JP3949076B2 - Laser welding quality evaluation apparatus and method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for grasping and evaluating a laser welding situation in real time, and in particular, a laser welding quality evaluation apparatus and method for grasping and evaluating a laser welding situation using reflected light of a laser beam reflected from a welded portion. About.
[0002]
[Prior art]
Conventionally, as a laser welding quality evaluation apparatus and method for grasping and evaluating a laser welding situation using reflected light of a laser beam, there is one described in Patent Document 1. In this laser, a condenser lens is provided in the laser torch so as to be coaxial with the optical axis of the welding laser beam, and the reflected light of the laser beam reflected from the welded portion is condensed by the condenser lens. The brightness level (light intensity) of each pixel from the CCD camera is sent to the camera and binarized by determining whether each pixel is within a predetermined range, and further weighted to determine whether there is a weld defect. Judgment is made.
[0003]
[Patent Document 1]
JP 2000-42769 A [0004]
[Problems to be solved by the invention]
However, according to the laser welding quality evaluation apparatus and method described in Patent Document 1, since the reflected light of the laser beam is condensed coaxially with the optical axis of the irradiated laser beam, the imaging range is limited, and welding is performed. It is not possible to accurately grasp the situation in the longitudinal direction of welding centering on the irradiation position of the laser beam, which correlates with the quality, particularly the situation of the rear wall part of the keyhole and the part adjacent to the rear wall part. It becomes difficult to accurately determine
Further, since it is necessary to binarize and weight all pixels from the CCD camera, it takes time to obtain a determination result (evaluation), and it is difficult to grasp the laser welding situation in real time.
The present invention has been made in view of the above-described problems, and the object of the present invention is to make it possible to accurately and promptly grasp the situation in the longitudinal direction of welding centering on the irradiation position of the laser beam. is there.
[0005]
[Means for Solving the Problems]
In order to solve the above problems, a laser welding quality evaluation apparatus according to the present invention irradiates an object to be welded with laser light emitted from a laser torch, and relatively moves the laser torch and the object to be welded in a welding direction. In laser welding for performing welding, imaging means for receiving reflected light of the laser beam reflected from the irradiated portion of the laser beam with respect to the workpiece to be welded non-coaxially with the irradiated laser beam, and obtaining image data of the fusion part, It is characterized by comprising quality judgment means for judging the welding quality based on the light intensity distribution in the longitudinal direction of welding of the image data obtained by the imaging means.
In the laser welding quality evaluation apparatus configured as described above, since the imaging means receives the reflected light of the laser beam non-coaxially with the irradiated laser beam and obtains image data, before and after welding around the irradiation position of the laser beam. It is possible to grasp direction information extensively. Moreover, since the quality determination means determines the welding quality based on the light intensity distribution in the longitudinal direction of welding, it is possible to accurately grasp the welding situation in the longitudinal direction of welding centering on the irradiation position of the laser beam, which correlates with the welding quality. . Moreover, since the welding quality is grasped by patterning the reflected light of the laser beam, troublesome processing such as binarization and weighting becomes unnecessary, and the welding situation can be grasped in real time.
In the present apparatus, the image pickup means can be configured to be inclined and positioned on the front side in the welding direction with respect to the laser torch so that an image can be picked up around the rear wall portion of the keyhole. In this case, the welding situation can be accurately grasped centering on the rear wall portion of the keyhole that is closely correlated with the welding quality.
In the apparatus of the present invention, the imaging means may be an area sensor camera capable of imaging an area or a line sensor camera capable of capturing one line.
In addition, a laser welding quality evaluation method according to the present invention for solving the above-described problems is directed to irradiating an object to be welded with laser light emitted from a laser torch and relatively moving the laser torch and the object to be welded in a welding direction. In laser welding in which welding is performed, the reflected light of the laser beam reflected from the irradiated portion of the laser beam with respect to the workpiece is received non-coaxially with the irradiated laser beam, and after the melted portion image data or the keyhole An imaging process for obtaining image data centered on a wall portion, and a quality determination process for determining welding quality based on a light intensity distribution in the longitudinal direction of welding of the image data obtained in the imaging process. To do.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
1 and 2 show one embodiment of a laser welding quality evaluation apparatus according to the present invention. In these drawings, reference numeral 1 denotes a laser torch that emits a laser beam A for welding toward a workpiece W. In the laser torch 1, laser beam A sent from a laser oscillator 2 through an optical fiber 3 is transmitted. A condensing optical system is built-in. In the present embodiment, the work piece W is composed of two steel plates W1 and W2 that are superposed on each other. During welding, the laser beam A emitted from the laser torch 1 is placed on the upper steel plate W1. Irradiation is performed in a predetermined pattern, and in this state, the laser torch 1 and the workpiece W are relatively driven in the welding direction F. The welding laser beam A can be a high-power laser beam such as a YAG laser beam or a carbon dioxide laser beam, and the laser oscillator 2 can be appropriately selected depending on the type of laser beam used. used.
[0007]
In laser welding, a keyhole 4 is formed at a portion irradiated with the laser beam A on the work W and a molten pool (molten portion) 5 of molten metal is formed around the keyhole 4. The molten pool 5 is formed so as to extend to the rear side in the welding direction F, and the molten metal solidifies sequentially from the rear end side of the molten pool 5 in accordance with the movement (relative movement) of the laser torch 1. In the figure, reference numeral 6 denotes a weld bead 6 which is a solidification trace of the molten metal, and two steel plates W1 and W2 as the workpiece W are overlapped and welded to each other via the weld bead 6. The
[0008]
Reference numeral 10 denotes an area sensor camera (imaging means) that receives the reflected light B of the laser light A from the melting portion 5 through the filter 11 and obtains image data of the melting portion 5. Here, the area sensor camera 10 is composed of an area CCD camera, and is disposed in front of the laser torch 1 in the welding direction F. The area sensor camera 10 is also arranged so as to be inclined with respect to the upper surface of the work piece W so that an image can be taken centering on the rear wall portion 4a of the keyhole 4. In this case, the inclination angle α of the area sensor camera 10 is arbitrary, but is preferably set to 40 to 60 degrees, preferably about 50 degrees. The filter 11 is an optical filter having a transmission band of the wavelength component of the reflected light B of the laser light A. The area sensor camera 10 may be connected to the laser torch 1 or may be supported by a drive system (for example, a robot) that drives the laser torch 1.
[0009]
It is known that the welding quality in laser welding closely correlates with the welding situation of the rear wall portion 4a of the keyhole 4 and the portion adjacent thereto, as well as the size of the keyhole 4 described above. In the present embodiment, as described above, the area sensor camera 10 is installed so as to be able to take an image centering on the rear wall portion 4a of the keyhole 4, so that the area sensor camera 10 can shoot at a high speed. The obtained image data accurately reflects the welding quality.
In order to confirm the above points, the present inventors performed high-speed imaging with the area sensor camera 10 while repeating the overlap welding, and correlated the image data and the welding quality with the area sensor camera 10. Various investigations were made. The upper side in FIG. 3 to FIG. 6 shows various image data obtained by the area sensor camera 10 in a visible manner. Depending on the welding situation (welding quality), a full moon shape (FIG. 3) and two separations are shown. A crescent shape (FIG. 4), a 3 separated crescent shape (FIG. 5), a single crescent shape (FIG. 6), etc. will be exhibited. Among them, the full moon image P1 shown in FIG. 3 is when the welding quality is good, and the 2-separated crescent image P2 shown in FIG. 4 is the 3-separated crescent shape shown in FIG. 5 when the welding quality is slightly good. The image P3 of FIG. 6 appears when the front and back are closed, and the single crescent-shaped image P4 shown in FIG. 6 appears when the burnout occurs. Therefore, by recognizing the pattern of these images, It becomes possible to accurately grasp the welding quality.
[0010]
The image data from the area sensor camera 10 is sent to the quality judgment means 13 through the signal line 12. The quality determination unit 13 obtains the image data obtained by the area sensor camera 10 by the information calculation unit 14 having a function of obtaining a light intensity distribution in the front-rear direction of welding around the laser irradiation position and the information calculation unit 14. A pattern recognition device 15 having a function of judging the quality of the welding quality by comparing the obtained light intensity distribution with a preset pattern is provided.
[0011]
In the information calculation device 14, for example, for each of the images (visualized images) P <b> 1 to P <b> 4 shown in FIGS. 3 to 6, the luminance value in the direction orthogonal to the welding direction F (the width direction of the fusion part 5) is added. Is repeated in the longitudinal direction of welding to obtain a light intensity distribution. Therefore, the light intensity distribution obtained by the information calculation device 12 is data obtained by patterning each image (image data) as shown on the lower side of FIGS. Since the pattern obtained in this way adds the luminance values in the width direction of the fusion part, errors due to the shift of the imaging position and the accuracy of particle formation of the image become extremely small, and the situation of the fusion part 5 can be accurately determined. It will be reflected.
Further, in the pattern recognition device 15, for example, by setting in advance the patterns corresponding to the full-moon-shaped image P 1 (FIG. 3) and the 2-separated crescent-shaped image P 2 (FIG. 4) as acceptable patterns. When a light intensity distribution (FIGS. 5 and 6) deviating from the pattern is obtained, it is determined that the welding is defective. In this case, the peak height, the number of peaks, the peak-to-peak distance, the area in the pattern, and the like can be used as indexes for comparing and determining patterns.
If necessary, the determination result by the quality determination unit 13 may be displayed on the display device together with the visualized image.
[0012]
Hereinafter, the welding quality evaluation method by the welding quality evaluation apparatus comprised as mentioned above is demonstrated.
In laser welding, the two steel plates W1 and W2 to be welded are brought into close contact with each other, and the two steel plates W1 and W2 are superposed on the workpiece W, for example, using a robot. The laser torch 1 and the area sensor camera 10 are positioned. When the laser oscillator 2 is activated to emit laser light A from the laser torch 1 toward the workpiece W and the laser torch 1 is moved in the welding direction F, the two steel plates W1 and W2 are gradually overlapped. Is done.
[0013]
During the above-described welding, the area sensor camera 10 operates at a high speed (for example, 30 frames per second), and the reflected light B of the laser light A reflected from the periphery of the melting part 5, particularly the keyhole 4, according to the operation. The image sensor in the area sensor camera 10 receives the light, whereby the area sensor camera 10 captures image data for each frame centered on the rear wall portion 4 a of the keyhole 4. The image data for each frame is sequentially sent from the area sensor camera 10 to the information calculation device 14 in the quality determination means 13, and the information calculation device 14 performs image processing on the image data, and the light intensity distribution in the pre- and post-welding directions. Ask for. Then, the pattern recognition device 15 compares the light intensity distribution in the direction before and after welding obtained by the information calculation device 14 with a good pattern set in advance, and determines the quality of the welding quality.
[0014]
As described above, according to the present laser welding evaluation method, the image data obtained by the area sensor camera 10 is patterned as the light intensity distribution of the laser reflected light in the pre- and post-welding directions. Compared with the case of condensing the laser reflected light, it is possible to grasp a wide range of information in the longitudinal direction of the welding centering on the irradiation position of the laser light, and to accurately grasp the welding quality. Particularly in the present embodiment, an area sensor camera 10 is arranged around the welding torch 1 so as to obtain imaging data centering on the rear wall portion 4a of the keyhole 4 that is closely correlated with the welding quality. Therefore, the evaluation of welding quality is also extremely accurate. Moreover, since binarization, weighting, and the like are not required, the processing is simplified and the welding status can be grasped in real time.
In the above embodiment, for each of the images P1 to P4 (FIGS. 3 to 6), adding the luminance value in the width direction of the fusion part 5 is repeated in the front-rear direction of welding to obtain a light intensity distribution. However, instead of this, a light luminance distribution of one line or a plurality of lines may be obtained for each of the images P1 to P4. However, in this case, the error is larger than when adding the luminance values in the width direction.
[0015]
Here, in the above-described embodiment, the area sensor camera 10 is used as the image pickup means of the melting part 5, but in the present invention, instead of the area sensor camera 10, image pickup elements are linearly arranged in the light receiving part. A line sensor camera can be used. However, in this case, it is necessary to adjust the installation direction of the line sensor camera so that image data along a line crossing the keyhole 4 in the welding direction F can be obtained. When a line sensor camera is used as the imaging means, the image data represents a light intensity distribution of one line, and therefore the information calculation device 14 performs image processing simply by converting the output of the line sensor camera into luminous intensity. Compared with the case where area image data is processed by the area sensor camera 10, the processing is simple. In addition, since the line sensor camera can shoot at a higher speed than the area sensor camera 10 (for example, 120 frames per second), it is possible to evaluate the welding quality in real time.
[0016]
In the above embodiment, the image data is obtained centering on the rear wall portion 4a of the keyhole 4. However, the part from which the image data is obtained is arbitrary. You may make it obtain.
Further, when a line sensor camera is used as the imaging means, the area sensor data can be taken in by scanning the line sensor camera in the width direction or the welding direction F of the fusion part 5, so the line sensor camera is used in this way. It is also included in the scope of the present invention.
Furthermore, in the said embodiment, although the example applied to the lap welding of the two steel plates W1 and W2 was shown, this invention is applied to butt welding, fillet welding, etc. of two members besides this. Of course you can.
[0017]
【The invention's effect】
As described above, according to the laser welding quality evaluation apparatus and method according to the present invention, the image data obtained by the imaging means is patterned as the light intensity distribution of the laser reflected light in the pre- and post-welding directions to improve the welding quality. Since the determination is made, it is possible to accurately and promptly grasp the situation in the longitudinal direction of the welding centering on the irradiation position of the laser beam, which correlates with the welding quality, and the reliability for the welding quality evaluation is remarkably improved.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a first embodiment of a laser welding quality evaluation apparatus according to the present invention.
FIG. 2 is an enlarged cross-sectional view showing a main part of FIG.
FIG. 3 shows a visualized image of image data obtained by this laser welding quality evaluation apparatus, and a light intensity distribution of the visualized image in the direction before and after welding, and shows results corresponding to good welding quality. is there.
FIG. 4 is a view similar to FIG. 3, showing a visualized image and a high intensity distribution corresponding to slightly better welding quality.
FIG. 5 is a view similar to FIG. 3, showing a visualized image corresponding to a close and a high intensity distribution.
6 is a view similar to FIG. 3, showing a visualized image corresponding to burn-through and a high-intensity distribution. FIG.
[Explanation of symbols]
1 Laser torch 4 Keyhole 4a Rear wall part of keyhole 5 Molten pool (molten part)
10 CCD camera (imaging means)
11 Filter 13 Quality determination means A Laser beam B for welding Reflected light W of laser beam W

Claims (6)

  In laser welding in which laser light emitted from a laser torch is irradiated onto a work piece and welding is performed by moving the laser torch and the work piece relative to each other in a welding direction, the laser beam is reflected from a portion irradiated with the laser light on the work piece. Receiving laser beam non-coaxially with the irradiated laser beam and obtaining image data of the melted part, and welding quality based on the light intensity distribution in the longitudinal direction of welding of the image data obtained by the imaging unit A laser welding quality evaluation apparatus comprising: a quality determination means for determining   2. The laser welding quality evaluation apparatus according to claim 1, wherein the imaging means is disposed so as to be inclined in front of the laser torch so as to be able to take an image centering on the rear wall portion of the keyhole. .   3. The laser welding quality evaluation apparatus according to claim 1, wherein the imaging means is an area sensor camera.   3. The laser welding quality evaluation apparatus according to claim 1, wherein the imaging means is a line sensor camera.   In laser welding in which laser light emitted from a laser torch is irradiated onto a work piece and welding is performed by moving the laser torch and the work piece relative to each other in a welding direction, the laser beam is reflected from a portion irradiated with the laser light on the work piece. Based on a light intensity distribution in the pre- and post-welding directions of the image data obtained by receiving the reflected light of the laser beam received non-coaxially with the irradiation laser light and obtaining image data of the melted portion And a quality determination step for determining the welding quality.   6. The laser welding quality evaluation method according to claim 5, wherein image data centering on a rear wall portion of the keyhole is obtained in the imaging step.

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