JP2003305581A - Laser beam welding method and laser beam welding device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser beam welding method which can lap-weld a plated steel sheet in high quality by displaying a vibration effect of a laser beam to the maximum by changing strength distribution of the laser beam. <P>SOLUTION: The beam strength distribution of an irradiation pattern of the laser beam L to be irradiated on the overlapped plated steel sheets 1, 2 by cutting the center of the convex side of a condensing lens 15 inside a laser torch 10 concavely is set so that beam strength is made higher in the peripheral part than in the central part. Also, converging beam L2 of the laser beam L is rotated by operation of oscillators 19 by supporting the condensing lens 15 by a plurality of the oscillators 19. A high quality weld bead without defects such as a blowhole can be obtained by discharging a plating component from a fused part by quickly evaporating the plating component at a welding part including a heat affected part by the beam strength distribution peculiar to the irradiation pattern and rotational movement of the converging beam L2. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of laminating plated steel sheets and performing laser welding, a so-called laser lap welding method, and a laser welding apparatus used for carrying out the method.

[0002]

2. Description of the Related Art For example, in the case of laser lap welding of galvanized steel sheets and aluminum plated steel sheets, if the steel sheets are simply superposed, the plating components are evaporated by the heat of the laser beam,
Scattering occurs, and welding defects such as blowholes and rough skin occur. Therefore, in the past, in the case of laser lap welding of such plated steel sheets, generally, a minute gap is secured between the laminated steel sheets, and a gas (vapor) generated by evaporation of the plating component is allowed to escape through this minute gap. I was doing. However, according to this measure, in order to secure a minute gap between the steel plates, it is necessary to previously form protrusions or recesses by plastic working on one or both of the two plated steel sheets to be overlapped (Japanese Patent Laid-Open No. 10-216974). Japanese Patent Publication No. 2000-162388, Japanese Patent Publication No. 6-73755.
However, there is a problem in that it requires extra cost to process them, and that dimensional variations in the minute gaps cannot be avoided.

By the way, recently, the development of laser lap welding that can avoid the above-mentioned welding defects caused by evaporation of plating components has been promoted even when the plated steel sheets are superposed on each other, and, for example, JP-A-2001-162389. The publication describes a method of evaporating a plating component in the first welding step to perform a subsequent second welding step (main welding) without a plating layer. However, according to this method, since the laser welding is performed in two steps, it is inevitable that the production efficiency is lowered, and further, the production cost is also increased.

[0004]

On the other hand, for example, in Japanese Unexamined Patent Application Publication Nos. 10-71480 and 2000-84684, the laser beam vibrates in a direction intersecting the welding direction (circular motion, elliptic motion). Exercise, reciprocating exercise, etc.) to overlap the beam irradiation to accelerate degassing. However, according to this method, the evaporation of plating components in the heat-affected zone is delayed due to the mountain-shaped intensity distribution characteristic of the laser beam, and there is a risk that this gas will be trapped in the weld metal.
Moreover, the width (bead width) of the obtained weld metal is narrow, which may cause a problem in strength. This will be described with reference to FIG. 7. In the conventionally used laser beam, the irradiation pattern S ′ is circular as shown in FIG. The beam intensity distribution has a mountain shape with the maximum in the center and a sharp decrease toward the periphery. As a result, as shown in FIG. 2B, the bead B ′ formed between the two plated steel sheets 1 and 2 that are superposed has a V shape and the width W ′ thereof is also narrow. . Therefore, such a laser beam L
Even if ‘is vibrated in the direction intersecting the welding direction as described above, rapid heating of the heat-affected zone is difficult, delaying evaporation of the plating components in the heat-affected zone, and expansion of the bead width. There is a limit. In addition, rapid heating of the heat affected zone described above,
The expansion of the beam width can be achieved to some extent by increasing the beam intensity, but in this case, the peak intensity at the center becomes too large, which facilitates burn-through and requires a laser oscillator with a large output. As a result, a new problem arises that the cost burden of equipment increases, and the fundamental problem cannot be solved.

The present invention has been made in view of the above problems, and its object is to maximize the vibration effect of the laser beam by changing the intensity distribution of the laser beam, Therefore, it is an object of the present invention to provide a laser welding method capable of performing high-quality lap welding of plated steel sheets, and also to provide a laser welding apparatus capable of efficiently performing this method.

[0006]

In order to solve the above-mentioned problems, a laser welding method according to the present invention applies a laser beam to a superposed portion of two steel plates, at least one of which is a plated steel plate, so that both steel plates are exposed. In the laser welding method for welding, the irradiation pattern of the laser beam is set so that the beam intensity is higher in the peripheral portion than in the central portion, and the welding is performed while vibrating the laser beam within a width wider than the target bead width. It is characterized by scanning in the direction. In the laser welding method performed in this way, the intensity distribution of the laser beam is higher in the peripheral portion than in the central portion, so when the laser beam is vibrated, the plating components of the welded portion including the heat affected zone evaporate rapidly. On the other hand, degassing progresses reliably in the weld metal due to overlapping beam irradiation. In the method of the present invention,
The form of vibration of the laser beam is circular motion, elliptical motion,
Although reciprocating motion or the like is optional, circular motion is desirable because it is easy to control. On the other hand, in order to solve the above-mentioned problems, a laser processing apparatus according to the present invention is a laser welding apparatus that welds both steel plates by irradiating a laser beam from a laser torch to a superposed portion of two steel plates, at least one of which is a plated steel plate. In the above, the condensing lens arranged in the laser torch is shaped so as to obtain an irradiation pattern in which the beam intensity becomes higher in the peripheral portion than in the central portion, and the laser beam is vibrated in a direction intersecting the welding direction. A vibrating means for vibrating the condenser lens is provided. In the laser welding device configured in this way,
By changing the shape of the condenser lens inside the laser torch,
The intensity distribution of the laser beam can be easily changed. In the present laser processing device, the vibrating means may be configured to include a plurality of vibrators arranged in the circumferential direction of the condenser lens.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 and 2 show a laser torch 10 used for carrying out the laser welding method according to the present invention. In both figures, 11 is a torch body having a double structure consisting of an inner cylinder 12 and an outer cylinder 13.
Inside, two condenser lenses 14 and 15 are arranged at a predetermined interval in the axial direction. The tip of the torch body 11 is closed by a lid plate 16 having an opening 16a in the center, and a protective glass 17 covering the opening 16a is arranged inside the lid plate 16.

Of the two condensing lenses, the first condensing lens 14 arranged on the inner side of the inner cylinder 12 collimates the laser beam L sent from a laser oscillator (not shown) into a parallel beam L.
The shape is set to change to 1, while the cover plate 1
The second condenser lens 15 arranged on the side of the opening 16a of 6 is
The parallel beam L1 emitted from the first condenser lens 14.
Is set to change the beam to a focused beam L2. The laser torch 10 is supported by, for example, an industrial robot, and is positioned at a predetermined height position with respect to the two plated steel plates 1 and 2 that are superposed during welding, and this height is maintained. Transferred in the welding direction F. In this case, the laser torch 10 has its height set so as to focus the laser beam L (focused beam L2) at a position deeper than the upper surface of the plated steel sheet 1 on the upper side, that is, to defocus the laser beam L. Irradiation pattern S (FIG. 3) having a predetermined area on the upper surface of the plated steel sheet 1
Is formed.

However, the central portion of the second condenser lens 15 on the convex side is cut into a concave shape. That is, the central portion of the second condenser lens 15 becomes substantially thin due to the presence of the concave cut portion 15a that is cut in a concave shape, and as a result, as shown in FIG. 3, in the irradiation pattern S on the plated steel plate 1, The beam intensity distribution has a different shape in which the beam intensity greatly drops in the central portion and becomes higher in the peripheral portion. In other words, the irradiation pattern S has a pseudo donut shape composed of the low beam intensity portion S1 on the center side and the high beam intensity portion S2 on the peripheral side.

The second condenser lens 15 also includes an inner cylinder 12
A peripheral portion is supported by a plurality of vibrators (vibration actuators) 19 arranged in an annular chamber 18 between the outer cylinder 13 and the outer cylinder 13. The oscillators 19 are equally distributed in the circumferential direction here and are 3
Each of them is provided with a control signal from a vibrator control device (not shown) via a signal line 20. Each oscillator 19 reciprocates with a predetermined phase according to a control signal from the oscillator controller, whereby the focused beam L2 emitted from the second condenser lens 15 makes a circular motion. As a result, the irradiation pattern S on the upper plated steel sheet 1 also moves circularly. Therefore, the vibrator 18 and the vibrator control device constitute a vibrating means for vibrating the second condenser lens so as to vibrate the laser beam L in the direction intersecting the welding direction F.

On the other hand, at the tip of the torch body 10, a plurality of (here, four) optical sensors 2 are equally arranged in the circumferential direction.
1 is provided. The optical sensor 21 serves to detect the reflected light of the laser beam reflected from the molten portion (molten pool), and its signal is a defect detection circuit (not shown).
It will be sent to. The defect detection circuit,
It has a function of detecting a welding defect from the intensity change of the reflected light detected by each of the optical sensors 21, and therefore, the optical sensor 21 and the defect detection circuit constitute a welding defect detection device. The optical sensor 21 has a structure including a bandpass filter that allows only the reflected light of the laser beam to be captured.

Here, the plated steel sheets 1 and 2 have a plated layer containing a metal that evaporates at a relatively low temperature. For example, a galvanized steel sheet, an aluminum plated steel sheet, a nickel-zinc plated steel sheet, etc. Equivalent to. At the time of laser welding, first, two plated steel plates 1 and 2 to be welded are superposed in close contact with each other, and the two plated steel plates 1 and 2 are superposed on each other, for example, using an industrial robot. Position the laser torch 10. Then, a laser oscillator (not shown) is activated to irradiate the plated steel sheets 1 and 2 on which the laser beam L has been overlapped, and the laser beam L is scanned in the welding direction F. Simultaneously with the start of the irradiation of the laser beam L, a control signal (not shown) is sent from the vibrator control device to each vibrator 19 to vibrate the second condenser lens 15 so that the focused beam L2 emitted therefrom is circular. Exercise.

Then, as shown in FIG. 4, the irradiation pattern S on the upper plated steel sheet 1 moves in the welding direction F while drawing a spiral locus. At this time, the irradiation pattern S
With respect to the amplitude H of the center locus O1 (shown by a broken line) of the peripheral loci O2, O which are the opposite pole points on the center line of the irradiation pattern S.
3 (shown by a solid line) oscillates outside the amplitude H of the central locus O1 by the radius R of the irradiation pattern S. That is, the high beam intensity portion S2 on the peripheral side of the irradiation pattern S
(FIG. 3) vibrates in a wide range over the diameter of the irradiation pattern S, whereby a range wider than the diameter of the irradiation pattern S is rapidly heated, and the plating component (metal) of the welded portion is rapidly spread over a wide range. Evaporate.

On the other hand, within the amplitude H of the center locus O1 of the irradiation pattern S, the high beam intensity portion S2 of the irradiation pattern S is obtained.
Are densely and overlappingly irradiated, the base material within the range of the amplitude H is rapidly melted and agitated, whereby the gas generated by the evaporation of the plating metal (gas degassing) proceeds. As a result, as shown in FIG. 3B, two plated steel plates 1 and 2
A weld bead B of good quality without defects such as blowholes is formed between the two. Also, this welding bead B
Has a trapezoidal shape due to the pseudo donut type irradiation pattern S in which the bead strength is higher in the peripheral portion than in the central portion, and the bead width W obtained is the width W ′ (of the conventional V-shaped weld bead B ′ ( It is significantly enlarged compared to Fig. 7), and the joint strength is also improved. Here, during the welding, a signal is continuously sent from each optical sensor 21 to the defect detection circuit, and the defect detection circuit averages the intensity of the laser reflected light from the melted portion and observes it over time. If there is an abnormality in the detection result, it is determined that welding is defective and a stop signal is sent to the laser oscillator.

In the present invention, two plated steel plates 1, 2 are used.
One of them may be a non-plated steel plate, and in this case, the order of stacking the plated steel plate and the non-plated steel plate is arbitrary. Further, in the above-mentioned embodiment, the irradiation pattern S is a pseudo donut type composed of the low beam intensity portion S1 on the center side and the high beam intensity portion S2 on the peripheral side. The intensity portion S1 may be of a perfect donut shape in which the beam intensity is zero. Further, in the above embodiment, the two plated steel sheets 1 and 2 are arranged so as to be in close contact with each other, but in the present invention, the two plated steel sheets 1 and 2 have a minute gap. They may be superposed, and in this case, the gas of the plating component is discharged through the minute gaps, so that the obtained welding quality is further improved. Furthermore, in the above embodiment, the welding torch 10 is moved in the welding direction F, but instead of this, the welding torch 10 is fixed in position and the plated steel sheet plates 1 and 2 are moved. Of course good things.

[0016]

Example As two plated steel plates 1 and 2 to be welded,
A galvanized steel sheet having a plate thickness of 1.2 mm is selected, a laser beam L having an output of 3.5 kW is oscillated from a YAG laser oscillator, and the oscillator 1 is produced by using the laser torch 10.
While oscillating the irradiation pattern S at 2 kHz by the operation of No. 9, laser lap welding was performed by scanning at a feed rate of 3.5 M / min, and after welding, the state of the welded portion was observed microscopically. FIG. 5 is a surface observation of the obtained weld bead B, and the weld bead B has been satisfactorily finished without any rough skin or bead breakage. On the other hand, FIG. 6 shows the cross-sectional structure of the welded portion, and internal defects such as blowholes are not found inside the weld bead (welding metal) B, and the method of the present invention is applicable to lap welding of plated steel sheets. It was confirmed that it was extremely useful.

[0017]

As described above, according to the laser welding method and apparatus of the present invention, the laser beam is used in which the irradiation pattern is set so that the beam intensity becomes higher in the peripheral portion than in the central portion, Since this is scanned in the welding direction while vibrating within a width wider than the target bead width, it is possible to rapidly evaporate the plating components of the welded part including the heat-affected zone, and the plated steel sheet can be of high quality and efficiently. Can be lap welded. Further, since it is not necessary to use a laser oscillator having a large output, it is advantageous in terms of cost and its utility value is great.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing a structure of a laser torch used for carrying out a laser welding method according to the present invention.

FIG. 2 is a plan view showing a tip shape of the laser torch shown in FIG.

FIG. 3 is a schematic diagram showing a laser beam irradiation pattern and a beam intensity distribution (A) and a bead shape (B) after welding in the laser welding method according to the present invention.

FIG. 4 is a schematic diagram showing a locus of a laser beam in the present laser welding method.

FIG. 5 is a photograph showing a surface condition of a welded portion after laser welding.

FIG. 6 is a micrograph showing an internal structure of a welded portion after laser welding.

FIG. 7 is a schematic diagram showing a laser beam irradiation pattern and a beam intensity distribution (A) and a bead shape (B) after welding in a conventional laser welding method.

[Explanation of symbols]

1,2 plated steel sheet 10 laser torch 11 Torch body 14 First condenser lens 15 Second condenser lens 15a concave cut portion of second condenser lens 19 vibrators (excitation means) 21 Optical sensor L laser beam Irradiation pattern of S laser beam

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G02B 26/10 G02B 26/10 G // B23K 103: 04 B23K 103: 04 103: 16 103: 16

Claims (4)

[Claims] 1. A laser welding method of irradiating a laser beam to a superposed portion of two steel plates, at least one of which is a plated steel plate, to weld the two steel plates together, wherein an irradiation pattern of the laser beam is from a central portion to a peripheral portion. The laser welding method is characterized in that the beam intensity is set to be higher on the one side, and the laser beam is scanned in the welding direction while vibrating within the width wider than the target bead width. 2. The laser welding method according to claim 1, wherein the laser beam is circularly moved. 3. A laser welding apparatus for irradiating a laser beam from a laser torch onto a superposed portion of two steel plates, at least one of which is a plated steel plate, to weld the two steel plates together. A vibrating means for vibrating the condensing lens so that an irradiation pattern in which the beam intensity is higher in the peripheral portion than in the central portion is obtained and the laser beam is vibrated in a direction intersecting the welding direction. A laser welding device characterized by being provided with. 4. The laser welding apparatus according to claim 3, wherein the vibrating means includes a plurality of vibrators arranged in a circumferential direction of the condenser lens.