JP2002137073A - Monitoring method of laser beam welding for die-cast material and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect a welding failure such as porosities inside of a weld metal when a die-cast material is welded by a YAG laser. SOLUTION: This monitoring device for laser beam welding is equipped with a laser beam source 1 for which the YAG laser is used, a condensing lens 6 for condensing laser light from the laser beam source 1 to the die-cast material, a wavelength selection and permeable mirror 4 which allows only the laser light from the laser beam source 1 to permeate and reflects light other than that, a prism 5 which takes out one part of the laser light and irradiates one part or plural parts of a part from start of solidification to the end thereof in backward of a molten pool of the die-cast material with the light, photodetectors 10 and 12 which reflect the light scattered by irradiating the die-cast material with the laser light by means of the wavelength selection and permeable mirror 4 and photoelectrically convert this reflected light, and a fault detecting means which determines the amount of the porosities and size thereof inside of the weld bead of the die-cast material based on an optical signal detected by the optical detectors 10 and 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for monitoring laser welding of a die-cast material, and more particularly to a method and apparatus for monitoring laser welding of a die-cast material such as magnesium and aluminum.

[0002]

2. Description of the Related Art As is well known, in laser welding in general, it is necessary to detect a defect such as a welding defect and to correct conditions for eliminating the cause of the defect and to develop an application control technique. By the way, conventionally, as a method of determining welding defects and stability during welding, a non-contact shape measuring device such as a laser scanner is installed before and after the welding line to determine the shape of the weld bead, or by laser irradiation. In some cases, light emission of the generated plasma plume is detected, and the appearance of the bead is determined based on the light emission intensity.

[0003]

However, the above prior art is directed to a rolled material such as a steel material, and laser welding of a die cast material has hardly been performed conventionally. The reason is that air and shrinkage cavities contained in the die-cast material at the time of manufacturing or hydrogen dissolved in solid solution are released by heating at the time of welding, and a large number of porosity is generated.

[0004] In recent years, a die-casting material free from entrainment of air or the like has been developed by a PF (porosity-free) method for forming a fine oxide by performing a die-casting in an oxygen atmosphere, and is being used partly. However, even in this case, porosity does not always occur, and a technique for online diagnosis of a welded portion where porosity occurs is desired.

As described above, according to the conventional technique, only the beat shape within the range visible from the outside can be detected, and the porosity left inside the die cast material, which is a problem, cannot be determined.
Further, unlike the CO ₂ laser, the YAG laser performs only weak ionization on the metal vapor and the shielding gas, and it is difficult to detect the light emission of the plasma room to determine the appearance of the bead.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides laser welding monitoring of a die cast material capable of accurately detecting a welding defect including presence of porosity inside a weld metal when the die cast material is welded by a laser. It is an object to provide a method and an apparatus.

[0007]

The first invention of the present application is directed to a laser welding monitoring method for detecting a welding defect when laser-die-welding a die-cast material, the solidification starting from a solidification start portion behind a molten pool formed by laser irradiation. After irradiating a part or a plurality of positions of the end part with a part of the scattered light of the processing beam and obtaining a frequency from a change in the intensity of the scattered light, obtaining a porosity amount and a size in the weld bead based on the frequency. A method for monitoring laser welding of a die-cast material, characterized in that:

A second invention of the present application is directed to a laser welding monitoring apparatus for detecting a welding defect when laser-die-casting a die-cast material, and a YAG for processing the die-cast material.
A laser light source using a laser, a condenser lens for condensing the laser light from the laser light source on the die casting material, and a wavelength that transmits only the laser light from the laser device and reflects the other light. A selective transmission mirror, a part of the laser beam cut out, a prism for irradiating a part or a plurality of positions of the solidification end portion from the solidification start behind the molten pool of the die casting material, and the laser light was irradiated to the die casting material and scattered. A light detector for reflecting light by the wavelength selective transmission mirror and photoelectrically converting the reflected light; and a defect for obtaining a porosity amount and a size in a weld bead of the die-cast material based on an optical signal detected by the light detector. A laser welding monitoring apparatus comprising: a detection unit.

According to a third aspect of the present invention, there is provided a laser welding monitoring method for detecting a welding defect at the time of laser welding of a die cast material, wherein a part or a plurality of solidification starting portions to a solidification ending portion behind a molten pool formed by laser irradiation. Irradiating the position with a probe light different from the processing laser light, calculating the frequency from the intensity change of the scattered light, and then calculating the porosity amount and size in the weld bead based on this frequency This is a laser welding monitoring method for die cast materials.

According to a fourth aspect of the present invention, there is provided a laser welding monitoring apparatus for detecting a welding defect at the time of laser-welding a die-cast material.
A laser light source using a laser, a condenser lens for condensing the laser light from the laser light source on the die-cast material, and a wavelength that transmits only the laser light from the laser light source and reflects the other light. A selective transmission mirror, a semiconductor laser device for irradiating probe light to a part or a plurality of positions of a solidification end portion from a solidification start portion behind a molten pool of a die casting material, and a probe light from the semiconductor laser device to the wavelength selective transmission mirror. A polarizing beam splitter to be sent, a circularly polarizing plate that converts probe light from the polarizing beam splitter from linearly polarized light to circularly polarized light, and a laser beam is irradiated to the die casting material and the light scattered is reflected by the wavelength selective transmission mirror. A photodetector that photoelectrically converts the reflected light, and a welding bead of the die casting material based on the optical signal detected by the photodetector. A laser welding monitoring device, characterized in that the and a defect detection means for determining the porosity volume and size.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method for monitoring laser welding of a die cast material according to the present invention will be described in more detail. In the present invention, the “defect detection means for obtaining the porosity and size of the porosity in the weld bead of the die cast material based on the optical signal detected by the photodetector” is electrically connected to a photodetector (such as a photodiode). And the amplifier
There is a device that includes an A / D converter electrically connected to the amplifier and a personal computer (or FET device) electrically connected to the converter. In such a defect detecting means, for example, scattered light is received by a photodetector, converted into an electric signal corresponding to the intensity, amplified by an amplifier, and then A / D
The signal is converted into a digital signal by a converter, and the signal is further processed by a fast Fourier transform (FET) program such as a personal computer or a dedicated FET device, and the vibration component is replaced from the time axis to the frequency axis by frequency analysis.

In the present invention, the size of the porosity to be detected is 5 μm to 500 μm. Here, if the size is smaller than 5 μm, there is no problem in material strength and it is considered that detection is not possible.
This is because if it exceeds 500 μm, welding itself is not performed normally. Further, the amount of porosity is estimated to be about 1/20 to 1/5 as a volume fraction of the weld metal.

In the present invention, when an abnormality occurs,
This is a case where the intensity of the relatively low frequency component of about 50 to 500 Hz in the frequency component and the intensity ratio before and after the frequency component are larger than the intensity ratio in the normal welding measured in advance, specifically, about 2 times. (Approximately 3 dB) on the basis of being large.

In the present invention, the beam diameter of the probe light is about 0.6 to 0.8 mm, and the diameter of the molten pool is about 0.8 to 0.8 mm.
It is about 1.0 mm. Accordingly, the shift amount of the probe light from the center of the weld bead is about 0.8 to 3 mm, and the optimum value is 1 mm. Here, the shift amount indicates a deviation of the center position of the probe beam from the center position of the processing beam.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. Embodiment 1 FIG. 1 is an explanatory view of a laser welding monitoring apparatus according to Embodiment 1 of the present invention, and shows an example in which a part of a YAG laser beam is cut out and used as a probe light.

Reference numeral 1 in the drawing denotes a laser light source 1 composed of a YAG laser. Most of the YAG laser light (hereinafter simply referred to as laser light) A from the laser light source 1 is used as a processing beam.
The light is applied to a work 7 through a recollimator lens 3, a wavelength selective transmission mirror 4, a prism 5, and a condenser lens 6. Further, the probe light B for examining the welding state cuts out a part of the laser light by the prism 5 and irradiates a part of the solidification start portion behind the molten pool. Although the wavelength selective transmission mirror 4 transmits laser light and reflects other wavelengths, the return light of the laser light is also reflected by about 0.1%. It can be measured with a container. The irradiation position of the probe can be changed by changing the apex angle of the prism 5.

The laser beam for processing is scattered on the work 7 and returns to the condenser lens 6, is reflected by the wavelength selective transmission mirror 4, passes through the dimming plate 8, the first light receiving lens 9, and the first laser beam.
Is detected by the photodetector 10. On the other hand, the probe light emitted to the rear of the molten pool is scattered by the work 7 and then returns to the condenser lens 6 again, where it is collimated and partially reflected by the wavelength selective transmission mirror 4. Furthermore, the second
The light is collected by the light receiving lens 11 and photoelectrically converted by the second photodetector 12. Here, the observation area can be determined by the ratio between the focal point f1 of the condenser lens 6 and the focal point f2 of the first light receiving lens 9 (or the second light receiving lens 11).

Each of the photodetectors 10 and 12 has an amplifier 1
3 and 14 are connected to each other.
A D converter 15 and a personal computer (or FET device) 16 are electrically connected. Here, the amplifiers 13 and 14 and A
The / D converter 15 and the personal computer 16 constitute a defect detecting means.

As described above, the monitoring device according to the first embodiment includes a laser light source 1, an optical fiber 2 connected to the laser light source 1, and a wavelength selection device that transmits light from the optical fiber 2 and reflects back scattered light. Transmission mirror 4
And a condenser lens 6 for condensing light from the optical fiber 2
A dimming plate 8, condensing lenses 9 and 11 for condensing the light reflected by the wavelength selective transmission mirror 4, and photodetectors 10 and 12 for detecting the light reflected by the wavelength transmission mirror 4, respectively.
Amplifiers 13 and 1 connected to these photodetectors 10 and 12
4 and A / A electrically connected to the amplifiers 13 and 14.
The configuration includes a D converter 14, a personal computer 15, a prism 5 that uses a part of laser light as probe light, and the like.

Further, in the laser welding monitoring apparatus, while the work 7 is processed with the laser light, a part of the solidification start part from the solidification start part behind the molten pool is irradiated using a part of the laser light as probe light, Processing laser light and probe light scattered by the work 7 are detected by the photodetectors 10 and 12 via the condenser lens 6 and the wavelength selective transmission mirror 4 and the like. Here, as the porosity inside the work 7 increases, the amplitude increases and the vibration oscillates at a low frequency. Therefore, the change in the intensity of the scattered light is detected by the amplifiers 13 and 12 connected to the photodetectors 10 and 12.
14, frequency analysis using the A / D converter 15, the personal computer 16, etc., obtains a high-intensity frequency, and from this frequency, obtains the porosity amount and size in the weld bead.

In fact, it has been confirmed that the monitoring device according to the above embodiment has the following effects. 3A and 3B show the state of the surface of the normal weld bead 21. FIG. 3A is a plan view and FIG. 3B.
Shows a sectional view. On the other hand, FIGS. 4A and 4B show a weld bead 21 having a porosity 22 inside and a swelling on the surface.
3 (A) is a plan view, and FIG.
FIG. 3B shows a cross-sectional view.

The probe light 23 irradiates the position behind the molten pool 24 or the solidification end position from the start of solidification, and measures the information on the shaking of that portion. At that time, it was found that the frequency was low due to large swinging, and the amplitude was large. Therefore, measurement can be performed by measuring the movement.

FIG. 5 shows an example of data of a signal obtained by the photodetector when a defective bead including a normal bead and a porosity is formed. From FIG. 5, it has been found that when a defective bead is formed, the bead largely swings near the solidified portion and the amplitude also becomes large. FIG. 6 shows an example of the frequency analysis. The curve (a) shows the case of a normal bead, and the curve (b) shows the case of a bad bead. As shown in FIG. 6, when the frequency of the signal was analyzed by fast Fourier transform, it was found that when a defective bead was formed, the intensity on the low frequency side was large. Note that on an actual production line, the average intensity may be obtained using a bandpass filter so as to pass a frequency region to be measured.

(Embodiment 2) FIG. 2 is an explanatory diagram of a laser welding monitoring apparatus according to Embodiment 2 of the present invention, and shows an example in which a semiconductor laser is used as an external probe light. However, the same members as those in FIG. 1 will be described with the same reference numerals.

Reference numeral 31 in the drawing indicates a semiconductor laser device. The probe light B from the semiconductor laser device 31 is
The work 7 is irradiated via the polarizing beam splitter 32, the circularly polarizing plate 33, and the wavelength selective transmission mirror 4. Here, since the semiconductor laser 31 is polarized, all the light can be reflected by using the polarization beam splitter 32. Further, by installing a circularly polarizing plate 33 on the downstream side of the polarizing beam splitter 32, linearly polarized light is converted into circularly polarized light.

It is to be noted that a Brewster brhythm (not shown) or the like is arranged downstream of the circularly polarizing plate 33 to bend the beam.
The light is reflected by the wavelength selective transmission mirror 4 for the processing beam. At this time, the beam is incident at an angle to the optical axis of the lens because of the incident angle. The probe light is applied to a position different from the condensing position of the processing beam A in accordance with the deflection angle, and the reflected light is received by the light receiving lens as in the case of FIG. Here, the returned light is converted into linearly polarized light orthogonal to the incident beam by the circularly polarizing plate 33, and then the polarization beam splitter 32 and the wavelength selective transmission filter 3 are used.
4. Collected by the photodetector 10 through the light receiving lens 35. In addition, since the polarizing beam splitter 32 transmits only the light of the semiconductor laser, scattering of the processing beam can be cut.

As described above, the laser welding monitoring apparatus according to the second embodiment includes a laser light source 1, a semiconductor laser device 31, a polarization beam splitter 32 for reflecting all the probe light from the laser device 31, and a polarization beam splitter 32. A circularly polarizing plate 33 for converting the probe light B passing through the beam splitter 32 from linearly polarized light to circularly polarized light;
Wavelength selective transmission mirror 4 for reflecting and transmitting light passing through
A condenser lens 6 for condensing the laser light A from the optical fiber 2, a light receiving lens 35 for receiving the light reflected by the wavelength selective transmission mirror 4, and a photodetector 10 for detecting the light from the light receiving lens 35 , An amplifier 13 connected to the photodetector 10, an A / D converter 14 electrically connected to the amplifier 13, a personal computer 15, and the like.

In the laser welding monitoring apparatus, the laser beam A from the laser light source 1 is radiated to the work as a processing beam, while the semiconductor laser device 31 emits probe light from the polarization beam splitter 32 and the circularly polarizing plate 3.
(3) Irradiate a part of the solidification end portion from the solidification start portion behind the molten pool through the wavelength selective transmission mirror 4 and the condenser lens 6. Then, as in the case of FIG.
After the light is received by the light receiving lens 6, the light is passed through the wavelength selective transmission mirror 4, the circularly polarizing plate 33, the polarizing beam splitter 32 and the light receiving lens 9 and detected by the photodetector 10. The change in the intensity of the scattered light is detected by the amplifier 1 connected to the photodetector 10.
3. A frequency having a high strength is obtained by frequency analysis using the A / D converter 15 and the personal computer 16, and the porosity amount and size in the weld bead are obtained from this frequency.

In the above embodiment, the case where the probe light is applied to a part of the solidification end portion from the solidification start portion behind the molten pool of the die casting material is described. However, the present invention is not limited to this. It is applicable when it does. More specifically, this can be achieved by using a plurality of prisms in the first embodiment, and by using a plurality of semiconductor laser devices in the second embodiment.

[0030]

As described above in detail, according to the present invention, laser welding monitoring of a die cast material capable of accurately detecting a welding defect including presence of porosity inside a weld metal when welding the die cast material with a laser. Methods and apparatus can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a monitoring device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a monitoring device according to a second embodiment of the present invention.

FIG. 3 is an explanatory diagram of a normal bead.

FIG. 4 is an explanatory view of an abnormal bead.

FIG. 5 is a characteristic diagram showing a relationship between signal intensity and time when a normal bead and an abnormal bead are formed.

FIG. 6 is a characteristic diagram showing the relationship between signal strength and frequency when the signal in FIG. 5 is subjected to frequency analysis by fast Fourier transform.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... YAG laser device, 2 ... Optical fiber, 3 ... Collimating lens, 6 ... Condensing lens, 4 ... Wavelength selective transmission mirror, 5 ... Prism, 7 ... Work, 8 ... Dark plate, 9,11,35 ... Light receiving lens Reference numerals 10, 12, photodetector 13, 14, amplifier, 16 A / D converter, 17 personal computer (or FET device), 21 welding bead, 22 porosity, 24 molten pool, 31 semiconductor laser 32, a polarizing beam splitter, 33, a circularly polarizing plate, 34, a wavelength selective transmission filter.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Shigeharu Kamado 1603-1, Kamitomioka-cho, Nagaoka City, Niigata Prefecture Inside Nagaoka University of Technology (72) Inventor: Yo Kojima 1603-1, Kamitomioka-cho, Nagaoka City, Niigata Prefecture Nagaoka Engineering F-term in University of Science and Technology (reference) 4E068 BA00 CA17 CB09 CB10 CC01 DA00 DB01

Claims (4)

[Claims] 1. A laser welding monitoring method for detecting a welding defect when laser-die-welding a die-cast material, comprising: forming a machining beam from a solidification start part behind a molten pool formed by laser irradiation to a part or a plurality of positions of a solidification end part; A method for monitoring laser welding of a die-cast material, comprising: irradiating a part of the laser beam; obtaining a frequency from a change in the intensity of the scattered light; and obtaining a porosity amount and a size in the weld bead based on the frequency. 2. A laser welding monitoring apparatus for detecting a welding defect when laser-die-welding a die-cast material, comprising: a laser light source using a YAG laser for processing the die-cast material; and a laser light from the laser light source. A condensing lens for condensing on the material, a wavelength selective transmission mirror that transmits only the laser light from the laser light source and reflects the other light, and cuts out a part of the laser light to melt the die casting material. A prism that irradiates a part or a plurality of positions of the coagulation end portion from the coagulation start portion behind the pond, and a laser beam is irradiated to the die casting material, and the scattered light is reflected by the wavelength selective transmission mirror, and the reflected light is photoelectrically converted. A photodetector and a method for obtaining a porosity amount and a size of a die-cast material in a weld bead based on an optical signal detected by the photodetector. Laser welding monitoring apparatus characterized by comprising a detecting means. 3. A laser welding monitoring method for detecting a welding defect at the time of laser welding a die casting material, comprising: a processing laser at a part or a plurality of positions from a solidification start part to a solidification end part behind a molten pool formed by laser irradiation. Laser welding of die casting material characterized by irradiating a probe light different from light, calculating the frequency from the intensity change of the scattered light, and calculating the porosity amount and size in the welding bead based on this frequency Monitoring method. 4. A laser welding monitoring device for detecting a welding defect at the time of laser-welding a die-cast material, comprising: a laser light source using a YAG laser for processing the die-cast material; A condensing lens for condensing on the material, a wavelength selective transmission mirror that transmits only the laser light from the laser light source and reflects the other light, and solidification from the solidification start part behind the molten pool of the die casting material A semiconductor laser device that irradiates a part or a plurality of positions with probe light, a polarization beam splitter that sends the probe light from the semiconductor laser device to the wavelength selective transmission mirror, and a probe light from the polarization beam splitter that is linearly polarized. Circularly polarizing plate to convert to circularly polarized light, and light scattered by irradiating laser beam to die casting material A photodetector that reflects the light by the wavelength selective transmission mirror and photoelectrically converts the reflected light, and a defect detection unit that obtains a porosity amount and a size in a weld bead of the die-cast material based on an optical signal detected by the photodetector. And a laser welding monitoring device comprising: