JPH04361889A - Method and device for monitoring laser welding - Google Patents

Abstract

PURPOSE:To accurately detect penetration depth and laser output in the course of laser welding by utilizing the light emission of a welding part. CONSTITUTION:The light of the welding part which is welded by a laser beam is transmitted through an optical fiber 5 for monitoring, the transmitted light is branched into three beams of light with each different wavelength range by reflection filters 13a, 13b, 13c, and each branched beam of light is inputted in detectors 6a, 6b, 6c through interference filters 14a, 14b, 14c. A light component emitted from a molten metal is made incident on the detectors 6a, 6b, and a light beam with a laser wavelength is made incident on the detector 6c. When the laser output is a base, the values of the detectors 6a, 6b are taken in to discriminate the penetration depth, and when the laser output is at a peak, the value of the detector 6c is taken in to discriminate the laser output.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser welding monitoring method and apparatus for monitoring the condition of a welded part (penetration depth and applied laser power) during welding using laser light.

0002

2. Description of the Related Art In recent years, welding has been performed using laser light emitted from a laser oscillator. Similarly, in laser welding, in order to ensure the quality of welding, it is necessary to monitor the welding situation and always take appropriate measures. The output of a laser oscillator can be monitored by branching the laser beam, but problems may occur in the optical transmission system that guides the laser beam to the welding area, resulting in increased transmission loss.
Monitoring accurate welding inputs is difficult.

[0003] From this point of view, a method of directly observing the welded portion has been proposed. That is, when laser welding is performed, laser plasma is generated in the welded part of the welded material and emits light, so there is a method of monitoring the penetration depth and the actual laser output value by observing the state of this light emission. That is, as shown in FIG.
When the material to be welded 03 is irradiated with a focus of 2, laser plasma 05 is generated from the welding part 04. This laser plasma 05
The light emission intensity is extracted and detected by a detector 07 via a filter 06 to monitor the penetration depth and laser output value. (Literature name E. Bey
er et al. :On-line plasma
diagnostics for process-
control in welding with C
O2 lasers, SPIE vol. 1020
p. 142). However, laser plasma is unstable due to heating due to laser beam absorption and the influence of atmospheric gas (see FIG. 12). Therefore, it is not practical to monitor the welding status from the emission intensity of laser plasma.

[0004] From this point of view, the applicant first
We proposed monitoring the penetration depth of the weld and the actual welding input from the luminescence intensity of the molten pool (Patent Application No. 2-607).
issue). That is, in FIG. 11, light from the weld is transmitted through a monitoring optical fiber 010, the transmitted light is branched into three by a multi-branch (three branches in this example) optical fiber 011, and each branched light is filtered through interference filters 012a, 012b. ,01
Detector (photodiode) 07a through 2c,
I tried to import it into 07b and 07c. Each interference filter 012a, 012b, 012c has a specific wavelength (λ1, λ
Since only the light of wavelengths 2, λ3) is allowed to pass through, various disturbance lights are excluded, and each detector 07a, 07b, 07c detects the light intensity of a specific wavelength. In such a configuration,
The welding status is monitored by detecting the intensity of light of a selected specific wavelength among the light emitted from the molten pool immediately after the welding laser light is interrupted.

[0005]

[Problem to be solved by the invention] However, FIG.
As shown in FIG. 2, in the technique using a multi-branch optical fiber 011, each detector 07a, 07b,
Since the amount of light entering 07c decreases in inverse proportion to the number of branches, there remains the problem that detection accuracy decreases depending on the scale of welding.

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, it is an object of the present invention to provide a laser welding monitoring method and apparatus that can accurately monitor penetration depth and actual welding input by laser light.

[0007]

[Means for Solving the Problems] The present invention, which solves the above-mentioned problems, makes a pulsed laser beam enter a welding part of a material to be welded, extracts the light from the welding part during welding, and transmits it. Split the light into multiple lights with different wavelength ranges, extract only the necessary wavelength from each branched light with different wavelength ranges, and melt the split/extracted light when the laser oscillator is at base output. The penetration depth is determined by detecting the intensity of the light at the wavelength emitted from the metal, and when the laser oscillator is at its peak output, the intensity of the light at the same wavelength as the laser oscillator's wavelength is determined when the laser oscillator is at its peak output. The method is characterized in that the actual input value of the laser beam is determined by detecting.

[0008]

[Operation] In the present invention, the light from the welding part is split into lights with different wavelength ranges by a reflection filter, each branched light is passed through an interference filter to extract the light of the necessary wavelength, and the intensity of the extracted light is detected by a detector. Detect with. This detection detects the intensity of light at the same wavelength as the laser beam when the laser beam is at its base output, and when the laser beam is at its peak output. Detect intensity.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an embodiment of the invention. In the figure, the laser oscillator 1 is a YAG laser with a wavelength of 1.06 μm.
The laser beam is outputted in a pulsed manner (see Fig. 5). This laser light is focused by an input optical system 2, enters a laser transmission optical fiber 3, is transmitted, and reaches a welding head 11 via a coupling optical system 4. The laser beam is then refocused by an optical system built into the welding head 11 and used for welding. When the laser beam has a peak output, laser plasma is generated and emits light, and when the laser beam has a base output (zero watts), the laser plasma disappears and only the light emitted from the molten pool can be observed. This light is taken into the monitoring optical fiber 5 by an optical system built into the welding head 11 and transmitted, and reaches the detector section 6.

The detector section 6 includes an optical system as shown in FIG. 2 in addition to detectors 6a, 6b, 6c made of photodiodes and an amplifier 7. That is, as shown in FIG. 2, the light emitted from the monitoring optical fiber 5 is
The collimating lens 12 converts the light into parallel light, which then travels to reflection filters 13a, 13b, and 13c. Detector 6a, 6
b, 6c are interference filters 14a, 14b, 1, respectively.
4c and condensing lenses 15a, 15b, 15c in between, they are diagonally opposed to the reflection filters 13a, 13b, 13c.

At this time (a) the reflection filter 13a has a wavelength of 0.85 μm.
The interference filter 14a reflects light with a wavelength of 0.8 μm or more and transmits light with a wavelength of 0.8 μm or more (characteristics are shown in FIG. 3).
(characteristics are shown in Figure 4). (b) The reflection filter 13b has a wavelength of 0.99 μm.
The interference filter 14b reflects light with a wavelength of 0.94 μm and transmits light with a wavelength of 0.94 μm. (c) The reflection filter 13c has a wavelength of 1.11 μm.
The interference filter 14c reflects light with a wavelength of 1.06 μm or more, and transmits light with a wavelength of 1.06 μm.

For this reason, the detector 6a is equipped with a condensing lens 1.
0.8 μm light enters the detector 6b through the detector 5a.
0.94 μm light is incident on the detector 6c via the condenser lens 15b, and 1.94 μm light is incident on the detector 6c via the condenser lens 15c.
06 μm light is incident. As shown in FIG. 5, in period A in which the laser beam is at the base output (output 0 W), data from the detectors 6a and 6b that detect light of 0.8 μm and 0.94 μm is captured. 0.8 μm and 0.9
The 4 μm light is a component contained in the light generated from the molten pool when the laser plasma disappears. In this example, out of the light generated from the molten pool, 0.8 μm and 0.94 μm
We are monitoring light with a wavelength of 0.4 to 1.0.
It is sufficient to detect light having an arbitrary wavelength component among wavelengths between μm. This is because when an inexpensive commercially available silicon photodiode is used as a detector, its sensitivity range is about 0.4 to 1.0 μm, and in particular, the spectral sensitivity of this diode is 0.8 to 1.0 μm. This is because sufficient detection sensitivity can be obtained. On the other hand, during the B period when the laser beam is at its peak output (output 1250 W), data from the detector 6c that detects the 1.06 μm light is taken in. The 1.06 μm light is transmitted by laser oscillator 1.
This is the wavelength of the laser light output from the

Referring back to FIG. 1, the detectors 6a,
The electrical output signal corresponding to the intensity of the light taken in from 6b and 6c is amplified by an amplifier 7 and sent to A through a monitor signal line 8.
The signal is transmitted to the /D conversion board 9, where it is converted into a digital signal and then input to the personal computer 10.

The personal computer 10 exhibits a light component generated from melting light when the laser plasma is extinguished.
The penetration depth is determined based on the data output from the detectors 6a and 6b (data for period A). Further, the personal computer 10 determines the usage efficiency of the laser beam based on the data output from the detector 6c (data for period B) indicating the laser beam component when laser plasma is generated. Usage efficiency indicates how much laser light output is actually output from the welding head 11 and contributes to welding compared to the laser light output output from the laser oscillator 1.

In the embodiments shown in FIGS. 1 and 2, the laser beam is the base output (period A in FIG. 5), and the light emitted from the molten metal is captured when there is no influence from the generation of laser plasma. Therefore, information that accurately reflects the penetration depth can be obtained based on the luminescence data at this time. Also,
Since the light of the wavelength component (1.06 μm) of the laser light is extracted when the laser light is at its peak output (period B in Figure 5) and laser plasma is generated, the light emission data at this time is Based on this, the usage efficiency of laser light can be determined accurately.

Furthermore, as shown in FIG. 2, since reflection filters 13a, 13b, and 13c are used to reflect light in a specific wavelength range, compared to the conventional technology using a multi-branch optical fiber 011 shown in FIG. The optical loss until the light enters the detector can be significantly reduced. In other words, in FIG. 2, most of the light component with a wavelength of 0.8 μm is incident on the detector 6a, but in the conventional FIG. The light is incident on the detector 07a.

FIG. 6 shows a specific application example of the embodiment of the present invention, and in this specific example, the heat exchanger tube 1 of the heat exchanger is
The sleeve 18 is attached to the damaged part of the tube 7 from the inner side, and the sleeve 18 and the heat transfer tube 17 are overlap-welded from the inner side of the sleeve. In this example, the sleeve diameter is approximately 18 mm, and welding is performed in a narrow space, and the welding environment is also a radiation atmosphere, so it is necessary to remotely monitor the welding state during welding.

In FIG. 6, a high-power laser beam used for welding is emitted from a YAG laser oscillator 1, transmitted through an optical fiber 3 (about 220 m in length), and guided to a welding head 11 on the inner surface of a sleeve 18. Used for welding from the inside of the sleeve. The welding head 11 is provided with an optical system such as a condensing lens system 16. When welding is being performed, light generated from the welding part is transmitted through the monitoring optical fiber 5, detected by the detector 6, and monitored and judged by the personal computer 10.

FIG. 7 shows the results of monitoring by this system when welding was actually performed properly. The horizontal axis of the graph represents the welding time, and the vertical axis represents the molten pool light emission intensity and the YAG laser reflected light intensity. Welding was performed by pulse welding with an average laser output of 625 W (base output: 0 W, peak output: 1250 W, duty 50%, pulse frequency;
42 Hz), and the welding speed was 0.6 m/min. Monitoring was carried out by sampling two wavelengths of λ = 0.8 μm and 0.94 μm in the light emitted from the welding pool at the base output, and sampling λ = 1.06 μm, which is the YAG laser reflected light, at the peak output. This is a plot of it.

As in this embodiment, throughout the welding time,
When the molten pool luminescence intensity is stable and a constant value is obtained, the penetration depth is also stable and at the same time the welding phenomenon is stable.

FIGS. 8 and 9 show the effects of this embodiment. Figure 8 shows the emitted light of the molten pool, λ = 0.8 μm, λ =
The light emission intensity for a laser output of 0.94 μm is summarized. According to this, λ=0.8μm, 0.94
By monitoring the μm emission light, the actual laser power applied to the material can be determined.

In FIG. 8, a conventional welding monitor, that is, FIG.
Compared to the extraction of emitted light using the three-branch type optical fiber 011 shown in FIG.

[0023] Through this monitoring, as shown in Fig. 9, it was confirmed that the lap welding of the heat exchanger tube and the sleeve part was carried out stably at any cross section, and welding stability could be confirmed in the welding in-process. This was effective for quality control.

[0024]

[Effects of the Invention] As specifically explained above in conjunction with the embodiments, according to the present invention, the light transmitted from the welding part can be
With multiple reflective filters that reflect light in specific wavelength ranges,
Since it branches into multiple lights with different wavelength ranges, compared to conventional technology that uses multi-branch optical fibers to split light, it can significantly reduce optical loss until the light of a specific wavelength enters the detector. . Therefore, detection accuracy is improved.

Furthermore, since the emission from the molten metal is captured when the laser beam is at its base output and is not affected by the generation of laser plasma, the penetration depth can be estimated based on the emission data at this time. You can obtain accurately reflected information. In addition, since the wavelength component of the laser beam is extracted when the laser beam is at its peak output and laser plasma is generated, based on the emission data at this time,
The intensity of the laser light that is actually being irradiated can be accurately determined.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a configuration diagram showing an optical system of a detector section according to an embodiment.

FIG. 3 is a characteristic diagram showing reflection/transmission characteristics of a reflection filter.

FIG. 4 is a characteristic diagram showing the transmission characteristics of an interference filter.

FIG. 5 is an explanatory diagram showing the timing of laser oscillation and sampling.

FIG. 6 is a configuration diagram showing a specific application example of the embodiment.

FIG. 7 is a characteristic diagram showing monitoring results according to the present invention.

FIG. 8 is a characteristic diagram showing the relationship between welding input power and monitoring emission intensity.

FIG. 9 is a characteristic diagram showing the results of proper welding through monitoring.

FIG. 10 is a configuration diagram showing a prior art.

FIG. 11 is a configuration diagram showing a transmission system of a previously filed welding monitoring device.

FIG. 12 is a characteristic diagram showing the state of laser plasma generation.

[Explanation of symbols]

1 Laser oscillator 2　Incidence optical system 3. Optical fiber for laser transmission 4 Coupling optical system 5 Optical fiber for monitoring 6 Detector section 6a, 6b, 6c Detector 7 Amplifier 8 Monitor signal line 9 A/D conversion board 10 Personal computer 11 Welding head 12 Collimating lens

Claims (2)

[Claims] Claim 1: A pulsed laser beam from a laser oscillator is irradiated onto a welding part of a material to be welded, the light from the welding part during welding is extracted and transmitted, and the transmitted light has the same wavelength as the laser beam. branching into a plurality of lights with different wavelength ranges, and extracting only the light of the necessary wavelength from each branched light with different wavelength ranges, and when the laser oscillator is at base output, the split/extracted light is The penetration depth is determined by detecting the intensity of the light with the same wavelength emitted from the molten metal, and when the laser oscillator is at its peak output, the intensity of the branched/extracted light with the same wavelength as the laser beam is detected. A method for monitoring laser welding, comprising: determining an actual input value of a laser beam. [Claim 2] Light emitted from the welding part during welding is incident near the output end of a laser transmission optical fiber that transmits the pulsed laser light oscillated and outputted by a laser oscillator to the vicinity of the welding part of the material to be welded. A monitoring optical fiber is arranged as shown in FIG. branching/extracting means for individually passing the light of the wavelength through an interference filter that passes only the light of the wavelength, and detecting the intensity of the light of the wavelength emitted from the molten metal among the branched/extracted light when the laser oscillator is at base output. Judgment that determines the penetration depth and, when the laser oscillator is at its peak output, detects the intensity of light with the same wavelength as the laser light wavelength among the branched and extracted light to determine the laser light output value. A laser welding monitoring device comprising: means.