JP6751902B2 - Laser welding equipment and laser welding method - Google Patents

Description

The present invention relates to a laser welding apparatus and a laser welding method for evaluating the quality of a welded portion when welding using a laser beam.

As a conventional welding device, there is a laser welding device that evaluates a welded portion by directly measuring the depth of a keyhole generated during welding.

Specifically, as shown in FIG. 6, in the laser welding apparatus 100, laser light for welding is output from the laser oscillator 102 during the welding process, and the welded portion 105 of the material to be welded 104 is output via the welding head 103. Is irradiated to. The welded portion 105 irradiated with the laser beam melts and evaporates from above, so that the molten metal 106 formed by melting the metal material of the welded portion 105 and the keyhole 107 which is a cavity generated by the pressure of the evaporated metal are formed. It is formed.

During this welding process, the measurement light source 108 continuously outputs measurement light having a wavelength different from that of the laser light for welding. The measurement light light source 108 periodically changes the wavelength of the output measurement light. The measurement light is transmitted to the welding head 103 via the optical interferometer 109 and the optical fiber 110, is concentrically and coaxially superposed on the laser beam for welding by the beam splitter 111, and irradiates the keyhole 107 of the welding portion 105. Will be done.

The measurement light reflected by the keyhole 107 is input to the optical interferometer 109 again via the optical fiber 110. In the optical interferometer 109, the light that has passed through the reference optical path 112 and the measurement light reflected by the keyhole 107 are combined to form interferometric light. The interference light is converted into a signal indicating the intensity by the detector 113.

Based on the signal converted by the detector 113, the computer 114 determines the position where the measured light is reflected by the keyhole 107 according to the principle of Swept Source Optical Coherence Tomography (SS-OCT: optical coherence tomography). This makes it possible to measure the keyhole depth during the welding process. Since the depth of the keyhole 107 correlates with the penetration depth of welding, the laser welding apparatus 100 can determine the quality of welding based on the measurement result of this depth.

Japanese Patent No. 5252026

However, in the above-mentioned conventional configuration, when the vibration of the molten pool 106 and the keyhole 107 is large, or when the spatter frequently crosses the measurement light, the noise becomes large due to these influences, and stable measurement cannot be performed. Have.

FIG. 7 shows the results of measurement with the measurement optical light source 108 having a change speed (scanning speed) of the optical frequency of about 50 P (peta) Hz / sec. In FIG. 7, the horizontal axis represents time, the vertical axis represents the depth of the reflected signal, and the bright points indicate the strength of the reflected signal, and the output is gradually reduced in four steps during welding. As shown in FIG. 7, it can be seen that large noise is generated in the depth direction, and measurement cannot be performed with sufficient accuracy with the conventional configuration.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a laser welding apparatus and method capable of stably measuring a keyhole depth even if there is vibration or sputtering of a welding pond or a keyhole. And.

In order to achieve the above object, the laser welding apparatus of the present invention outputs a laser output means for irradiating a laser beam toward a material to be welded and a measurement light having a wavelength different from the laser light, and at the time of output, the measurement is performed. A measurement light light source that periodically changes the wavelength of light, the laser light, and the measurement light from the measurement light light source are coaxially superposed on the welded portion formed on the material to be welded by the laser light. A surface movement is provided with an optical member to be irradiated and an optical interferometer that measures the keyhole depth of the welded portion based on the interference caused by the optical path difference between the measured light reflected by the welded portion and the reference light. When the speed is 0.4 m / s or less, the average value of the scanning speeds of the optical frequencies of the measured optical light source is 1000 PHz / sec or more.

Further, in the laser welding apparatus of the present invention, the measurement light source is a light source that scans wavelengths by the operation of a MEMS mirror.

Further, in the laser welding apparatus of the present invention, the measurement light source is a semiconductor laser whose wavelength is scanned by an injection current.

The laser welding apparatus of the present invention outputs a laser output means for irradiating a laser beam toward a material to be welded and a measurement light having a wavelength different from the laser light, and periodically changes the wavelength of the measurement light at the time of output. An optical member that coaxially superimposes the measurement light light source to be generated, the laser light and the measurement light from the measurement light light source, and irradiates the welded portion formed on the material to be welded by the laser light, and the welding. It is equipped with an optical interferometer that measures the keyhole depth of the welded portion based on the interference caused by the optical path difference between the measured light reflected by the portion and the reference light, and the surface movement speed is 0.2 m / s. In the following cases, the average value of the scanning speeds of the optical frequencies of the measured optical light source is 500 PHz / sec or more.

In the laser welding method of the present invention, a laser output step of irradiating a laser beam toward a material to be welded and a measurement light having a wavelength different from the laser light are output, and the wavelength of the measurement light is periodically changed at the time of output. A coaxial irradiation step of coaxially superimposing the laser light and the measurement light from the measurement light light source and irradiating the welded portion formed on the material to be welded with the laser light, and the said measurement light output step. It includes a keyhole depth measuring step of measuring the keyhole depth of the welded portion based on the interference caused by the optical path difference between the measured light reflected by the welded portion and the reference light, and the surface movement speed is 0. When it is .4 m / s or less, the average value of the scanning speeds of the optical frequencies in the measured optical light source is 1000 PHz / sec or more.

In the laser welding method of the present invention, a laser output step of irradiating a laser beam toward a material to be welded and a measurement light having a wavelength different from the laser light are output, and the wavelength of the measurement light is periodically changed at the time of output. A coaxial irradiation step of coaxially superimposing the laser light and the measurement light from the measurement light light source and irradiating the welded portion formed on the material to be welded with the laser light, and the said measurement light output step. It includes a keyhole depth measuring step of measuring the keyhole depth of the welded portion based on the interference caused by the optical path difference between the measured light reflected by the welded portion and the reference light, and the surface movement speed is 0. When it is .2 m / s or less, the average value of the scanning speeds of the optical frequencies in the measured optical light source is 500 PHz / sec or more.

With this configuration, the keyhole depth can be measured with high accuracy even if there is vibration or spatter of the welding pond or keyhole.

As described above, according to the laser welding apparatus and the laser welding method of the present invention, the penetration depth of the welded portion can be measured quantitatively and stably, and the welded portion can be measured based on the depth. Good or bad can be evaluated with high accuracy.

Schematic of the laser welding apparatus according to the first embodiment of the present invention. Simulation results of the effect of surface movement on keyhole depth measurement Results of simulating measurement error due to the effect of surface speed when the scanning speed of the optical frequency is changed Actual measurement result of surface movement Keyhole measurement result with a measurement optical light source of about 4000 PHz / sec Schematic of the conventional laser welding apparatus described in Patent Document 1. Keyhole measurement result with a measurement light source of about 50 PHz / sec

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1)
FIG. 1 is a schematic view of a laser welding apparatus according to a first embodiment of the present invention.

As shown in FIG. 1, in the laser welding apparatus 1, during the welding process, a laser beam for welding is output from the laser oscillator 2 and irradiated to the welded portion 5 of the material to be welded 4 via the welding head 3. When the welded portion 5 irradiated with the laser beam melts and evaporates from above, the molten pool 6 formed by melting the metal material of the welded portion 5 and the keyhole 7 which is a cavity generated by the pressure of the evaporated metal are formed. It is formed.

During this welding process, the measurement light source 8 continuously outputs measurement light having a wavelength different from that of the laser light for welding. The measurement light light source 8 periodically changes the center wavelength of the output measurement light. The operation of periodically changing the center wavelength of the measurement light is sometimes called wavelength scanning. The measurement light is transmitted to the welding head 3 via the optical interferometer 9 and the optical fiber 10, is concentrically and coaxially superposed on the laser beam for welding by the beam splitter 11, and irradiates the keyhole 7 of the welded portion 5. Will be done.

The measurement light reflected by the keyhole 7 is input to the optical interferometer 9 again via the optical fiber 10. In the optical interferometer 9, the light that has passed through the reference optical path 12 and the measurement light reflected by the keyhole 7 are combined to form interferometric light. The interference light is converted into a signal indicating the intensity by the detector 13.

Based on the signal converted by the detector 13, the computer 14 determines the position where the measured light is reflected by the keyhole 7 according to the principle of Swept Source Optical Coherence Tomography (SS-OCT: optical coherence tomography). This makes it possible to measure the keyhole depth during the welding process.

In the laser welding apparatus 1 shown in FIG. 1, the measurement light source 8 changes the light frequency, which is the reciprocal of the wavelength, substantially linearly with time. Here, the rate of change (scanning speed) of the optical frequency of the measurement optical light source 8 is 2000 PHz / sec or more.

The light output from the measurement light source 8 is branched into two, an optical path reflected by the welded portion 5 and a reference optical path 12 in the optical interferometer 9. The branched light passes through each optical path, is combined again by the optical interferometer 9, and the interfering light is detected by the detector 13. At this time, a time delay occurs in the two lights due to the difference in the optical path lengths of the two optical paths, and an optical beat having a frequency proportional to this time delay is obtained. Here, the keyhole depth on the optical axis of the measured light is obtained by Fourier transforming (FFT) the optical beat signal detected by the detector 13 with the computer 14 based on the linearity between the frequency of the optical beat and the time delay. Can be obtained.

Here, the reason why the scanning speed of the optical frequency of the measurement optical light source 8 is 2000 PHz / sec or more will be described.

A molten metal having a temperature close to the boiling point is present on the surface of the keyhole 7, and a hollow keyhole 7 is formed by balancing with the evaporated metal. When the welding head 3 moves, the keyhole 7 also moves. Therefore, it is considered that the keyhole 7 does not maintain a stable shape, but the shape constantly fluctuates, and the bottom surface thereof often vibrates. Further, in laser welding, since welding is performed by laser light having high peak power energy, excessive energy may be applied depending on the welding conditions, and metal powder called spatter 15 may be scattered. When vibration occurs on the bottom surface of the keyhole 7 or spatter 15 occurs in the measurement light emitted from the welding head 3, the accuracy of measuring the keyhole depth may decrease.

The results of quantitative evaluation of the effects of vibration on the bottom surface of the keyhole 7 and generation of spatter 15 are shown below.

Depth measurement of the keyhole when the surface of the welded portion 5 (here, the surface of the keyhole 7 or the surface of the spatter 15) moves up and down along the optical axis of the measurement light at a constant speed. The result of simulating the influence on the result is shown in FIG. The waveform in which the vertical movement of the surface is stopped, that is, the waveform when the moving speed is 0.0 mm / s is the waveform to be measured. However, as shown in FIG. 2, as the moving speed of the surface increases, the peak position of the measured waveform, that is, the measurement result of the keyhole depth becomes deviated.

The simulation results illustrated in FIG. 2 are the results when the surface moves at a constant speed, but if the moving speed changes irregularly, the measurement results containing a large amount of noise can be obtained as shown in FIG. Conceivable.

On the other hand, the effects of vibration on the bottom surface of the keyhole 7 and generation of spatter 15 differ depending on the optical frequency scanning speed of the measurement optical light source 8. The graph of FIG. 3 shows the result of simulating the measurement error due to the influence of the surface speed when the scanning speed of the optical frequency is changed. As shown in FIG. 3, it can be seen that the faster the scanning speed, the more the measurement error due to the surface speed can be reduced.

FIG. 4 shows the results of measuring the moving speed of the surface in actual welding. In FIG. 4, the horizontal axis represents time and the vertical axis represents depth. With reference to FIG. 4, it can be seen that the maximum moving speed of the surface is about 0.8 m / sec. That is, even if the moving speed of the surface is 0.8 m / sec, it can be said that stable measurement can be realized if it is affected only by the measurement error (accuracy) or less.

Here, laser welding is often used for automobile-related welding. In automobile-related welding, the welding depth is often in millimeters. For this reason, in automobile-related welding, the measurement accuracy of the keyhole depth is required to be about 0.1 mm, which is an order of magnitude smaller (dotted line in FIG. 3). When the measurement error (accuracy) is required to be 0.1 mm or less when the surface speed is 0.8 m / sec as described above, the scanning speed of the optical frequency is 2000 PHz / sec or more, referring to FIG. It turns out that it should be done.

By setting the scanning speed of the optical frequency of the measurement optical light source 8 to 2000 PHz / sec or more in this way, even if there is vibration of the welded portion 5 or scattering of spatter 15, there is little noise and stable keyhole depth measurement is performed. Is possible. As an example, FIG. 5 shows the result of performing keyhole measurement using a measurement optical light source having a scanning speed of about 4000 PHz / sec. According to FIG. 5, it can be confirmed that the keyhole depth could be measured stably.

The measurement light source 8 that realizes a scanning speed of 2000 PHz / sec or more can be realized by using, for example, a mirror that operates in MEMS (Micro Electro-Mechanical Systems). Since the measurement light light source 8 using the MEMS mirror has a smaller mass than the light source using a polygon mirror or the like, it is possible to realize a faster wavelength change. As the measurement light source 8 using the MEMS mirror, for example, a light source in which a wavelength filter is arranged in a resonator and the transmission wavelength of the wavelength filter is continuously changed, or a VCSEL (Vertical Cavity Surface Emitting Laser) is used as a gain medium. , There is a light source that scans the wavelength by changing the length of the resonator with a mirror that operates in MEMS.

In the present embodiment, a MEMS type light source is used as the measurement light light source 8 that realizes a scanning speed of 2000 PHz / sec or more, but for example, a light source using a DBR (Distributed Bragg Reflector) laser may be used. The DBR laser changes the refractive index by the carrier effect by changing the injection current, and changes the wavelength by changing the optical path length of the resonator. Since the change in the refractive index due to the change in the injection current is fast and does not include mechanical operation, it is possible to realize a very high-speed wavelength change.

The laser welding apparatus and laser welding method of the present invention can be applied to laser welding of automobiles, electronic parts, and the like.

1 Laser welding equipment 2 Laser oscillator 3 Welding head 4 Welded material 5 Welded part 6 Molten pond 7 Keyhole 8 Measuring optical light source 9 Optical interferometer 10 Optical fiber 11 Beam splitter 12 Reference optical path 13 Detector 14 Computer 15 Spatter 100 Laser welding Equipment 102 Laser oscillator 103 Welded head 104 Welded material 105 Welded part 106 Welded pond 107 Keyhole 108 Measured optical light source 109 Optical interferometer 110 Optical fiber 111 Beam splitter 112 Reference optical path 113 Detector 114 Computer

Claims (6)

A laser output means that irradiates a laser beam toward the material to be welded,
A measurement light source that outputs measurement light having a wavelength different from that of the laser light and periodically changes the wavelength of the measurement light at the time of output.
An optical member that coaxially superimposes the laser beam and the measurement light from the measurement light light source and irradiates the welded portion formed on the welded material with the laser light.
An optical interferometer that measures the keyhole depth of the welded portion based on the interference caused by the optical path difference between the measured light and the reference light reflected by the welded portion.
With
When the surface moving speed is 0.4 m / s or less, the average value of the scanning speeds of the optical frequencies in the measured light source is 1000 PHz / sec or more.
Laser welding equipment. The measurement light source is a light source that scans wavelengths by the operation of a MEMS mirror.
The laser welding apparatus according to claim 1. The measurement light source is a semiconductor laser that scans wavelengths with an injection current.
The laser welding apparatus according to claim 1. A laser output means that irradiates a laser beam toward the material to be welded,
A measurement light source that outputs measurement light having a wavelength different from that of the laser light and periodically changes the wavelength of the measurement light at the time of output.
An optical member that coaxially superimposes the laser beam and the measurement light from the measurement light light source and irradiates the welded portion formed on the welded material with the laser light.
An optical interferometer that measures the keyhole depth of the welded portion based on the interference caused by the optical path difference between the measured light and the reference light reflected by the welded portion.
With
When the surface moving speed is 0.2 m / s or less, the average value of the scanning speeds of the optical frequencies in the measured light source is 500 PHz / sec or more.
Laser welding equipment. A laser output process that irradiates a laser beam toward the material to be welded,
A measurement light output process that outputs measurement light having a wavelength different from that of the laser light and periodically changes the wavelength of the measurement light at the time of output.
A coaxial irradiation step of coaxially superimposing the laser beam and the measurement light from the measurement light source and irradiating the welded portion formed on the welded material with the laser light.
A keyhole depth measurement step of measuring the keyhole depth of the welded portion based on the interference caused by the optical path difference between the measured light reflected by the welded portion and the reference light.
With
When the surface moving speed is 0.4 m / s or less, the average value of the scanning speeds of the optical frequencies in the measured light source is 1000 PHz / sec or more.
Laser welding method. A laser output process that irradiates a laser beam toward the material to be welded,
A measurement light output process that outputs measurement light having a wavelength different from that of the laser light and periodically changes the wavelength of the measurement light at the time of output.
A coaxial irradiation step of coaxially superimposing the laser beam and the measurement light from the measurement light source and irradiating the welded portion formed on the welded material with the laser light.
A keyhole depth measurement step of measuring the keyhole depth of the welded portion based on the interference caused by the optical path difference between the measured light reflected by the welded portion and the reference light.
With
When the surface moving speed is 0.2 m / s or less, the average value of the scanning speeds of the optical frequencies in the measured light source is 500 PHz / sec or more.
Laser welding method.