Laser welding in-situ process monitoring device and method based on molten pool mirror reflection area

Abstract

The invention provides a laser welding in-situ process monitoring device and method based on a molten pool mirror reflection area, and belongs to the technical field of laser material machining. The device comprises a welding plate, a high-power laser is arranged over the welding plate, and a semiconductor laser and a high-speed camera are arranged on the two sides of the high-power laser respectively; illumination laser beams of the semiconductor laser and the axis of the high-speed camera are symmetrically distributed relative to the laser beam direction of the high-power laser and act on the surface of a molten pool at the same time, the semiconductor laser is connected with a semiconductor laser power source, the high-speed camera is connected with a computer, and two band-pass filters and an attenuation piece are arranged in front of a lens of the high-speed camera. According to the laser welding in-situ process monitoring device and method based on the molten pool mirror reflection area, the dynamic behavior of the molten pool can be directly and clearly represented, and a new way is provided for monitoring of the laser welding process.

Description

Technical Field

[0001] The invention relates to the technical field of laser material processing, and in particular to a laser welding in-situ process monitoring device and method based on a molten pool mirror reflection zone. Background Art

[0002] Welding is a basic process in the manufacturing industry. It has gone through the development process from early gas welding and arc welding to the current high-energy beam welding technology represented by plasma, electron beam, and laser beam. Compared with other welding technologies, laser welding technology has significant advantages such as small welding heat affected zone, small thermal deformation of the plate after welding, fast welding speed, good welding quality, easy to realize automatic control, and a wide range of weldable materials. Therefore, laser welding technology has attracted widespread attention and has been widely used in manufacturing industries such as aerospace, rail transportation, shipbuilding, and vehicle manufacturing.

[0003] The laser welding process is a complex process involving molten pool flow, metal evaporation, and laser energy coupling. During the laser welding process, the surface of the material melts under the action of the laser to form a molten pool, and then the molten pool sinks downward under the action of the evaporation recoil pressure to form a deep molten keyhole. In the field of laser deep fusion welding, a large number of studies have found that welding is prone to produce problems such as thick smoke, spatter, humps, pores, poor weld surface formation, and serious fluctuations in welding depth. These problems manifest as welding defects in the weld, which will seriously affect the overall service performance of the welded component, thus restricting the development of laser deep fusion welding technology. Intelligence is the development trend of laser welding technology, and welding process defect monitoring is a necessary link in the intelligent laser welding process.

[0004] In order to overcome the above limitations, the present invention proposes a laser welding in-situ process monitoring device and method based on the mirror reflection area of ​​the molten pool, based on the idea that the flatness of the molten pool surface can reflect the stability of the molten pool. The illumination laser beam and the observation axis of the high-speed camera are symmetrically arranged on both sides of the laser beam direction of the high-power laser. A filter with the same wavelength as the illumination laser beam and a suitable attenuation plate form a composite filtering and dimming system to filter out interference from factors such as plasma and plume, reduce their interference with the observation process, and the high-speed camera collects the filtered light signal. Since the generation of welding defects is closely related to the characteristic behavior (especially the dynamic behavior) of the keyhole, and the dynamic behavior of the keyhole is closely related to the molten pool, the dynamic behavior of the keyhole is reflected by observing the area of ​​the light spot reflected on the surface of the molten pool. It is expected to establish a corresponding relationship between the dynamic behavior of the light spot area and the welding defect generation process, and realize the detection of the welding process. Summary of the invention

[0005] The purpose of the present invention is to provide a laser welding in-situ process monitoring device and method based on the mirror reflection area of ​​the molten pool, which can directly and clearly characterize the dynamic behavior of the molten pool and provide a new way to monitor the laser welding process. In addition, the present invention has the advantages of simple system structure, easy operation, low cost, etc.

[0006] To achieve the above-mentioned purpose, the present invention provides an in-situ process monitoring device for laser welding based on the mirror reflection zone of a molten pool, comprising a welding plate, a high-power laser is arranged directly above the welding plate, a semiconductor laser and a high-speed camera are respectively arranged on both sides of the high-power laser, the illumination laser beam of the semiconductor laser and the axis of the high-speed camera are symmetrically distributed about the direction of the processing laser beam of the high-power laser and act on the surface of the molten pool at the same time, the semiconductor laser is connected to a semiconductor laser power supply, the high-speed camera is connected to a computer, and two band-pass filters and an attenuation plate are arranged in front of the lens of the high-speed camera.

[0007] Preferably, the wavelength of the illumination laser beam is 100-1000 nm, and the power is 0.1-100 W; the angle between the illumination laser beam and the processing laser beam is 10-80°.

[0008] Preferably, the central light wavelength of the bandpass filter is consistent with the wavelength of the illumination laser beam, and its bandwidth is 1 to 20 nm.

[0009] Preferably, the light transmittance of the attenuation sheet is 0.01-50%.

[0010] Preferably, the high-power laser type is any one of a fiber laser, a disk laser, a semiconductor laser, a green laser, a blue laser or a Nd:YAG laser; and the power of the laser is 0.5-50 kW.

[0011] Based on the above-mentioned laser welding in-situ process monitoring device based on the mirror reflection area of ​​the molten pool, the present invention also provides a laser welding in-situ process monitoring method based on the mirror reflection area of ​​the molten pool, comprising the following steps: Step S1, using a semiconductor laser to irradiate a molten pool in a laser processing state, so that the surface of the molten pool produces a mirror reflection of the illumination laser beam to form a mirror reflection area; Step S2, observing the molten pool surface through a high-speed camera, filtering out interference from plume and plasma with a bandpass filter, and reducing the intensity of the illumination light entering the high-speed camera with an attenuation plate, only collecting the light signal of the illumination laser beam reflected by the molten pool surface, and extracting the mirror reflection area of ​​the molten pool surface through a computer; Step S3, based on the size of the extracted mirror reflection area of ​​the molten pool surface and the change pattern of the area over time, the flatness of the molten pool surface and the stability of the laser processing process are reflected.

[0012] Therefore, the present invention adopts the above-mentioned laser welding in-situ process monitoring device and method based on the mirror reflection area of ​​the molten pool, and the beneficial technical effects are as follows: The present invention uses the size of the mirror reflection area of ​​the illuminating laser beam produced by the molten pool surface to characterize the stability of the molten pool and the welding process. The dynamic behavior of the welding process is reflected by observing the dynamic behavior of the mirror reflection area (i.e., bright spot) produced in the spot action area of ​​the illuminating light on the surface of the laser welding molten pool. On the one hand, compared with the existing method of observing the steady state of the welding process, the present invention chooses to observe the area of ​​the illuminating laser spot action area, which is simpler, less costly, and easier to operate than directly observing the dynamic behavior in the hole. On the other hand, the fundamental reason for the oscillation of the molten pool surface is caused by the laser energy coupling process in the keyhole. By extracting the oscillation behavior of the molten pool surface, it is expected to reveal the energy coupling mode in the keyhole. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a structural schematic diagram of a laser welding process monitoring device based on in-situ measurement of the mirror reflection area of ​​the molten pool; Figure 2 This is the processing flow of the melt pool image obtained in the experiment; Figure 2 (a) is the result of melt pool image processing; Figure 2 (b) is the image processing flow chart; Figure 3 is the mirror reflection area of ​​the molten pool obtained in the experiment.

[0014] Reference numerals 1. High-power laser; 2. Molten pool surface; 3. Welding plate; 4. Semiconductor laser; 5. Semiconductor laser power supply; 6. Bandpass filter; 7. Attenuation plate; 8. High-speed camera; 9. Computer. DETAILED DESCRIPTION

[0015] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0016] 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.

[0017] Embodiment 1 like Figure 1As shown, it is a structural schematic diagram of the laser welding in-situ process monitoring device based on the mirror reflection zone of the molten pool of the present invention, including a welding plate 3, a high-power laser 1 is arranged directly above the welding plate 3, a semiconductor laser 4 and a high-speed camera 8 are respectively arranged on both sides of the high-power laser 1, the illumination laser beam of the semiconductor laser 4 and the axis of the high-speed camera 8 are symmetrically distributed about the processing laser beam direction of the high-power laser 1 and act on the molten pool surface 2 at the same time, the semiconductor laser 4 is connected to a semiconductor laser power supply 5, the high-speed camera 8 is connected to a computer 9, and two band-pass filters 6 and an attenuation plate 7 are arranged in front of the lens of the high-speed camera 8.

[0018] In this embodiment, the welding plate 3 is low-carbon steel with a thickness of 5 mm, the surface is ground, and the surface is wiped with acetone before welding; the high-power laser 1 is a YLS-6000 fiber laser with a wavelength of 1.07 μm.

[0019] During welding, the high-power laser beam can be negatively defocused, zero defocused or positively defocused; the laser light emission mode can be pulsed or continuous. The external arc plasma can be TIG arc, MIG arc or plasma arc.

[0020] The wavelength of the semiconductor laser 4 used for the auxiliary illumination laser is 808nm.

[0021] The high-speed camera 8 uses the American PHOTRON Fastcam Mini UX100 color high-speed camera. Two 808nm band-pass filters 6 and an attenuation film 7 with a transmittance of 20% are installed in front of the lens of the high-speed camera 8. The fixed frame rate during shooting is 10000 frames / s.

[0022] The processing parameters are as follows: the fiber laser power is set to 2, 3, 4, 5, and 6 kW respectively, the welding speed is 0.5 m / min, and the power of the semiconductor laser 4 is 10 W.

[0023] During welding, the angle between the axis of the illumination laser beam and the processing laser beam is 30°, and the illumination laser beam and the lens axis of the high-speed camera 8 are symmetrically distributed on both sides of the processing laser beam. The light reflected by the molten pool is transmitted through the light guide path. The high-speed camera 8 filters and reduces the interference of the plume and the illumination laser beam through the bandpass filter 6 and the attenuation plate 7, collects the molten pool image in real time and transmits it to the computer 9. The molten pool image is obtained by cropping, grayscale processing, median filtering, mask operation, area filtering and threshold segmentation using Matlab software. Figure 2 The processing of Matlab software is prior art and will not be elaborated in detail here.

[0024] The area of ​​the mirror reflection region of the molten pool is represented by the number of pixels with a pixel value of 1 in the binary image. This embodiment counts 200 consecutive molten pool images under different laser powers (within 20ms) and analyzes the variation of the size of the mirror reflection region of the molten pool with the laser power, such as Figure 3 As shown in the figure. Under the same laser power, the larger the mirror reflection area of ​​the molten pool, the flatter the molten pool surface and the more stable the welding process. Under different laser powers, in the range of 2-5kW, as the laser power increases, the welding process becomes more stable, and the mirror reflection area of ​​the molten pool also increases with the increase of laser power. When the laser power is further increased to 6kW, the weld collapses, the welding process becomes more unstable than at 5kW, and the mirror reflection area of ​​the molten pool also decreases. Therefore, the size of the mirror reflection area of ​​the molten pool can reflect the stability of the welding process.

[0025] 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.

[0026] Therefore, the present invention adopts the above-mentioned laser welding in-situ process monitoring device and method based on the mirror reflection area of ​​the molten pool, which can directly and clearly characterize the dynamic behavior of the molten pool and provide a new way to monitor the laser welding process.

[0027] 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 laser welding in-situ process monitoring device based on the mirror reflection area of ​​the molten pool, characterized in that: It includes a welding plate, a high-power laser is arranged directly above the welding plate, a semiconductor laser and a high-speed camera are arranged on both sides of the high-power laser respectively, the illumination laser beam of the semiconductor laser and the axis of the high-speed camera are symmetrically distributed about the processing laser beam direction of the high-power laser and act on the molten pool surface at the same time, the semiconductor laser is connected to a semiconductor laser power supply, the high-speed camera is connected to a computer, and two band-pass filters and an attenuation plate are arranged in front of the lens of the high-speed camera.

2. The laser welding in-situ process monitoring device based on the mirror reflection area of ​​the molten pool according to claim 1 is characterized in that: The wavelength of the illumination laser beam is 100-1000nm, and the power is 0.1-100W; the angle between the illumination laser beam and the processing laser beam is 10-80°.

3. The laser welding in-situ process monitoring device based on the mirror reflection area of ​​the molten pool according to claim 2 is characterized in that: The central light wavelength of the bandpass filter is consistent with the wavelength of the illumination laser beam, and its bandwidth is 1 to 20 nm.

4. The laser welding in-situ process monitoring device based on the molten pool mirror reflection area according to claim 3 is characterized in that: The light transmittance of the attenuation sheet is 0.01 to 50%.

5. The laser welding in-situ process monitoring device based on the molten pool mirror reflection area according to claim 4 is characterized in that: The high-power laser type is any one of a fiber laser, a disk laser, a semiconductor laser, a green laser, a blue laser or a Nd:YAG laser; the power of the laser is 0.5~50kW.

6. A monitoring method for the laser welding in-situ process monitoring device based on the molten pool mirror reflection area according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step S1, using a semiconductor laser to irradiate a molten pool in a laser processing state, so that the surface of the molten pool produces a mirror reflection of the illumination laser beam to form a mirror reflection area; Step S2, observing the molten pool surface through a high-speed camera, filtering out interference from plume and plasma with a bandpass filter, and reducing the intensity of the illumination light entering the high-speed camera with an attenuation plate, only collecting the light signal of the illumination laser beam reflected by the molten pool surface, and extracting the mirror reflection area of ​​the molten pool surface through a computer; Step S3, based on the size of the extracted mirror reflection area of ​​the molten pool surface and the change pattern of the area over time, the flatness of the molten pool surface and the stability of the laser processing process are reflected.

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