JP2020121336A - Method for manufacturing vehicle structure member - Google Patents

Abstract

To reduce a shear stress generated on a welding point by bending with an inexpensive method.SOLUTION: A method for manufacturing a vehicle structure member that has a top plate part and two vertical wall parts, has a long-sized shape having a U-shaped cross section or hat-shaped cross section and has bending between the top plate part and the respective vertical wall parts includes: a step of welding first and second steel plate members curved in the same direction as a bending direction of the bending in at least the vertical wall parts by a welding part, thereby forming an overlapping blank material; and a step of press molding the welded overlapping blank material, thereby forming the vehicle structure member having the bending.SELECTED DRAWING: Figure 3

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a vehicle structural member, and more particularly, to an elongated shape having a U-shaped cross section or a hat-shaped cross section having a top plate portion and two vertical wall portions. The present invention relates to a method for manufacturing a vehicle structural member having a bend between a portion and each vertical wall portion.

Structural members formed into various shapes by hot pressing or cold pressing are used for vehicles. In order to reduce the weight of such a structural member, the necessary thickness may be locally reinforced instead of increasing the overall plate thickness. For example, a pillar (particularly a center pillar) of an automobile is a member that is required to have strength against a side impact, and an upper portion that curves along the outer shape of the automobile is often reinforced. More specifically, the pillar is usually constructed by welding an outer member and an inner member so as to form a closed cross section, and the outer member is locally reinforced.

In order to manufacture such a locally reinforced structural member, for example, a method in which a main body member (for example, an outer member) and a reinforcing member are separately press-molded and then welded to each other, or a blank material and a reinforcing material to be a main body are used. There is a method called patchwork in which press blanking is performed on a product obtained by overlapping and welding a blank material for use (called a superposed blank material or a patchwork blank material). Generally, according to the latter patchwork method, since the main body member and the reinforcing member are molded in a single pressing step, the cost for the mold can be suppressed, and the overlapping surfaces are prepared for welding. It has the advantage that it is not necessary. Structural members manufactured by such a method are described in Patent Documents 1 to 3 below, for example.

JP, 2016-124029, A JP, 2013-128955, A JP, 2014-028379, A

In the patchwork method, the main body member and the reinforcing member are already constrained at multiple welding points at the time of press forming.Therefore, when bending, the members inside the bend are in The members on the outside and the outside tend to be pulled in the in-plane direction. Therefore, shear stress occurs in the nugget at the welding point. It is conceivable to increase the spot welding nugget diameter in order to prevent the welded part from being broken by this stress before press forming is completed. However, this method increases power and pressurization time required for welding, and is expensive. Therefore, it is desired to reduce the shear stress generated at the welding point by bending by an inexpensive method.

One aspect of the present invention is an elongated shape having a U-shaped cross section or a hat-shaped cross section having a top plate portion and two vertical wall portions, and is bent between the top plate portion and each vertical wall portion. A method of manufacturing a vehicle structural member having a laminated blank material by welding first and second steel plate members curved in the same direction as the bending direction of the bend at a welded portion at least in the vertical wall portion. And a step of forming the vehicle structural member having the bend by press-forming the welded laminated blank material.

Depending on the embodiment, the method further includes a step of superimposing the flat plate-shaped first and second steel plate members, and holding the superposed first and second steel plate members in a curved state in the welding process. While welding.

Depending on the embodiment, the method further includes a step of forming the first and second steel plate members into a curved shape by plastic working, and the curved first and second steel plate members are overlapped in the welding process. Weld in the state.

In some embodiments, hot pressing is performed in the press-forming step.

Depending on the embodiment, the vehicle structural member is a center pillar or bumper reinforcement, the second steel plate member is a reinforcing member for reinforcing the first steel plate member, in the welding step The first and second steel plate members are curved in a direction in which they are convex toward the first steel plate member.

According to each embodiment, by welding in a curved state, the strain caused by the difference in the line length between the restraint portions of the two steel plate members during bending by the subsequent press is suppressed, and the shear stress generated at the welding point is suppressed. Can be reduced.

It is a side view of a center pillar of a car as one embodiment, and an inner member is removed. It is sectional drawing in the II-II line of the center pillar of FIG. As one embodiment, it is sectional drawing explaining the manufacturing method of forming a superposed blank material by superposing two blank materials and welding them while keeping them in a curved state by a jig. As another embodiment, it is a cross-sectional view illustrating a manufacturing method in which two blanks are plastically worked into a curved shape in advance, and the blanks are overlapped and welded to form a superposed blank. It is a figure explaining generation|occurrence|production of the shear stress of a welding part by bending, and the effect by using a curved laminated|blank blank material.

Hereinafter, various embodiments of the present invention will be described with reference to the drawings. It should be noted that, in the following embodiments, parts that do not substantially differ are given the same or similar reference numerals to avoid repetition of description.

FIG. 1 is a view of an outer member 12 of a center pillar 10 (B pillar) of an automobile as one embodiment as viewed from the inside of the vehicle. As other embodiments, various vehicle structural members having a long shape having a U-shaped cross section or a hat-shaped cross section such as bumper reinforcement may be considered as the other embodiments, but the center pillar 10 is basically taken as an example below. To explain.

As shown in FIG. 2, the center pillar 10 is basically configured by combining an outer member 12 and a inner member 14 which are steel plate members so as to form a closed cross section. An exterior member (not shown) of an automobile called a side member is attached to the outside of the center pillar 10. The outer member 12 is usually a top plate portion 18 that is directed to the vehicle exterior side, two vertical wall portions 20 that extend from the end thereof to the same side (vehicle interior side), and a flange that extends away from the end of the vertical wall portion 20. With a portion 22 and having a generally hat-shaped cross section. As shown in FIGS. 1 and 2, a patch member 16 for partial reinforcement is attached to the inside of the outer member 12 if necessary. The patch member 16 is arranged so as to hang from the top plate portion 18 to a part of the vertical wall portions 20 on both sides.

In order to manufacture such a center pillar 10, in the present application, a patchwork method is used, and a blank material for the outer member 12 made of steel plates and a blank material (reinforcement blank material) for the patch member 16 having a small area are preliminarily superposed. It is welded in the state of being formed, and this is press-formed into a desired shape. As the steel plate, a plated steel plate such as an Al-Si plated steel plate or a bare material without plating can be used depending on the rust prevention performance required for the component.

FIG. 3 shows a method of manufacturing the center pillar 10 as one embodiment. However, in this figure, the flange portion 22 of the outer member 12 is omitted. First, as shown in FIGS. 3(A) and 3(B), flat plate-shaped blank materials of the outer member 12 and the patch member 16 are overlapped and a vertical wall in a final press molding process using a plurality of jigs 40. The portion 20 is elastically bent in the same direction as the bending. The bending in the same direction here means that the convex direction of the curve is directed to the same side as the convex direction of the bending. The radius of curvature at this time can be set to 2000 mm, for example. Next, as shown in FIG. 3C, the two blank materials are welded at a plurality of welding points W while being held in a curved state by the jig 40, and the superposed blank material (patchwork blank material) 24 is obtained. Form. In each figure, the position of each welding spot by spot welding is indicated by an X mark. Instead of spot welding, any appropriate welding method such as laser welding can be used. As the jig 40 for bending the blank material, a jig generally used for welding is used, and it can be operated by air pressure or hydraulic pressure. When the welding is completed, the blank materials of the outer member 12 and the patch member 16 are constrained to each other by a plurality of welding points, so that the curved shape may be maintained to some extent even if the load by the jig 40 is removed, but it is almost flat. It may return to the top. It is possible to bend the two steel plate members with the same ease as a clamp normally performed in the welding process. Finally, the curved superposed blank material 24 is press-formed into a desired shape as shown in FIG. The press molding may be performed hot (press quench) or cold. Specifically, the stacking blank material 24 is set on the lower mold 50, and the top plate portion 18 is pressed by the central upper mold 52 that comes into contact with the top die portion 18, and then the vertical wall portion 20 is placed on both sides. Bend down with the mold 54. Instead of dividing the central upper mold 52 and the upper and lower molds 54 on both sides, pressing the top plate portion 18 and pressing and bending the vertical wall portion 20 may be sequentially performed using an integrated upper mold. Then, as shown in FIG. 2, the inner member 14 is welded to the flange portion 22 of the outer member 12 to form the center pillar 10 having a closed cross section. When the outer member and the reinforcing member, which are separately press-molded, are stacked, it is difficult to bring them into close contact, especially when a high-strength material is used, because of variations in molding accuracy. Therefore, an extra structure is required such as setting a plurality of welding seat surfaces for each reinforcing point on the reinforcing member. However, when the patchwork method is used as described above, the outer member 12 and the patch member 16 can be brought into close contact with each other by pressing.

FIG. 4 shows a method of manufacturing the center pillar 10 as another embodiment. However, in this figure, the flange portion 22 of the outer member 12 is omitted. First, as shown in FIGS. 4A and 4B, the blank materials of the outer member 112 and the patch member 116 are individually set in a mold, and the vertical wall portion 20 is bent in the final press molding process. Plastic-work into a curved shape by pressing in the same direction. The curved shape can also be formed by plastic working other than pressing. It is preferable that the outer member 112 and the patch member 116 have substantially the same curved shape of the blank material. Therefore, it is possible to use the same mold for two blanks in some cases. The radius of curvature of the two blanks can be set to, for example, about 200 mm in consideration of the springback amount due to unloading. Next, as shown in FIG. 4C, the curved outer member 112 and the blank material of the patch member 116 are overlapped and spot-welded at a plurality of welding points W to form a curved overlapped blank material 124. .. Note that instead of spot welding, any suitable welding method such as laser welding can be used. At the time of welding, a blank material for the outer member 112 and the patch member 116 is appropriately clamped by a jig (not shown). Finally, the curved overlapping blank material 124 is press-molded as shown in FIG. 4(D) to have a desired shape. This last press-molding step can be performed in the same manner as the method described above with reference to FIG.

In any of the methods described above, the overlapping blank materials 24 and 124 before the final press molding are curved in the same direction as the direction in which the vertical wall portion 20 is bent. When the curved superposed blank material 24 is further bent in the press forming step, the outer member 12 and the patch member 16 are restrained from each other by the central upper die 52 in the top plate portion 18 as shown in FIG. 5(A). The vertical wall portions 20 are restrained from each other by the welded portions 32. Therefore, as the bending progresses, a line length difference occurs between the outer member 12 and the patch member 16 between these restraint portions. This causes the patch member 16 on the inside of the bend to be compressed and the outer member 12 on the outside to be pulled. Initially, the stress concentrates at the terminal end of the top plate portion 18 to be constrained and the center of the welding spot, but thereafter, as shown in FIG. 5B, shear stress as indicated by an arrow occurs in the weld portion 32. However, as shown in FIG. 5(A), the overlapping blank material 24 used here was already curved at the time of welding in the same direction as the direction in which the vertical wall portion 20 is bent. The shearing stress generated at the welding point is reduced as compared with the case of pressing a laminated blank formed by welding. For example, two blanks having plate thicknesses of 2.0 mm and 1.8 mm, respectively, are overlapped and curved with a constant radius of curvature R=2000 mm, and two welding points separated by 200 mm from each other while maintaining the curved state. Consider the case of welding. At this time, the difference in line length between the welding points on the neutral surfaces of the two steel plate members due to the bending is about 0.2 mm. Therefore, if one bend is formed between the welding points of this superposed blank material in the final press forming, the shear stress corresponding to this 0.2 mm line length difference is reduced compared to the case of welding in the flat plate state. Will be. Although not shown, the patch member 16 may be attached to the outside of the outer member 12 in some cases. In this case as well, by using the curved overlapping blank material as in the above case, it is possible to obtain the effect of reducing the shear stress generated at the welding point. Although the bending direction of the flange portion 22 (not shown in FIG. 5) is opposite to the bending direction of the superposed blank material 24, the patch member 16 does not extend to the flange portion 22 and there is no welding spot on the flange portion 22. Therefore, of course, it does not matter.

Although the present invention has been described with reference to specific embodiments, the present invention is not limited to these embodiments, and those skilled in the art can make various substitutions and improvements without departing from the object of the present invention. It is possible to make changes.

10 Center Pillar 12 Outer Member 14 Inner Member 16 Patch Member 18 Top Plate Part 20 Vertical Wall Part 22 Flange Part 24 Laminated Blank Material 32 Welded Part 40 Jig W Welding Point

Claims (5)

A vehicle structural member having a long shape having a U-shaped cross section or a hat-shaped cross section having a top plate portion and two vertical wall portions and having a bend between the top plate portion and each vertical wall portion is manufactured. Method,
A step of forming a superposed blank material by welding first and second steel plate members curved in the same direction as the bending direction of the bend at a welded portion at least in the vertical wall portion,
Forming the vehicle structural member having the bend by press forming the welded laminated blank. The method of claim 1, wherein
Further comprising a step of superimposing the flat plate-shaped first and second steel plate members,
A method of welding while holding the superposed first and second steel sheet members in a curved state in the welding step. The method of claim 1, wherein
Further comprising a step of forming the first and second steel plate members into a curved shape by plastic working,
A method of performing welding in a state in which the curved first and second steel plate members are superposed in the welding step. The method according to any one of claims 1 to 3,
A method of forming by hot pressing in the press forming step. The method according to any one of claims 1 to 4, wherein
The vehicle structural member is a center pillar or bumper reinforcement, the second steel plate member is a reinforcing member for reinforcing the first steel plate member, the first and second in the step of welding. A method in which the steel plate member is curved in a direction such that it is convex toward the first steel plate member.

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