JP2002210579A - Ripple-oscillated yag laser beam device and equipment for welding thin steel plate using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device with which a ripple-oscillated laser beam is obtained by efficiently coaxially synthesizing a pulse-oscillation YAG laser beam and a continuous-wave oscillation YAG laser beam, and to provide equipment for laser beam welding with which a setting accuracy of a butting gap for preventing the generation of a burn through or a humping in a butt welding of thin steel plates is remarkably relaxed. SOLUTION: Either a YAG laser beam unit which generates a conventional solid laser beam or a YAG laser beam unit which generates a hollow laser beam which has a spatial distribution in reflectivity of a partially transparent mirror is set at a continuous oscillation and the other is set at a pulse oscillation. A ripple waveform is realized at a high efficiency by coaxially synthesizing these laser beams with a beam coupler which has a prescribed aperture. Further, as a ripple condition, the ratio of a mean output of the pulse component to a total output is set at a prescribed value and applied to a butt welding of the thin steel plates.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state laser device for obtaining a laser output having a specific time waveform, and in particular, to efficiently coaxially couple a pulsed laser beam and a continuous wave laser beam outside a resonator. The present invention relates to an apparatus for realizing a desired time waveform by synthesizing in a shape, and achieving a sound welding even when operating conditions fluctuate in laser beam butt welding of a thin steel plate.

[0002]

2. Description of the Related Art In butt welding of thin steel sheets, it becomes difficult to secure the butt accuracy with a decrease in the thickness of the steel sheet. As a result, the butt gap becomes too large, and there is a problem that sound welding cannot be achieved. To cope with this problem, Japanese Patent Application Laid-Open No. Hei 4-322892 discloses that a continuous wave laser and a pulsed laser output from a plurality of laser oscillators are coupled outside the laser oscillator and supplied to a butt weld. A method for preventing defects such as burn-through and humping has been proposed.
This is because a laser beam with ripples in time, that is, a pulse superimposed on a continuous wave, is supplied to the welded portion, stabilizing the laser beam absorptivity at the pulsed portion, and the power required for welding with the continuous wave component. It is known that such “ripple laser light” is particularly effective for laser welding thin steel plates.

[0003] In Japanese Patent Application Laid-Open No. 4-322892, laser beams obtained from a plurality of laser beams are combined at the input end of a transmission fiber, or independent fibers are used to realize a ripple laser beam at a welding portion. Means are disclosed for combining the transmitted beams with the final focusing optics or any other way. In order to realize such a coupling method, in the former case, it is necessary to increase the aperture diameter of the fiber incidence lens. As a result, the angle of incidence on the fiber increases, so that the fiber is limited due to the limitation of numerical aperture (NA). There was a problem that the input efficiency to the system was reduced. Further, in the latter case, since there are a plurality of light sources of the imaging optical system, there is a problem that the convergence points do not exactly coincide with each other and the above-described desired effects cannot be sufficiently exerted. . These problems result from the difficulty in coaxially combining laser beams output from different laser oscillators.

To cope with such a problem, two laser beams are coaxially combined as shown in FIG.
(A) and (B) have been implemented. In FIG. 3A, two laser beams 22 and 23 having different laser beam diameters are combined from a beam combining element 24 in an orthogonal direction.
In this method, the laser beam 22 is transmitted through the opening of the beam combining element 24, and the laser beam 23 is reflected on a reflection surface provided around the opening of the beam combining element 24 so as to be coaxially combined. However, since a component of the laser beam 23 corresponding to the opening passes through the opening, there is a problem that the output loss due to the coupling increases. FIG. 6B shows a method of obtaining a coaxial beam by using the beam splitter 25, but also in this case, there is a problem that a reflected component of the laser beam 22 and a transmitted component of the laser beam 23 cause an output loss. Also, a method of increasing the output combining efficiency by using the beam splitter 25 as a polarization beam splitter and using the laser beam 22 as P-polarized light and the laser beam 23 as S-polarized light can be considered.
Since the S-polarized light reflecting surface of the polarizing beam splitter is formed by depositing a dielectric multilayer film, there is a problem that the light resistance against high output is inferior and the long-term reliability is poor. Further, in order to obtain a linearly polarized light output from the laser oscillator, it is necessary to insert a polarization regulating element inside the resonator, and there is a problem that the output efficiency of the laser oscillator is reduced.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a means for drastically improving the coaxial coupling efficiency of a plurality of laser beams, which has been a problem in the above-mentioned prior art. Providing an efficient ripple oscillation YAG laser device and applying such a laser oscillation device to the welding of thin steel sheets under specific conditions to achieve stable laser welding without welding defects using a relatively low output laser. It is to provide a welding device that can be achieved.

[0006]

The above object is achieved by the following inventions (1) to (3). (1). The reflectivity of the partial transmission output mirror of the YAG laser oscillator that constitutes the resonator is made high at the center of the optical axis to reduce the reflectivity at the periphery, or the laser beam is located at the center of the optical axis in the resonator. A first pulsed YAG laser that obtains a hollow ring-mode oscillating beam by inserting a circular substance with a large loss, and a solid oscillating beam obtained by using a partially transmitting output mirror whose reflectance is spatially constant A second continuous wave YAG laser, and a collimator for changing the diameter of the first YAG laser beam so that the inner diameter of the hollow portion of the first YAG laser is equal to or larger than the outer diameter of the second YAG laser. The opening diameter is equal to or less than the inner diameter of the hollow portion of the first YAG laser beam whose diameter is adjusted by the collimator, and is equal to or more than the outer diameter of the second YAG laser; The first and second YAG laser beams are coaxially coupled by having a reflecting surface through which the AG laser passes and the first YAG laser beam is reflected at the aperture output section. A ripple oscillation YAG laser device. (2). The reflectivity of the partial transmission output mirror of the YAG laser oscillator that constitutes the resonator is made high at the center of the optical axis to reduce the reflectivity at the periphery, or the laser beam is located at the center of the optical axis in the resonator. A first continuous wave YAG laser that obtains a hollow ring-mode oscillation beam by inserting a lossy circular substance, and a solid oscillation beam is obtained using a partially transmitted output mirror with a spatially constant reflectance. A second pulsed YAG laser, and a collimator that changes the first YAG laser beam diameter so that the inner diameter of the hollow portion of the first YAG laser matches or becomes larger than the outer diameter of the second YAG laser; The opening diameter is equal to or less than the inner diameter of the hollow portion of the first YAG laser beam whose diameter is adjusted by the collimator, and is equal to or more than the outer diameter of the second YAG laser. Laser passes, ripple wave YAG laser apparatus characterized by first YAG laser beam at the aperture output unit is constituted by a beam coupling element having a reflecting surface for reflecting. (3). The ripple oscillation Y described in the item (1) or (2).
The oscillation condition of the AG laser is such that the average output of the pulse component is 20% to 50% of the entire laser output, and the laser beam obtained from the ripple oscillation solid-state laser device is transmitted by an optical fiber or mirror reflection, and is condensed. A thin steel plate welding apparatus characterized in that the light is condensed and irradiated to a butt weld portion of a thin steel plate.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a ripple oscillation YAG laser device according to the present invention and a welding device using the same will be described in detail. FIG. 2 is an explanatory view schematically showing the structure of a laser resonator constituting a part of the present invention. In FIG. 1, a light source device for exciting the laser medium and a cooling structure for cooling the medium are omitted to avoid complication of the configuration display. FIG. 2A shows the configuration of a normal stable laser resonator. The laser resonator includes a partially transmitting mirror 11, a high reflection mirror 10, and an Nd3 +: YAG laser rod 9 as a laser medium. The output laser beam 2 obtained from the laser oscillator having the above configuration has a higher order T
Obtained as a solid beam in EM mode. FIG. 2B shows a resonator configuration for obtaining a hollow laser beam 1 to be synthesized coaxially with the output beam of FIG. Compared to FIG. 2A, the reflection surface of the partial transmission mirror 12 is coated with a high reflection coating 13 at the center of the optical axis, and the partial transmission coating 1 is applied to the periphery thereof.
4 is given. As a result, the component resonating at the center of the laser rod 9 is confined in the resonator, and the spatial distribution of the output beam 1 becomes a ring-shaped laser beam.

With the above configuration, the diameter of the laser rod 9 is set to 6 m.
m, the diameter of 13 parts of the high reflection coating is 3 mm, the reflectance is 99%, and the reflectance of 14 parts of the partially transmitting coating is 7
As a result of oscillating at 0%, the output is the same as the output when the reflectance is set to 80% by the normal partially transmitting mirror 11 having no spatial distribution, and the output is provided in the region of the optical axis center of 3 mm. A laser beam 1 not obtained was obtained. FIG. 2 (A),
(B) FIGS. 3A and 3B show the spatial distribution of the output laser beam extracted from each resonator.
In the above example, an example in which a hollow-shaped ring mode output is obtained from a stable resonator has been described. However, a ring-shaped beam can be extracted from an unstable resonator. As a means for obtaining a hollow beam, a partially transmitting mirror 11 is used.
An example of giving a spatial distribution to the reflectivity of the laser beam was shown, but as another method, a circular substance with a low transmittance and a large loss to the laser beam was placed at the center of the optical axis to suppress laser resonance at the center of the optical axis. A similar hollow beam can be obtained by insertion.

FIG. 1 is a schematic diagram for explaining coaxial synthesis of two laser beams using a beam combining element which is the next component of the present invention. The beam diameter of the hollow laser beam 1 extracted from the laser oscillator having the configuration shown in FIG. 2B is enlarged by a collimator constituted by a concave lens 3 and a convex lens 4 arranged under confocal conditions. This magnification is set to be equal to or larger than the outer shape of the solid laser beam 2 to be synthesized. The hollow laser beam 1 expanded as described above is reflected by the reflection surface of the beam combining element 5, and the optical axis is changed to the left in the figure. Here, the diameter of the aperture provided in the beam combining element is set to a value equal to or smaller than the inner diameter of the hollow laser beam 1 expanded as described above. Will be reflected. In the process of converting the beam shape, a slight output may be mixed into the hollow portion due to the influence of diffraction. Therefore, the output component passing through the opening is absorbed by the beam damper 6. Since the aperture diameter of the beam combining element 5 is set to a value equal to or larger than the outer shape of the solid laser beam 2 at the same time, the output of the solid laser beam 2 is basically basically all transmitted through the opening. The light propagates to the left in the figure and is coaxially synthesized with the reflected light of the hollow laser beam 1 described above. The laser beam coaxially synthesized by the above configuration is condensed by the condensing lens 7 and enters the core of the optical fiber 8.

In the above configuration, the hollow laser oscillator shown in FIG.
(Pulse repetition frequency 300Hz, pulse energy 33
mJ), the solid laser oscillator shown in FIG. The inner diameter of the hollow laser beam 1 is 3 mm, the outer diameter is 6 mm, and the magnification of the collimator is 2.2.
And the inner diameter at the reflection surface of the beam combining element is 6.6.
mm, the outer diameter of the solid laser beam 2 was 6 mm, and the aperture diameter of the beam combining element 5 was 6.3 mm. As a result of performing coaxial synthesis of each beam, 340 W was obtained as the output of the synthesized laser beam. A synthesis efficiency of .1% was confirmed. FIG. 4 shows the result of measuring the time waveform of the laser beam synthesized as described above. The continuous wave level is 250 W which is the output of the solid laser beam, and a ripple waveform is realized in which the pulse waveform which is the output of the hollow laser beam 1 is superimposed. In this embodiment, an example is shown in which the hollow laser beam 1 is a pulse laser and the solid laser beam 2 is a continuous wave laser. As a result of evaluating the same synthesis efficiency using the laser beam 2 as a pulse laser, a synthesis efficiency of 96.9% was confirmed.

FIG. 5 is a schematic diagram showing the overall configuration of a ripple oscillation YAG laser device using a ring mode oscillation YAG laser according to the present invention. The solid laser beam 2 output from the solid laser oscillator 15 is a concave lens 3 and a convex lens 4 shown in FIG.
After the beam divergence angle is adjusted by the divergence angle correction optical system 17 similar to the combination, the beam enters the beam combiner 19 having the configuration shown in FIG. The divergence angle of the hollow laser beam 1, which is the output of the hollow laser oscillator 16, is adjusted by the divergence angle correcting optical system 17 as in the case of the solid laser beam 2, and the beam is combined via the beam deflector 18 which is a reflecting mirror. Table 19
to go into. The laser beam synthesized and condensed by the beam combiner 19 is transmitted to the material to be welded by the optical fiber 8, condensed again by the converging lens installed in the laser condensing / processing head 20, and is conveyed to the material 21 to be welded. Irradiation achieves welding.

Next, a thin steel sheet welding apparatus using the ripple oscillation YAG laser apparatus according to the present invention will be described. In the laser oscillation waveform of FIG. 4, the pulse oscillation section has a function of instantaneously shifting the steel sheet surface to a molten state due to the height of the peak output. Since the metal in the molten state has a higher laser absorptivity than the solid phase metal, the metal surface having a high absorptivity by the pulse component maintains the molten phase more stably by the subsequent continuous wave component. As a result, occurrence of welding defects such as humping and burn-through occurring during welding is suppressed. Here, as a result of an experimental study by the present inventors, if the average output of the pulse component is 20% or less of the total output, the above-described effect of improving the absorptance is not significant and becomes equivalent to a welding phenomenon in a continuous wave. , Again 50
%, The pulse welding was mainly performed, and it was found that the humping phenomenon clearly occurred in high-speed welding. From the above, it is a condition for applying the ripple oscillation YAG laser device according to the present invention to thin steel plate butt welding that the average output of the pulse component should be 20 to 50% of the total average output.

FIG. 7 shows a configuration of a welding apparatus according to the present invention. This device is a thin steel coil 30,3
5, a ripple YAG laser device 26 comprising up to the beam combiner 19 in the configuration of FIG. 5, an excitation power source (one provided with both a continuous wave power source and a pulse power source) 27, and laser light transmission Optical fiber 8, laser condensing / processing head 20, scanning table 28 and rail 29 as head moving device, steel plate clampers 32, 3
3 In the above-described embodiment, an example in which the optical fiber 8 is used for transmitting the ripple laser beam has been described. However, it is also possible to perform beam transmission including a total reflection mirror and a waveguide.

With the above configuration, butt welding of a thin steel plate having a thickness of 0.2 mm using the ripple oscillation laser output shown in FIG. 4 was performed by sequentially changing the butt interval. as a result,
As shown in FIG. 8, a sound weld bead having no burn-through or humping was obtained up to a gap amount of 30% normalized by the plate thickness, that is, up to 60 μm. For comparison, a similar welding test was performed by applying a continuous-wave laser beam having an output of 350 W to the same welding apparatus. As a result, as shown in the conventional welding method (CW) in FIG. Gap amount 1
It was found that if there was a gap larger than 0%, that is, 20 μm, sound welding could not be obtained. As described above, by applying the welding apparatus according to the present invention, the allowable amount of the butt gap can be increased up to three times as compared with the conventional welding apparatus.

[0015]

As described in detail above, according to the ripple oscillation YAG laser device of the present invention, an output having a ripple waveform synthesized with high efficiency can be obtained. There is an advantage that a ripple output synthesized coaxially from the device can be obtained. Furthermore, the ripple oscillation YAG laser device is used for thin steel plates (particularly 0.1 to 1.
By applying to butt welding (0mm class), there is an advantage that strict gap management does not have to be performed over the entire area in the plate width direction, and the accuracy of the cutting machine and the accuracy of the clamper for forming the welding line can be greatly reduced. From
This has the advantage that the cost of the entire welding device can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration of a beam combiner which is one element constituting a ripple oscillation YAG laser device of the present invention.

FIG. 2 shows a resonator configuration (A) for obtaining a solid laser beam and a resonator configuration (B) for obtaining a hollow laser beam, which are other elements constituting the ripple oscillation YAG laser device of the present invention. FIG.

FIG. 3 is an explanatory diagram showing a spatial distribution (A) of a solid laser beam and a spatial distribution (B) of a hollow laser beam.

FIG. 4 is a graph showing a time waveform of a ripple laser obtained by the ripple oscillation YAG laser device of the present invention.

FIG. 5 is an explanatory diagram showing an overall configuration of a ripple oscillation YAG laser device of the present invention.

FIG. 6 is an explanatory diagram of a conventional laser beam coaxial synthesis method.

FIG. 7 is an explanatory view showing a configuration of a thin steel plate welding apparatus using the ripple oscillation YAG laser device of the present invention.

FIG. 8 is a graph showing the results of a comparison between the present invention and a conventional method with respect to welding defect occurrence characteristics in butt welding of thin steel sheets.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Hollow laser beam 2 Solid laser beam 3 Concave lens 4 Convex lens 5 Beam coupling element 6 Beam damper 7 Condensing lens 8 Optical fiber 9 YAG laser rod 10 High reflection mirror 11, 12 Partial transmission mirror 13 High reflection coating 14 Partial transmission coating 15 Medium Actual laser oscillator 16 Hollow laser oscillator 17 Divergence angle correction optical system 18 Beam deflector 19 Beam combiner 20 Laser focusing / working head 21 Workpiece to be welded 22, 23 Laser beam 24 Beam combining element 25 Beam splitter 26 Ripple YAG laser device 27 Excitation power supply 28 Scanning table 29 Rail 30,31 Steel coil 32,33 Clamper

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // B23K 103: 04 B23K 103: 04 (72) Inventor Naoya Hamada 20-1 Shintomi, Futtsu-shi, Chiba New Japan (72) Inventor Masakazu Tsuji 4-3-9 Fushimicho, Chuo-ku, Osaka City, Osaka Prefecture Osaka Incorporated Company (72) Inventor Masashi Oikawa 20-1 Shintomi, Futtsu-shi, Chiba New Nippon Steel Corporation Technology Development Division (72) Inventor Hiroyuki Yamamoto 20-1 Shintomi, Futtsu City, Chiba Prefecture Nippon Steel Corporation Technology Development Division F-term (reference) YY06

Claims (3)

[Claims] The reflectance of a partially transmitting output mirror of a YAG laser oscillator constituting a resonator is made high at the center of the optical axis to reduce the reflectance at the peripheral portion, or at the center of the optical axis in the resonator. The first pulsed YAG laser that obtains a hollow ring-mode oscillation beam by inserting a circular substance with a large loss into the laser beam, and a solid-state output mirror with a partially transmitted output mirror whose reflectance is spatially constant And a second continuous wave YAG laser for obtaining an oscillation beam of the first YAG laser and a first YAG laser beam diameter for satisfying a condition that the inner diameter of the hollow portion of the first YAG laser is equal to or larger than the outer diameter of the second YAG laser. A collimator that changes the diameter of the first YAG laser beam whose diameter is adjusted by the collimator and is equal to or smaller than the inner diameter of the hollow portion of the first YAG laser beam and equal to or larger than the outer diameter of the second YAG laser. The second YAG laser passes through the mouth and has a reflecting surface at which the first YAG laser beam is reflected at the aperture output portion, so that the first and second YAG laser beams are coaxially combined by a beam combining element. A ripple oscillation YAG laser device comprising: 2. The reflectivity of a partially transmitting output mirror of a YAG laser oscillator constituting a resonator is made high at the center of the optical axis to reduce the reflectance at the peripheral portion, or at the center of the optical axis in the resonator. The first continuous-wave YAG laser that obtains a hollow ring-mode oscillation beam by inserting a circular substance with high loss into the laser beam, and a partially transmitted output mirror whose spatial reflectance is spatially constant are used. A second pulse oscillation YAG laser for obtaining an actual oscillation beam, and a first YAG laser beam diameter for satisfying a condition that the inner diameter of the hollow portion of the first YAG laser is equal to or larger than the outer diameter of the second YAG laser. A collimator for changing the diameter of the first YAG laser beam whose diameter is adjusted by the collimator is equal to or smaller than the inner diameter of the hollow portion of the first YAG laser beam and equal to or larger than the outer diameter of the second YAG laser. The second YAG laser passes through the section,
A ripple oscillation YAG laser device comprising a beam combining element having a reflection surface for reflecting a first YAG laser beam at an aperture output section. 3. The ripple oscillation Y according to claim 1 or 2,
The oscillation condition of the AG laser is such that the average output of the pulse component is 20% to 50% of the entire laser output, and the laser beam obtained from the ripple oscillation solid-state laser device is transmitted by an optical fiber or mirror reflection, and is condensed. A thin steel plate welding apparatus characterized in that the light is condensed and irradiated to a butt weld portion of a thin steel plate.