JPH081337A - Arc welding method for galvanized plate - Google Patents

Abstract

PURPOSE:To prevent a weld defect such as a blowhole, etc., by dropping a droplet into a molten pool after arc welding, and expelling a zinc gas bubble existing in the molten pool by a vibration given to the molten pool, caused by dropping the droplet. CONSTITUTION:First of all, a molten pool 5 is formed by a preceding torch 3 by directing the preceding welding torch 3 and a succeeding welding torch 4 successively to the joining part 2 of galvanized plates 1 and 1a. Successively, when dropping a droplet into the molten pool 5 by the succeeding welding torch 4, a vibration is given to the molten pool 5 by the dropped droplet, and a zinc gas bubble in the molten pool 5 is floated and expelled. Consequently, a weld defect such as a blowhole, etc., is prevented, a quality is improved, and a yield can be enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an arc welding method for galvanized steel sheets, and more particularly to a method for arc welding galvanized steel sheets while preventing the occurrence of welding defects such as broholes and pits. .

[0002]

2. Description of the Related Art As a method for joining thin steel plates, an arc welding method has been conventionally used, and among them, a MAG welding method and a MIG welding method, which are capable of high-speed welding, are widely adopted. However, it is known that when the galvanized steel sheets are joined by these arc welding methods, welding defects such as broholes and pits occur and the joint strength is likely to decrease. This is because zinc in the plating layer existing in the bead forming portion melts into the bead during the bead forming process, vaporizes and remains.

Therefore, in Japanese Patent Laid-Open No. 63-108995, a special paint is applied to the surface of a galvanized steel sheet that serves as a bonding interface, and P existing in the paint causes an alloy having a higher melting point than zinc (Fe-P- A method of forming Zn) to prevent the generation of zinc gas during welding has been proposed. In addition, JP-A-63-5
Japanese Patent No. 6395 proposes a method in which a simple substance of Te, Se, REM, or Sb or an oxide is applied to the bonding interface of a galvanized steel sheet to reduce the viscosity during melting and accelerate the discharge of zinc gas. . However, in all of these methods, it is necessary to apply a paint to the joint interface of the galvanized steel sheet prior to welding, and there is a problem that the man-hours for welding are increased. There is a problem such as an increase in the cost of the welded parts.

[0004]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, does not require the application of paint as in the prior art, and prevents the occurrence of welding defects such as bro holes and pits while galvanizing. It has been completed to provide a method by which a steel sheet can be arc welded.

[0005]

The arc welding method for galvanized steel sheet according to the present invention, which has solved the above-mentioned problems, comprises:
It is characterized in that a droplet is dropped into the molten pool after arc welding, and the zinc gas bubbles in the molten pool are discharged by the vibration imparted to the molten pool by this droplet drop.

[0006]

According to such an arc welding method for galvanized steel sheet, a new droplet is dropped in the molten pool after arc welding, and the molten pool vibrates to vibrate near the interface in the molten pool.
In particular, the fluidity near the interface of the molten pool immediately before solidification is improved, and zinc gas bubbles float up without being trapped inside the molten pool and are discharged to the outside of the molten pool, or are refined, so that melting defects are reliably Can be prevented.

Generally, a large number of thickness gaps of about several μm due to the surface roughness of the steel sheets are present in the superposed portion near the joint of the galvanized steel sheets, and minute gaps are formed. When the galvanized layer is gasified by the heat effect of welding heat, this gap serves as a passage for the gasified high-pressure zinc gas to enter the molten pool. Further, at the root portion (corner portion) of fillet welding, zinc gas that has penetrated into the molten pool due to stress concentration is likely to accumulate at the root portion, and further, the zinc gas in the plating layer travels through the minute gaps in the superposed portion of the plated steel sheets. Becomes high-temperature zinc gas under the influence of the molten pool and molten and solidified metal, and since the gap is extremely small, it becomes high-temperature high-pressure zinc gas, and this zinc gas is constantly supplied to the molten pool, especially when it enters the molten pool immediately before solidification. Weld defects such as blow holes and pits.

Therefore, in order to prevent such welding defects, it is possible to prevent zinc gas vaporized from zinc in the plating layer of the superposed portion of the plated steel sheet from entering the molten pool,
The invading zinc gas is separated from the bottom interface of the molten pool,
It is necessary to miniaturize the bubbles of zinc gas that exist near the weld interface of the molten pool.

In view of the above, the present invention has achieved the intended purpose of preventing welding defects by dropping droplets into a molten pool after arc welding and forcibly vibrating the molten pool. As a method of dropping the droplets into the molten pool, for example, a trailing welding torch is provided in series to the leading welding torch, the trailing welding torch is moved to follow the leading welding torch, and a molten pool is formed by the leading welding torch, Droplets may be dropped into the molten pool by a trailing welding torch. Thus, the welding torch interval for moving the trailing welding torch following the leading welding torch is slightly different depending on the welding speed. For example, at a welding speed of 80 to 180 cm / min, 2 to 10
mm is appropriate. The reason for this is that if the welding torch interval is less than 2 mm, the droplets of the trailing welding torch may be shaken by the sparks of the preceding welding torch and the droplets may not drop into the molten pool reliably. If it exceeds 10 mm, the surface temperature of the molten pool decreases and becomes slightly hard, and it may be difficult to discharge zinc gas bubbles from the molten pool due to the dropping of molten droplets. Is 3 to 5 mm.

The relationship between the welding current and welding voltage of the preceding welding torch (electrode) and the following welding torch (electrode) is as follows: the welding current of the preceding welding torch is 1 A, the welding voltage is VA, and the welding current of the following welding torch. Is 1B and the welding voltage is VB,
When the formula 1.1 ≦ 1B / 1A ≦ 1.5 1.1 ≦ VB / VA ≦ 1.5, the zinc gas bubbles in the molten pool can be more reliably floated and discharged. That is, if the respective welding current and welding voltage are less than the lower limit, the volume of the dropped droplets may become small, making it difficult to impart sufficient vibration to the molten pool, and the discharge of zinc gas bubbles in the molten pool. May be insufficient, which is not preferable. Further, when the respective welding current and welding voltage exceed the upper limits, the discharge of zinc gas bubbles in the molten pool is not hindered, but the appearance shape of the beads may be impaired, which is not practical.

The relationship between the welding rod cross-sectional area of the leading welding torch and the welding rod cross-section of the trailing welding torch is expressed by the following equation, where AA is the welding rod cross-sectional area of the leading welding torch and AB is the trailing welding torch. When 1.1 ≤ AB / AA ≤ 2.0, it is possible to add a droplet capable of imparting sufficient vibration to the molten pool in combination with the relationship between the welding current and the welding voltage, and to further prevent zinc gas bubbles in the molten pool. It can be reliably discharged. If the cross-sectional area ratio of the welding rod of the leading welding torch and the welding rod of the following welding torch is less than the lower limit, the volume of the dripping droplet is small and it becomes difficult to give sufficient vibration to the molten pool, and The discharge of gas bubbles may be insufficient, which is not preferable. If it exceeds the upper limit, the external shape of the bead may be impaired, which is not practical.

Hereinafter, the present invention will be described in more detail with reference to the illustrated embodiments. In FIG. 1, 1 and 1a are galvanized steel sheets to be welded, 2 is their joint, 3 is a leading welding torch, and 4 is a trailing welding torch. Now, the leading welding torch 3 and the trailing welding torch 4 are sequentially oriented to the joint portion 2 of the galvanized steel sheets 1 and 1a to first form the welding pool 5 by the leading welding torch 3, and then the trailing welding torch 4 is used. When a droplet is dropped onto the molten pool 5, vibration is imparted to the molten pool 5 by the dropped droplet, and zinc gas bubbles in the molten pool 5 are floated and discharged. In the figure, 6 is a weld bead.

[0013]

[Example] Next, using a commercially available MAG welding wire, the shielding gas was Ar 80% + CO ₂ 20% and the flow rate was 20 l /
Two pieces of fillet welding were automatically welded by MAG welding under the condition of min. As shown in FIGS. 2 and 3, the welding attitude was set such that the angle θ of the preceding welding torch 3 was 60 ° and the advance angle β of the preceding welding torch 3 was −45 to 45 °. In addition, trailing welding torch 4
Welded while adjusting the forward or backward angle in the range of -45 to 45 °. The results of welding under such conditions are shown in Table 1 as an example and in Table 2 as a comparative example. In addition, in Table 1 and Table 2, the evaluation method of brohol was to detect all brohol by X-ray transmission test on the weld bead whole line (30 cm).
The number of brohols per 1 cm length was evaluated, and all the evaluation results are shown by the average value of n = 10. Also, in both tables
IA is the welding current of the leading torch (A), VA is the welding voltage of the leading torch (V), AA is the cross section of the welding rod of the leading torch (m
m ² ), IB is the welding current (A) of the trailing torch, VB is the welding voltage (V) of the trailing torch, and AB is the cross-sectional area (mm ² ) of the welding rod of the trailing torch. Further, the explanation of the symbols described in the “material to be welded” column of Tables 1 and 2 is as shown in Table 3.

[0014]

[Table 1]

[0015]

[Table 2]

[0016]

[Table 3] In Table 3, E plating means electroplating of iron 85% and residual zinc (basis weight 3 g / m ² ).

[0017]

As described above, according to the present invention, in arc welding of galvanized steel sheet, zinc gas bubbles in the molten pool can be sufficiently discharged, and welding defects such as blowholes can be reliably prevented. Therefore, it is possible to significantly improve the quality and increase the yield. Further, the weld bead formation is good, and the repair work for finishing smoothly with a grinder or the like can be omitted. Therefore, the work efficiency is improved, and the excellent effects such as the productivity increase and the labor saving can be obtained.

[Brief description of drawings]

FIG. 1 is a side view showing an example of the method of the present invention.

FIG. 2 is a front view showing a welding torch angle in the embodiment of the present invention.

FIG. 3 is a side view showing a welding torch angle in the embodiment of the present invention.

[Explanation of symbols]

 1 Galvanized steel sheet 1a Galvanized steel sheet 2 Joined portion 3 Leading welding torch 4 Trailing welding torch 5 Weld pool 6 Weld bead

Claims (3)

[Claims] 1. A galvanized steel sheet, characterized in that a droplet is dropped into a molten pool after arc welding and zinc gas bubbles in the molten pool are discharged by vibrations imparted to the molten pool by the droplet dropping. Arc welding method. 2. A molten pool is formed by a preceding welding torch,
A droplet is dropped into a molten pool by a trailing welding torch.
Arc welding method of galvanized steel sheet according to. 3. The welding according to claim 2, wherein the welding current and welding voltage of the leading welding torch and the trailing welding torch and the relationship between the welding rod cross-sectional area of the leading welding torch and the trailing welding torch are controlled within the range of the following formula. Arc welding method for galvanized steel sheet described. 1.1 ≤ 1B / 1A ≤ 1.5 1.1 ≤ VB / VA ≤ 1.5 However, welding current of the preceding welding torch: 1A: welding voltage: V
A Welding current of trailing welding torch: 1B: Welding voltage: VB 1.1 ≤ AB / AA ≤ 2.0 However, welding rod cross-sectional area of leading welding torch: AA Welding rod cross-sectional area of trailing welding torch: AB