JP2008161911A - Shock absorbing member and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a shock absorbing member that excels in a shock absorption characteristic in the event of collision of automobiles and that can protect crew members by surely and effectively absorbing colliding energy. <P>SOLUTION: The shock absorbing member includes a cylindrical body having in the flange a laser welding bead for joining the first and second members each having a flange. The laser welding bead is composed of a plurality of first regions and a plurality of second regions which are alternately formed at intervals in the longitudinal direction of the flange, wherein the length of projection in the width direction of the flange in the first region is longer than that in the second region. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an impact absorbing member and a method for manufacturing the same, and more particularly to an impact absorbing member that can effectively absorb collision energy in the event of an automobile collision, such as a crash box and a method for manufacturing the same.

  The impact absorbing member is a member for efficiently absorbing the collision energy by being preferentially crushed before other members in the event of a vehicle collision. A crash box is known as such a shock absorbing member. The crash box is a cylindrical body having a length of about 200 to 300 mm. For example, the front end of the front side member that is fixed to one end side in the axial direction on the back surface of the front bumper reinforcement and forms the skeleton of the automobile body The other end side is detachably fixed to. When an impact load is applied to the crash box in the axial direction via the front bumper reinforcement, it crushes and deforms into a bellows shape, thereby absorbing the collision energy and suppressing damage to the front side member. The increase in repair costs due to damage to the members is greatly suppressed, and as a result, the impact on the occupant is mitigated to improve collision safety. In recent years, crash boxes have been highly evaluated for their usefulness, especially in Europe, and are now standard equipment on low-end cars.

  In addition, since this crash box is naturally one of the parts mounted on the car body, further weight reduction is required as part of the reduction in fuel consumption against the background of global environmental problems.

  For this reason, a high strength steel plate of 440 MPa class or more is generally used for the crash box, but the application of a higher strength steel plate is also being studied for the purpose of achieving further weight reduction and high shock absorption characteristics. Then, it is beginning to be put into practical use.

  FIG. 8 is a graph showing an example of a load-displacement curve when the crash box receives an impact load and is crushed in the axial direction. The superiority or inferiority of the impact absorption characteristic is expressed as an integrated value of displacement in the load-displacement curve at the time of crushing shown in this graph.

  Until now, the front side member which is one of the shock absorbing members has been assembled by overlapping two or more panels having flanges via the flanges and then performing resistance spot welding on the overlapping portions. In recent years, in order to further improve performance such as weight reduction, shock absorption characteristics, rigidity, etc., when manufacturing a front side member by welding a substantially hat-shaped panel having a flange and a flat panel with a flange, There has already been proposed an invention that stabilizes and improves the impact absorption characteristics by using, for example, line welding by laser welding instead of spot welding by spot welding.

  For example, Patent Document 1 discloses that laser welding is performed so that a laser welding bead is intermittently formed in the longitudinal direction at the outermost end of the flange, thereby suppressing bending deformation at the time of collision and absorbing the amount of impact energy. An invention is disclosed in which the impact absorption characteristics of the front side member are improved by increasing.

Further, in Patent Document 2, the laser welding bead width in the flange is set to 1.4 to 3.0 times the plate thickness, and the laser welding is performed to sufficiently secure the bonding strength secured by the laser welding bead width. Thus, there is disclosed an invention that improves the shock absorption characteristics of the front side member by preventing breakage of the laser weld bead at the time of collision.
JP-A-6-170568 JP 2002-79388 A

  The invention disclosed in Patent Document 1 aims to improve the impact absorption characteristics of the front side member by appropriately controlling the crushing mode at the time of collision and the welding position at that time. Here, the width of the laser weld bead is usually about 1.0 mm. For this reason, when the base material is made of a high strength material or when the thickness of the base material is large, the laser weld bead breaks at the time of crushing due to a collision, that is, the interface between the overlapping surfaces of the panels constituting the shock absorbing member Peeling may occur at an early stage, and the desired shock absorption characteristics may not be exhibited. However, the present invention does not consider any countermeasures against the interface peeling, and thus may not exhibit the desired shock absorption characteristics.

  On the other hand, in the invention disclosed in Patent Document 2, in order to prevent interfacial peeling at the overlapping surface of the panels constituting the front side member, the bonding strength in the direction perpendicular to the longitudinal direction of the laser weld bead is Focusing on the large influence of the width of the laser weld bead, the width of the laser weld bead is specified in relation to the thickness of the base metal, and is considered to be an effective means to prevent interfacial delamination. It is done. However, in the present invention, the width of the laser weld bead is constant in the longitudinal direction of the flange, and it is completely considered that the magnitude and direction of the impact load applied in the longitudinal direction of the front side member fluctuates in an extremely complicated manner in an actual accident. Therefore, even with the present invention, there is a possibility that the desired shock absorption characteristics cannot be exhibited.

  The front side member is crushed by an impact load in the longitudinal direction. The laser weld bead is rapidly hardened due to the heat history during laser welding, so that it hardens significantly. For this reason, a laser weld bead formed continuously in the longitudinal direction of the front side member is likely to generate an initial crack at any position in the longitudinal direction when an impact load is applied, and the crack once generated easily propagates. As a result, the laser welding bead breaks, that is, the above-described interfacial delamination occurs, and a stable crushing mode cannot be obtained, resulting in unstable buckling, resulting in reduced shock absorption characteristics and instability.

  Laser welding means an irradiation spot diameter of about 0.2 to 0.6 mm by laser light with an optical system (meaning a major axis on the surface of a workpiece to be irradiated with a laser, This is a welding method that has the advantage that high-speed welding is possible by concentrating to a shape because the shape is used to obtain a high energy density, and that the thermal strain generated in the member to be welded is small. Therefore, the width of the laser weld bead is usually about 1.0 mm. However, when trying to obtain a laser welding bead having a width of 1.4 to 3.0 times the plate thickness as in the invention disclosed in Patent Document 2, the irradiation spot diameter of the laser beam is inevitably increased. As a result, the welding speed is lowered, high-speed weldability, which is an advantage of laser welding, is impaired, thermal strain during welding is increased, and the heat affected zone is softened (so-called HAZ softening). ), The shock absorption characteristics may be reduced.

  The present invention has a closed cross section composed of at least a first member having a flange and a second member disposed so as to overlap the first member via the flange. A longitudinal direction (hereinafter referred to as a “flange longitudinal direction”) is oriented in an axial direction intersecting the transverse section, and a cylindrical body having a laser weld bead for joining the first member and the second member on the flange. The laser-absorbing member is divided into a first region where a plurality of laser weld beads are formed apart from each other in the longitudinal direction of the flange, and two first regions that are adjacent to each other in the longitudinal direction of the flange. And a plurality of second regions formed on a part of the plurality of portions formed apart from each other in the longitudinal direction of the flange, or on all of the plurality of portions. In addition, the projected length in the flange width direction (hereinafter referred to as “flange width direction”) in the first region is larger than the projected length in the flange width direction in the second region. Is a shock-absorbing member wherein the second region is formed every other one of the plurality of portions in the longitudinal direction, and more specifically, the projected length in the first region. Is an impact-absorbing member characterized in that it is 1.9 times or more the plate thickness of the first member.

  From another point of view, the present invention has a closed cross section at least by superimposing the second member on the flange of the first member and directs the longitudinal direction of the flange in the axial direction intersecting the cross section. After assembling the cylinder, the laser is welded to the flange, and a plurality of first regions that are formed apart from each other in the longitudinal direction of the flange and two first regions that are adjacent to each other in the longitudinal direction of the flange A plurality of second regions are formed on a part of the plurality of parts that are partitioned and spaced apart in the longitudinal direction of the flange, or on all of the plurality of parts. The first member is formed by forming a laser weld bead having a projected length in the flange width direction in the region larger than a projected length in the flange width direction in the second region. And a second member are bonded to each other, and more specifically, the projected length in the first region is 1.9 times or more the plate thickness of the first member. A method for manufacturing an impact-absorbing member, characterized in that a laser weld bead is formed.

In these present invention, it is illustrated that an impact-absorbing member is a crash box.
In the present invention, the first member is exemplified by a panel having a hat-shaped cross section manufactured by roll forming, for example.

In these inventions, it is desirable that the laser weld bead is formed over a length of 50% or more of the total length in the longitudinal direction of the flange.
In these present inventions, it is exemplified that the first member has two flanges, and in this case, the first region and the second region constituting the laser welding bead formed on one of the two flanges. It is desirable that the first region and the second region constituting the laser weld bead formed on the other of the two flanges are formed at positions substantially coincident with each other with respect to the axial direction of the cylindrical body. .

In these present inventions, the second member may be a member having a flange superimposed on the first member, or may be a flat member.
In these present inventions, a third member for further increasing the rigidity of the cylindrical body is disposed inside the cylindrical body by being disposed so as to overlap between the flange of the first member and the second member. A member can be provided.

In these present inventions, it is exemplified that the plurality of first regions are formed in a dot shape.
That is, it is desirable to perform laser welding in the present invention in combination with spot welding and stitch welding (a welding technique in which welding and idle running cycles are continuously repeated to form intermittent welding beads) or continuous welding. For example, the first region is formed by spot welding, and the second region is formed by stitch welding or continuous welding.

  Further, these laser welding forms of the present invention include I-shaped welding, U-shaped welding, and odd-shaped U-shaped welding. For example, in I-shaped welding, U-shaped welding, or odd-shaped U-shaped welding, welding is performed in the flange width direction to form the first region, and welding in the flange longitudinal direction is performed between the first regions. Two regions are formed. In addition, in U-shaped or odd-shaped U-shaped welding, a robot equipped with a laser head is taught to continuously form the first area, then the second area, and the first area. Can do.

  According to the present invention, it is possible to provide an impact absorbing member that exhibits good crushing behavior and weld fracture resistance in the event of an automobile collision, and can protect passengers by absorbing collision energy reliably and effectively. it can. In addition, the shock absorbing member according to the present invention can reduce the flange width because laser welding is performed, compared to a conventional shock absorbing member assembled by spot welding, thereby reducing the weight. .

  As described above, according to the present invention, since it has excellent shock absorption characteristics, it is possible to reduce damage to the human body at the time of a collision accident and to reduce the weight, and the present invention has an industrial utilization effect. large.

  Hereinafter, the best mode for carrying out the present invention will be described. In the following description, the shock absorbing member is a crash box, and the cylindrical body constituting the shock absorbing member is a well-known and commonly used first member having a hat-shaped cross-sectional shape as this type of shock absorbing member. For example, a case where the second member is a closing plate is used.

The shock absorbing member of the present embodiment includes a cylindrical body having a closed rectangular cross section constituted by a first member and a second member.
The first member is a molded panel having a so-called hat-shaped cross section. The first member is manufactured by roll forming, for example. The first member has two flanges in the cross section thereof, and is joined to the second member by welding through the two flanges in order to stably collapse in a bellows shape in the axial direction. Is desirable.

  The second member is a panel member that is disposed so as to overlap the first member via the two flanges of the first member, and is a flat closing plate in the present embodiment. The second member may be a flat member having no flange as in the present embodiment, or, unlike the present embodiment, a flange that is overlapped with the flange of the first member. It may be a molded member.

  Fig.1 (a)-FIG.1 (p) are explanatory drawings which show the cross-sectional shape example of the various cylinders 4 which comprise the impact-absorbing member which concerns on this invention. Reference numeral 1 indicates a first member, and reference numeral 2 indicates a second member. FIG. 1A shows the present embodiment, and FIGS. 1B to 1P show modifications of the present embodiment.

  As shown in FIG. 1A to FIG. 1P, the position of the flange 1 a may be formed on either the ridge line part of the first member 1 or the flat part between the ridge line parts. Further, the number of stacked sheets in the flange 1a may be two or three or more. For example, as shown in FIGS. 1 (i), (j), and (p), the cylinder 4 is placed inside by overlapping the flange 1 a of the first member 1 and the second member 2. The third member 3 for increasing the rigidity of the cylindrical body 4 may be provided as the reinforcement.

  As will be described later, the shock absorbing member according to the present embodiment has a longitudinal direction by making the laser weld bead in the flange 1a for joining the first member 1 and the second member 2 into a specific formation state. The distribution of the bonding strength of the flange 1a in the direction is optimized in order to crush in a bellows shape. For this reason, this shock absorbing member has a rectangular cross-sectional shape by combining the first member 1 having a hat-shaped cross section and the second member 2 being a closing plate as in the present embodiment. (Refer to FIG. 1 (a)). Of course, a combination of members 1 and 2 having a pair of hat-shaped cross sections has a rectangular cross section (see FIGS. 1 (b) and 1 (i)). ) Or a combination of the first member 1 and the second member 2 having a cross section of a polygonal cross section other than a hat shape (FIG. 1C to FIG. 1H, FIG. 1J) As shown in FIG. 6), a combination of members 1 and 2 having a cross-sectional shape other than the hat-shaped cross-sectional shape may be used.

  The cross-sectional shape of the cylinder 4 is not limited to a quadrangle, and may be a polygon other than a quadrangle such as a hexagon or an octagon (see FIGS. 1 (k) to 1 (p)). ). In this case, the cylinder 4 may also include a fourth member 5 together with the first member 1 and the second member 2 as illustrated in FIG.

The cylindrical body 4 of the present embodiment is directed to the longitudinal direction of the flange 1a of the first member 1 in the axial direction intersecting the transverse section (direction orthogonal to the paper surface in FIG. 1).
FIG. 2A to FIG. 2D are two-side views of the cylindrical body 4 and explanatory views showing the various laser welding beads 6 in the cylindrical body 4 in an enlarged manner.

  As shown in the figure, the left and right flanges 1a and 1a are respectively provided with laser weld beads 6 in a direction substantially coinciding with the longitudinal direction of the flange (the vertical direction in FIGS. 2 (a) to 2 (d)). Each is formed. The flanges 1 a and 1 a of the first member 1 and the second member 2 are joined by the laser welding bead 6.

In the present embodiment, the laser weld bead 6 has a first region 7 and a second region 8.
As shown in FIGS. 2A to 2D, a plurality of first regions 7 are formed apart from each other in the longitudinal direction of the flange.

FIG. 3A and FIG. 3B are top views showing two forms of forming the laser weld bead 6 in the second region 8.
As shown in the top views of FIGS. 2A to 2D and the top view of FIG. 3A, the second region 7 includes two first regions that are adjacent to each other in the longitudinal direction of the flange. 7 and 7, separated from each other in the longitudinal direction of the flange and separated every other portion in the longitudinal direction of the flange, or as shown in FIG. A plurality are formed in all. In this specification, the form shown in FIG. 3A is called intermittent welding, and the form shown in FIG. 3B is called continuous welding.

  Conventionally, the joining of the first member 1 and the second member 2 constituting the shock absorbing member is performed by wire joining such as laser welding as shown in the present embodiment rather than point joining such as resistance spot welding. It is known that the use is more advantageous because the torsional rigidity of the shock absorbing member, which is a cylindrical body, can be increased. Further, the impact absorbing member is crushed in a bellows shape while being folded and deformed when it is crushed in the axial direction under an impact load.

FIG. 4 is an explanatory diagram showing the stress acting on the laser welding bead 6 that joins the first member 1 and the second member 2 during the folding deformation.
As shown in FIG. 4, during the folding deformation, the laser weld bead 6 of the first member 1 and the second member 2 has a stress perpendicular to the crushing axis, that is, the laser weld bead 6. On the other hand, the tensile stress indicated by the arrow is generated.

  Therefore, the resistance force against the tensile stress of the laser weld bead 6 is increased or decreased in the longitudinal direction of the flange, so that the laser weld bead 6 is not broken in the first region 7 and compared with the first region 7 in the second region 8. The cylindrical body 4 constituting the shock absorbing member by receiving an impact load by reducing the resistance against the tensile stress and alternately providing the first region 7 and the second region 8 in the longitudinal direction of the flange. It can be stably crushed in the axial direction and deformed into a bellows shape.

  In order to realize this, in the present embodiment, the length of the laser weld bead 6 in the flange width direction in the first region 7, that is, the length of the laser weld bead 6 in the first region 7 in the flange width direction. The projected length is larger than the length of the laser weld bead 6 in the second region 8 in the flange width direction, that is, the projected length of the laser weld bead 6 in the second region 8 in the flange width direction. Set. That is, the projected length in the flange width direction means the length when projected onto a plane orthogonal to the axial direction.

  The projected length in the flange width direction of the laser weld bead 6 in the first region is such a length that the laser weld bead does not break in the first region during crushing, for example, the laser weld bead 6 in the first region 7. It is desirable that the projected length in the flange width direction be 1.9 times or more the plate thickness of the first member 1.

  In the present specification, this projection length is also referred to as “effective joint width”. That is, the effective weld width is the melt-joined length of the mating surfaces of the first member 1 and the second member 2, in other words, the projected length of the joint portion of the laser weld bead 6 in the flange width direction. means.

  The upper limit of the effective joint width W in the first region 7 does not need to be specified, but excessively increasing the effective joint width W in the first region 7 increases the flange width, that is, impact. Since this means increasing the weight of the absorbing member, it may be determined as appropriate in consideration of the target weight of the shock absorbing member.

  The effective junction width in the second region 8 is smaller than the effective junction width in the first region 7. In order to suppress a decrease in welding speed, the effective joint width in the second region 8 is preferably smaller than the effective joint width in the first region 7 and about 1 mm or less.

  In order to ensure the desired shock absorption characteristics, the tensile stress applied to the laser weld bead 6 during crushing deformation or the laser weld bead 6 itself according to the plate thickness and strength level of the shock absorbing member of the present embodiment. It is also necessary to take into account that the characteristics of these are not constant. For example, as the plate thickness of the first member 1 increases, the laser welding bead 6 breaks due to the tensile stress applied to the laser welding bead 6, and further, the first member 1 and the second member 2 are accordingly accompanied. Interfacial peeling is likely to occur on the overlapping surface.

  Further, as the tensile strength TS of the first member 1 increases, the carbon equivalent Ceq (for example, Ceq = C + Si / 24 + Mn / 16 (mass%)), which is an index of the hardenability of the first member 1, increases, and the laser weld bead 6 indicates higher hardness. The hardened laser weld bead 6 exhibits brittle characteristics, and the laser weld bead 6 is liable to break due to the applied tensile stress. As a result, even if the tensile strength of the steel plate is increased or the thickness of the steel plate is increased. It is impossible to improve the impact absorption characteristics commensurate with it.

  In the present embodiment, a plurality of first regions 7 in which the effective bonding width W is 1.9 times or more the plate thickness t of the first member 1 are intermittently formed in the longitudinal direction of the flange. Since a plurality of second regions 8 in which the effective bonding width W is less than 1.9 times the plate thickness t of the first member 1 are formed between the regions 7, regardless of the plate thickness and strength level of the shock absorbing member. In addition, it is possible to suppress breakage of the laser weld bead 6 in the first region 7 even when subjected to an impact load, and to reliably establish a buckling starting point between the first regions 7. Since it can be stably buckled and deformed in a bellows shape in the axial direction, it is possible to reliably ensure good shock absorption characteristics.

  Thus, in this Embodiment, the 1st area | region 7 is an area | region which does not peel the 1st member 1 and the 2nd member 2 by the stress which acts on the flange width direction by the impact load loaded to an axial direction. A plurality of them are provided apart from each other in the longitudinal direction of the flange. On the other hand, the second region 8 has a smaller resistance to breakage of the laser weld bead 6 than the first region 7 and is provided adjacent to each of the plurality of first regions 7.

  Here, as shown in FIG. 2 described above, the characteristics of the shock absorbing member can be improved by arranging the first regions 7 in the longitudinal direction of the flange, for example, at intervals of 30 mm. The distance between the first regions 7 is preferably 20 to 40 mm because it is a starting point when the first region 7 is deformed on the bellows at the time of collision. If this interval is less than 20 mm, the bellows deformation may become an obstacle, and the bellows-like deformation at the time of crushing may become unstable. If it exceeds 40 mm, the second region formed between the first regions 7 may be formed. This is because the laser welding bead 6 in the region 8 breaks and the fracture mode changes, resulting in a reduction in shock absorption characteristics.

In the present embodiment, it is desirable that the laser weld bead 6 is formed over a length of 50% or more of the total length of the cylinder 4 in the flange longitudinal direction.
Further, as shown in FIG. 2, the first region 7 and the second region 8 constituting the laser welding bead 6 formed in one of the left and right flanges 1 a and 1 a are in the axial direction of the cylindrical body 4. With respect to the impact load, it is formed at a position substantially coincident with the first region 7 and the second region 8 constituting the laser weld bead 6 formed on the other one of the two flanges 1a and 1a. Therefore, it is desirable for the cylindrical body 4 to be deformed stably in a bellows shape when the cylindrical body 4 is crushed in the axial direction.

Next, a method for manufacturing the impact absorbing member of the present embodiment will be described.
FIG. 5A is an explanatory view showing a manufacturing process of a conventional shock absorbing member, and FIG. 5B is an explanatory view showing a manufacturing process of the shock absorbing member of the present embodiment.

  In the present embodiment, as shown in FIG. 5B, the second member 2 is overlapped with the left and right flanges 1a, 1a of the first member 1, thereby having a closed rectangular cross section. The cylindrical body 4 that directs the longitudinal direction of the flange in the axial direction intersecting the transverse section is assembled and held in an assembled state using an appropriate jig (not shown).

  Next, laser welding is performed on the left and right flanges 1a and 1a using a laser torch 9, and a plurality of first regions 7 that are formed apart from each other in the longitudinal direction of the flange are adjacent to each other in the longitudinal direction of the flange. As shown in FIG. 5B, every other part of the plurality of portions defined by the two first regions 7 and 7 separated from each other in the longitudinal direction of the flange is arranged in the longitudinal direction of the flange. Alternatively, as shown in FIG. 3 (b), a plurality of second regions 8 are formed on all of the plurality of portions, and the projected length in the flange width direction in the first region 7 is the first. 2 is larger than the projected length in the flange width direction in the region 8, for example, the projected length in the first region 7 is 1.9 times or more the plate thickness of the first member 1, and the second region 8 The projection length at is the first member 1 The laser weld bead 6 is a thickness of less than 1.9 times, to form.

  That is, by this laser welding, the first region 7 in which the first member 1 and the second member 2 are not separated by the stress acting in the flange width direction due to the impact load applied in the axial direction is formed in the longitudinal direction of the flange. A plurality of second regions having a projection length smaller than the projection length in the flange width direction in the first region are provided adjacent to the first region, for example.

In the present embodiment, the impact absorbing member 4 is manufactured by joining the first member 1 and the second member 2 in this manner.
It is desirable to form the first region 7 in a dot shape by this laser welding. For example, in the present embodiment, as shown in FIG. 2A, a combination of spot welding and stitch welding (a welding technique in which a cycle of welding and idle running is continuously repeated to form intermittent weld beads). Alternatively, as shown in FIG. 3B, a weld bead is formed by a combination of spot welding and continuous welding. That is, it is exemplified that the first region 7 is formed by spot welding and the second region 8 is formed by stitch welding or continuous welding.

  The laser welding is not limited to that shown in FIG. 2A, but is I-shaped welding shown in FIGS. 2B and 2C, U-shaped welding shown in FIG. U-shaped welding or the like. In the I-shaped welding, the U-shaped welding, and the odd-shaped U-shaped welding, for example, the first region 7 is formed by welding while moving the laser torch 9 in the flange width direction, and the laser torch 9 is flanged. The second region 8 may be formed between the first regions 7 by welding while moving in the longitudinal direction. Even in these laser weld beads 6, the first region 7 in which the first member 1 and the second member 2 are not separated by the stress acting in the flange width direction due to the impact load applied in the axial direction is provided in the flange. A plurality are formed apart from each other in the longitudinal direction.

  As described above, according to the present embodiment, the projected length of the laser weld bead 6 in the flange width direction is larger than the projected length of the laser weld bead 6 in the second region 8 in the flange width direction. Since a plurality of first regions 7 are intermittently formed in the longitudinal direction of the flange and a second region 8 is formed adjacent to the plurality of first regions 7, an impact load is applied in the longitudinal direction of the flange. Since at least the first region 7 can control the crushing mode in the longitudinal direction without being crushed, it can be reliably crushed and deformed in a bellows shape (accordion shape). A large amount of absorption can be secured.

  Further, by forming not only the first region 7 but also the second region 8, the torsional deformation at the time of the crushing deformation can be suppressed, and the crushing can be stably performed in an accordion shape throughout the entire axial direction. Can be deformed.

  In addition, since the concept of the crushing control of the shock absorbing member of the present embodiment is not influenced by the collision speed, the shock absorbing member of the present embodiment has excellent shock absorbing characteristics in the region from low speed to high speed. It can be demonstrated.

  Furthermore, as shown in FIG. 5 (a), in the conventional assembly method in which the flange of the first member and the second member are overlapped and joined using resistance spot welding, they are overlapped by the electrodes of the resistance spot welder. Since the mating portion is sandwiched with pressure applied from both sides and joined by resistance heating, a flange width of about 20 mm is usually required. However, since laser welding is used in the present embodiment, the welding operation can be performed in a non-contact manner from one side of the overlapping portion, and the flange width of the first member can be set as small as possible. Thus, the weight of the impact absorbing member can be reduced. In other words, in this embodiment, the shock absorbing member can be configured using a member having a narrow flange that is difficult to assemble and weld by resistance spot welding, and the shock absorbing performance per unit weight can be improved. it can.

Furthermore, the present invention will be described more specifically with reference to examples.
In order to take advantage of high-speed weldability, which is a feature of laser welding, and a high degree of freedom in the form of a weld line by robot trajectory control, the inventors have a hat shape having the dimensions shown in FIG. The flanges 10a and 10a of the first member 10 made of a steel plate and the second member 11 made of a closing plate are overlapped and laser welded in the longitudinal direction as shown in FIG. The shock absorbing member shown in FIG. 6 (e) was manufactured.

  Here, FIG. 6B shows an example of the present invention in which the first region 7 is formed in a dot shape by laser welding and the second region 8 is formed by laser stitch welding, and FIG. 6C is a laser welding. FIG. 6D is a comparative example in which the first region is formed in a dot shape and the second region is formed by continuous welding. FIG. 6D is a comparative example in which the entire length is continuously welded by laser welding. (E) is a comparative example in which intermittent welding is performed by laser stitch welding. In the laser stitch welding, the bead length was set to 30 mm and the pitch was set to 30 mm by continuously repeating welding and idling at a pitch of 30 mm.

  Laser welding uses an LD-pumped YAG laser and supplies a pure Ar: 10 L / min flow rate as a shielding gas, so that an output of 4500 W and a spot diameter of 0.6 mm (beam waist position) become the plate surface of the joint. The standard condition is that welding is performed at a welding speed of 3.5 m / min for a 780 MPa class steel 1.4 mm thick plate and welding is performed at 2.5 m / min for a 780 MPa grade steel 1.8 mm thick plate. It was.

  In order to obtain the effective bonding width W, in the present embodiment, the D.D. F. Using the (defocus) conditions, shock absorbing members having two shapes with different flange widths (flange width 24 mm and flange width 12 mm) were produced. A cross-section macro test piece was cut out from the produced member, and its effective bonding width W was measured. Note that the flange width 24mm material can be spot welded, and the flange width 12mm material cannot be spot welded because the width is too small. By reducing the flange width from 24mm to 12mm, the weight of the member is reduced by about 13%. It becomes.

  In order to secure a stable contact surface between the shock absorbing member shown in FIG. 6B to FIG. 6E and the fixing and the cone in the impact crushing test, the thickness is 12 mm at both end portions (side surfaces in FIG. 6). End plates 12, 12 of 150 mm × 150 mm were attached by arc welding.

  In order to investigate the crushing behavior of these impact absorbing members, a falling cone test was performed as shown in FIG. In the falling weight test, 230 kg of steel cone 13 (weight) was dropped freely from a height of 16.1 m above the impact absorbing member to be evaluated, collided at a speed of 64 km / h (calculated value), and crushed shock absorption The members were investigated, and the amount of interfacial debonding and the crushing mode on the overlapping surface occupying the total weld length were evaluated.

In this way, the behavior of various types of weld lines schematically shown in FIG. 6B to FIG. 6E was crushed in the axial direction when an impact load was applied.
The obtained results are summarized in Tables 1 and 2. Table 1 shows the test results for an impact absorbing member having a wide flange (24 mm) that can be spot welded. Table 2 shows an impact absorbing member having a narrow width (12 mm) flange incapable of spot welding.

  The “total length ratio” in Tables 1 and 2 means (total of the projected weld lengths in the flange longitudinal direction) / (total length in the flange longitudinal direction).

In the column of “crush mode” in Tables 1 and 2, the impact absorbing member after crushing is visually observed from the side and front, and a case where bellows-like buckling occurs is good, and the other cases are bad x. .
In Tables 1 and 2, “welded part breakage” indicates that the welded part is broken 50% or more as bad (x), less than 50% 30% or more is almost good ○, and less than 30% is good ○.

In the comprehensive evaluation, the crushing mode ○ and the welded portion fracture ○ were evaluated as “good”, and the crushing mode ○ and the welded portion fractured ◎ were evaluated as “good”.
As shown in Table 1, according to the shock absorbing member of the example of the present invention, the effective joint width of the first region and the projected length of the second region are compared with a member assembled by the same stitch welding or continuous welding. Good crushing mode and weld fracture characteristics can be obtained. In addition, as shown in Table 2, it can be seen that even the shock absorbing member having a narrow flange that cannot perform resistance spot welding has a good crushing mode and welded portion fracture characteristics in the present invention example.

  Furthermore, as shown in Table 1, the flange portion is welded so that the effective joint width W shown in FIG. It can be seen that can be secured. Thereby, the impact absorption characteristic of the impact absorbing member can be improved. The larger the effective joint width W, the greater the effect that can be expected. On the other hand, the welding time for obtaining the effective joint width becomes longer, and depending on the plate thickness, the flange width needs to be expanded for welding, Since this increases the weight, it is desirable that the effective bonding width W be 1.9 times or more and 6.0 times or less the plate thickness of the first member.

  In addition, although the 1st member 10 in a present Example uses what was shape | molded by press brake (bending process), it cannot be overemphasized that the same effect can be anticipated even if it is processing methods, such as press work.

Fig.1 (a)-FIG.1 (p) are explanatory drawings which show the cross-sectional shape example of the various cylinders which comprise the impact-absorbing member which concerns on this invention. FIG. 2A to FIG. 2D are a two-sided view of the cylindrical body and an explanatory view showing an enlarged view of various laser welding beads in the cylindrical body. 3 (a) and 3 (b) are top views showing two forms of forming the laser weld bead in the second region. It is explanatory drawing which shows the stress which acts on the laser welding bead which joins the 1st member and the 2nd member in the case of folding deformation. FIG. 5A is an explanatory view showing a manufacturing process of a conventional shock absorbing member, and FIG. 5B is an explanatory view showing a manufacturing process of the shock absorbing member of the present embodiment. It is explanatory drawing which shows the shape of the impact-absorbing member used in the Example. It is explanatory drawing which shows the point of the falling-fall test performed in the Example. It is a graph which shows an example of the load-displacement curve at the time of a crush box receiving an impact load and crushing to an axial direction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st member 1a Flange 2 2nd member 3 3rd member 4 Cylinder 5 4th member 6 Laser welding bead 7 1st area | region 8 2nd area | region 9 Laser torch 10 1st member 10a Flange 11 Second member 12 End plate 13 Steel cone

Claims (5)

At least a first member having a flange and a second member disposed so as to overlap the first member via the flange; Is an impact-absorbing member comprising a cylindrical body having a laser welding bead for joining the first member and the second member in an axial direction intersecting the transverse section, the laser welding bead for joining the first member and the second member, Laser weld beads
A plurality of first regions that are spaced apart from each other in the longitudinal direction of the flange and two first regions that are adjacent to each other in the longitudinal direction of the flange are separated from each other in the longitudinal direction of the flange. A plurality of second regions formed on a part of the plurality of parts formed on the whole or all of the plurality of parts,
The impact absorbing member, wherein a projected length in the width direction of the flange in the first region is larger than a projected length in the width direction of the flange in the second region.   The impact absorbing member according to claim 1, wherein the second region is formed every other portion in the longitudinal direction of the plurality of portions.   3. The impact absorbing member according to claim 2, wherein a length at which the laser weld bead is not broken in the first region during the crushing is 1.9 times or more of a plate thickness of the first member.   The impact-absorbing member according to any one of claims 1 to 3, wherein the first member has a hat-shaped cross section.   At least after assembling the cylinder having a closed cross section and directing the longitudinal direction of the flange in an axial direction intersecting the cross section by overlapping the second member on the flange of the first member, Laser welding is performed on the flange, and a plurality of first regions are formed apart from each other in the longitudinal direction of the flange, and two first regions that are adjacent to each other in the longitudinal direction of the flange. A plurality of second regions formed on a part or all of the plurality of portions formed apart from each other in the longitudinal direction of the flange, and further, the first region in the first region. By forming a laser weld bead having a projected length in the width direction of the flange larger than a projected length in the width direction of the flange in the second region, Method for manufacturing a shock absorbing member characterized by joining the first member and the second member.

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