An in-situ real-time monitoring method for the protection state of a laser welding molten pool

Abstract

The present invention provides an in-situ real-time monitoring method for the protection state of a laser welding molten pool, belonging to the technical field of laser material processing. The present invention utilizes the difference in the absorption rate of the probing laser by different protection states of the laser welding molten pool surface, and in real-time monitors the reflected light intensity of the probing laser during the welding process. By comparing the change in the output voltage signal of the probing laser caused by the reflected laser, the protection state of the molten pool surface is identified. During the laser welding process, the probing laser beam acts on the molten pool surface. The change in the protection effect of the protective gas flow on the molten pool will result in different oxidation degrees of the molten pool surface, causing an obvious difference in the reflected laser intensity. The protection effect of the protective gas on the molten pool is monitored by the change in the reflected light intensity of the probing laser. By adopting the above in-situ real-time monitoring method for the protection state of a laser welding molten pool, the present invention can quickly, in-situ and real-time monitor the protection effect of the protective gas flow on the molten pool.

Description

Technical Field

[0001] The present 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 high welding speed, high efficiency, small deformation, large depth-to-width ratio of the weld seam, and high degree of automation, shows great application potential in many fields such as aerospace, rail transit, and automobile manufacturing. However, problems such as excessive spatter, severe fluctuation of the keyhole, weld bead hump, and incomplete penetration often occur during the laser welding process, which seriously restricts the improvement of the quality of the welded joint.

[0003] To solve the above problems, an external protective gas flow is widely used in the laser welding process in order to reduce welding defects and improve welding quality. However, different protection effects of the protective gas flow on the molten pool will directly lead to significant differences in welding quality. When the protection effect is poor, the weld seam 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 protection effect of the protective gas flow on the molten pool is of crucial significance for improving the quality of the welded joint and optimizing the welding process.

[0004] Although the current online monitoring technology for the laser welding process has developed rapidly, covering various monitoring methods such as optoelectronic, visual, spectral, and acoustic, the monitoring methods for the protection effect of the protective gas flow on the molten pool are relatively scarce. Traditional direct observation methods (such as visual method and microscope method) have limitations such as poor timeliness and low quantification degree, and cannot achieve real-time and in-situ monitoring of the protection effect of the protective gas flow.

[0005] To overcome the deficiencies of the existing methods, the present invention proposes an in-situ real-time monitoring method for the protection state of a laser welding molten pool. This method uses the laser emitted by the detection laser to directly act on the surface of the molten pool, serving as both the transmitting end and the receiving end at the same time. The change in the protection effect of the protective gas flow on the molten pool will directly affect the degree of oxidation of the molten pool surface, and thus change 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 a change in the output voltage signal of the detection laser. By accurately measuring the change in the voltage signal of the detection laser, the protection effect of the protective gas flow on the molten pool can be monitored in real time. Summary of the Invention

[0006] The object 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 the difference in the absorption rate of the probing laser by the molten pool surface under different protection states. By emitting a probing laser to the surface of the laser welding molten pool and analyzing the change in the output voltage signal of the probing laser caused by the difference in the reflected light intensity on the molten pool surface, the monitoring is implemented. This method can accurately identify the specific protection state of the molten pool surface, and thus monitor the effective protection effect of the protective gas flow on the welding molten pool in real time and accurately during the actual welding process. Compared with the traditional monitoring means, this method realizes the three major 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:

[0008] Step S1, while the welding laser emits a welding laser beam to perform welding operations on the welding plate, start the protective gas nozzle to spray the protective gas;

[0009] Step S2, the probing laser serves as both the emitting end and the receiving end. The emitted probing laser beam acts on the surface of the welding molten pool through the protective gas. After the reflected light is received in the probing laser cavity to form a new resonance, photoelectric signal conversion is performed. After the signal is amplified by 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;

[0010] Step S3, close the protective gas nozzle. The probing laser beam emitted by the probing laser directly acts on the surface of the welding molten pool. After the reflected light is received in the probing laser cavity to form a new resonance, photoelectric signal conversion is performed. After the signal is amplified by 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;

[0011] Step S4, by comparing the measurement voltage signal diagrams obtained in Step S2 and Step S3, obtain the protection effect of the protective gas on the molten pool.

[0012] Preferably, the distance between the focus of the probing laser beam and the focus of the welding laser beam is 0.5 to 10 mm; the angle between the probing laser beam and the welding laser beam is 10 to 90°.

[0013] Preferably, the angle between the scanning direction of the probing laser beam and the welding laser beam is 0 to 180°.

[0014] Preferably, the wavelength of the probing laser beam is 0.1 to 20 μm; the diameter of the probing laser beam is 0.1 to 10 mm.

[0015] Preferably, the output power of the probing laser is 0.01 mW to 50 W.

[0016] Preferably, 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.

[0017] Therefore, the present invention adopts the above-mentioned in-situ real-time monitoring method for the protection state of the laser welding molten pool, and the beneficial technical effects are as follows:

[0018] (1) The present invention can in-situ real-time monitor the protection effect of the shielding gas on the molten pool during the laser welding process, and solves the problem that the existing methods cannot achieve the in-situ real-time monitoring of the protection effect of the shielding gas on the molten pool during the laser welding process.

[0019] (2) The present invention has the advantages of simple system structure, small volume, easy adjustment, no need for external interference, not affected by the fluctuation of the power of the detection laser, low cost, etc. Description of the Drawings

[0020] Figure 1 Schematic diagram of the experimental method for in-situ real-time monitoring of the protection state of the laser welding molten pool;

[0021] Figure 2 Measurement signal voltage diagram generated during laser welding in an inert shielding gas;

[0022] Figure 3 Measurement signal voltage diagram generated during laser welding in air.

[0023] Reference Signs

[0024] 1. Detection laser power supply; 2. Detection laser; 3. Detection laser beam; 4. Welding laser beam; 5. Shielding gas nozzle; 6. Shielding gas; 7. Welding plate; 8. Computer; 9. Data acquisition card; 10. Signal amplifier; 11. Welding laser. Detailed Embodiments

[0025] The technical solutions of the present invention will be further described below with reference to the drawings and embodiments.

[0026] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those of ordinary skill in the art to which the present invention belongs.

[0027] Example 1

[0028] As Figure 1As shown in the figure, it is a schematic diagram of an experimental method for in-situ real-time monitoring of the protection state of a laser welding molten pool. A welding laser 11 is arranged directly above the welding plate 7. The welding laser 11 emits a welding laser beam 4 towards the welding plate 7. A detection laser 2 is arranged on one side of the welding laser 11. The detection laser 2 emits a detection laser beam 3 towards the welding plate 7. The detection laser 2 is connected to a detection laser power supply 1, and the detection laser 2 is also sequentially connected to a signal amplifier 10, a data acquisition card 9, and a computer 8.

[0029] A protective gas nozzle 5 is arranged on one side of the intersection of the welding laser beam 4 and the welding plate 7. The protective gas nozzle 5 sprays a protective gas 6.

[0030] In this example, the welding laser 11 uses a YLS-6000 fiber laser. The welding plate 7 is low-carbon steel with a thickness of 10 mm and is ground and polished. The processing parameters are: welding speed 2 m / min, laser power 3 kW, spot diameter 1.06 mm, and the spot acts on the surface of the welding plate 7. The wavelength of the detection laser beam 3 is 639 nm, is focused by a lens with a focal length of 100 mm, and the laser power is 500 mW.

[0031] The detection laser beam 3 acts on the surface of the molten pool. When there is protection by the protective gas, there is no oxidation on the surface of the molten pool. At this time, the absorption of the detection laser by the surface of the molten pool is less, the intensity of the reflected laser is greater, and the voltage signal of the detection laser is stronger. After stopping the protection of the protective gas, oxidation occurs on the surface of the molten pool, the absorption of the detection laser by the molten pool increases, the intensity of the detected laser feedback decreases, and the voltage signal of the detection laser decreases.

[0032] During the welding process, first, the protective gas is used for protection, and then the protection of the protective gas is stopped. The data acquisition card 9 of the model 6251 of National Instruments is used to collect and store signals, and the Matlab software is used for signal processing to obtain the voltage spectrograms in an inert protective gas atmosphere and an air atmosphere respectively, as shown in Figure 2 and 3 shown. It can be seen that when welding in an argon atmosphere, the voltage signals are relatively dense, and the peak value is about 11 V. When welding in an air atmosphere, the voltage signals are relatively sparse, and the peak value of the voltage signal is only about 5 V. By reading the differences in different voltage signals, the protection effect of the protective gas on the molten pool can be monitored in-situ and real-time.

[0033] It should be noted that the content not elaborated in detail in the present invention is the prior art and is well-known to those skilled in the art.

[0034] Therefore, by adopting the above-mentioned method for in-situ real-time monitoring of the protection state of a laser welding molten pool, the present invention can quickly, in-situ, and real-time monitor the protection effect of the protective gas on the molten pool.

[0035] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. An in-situ real-time monitoring method for the protection state of a laser welding molten pool, characterized in that, It includes the following steps: Step S1: While the welding laser emits a welding laser beam to perform welding operations on the welding plate, start the protective gas nozzle to spray the protective gas; Step S2: The detection laser, which acts as both a transmitting end and a receiving end, emits a detection laser beam that acts on the surface of the welding molten pool through the protective gas. After receiving the reflected light in the detection laser cavity, a new resonance is formed, and 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 Matlab software to obtain the measured signal voltage diagram; Step S3: Close the protective gas nozzle. The detection laser beam emitted by the detection laser directly acts on the surface of the welding molten pool. After receiving the reflected light in the detection laser cavity, a new resonance is formed, and 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 Matlab software to obtain the measured signal voltage diagram; Step S4: By comparing the measured voltage signal diagrams obtained in Step S2 and Step S3, the protection effect of the protective gas on the molten pool is obtained; The distance between the focus of the detection laser beam and the focus of the welding laser beam is 0.5 to 10 mm; the angle between the detection laser beam and the welding laser beam is 10 to 90°; The angle between the detection laser beam and the scanning direction of the welding laser beam is 0 to 180°.

2. The in-situ real-time monitoring method for the protection state of a laser welding molten pool according to claim 1, wherein, 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.

3. The in-situ real-time monitoring method for the protection state of a laser welding molten pool according to claim 1, characterized in that, The output power of the detection laser is 0.01 mW to 50 W.

4. The in-situ real-time monitoring method for the protection state of a laser welding molten pool according to claim 3, wherein 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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