JP2000146852A - Monitoring mehotd of laser welding and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely estimate the generation of a welding defect including the presence of a porosity within a weld metal by fitting the focal point or image pickup position to a plurality of desired depths within the key hole of a groove during laser welding, reading the respective light quantities in the depths, and analyzing the light quantities. SOLUTION: A power beam is emitted to the groove 11 of a work 10. The power beam is formed by a first optical system consisting of a laser beam source 12 such as YAG laser, a total reflecting mirror 13 and a condenser lens 14. On the other hand, the focusing or imaging surface fitting of a monitoring fiber 17a is performed by a second optical system consisting of a partial reflecting mirror 15a and a lens 16a so as to have the light quantity in the depth directional position 1 of the groove 11. The focusing or imaging surface fitting of monitoring fibers 17b, 17c is also performed by second and third optical systems so as to have the light quantities in the depth directional positions 2 and 3 of the groove 11. Accordingly, noise can be reduced by the set of a pinhole 22, and the light quantity in a depth position can be judged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser welding monitoring method and apparatus for estimating welding defects during laser welding.

[0002]

2. Description of the Related Art Recently, laser welding technology, which has been actively developed, detects welding defects such as welding defects and corrects conditions so as to eliminate the cause of the defects. It is necessary to add welding or perform adaptive control to further improve the welding quality. Conventionally, welding defects and welding stability are determined by detecting light emission from a laser plume or light emission from a molten pool, and judging the bead appearance based on the light emission state.

[0003] However, even if the welding defects and the welding stability relating to the bead appearance in laser welding, the undercut of the butt weld, the step, and the like can be estimated or detected to some extent, the accuracy of the welding defects inside the weld metal is accurate. No detection technology currently exists. In other welding methods, a blow hole is a typical welding defect that causes stress concentration and is regarded as a problem.
In the state where line penetration has been performed, air bubbles (called porosity) are more likely to be generated in the weld metal in thick plate welding and non-penetrating welding than in other welding methods in laser welding. It is necessary to accurately monitor the internal state of the metal.

[0004] In view of the above problems, an object of the present invention is to provide a laser welding monitoring method and apparatus capable of accurately estimating the occurrence of welding defects including the presence of porosity inside a weld metal.

[0005]

The present invention that achieves the above object has the following matters specifying the invention.

(1) The method is characterized in that, during laser welding, a focus or an imaging position is adjusted to a plurality of desired depths in a keyhole at a groove, a light amount at each depth is extracted, and the light amount is analyzed. I do.

(2) A second optical system for irradiating a groove with a power beam and a plurality of optical paths for focusing or imaging at a plurality of desired depths in the keyhole of the groove with the power beam. It is characterized by having an optical system and means for analyzing the amount of light obtained by the plurality of optical paths.

(3) In the above (2), the plurality of optical paths are:
The optical path is one of an optical path formed by providing a partial reflecting mirror at a different position, an optical path formed by reciprocating a lens, and an optical path formed by rotating the reflecting mirror.

(4) In the above (2), the analysis of the light quantity is characterized in that light of a plurality of wavelengths is taken out and multivariate analysis is performed.

The present inventors have made new findings as a result of studying the existence of porosity due to X-ray transmission and the behavior of the molten pool during laser welding while observing them in comparison. That is,
It has been found that the state of the inside of a molten hole (referred to as a keyhole) generated by laser welding is related to the presence of porosity. And this relevance is not a problem if the keyhole is constantly changing, for example, if it is gradually increasing or becoming deeper, but if it is not constant, for example, the keyhole during welding is It has been found that porosity occurs when closing or changing the shape of the tip.

Next, the present inventors have found this new finding. However, whether or not the keyhole is in a steady state is indistinguishable from obscure observation because the laser plume emits high-luminance light. I can't get it. Therefore, the inventors considered how to detect the non-steady state of the keyhole, and also considered welding monitoring by analyzing information, and obtained test results.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Here, an example of an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows an example of the apparatus of the present invention. A groove 11 of a work 10 is irradiated with a power beam from above. Power beam is YAG
It is created by a first optical system consisting of a laser light source 12, such as a laser, a total reflection mirror 13, and a condenser lens 14.

On the other hand, the second optical system including the partial reflecting mirror 15a and the lens 16a focuses or adjusts the image plane so as to obtain an amount of light at the position in the depth direction of the groove 11 by the monitor fiber 17a. Similarly, the partial reflecting mirror 15
b, a focus or an imaging plane for obtaining the light quantity at the depth direction position of the groove 11 is performed on the monitor fiber 17b by the second optical system by the lens 16b. Also, lens 1
Focusing is also performed by 6c to obtain the amount of light at the position in the depth direction on the monitor fiber 17c. That is, each monitor fiber 17a, 1 is controlled by the second optical system focused according to the keyhole depth of the groove.
The light amount corresponding to each depth is taken into 7b and 17c.

In this case, a high-luminance plume is generated on the surface of the groove 11 by welding. Even if this plume is generated, the amount of light at the depth of the groove can be obtained by focusing. Is known. Of course, unnecessary light is also generated as noise due to plumes,
In order to reduce such noise, a pinhole 22 is provided in front of the monitor fiber to limit the amount of incident light. Therefore, it is possible to determine the light amount at the depth position.

As means for obtaining the amount of light at the depth of the keyhole, FIG. 2 shows a lens 16d which reciprocates so as to approach and separate from the groove 11, and the key 16 is moved by the movement of the lens 16d. For example, the depth of the hole
, And the monitor fiber 17d
The depth and the amount of light are taken in. In this case, although a drive system of the lens 16d is not shown, for example, a structure in which the rotation of the motor is changed to a linear operation to move the lens 16d, or a structure in which the lens 16d moves forward and backward while rotating with the rotation of the motor, for example, a lens drive of the camera Various types of means can be applied.

FIG. 3 shows the depth of the keyhole,
The rotation of the reflecting mirror 15d changes the state of the imaging position according to the photo sensors 18a, 18b, 18c, and 1
8d, and the photo sensors 18a, 18
In b, 18c and 18d, the amount of light at each imaging position of the keyhole is taken in. Also in this case, the rotation angle of the reflecting mirror 15d is determined, and a predetermined photo sensor 18a,
It is necessary to ensure that the light quantity of a desired depth accurately enters 18b, 18c, 18d.

In this manner, the amount of light at the depth of the keyhole is taken into the monitor fiber or the photosensor by focusing by a lens or by adjusting the rotation angle (imaging position) of the reflecting mirror, so that noise such as plume Is present, the light amount at each depth can be individually captured. Therefore, the amount of light captured by each monitor fiber and each photosensor is a unique amount of light corresponding to the corresponding depth state including noise.

FIG. 4 schematically shows an apparatus for processing the amount of light taken from the monitor fiber shown in FIGS. 1 and 2, and an O / E (optical / electric) converter 20 as shown in FIG. The processing is performed by the computer 21. Here, it is necessary to divide the amount of light taken in from the monitor fiber into noise and the amount of light at a desired depth of the keyhole. In this example, a small amount of noise is removed by extracting light of plural wavelengths. In this way, the S / N ratio is improved to obtain the light amount of the original depth. Therefore, in the O / E converter, for example, an optical filter is incorporated to perform wavelength discrimination. In the case of a photosensor, the output is an electric output, and the filter is not an O / E converter but an electric filter.

The plural kinds of wavelength lights are obtained by test results, and for example, three kinds of wavelength lights λ ₁ ,
When attention was paid to λ ₂ and λ ₃ , the relative intensity and behavior of the light relative to the welding time by laser irradiation were obtained as shown in FIG. FIG. 5 shows the relative value and behavior of the wavelength light when the keyhole is normal.

In this way, the S / N is improved by dividing the amount of light taken in by each monitor fiber into a plurality of wavelengths, and the normal state of the keyhole and the abnormal state are determined based on, for example, the relative intensity of the plurality of wavelengths. A state (a state in which the keyhole is closed) is determined to determine whether the keyhole is normal or abnormal at a desired depth.

FIG. 6 exemplifies a method of judging “normal” and “abnormal” by a computer, and a process in the case of an abnormality. In FIG. 6, when welding is started, FIGS.
The monitoring data of a plurality of wavelengths (for example, FIG. 5) is read from the amount of light obtained from the monitoring fiber and the photo sensor, and the data is compressed to perform a multivariate analysis for determining whether the data is normal or abnormal. In this case, Mahalanobis (Mah
alanobis) Normal distribution bias due to distance and Chebyshev (C
He uses multivariable averaging by the inequality of Hebyshev) to test the degree of goodness, finds interrelated features from a large amount of data, and performs multivariate analysis to determine “normal” or “abnormal”. In order to determine the cause of the "abnormality", a neural network is constructed by learning the abnormal data to perform parallel data processing. Then, the result of the abnormality is corrected or corrected based on, for example, power down, spatter adhesion, deterioration of the optical system, speed change, and the like.

The processing shown in FIG. 6 is to analyze the characteristics and factors from various data included in a plurality of wavelengths of light to determine “normal” or “abnormal”, and to determine the keyhole depth by laser welding. The analysis makes it possible to monitor typical defects of porosity welding, and consequently contributes to improvement of welding quality of laser welding.

[0023]

As described above, according to the present invention, the amount of light at the desired depth of a groove during laser welding is extracted and analyzed. It is possible to accurately monitor weld metal internal defects in laser welding, which have not been performed until now, and this can be a very useful basic technique for preventing or eliminating welding defects in laser welding. A first optical system that irradiates a groove with a power beam; a second optical system that includes a plurality of optical paths that focus or focus an imaging position to a desired depth in the keyhole of the groove with the power beam; And means for analyzing the amount of light obtained by the plurality of optical paths, so that a defect inside the weld metal can be accurately monitored. At this time, a plurality of optical paths can be provided with partial reflecting mirrors at different positions, a lens can be reciprocated, a reflecting mirror can be rotated, and the analysis is, for example, a multivariate analysis.

[Brief description of the drawings]

FIG. 1 is a simplified configuration diagram of an example of an embodiment of the present invention.

FIG. 2 is a simplified configuration diagram of another example.

FIG. 3 is a simplified configuration diagram of another example.

FIG. 4 is a simplified configuration diagram including a processing device.

FIG. 5 is a characteristic diagram of three types of wavelength light.

FIG. 6 is an exemplary processing flowchart by a computer.

[Explanation of symbols]

 11 groove 15a, 15b, 15d Reflector mirror 16a, 16b, 16c, 16d Lens 17a, 17b, 17c, 17d Monitoring fiber 18a, 18b, 18c, 18d Photosensor 20 O / E converter 21 Computer 22 Pinhole

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) // G01N 21/89 G01N 21/89 610Z (72) Inventor Risuke Nayama 2-chome, Araimachi, Araimachi, Takasago City, Hyogo Prefecture No. 1-1 Inside the Takasago Research Laboratory, Mitsubishi Heavy Industries, Ltd. (72) Inventor Yoshio Hashimoto 2-1-1, Shinhama, Arai-machi, Takasago City, Hyogo Prefecture Inside the Takasago Research Laboratory, Mitsubishi Heavy Industries, Ltd. 1-1-1 Wadazakicho Mitsubishi Heavy Industries, Ltd. Kobe Shipyard (72) Inventor Takashi Akabane 1-1-1, Wadasakicho, Hyogo-ku, Kobe-shi, Hyogo F-term in Mitsubishi Heavy Industries, Ltd. Kobe Shipyard (reference) 2G051 AA90 AB04 BA10 BA20 BB11 BC04 CA03 CA07 CC07 CC11 CC15 CC17 CD02 EA11 EA12 EA25 EC02 EC03 EC10 4E068 CA17 CB02 CC01

Claims (4)

[Claims] 1. A laser welding monitoring method in which a focal point or an imaging position is adjusted to a plurality of desired depths in a keyhole of a groove during laser welding, a light amount at each depth is extracted, and the light amount is analyzed. 2. A second optical system comprising: a first optical system for irradiating a groove with a power beam; and a plurality of optical paths for focusing or imaging at a plurality of desired depths in the keyhole of the groove with the power beam. A laser welding monitoring device comprising: a system; and means for analyzing light amounts obtained by the plurality of optical paths. 3. The optical path according to claim 1, wherein the plurality of optical paths include an optical path formed by providing a partial reflecting mirror at different positions, an optical path formed by reciprocating a lens, and an optical path formed by rotating the reflecting mirror. The laser welding monitoring device according to claim 2, wherein 4. The laser welding monitoring apparatus according to claim 2, wherein the analysis of the light quantity is performed by extracting light of a plurality of wavelengths and performing a multivariate analysis or the like.