JP2002079388A - Method for laser beam welding of shock-absorbing member having excellent shock absorption characteristic against axial collapse - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a break of welded metal and to obtain an excellent shock absorption characteristic. SOLUTION: In the method for welding with a laser beam a steel palate 1 having a hat-shaped cross section which forms a shock absorption member having a closed cross sectional structure and a flat steel plate 2 or a steel plate having a hat-shaped cross section at the flange parts 3 of the steel plate having a hat-shaped cross section, the welding is continuously performed in a way that the width Wb of molten zone on the lapped face of the flange part is set at >=1.4 and <=3.0 times the plate thickness t.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for welding using a laser, and more particularly to a method for welding an impact absorbing member applied when manufacturing an automobile member.

[0002]

2. Description of the Related Art Generally, a shock absorbing member having a closed sectional structure called a front side member is provided on both sides of a front part of a vehicle body of an automobile. Ensure safety. As shown in FIG. 1, the front side member is joined by forming a spot-welded portion 4 on a flange 3 of a steel plate 1 having a hat cross-sectional shape and a steel plate 2 having a flat shape. Conventionally,
In order to enhance the energy absorption characteristics of the impact absorbing member at the time of collision, mainly, the distance between the spots of the spot welded portion 4 is reduced, or the material of the steel plates 1 and 2 is 590M.
A method using a high-strength steel sheet of Pa class has been performed.

[0003] In recent years, there has been a social demand for further improvement of the collision safety of a vehicle body, and several methods have conventionally been proposed to enhance the energy absorption characteristics of a shock absorbing member at the time of a collision.

Japanese Unexamined Patent Publication (Kokai) No. 58-116268 discloses a closed cross-section structure in which a number of notches are arranged in the longitudinal direction on both flange portions of a hat section member provided on a lower portion of a side panel of a vehicle body. There is disclosed a method of improving a shock absorbing property by controlling a crush mode so as to perform regular bellows deformation at the time of a collision while securing strength due to the shock. This technology is a technology for improving the shock absorption characteristics by controlling the crush mode at the time of collision, and is not a technology for improving the strength of the flange welded portion in consideration of the shape of the welded portion and improving the shock absorption characteristics.

Japanese Patent Application Laid-Open No. Hei 6-170568 discloses a front frame which requires rigidity against bending and the like and absorption of impact energy at the time of a collision, a flange section of a member having a hat-shaped cross section in the width direction, and a panel plate. When assembling by laser welding, the welding position is intermittently welded as the end of the flange of the hat-shaped member, thereby increasing the cross-sectional area between welds in the flange width direction contributing to deformation at the time of collision, A method for improving the shock absorbing properties is disclosed.

Japanese Unexamined Patent Publication No. 7-125651 discloses a welding position for a strength member having a closed cross-sectional structure obtained by spot welding or line welding a flange portion of a hat cross-sectional member used for a front side member or the like of an automobile. A method of increasing the average crushing load and improving the collision energy absorption characteristics by defining a specific range in the flange width direction from the corner of the hat cross section member is disclosed. JP-A-6-170
The technologies disclosed in Japanese Patent Application Laid-Open No. 568 and Japanese Patent Application Laid-Open No. Hei 7-125651 are all technologies for improving the energy absorbing ability of a strength member by optimizing a laser welding position. It is not a technique for improving the strength of the part and improving the shock absorption characteristics.

As described above, the conventional technique for improving the energy absorption characteristics of the shock absorbing member is a method by controlling the crush mode at the time of collision and optimizing the welding position. It was not a technique for improving the strength of the weld, and no consideration was given to the shape of the weld required for improving the strength of the weld. For this reason, if the joining strength of the laser welded portion is insufficient, when the impact absorbing member such as the front frame is crushed at the time of a collision, fracture may occur from within the weld metal, and sufficient impact absorbing properties may not be exhibited. Was.

[0008]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, the present invention has been made to improve the strength of a laser welded portion of a shock absorbing member and further improve the shaft safety in order to further improve the collision safety of an automobile. It is an object of the present invention to provide a laser continuous welding method for an overlapped portion, which improves the shock absorbing ability by preventing breakage from a laser welded portion during crushing.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and the gist thereof is as follows.

(1) A method of laser welding a steel plate having a hat cross-section and a steel plate having a flat cross-section or a steel plate having a hat cross-section forming a shock absorbing member having a closed cross-section structure at a flange portion of the steel plate having a hat cross-section. And continuous welding so that the melting width W at the overlapping surface of the flange portions is 1.4 times or more and 3.0 times or less of the plate thickness t, and is excellent in shock absorption at the time of axial crushing. Laser welding method for shock absorbing members.

(2) An impact excellent in shock absorption at the time of axial crushing according to (1), wherein the hat-shaped steel sheet and the flat-shaped steel sheet have a tensile strength higher than 590 MPa. Laser welding method for absorbing members.

(3) Assuming that the thickness of the hat-shaped steel plate and the flat steel plate is t, a distance d = 12t from the vertical wall of the flange in the width direction of the flange.
The laser welding method for a shock absorbing member excellent in shock absorption at the time of axial crushing according to any of the above (1) or (2), wherein the laser welding is performed continuously by laser within a range of ^0.5 .

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below.

Generally, in the method of spot welding the flange portion 3 of the hat-shaped steel plate 1 and the flat steel plate 2 when manufacturing the shock absorbing member as shown in FIG. By reducing the
There has been known a method for improving the energy absorption characteristics of a member when the member is axially crushed. Further, in order to further improve the absorption energy characteristics when the member is axially crushed, the flange portion 3 is continuously welded in the longitudinal direction by a laser as shown in FIG.

However, in any of these welding methods, no consideration has been given to the shape of the welded portion.

The inventor of the present invention used a laser welding method in which the shape of the welded portion was relatively easily controlled, and moved the flange portion 3 of the steel plate 1 having the hat cross-sectional shape of the shock absorbing member as shown in FIG. In the case of performing continuous welding, the influence of the shape of the laser welded portion of the laser welded portion 5 on the impact absorption energy characteristics of the impact absorbing member was studied diligently.

As a result, as shown in FIG. 7, the melting width Wb of the laser welded portion 5 of the flange portion 3 in FIG.
It has been found that by continuously welding the flange portion 3 in the longitudinal direction with a laser so as to be in a range of 1.4 times or more and 3.0 times or less of the above, the shock absorbing energy characteristics of the shock absorbing member can be stably improved. Here, the above-mentioned melting width W
b is defined as the melting width measured on the superposed surface of the steel plate member as shown in FIG.

The present invention has been made based on this finding, and comprises a hat-shaped steel sheet 1 and a flat-shaped steel sheet 2 constituting a shock absorbing member having a closed cross-sectional structure as shown in FIG. When laser welding is performed on the flange portion of a steel plate having a hat cross-sectional shape, the weld width Wb at the overlapped surface of the flange portion is continuous in the longitudinal direction so as to be 1.4 to 3.0 times the plate thickness t. It is characterized by welding.

Here, the reason why the melting width Wb at the overlapping surface of the flange portions is specified to be 1.4 times or more and 3.0 times or less of the plate thickness t is that when the melting width Wb is less than 1.4 times, welding is performed. Insufficient part strength, peeling and rupture at the overlapped surface of the weld metal when the shock absorbing member is axially crushed, sufficient impact absorption cannot be obtained, and when the molten width Wb exceeds 3.0 times, the molten metal during laser welding This is because the possibility of dripping increases.

The shock absorbing member having a closed cross-section structure according to the present invention also includes a case where a pair of hat-shaped steel plates 1 as shown in FIG. .

Even if the steel plate 1 having a hat cross section (square cross section) shown in FIGS. 2 and 3 is replaced with another steel plate having a polygonal cross section, the shock absorbing energy of the shock absorbing member is similarly improved. be able to. Here, the shock absorption energy is a value obtained by integrating the load with the displacement in a load-displacement curve measured when the shock absorbing member is axially crushed at a high speed as shown in FIG. The shock absorbing ability is high.

According to the United States crash safety standard, the collision speed is 56 km / h (about 5.0 × 10 5 in the material strain rate).
² / sec or more) to ensure the safety of the occupant, and the shock absorbing member of the present invention also exhibits excellent effects in this collision speed range.

In general, it is known that the shock absorbing energy characteristics of a shock absorbing member can be improved by improving the tensile strength of a steel plate used for manufacturing the shock absorbing member.

However, normally, the carbon equivalent Ceq = C + Si / 24 + Mn / 16 (% by weight), which is an index of hardenability of the steel sheet component, tends to be high due to the improvement of the tensile strength of the steel sheet, and the conventional shock absorption When a member is manufactured by spot welding, it has been difficult to maintain the soundness of a spot welded portion of a steel sheet having a tensile strength exceeding 590 MPa. For example, as described in a study by Takahashi et al. (“Spot welding of high strength steel”, welding technology (19773 issue), page 24), spot-welded joints are welded like a cross tension test. This is because when a force such as peeling in the peeling direction from the weld in the direction perpendicular to the surface is applied, as the carbon equivalent of the steel sheet increases, the tendency of the fracture to progress into the nugget increases, and the joint strength decreases. .

Therefore, in the conventional method of manufacturing a shock absorbing member by spot welding, the tensile strength is 590 MPa.
When a steel sheet exceeding a is used for a member, a fracture occurs from a spot welded portion of the shock absorbing member when a load due to an axial impact is applied, and the crush mode of the shock absorbing member becomes poor. Conversely, there is a problem that the shock absorption energy is reduced.

On the other hand, as a result of examinations conducted by the inventors and the like, it has been found that even when a shock absorbing member is manufactured using a steel plate having a high carbon equivalent having a tensile strength exceeding 590 MPa, the melting width at the overlapping surface of the flange portion is also large. Wb is continuously welded in the longitudinal direction so as to be 1.4 times or more and 3.0 times or less the thickness t of the plate, so that a crushing mode failure due to a fracture from a welded portion at the time of an axial impact such as spot welding, etc. It was found that there was no problem and excellent shock absorption characteristics were obtained.

Therefore, in the present invention, the melting width Wb of the laser at the overlapping surface of the flange portions is set to 1.4 times or more and 3.0 times or less of the plate thickness t, and the tensile strength is 590M.
By manufacturing the shock absorbing member using a steel plate higher than Pa, the shock absorbing characteristics can be further improved.

Further, the inventors of the present invention have proposed that the flange portion of the shock absorbing member be continuous with a laser beam in the longitudinal direction when the melt width Wb at the overlapped surface is 1.4 to 3.0 times the plate thickness t. When welding, the position of the welded portion 5 of the flange portion 3 of the steel plate 1 having the hat cross-sectional shape shown in FIGS. 2 and 3 is such that the thickness of the steel plate is t as shown in FIG. Distance d = 12t ^{0.5 in the} flange width direction from the vertical wall part 1
It has been found that by performing continuous welding by laser in the longitudinal direction of the flange so as to fall within the range, the shock absorbing ability of the shock absorbing member at the time of axial crush can be further improved.

Therefore, in the present invention, the melting width Wb of the laser at the overlapping surface of the flange portions of the shock absorbing member is set to be 1.4 times or more and 3.0 times or less of the plate thickness t, and is used for the member. the plate thickness of the steel sheet in the case of the t, and be continuously welded by a laser in the range of the distance d = 12t ^0.5 from the vertical wall portion of the flange in the width direction of the flange. At this time, by manufacturing the shock absorbing member using a steel plate having a tensile strength higher than 590 MPa, the shock absorbing energy characteristics of the shock absorbing member at the time of axial crushing are further improved.

[0030] Outside the range of the distance d = 12t ^0.5 from the vertical wall portion of the flange in the width direction of the flange, binding is reduced with respect to the flange of the weld, especially excellent impact-absorbing ability when the shaft crushing member obtained Absent.

[0031]

The present invention will be described below with reference to examples. FIG. 7 is a cross-sectional view of the shock absorbing member used as an example. Hat-shaped steel sheet 1 that constitutes the shock absorbing member
And the flat steel plate 2 has a tensile strength of 440 to 9
80MPa, thickness t is 0.8mm or 1.2m
m, and the flange length Wf of both flange portions 3 of the steel plate 1 having the hat cross-sectional shape is 20 mm, the length Wc of the horizontal wall portion is 60 mm, the height h of the vertical wall portion is 40 mm, and the member length L is It was 300 mm.

For laser welding, a YAG laser was used, the laser oscillation output was 2 kW, and the welding speed was 0.8 to 3.0 m / m.
in. The laser beam is focused on a steel plate,
The focused spot diameter was 0.5 mm. The relative value (Wb / t) of the laser melting width Wb to the plate thickness t at the overlapping surface of the flange portion and the distance d in the flange width direction from the vertical wall portion of the flange to the laser welded portion 4 are within the scope of the present invention. And changed it to the range outside of it.

In order to investigate the shock absorbing properties of these shock absorbing members, a weight of 200 kg was dropped freely from a height of 12.5 m, and was hit against the members at a speed of 56 km / h, and a load-displacement curve obtained at this time was used. The shock absorption energy was determined.

Table 1 shows the results. In Table 1, the absorbed energy was measured using a steel plate having a tensile strength of 440 MPa, at a position where the distance from the vertical wall to the welded portion was 8.0 mm, and at a condition of laser melting width Wb / plate thickness t = 0.75. 100m displacement of shock absorbing member when continuously welded in the longitudinal direction
Assuming that the absorbed energy at m is 1.0, a relative value to it was used.

From Table 1, in the case of the shock absorbing member manufactured using the steel plate having the same thickness, the present invention example shows that the relative value (Wb / t) of the melting width Wb of the laser at the overlapping surface of the flange portion to the thickness t. ) And the condition of the distance d in the width direction of the flange from the vertical wall portion of the flange to the laser welded portion 5 was out of the range of the present invention, so that excellent shock absorption characteristics were obtained.

[0036]

[Table 1]

[0037]

According to the present invention, an excellent shock absorbing ability can be stably obtained at the time of a head-on collision of an automobile, which is extremely advantageous for industrial use.

[Brief description of the drawings]

FIG. 1 is a perspective view of an impact absorbing member manufactured by using a spot welding method.

FIG. 2 is a perspective view showing an example of a shock absorbing member manufactured by using the laser welding method of the present invention.

FIG. 3 is a perspective view showing an example of a shock absorbing member manufactured by using the laser welding method of the present invention.

FIG. 4 is a graph showing a relationship between a crush displacement of an impact absorbing member and an axial crush load.

FIG. 5 is an enlarged sectional view around a welded portion in the laser welding method of the present invention.

FIG. 6 is a graph showing the relationship between the melting width Wb / plate thickness t and the impact absorption energy during laser welding.

FIG. 7 is a sectional view of a shock absorbing member according to an embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Steel plate with hat cross section 2 Flat steel plate 3 Flange part 4 Spot welding part 5 Laser welding part t Plate thickness Wf Flange length Wc Length of horizontal wall part h Height of vertical wall part d Welding from vertical wall part of flange Distance in the width direction of the flange to the section Wb Laser melting width

 ──────────────────────────────────────────────────続 き Continued on front page (72) Inventor Takashi Tanaka 20-1 Shintomi, Futtsu City Nippon Steel Corporation Technology Development Headquarters (72) Inventor Masahiro Ohara 1 Nishinoshu, Oita, Nippon Steel Corporation F-term in Oita Works (reference) 4E068 BA01 BF00 CA08 DA00

Claims (3)

[Claims] 1. A method of laser welding a steel plate having a hat cross-sectional shape and a steel plate having a flat cross-section or a steel plate having a hat cross-sectional shape constituting a shock absorbing member having a closed cross-sectional structure at a flange portion of the steel plate having a hat cross-sectional shape, The melting width W at the overlapping surface of the flange portions is 1.4 times or more the plate thickness t;
A laser welding method for a shock absorbing member having excellent shock absorption at the time of axial crushing, wherein continuous welding is performed so as to be 3.0 times or less. 2. The shock-absorbing member according to claim 1, wherein the hat-shaped steel sheet and the flat-shaped steel sheet have a tensile strength of more than 590 MPa. Laser welding method. Wherein the thickness of the steel sheet and the flat shape of the hat cross-section in the case of a t, the laser by within the distance d = 12t ^0.5 in the width direction of the flange from the vertical wall portion of the flange 3. The laser welding method for an impact absorbing member having excellent impact absorption at the time of axial crushing according to claim 1, wherein the laser welding is performed continuously.