A dynamic microwave-assisted laser metal additive manufacturing method and device

Abstract

The embodiment of the application relates to a kind of laser metal additive manufacturing methods based on dynamic microwave auxiliary, comprising the following steps: S1: determining the process parameters of laser additive manufacturing, and determining preset molten pool size based on process parameters;S2: control laser beam acts on metal material to form liquid molten pool, while using multistage microwave screening device to the space constraint and screening of microwave beam, the action range of microwave beam is focused to the scale matched with preset molten pool size;S3: after screening, microwave beam is directionally applied to liquid molten pool and solid-liquid interface region;S4: control after screening, microwave beam and laser beam synchronous movement, cooperate laser beam and carry out the layer-by-layer accumulation of material to complete part forming. By realizing the localized, special-shaped and dynamic control of microwave energy field, not only the inherent defects of laser are compensated from the heat field angle, but also the metallurgical defects are improved from the microscopic dynamics angle. The application also provides a kind of laser metal additive manufacturing device based on dynamic microwave auxiliary.

Description

Technical Field

[0001] This application relates to the field of metal additive manufacturing technology, and in particular to a method and apparatus for laser metal additive manufacturing based on dynamic microwave assistance. Background Technology

[0002] Additive manufacturing technology, especially selective laser melting (SLM) and laser melting deposition (LMD), has been widely used in aerospace, biomedical and other fields because it can directly form metal parts with complex structures. However, due to the extremely high energy density and extremely short duration of the laser heat source, the metal material undergoes a rapid melting and solidification cycle during the forming process, which inevitably brings a series of metallurgical defects and mechanical property problems.

[0003] In existing technologies, the main challenges are concentrated in the following aspects: First, thermal stress and cracks caused by temperature gradients. The energy of laser beams is usually Gaussian distributed (extremely high energy at the center and rapidly decaying at the edges), resulting in a huge temperature gradient inside the molten pool. This non-uniform thermal field distribution generates extremely large residual stress during solidification, which can induce microcracks and even cause warping and deformation of parts. Second, porosity and incomplete fusion defects. Due to the extremely rapid cooling rate of the molten pool, bubbles in the melt often do not have time to escape and are "frozen" in the solid phase, forming pores; at the same time, if the interlayer energy input is insufficient or the fluidity is poor, incomplete fusion defects are easily generated, which seriously affects the fatigue performance of the component. Third, difficulty in controlling the microstructure. Rapid directional solidification easily leads to the growth of coarse columnar crystals, causing anisotropy in the mechanical properties of the material.

[0004] To address these issues, existing technologies attempt to introduce auxiliary heat sources. Common solutions include induction heating, resistance heating, or overall microwave heating. For example, patent CN119910751A proposes a method for additive manufacturing within a sealed microwave high-temperature cavity, utilizing microwaves to preheat the entire environment or workpiece. However, this "macroscopic, static, and holistic" heating method has significant limitations: 1. Lack of localization and flexibility: Overall heating heats the entire forming chamber or the entire workpiece, making precise energy control impossible for the core area of ​​the tiny "molten pool." This "flooding" heating not only consumes a lot of energy but also easily leads to grain coarsening or heat accumulation deformation in the formed parts. 2. Inability to compensate for the Gaussian thermal field of lasers: Existing microwave-assisted methods mostly pursue uniform heating and cannot compensate for the inherent "high center, low edge" defect of laser heat sources in terms of spatial energy, making it difficult to fundamentally level the temperature gradient inside the molten pool. 3. Lack of kinetic intervention mechanism: Existing microwave applications mainly utilize its "thermal effect" (preheating), while ignoring the "non-thermal effects" (such as electromagnetic oscillation and vibration) that microwave electromagnetic fields may produce on metal atoms and melt flow. Therefore, its effectiveness in eliminating micropores and refining grains is limited. 4. Control lag: Traditional temperature control methods are mostly open-loop or simple single-point feedback, which are difficult to adapt to the dynamic characteristics of the rapidly changing molten pool morphology during additive manufacturing. Summary of the Invention

[0005] One objective of this application is to provide a method and apparatus for laser metal additive manufacturing based on dynamic microwave assistance, which at least solves the above-mentioned problems.

[0006] To achieve the above objectives, some embodiments of this application provide a method for laser metal additive manufacturing based on dynamic microwave assistance, comprising the following steps:

[0007] S1: Determine the process parameters for laser additive manufacturing, and determine the preset molten pool size based on the process parameters;

[0008] S2: Control the laser beam to act on the metal material to form a liquid molten pool. At the same time, use a multi-level microwave screening device to spatially constrain and screen the microwave beam, focusing the effective range of the microwave beam to a scale that matches the preset molten pool size.

[0009] S3: Apply the selected microwave beam in a directional manner to the liquid molten pool and the solid-liquid interface region;

[0010] S4: Control the microwave beam and laser beam to move synchronously after screening, and cooperate with the laser beam to deposit materials layer by layer to complete the part forming.

[0011] Some embodiments of this application provide a dynamic microwave-assisted laser metal additive manufacturing apparatus, applied to the aforementioned method, including:

[0012] The additive manufacturing host is equipped with a laser generation system, which is used to provide a laser beam heat source and control the layer-by-layer deposition of metal materials to form a liquid molten pool during the forming process;

[0013] A microwave generating system used to generate microwave beams with adjustable frequency and power;

[0014] A multi-stage microwave screening device, connected to the microwave generating system and set at the end of the microwave transmission path, is configured to spatially constrain and directionally screen the microwave beam, focusing the effective range of the microwave beam to a scale that matches the size of the molten pool.

[0015] A linkage mechanism is used to drive the multi-stage microwave screening device to move synchronously with the laser beam;

[0016] The control system receives temperature feedback data from the molten pool and adjusts the output power and frequency of the microwave generator system in real time according to a preset dual closed-loop control strategy.

[0017] Compared with related technologies, the solution provided in this application overcomes the limitation of traditional microwave-assisted technologies (such as microwave cavity heating) which can only perform overall, large-scale heating, and achieves precise delivery of microwave energy. In addition, by moving synchronously, ineffective heating or secondary thermal damage to the solidified area is avoided, and intervention is only carried out on the molten pool area that most needs energy regulation, which significantly improves the energy efficiency ratio.

[0018] By achieving localization, irregular shaping, and dynamic control of the microwave energy field, not only are the inherent defects of lasers compensated from the perspective of thermal field, but metallurgical defects are also improved from the perspective of micro-dynamics. Compared with the overall or static heating of existing technologies, it has the advantages of simple method, precise control, high forming quality, and superior material properties. Attached Figure Description

[0019] One or more embodiments are illustrated by way of example with reference numerals in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the figures in the drawings are not to be limited by scale.

[0020] Figure 1 This is a schematic diagram of the framework flow of the laser metal additive manufacturing method based on dynamic microwave-assisted manufacturing provided in the embodiments of this disclosure.

[0021] Figure 2 This is a schematic diagram of the laser metal additive manufacturing apparatus provided in this embodiment acting on a solid metal region and a molten pool.

[0022] Figure 3 This is a schematic diagram of a microwave generating system provided in an embodiment of this disclosure.

[0023] Figure 4 This is a schematic diagram of the microwave generating system acting on the molten pool according to an embodiment of this disclosure.

[0024] Figure label:

[0025] 10: Additive manufacturing host; 20: Microwave generating system; 21: Solid-state microwave source; 22: Multi-stage microwave screening device; 221: Wave-transmitting focusing layer; 222: Irregularly shaped hollow metal structure layer; 223: Wave-absorbing cutting layer; 100: Molten pool. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0027] The terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this disclosure are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of this disclosure described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion.

[0028] In this disclosure, the terms "upper," "lower," "inner," "middle," "outer," "front," and "rear," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for better description of the embodiments of this disclosure and their implementations, and are not intended to limit the indicated devices, elements, or components to having a specific orientation, or to require them to be constructed and operated in a specific orientation. Furthermore, some of the aforementioned terms may be used to indicate other meanings besides orientation or positional relationship; for example, the term "upper" may in some cases indicate a dependency or connection relationship. Those skilled in the art can understand the specific meaning of these terms in the embodiments of this disclosure according to the specific circumstances.

[0029] Furthermore, the terms "set up," "connect," and "fix" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this disclosure according to the specific circumstances.

[0030] Unless otherwise stated, the term "multiple" means two or more.

[0031] In this embodiment of the disclosure, the character " / " indicates that the objects before and after it are in an "or" relationship. For example, A / B means: A or B.

[0032] The term "and / or" describes an association between objects, indicating that three relationships can exist. For example, A and / or B means: A or B, or A and B.

[0033] It should be noted that, unless otherwise specified, the embodiments and features described in the present disclosure can be combined with each other.

[0034] Combination Figures 1 to 4 As shown in the figure, an embodiment of this disclosure provides a laser metal additive manufacturing method based on dynamic microwave assistance, comprising the following steps:

[0035] S1: Determine the process parameters for laser additive manufacturing, and determine the preset molten pool size 100 based on the process parameters;

[0036] S2: Control the laser beam to act on the metal material to form a liquid molten pool 100, and at the same time use the multi-level microwave screening device 22 to spatially constrain and screen the microwave beam, focusing the effective range of the microwave beam to a scale that matches the preset size of the molten pool 100.

[0037] S3: Apply the selected microwave beam in a directional manner to the liquid molten pool 100 and the solid-liquid interface region;

[0038] S4: Control the microwave beam and laser beam to move synchronously after screening, and cooperate with the laser beam to deposit materials layer by layer to complete the part forming.

[0039] The method provided in this embodiment achieves precise localization of microwave energy field application. By utilizing a multi-stage microwave filtering device 22 to spatially constrain and filter the microwave beam, the effective range of the microwave is successfully focused from the centimeter-level coverage of a conventional microwave source to a millimeter-level scale matching the size of the laser molten pool 100. This localized control overcomes the defects of energy divergence, excessively large and discontinuous heating area in traditional microwave-assisted technology, ensuring that microwave energy acts only directionally on the liquid molten pool 100 and the solid-liquid interface region. This effectively avoids ineffective heat accumulation or secondary damage to non-processed areas (such as solidified parts), significantly improving energy utilization efficiency and processing accuracy.

[0040] Secondly, this embodiment significantly improves the metallurgical quality of the formed parts through a unique microwave vibration and kinetic intervention mechanism. The selected microwave electromagnetic field induces high-frequency vibrations within the molten pool 100, a non-thermodynamic effect similar to "concrete vibration." This effect significantly reduces the diffusion barrier of atoms at the solid-liquid interface, accelerating the rapid migration and mutual solubility of alloying elements, thus solving problems of poor interlayer bonding and element segregation. Furthermore, it effectively disrupts the adhesion of bubbles in the melt, promoting their active escape, thereby eliminating porosity defects and refining the grain structure. Simultaneously, combined with the bulk heating effect of microwaves, the temperature gradient within the molten pool 100 is effectively controlled and leveled, fundamentally suppressing the generation of thermal stress and cracks.

[0041] Furthermore, this embodiment achieves dynamic coordination of energy field assistance throughout the entire process. By controlling the selected microwave beam and laser beam to move synchronously, it is ensured that the auxiliary energy field accurately follows the processing hotspot throughout the entire layer-by-layer deposition manufacturing process. This dynamic accompanying characteristic ensures that the molten pool 100 is always in the optimal "thermal-mechanical" coupling environment regardless of changes in the scanning path, thereby guaranteeing the uniformity of the microstructure and consistency of the mechanical properties of the final formed part in terms of overall dimensions, effectively solving the problem of unstable forming quality of complex components.

[0042] The laser metal additive manufacturing method based on dynamic microwave assistance provided in this disclosure firstly sets process parameters such as laser power and scanning speed according to the material properties (e.g., thermal conductivity, melting point) and geometric characteristics of the part to be processed, and predicts the size of the liquid molten pool 100 generated under laser action through experiments or simulations. Next, during the printing process, a multi-stage microwave screening device 22 physically constrains the wide beam generated by the microwave generator. This device, similar to a funnel, "compresses" and focuses the originally centimeter-wavelength microwave energy beam to a scale matching the millimeter-scale molten pool 100. Subsequently, this focused microwave beam is precisely aligned with the liquid molten pool 100 and the surrounding solid-liquid interface. Finally, through a mechanical linkage mechanism, the microwave screening device moves synchronously with the laser head, ensuring that the microwaves always move along with the laser during the layer-by-layer melting and powder deposition process, playing an auxiliary role at the molten pool 100.

[0043] This embodiment overcomes the limitation of traditional microwave-assisted technologies (such as microwave cavity heating) which can only perform overall, large-area heating, achieving millimeter-level precise delivery of microwave energy. Furthermore, by moving synchronously, it avoids ineffective heating or secondary thermal damage to the already solidified area, intervening only in the molten pool 100 region that most urgently requires energy control, significantly improving the energy efficiency ratio.

[0044] Optionally, the specific method of screening using the multi-stage microwave screening device 22 in step 2 includes: when using a screening layer with a ring-shaped fence structure, the microwave energy is reshaped into a ring beam by utilizing its characteristics of solid blocking at the center and wave transmission at the periphery, so that its energy is concentrated at the solid-liquid interface around the molten pool 100 to compensate for the difference in heat distribution between the center and the edge of the laser heat source; when using a screening layer with a diamond-shaped fence structure, its characteristics as a high-pass filter are used to filter out low-frequency microwave components and only allow high-frequency microwaves with frequencies higher than the cutoff frequency to pass through, thereby controlling the penetration depth of microwaves in the molten pool 100.

[0045] When addressing the issue of a hot center and cold edges in a laser heat source, a ring-shaped grid structure is employed. This structure features a solid metal disk at its center to block direct microwave radiation to the center of the molten pool 100; the outer perimeter consists of annular gaps that allow microwaves to pass through. This creates a "hollow ring" microwave field, concentrating energy at the solid-liquid interface around the molten pool 100. This effectively compensates for the Gaussian heat distribution defects of the laser, smooths the temperature gradient within the molten pool 100, and directly suppresses thermal cracks and residual stress caused by excessive temperature differences.

[0046] When it is necessary to control the penetration depth of microwaves within the molten pool 100, a diamond-shaped grid structure is selected. This structure utilizes the waveguide cutoff frequency principle as a high-pass filter to filter out frequency components with excessively strong or weak penetration, allowing only specific high-frequency microwaves to pass through, thereby precisely controlling the heating depth. In this way, layered injection of microwave energy in the depth direction is achieved, avoiding excessive energy deposition at the bottom of the molten pool 100 or insufficient surface heating.

[0047] Optionally, the screening of the microwave beam in step S2 further includes: using a wave-transmitting focusing layer 221 with a Fresnel lens structure to perform phase modulation and primary focusing on the microwave beam; and using a wave-absorbing cutoff layer 223 made of high dielectric loss material to absorb the sidelobe microwave energy around the focused spot to prevent secondary thermal effects on the solidified area.

[0048] In the multi-stage screening device, a Fresnel lens structure made of high-transmittance ceramic or glass is first used to perform primary focusing of microwaves, and the diverging beam is focused towards the center through phase modulation. At the outermost or lower part of the screening device, an absorbing cutoff layer 223 made of high-dielectric-loss materials such as silicon carbide-doped ceramic is set. This layer acts like an aperture, absorbing the energy of the diffraction side lobes around the focused spot.

[0049] This embodiment significantly improves the energy density of the microwave beam at the target point through the Fresnel lens. In addition, the absorbing cutoff layer 223 eliminates stray microwaves, forming a "steep" beam with clear edges, preventing microwaves from causing accidental arcing or interference to surrounding non-processed areas (such as powder beds or precision parts).

[0050] Optionally, the microwave generator uses a solid-state microwave source 21, and its frequency control method is as follows: using a voltage-controlled oscillator (VCO) combined with a phase-locked loop (PLL) synthesizer, the frequency is adjusted with millisecond precision in the frequency band from 1 GHz to 25 GHz; during the processing, the microwave frequency is adjusted in real time according to the change in the size of the molten pool 100 to maintain the subwavelength matching relationship between the microwave wavelength and the aperture of the screening device.

[0051] A solid-state microwave source 21 replaces the traditional magnetron, and the core components include a voltage-controlled oscillator (VCO) and a phase-locked loop (PLL) synthesizer. The system can adjust the frequency with a millisecond-level response speed within a wide frequency band from 1 GHz to 25 GHz. During processing, if fluctuations in the size of the molten pool 100 are detected due to changes in heat dissipation conditions, the system immediately adjusts the output frequency to maintain the subwavelength matching relationship between the microwave wavelength and the screening aperture.

[0052] Thus, this embodiment achieves millisecond-level frequency modulation capability, enabling microwave energy to adapt to the transiently changing state of the molten pool 100, ensuring the stability of energy coupling. Furthermore, it ensures that the screening device always operates in the optimal frequency selection or focusing mode, avoiding a decrease in energy transmission efficiency due to frequency drift.

[0053] Optionally, the directional application of microwaves in step S3 includes: adjusting the spatial distribution of microwave energy through a multi-stage microwave screening device 22 so that it presents a distribution state with low energy in the center and high energy around the periphery on the surface of the molten pool 100; and spatially superimposing and complementing the energy characteristics of the laser heat source, which are in a Gaussian distribution, to compensate for the energy difference of the laser heat source, thereby forming a flat-topped temperature field distribution inside the molten pool 100 to reduce the temperature gradient of the molten pool 100.

[0054] By adjusting the microwave screening device, a microwave field with a "low center and high periphery" output is generated. This microwave field is then superimposed on a laser Gaussian thermal field with a "high center and low periphery." The two fields are mathematically superimposed in space, and the resulting total energy field exhibits a flat-topped distribution across the cross-section of the molten pool 100. This fundamentally eliminates the extreme temperature gradient within the molten pool 100, resulting in a more uniform solidification process and significantly reducing the initiation sources of microcracks.

[0055] Optionally, the filtered microwave beam is applied directionally to the molten pool 100 and the solid-liquid interface region, including: exciting the near-field coupling effect of microwaves through the subwavelength aperture structure in the multi-stage microwave screening device 22, confining and concentrating the microwave energy field on the solid-liquid interface region of the molten pool 100; inducing high-frequency vibration of atoms through the non-thermodynamic effect of the high-frequency microwave electromagnetic field on the metal atoms in the molten pool 100, thereby reducing the diffusion barrier at the solid-liquid interface of the molten pool 100, accelerating the migration and mutual solubility of alloying elements, and driving the bubbles in the molten pool 100 to escape to eliminate pore defects.

[0056] By utilizing a subwavelength aperture structure, a near-field coupling effect is excited at the aperture exit, generating a high-intensity evanescent wave that directly acts on the molten pool 100. Simultaneously, the non-thermodynamic effect (i.e., electromagnetic oscillation force) generated by the high-frequency electromagnetic field on the metal atoms forces the atoms within the molten pool 100 to vibrate at high frequencies. This embodiment achieves microwave energy transfer at the subwavelength scale, solving the physical problem that conventional microwaves cannot be focused to millimeter-scale spots. Furthermore, the high-frequency vibration of atoms lowers the diffusion barrier, accelerates the mutual solubility of alloying elements (solving segregation), and, like concrete vibration, drives air bubbles to the surface (eliminating porosity), refining the grain size.

[0057] In some embodiments, the size of the subwavelength aperture must maintain a specific proportional relationship with the operating wavelength of the microwave (e.g., aperture size ≤ half or ≤ one-tenth of the operating wavelength). Simultaneously, the vertical distance between the end-emission surface of the microwave screening device and the surface of the molten pool 100 is strictly limited to a near-field coupling range of 1 mm to 5 mm to ensure efficient coupling of the evanescent wave.

[0058] Optionally, the selected microwave beam is applied directionally to the liquid molten pool and the solid-liquid interface region. The application process of the selected microwave beam adopts a dual closed-loop real-time control strategy, including: a power control loop, which adjusts the output power of the microwave generator according to the real-time monitored average temperature of the molten pool 100 to control the overall heat input of the molten pool 100; and a frequency control loop, which adjusts the microwave frequency in real time according to the temperature difference or temperature distribution uniformity between the center and the edge of the molten pool 100 to change the penetration depth and energy distribution uniformity of the microwave in the molten pool 100.

[0059] Optionally, the microwave beam application process in step S3 employs a dual closed-loop real-time control strategy, specifically including:

[0060] A temperature feedback mechanism is constructed, which uses an external infrared thermometer to monitor the macroscopic temperature of the surface of the molten pool 100 in real time, and uses a built-in fiber optic temperature sensor to monitor the transient temperature of the center of the molten pool 100 in real time.

[0061] The power PID control is executed to calculate the deviation between the average temperature of the molten pool 100 and the target set temperature. Based on the PID algorithm, the output power of the microwave generator is adjusted to stabilize the overall heat input of the molten pool 100.

[0062] The frequency PI control is executed to calculate the difference or temperature range between the center temperature and the surface temperature of the molten pool 100. When the difference exceeds the preset non-uniformity threshold, the output frequency of the microwave generator is adjusted based on the PI algorithm to change the standing wave distribution and penetration depth of the microwave in the molten pool 100, so as to improve the uniformity of temperature distribution.

[0063] The power loop monitors the average temperature of the molten pool 100 using an infrared thermometer. If the temperature is below the set value, the PID algorithm increases the microwave power; conversely, it decreases it. This ensures stable overall heat input. The frequency control loop monitors the temperature difference between the center and edge of the molten pool 100. If the temperature difference is too large (non-uniform), the PI algorithm adjusts the microwave frequency. Changing the frequency alters the microwave's penetration depth in the material (skin effect) and the standing wave distribution nodes, thereby correcting the heating uniformity.

[0064] This embodiment solves the problem that open-loop control cannot handle complex heat accumulation, ensuring that the state of the molten pool 100 remains stable and consistent during long-term printing. At the same time, introducing frequency as a control variable to adjust "uniformity" provides more precise control than power control alone.

[0065] Optionally, determining the preset size of the molten pool 100 in step S1 includes: calculating the size and shape of the molten pool 100 under different laser parameters using finite element simulation based on the thermophysical properties of the material to be processed, and preset the initial frequency and range of the microwave based on the simulation results.

[0066] Optionally, before additive manufacturing is implemented, based on the thermophysical properties of the metal material to be formed and the laser process parameters, the morphology of the molten pool 100 and the range of the heat-affected zone under the action of the laser spot are simulated using finite element simulation software; according to the molten pool 100 size data obtained from the simulation, a device with a matching aperture size is selected from the preset multi-level microwave screening device 22 specification library, and the initial frequency and initial range of microwave are set.

[0067] Before actual printing, finite element simulation software is used to simulate the interaction between the laser and the powder, predicting the morphology of the molten pool 100 under different working conditions. Based on the simulation results, a suitable subwavelength aperture for the screening device is selected in advance from the specification library, and initial microwave parameters are set. This embodiment can reduce a significant amount of trial-and-error experimental costs and ensure a high success rate for printing on the first attempt. In addition, it ensures optimal dimensional matching between the physical device (aperture) and the process object (molten pool 100).

[0068] Optionally, controlling the microwave beam and laser beam to move synchronously after screening includes: controlling the multi-stage microwave screening device 22 to move synchronously with the laser beam, wherein the vertical distance between the end emission surface of the multi-stage microwave screening device 22 and the surface of the molten pool 100 is within the near-field coupling range of the microwave, so as to achieve energy coupling by using evanescent waves.

[0069] Optionally, during the synchronous movement of the microwave beam following the laser beam in step S4, the process also includes: real-time monitoring and adjustment of the vertical distance between the end emission surface of the multi-stage microwave screening device 22 and the surface of the molten pool 100, keeping it within the near-field coupling range of 1mm to 5mm, so as to ensure that the microwave energy is efficiently coupled to the molten pool 100 in the form of evanescent waves and prevent the energy from dissipating in the far-field transmission.

[0070] During synchronous movement, a distance sensor (such as a capacitive or laser displacement sensor) is used to monitor the vertical distance between the end of the screening device and the surface of the molten pool 100 in real time, and the distance is strictly locked within the range of 1mm to 5mm (i.e., the near-field coupling zone) by the Z-axis actuator in the linkage movement mechanism. Since evanescent waves decay exponentially with distance, strictly controlling the near distance is crucial for effective energy injection. This embodiment ensures coupling efficiency while also preventing microwave diffraction and divergence during far-field transmission, thus guaranteeing energy concentration.

[0071] Optionally, it also includes a microwave-assisted quality verification step: microwave assistance is turned off in the first half of the processing and turned on in the second half to form a contrast area on a workpiece; by performing nanoindentation matrix testing and electron backscatter diffraction (EBSD) analysis on both sides of the interface, the degree of grain refinement and the effect of microhardness improvement are verified, and the microwave power parameters of the next batch are optimized accordingly.

[0072] In the initial prototype fabrication, a "half-cycle switching" method was employed: the microwave was not activated for the first half and activated for the second half. After forming, the interface was sliced, and the hardness distribution was measured using a nanoindenter. Grain orientation and size were analyzed using EBSD. The comparative data was used to correct the microwave power parameters for the next batch. This embodiment provides a rapid, homogeneous comparison method for process verification, eliminating batch-to-batch error interference; it also establishes a closed-loop optimization logic between material microstructures and microwave macrostructures.

[0073] The preliminary preparations for additive manufacturing are as follows:

[0074] Before proceeding with the layer-by-layer deposition process, detailed data model processing and path planning are required. This process begins with importing and analyzing the 3D digital model of the part to be formed, discretizing it along the height direction using slicing software to generate a series of 2D cross-sectional contour data. Based on this cross-sectional information, the system plans the scanning path of the laser beam and synchronously generates the movement trajectory of the microwave beam, ensuring that the two can achieve precise trajectory overlap and linkage control in subsequent processing.

[0075] Simultaneously, the forming environment and material preparation must be completed. This includes rigorous drying and sieving of the selected metal powder to ensure that the powder's flowability and sphericity meet process requirements; at the same time, the forming cavity is evacuated and filled with an inert protective gas (such as argon or nitrogen) to control the oxygen content below a preset safety threshold, preventing the metal from oxidizing at high temperatures. In addition, the substrate where processing takes place also needs to be leveled and preheated to reduce the accumulation of thermal stress in the early stages of forming.

[0076] The most crucial step is the coordinated setting of the dual-energy field process parameters. At this stage, it is necessary not only to determine the laser processing parameters (such as laser power, scanning speed, spot diameter, and overlap rate), but also to set key microwave control parameters for the microwave-assisted system. This includes adjusting the output frequency and power of the microwave generating system 20, and, based on the preset size of the molten pool 100, precisely setting the focusing scale and beam shape of the microwave beam by adjusting the relative position or parameters of the wave-transparent focusing layer 221 and the irregularly shaped hollowed-out metal structure layer 222. Through this parameter coupling and matching, the optimal ratio of laser energy density to microwave energy injection is established, laying the foundation for the subsequent realization of a composite processing mode of "laser melting and microwave steady-state temperature control."

[0077] The additive manufacturing process involves a layer-by-layer deposition process as follows:

[0078] The first step is powder laying / feeding: For powder bed process, the system lays a uniform layer of metal powder on the substrate or the formed layer; for directional energy deposition process, the metal powder is fed into the processing area through a nozzle.

[0079] Next comes the crucial microwave screening and focusing (step S2). In this step, the microwave generating system 20 outputs a microwave beam. The beam passes sequentially through a wave-transparent focusing layer 221 (e.g., a Fresnel lens) for initial focusing, which is equivalent to primary energy convergence. Subsequently, the beam passes through an irregularly shaped, perforated metal structure layer 222. This layer serves to spatially constrain, localize, screen, and shape the beam, aiming to precisely focus the beam's effective range onto a scale matching the preset molten pool 100 size. During focusing, excess microwaves from the periphery are fully absorbed by the absorbing cutoff layer 223, effectively preventing these stray microwaves from causing secondary thermal effects on the surrounding area and ensuring directional energy concentration.

[0080] The next step is energy coupling and directional application (step S3). The laser beam first acts on the metal powder, providing the main energy to melt it and form a liquid molten pool 100. At the same time, a microwave beam, after precise orientation screening, is precisely applied to this liquid molten pool 100 and the surrounding solid-liquid interface region, achieving synergistic coupling of the two energy sources.

[0081] Finally, there is dynamic synchronous scanning (step S4). The linkage mechanism precisely controls the selected microwave beam and laser beam, ensuring they move synchronously throughout the scanning path. The entire system stacks layers one after another according to the preset scanning path until the part is finally formed.

[0082] The real-time monitoring and dual closed-loop control process of additive manufacturing occurs in parallel with the processing cycle, as detailed below:

[0083] During the dynamic process of layer-by-layer deposition, the system performs multi-dimensional real-time monitoring. Utilizing coaxial or off-axis sensor arrays integrated into the optical path (such as high-speed infrared thermal imagers, colorimetric thermometers, and high-resolution CCD cameras), the processing area is continuously captured at the nanosecond level. The core monitoring focuses on the morphological features of the center of the molten pool 100 (including the area, aspect ratio, and spatter characteristics of the molten pool 100) and the thermal field distribution (including temperature gradient and cooling rate) at the solid-liquid interface. These sensors convert the acquired optical and thermal signals into digital signals in real time and feed them back to the central processing unit for data fusion and analysis.

[0084] Based on monitoring data, the system operates a sophisticated dual-loop feedback control strategy. The first loop targets the laser energy system: when the system detects fluctuations in the size of the molten pool 100 or signs of incomplete fusion, the main control unit uses a PID algorithm to fine-tune the laser power and scanning speed in real time, ensuring that the melting quality of the metal powder remains stable. The second loop specifically targets the microwave-assisted system: based on the temperature gradient changes and thermal stress accumulation trends at the solid-liquid interface, the system dynamically adjusts the output power of the microwave generator and the focusing shape of the microwave beam. This control is not simply heating, but rather actively intervenes in heat conduction during solidification by injecting compensatory or smoothing energy into the periphery of the molten pool 100 using microwaves.

[0085] This closed-loop control with dual energy fields enables "steady-state thermal management" of the processing. The dynamic intervention of microwave energy effectively reduces the severe thermal shock caused by rapid laser heating and cooling, significantly reducing residual stress during the forming process. Based on real-time feedback, the system can correct process deviations within milliseconds, ensuring that each cladding layer solidifies under optimal temperature conditions. This effectively suppresses the generation of micro-defects such as cracks and pores, guaranteeing the consistency and reliability of the final formed component's microstructure and properties.

[0086] In some embodiments, a specific time phase difference is controlled between the microwave pulse and the laser pulse. The laser pulse melts the metal first, and the microwave pulse is delayed and specifically acts on the solidification stage of the molten pool 100. Microwave vibration is used to break up growing dendrites and promote the formation of equiaxed crystals, rather than simply heating.

[0087] This embodiment is primarily applied to the manufacturing of aero-engine blades, where strict requirements on grain morphology are necessary. Unlike continuous wave heating, this scheme employs a time-domain pulse-coordinated process. The control system sets the microwave generator to pulse operating mode and performs phase locking with the laser pulse signal. Specifically, the trigger time of the microwave pulse is set to lag behind the laser pulse (e.g., 2-5 ms). The microwave pulse precisely intervenes just as the laser pulse extinguishes and the molten pool 100 enters the rapid cooling and crystallization stage. A high-intensity microwave electromagnetic field is used to transiently "electromagnetically vibrate" the mushy region, breaking the directionally growing dendrite tips, inhibiting the formation of coarse columnar crystals, and promoting the nucleation and growth of fine equiaxed crystals. This precise timing avoids excessive energy input during the laser heating stage, preventing the molten pool 100 from becoming too large, while simultaneously leveraging the non-thermal effects of microwaves during the critical solidification window, thus achieving control over the microstructure.

[0088] In some embodiments, during single-layer printing, the microwave frequency is controlled to periodically and rapidly switch between high frequency (e.g., 25 GHz) and low frequency (e.g., 2.45 GHz). High-frequency microwaves utilize a small skin depth to heat the surface of the molten pool 100 to reduce surface tension (smooth the surface); low-frequency microwaves utilize a large penetration depth to heat the bottom of the molten pool 100 to promote substrate bonding. This achieves precise control of layering throughout the entire depth of the molten pool 100.

[0089] In some embodiments, the control system reads three-dimensional slice data of the part and identifies characteristic areas with poor heat dissipation (such as overhanging structures or sharp corners). Before the laser head reaches this area, the microwave power is reduced or the microwave frequency is changed in advance to achieve thermal field pre-compensation based on geometric features.

[0090] This embodiment is applicable to the printing of precision parts with complex geometric features such as overhanging structures and thin-walled sharp corners. To overcome the lag inherent in traditional feedback control, this solution introduces a feedforward control mechanism based on thermal history. Before printing begins, the control system pre-reads the three-dimensional slice data of the part and identifies "hot spots" with poor heat dissipation conditions (such as overhanging beams and sharp edges) through thermal simulation algorithms. Just before the laser head moves to these specific areas, the control system generates instructions in advance to proactively reduce the microwave output power or increase the microwave frequency (reducing the penetration depth). This "predictive" adjustment counteracts local heat accumulation caused by the geometry, preventing overheating collapse or warping deformation at thin-walled areas. Simultaneously, the system monitors the state of the molten pool 100 using acoustic emission sensors. Once an abnormal "crackling" signal is detected (indicating the formation of pores), the microwave parameters are immediately fine-tuned to suppress it, achieving dual protection through "feedforward pre-setting and feedback correction."

[0091] In some embodiments, fluctuations in plasma light intensity above the molten pool 100 or acoustic emission signals inside the molten pool 100 are monitored. When a characteristic signal representing "pore collapse" or "pore burst" is detected, the microwave vibration power is instantaneously increased to stabilize the fluctuations in the molten pool 100 using strong electromagnetic force.

[0092] In some embodiments, for high laser reflectivity materials such as copper and aluminum, the preheating effect of microwaves on the surface of metal powder through conductivity loss is used to increase the resistivity of the material, thereby significantly improving its absorption rate of laser energy and solving the problem of difficult printing of high reflectivity materials.

[0093] This embodiment specifically addresses the challenges of additive manufacturing of high laser reflectivity materials such as pure copper and aluminum alloys. It is well known that cold copper powder has extremely low absorption of infrared lasers, making it difficult to melt. This solution utilizes the preheating effect of microwaves on the conductive loss of the metal powder surface. Before laser scanning, high-frequency microwaves (e.g., 25 GHz) output from a multi-stage screening device pre-cover the powder area to be scanned. The microwave energy rapidly raises the surface temperature of the metal powder, and by utilizing the physical property that the resistivity of metal increases with temperature, the absorption rate of the copper powder for subsequent laser energy is significantly improved. This "microwave-assisted absorption" method allows pure copper, which originally required extremely high laser power to melt, to form a stable molten pool 100 under conventional laser power. Furthermore, the continuous assistance of microwaves greatly improves the density and conductivity of copper parts, expanding the application of this device in the field of electronic component manufacturing.

[0094] In some embodiments, in the printing of dissimilar materials (such as ceramic-reinforced metal matrix composites), microwaves are used to selectively heat different materials, such as heating ceramic particles with microwaves, to compensate for the insufficiency of lasers in heating only the metal matrix, improve the wettability of ceramic particles and the metal matrix, and solve the problem of weak interfacial bonding.

[0095] This disclosure also provides a dynamic microwave-assisted laser metal additive manufacturing apparatus, applied to the above-described method, comprising: an additive manufacturing host 10, equipped with a laser generating system for providing a laser beam heat source and controlling the layer-by-layer deposition of metal material to form a liquid molten pool 100 during the forming process; a microwave generating system 20 for generating a microwave beam with adjustable frequency and power; a multi-stage microwave screening device 22, connected to the microwave generating system 20 and located at the end of the microwave transmission path, configured to spatially constrain and directionally screen the microwave beam, focusing the effective range of the microwave beam to a scale matching the size of the liquid molten pool 100; a linkage movement mechanism for driving the multi-stage microwave screening device 22 to move synchronously with the laser beam; and a control system for receiving temperature feedback data of the molten pool 100 and adjusting the output power and output frequency of the microwave generating system 20 in real time according to a preset dual closed-loop control strategy.

[0096] This embodiment constructs an integrated additive manufacturing hardware system. The main body of the device includes a laser additive manufacturing host 10 (such as an SLM or LMD device), whose laser head is responsible for providing a high-energy heat source and melting metal powder to form a liquid molten pool 100. Based on this, the system integrates a microwave generation system 20, which generates microwave energy with adjustable frequency and power. Crucially, a multi-stage microwave screening device 22 is installed at the end of the microwave transmission path and physically bound to the laser head via a linkage mechanism (such as a servo robotic arm or a rigid connecting bracket). When the laser head moves along the path to print, the microwave screening device moves synchronously, always precisely projecting the focused and screened millimeter-level microwave beam onto the current liquid molten pool 100. Simultaneously, the control system acts as the "brain," receiving real-time temperature data of the molten pool 100 and dynamically adjusting the microwave output parameters.

[0097] Optionally, the multi-stage microwave screening device 22 includes, from top to bottom, the following components along the microwave transmission direction: a wave-transparent focusing layer 221, made of wave-transparent material, configured to focus the diverging microwave beam toward the central axis; an irregularly shaped hollow metal structure layer 222, made of conductive metal material, with a subwavelength scale hollow pattern on its surface, configured to perform localized screening and beam shaping of microwaves; and a wave-absorbing interception layer 223, made of dielectric loss material, configured to intercept and absorb excess microwaves outside the screening range to prevent secondary thermal impact on the solidified area.

[0098] The multi-stage microwave screening device 22 adopts a layered structure design similar to a "sandwich" or "funnel." From top to bottom along the microwave propagation direction, the layers are as follows: a wave-transmitting focusing layer 221 is located at the top, using high-transmittance quartz glass or alumina ceramic to initially converge the diverging microwave beam transmitted from the waveguide towards the central axis; an irregularly shaped hollowed-out metal structure layer 222 is located in the middle core layer, which is a conductive metal plate (such as copper or silver) processed with a specific subwavelength pattern, using the pinhole coupling principle to forcibly screen the microwaves; and a wave-absorbing cutoff layer 223 is located at the bottom or on the periphery, using a dielectric loss material to absorb the diffraction side lobes around the main beam, acting like an "aperture." This embodiment shapes electromagnetic waves like an optical lens, eliminating stray waves and preventing edge energy from causing arcing in the non-molten pool 100 area of ​​the workpiece.

[0099] In some embodiments, the multi-stage microwave screening device 22 is internally equipped with a circulating cooling channel, and the cooling medium is a non-polar cooling oil with good microwave transmittance. This achieves both cooling of the device and does not interfere with microwave transmission and focusing. This effectively avoids the problem of frequency drift caused by thermal deformation of the irregularly shaped metal layer due to the microwave screening device being only 1-5 mm away from the molten pool 100 and being exposed to high-temperature radiation and metal splashing for extended periods. For example, a microchannel cooling system is integrated inside the microwave-transparent focusing layer 221 (ceramic / glass) or the irregularly shaped metal layer.

[0100] This embodiment aims to address the thermal stability and contamination resistance issues of microwave screening devices during long-term operation at near-field distances (1-5 mm). In the structural design of the multi-stage microwave screening device 22, a microchannel cooling system is integrated within the wave-transparent focusing layer 221 (such as alumina ceramic) and the irregularly shaped perforated metal structure layer 222. The cooling medium is a non-polar cooling oil (such as fluorinated liquid) with excellent wave transmittance. Without absorbing microwave energy, it carries away the heat generated by radiation from the molten pool 100 and microwave losses through circulating flow, preventing the metal layer from deforming its aperture and drifting its frequency due to thermal expansion. Furthermore, an annular air knife structure is integrated on the lower surface of the bottom-most absorbing cutoff layer 223 of the device. This air knife is connected to the protective gas path of the additive manufacturing host 10, spraying high-speed laminar gas downwards. This airflow not only strengthens the antioxidant protection of the molten pool 100, but more importantly, it forms an "air curtain barrier" that uses aerodynamic principles to force the metal splashes and dust generated by the molten pool 100 away from the screening hole area, preventing the subwavelength apertures from being blocked, thereby ensuring the stability and lifespan of the device during long-term continuous printing.

[0101] Optionally, the multi-stage microwave screening device 22 adopts a modular design, and the irregularly shaped hollow metal structure layer 222 is configured as a detachable and replaceable plug-in structure; the device is equipped with various irregularly shaped hollow metal structure layer 222 plug-ins with different aperture sizes or different hollow patterns (such as ring, rhombus, multi-point hole type) to adapt to the additive manufacturing process requirements of different laser spot sizes or different material properties.

[0102] The multi-stage microwave screening device 22 adopts a modular slot design, with the central irregularly shaped hollow metal structure layer 222 designed as a quick-detachable plug-in. Operators can select the corresponding plug-in (such as annular holes, diamond holes, etc.) from the parts library and insert it into the device based on the laser spot size (e.g., 0.5mm or 2mm) or material type of the current printing task. A single multi-stage microwave screening device 22 can adapt to additive manufacturing scenarios with different process requirements without replacing the entire microwave head, thus reducing equipment costs.

[0103] Optionally, the outer shell of the multi-stage microwave screening device 22 has an inverted conical or funnel-shaped structure, and its cross-sectional area gradually decreases along the microwave transmission direction; the wave-transmitting focusing layer 221, the irregularly shaped hollow metal structure layer 222, and the wave-absorbing cutting-off layer 223 are arranged coaxially along the axis of the conical structure to physically adapt to the focusing path of the microwave beam from the centimeter level to the millimeter level.

[0104] The outer casing of the multi-stage microwave screening device 22 is designed in an inverted cone or funnel shape. Its cross-sectional area gradually decreases along the microwave transmission direction (from the microwave source end to the molten pool 100 end). The internal three-layer structure (focusing layer, metal layer, and truncating layer) is coaxially distributed along the central axis of this cone-shaped structure. The structural shape conforms to the physical path of microwave beam focusing and narrowing, reducing microwave reflection loss inside the device. In addition, the inverted cone design minimizes the size of the device's end, facilitating installation next to a compact laser processing head and reducing interference with other components.

[0105] In some embodiments, additive manufacturing requires inert gas protection. However, the screening device, being in close contact with the molten pool 100, may obstruct the protective airflow and is prone to clogging of pores by spatter. Therefore, the lower surface of the absorbing cutoff layer 223 of the multi-stage microwave screening device 22 is provided with an annular airflow nozzle to form a high-speed air curtain. This protects the molten pool 100 from oxidation and utilizes aerodynamics to remove metal spatter, preventing subwavelength pore clogging. Exemplarily, the inverted conical structure of the screening device is designed as part of a coaxial air delivery nozzle, or an air curtain structure is added to the bottom of the device.

[0106] Optionally, the cross-section of the wave-focusing layer 221 is a Fresnel lens structure, configured to focus the incident microwaves toward the central axis through phase modulation.

[0107] The cross-section of the wave-focusing layer 221 is not a typical flat plate, but rather fabricated as a Fresnel lens structure, with a series of concentric annular grooves etched on its surface. By modulating the microwave phase through different annular bands, the incident plane wave or diverging wave converges towards the focal point after passing through the lens. Compared to traditional thick dielectric lenses, the Fresnel structure is thinner and lighter, facilitating high-speed movement with the laser head; it effectively increases the microwave energy density reaching the surface of the irregularly shaped metal layer, thereby improving screening efficiency.

[0108] In some embodiments, if the part being printed is curved, a fixed focal length may lead to a decrease in coupling efficiency. This embodiment utilizes the refractive index variation of the electro-controlled liquid crystal cell to finely adjust the focal depth of the microwave beam in real time without moving the mechanical structure, in order to adapt to the minute changes in the Z-axis height during the printing of complex curved parts. For example, a liquid crystal phased array or deformable liquid lens is introduced above the wave-transmitting focusing layer 221 (Fresnel lens).

[0109] Optionally, the distance between the irregularly shaped perforated metal structure layer 222 and the surface of the molten pool 100 is configured to be within the near-field coupling range of microwaves, so as to enhance the energy density of microwaves on the surface of the molten pool 100 by utilizing the evanescent wave effect.

[0110] Optionally, the irregularly shaped hollow metal structure layer 222 adopts any of the following structural forms: a ring-shaped fence structure, consisting of several concentric metal rings or ring gaps, used to generate a ring microwave field with low energy at the center and high energy around the perimeter; a rhomboid fence structure, consisting of periodically arranged rhomboid metal mesh, used to filter out low-frequency microwaves; or a multi-point aperture structure, consisting of an array of circular through holes, used to divide and confine the microwave beam within the lattice region.

[0111] To address different metallurgical defects, three specific functional plug-ins are provided: the ring-shaped fence type has a solid metal disk at the center and annular gaps around it. Microwaves can only pass through from the outside, forming a "hollow" beam; the diamond-shaped fence type is similar to a metal mesh, with the mesh size designed as a cutoff frequency filter; and the multi-point aperture type has small circular holes arranged in an array.

[0112] The ring structure (energy complementarity) generates a microwave field that is "high around the edges and low in the center," perfectly compensating for the Gaussian thermal distribution of the laser, which is "high in the center and low around the edges," thus smoothing out the temperature gradient. The rhomboid structure (frequency-selective depth control) filters out low-frequency waves with excessive penetrating power, allowing only specific high-frequency waves to pass through, precisely controlling the heating depth (skin depth) of the microwaves within 100mm of the molten pool. The multi-point structure (discrete action) disperses energy across multiple tiny points, suitable for homogenization during large-area cladding.

[0113] Optionally, the microwave absorbing cutoff layer 223 is disposed on the periphery or lower part of the irregularly shaped hollow metal structure layer 222, and surrounds the output path of the microwave beam in a ring shape; the microwave absorbing cutoff layer 223 is made of silicon carbide doped ceramic or ferrite composite material, and is configured to convert microwave energy that does not pass through the screening aperture into heat energy and dissipate it, so as to form a clear microwave beam edge.

[0114] The microwave absorbing cutoff layer 223 is located at the lower edge of the irregularly shaped metal layer, surrounding the output port in a ring shape. The material is silicon carbide-doped ceramic or ferrite composite material. When microwaves are diffracted through the irregularly shaped hole, the energy of the outwardly diffused side lobes is rapidly converted into heat energy and dissipated by this layer. In this way, the output microwave beam is ensured to have a clear and sharp edge without trailing, eliminating the risk of stray microwaves causing tip discharge (arson) at the sharp corners of the formed parts.

[0115] Optionally, the microwave generating system 20 employs a solid-state microwave source 21, which includes a voltage-controlled oscillator (VCO) and a phase-locked loop (PLL) synthesizer, configured to achieve millisecond-level real-time adjustment of the output frequency within a preset bandwidth through digital control.

[0116] The microwave generating system 20 abandons the traditional magnetron and adopts a solid-state microwave source 21. Its core circuit includes a voltage-controlled oscillator (VCO) and a phase-locked loop (PLL) synthesizer. The control system sends digital signals to achieve millisecond-level frequency switching within a preset bandwidth (such as 1-25 GHz); it can adjust the frequency extremely quickly to cope with transient changes in the shape of the molten pool 100; compared with the magnetron, the output frequency is more stable and the bandwidth is narrower, which is conducive to achieving precise frequency-selective heating.

[0117] Optionally, it also includes: an external infrared thermometer for acquiring macroscopic temperature distribution data on the surface of the molten pool 100; and a built-in fiber optic temperature sensor for acquiring transient temperature data at the center of the molten pool 100. Both the external infrared thermometer and the built-in fiber optic temperature sensor are electrically connected to the control system. The control system calculates the average temperature and temperature uniformity index of the molten pool 100 based on the feedback data from the external infrared thermometer and the built-in fiber optic temperature sensor, so as to adjust the power and frequency of the microwave generating system 20.

[0118] The device in this embodiment integrates two temperature measurement systems: an external infrared thermometer is installed on the side to capture an overall thermal image (macroscopic data) of the molten pool 100 and the heat-affected zone; a built-in fiber optic temperature sensor is integrated inside the laser head to coaxially monitor the highest temperature point at the center of the molten pool 100 (transient data); the control system simultaneously collects both data and calculates the "average temperature" and "temperature uniformity (such as the temperature difference between the center and the edge)," which are used to adjust the microwave power (power loop) and frequency (frequency loop), respectively; it provides a more comprehensive view of both the overall picture and the local picture; it achieves decoupled control of "temperature uniformity" and "temperature control," significantly improving the consistency of forming quality.

[0119] Optionally, the linkage movement mechanism and control system are connected to maintain the vertical working distance between the end emission surface of the multi-stage microwave screening device 22 and the surface of the molten pool 100 within the near-field coupling range of 1 mm to 5 mm.

[0120] The linkage movement mechanism is equipped with a high-precision Z-axis adjustment function (or preset fixed during installation). During processing, the vertical distance between the end emission surface of the multi-stage microwave screening device 22 and the surface of the molten pool 100 is strictly controlled to be between 1 mm and 5 mm; this distance is within the near-field coupling range of the microwave wavelength. Only at extremely close distances can the evanescent wave excited by the subwavelength aperture couple into the molten pool 100. If the distance is too far, the energy will attenuate or diverge sharply.

[0121] Optionally, the linkage moving mechanism is configured to install the multi-stage microwave screening device 22 on one side of the laser processing head at a preset tilt angle; the tilt angle is configured such that the central axis of the focused microwave beam intersects with the central axis of the laser beam at the surface of the liquid molten pool 100, thereby realizing the fixed-point coupling of microwave and laser.

[0122] The linkage mechanism mounts the multi-stage microwave screening device 22 at a preset tilt angle on the side of the laser head (non-coaxial enclosure). Adjusting the tilt angle ensures that the central axis of the focused microwave beam precisely intersects the central axis of the laser beam at the surface of the molten pool 100. This achieves "dual-beam fusion," ensuring that microwave energy consistently covers the laser molten pool 100. Furthermore, the lateral tilt mounting avoids obstructing the vertically incident laser beam path, simplifying the structural implementation.

[0123] Optionally, the control system integrates a microwave parameter matching database; the database stores the correspondence between different material thermophysical properties, laser power parameters and optimal microwave frequency, optimal screening aperture and optimal working distance; the control system is configured to retrieve matching control parameters from the database based on the input material and laser parameters before processing, and prompt the operator to replace the corresponding irregularly shaped hollow metal structure layer 222 plug-in.

[0124] The control system incorporates a microwave parameter matching database. This database stores a large amount of experimental data, corresponding to the optimal microwave frequency, optimal sieving aperture shape, and optimal operating distance for different materials (such as titanium alloys and aluminum alloys) and different laser powers. Before processing, the user inputs the material and laser parameters, and the system automatically calls up the optimal solution, prompting the user on the screen: "Please replace the ring insert with an aperture of 1.5mm." This embodiment simplifies complex multi-parameter control, allowing operators to use it without extensive microwave knowledge. Furthermore, it reduces human error and ensures the stability of processing results across different batches.

[0125] Optionally, the control system is equipped with a specific non-uniformity adjustment module; this module is configured to calculate the difference between the center temperature and the surface temperature of the molten pool 100 in real time. When the difference exceeds a preset threshold, a frequency adjustment command is generated through a PI control algorithm (proportional-integral control) to drive the voltage-controlled oscillator of the microwave generation system 20 to perform frequency conversion, so as to adjust the skin depth of the microwave in the molten pool 100.

[0126] The control system incorporates specific algorithm modules. It calculates the temperature difference between the center and surface of the molten pool 100 in real time. When the difference exceeds a preset threshold (e.g., 50°C), the PI (proportional-integral) control algorithm intervenes, generating a frequency adjustment command to drive the VCO to change the microwave frequency. This frequency change causes a change in the skin depth of the microwaves within the molten pool 100, thereby correcting the temperature distribution. This dynamically eliminates hot or cold spots within the molten pool 100, preventing element burn-off due to localized overheating or incomplete fusion due to localized undercooling.

[0127] In an embodiment of additive manufacturing applied to hot-crack-sensitive materials such as nickel-based superalloys or titanium alloys, the additive manufacturing host 10 works in conjunction with the microwave generation system 20. The key feature is the use of an irregularly shaped metal insert with a ring-shaped grid structure in the multi-stage microwave screening device 22. The insert has a solid metal disk at its center and an annular wave-transparent slit around its perimeter.

[0128] During processing, a laser beam irradiates metal powder, creating a Gaussian thermal field with extremely high energy at the center and a sharp drop in energy at the edges of the molten pool 100. This significant temperature difference is often the main cause of cracks. Meanwhile, the microwave beam, after initial focusing by the wave-transparent focusing layer 221, is filtered by an annular grid. The microwaves in the center are blocked, allowing only the peripheral microwaves to pass through, thus forming a hollow annular microwave thermal field. A linkage mechanism controls this annular microwave field to move coaxially and synchronously with the laser spot, precisely heating the solid-liquid interface region around the molten pool 100. This "low center, high periphery" microwave field and the "high center, low periphery" laser field perfectly complement each other spatially, reshaping the temperature field within the molten pool 100 from a peak-like shape to a flat-topped shape. In this way, the temperature gradient inside the molten pool 100 is significantly reduced, suppressing the generation of residual stress at its source and effectively eliminating microcrack defects inside the formed part.

[0129] In embodiments targeting printing scenarios with large-layer stacking or dissimilar metal gradient materials, the aim is to address incomplete fusion defects and enhance bonding strength in the Z-axis direction. In this embodiment, the multi-stage microwave screening device 22 employs a diamond-grid structure plug-in, with the diamond grid size designed to a specific cutoff wavelength, serving as a high-pass filter to filter out interfering low-frequency clutter.

[0130] During processing, the real-time control system calculates the required microwave penetration depth based on the current printed layer thickness (e.g., increasing from the conventional 30μm to 60μm). The system dynamically reduces the microwave frequency (e.g., adjusting it to lower frequencies within the allowable bandwidth) by driving the voltage-controlled oscillator (VCO) in the solid-state microwave source 21. Utilizing the physical property of long-wavelength microwaves having a large skin depth, microwave energy can penetrate the surface molten pool 100, directly acting on the remelted zone at the bottom of the molten pool 100 and the previous solidified layer. The diamond-shaped grid ensures pure transmission of microwaves in specific frequency bands during this process, achieving precise energy deposition in the depth direction. This deep heating effect promotes metallurgical bonding between the current layer and the substrate, effectively eliminating incomplete fusion defects encountered during thick-layer printing.

[0131] In an embodiment used for manufacturing aerospace components or aluminum alloys that are prone to porosity, the core of the device is a screening insert with a multi-point hole structure. The aperture is designed to be on the subwavelength scale (e.g., 0.5 mm), and the vertical distance between the end of the screening device and the surface of the molten pool 100 is strictly locked within a near-field coupling range of 1 mm to 5 mm by a linkage moving mechanism.

[0132] As the microwave beam follows the laser, the microwaves excite high-intensity evanescent waves at the exit through a subwavelength aperture. This high-frequency electromagnetic field breaks the diffraction limit and directly couples into the molten pool 100, inducing intense high-frequency vibrations in metal atoms, i.e., generating non-thermodynamic effects. This microscopic oscillation is similar to the vibration during concrete pouring, which can disrupt the surface tension adhesion of microbubbles in the melt and accelerate the escape of the bubbles. This embodiment can significantly reduce the porosity of the formed part, while the atomic vibration promotes the breakage and proliferation of crystal nuclei, resulting in a final metallographic structure with fine equiaxed crystals rather than coarse columnar crystals.

[0133] In an embodiment suitable for printing parts with complex geometries and drastic changes in heat dissipation conditions (such as blades with overhang structures or thin walls), the device integrates an external infrared thermal imager and a built-in fiber optic sensor to monitor the macroscopic thermal field distribution on the surface of the molten pool 100 and the transient temperature at its center, respectively.

[0134] The control system operates a dual closed-loop strategy: when printing to areas with poor heat dissipation, such as thin-walled sharp corners, the infrared thermal imager detects an abnormal increase in the average temperature of the molten pool (100°C). The power control loop (PID algorithm) immediately intervenes, automatically reducing the microwave output power to prevent overheating and collapse. When printing to large solid areas, if the temperature difference between the center and edge exceeds a threshold as shown by the fiber optic sensor and infrared data comparison, the frequency control loop (PI algorithm) intervenes, adjusting the microwave frequency to change the standing wave distribution and forcibly increasing edge heating efficiency. This intelligent intervention throughout the entire process achieves decoupled control of "temperature uniformity" and "temperature control," ensuring the consistency of grain structure and mechanical properties in different parts of complex components.

[0135] The dynamic microwave-assisted laser metal additive manufacturing method and apparatus disclosed herein aim to overcome the problems of lack of localization, imprecise thermal field control, and insufficient microscopic dynamic intervention in the prior art. This embodiment achieves highly coordinated spatial, temporal, and controllable application and regulation of directional, quantitative, dynamic, and irregular energy to the molten pool 100 and the solid-liquid interface region in additive manufacturing by achieving spatial, temporal, and controllable synergy between the microwave energy field and the laser thermal field, thereby significantly improving the quality and performance of the formed parts.

[0136] Regarding spatial localization and thermal field compensation, by setting up a multi-level microwave screening device 22, the originally divergent microwave beam is focused, screened, and shaped, successfully confining the effective range of microwave energy from the centimeter or decimeter-level environmental space to a millimeter-level region matching the size of the laser molten pool 100. More importantly, by adopting an irregularly shaped hollow metal structure layer 222 with a ring-shaped fence structure, this solution can reshape the microwave energy into a ring beam, concentrating its energy in the solid-liquid transition region around the molten pool 100. This "high around the edges, low in the center" microwave field complements the inherent "high in the center, low around the edges" Gaussian thermal field of the laser in space, effectively flattening the temperature gradient inside the molten pool 100, significantly reducing residual thermal stress from the root, thereby greatly suppressing the generation of microcracks and macroscopic deformation, and solving the core quality problem in additive manufacturing.

[0137] In terms of microdynamic intervention and metallurgical bonding, the selected microwave beam, after being directionally applied to the molten pool 100, utilizes the high-frequency vibration (non-thermodynamic effect) generated by the microwave electromagnetic field on charged particles and atoms in the melt. This significantly accelerates the rapid mutual dissolution and diffusion migration of metal elements at the solid-liquid interface, promoting the metallurgical bonding strength between layers, which is particularly crucial for the forming of dissimilar materials or graded functional materials. Simultaneously, this high-frequency vibration is equivalent to "electromagnetic tamping" of the liquid metal, effectively disrupting the surface tension adhesion of microbubbles and accelerating their escape, thereby significantly reducing the porosity of the formed part (increasing density). Furthermore, the microwave-assisted oscillation effect helps to break up growing coarse dendrites and promotes the nucleation and growth of fine equiaxed crystals. According to the Hall-Page effect, this significantly improves the yield strength and overall mechanical properties of the material.

[0138] In terms of process control and intelligent adaptation, a dual closed-loop control strategy based on temperature feedback was established: one closed loop is used to regulate the output power of the microwave (temperature control), and the other closed loop is used to regulate the output frequency of the microwave (temperature equalization / depth control). By monitoring the temperature and thermal field distribution of the molten pool 100 in real time (e.g., infrared thermography or fiber optic sensing), the system can adjust the energy input and penetration depth of the microwave in real time and adaptively according to the preset control strategy. This enables this embodiment to quickly respond to differences in local heat accumulation caused by changes in scanning path and geometry (e.g., thin walls, sharp corners) during additive manufacturing, ensuring the stability of the molten pool 100 state and the robustness of the processing, thereby guaranteeing the uniformity of the forming quality of complex structural parts.

[0139] The dynamic microwave-assisted method and apparatus provided in this embodiment achieve localization, irregular shaping and dynamic control of the microwave energy field, which not only compensates for the inherent defects of laser from the perspective of thermal field, but also improves metallurgical defects from the perspective of micro-dynamics. Compared with the overall or static heating of the prior art, it has the advantages of simple method, precise control, high forming quality and superior material properties.

[0140] The foregoing description and accompanying drawings fully illustrate embodiments of the present disclosure to enable those skilled in the art to practice them. Other embodiments may include structural and other changes. The embodiments represent only possible variations. Individual components and functions are optional unless explicitly required, and the order of operation may vary. Parts and features of some embodiments may be included or substituted for parts and features of other embodiments. Embodiments of the present disclosure are not limited to the structures described above and shown in the accompanying drawings, and various modifications and changes may be made without departing from its scope. The scope of the present disclosure is limited only by the appended claims, and the foregoing embodiments should be considered exemplary and non-limiting.

Claims

1. A method for laser metal additive manufacturing based on dynamic microwave assistance, characterized in that, Includes the following steps: S1: Determine the process parameters for laser additive manufacturing, and determine the preset molten pool size based on the process parameters; S2: Control the laser beam to act on the metal material to form a liquid molten pool. At the same time, use a multi-level microwave screening device to spatially constrain and screen the microwave beam, focusing the effective range of the microwave beam to a scale that matches the preset molten pool size. S3: Apply the selected microwave beam in a directional manner to the liquid molten pool and the solid-liquid interface region; The selected microwave beam is applied directionally to the molten pool and the solid-liquid interface region, including: The near-field coupling effect of microwaves is excited by the subwavelength aperture structure in the multi-stage microwave screening device, which confines and concentrates the microwave energy field on the solid-liquid interface region of the molten pool. The non-thermodynamic effects of high-frequency microwave electromagnetic fields on metal atoms in the molten pool induce high-frequency atomic vibrations, thereby reducing the diffusion barrier at the solid-liquid interface of the molten pool, accelerating the migration and mutual solubility of alloying elements, and driving bubbles to escape from the molten pool to eliminate porosity defects. S4: Control the microwave beam and laser beam to move synchronously after screening, and cooperate with the laser beam to deposit materials layer by layer to complete the part forming; controlling the microwave beam and laser beam to move synchronously after screening includes: controlling the multi-stage microwave screening device to move synchronously with the laser beam, and the vertical distance between the end emission surface of the multi-stage microwave screening device and the surface of the molten pool is within the near-field coupling range of microwaves, so as to realize energy coupling by using evanescent waves.

2. The method according to claim 1, characterized in that, The directional application of microwaves in step S3 includes: By adjusting the spatial distribution of microwave energy through a multi-stage microwave screening device, the microwave energy on the surface of the molten pool is made to exhibit a distribution state with low energy in the center and high energy around the perimeter. By spatially superimposing and complementing the energy characteristics of the microwave energy distribution state and the laser heat source, which exhibit a Gaussian distribution, the energy difference of the laser heat source is compensated, and a flat-topped temperature field distribution is formed inside the molten pool to reduce the temperature gradient of the molten pool.

3. The method according to claim 1, characterized in that, The selected microwave beams were applied directionally to the molten pool and the solid-liquid interface region. The application process of the selected microwave beams employed a dual closed-loop real-time control strategy, including: The power control loop adjusts the output power of the microwave generator based on the real-time monitored average temperature of the molten pool, thereby controlling the overall heat input of the molten pool. The frequency control loop adjusts the microwave frequency in real time based on the temperature difference or temperature distribution uniformity between the center and edge of the molten pool, thereby changing the penetration depth and energy distribution uniformity of the microwaves within the molten pool.

4. The method according to claim 1, characterized in that, Step S1 involves determining the preset molten pool size, including: Based on the thermophysical properties of the material to be processed, the size and shape of the molten pool under different laser parameters are calculated using finite element simulation, and the initial frequency and range of the microwave are preset according to the simulation results.

5. A dynamic microwave-assisted laser metal additive manufacturing apparatus, applied to the method according to any one of claims 1 to 4, characterized in that, include: The additive manufacturing host is equipped with a laser generation system, which is used to provide a laser beam heat source and control the layer-by-layer deposition of metal materials to form a liquid molten pool during the forming process; A microwave generating system used to generate microwave beams with adjustable frequency and power; A multi-stage microwave screening device, connected to a microwave generating system and located at the end of the microwave transmission path, is configured to spatially constrain and directionally screen the microwave beam, focusing the effective range of the microwave beam to a scale matching the size of the molten pool. The multi-stage microwave screening device includes an irregularly shaped perforated metal structure layer, which is made of conductive metal material and has a subwavelength scale perforated pattern on its surface, configured to perform localized screening and beam shaping of microwaves. A linkage mechanism is used to drive the multi-stage microwave screening device to move synchronously with the laser beam; The control system receives temperature feedback data from the molten pool and adjusts the output power and frequency of the microwave generator system in real time according to a preset dual closed-loop control strategy.

6. The apparatus according to claim 5, characterized in that, The multi-stage microwave screening device includes, from top to bottom, the following components along the microwave transmission direction: The wave-transparent focusing layer, made of wave-transparent material, is configured to focus the diverging microwave beam toward the central axis. The irregularly shaped hollow metal structure layer; The microwave absorbing cutoff layer, made of dielectric loss material, is configured to intercept and absorb excess microwaves outside the screening range, preventing secondary thermal effects on the solidified area.

7. The apparatus according to claim 5, characterized in that, The irregularly shaped, perforated metal structure layer adopts any of the following structural forms: The ring-shaped fence structure consists of several concentric metal rings or ring gaps, and is used to generate a ring microwave field with low energy at the center and high energy around the edges. The diamond-shaped grid structure, composed of periodically arranged diamond-shaped metal mesh, is used to filter out low-frequency microwaves. The multi-hole structure, consisting of an array of circular through-holes, is used to divide and confine the microwave beam within the lattice region.

8. The apparatus according to claim 5, characterized in that: The microwave generation system uses a solid-state microwave source, which includes a voltage-controlled oscillator and a phase-locked loop synthesizer, and is configured to achieve millisecond-level real-time adjustment of the output frequency within a preset bandwidth through digital control.

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