In-situ real-time monitoring method for protection state of laser welding pool

Abstract

The invention provides an in-situ real-time monitoring method for the protection state of a laser welding pool, and belongs to the technical field of laser material processing.According to the in-situ real-time monitoring method for the protection state of the laser welding pool, the reflection light intensity of detection laser is monitored in real time in the welding process according to the difference of the surface protection states of different laser welding pool on the absorption rate of the detection laser; and the protection state of the surface of the molten pool is identified by comparing the change of the output voltage signal of the detection laser caused by the reflected laser. In the laser welding process, the detection laser beam acts on the surface of the molten pool, the change of the protective effect of the protective gas flow on the molten pool causes different oxidation degrees of the surface of the molten pool, the reflected laser intensity has obvious difference, and the protective effect of the protective gas on the molten pool is monitored by detecting the change of the reflected laser intensity. According to the in-situ real-time monitoring method for the protection state of the laser welding pool, the protection effect of the protection airflow on the molten pool can be rapidly monitored in situ in real time.

Description

Technical Field

[0001] The invention relates to the technical field of laser material processing, and in particular to an in-situ real-time monitoring method for the protection state of a laser welding molten pool. Background Art

[0002] Laser welding technology, with its advantages of fast welding speed, high efficiency, small deformation, large weld depth-to-width ratio and high degree of automation, has shown great application potential in a variety of fields such as aerospace, rail transportation, and automobile manufacturing. However, laser welding often encounters problems such as excessive spatter, violent keyhole fluctuations, weld humps, and incomplete penetration, which seriously restrict the improvement of the quality of welded joints.

[0003] To solve the above problems, an additional shielding gas flow is widely used in laser welding process in order to reduce welding defects and improve welding quality. However, the different protective effects of the shielding gas flow on the molten pool will directly lead to significant differences in welding quality. When the protection effect is not good, the weld may face problems such as oxidation corrosion and severe spatter, which seriously hinders the further development of laser welding technology. Therefore, in-depth research on the protective effect of the shielding gas flow on the molten pool is of vital importance to improving the quality of welded joints and optimizing welding processes.

[0004] Although the online monitoring technology of laser welding process has developed rapidly, covering a variety of monitoring methods such as photoelectric, visual, spectral, acoustic, etc., there is a relative lack of monitoring methods for the protective effect of shielding gas flow on the molten pool. Traditional direct observation methods (such as visual method and microscope method) have limitations such as poor timeliness and low quantification, and cannot achieve real-time and in-situ monitoring of the protective effect of shielding gas flow.

[0005] In order to overcome the shortcomings of the existing methods, the present invention proposes an in-situ real-time monitoring method for the protection status of the laser welding molten pool. The method uses the laser emitted by the detection laser to directly act on the surface of the molten pool, and acts as both the transmitting end and the receiving end. The change in the protective effect of the protective gas flow on the molten pool will directly affect the degree of oxidation on the surface of the molten pool, thereby changing the intensity of the reflected laser. The difference in the intensity of the reflected laser will cause the formation of a new resonance in the detection laser cavity and lead to changes in the output voltage signal of the detection laser. By accurately measuring the changes in the voltage signal of the detection laser, the protective effect of the protective gas flow on the molten pool can be monitored in real time. Summary of the invention

[0006] The purpose of the present invention is to provide an in-situ real-time monitoring method for the protection state of a laser welding molten pool, based on the principle of differences in the absorption rate of a detection laser by the molten pool surface under different protection states. Monitoring is performed by emitting a detection laser to the surface of the laser welding molten pool, and analyzing the changes in the output voltage signal of the detection laser caused by the difference in the intensity of the reflected light of the detection laser on the molten pool surface. This method can accurately identify the specific protection state of the molten pool surface, and then monitor the effective protection of the protective gas flow on the welding molten pool in real time and accurately during the actual welding process. Compared with traditional monitoring methods, this method achieves the three advantages of in-situ monitoring, real-time feedback and high-precision measurement.

[0007] To achieve the above object, the present invention provides an in-situ real-time monitoring method for the protection state of a laser welding molten pool, comprising the following steps: Step S1, while the welding laser emits a welding laser beam to perform a welding operation on the welding plate, the shielding air flow nozzle is started to spray a shielding air flow; Step S2, the detection laser acts as both a transmitting end and a receiving end. The detection laser beam emitted by the detection laser acts on the surface of the welding pool through the protective airflow. After the reflected light is received in the detection laser cavity, a new resonance is formed and a photoelectric signal conversion is performed. After the signal passes through the signal amplifier, it is collected by the data acquisition card and then processed by the Matlab software to obtain a measurement signal voltage diagram; Step S3, close the protective air flow nozzle, the detection laser emitted by the detection laser directly acts on the surface of the welding pool, and the detection laser cavity receives the reflected light to form a new resonance, and performs photoelectric signal conversion. After the signal passes through the signal amplifier, it is collected by the data acquisition card and then processed by Matlab software to obtain a measurement signal voltage diagram; Step S4: By comparing the measured voltage signal diagrams obtained in step S2 and step S3, the protective effect of the protective airflow on the molten pool is obtained.

[0008] Preferably, the distance between the focus of the detection laser beam and the focus of the welding laser beam is 0.5-10 mm; and the angle between the detection laser beam and the welding laser beam is 10-90°.

[0009] Preferably, the angle between the scanning direction of the detection laser beam and the welding laser beam is 0-180°.

[0010] Preferably, the wavelength of the detection laser beam is 0.1-20 μm; the diameter of the detection laser beam is 0.1-10 mm.

[0011] Preferably, the output power of the detection laser is 0.01 mW to 50 W.

[0012] Preferably, the welding laser is a fiber laser, a Nd:YAG laser, a disk laser, a blue laser, a green laser, a semiconductor laser or a CO2 Any one of the lasers; the output power of the welding laser is 0.5 to 100 kW.

[0013] Therefore, the present invention adopts the above-mentioned in-situ real-time monitoring method of the protection state of the laser welding molten pool, and the beneficial technical effects are as follows: (1) The present invention can monitor the protective effect of the shielding gas flow on the molten pool in real time during laser welding, thereby solving the problem that the existing method cannot realize the in-situ real-time monitoring of the protective effect of the shielding gas flow on the molten pool during laser welding.

[0014] (2) The present invention has the advantages of simple system structure, small size, easy adjustment, no need for external interference, no influence of detection laser power fluctuation, and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the experimental method for in-situ real-time monitoring of the protection status of the laser welding molten pool; Figure 2 A graph of the voltage of the measurement signal generated by laser welding in an inert shielding gas; Figure 3 This is a graph of the measured signal voltage generated by laser welding in air.

[0016] Reference numerals 1. Detection laser power supply; 2. Detection laser; 3. Detection laser beam; 4. Welding laser beam; 5. Protective airflow nozzle; 6. Protective airflow; 7. Welding plate; 8. Computer; 9. Data acquisition card; 10. Signal amplifier; 11. Welding laser. DETAILED DESCRIPTION

[0017] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0018] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0019] Embodiment 1 like Figure 1 As shown, it is a schematic diagram of an experimental method for in-situ real-time monitoring of the protection state of the laser welding molten pool. A welding laser 11 is arranged directly above the welding plate 7, and the welding laser 11 emits a welding laser beam 4 to the welding plate 7. A detection laser 2 is arranged on one side of the welding laser 11, and the detection laser 2 emits a detection laser beam 3 to the welding plate 7. The detection laser 2 is connected to a detection laser power supply 1, and the detection laser 2 is also connected to a signal amplifier 10, a data acquisition card 9, and a computer 8 in sequence.

[0020] A shielding gas flow nozzle 5 is provided on one side of the intersection of the welding laser beam 4 and the welding plate 7 , and the shielding gas flow nozzle 5 sprays a shielding gas flow 6 .

[0021] In this example, the welding laser 11 uses a YLS-6000 fiber laser, the welding plate 7 is a 10 mm thick low carbon steel that has been ground and polished, and the processing parameters are: welding speed 2m / min, laser power 3kW, spot diameter 1.06mm, and the spot acts on the surface of the welding plate 7. The wavelength of the detection laser beam 3 is 639nm, which is focused by a lens with a focal length of 100mm, and the laser power is 500mW.

[0022] The detection laser beam 3 acts on the surface of the molten pool. When there is a protective gas flow, there is no oxidation on the surface of the molten pool. At this time, the molten pool surface absorbs less detection laser, the reflected laser intensity is larger, and the detection laser voltage signal is stronger. After the protective gas protection is stopped, the molten pool surface is oxidized, the molten pool absorbs more detection laser, and the intensity of the feedback detection laser is weakened, so that the detection laser voltage signal is weakened.

[0023] During the welding process, the protective gas flow protection is first carried out, and then the protective gas flow protection is stopped. The National Instruments model 6251 data acquisition card 9 is used to collect and store the signal, and the signal is processed using Matlab software to obtain the voltage spectrum diagrams in the inert protective gas atmosphere and the air atmosphere, respectively, as shown in FIG. Figure 2 and 3 As shown in the figure, it can be seen that when welding in an argon atmosphere, the voltage signal is relatively dense, with a peak value of about 11V, while when welding in an air atmosphere, the voltage signal is relatively sparse, with a peak value of only about 5V. By reading the difference between different voltage signals, the protective effect of the protective airflow on the molten pool can be monitored in real time on-site.

[0024] It is worth noting that the contents not elaborated in detail in the present invention are all prior art and are well known to those skilled in the art.

[0025] Therefore, the present invention adopts the above-mentioned in-situ real-time monitoring method of the protection status of the laser welding molten pool, which can quickly, in-situ and in real time monitor the protection effect of the protective gas flow on the molten pool.

[0026] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for in-situ real-time monitoring of the protection state of a laser welding molten pool, characterized in that: The following steps are involved: Step S1, while the welding laser emits a welding laser beam to perform a welding operation on the welding plate, the shielding air flow nozzle is started to spray a shielding air flow; Step S2, the detection laser acts as both a transmitting end and a receiving end. The detection laser beam emitted by the detection laser acts on the surface of the welding pool through the protective airflow. After the reflected light is received in the detection laser cavity, a new resonance is formed and a photoelectric signal conversion is performed. After the signal passes through the signal amplifier, it is collected by the data acquisition card and then processed by the Matlab software to obtain a measurement signal voltage diagram; Step S3, close the protective air flow nozzle, the detection laser emitted by the detection laser directly acts on the surface of the welding pool, and the detection laser cavity receives the reflected light to form a new resonance, and performs photoelectric signal conversion. After the signal passes through the signal amplifier, it is collected by the data acquisition card and then processed by Matlab software to obtain a measurement signal voltage diagram; Step S4: By comparing the measured voltage signal diagrams obtained in step S2 and step S3, the protective effect of the protective airflow on the molten pool is obtained.

2. The in-situ real-time monitoring method of the protection state of the laser welding molten pool according to claim 1 is characterized in that: The distance between the focus of the detection laser beam and the focus of the welding laser beam is 0.5~10mm; the angle between the detection laser beam and the welding laser beam is 10~90°.

3. The in-situ real-time monitoring method of the protection state of the laser welding molten pool according to claim 2 is characterized in that: The angle between the scanning direction of the detection laser beam and the welding laser beam is 0~180°.

4. The in-situ real-time monitoring method of the protection state of the laser welding molten pool according to claim 3 is characterized in that: The wavelength of the detection laser beam is 0.1 to 20 μm; the diameter of the detection laser beam is 0.1 to 10 mm.

5. The in-situ real-time monitoring method of the protection state of the laser welding molten pool according to claim 4 is characterized in that: The output power of the detection laser is 0.01mW~50W.

6. The in-situ real-time monitoring method of the laser welding molten pool protection state according to claim 5, characterized in that: The welding laser is any one of a fiber laser, a Nd:YAG laser, a disk laser, a blue laser, a green laser, a semiconductor laser or a CO2 laser; the output power of the welding laser is 0.5 to 100 kW.

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