Side member made for vehicle

Abstract

The present invention provides a side member for a vehicle, which can increase energy absorption capacity by inducing a stable crushing shape and at the same time has a structure with high mass producibility, the side member comprising: a first tubular shape portion which extends in the lengthwise direction and has a hexagonal cross-sectional shape; a second tubular shape portion which is connected to the first tubular shape portion, extends in the lengthwise direction, and has a hexagonal cross-sectional shape; and welding portions which are formed on the outer walls of the first tubular shape portion and the second tubular shape portion, wherein the first tubular shape portion and the second tubular shape portion are integrally formed by bending a single first plate.

Description

Vehicle side member

[0001] The present invention relates to a vehicle side member applicable to the front or rear of a vehicle body so as to sufficiently absorb collision energy during a front or rear collision.

[0002] The vehicle's side members play a role in absorbing collision energy as much as possible during a frontal or rear collision to minimize the transfer of collision loads to the passenger compartment or, in the case of electric vehicles, the battery compartment.

[0003] Side members in currently mass-produced electric vehicles utilize extruded aluminum in key areas responsible for absorbing energy during frontal or rear collisions. In this scenario, the entire longitudinal compressive deformation of the member is induced upon impact, allowing this single component to absorb a significant portion of the vehicle's kinetic energy. Furthermore, due to the ample space available at the front of electric vehicles, the structural freedom of side members is greater than that of internal combustion engine vehicles. Consequently, to maximize energy absorption capacity through sufficient compressive deformation along the length, side members can be designed as straight lines without altering their cross-sectional shape. Such members serve to protect the battery and passengers during frontal or rear collisions. To achieve this, there is a growing trend to apply extruded aluminum components, despite the resulting increase in cost, in order to ensure a consistently robust cross-sectional structure along the length and achieve weight reduction.

[0004] To address the issue of rising costs, side members made of steel, which is cheaper than aluminum or aluminum alloys, have been proposed; however, there is a problem in that it is difficult to construct side members with complex cross-sections due to the high density of steel and the complexity of the manufacturing process. Furthermore, side members made of steel have a limitation in that they absorb only a portion of the impact energy because they absorb collision energy through bending deformation rather than longitudinal crushing deformation.

[0005] In order to solve these problems, the applicant proposed in Patent Document 1 a side member with an octagonal cross-section that can double energy absorption capacity by inducing a stable crushed shape. However, the side member with an octagonal cross-section has a problem of interference with the mold during the roll forming process in mass production, and if the bending point is lower than 40° to avoid said interference, there is a problem of excessive springback. In addition, the side member undergoes a sizing roll process to ensure dimensional accuracy after the closed cross-section is formed during the roll forming process, but if the bending point is lower than 40°, it is difficult to apply the sizing roll, resulting in a problem of low mass production capability.

[0006] (Patent Document 1) KR 10-2423412 B1

[0007] The present invention aims to solve the above problems by providing a vehicle side member having a structure with high mass production capability that doubles energy absorption capacity through the induction of a stable crushed shape.

[0008] To achieve the above objectives, the present invention provides the following vehicle side member.

[0009] In one embodiment, the present invention provides a vehicle side member comprising: a first tubular upper portion extending in the longitudinal direction and having a hexagonal cross-sectional shape; a second tubular upper portion connected to the first tubular upper portion and extending in the longitudinal direction and having a hexagonal cross-sectional shape; and a welded portion formed on the outer wall of the first tubular upper portion and the second tubular upper portion; wherein the first tubular upper portion and the second tubular upper portion are formed integrally by bending and forming from a single first plate material.

[0010] In one embodiment, the weld may include: a first weld formed by welding one end of the first plate to abut the outer wall of the first tubular upper portion and the first flange of the second tubular upper portion; and a second weld formed by welding the other end of the first plate to abut the outer wall of the second tubular upper portion and the second flange of the second tubular upper portion.

[0011] In one embodiment, the first flange is formed by being bent outward from the first tubular upper portion, and the second flange can be formed by being bent outward from the second tubular upper portion.

[0012] In one embodiment, the first flange is provided such that its front surface contacts the outer wall of the second tubular upper portion, and the second flange may be provided such that its front surface contacts the outer wall of the first tubular upper portion.

[0013] In one embodiment, the first weld and the second weld may have a length of 5 mm to 20 mm.

[0014] In one embodiment, the first weld and the second weld may have a plurality of weld lines formed parallel to each other at a predetermined interval.

[0015] In one embodiment, the first weld and the second weld may have a single weld line bent in a zigzag shape.

[0016] In one embodiment, the first tubular upper part and the second tubular upper part share one side, and the first tubular upper part and the second tubular upper part may have the same cross-sectional shape and size with respect to the side.

[0017] In one embodiment, when viewed from the longitudinal direction, the first tubular upper portion is composed of first to sixth sides formed by being bent sequentially in one direction, and the second tubular upper portion is composed of seventh to eleven sides formed by being bent sequentially in the opposite direction of the one direction with respect to the sixth side, including the sixth side, and the first flange is located at the end of the first side, and the second flange may be located at the end of the eleventh side.

[0018] In one embodiment, the third side of the first tubular upper part and the ninth side and the sixth side of the second tubular upper part are parallel to each other, the first side of the first tubular upper part and the seventh side of the second tubular upper part are parallel, and the first weld is formed by welding the first flange located on the first side to the seventh side, the eleventh side of the second tubular upper part and the fifth side of the first tubular upper part are parallel, and the second weld can be formed by welding the second flange located on the eleventh side to the fifth side.

[0019] In one embodiment, the sixth side can be extended orthogonally to the first side and the eleventh side.

[0020] The present invention provides a vehicle side member comprising, in one embodiment, a first tubular upper portion extending in the longitudinal direction and having a hexagonal cross-sectional shape; a second tubular upper portion connected to the first tubular upper portion and extending in the longitudinal direction and having a hexagonal cross-sectional shape; and a welded portion formed on the outer wall of the first tubular upper portion and the second tubular upper portion; wherein the first tubular upper portion and the second tubular upper portion are formed integrally by bending and forming a single first plate material, so that the first tubular upper portion and the second tubular upper portion share a sixth side, and when viewed from the longitudinal direction, the first tubular upper portion is composed of first to sixth sides formed by bending sequentially in one direction, and the second tubular upper portion includes seventh to eleven sides formed by bending sequentially in the opposite direction of the one direction based on the sixth side, and the outer angle formed by one side and the other side adjacent to it in the first tubular upper portion and the second tubular upper portion is 40° or more.

[0021] In one embodiment, the weld may include: a first weld formed by welding one end of the first plate to abut the outer wall of the first tubular upper portion and the first flange of the first tubular upper portion; and a second weld formed by welding the other end of the first plate to abut the outer wall of the second tubular upper portion and the second flange of the second tubular upper portion.

[0022] In one embodiment, the first flange is formed by bending outward from the first side of the first tubular upper portion, and the second flange can be formed by bending outward from the eleventh side of the second tubular upper portion.

[0023] In one embodiment, the third side of the first tubular upper part and the ninth side and the sixth side of the second tubular upper part are parallel to each other, and the first side and the fifth side of the first tubular upper part and the seventh and eleven sides of the second tubular upper part are parallel, and when viewed in the longitudinal direction, the first side has a longer length than the fifth side, so that the part of the first side that overlaps with the seventh side forms the first flange, and the eleven side has a longer length than the seventh side, so that the part of the first side that overlaps with the fifth side forms the second flange, and the first weld is formed by welding the first flange to the seventh side, and the second weld can be formed by welding the second flange to the fifth side.

[0024] In one embodiment, the first plate may be a steel having a tensile strength of 780 MPa or more.

[0025] In one embodiment, in the hexagonal cross-sectional shape, the radius of curvature (R) at the bending point between one side and an adjacent side and the thickness (t) of the first plate can satisfy the following relationship.

[0026] R / t < R / t_p

[0027] Here, R / t_p is the limit value of the radius of curvature with respect to the thickness when the first plate is bent and formed by a press.

[0028] The present invention provides a method for manufacturing a vehicle side member, comprising, in one embodiment, a first bending step of forming a first tubular upper portion by bending a single first plate five times in a first direction; a second bending step of forming a second tubular upper portion by bending the first plate five times in a second direction opposite to the first direction; and a welding step of forming a first weld by welding one end of the first plate to the outer wall of the second tubular upper portion and forming a second weld by welding the other end of the first plate to the outer wall of the first tubular upper portion.

[0029] In one embodiment, the first bending step and the second bending step may bend so that the bending angle of the bending point is 40° or more.

[0030] In one embodiment, the method may further include a flange forming step performed prior to the welding step, wherein one end of the first plate is bent outward to the outside of the first tubular upper part to form a first flange and the other end of the first plate is bent outward to the outside of the second tubular upper part to form a second flange, and a closed cross-section forming step wherein the first flange is brought into contact with the outer wall of the second tubular upper part to form a closed cross-section and the second flange is brought into contact with the outer wall of the first tubular upper part to form a closed cross-section.

[0031] In one embodiment, a sizing step may be further included, which is performed after the closed cross-section forming step but before the welding step, and involves re-compressing the closed cross-section from the outside so that it has preset dimensions.

[0032] The present invention provides a vehicle side member manufactured by the method for manufacturing a vehicle side member described above, comprising a first tubular upper portion that is extended in the longitudinal direction and has a hexagonal cross-sectional shape, a second tubular upper portion that is connected to the first tubular upper portion and is extended in the longitudinal direction and has a hexagonal cross-sectional shape, and a welded portion formed on the outer wall of the first tubular upper portion and the second tubular upper portion, wherein the first tubular upper portion and the second tubular upper portion are formed integrally by bending and forming a single first plate material.

[0033] In one embodiment, the first weld and the second weld may have a length of 5 mm to 20 mm.

[0034] In one embodiment, the first weld and the second weld may have a plurality of weld lines formed parallel to each other at a predetermined interval.

[0035] In one embodiment, the first weld and the second weld may have a single weld line formed by bending in a zigzag shape.

[0036] The present invention can provide a structure that doubles energy absorption capacity by inducing a stable crushed shape through the vehicle side member described above, while simultaneously offering high mass production capability.

[0037] FIG. 1 is a perspective view illustrating a conventional side member.

[0038] Figure 2 is a cross-sectional view of Figure 1.

[0039] FIG. 3 is a perspective view illustrating a side member according to an embodiment of the present invention.

[0040] Figure 4 is a cross-sectional view of Figure 3.

[0041] Figure 5 is an enlarged view of part A of Figure 4.

[0042] Figure 6 is an analysis image showing deformation due to an initial collision of a conventional side member.

[0043] FIG. 7 is an analysis image showing deformation due to an initial collision of a side member according to an embodiment of the present invention.

[0044] FIG. 8 is a diagram showing the behavioral pattern in the results of verifying performance through analysis of a side member according to an embodiment of the present invention.

[0045] Figure 9 is a drawing showing the bending angle in the open cross-section state during the roll forming process of a side member having an octagonal cross-section shape.

[0046] Figure 10 is a drawing showing the bending angle in the open cross-section state during the roll forming process of a side member having a hexagonal cross-section shape.

[0047] FIG. 11 is a flowchart of a method for manufacturing a side member according to an embodiment of the present invention.

[0048] FIG. 12 is a cross-sectional view of a side member according to another embodiment of the present invention.

[0049] FIG. 13 is a schematic perspective view of the side member of FIG. 12.

[0050] Specific embodiments of the present invention will be described below with reference to the attached drawings. However, the concept of the present invention is not limited to the presented embodiments, and those skilled in the art who understand the concept of the present invention may easily propose other inventions that are inferior or other embodiments included within the scope of the concept of the present invention by adding, changing, or deleting other components within the same scope of the concept, and such are also to be considered to be included within the scope of the concept of the present invention.

[0051] Furthermore, throughout the specification, the statement that one component is 'connected' to another component means that it includes not only cases where these components are 'directly connected,' but also cases where they are 'indirectly connected' with another component in between. Also, the statement that a component 'includes' means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0052] Additionally, components with the same function within the scope of the same concept appearing in the drawings of each embodiment are described using the same reference numeral.

[0053]

[0054] FIGS. 1 and 2 present a conventional side member, and FIGS. 3 and 4 present a side member according to an embodiment of the present invention. More specifically, FIG. 1 is a perspective view showing a conventional side member, FIG. 2 is a cross-sectional view of FIG. 1, FIG. 3 is a perspective view showing a side member according to an embodiment of the present invention, and FIG. 4 is a cross-sectional view of FIG. 3. Meanwhile, since the side member (100) according to an embodiment of the present invention differs from the conventional side member (10) in the position of the welded portion (130), the present specification will focus on the differences distinguishing it from the prior art, while common parts will be described at once.

[0055] Vehicle side members are positioned on both the left and right sides of a vehicle and can extend forward or backward. When viewed from above, the side members may have a shape that extends in an almost straight line in the front-rear direction. This allows the side members to absorb collision energy to suppress body deformation during a frontal or rear collision. For example, one end of the side member may be connected to a kick-up portion installed at the front end of the vehicle's floor section to extend forward, or one end may be connected to a kick-up portion installed at the rear end of the floor section to extend backward. Assembly of the side member and the vehicle body may be achieved by inserting any connecting member into the side member and bolting it, or by forming a flange at the front or rear end of the side member and joining them by welding or the like using the flange. A more detailed description of such assembly is omitted in this specification.

[0056] In addition, since a pair of side members are arranged symmetrically to each other and have the same actual configuration, one side member will be described below as a representative example. Also, for the convenience of explanation, a side member installed at the front of the vehicle body is used as an example, but it is not limited to this and can be applied to a side member installed at the rear of the vehicle body as well.

[0057] Referring to FIGS. 1 to 4, a side member (10, 100) made of general steel includes a first tubular upper section (110) and a second tubular upper section (120). For example, it can be formed integrally by machining a single first plate (1) of a metal such as steel, or formed by bending or roll forming. At this time, the first tubular upper section (110) and the second tubular upper section (120) may have a hexagonal cross-sectional shape that extends in the X direction, which is the longitudinal direction. More specifically, the side member (10, 100) may be formed by bending a first plate (1) having a predetermined width and length multiple times to form a plurality of closed cross-sections, each having a hexagonal cross-sectional shape.

[0058] For example, a single first plate (1) can be bent in a counterclockwise direction from one end (p1) toward the other end (p2), and for example, a first tubular upper part (110) with a hexagonal cross-section can be formed by bending it five times in the same first direction (e.g., counterclockwise) in the order of the first side (s1), second side (a2), second side (s2), third side (a3), third side (s3), fourth side (a4), fourth side (s4), fifth side (a5), fifth side (s5), sixth side (a6), and sixth side (s6) centered on the first bending point (a1).

[0059] Next, the first plate (1) can be folded five times in the same second direction (e.g., clockwise) in the order of the seventh bend point (a7), the seventh side (s7), the eighth bend point (a8), the eighth side (s8), the ninth bend point (a9), the ninth side (s9), the tenth bend point (a10), the tenth side (s10), the eleventh bend point (a11), the eleventh side (s11), and the twelveth bend point (a12) to form a second tubular upper part (120) with a hexagonal cross-section.

[0060] The side member (10, 100) includes a weld (w1, w2, 130) for connecting the first tubular upper part (110) and the second tubular upper part (120). The weld (w1, w2, 130) includes a first weld (w1, 131) located on one end (p1) and a second weld (w2, 132) located on the other end (p2). Both ends (p1, p2) of the first plate (1) may be bent at a predetermined angle to form flanges (f1, f2), and the weld (w1, w2, 130) may be located on the side where the flanges (f1, f2) are connected to the first tubular upper part (110) and the second tubular upper part (120).

[0061] In the conventional side member (10), the flanges (f1, f2) are formed by being bent inward toward the first tubular upper part (110) and the second tubular upper part (120). For example, the flanges (f1, f2) are formed by being bent so as to be in contact with the sixth side (s6). That is, the conventional side member (10) can be connected to the first tubular upper part (110) of the sixth side (s6) as the first flange (f1) is formed by being bent inward toward the first bending point (a1), and can be connected to the second tubular upper part (120) of the sixth side (s6) as the second flange (f2) is formed by being bent inward toward the second bending point (a12). Meanwhile, in this specification, being bent inward may mean being bent inwardly to the closed cross-section of the first tubular upper part (110) or the second tubular upper part (120), and being bent outward may mean being bent outwardly to the closed cross-section of the first tubular upper part (110) or the second tubular upper part (120).

[0062] Meanwhile, since the side member made of steel forms a closed cross-section and then performs welding, the conventional side member (10) could perform welding at the first bend point (a1) and the seventh bend point (a7) where the first flange (f1), the first side (s1), and the seventh side (s7) meet, and could perform welding at the sixth bend point (a6) and the twelfth bend point (a12) where the second flange (f2), the fifth side (s5), and the eleventh side (s11) meet. That is, the conventional side member (10) could perform fillet welding, for example, to form welded parts (w1, w2) at the edge portion, but this has the problem that the welded parts (w1, w2) break upon front-to-rear collision.

[0063] Meanwhile, in one embodiment of the present invention, the side member (100) may be formed such that the flanges (f1, f2) are bent outward toward the first tubular upper part (110) and the second tubular upper part (120). For example, the first flange (f1) may be formed by being bent to abut the seventh side (s7) of the second tubular upper part (120), and the second flange (f2) may be formed by being bent to abut the fifth side (s5) of the first tubular upper part (110). That is, the first flange (f1) can be connected to the outer wall of the second tubular upper part (120) by being formed by being bent in the first direction around the first bending point (a1), and the second flange (f2) can be connected to the outer wall of the first tubular upper part (110) by being formed by being bent in the first direction around the twelfth bending point (a12). Furthermore, in the side member (100) according to an embodiment of the present invention, the first tubular upper part (110) and the second tubular upper part (120) share a sixth side (s6), which is a side between the sixth bending point (a6) and the seventh bending point (a7), and the first tubular upper part (110) and the second tubular upper part (120) may have the same cross-sectional shape and size based on the side (s6).

[0064] Accordingly, in a side member (100) according to an embodiment of the present invention, a first weld (131) may be formed on the surface where the first flange (f1) and the seventh side (s7) meet, and a second weld (132) may be formed on the surface where the second flange (f2) and the fifth side (s5) meet. That is, unlike a conventional side member (10), the side member (100) according to an embodiment of the present invention provides a structure in which the entire surface of the flanges (f1, f2) is weldable, thereby preventing fracture of the welds (131, 132) and increasing crushing stability. At this time, since the entire surface of the flanges (f1, f2) can be weldable, the length (d1) of the weld (130) may correspond to the length of the flanges (f1, f2) and may be approximately 5 mm to 20 mm.

[0065] FIG. 5 is an enlarged view of part A of FIG. 4, showing an enlarged view of a welded portion (130) of a side member (100) according to an embodiment of the present invention. More specifically, FIG. 5(a) shows an embodiment of the welded portion (130), and FIG. 5(b) is a modified example of FIG. 5(a).

[0066] As illustrated in FIG. 5(a), the weld (130) can be formed on the front surface of the flanges (f1, f2), so a single weld line (130a) can be formed in a zigzag shape. Furthermore, although not illustrated in the drawings, the weld (130) may have a shape pattern such as a triangle or a semicircle for the single weld line (130a). As illustrated in FIG. 5(b), the weld (130) may have a plurality of weld lines (130b, 130c) spaced apart in parallel at a predetermined interval. In particular, the bonding strength can be increased as the plurality of weld lines (130b, 130c) are located at both ends of the weld (130).

[0067] That is, the side member (100) according to one embodiment of the present invention can secure a wide welded area as the front surface of the flanges (f1, f2) is welded in contact with the outer wall of the first tubular upper part (110) and the second tubular upper part (120). Accordingly, the welded part (130) according to one embodiment of the present invention can secure uniformity of welding over a wide welded area and increase the joint strength, thereby preventing fracture of the welded part and increasing crush stability.

[0068] FIGS. 6 to 8 are drawings showing the analysis results of a side member following a collision. The applicant performed a performance analysis of the side member of the present invention through simulation. More specifically, FIG. 6 is an analysis image showing the deformation of a conventional side member following an initial collision, FIG. 7 is an analysis image showing the deformation of a side member following an initial collision according to an embodiment of the present invention, and FIG. 8 is a drawing showing the behavioral pattern in the results of performance verification through the analysis of the side member according to an embodiment of the present invention. Hereinafter, the effects of the side member according to an embodiment of the present invention will be described with reference to FIGS. 6 to 8, while also referring to the configurations illustrated in FIGS. 1 to 4.

[0069] As described above, since welding is performed after the side member forms a closed cross-section, the conventional side member (10) cannot be welded between the flange (f1, f2) and the sixth side (s6), and the welded portion (w1, w2) is formed at the edge where the first tubular upper portion (110) and the second tubular upper portion (120) are joined. Therefore, as shown in FIG. 6, in the conventional side member (10), the flange (f1, f2) surface separates from the sixth side (s6) upon a frontal or rear collision, and there is a constant risk of fracture of the welded portion (w1, w2) upon crushing deformation.

[0070] Meanwhile, in the side member (100) according to one embodiment of the present invention, the first flange (f1) is provided to be weldable by contacting the seventh side (s7), and the second flange (f2) is provided to be weldable by contacting the fifth side (s5), thereby increasing the welding area and increasing the bonding strength. Accordingly, the side member (100) according to one embodiment of the present invention can prevent the flange (f1, f2) surfaces from spreading apart during crushing deformation, and can maximize energy absorption capacity through sequential crushing without bending deformation along the X direction, which is the longitudinal direction, as shown in FIG. 8.

[0071] In other words, a side member made of steel may have a polygonal cross-section to facilitate the efficient absorption of collision energy and connection with other parts before and after it, particularly face-to-face contact. A side member according to one embodiment of the present invention, having a double hexagonal cross-section, can have energy absorption capabilities similar to those of a side member with an octagonal cross-section, while simultaneously increasing the possibility of connection with other parts and facilitating manufacturing. In particular, by expanding the weld area to improve joint strength, energy absorption capabilities can be doubled through stable crushing induction by preventing fracture of the weld area.

[0072]

[0073] FIGS. 9 and 10 are drawings showing the bending angle according to the cross-sectional shape of a side member during a roll forming process. More specifically, FIG. 9 shows the bending angle in an open cross-section state during the roll forming process of a side member having an octagonal cross-section shape, and FIG. 10 shows the bending angle in an open cross-section state during the roll forming process of a side member having a hexagonal cross-section shape. The following description will be explained with reference to FIGS. 9 and 10.

[0074] The roll forming process is known as a process for producing a beam with a uniform cross-section by introducing a coil or a long plate into a continuous arrangement of upper and lower forming roll sets and sequentially bending and forming it. A side member using steel (P) is produced by bending and forming a single piece of steel (P), and the bending and forming is performed by compression of the upper and lower dies. For example, as shown in FIG. 9, the steel (P) is sequentially bent to a first bend point (a1), a second bend point (a2), a third bend point (a3), a fourth bend point (a4), a fifth bend point (a5), a sixth bend point (a6), a seventh bend point (a7), and an eighth bend point (a8) to form a closed cross-section. At this time, the steel (P) can be bent by compression of the upper die (UD1, UD2) and lower die (LD1, LD2) before the closed cross-section is formed, that is, in an open state. Since compression is possible only on the outer side of the closed cross-section after the closed cross-section is formed, the steel (P) undergoes a sizing process using a sizing roll on the outer side of the closed cross-section to have a target bending angle and cross-sectional shape.

[0075] Meanwhile, when the steel (P) is in an open cross-section state before a closed cross-section is formed, and is pressed by the mold (UD1, UD2, LD1, LD2), the bending angle at each bending point (e.g., the first to eighth bending points) must be at least 40° to ensure dimensional accuracy by the sizing roll. If the bending angle in the open cross-section state is lower than 40°, during the sizing roll process, the bending angle at each bending point may not bend to the target angle, but rather bend at an unexpected point, or problems such as springback may occur, making it difficult to secure the target dimensional accuracy. Therefore, for mass production, it is important to ensure that the bending angle at the bending point is at least 40° when forming the side member using the steel (P).

[0076] As shown in FIG. 9, since the side member with an octagonal cross-section has seven bending points in a single closed cross-section, the bending angle must be formed in a limited manner to avoid interference between the steel (P) and the die during the roll forming process. For example, if the bending angle at the second to fifth bending points (a2, a3, a4, a5) is secured to 40°, interference may occur between the first lower die (LD1) and the first flange (f1) as shown in part B, and as a result, the bending angle at the sixth and seventh bending points (a6, a7) becomes smaller than 40°. Additionally, for the side member with an octagonal cross-section, compression must be performed between the first lower die (LD1) and the first upper die (UD1) to form the sixth bending point (a6). However, if the size of the first lower die (LD1) is reduced due to interference with the first flange (f1), a problem arises in which the first lower die (LD1) cannot be matched to the first upper die (UD1).

[0077] As illustrated in FIG. 10, the side member with a hexagonal cross-section can be formed by bending such that the bending angle at the bending point is greater than at least 40° during the roll forming process. For example, the side member with a hexagonal cross-section can provide a structure in which interference between the first lower die (LD1) and the first flange (f1) does not occur even if the bending angle at the second to fifth bending points (a2, a3, a4, a5) is greater than 40°. Furthermore, since the first upper die (UD1) and the first lower die (LD1) can be precisely matched, the side member with a hexagonal cross-section can be mass-produced while maintaining a bending angle of 40° or more at the bending point.

[0078] Accordingly, the method for manufacturing a side member according to one embodiment of the present invention recognizes the above problems and can provide a method for manufacturing a side member having a hexagonal cross-sectional shape as a structure with high mass production capability, while doubling the energy absorption capacity by inducing a stable crushed shape.

[0079] FIG. 11 is a flowchart of a method for manufacturing a side member according to an embodiment of the present invention. A method for manufacturing a side member according to an embodiment of the present invention will be described with reference to FIG. 11. Since the side member according to an embodiment of the present invention is manufactured by the method for manufacturing a side member according to an embodiment of the present invention, the description will be made with reference to FIG. 3 to FIG. 5.

[0080] A method for manufacturing a side member according to an embodiment of the present invention includes a first bending step (S210), a second bending step (S220), a flange forming step (S230), a closed cross-section forming step (S240), a sizing step (S250), and a welding step (S260). The first bending step (S210) may form a first tubular upper part (110) by bending a single first plate (1) five times in a first direction (e.g., counterclockwise). The second bending step (S220) may form a second tubular upper part (120) by bending the first plate (1) five times in a second direction (e.g., clockwise), which is opposite to the first direction. For example, as illustrated in FIG. 4, the first bending step (S210) bends the first plate (1) in the first direction at the second bending point (a2), the third bending point (a3), the fourth bending point (a4), the fifth bending point (a5), and the sixth bending point (a6) in sequence from the end (p1) side toward the other end (p2) side, and the second bending step (S220) can continue to bend the first plate (1) in the second direction opposite to the first direction at the seventh bending point (a7), the eighth bending point (a8), the ninth bending point (a9), the tenth bending point (a10), and the eleventh bending point (a11) in sequence.

[0081] At this time, the method for manufacturing a side member according to an embodiment of the present invention may bend the bending point so that the bending angle is 40° or more during the first bending step (S210) and the second bending step (S220). According to the above-described problem, if the bending angle of the bending point becomes smaller than 40° in the open cross-section state, a problem arises in which it becomes difficult to secure the target dimensional accuracy due to the bending occurring at an unexpected point other than the bending point during the sizing step (S250) described later, or due to springback. Therefore, the method for manufacturing a side member according to an embodiment of the present invention may bend the bending point so that the bending angle is 40° or more during the first bending step (S210) and the second bending step (S220). Furthermore, since five bending points are formed in the first bending step (S210) and the second bending step (S220), even if the bending angle of the bending points is maintained at 40° or more, there is no interference problem with the flanges (f1, f2) described later, so mass production is ensured.

[0082] The above flange forming step (S230) may be performed prior to the welding step (S260), and a first flange (f1) may be formed by bending one end of the first plate (1) outwardly toward the first tubular upper part (110), and a second flange (f2) may be formed by bending the other end of the first plate (1) outwardly toward the second tubular upper part (120). Meanwhile, although not shown in the drawing, the flange forming step (S230) may be performed prior to the first bending step (S210) and the second bending step (S220); for example, the first bending step (S210) may be performed after the first flange (f1) is formed first. That is, if the flange forming step (S230) is performed before the welding step (S260), the order of the first bending step (S210) and the second bending step (S220) is not limited by the flowchart (see FIG. 11).

[0083] The above closed cross-section forming step (S240) may form a closed cross-section by bringing the first flange (f1) into contact with the outer wall of the second tubular upper part (120), and may form a closed cross-section by bringing the second flange (f2) into contact with the outer wall of the first tubular upper part (110). More specifically, as shown in FIG. 4, the first flange (f1) may be brought into contact with the seventh side (s7) to form a closed cross-section with a hexagonal cross-section inside the first tubular upper part (110), and the second flange (f2) may be brought into contact with the fifth side (s5) to form a closed cross-section with a hexagonal cross-section inside the second tubular upper part (120).

[0084] The sizing step (S250) is performed after the closed cross-section forming step (S240) but before the welding step (S260), and the closed cross-section can be re-compressed from the outside to have preset dimensions. The sizing step (S250) can be re-compressed by a sizing roll (not shown) to have a preset curvature of the bending point or a bending angle of the final closed cross-section. For example, the first plate (1) can be pre-bent at the first bending step (S210) or the second bending step (S220) so that one bending point has a bending angle of 55°, and then in the sizing step (S250), the bending point can be bent so that it has a bending angle of 60°. Accordingly, the first plate (1) can be formed into a closed cross-section with a hexagonal cross-section shape.

[0085] Meanwhile, FIGS. 12 and FIGS. 13 illustrate a side member according to another embodiment of the present invention. Specifically, FIG. 12 illustrates a cross-sectional view of a side member according to another embodiment of the present invention, and FIG. 13 illustrates a schematic perspective view of the side member of FIG. 12.

[0086] The side member (100) of this embodiment can be formed by roll forming a single sheet metal, similar to the previous embodiment.

[0087] In this embodiment, the side member (100) includes a first tubular upper section (110) and a second tubular upper section (120), and the first tubular upper section (110) and the second tubular upper section (120) can be formed by forming a plate of high-strength steel, for example, steel having a tensile strength of 780 MPa or more, in different directions by machining, for example, roll forming or bending. Accordingly, each side is welded only on one side with respect to a shared side, and the rest are continuously connected.

[0088] Each side is formed around a bending point. In the first tubular upper section (110), the first to fifth sides (s1 to s5) are formed by bending at multiple bending points (a2 to a6) in a clockwise direction around the shared sixth side (s6), and in the second tubular upper section (110), the seventh to eleventh sides (s7 to s11) are formed by bending at multiple bending points (a7 to a11) in a counterclockwise direction around the sixth side (s6). The first and second tubular upper sections (110, 120) have a hexagonal cross-sectional shape and include the third side (s3) parallel to the shared sixth side (s6), and the ninth side (s9), and the first and eleventh sides (s1, s11) in a direction orthogonal to the extension direction of the sixth side (s6) when viewed from a cross-section perpendicular to the length direction.

[0089] The first tubular upper section (110) has a first side (s1) that extends in the Z direction perpendicular to the Y direction, which is the extension direction of the sixth side (s6), when viewed from the X direction, which is the length direction, and a flange (f1) that forms a first weld (131) is disposed at the edge. The first side (s1) and the flange (f1) are continuous without bending. The second side (s2) is configured to connect the first side (s1) with the third side (s3) which is parallel to the sixth side (s6), and is formed by bending at the second bending point (a2) opposite the flange (f1) of the first side (s1). The second side (s2) is formed at an angle with respect to the Y direction or the Z direction.

[0090] The third side (s3) is parallel to the sixth side (s6), is bent at the third bend point (a3) ​​to connect to the second side (s2), and is bent at the fourth bend point (a4) to connect to the fourth side (s4). The fourth side (s4) is connected to the third side (s3) and is formed to have the same angle with respect to the second side (s2) with respect to the Z direction, but inclined in opposite directions. The fifth side (s5) is parallel to the first side (s1), is connected to the fourth side (s4) through the fifth bend point (a5), and is connected to the sixth side (s6) through the sixth bend point (a6). At the 6th bending point (a6), the 5th side (s5) and the 6th side (s6) are connected by bending at 90°, so they can be bent with a larger radius of curvature than the 2nd to 5th bending points (a2~a5), but are not limited thereto.

[0091] The sixth side (s6) is used to form the closed cross-section of the first tubular upper part (110) and the closed cross-section of the second tubular upper part (120), so it can be said to be a side shared by the first and second tubular upper parts (110, 120).

[0092] The 7th to 11th sides (s7~s11) are symmetrical with respect to the 1st to 5th sides (s1~s5) from the center of the 6th side (s6). The 7th to 11th sides (s7~s11) are formed by bending from the 6th side (s6). Specifically, the 7th side (s7) is connected to the 6th side (s6) through the 7th bend point (a7), the 8th side (s8) is connected to the 7th side (s7) through the 8th bend point (a8), the 9th side (s9) is connected to the 8th side (s8) through the 9th bend point (a9), the 10th side (s10) is connected to the 9th side (s9) through the 10th bend point (a10), and the 11th side (s10) is connected to the 10th side (s10) through the 11th bend point (a11).

[0093] The 7th side (s7) and the 11th side (s11) are parallel to the Z direction. That is, the 1st side (s1) and the 5th side (s5) of the 1st tubular upper part (110) and the 7th side (s7) and the 11th side (s11) of the 2nd tubular upper part (120) are parallel to the Z direction. These parallel sides not only facilitate the formation of the 1st and 2nd welded parts (131, 132), but also facilitate the attachment of other configurations to the 1st, 5th, 7th, and 11th sides (s1, s5, s7, s11), making it advantageous to attach other configurations to the side member (100).

[0094] The ninth side (s9) is parallel to the sixth side (s6) as with the third side (s3), and the eighth and tenth sides (s8, s10) are positioned at an angle with respect to the Z direction or the Y direction. The angle of inclination of the eighth and tenth sides (s8, s10) with respect to the Z direction may correspond to the second and fourth sides (s2, s4).

[0095] The first side (s1) faces the fifth side (s5), and the length of the first side (s1) in the Z direction is longer than the length of the fifth side (s5) in the Z direction. The first side (s1) is formed to pass through the seventh bending point (a7) and overlap with the seventh side (s7). The portion where the seventh side (s7) and the first side (s1) overlap acts as the first flange (f1), and at this portion, the seventh side (s7) and the first side (s1) are welded to form the first weld portion (131).

[0096] The first weld (131) is structured such that the entire surface of the first flange (f1) of the first side (s1) is welded to the seventh side (s7), thereby preventing the first weld (131) from breaking upon impact in the X direction and increasing crush stability. At this time, the front surface of the first flange (f1) may be weldable, and the length of the first weld (131) may be the length of the first flange (f1) and may be in the range of about 5 to 20 mm.

[0097] Likewise, the eleventh side (s11) faces the seventh side (s7), and the length of the eleventh side (s11) in the Z direction is formed to be longer than the length of the seventh side (s7) in the Z direction. Accordingly, the eleventh side (s11) can pass through the sixth bend point (a6) and overlap with the fifth side (s5), and the part where the eleventh side (s11) and the fifth side (s5) overlap acts as the second flange (f2), and the eleventh side (s11) and the fifth side (s5) are welded at this part to form the second weld (132).

[0098] The second weld (132) is structured such that the entire surface of the second flange (f2) of the eleventh side (s11) is welded to the fifth side (s5), thereby preventing the second weld (132) from breaking upon impact in the X direction and increasing crush stability. At this time, the front surface of the second flange (f2) may be weldable, and the length of the second weld (132) may be the length of the second flange (f2) and may be in the range of approximately 5 to 20 mm, which is the same as the length of the first weld (131).

[0099] In this embodiment, the length of the weld (130) is secured in the same way as in the previous embodiment to increase crushing stability while also ensuring formability. Additionally, by including a side parallel to the Z direction or the Y direction, the ease of joining with surrounding components is improved when installed in a vehicle.

[0100] As mentioned above, in this embodiment as well, since the side member (100) is formed by roll forming, it can be formed to have a radius of curvature for thickness smaller than the radius of curvature for thickness (R / t_p), which is the bending forming limit by press. That is, as the side member (100) is sequentially bent by roll forming, the radius of curvature for thickness (R / t) at each bending point (a2~a11) can be formed to be smaller than the radius of curvature for thickness limit value (R / t_p) by press.

[0101] Although the present invention has been described above with reference to embodiments, the present invention is not limited to the embodiments described above, and it is understood that it can be modified and implemented by those skilled in the art without changing the technical concept of the present invention as claimed in the claims.

[0102] (Explanation of symbols)

[0103] 1: Plate, 10, 100: Side member

[0104] 110: 1st tubular upper part 120: 2nd tubular upper part

[0105] 130: Weld 130a, 130b, 130c: Weld line

[0106] 131, 132: First and second welds

[0107] a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12: 1st to 12th bending points

[0108] f1, f2: 1st and 2nd flanges

[0109] s1, s2, s3, s4, s5, s6, s7, s8, s9, s10, s11: 1st to 11th variables

Claims

1. A first tubular upper portion extending in the longitudinal direction and having a hexagonal cross-sectional shape; A second tubular upper portion connected to the first tubular upper portion, extending in the longitudinal direction and having a hexagonal cross-sectional shape; and A welded portion formed on the outer wall of the first tubular upper portion and the second tubular upper portion; Includes, A vehicle side member in which the first tubular upper portion and the second tubular upper portion are formed integrally by bending and molding a single first plate material.

2. In Paragraph 1, The above welded part is, A first welded portion formed by welding one end of the first plate to the outer wall of the second tubular upper portion, wherein the first flange of the first tubular upper portion abuts against the first tubular upper portion; and A vehicle side member comprising: a second welded portion formed by welding the other end of the first plate to the second tubular upper portion so that the second flange of the second tubular upper portion comes into contact with the outer wall of the first tubular upper portion.

3. In Paragraph 2, The first flange is formed by being bent outward toward the first tubular upper portion, and A vehicle side member, wherein the second flange is formed by being bent outward from the second tubular upper portion.

4. In Paragraph 3, The above first flange is, The front surface is provided to be in contact with the outer wall of the second tubular upper portion, and The above second flange is, A vehicle side member provided such that its front surface contacts the outer wall of the first tubular upper portion.

5. In Paragraph 4, The above-mentioned first weld and second weld are a vehicle side member having a length of 5 mm to 20 mm.

6. In Paragraph 5, The above first weld and second weld are, A vehicle side member characterized by multiple weld lines being formed parallel and spaced apart at predetermined intervals.

7. In Paragraph 5, The above first weld and second weld are, A vehicle side member in which a single weld line is bent into a zigzag shape.

8. In Paragraph 7, The first tubular upper part and the second tubular upper part share one side, and A vehicle side member having the same cross-sectional shape and size with respect to the side, wherein the first tubular upper portion and the second tubular upper portion are the same.

9. In Paragraph 2, When viewed from the longitudinal direction, the first tubular upper portion is composed of first to sixth sides formed by being folded sequentially in one direction, and the second tubular upper portion is composed of seventh to eleven sides formed by being folded sequentially in the opposite direction of the one direction with respect to the sixth side, including the sixth side. The first flange is located at the end of the first side, and The above second flange is a vehicle side member located at the end of the above eleventh side.

10. In Paragraph 9, The third side of the first tubular upper part, the ninth side of the second tubular upper part, and the sixth side are parallel to each other, The first side of the first tubular upper part and the seventh side of the second tubular upper part are parallel, The first weld is formed by welding the first flange located on the first side to the seventh side, and The 11th side of the second tubular upper part and the 5th side of the first tubular upper part are parallel, The above second weld is a vehicle side member formed by welding the second flange located on the 11th side to the 5th side.

11. In Paragraph 10, The above-mentioned sixth side is a vehicle side member extending orthogonally to the above-mentioned first side and the above-mentioned eleventh side.

12. In Paragraph 2, The above-mentioned first plate is a steel material having a tensile strength of 780 MPa or more, and is a vehicle side member.

13. In Paragraph 12, A vehicle side member having the following relationship between the radius of curvature (R) at the bending point between one side and an adjacent side in the above hexagonal cross-sectional shape and the thickness (t) of the first plate. R / t < R / t_p Here, R / t_p is the limit value of the radius of curvature with respect to the thickness when the first plate is bent and formed by a press.

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