KR20190064006A - Automotive bumper beam - Google Patents

Abstract

The present invention relates to a vehicle bumper beam. The vehicle bumper beam includes: a support part protruding forwards; upper and lower buffer parts having a section curved triply into an approximately rectangular shape to form upper and lower shock absorption spaces in the upper and lower parts of the support part, respectively; and a connection part connecting the upper and lower buffer parts. One panel is curved several times through a roll forming method to form a B-shaped section, and after the formation work, the panel has a predetermined length in a horizontal direction and has preset curvature in accordance with the shape of the front or rear side of a vehicle for shock absorption spaces to be placed in the upper and lower parts of the vehicle bumper beam to form a B-shape. Therefore, collision energy generated when the vehicle collides is effectively absorbed to prevent damage to the body of the vehicle and to protect passengers safely.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automotive bumper beam,

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a bumper beam for a vehicle, and more particularly, to a bumper beam for a vehicle that absorbs impact energy generated in a vehicle collision.

Generally, a bumper unit of a vehicle absorbs an impact force to elastically deform when a vehicle collides, minimizes physical damage to the vehicle body, protects the engine and various devices mounted on the hood and the engine room, And is mounted on the front and rear of the vehicle so as to cover the vehicle.

These bumper units must satisfy impact requirements according to the regulations of each country, have high rigidity and impact resistance in a wide temperature range, and have a small expansion and contraction due to temperature.

For example, the following Patent Document 1 discloses a bumper unit configuration according to the prior art.

Fig. 1 is a schematic view of a conventional bumper unit, and Fig. 2 is a sectional view of the bumper beam shown in Fig.

1, the bumper unit 1 according to the prior art includes bumper beams 2 arranged in the vehicle width direction from the front and rear of the vehicle, bumper beams 2 arranged in front of the bumper beam 2, A bumper cover 4 that encloses the bumper beam 2 and the energy absorber 3 and a stay 6 that interconnects the bumper beam 2 and the front side member 5.

This bumper unit 1 absorbs a part of the impact energy while the energy absorber 3 is being compressed in the event of a vehicle collision and the remaining impact energy that has not been absorbed by the energy absorber 3 is absorbed by the rear bumper beam 2 and the stay 6), it is possible to protect the safety of passengers and various devices.

The bumper beam 2 is manufactured by processing a compression press (not shown). However, recently, as shown in FIG. 2, one panel is bent and formed several times through roll forming to form a closed space 7) are formed.

The bumper beam 2 is formed by bending the panel so that two closed spaces 7 are formed on the upper and lower sides, and then welded to each other in a final stage.

On the other hand, the present applicant has filed and filed a bumper beam configuration for a vehicle disclosed in the following patent document 2 and filed.

Patent Document 2 discloses a bumper beam configuration for a vehicle composed of an inner beam forming an up-and-down asymmetric space and an outer beam fixed to the front surface of the inner beam so as to correspond to a collision portion along the height of the vehicle body.

Korean Patent Registration No. 10-0527125 (published on November 9, 2005) Korean Patent Registration No. 10-1436815 (Announcement on Nov. 3, 2014)

However, in Patent Document 1, both ends of the panel are formed so as to meet each other at the front center portion of the bumper beam, and both ends of the panel, which meet at the center portion of the bumper beam, are bent to come into contact with the rear inner surface of the panel.

Patent Document 1 configured in this way complicates the construction of the roll former due to the need to bend both ends of the panel, and the welding operation is performed in such a state that both bent ends of the panel are in contact with the rear inner surface of the panel Accordingly, it is difficult to stably fix the object to be welded, resulting in deterioration in workability and delay in working time.

In the case where space is formed as mutually asymmetric as in Patent Document 2, the roll formers used in the roll forming apparatus are also required to be formed symmetrically with respect to each other, thereby complicating the structure of the forming apparatus.

Further, when the inner beam and the outer beam are individually manufactured and fixed by the welding method, there is a problem that the amount of welding work increases and the working time becomes long.

Further, the portion where the welding operation is performed is liable to be broken or separated by an impact force at the time of a vehicle collision. Thus, there is a limit in completely preventing the safety of the occupant and the breakage of various devices in the event of a vehicle collision.

Further, there is a problem that wrinkles are generated on the rear surface of the bumper beam which is concavely formed in the bending molding process so that the bumper beam has a certain curvature.

Conventionally, in order to prevent the wrinkles of the bumper beam, additional processes are performed using a wrinkle-improving fixture, thereby increasing work processes and lowering workability.

SUMMARY OF THE INVENTION An object of the present invention is to provide a bumper beam for a vehicle that absorbs collision energy generated when a vehicle collides with the vehicle, thereby preventing damage to the vehicle body and protecting the occupant.

It is another object of the present invention to provide a vehicle bumper beam capable of minimizing a welding portion between both ends of a panel and preventing breakage and separation of a welding portion in a process of bending and forming one panel sequentially through a roll forming forming method .

It is still another object of the present invention to provide a vehicle bumper beam capable of improving workability in welding work at both ends of a panel and improving bonding strength at a welding portion.

It is still another object of the present invention to provide a bumper beam for a vehicle which can improve workability by changing a bending angle at the time of bending molding of a panel.

It is still another object of the present invention to provide a vehicle bumper beam capable of preventing wrinkles from being generated on the rear surface of a bumper beam concavely formed in the bending process of the bumper beam.

In order to achieve the above object, a bumper beam for a vehicle according to the present invention includes a support portion protruding forwardly, and an upper and a lower shock absorbing spaces formed at upper and lower ends of the support portion, And a connecting portion connecting the upper and lower cushioning portions, wherein the one panel is formed by bending a plurality of times by a roll-forming forming method so that the cross-section is formed into a B shape, And the support portion has a front web vertically disposed on the front surface so as to have a cross section in the form of a C shape and a rear web disposed on the upper and lower ends of the front web, The first support bar and the second support bar comprising a first support bar and a second support bar, And are inclined from the upper end of the front web toward the upper side and the lower side, respectively.

As described above, according to the bumper beam for a vehicle according to the present invention, since the shock absorbing spaces are provided at the upper and lower portions of the vehicle bumper beam in the shape of B, the impact energy generated upon collision of the vehicle is effectively absorbed, And the occupant can be safely protected.

According to the present invention, it is possible to minimize damage to both ends of the panel and to minimize damage and separation of the welded part during the process of bending and forming one panel sequentially by the roll forming method .

Particularly, according to the present invention, when an impact is applied forward of the bumper beam, the impact force can be effectively buffered by using the upper and lower shock absorbing spaces formed in a rectangular shape having a longer transverse length than the longitudinal length, By forming embossed portions in the cushioning portions to enlarge the cross-sectional area, it is possible to reinforce the rigidity at the time of vehicle collision.

According to the present invention, by arranging the first and second support bars of the support portion obliquely upward or downward, it is possible to improve the rigidity against the impact applied from above or below the bumper beam, It is possible to reduce the degree of difficulty of the molding operation and make the operation easier, as compared with the case where the second support bars are respectively bent along the horizontal direction to perform the roll forming, and the workability can be improved.

In addition, according to the present invention, the connecting portion disposed at the central portion of the bumper beam and the front web formed by bending the both end portions of the panel are overlapped with each other and welded together to improve the rigidity of the central portion of the bumper beam, Can be minimized.

Further, according to the present invention, seam welding is applied to increase the durability by joining the welded portions, thereby preventing separation or damage of the welded portions due to an impact at the time of vehicle collision and improving the working speed .

In addition, according to the present invention, it is possible to prevent the deterioration of the appearance quality of the front surface of the bumper beam due to the deformation of the front web caused by the heat applied during the welding operation and to prevent the detachment or damage of the welded portion during the bending operation of the bumper beam And it is possible to improve the workability of the welding work and to improve the bonding strength of the welded portion.

Further, according to the present invention, it is possible to minimize the occurrence of wrinkles by minimizing the compression surface of the bumper beam, that is, the back surface of the bumper beam that is concavely formed during the bending operation of the bumper beam.

Further, according to the present invention, the embossed portions provided in the upper and lower cushioning portions can be formed in a planar shape to reduce the maximum amount of thrust at the time of impact and reduce the strain caused by the energy dispersing action.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a configuration diagram of a conventional bumper unit,
FIG. 2 is a cross-sectional view of the bumper beam shown in FIG. 1,
3 is a perspective view of a bumper beam for a vehicle according to a preferred embodiment of the present invention,
4 is a cross-sectional view taken along the line A-A 'shown in Fig. 3,
5 is a perspective view of a bumper beam joined by seam welding,
FIG. 6 is a cross-sectional view of the bumper beam shown in FIG. 5,
FIGS. 7 to 12 are graphs of collision test process and result of a bumper beam for a vehicle and a bumper beam not embossed according to a preferred embodiment of the present invention.

Hereinafter, a vehicle bumper beam according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 3 is a perspective view of a bumper beam for a vehicle according to a preferred embodiment of the present invention, and FIG. 4 is a sectional view taken along the line A-A 'shown in FIG.

Hereinafter, the right side coupled to the front side member of the vehicle body through the stay will be referred to as the rear side of the bumper beam, and the opposite side will be referred to as the front side of the bumper beam.

Accordingly, terms indicating directions such as 'forward, backward', 'upward' and 'downward' are defined as indicating the respective directions with reference to the front and rear surfaces.

In the present embodiment, the front bumper beam installed on the front surface of the vehicle is used. However, the present invention is not limited to this but it is also applicable to the rear bumper beam installed on the rear surface of the vehicle.

As shown in FIGS. 3 and 4, a bumper beam 10 for a vehicle according to a preferred embodiment of the present invention is formed by folding and molding one panel several times in a roll-forming forming manner, And 41 may be formed so as to have a substantially 'B' shape in cross section, and may be formed to have a predetermined curvature according to the front shape of the vehicle with a predetermined length in the horizontal direction after the molding operation.

Here, the vehicle bumper beam 10 can be manufactured using a panel made of high tensile steel or ultra high strength steel.

The high tensile steel means a steel having a tensile strength higher than that of ordinary steel, and a tensile strength not lower than 50 kg / mm 2.

These high-strength steels are improved in performance by adding silicon, manganese, nickel, chromium, copper, etc. to carbon steel containing about 0.2% of carbon.

The ultrahigh-strength steel is a steel having a tensile strength of 50 kg / mm 2 and a higher tensile strength than the high-strength steel.

Such super high tensile steel is produced by adding a small amount of silicon and manganese to a processing heat treatment called ausforming so as to have a tensile strength of 200 kg / mm 2 or more and a yield strength of 200 kg / Therefore, it is widely used for materials such as shipbuilding and bridges.

The bumper beam 10 for a vehicle has a supporting portion 20 protruding forward and an upper and a lower shock absorbing spaces 31 and 41 at the upper and lower ends of the supporting portion 20, And may include upper and lower cushioning portions 30 and 40 that are triple-folded.

The support portion 20 is formed by bending a panel several times to form an upper buffer portion 30 and a lower buffer portion 40 and then bending both ends of the panel toward the front surface again, 30 and the lower cushioning portion 40 by welding in a state where they are overlapped with each other.

As shown in FIG. 4, the supporting part 20 includes a front web 21 vertically disposed on the front surface so as to have a substantially 'C' shape in section, and a front web 21 extending toward the rear of the front web 21 And may include first and second support bars 22,23.

The front web 21 is formed in such a manner that both ends of a panel bent and folded so as to overlap with the connection portion 100 are in contact with each other and the front and rear cushioning portions 30, The connecting portion 100 is disposed in a state of being welded.

The first and second support bars 22 and 23 are arranged to extend upward and downward with respect to imaginary first and second horizontal lines X1 and X2 extending from the left upper end and the lower end of the front web 21 to the rear side, And may be formed to be inclined by a predetermined inclination angle alpha.

For example, the first support bar 22 may be formed at an upper end of the front web 21 to be inclined upward toward the rear side so as to form an angle of about 10 ° to 80 °, preferably 25 ° to 40 ° with the first horizontal line .

The second support bar 23 is formed at an angle of about -10 ° to -80 °, preferably -25 ° to -40 ° with respect to the second horizontal line at the lower end of the front web 21, .

As described above, according to the present invention, the first and second support bars of the support portion are inclined rearwardly or downwardly, respectively, so that the rigidity against the impact applied at the upper portion or the lower portion of the bumper beam can be improved.

In addition, the present invention can improve the rigidity of the center portion of the bumper beam by bending the panel several times, and arranging the front webs formed by bending the both ends of the panels on the rear surface of the connecting portion disposed at the center of the panel.

In addition, the present invention can prevent deterioration of the appearance quality due to the deformation of the front web caused by heat applied during the welding operation, and can prevent separation or damage of the welded portion during the bending operation of the bumper beam.

In addition, in the process of folding and forming the panel, a portion where the first and second support portions and the upper and lower buffer portions are connected to each other is formed at an obtuse angle so that the first and second support bars are bent along the horizontal direction, It is possible to improve the workability by lowering the degree of difficulty of the molding operation and to reduce the number of steps of the roll forming molding apparatus as compared with the case of molding at right angles with the cushioning portion.

The upper buffer part 30 includes a first vertical bar 32 connected to the upper end of the connection part 100 and disposed along the vertical direction, a first horizontal bar 32 bent rearward from the upper end of the first vertical bar 32, And a second vertical bar 34 bent downward from a rear end of the first horizontal bar 33 and connected to a rear end of the first support bar 22. [

Accordingly, the first support bar 22 is inclined at a certain angle toward the rear upper side in the upper shock absorbing portion 30, so that the upper shock absorbing space 31 may be formed.

Therefore, in order to prevent the wrinkles from being generated by minimizing the compression surface on which the compressive force acts during the bending process of the bumper beam 10, that is, the back surface of the concave bumper beam 10, May be shorter than the length of one vertical bar (32).

For example, in the present embodiment, the second vertical bar 34 may be provided with a length (h) of about 1/2 of the length 2h of the first vertical bar 32.

As described above, according to the present invention, since the first supporting bar is formed so as to be inclined upward toward the rear side, the compression face can be minimized to prevent the occurrence of wrinkles in the banding molding process.

Of course, the present invention is not necessarily limited to this, and the length ratio between the first vertical bar 32 and the second vertical bar 34 may be changed according to the inclination angle of the first support bar 22.

That is, the longer the inclination angle alpha of the first support bar 22 is, the shorter the length of the second vertical bar 34 is. As the inclination angle alpha of the first support bar 22 becomes smaller, The length of the vertical bar 34 can be increased.

The upper shock absorbing space 31 is formed in a rectangular shape whose lower side is inclined. However, the present invention can be applied to the case where the first support bar 22, the first and second vertical bars 32 and 34, The upper shock absorbing space 31 may be formed in a square shape whose lower side is inclined and whose remaining sides are the same or a substantially rectangular shape whose upper side length is longer than both side sides by adjusting the length ratio of the upper shock absorbing space 31. [

That is, the length of the first supporting bar 22 and the length of the first horizontal bar 33 is set to be shorter than the length of the first and second vertical bars (or the second vertical bar) so that the impact applied in front of the bumper beam 10 can be sufficiently absorbed. 32 and 34, so that the upper shock absorbing space 31 is formed to have a substantially rectangular shape with a longer transverse length than the longitudinal length.

Likewise, the lower cushioning portion 40 includes a third vertical bar 42 connected to the lower end of the connection portion 100 and disposed along the vertical direction, a second vertical bar 42 bent rearward from the lower end of the third vertical bar 42, And a fourth vertical bar 44 which is bent upward from the rear end of the horizontal bar 43 and the second horizontal bar 43 and is connected to the rear end of the second support bar 23.

Accordingly, the second support bar 23 is inclined at a predetermined angle toward the rear lower side in the lower shock absorbing portion 40, so that the lower shock absorbing space 41 may be formed.

Therefore, in order to minimize the generation of wrinkles by minimizing the compression surface on which the pressing force acts on the bumper beam 10 during the bending process of the bumper beam 10, that is, the rear surface of the concave bumper beam 10, The length of the vertical bar 43 may be shorter than the length of the vertical bar 43.

For example, in the present embodiment, the fourth vertical bar 44 may be provided with a length (h) of about 1/2 of the length 2h of the third vertical bar 32.

The lower shock absorbing space 41 is formed in such a manner that the lengths of the second support bar 23 and the third horizontal bar 43 are equal to the lengths of the third and fourth vertical bars 42 and 44 And may be formed in a substantially rectangular shape having a length longer than a longitudinal length.

As described above, in the case where an impact is applied to the front side of the bumper beam, the impact force can effectively be buffered by using the upper and lower shock absorbing spaces formed in a rectangular shape having a longer transverse length than the longitudinal length.

The upper and lower shock absorbing spaces 31 and 41 are formed symmetrically with respect to each other and the height 2h of the upper and lower shock absorbing spaces 31 and 41 is about 2 Can be formed.

On the other hand, the first and third vertical bars 32 and 42 may have first and second embossed portions 35 and 45 for reinforcing the rigidity, respectively, so as to buffer an impact force at the time of a vehicle collision.

The first and second embossed portions 35 and 45 are formed on the first and third vertical bars 32 and 42 so as to protrude toward the rear in at least one concave manner or convexly protruding forward, By increasing the cross-sectional area of the vertical bars 32 and 42, it is possible to reinforce the rigidity of the first and third vertical bars 32 and 42 in the event of a vehicle collision.

Here, the first and second embossed portions 35 and 45 are recessed or protruded from the first and third vertical bars 32 and 42 along the longitudinal direction of the first and third vertical bars 32 and 42, To increase the cross-sectional area of the first and third vertical bars 32 and 42, and is preferably formed at a position corresponding to the upper and lower shock-absorbing spaces 31 and 41.

3 and 4, one of the first and second embossed portions 35 and 45 is recessed rearwardly. However, the shape of the first and second embossed portions 35 and 45, It should be noted that the number can be variously changed according to the size of the bumper beam 10.

In particular, in this embodiment, the first and second embossed portions 35 and 45 may include first and second vertical surfaces 36 and 46 vertically arranged at the central portion, respectively.

As described above, according to the present invention, an embossed portion having a vertical surface on the entire upper and lower cushioning portions can be formed to reduce the maximum thrust amount during collision and reduce the strain due to the energy dispersing action.

The lower end of the first vertical bar 32 and the upper end of the third vertical bar 42 are connected to the connecting part 100 and the connecting part 100 is welded to the front surface of the front web 21 of the supporting part 20, . ≪ / RTI >

For example, the connection portion 100 and the front web 21 may be joined by seam welding.

The seam welding is a method in which a workpiece to be welded is disposed between a pair of roller electrodes and the spot welding is continuously repeated while rotating the electrode while applying pressure to the electrode.

For example, FIG. 5 is a perspective view of a bumper beam joined by seam welding, and FIG. 6 is a cross-sectional view of the bumper beam shown in FIG.

5 and 6, when the connecting portion 100 and the front web 21 are joined together by seam welding, the connecting portion 100 and the front web 21 are vertically arranged and welded in pairs, Points P are formed at predetermined intervals.

In the meantime, the present invention can be modified so that the connecting portion and the front web are joined by a laser welding method other than the seam welding method.

The laser welding is a method in which a high energy laser beam is used to transfer high energy to a workpiece to be heated and welded. It is possible to weld even a minute size up to about 0.2 mm, Since the object absorbs the energy of the laser to generate heat, it can be heated and cooled more efficiently than other methods.

In the case of joining the connecting portion 100 and the front web 21 by the laser welding method, welding lines in which welding points P are continuous are arranged vertically in a zigzag shape in the connecting portion 100 and the front web 21, As shown in FIG.

Needless to say, the present invention is not necessarily limited to this, and welding may be performed such that weld lines continuous from the welding points on the front surface of the connection portion and the rear surface of the front web are continuously formed in parallel vertically.

As described above, according to the present invention, the welded portion of the connecting portion and the front web is minimized, and the welded portion is bonded using the seam welding method to increase the durability, thereby preventing the welded portion from being separated or damaged .

Next, with reference to Figs. 7 to 12, collision test results of a vehicle bumper beam according to a preferred embodiment of the present invention will be described.

FIGS. 7 to 12 are graphs of a crash test process and a result of a bumper beam for a vehicle and a bumper beam not embossed according to a preferred embodiment of the present invention.

FIGS. 7 and 8 show operation states for testing the bumping moment of the bumper beam for a vehicle and the bumper beam for an embossed bumper according to the present embodiment, respectively.

In FIGS. 9 and 10, an operating condition for testing a center barrier collision at a speed of about 10 km / h in accordance with the regulations of the Insurance Institute for Highway Safety (IIHS) is shown.

Fig. 11 is a graph showing a bending moment test result of the bumper beam for vehicle and the bumper beam not embossed shown in Figs. 7 and 8, A barrier test result graph is shown.

Table 1 is the test result table shown in FIG. 11 and FIG.

In this embodiment Embossless Bending moment test max moment 7,359 Nm 6,341 Nm IIHS Central Barrier Test max stroke 78.5 mm 122.4 mm max force 82.8 kN 76.0 kN

As shown in Table 1 and Figs. 11 and 12, the bumper beam for a vehicle according to the present embodiment increases the maximum moment as a result of the bending moment test by about 10 Nm as compared with the case where the embossment is not applied, Is reduced by about 43 mm, and the maximum force is increased by about 4.8 kN.

As described above, according to the present invention, by providing the shock absorbing spaces at the upper and lower portions of the vehicle bumper beam in the shape of B, it is possible to effectively absorb the impact energy generated at the time of vehicle collision to prevent damage to the vehicle body, can do.

Although the invention made by the present inventors has been described concretely with reference to the above embodiments, the present invention is not limited to the above embodiments, and it goes without saying that various changes can be made without departing from the gist of the present invention.

The present invention relates to a vehicle bumper beam technology for protecting a vehicle occupant from damage by effectively absorbing impact energy generated at the time of a vehicle collision by providing a shock absorbing space at the top and bottom of the vehicle bumper beam, .

10: vehicle bumper beam 20:
21: front web 22, 23: first and second supporting bars
30: upper buffer portion 31: upper shock absorbing space
32, 34: first and second vertical bars 33: first horizontal bars
35: upper embossed portion 36: first vertical surface
40: Lower buffer part 41: Lower shock absorbing space
42, 44: third and fourth vertical bars 43: second horizontal bar
45: lower emboss part 46; The second vertical surface
100: Connection P: Welding point

Claims (7)

A support portion protruding forward,
Upper and lower cushioning parts formed in a triangular shape in cross section to form upper and lower shock absorbing spaces at the upper and lower ends of the support part, respectively,
And a connection portion connecting the upper and lower buffer portions
One panel is formed by bending a plurality of times by a roll forming forming method to have a cross section of a B shape and having a preset length in the horizontal direction after the molding operation and having a predetermined curvature according to the front or rear shape of the vehicle,
The supporting portion may include a front web disposed perpendicularly to the front surface so as to have a cross-
And first and second support bars disposed on the upper and lower ends of the front web toward the rear, respectively,
Wherein the first support bar and the second support bar are each inclined from an upper end of the front web toward a rear upper side and a lower side of the front web. The method according to claim 1,
Wherein the front web is formed on the rear surface of the connection portion so that both ends of the panel are in contact with each other,
Wherein the bumper beam is welded in a state of overlapping with the connecting portion. 3. The method of claim 2,
The upper buffer portion includes a first vertical bar connected to an upper end of the connection portion and disposed along a vertical direction,
A first horizontal bar bent from the upper end of the first vertical bar toward the rear,
And a second vertical bar connected to a rear end of the first support bar bent downward from a rear end of the first horizontal bar,
An upper shock absorbing space is formed in a rectangular shape in cross section inside the upper shock absorbing portion,
Wherein the second vertical bar is formed to have a length shorter than a length of the first vertical bar so as to prevent a wrinkle caused by a compressive force during a bending molding process. The method of claim 3,
Wherein the lower cushioning portion includes a third vertical bar connected to a lower end of the connection portion and arranged in a vertical direction,
A second horizontal bar bent rearward from a lower end of the third vertical bar,
And a fourth vertical bar bent upward from a rear end of the second horizontal bar,
A lower impact absorbing space is formed in a rectangular shape in cross section inside the lower shock absorbing part,
Wherein the fourth vertical bar is formed to have a length shorter than a length of the third vertical bar so as to prevent a wrinkle caused by a compressive force during a forming process of the bending beam. 5. The method of claim 4,
Wherein the upper shock absorbing space is formed in a rectangular shape in which the length of the first support bar and the first horizontal bar is longer than the length of the first and second vertical bars and the transverse length is longer than the vertical length,
Wherein the lower shock absorbing space is formed in a rectangular shape in which the length of the second support bar and the third horizontal bar is longer than the length of the third and fourth vertical bars and is longer than the vertical length,
And the upper and lower shock absorbing spaces are formed in a shape symmetrical to each other. 3. The method of claim 2,
The front web and the connecting portion are jointed by seam welding,
Wherein the connecting portion and the front web are vertically disposed to form pairs of welding points at predetermined intervals. 7. The method according to any one of claims 1 to 6,
Wherein at least one embossed portion is concavely recessed toward the rear or protruded forward and convex so as to reinforce the rigidity at the time of a vehicle collision by extending a sectional area of each of the upper and lower cushioning portions,
Each embossed portion is formed at a position corresponding to the upper and lower shock absorbing spaces,
And a vertical surface formed vertically is formed in each embossed portion.

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