JP2004148353A - Method and device for inspecting laser welding quality - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for inspecting the laser welding quality for easily and reliably determining any defective welding or precursory phenomenon, and more correctly inspecting the welding quality. <P>SOLUTION: Images of a place corresponding to the irradiation position of laser beams 1a and a place in a vicinity thereof between members 2a and 2b to be welded are taken in at high speed from the side during the laser lap welding. The distance from the position of a first luminous image corresponding to the laser beam irradiation position to the position of a bridge-like second luminous image formed on the back side of the welding direction in the taken-in image is obtained by an image processor 7. The obtained value is compared with a reference value by a determination circuit 8, and the result is specified as the inspection result of the welding quality. The value for obtaining the inspection result of "Good" by an experiment or the like in advance is selected as the reference value. Both luminous images are brighter than other peripheral portions, and the distance between the luminous images can be easily obtained. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser welding quality inspection method and apparatus for inspecting the quality of welding in laser overlay welding performed by irradiating a workpiece on which a plurality of members to be welded are overlapped with a laser beam.
[0002]
[Prior art]
In laser welding, a workpiece is irradiated with a laser beam, and the irradiated portion is melted to perform welding. Conventionally, in such welding, the weld pool and its vicinity during laser irradiation are mainly moved upward. There is a device for judging welding quality by photographing with a CCD camera from directly above and observing the obtained image (see Patent Document 1).
[0003]
[Patent Document 1]
JP-A-9-225666 ([Claim 1], [0024])
[0004]
[Problems to be solved by the invention]
However, the above prior art has the following problems.
That is, in order to compare and observe a plurality of images and to make a determination about the difference between them, it is usually easy and reliable to use the light and dark patterns in these images. However, in the top view image of the molten pool and the vicinity thereof, there is little difference in the light and dark pattern between the normal time and the time when the defect is generated, and it is difficult to determine poor welding. In particular, it is extremely difficult to determine the precursor phenomenon of poor welding because the behavior of the weld pool and its surroundings during welding is high speed.
Therefore, there has been a demand for a quality inspection method for laser welding that can easily and reliably determine a welding failure or its precursor phenomenon and accurately inspect the welding quality.
An object of the present invention is to provide a laser welding quality inspection method and apparatus capable of inspecting welding quality more accurately.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, a laser welding quality inspection method according to claim 1 is directed to irradiating a workpiece to which a plurality of workpieces are overlapped with each other while irradiating the workpiece with the laser beam. In laser overlay welding, in which welding is performed by moving the workpiece in a desired welding direction, images of the laser beam irradiation position corresponding portion and the vicinity thereof between the welded members during welding are displayed. The members to be welded that are captured at high speed from the side crossing the welding direction, and that are generated on the rear side in the welding direction from the position of the first emission image corresponding to the irradiation position of the laser beam in the captured image are melt-bonded to each other. The welding quality inspection is performed based on the distance to the position of the bridge-shaped second light emission image.
[0006]
The laser welding quality inspection apparatus according to claim 2, while irradiating a laser beam on a workpiece on which a plurality of workpieces are superimposed, moves the workpiece and / or the laser beam in a desired welding direction, In laser lap welding for performing lap welding of the workpieces, during welding, high speed images from the side intersecting the welding direction between the welded members and corresponding portions of the irradiation position of the laser beam and the vicinity thereof. The high-speed camera to be captured in step S1 and the image from the high-speed camera are input, and the input image is appropriately processed so that the position of the first emission image corresponding to the irradiation position of the laser beam is rearward in the welding direction. An image processing means for obtaining a distance to a position of a second light emission image in the form of a bridge formed by melting and joining the welded members, and the distance obtained by the image processing means Good quality welding based on, characterized by comprising determination means for determining failure.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
As a result of intensive studies and experiments to achieve the above-described object in laser overlay welding, the present inventors have obtained the following knowledge and completed the present invention.
That is, the position of the emission image corresponding to the position corresponding to the irradiation position of the laser beam in the image (side view image) in which the portion corresponding to the irradiation position of the laser beam and the vicinity thereof are taken from the side during welding. From this, it has been found that the distance to the position of the bridge-like light emission image generated on the rear side in the welding direction expresses good and bad welding quality with high accuracy, and the present invention has been completed.
Since these two luminescent images are both brighter than their surrounding parts, they can be easily distinguished from the side view image (bright / dark pattern), and the image can be captured at high speed. The time resolution is increased, and not only defective welding but also the precursor phenomenon can be easily and reliably determined, and accurate welding quality inspection can be performed.
In lap welding, normal welding is performed if welded members are in close contact with each other at the time of welding, and when a gap is formed, welding with a high degree of failure is performed as the size increases. Become. According to the experiments by the inventors, in the lap welding of thin steel plates, normal welding is performed when the gap between them is 0 to 0.3 mm or less. The result was that “scoring” occurred, and when the thickness exceeded 0.5 mm, “melting” occurred. In addition, the said numerical value changes with conditions, such as the thickness of a thin steel plate, welding speed, and laser output. In this embodiment, an example with the above gap amount will be described.
[0008]
FIG. 1 is an explanatory diagram of an embodiment of an apparatus (invention apparatus) to which a laser welding quality inspection method according to the present invention is applied.
In FIG. 1, reference numeral 1 denotes a laser welding torch, which is welded by irradiating a workpiece 2 with a laser beam (light) 1a from the torch 1 as shown by an arrow A.
The workpiece 2 is a plurality of members to be welded, in this case, two thin steel plates 2a and 2b, which are stacked one above the other, and the lap welding is performed using such a workpiece 2 (thin steel plates 2a and 2b). ) Is irradiated with the laser beam 1a.
Laser devices that generate the laser beam 1a include a carbon dioxide laser device and a YAG laser device. Here, a YAG laser device having an output of about 4 kW is used. Welding is performed by moving either the torch 1 or the workpiece 2 or both of them, and moving the torch 1 in the direction indicated by the arrow B.
[0009]
The filter 3 is an optical filter for dimming.
The high-speed camera 4 has a high-speed image of 30 frames per second through the filter 3 from the side intersecting the welding direction between the thin steel plates 2a and 2b during the welding, corresponding to the irradiation position of the laser beam 1a and the vicinity thereof. This is a camera that captures (captures) an image, in this case a CCD camera. In addition, the said image taken in from the side which cross | intersects a welding direction (side of a welding direction) is called side view image.
Here, the high-speed camera 4 captures a side view image from the side orthogonal to the welding direction at a speed at which the behavior of the molten part during welding and its surroundings can be observed, for example, about 500 frames per second. The high-speed camera 4 is attached to the torch 1 via the telescopic arm 5 with the lens surface covered with the filter 3, and follows the movement of the welded portion 6 during the laser welding. Capture.
The telescopic arm 5 is composed of a horizontal arm portion 5a and a vertical arm portion 5b, and the high-speed camera 4 is moved to a position where both arm portions 5a and 5b can be expanded and contracted so that a side view image can be taken. As shown by arrow C, the position is controlled so as to match the position between the thin steel plates 2a and 2b.
[0010]
The image processing device 7 receives a side view image (signal) from the high-speed camera 4, and from the position of the light emission image (first light emission image) at the position corresponding to the irradiation position of the laser beam 1a in the side view image. This is an apparatus for obtaining the distance to the position of a bridge-like light emission image (second light emission image) formed by fusion bonding of the thin steel plates 2a and 2b. The second light emission image is generated on the rear side in the welding direction from the position of the first light emission image.
Specifically, the image processing device 7 binarizes the side view image from the high-speed camera 4, removes noise, and then makes the first and second emission images sharper by thinning processing or the like, and then The distance from the position of the first emission image (first emission image position) to the position of the second emission image (second emission image position) is calculated. The image processing apparatus 7 may have any configuration as long as the distance from the first light emission image position to the second light emission image position can be calculated.
[0011]
The determination circuit 8 determines whether the quality of the welding being performed is good or bad based on the distance (calculated value) from the first light emission image position to the second light emission image position obtained by the image processing device 7. It is. As the distance (reference value) from the first light emission image position to the second light emission image position, which serves as a reference for determining whether the welding quality is good or defective, a value obtained in advance through experiments or the like is used.
The image display device 9 is a device that displays the determination result by the determination circuit 8, and here can also display a raw image from the high-speed camera 4, that is, a side view image.
The image processing apparatus 7 may be housed in the housing of the high speed camera 4 and configured integrally with the high speed camera 4. Further, the determination circuit 8 may be built in the image processing apparatus 7.
[0012]
2 to 4 are diagrams schematically showing side-view images (enlarged images) captured by the high-speed camera 4, respectively. FIG. 2 shows a normal welding, FIG. 3 shows a “shrinkage”, and FIG. Shows the occurrence of “burn-out”.
As can be seen from these drawings, regardless of whether the welding is normal or not, between the thin steel plates 2a and 2b in the side view image, two light emission images (first images) that are both brighter than the surrounding portions. And second emission images 21 and 22 are observed. The first light emission image 21 is observed at a position corresponding to the irradiation position of the laser beam 1a (position indicated by arrow D), and the second light emission image 22 is on the right side in the drawing of the first light emission image 21, that is, on the rear side in the welding direction. The thin steel plates 2a and 2b are observed at a portion where the thin steel plates 2a and 2b are melt-bonded in a bridge shape. 23 in each figure shows plasma.
In each figure, when the distance L (L1 to L3) from the position of the first light emission image 21 to the position of the second light emission image 22 is compared, it increases in the order of FIGS. 2, 3 and 4 (second light emission image). The position of 22 goes backward). That is, with reference to the distance L1 at the time of normal welding in FIG. 2, the distance L increases in the order of “shrinkage” in FIG. 3 and “burn-out” in FIG. 4 (L1 <L2 <L3). It can be seen that the degree of failure increases.
Therefore, by observing this change in the distance L, it is possible to judge whether the welding quality is good or bad, specifically whether the distance L is L1, or L2 or L3, and the distance L is a sign of shifting from L1 to L2. If it is seen, it can be determined as a sign of poor welding at that time. In this case, since the side view image is captured by the high-speed camera 4, the change in the distance L is observed with high time resolution, and can be determined without missing a sign of poor welding.
[0013]
In FIG. 2 to FIG. 4, the gap between the thin steel plates 2 a and 2 b is drawn substantially the same for convenience, but this gap actually shows the following value. That is, 0 to 0.3 mm or less at the time of normal welding in FIG. 2, more than 0.3 mm at the time of occurrence of “shrunk” in FIG. 3, and 0.5 mm or less at the time of occurrence of “burn-out” in FIG. There is a gap. Therefore, when the distance L is less than or equal to L1, the gap is 0 to 0.3 mm or less, and the welding quality is determined as “good”. When the distance L exceeds L1, the gap exceeds 0.3 mm. Therefore, the welding quality is determined as “bad”.
[0014]
Details of the determination operation will be described below with reference to FIG.
In FIG. 5, when welding is started in step 501, the high-speed camera 4 captures a side view image between the thin steel plates 2 a and 2 b dimmed by the filter 3 at a high speed. Note that the imaging position of the high-speed camera 4 with respect to the irradiation position of the laser beam 1a is constant during welding, and the high-speed camera 4 always captures a side view image.
In step 502, the image processing apparatus 7 that has received the side view image (signal) from the high-speed camera 4 starts from the position of the first light emission image 21 in the side view image shown in FIGS. The distance L to the position is calculated.
In step 503, the determination circuit 8 given the distance L calculated by the image processing device 7 determines whether the welding quality at that time is good or bad. The determination is made by comparing whether or not the calculated value L exceeds a reference value (threshold value) L1. Here, as the reference value L1, the calculated value L when the gap between the thin steel plates 2a and 2b is 0.3 mm is set.
The determination result, that is, whether the welding quality is good or bad is displayed in real time on the image display device 9 (see step 504).
The above operations (steps 501 to 504) are repeated until the end of welding.
In addition to displaying good and bad welding quality, a raw image (side view image) from the high-speed camera 4 may be displayed on the image display device 9 at the same time. May be recorded and used for analysis and confirmation of welding results after welding.
[0015]
【The invention's effect】
As described above, according to the present invention, in laser overlay welding, a side view image between members to be welded is captured at high speed during welding, and the first light emission at the position corresponding to the irradiation position of the laser beam in the captured image. The quality of the welding is inspected based on the distance from the position of the image to the position of the bridge-like second light emission image generated on the rear side in the welding direction.
It has been found by the present inventors that the distance from the position of the first light emission image to the position of the second light emission image in the side view image expresses good or bad welding quality with high accuracy. And both the 1st and 2nd light emission images are high-intensity compared with the surrounding part, and can distinguish easily from the side view image. In addition, if the image is captured at a high speed, the time resolution can be improved. Therefore, according to the present invention, not only the poor welding but also the precursor phenomenon can be easily and reliably determined as compared with the prior art. It is possible to inspect the welding quality.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of an embodiment of a laser welding quality inspection apparatus according to the present invention.
FIG. 2 is a diagram schematically showing a side view image (during normal welding) captured by the high-speed camera in FIG. 1;
FIG. 3 is a diagram schematically showing a side view image when welding quality is poor (shrinkage occurs).
FIG. 4 is a diagram schematically showing a side view image when welding quality is poor (melting-off occurs).
FIG. 5 is a flowchart showing a welding quality determination operation.
[Explanation of symbols]
1a Laser beam 2 Work piece 2a, 2b Thin steel plate (welded member)
4 High-speed camera 7 Image processing device (image processing means)
8. Judgment circuit (determination means)
21 First light emission image 22 Second light emission image

Claims (2)

Laser superposition for lap welding of the workpieces by moving the workpiece and / or the laser beam in a desired welding direction while irradiating a workpiece on which a plurality of workpieces are superimposed with each other. In welding,
During welding, the laser beam irradiation position between the members to be welded is captured at high speed from the side intersecting the welding direction and the laser beam irradiation position in the captured image. The welding quality inspection is performed based on the distance from the position of the first light emission image of the corresponding portion to the position of the bridge-shaped second light emission image formed on the rear side in the welding direction by fusion bonding of the members to be welded. Laser welding quality inspection method characterized by the above. Laser superposition for lap welding of the workpieces by moving the workpiece and / or the laser beam in a desired welding direction while irradiating a workpiece on which a plurality of workpieces are superimposed with each other. In welding,
A high-speed camera that captures images of the laser beam irradiation position corresponding portion and the vicinity thereof between the members to be welded at high speed from the side intersecting the welding direction during welding,
An image from the high-speed camera is input, the input image is appropriately processed, and the welded members are generated on the rear side in the welding direction from the position of the first light emission image corresponding to the irradiation position of the laser beam. Image processing means for determining the distance to the position of the bridge-like second light emission image formed by fusion bonding;
A laser welding quality inspection apparatus comprising: a determination means for determining whether the quality of welding is good or not based on the distance obtained by the image processing means.

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