JP2000061672A - Laser welding state detecting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser welding state detecting method capable of highly precisely and minutely detecting defects of a weld zone. SOLUTION: This method is applied to the welding method for welding a work 500 by being irradiated with an irradiating light Lw and is used for detecting the weld state of the work 500. The welding state is detected based on the state information of both of plasma light Lp emitted from and reflection light Lr on the work 500 at the time of laser welding.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to a laser welding method for irradiating a workpiece with laser light to perform welding, and relates to a welding state detecting method of laser welding for detecting a welding state such as presence or absence of a defect in a workpiece.

[0002]

2. Description of the Related Art In laser welding, a target work is irradiated with pulsed laser light output from a laser oscillator to perform welding. Inspecting a welding state, particularly a welding defect, in laser welding is often performed by visual inspection or by using an inspection device while the inspection is offline. In this case, in a mass production line such as automobile manufacturing, it is necessary to inspect a large number of places, which imposes a heavy burden on the inspector. Further, the inspection time needs to be short from the viewpoint of the productivity of the production line, and it is most desirable to perform the defect inspection in parallel with the welding.

Generally, as an on-line measuring technique of a welding state in laser welding, a technique utilizing plasma generated at a welding portion during welding, a technique utilizing sound generated during welding (welding sound), or a YAG laser is used. There is also one that utilizes scattered light (hereinafter referred to as reflected light) generated from the welded portion during laser welding. Specifically, there has been proposed, disclosed, or implemented a device which measures plasma light intensity, plasma potential, welding sound level, or reflected light intensity and detects a welding defect based on the measured value. A technique for measuring the intensity of reflected light and detecting a welding defect based on the measured value is proposed as Japanese Patent Application No. 9-213223.

Although there are few actual examples in which the above-described online measurement technique is applied to automatically detect welding defects, for example, "Welding Society Papers (1996), Vol. 500, No. 4, 689." ~ Page 693 "discloses a method for automatically detecting defects from changes in the intensity of plasma light.

[0005]

By the way, the reflected light is
The laser light applied to the work (irradiation light) is not entirely absorbed by the work, and is based on the effect that the unabsorbed laser light reflects in various directions. Therefore, even reflected light has the property of directivity that is generally found in laser light. Therefore, in the technique of measuring reflected light, it is practically impossible to receive all of the reflected light by the light receiving sensor, and it is not always possible to receive a fixed amount of reflected light. That is, the reflected light necessary for measurement may not be reliably obtained. Therefore, the technique of measuring the reflected light cannot be said to be a technique with sufficient measurement stability.

Further, in the technique for measuring plasma light, the relationship between the characteristics of the obtained plasma light and the welding state at that time has not yet been unambiguously defined, so that it is difficult to identify and analyze each characteristic. It is in reality.

An object of the present invention is to provide a welding state detecting method of laser welding capable of detecting defects in a welding portion with high accuracy and detail.

[0008]

According to the present invention, the method is applied to a laser welding method for irradiating a workpiece with a laser beam to perform welding, and in a welding state detecting method of laser welding for detecting a welding state in a workpiece, a laser is used. A welding state detecting method for laser welding is provided, which is characterized in that the welding state is detected based on the state information of both plasma light and reflected light emitted from a work during welding.

According to the present invention, there is also provided a welding state detecting method for laser welding, which uses the intensities of both the plasma light and the reflected light as the state information of both lights.

Further, according to the present invention, the intensity of the plasma light is compared with a preset intensity range of the plasma light at the time of good welding, and the intensity of the reflected light is set at the preset reflection light at the time of good welding. According to both comparison results, the welding state detection method for laser welding is obtained in which the good / bad state of welding and the type of fault at the time of failure and the cause of the fault are detected as the welding state.

According to the present invention, there is also provided a welding state detecting method for laser welding in which a table in which the comparison result and the welding state are associated with each other is prepared in advance.

According to the present invention, there is further provided a welding state detection method for laser welding, which detects the welding state based on the source intensity of laser light in addition to the intensities of both the plasma light and the reflected light.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION A welding state detecting method for laser welding according to an embodiment of the present invention will be described below with reference to the drawings.

Referring to FIG. 1, a laser welding system for realizing a welding state detecting method according to the present invention includes a YAG laser oscillator 301 for generating pulsed laser light,
It has an optical fiber 302 for propagating the generated laser light, and a laser torch 303 to which a scanning mechanism (not shown) is connected and into which the propagated laser light is input. The laser light emitted from the laser torch 303 is irradiated as the irradiation light Lw onto the work 500 placed on a scanning table (not shown), and laser welding is performed. At the time of welding, the reflected light Lr and the plasma light Lp are emitted from the welded portion of the workpiece 500.
Occurs.

The laser torch 303 is a torch body 303.
It has a housing composed of a and the torch upper part 303c. Inside the torch body 303a, the YAG laser reflecting mirror 303b that reflects the laser light propagated through the optical fiber 302, while transmitting the reflected light Lr and the plasma light Lp, and the laser light reflected by the YAG laser reflecting mirror 303b. A condenser lens (not shown) that condenses as irradiation light Lw, a condenser lens (not illustrated) that condenses the reflected light Lr and the plasma light Lp that have passed through the YAG laser reflection mirror 303b, and a reflected light that has passed through the YAG laser reflection mirror 303b. Of the Lr and the plasma light Lp, the plasma light Lp is transmitted, while the YAG light reflection mirror 303d that reflects the reflected light Lr and the light including the plasma light Lp that is transmitted through the YAG light reflection mirror 303d are plasma. A filter (not shown) for extracting only the light Lp, and a YAG light reflecting mirror Reflected light Lr reflected by the 03d
And a filter (not shown) that extracts only the reflected light Lr from the light including the light.

Further, the present laser welding system has a laser welding state detecting device 100 for detecting the welding state of the work 500. Laser welding state detection device 10
Reference numeral 0 denotes a plasma light sensor 102 which is attached to the torch upper portion 303c, receives the plasma light Lp filtered by the filter after passing through the YAG light reflection mirror 303d, and outputs an electric signal Sp according to the light intensity, and the torch. Attached to the upper part 303c, the YAG light reflection mirror 30
Reflected light Lr filtered by a filter after reflecting 3d
The sensor 103 for reflected light that receives the light and outputs the electric signal Sr corresponding to the light intensity, and the electric signal Sp and electric signal Sr from the sensor 102 for plasma light and the sensor 103 for reflected light are used to generate the plasma light Lp and Welding state determination processing unit 101 that detects the welding state based on the two light intensities as the state information of both reflected light Lr, the display unit 104 that displays the detected welding state on a display, and the detected welding state. And a storage unit 105 for storing

The welding state determination processing unit 101 includes an A / D converter for converting the analog electric signal Sp and the electric signal Sr into a digital signal, and a CP for processing the digital signal.
U and a memory in which, for example, data used in processing are stored in advance.

FIG. 2A shows a welding state determination processing unit 101.
An electrical signal Sp input to the, that is, an example of the light intensity of the plasma light Lp detected by the plasma light sensor 102 is shown in time series. Further, FIG. 2B shows an electric signal Sr input to the welding state determination processing unit 101, that is, the reflected light L detected by the reflected light sensor 103.
An example of the light intensity of r is shown in time series. The CPU of the welding state determination processing unit 101 is shown in FIG.
An electric signal as shown in (b) is actually obtained in the form of a digital signal through an A / D converter.

Referring to FIG. 2 (a), PTh _H and P
Th _L is a threshold value of good / bad welding condition for the preset light intensity of the plasma light Lp,
It is stored in the memory of the welding state determination processing unit 101.

Basically, the CPU has a defect other than welding defects when the light intensity of the plasma light Lp exceeds the upper threshold value PTh _H , and a welding defect defect when the light intensity is less than the lower threshold value PTh _L. Further, if it is in the range of the lower limit threshold value PTh _L or more and the upper limit threshold value PTh _H or less, it is determined that the welding is good. However, in the present invention, the CPU makes a final determination in consideration of the following determination of the reflected light intensity as well.

Referring to FIG. 2 (b), RTh _H and R
Th _L is a threshold value of the welding state good / defective with respect to the preset light intensity of the reflected light Lr, and is stored in the memory of the welding state determination processing unit 101.

Basically, the CPU has a welding defect defect when the light intensity of the reflected light Lr exceeds the upper threshold value RTh _H and a defect other than the welding defect when it is less than the lower threshold value RTh _L. Also, if the lower limit threshold value RTh _L or more and the upper limit threshold value RTh _H or less is satisfied, it is determined that the welding is good. However, in the present invention, the CPU makes a final determination in consideration of the determination of the plasma light intensity described above.

In the present invention, a low pass filter may be provided between the A / D converter and the CPU in the welding state determination processing section. In this case, the signal from which the high frequency component is removed as shown in FIGS. 3A and 3B is processed. It is often more excellent in detection accuracy to process a signal from which high frequency components have been removed.

FIG. 3A shows a signal obtained by filtering the digitized electric signal Sp with a low-pass filter, that is,
An example of the light intensity of the plasma light Lp from which the high frequency components have been removed is shown in time series. Further, FIG. 3B shows a signal obtained by filtering the digitized electric signal Sr with a low-pass filter, that is, an example of the light intensity of the reflected light Lr in time series.

Referring to FIG. 3A, FPTh _H and FP
Th _L is a threshold value of good / bad welding condition for the preset light intensity of the plasma light Lp,
It is stored in the memory of the welding state determination processing unit 101.
The CPU basically has a defect other than welding defects when the light intensity of the plasma light Lp exceeds the upper threshold value FPTh _H , and a welding defect defect when the light intensity is less than the lower threshold value FPTh _L. Lower threshold value FPTh _L or more Upper threshold value FPT
If it is within the range of h _H or less, it is determined that the welding is good. However, in the present invention, the CPU makes a final determination in consideration of the following determination of the reflected light intensity as well.

Referring to FIG. 3 (b), FRTh _H and FR
Th _L is a threshold value of the welding state good / defective with respect to the preset light intensity of the reflected light Lr, and is stored in the memory of the welding state determination processing unit 101. CP
U is basically the upper limit of the light intensity of the reflected light Lr.
If it exceeds FRTh _H , the welding defect is defective. If it is less than the lower limit threshold value FRTh _L , it is a defect other than welding defect.
Welding is judged to be good if it is within the range from the lower limit threshold value FRTh _{L to the} upper limit threshold value FRTh _H. However, in the present invention, the CPU makes a final determination in consideration of the determination of the plasma light intensity described above.

As described above, the intensity of the plasma light Lp is referred to by referring to the threshold values stored in advance in the memory of the welding state determination processing unit 101, and the plasma light L when the welding is good is performed.
In addition to comparing with the intensity range of p, the intensity of the reflected light Lr is compared with a preset intensity range of the reflected light Lr at the time of good welding,
Based on the results of both comparisons, the type of failure and the cause of the failure are detected as the welding state. Specifically, a table in which the comparison result and the welding state are associated with each other is stored in advance in the memory of the welding state determination processing unit 101. An example of this table is shown in FIG.

Referring to FIG. 4, this table makes it possible to make a composite determination of the results of comparison between the intensity of the plasma light Lp and the respective thresholds of the intensity of the reflected light Lr. For example, the plasma light Lp is the lower threshold PTh _L (or F
RTh _L ) and the reflected light Lr is the upper threshold R
If it exceeds Th _H (or FRTh _H ), it is determined to be a welding defect.

Further, in this table, not only the presence / absence of a welding defect, but also a defect other than a defect can be determined, and in the case of a defect, its type can be estimated. For example, plasma light L
p is less than the lower threshold PTh _L (or FRTh _L ) and the reflected light Lr is the upper threshold RTh _H (or F
If it exceeds RTh _H ), it is presumed that the defect type is “poor melting”.

Further, according to this table, for example, in the case of the above comparison result, not only is the defect type "melting poor" estimated, but the defect factor is "work 50".
It can be estimated that the irradiation light Lw is defocused on the welded place of 0 "," dirt on the cover glass "," deterioration of the laser optical system ", or a combination of any two or more thereof.

In the table example shown in FIG. 4, the judgment of each cell marked with *, the defect type, the defect factor, etc. are omitted in order to avoid the complexity of the description, but in the case of implementation. Is
The judgment, defect type, defect factor, etc. are set for each cell.

Judgment and estimation results by the welding state judgment processing unit 101 (good / bad welding, defect type, defect factor)
Is displayed by the display unit 104, and the storage unit 10
Stored by 5. As a display method, not only display but also printout may be performed. In addition to being stored in the storage unit 105, it may be stored in a database storage unit directly connected to the main controller of the laser welding system. Further, it may be sent to the main controller of the laser welding system via a network, and the control of the laser welding system may be feedback control.

In the present invention, as described above, the result of comparison of the threshold values of the plasma light intensity and the reflected light intensity is compositely determined, whereby the welded state is high / bad (including defects). In addition to the accurate determination, the defect type, the defect factor, and the like can be estimated based on the difference in the characteristics of the plasma light and the reflected light. That is, the plasma light is used to comprehensively evaluate the components of the light generated by the melting phenomenon at the time of laser welding, and as a result, various phenomenon changes can be captured. On the other hand, since the reflected light is originally the irradiation light that has absorptivity to the work, the reflected light intensity depends on the degree of absorption to the work, so from the viewpoint of the state of laser welding, there is a strong correlation with the penetration phenomenon. It is in. Therefore, it is used for managing the penetration depth.

As a modification of the embodiment described above,
Irradiation light Lw in addition to the intensities of both plasma light and reflected light
The light intensity of may also be used as a determination parameter. Specifically, the power monitor signal is acquired from the YAG laser oscillator 301.

Further, in addition to the batchwise intensities of both the plasma light and the reflected light, the defect factors and the like caused by the temporal parameters may be estimated based on the trend intensities of both lights. Specifically, as the detection signal on the graph, its horizontal axis is for each work (product number), and the vertical axis is the average value of the signal level for each product.

In the above description, the YAG laser oscillator is used as the laser oscillator, but the present invention is not limited to this, and other CO2 laser oscillator or excimer laser oscillator may be used. In this case, the configuration of the optical system and the photoelectric conversion element are selected so that the reflected light of the irradiation laser light can be detected.

The configuration of the welding state determination processing unit 101 is generally a signal processing device and can be easily realized by using a personal computer.

[0038]

The welding state detecting method of laser welding according to the present invention is applied to a laser welding method of irradiating a workpiece with laser light to perform welding, and a welding state detecting method of laser welding for detecting a welding state of a workpiece. Since the welding state is detected based on the state information of both the plasma light and the reflected light emitted from the work during laser welding, it is possible to detect defects at the welding location with high accuracy and detail. In addition, the welding state can be determined in multiple directions by using the plasma light and the reflected light of the irradiation laser light. In addition, labor and labor can be saved for inspectors, and inspection time can be shortened by online measurement, which greatly contributes to automation of production lines (automation) through automation of defect detection.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a laser welding system for realizing a welding state detection method for laser welding according to an embodiment of the present invention.

2A and 2B are views for explaining a welding state detecting method of laser welding according to an embodiment of the present invention, in which FIG. 2A shows the light intensity of plasma light in time series, and FIG. The light intensity is shown in time series.

FIG. 3 is a diagram for explaining a welding state detection method of laser welding according to the embodiment of the present invention, in which (a) shows the light intensity of plasma light from which high frequency is removed in a time series manner;
(B) shows the light intensity of the reflected light from which the high frequency is removed in time series.

FIG. 4 is a diagram for explaining a welding state detecting method of laser welding according to the embodiment of the present invention, showing the state information of both plasma light and reflected light and the welding state (good / defective). , Defect type, defect factor).

[Explanation of symbols]

100 Laser welding condition detector 101 welding state determination processing unit 102 Plasma light sensor 103 Reflected light sensor 104 display 105 storage 301 YAG laser oscillator 302 optical fiber 303 laser torch 303a Torch body 303b YAG laser reflection mirror 303c Torch top 303d YAG light reflection mirror 500 work

Claims (5)

[Claims] 1. A welding state detection method for laser welding, which is applied to a laser welding method for irradiating a workpiece with laser light to perform welding, and detects a welding state in a workpiece. A welding state detection method for laser welding, characterized in that the welding state is detected based on state information of both reflected light. 2. The welding state detection method for laser welding according to claim 1, wherein the intensities of both the plasma light and the reflected light are used as the state information of both lights. 3. The intensity of the plasma light is compared with a preset intensity range of the plasma light when the welding is good, and the intensity of the reflected light is compared with a preset intensity range of the reflection light when the welding is good. Good welding /
The welding state detecting method of laser welding according to claim 2, wherein a defect, a type of the defect at the time of the defect, and a cause of the defect are detected as a welding state. 4. The welding state detecting method for laser welding according to claim 3, wherein a table in which the comparison result and the welding state are associated with each other is prepared in advance. 5. The welding state detecting method for laser welding according to claim 2, wherein the welding state is detected based on the source intensity of the laser light in addition to the intensities of both the plasma light and the reflected light.