JP4045424B2 - Laser welding quality inspection method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser welding quality inspection method and apparatus for detecting the quality of welding by detecting light from a welded part in laser welding performed by irradiating a workpiece with laser light .
[0002]
[Prior art]
As a conventional laser welding quality inspection method of this type, there is a method described in Japanese Patent Laid-Open No. 2000-42769. This is to detect the reflected light of the irradiated laser light out of the light from the welding location, and to detect the defect at the welding location based on its intensity.
[0003]
[Problems to be solved by the invention]
The above prior art is effective in detecting defects in welded portions because the intensity of reflected light from the welded portions irradiated with laser light changes with the occurrence of welding defects.
However, defect detection by reflected light from a welded spot (laser beam irradiated spot) is actually detected from a site where a significant difference due to welding quality is unlikely to occur, and the expected accuracy can be found in inspection accuracy. There wasn't.
On the other hand, welding with a laser beam has recently been widely used for lap welding of two thin plate materials, for example, two panel materials constituting a vehicle body such as an automobile. Recently, not only the high quality but also the demand for high speed is increasing. For this reason, there has been a demand for a high-quality laser welding quality inspection method that can withstand the laser welding quality inspection in such a line, particularly in high-precision welding of thin plate materials.
The object of the present invention has been made in view of the above-described demands, and provides a highly accurate laser welding quality inspection method and apparatus for highly accurate inspection of welding quality, particularly in high-speed welding of thin plate materials. It is in.
[0004]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to the laser welding quality inspection method according to claim 1 is directed to a workpiece to be welded on which a plurality of members to be welded are irradiated with laser light , and / or In laser lap welding, in which laser beam is moved in a desired welding direction to perform lap welding of the workpiece, illumination is performed on the rear end portion of the weld pool formed around the keyhole of the workpiece during welding. Is a method for inspecting the quality of welding based on the intensity of reflected light from the rear end portion of the molten pool, and as means for irradiating the illumination light, an illumination laser beam is used. A light irradiating means including an illuminating optical fiber that guides and emits toward the rear end portion of the molten pool is used, and as means for obtaining the intensity of the reflected light, a plurality of light receiving optical fibers and the plurality of light receiving optical fibers are used. Before receiving optical fiber A light receiving means including a condensing lens for condensing and entering the reflected light is used, and the illumination optical fiber is lighted together with the condensing lens in a state surrounded by the plurality of light receiving optical fibers. It is characterized in that it is integrated at the exit / incident part, is coaxial with the condenser lens, and penetrates the condenser lens .
[0005]
The invention relating to the laser welding quality inspection apparatus according to claim 2 is directed to irradiating a laser beam to a workpiece on which a plurality of members to be welded are overlapped with each other and the laser beam in a desired welding direction. In laser overlay welding that moves and performs overlay welding of the workpiece,
A light irradiating means for irradiating light for illumination to a rear end portion of the molten pool formed around the keyhole of the workpiece during welding, and a rear end of the molten pool irradiated with light by the light irradiating means A light receiving means for receiving reflected light from the part and outputting an electric signal according to the intensity of the reflected light, and performing a predetermined calculation based on the intensity of the electric signal from the light receiving means, the quality of welding is good, Processing means for determining a defect and outputting the result, and the light irradiation means is configured to include an illumination optical fiber that guides the illumination laser light and emits it toward the rear end portion of the molten pool. The light receiving means includes a plurality of light receiving optical fibers, and a condensing lens for condensing and entering the reflected light into the plurality of light receiving optical fibers. Surrounded by multiple receiving optical fibers It is integrated in the light emitted incident portion with the condenser lens condition and the condenser lens and coaxially located, characterized in that through the condenser lens.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
The inventors of the present invention have completed the present invention as a result of intensive studies and experiments and studies in order to achieve the above-described object in laser welding, particularly, high-speed welding of thin plate materials.
In other words, the present inventors have found that if the surface (pond surface) of the rear end portion of the molten pool formed around the keyhole of the work piece is vibrated violently, the welding quality is poor, and if there is no wave, the quality is good. The knowledge that it becomes (normal welding) was obtained. And according to this, it discovered that the quality of a welding quality and a defect could be determined with high precision more than the prior art based on the phenomenon of the welding location which is irradiating the laser beam. Therefore, the present inventors irradiate the above-mentioned phenomenon of the surface at the rear end portion of the molten pool, and irradiate the illumination light (illumination light) to the rear end portion of the molten pool. The conclusion that it can be grasped by the intensity of the light reflected from the end portion (reflected light) has come to be completed.
[0008]
When the illumination light emitting part and the reflected light receiving part are integrated as a light incident / incident part, that is, when the emission direction of the illumination light and the light receiving direction of the reflected light are set to 180 ° opposite directions, The intensity of the reflected light and the quality of the welding quality have the following relationship. That is, when the light incident / incident part is directly above the molten pool surface (in a direction perpendicular to the molten pool surface) and illumination light is emitted from the molten pool surface, there is no wave on the molten pool surface and it is gentler. Since the received light intensity of the reflected light increases, it is determined that the quality is normal (normal welding) when the received light intensity of the reflected light is large. When the light exit / incident part is in a direction inclined from directly above the molten pool surface and illumination light is emitted from the surface, the light exit / incident part side should be gentle if there is no wave on the melt pool surface. Light does not reflect and reflects to the opposite side. Therefore, in this case, the smaller the received light intensity of the reflected light, the better the quality (normal welding) is determined. If the molten pool surface vibrates violently, light reflection to the light incident / incident part side will occur frequently or greatly due to irregular reflection, etc., so the higher the intensity of the reflected light, the worse the welding quality. Is done.
In the later-described embodiment, the light incident / incident part is integrally attached to a welding torch and moved in the welding direction together with the torch. Therefore, the direction of the light incident / incident part that emits and emits illumination light and reflected light with respect to the surface of the rear end portion of the molten pool located behind the welding direction of the laser irradiation position by the torch is true of the surface of the molten pool. From the top, the direction is inclined. That is, in the embodiment described later, a case where the welding quality is determined to be poor as the received light intensity of the reflected light is increased is illustrated.
[0009]
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 performs welding by irradiating a workpiece 2 with a laser beam (light) 1a emitted 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.
The laser device includes a carbon dioxide laser device and a YAG laser device, and here, a YAG laser device 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.
[0010]
The light irradiating device 3 irradiates the rear end portion 6 of the molten pool 5 formed around the keyhole 4 of the workpiece 2 during welding with a beam light for illumination, in this case, a laser beam (illumination laser beam 7). It is a device to do. In the figure, a region surrounded by a one-dot chain line indicates a keyhole region, a region surrounded by a two-dot chain line indicates a molten pool region, and a region surrounded by a solid line indicates an irradiation region of the illumination laser beam 7.
The light irradiation device 3 includes an illumination laser device 3a, and an illumination optical fiber 3b that guides the illumination laser light 7 from the illumination laser device 3a and emits it toward the rear end portion 6 of the molten pool 5. It is prepared for.
The illumination optical fiber 3b forms an optical fiber bundle 8 with a light receiving optical fiber, which will be described later, in the middle of the illumination optical fiber 3b, reaches the light exit / incident part 9, and emits the illumination laser light 7 from the light exit / incident part 9. The range between the solid line arrows haha indicates the irradiation range of the illumination laser beam 7.
[0011]
The light receiving device 10 receives the reflected light 11 from the rear end portion 6 of the molten pool 5 irradiated with light by the light irradiating device 3 during welding, and outputs an electrical signal corresponding to the intensity of the reflected light 11. Device.
Here, the light receiving device 10 includes a plurality of light receiving optical fibers 10a, a condensing lens 10b (see FIG. 2), and a photosensor, for example, a photodiode 10c.
The condensing lens 10b is an optical lens that condenses and enters the reflected light 11 from the rear end portion 6 of the molten pool 5 on the light receiving end side of the plurality of light receiving optical fibers 10a. The photodiode 10c is a photoelectric conversion element that receives the reflected light 11 from the plurality of light receiving optical fibers 10a and converts the reflected light 11 into an electric signal, and outputs an electric signal having a strength corresponding to the received light intensity. In FIG. 1, a region surrounded by a broken line indicates a reflected light capturing region 12 from the rear end portion 6 of the molten pool 5, and a region between the broken arrows 2 and 2 indicates a light receiving range of the reflected light 11. The reflected light capturing area 12 is set in the rear end portion 6 of the molten pool 5 and in the irradiation area of the illumination laser light 7 surrounded by the solid line in the drawing, in an area where the illuminance distribution is more uniform.
[0012]
The processing device 13 is a device that performs a predetermined calculation based on the intensity of the electric signal from the light receiving device 10 (photodiode 10c), determines whether the welding quality is good or bad, and outputs the result. Here, the processing device 13 is configured to perform first-order differentiation processing, normalization processing, and threshold processing on the electrical signal from the photodiode 10c to determine whether the welding quality is good (normal) or not. ing. The electrical signal from the photodiode 10c may be configured to perform a frequency analysis such as a fast Fourier transform to determine whether the welding quality is good or not. According to the configuration for performing simple processing, simple processing and high-speed computation can be realized as compared with the configuration for performing frequency analysis.
[0013]
The image display device 14 is a device that displays the determination result of the processing device 13 in real time. For example, when a welding failure occurs during welding, the position is changed to another position (normal). The position is displayed separately from the position. Specifically, as time passes, if welding is normal, a straight line is drawn in the right direction, and when a welding failure occurs, a vibration waveform having an amplitude corresponding to the degree of the failure is drawn at that point. To display. According to this, it is possible to observe from the display screen the time when the welding failure occurs (welding failure location) and the degree of the failure. If it is possible to correlate between the degree of welding failure (amplitude magnitude) and the type of welding failure such as “squeezing” or “burning-out”, when the welding failure occurs, The type of defective welding such as “” may be displayed at the same time.
Note that the result of the primary differentiation processing and normalization processing by the processing device 13 (signal waveform after processing) may be displayed on the image display device 14. Moreover, the display image of the image display device 8 may be recorded and used for analysis and confirmation of the welding result after welding.
[0014]
FIG. 2 is an enlarged cross-sectional view of the light exit / incident part 9.
As shown in this figure, the illumination optical fiber 3b, the plurality of light receiving optical fibers 10a, and the condenser lens 10b are integrated in the light incident / incident part 9. In this case, the illumination optical fiber 3b and the condenser lens 10b are positioned coaxially (the optical axis 21 of the illumination optical fiber 3b and the optical axis 22 of the condenser lens 10b are common), and The plurality of light receiving optical fibers 10a are integrated so as to surround the periphery of the illumination optical fiber 3b.
[0015]
That is, the condensing lens 10b is disposed at the end of the light exit / incident portion 9 on the side facing the workpiece 2 and the illumination optical fiber 3b penetrates the central axis (optical axis) 21 portion. . A plurality of light receiving optical fibers 10a are arranged in a condensing range on the back side of the condensing lens 10b so as to surround the illumination optical fiber 3b as a center.
In this case, the plurality of light receiving optical fibers 10a are arranged in a plurality of layers, in this case, five layers so as to draw a concentric circle around the optical axis 22 of the illumination optical fiber 3b (the optical axis 21 of the condenser lens 10b). The cylindrical light receiving optical fiber 10a bundle forming each layer is positioned coaxially with the optical axis 22 of the illumination optical fiber 3b and reaches the photodiode 10c. Of course, one end face (light receiving end face) of the light receiving optical fiber 10a bundle forming each layer faces the back face of the condenser lens 10b, and the other end face faces the light receiving face of the photodiode 10c.
As can be seen from FIG. 1, such a light exit / incident part 9 is attached to the torch 1 here, such as the irradiation region of the illumination laser beam 7 on the rear end portion 6 of the molten pool 5 and the reflected light capturing region 12. It is comprised so that it may move to a welding direction (arrow B direction) with the torch 1 without changing a positional relationship.
[0016]
Next, the operation will be described with reference to FIG.
In FIG. 3, when welding is started, the processing device 13 takes in a signal (electric signal) from the light receiving device 10 (photodiode 10 c) in step 301. The signal taken into the processing device 13 is a signal corresponding to the intensity of the reflected light 11 from the rear end portion 6 of the molten pool 5 irradiated with light by the light irradiation device 3. Indicates the degree of surface wave.
In step 302, a first-order differentiation process is performed on the acquired signal to extract a change amount of the signal intensity.
FIG. 4 is a graph showing an example of the result of such primary differentiation processing, where the vertical axis indicates the signal change amount and the horizontal axis indicates time t.
The result of the primary differentiation process can be displayed by the image display device 14 as will be described later, and when the amount of change in the display image exceeds a certain value on the time axis, the position (time point) is defective. It can be specified as a location. The identified defect occurrence location can be effectively used in a subsequent process such as rework.
[0017]
In step 303, the signal from the photodiode 10c taken in in step 301 is normalized. This is to prevent the signal captured in step 301 from causing variations due to disturbances during inspection, for example, clouding or contamination of the condenser lens 10b of the light receiving device 10.
In the normalization process, test welding is performed in advance under various conditions so that normal welding results can be obtained in advance, and an average value of the intensity of the signal from the photodiode 10c obtained each time is obtained. In actual welding, the value of the signal from the photodiode 10c is divided by the average value. If the actual welding is normal welding, the result of normalization (division) is “1”, and the larger the degree of welding failure, the larger the value is from “1”.
FIG. 5 is a graph showing an example of the result of such normalization processing. In this figure, the vertical axis represents the signal intensity ratio, and the horizontal axis represents time t. U1, U2, L1, and L2 on the vertical axis each indicate a threshold value. In this case, the range between U1 and L1 indicates a range of normal welding, the range between U1 and U2 or between L1 and L2 indicates a range of welding failure that is “shrunk”, and the range between U2 and L2 or less indicates a range of welding failure that is “burned out”.
The result of this normalization process can be displayed by the image display device 14 as will be described later, and when the amount of change in the display image is greater than or equal to a certain value on the time axis t, the position (time point) is defective. The point that can be specified as the occurrence location is the same as in the case of the first-order differential processing result display. In addition, in this normalization processing result display, the type of welding failure such as “shrunk” or “burn-out” can be determined according to the degree of change on the time axis t. The identified defect occurrence location and the type of the determined welding defect can be effectively used in a subsequent process such as rework.
[0018]
In step 304, the value after the normalization process in step 303 is compared with the threshold value U1, U2, L1, and L2, and the result is output. Specifically, if the value after the normalization processing is between the threshold values U1 to L1, it is determined that the welding quality at that time is good (normal), and if it is any other value, the welding quality is high. It is determined to be defective, and the result is output.
In step 305, the image display device 14 displays the result of the threshold processing in step 304. In step 305, the primary differential processing result shown in FIG. 4 and the normalization processing result shown in FIG. When the display of the normalization processing result is selected, the type, for example, “shrunk” or “burned out” is additionally displayed in the case of poor welding. Specifically, if the value after the normalization processing is between the threshold values U1 and U2 or between L1 and L2, it means that “shrinkage” has occurred at that point in time. If it is less than that, the fact that “burn-out” has occurred at that time is displayed in addition to the fact that the welding quality is poor. In the example of FIG. 5, from the start of processing, a determination result such as approximately normal welding → “shrinking” → normal welding → “shrinking” → “burning out” → “shrinking” is additionally displayed.
The processing device 13 also executes the processing in steps 302 to 304.
The above operations (steps 301 to 305) are repeated until the end of welding.
1 and 2, the same reference numerals indicate the same or corresponding parts.
[0019]
【The invention's effect】
As described above, in the present invention, in laser welding, at the time of welding, the rear end portion of the molten pool formed around the keyhole of the workpiece is irradiated with illumination light, and from the rear end portion of the molten pool. Weld quality inspection based on the intensity of reflected light.
It is the present invention that when the rear end portion of the molten pool is irradiated with illumination light, the intensity of the light reflected from the rear end portion of the molten pool expresses good or bad welding quality with high accuracy. Therefore, according to the present invention, it is possible to inspect the welding quality more accurately than the prior art. In particular, it is possible to inspect laser welding quality with high accuracy in high-speed welding of thin plate materials.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of an embodiment of an apparatus to which a laser welding quality inspection method according to the present invention is applied.
FIG. 2 is an enlarged cross-sectional view of a light exit / incident part in FIG.
FIG. 3 is a flowchart showing a welding quality inspection operation.
FIG. 4 is a graph showing an example of a result of first-order differentiation processing by the processing device in FIG.
FIG. 5 is a graph showing an example of normalization processing results.
[Explanation of symbols]
1a Laser beam 2 Work piece 2a, 2b Thin steel plate (welded member)
3 Light irradiation device (light irradiation means)
4 Keyhole 5 Molten Pool 6 Back End 7 of the Molten Pool 7 Laser Light 10 for Illumination Light Receiving Device (Light Receiving Means)
11 reflected light 13 processing device (processing means)

Claims (2)

Its welded object and / or the laser beam is moved to a desired welding direction while irradiating a laser beam to the welded object in which a plurality of weld members are overlapped, superimposed laser performing overlay welding of the welded object In welding,
During welding, the rear end portion of the weld pool formed around the keyhole of the workpiece is irradiated with illumination light, and the quality inspection of the weld is performed based on the intensity of reflected light from the rear end portion of the weld pool. A way to
As the means for irradiating the illumination light, a light irradiation means including an illumination optical fiber that guides the illumination laser light and emits it toward the rear end portion of the molten pool is used.
As a means for obtaining the intensity of the reflected light, a light receiving means including a plurality of light receiving optical fibers and a condensing lens for condensing and entering the reflected light to the plurality of light receiving optical fibers is used. ,
The illumination optical fiber is integrated with the condenser lens at the light incident / incident part in a state surrounded by the plurality of light receiving optical fibers, and is coaxially positioned with the condenser lens, A laser welding quality inspection method characterized by penetrating a condenser lens . Its welded object and / or the laser beam is moved to a desired welding direction while irradiating a laser beam to the welded object in which a plurality of weld members are overlapped, superimposed laser performing overlay welding of the welded object In welding,
A light irradiating means for irradiating light for illumination to a rear end portion of a molten pool formed around the keyhole of the workpiece during welding;
A light receiving means for receiving reflected light from a rear end portion of the molten pool irradiated with light by the light irradiating means, and outputting an electric signal according to the intensity of the reflected light;
A predetermined calculation is performed based on the intensity of the electrical signal from the light receiving means, and the processing means for determining whether the quality of the welding is good or bad and outputting the result ,
The light irradiation means is configured to include an illumination optical fiber that guides the illumination laser light and emits it toward the rear end portion of the molten pool,
The light receiving means includes a plurality of light receiving optical fibers, and a condensing lens that collects the reflected light and enters the light receiving optical fibers.
The illumination optical fiber is integrated with the condenser lens at the light incident / incident part in a state surrounded by the plurality of light receiving optical fibers, and is coaxially positioned with the condenser lens, A laser welding quality inspection apparatus characterized by passing through a condenser lens .

Images