JPH067978A - Method for laser beam welding galvanized steel sheets - Google Patents

Abstract

PURPOSE:To prevent generation of blow holes in lap welding by inserting a thin organic insert material between galvanized steel sheets and welding them with a laser beam. CONSTITUTION:In a process where a laser beam 10 arrives at the insert material 11, first, the resin of the insert material 11 is melted and vaporized at a temperature lower than zinc of the galvanized layers 3, 4 of the galvanized steel sheets 1, 2. Then, when zinc is vaporized, part of carbon in the resin enters a molten pool like the arrows (a), on one hand, since part of zinc vapor from the galvanized layers 3,4 enters a clearance made by vaporization of the resin like the arrows (b), zinc vapor entering the molten pool decreases. Since the viscosity of molten steel containing a small amount of carbon is lowered, zinc vapor is easy to get away from the surface and is scarecely closed in the molten steel. Consequently, a good bead nearly free of generation of blow holes can be obtained.

Description

Detailed Description of the Invention

[0001]

The present invention relates to galvanized steel sheets,
Alternatively, the present invention relates to a laser welding method for lap welding a galvanized steel sheet and another metal.

[0002]

2. Description of the Related Art Lap welding of galvanized steel sheets is generally performed by a resistance welding method. For example, Japanese Patent Publication No. 54-2621
As shown in Japanese Patent Publication No. 3, a wire electrode is wound around each of the upper and lower electrode rollers, and a lap portion of a galvanized steel sheet is passed between the wire electrodes, whereby the lap portion can be seam resistance welded. However, in the seam resistance welding method, the electrode rollers and the like have to be arranged on both sides of the material to be welded, so that the structure is complicated, and generally, the welding portion is limited to a straight and flat welding portion. Therefore,
Not suitable for single-sided welding and welding of curved and curved surfaces.

On the other hand, according to the arc welding method, a large amount of zinc vapor is generated from the plating layer due to the arc heat, which is trapped in the molten metal and causes porosity (such as porosity and surface craters) in the beads. It is known that the bead becomes aggravated by generating a large number of pores (called blow holes).

Further, it is difficult to reduce this phenomenon even in the case of the laser welding method. The phenomenon of bead roughening will be described with reference to the drawing. As shown in FIG. 7, the laser welding is keyhole welding with the laser beam 10. Since low-melting-point and low-boiling-point zinc evaporates violently from 4, molten zinc in the molten pool 6 is blown away by this zinc vapor 5, or zinc vapor penetrates into the molten steel, resulting in a large number of blowholes in the bead 7. 8 will be generated. Therefore, even with the laser welding method, lap welding of galvanized steel sheets has many bead defects and is generally not applicable.

[0005]

However, the laser welding method is considered to be an effective welding method for suppressing the generation of blow holes because the weld pool can be made small. It is considered to be the most suitable for lap welding of galvanized steel sheets because it can be freely shaped and has excellent controllability and operability of welding. In particular, there are many curved and curved surface welds, and there are great expectations for their practical application in the automobile industry, which uses a large amount of galvanized steel sheets.

The present invention was developed to meet such a demand, and in the lap welding of galvanized steel sheets by the laser welding method, the occurrence of blow holes as described above is prevented as much as possible and a good bead is obtained. That is the purpose.

[0007]

According to the present invention, firstly, a thin insert material of an organic material is sandwiched between galvanized steel sheets or between a galvanized steel sheet and another metal, and the overlapping portion is laser-welded. is there. Here, the galvanized steel sheet,
It includes those by electroplating and those by hot dipping. In addition, the organic insert material includes a polymer material and a cellulose material. Secondly, the target steel sheet is a thin steel sheet, and the zinc plating amount is 10 g.
/ M ^{2 to} 120 g / m ² . Thirdly, the thickness of the insert material is set to 10 μm to 200 μm. Fourthly, one side or both sides of the insert material are bonded. Fifth, the insert material itself is formed by resin coating. Sixth,
It is assumed that the galvanized steel sheet includes a damping steel sheet integrally formed by sandwiching a resin between two steel sheets.

[0008]

The mechanism of preventing blowholes in the bead according to the present invention will be described. Since the organic material that constitutes the insert material has a low melting point and a low boiling point with respect to zinc having a melting point of 420 ° C. and a boiling point of 905 ° C., as shown in FIG.
First, the resin of the insert material 11 is melted and the plated layers 3 and 4 are
It vaporizes at a lower temperature than zinc. When zinc is subsequently vaporized, a part of carbon in the resin enters the molten pool as shown by an arrow a in FIG. 1 (b), while the plating layers 3, 4 are formed in the gap formed by the vaporization of the resin. Since a part of the zinc vapor from the inside enters as shown by the arrow b (this action is referred to as a "gap effect"), the amount of zinc vapor entering the molten pool decreases. In addition, since the viscosity of molten steel containing a small amount of carbon decreases,
It is considered that zinc vapor easily escapes from the surface and is rarely trapped in molten steel. When the cross section of the bead 7 is observed, carbon 1 is contained in the composition of the joint metal as shown in FIG.
2 is in a solid solution state, and it is presumed that blowholes are reduced by the effect of the above gap and the action of decreasing the viscosity of molten steel.

[0009]

EXAMPLES Examples of the present invention will be described below. (1) Zinc plating amount First, in the present invention, since the zinc plating amount directly affects the zinc evaporation amount, the relationship between the zinc plating amount and the number of blow holes was investigated. In FIG. 3, the horizontal axis represents the zinc plating amount (g / m ² ), and the vertical axis represents the number of blow holes (pieces /
It is the experimental result shown by taking m). The experiment was conducted under the following conditions. Laser conditions: CO ₂ laser, output 3 kw (constant), continuous oscillation, no shield gas Material: Double-sided galvanized steel plate (steel plate thickness 0.2 mm, 0.8
mm, 3.2 mm) Insert material (cellophane tape, tape thickness 150 μm) Welding speed: 1 m / min to 10 m / min

When the steel plate thickness t = 0.2 mm (FIG. 3A)
However, the number of blowholes is generally small even if the amount of galvanizing and the welding speed increase. As the plate thickness of the steel plate increases (see FIGS. 3B and 3C), the molten steel amount increases, and the number of blow holes also increases. Therefore, in order to reduce the number of blow holes, it is necessary to reduce the galvanizing amount or slow the welding speed. Maximum number of blow holes is n = 3
If the number is 0 / m, the upper limit of the galvanizing amount may be 120 g / m ^{2 at} a normal welding speed (3 m / min or less) for a thin steel plate (4.5 mm or less).

(2) Thickness of Insert Next, the relationship between the thickness (μm) of the organic material insert and the number of blowholes (number / m) was investigated. The experimental results are shown in FIG. The experiment was performed with the same steel plate thickness of 0.2 mm,
With respect to 0.8 mm and 3.2 mm, the laser output was 3 kw and the galvanizing amount was 40 g / m ^2, which were constant. Cellophane tape was used as the insert material.

From the results shown in FIG. 4, first, if the organic insert is too thin, the amount of resin evaporation is smaller than the amount of zinc evaporation, so that the effect of the gap is not sufficiently exhibited. Therefore, the insert material thickness is required to be 10 μm or more. Moreover, when the insert material thickness is increased to some extent, the number of blow holes tends to increase rapidly as the welding speed increases. This is because the faster the welding speed is, the faster the molten steel is cooled than the rate at which the resin vapor exits the molten steel. Further, as the thickness of the steel plate increases, it becomes more difficult for the resin vapor to escape, and the number of blow holes increases sharply. Further, as in the conventional case, when there is no insert material, blow holes frequently occur. If the number of blow holes is set to the same standard n = 30 holes / m as described above, the upper limit of the insert material thickness may be 200 μm.

FIG. 5 shows the above results of welding speed v = 7 m / mi
n is a graph in which the steel plate thickness t = 0.8 mm is arranged, and is a graph showing changes with respect to insert material thickness, where the horizontal axis represents the zinc plating amount and the vertical axis represents the number of blow holes.
When n = 30 pieces / m or less, zinc plating amount 120 g / m
^A thickness of ² or less and an insert material thickness of 200 μm or less are suitable.
Further, when the usable range of the zinc plating amount and the insert material thickness is shown under the condition of n = 30 pieces / m or less, it becomes a rectangular range as shown by the hatched line in FIG. In addition, the lower limit of the galvanized amount is 10 g / m from the practical requirement as a galvanized steel sheet.
It is supposed to be ² .

When the insert material is attached, one side or both sides may be adhered or may be formed by resin coating. Further, the present invention can also be applied to a so-called vibration-damping steel plate (composite by sandwiching a synthetic resin between two steel plates).

[0015]

As described above, according to the present invention, a thin insert material of an organic material is sandwiched between a galvanized steel sheet and a galvanized steel sheet, or between a galvanized steel sheet and a normal steel sheet, and laser welding is performed. Therefore, during welding, the resin with a lower melting point and lower boiling point than zinc evaporates first, which causes zinc vapor to enter the gap created by the resin vapor and substantially reduce the amount of zinc vapor entering the molten steel. As a result of reducing the viscosity of the molten steel with the carbon of the resin solid-dissolved in the molten steel, the zinc vapor is satisfactorily discharged, so that good beads with almost no blowholes can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a mechanism for preventing the generation of blowholes according to the present invention.

FIG. 2 is a cross-sectional view of a bead in this example.

FIG. 3 is a graph showing experimental results of galvanizing amount and blowhole number.

FIG. 4 is a graph showing experimental results of insert material thickness and number of blow holes.

FIG. 5 is a graph showing the relationship between the zinc plating amount, the number of blow holes, and the insert material thickness.

FIG. 6 is a diagram showing a usable range of a zinc plating amount and an insert material thickness under the condition of the number of blow holes n ≦ 30.

FIG. 7 is an explanatory diagram showing a blowhole generation situation by a conventional laser welding method.

[Explanation of symbols]

 1, 2 Galvanized steel plate 3, 4 Plating layer 7 Bead 10 Laser beam 11 Insert material

Claims (6)

[Claims] 1. Zinc plating, characterized in that, in the lap welding of galvanized steel plates to each other or of a galvanized steel plate and another metal by laser welding, laser welding is performed by interposing a thin insert material of an organic material in the lap part. Laser welding method for steel sheets. Wherein a steel sheet steel sheet of interest, the laser welding method of the galvanized steel sheet according to claim 1, characterized in that the galvanized amount of ^{10g / m 2 ~120g / m 2} . 3. The thickness of the insert material is 10 μm to 2
The method for laser welding a galvanized steel sheet according to claim 1, wherein the laser welding method is 00 μm. 4. The laser welding method for galvanized steel sheet according to claim 1, wherein one side or both sides of the insert material are bonded. 5. The method for laser welding a galvanized steel sheet according to claim 1, wherein the insert material is formed on the overlapped portion by coating. 6. A vibration-damping steel plate formed by sandwiching a resin between two galvanized steel plates.
A method for laser welding galvanized steel sheet according to the above.