Point-surface additive manufacturing system and method based on dual-optical-path polarization multiplexing

Abstract

The invention provides a point-surface additive manufacturing system and method based on dual-optical-path polarization multiplexing, and relates to the technical field of additive manufacturing, and the method comprises the steps: importing a three-dimensional model of a part, generating hierarchical data by adopting a self-adaptive hierarchical algorithm, dividing each layer of data into a contour region and a filling region, and setting corresponding parameters; the coaxiality of the patterned light spot and the point light spot is calibrated, the energy density mapping relation in different polarization states is calibrated, and the optimal energy parameter is verified and stored based on the material type; loading a filling pattern, scanning according to a planned path, monitoring the temperature of a molten pool in real time, dynamically adjusting power, switching a polarization state mode to generate a spot light spot, and scanning according to the planned path to obtain a formed part; a point light spot light path and a patterned light spot light path are integrated in the additive manufacturing system at the same time, and the printing efficiency and the printing precision of laser additive manufacturing parts are synchronously improved through efficient switching of point light spot contour scanning and patterned light spot filling scanning.

Description

Technical Field

[0001] This invention relates to the field of laser additive manufacturing technology, and more particularly to a point-to-surface additive manufacturing system and method based on dual-path polarization multiplexing. Background Technology

[0002] Laser Powder Bed Fusion (LPBF) is an advanced metal additive manufacturing technology that uses a laser to scan a metal powder bed along a planned path, causing the powder to completely melt and solidify into a metallurgical bond, layer by layer, to form complex metal parts. It is widely used in aerospace, biomedical, and mold manufacturing fields. Patterned LPBF technology generates a pre-defined patterned laser using a spatial light modulator or dynamic spot shaping device. After scanning with a galvanometer and focusing with a field lens, the laser acts on the metal powder bed, achieving layer-by-layer selective melting and forming. With its ability to form multiple pixel areas in a single scan, it significantly improves the manufacturing efficiency of complex structural parts, demonstrating enormous application potential in high-precision fields such as aerospace and medical implants.

[0003] However, existing patterned laser powder bed melting technology generally adopts a single pattern filling scanning mode in the patterned splicing process, ignoring the fine scanning control of the contour area. This results in low contour accuracy and high edge surface roughness of the parts. Furthermore, the splicing area is prone to step effect due to the mismatch between filling and contour energy, which seriously affects the assembly accuracy and mechanical property consistency of complex structural parts. This severely limits the industrial application of patterned laser powder bed melting technology in the manufacturing of high-precision and high-performance parts.

[0004] Therefore, there is an urgent need for a point-to-surface additive manufacturing system and method that can simultaneously handle pattern filling and contour scanning, in order to improve the assembly accuracy and mechanical property consistency of complex structural parts. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a dot-surface additive manufacturing system and method based on dual-path polarization multiplexing. The additive manufacturing system simultaneously integrates dot-spot optical paths and patterned spot optical paths, and through efficient switching between dot-spot contour scanning and patterned spot filling scanning, the printing efficiency and accuracy of laser additive manufacturing parts are improved simultaneously.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a point-to-surface additive manufacturing system based on dual-optical-path polarization multiplexing, including a laser emission module, a mode conversion module, a spot generation module, an optical 4f module, an optical path scanning module, and a part forming module that are connected by communication. Laser emitting module: used to emit high-power polarized laser and adjust the laser spot into a rectangular uniform spot; Mode conversion module: used to dynamically adjust the polarization mode of incident light and separate light with different polarization states into different optical paths. The polarization modes include patterned light spot mode and dotted light spot mode. Spot generation module: Used to generate and output the corresponding spot based on the polarization mode output by the mode conversion module; Optical 4F module: used for filtering and imaging the laser beam output from the spot generation module; Optical path scanning module: used to project the combined light spot into the powder bed; Part forming module: Used to form parts based on light spot scanning.

[0007] Furthermore, the laser emitting module includes a laser emitting unit and a beam adjustment unit; The laser emitting unit includes a polarized laser, which is connected to a beam expander. The polarized laser emits high-power polarized laser light, and the beam expander increases the diameter of the laser spot. The beam adjustment unit adjusts the expanded laser beam into a rectangular uniform beam using a homogenization and shaping device.

[0008] Furthermore, the polarization laser is either a fiber laser or a semiconductor laser, and the output polarized light is either horizontally polarized or vertically polarized. If it is a fiber laser, polarization-maintaining fiber is used for transmission; if it is a semiconductor laser, polarization combining is used for beam combining.

[0009] Furthermore, the mode conversion module includes an electronically controlled liquid crystal variable delay unit. The output of the electronically controlled liquid crystal variable delay unit is connected to a first polarization beam splitter. The electronically controlled liquid crystal variable delay unit is used to dynamically adjust the polarization mode of the incident light, select and activate the patterned light spot channel or the dotted light spot channel, and output to the first polarization beam splitter. The first polarization beam splitter is used to separate polarized light of different polarization states into corresponding optical paths. The optical 4f module consists of two lenses, including a first lens and a second lens, used to filter and image the beam combining path output from the second polarizing beam splitter. Furthermore, the optical path scanning module includes a galvanometer and a field mirror, used to project the combined light spot into the powder bed.

[0010] Furthermore, the light spot generation module includes a pattern light spot generation unit, a dot light spot generation unit, and a beam combining unit; Patterned spot generation unit: used to generate patterned spots according to the patterned spot pattern output by the mode conversion module and transmit them to the beam combining unit; Spot generation unit: used to generate spotlights according to the spotlight pattern output by the mode conversion module and transmit them to the beam combining unit; Beam combining unit: Used to re-bundle the generated patterned light spot and dot light spot into a coaxial output.

[0011] Furthermore, the part forming module includes a powder bed and an atmosphere system; The powder bed is used for part forming and includes a forming cylinder, a powder cylinder, and a powder spreading shaft; The atmosphere system is used to provide an inert gas to the powder bed to prevent powder oxidation.

[0012] Furthermore, it also includes an automatic control module, which is a computer used for slicing, patterning, and planning the scanning path of printed parts, as well as a synchronous control mode conversion module, a spot generation module, an optical path scanning module, and a part forming module.

[0013] On the other hand, the present invention provides a point-to-surface additive manufacturing method based on dual-path polarization multiplexing, comprising the following steps: S1: Import the 3D model of the part, use an adaptive layering algorithm to generate layered data, divide each layer of data into contour area and fill area and set corresponding parameters, including spot parameters and scanning path; S2: Calibrate the coaxiality of patterned light spots and dot light spots, calibrate the energy density mapping relationship under different polarization states, and verify and store the optimal energy parameters based on material type; S3: Load the filling pattern and scan according to the planned path, monitor the molten pool temperature in real time and dynamically adjust the power, switch the polarization mode to generate dot spot and scan according to the planned path to obtain the formed part; S4: Cool the obtained parts and test their dimensional accuracy, density and mechanical properties.

[0014] The coaxiality calibration includes pattern spot channel calibration, dot spot channel calibration, and 4f system focusing calibration.

[0015] To compensate for energy loss during polarization state switching, two polarization states are alternately switched, and the energy density difference under the same laser power is measured. A compensation coefficient is added to the mapping table to ensure that the energy fluctuation during switching is ≤±2%. After the current layer is scanned, the surface morphology of the current layer is scanned using a laser profilometer to record the contour size deviation. The computer automatically calculates the compensation amount and writes the compensation parameters into the contour path of the next layer to avoid the accumulation of deviation.

[0016] The beneficial effects of this invention are as follows: Dual improvement in efficiency and accuracy: Patterned light spots enable rapid scanning of large areas of the filling region, forming multi-pixel areas in one step, significantly improving printing efficiency; Dotted light spots perform fine scanning of the contour area, with a minimum diameter of 5μm, greatly reducing edge roughness and improving contour accuracy; Dual optical path polarization state switching delay ≤50μs, working together without interruption, avoiding compromise between efficiency and accuracy.

[0017] Significantly optimized part quality: precise matching of energy parameters between the contour area and the filling area solves the step effect of traditional technology and improves the assembly accuracy of parts; real-time monitoring of the molten pool temperature and dynamic adjustment of power, combined with interlayer error compensation, ensures that the part density is ≥99.5% and the mechanical properties are consistent; inert gas protection and precise optical path calibration reduce oxidation and forming defects, and the surface roughness Ra≤1.5μm (contour area).

[0018] Enhanced system stability and applicability: Compatible with fiber lasers and semiconductor lasers, supports various metal materials, and applicable to a wide range of scenarios; the automatic control module integrates slicing, path planning, and multi-module synchronous control, standardizing the operation process and reducing human error; optical path coaxiality deviation ≤3μm, energy fluctuation ≤±2%, the system has high long-term operational stability, meeting the needs of industrial production. Attached Figure Description

[0019] Figure 1 This is a structural diagram of the point-to-surface additive manufacturing system based on dual-path polarization multiplexing according to the present invention.

[0020] Figure 2 It is the optical path of the patterned spot scanning mode.

[0021] Figure 3 It is the optical path of the spot scanning mode.

[0022] Figure 4 This is a flowchart of the point-to-surface additive manufacturing method based on dual-path polarization multiplexing according to the present invention.

[0023] The components in the attached diagram are labeled as follows: polarization laser 1, beam expander 2, homogenization and shaping device 3, electronically controlled liquid crystal variable delay device 4, first polarization beam splitter 5, first liquid crystal spatial light modulator 6, second polarization beam splitter 7, first reflector 8, second reflector 9, second liquid crystal spatial light modulator 10, first lens 11, second lens 12, galvanometer 13, field lens 14, powder bed 15, atmosphere system 16, and computer 17. Detailed Implementation

[0024] Please see Figure 1-3 As shown, the present invention provides a point-to-surface additive manufacturing system based on dual-path polarization multiplexing, including a laser emission module, a mode conversion module, a spot generation module, an optical 4f module, an optical path scanning module, and a part forming module that are connected by communication. Laser emitting module: used to emit high-power polarized laser and adjust the laser spot into a rectangular uniform spot; Mode conversion module: used to dynamically adjust the polarization mode of incident light and separate light with different polarization states into different optical paths. The polarization modes include patterned light spot mode and dotted light spot mode. Spot generation module: Used to generate and output the corresponding spot based on the polarization mode output by the mode conversion module; Optical 4F module: used for filtering and imaging the laser beam output from the spot generation module; Optical path scanning module: used to project the combined light spot into the powder bed; Part forming module: Used to form parts based on light spot scanning.

[0025] Specifically, such as Figure 2 The image shows the optical path in the patterned spot scanning mode. Figure 3 The diagram shows the optical path in the dot-spot scanning mode. The S-polarized light emitted from the polarized laser 1 is enlarged by the beam expander 2 and shaped into a rectangular spot of uniform intensity by the homogenizing and shaping device 3 before being input into the electro-controlled liquid crystal variable delay unit 4. The electro-controlled liquid crystal variable delay unit 4 outputs the polarization state (S-polarization) of the patterned spot with zero delay and is separated into the first optical path (first liquid crystal spatial light modulator 6) by the first polarization beam splitter 5. The patterned spot generated by the first liquid crystal spatial light modulator 6 is output to the second polarization beam splitter 7. Simultaneously, the electro-controlled liquid crystal variable delay unit 4 outputs the polarization state (P-polarization) of the dot-spot after a delay of λ / 2 and is separated into the second optical path (second liquid crystal spatial light modulator 10) by the first polarization beam splitter 5. The dot-spot generated by the second liquid crystal spatial light modulator 10 is then processed by the first... After the light path direction is changed by the mirror 8 and the second reflecting mirror 9, the light is output to the second polarizing beam splitter 7. The second polarizing beam splitter 7 recombines the two beams into a coaxial output. The laser beam is filtered and imaged by the optical 4f system composed of the first lens 11 and the second lens 12. The optical path scanning system composed of the galvanometer 13 and the field lens 14 projects the combined beam spot into the powder bed 15. Inert gas is added to the powder bed 15 to prevent powder oxidation. The part is formed by spreading powder and under the action of the combined laser. The computer 17 can realize automatic control, that is, it can realize the functions of slicing, patterning, and scanning path planning of printed parts, as well as synchronously control the electronically controlled liquid crystal variable delay device 4, the first liquid crystal spatial light modulator 6, the second liquid crystal spatial light modulator 10, the scanning system and the powder bed.

[0026] The laser emitting module includes a laser emitting unit and a beam adjustment unit; The laser emitting unit includes a polarized laser 1, which is connected to a beam expander 2. The polarized laser 1 emits high-power polarized laser light, and the beam expander 2 increases the diameter of the laser spot. The beam adjustment unit adjusts the expanded laser beam into a rectangular uniform beam using the homogenization and shaping device 3.

[0027] The polarization laser 1 is a fiber laser or a semiconductor laser, and the output polarized light is either horizontally polarized or vertically polarized. If it is a fiber laser, polarization-maintaining fiber is used for transmission; if it is a semiconductor laser, polarization beam combining is used for combination.

[0028] It should be noted that the entrance size of the beam expander 2 is larger than the polarized beam output by the polarized laser 1; the homogenization and shaping device 3 is used to shape the expanded laser spot into a rectangular spot of uniform intensity, and the optional methods include aspherical lens, microlens array, birefringent lens or optical waveguide.

[0029] The mode conversion module includes an electronically controlled liquid crystal variable delay unit 4. The output of the electronically controlled liquid crystal variable delay unit 4 is connected to a first polarization beam splitter 5. The electronically controlled liquid crystal variable delay unit 4 is used to dynamically adjust the polarization mode of the incident light, select and activate the patterned light spot channel or the dotted light spot channel, and output to the first polarization beam splitter 5. The first polarization beam splitter 5 is used to separate light of different polarization states to the corresponding optical paths.

[0030] Specifically, when the electronically controlled liquid crystal variable delay device 4 activates the dot spot channel, the output voltage V1 causes the liquid crystal molecules to be oriented with a π / 2 phase delay, and the polarization state of the incident light is converted to p polarization, which matches the reflection direction of the first polarization beam splitter 5; when switching to the pattern spot channel, the output voltage V2 (V2≠V1) resets the phase delay, and the polarization state of the incident light is converted to s polarization, which matches the transmission direction of the first polarization beam splitter 5.

[0031] The optical 4f module consists of two lenses, including a first lens 11 and a second lens 12, which are used to filter and image the beam combining path output by the second polarizing beam splitter 7.

[0032] The optical path scanning module includes a galvanometer 13 and a field mirror 14, which are used to project the combined light spot into the powder bed.

[0033] The light spot generation module includes a pattern light spot generation unit, a dot light spot generation unit, and a beam combining unit; Patterned spot generation unit: used to generate patterned spots according to the patterned spot pattern output by the mode conversion module and transmit them to the beam combining unit; Spot generation unit: used to generate spotlights according to the spotlight pattern output by the mode conversion module and transmit them to the beam combining unit; Beam combining unit: Used to re-bundle the generated patterned light spot and dot light spot into a coaxial output.

[0034] Specifically, the patterned light spot generation unit receives the patterned light path output from the first polarizing beam splitter 5 through the first liquid crystal spatial light modulator 6 to generate a patterned light spot and transmits it to the beam combining unit; the dot light spot generation unit receives the dot light path output from the first polarizing beam splitter 5 through the second liquid crystal spatial light modulator 10 to generate a dot light spot and transmit it to the beam combining unit, and a first first reflector 8 and a second reflector 9 are provided between the second liquid crystal spatial light modulator 10 and the first polarizing beam splitter 5 to adjust the direction of the light path; the beam combining unit re-bundles the two received light paths into a coaxial output through the second polarizing beam splitter 7.

[0035] The first liquid crystal spatial light modulator 6 can be an amplitude-type light valve or a phase-type light valve. When a phase-type light valve is used, a holographic phase map is loaded to generate a light spot of arbitrary shape. The second liquid crystal spatial light modulator 10 loads a uniform phase map through SLM1 to generate a diffraction-limited spot (5-50 μm in diameter), and the size of the spot can be adjusted according to the required contour accuracy.

[0036] The part forming module includes a powder bed 15 and an atmosphere system 16; The powder bed 15 is used for part forming, including a forming cylinder 151, a powder cylinder 152 and a powder spreading shaft 153; The atmosphere system 16 is used to provide an inert gas to the powder bed 15 to prevent powder oxidation.

[0037] It also includes an automatic control module, which is a computer 17, used for slicing, patterning, and scanning path planning of printed parts, as well as a synchronous control mode conversion module, a spot generation module, an optical path scanning module, and a part forming module.

[0038] Specifically, the computer 17 is used to synchronously control the electronically controlled liquid crystal variable delay device 4, the first liquid crystal spatial light modulator 6, the second liquid crystal spatial light modulator 10, the optical path scanning module, and the powder bed 15.

[0039] On the other hand, please see Figure 4 As shown, the present invention provides a point-to-surface additive manufacturing method based on dual-path polarization multiplexing, comprising the following steps: S1: Import the 3D model of the part, use an adaptive layering algorithm to generate layered data, divide each layer of data into contour area and fill area and set corresponding parameters, including spot parameters and scanning path; Specifically, the 3D CAD model of the part is imported into the computer, and then repaired using professional slicing software. Unlike traditional fixed-thickness layering, the adaptive layering algorithm dynamically adjusts the layer thickness according to the structural complexity and precision requirements of the part: a thinner layer thickness (10-20μm) is set for areas with high precision requirements (such as part edges and complex curved surfaces) to ensure the reproduction of cross-sectional details; a thicker layer thickness (30-50μm) is set for rough internal areas with low precision requirements to reduce the total number of layers and improve efficiency. The algorithm slices the 3D model along the forming direction (Z-axis), generating 2D cross-sectional data for each layer (including the contour boundary and internal structural coordinates of that layer), and automatically numbers the layering order (from the bottom layer to the top layer), providing a basis for subsequent area division.

[0040] Based on the surface accuracy requirements of the parts, each layer of 2D cross-sectional data is clearly divided into two types of regions. The software automatically marks the boundary coordinates of the two types of regions in each layer of 2D data to ensure that there are no missed or overlapping scans during subsequent spot scanning. The contour region is defined as a ring-shaped area 50-100μm inward from the outer edge of the part. This region directly affects the appearance accuracy and assembly fit of the part. Fine spot scanning is used, and the spot parameters are set (diameter 5-20μm, energy density 100-300J / mm). 2 The scanning path is spiral; the filled area is the inner region surrounded by the contour area, which is quickly filled using patterned light spots. The patterned light spot parameters are set (size 2×2mm). 2 -5×5mm 2 Energy density 50-200 J / mm 2 ) and orthogonal filling path. Synchronously set the polarization state switching timing (switching delay ≤ 50μs).

[0041] Simultaneously, the system is initialized and the atmosphere is prepared, namely, the polarization laser 1, beam expander 2, homogenization and shaping device 3, and electronically controlled liquid crystal variable delay device 4 are started to complete the hardware self-test; after the powder bed is evacuated to ≤1Pa, metal powder is loaded, and the powder layer thickness uniformity is verified (deviation ≤±2μm); the atmosphere system is filled with high-purity argon to make the oxygen content ≤10ppm and maintain the working pressure of 50-100kPa.

[0042] S2: Calibrate the coaxiality of patterned light spots and dot light spots, calibrate the energy density mapping relationship under different polarization states, and verify and store the optimal energy parameters based on material type; The coaxiality calibration includes pattern spot channel calibration, dot spot channel calibration, and 4f system focusing calibration.

[0043] Coaxiality deviation can cause misalignment between the filling area and the contour area, thus requiring calibration. A high-precision calibration plate (such as a glass substrate with a micron-level crosshair origin, accuracy ±1μm) is placed in the forming area of ​​the powder bed. An industrial camera (resolution ≥5 million pixels) and a laser confocal microscope (for measuring the spot size) are mounted above the calibration plate. The spot generation module and the optical path scanning module are activated via computer.

[0044] Patterned light spot channel calibration: The computer sends a "crosshair target pattern" (crosshair width 10μm, center theoretically aligned with the origin of the calibration plate) to the first liquid crystal spatial light modulator 6; the control galvanometer 13 precisely projects the patterned light spot onto the center area of ​​the calibration plate, ensuring that the light spot completely covers the crosshair target; the industrial camera captures the image of the projected crosshair spot, and the software automatically identifies the deviation value between the center of the crosshair spot and the origin of the calibration plate (e.g., X-axis deviation 5μm, Y-axis deviation 3μm); by adjusting the installation angle of the first polarizing beam splitter 5 (fine-tuning accuracy ±0.1°) and the position of the first reflector 8, the deviation is gradually reduced until the deviation is ≤3μm.

[0045] Dot spot channel calibration: The computer-controlled liquid crystal variable delay unit 4 switches to dot spot mode (outputs P-polarized light), the second liquid crystal spatial light modulator 10 loads a uniform phase map to generate a standard dot spot with a diameter of 10μm; the galvanometer 13 projects the dot spot onto the crosshair origin area of ​​the calibration plate, and the industrial camera captures the center of the dot spot; by adjusting the angle of the second reflector 9 (fine-tuning the direction of the optical path) and the position of the second polarizing beam splitter 7 (adjusting the beam combining optical path), the center of the dot spot is made to completely coincide with the crosshair center of the patterned spot, with a final deviation ≤2μm.

[0046] 4f system focusing calibration: Adjust the distance between the first lens 11 and the second lens 12 in the optical 4f module (fine-tuning accuracy 0.1mm), and measure the focusing size of the two spots on the powder bed surface using a laser confocal microscope to ensure that the focusing size deviation of the two types of spots is ≤1μm, so as to avoid local energy unevenness caused by focusing differences.

[0047] Polarization state switching may result in energy loss. It is necessary to establish the correspondence between laser power and actual energy density through calibration to ensure that energy fluctuation during switching is ≤±2%.

[0048] Pattern spot polarization state (e.g., S-polarization) energy calibration: A fully bright pattern is loaded onto the first liquid crystal spatial light modulator 6 (maximizing energy output). The laser output power is set to gradually increase from 50W to 300W (in 20W increments). Each time the power is adjusted, the actual energy density on the powder bed surface is measured using a laser power meter (energy density = power / spot area), and the data is recorded (e.g., at a power of 100W, 2×2mm). 2 Energy density of light spot (Unit conversion is required); establish a "laser power-patterned spot energy density" mapping table, and mark the compatibility range of different materials (e.g., Ti6Al4V patterned spot energy density 80-120J / mm). 2 (Corresponding laser power 128-192W).

[0049] Point spot polarization state (e.g., P-polarization) energy calibration: The second liquid crystal spatial light modulator 10 outputs a point spot with maximum amplitude (diameter 5-20μm), and the laser power is gradually increased from 30W to 200W (in 10W increments); the energy density at the center of the point spot is measured using a micropower meter (point spot energy density = power / πr). 2 (where r is the spot radius), record data (e.g., energy density of a 10μm spot at 50W power). (Note the need for unit conversion and actual attenuation); establish a "laser power-spot energy density" mapping table to ensure that the spot energy density is 10%-20% higher than that of the filled area (e.g., 100 J / mm² for the filled area). 2 The spot size is set to 110-120 J / mm. 2 (This ensures more complete melting of the contour).

[0050] Polarization state switching energy loss compensation: Alternately switch between two polarization states and measure the energy density difference at the same laser power (e.g., 100W corresponds to 100J / mm² in S polarization). 2 When polarized (P), 100W corresponds to 95J / mm². 2 (Energy loss of 5%); add compensation coefficients to the mapping table (e.g., the laser power needs to be increased by 5% for P polarization to achieve the same energy density as S polarization) to ensure that energy fluctuation during switching is ≤±2%.

[0051] Set multiple sets of energy parameters (e.g., energy density of Ti6Al4V filled region 80J / mm²). 2 100J / mm 2 120J / mm 2 The contour area corresponds to 150J / mm 2 180J / mm 2 210J / mm 2 Each sample is printed separately, and its quality (density, surface quality, mechanical properties) is tested to select the optimal parameters. The "material type - optimal spot parameters (size / energy density) - polarization state compensation coefficient" are linked and stored in the computer database. When printing parts made of the same type of material, this parameter set can be directly called without repeated calibration.

[0052] S3: Load the filling pattern and scan according to the planned path, monitor the molten pool temperature in real time and dynamically adjust the power, switch the polarization mode to generate dot spot and scan according to the planned path to obtain the formed part; Before performing spot scanning, the forming cylinder needs to be lowered by one layer thickness (10-50μm), the powder spreading shaft completes the new layer powder spreading, and the powder layer flatness (Ra≤5μm) is detected by a laser displacement sensor. Then, the computer automatically calls the current layer parameters stored in step S1, including the patterned spot size, energy density, scanning path of the filling area, and the spot parameters of the contour area, and loads the current layer filling pattern into the first liquid crystal spatial light modulator 6 to ensure that the pattern is completely matched with the boundary of the filling area.

[0053] The computer sends a command to the mode conversion module, and the electronically controlled liquid crystal variable delay unit 4 switches to the patterned spot polarization state (S-polarization). At this time, the first polarization beam splitter 5 separates the S-polarized light into the patterned spot channel (first optical path). The first liquid crystal spatial light modulator 6 generates a patterned spot of the corresponding shape according to the loaded filling pattern. After being combined by the second polarization beam splitter 7, the light is transmitted to the optical 4f module for filtering and imaging, ensuring that the spot uniformity is ≥90%. The galvanometer 13 moves the spot according to the orthogonal filling path (adjacent scanning lines intersect at 90°) planned in step S1. The scanning speed is set to 500-1000 mm / s (adaptively adjusted according to the pattern complexity), and the power is output according to the energy density mapping table calibrated in step S2. The molten pool temperature is monitored in real time using an infrared thermal imager (frame rate ≥ 1000fps). The target temperature range is 1800-2200K (matching the melting point of the metal material, such as Ti6Al4V with a melting point of about 1668℃, the molten pool temperature needs to be 100-500K higher than the melting point to ensure full fusion). If the temperature deviates from the preset range (such as below 1750K or above 2250K), the computer immediately sends an adjustment command to the laser: if the temperature is low, the power is increased (adjustment step size 5W), and if the temperature is high, the power is decreased to ensure the stability of the molten pool shape and avoid "incomplete fusion" or "overheating".

[0054] After the filling region scan is completed, the polarization state switching is completed within 50μs to avoid poor interlayer bonding caused by excessively rapid temperature drop within the layer. The computer sends a switching signal to the electronically controlled liquid crystal variable delay device 4, and the output voltage switches from V2 (patterned spot mode) to V1 (dot spot mode), causing a π / 2 phase delay in the orientation of the liquid crystal molecules, and the polarization state of the incident light changes from S polarization to P polarization. The first polarization beam splitter 5 identifies the P-polarized light and separates it into the dot spot channel (second optical path). At the same time, the computer confirms through an industrial camera that the patterned spot channel is closed and the dot spot channel is activated, ensuring no optical path crosstalk (energy crosstalk ≤1%). The second liquid crystal spatial light modulator 10 loads a uniform phase map to generate dot spots with a diameter of 5-20μm. After the optical path direction is adjusted by the reflectors (8, 9), it is transmitted to the second polarization beam splitter 7 and outputs coaxially with the original optical path. The optical 4f module filters again to ensure the focusing accuracy of the dot spot.

[0055] Galvanometer 13 moves along the spiral scanning path planned in step S1 (spiraling inward from the outer edge of the contour), with a scanning speed set to 200-300 mm / s (lower than the speed in the filling area to ensure sufficient time for the spot to melt the edge powder). According to the parameters calibrated in step S2, the spot power is 10%-20% higher than that in the filling area to ensure the contour melting depth is 5-10 μm deeper than that in the filling area, thus enhancing edge density. A high-speed camera (frame rate ≥ 10000 fps) is used to capture the molten pool morphology in the contour area, focusing on monitoring for "edge spatter" and "spheroidization" (if spatter occurs, the power is too high and needs to be reduced by 2-5 W; if spheroidization occurs, the power is too low and needs to be increased by 2-5 W). During the scanning process, a laser confocal microscope simultaneously detects the contour dimensions to ensure that the actual contour deviates from the designed contour by ≤ ±10 μm.

[0056] After the filling and contour scanning of a single layer are completed, the interlayer loop process begins until all layers are formed. A laser profilometer is used to scan the surface morphology of the current layer, recording the contour size deviation (e.g., the actual contour is 12μm larger than the design). The computer automatically calculates the compensation amount (compensation amount = deviation × 80%, e.g., a 12μm deviation is compensated by 9.6μm), and writes the compensation parameters into the contour path of the next layer to avoid deviation accumulation. The process of "forming cylinder descent → powder spreading → filling area scanning → polarization state switching → contour area scanning" is repeated until all layers defined in step S1 are formed, ultimately resulting in a complete 3D part.

[0057] S4: Cool the obtained parts and test their dimensional accuracy, density and mechanical properties.

[0058] After molding, the parts are cooled to ≤100℃, then removed and residual powder is cleaned. After removing the support structure, the dimensional accuracy (±10μm), density (≥99.5%) and mechanical properties of the parts are tested to ensure that they meet the design requirements.

[0059] The following provides a detailed and specific embodiment of the system and method of the present invention: I. System Initialization and Preparation Phase First, the hardware was debugged and checked. The working status of polarization laser 1 (fiber laser / semiconductor laser) was checked, and the power was turned on and preheated for 30 minutes. The output power stability (fluctuation ≤ ±1%) was verified by a power meter, and the polarization state (horizontal / vertical polarization ≥ 98%) was detected by a polarization degree meter. The optical components were calibrated. For beam expander 2, the position was adjusted so that the center of the laser beam coincided with the optical axis of the lens group. The circularity of the beam spot after beam expansion was confirmed to be ≥ 95% by a beam analyzer. For homogenization and shaping device 3, a microlens array (fine structure) or birefringent lens (large area shaping) was selected according to the characteristics of the parts. The output beam spot was observed by an infrared camera to ensure that the uniformity of the rectangular beam spot was ≥ 90% and the edge steepness was ≥ 80%. For polarization beam splitter prism 5 / 7, the installation angle was adjusted so that the transmittance of p-polarized light was ≥ 99% and the reflectance of s-polarized light was ≥ 99%. The extinction ratio was verified to be ≥ 1000:1 by a polarimeter.

[0060] Then, set the software parameters, import the part CAD model (format: STL / STEP) into computer 17, and use slicing software (such as Magics) to perform layer processing, with the layer thickness set to 10-50μm (10μm for fine areas and 50μm for rough areas).

[0061] The system automatically divides the area into a filled area (internal area) and a contour area (edge ​​range of 50-100μm). The filled area uses an orthogonal grid path with an overlap rate of 10%-15% between adjacent pattern spots. The contour area uses a spiral path with a spot spacing of 5-10μm. The switching timing of the electronically controlled liquid crystal variable delay unit 4 is set by the control software (pattern → contour channel switching delay ≤ 50μs), and the synchronization error between the galvanometer 13 and the liquid crystal spatial light modulator is ≤ ±5μs.

[0062] Then, prepare by cleaning the powder bed 15, evacuating it to ≤1Pa, and removing residual impurities; start the atmosphere system 16 and fill it with high-purity argon (purity ≥99.999%), and maintain the oxygen content ≤10ppm after 3 replacements, with a working pressure of 50-100kPa; load the metal powder (such as Ti6Al4V, particle size 15-53μm) into the powder cylinder 152, and spread 2-3 layers of powder by the powder spreading shaft 153, and check the uniformity of the powder layer thickness (deviation ≤±2μm) with a laser confocal microscope.

[0063] II. Optical Path Calibration and Parameter Verification First, the coaxiality of the dual light spots is calibrated. For the patterned light spot channel calibration, the computer 17 loads the cross target pattern onto the first liquid crystal spatial light modulator 6, and projects the light spot onto the calibration plate of the powder bed 15 through the galvanometer 13. The industrial camera captures the target image, and the angles of the first polarizing beam splitter 5 and the first first reflecting mirror 8 are adjusted so that the deviation between the center of the cross and the origin of the calibration plate is ≤3μm.

[0064] For dot spot channel calibration, switch the electronically controlled liquid crystal variable delay 4 to dot spot mode, and the second liquid crystal spatial light modulator 10 generates a 10μm dot spot; project the spot onto the calibration plate of the powder bed 15 through the galvanometer 13; adjust the second reflector 9 and the second polarizing beam splitter 7 to ensure that the center of the dot spot coincides with the cross center of the patterned spot (deviation ≤2μm); for 4f system focusing calibration, adjust the distance between the first lens 11 and the second lens 12 (accurate to 0.1mm) so that the size deviation of the focused spot on the powder bed surface of the two types of spots is ≤1μm.

[0065] Then, the energy parameters were calibrated. For the energy calibration of the patterned light spot, a fully bright pattern was loaded onto the first liquid crystal spatial light modulator 6, and the actual energy density (50-200 J / mm²) was measured at different laser powers using a laser power meter. 2 A power-energy density mapping table was established, and the optimal energy range for different materials was tested (e.g., Ti6Al4V: 80-120 J / mm). 2 316L stainless steel: 60-100J / mm 2 For spot energy calibration, the second liquid crystal spatial light modulator 10 outputs the maximum amplitude spot, and the energy density at the center of the spot (150-300 J / mm²) is measured by a micropower meter. 2 To ensure that the contour melting depth is 5-10 μm deeper than the filling area, the energy loss during polarization state switching is detected, and the energy attenuation (≤5%) under the two polarization states is recorded. Energy stability (fluctuation ≤±2%) is achieved during channel switching through laser power compensation.

[0066] III. Core Process of Layered Forming Powder spreading: The forming cylinder 151 descends by one layer thickness (e.g., 30μm), the powder cylinder 152 rises, and the powder spreading shaft 153 moves at a constant speed (50-100mm / s) to complete the spreading of the new layer of powder; the laser displacement sensor scans the surface of the powder layer to confirm the flatness (roughness Ra≤5μm). If it exceeds the standard, it triggers the re-spreading of powder.

[0067] Pattern spot filling scanning: Computer 17 sends a control signal to the electronically controlled liquid crystal variable delay device 4 to switch it to the pattern spot polarization state (such as p polarization). The first liquid crystal spatial light modulator 6 loads the current layer filling area pattern (resolution 1920×1080). The galvanometer 13 scans according to the planned path, and the scanning speed is set to 500-1000mm / s (adaptively adjusted according to the pattern complexity). The laser power is output according to the calibration parameters (such as Ti6Al4V filling power 200W). The infrared thermal imager monitors the molten pool temperature in real time (1800-2200K). If it deviates from the preset range of ±50K, the computer automatically adjusts the laser power (adjustment step size 5W).

[0068] Contour scanning: After the filling scan is completed, the computer 17 sends a switching signal, and the electronically controlled liquid crystal variable delay 4 switches the polarization state to the spot mode (such as s polarization) within 50μs. The second liquid crystal spatial light modulator 10 generates a spot with a diameter of 10μm. The galvanometer 13 scans the contour area along a spiral path. The scanning speed is set to 200-300mm / s (lower than the filling speed to ensure accuracy). The laser power is 10%-20% higher than that of the filling area (such as 220W) to ensure that the contour is fully melted. The high-speed camera (10000fps) captures the shape of the contour molten pool. If splashing or spheroidization occurs, the spot energy is adjusted immediately (adjustment step size 2W).

[0069] Interlayer detection and feedback: After each layer is formed, the surface morphology is scanned by a laser profilometer and the contour size deviation is recorded (allowable range ±10μm). If the deviation exceeds the standard (e.g. +15μm), the computer automatically corrects the contour path of the next layer (compensation amount 10μm). The atmosphere system 16 continuously monitors the oxygen content. When it exceeds 10ppm, argon is automatically added to maintain an inert environment.

[0070] IV. Post-forming processing stage After all layers are formed, the laser power is gradually reduced to 0, the galvanometer is reset to its origin, and the atmosphere system 16 is kept running for 30 minutes. Once the parts have cooled to below 100°C, the argon supply is stopped, and air is slowly refilled to atmospheric pressure. The forming cylinder 151 is raised, the parts and substrate are removed, and residual powder on the surface is cleaned (using compressed air + ultrasonic cleaning). The parts and substrate are separated (wire cutting or machining), and the support structure is removed. The quality of the parts is inspected, including their dimensions, internal quality, and surface quality. Specifically, the key dimensions of the parts are inspected using a coordinate measuring machine (accuracy ±5μm) to ensure they meet design requirements; the density of the parts is inspected using CT scanning (≥99.5%) to ensure there are no pores larger than 50μm; and the surface roughness of the parts is measured using a white light interferometer (Ra≤3μm in the filled area, Ra≤1.5μm in the contour area).

[0071] This invention achieves high-precision part forming through a "polarization multiplexing-dual-channel collaboration" mechanism. Based on the part slice data, the computer first activates the pattern spot channel through the electronically controlled liquid crystal variable delay device 4, and the first liquid crystal spatial light modulator 6 generates the filling area pattern to complete large-area rapid melting. Subsequently, the electronically controlled liquid crystal variable delay device 4 switches to the polarization state to activate the dot spot channel, and the second liquid crystal spatial light modulator 10 generates tiny dot spots (5-20μm in diameter) to perform fine scanning of the contour area, realizing step-by-step filling and contour forming. It can be applied to the additive manufacturing of metal parts in aerospace, automotive, medical and other fields, and is especially suitable for parts with complex structures and high surface quality requirements, such as turbine blades and orthopedic implants.

[0072] The above embodiments are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A point-to-surface additive manufacturing system based on dual-path polarization multiplexing, characterized in that, It includes a laser emission module, a mode conversion module, a spot generation module, an optical 4f module, an optical path scanning module, and a part forming module connected in sequence; Laser emitting module: used to emit high-power polarized laser and adjust the laser spot into a rectangular uniform spot; Mode conversion module: used to dynamically adjust the polarization mode of incident light and separate light with different polarization states into different optical paths. The polarization modes include patterned light spot mode and dotted light spot mode. Spot generation module: Used to generate and output the corresponding spot based on the polarization mode output by the mode conversion module; Optical 4F module: used for filtering and imaging the laser beam output from the spot generation module; Optical path scanning module: used to project the combined light spot into the powder bed; Part forming module: Used to form parts based on light spot scanning.

2. The point-to-surface additive manufacturing system based on dual-path polarization multiplexing according to claim 1, characterized in that, The laser emitting module includes a laser emitting unit and a beam adjustment unit; The laser emitting unit includes a polarized laser (1), which is connected to a beam expander (2). The polarized laser (1) emits high-power polarized laser light, and the beam expander (2) increases the diameter of the laser spot. The beam adjustment unit adjusts the expanded laser beam into a rectangular uniform beam using the homogenization and shaping device (3).

3. The point-to-surface additive manufacturing system based on dual-path polarization multiplexing according to claim 2, characterized in that, The polarization laser (1) is a fiber laser or a semiconductor laser, and the output polarization light is horizontally polarized light or vertically polarized light. If it is a fiber laser, polarization-maintaining fiber is used for transmission. If it is a semiconductor laser, then polarization beam combining is used.

4. The point-to-surface additive manufacturing system based on dual-path polarization multiplexing according to claim 1, characterized in that, The mode conversion module includes an electronically controlled liquid crystal variable delay device (4). The output of the electronically controlled liquid crystal variable delay device (4) is connected to a first polarization beam splitter (5). The electronically controlled liquid crystal variable delay device (4) is used to dynamically adjust the polarization mode of the incident light, select to activate the pattern light spot channel or the dot light spot channel, and output to the first polarization beam splitter (5). The first polarization beam splitter (5) is used to separate polarized light of different polarization states to the corresponding optical path. The optical 4f module consists of two lenses, including a first lens (11) and a second lens (12), which are used to filter and image the beam combining path output by the second polarizing beam splitter (7); The optical path scanning module includes a galvanometer (13) and a field mirror (14) for projecting the combined light spot into the powder bed.

5. The point-to-surface additive manufacturing system based on dual-path polarization multiplexing according to claim 1, characterized in that, The light spot generation module includes a pattern light spot generation unit, a dot light spot generation unit, and a beam combining unit; Patterned spot generation unit: used to generate patterned spots according to the patterned spot pattern output by the mode conversion module and transmit them to the beam combining unit; Spot generation unit: used to generate spotlights according to the spotlight pattern output by the mode conversion module and transmit them to the beam combining unit; Beam combining unit: Used to re-bundle the generated patterned light spot and dot light spot into a coaxial output.

6. The point-to-surface additive manufacturing system based on dual-path polarization multiplexing according to claim 1, characterized in that, The part forming module includes a powder bed (15) and an atmosphere system (16). The powder bed (15) is used for part forming and includes a forming cylinder (151), a powder cylinder (152) and a powder spreading shaft (153). The atmosphere system (16) is used to provide an inert gas to the powder bed (15) to prevent powder oxidation.

7. The point-to-surface additive manufacturing system based on dual-path polarization multiplexing according to claim 1, characterized in that, It also includes an automatic control module, which is a computer (17) used for slicing, patterning, dividing, and scanning path planning of printed parts, as well as a synchronous control mode conversion module, a spot generation module, an optical path scanning module, and a part forming module.

8. A point-to-surface additive manufacturing method based on dual-path polarization multiplexing, using the point-to-surface additive manufacturing system based on dual-path polarization multiplexing as described in any one of claims 1-7, characterized in that, Includes the following steps: S1: Import the 3D model of the part, use an adaptive layering algorithm to generate layered data, divide each layer of data into contour area and fill area and set corresponding parameters, including spot parameters and scanning path; S2: Calibrate the coaxiality of patterned light spots and dot light spots, calibrate the energy density mapping relationship under different polarization states, and verify and store the optimal energy parameters based on material type; S3: Load the filling pattern and scan according to the planned path, monitor the molten pool temperature in real time and dynamically adjust the power, switch the polarization mode to generate dot spot and scan according to the planned path to obtain the formed part; S4: Cool the obtained parts and test their dimensional accuracy, density and mechanical properties.

9. The point-to-surface additive manufacturing method based on dual-path polarization multiplexing according to claim 8, characterized in that, The coaxiality calibration includes pattern spot channel calibration, dot spot channel calibration, and 4f system focusing calibration.

10. The point-to-surface additive manufacturing method based on dual-path polarization multiplexing according to claim 8, characterized in that, To compensate for energy loss during polarization state switching, two polarization states are alternately switched, and the energy density difference under the same laser power is measured. A compensation coefficient is added to the mapping table to ensure that the energy fluctuation during switching is ≤±2%. After the current layer is scanned, the surface morphology of the current layer is scanned using a laser profilometer to record the contour size deviation. The computer automatically calculates the compensation amount and writes the compensation parameters into the contour path of the next layer to avoid the accumulation of deviation.

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