JPH08164489A - Laser welding quality judgment device - Google Patents

Abstract

(57) [Abstract] [Purpose] The present invention determines the welding quality in a melted state online with high accuracy, and controls the laser output according to this determination to make the melted state uniform. [Structure] Plasma Pz generated in a molten portion on the work 3
The plasma monitor means 10 monitors the generation state of the electric field, outputs a potential difference Vs corresponding to the plasma generation state, and determines whether the welded state of the welded portion is good or bad by the microprocessor unit 21b based on the level of the potential difference Vs. Depending on the judgment result, the laser oscillator 1
Control the laser output of.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser welding quality for determining a melted state of a welded portion when a work is irradiated with a laser beam and performing a welding process, and further controlling a laser output based on the result of the determination. Regarding a determination device.

[0002]

2. Description of the Related Art In laser welding, it has been proposed to monitor the welding state online by a sensor arranged in the vicinity of the welded portion as a technique for monitoring the welding quality such as the penetration state of a work.

FIG. 9 is a block diagram of an apparatus for monitoring the welding quality such as the penetration state of the work. The laser beam Lb emitted from the laser oscillator 1 is condensed by the lens 2 and is irradiated so as to focus on the surface of the work 3.

At this time, the work 3 is fixed on an XY table (not shown), and a welding process, that is, a bead is applied to the work 3 in accordance with the movement of the XY table. on the other hand,
A microphone 4 is arranged as a sensor in the vicinity of the welded portion, and the microphone 4 collects the welding sound generated by the welding process and outputs it as an electric signal.
This electric signal is digitally converted by the A / D converter 5 and sent to the computer 6.

The computer 6 compares the digitized electric signal with the reference value for the welding sound stored in the internal memory, and judges the quality of the welding state based on its magnitude and its fluctuation range.

However, normally, the working environment in which the welding work is performed is to start the laser oscillator 1 around the welded portion,
There are incidental devices, and noises other than welding noise are constantly generated from these devices.

Therefore, these noise sounds are also collected together with the welding sound by the microphone 4 and converted into an electric signal for output, so that an electric signal in which the noise sound and the welding sound are mixed is sent to the microcomputer 6.

Therefore, it is very difficult for the microcomputer 6 to extract only the signal due to the welding sound from the electric signal in which the noise sound and the welding sound are mixed.
For this reason, the accuracy of determining the welding quality such as the melted state by the welding sound is low.

[0009]

As described above, in the conventional welding quality monitor, the noise sound and the welding sound are mixed and it is difficult to extract only the welding sound from the noise sound. The accuracy of determining the welding quality such as the condition is low.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a laser welding quality judging device which can judge the welding quality such as a penetration state on-line with high accuracy. Another object of the present invention is to provide a laser welding quality determination device capable of highly accurately determining the welding quality such as the penetration state online and controlling the laser output according to this determination to make the penetration state uniform. And

[0011]

According to a first aspect of the present invention, there is provided a laser welding quality judging device for judging at least a melted state of a welded part when a work is irradiated with a laser beam to perform a welding process. Plasma monitor means for monitoring the plasma generation state generated in the molten portion and outputting an electric signal according to the plasma generation state, and at least welding of the welded portion based on the level of the electric signal output from the plasma monitor means A laser welding quality judging device, which comprises a judging means for judging whether the condition is good or bad and which is intended to achieve the above object.

According to a second aspect of the present invention, there is provided a laser welding quality judging device for judging at least a melted state of a welded portion when a work is irradiated with a laser beam outputted from a laser oscillator to perform welding. Plasma monitor means for monitoring the plasma generation state generated in the molten portion and outputting an electric signal according to the plasma generation state, and at least welding of the welded portion based on the level of the electric signal output from the plasma monitor means An object of the present invention is to provide the above object by providing a determining means for determining the quality of the state and a laser control means for controlling the laser output of the laser oscillator according to the determination result of at least the quality of the melted state by the determining means. Is a laser welding quality determination device.

According to a third aspect of the present invention, the plasma monitor means has electrodes arranged on the optical path of the laser beam above the work, and a voltage signal corresponding to changes in resistance and excitation voltage in the plasma space between the electrode and the work. Is output.

According to a fourth aspect of the present invention, the plasma monitor means inserts a nozzle tip into at least a processing nozzle used as a conduit for laser light via an insulator, and a resistance in a plasma space between the nozzle tip and the work. And a voltage signal corresponding to a change in the excitation voltage is output.

According to the fifth aspect, the judging means compares the electric signal level output from the plasma monitoring means with the range of the upper limit and the lower limit set values which are the reference signals, and judges at least whether the melted state of the welded portion is good or bad. judge.

According to the sixth aspect of the present invention, the judging means compares the electric signal level output from the plasma monitoring means with the range of the upper and lower limit set values which are the reference signals, and the electric signal level is within the range of the reference signal. If it exceeds every predetermined period, it is determined that an abnormal beat has occurred.

According to the seventh aspect, the laser control means feedback-controls the laser output of the laser oscillator so that the electric signal level output from the plasma monitor means falls within the range of the reference signal.

[0018]

According to the first aspect of the present invention, when the work is irradiated with the laser beam to perform the welding process, the plasma generation means monitors the plasma generation state generated in the melted portion on the work and confirms the plasma generation state. A corresponding electric signal is output, and based on the level of this electric signal, the judging means judges at least whether the melted state of the welded portion is good or bad. As a result, the welding quality such as the penetration state can be determined online with high accuracy.

According to the second aspect of the present invention, when the work is irradiated with the laser beam to perform the welding process, the plasma generation means monitors the plasma generation state generated in the melted portion on the work and confirms the plasma generation state. According to the level of this electric signal, the judging means judges at least whether the welded state of the welded portion is good or bad, and further controls the laser output of the laser oscillator by the laser control means according to the judgment result. . As a result, the welding quality such as the melted state can be determined with high accuracy online, and the laser output can be controlled to make the melted state uniform.

According to the third aspect of the present invention, a voltage signal is output according to a change in resistance and excitation voltage in the plasma space between the electrode arranged on the optical path of the laser beam above the work and the work, and the level of this electric signal is output. Based on the above, at least the quality of the melted state of the welded portion is determined, and the laser output of the laser oscillator is controlled.

According to a fourth aspect of the present invention, a voltage signal corresponding to changes in resistance and excitation voltage in a plasma space between a nozzle tip and a workpiece inserted through an insulator into a processing nozzle used as a laser beam conduit. Based on the level of the electric signal, the quality of the melted state of at least the welded portion is determined, and the laser output of the laser oscillator is controlled.

According to the fifth aspect, the quality of the welded state of the welded portion is judged by comparing the electric signal level according to the plasma generation state with the range of the upper limit and the lower limit set value as the reference signal.

According to the sixth aspect of the present invention, the electric signal level corresponding to the plasma generation state is compared with the range of the upper limit and the lower limit set value which is the reference signal, and the electric signal level exceeds the range of the reference signal every predetermined period. In this case, the occurrence of an abnormal beat, for example, a humping beat is determined.

According to the seventh aspect, by performing feedback control of the laser output of the laser oscillator so that the electric signal level according to the plasma generation condition falls within the range of the reference signal, the melted state and the like become uniform.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. The same parts as those in FIG. 9 are designated by the same reference numerals and detailed description thereof will be omitted. FIG. 1 is a configuration diagram of a laser welding quality determination device.

The plasma monitor means 10 has a function of monitoring the generation state of the plasma Pz generated in the molten portion on the work 3 and outputting an electric signal Vs according to the plasma generation state.

The plasma monitor means 10 is used for the work 3
An electrode 11 is arranged on the optical path of the laser beam Lb above, and an electric signal Vs corresponding to changes in resistance and excitation voltage in a plasma space between the electrode 11 and the work 3 is output.

The specific configuration of the plasma monitor means 10 is provided with a constant voltage power source 12, and the constant voltage power source 12 is provided.
The first resistor 13 and the second resistor 14 are connected in series to the output terminal of the, and the electrode 11 is connected to the connection point of the first and second resistors 13 and 14. The second resistor 14 is
It is connected to the work 13 and the ground potential.

Normally, the laser light Lb emitted from the laser oscillator 1 is applied to the work 3 through the processing nozzle 15 as shown in FIG. The processing nozzle 15 is used as a conduit for the laser light Lb and the shield gas. The nozzle tip 1 is provided on the tip side of the processing nozzle 15.
6 is provided, and a spacer 17 made of an insulator is inserted between the processing nozzle 15 and the nozzle tip 16.

Therefore, the nozzle tip 16 is insulated from the potential of the processing nozzle 15, and this is used as the electrode 11. However, the electrode 11 (nozzle tip 1
6) and the electric signal Vs corresponding to the change in the excitation voltage and the resistance in the plasma space between the work 3 are output as the potential difference across the first resistor 13.

A differential amplifier 18, a low-pass filter 19 for extracting a voltage signal of a low frequency component from the output signal of the differential amplifier 18, and an A / D are provided across the first resistor 13.
A welding quality determination circuit 21 is connected via the converter 20.

This welding quality judging circuit 21 compares the level of the potential difference Vs digitally converted and output from the A / D converter 20 with the range of the upper limit and the lower limit set value which is the reference signal DR, and at least on the work 3. It has the function of determining the quality of the welded state.

The welding quality judging circuit 21 is specifically composed of a memory 21a and a microprocessor unit 21b. The memory 21a stores in advance the data of the reference signal DR with respect to the potential difference Vs between the first resistors 13 measured under various welding conditions including the laser output of the laser oscillator 1.

Here, the data of the reference signal DR has a range including, for example, an upper limit setting value and a lower limit setting value, and the upper limit setting value and the lower limit setting value can be arbitrarily changed.

The microprocessor unit 21b is A
Potential difference V digitally converted and output from the / D converter 20
It has a function of comparing the s level with the range of the upper and lower limit setting values which are the reference signal DR, and determining the occurrence of an abnormal beat, for example, a humping beat, when the potential difference Vs level exceeds the range of the reference signal DR every predetermined period. are doing.

Further, the microprocessor unit 21b
Has a function as a laser control means for feedback controlling the laser output of the laser oscillator 1 so that the potential difference Vs level digitally converted and output from the A / D converter 20 falls within the range of the reference signal DR.

Next, the operation of the apparatus configured as described above will be described. When the laser light Lb is emitted from the laser oscillator 1, the laser light Lb is condensed by the condenser lens 2 and is applied to the work 3.

The work 3 is melted by the irradiation of the laser beam Lb, and a part of the work 3 is evaporated to become metal vapor. This metal vapor absorbs the subsequent laser light Lb to generate plasma Pz.

The generation state of this plasma Pz changes depending on the melted state of the work 3, and the resistance and excitation voltage in the plasma space between the work 3 and the electrode 11 (nozzle tip 16) change, and in response to this change. The potential difference Vs generated at both ends of the first resistor 13 connected to the electrode 11 changes.

Therefore, the potential difference Vs generated across the first resistor 13 is output to the differential amplifier 18. Here, each potential of the electrode 11 when the plasma Pz is not generated and when the plasma Pz is generated will be described with reference to FIGS. 3 and 4.

When the plasma Pz is not generated,
Since there is no excitation voltage due to the plasma Pz, it is equivalent to the electric circuit shown in FIG. R13 and R14 are resistance values of the first and second resistors 13 and 14, respectively, and Vc is an output voltage value of the constant voltage power supply 12.

In the electric circuit, the electric potential VE at the point E corresponding to the electric potential of the electrode 11 is a value obtained by dividing the output voltage value Vc of the constant voltage power source 12 by the first and second resistors 13 and 14, It is expressed by the following equation.

VE = {R14 / (R13 + R14)} Vc (1) On the other hand, when the plasma Pz is generated, it is equivalent to the electric circuit shown in FIG. Here, Vp is an excitation voltage generated by the plasma Pz, and Rp is a gap resistance between the work 3 and the electrode 11.

These excitation voltage Vp and gap resistance Rp
Has a value that changes depending on the generation state of the plasma Pz, that is, the melted state of the work 3. In such an electric circuit, the electric potential VE at the point E is represented by VE = IR.R14 (2) IR = (Rp.Vc + R13.Vp) / (R13.R14 + R13.Rp + R14.Rp) (3). IR is a current flowing in or out of the excitation voltage Vc generated by the constant voltage power supply 12 and the plasma Pz. The current IR is obtained using the superposition theorem.

As described above, the potential difference Vs across the first resistor 13, which changes according to the generation state of the plasma Pz, that is, the melted state of the work 3, is amplified by the differential amplifier 18.

FIGS. 5 (a) and 6 (a) show the output signal of the differential amplifier 18, and the welding conditions for bead-on welding to the work 3, that is, laser output, welding speed, defocus, work material. -It was obtained by changing only the laser output of the thickness and the like. The laser output is 3 kW in FIG. 5 (a) and the laser output is 4 kW in FIG. 6 (a).

Low frequency components of the respective output signals of the differential amplifier 18 are extracted by the low pass filter 19, and the respective output signals are output due to the difference in laser output as shown in FIGS. 5B and 6B. The voltages are 6.4V and 9.0V.

That is, as compared with the laser output of 3 kW, the laser output of 4 kW increases the penetration of the work 3, and the metal vapor generated from the work 3, the size of the plasma Pz, the electron density inside the plasma Pz, and the like increase.

As a result, the excitation voltage Vp increases, but
The gap resistance Rp decreases as the electron density increases.
By reducing the gap resistance Rp, the gap resistance R
The combined resistance value of the second resistor R14 connected in parallel with p decreases, and the constant-voltage power supply 12 lowers the potential at point E. As a result, the potential difference Vc across the first resistor R13 increases.

As described above, by monitoring the potential difference Vc generated across the first resistor R13, it is possible to determine the melted state of the work 3, that is, the welding quality. The process of determining the welding quality of the work 3 will be described below.

The output signal of the low-pass filter 19 is A /
The signal is digitally converted by the D converter 20 and becomes an input signal Ds to the microprocessor unit 21b. The microprocessor unit 21b takes in the input signal Ds, and the input signal Ds, that is, the potential difference Vs and the memory 21.
Reference signal DR of predetermined welding condition stored in advance in a
The upper limit and the lower limit set value which are are compared.

FIG. 7 shows these input signal Ds and reference signal DR.
When the input signal Ds is within the range of the upper limit setting value and the lower limit setting value of the reference signal DR, the microprocessor unit 21b determines that the welding quality is good and outputs the welding quality determination signal Sp Output as 0 level.

On the other hand, like the periods T1 and T2,
If the input signal Ds exceeds the range between the upper limit setting value and the lower limit setting value of the reference signal DR, the microprocessor unit 2
1b is "+ (plus)" or "-(minus)" depending on the direction in which the welding quality is poor and the determination signal Sp is exceeded.
Are distinguished and output.

Next, the determination of the occurrence of abnormal welding beat, for example, humping beat will be described. When a humping beat occurs, the molten metal periodically swells in the appearance of the bead, and the periodical difference in the depth of penetration inside the bead also fluctuates, so that the generation state of the plasma Pz becomes unstable.

FIGS. 8A and 8B show signal waveforms observed by the differential amplifier 18 and the low-pass filter 19 when a humping beat occurs. Microprocessor unit 21
In FIG. 8B, when the input signal Ds is fetched, the input signal Ds is compared with the reference signal DR, and the result exceeds the judgment signal Sp every "0" level every predetermined period, that is, FIG. 8 (b). When a rectangular wave signal as shown in is observed, it is determined that a humping beat has occurred.

Next, the laser output control of the laser oscillator 1 will be described. The microprocessor unit 21b is
As shown in FIG. 7, if the input signal Ds is within the range of the upper limit setting value and the lower limit setting value of the reference signal DR, the welding quality determination signal Sp is output as a "0" level, but the input signal Ds is the reference signal. If the range between the upper limit setting value and the lower limit setting value of the signal DR is exceeded, the determination signal Sp is discriminated and output according to the sign of "+ (plus)" or "-(minus)" depending on the direction in which it is exceeded.

In the microprocessor unit 21b, the potential difference Vs level is set to the reference signal D according to the determination signal Sp.
The laser output of the laser oscillator 1 is feedback-controlled so that it falls within the range of R 2.

That is, when the determination signal Sp is "+ (plus)", the microprocessor unit 21b
Reduces the laser output and suppresses the melting of the work 3 so that the signal level of the input signal Ds falls below the upper limit set value of the reference signal DR.

If the determination signal Sp is "-(minus)", the microprocessor unit 21b increases the laser output to increase the penetration of the work 3 and lowers the signal level of the input signal Ds to the lower limit of the reference signal DR. Make sure to exceed the set value.

Therefore, the microprocessor unit 21
b controls the laser output of the laser oscillator 1 by the determination signal Sp so that the signal level of the input signal Ds falls within the range of the upper limit and lower limit set values of the reference signal DR.

As described above, in the above-described embodiment, the plasma generation state generated in the molten portion on the work 3 is monitored, and the potential difference Vs corresponding to the plasma generation state is output, and based on the level of this potential difference Vs. Since the quality of the melted state of the welded part is determined by the judgment, it is not restricted by the welding work environment under adverse conditions, that is, noise other than the welding sound from the laser oscillator 1 around the welded part and its associated equipment. The weld quality of the melted state in the work 3 can be determined with high accuracy online without being affected by the sound.

At this time, since the potential difference Vs corresponding to the changes in the resistance Rp and the excitation voltage Vp in the plasma space between the electrode 11 and the work 3 is output, the changes in the resistance Rp and the excitation voltage Vp in the plasma Pz, that is, A signal corresponding to the melted state of the welded portion can be obtained, and from this, the welding quality can be determined with high accuracy.

Moreover, as the electrode 11, the processing nozzle 15 is used.
On the other hand, since the nozzle tip 16 inserted through the spacer 17 is used, it is not necessary to dispose a sensor or the like around the welded portion, and the welding quality can be determined.

Further, the potential difference Vs corresponding to the plasma generation state
And the reference signal DR are compared, and if the obtained waveform is a rectangular wave, the occurrence of a humping beat can be determined. On the other hand, since the quality of the welded state of the welded portion is determined and the laser output of the laser oscillator 1 is controlled according to the determination result, the welded state on the work 3 can be made uniform online and high quality welding can be performed. .

[0065]

As described above in detail, according to the present invention, it is possible to provide a laser welding quality judging device which can judge the welding quality such as a penetration state online with high accuracy. Further, according to the present invention, it is possible to provide a laser welding quality determination device capable of highly accurately determining a welding quality such as a penetration state online and controlling a laser output according to the determination to make the penetration state uniform.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a laser welding quality determination device according to the present invention.

FIG. 2 is a configuration diagram showing an electrode for obtaining an electric signal according to a plasma generation state.

FIG. 3 is a diagram showing an electric circuit of a plasma monitor when plasma is not generated.

FIG. 4 is a diagram showing an electric circuit of a plasma monitor when plasma is generated.

FIG. 5 is a waveform diagram of an electric signal during plasma monitoring.

FIG. 6 is a waveform diagram of an electric signal during plasma monitoring.

FIG. 7 is a diagram showing a function of determining weld quality in a melted state.

FIG. 8 is a waveform diagram when a humping beat occurs.

FIG. 9 is a block diagram of a conventional device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Laser oscillator, 3 ... Work, 10 ... Plasma monitoring means, 11 ... Electrode, 12 ... Constant voltage power supply, 13 ... 1st resistance, 14 ... 2nd resistance, 16 ... Nozzle chip, 18 ... Differential amplifier, 19 ... Low-pass filter, 20 ... A / D converter, 21 ... Welding quality judgment circuit, 21a ... Memory, 21b
… Microprocessor unit.

Claims (7)

[Claims] 1. A laser welding quality judging device for judging at least a melted state of a welded part when a work is irradiated with a laser beam to perform a welding process. Plasma monitor means for monitoring and outputting an electric signal according to the plasma generation state, and judging means for judging at least whether or not the melted state of the welded portion is good or bad on the basis of the level of the electric signal outputted from the plasma monitor means. A laser-welding quality judging device comprising: 2. A laser welding quality judging device for judging at least a melted state of a welded part when irradiating a work with a laser beam outputted from a laser oscillator and performing welding processing. Plasma monitoring means for monitoring the plasma generation status and outputting an electric signal corresponding to the plasma generation status, and at least whether the melted state of the welded portion is good or bad based on the level of the electric signal output from the plasma monitoring means. A laser welding quality determination device comprising: a determination unit that determines whether or not the laser beam is emitted from the laser oscillator according to a determination result of at least whether the melted state is good or not determined by the determination unit. 3. The plasma monitor means has electrodes arranged on the optical path of laser light above the work, and outputs a voltage signal according to changes in resistance and excitation voltage in the plasma space between the electrodes and the work. The laser welding quality determination device according to claim 1 or 2. 4. The plasma monitor means inserts a nozzle tip into at least a processing nozzle used as a laser beam conduit via an insulator, and changes in resistance and excitation voltage in a plasma space between the nozzle tip and the work. The laser welding quality judging device according to claim 1 or 2, which outputs a voltage signal according to the above. 5. The judging means compares the electric signal level output from the plasma monitoring means with a range of upper and lower limit set values which are reference signals, and judges at least whether or not the melted state of the welded portion is good or bad. Claim 1 or 2
The laser welding quality determination device described. 6. The judging means compares the electric signal level output from the plasma monitoring means with a range of upper and lower limit set values which are reference signals, and the electric signal level is within the range of the reference signal at predetermined intervals. 3. The laser welding quality judging device according to claim 1, wherein the occurrence of an abnormal beat is judged when it exceeds. 7. The laser according to claim 2, wherein the laser control means feedback-controls the laser output of the laser oscillator so that the electric signal level output from the plasma monitor means falls within the range of the reference signal. Welding quality judgment device.