since the trailing arm can be manufactured by the above method, it is possible to manufacture a trailing arm having less defective appearance as compared with the case of bending a conventional metal tube. Further, since the trailing arm can be made into a hollow closed cross-section part, it can contribute to the weight reduction of the automobile.

Hereinafter, the present invention will be described in more detail with reference to Examples.
A steel sheet having a plate thickness of 3.6 mm and a tensile strength of 440 MPa was prepared, and the first forming step was performed in the same manner as in FIG. 10B to process the steel sheet into an intermediate molded product having a predetermined shape. There are two types of intermediate molded products, one consisting of only a curved portion and the other having a curved portion and an extension portion. The extension portions were provided so as to be adjacent to both sides in the longitudinal direction of the curved portion. All extensions are straight. Next, in the same manner as in FIG. 10C, a second molding step was performed, processing was performed to bring the open ends of the intermediate molded product close to each other, and then the open ends were butted against each other and welded to produce a pipe material. .. The appearance of the obtained pipe material was visually confirmed, and it was evaluated whether or not appearance defects such as wrinkles had occurred. The poor appearance was evaluated in the following two stages. ◯: No wrinkles. ×: Wrinkles occur. The results are shown in Table 1.

The value on the right side of the equation (1) in Table 1 was (R + 1.25 × θ- (14 × H / t-26)) / (−0.4). H is the height (unit: mm) in the direction orthogonal to the longitudinal direction of the pipe material, and R is the radius of curvature inside the curved portion of the pipe material (the radius of curvature of the line connecting the U-shaped bisection points of the curved portion). Difference from H) (Unit: mm), θ is the sandwiching angle of the curved portion (angle formed by the normals of the cross section of the curved portion) (Unit: °), t is the plate thickness of the metal plate (unit: °) Unit: mm).
Further, the length L of the extension portion is the length of the line connecting the U-shaped bisectors in the extension portion (unit: mm).

As shown in Table 1, in Examples 1 to 6, since the extension portions adjacent to the curved portions were provided on both sides of the curved portion of the intermediate molded product in the longitudinal direction, the pipe material did not wrinkle and the appearance was poor. There wasn't.
On the other hand, in Comparative Examples 1 to 6, wrinkles were generated in the pipe material, resulting in poor appearance. Since the extension portions were not provided in Comparative Examples 1, 3 and 5, wrinkles due to buckling generated during the second molding step were generated at both ends in the longitudinal direction of the pipe material. Further, in Comparative Examples 2, 4 and 6, the extension portion was provided, and the length L was not sufficient, so that wrinkles were generated as in the other Comparative Examples.

11 ... Metal plate, 11a ... Bent part, 12 ... Intermediate molded product, 12a ... Curved part, 12b ... Extension part, 12c ... Open end, 12f ... Line connecting bisectors, 13 ... Pipe material.

Claims (4)

The cross-sectional shape is U-shaped, the line connecting the U-shaped bisectors is curved, and the inside of the arc of the line connecting the bisectors is inside the U-shaped bent portion. Adjacent to both ends of the curved portion, the cross-sectional shape is U-shaped, the line connecting the U-shaped bisectors is a straight line, or the line connecting the U-shaped bisectors is the U-shape. A first molding step of press-molding a metal plate into an intermediate molded product provided with an extension portion that is a curved line with the outside of the bent portion inside.
A second molding step of bringing the U-shaped open ends of the intermediate molded product close to each other,
The pipe making process of joining the open ends and
Equipped with a,
Manufacturing method of the after pipe process, you cut off the extension tube. The method for manufacturing a pipe material according to claim 1, wherein the length L on one side of the extension portion of the intermediate molded product satisfies the formula (1).
L> (R + 1.25 * θ- (14 * H / t-26)) / (-0.4) ... (1)
L, H, R, θ, and t in the formula (1) are as follows.
L: Length of a straight line or curved line connecting the U-shaped bisectors in the extension portion (unit: mm)
H: Height (unit: mm) of the pipe material in a cross section orthogonal to the line connecting the U-shaped bisectors.
R: Radius of curvature inside the curved portion of the pipe material (difference between the radius of curvature of the line connecting the U-shaped bisection points of the curved portion and the H) (unit: mm)
θ: Scissors angle of the curved portion (angle formed by normals of the cross section of the end of the curved portion) (unit: °)
t: Thickness of the metal plate (unit: mm) The method for producing a pipe material according to claim 1 or 2, further comprising a step of adjusting the contour shape of the U-shaped opening end of the intermediate molded product between the first molding step and the second molding step. The method for manufacturing a pipe material according to any one of claims 1 to 3 , wherein the pipe material is a pipe material for automobile parts.

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