JPH11347764A - Method of preventing blowhole in lap welding of surface treated steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce blowholes generating in welding, in the manner suitable for mass production while damage to a steel sheet is controlled, by vibrating the steel sheet at the time when two or more steel sheets including at least one surface treated steel sheet are lap-welded or fillet-welded. SOLUTION: Two steel sheets 1a, 1b are tightly superposed with the ends fixed by a clamp base 5, and welded at a position about 5 mm from the end of the opposite side of the fixed end, by means of CO2 gas laser provided with a welding nozzle 2, under prescribed welding conditions while focussing on the surface of the steel sheet 1a. In this case, a vibrating device 3 constituted of a motor and a cam mechanism is brought into contact with the steel sheet 1a at 50 mm forward in the welding direction from the welding nozzle 2 and vibrated. The displacement of the steel sheets 1a, 1b is measured by laser displacement gauges 4a, 4b, which are installed holding the steel sheets 1a, 1b in-between in front of the welding nozzle 2, the measurement is converted into a gap between the steel sheets. The conditions of the vibration are desirably set so that a gap of >=0.05 mm in amplitude is formed in the weld zone.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a car, an electric product, a building material product, and the like, in which a surface treated steel sheet such as a coated steel sheet or a galvanized steel sheet is superposed and subjected to laser beam welding or arc welding. The present invention relates to a method for preventing porosity and performing firm and high-quality welding.

[0002]

2. Description of the Related Art Surface-treated steel sheets typified by galvanized steel sheets are used in a wide range of fields such as automobiles, home appliances, heavy electric products, industrial machines, furniture, and building materials because of their excellent corrosion resistance. As the joining method of the surface-treated steel sheet, in addition to bonding and brazing, resistance welding such as spot welding and seam welding, or arc welding such as TIG welding, MIG welding, and plasma welding are used. The form of a joint when welding a surface-treated steel sheet is most often a lap joint in which two or more steel sheets are overlapped and welded from the surface.

[0003] As a future welding method for a thin plate structure, a laser welding method has received the most attention for the following reasons.

[0004] Compared to arc welding, laser welding can reduce the heat input, so that it can be applied to a wide range of applications. (B) The welding cost can be reduced and the weight of parts can be reduced.

(C) Compared with intermittent welding such as spot welding, continuous welding is possible, so that the rigidity of the structure is high.
(d) Compared to resistance welding, there is no need to sandwich steel sheets, single-sided construction is possible, and welding tools such as electrodes and nozzles are not in contact, so there is a large degree of freedom in processing (construction). .

For the above reasons, a YAG laser which can be mounted on an articulated robot has recently been applied to the assembly of an automobile body.

However, if an organic resin or zinc-based plating is present on the overlapping surface, pores and spatters are likely to occur. Especially,
In laser welding, the welding margin is small, pores are generated, and the molten metal is blown away by spatter, and the weld may not be formed.Therefore, the generation of pores is more fatal than resistance welding and arc welding, which have a large molten area. is there.

As described above, it has been a major problem in laser welding of a surface-treated steel sheet to suppress generation of defects such as pores. Similar problems exist in TIG welding, plasma welding, MIG welding and the like.

The generation of pores increases as the gap between the superposed steel plates becomes smaller. In other words, the mechanism of pore generation is that the resin or zinc in the surface treatment layer evaporates due to heating, and the gap between the overlapping surfaces is small, so that when the vapor of the resin or zinc enters the molten part in search of a way to escape, pores are generated. It is considered.

In order to solve this problem, for example, there is the following invention. Japanese Patent Application Laid-Open No. 4-279291 discloses a method in which paper is sandwiched between steel plates in advance to secure a gap and suppress pore defects.

Japanese Patent Application Laid-Open No. 4-258391 discloses a method in which zinc in a plating film in front of a welding line is removed by heating and evaporating with another heat source.

[0012]

However, Japanese Patent Laid-Open Publication No.
The method disclosed in JP 79291 requires an extra step of inserting paper between steel plates before assembly. Also, this method is not suitable for mass production because it is necessary to remove the paper remaining after welding.

Further, the method disclosed in Japanese Patent Application Laid-Open No. 4-258391 is problematic in that the plating is removed more than necessary and the corrosion resistance in the vicinity of the welded part is deteriorated. There is a problem of thermal strain.

An object of the present invention is to form pores generated during lap welding of a surface-treated steel sheet by a method suitable for mass production, and
An object of the present invention is to reduce damage while suppressing damage to a steel sheet.

[0015]

Means for Solving the Problems The inventors of the present invention consider that it is best to secure a proper amount of gap in order to suppress the steam entering the welded portion. Was found to be effective. The gist of the invention completed on the basis of this finding is as described in (1) to (3) below.

(1) A method for preventing porosity in lap welding of surface-treated steel sheets, wherein the steel sheets are vibrated when lap welding or lap fillet welding of two or more steel sheets including at least one surface-treated steel sheet. .

(2) The distance between the surface-treated steel sheet and other steel sheets is 0.0
The method for preventing porosity of lap welding of a surface-treated steel sheet according to the above item (1), wherein the welding is performed while a gap of 5 mm or more is generated.

(3) The method for preventing porosity of lap welding of a surface-treated steel sheet according to the above (1) or (2), wherein the steel sheet is vibrated at a frequency of 2 Hz or more.

Here, "vibrating at a frequency of 2 Hz or more" means that the fundamental frequency of the vibration is 2 Hz or more, and a lower frequency of the vibration causes a harmonic to be generated. This is not included.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS When two or more steel sheets are vibrated under appropriate conditions, a gap is formed between the steel sheets and vibrates. This is because the shapes of the steel plates are different, the natural frequencies are different, and the amplitude and phase of the vibration applied to each steel plate are different due to the propagation of the vibration.

Vibration while the size of the gap fluctuates means that the gap is almost always present, so that the vapor from the surface treatment layer escapes inside the gap and does not enter the melting portion. No stomata formation.

In some cases, the gap disappears instantaneously, but the evaporation rate of the steam is relatively low, and no pores are generated.

As for the portion that gives vibration, the whole steel plate may be vibrated, or vibration may be given to a local portion near the welded portion. It is more preferable to apply the vibration locally because the vibration energy is smaller than the vibration of the entire steel sheet and the position of the steel sheet is not easily shifted by the vibration. In the case where vibration is applied locally, a mechanism is required in which the vibration device follows the welded portion as the welded portion moves. The following mechanism may use a known method. If the welding line is a simple line such as a straight line or a circle, it can be realized by a method of attaching a vibration device to a holding device for the welding nozzle.

As a vibration method, any method such as a mechanical method using a motor or the like, vibration by an electromagnetic force, or an ultrasonic element may be used.

The condition of the vibration is that the amplitude at the welded portion is 0.1.
The condition for forming a gap of 05 mm or more is preferable. If the gap is smaller than 0.05 mm, it becomes difficult for zinc vapor to escape, and pores are likely to be generated. Regarding pore reduction, the larger the gap is, the better, the upper limit of the gap is not particularly defined. However, if the gap is too large, it becomes difficult to bridge the molten portion between the two steel sheets, and it becomes difficult to hold the steel sheets. It is preferable that the gap be provided within about twice the thickness of the thinner steel sheet because of the possibility of the welding position shifting or welding position shift. Also, in the case of laser welding, if the vibration of the steel plate is too large, the focal position of the laser fluctuates, and the penetration of the welded portion is likely to change, so care must be taken. As a countermeasure, reduce the vibration of the steel plate on the side irradiated with the laser and increase the vibration of the steel plate on the non-irradiated side (for example, vibrate from the steel plate on the non-irradiated side, or hold the steel plate on the irradiated side more firmly). And increasing the depth of focus of the laser.

The frequency of the vibration is preferably 2 Hz or more. The reason for this is that if the frequency of vibration is small, a gap is hardly formed between the plates. The upper limit of the frequency of the vibration is not particularly limited. However, if the frequency is too high, the vibration energy for maintaining the necessary gap (amplitude) between the steel plates becomes too large.
Hz or less is economically preferable. A more preferred range is 10
２００200 Hz.

The direction of vibration may be any direction as long as it includes a vibration component in the thickness direction. For example, in FIG. 1, even if the vibration direction in the vibration device 3 is a direction parallel to the steel plate surface, the vibration mode is converted during the propagation of the vibration, and the vibration component in the plate thickness direction at the welding point immediately below the welding nozzle 2. Should just be included.

As welding methods other than laser welding, electron beam welding, plasma arc welding, TIG welding, MIG welding, etc.
Vibration of the steel sheet is effective in reducing porosity in any of the welding methods such as welding and plasma welding.

In actual observation, even when it appears that no gap is formed between the steel sheets, reduced hardening of pores due to vibration was observed. This is thought to be due to the fact that extremely small gaps are created by the vibration, and the bubbles are more likely to escape out of the molten pool than when no vibration is applied.

[0030]

EXAMPLES (Example 1) As the materials to be welded, A: ^two alloyed hot-dip galvanized steel sheets having a thickness of 0.7 mm and a basis weight of 60 g / m ^{2 on} one side; B; a thickness of 0.7 mm; weight per unit area coated steel plate two having adhesion amount 10 g / m ² of an acrylic paint on a galvanized steel sheet of the single-sided 50 g / m ^2, were prepared two steel plates.

First, a test was conducted in which a steel plate was vibrated from one side. FIG. 1 is a schematic view showing a welding method according to a first embodiment of the present invention. FIG. 1 (a) is a front view, and FIG. 1 (b) is a side view. As shown in FIG. 4B, two steel plates 1a and 1b were closely adhered and overlapped, and the ends were fixed with a clamp table 5. About 5 mm from the end opposite to the fixed end was welded with a carbon dioxide laser having a welding nozzle 2. The welding conditions are 3m / mi speed
n, the output was 3 kW, and the focus was on the surface of the steel plate 1a. When no vibration is applied, both steel sheets A (alloyed hot-dip galvanized steel sheet) and steel sheet B (hot-dip galvanized coated steel sheet) penetrate under this welding condition, and an underflow is generated.

50 mm forward from the welding nozzle 2 in the welding direction
The vibration device 3 composed of a motor and a cam mechanism
a, and vibrated under various conditions (amplitude, frequency). At 10 mm in front of the welding nozzle 2, laser displacement meters 4 a, 4 b are installed with the steel plates 1 a, 1 b sandwiched, the displacement of the steel plates 1 a, 1 b is measured and converted into a gap between the steel plates, and the amplitude and The frequency was measured.

After welding, the steel plates 1a and 1b were peeled off, the length of the pores formed on the weld surface in the direction of the weld line was measured, and the ratio to the total weld length was defined as the pore generation rate. Table 1 shows the test results.

When the vibrations of Test Nos. 1 and 10 were not given (Comparative Example), the porosity was 55% for steel sheet A (alloyed hot-dip galvanized steel sheet) and 65% for steel sheet B (hot-dip galvanized steel sheet). Also reached.

Test Nos. 2, 3, 4, 11, 12 and 1
No. 3 was obtained by applying vibration under the conditions according to claims 2 and 3 of the present invention, and no generation of pores was observed.

In Test Nos. 4 and 13, the laser focal position fluctuated greatly due to the large amplitude, and the penetration was somewhat unstable.

Test Nos. 5, 6, 14 and 15 are vibrations applied under the conditions according to claim 2 of the present invention. Since the frequency is as low as 1 Hz, reduced hardening of pores is observed, but slight Occurred. The steel sheet type A had a slightly higher porosity generation rate than the steel sheet type A.

Test Nos. 7, 8, 16 and 17 are obtained by applying vibration under the conditions according to claim 3 of the present invention but without claim 2. Samples Nos. 7 and 16 had some pores due to the small amplitude of the steel plate.

In Test Nos. 9 and 18, the amplitude was smaller than the measurable range of the displacement meter and no gap could be confirmed, but the effect of reducing pores was recognized.

[0040]

[Table 1]

Example 2 Next, a test was conducted in which both of the two steel sheets were vibrated. Among the devices shown in FIG.
Was removed, and the clamp table 5 holding the sample was mounted on a vibration table (not shown) and vibrated in the vertical direction. The laser welding conditions were a speed of 3 m / min, an output of 5 kW, and a focus on the surface of the steel plate 1a. Table 2 shows the test results.

[0042]

[Table 2]

Test Nos. 19 and 21 are cases where no vibration is applied (Comparative Example), and the porosity was 40 to 45%.

In Test Nos. 20 and 22, vibrations were applied under the conditions according to claims 2 and 3 of the present invention, and no generation of pores was observed.

As can be seen in Examples 1 and 2, it has been found that the method of the present invention may be applied to one steel plate or to two or more steel plates.

[0046]

According to the present invention, pores generated during lap welding of a surface-treated steel sheet by a fusion welding method can be prevented, and the quality of welding can be improved. In particular, high quality welding can be obtained when applied to lap welding laser welding of surface treated steel sheets.

[Brief description of the drawings]

FIG. 1 is a schematic view of a weldability test apparatus of the present invention,
(a) is a front view, and (b) is a side view.

[Explanation of symbols]

 1a, 1b Steel plate 2 Welding nozzle 3 Vibration device 4a, 4b Displacement gauge 5 Clamp table

Claims (3)

[Claims] 1. A method comprising at least one surface-treated steel sheet.
When lap welding or lap fillet welding of more than one steel sheet,
A method for preventing porosity in lap welding of a surface-treated steel sheet, wherein the steel sheet is welded while being vibrated. 2. The lap welding of a surface-treated steel sheet according to claim 1, wherein the welding is performed while maintaining a gap having an amplitude of 0.05 mm or more between the surface-treated steel sheet and the steel sheet overlapped with the surface-treated steel sheet. Stoma prevention method. 3. The method for preventing porosity in lap welding of a surface-treated steel sheet according to claim 1, wherein the steel sheet is vibrated at a frequency of 2 Hz or more.