JP2001138079A - Method and device for monitoring weld zone in laser beam welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide such a method and device for monitoring a weld zone in laser beam welding that are capable of sensing positional deviation from the abutting face of materials to be welded, by means of plasma light produced by laser beam welding. SOLUTION: A laser beam 2 irradiates the abutting part of a pair of materials 1 and 1 to be welded, and at the same time, the optical characteristics of the weld zone are detected by a sensor 3. If the luminous intensity detected by the sensor 3 is higher than the first reference value of a predetermined luminous intensity, it is judged the laser beam 2 is deviated from the abutting faces 4 and 4, and the aiming position of the welding with the laser beam 2 is controlled. On the other hand, if the luminous intensity detected is lower than the second reference value of a predetermined luminous intensity, it is judged there is a possibility of generating a weld defect in the weld zone.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for monitoring a welding portion of laser beam welding for grasping a welding state at the time of laser beam welding, and a welding portion monitoring device for performing the method.

[0002]

2. Description of the Related Art Recent advances in laser technology have made laser beam welding practical in various fields. With the practical application, development of a more accurate laser beam welding quality evaluation system is required. For example, as a quality evaluation system required when performing butt penetration welding using a laser beam, there is an evaluation system for a target displacement of a laser beam. In general, the energy of a laser beam is concentrated on a very small point, and therefore, in order to perform high-quality welding, it is necessary to accurately irradiate the butted surface of the material to be welded with the laser beam. If the laser beam deviates from the abutting surface at the target position, it causes defects such as poor penetration and has a great adverse effect on the joint strength. For this reason, conventionally, various methods have been used to grasp the target position deviation of the material to be welded from the abutting surface and to obtain a joint member having good welding quality.

[0003] As a method of grasping the target position deviation from the abutting surface of the material 1 to be welded, for example, Japanese Patent Laid-Open No. 6-26 is disclosed.
There is a method as shown in Japanese Patent No. 9966. According to this, in the method of detecting plasma light generated at the time of locally heating the butted portion of the material to be welded by the laser beam with the sensor, of the respective elements included in the plasma light, compared with the other material to be welded The intensity of the wavelength of the element contained in a relatively large amount is detected, and it is grasped from the intensity whether or not the laser beam is deviated from the target position with respect to the butting surface. Japanese Patent Application Laid-Open No. 61-202790 discloses a method of detecting plasma light near a processing point generated during laser beam welding with a sensor. The method uses a specific wavelength from a gap generated between butted surfaces of both materials to be welded. Is determined based on the fact that the light emission intensity of the laser beam is reduced as compared with the light emission intensity from the flat portion, and whether or not the laser beam is displaced from the target position with respect to the abutting surface.

[0004]

However, the former method has the following problems.
Applicable only when butt penetration welding of two materials having different element contents using a laser beam is used. Butt penetration welding between materials to be welded of the same material and containing the same amount of elements However, there is a problem that it is impossible to use the above method. In addition, according to the latter method, since the target position deviation is grasped from the change in the emission intensity from the gap between the butting surfaces, the target position deviation cannot be grasped if there is no gap between the butting surfaces. There is. Furthermore, pre-processing such as chamfering is required,
If there is a gap large enough to allow the target position to be grasped by the above method, there is a danger that the welding quality itself will be deteriorated, such as the occurrence of underfill due to the passage of the laser beam or insufficient molten metal.

[0005] On the other hand, the cause of the deterioration of the welding quality is caused by a mill scale or a thermally cut oxide film formed on the butted surface of the materials to be welded, in addition to the displacement of the target position of the laser beam. Such an oxide film tends to cause a defect such as a blowhole in a welded portion and causes a decrease in welding quality. Therefore, welding is usually performed after removing the oxide film. However, this method has a problem that a great deal of labor has to be spent on preparations such as the above-mentioned work for removing the oxide film. Therefore, in recent years, a method has been proposed which enables welding to be performed when the oxide film exists. For example, in JP-A-8-300002,
Al, Ti, which are deoxidizing materials,
Laser beam welding of both materials to be welded while supplying an iron alloy wire filler containing any one or two or more types of Si prevents blow holes from being generated in the welded portions. By the way, according to the above method, the processing is performed on the assumption that the oxide film that deteriorates the welding quality is uniformly formed on the butted surface. However, an oxide film of various thicknesses is formed on the actual butted surface, and the welding quality of the joint obtained varies depending on the thickness of the oxide film. For this reason, it can be said that it is most preferable to grasp the thickness of the oxide film at each welding position and to perform the above-described processing when necessary according to the oxide film thickness.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional disadvantages, and has a main object of ascertaining a shift of an irradiation position of a material to be welded with respect to a butt surface from plasma light generated by laser beam welding. It is an object of the present invention to provide a method and a device for monitoring a welded portion of laser beam welding, which can perform the method. Another object of the present invention is to
From the plasma light, the thickness of the oxide film generated on the butt surface can be ascertained, and a welding portion monitoring method and a welding portion monitoring device for laser beam welding capable of determining whether welding can be continued or not. Is to provide.

[0007]

Means and Effects for Solving the Problems Claim 1
In the method of monitoring a weld portion of laser beam welding, a laser beam 2 is applied to a butt portion of a pair of workpieces 1 and 1, and an optical characteristic of the weld portion is detected by a sensor 3 to grasp a welding state. In the method for monitoring a welded portion of beam welding, when the emission intensity detected by the sensor 3 is higher than a first reference value, it is determined that the laser beam 2 is deviated from the butt surfaces 4, 4. I have.

According to the first aspect of the present invention, a butt welding is performed by irradiating a laser beam 2 to a butt portion of materials to be welded 1 and a plasma detected at this time. When the light emission intensity of the light is higher than a predetermined light emission intensity (first reference value), it is determined that the laser beam 2 is deviated from the butting surfaces 4, 4. This is based on the finding that the emission intensity obtained when an oxide film is present on the butting surfaces 4 and 4 is lower than the emission intensity obtained when no oxide film is present. That is, when the laser beam 2 is accurately irradiated on the butting surfaces 4 and 4 where the oxide film is present, a relatively low emission intensity is obtained, whereas the laser beam 2 is displaced from the butting surfaces 4 and 4. In this case, the amount of the oxide film to be melted is reduced, so that a higher emission intensity than the above can be obtained. As a result, the value of the light emission intensity obtained when the laser beam 2 is irradiated on the butting surfaces 4 and 4 having the oxide film is determined in advance as the first reference value. It is possible to reliably determine whether or not the position of the laser beam 2 is shifted from. Further, according to the above method, the present invention can be applied not only to different materials but also to a case where the same materials 1 and 1 are laser beam-welded, and there is no gap between the butting surfaces 4 and 4. It is also possible to grasp the target position deviation. The sensor 3 may be arranged at any angle. However, preferably, the angle (observation angle θ) between the beam axis of the laser beam 2 and the optical axis of the sensor 3 is small, that is, θ = 4 °. If it is arranged to receive the plasma light, a highly sensitive result can be obtained.

According to a second aspect of the present invention, there is provided a method for monitoring a welded portion in laser beam welding, wherein when the light emission intensity detected by the sensor is higher than a first reference value, the light emission intensity is lower than the reference value. It is characterized in that the irradiation position of the laser beam 2 is controlled.

According to the second aspect of the present invention, when the luminous intensity is higher than the first reference value, the laser beam 2 is displaced from the butt surfaces 4,4. Is determined, and the laser beam 2 and the workpieces 1 and 1 are relatively moved in a direction perpendicular to the welding line (for example, a left-right direction with respect to the welding line), so that the emission intensity becomes equal to or less than the reference value. The welding target position of the laser beam 2 is controlled as described above. As a result, the displacement of the laser beam 2 can be corrected during welding,
A weld having good welding quality can be obtained.

According to a third aspect of the present invention, there is provided a method for monitoring a welding portion of laser beam welding, wherein the light emission intensity detected by the sensor 3 is:
If the second reference value, which is lower than the first reference value, is lower than the second reference value, it is determined that there is a possibility that welding quality defects may occur in the welded portions of the workpieces 1 and 1.

According to the method for monitoring a welded portion of laser beam welding according to the third aspect, when the light emission intensity detected by the sensor 3 is lower than a second predetermined reference value, the oxidation of the workpieces 1 and 1 is performed. Assuming that the thickness of the film exceeds the appropriate range,
We judge that there is a possibility of poor welding quality. The thickness of the oxide film formed on the butting surfaces 4 and 4 of the workpieces 1 and 1 is deeply related to the welding quality, and the welding quality decreases as the oxide film thickness increases. Therefore, by determining in advance the light emission intensity obtained when the oxide film thickness provides good welding quality as the second reference value of the light emission intensity, the quality of the welding quality can be determined from the light emission intensity detected during welding. You can figure out.

According to a fourth aspect of the present invention, there is provided a laser beam welding welding portion monitoring apparatus, comprising: a sensor for detecting an optical characteristic of a welding portion irradiated with the laser beam; and a luminous intensity detected by the sensor. An irradiation position control means for controlling the irradiation position of the laser beam 2 so that the emission intensity is equal to or lower than the reference value when the reference value is higher than one reference value.

According to the laser beam welding monitoring device of the fourth aspect, when the light emission intensity is higher than the predetermined first reference value, the laser beam 2 is displaced from the butting surfaces 4,4. By irradiating the laser beam 2 and the workpieces 1 and 1 relative to each other in a direction perpendicular to the welding line (for example, a left-right direction with respect to the welding line) by the irradiation position control means, The welding target position of the laser beam 2 is controlled so that the light emission intensity is equal to or less than the reference value. As a result, the displacement of the laser beam 2 can be corrected during welding, so that a weld having good welding quality can be obtained.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, specific embodiments of a method and apparatus for monitoring a weld in laser beam welding according to the present invention will be described in detail with reference to the drawings.
First, in FIG. 1, 1 indicates a pair of materials to be welded,
The butting surfaces 4, 4 are closely attached so as to face each other, and are arranged so that the longitudinal direction thereof coincides with the welding progress direction. In this state, I-shaped butt penetration welding is performed in the longitudinal direction using the laser beam 2. At this time, the butted surfaces 4 of the workpieces 1 and 1
4 is assumed to have an oxide film such as a mill scale or a thermally cut oxide film. In FIG. 1, the welding direction is a direction perpendicular to the paper surface, and is approximately 45
He assist gas is supplied at an angle of ° toward the welding direction. Further, a photodiode (sensor) 3 is provided on a circumference in a plane perpendicular to the welding direction with the laser beam irradiation point O as a center, and the photodiode 3 is attached to the workpieces 1, 1 Butt surfaces 4, 4
Is arranged with its optical axis directed to the laser beam irradiation point O. At this time, the angle (observation angle) θ between the beam axis of the laser beam 2 and the optical axis of the photodiode 3
Is in the range of θ = 4 ° to 90 °.

When a steel material is used as the material to be welded 1, 1, the average thickness of the mill scale or the thermally cut oxide film formed on the butting surfaces 4, 4 is about 5 to 15 μm. In the present embodiment, the steel materials 1 having an oxide film having the above-mentioned thickness are welded by laser beam, and the plasma light generated at this time is detected by the photodiode 3, so that the material to be welded is obtained. Attempts are made to determine whether or not there is a displacement of the target position of the laser beam 2 from the abutting surfaces 4, 4.

Therefore, first, in order to clarify the relationship between the oxide film and the emission intensity of the plasma light, the thickness of the oxide film formed on the butting surfaces 4, 4 of the workpieces 1, 1 is set to 0 μm ( The average value of the emission intensity of the plasma light obtained when the thickness was changed to 16 μm and 32 μm was determined. At this time, since the emission intensity of the plasma light varies depending on the angle at which it is received, the angle (observation angle) between the beam axis of the laser beam 2 and the optical axis of the photodiode 3 changes in the range of θ = 4 ° to 90 °. Then, the above-mentioned oxide film thickness and emission intensity were investigated at each angle.

FIG. 2 is a graph showing a change in light emission intensity with respect to each observation angle θ. In the above graph, the horizontal axis indicates the observation angle (degree), and the vertical axis indicates the emission intensity (V). In the graph, circles, squares, and triangles indicate oxide film thicknesses of 0 μm, 16 μm, and 32 μm, respectively. Data obtained from time to time. The graph shows that the observed emission intensity increases as the observation angle θ decreases. This is because when the observation angle θ is large, only light emission near the welding surface can be detected, but when the observation angle θ is small, light emission at a deeper portion can be detected. On the other hand, with respect to the oxide film thickness, the emission intensity is lower when the oxide film is present on the butting surfaces 4 and 4 than when the oxide film is removed at any observation angle θ. The emission intensity obtained with a thicker oxide film is lower. From this result, it is clear that the emission intensity detected by the oxide film thickness changes.

Next, the relationship between the emission intensity and the displacement of the irradiation position of the laser beam 2 was investigated by examining the relationship between the oxide film thickness and the emission intensity in more detail. The specific method is described below. In the graph of FIG. 2, the relationship between the oxide film thickness and the emission intensity is most clearly shown when the observation angle θ is 4 °. Thus, when the photodiode 3 is placed at the position of the observation angle θ = 4 °, and the oxidized film thickness generated on the butted surfaces 4 and 4 of the workpieces 1 and 1 is changed, the luminescence intensity obtained respectively is obtained. A survey was conducted. The data is shown in the dotted line graph of FIG. In the graph, the horizontal axis represents the oxide film thickness (μm), and the vertical axis represents the light emission intensity (V). This graph shows that the emission intensity decreases as the oxide film thickness increases. From this result, when the laser beam 2 is accurately irradiated on the butting surfaces 4 and 4 where the oxide film is present, a relatively low emission intensity is obtained, and the laser beam 2 is applied to the butting surfaces 4 and 4.
If the target position is shifted from the target position 4, the amount of the oxide film that is melted by the irradiation of the laser beam 2 decreases, so that a higher emission intensity than the above can be obtained.

By the way, as described above, a thermally cut oxide film having an average of about 5 to 15 μm exists on the butted surfaces 4 and 4 of the workpieces 1 and 1. Thus, when the value of the oxide film thickness is compared with the dotted line graph in FIG. 3, the emission intensity obtained when the oxide film thickness is 5 μm is about 0.13.
V, the emission intensity obtained when the oxide film thickness is 15 μm is about 0.08 V. Here, it has been described above that the emission intensity takes a high value when the laser beam 2 is displaced from the abutment surfaces 4 and 4 at the target position. When this is applied to the present embodiment, the detected light emission intensity is higher than the light emission intensity range of 0.08 to 0.13 V obtained when the thickness range of the oxide film is 5 to 15 μm. When the value is high, that is, when the light emission intensity exceeds 0.13 V, it can be determined that the laser beam 2 is displaced from the abutting surfaces 4 and 4 at the target position. Further, since the dotted line graph in FIG. 3 shows the relationship between the light emission intensity and the oxide film thickness, it is possible to estimate the oxide film thickness occurring on the butting surfaces 4, 4 from the light emission intensity detected thereby. Become.

Next, in order to investigate the welding quality of the welded portion obtained when the workpieces 1 and 1 having an oxide film were subjected to laser beam welding, the void area ratio in the above welded portion was determined. The solid line graph in FIG.
Is a graph showing how the porosity of the weld changes depending on the thickness of the oxide film present in the graph, where the abscissa indicates the thickness of the oxide (μm) and the ordinate indicates the porosity (%). ing. The above graph shows that the pore area ratio increases as the oxide film thickness increases. In other words, this indicates that defects such as blowholes are more likely to occur in the welded portion as the oxide film thickness increases, and this result indicates that the weld quality tends to decrease as the film thickness increases. Can be.

As described above, the materials to be welded 1, 1
The average thickness of the oxide film formed on the butting surfaces 4 is about 5 to 15 μm. From this, it can be seen from the solid line graph of FIG. 3 that the porosity area ratio of the welded portion in this film thickness range is approximately 10% or less. From this, it is considered that when the oxide film thickness is within the above range, a joining member having relatively good welding quality can be obtained. When this result is compared with a dotted line graph showing the relationship between the oxide film thickness and the light emission intensity in FIG. 3, the light emission intensity obtained when the oxide film thickness is 5 μm is about 0.13 V and the oxide film thickness is 15 μm. Occasionally the emission intensity obtained is about 0.08
V is shown. Thus, when the detected light emission intensity has a value lower than the above light emission intensity range of 0.08 to 0.13 V, that is, when the light emission intensity has a value lower than 0.08 V, welding quality is poor. It can be understood that there is. Thus, in the case of the present embodiment, the second reference value of the light emission intensity when determining the quality of the welding quality can be set to 0.08V.

From the results described above, the laser beam 2 is welded to the butting surfaces 4 and 4 without shifting the target position, and in order to obtain a higher quality bonding member, the first reference value and the second reference value are required. It is necessary to obtain an emission intensity within the range of two reference values. That is, in the case of this embodiment, if the obtained light emission intensity falls within the range of 0.08 to 0.13 V, it can be determined that high-quality welding is being performed.

Next, a control and processing method when the detected light emission intensity does not fall within the range between the first reference value and the second reference value will be described. First, if the light emission intensity detected during welding is higher than a predetermined first reference value of 0.13 V, it is determined that the laser beam 2 is displaced from the butt surfaces 4 and 4 and the irradiation position control means. Thus, by controlling the laser beam 2 to move in a direction perpendicular to the welding progress direction (left-right direction with respect to the welding line), the detected emission intensity is controlled to be equal to or less than the first reference value. Conversely, the light emission intensity is equal to the predetermined second reference value 0.
If the voltage is lower than 08 V, it is determined that the thickness of the oxide film of the workpieces 1 and 1 is out of the appropriate range, and it is determined that there is a possibility that poor welding quality of the workpieces 1 and 1 may occur. Or by performing processing such as supplying a deoxidizing material such as Al, Si, or Ti to the butted portion, thereby suppressing the occurrence of blowholes in the welded portion.

As described above, according to the method for monitoring a welded portion of laser beam welding of the above embodiment, the laser beam 2
However, the position of the laser beam 2 is deviated by obtaining the value of the emission intensity obtained when the butt surfaces 4, 4 of the workpieces 1, 1 are accurately irradiated as the first reference value in advance. Can be reliably determined. Further, while the laser beam 2 is moved in a direction (left-right direction) perpendicular to the welding line of the workpieces 1 and 1, the emission intensity is controlled to be equal to or less than a first reference value. The displacement of the laser beam 2 can be corrected during the process. For this reason, it is possible to obtain a welded part having good welding quality. In addition, from the appropriate range of the oxide film thickness at which good welding quality can be obtained, the second reference value of the light emission intensity obtained at that thickness is obtained in advance, so that the welding quality can be determined from the light emission intensity detected during welding. Is good or bad. Furthermore, according to this method, not only different materials but also the same materials 1 and 1 can be applied to the case where the same material is laser beam-welded, and there is no gap between the butting surfaces 4 and 4. However, the target position deviation and welding quality can be grasped.

Although the embodiment of the method for monitoring a weld portion of laser beam welding according to the present invention has been described above, the present invention is not limited to the above-described embodiment, and can be implemented with various modifications. is there. First, in the above embodiment, the reference value range of the light emission intensity was set to 0.08 to 0.13 V, but this value is obtained by the type of the workpiece 1, the method of processing the butt surface 4, the observation angle θ, and the like. Therefore, a correlation table of the emission intensity with respect to the oxide film thickness and a correlation table of the void area ratio with respect to the oxide film thickness shown in the graph of FIG. It is preferable to determine the thickness range of the oxide film from which quality can be obtained. Further, at this time, if the range of the thickness of the oxide film generated in the processing stage of the workpieces 1 and 1 is set to be narrow, more accurate control can be performed. And welding quality can be grasped more accurately. Further, in the above, while the laser beam 2 is moved by the irradiation position control means in a direction perpendicular to the welding line of the workpieces 1 and 1, the emission intensity is controlled to be equal to or less than the reference value. The irradiation position control means may be configured to control the target position shift by fixing the laser beam 2 and moving the workpieces 1 and 1. Further, in the case where a gap is formed between the butting surfaces 4, the light emission intensity is further reduced by the laser beam 2 passing through the gap, so that it is possible to grasp welding defects due to this. is there.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an arrangement of sensors in one embodiment of a laser beam welding monitoring method of the present invention.

FIG. 2 is a graph showing a change in emission intensity with respect to an observation angle when laser beam welding is performed while changing the oxide film thickness to 0, 16, and 32 μm.

FIG. 3 is a graph showing a change in emission intensity with respect to an oxide film thickness and a change in a hole area ratio with respect to an oxide film thickness.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Material to be welded 2 Laser beam 3 Sensor (photodiode) 4 Butt surface O Laser beam irradiation point

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Taiichi Matsumoto 3-1-1 Ueno, Hirakata-shi, Osaka F-term in Komatsu Manufacturing Technology Development Center (reference) 4E068 BE00 CA09 CA17 CC01 DA14 DB01

Claims (4)

[Claims] 1. A laser beam (2) is applied to a butt portion of a pair of workpieces (1) and (1), and an optical characteristic of the weld portion is detected by a sensor (3) to grasp a welding state. In the method for monitoring a welded portion of laser beam welding, when the emission intensity detected by the sensor (3) is higher than a first reference value, the laser beam (2) is deviated from the butt surfaces (4) and (4). And a method for monitoring a welded portion of laser beam welding. 2. When the light emission intensity detected by the sensor (3) is higher than a first reference value, the irradiation position of the laser beam (2) is controlled so that the light emission intensity is lower than the reference value. The method for monitoring a welded portion in laser beam welding according to claim 1, wherein: 3. When the light emission intensity detected by the sensor (3) is further lower than a second reference value lower than the first reference value, the light is applied to a welded portion of the workpieces (1) and (1). 3. The method according to claim 1, wherein it is determined that there is a possibility that poor welding quality may occur. 4. A sensor (3) for detecting an optical characteristic of a welded portion irradiated with a laser beam (2), and a light emission intensity detected by the sensor (3) is higher than a first reference value. In such a case, the welding part monitoring apparatus further includes an irradiation position control unit that controls an irradiation position of the laser beam (2) so that the emission intensity is equal to or less than a reference value.