JPH0732180A - Laser beam welding method for galvanized steel sheets - Google Patents

Abstract

PURPOSE:To prevent the occurrence of blowholes by supporting the laser beam irradiation side galvanized steel sheet ends without restraining, melting and deforming the ends by using a laser beam in advance and then, superposing the galvanized steel sheets on each other to perform welding. CONSTITUTION:The galvanized steel sheets 1 and 2 are held in a state with the end 5 not restrained by restraining tools 3a, 3b, 4a and 4b. A the more restraining side position 7 than the superposed welding position 8, only the galvanized steel sheet 1 is melted by the laser beam to form a melting part 7, the end 5 is deformed to the irradiation side by heat shrinkage, a gap 9 is formed and then, a lap weld bead 8 is formed. Zinc vapor generated between the steel sheets 1 and 2 escapes to the gap 9 and the weld bead 8 can be formed without generating weld defects such as pits and blowholes. In addition, in the melting part 7, the more the irradiation side melting width is widened and the more the opposite side melting width is narrowed, the gap 9 can be widened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of lap welding a galvanized steel sheet using a laser (hereinafter referred to as lap laser welding or laser lap welding).

[0002]

2. Description of the Related Art When two galvanized steel sheets are layered and laser-welded, zinc vapor rapidly generated between the steel sheets blows molten metal and spatters violently. Moreover, pits and blow holes frequently occur in the welding bead. It has long been known that the good appearance and mechanical strength of weld beads cannot be ensured. It is also well known that good lap welding can be performed by forming an appropriate gap between galvanized steel sheets, and various methods are known as a method for forming the gap. For example, JP-A-6
According to Japanese Patent Laid-Open No. 1-27189, plastic working is performed in advance so that voids with appropriate intervals can be formed between galvanized steel sheets. Such a method is not limited to lap laser welding, but is also effective in arc welding as seen in JP-A-62-179869. According to this invention, at least one of the base materials to be welded is provided with a convex portion to form a gap around the welded portion, and arc welding is performed.

In addition to the method of previously providing a gap between galvanized steel sheets as described above, a method of inserting a third member between galvanized steel sheets to form a gap is also disclosed. For example, Japanese Patent Application Laid-Open No. 4-279291 discloses a welding method in which paper is sandwiched between steel plates, and Japanese Patent Application Laid-Open No. 4-288986 discloses a method in which a thin sheet made of a combustible porous material is sandwiched between steel plates for welding. ing.

In addition to the method of forming a gap between galvanized steel sheets, a method of removing zinc in a welded portion before welding is also disclosed. For example, in the method disclosed in Japanese Unexamined Patent Publication No. 4-231190, laser light is separated into two, a concentrated laser light having a high energy density and a concentrated laser light having a low energy density, and zinc in the welded portion is removed by the laser light having a low energy density. It is said that they are vaporized and separated and then melted and welded by a laser beam with high energy density. In addition, JP-A-4-251468
In the method disclosed in the publication, the output of laser light is controlled to alternately irradiate a laser light with a pulse with a low peak and a laser light with a high peak, and the zinc plating is removed with the laser light with a low peak. It says that welding will be performed with high laser light.

[0005]

The above-mentioned conventional methods have problems. That is, JP-A-6
As disclosed in JP-A-1-27189 and JP-A-62-179869, in a method of forming a gap between galvanized steel sheets by subjecting a material to be welded to a press work in advance,
The number of processing steps before welding increases by one. Also, inserting paper, porous material, etc. between galvanized steel sheets is disclosed in Japanese Patent Laid-Open No. 4-27.
In the methods disclosed in Japanese Patent Laid-Open No. 9291 and Japanese Patent Laid-Open No. 4-2889886, respectively, the third method of sandwiching between steel plates is used.
This member acts as a water retention material, which accelerates corrosion in the vicinity of the weld where the zinc plating is damaged. Further, Japanese Patent Laid-Open No. 4-2 tries to remove zinc in a welded portion by using laser light.
In the methods disclosed in Japanese Patent No. 31190 and Japanese Patent Application Laid-Open No. 4-251648, the zinc plating on the inner surface of the stacked steel sheets, which causes spatter and blowholes, is not sufficiently removed, and spatter and blowholes are not completely removed. The generation of blowholes could not be suppressed.

The present invention has been made in order to prevent the generation of spatter and blowholes in lapped laser welding of zinc plating, and solves the problems of the prior art as described above and simplifies sound welding. The purpose is to form.

[0007]

Means for Solving the Problems The present invention is to solve the above problems, and in lap welding of a galvanized steel sheet using a laser, the end of the galvanized steel sheet on the laser irradiation side is not restricted. The galvanized steel sheet on the laser irradiation side, and only the galvanized steel sheet on the laser irradiation side is melted by using a laser in advance at the position on the restraining side from the overlap welding position to deform the end portion to form a gap between the galvanized steel sheets. Is formed, and then the galvanized steel sheet is lap-welded, which is a laser welding method for galvanized steel sheet. Further, in this case, the cut surface of the galvanized steel sheet is not melted. Here, the end portion is defined as an area within 20 mm from the cut surface.

[0008]

FIG. 1 is a sectional view of a welded portion when a galvanized steel sheet is overlapped and laser-welded using the present invention. 1, in FIG.
2 is a galvanized steel plate, these are restraints 3a, 3b
And 4a, 4b are superposed. In FIG. 1, the ends of the galvanized steel sheet 2 on the side opposite to the laser light source are not restrained by the restraints 3a and 3b, but as shown in FIG. 2, the ends of the galvanized steel sheet 2 are restrained by the restraints 3a and 3b. The same effect can be obtained in the case.

In the state of restraint as described above, only the galvanized steel sheet 1 is melted by a laser in advance at the restraint side position from the lap welding position to form a molten portion 7, and the end portion 5 is laser-heated by thermal contraction. After being deformed to the irradiation side by the irradiation torch 6, the lap welding bead 8 is formed thereafter. In this case, the fusion zone 7 is formed so as not to penetrate the steel plate 1. Therefore, this fused portion can be formed without defects such as pits and blow holes.

By the way, when a steel sheet is irradiated with a laser, a welded portion having a wide weld metal width is formed on the side irradiated with the laser and a welded portion having a narrow weld metal width is formed on the opposite side. At this time, volume contraction occurs in the molten metal during solidification and cooling of the molten metal, but due to the structure of the molten portion as described above, the contraction on the laser irradiation side is large and the contraction on the opposite side is small. Therefore, the steel sheet 1 undergoes angular deformation on the laser irradiation side around the bead of the fusion zone, but since the steel sheet 1 is restrained by the restraints 3a and 3b,
The deformation concentrates on the side of the end 5 that is not restrained, and as a result, the gap 9 is formed.

After the gap 9 is formed, the weld bead 8 is formed. Since the gap 9 is formed, the zinc vapor generated between the steel plates 1 and 2 escapes into the gap 9, and the weld bead 8 is pitted and blown. It can be formed without the occurrence of welding defects such as holes.

The melting portion 7 is advantageous because the gap 9 can be widened as the melting width on the laser irradiation side is widened and the melting width on the opposite side is narrowed. By the way, when a galvanized steel sheet is irradiated with a laser, zinc on the surface of the steel sheet evaporates, which works in the direction of causing a large growth of welding plasma.
It is advantageous to widen the melting width on the laser irradiation side. The laser irradiation conditions for forming the fusion zone 7 are not particularly limited, and a method such as defocusing or suppressing the laser irradiation output can be appropriately selected. Further, the present invention can be expected to be effective regardless of the type of laser.

If the gap between the fusion zone 7 and the weld zone 8 is too narrow,
Even if angular deformation is caused by the fusion zone 7, no gap is formed at the welding position, so the effect of the present invention is lost. Therefore, after determining the position of the welded portion 8, it is necessary to select at least a position where the fused portion 7 and the welded portion 8 do not overlap each other. Usually, an appropriate gap 9 can be formed by setting the distance between the center of the melted portion 7 and the center of the welded portion (weld bead 8) to be about 1 mm to 15 mm. If it is less than 1 mm, there arises a problem that the gap 9 is not formed at the welding position as described above. On the other hand, thermal deformation other than angular deformation also occurs in the steel sheet, and therefore, if it exceeds 15 mm, thermal deformation other than angular deformation is applied, and there is a problem in that a gap 9 is not partially formed in the welded portion 8.

The gap 9 required for performing lap welding to form a sound weld bead varies depending on the basis weight of the steel sheet used. The minimum required gap G (μm) at the weld bead position is G = 2, where X (gr / m ² ) is the total weight of the basis weights on the superposed surfaces of the steel plates 1 and 2.
It is represented by 5/120 × X. The larger the amount of the gap in the weld portion of the gap 9 required to form a sound weld bead, the better. If it is too wide, not only the welded portion 9 will be concave, but also a welded portion with low fatigue strength will result. Therefore, the gap G needs to be 50% or less of the thinner plate thickness of the steel plate 1 or 2.

The position of the welded portion 8 is preferably selected so as not to melt the cut surface of the steel plate 1. This is because the weld bead tends to be disturbed when the cut surface is melted. Therefore, in an application in which a good appearance is strongly desired, it is necessary to select a welding position that does not melt the cut surface of the steel sheet 1.

[0016]

EXAMPLES The present invention will be described below with reference to examples. [Embodiment 1] FIG. 3 is a plan view of a welded portion showing an embodiment of the present invention. In FIG. 3, reference numerals 1 and 2 denote alloyed hot-dip galvanized steel sheets (GA60 / 60) having a plate thickness of 0.8 mm and a basis weight of 60 gr / m ² per side. These are restrained by restraints 3 and 4 as shown in FIG.

In this state, a carbon dioxide laser is used as a heat source,
Laser light was focused on a steel plate at 3 mm using a lens having a focal length of 10 inches, irradiated with 3 kW, and a fusion zone 7 was formed at a position 5 mm from the edge of the steel plate 1 at a scanning speed of 4 m / min. Then, as Example 1 of the present invention, 5 kW irradiation, 4 m / m
in, with the focus position directly above the steel plate 2 from the edge of the steel plate 1
A weld bead 8 was formed at a position of mm, and the steel plates 1 and 2 were welded.

In addition, as Example 2 of the present invention, the fusion zone 7 was formed under the same conditions as in Example 1 of the present invention, and thereafter, irradiation with 5 kW was performed.
The weld bead 8 is formed at a position of 0.5 mm from the edge of the steel plate 1 with the focus position right above the steel plate at m / min.
And No. 2 were welded. At this time, the cut surface of the steel plate 1 is also melted.

In order to investigate the bead shape and the internal soundness, a visual appearance inspection and an X-ray transmission test based on JIS Z3104 were conducted. In other words, visually check the pit occurrence situation, the pit is the total length of the bead,
Those that stayed below 5% were good (○), over 5% 2
It was judged that 0% or less was a little bad (Δ) and more than 20% was a bad (x). Furthermore, the pit occurrence is 5 for the entire bead length.
%, The appearance shape is slightly defective (△),
It was determined to be defective (x). In addition, the occurrence of pits and blowholes was investigated by an X-ray transmission test, and if the occurrence of pits and blowholes was 5% or less with respect to the entire length of the bead, it was good (○), more than 5% and 20% or less Was judged to be slightly defective (Δ), and more than 20% was judged to be defective (×).

Table 1 shows the determination results together with a comparative example in which the welded bead 8 alone was formed at the positions 0.5 mm and 2 mm from the edge of the steel plate 1 under the above conditions without forming the fusion zone 7.

[0021]

[Table 1]

[Embodiment 2] In FIG. 3, the fusion zone 7 and the weld bead 8 are continuous, but this is not necessary. 4 is also a plan view of the welded portion similar to FIG.
b, 7c, ..., Weld beads 8a, 8b, 8c, ...
• May be intermittent as in. At this time, if the laser irradiation is performed in the order of 7a, 8a, 7b, 8b, 7c, ..., The molten portion and the welding bead can be sequentially formed. This embodiment will be described in detail below.

In FIG. 4, reference numerals 1 and 2 denote double-sided galvannealed steel sheets (GA60 / 60) having a plate thickness of 0.7 mm and a basis weight per surface of 60 gr / m ² . These are restrained by restraints 3 and 4 as shown in FIG.
As Example 3 of the present invention, first, the fusion zone 7a was welded at a welding speed of 4 m / m
5 mm in length is formed, and then welding bead 8a is formed to a length of 5 mm at a welding speed of 4 m / min, and then 7b, 8
Laser irradiation was repeatedly performed in the order of b, 7c, 8c, .... At this time, the welding bead position is 2 mm from the steel plate edge, the fusion zone position is 4 mm from the steel sheet edge, the laser irradiation output is constant at 3 kW, and a lens with a focal length of 10 inches is used. Then, at the welded portion, laser irradiation was performed with a focus on the steel plate.

Under the same conditions as in Invention Example 3, the welding bead 8a,
Only 8b, 8c, ..., 5 mm apart, 5 m each
Table 2 shows the results of judgment using the judgment criteria described in Example 1 together with the comparative example in which the m length was formed.

[0025]

[Table 2]

[Embodiment 3] Further, the fusion zone and the welding bead can be continuously formed in a triangular wave or in a sinusoidal shape as shown by a laser irradiation locus 10 in the plan view of the welding zone in FIG. In this case, only the steel plate 1 is melted on the restraint side by changing the focal position or the laser irradiation output,
On the end side, steel plates 1 and 2 are overlapped and welded. Hereinafter, this example will be described in detail.

In FIG. 5, reference numerals 1 and ² are double-sided galvannealed steel sheets (GA60 / 60) having a plate thickness of 0.8 mm and a basis weight per surface of 60 gr / m ² . These are restrained by restraints 3 and 4 as shown in FIG.
In such a state, laser irradiation was performed with a sinusoidal locus as shown in the upper graph of FIG. That is, in FIG. 6, the X axis represents the position along the edge of the steel plate 1, and the increasing direction of the Y axis is the direction toward the end of the steel plate 1. The amplitude of the sine wave locus subjected to laser irradiation is 2 mm. Therefore, when the laser irradiation locus is closest to the edge, the distance between the locus and the edge is 2 mm, and the distance farthest from the edge is 6 mm. The period of the sine wave locus is 8 mm.

In FIG. 6, sections a, b and d and e in the X-axis direction are fusion zone formation sections, and section c is a weld zone formation section. For each of these sections, the laser output was controlled as shown in the middle graph of FIG. 6, and the focus position was controlled as shown in the lower graph to perform laser irradiation. Here, the laser output is controlled within the range of maximum 4 kW and minimum 2 kW, and the focus position is controlled within the range of 10 mm above the maximum steel plate and directly above the minimum steel plate. The focal length of the condenser mirror used at this time is 10
Inches.

When welding was performed as described above and the judgment criteria used in Example 1 were applied, the appearance inspection and the X-ray transmission test were both judged to be good.

[0030]

Industrial Applicability According to the present invention, lap welding of a galvanized steel sheet by a laser can be easily carried out without the occurrence of blowhole defects, which is extremely industrially advantageous.

[Brief description of drawings]

FIG. 1 is a sectional view of a welded portion in the method of the present invention.

FIG. 2 is a sectional view of a weld portion in the method of the present invention.

FIG. 3 is a plan view of a welded portion showing an embodiment of the present invention.

FIG. 4 is a plan view of a welded portion showing an embodiment of the present invention.

FIG. 5 is a plan view of a welded portion showing an embodiment of the present invention.

FIG. 6 is a graph showing control of laser irradiation locus, laser output, and focus position in an example of the present invention.

[Explanation of symbols]

 1, 2 Galvanized steel sheet 3, 4, 3a, 3b, 4a, 4b Restraint tool 5 End part 6 Laser irradiation torch 7 Melting part 8 Weld bead (welding part) 9 Gap 10 Laser irradiation trajectory

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobutaka Yurioka 20-1 Shintomi, Futtsu City, Chiba Prefecture Nippon Steel Co., Ltd. Technology Development Division (72) Inventor Takuji Karasawa 20-1 Shintomi, Futtsu City, Chiba Prefecture New Japan Steel Engineering Co., Ltd.

Claims (2)

[Claims] 1. In lap welding of a galvanized steel sheet using a laser, the end portion (5) of the galvanized steel sheet (1) on the laser irradiation side is not constrained to the galvanized steel sheet (1, 2). Only the galvanized steel sheet (1) on the laser irradiation side is supported and melted in advance at the restraining side position from the lap welding position using a laser to deform the end portion (5), and the galvanized steel sheet (1, 2) is supported. ), A gap is formed between the two, and then the galvanized steel sheets (1, 2) are lap-welded, and a laser welding method for the galvanized steel sheet. 2. The laser welding method for a galvanized steel sheet according to claim 1, wherein the cut surface of the galvanized steel sheet is not melted.