JP2000084683A - Method and device for abnormality monitoring at laser beam welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase an information quantity in welding, to extract an abnormal cause as well as to monitor in process by measuring plasmatic potential generated from laser irradiation on front/rear face of a work and monitoring welding abnormality based on plasmatic potential. SOLUTION: A shield gas is injected from a nozzle 2 to a weld zone of a work and a laser beam L irradiates a weld zone. Among ionized plasmas, an electron of a negative electric charge is light, a gas body of a positive electric charge is heavy. Thus, metal vapor plasma 11 forms a positive electric field near the work 1 and a negative electric field apart from the work. The shield gas plasma 12 coming out from the nozzle 2 forms a positive electric field near the nozzle 2 and a negative electric field apart from the nozzle. An oscilloscope 5 is connected between the work 1 and the nozzle 2 to measure an electric potential, at a rear side of the work 1, the electric potential between the work 1 and an electrode 4 is measured by an oscilloscope 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for monitoring a welding abnormality in an in-process process for detecting a welding abnormality in laser welding and extracting a cause of the abnormality. .

[0002]

2. Description of the Related Art Laser welding can perform high-speed, high-precision welding, and can reduce the distortion accompanying welding. However, it is difficult to monitor the phenomenon because of the high speed, and it is difficult to check the quality. Under such circumstances, for example, welding technology vol. 4
5, No. 11, p. 92, a technique for monitoring the welding status by plasma light or the like during welding is proposed. The plasma light used during welding, which is used here, exhibits good welding characteristics and enables excellent monitoring. However, a work holding base is provided on the back side of the material to be welded (hereinafter referred to as a work). Because of the necessity, monitoring the plasma light from the back side becomes difficult.

For this reason, when the above-mentioned plasma light is used, only the plasma blown out to the front side is monitored. For example, when the plasma light is abnormally reduced, it may be due to excessive melting or excessively large gap, It is difficult to extract the cause. This is because the amount of information for monitoring is small. Therefore, there is a demand for a monitoring technique that can further increase the amount of information and extract a certain cause of abnormality.

[0004]

SUMMARY OF THE INVENTION The basic technical problem of the present invention is to provide a method and apparatus for monitoring a welding abnormality in which the amount of information for monitoring during laser welding is increased in view of the above situation. To provide.

A more specific technical object of the present invention is to obtain monitoring information simultaneously from the front and back surfaces of a work at the time of butt welding of the work by laser welding by improving a technique for monitoring a welding abnormality during laser welding. It is therefore to provide a welding abnormality monitoring technique which enables a larger amount of information. Further, a more specific technical problem of the present invention is to effectively utilize a plasma potential that can be simultaneously measured from the front and back surfaces of the work at the time of butt welding of the work so that welding abnormality during the laser welding can be monitored. To provide a monitoring method and a monitoring device.

[0006]

According to the welding abnormality monitoring method of the present invention for solving the above-mentioned problems, when performing laser welding of a butt joint of a work, plasma generated by laser irradiation is irradiated on both front and back surfaces of the work. It is characterized in that potentials are measured and welding abnormalities are monitored based on the plasma potentials. In the above monitoring method, it is effective to carry out laser welding while flowing a shielding gas to the welded portion of the work, measure the potential of the vapor plasma of the work material and the potential of the shield gas plasma, and use them as information for monitoring welding abnormalities. is there.

According to another aspect of the present invention, there is provided a welding abnormality monitoring apparatus for irradiating a welding portion of a workpiece with a laser beam for welding, and a laser irradiating means for irradiating the welding portion with the welding portion. Nozzle that blows out shielding gas to the welded part, electrodes placed opposite to the welded part on both front and back sides of the work, and connected to the electrodes on the front and back sides, welding based on the potential of plasma generated by laser irradiation Monitoring means for monitoring the state.

In the method and apparatus for monitoring a welding abnormality according to the present invention as described above, the plasma potential that can be measured simultaneously on the front and back surfaces of the work at the time of butt welding of the work is used. Compared to monitoring the welding status only from the surface side of the workpiece, the amount of information on abnormality monitoring during laser welding can be increased, and welding abnormalities can be monitored in-process, including extraction of the cause of the abnormality. it can.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to the drawings. Generally, when a laser having a high energy density is irradiated on a work made of a metal material, the metal receives the energy and melts, and a part of the metal evaporates. During laser welding of metal materials, some of the metal vapor generated by the laser irradiation and the shielding gas for welding are ionized by the laser irradiation.These ionized materials are called plasma. I have.

FIG. 1 shows the state of ionization at the time of laser welding, that is, when a shield gas is ejected from a nozzle 2 disposed opposite to a welded portion of a work 1 to the welded portion, and a laser beam L The state of generation of the metal vapor plasma 11 and the shield gas plasma 12 when irradiating is shown schematically. Here, of the plasma ionized by the laser L, the negatively charged electrons are light and the positively charged gas is heavy. For this reason,
As shown in FIG. 1, the metal vapor plasma 11 forms a positive electric field near the work 1 and a negative electric field far from the work 1. The shield gas plasma 12 emitted from the nozzle 2 forms a positive electric field near the nozzle 2 and a negative electric field far from the nozzle 2.

Therefore, when the oscilloscope 5 is connected between the work 1 and the nozzle (electrode) 2 at the time of laser welding of the butt joint of the metal material and the potential between them is measured, the momentum of the metal vapor plasma 11 is determined. When the pressure is strong, a positive potential is generated on the work 1 side, and a negative potential is generated on the nozzle 2 side. Conversely, when the momentum of the shield gas plasma 12 is strong, the opposite potential is generated.

On the back side of the work 1, an electrode 4 is installed at a distance of several millimeters from the work 1 in a state of being insulated from the work table 3, and an oscilloscope 6 is connected between the work 1 and the electrode 4. Work 1 and its electrode 4
Is measured, the metal vapor plasma 13 emerging on the back side of the work 1 also generates a potential. As described above, the potentials generated by the plasma on the front and back surfaces of the work 1 can be measured by the oscilloscopes 5 and 6, respectively, and these measured potentials are herein referred to as plasma potentials.

[0013] The shielding gas referred to herein means a nozzle 2 installed near an exit from which a laser is emitted to prevent a high-temperature metal material from reacting with the atmosphere and being oxidized or nitrided during welding. An inert gas such as Ar or He is used as a gas to be ejected toward the welded portion.

FIG. 2 shows the configuration of an apparatus for implementing the welding abnormality monitoring method of the present invention. Work 1
The laser beam L irradiating the welding portion of the workpiece 1 is passed from a laser irradiating means (not shown) through a laser condensing system 21 and further through a nozzle 2 electrically insulated by an insulator 22 to the workpiece 1. Is projected. The nozzle 2 is disposed so as to face a welded portion of the work 1 and ejects a shielding gas to the welded portion. The nozzle 2 also serves as an electrode for detecting a plasma potential on the surface side of the work 1.

On the other hand, the work 1 is fixed on a work fixing table 25 which is placed on an XY table 23 via an insulator 24 so as to be electrically insulated. The work fixing base 25 is provided with an electrode receiving groove 26 having a slit 27 which is opened at a portion where the welded portion of the work 1 is placed, and in the electrode receiving groove 26 except for a portion facing the slit 27. An electrode 28 whose periphery is covered with an insulator 29 is accommodated. Thereby, on the back side of the welded portion of the work 1,
At a distance of several millimeters from the work, electrodes 28 for detecting the plasma potential on the back side are arranged to face each other.

Further, the nozzle 2 serving also as the electrode on the front surface side
The plasma potential generated by laser irradiation between the workpiece fixing table 25 (or the work 1) and between the electrode 28 provided on the work fixing table 25 in an insulated state and the work fixing table 25 (or the work 1). Is connected to an oscilloscope recorder 30 for recording the fluctuation of the oscilloscope. Note that, instead of the oscilloscope recorder 30, various monitoring means for monitoring the welding state based on the plasma potential can be employed.

According to such a welding abnormality monitoring apparatus, when laser welding a butt joint of a work, on both front and back surfaces of the work 1, the potential of the plasma of the vapor of the work material generated by the laser irradiation and the potential of the shield gas plasma. , The fluctuation of the plasma potential is taken into the oscilloscope recorder 30, and the welding abnormality can be monitored based on the change of the signal. In particular, when monitoring this welding abnormality, the work 1
Since electrodes are installed on both front and back sides of the welded part to measure the behavior of plasma potential, the amount of monitoring information of welding abnormalities increases, and based on the measurement results, various welding abnormalities and various defects during welding Can be detected in-process, and the cause of abnormality during laser welding can be easily extracted.

[0018]

Next, an embodiment of the monitoring method of the present invention will be described. For monitoring the welding abnormality according to the present invention, substantially the same apparatus as that shown in FIG. 2 was used.
FIGS. 3A to 3G show examples of macro cross sections when the welding speed during butt welding is changed, and FIGS. 4 to 7 correspond to FIGS. 3A, 3B, 3D, and 3G, respectively. The example of the signal intensity about the plasma potential of the front and back is shown. In FIG. 3A, where the welding speed is too slow, the heat input per unit welding length is too large, so that the penetration is excessive. Conversely, as shown in FIGS. Is insufficient to penetrate to the back side and not penetrate. In the example of the signal intensity on the front and back surfaces shown in FIGS. 4 to 7, when the penetration is excessive, the signal intensity on both the front and back surfaces vibrates sharply. Further, if the penetration is not penetrated, no signal is output on the back side as shown in FIG.

The measurement result of this signal is divided into thousandths of a second, the maximum value, the minimum value, and the average value are determined during the measurement. The average value obtained by simply averaging 0.3 seconds is the average value and the maximum value. The values obtained by subtracting the minimum value from 平均 are averaged for 0.3 seconds and arranged as amplitudes, which are shown in FIGS. 8A and 8B. From this result, when the penetration becomes excessive, the large metal plasma violently comes out to the front side or the back side, so that the plasma potential fluctuates greatly on both the front and back sides, and compared to the appropriate condition. The average value of the signal decreases and the amplitude increases significantly. Further, when the penetration is not penetrated, no plasma is generated on the back side, so that the plasma potential on the back side is 0.
From this result, when the welding speed changes for some reason during welding and the penetration becomes excessive or non-penetration occurs, it can be easily detected from the signal intensity.

FIGS. 9A to 9C show examples of macro cross-sections when the gap at the time of butt welding is changed, and FIG. 10 shows the result of summing up the average values of the signals at this time.
If the gap at the time of welding is too wide (b and c in FIG. 9), the weld metal becomes insufficient, and moreover, a part of the laser beam penetrates so that only the side surface of the groove is melted. On the other hand, almost no plasma potential appears on the back side. On the other hand, since the shielding gas plasma is mainly used on the front side, the polarity changes. From this result, if there is a gap defect during welding, it can be detected.

[0021]

According to the welding abnormality monitoring method and apparatus of the present invention described in detail above, the plasma potential that can be measured simultaneously on the front and back surfaces of the work at the time of butt welding of the work is used. Compared to monitoring the welding status only from the front side of the workpiece with plasma light at the time, the amount of information on abnormality monitoring during laser welding is increased and the in-process Welding abnormalities can be monitored.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram for explaining the concept of a welding abnormality monitoring method according to the present invention.

FIG. 2 is a perspective view illustrating a configuration of a device for monitoring welding abnormality.

FIGS. 3A to 3G are cross-sectional views showing examples of macro cross-sections when the welding speed during butt welding is changed.

FIGS. 4A and 4B are diagrams showing examples of signal intensities of plasma potentials on the front surface and the back surface corresponding to FIG. 3A.

5A and 5B are diagrams showing an example of the same signal intensity corresponding to FIG. 3B.

6A and 6B are diagrams showing an example of the same signal intensity corresponding to FIG. 3D.

FIG. 7 is a diagram showing an example of a signal intensity for a plasma potential on the front surface corresponding to g in FIG. 3;

FIGS. 8A and 8B are graphs showing the results of organizing the average value and the amplitude of the plasma potential.

FIGS. 9A to 9C are cross-sectional views illustrating examples of macro cross-sections when a gap at the time of butt welding is changed.

FIG. 10 is a graph showing the results of summing up the average values of signals when the gap during butt welding is changed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Work 2 Nozzle 4 Electrode 11, 13 Metal vapor plasma 12 Shield gas plasma 30 Oscilloscope recorder L Laser

Claims (3)

[Claims] 1. In laser welding of a butt joint of a work, on both front and back surfaces of the work, a plasma potential generated by laser irradiation is measured, and a welding abnormality is monitored based on the plasma potential. Abnormality monitoring method during laser welding. 2. A laser welding method in which a shield gas is supplied to a welded portion of a work to measure a potential of a plasma of a work material vapor and a shield gas plasma, and use them as information for monitoring welding abnormalities. The method for monitoring abnormality during laser welding according to claim 1. 3. A laser irradiating means for irradiating a laser beam for welding to a welded portion of a work, a nozzle arranged opposite to the welded portion, and blowing a shielding gas to the welded portion, and a front and back surface of the work. A laser, comprising: an electrode disposed to face the welded portion; and a monitoring means connected to the electrodes on the front and back surfaces, and monitoring a welding state based on a potential of plasma generated by laser irradiation. Abnormality monitoring device during welding.