JP2002346780A - Superposition laser welding method of galvanized steel sheet - Google Patents

Abstract

(57) [Summary] The present invention relates to a laser welding method for galvanized steel sheet. SOLUTION: When a galvanized steel sheet is closely overlapped and laser-welded, in order to reduce zinc vapor pressure generated at the time of laser welding so that welding defects do not occur, a fine uneven surface is provided on the entire surface of the steel sheet. Provide uneven space between steel plates,
A superposition laser welding method for galvanized steel sheets that can be continuously welded at any position on the steel sheets. The laser welding method as described above, wherein the conditions of the rough surface and the uneven space are specified. Enables welding at any position on galvanized steel sheet without specifying the welding position.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for laser welding galvanized steel sheets.

[0002]

2. Description of the Related Art Galvanized steel sheets are very frequently used as corrosion-resistant materials in many industrial fields including automobiles. Above all, body parts are one of the representative ones. Conventionally, the method of joining vehicle body parts has generally been to press-mold galvanized steel sheets and then join them by resistance spot welding or arc welding, but in recent years, both weight reduction and high rigidity and high strength have been achieved. There is an increasing movement to replace with laser welding in order to achieve these simultaneously.

[0003] However, galvanized steel sheets of automobile materials are generally thickened in order to increase corrosion resistance, and laser welding is continuously performed in a state where two steel sheets are closely overlapped. The explosive vaporization of the zinc in close contact with the pressure increases the pressure and causes a blast. As a result, there is a problem that the molten base metal is blown off, spatters are generated, and welding defects such as hole defects and blow holes are easily generated, thereby deteriorating welding strength and welding quality. Numerous attempts have been made to suppress such explosion, and it is known in the art that it is effective to provide an appropriate gap to release zinc vapor. As one of the methods, JP-A-03-165994 and JP-A-04-279291 are known.
JP-A-05-318155 and JP-A-06-797.
As disclosed in No. 8, a gap is secured by providing an intermediate layer such as tape, paper, carbon graphite or a carbon-based surface absorbent, a metal layer, or a thin organic insert material between galvanized steel sheets. Methods of welding are known.

As disclosed in JP-A-60-255294, JP-A-61-135495, and JP-A-03-193285, embossing such as embossing is performed near the welding line at intervals in the welding line direction. There is also known a method in which a projection is provided to allow generated steam to escape from the gap.

[0005]

However, in the laser welding method for providing an intermediate layer such as an insert material between steel sheets as described above, the number of work steps for applying an intermediate layer to a welded portion of a steel sheet before welding increases, and Depending on the complicated shape, manual work occurs and the work efficiency is poor, and there is a concern that the appearance quality may be impaired due to the combustion reaction of the intermediate layer in terms of quality.

In the method of providing projections only in the vicinity of a welding line, such as embossing, it is necessary to add an uneven portion having a projection shape to a mold or the like, and the laser welding position is specified. In addition, there is a problem that it is difficult to always obtain a constant amount of protrusions due to wear and life of mold protrusions. The present invention has been made to advantageously solve such a problem, and an object of the present invention is to provide a laser welding method that enables welding without specifying a welding position at an arbitrary position on a galvanized steel sheet. Is what you do.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above object advantageously, and its gist is as follows: (1) Laser welding is performed by closely stacking galvanized steel sheets. At this time, in order to reduce the zinc vapor pressure generated during laser welding so that welding defects do not occur, a fine uneven surface is provided over the entire surface of the steel sheet to provide an uneven space between the steel sheets, and at any position of the steel sheet. A superposition laser welding method for galvanized steel sheets, which is capable of continuous welding. (2) The area ratio of the concave portion on the surface of the galvanized steel sheet is 30% to 8%.
The uneven roughness pitch of 15% to 50μm is uniformly molded with the distance between the uneven pitches of 0% and the size of the uneven surface, and both galvanized steel sheets are closely overlapped with the uneven surfaces facing each other. A superposition laser welding method for a galvanized steel sheet, characterized in that zinc vapor pressure generated during laser welding is reduced by providing an uneven space of 30 μm to 100 μm between steel sheets. (3) The area ratio of the concave portion on the surface of the galvanized steel sheet is 30% to 8%.
The uneven surface having irregularities of 30 μm to 50 μm is uniformly formed by the distance between the uneven pitches and the size of the uneven surface, which is 0%. The two galvanized steel sheets are closely overlapped in a state where they face each other, and the unevenness space between the steel sheets is set to 30 μm to 50 μm to reduce the zinc vapor pressure generated at the time of laser welding. Laser welding method. (4) The method for superposing laser welding of galvanized steel sheet according to (2) or (3), wherein the uneven space is partially provided in a range to be a laser welding area of the steel sheet. (5) The laser welding method for lapping galvanized steel sheets according to any one of (1), (2), (3) and (4), wherein the uneven space intersects the welding line. That is, the present invention focuses on the zinc vapor pressure generated at the time of laser welding in order to solve the problem of welding defects (holes, blowholes, etc.) when superposing galvanized steel sheets and performing laser welding. An object of the present invention is to provide a method of superposing laser welding of galvanized steel sheets in which an uneven space to be reduced is provided on the joint surface of the steel sheet, and appropriate conditions for the uneven space are found to prevent welding defects.

[0008]

Next, an example of the method of the present invention will be described with reference to the drawings. FIGS. 1 (a) and 1 (b) are a plan image diagram and a cross-sectional image diagram showing a mode in which fine roughened surfaces 6, 7 are formed on the surface of a galvanized steel sheet 5, respectively.
Is a state in which galvanized steel sheets 5 and 5 having fine uneven surfaces 6 and 7 uniformly provided on the surface are opposed to each other so that an uneven space 9 is formed therebetween. FIG. 1 (a) shows a cross-sectional image when a laser welded portion 8 is formed by closely overlapping laser welding to form a laser welded portion. In FIG. ,
In FIG. 1 (b), reference numeral 4 denotes a difference in the unevenness of the steel sheet. FIG. 3 shows a galvanized steel sheet 5 having finely roughened rough surfaces 6 and 7 uniformly formed on the surface, and a roughened rough surface 6 on a standard galvanized steel sheet 5 having no roughened rough surface. 7 is a cross-sectional image when laser welding is performed while superposing the members 7 and 7 closely. The steel plate 5 can be welded at an arbitrary position by providing fine uneven rough surfaces 6 and 7 over the entire surface. The welding line 8 crosses the concavo-convex space 9 formed by the close contact of the steel plate 5, and the concavo-convex space 9 is a space for reducing the zinc vapor pressure generated during laser welding so that welding defects do not occur. It is. That is, the presence of the uneven space 9 between the portion to be melted by the laser welding and the region adjacent to the molten metal lowers the pressure in the molten metal, and further adjacent spaces serve as escape paths a and b for zinc vapor, thereby increasing the pressure. This will help to reduce the decline.

First, the height of the uneven space will be described.
When the laser welding test was performed by changing the height of the roughened surface of the steel sheet to close contact, a decrease in the weight of the steel sheet after welding was found to decrease as the height of the uneven space increased, as shown in Fig. 4 (a). understood. In other words, a small decrease in the weight of the steel sheet after welding means that the amount of molten metal scattered by the explosion is small, and as a result, stable welding is achieved. The evaluation index at this time is a gap of about 100 μm that enables stable welding of steel sheets that have not been subjected to roughening on the surface of the steel sheet.
m, and the difference in weight of the steel material before and after laser welding (reduction amount) was used as a reference, and up to a 20% increase was used as an index as an allowable range of mechanical strength. According to this, as shown in FIG. 4 (a), it was found that the height of the uneven space was required to be 30 μm or more. In addition, the present invention is to transfer and mold a fine uneven pattern on the surface of the steel sheet by rolling and applying a fine uneven surface to the surface of the iron roll, the processing depth of the fine uneven surface rough surface of the iron roll and it. The maximum difference in the unevenness of the steel sheet transferred from the reality of the rolling load (elongation of the steel sheet) caused by the above was set to 50 μm. Therefore, the spatial height of the steel sheet close-contact surface formed by laminating the steel sheet surface with irregularities and roughening is 100 μm at the maximum. Next, the concave space area ratio on the surface of the galvanized steel sheet, that is, the concave area ratio, will be described. As shown in FIG. Quantity x
Assuming that the allowable range is 1.2 times, it is understood that the concave area ratio is required to be 30% or more. It is well known that the larger the concave area ratio is, the better. However, when a circular concave pattern is formed, the condition that the circular shapes contact each other is the maximum space ratio, and the concave area ratio is about 80%.

That is, according to the present invention, an uneven space height of 30 μm to 100 μm, which is formed by closely contacting two galvanized steel sheets,
We have found welding conditions that enable stable laser welding with less explosion at a recess area ratio of 30% to 80%.
In addition, since the present invention is a mode in which the concave space is closed,
In particular, in the case of a thin material, the influence of the heat input per unit time during welding is great, and it is considered that the generation of spatter is reduced by shortening the time of staying at the same place as much as possible. In other words, it is recommended to increase the welding speed at a high output power within the range where the backwash in laser welding can be produced.

When laser welding is performed on the surface of the galvanized steel sheet 5 without forming the roughened surfaces 6 and 7 in close contact with each other and performing laser welding as shown in FIG.
There is no escape route of the pressure which is increased due to vaporization of the galvanized layer 10a out of the molten metal 0a10b, and the molten metal is discharged toward the surface of the molten metal to explode and explode when the zinc vapor is separated from the molten metal. It is presumed to cause welding defects such as. The galvanized steel sheet formed into a rough surface under the conditions found in the present invention described above,
Compared to the case where standard galvanized steel sheets were overlapped with each other and laser-welded, stable laser welding with much less spatter was possible, and it was confirmed that the roughened surface was effective.

FIG. 6A shows an example in which a concavo-convex space is provided by a continuous concave portion 11 which intersects a welding line which is a laser welded portion 8, in which zinc vapor is more easily escaped. FIG.
(b) shows an example of a continuous uneven space in the direction of arrows AA, and the state in the direction of arrows BB is the same as that in FIG. Here, the height of the space formed by molding is in accordance with the conditions found above. In addition, as a similar example, it is easily conceivable to provide a concavo-convex space formed of a skewed concave portion 12 that is continuous in an oblique direction with respect to a welding line as a laser welded portion 8 as shown in FIG.

[0013] These fine irregularities on the surface of the steel sheet satisfy the space for reducing the zinc vapor pressure during welding so that welding defects do not occur, and various pattern patterns can be formed. Also, as shown in FIGS. 7 (a) and 7 (b), it is possible to form a uniform fine convex pattern on the surface of the steel sheet by reversing the rough surface of the unevenness. In other words, these fine uneven patterns can be formed on the entire surface of the steel sheet or on the welding area, and stable laser welding can be performed at any position without specifying the welding position within the rough surface forming area. is there.

The above-described rough surface roughening of a galvanized steel sheet is performed by forming an uneven surface on a skin pass roll or the like by electrolytic processing or the like.
It is rolled by a roll formed by freely forming a fine uneven pattern of up to 100 μm.
Can be adjusted arbitrarily by changing the rolling load during rolling.

Further, after forming into a roll by laser dulling or arc plasma processing as a means for roughening the rough surface,
It is also possible to carry out a molding method of transferring to a steel plate or directly form irregularities on a steel plate. The galvanized steel sheet of the present invention has no problem when used not only for hot-dip galvanized steel sheet and electrogalvanized steel sheet but also for various zinc-based alloy-plated steel sheets.

[0016]

Next, working examples of the method of the present invention will be described together with comparative examples. A fine uneven surface was formed on the surface of the galvanized steel sheet, and a laser welding test was continuously performed as described below. 1) Galvanized steel sheet: 45g / m ^{2 of} zinc basis weight, steel sheet thickness of 1.4mm 2) Roughness of uneven surface of steel sheet: steel sheet concave area ratio: 0%, about 28
%, About 36% 3) Arrangement of unevenness: diameter: 180 μm, pitch: 300
μm diameter: 270 μm, pitch: 400 μm 4) steel plate uneven space height: 0 μm, 20 μm, 34 μm
48μm 5) Laser welding: CO ₂ laser welding 5KW 3m / min

A laser welding test was performed on the galvanized steel sheet under the above conditions, and the weight difference of the steel sheet before and after welding was measured and compared as an evaluation index value. Fig. 8 (a) shows the results of laser welding with the height of the uneven space as the level. The amount of weight loss of the steel sheet after laser welding was observed. 3 compared to the weight loss when zero
It was found that as the space height was increased to 4 μm and 48 μm, the amount of weight reduction was significantly reduced. Also,
Looking at the evaluation index, it was confirmed that 20 μm was out of the allowable range, but that it was within the allowable range above 34 μm.

Further, in the present embodiment, it is assumed that good results are obtained in the range where the void ratio is large. A laser welding test was performed on 28%, 32%, and 36% of 0% galvanized steel sheet having no concavo-convex space, and the weight loss of the steel sheet after welding was compared. As shown in FIG. 8 (b), it was found that the larger the recess area ratio, the smaller the weight loss compared to the weight loss after welding in the zero-% state where there is no concave space. According to the evaluation index, 32% and 3%
It was confirmed that 6% was within the allowable range.

Thus, by ensuring a concavo-convex space of 30 μm or more and a concave area ratio of 30% or more, the amount of spatters generated is remarkably smaller than in the case where two standard galvanized steel sheets are welded together, and the weight of the steel material is reduced. It was found that stable laser welding was possible with a small decrease.

[0020]

[Comparative Example] A state in which two sheets of non-roughened steel sheet were adhered to each other under the same conditions as those in the example, and a galvanized steel sheet whose surface was roughened with a difference of about 6 μm in roughness was obtained. The laser welding test was performed at two levels of a small gap in which a galvanized steel sheet not subjected to heat treatment was closely attached. When the weight loss of the steel material after welding was measured, the weight loss was extremely large, about 15 to 20 times, as compared with that of the present invention, which forms an uneven space for reducing the zinc vapor pressure during laser welding. Also,
Many welding defects such as hole defects and blow holes also occurred due to generation of spatter.

[0021]

According to the present invention, even if two galvanized steel sheets are stacked and welded in close contact with each other, there is little generation of spatter, and there are few welding defects such as blow holes, and stable welding quality can be obtained. Further, welding can be performed at an arbitrary position without specifying a welding position without requiring a preliminary setup such as securing a gap at the time of welding, and workability is also superior. In addition, it goes without saying that the welding method of the present invention enables welding without specifying the front and back surfaces of the steel sheet by forming fine irregularities on the front and back surfaces of the steel sheet. In addition, the present invention has found a stable laser welding method by forming a required fine uneven surface on a steel sheet surface. However, the fine uneven surface formed here can simultaneously be press-formed or painted. This provides a composite effect that also improves the image quality. As described above, the lap laser welding method of the present invention can be applied to many industrial fields including the automobile industry, and further applied to nickel-plated and chromium-plated surface-treated steel sheets, and the base metal is formed by hot-rolled material. However, it is applicable to a wide range such as possible.

[Brief description of the drawings]

FIG. 1A is a plan view showing an image of a roughened surface, and FIG. 1B is a cross-sectional view showing an image of a roughened surface.

FIG. 2 is a cross-sectional view showing an image in which two uneven rough surfaces (steel plate concave) are closely overlapped and welded.

FIG. 3 is a cross-sectional view showing an image obtained by overlapping and welding a steel plate subjected to uneven surface roughening and a general steel plate.

FIG. 4 (a) is a graph showing a relationship between a concave space height and a steel material weight reduction after welding, and FIG. 4 (b) is a graph showing a relationship between a concave area ratio and a steel material weight reduction after welding. is there.

FIG. 5 is a cross-sectional view showing an image of a general galvanized steel sheet overlapped and welded.

6A is a plan view showing an uneven pattern intersecting a welding line, FIG. 6B is a cross-sectional view showing an image of a concave space intersecting a welding line, and FIG. It is a top view which shows an uneven | corrugated pattern.

7 (a) is a cross-sectional view showing an image of a convex and concave rough surface steel plate convex processing, and FIG. 7 (b) is a cross-sectional view showing an image of two convex and concave rough surface (concave steel plate) welded closely. .

FIG. 8 (a) is a graph showing an example of a concave space height welding test, and FIG. 8 (b) is a graph showing an example of a concave area ratio welding test.

[Explanation of symbols]

 5 Galvanized steel sheet 6 Concave part 7 Convex part 8 Laser welded part 9 Uneven space

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Yoichi Ito 5-3 Tokaicho, Tokai City, Aichi Prefecture Inside Nippon Steel Corporation Nagoya Works (72) Inventor Kazuyuki Kawano 5- Tokaicho, Tokai City, Aichi Prefecture 3 Nippon Steel Corporation Nagoya Works (72) Inventor Akihiro Miyasaka 20-1 Shintomi, Futtsu City, Chiba Prefecture Nippon Steel Corporation Technology Development Division (72) Inventor Yasunobu Miyazaki 20 Shintomi, Futtsu City, Chiba Prefecture -1 F-term in the Technology Development Division of Nippon Steel Corporation (reference) 4E068 BF00 DB01 DB15

Claims (5)

[Claims] 1. When a galvanized steel sheet is closely overlapped and laser-welded, a fine uneven surface is provided over the entire surface of the steel sheet so as to reduce the zinc vapor pressure generated at the time of laser welding so that welding defects do not occur. To provide an uneven space between the steel plates,
A superposition laser welding method for galvanized steel sheets, wherein welding can be continuously performed at an arbitrary position on the steel sheets. 2. The method according to claim 1, wherein the surface area of the concave portion is 3 on the surface of the galvanized steel sheet.
The uneven roughness pitch of 15% to 50μm is uniformly formed according to the distance between the uneven pitches of 0% to 80% and the size of the uneven surface, and both galvanized steel sheets are closely contacted with the uneven surfaces facing each other. Laminate, uneven space between steel plates 30 μm to 10
A superposition laser welding method for galvanized steel sheets, wherein a zinc vapor pressure generated during laser welding is reduced by providing 0 μm. 3. A concave area ratio of 3 on the surface of a galvanized steel sheet.
The uneven surface having an uneven pitch of 30 μm to 50 μm is uniformly formed according to the distance between the uneven pitches of 0% to 80% and the size of the uneven surface, and the uneven surface of the uneven surface and the unevenness of a general galvanized steel sheet are formed. Both galvanized steel sheets are closely overlapped with the surfaces not facing each other, and an uneven space between the steel sheets of 30 μm to 50 μm
A superposition laser welding method for galvanized steel sheets, characterized in that a zinc vapor pressure generated during laser welding is reduced by providing a thickness of μm. 4. The method for laser welding of galvanized steel sheets according to claim 2, wherein an uneven space is partially provided in a range to be a laser welding area of the steel sheet. 5. The method according to claim 1, wherein the uneven space intersects the welding line.