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

Abstract

The present invention provides an in-situ process monitoring device and method for laser welding based on the mirror reflection zone of a molten pool. The device and method belong to the field of laser material processing technology and include a welding plate. A high-power laser is disposed directly above the welding plate. A semiconductor laser and a high-speed camera are disposed on either side 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 high-power laser beam and simultaneously act on the surface of the molten pool. The semiconductor laser is connected to a semiconductor laser power supply, the high-speed camera is connected to a computer, and two bandpass filters and an attenuation plate are disposed in front of the lens of the high-speed camera. The present invention utilizes the above-mentioned in-situ process monitoring device and method for laser welding based on the mirror reflection zone of the molten pool, which can directly and clearly characterize the dynamic behavior of the molten pool, providing a new approach to monitoring the laser welding process.

Description

Technical Field

[0001] The present invention relates to the technical field of laser material processing, 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 fundamental process in the manufacturing industry, evolving from early gas welding and arc welding to current high-energy beam welding technologies represented by plasma, electron beam, and laser beams. Compared to other welding technologies, laser welding offers significant advantages, including a smaller heat-affected zone, minimal thermal deformation of the plate after welding, faster welding speeds, better weld quality, ease of automated control, and a wide range of weldable materials. Consequently, laser welding has attracted widespread attention and has been widely used in a variety of manufacturing industries, including 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, which then sinks downward under the action of the evaporation recoil pressure to form a deep-penetration keyhole. In the field of laser deep-penetration welding, a large number of studies have found that welding is prone to problems such as thick smoke, spatter, humps, porosity, poor weld surface formation, and severe fluctuations in weld penetration. 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-penetration welding technology. Intelligence is the development trend of laser welding technology, and welding process defect monitoring is an essential part of the intelligent laser welding process.

[0004] To overcome these limitations, the present invention proposes an in-situ laser welding process monitoring device and method based on the idea that the surface flatness of the molten pool can reflect its stability. This device and method utilize the specular reflection area of ​​the molten pool to monitor the process. The illumination laser beam and the observation axis of a high-speed camera are symmetrically arranged on either side of the high-power laser beam. A composite filtering and dimming system is constructed using filters with the same wavelength as the illumination laser beam and appropriate attenuation plates. This filter removes interference from factors such as plasma and plume, reducing their impact on the observation process. The filtered optical signal is collected by a high-speed camera. Since the generation of welding defects is closely related to the characteristic behavior (particularly dynamic behavior) of the keyhole, which is closely related to the molten pool, the dynamic behavior of the keyhole can be reflected by observing the area of ​​the light spot reflected on the molten pool surface. This approach is expected to establish a correspondence between the dynamic behavior of the light spot area and the process of welding defect generation, thus enabling detection of the welding process. Summary of the Invention

[0005] The present invention aims to provide an in-situ laser welding process monitoring device and method based on the specular reflection zone of the molten pool. This device can directly and clearly characterize the dynamic behavior of the molten pool, providing a new approach to laser welding process monitoring. Furthermore, the present invention offers advantages such as a simple system structure, ease of operation, and low cost.

[0006] To achieve the above-mentioned objectives, the present invention provides an in-situ process monitoring device for laser welding based on the mirror reflection zone of the molten pool, comprising a welding plate, a high-power laser arranged directly above the welding plate, a semiconductor laser and a high-speed camera 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 being symmetrically distributed about the direction of the processing laser beam of the high-power laser and acting on the surface of the molten pool at the same time, the semiconductor laser being connected to a semiconductor laser power supply, the high-speed camera being connected to a computer, and two band-pass filters and an attenuation plate being 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 to 50%.

[0010] Preferably, the high-power laser 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 molten pool mirror reflection area, the present invention also provides a laser welding in-situ process monitoring method based on the molten pool mirror reflection area, comprising the following steps:

[0012] 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 specular reflection of the illumination laser beam, forming a specular reflection area;

[0013] Step S2: Observe the molten pool surface with a high-speed camera, filter out interference from plume and plasma with a bandpass filter, and reduce the intensity of the illumination light entering the high-speed camera with an attenuator. Only the light signal of the illumination laser beam reflected by the molten pool surface is collected, and the area of ​​the specular reflection area on the molten pool surface is extracted by a computer.

[0014] 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.

[0015] Therefore, the present invention adopts the above-mentioned laser welding in-situ process monitoring device and method based on the molten pool mirror reflection area, and the beneficial technical effects are as follows:

[0016] The present invention uses the size of the mirror reflection area produced by the illuminating laser beam on 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 zone of the illuminating light on the surface of the laser welding molten pool. On the one hand, compared to existing methods of observing the steady state of the welding process, the present invention chooses to observe the area of ​​the illuminated laser spot action zone, which is simpler, less expensive, and easier to operate than directly observing the dynamic behavior within the hole. On the other hand, the fundamental cause of the oscillation of the molten pool surface is caused by the laser energy coupling process within the keyhole. By extracting the oscillatory behavior of the molten pool surface, it is hoped that the energy coupling method within the keyhole will be revealed. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The figure is a schematic diagram of the structure of a laser welding process monitoring device based on in-situ measurement of the mirror reflection area of ​​the molten pool;

[0018] 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;

[0019] Figure 3 is the mirror reflection area of ​​the molten pool obtained from the experiment.

[0020] Reference numerals

[0021] 1. High-power laser; 2. Molten pool surface; 3. Welding plate; 4. Semiconductor laser; 5. Semiconductor laser power supply; 6. Bandpass filter; 7. Attenuator; 8. High-speed camera; 9. Computer. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0023] Unless otherwise defined, technical or scientific terms used in the present invention shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0024] Example 1

[0025] like Figure 1As shown in the figure, 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.

[0026] In this embodiment, the welding plate 3 is low-carbon steel with a thickness of 5 mm, the surface of which is ground and wiped with acetone before welding; the high-power laser 1 is a YLS-6000 fiber laser with a wavelength of 1.07 μm.

[0027] During welding, the high-power laser beam can be negatively defocused, zero defocused, or positively defocused; the laser beam output mode can be pulsed or continuous. The applied arc plasma can be a TIG arc, MIG arc, or plasma arc.

[0028] The wavelength of the semiconductor laser 4 used for the auxiliary illumination laser is 808 nm.

[0029] The high-speed camera 8 uses a PHOTRON Fastcam Mini UX100 color high-speed camera from the United States. Two 808 nm band-pass filters 6 and an attenuation plate 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 10,000 frames / s.

[0030] 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.

[0031] 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 plume and illumination laser beam through the bandpass filter 6 and attenuation plate 7, and 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, masking, area filtering and threshold segmentation using Matlab software. Figure 2 The processing of Matlab software is prior art and will not be elaborated here.

[0032] 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. In this embodiment, 200 consecutive molten pool images under different laser powers (within 20ms) are counted to analyze the variation of the size of the mirror reflection region of the molten pool with the laser power. Figure 3 As shown in the figure. At the same laser power, the larger the molten pool's mirror reflection area, the smoother the molten pool surface and the more stable the welding process. At different laser powers, within the 2-5kW range, as the laser power increases, the welding process becomes more stable, and the molten pool's mirror reflection area also increases with the increase in laser power. However, when the laser power is further increased to 6kW, the weld collapses, the welding process becomes less stable than at 5kW, and the molten pool's mirror reflection area also decreases. Therefore, the size of the molten pool's mirror reflection area can reflect the stability of the welding process.

[0033] 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.

[0034] 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.

[0035] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. 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 solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions 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: The device comprises 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 with respect to the processing laser beam direction of the high-power laser and act on the surface of the molten pool simultaneously, 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; A monitoring method for a laser welding in-situ process monitoring device based on a molten pool mirror reflection zone comprises 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 specular reflection of the illumination laser beam, forming a specular reflection area; Step S2: Observe the molten pool surface with a high-speed camera, filter out interference from plume and plasma with a bandpass filter, and reduce the intensity of the illumination light entering the high-speed camera with an attenuator. Only the light signal of the illumination laser beam reflected by the molten pool surface is collected, and the area of ​​the specular reflection area on the molten pool surface is extracted by 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; The wavelength of the illumination laser beam is 100 to 1000 nm, and the power is 0.1 to 100 W; the angle between the illumination laser beam and the processing laser beam is 10 to 80 degrees; The central wavelength of the bandpass filter is consistent with the wavelength of the illumination laser beam, and its bandwidth is 1 to 20 nm; The light transmittance of the attenuation sheet is 0.01 to 50%.

2. The laser welding in-situ process monitoring device based on the molten pool mirror reflection area according to claim 1 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 to 50 kW.

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