JP3184962B2 - Laser welding detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In laser welding, welding is performed by irradiating a target workpiece with pulsed laser light output from a laser oscillator. Inspection of welding conditions, particularly welding defects in laser welding, is often carried out off-line visually or by using inspection equipment. In this case, mass production lines such as automobile manufacturing require inspection of a large number of places, and the burden on inspectors is large. 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.

[0003] In general, as an on-line measurement technique of a welding state in laser welding, a technique utilizing plasma generated at a welded portion during welding, a technique utilizing sound generated during welding (welding sound), or a YAG laser is used. Some use scattered light (hereinafter referred to as reflected light) generated from a welded portion during laser welding. Specifically, an apparatus that measures a plasma light intensity, a plasma potential, a welding sound level, or a reflected light intensity and detects a welding defect based on the measured value has been proposed, disclosed, or implemented. A technique of measuring the intensity of reflected light and detecting a welding defect based on the measured value is proposed in Japanese Patent Application No. 9-213223.

Although there are few actual examples in which the above-described online measurement technology is applied to automatically detect a welding defect, for example, “Welding Society Transactions (1996), Vol. 14, No. 4
No., pages 689 to 693 ", a method for automatically detecting a defect from a change in the intensity of plasma light is disclosed.

[0005]

By the way, the reflected light is
The laser light (irradiation light) applied to the work is not entirely absorbed by the work, and the laser light not absorbed is reflected in various directions. Therefore, even the reflected light has the property of the directivity seen in the entire laser light. For this reason, in the technique of measuring the reflected light, it is practically impossible to receive all of the reflected light by the light receiving sensor, and a fixed amount of reflected light cannot always be received. That is, the reflected light required for the 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.

In the technique of measuring plasma light, the relationship between the characteristics of the obtained plasma light and the welding state at that time has not yet been uniquely determined, so that it is difficult to identify and analyze each characteristic in detail. In fact.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for detecting a welding state of laser welding, which can detect a defect at a welding portion with high accuracy and detail.

[0008]

According to the present invention, there is provided a laser welding method for detecting a welding state in a work, which is applied to a laser welding method for irradiating a work with laser light to perform welding. The intensity of both the plasma light and the reflected light emitted from the workpiece at the time of welding is used as welding state information, and the intensity of the plasma light is compared with a preset intensity range of the plasma light at the time of good welding. Is compared with the preset intensity range of the reflected light when welding is good, and the comparison result and the table in which the comparison result and the welding state are associated in advance show whether welding is good / bad and at least bad. A method for detecting the welding state of laser welding, characterized by detecting the type of failure as a welding state.

[0009]

[0010]

Further, according to the present invention, there is provided the welding state detecting method for laser welding, wherein the welding state is detected based on the source intensity of the laser light in addition to the intensity of both the plasma light and the reflected light. .

[0012]

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for detecting a welding state of laser welding according to an embodiment of the present invention will be described 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,
An optical fiber 302 that propagates the generated laser light, and a laser torch 303 to which a scanning mechanism (not shown) is connected and to which the propagated laser light is input, are provided. The laser light emitted from the laser torch 303 is irradiated as irradiation light Lw on the work 500 placed on a scanning table (not shown), and laser welding is performed. During welding, reflected light Lr and plasma light Lp
Occurs.

The laser torch 303 includes a torch main body 303.
a and a torch upper portion 303c. Inside the torch body 303a, while reflecting the laser light propagated through the optical fiber 302, the YAG laser reflecting mirror 303b transmitting the reflected light Lr and the plasma light Lp, and the laser light reflected by the YAG laser reflecting mirror 303b. A not-shown condensing lens that condenses as irradiation light Lw, a not-shown condensing lens that condenses reflected light Lr and plasma light Lp transmitted through YAG laser reflecting mirror 303b, and reflected light transmitted through YAG laser reflecting mirror 303b Among the Lr and the plasma light Lp, a plasma is selected from among a YAG light reflecting mirror 303d that transmits the plasma light Lp substantially while reflecting the reflected light Lr and a light that includes the plasma light Lp transmitted through the YAG light reflecting mirror 303d. A filter (not shown) for extracting only 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

Further, the laser welding system has a laser welding state detecting device 100 for detecting a welding state of the work 500. Laser welding state detection device 10
A plasma light sensor 102 attached to the torch upper part 303c, receives the plasma light Lp filtered by the filter after passing through the YAG light reflecting mirror 303d, and outputs an electric signal Sp according to the light intensity; The YAG light reflecting mirror 30 is attached to the upper part 303c.
Reflected light Lr filtered by a filter after reflecting 3d
And a reflected light sensor 103 that outputs an electric signal Sr corresponding to the light intensity thereof, and the plasma light Lp using the electric signal Sp and the electric signal Sr from the plasma light sensor 102 and the reflected light sensor 103. A welding state determination processing unit 101 that detects a welding state based on both light intensities as state information of both the reflected light Lr, a display unit 104 for displaying the detected welding state on a display or the like, and a detected welding state And a storage unit 105 for storing.

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

FIG. 2A shows a welding state determination processing unit 101.
, An example of the light intensity of the plasma light Lp detected by the plasma light sensor 102 is shown in chronological order. 2B shows the 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 performs the operations shown in FIGS.
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 a preset light intensity of plasma light Lp,
It is stored in the memory of the welding state determination processing unit 101.

[0020] CPU is basically when the light intensity of the plasma light Lp exceeds the high threshold PTh _H is other than welding defect defect, weld defects in the case of less than the lower threshold PTh _L poor and determines that the welding be within the scope of the following lower threshold PTh _L or more upper threshold PTh _H is good. However, in the present invention, the CPU makes a final determination in consideration of the following determination of the reflected light intensity.

Referring to FIG. 2B, RTh _H and R
Th _L is a threshold value of good / bad of the welding state 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.

The CPU is basically when the light intensity of the reflected light Lr has exceeded the high threshold RTh _H welding defect defect, in the case of less than the lower threshold RTh _L is other than welding defect failure and determines that the welding be within the range of less than the lower limit threshold value RTh _L or more upper threshold RTh _H is good. However, in the present invention, the CPU makes a final determination in consideration of the above-described determination of the plasma light intensity.

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, a signal from which high-frequency components are removed as shown in FIGS. 3A and 3B is processed. Processing a signal from which high frequency components have been removed is often superior in detection accuracy.

FIG. 3A shows a signal obtained by further 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 component has been removed is shown in chronological order. FIG. 3B shows, in a time-series manner, an example of a signal obtained by further filtering the digitized electric signal Sr with a low-pass filter, that is, the light intensity of the reflected light Lr.

Referring to FIG. 3 (a), FPTh _H and FP
Th _L is a threshold value of good / bad welding condition for a preset light intensity of plasma light Lp,
It is stored in the memory of the welding state determination processing unit 101.
CPU is basically when the light intensity of the plasma light Lp exceeds the high threshold FPTh _H is other than welding defect defect, in the case of less than the lower threshold FPTh _L welding defects failure, also, Lower threshold FPT _L or higher Upper threshold FPT
It is determined that the welding is good if it is within the range of _hH or less. However, in the present invention, the CPU makes a final determination in consideration of the following determination of the reflected light intensity.

Referring to FIG. 3B, FRTh _H and FR
Th _L is a threshold value of good / bad of the welding state 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 basically means that the light intensity of the reflected light Lr is the upper threshold value
Weld defects failure when exceeded FRTh _H, in the case of less than the lower threshold FRTh _L is other than welding defects failure, also,
It determines that the weld if the lower threshold FRTh _L or more upper threshold FRTh _H following range is good. However, in the present invention, the CPU makes a final determination in consideration of the above-described determination of the plasma light intensity.

As described above, the intensity of the plasma light Lp is determined by referring to the respective threshold values stored in advance in the memory of the welding state determination processing unit 101 when the welding is good.
While 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 when welding is good,
In accordance with the comparison results, the good / bad state of the welding and the type and cause of the failure at the time of the failure are detected as the welding state. Specifically, a table in which the comparison result is associated with the welding state is stored in the memory of the welding state determination processing unit 101 in advance. FIG. 4 shows an example of this table.

Referring to FIG. 4, this table makes it possible to compositely determine the result of comparison between the intensity of plasma light Lp and the threshold of the intensity of reflected light Lr. For example, when the plasma light Lp reaches the lower threshold PTh _L (or F
RTh _L ) and the reflected light Lr is higher than the upper threshold R
If Th _H (or FRTh _H ) is exceeded, it is determined that the defect is a welding defect.

Further, in this table, it is possible to determine not only the presence or absence of a welding defect but also a defect other than a defect, and further, in the case of a defect, its type. For example, the 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 RTh _H ) is exceeded, it is estimated that the defect type is “poor penetration”.

Further, according to this table, for example, in the case of the above comparison result, not only the defect type “poor penetration” is estimated, but the defect factor is “work 50
It can also be estimated that the irradiation light Lw is defocused for the welding position of 0, "contamination of the cover glass", "deterioration of the laser optical system", or a combination of any one of these.

In the table example shown in FIG. 4, for simplicity of explanation, the judgment of each cell marked with *, the defect type, the defect factor, etc. are omitted. Is
For each cell, a judgment, a defect type, a defect factor, and the like are set.

Determination and estimation results by welding state determination processing section 101 (good / bad welding, defect type, defect factor)
Is displayed by the display unit 104, and the storage unit 10
5 is stored. As a display method, not only display but also printout may be performed. Further, the information may be stored not only in the storage unit 105 but also in a database storage unit directly connected to the main controller of the laser welding system. Further, the information may be transmitted to a main controller of the laser welding system via a network, and the control of the laser welding system may be performed as feedback control.

In the present invention, as described above, the results of comparison between the threshold values of the plasma light intensity and the reflected light intensity are determined in a complex manner, so that the good / bad (including defects) in the welding state can be increased. The fact that the defect type and the defect factor can be estimated in addition to the accurate determination is based on the difference between the characteristics of the plasma light and the reflected light. That is, the plasma light is used to comprehensively evaluate the light component generated by the melting phenomenon at the time of laser welding. As a result, it is possible to capture various changes in the phenomenon. On the other hand, the reflected light has a strong correlation with the penetration phenomenon from the viewpoint of the state of laser welding because the reflected light intensity depends on the degree of absorption to the work, because the reflected light is the original irradiation light that has absorptivity to the work. It is in. Therefore, it is used for controlling the penetration depth.

As a modification of the embodiment described above,
In addition to the intensity of both the plasma light and the reflected light, the irradiation light Lw
May be used as a parameter for determination. Specifically, a power monitor signal is obtained from the YAG laser oscillator 301.

Further, in addition to the batch-like intensity of both the plasma light and the reflected light, a defect factor or the like caused by a parameter over time may be estimated based on the trend intensity of the two lights. Specifically, as a detection signal on the graph, the horizontal axis is set for each work (product number), and the vertical axis is set to an average value of signal levels for each product.

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

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

[0038]

The welding state detecting method for laser welding according to the present invention is applied to a laser welding method for performing welding by irradiating a laser beam to a work. Since the welding state is detected based on the state information of both the plasma light and the reflected light emitted from the workpiece at the time of laser welding, it is possible to detect a defect at a welding location with high accuracy and in detail. Further, the welding state can be determined from various angles by using the plasma light and the reflected light of the irradiation laser light. Furthermore, labor saving and labor saving of the inspector can be realized, and the inspection time can be shortened by the online measurement, which greatly contributes to the automation (unmanned) of the production line by the automatic defect detection.

[Brief description of the drawings]

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

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

3A and 3B are diagrams for explaining a welding state detection method of laser welding according to an embodiment of the present invention, wherein FIG. 3A shows the light intensity of plasma light from which high-frequency waves have been removed in time series;
(B) shows in chronological order the light intensity of the reflected light from which the high frequency has been removed.

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

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 laser welding state detection device 101 welding state determination processing unit 102 plasma light sensor 103 reflected light sensor 104 display unit 105 storage unit 301 YAG laser oscillator 302 optical fiber 303 laser torch 303a torch main body 303b YAG laser reflection mirror 303c torch upper part 303d YAG Light reflection mirror 500 work

Claims (2)

(57) [Claims] The present invention is applied to a laser welding method of irradiating a laser beam to a work to perform welding, and in a laser welding welding state detecting method of detecting a welding state of the work, a plasma light emitted from the work at the time of laser welding;
The intensity of the reflected light and the intensity of the plasma light are used as welding state information, and the intensity of the plasma light is set to a preset value when welding is good.
The intensity of the reflected light is compared with the intensity range of the plasma light.
Is compared with the preset range of reflected light intensity when welding is good.
The comparison result, the comparison result, and the welding state are associated in advance.
Good and bad welding and minimal
A method for detecting a welding state of laser welding, wherein the type of the defect at the time of the defect is also detected as a welding state. 2. The method according to claim 1, wherein said plasma light and said reflected light are both
Welding condition based on laser light source intensity in addition to intensity
The welding state detection of the laser welding according to claim 1, wherein the state is detected.
How to get out.