SLM quality improvement method and system based on dynamic focusing and light spot tracking

Abstract

The invention belongs to the technical field of additive manufacturing, and provides an SLM quality improving method and system based on dynamic focusing and light spot tracking. Comprising three core processes of real-time measurement, compensation calculation and dynamic focusing scanning, wherein height information of an actual working surface on a current scanning path relative to an ideal focal plane is measured in real time; the central processing and control unit calculates the real-time compensation amount of the laser focus; the three-dimensional dynamic focusing device adjusts the laser Z-axis focus position and is matched with the two-dimensional galvanometer to realize that a light spot is always focused on an actual working surface; according to the invention, the three-dimensional dynamic focusing device works cooperatively with the central processing and control unit and the distance measuring device to form a shape follow-up processing mechanism; a closed-loop control system effectively reduces forming defects through a ranging-control-focusing circulation mechanism; the adaptive adjustment capability of the system broadens the application boundary of the SLM technology.

Description

A Method and System for Improving SLM Quality Based on Dynamic Focusing and Spot Tracking Technical Field

[0001] This invention belongs to the field of additive manufacturing technology, and particularly relates to a method and system for improving the quality of SLM based on dynamic focusing and spot tracking. Background Technology

[0002] Traditional SLM equipment lacks "conformal processing" capabilities and suffers from poor molten pool stability: In the SLM process, the rapid melting and solidification of the metal material generates enormous thermal stress, causing warping and deformation of the formed portion (especially large-sized, complex structural parts). This causes the actual working surface formed by the current powder layer and the solidified portion to deviate from the ideal optical focal plane. Traditional SLM equipment uses a fixed-focusing two-dimensional galvanometer scanning system, which cannot dynamically adjust the laser focus position according to the deformation of the working surface. This results in fluctuations in laser energy density due to defocusing, leading to inconsistent molten pool size and uneven quality, becoming a core bottleneck affecting the basic quality of the formed parts. Furthermore, the lack of a closed-loop compensation mechanism results in numerous forming defects and difficulty in achieving the required accuracy: Existing SLM equipment lacks a closed-loop "range measurement-control-focusing" mechanism, making it unable to compensate for the defocusing problem caused by focal plane offset in real time. This directly leads to molding defects such as spheroidization and voids during the printing process, resulting in a generally low density of molded parts (below 98%) and mechanical properties such as tensile strength and hardness that fail to meet the demands of high-end manufacturing. Simultaneously, the accuracy of contour scanning is significantly reduced due to defocusing, with dimensional deviations of molded parts often exceeding ±0.1mm and surface roughness Ra values ​​often greater than 5μm. This necessitates additional post-processing steps such as milling and polishing, increasing production costs and extending the production cycle. Furthermore, the lack of adaptive adjustment capabilities limits the printing of complex parts: traditional SLM equipment relies on fixed process parameters (such as laser power and scanning speed) for printing, making it impossible to dynamically adjust the focus position based on the real-time deformation of large-sized, thin-walled, or overhanging complex structural parts. During the printing of such parts, accumulated thermal stress easily causes sudden warping, leading to problems such as localized defocusing and poor interlayer bonding. The success rate of first-pass molding is generally below 60%, severely limiting the application of SLM technology in the manufacturing of high-value-added, complex structural parts and hindering its penetration into high-end fields such as aerospace and precision molds. Therefore, SLM quality improvement methods and systems based on dynamic focusing and spot tracking are needed to address these issues. Summary of the Invention

[0003] The purpose of this invention is to provide a method and system for improving the quality of SLM based on dynamic focusing and spot tracking, so as to solve the problems mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a SLM quality improvement method based on dynamic focusing and spot tracking, comprising the following steps: S1, Real-time measurement: Before or simultaneously with the processing laser scanning and melting the current powder layer, a ranging device is used to measure the actual working surface on the current scanning path in real time. The actual working surface includes the formed part and the current powder layer laid on it, and the height information of the actual working surface relative to the preset ideal focal plane is obtained; S2, Compensation calculation: The central processing and control unit receives the real-time height data transmitted by the ranging device in step S1, compares the real-time height data with the preset ideal focal plane height value, and calculates the real-time focus compensation amount required by the processing laser at each point on the scanning path; S3, Dynamic focusing scanning: The central processing and control unit sends control commands to the three-dimensional dynamic focusing device. The three-dimensional dynamic focusing device adjusts the Z-axis focus position of the processing laser according to the real-time focus compensation amount, and at the same time, the two-dimensional galvanometer adjusts the X and Y axis scanning directions of the laser so that the laser spot is always focused on the actual working surface during the scanning process, thus completing the scanning of the current layer.

[0005] By employing a core process of "real-time measurement - compensation calculation - dynamic focusing scanning," a closed-loop control logic integrating measurement and processing is constructed. This breaks through the limitations of traditional fixed focusing, enabling real-time capture of work surface deformation. By calculating the real-time focus compensation amount, the focus position is dynamically adjusted to ensure that the laser spot always fits the actual work surface, thus solving the problem of spot defocusing from the source and laying the foundation for improving the overall quality of the formed parts.

[0006] In a further technical solution, in step S1, the measuring point of the ranging device and the processing point of the processing laser maintain a predetermined spatiotemporal correlation. The ranging device takes precedence over the processing laser by a preset time or a preset distance. The preset time range is 0.1ms to 1ms, and the preset distance range is 0.05mm to 0.2mm, ensuring that the measurement data accurately corresponds to the position of the point to be processed. The spatiotemporal correlation design between the ranging device and the processing laser avoids compensation delays caused by time or space differences between measurement and processing. The clear range of the preset time and preset distance ensures that the measurement data accurately corresponds to the position of the point to be processed, providing an accurate basis for subsequent compensation calculations and further improving the synchronization and accuracy of focus adjustment.

[0007] In a further technical solution, in step S3, the three-dimensional dynamic focusing device controls an electrically controlled liquid lens or a voice coil motor-driven moving lens group to achieve rapid and precise movement of the laser focus in the Z-axis direction, adjusting the response speed to match the laser scanning speed. The laser scanning speed ranges from 800mm / s to 1500mm / s, avoiding local defocusing. The Z-axis focus adjustment is achieved by using an electrically controlled liquid lens or a voice coil motor-driven moving lens group. Both methods have the characteristics of fast response speed and high adjustment accuracy. Furthermore, the adjustment response speed matches the laser scanning speed, which can avoid local defocusing caused by adjustment lag, ensuring the continuous stability of the focus position throughout the scanning process and ensuring uniform molten pool quality.

[0008] A further technical solution involves continuously looping steps S1, S2, and S3 during the current layer scanning process, forming a real-time closed-loop control system. This dynamically corrects focus shifts caused by work surface deformation, ensuring focus accuracy throughout the entire scanning cycle. The closed-loop execution mechanism enables the system to have real-time correction capabilities, continuously updating height data, calculating compensation amounts, and adjusting the focus during the current layer scanning. This dynamically addresses the increased deformation caused by accumulated thermal stress during printing, ensuring that the focus remains precisely focused throughout the entire printing cycle. This improves the consistency of quality across all layers of the formed part and avoids interlayer bonding defects caused by localized defocusing.

[0009] A further technical solution involves using a laser displacement sensor or a confocal chromatography sensor for the ranging device. The ranging device can be set coaxially or off-axis. When set coaxially, it is combined with the processing laser optical path through a beam splitter to achieve measurement along the same path and eliminate positional deviation. The selection of the laser displacement sensor and the confocal chromatography sensor takes into account both measurement speed and accuracy to meet the printing scenarios with different accuracy requirements. The coaxial setting combines the optical paths through a beam splitter to eliminate the positional deviation that may exist in off-axis measurement, ensuring that the measurement data can accurately reflect the actual height of the processing point, providing reliable data support for compensation calculation and improving the accuracy of compensation.

[0010] A further technical solution includes a path planning and pre-compensation step before step S1: the 3D model of the part is sliced ​​to generate scanning paths for each layer, with a slice thickness ranging from 20μm to 100μm. Simultaneously, based on historical deformation data or finite element simulation results of parts of the same material and structure, a basic Z-axis compensation curve is preset for easily deformable areas to reduce the real-time compensation adjustment range. The path planning and pre-compensation step, through a clearly defined slice thickness range, ensures that the slice quality meets the accuracy requirements of different parts. Combining historical deformation data or finite element simulation results with preset basic compensation curves reduces the adjustment range of subsequent real-time compensation, lowers the computational pressure on the central processing and control unit, improves overall scanning efficiency, and provides preliminary compensation for easily deformable areas, further ensuring molding quality.

[0011] A further technical solution involves a central processing and control unit that employs a dual-core architecture of a high-performance industrial computer and a field-programmable gate array (FPGA). The high-performance industrial computer is responsible for historical data processing and pre-compensation curve optimization, while the FPGA is responsible for real-time height data calculation and control command generation. The compensation calculation latency is no more than 0.1ms, meeting the requirements of high-speed scanning. The dual-core architecture of the central processing and control unit has a clear division of labor: the high-performance industrial computer processes historical data and optimizes the pre-compensation curve, while the FPGA is responsible for real-time calculation and command generation. The compensation calculation latency is controlled within 0.1ms, which can meet the requirements of high-speed laser scanning, ensure that focus adjustment and scanning actions are synchronized, and avoid defocusing caused by calculation latency.

[0012] The SLM quality improvement system based on dynamic focusing and spot tracking, applied to any of the aforementioned SLM quality improvement methods based on dynamic focusing and spot tracking, includes a three-dimensional dynamic focusing device, a ranging device, and a central processing and control unit. The ranging device is used to perform real-time distance measurement on the actual working surface (including the formed portion and the current powder layer on it) on the current scanning path before or simultaneously with the laser scanning and melting of the current powder layer, obtaining the height information of the actual working surface relative to a preset ideal focal plane. The central processing and control unit is signal-connected to both the ranging device and the three-dimensional dynamic focusing device, and is used to receive the real-time height data transmitted by the ranging device, compare the real-time height data with the preset ideal focal plane height value to calculate the real-time distance required by the processing laser at each point on the scanning path. The system calculates the focal compensation amount and sends a focal compensation control command to the three-dimensional dynamic focusing device. The three-dimensional dynamic focusing device is connected to the laser and two-dimensional galvanometer optical path of the traditional SLM equipment. It is used to receive control commands from the central processing and control unit and dynamically adjust the Z-axis focal position of the processing laser according to the real-time focal compensation amount. It also works with the two-dimensional galvanometer to adjust the X and Y axis scanning directions of the laser, so that the laser spot is always focused on the actual working surface during the scanning process. The system also works in conjunction with the powder spreading device and forming cylinder of the traditional SLM equipment. After the powder spreading device completes the powder spreading of the current layer, the system starts real-time measurement, compensation calculation and dynamic focusing scanning. After the current layer scanning is completed, the forming cylinder descends by one layer thickness, and the powder spreading device spreads the next layer of powder. The system repeats the above process until the part is printed.

[0013] Compared with existing technologies, the beneficial effects of this invention are as follows: In this invention, the collaborative work of the three-dimensional dynamic focusing device, the central processing and control unit, and the ranging device forms a "shape-following processing" mechanism: the central processing and control unit receives height data transmitted by the ranging device, quickly calculates the real-time focus compensation amount, and drives the three-dimensional dynamic focusing device to dynamically adjust the focus position, ensuring that the laser energy density always remains at the design value, avoiding energy fluctuations caused by defocusing, and ultimately obtaining a molten pool with consistent size and uniform quality. This fundamentally solves the problem of unstable molten pools in traditional equipment and improves the basic quality of the formed parts. Furthermore, the closed-loop control system of this invention effectively reduces forming defects through a "range-control-focusing" cyclic mechanism: real-time compensation eliminates spheroidization and voids caused by spot defocusing, increasing the density of the formed parts to [a higher level]. With a success rate exceeding 99.9%, mechanical properties such as tensile strength and hardness are improved by 10%-15%. Simultaneously, contour scanning accuracy is enhanced, controlling dimensional deviations within ±0.05mm and reducing surface roughness by 20%-30%, meeting the demands of high-precision manufacturing, reducing post-processing steps, and lowering production costs. This invention expands the application boundaries of SLM technology through its adaptive adjustment capabilities: it does not rely on fixed process parameters and can dynamically adjust the focus based on the real-time deformation of complex structural parts such as large-size, thin-walled, and overhanging components, significantly reducing the risk of printing failures for complex parts. For example, the success rate of one-time molding of large aerospace structural parts has increased from 60% with traditional equipment to over 90%, providing technical support for the manufacturing of high-value-added, complex structural parts and promoting the application of SLM technology in more high-end fields.

[0014] To more clearly illustrate the structural features and effects of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0015] Figure 1 is a system architecture diagram of the present invention; Figure 2 is a compensation comparison diagram of the present invention; Figure 3 is a flowchart of the workflow of the present invention. Detailed Implementation

[0016] The present invention will be further described below with reference to embodiments.

[0017] The following embodiments are used to illustrate the present invention, but should not be used to limit the scope of protection of the present invention. The conditions in the embodiments can be further adjusted according to specific conditions, and simple improvements to the method of the present invention under the premise of the concept of the present invention are all within the scope of protection claimed by the present invention.

[0018] As shown in Figures 1, 2, and 3, this embodiment of the invention provides a method for improving the quality of SLM based on dynamic focusing and spot tracking. The method includes a three-dimensional dynamic focusing device, a ranging device, a central processing and control unit, and a traditional SLM equipment consisting of a 500W fiber laser, a two-dimensional galvanometer, a hopper, a powder spreading device, a scraper, and a forming cylinder. The three-dimensional dynamic focusing device is equipped with an Optotune EL-10-30-TC electrically controlled liquid lens, the ranging device is a Keyence IL-600 laser displacement sensor, and the central processing and control unit contains a Xilinx Kintex-7 field-programmable gate array chip. The connections between the components are as follows: the laser output enters the three-dimensional dynamic focusing device via an optical path transmission component, and is then guided by the two-dimensional galvanometer to the processing area of ​​the forming cylinder. The ranging device is coaxially connected to the processing optical path via a beam splitter and connected to the central processing and control unit via a signal cable. The central processing and control unit is connected to the three-dimensional dynamic focusing device and the two-dimensional galvanometer via control cables.

[0019] In this embodiment, a titanium alloy TC4 aircraft door bracket for the aerospace field is printed. The bracket measures 300mm × 200mm × 150mm. Before printing, a 3D model of the bracket is imported into the central processing and control unit, and slicing is performed. The slice thickness is set to 50μm. Simultaneously, a Z-axis basic compensation curve is preset based on historical deformation data of the titanium alloy TC4. During printing, a powder spreading device removes titanium alloy powder from the hopper and evenly spreads it into the forming cylinder using a scraper. A ranging device prioritizes laser processing for 0.5ms and advances the scanning path by 0.1mm to measure the actual working surface height, transmitting the height data to the central processing and control unit in real time. The central processing and control unit calculates the real-time focus compensation amount, which ranges from -50μm to +50μm. Then, it drives the electronically controlled liquid lens to adjust the laser Z-axis focus position. The two-dimensional galvanometer synchronously drives the laser to scan along the X and Y axes, so that the light spot is always focused on the deformed actual working surface. After the current layer is scanned, the forming cylinder descends by 50μm, and the powder spreading device repeats the powder spreading action. The system cyclically executes the above process until printing is completed. The final formed door bracket has a density of 99.93%, a dimensional deviation of no more than 0.08mm, a surface roughness Ra of no more than 3.2μm, and no spheroidization or hole defects, which fully meets the design standards of aerospace parts.

[0020] Example 2 differs from Example 1 in that: the ranging device is replaced with a Micro-Epsilon confoSCAN40 confocal chromatograph sensor; the three-dimensional dynamic focusing device uses a Thorlabs MLZ100 voice coil motor to drive the moving lens group; a temperature compensation algorithm is added to the central processing and control unit to eliminate the influence of ambient temperature in the range of 5℃-35℃ on the ranging accuracy; and the printing object is replaced with a precision conformal cooling water channel of H13 mold steel, which has a diameter of 5mm and a length of 200mm.

[0021] In this embodiment, the confocal chromatography sensor is coaxially set with the processing optical path via a beam splitter, achieving a measurement accuracy of ±0.1μm, which can accurately capture the subtle deformation of the inner wall surface of the cooling channel. The focus adjustment speed of the moving lens group driven by the voice coil motor reaches 100μm / ms, matching the laser scanning speed of 1200mm / s, avoiding local defocusing during the scanning of the inner wall of the channel. The temperature compensation algorithm corrects the ranging deviation caused by the ambient temperature in real time, with a compensation range of 0.1μm / ℃. The final formed inner wall roughness Ra of the cooling channel does not exceed 1.6μm, which is 35% lower than that of products printed by traditional equipment. A water flow test was conducted on the channel with an inlet pressure of 0.8MPa and a flow rate of 10L / min. The test results showed that the cooling uniformity of the channel was improved by 18%, fully meeting the cooling requirements of the precision mold.

[0022] Example 3 differs from Example 2 in that: the central processing and control unit adopts a dual-core architecture of Advantech IPC-610 high-performance industrial computer and field-programmable gate array, and adds a historical data iterative optimization function, which can correct the current pre-compensation curve based on the real-time focus compensation data of the previous print; the ranging device adds a dual-sensor redundancy design, using two Micro-Epsilon confoSCAN40 confocal chromatography sensors to verify the measurement data in real time; the printing object is replaced with an aluminum alloy AlSi10Mg rocket fuel tank end frame, which has a size of 800mm×800mm×100mm.

[0023] In this embodiment, a dual confocal chromatograph sensor synchronously acquires the height data of the working surface of the tank end frame. If the deviation between the two sets of data exceeds 0.2 μm, the system automatically selects the set that is closer to the historical data trend as the valid data to ensure measurement reliability. A high-performance industrial computer processes the historical data of the real-time focus compensation amount of the first three tank end frame prints, optimizes the pre-compensation curve of easily deformable areas such as the corners of the end frame, and reduces the real-time compensation adjustment range by 30%. The field-programmable gate array keeps the compensation calculation delay at no more than 0.1 ms, drives the voice coil motor to drive the moving lens group to quickly respond to the thermal stress accumulation deformation caused by the large size of the end frame. Finally, the tank end frame is successfully formed in one go, and the overall deformation is controlled within 0.2 mm, which is 45% less than that of traditional equipment. The density reaches 99.91%, and a 10 MPa water pressure holding test for 30 minutes shows no leakage, which meets the sealing and structural strength requirements of rocket fuel tanks.

[0024] The working principle and usage process of this invention: Based on the core logic of "real-time perception - dynamic compensation - closed-loop iteration", the complete workflow is divided into five stages, as follows: Path planning and pre-compensation stage: The three-dimensional model of the part to be printed is imported through the central processing and control unit. The slicing thickness is set within the range of 20μm-100μm according to the part's accuracy requirements. The laser scanning path of each layer is generated using slicing software. At the same time, the historical deformation database of parts of the same material and structure stored in the central processing and control unit is called, or the easily deformable areas in the part printing process are predicted through finite element simulation software, such as the edges and corners of large-sized parts and thin-walled structures. The Z-axis basic compensation curve is preset for these areas to reduce the adjustment range of subsequent real-time compensation and improve the system response speed.

[0025] Real-time distance measurement stage: After the SLM equipment is started, the powder spreading device takes out metal powder from the hopper and spreads the powder evenly on the surface of the formed part of the forming cylinder with a scraper, completing the powder spreading of the current layer; then the central processing and control unit sends a start command to the ranging device. The ranging device performs high-speed scanning measurement of the actual working surface of the current layer according to the preset spatiotemporal association rules, that is, prioritizing the processing laser by 0.1ms-1ms and leading by 0.05mm-0.2mm along the scanning path. It collects the height information of 100-500 measurement points every millisecond and transmits the real-time height data to the central processing and control unit through the signal cable.

[0026] In the focus compensation calculation stage: After receiving real-time height data, the central processing and control unit calculates the difference between the actual height value of each measurement point and the preset ideal focal plane height value to obtain the real-time focus compensation amount corresponding to that point. If a dual-core architecture of a high-performance industrial computer and a field-programmable gate array is adopted, the high-performance industrial computer synchronously iteratively optimizes the pre-compensation curve based on historical printing data, while the field-programmable gate array focuses on the rapid calculation of the real-time focus compensation amount, ensuring that the compensation calculation delay does not exceed 0.1ms, meeting the real-time requirements of high-speed laser scanning of 800mm / s-1500mm / s.

[0027] Dynamic focusing and scanning stage: The central processing and control unit sends control commands to the three-dimensional dynamic focusing device based on the calculated real-time focus compensation amount. If the three-dimensional dynamic focusing device is equipped with an electrically controlled liquid lens, the command will control the change in the refractive index of the liquid inside the lens to adjust the Z-axis position of the laser focus. If a voice coil motor is used to drive the moving lens group, the command will drive the motor to move the lens along the Z-axis with an adjustment accuracy of micrometer level. At the same time, the central processing and control unit sends X and Y axis scanning commands to the two-dimensional galvanometer to move the laser along a preset path. The three-dimensional dynamic focusing device and the two-dimensional galvanometer work together to ensure that the laser spot always fits the deformed actual working surface during the scanning process. The processing laser simultaneously melts and solidifies the powder to form a stable and uniform molten pool.

[0028] Closed-loop iteration stage: After the current layer scanning is completed, the forming cylinder drives the formed part to descend one layer of slice thickness, and the powder spreading device takes powder from the hopper again and completes the next layer of powder spreading; the central processing and control unit sends start commands to the ranging device, the three-dimensional dynamic focusing device, and the two-dimensional galvanometer again, and the system repeatedly executes the real-time distance measurement, focus compensation calculation, and dynamic focusing scanning steps to form a closed-loop cycle of "powder spreading-measurement-calculation-focusing-scanning"; this cycle continues to execute until all slice layers of the part are printed, ensuring that the laser spot is always accurately focused throughout the process, and finally achieving high-quality SLM forming.

[0029] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for improving the quality of SLM based on dynamic focusing and spot tracking, characterized in that, Includes the following steps: S1. Real-time Measurement: Before or simultaneously with the laser scanning and melting of the current powder layer, a ranging device is used to measure the actual working surface on the current scanning path in real time. The actual working surface includes the formed part and the current powder layer laid on it. The height information of the actual working surface relative to the preset ideal focal plane is obtained. S2. Compensation Calculation: The central processing and control unit receives the real-time height data transmitted by the ranging device in step S1, compares the real-time height data with the preset ideal focal plane height value, and calculates the real-time focus compensation amount required by the processing laser at each point on the scanning path. S3. Dynamic Focusing Scan: The central processing and control unit sends control commands to the three-dimensional dynamic focusing device. The three-dimensional dynamic focusing device adjusts the Z-axis focus position of the processing laser according to the real-time focus compensation amount. At the same time, the two-dimensional galvanometer adjusts the X and Y axis scanning directions of the laser so that the laser spot is always focused on the actual working surface during the scanning process, completing the scanning of the current layer.

2. The SLM quality improvement method based on dynamic focusing and spot tracking according to claim 1, characterized in that, In step S1, the measuring point of the ranging device and the processing point of the processing laser are kept in a predetermined spatiotemporal relationship. The ranging device takes priority over the processing laser by a preset time or a preset distance. The preset time range is 0.1ms to 1ms, and the preset distance range is 0.05mm to 0.2mm, to ensure that the measurement data corresponds accurately with the position of the point to be processed.

3. The SLM quality improvement method based on dynamic focusing and spot tracking according to claim 1, characterized in that, In step S3, the three-dimensional dynamic focusing device controls the movable lens group driven by an electrically controllable liquid lens or a voice coil motor to achieve rapid and precise movement of the laser focus in the Z-axis direction, adjusting the response speed to match the laser scanning speed. The laser scanning speed ranges from 800 mm / s to 1500 mm / s to avoid local defocusing.

4. The SLM quality improvement method based on dynamic focusing and spot tracking according to claim 1, characterized in that, Steps S1, S2, and S3 are executed continuously and cyclically during the current layer scanning process, forming a real-time closed-loop control system that dynamically corrects focus shift caused by working surface deformation, ensuring focus accuracy throughout the entire scanning cycle.

5. The SLM quality improvement method based on dynamic focusing and spot tracking according to claim 1, characterized in that, The ranging device uses a laser displacement sensor or a confocal chromatography sensor. The ranging device can be set coaxially or off-axis. When set coaxially, it is combined with the processing laser optical path through a beam splitter to achieve measurement along the same path and eliminate positional deviation.

6. The SLM quality improvement method based on dynamic focusing and spot tracking according to claim 1, characterized in that, Before step S1, there are also path planning and pre-compensation steps: the 3D model of the part is sliced ​​to generate scanning paths for each layer, with the slice thickness ranging from 20μm to 100μm. At the same time, based on the historical deformation data or finite element simulation results of parts of the same material and structure, a basic Z-axis compensation curve is preset for easily deformable areas to reduce the real-time compensation adjustment range.

7. The SLM quality improvement method based on dynamic focusing and spot tracking according to claim 1, characterized in that, The central processing and control unit adopts a dual-core architecture of a high-performance industrial computer and a field-programmable gate array (FPGA). The high-performance industrial computer is responsible for historical data processing and pre-compensation curve optimization, while the FPGA is responsible for real-time height data calculation and control command generation. The compensation calculation delay is no more than 0.1ms, which meets the requirements of high-speed scanning.

8. A SLM quality improvement system based on dynamic focusing and spot tracking, applied to the SLM quality improvement method based on dynamic focusing and spot tracking as described in any one of claims 1-7, characterized in that, The system includes a three-dimensional dynamic focusing device, a ranging device, and a central processing and control unit. The ranging device measures the actual working surface (including the formed part and the current powder layer on it) on the current scanning path in real time before or simultaneously with the processing laser scanning and melting the current powder layer, obtaining the height information of the actual working surface relative to the preset ideal focal plane. The central processing and control unit is connected to the ranging device and the three-dimensional dynamic focusing device, respectively, and receives the real-time height data transmitted by the ranging device. It compares the real-time height data with the height value of the preset ideal focal plane to calculate the real-time focus compensation amount required by the processing laser at each point on the scanning path, and sends focus compensation control commands to the three-dimensional dynamic focusing device. The three-dimensional dynamic focusing device is connected to the laser and two-dimensional galvanometer optical path of the traditional SLM equipment. It receives the control commands from the central processing and control unit, dynamically adjusts the Z-axis focus position of the processing laser according to the real-time focus compensation amount, and coordinates with the two-dimensional galvanometer to adjust the X and Y axis scanning directions of the laser, so that the laser spot is always focused on the actual working surface during the scanning process.

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