Coaxial slm monitoring and real-time feedback control printing cabin wind field device and method

Abstract

The coaxial SLM monitoring and real-time feedback control printing chamber airflow device and method of the present invention includes an optical path unit, an imaging unit, a control unit, and a gas circulation and purification unit. The control unit controls the optical path unit to generate a laser with a preset power and focus it on the processing surface for SLM processing. The mixed beam of the self-luminous infrared molten pool and the laser reflected from the semiconductor laser emitted by the imaging unit on the processing surface enters the optical path unit and is reflected to the imaging unit, realizing visible light imaging and infrared thermal imaging. The control unit receives, stores, and analyzes the real-time SLM processing process molten pool temperature distribution and molten pool image acquired by the imaging unit to generate a feedback control signal to the gas circulation and purification unit to adjust the airflow velocity in the printing chamber in real time. This ensures that the splashes and dust generated when the metal powder on the processing surface melts and solidifies rapidly during the SLM processing can be completely absorbed, reducing the impact of splashes and dust on the laser, powder spreading process, and molten pool formation during subsequent processing. This method is suitable for widespread application.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology, and in particular to a coaxial SLM monitoring and real-time feedback control device and method for the air field of a printing chamber. Background Technology

[0002] Selective Laser Melting (SLM) is a popular additive manufacturing technology with advantages such as rapid cooling and high dimensional accuracy, making it widely used in aerospace, medical, and other fields. During SLM processing, a high-energy laser is generated and focused onto metal powder on the work surface through a collimating lens, scanning galvanometer, and field lens. The metal powder rapidly melts and solidifies, ultimately printing the final part.

[0003] During SLM processing, the rapid temperature fluctuations during the formation and solidification of the molten pool by the metal powder cause thermal stress in the molten pool, leading to defects such as spatter and fumes. Spatter reduces the amount of metal in the molten pool and causes fluctuations in the molten pool at the point of impact. Fumes generated during processing affect laser intensity, thus impacting print quality, accuracy, and stability, and are also harmful to human health. Therefore, controlling and promptly removing spatter and fumes during SLM processing is crucial for ensuring the reliability of SLM processing and the quality of the formed parts.

[0004] To eliminate spatter and dust defects generated during SLM processing, in addition to adjusting process parameters such as laser power, scanning speed, scanning strategy, layer thickness, and scanning spacing, real-time adjustment of the airflow velocity within the printing chamber can also be used to remove spatter and dust. Characterizing spatter and dust is crucial for real-time feedback adjustment of the airflow velocity within the printing chamber, as their generation directly affects the temperature and morphology of the molten pool. To directly observe changes in the temperature distribution and the morphology of the molten pool and surrounding powder areas, some researchers have used off-axis high-speed cameras and pyrometers to monitor the molten pool area. Others have coaxially mounted high-speed cameras in the laser optical path to achieve coaxial monitoring of the molten pool and spatter. However, these methods struggle to obtain clear and high-frame-rate coaxial molten pool morphology and temperature distribution, and cannot utilize real-time processing signals for real-time feedback control of the airflow velocity within the printing chamber to reduce spatter and dust defects, improve the quality of molded parts, and ensure the stability of SLM processing. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a coaxial SLM monitoring and real-time feedback control device and method for the airflow in the printing chamber. The purpose is to achieve real-time coaxial monitoring of the molten pool temperature distribution and molten pool morphology during SLM processing, and to control the airflow velocity in the printing chamber based on the two data in real time, thereby suppressing the impact of molten pool splash and dust on the quality of the molded parts during SLM processing and ensuring the stability of SLM processing.

[0006] To achieve the above objectives, the specific contents of the present invention are as follows:

[0007] The coaxial SLM monitoring and real-time feedback control device for the printing chamber air field includes an optical path unit, an imaging unit, a control unit, and a gas circulation and purification unit. The optical path unit includes a laser, a collimating lens, a first beam combiner, a second beam combiner, a scanning galvanometer, and a field lens. The laser and the scanning galvanometer are respectively connected to the control unit. The laser is connected to the collimating lens through an optical fiber. The control unit controls the laser to generate a laser with a preset power, which passes through the collimating lens, the second beam combiner, the first beam combiner, and the scanning galvanometer in sequence, and is then focused onto the processing surface by the field lens.

[0008] The imaging unit includes a semiconductor laser, an infrared thermal imager, a high-speed camera, a first filter, and a second filter. The semiconductor laser is mounted above the processing surface, and the laser generated by the semiconductor laser irradiates the processing surface. The second filter and the high-speed camera are respectively arranged in the vertical direction of the second beam combiner. The first filter and the infrared thermal imager are respectively arranged in the vertical direction of the first beam combiner. The high-speed camera and the infrared thermal imager are respectively connected to the control unit.

[0009] The gas circulation purification unit includes a dust removal and purification device, an air intake component, an air intake duct, a first air blowing component, a second air blowing component, a first air blowing duct, and a second air blowing duct. The dust removal and purification device is connected to the control unit. The air inlet of the dust removal and purification device is connected to the air intake component through the air intake duct, and the air outlet is connected to the first air blowing component through the first air blowing duct. The second air blowing component is installed on top of the first air blowing component through the second air blowing duct and is located between the scanning galvanometer and the first air blowing component. The air intake duct and the first air blowing duct are arranged opposite each other to form a semi-enclosed shape, so that the air intake component and the first air blowing component are symmetrically arranged on both sides of the processing surface.

[0010] Furthermore, the control unit includes a high-speed camera controller, a temperature signal processor, and a computer. The high-speed camera controller, temperature signal processor, laser, scanning galvanometer, and dust removal and purification device are respectively connected to the computer. The high-speed camera is connected to the high-speed camera controller, and the infrared thermal imager is connected to the temperature signal processor.

[0011] Furthermore, the high-speed camera controller includes a high-speed camera control module, an image processing module, and a data transfer module. The high-speed camera control module is connected to a computer, the image processing module, and the high-speed camera. The image processing module is connected to the data transfer module, and the data transfer module is connected to the computer. The temperature signal processor includes a thermal imager control module, a temperature distribution processing module, and a data storage module. The thermal imager control module is connected to a computer, the temperature distribution processing module, and the infrared thermal imager. The temperature distribution processing module is connected to the data storage module, and the data storage module is connected to the computer.

[0012] Furthermore, the first filter is a narrowband filter with a wavelength range of 810-920nm; the second filter is a single-pass filter with a wavelength of 450nm; the semiconductor laser generates 450nm laser; and the laser with the preset power is a high-energy laser with a wavelength of 1080nm.

[0013] Furthermore, both the suction duct and the second blowing duct are L-shaped, the first blowing duct is C-shaped, and the suction component, the first blowing component, and the second blowing component are respectively provided with multiple perforated airflow channels.

[0014] The control method for monitoring and real-time feedback control of the coaxial SLM in the printing chamber air field device, as described above, includes the following steps:

[0015] Step 1: During SLM printing, the control unit controls the high-speed camera and infrared thermal imager to start recording, controls the laser to emit a laser with a preset power, controls the scanning speed and scanning path of the scanning galvanometer, and controls the dust removal and purification device to draw in and expel air. The laser with the preset power passes through the collimating lens, the second beam combiner, the first beam combiner, and the scanning galvanometer in sequence, is reflected by the field lens, and then focused onto the metal powder on the processing surface. This causes the metal powder on the processing surface to melt rapidly and form a molten pool. At the same time, the laser generated by the semiconductor laser is irradiated onto the molten pool area on the processing surface. The inert protective gas contaminated in the printing chamber of the processing surface is drawn in by the air intake component. After the contaminated inert gas is purified by the dust removal and purification device, the purified inert gas is blown out between the processing surface and the scanning galvanometer by the first and second air blowing components, respectively.

[0016] Step 2: During the processing, the mixed beam of the 450nm wavelength laser generated by the semiconductor laser in Step 1, reflected on the processing surface, and the self-luminous emission of the molten pool in the 450nm and 810-920nm wavelengths, enters the optical path unit through the field lens. The scanning galvanometer reflects the mixed beam to the first beam combiner. The first beam combiner reflects the self-luminous emission of the molten pool in the 810-920nm wavelength range of the mixed beam to the first filter and then transmits it to the infrared thermal imager for coaxial molten pool temperature distribution imaging. At the same time, the 450nm mixed beam of the molten pool self-luminous emission and the 450nm wavelength laser generated by the semiconductor laser, reflected on the processing surface, is reflected together to the second beam combiner. The second beam combiner reflects the 450nm mixed beam to the second filter and then transmits it to the high-speed camera for coaxial molten pool area imaging.

[0017] Step 3: The control unit processes the molten pool area image from the high-speed camera and the molten pool temperature distribution data from the infrared thermal imager in real time, and obtains and stores the ROI region of the molten pool image and the ROI region of the temperature distribution data from the laser spot position as the center.

[0018] Step 4: The control unit receives and stores the ROI region of the molten pool image and the ROI region of the temperature distribution from Step 3. At the same time, it analyzes whether there are any abnormalities in the temperature distribution of the molten pool and monitors the generation of splashes and dust. Combined with the analysis of the abnormalities in the splashes of the molten pool and the distribution of surrounding powder at the same moment, it determines whether to generate a feedback control signal.

[0019] Furthermore, the method for determining whether to generate a feedback control signal includes the following steps:

[0020] Step 4.1: When the control unit determines that the molten pool splash and fumes have been normally cleared during the SLM processing, it will continue the printing process with the current process parameters by default.

[0021] Step 4.2: When the control unit determines that the molten pool splash and dust have not been removed during the SLM processing, it generates a feedback control signal and adjusts the airflow rate of the printing chamber output by the dust removal and purification device in real time until the entire part is printed layer by layer.

[0022] Furthermore, the control method for the airflow velocity of the printing chamber described in step 4.2 is as follows: when there is a lot of molten pool splashing or obvious smoke in the molten pool area, and the powder area is not obviously blown, the control unit determines to increase the airflow velocity of the printing chamber; when there is little molten pool splashing or no smoke can be detected in the molten pool area, but the powder in the powder area is detected to be blown, the control unit determines to reduce the airflow velocity of the printing chamber.

[0023] Advantages of the present invention

[0024] 1. The present invention and the device and method for monitoring and real-time feedback control of the printing chamber airflow in coaxial SLM processing utilize an infrared thermal imager and a high-speed camera in the imaging unit to coaxially monitor the processing process, acquire images of the molten pool temperature distribution and molten pool area, and process the molten pool status data in real time through the control unit to monitor the formation of splashes and dust during processing and generate feedback control signals for the printing chamber airflow to the dust removal and purification device of the gas circulation and purification unit. This achieves real-time feedback control of the printing chamber airflow, improves the stability of SLM processing, and thus ensures the forming quality of the processed parts.

[0025] 2. The imaging unit of this invention shares the same optical path as the laser required for printing, thus achieving true coaxial monitoring.

[0026] 3. The control unit of the present invention analyzes the temperature distribution of the molten pool and the image of the molten pool area to obtain the control signal of the air field of the printing chamber. The control signal controls the air flow rate of the SLM printing chamber in real time, realizing the closed-loop control of SLM.

[0027] 4. This invention can achieve real-time acquisition of processing status data; extract ROI regions from multi-source monitoring data, analyze processing status, and thus adjust the printing chamber airflow in a timely manner to remove splashes and dust to avoid quality defects and improve the stability of SLM process. Attached Figure Description

[0028] Figure 1 Optical path diagram for coaxial SLM monitoring and real-time feedback control of the printing cabin wind field device.

[0029] Figure 2 A flowchart of a control method for monitoring and real-time feedback control of the wind field device in a coaxial SLM for printing chamber.

[0030] In the picture:

[0031] 1. Imaging unit; 2. Infrared thermal imager; 3. First filter; 4. First beam combiner; 5. Scanning galvanometer; 6. Semiconductor laser; 7. Optical path unit; 8. Field lens; 9. Gas circulation and purification unit; 10. First air blowing component; 11. Processed surface; 12. Air intake; 13. Air intake duct; 14. Dust removal and purification device; 15. First air blowing duct; 16. Second air blowing duct; 17. Second air blowing component; 18. Control unit; 19. Temperature signal processor; 20. High-speed camera controller; 21. Computer; 22. Laser; 23. Optical fiber; 24. Collimating lens; 25. Second beam combiner; 26. Second filter; 27. High-speed camera. Detailed Implementation

[0032] The present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments. It should be noted that the specific embodiments are not intended to limit the scope of the present invention.

[0033] like Figure 1 As shown in the figure, the coaxial SLM monitoring and real-time feedback control printing chamber air field device provided in this specific embodiment includes an optical path unit 7, an imaging unit 1, a control unit 18, and a gas circulation and purification unit 9.

[0034] The optical path unit 7 includes a laser 22, a collimating lens 24, a first beam combiner 4, a second beam combiner 25, a scanning galvanometer 5, and a field lens 8. The imaging unit 1 includes a semiconductor laser 6, an infrared thermal imager 2, a high-speed camera 27, a first filter 3, and a second filter 26. The gas circulation and purification unit 9 includes a dust removal and purification device 14, an air intake component 12, an air intake duct 13, a first air blowing component 10, a second air blowing component 11, a first air blowing duct 15, and a second air blowing duct 16. The control unit 18 includes a high-speed camera controller 20, a temperature signal processor 19, and a computer 21.

[0035] The optical path unit 7 is used to receive signals from the computer 21 to control the laser 22 to generate a high-energy laser with a preset power of 1080nm and focus it onto the processing surface 11 for SLM processing. During the SLM processing, the mixed beam of the molten pool self-luminescence of 450nm and 810-920nm generated on the processing surface 11 and the reflected light of the high-energy laser of 450nm generated by the semiconductor laser 6 on the processing surface 11 enters the optical path unit 7 and is reflected into the imaging unit 1.

[0036] The imaging unit 1 is used to receive the mixed beam of light transmitted from the optical path unit 7, which consists of the molten pool self-luminescence in the 450nm band and the 810-920nm band generated by the processing surface 11 during the processing, and the reflected light of the high-energy laser in the 450nm band generated by the semiconductor laser 6 on the processing surface 11, and to perform visible light imaging and infrared thermal imaging.

[0037] The control unit 18 receives the real-time SLM processing melt pool temperature distribution and melt pool image acquired by the imaging unit 1, stores the data, analyzes the data, generates a feedback control signal and transmits it to the gas circulation and purification unit 9 to adjust the airflow rate in the printing chamber in real time.

[0038] The gas circulation and purification unit 9 receives feedback control signals generated by the control unit 18 in real time, thereby realizing real-time regulation of the airflow velocity in the printing chamber. This ensures that the splashes and dust generated when the metal powder on the processing surface 11 melts and solidifies rapidly during the SLM processing can be completely absorbed, reducing the impact of splashes and dust on the laser, powder spreading process, and molten pool formation during subsequent processing.

[0039] The specific connection method of the device is as follows: the laser 22, scanning galvanometer 5, dust removal and purification device 14, high-speed camera controller 20, and temperature signal processor 19 are respectively connected to computer 21. The high-speed camera controller 20 includes a high-speed camera control module, an image processing module, and a data transfer module. The high-speed camera control module is connected to computer 21, the image processing module, and the high-speed camera 27. The image processing module is connected to the data transfer module, and the data transfer module is connected to computer 21. The function of the high-speed camera controller 20 is to process the molten pool area image acquired by the high-speed camera 27 in real time. The image processing module 32 crops the molten pool area image with the laser spot position as the center to obtain the ROI region of the molten pool image. The data transfer module 33 stores the ROI region of the molten pool image into computer 21. The temperature signal processor 19 includes a thermal imager control module, a temperature distribution processing module, and a data storage module. The thermal imager control module is connected to computer 21, the temperature distribution processing module, and the infrared thermal imager 2. The temperature distribution processing module is connected to the data storage module, and the data storage module is connected to computer 21. The temperature signal processor 19 processes the molten pool temperature distribution data acquired by the infrared thermal imager 2 in real time. The temperature distribution processing module 29 cuts the molten pool temperature distribution data with the laser spot position as the center to obtain the ROI region of the temperature distribution. The data storage module 30 stores the ROI region of the temperature distribution into the computer 21. The laser 22 receives the signal from the computer 21 and generates a high-energy laser with a preset power of 1080nm. The laser is transmitted through the optical fiber 23 to the collimating lens 24. The collimating lens 24 collimates the high-energy laser with a fixed divergence angle and a preset power of 1080nm and then transmits it to the second beam combiner 25. The transmittance of the second beam combiner 25 exceeds 99.9%. The second beam combiner 25 transmits the high-energy laser with a preset power of 1080nm generated by the laser 22 to the first beam combiner 4. The transmittance of the first beam combiner 24 exceeds 99%. 0.9%, computer 21 generates control signals to control scanning galvanometer 5 to reflect the 1080nm high-energy laser transmitted through the first beam combiner 4 towards a designated position on the processing surface 11. The laser is then focused onto the metal powder on the processing surface 11 by field lens 8, causing the metal powder on the processing surface 11 to rapidly melt and form a molten pool. A semiconductor laser 6 is mounted above the processing surface 11, and the semiconductor laser 6 generates a 450nm high-energy laser that irradiates the processing surface 11, ensuring that the generated 450nm high-energy laser can cover the processing area. In this example, semiconductor laser 6 is used as an auxiliary light source. Simultaneously with laser generation, the 450nm laser generated by semiconductor laser 6 is manually irradiated onto the molten pool area of ​​the processing surface 11. The reflected light from the 450nm laser generated by semiconductor laser 6 on the processing surface 11, along with the self-emission of the 450nm molten pool, is reflected through optical path unit 7 into imaging unit 1 for visible light imaging.

[0040] The first beam combiner 4 serves two purposes: first, it transmits the 1080nm high-energy laser generated by the transmission laser 22, with a transmittance exceeding 99.9%; second, it transmits the 450nm band molten pool self-luminescence of the processed surface 11 and the 450nm laser generated by the semiconductor laser 6, and the reflected light from the processed surface 11 to the second beam combiner 25, with a transmittance exceeding 99.9%, and reflects the 810-920nm band molten pool self-luminescence of the processed surface 11 into the imaging unit 1, with a reflectance exceeding 95%.

[0041] The second beam combiner 25 serves two purposes: first, it transmits the 1080nm high-energy laser generated by the transmission laser 22, with a transmittance exceeding 99.9%; second, it reflects the 450nm band molten pool self-luminescence transmitted by the first beam combiner 4 and the 450nm laser generated by the semiconductor laser 6 onto the processing surface 11, with a reflectance exceeding 95%.

[0042] The field lens 8 focuses the high-energy laser generated by the laser 22 with a preset power of 1080nm to the processing surface 11. The light reflected from the 450nm and 810-920nm band molten pool self-luminescence generated by the processing surface 11 and the 450nm laser generated by the semiconductor laser 6 on the processing surface 11 has a transmittance of over 95%, of which the transmittance of the 1080nm high-energy laser exceeds 99%.

[0043] The semiconductor laser 6 is used to generate 450nm wavelength laser during the printing process in the optical path unit 7. The 450nm wavelength laser is reflected by the optical path unit 7 into the imaging unit 1 for visible light imaging.

[0044] The infrared thermal imager has a pixel resolution of no less than 640×480 and a frame rate of no less than 60 frames / second under full resolution conditions; the spectral range is 810-920nm; and the sub-temperature range is 800-1150℃, 1000-1500℃, 1350-2050℃, and 1900-3000℃.

[0045] Its function is to perform infrared imaging of the processing area and to obtain the temperature distribution of the processing area.

[0046] The high-speed camera has a 27-pixel resolution of at least 1920×1080, a frame rate of at least 2247 frames per second at full resolution, a dynamic range of 56dB, and four CoaXPress2.0 data transmission interfaces with a total data transmission speed of 50Gbps. Its purpose is for visible light imaging of the processing area.

[0047] The high-speed camera controller 20 is used to acquire and transfer video data transmitted from the high-speed camera 27. After data processing, the ROI region is obtained and then transmitted to the computer 21.

[0048] The high-speed camera control module 31 is used to receive high-speed camera parameters output by the computer 21, set high-speed camera parameters, control the high-speed camera 27 to collect real-time data of the molten pool, and store it in memory.

[0049] The data transfer module 33 is used to transfer image data to the image processing module 32 in real time, and to store the processed image data into the computer 21 after processing.

[0050] The image processing module 32 is used to crop the image with the laser spot position as the image center to obtain the ROI region.

[0051] The temperature signal processor 19 is used to acquire and store the temperature data transmitted from the infrared thermal imager 2, and after the data processing acquires the ROI area, it is transmitted to the computer 21.

[0052] The thermal imager control module 28 is used to receive the opening and closing signals output by the computer 21 and control the thermal imager to collect the real-time temperature distribution of the molten pool.

[0053] The temperature distribution processing module 29 is used to cut the data center of the melt pool based on the laser spot position to obtain the ROI area.

[0054] The data storage module 30 is used to store temperature distribution data into the computer 21.

[0055] Computer 21 is used to receive and store real-time data generated by high-speed camera 27 and infrared thermal imager 2 during SLM processing and to provide real-time feedback control to dust removal and purification device 14. Before SLM processing begins, the parameters recorded by high-speed camera 27 and the start signal are transmitted to the high-speed camera controller 20, and the parameters recorded by infrared camera and the start signal are transmitted to the temperature signal processor 19. The control signal of dust removal and purification device 14 is output to dust removal and purification device 14 to start SLM processing. During processing, real-time data of the processing process processed by high-speed camera controller 20 and infrared thermal imager 2 are received. After image analysis and processing, a printing chamber airflow velocity control signal is generated and transmitted to dust removal and purification device 14 to realize real-time feedback control of the airflow velocity of the SLM processing printing chamber. Computer 21 processes two types of data in real time at a rate of 60 frames per second for each type of data, with a total real-time data processing rate of 120 frames per second. It analyzes whether the temperature distribution of the molten pool is abnormal and monitors the generation of splashes and dust. Combined with the analysis of the abnormality of the molten pool splashes and the distribution of surrounding powder at the same moment, it generates feedback control signals to realize real-time control of the dust removal and purification device 14 to adjust the airflow speed of the printing chamber, thereby improving the stability of the laser selective melting equipment and the quality of the processed parts.

[0056] The second filter 26 and the high-speed camera 27 are respectively positioned in the vertical direction of the second beam combiner 25. The purpose is to ensure that the high-speed camera 27 only receives light in the 450nm band, thereby ensuring that the molten pool fluctuation state and powder melting process can be clearly observed. During the processing, the semiconductor laser 6 generates a 450nm band laser, and the reflected light on the processing surface 11, along with the 450nm band and the 810-920nm band self-emission from the molten pool, enter the optical path unit 7 through the field lens 8. Then, through the field lens 8, the reflected light of the mixed beam passes sequentially through the scanning galvanometer 5 and the first beam combiner 4. The first beam combiner 4 reflects the 810-920nm band self-emission from the molten pool in the mixed beam to the first filter 3 for further filtering before being transmitted to the infrared thermal imager 2 for coaxial molten pool temperature distribution imaging.

[0057] Because the rapid melting and solidification of the molten pool can lead to defects such as spatter, the generation of defects can be clearly observed by monitoring the temperature distribution of the molten pool. Therefore, in this embodiment, an infrared thermal imager 2 is used to monitor the temperature distribution of the molten pool in real time. Like the high-speed camera 27, it is a non-contact coaxial monitoring device. It is integrated with the second beam combiner 25 in the laser coaxial optical path. The specific installation method is as follows: the first filter 3 and the infrared thermal imager 2 are respectively set in the vertical direction of the first beam combiner 4. The 450nm band self-luminous light from the molten pool and the 450nm band laser light generated by the semiconductor laser 6 in the mixed beam obtained during the processing are reflected on the processing surface 11 in sequence to the second beam combiner 25 and the second filter 26 for further filtering before being transmitted to the high-speed camera 27 for coaxial imaging of the molten pool area.

[0058] The first filter 3 is a narrowband filter with a wavelength range of 810-920nm and a transmittance of over 99%. Its function is to transmit the 810-920nm band molten pool self-luminescence reflected by the first beam combiner 4 into the infrared thermal imager 2, ensuring that the infrared thermal imager 2 avoids the influence of possible reflected laser radiation and improves the accuracy of temperature distribution monitoring.

[0059] The second filter 26 is a single-pass filter with a 450nm wavelength and a transmittance of over 99%. Its function is to transmit the 450nm wavelength self-luminous emission from the molten pool on the processing surface 11 reflected by the second beam combiner 25 and the reflected light from the 450nm laser generated by the semiconductor laser 6 on the processing surface 11 to the high-speed camera 27, so as to ensure that the high-speed camera 27 avoids possible reflected laser radiation and the influence of reflected light radiation from other wavelengths in the camera spectrum.

[0060] The suction component 12 is placed above the forming platform. The air inlet of the dust removal and purification device 14 is connected to the suction component 12 through the suction pipe 13. During the processing, the inert gas in the printing chamber, as well as the splashes and dust generated during the processing, are sucked in by the suction component 12 and transported to the suction pipe 13. The polluted inert gas passing through the suction pipe 13 is then transported to the dust removal and purification device 14 for purification. The suction component 12 is provided with multiple perforated airflow channels to ensure that the polluted inert gas in the printing chamber is evenly sucked into the suction pipe 13.

[0061] The first air blowing component 10 is placed above the forming platform. The air outlet of the dust removal and purification device 14 is connected to the first air blowing component 10 through the first air blowing pipe 15. This is used to transport the inert gas purified by the dust removal and purification device 14 to the first air blowing component 10 through the first air blowing pipe 15 during the SLM processing.

[0062] The second air blowing element 17 is installed on top of the first air blowing element 10 through the second air blowing pipe 16 and is located between the scanning galvanometer 5 and the first air blowing element 10. It is used to divert the inert gas purified by the first air blowing element 10. Part of the purified inert gas is blown through the second air blowing pipe 16 to the second air blowing element 17 and blown below the scanning galvanometer 5, ensuring that the splashes and dust generated during SLM processing do not come into contact with the scanning galvanometer 5 but are directly sucked into the suction element 12 by the inert gas. The other part of the purified inert gas is blown through the first air blowing element 10 to the top of the processing surface 11, so that the splashes and dust generated during processing can be blown into the suction element 12. The suction pipe is L-shaped and the first air blowing pipe is C-shaped, so that the suction pipe 13 and the first air blowing pipe 15 are arranged opposite each other to form a semi-enclosed shape, and the suction element 12 and the first air blowing element 10 are symmetrically arranged on both sides of the processing surface 11. The second air duct is L-shaped, and the first air blowing component 10 has multiple perforated airflow channels to ensure that the contaminating inert gas in the printing chamber is evenly drawn into the suction component 12. The second air blowing component 17 also has multiple perforated airflow channels to ensure that the contaminating inert gas in the printing chamber is evenly drawn into the suction component 12.

[0063] Simultaneously with laser generation, computer 21 sends signals to control the dust removal and purification device 14 to circulate gas by drawing in and expelling air. The suction component 12 draws in the inert protective gas contaminated in the printing chamber on the processing surface 11, which is then transported through the suction duct 13 to the dust removal and purification device 14 for purification. After purification, the inert gas is then conveyed through the first blowing duct 15 to the first blowing component 10. The first blowing component 10 divides the purified inert gas into two parts: one part is blown out from the first blowing component 10 to the processing area above the processing surface 11 to remove splashes and dust generated during processing; the other part is transported through the second blowing duct 16 to the second blowing component 17, which blows this purified inert gas below the galvanometer to protect the galvanometer from splashes and dust contamination and to remove splashes and dust. The dust removal and purification device 14 is a Xinghui dust removal and purification device APS-F150A with a maximum air volume of 186 m³ / h. 3 / h. The computer 21 processes and stores the temperature data acquired by the infrared thermal imager 2 and the data from the high-speed camera 27 in real time. It combines the two types of multi-source data to adjust the processing parameters in real time and generates control signals to the dust removal and purification device 14 to adjust the airflow velocity in the printing chamber in real time. By adjusting the airflow velocity in the printing chamber output by the dust removal and purification device 14 in real time, the printing process is adjusted by feedback control until the entire part is printed layer by layer.

[0064] The dust removal and purification device 14 has two functions: first, to purify the inert gas containing splashes and dust drawn in by the suction device 12, and to divide the purified inert gas into two parts and blow it out through the first blowing device 10 and the second blowing device 17; second, to receive the real-time feedback control signal output by the computer 21 and adjust the flow rate in real time.

[0065] Because the molten pool exhibits significant self-illumination during SLM processing, the images of the molten pool acquired by the high-speed camera 27 are often overexposed, making it impossible to observe the molten pool properly. Simultaneously, the surrounding area of ​​the molten pool is also difficult to observe, hindering further observation of the powder melting process and the evolution of the molten pool. Therefore, this example employs a coaxial SLM processing monitoring and feedback control scheme. Before SLM processing, a computer 21 synchronously controls the high-speed camera 27 and the infrared thermal imager 2 to begin data acquisition. The high-speed camera 27 and the infrared thermal imager 2, along with the second beam combiner 25, are connected to the optical path unit 7. The computer 21 synchronously controls the high-speed camera 27 and the infrared thermal imager 2 to monitor the temperature distribution and morphology of the molten pool, powder spreading quality, and surface quality of the formed workpiece in real time during the SLM forming process. It also acquires, analyzes, and stores multi-source real-time data on the morphology and temperature distribution of the molten pool area, sending feedback control signals to the computer 21 to adjust printing parameters, thereby reducing the generation of defects. At the same time, the computer 21 generates control signals for the gas circulation purification unit 9 in real time, which are transmitted to the dust removal and purification device 14 to achieve real-time high-speed printing airflow velocity and complete non-contact coaxial real-time monitoring of SLM printing.

[0066] Working principle:

[0067] While the computer 21 controls the dust removal and purification device 14, the high-speed camera 27, and the infrared thermal imager 2 to perform SLM processing, the semiconductor laser 6 is manually controlled to emit a 450nm wavelength laser to irradiate the processing surface 11. The processing surface 11 reflects a mixed beam of the 450nm wavelength laser and the 450nm and 810-920nm infrared wavelength molten pool self-emissions on the processing surface 11, which enters the optical path unit 7. Then, through the field lens 8, the reflected light of the mixed beam passes sequentially through the scanning galvanometer 5 and the first beam combiner 4. The scanning galvanometer 5 and the first beam combiner reflect the 810-920nm wavelength molten pool self-emissions from the mixed beam to the first filter 3 in the imaging unit 1 for filtering before being transmitted to the infrared thermal imager. 2. The 450nm band self-luminous light from the molten pool and the 450nm laser generated by the semiconductor laser in the transmitted mixed beam are reflected on the processing surface 11 to the second beam combiner 25. The second beam combiner 25 reflects the 450nm band self-luminous light from the molten pool and the 450nm laser generated by the semiconductor laser in the mixed beam to the high-speed camera 27 for synchronous imaging. The control unit 18 processes and stores the acquired temperature data from the infrared thermal imager 2 and the data from the high-speed camera 27 in real time. It combines the two multi-source data to adjust the processing parameters in real time and generates control signals to the dust removal and purification device 14 to adjust the airflow velocity in the printing chamber in real time, thus completing the coaxial SLM monitoring and real-time feedback control of the airflow in the printing chamber.

[0068] like Figure 2 As shown, the control method for the coaxial SLM monitoring and real-time feedback control of the printing chamber air field device includes the following steps:

[0069] Step 1: During SLM printing, computer 21 sends signals to the high-speed camera control module 31 in the high-speed camera controller 20 to control the recording of high-speed camera 27 and sends signals to the thermal imager control module 28 in the temperature signal processor 19 to control the recording of infrared thermal imager 2. It also sends signals to control laser 22 to emit a high-energy laser with a preset power of 1080nm wavelength and to control the scanning speed and scanning path of scanning galvanometer 5. The high-energy laser with a preset power of 1080nm wavelength is transmitted through optical fiber 23 to collimating lens 24. Collimating lens 24 reduces the divergence angle of the high-energy laser with a preset power of 1080nm wavelength and collimates it into parallel light. Then, the light passes sequentially through the second beam combiner 25, the first beam combiner 4, and scanning galvanometer 5. Based on the preset scanning speed and scanning path, scanning galvanometer 5 reflects the high-energy laser with a preset power of 1080nm wavelength to field mirror 8. Field mirror 8 focuses the laser onto the metal powder on the processing surface 11, thus processing... The metal powder on surface 11 melts rapidly to form a molten pool. Simultaneously, the laser generated by semiconductor laser 6 irradiates the molten pool area of ​​the processing surface 11. At the same time as the laser is generated, computer 21 sends a signal to control the dust removal and purification device 14 to circulate gas by sucking in and expelling air. The inert protective gas contaminated in the printing chamber on the processing surface is sucked in by the suction component 12 and transmitted to the dust removal and purification device 14 through the suction pipe 13 to purify the contaminated inert gas. Then, it is transmitted to the first blowing component 10 through the first blowing pipe 15. The first blowing component 10 divides the purified inert gas into two parts. One part is blown out from the first blowing component 10 to the processing area above the processing surface 11 to remove splashes and dust generated during the processing. The other part is transmitted to the second blowing component 17 through the second blowing pipe 16. The second blowing component 17 blows the purified inert gas to the area below the galvanometer to protect the galvanometer from splashes and dust contamination and to remove splashes and dust.

[0070] Step 2: During the processing, the mixed beam of the 450nm wavelength laser generated by the semiconductor laser in Step 1, reflected on the processing surface, and the self-luminous emission of the molten pool in the 450nm and 810-920nm wavelengths, enters the optical path unit through the field lens. The scanning galvanometer reflects the mixed beam to the first beam combiner. The first beam combiner reflects the self-luminous emission of the molten pool in the 810-920nm wavelength range of the mixed beam to the first filter and then transmits it to the infrared thermal imager for coaxial molten pool temperature distribution imaging. At the same time, the 450nm mixed beam of the molten pool self-luminous emission and the 450nm wavelength laser generated by the semiconductor laser, reflected on the processing surface, is reflected together to the second beam combiner. The second beam combiner reflects the 450nm mixed beam to the second filter and then transmits it to the high-speed camera for coaxial molten pool area imaging.

[0071] Step 3: The control unit 18 processes the molten pool area image from the high-speed camera 27 and the molten pool temperature distribution data from the infrared thermal imager 2 in real time, and obtains and stores the ROI region of the molten pool image and the ROI region of the temperature distribution from the temperature distribution data by cropping the molten pool area image with the laser spot position as the center. Specifically, the high-speed camera controller 20 processes the molten pool area image acquired by the high-speed camera 27 in real time, the image processing module 32 cropes the molten pool area image with the laser spot position as the center to obtain the ROI region of the molten pool image, and the data transfer module 33 stores the ROI region of the molten pool image into the computer 21; at the same time, the temperature signal processor 19 processes the molten pool temperature distribution data acquired by the infrared thermal imager 2 in real time, the temperature distribution processing module 29 cropes the molten pool temperature distribution data with the laser spot position as the center to obtain the ROI region of the temperature distribution, and the data storage module 30 stores the ROI region of the temperature distribution into the computer 21.

[0072] Step 4: The computer 21 in the control unit 18 simultaneously receives and stores the ROI region of the molten pool image and the ROI region of the temperature distribution transmitted from the high-speed camera controller 20 and the temperature signal processor 19 in step 3. At the same time, it analyzes whether there are any abnormalities in the temperature distribution of the molten pool and monitors the generation of splashes and dust. Combined with the analysis of the abnormalities in the splashes of the molten pool and the distribution of surrounding powder at the same moment, it determines whether to generate a feedback control signal.

[0073] The method for determining whether to generate a feedback control signal includes the following steps:

[0074] Step 4.1: When the computer 21 determines that the molten pool spatter and fumes have been properly cleared during the SLM processing, it will continue the printing process of the current process parameters by default.

[0075] Step 4.2: When the computer 21 determines that the molten pool splash and dust have not been clearly removed during the SLM processing, it generates a feedback control signal to adjust the airflow rate of the printing chamber output by the dust removal and purification device in real time, and performs feedback control to adjust the printing process of the printing chamber airflow until the entire part is printed layer by layer; when there is a lot of molten pool splash or obvious dust in the molten pool area, and the powder area is not obviously blown, the control unit determines to increase the airflow rate of the printing chamber to ensure that the airflow rate of the printing chamber is within the appropriate range; when there is little molten pool splash or no dust can be detected in the molten pool area, but the powder area is detected to be blown, the control unit determines to reduce the airflow rate of the printing chamber to ensure that the airflow rate of the printing chamber is within the appropriate range.

[0076] In conjunction with the above embodiments, the present invention adds an imaging unit 1 to the laser optical path of SLM processing and uses a semiconductor laser 6 as an auxiliary light source to realize coaxial status monitoring of SLM processing. A high-speed camera 27 is used to acquire images of the molten pool area and an infrared thermal imager 2 is used to acquire the temperature distribution of the molten pool. The high-speed camera controller 20 and the temperature signal processor 19 store and process the above molten pool status data in real time. The computer 21 further analyzes and processes the molten pool splash, smoke and powder status data, and generates real-time feedback control signals to adjust the airflow velocity of the printing chamber in real time during the processing, thereby realizing real-time feedback control of the SLM processing process, avoiding serious quality defects, and improving the stability of the SLM process.

Claims

1. A coaxial SLM monitors and real-time feedback control printing cabin wind field device, characterized in that, It includes an optical path unit, an imaging unit, a control unit, and a gas circulation and purification unit. The optical path unit includes a laser, a collimating lens, a first beam combiner, a second beam combiner, a scanning galvanometer, and a field lens. The laser and the scanning galvanometer are respectively connected to the control unit. The laser is connected to the collimating lens through an optical fiber. The control unit controls the laser to generate a laser with a preset power. The laser passes through the collimating lens, the second beam combiner, the first beam combiner, and the scanning galvanometer in sequence, and is then focused onto the processing surface by the field lens. The imaging unit includes a semiconductor laser, an infrared thermal imager, a high-speed camera, a first filter, and a second filter. The semiconductor laser is mounted above the processing surface, and the laser generated by the semiconductor laser irradiates the processing surface. The second filter and the high-speed camera are respectively arranged in the vertical direction of the second beam combiner. The first filter and the infrared thermal imager are respectively arranged in the vertical direction of the first beam combiner. The high-speed camera and the infrared thermal imager are respectively connected to the control unit. The gas circulation purification unit includes a dust removal and purification device, an air intake component, an air intake duct, a first air blowing component, a second air blowing component, a first air blowing duct, and a second air blowing duct. The dust removal and purification device is connected to the control unit. The air inlet of the dust removal and purification device is connected to the air intake component through the air intake duct, and the air outlet is connected to the first air blowing component through the first air blowing duct. The second air blowing component is installed on top of the first air blowing component through the second air blowing duct and is located between the scanning galvanometer and the first air blowing component. The air intake duct and the first air blowing duct are arranged opposite each other to form a semi-enclosed shape, so that the air intake component and the first air blowing component are symmetrically arranged on both sides of the processing surface. The first filter is a narrowband filter with a wavelength range of 810-920nm; the second filter is a single-pass filter with a wavelength of 450nm; the semiconductor laser generates 450nm laser; and the laser with preset power is a high-energy laser with a wavelength of 1080nm. The suction pipe and the second blowing pipe are both L-shaped, the first blowing pipe is C-shaped, and the suction component, the first blowing component and the second blowing component are respectively provided with multiple perforated airflow channels; The control unit is configured to: process the molten pool area image from the high-speed camera and the molten pool temperature distribution data from the infrared thermal imager in real time, and crop the molten pool area image with the laser spot position as the center to obtain and store the ROI region of the molten pool image. At the same time, it crops the temperature distribution data to obtain and store the ROI region of the temperature distribution. It also analyzes whether there are any abnormalities in the molten pool temperature distribution and monitors the generation of splashes and dust. When there are many molten pool splashes or obvious dust in the molten pool area, and the powder area is not blown away, the control unit determines to increase the airflow velocity in the printing chamber. When there are few molten pool splashes or no dust can be detected in the molten pool area, but the powder area is detected to be blown away, the control unit determines to decrease the airflow velocity in the printing chamber.

2. The coaxial SLM monitoring and real-time feedback control device for the printing chamber air field according to claim 1, characterized in that, The control unit includes a high-speed camera controller, a temperature signal processor, and a computer. The high-speed camera controller, temperature signal processor, laser, scanning galvanometer, and dust removal and purification device are respectively connected to the computer. The high-speed camera is connected to the high-speed camera controller, and the infrared thermal imager is connected to the temperature signal processor.

3. The coaxial SLM of claim 2, wherein the printing cabin wind field device is monitored and controlled in real time by feedback. The high-speed camera controller includes a high-speed camera control module, an image processing module, and a data transfer module. The high-speed camera control module is connected to a computer, the image processing module, and the high-speed camera. The image processing module is connected to the data transfer module, and the data transfer module is connected to the computer. The temperature signal processor includes a thermal imager control module, a temperature distribution processing module, and a data storage module. The thermal imager control module is connected to a computer, the temperature distribution processing module, and the infrared thermal imager. The temperature distribution processing module is connected to the data storage module, and the data storage module is connected to the computer.

4. The control method of the coaxial SLM monitoring and real-time feedback control printing cabin wind field device according to any one of claims 1 to 3, characterized in that, Includes the following steps: Step 1: During SLM printing, the control unit controls the high-speed camera and infrared thermal imager to start recording, controls the laser to emit a laser with a preset power, controls the scanning speed and scanning path of the scanning galvanometer, and controls the dust removal and purification device to draw in and expel air. The laser with the preset power passes through the collimating lens, the second beam combiner, the first beam combiner, and the scanning galvanometer in sequence, is reflected by the field lens, and then focused onto the metal powder on the processing surface. This causes the metal powder on the processing surface to melt rapidly and form a molten pool. At the same time, the laser generated by the semiconductor laser is irradiated onto the molten pool area on the processing surface. The inert protective gas contaminated in the printing chamber of the processing surface is drawn in by the air intake component. After the contaminated inert gas is purified by the dust removal and purification device, the purified inert gas is blown out between the processing surface and the scanning galvanometer by the first and second air blowing components, respectively. Step 2: During the processing, the mixed beam of the 450nm wavelength laser generated by the semiconductor laser in Step 1, reflected on the processing surface, and the self-luminous emission of the molten pool in the 450nm and 810-920nm wavelengths, enters the optical path unit through the field lens. The scanning galvanometer reflects the mixed beam to the first beam combiner. The first beam combiner reflects the self-luminous emission of the molten pool in the 810-920nm wavelength range of the mixed beam to the first filter and then transmits it to the infrared thermal imager for coaxial molten pool temperature distribution imaging. At the same time, the 450nm mixed beam of the molten pool self-luminous emission and the 450nm wavelength laser generated by the semiconductor laser, reflected on the processing surface, is reflected together to the second beam combiner. The second beam combiner reflects the 450nm mixed beam to the second filter and then transmits it to the high-speed camera for coaxial molten pool area imaging. Step 3: The control unit processes the molten pool area image from the high-speed camera and the molten pool temperature distribution data from the infrared thermal imager in real time, and obtains and stores the ROI region of the molten pool image by cropping the molten pool area image with the laser spot position as the center, and simultaneously cropping the temperature distribution data to obtain and store the ROI region of the temperature distribution. Step 4: The control unit receives and stores the ROI region of the molten pool image and the ROI region of the temperature distribution from Step 3. At the same time, it analyzes whether there are any abnormalities in the temperature distribution of the molten pool and monitors the generation of splashes and dust. Combined with the analysis of the abnormalities in the splashes of the molten pool and the distribution of surrounding powder at the same moment, it determines whether to generate a feedback control signal.

5. The control method of the coaxial SLM monitoring and real-time feedback control printing cabin wind field device according to claim 4, characterized in that, The method for determining whether to generate a feedback control signal includes the following steps: Step 4.1: When the control unit determines that the molten pool splash and fumes have been normally cleared during the SLM processing, it will continue the printing process with the current process parameters by default. Step 4.2: When the control unit determines that the molten pool splash and dust have not been removed during the SLM processing, it generates a feedback control signal to adjust the airflow rate of the printing chamber output by the dust removal and purification device in real time until the entire part is printed layer by layer.

6. The control method of the coaxial SLM monitoring and real-time feedback control printing cabin wind field device according to claim 5, wherein, The control method for the airflow velocity in the printing chamber described in step 4.2 is as follows: when there is a lot of molten pool splashing or obvious smoke in the molten pool area, and the powder area is not blown away, the control unit determines to increase the airflow velocity in the printing chamber; when there is little molten pool splashing or no smoke can be detected in the molten pool area, but the powder area is detected to be blown away, the control unit determines to decrease the airflow velocity in the printing chamber.

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