Laser metal additive manufacturing method and device based on dynamic microwave assistance

Abstract

The embodiment of the invention relates to a laser metal additive manufacturing method based on dynamic microwave assistance, and the method comprises the following steps: S1, determining technological parameters of laser additive manufacturing, and determining the size of a preset molten pool based on the technological parameters; s2, a laser beam is controlled to act on the metal material to form a liquid molten pool, meanwhile, a multi-stage microwave screening device is used for conducting spatial constraint and screening on microwave beams, and the acting range of the microwave beams is focused to the size matched with the preset molten pool size; s3, directionally applying the screened microwave beams to a liquid molten pool and a solid-liquid interface area; and S4, the screened microwave beams and the laser beams are controlled to move synchronously, and the laser beams are matched to conduct layer-by-layer stacking of materials so as to complete part forming. By realizing localization, special shape and dynamic regulation and control of a microwave energy field, inherent defects of laser are compensated from the perspective of a thermal field, and metallurgical defects are improved from the perspective of microdynamics. The invention further provides a laser metal additive manufacturing device based on dynamic microwave assistance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal additive manufacturing, and particularly relates to a laser metal additive manufacturing method and device based on dynamic microwave assistance. BACKGROUND

[0002] Additive manufacturing technology, especially selective laser melting (SLM) and laser melting deposition (LMD), has been widely applied in the fields of aerospace, biomedicine, etc. due to its ability to directly shape complex metal parts. However, since the laser heat source has extremely high energy density and extremely short action time, the metal material undergoes extremely rapid melting and solidification cycles during the shaping process, which inevitably brings a series of metallurgical defects and mechanical property problems.

[0003] In the prior art, the main challenges are concentrated in the following aspects: first, thermal stress and cracks caused by temperature gradient. The energy of the laser beam is usually in a Gaussian distribution (extremely high central energy, rapid decay at the edge), which leads to a huge temperature gradient inside the molten pool. This non-uniform thermal field distribution will generate a large amount of residual stress during the solidification process, and then induce micro-cracks or even cause the part to warp and deform. Secondly, pores and un-melted defects. Due to the extremely fast cooling rate of the molten pool, the gas bubbles in the melt are often "frozen" in the solid phase to form pores before they have time to escape; at the same time, if the interlayer energy input is insufficient or the fluidity is poor, un-melted defects are easily produced, which seriously affects the fatigue performance of the component. Thirdly, it is difficult to control the microstructure. Rapid directional solidification easily leads to the growth of coarse columnar crystals, causing anisotropy of the mechanical properties of the material.

[0004] To solve the above problems, the prior art attempts to introduce an auxiliary heat source. Common solutions include induction heating, resistance heating or overall microwave heating. For example, the patent with publication number CN119910751A proposes a method for additive manufacturing in a closed microwave high-temperature cavity, which uses microwaves to preheat the entire environment or workpiece. However, this "macro, static, overall" heating method has obvious limitations: 1. Lack of localization and flexibility: overall heating is to heat the entire forming chamber or the entire workpiece, which cannot accurately control the energy of the tiny "liquid pool" core area. This "flood irrigation" type of heating not only consumes a lot of energy, but also easily causes grain coarsening or thermal accumulation deformation of the formed part. 2. Unable to compensate for the Gaussian heat field of the laser: existing microwave auxiliary methods mainly pursue uniform heating, and cannot compensate for the spatial energy of the inherent defects of the laser heat source "center high, edge low", which is difficult to flatten the temperature gradient inside the pool from the root. 3. Lack of dynamic intervention mechanism: existing microwave applications mainly use its "thermal effect" (preheating), and ignore the "non-thermal effect" (such as electromagnetic oscillation and vibration) that the microwave electromagnetic field may have on metal atoms and melt flow, so the effect is limited in eliminating micro pores and refining grains. 4. Control lag: traditional temperature control methods are mostly open-loop or simple single-point feedback, which is difficult to adapt to the dynamic characteristics of the melt pool shape changing instantaneously in the additive manufacturing process. SUMMARY

[0005] An object of the present application is to provide a laser metal additive manufacturing method and device based on dynamic microwave assistance, at least to solve the above problems.

[0006] To achieve the above object, some embodiments of the present application provide a laser metal additive manufacturing method based on dynamic microwave assistance, comprising the following steps: S1: determining the process parameters of laser additive manufacturing, and determining the preset pool size based on the process parameters; S2: controlling the laser beam to act on the metal material to form a liquid pool, and simultaneously using a multi-stage microwave screening device to spatially constrain and screen the microwave beam, focusing the action range of the microwave beam to a size matching the preset pool size; S3: directing the screened microwave beam to the liquid pool and the solid-liquid interface region; S4: controlling the screened microwave beam to move synchronously with the laser beam, and cooperating with the laser beam to perform layer-by-layer accumulation of materials to complete part forming.

[0007] Some embodiments of the present application provide a laser metal additive manufacturing device based on dynamic microwave assistance, applied to the above-mentioned method, comprising: An additive manufacturing host machine is configured with a laser generation system for providing a laser beam heat source and controlling the layer-by-layer deposition of metal material to form a liquid molten pool in a forming process; A microwave generation system is used to generate a microwave beam with adjustable frequency and power; A multi-stage microwave screening device is connected to the microwave generation system and arranged at the end of the microwave transmission path, configured to spatially constrain and directionally screen the microwave beam, and focus the action range of the microwave beam to a scale matching the size of the liquid molten pool; A linkage movement mechanism is used to drive the multi-stage microwave screening device to move synchronously with the laser beam; A control system is used to receive temperature feedback data of the molten pool and real-time regulate and control the output power and output frequency of the microwave generation system according to a preset double closed-loop control strategy.

[0008] Compared with related technologies, the scheme provided in the embodiments of the present application solves the defects of traditional microwave-assisted technologies (such as microwave cavity heating) that can only perform overall and large-scale heating, and realizes precise delivery of microwave energy. In addition, through synchronous movement, invalid heating or secondary thermal damage to the solidified forming area is avoided, and only the molten pool area that most needs energy regulation and control is intervened, thereby significantly improving the energy efficiency ratio.

[0009] By realizing localized, special-shaped and dynamic regulation and control of the microwave energy field, not only the inherent defects of the laser are compensated from the thermal field perspective, but also the metallurgical defects are improved from the microscopic dynamics perspective, compared with the overall or static heating of the prior art, the method is simple, the control is accurate, the forming quality is high, and the material performance is superior. BRIEF DESCRIPTION OF DRAWINGS

[0010] One or more embodiments are exemplarily illustrated by pictures in the drawings corresponding thereto, which do not constitute a limitation on the embodiments, elements with the same reference numerals in the drawings represent similar elements, unless specifically stated otherwise, and the drawings do not constitute a proportional limit.

[0011] Fig. 1 is a schematic diagram of the framework process of the laser metal additive manufacturing method based on dynamic microwave assistance provided by the embodiments of the present disclosure.

[0012] Fig. 2 is a schematic diagram of the laser metal additive manufacturing device acting on the metal solid area and the molten pool provided by the embodiments of the present disclosure.

[0013] Fig. 3 is a schematic diagram of the microwave generation system provided by the embodiments of the present disclosure.

[0014] Fig. 4 is a schematic diagram of the microwave generation system acting on the molten pool provided by the embodiments of the present disclosure.

[0015] Reference signs: 10: additive manufacturing host; 20: microwave generating system; 21: solid-state microwave source; 22: multi-stage microwave screening device; 221: wave-transparent focusing layer; 222: special-shaped hollow metal structure layer; 223: wave-absorbing truncation layer; 100: molten pool. DETAILED DESCRIPTION

[0016] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the following will be combined with the drawings in the embodiments of the present application to make a clear and complete description of the technical solutions in the embodiments of the present application. Obviously, the described embodiments are some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0017] The terms “first”, “second”, and the like in the description and claims of the present disclosure and the above drawings are used to distinguish similar objects, and do not necessarily indicate a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present disclosure described herein can be implemented. In addition, the terms “include” and “have” and any variations thereof are intended to cover non-exclusive inclusion.

[0018] In the embodiments of the present disclosure, the terms “upper”, “lower”, “inner”, “middle”, “outer”, “front”, “back” and the like indicate the orientation or positional relationship shown in the drawings. These terms are mainly used to better describe the present disclosure and its embodiments, and are not intended to limit the indicated devices, elements or components to have a specific orientation, or to be constructed and operated in a specific orientation. In addition, in addition to indicating the orientation or positional relationship, the above-mentioned terms can also be used to indicate other meanings, for example, the term “upper” can also be used to indicate a certain attachment relationship or connection relationship in some cases. For those of ordinary skill in the art, the specific meanings of these terms in the embodiments of the present disclosure can be understood according to the specific circumstances.

[0019] In addition, the terms “set”, “connected”, “fixed” should be broadly understood. For example, “connected” can be fixed connection, detachable connection, or integral structure; can be mechanical connection, or electrical connection; can be direct connection, or indirect connection through an intermediate medium, or internal communication between two devices, elements or components. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present disclosure can be understood according to the specific circumstances.

[0020] Unless otherwise specified, the term “a plurality of” means two or more.

[0021] In the embodiments of the present disclosure, the character " / " represents an "or" relationship between the preceding and following objects. For example, A / B means A or B.

[0022] The term "and / or" is a description of the association relationship between objects, which means that there can be three relationships. For example, A and / or B means that there are three relationships of A or B, or A and B.

[0023] It should be noted that the embodiments in the embodiments of the present disclosure and the features in the embodiments can be combined with each other without conflict.

[0024] In combination with Figs. 1 to 4 The embodiment of the present disclosure provides a laser metal additive manufacturing method based on dynamic microwave assistance, which comprises the following steps: S1: determining the process parameters of laser additive manufacturing, and determining the preset molten pool 100 size based on the process parameters; S2: controlling the laser beam to act on the metal material to form a liquid molten pool 100, and simultaneously using a multi-stage microwave screening device 22 to spatially constrain and screen the microwave beam, focusing the action range of the microwave beam to a scale matching the preset molten pool 100 size; S3: directing the screened microwave beam to the liquid molten pool 100 and the solid-liquid interface region; S4: controlling the screened microwave beam to move synchronously with the laser beam, and cooperating with the laser beam to perform layer-by-layer accumulation of materials to complete part forming.

[0025] The method provided by the embodiment realizes precise localized application of microwave energy field; by using the multi-stage microwave screening device 22 to spatially constrain and screen the microwave beam, the action range of the microwave is successfully focused from the centimeter-level coverage range of the conventional microwave source to the millimeter-level scale matching the laser molten pool 100 size. This localized control overcomes the defects of energy divergence, excessive heating area and discontinuity in traditional microwave assistance technology, ensures that the microwave energy is only directed to act on the liquid molten pool 100 and the solid-liquid interface region, effectively avoids invalid heat accumulation or secondary damage to the non-processing area (such as the solidified formed part), and significantly improves the energy utilization efficiency and processing precision.

[0026] Secondly, the embodiment significantly improves the metallurgical quality of the formed part through a unique microwave vibration and dynamic intervention mechanism. The high-frequency vibration of the atoms inside the molten pool 100 is induced by the screened microwave electromagnetic field, and this non-thermal dynamic effect plays a role similar to "concrete vibration". On the one hand, this effect greatly reduces the diffusion barrier of atoms at the solid-liquid interface, accelerates the rapid migration and mutual dissolution of alloying elements, and solves the problems of poor interlayer bonding and element segregation; on the other hand, it effectively destroys the adhesion of bubbles in the melt, promotes the active escape of bubbles, thereby eliminating pore defects and refining the grain structure. At the same time, combined with the bulk heating effect of microwaves, the temperature gradient inside the molten pool 100 is effectively controlled and flattened, thereby inhibiting the generation of thermal stress and cracks from the root.

[0027] Moreover, the embodiment realizes the whole-process dynamic coordination of energy field assistance. By controlling the screened microwave beam and the laser beam to move synchronously, it is ensured that the auxiliary energy field always accurately follows the processing hot spot during the whole manufacturing process of layer-by-layer accumulation. This dynamic accompanying feature ensures that the molten pool 100 is always in the best "thermal-mechanical" coupling environment regardless of the change of the scanning path, thereby ensuring the uniformity of the organization and the consistency of the mechanical properties of the final shaped part in the overall size, effectively solving the problem of unstable forming quality of complex components.

[0028] By using the dynamic microwave-assisted laser metal additive manufacturing method provided by the embodiment of the present disclosure, first, according to the material properties (such as thermal conductivity, melting point) and geometric characteristics of the part to be processed, the process parameters such as laser power and scanning speed are set, and the size of the liquid molten pool 100 generated under the action of the laser is predicted through experiment or simulation. Then, in the printing process, the wide beam generated by the microwave generator is physically constrained by using a multi-stage microwave screening device 22. This device is similar to a funnel, which "compresses" and focuses the microwave energy beam with a wavelength of centimeters to a scale matching the millimeter-level molten pool 100. Subsequently, the focused microwave beam is accurately aimed at the liquid molten pool 100 and the solid-liquid interface around it. Finally, through a mechanical linkage moving mechanism, the microwave screening device moves synchronously with the laser head, ensuring that the microwave always acts together with the laser head during the process of layer-by-layer melting and accumulation of the powder to form a shape.

[0029] The embodiment solves the defect that the traditional microwave-assisted technology (such as microwave cavity heating) can only perform overall and large-scale heating, and realizes millimeter-level precise delivery of microwave energy. In addition, through synchronous movement, invalid heating or secondary thermal damage to the already solidified formed area is avoided, and only the molten pool 100 area that most needs energy regulation is intervened, thereby significantly improving the energy efficiency ratio.

[0030] Optionally, the specific way of screening in step 2 using the multi-stage microwave screening device 22 includes: when a ring fence type structure is used for the screening layer, the central solid block and the peripheral wave-transparent characteristics are used to reshape the microwave energy into a ring-shaped beam, so that the energy is concentrated on the solid-liquid interface at the periphery of the molten pool 100, to compensate for the difference in heat distribution of the laser heat source center high and the edge low; when a diamond fence type structure is used for the screening layer, the characteristics of the high-pass filter are used to filter out low-frequency microwave components, and only high-frequency microwaves with a frequency higher than the cutoff frequency are allowed to pass through, thereby controlling the penetration depth of the microwave in the molten pool 100.

[0031] When it is necessary to solve the problem of laser heat source center heat and edge cold, a ring fence type structure is selected. The center of the structure is a solid metal disc that blocks the direct transmission of microwaves to the center of the molten pool 100; the periphery is a ring-shaped gap that allows microwaves to pass through. The microwave field formed in this way presents a "hollow ring shape", and the energy is concentrated on the solid-liquid interface at the periphery of the molten pool 100. In this way, the Gaussian heat distribution defect of the laser is effectively compensated, the temperature gradient in the molten pool 100 is flattened, and the thermal cracks and residual stress caused by excessive temperature difference are directly inhibited.

[0032] When it is necessary to control the penetration depth of the microwave in the molten pool 100, a diamond fence type structure is selected. The structure uses the waveguide cutoff frequency principle to act as a high-pass filter, filters out frequency components with excessive penetration or weak penetration, and only allows specific high-frequency microwaves to pass through, thereby accurately controlling the heating depth. In this way, layered injection of microwave energy in the depth direction is achieved, and excessive deposition of energy at the bottom of the molten pool 100 or insufficient heating on the surface is avoided.

[0033] Optionally, the screening of the microwave beam in step S2 also includes: using the wave-transparent focusing layer 221 of the Fresnel lens structure to perform phase modulation and primary focusing on the microwave beam; using the wave-absorbing cutoff layer 223 made of high dielectric loss material to absorb the sidelobe microwave energy outside the focused spot, to prevent secondary thermal effects on the solidified and formed area.

[0034] In the multi-stage screening device, a layer of Fresnel lens structure made of high-transparency ceramic or glass is first used to perform primary focusing on the microwaves, and the divergent beam is gathered to the center through phase modulation. At the outermost layer or lower part of the screening device, a wave-absorbing cutoff layer 223 made of high dielectric loss material such as silicon carbide doped ceramic is arranged. This layer acts like a diaphragm, absorbing the diffraction sidelobe energy outside the focused spot.

[0035] This embodiment significantly improves the energy density of the microwave beam at the target point through the Fresnel lens. In addition, the wave-absorbing cutoff layer 223 eliminates stray microwaves, forms a "steep" beam with clear edges, and prevents accidental ignition or interference of microwaves on the surrounding non-processing area (such as the powder bed or precision parts).

[0036] Optionally, the microwave generator adopts a solid-state microwave source 21, whose frequency control mode is as follows: a voltage-controlled oscillator (VCO) combined with a phase-locked loop (PLL) synthesizer is used to adjust the frequency with millisecond-level precision in the frequency range of 1 GHz to 25 GHz; during the processing, the microwave frequency is adjusted in real time according to the change of the size of the molten pool 100, so as to maintain the sub-wavelength matching relationship between the microwave wavelength and the aperture of the screening device.

[0037] The 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 in a wide frequency band of 1 GHz to 25 GHz with millisecond-level response speed. During the processing, if the size of the molten pool 100 fluctuates due to changes in heat dissipation conditions, the system immediately adjusts the output frequency to maintain the sub-wavelength matching relationship between the microwave wavelength and the screening aperture.

[0038] In this way, the millisecond-level frequency adjustment capability of the embodiment enables the microwave energy to adapt to the transient changes in the state of the molten pool 100, ensuring the stability of energy coupling. In addition, it ensures that the screening device always works in the best frequency selection or focusing mode, avoiding the decline in energy transmission efficiency caused by frequency drift.

[0039] Optionally, the directional application of the microwave in step S3 includes: adjusting the spatial distribution of the microwave energy through the multi-stage microwave screening device 22, so that it presents a distribution state of low center energy and high peripheral energy on the surface of the molten pool 100; and through the spatial superposition of the microwave energy distribution state and the energy characteristics of the Gaussian distribution of the laser heat source, the energy difference of the laser heat source is compensated, and a flat-top temperature field distribution is formed inside the molten pool 100 to reduce the temperature gradient of the molten pool 100.

[0040] By adjusting the microwave screening device, a microwave field of "low center and high periphery" is output. This microwave field is superimposed on the Gaussian thermal field of "high center and low periphery" of the laser. The two are mathematically superimposed in space, and the total energy field after synthesis presents a flat-top distribution on the cross section of the molten pool 100. The great temperature gradient inside the molten pool 100 is fundamentally eliminated, making the solidification process more uniform and significantly reducing the source of micro-cracks.

[0041] Optionally, the screened microwave beam is applied to the liquid molten pool 100 and the solid-liquid interface region, including: exciting the near-field coupling effect of the microwave through the sub-wavelength aperture structure in the multi-stage microwave screening device 22, and concentrating the microwave energy field on the solid-liquid interface region of the molten pool 100; through the non-thermal dynamic effect of the high-frequency microwave electromagnetic field on the metal atoms in the molten pool 100, inducing high-frequency vibration of the atoms, thereby reducing the diffusion barrier at the solid-liquid interface of the molten pool 100, accelerating the migration and mutual solubility of alloy elements, and driving the bubbles in the molten pool 100 to escape to eliminate pore defects.

[0042] By using sub-wavelength aperture structure, near-field coupling effect is excited at the aperture exit, generating high-intensity evanescent wave directly acting on the molten pool 100. At the same time, the non-thermal dynamic effect (i.e. electromagnetic oscillation force) of the high-frequency electromagnetic field on metal atoms forces the atoms in the molten pool 100 to vibrate at high frequency. This embodiment realizes energy transmission of microwaves at sub-wavelength scale, solving the physical problem that conventional microwaves cannot be focused to a millimeter-level spot. In addition, the high-frequency vibration of atoms reduces the diffusion barrier, accelerates the mutual solubility of alloy elements (solves segregation), and drives bubbles to float up like concrete vibration (eliminates pores), and refines the grains.

[0043] In some embodiments, the size of the sub-wavelength aperture must maintain a certain proportional relationship with the working wavelength of the microwaves (for example, aperture size ≤ half of the working wavelength or aperture size ≤ one-tenth of the working wavelength). At the same time, the vertical distance between the end exit surface of the microwave screening device and the surface of the molten pool 100 is strictly limited to the near-field coupling range of 1 mm to 5 mm, to ensure efficient coupling of evanescent waves.

[0044] Optionally, the screened microwave beam is applied to the liquid molten pool and the solid-liquid interface region, and the application process of the screened microwave beam adopts a double-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; a frequency control loop, which adjusts the microwave frequency in real time according to the temperature difference between the center and the edge of the molten pool 100 or the uniformity of the temperature distribution, to change the penetration depth and energy distribution uniformity of the microwaves in the molten pool 100.

[0045] Optionally, the application process of the microwave beam in step S3 adopts a double-closed-loop real-time control strategy, specifically including: A temperature feedback mechanism is constructed to monitor the macro temperature of the surface of the molten pool 100 in real time by an external infrared thermometer, and to monitor the transient temperature of the center of the molten pool 100 in real time by an internal optical fiber temperature sensor; A power PID control is performed to calculate the deviation of the average temperature of the molten pool 100 from the target set temperature, and to adjust the output power of the microwave generator based on the PID algorithm to stabilize the overall heat input of the molten pool 100; A frequency PI control is performed to calculate the difference between the center temperature and the surface temperature of the molten pool 100 or the temperature range, and when the difference exceeds a 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 microwaves in the molten pool 100, to improve the uniformity of the temperature distribution.

[0046] The power loop monitors the average temperature of the melt pool 100 by an infrared temperature detector. If the temperature is lower than the set value, the PID algorithm increases the microwave power; otherwise, it decreases. This ensures the stability of the overall heat input. The frequency control loop monitors the temperature difference between the center and the edge of the melt pool 100. If the temperature difference is too large (non-uniform), the PI algorithm adjusts the microwave frequency. Changing the frequency changes the penetration depth of the microwave in the material (skin effect) and the standing wave distribution node, thereby correcting the uniformity of heating.

[0047] The present embodiment solves the problem that open-loop control cannot cope with complex heat accumulation, ensuring that the state of the melt pool 100 is always stable and consistent during long-time printing. At the same time, the frequency is introduced as a control variable to adjust the "uniformity", which is more precise than single power control.

[0048] Optionally, the preset melt pool 100 size in step S1 comprises: based on the thermal physical properties of the material to be processed, using finite element simulation to calculate the size and shape of the melt pool 100 under different laser parameters, and presetting the initial frequency and action range of the microwave according to the simulation results.

[0049] Optionally, before the additive manufacturing is implemented, based on the thermal physical properties of the metal material to be shaped and the laser process parameters, the finite element simulation software is used to simulate the shape of the melt pool 100 and the range of the heat-affected zone under the action of the laser spot; according to the size data of the melt pool 100 obtained by simulation, a device with a pore size matching the aperture size is selected from a preset multi-stage microwave screening device 22 specification library, and the initial frequency and initial action range of the microwave are set.

[0050] Before actual printing, the interaction between the laser and the powder is simulated by using the finite element simulation software to predict the shape of the melt pool 100 under different working conditions. According to the simulation results, the appropriate subwavelength aperture of the screening device is selected from the specification library in advance, and the initial microwave parameters are set. The present embodiment can reduce a large amount of trial and error experiment cost and ensure the success rate of one-time printing. In addition, the best matching between the physical device (aperture) and the process object (melt pool 100) in size is ensured.

[0051] Optionally, the step of controlling the screened microwave beam to move synchronously with the laser beam comprises: controlling the multi-stage microwave screening device 22 and the laser beam to move synchronously, and the vertical distance between the end surface of the multi-stage microwave screening device 22 and the surface of the melt pool 100 is within the near-field coupling range of the microwave, so as to realize energy coupling by means of evanescent wave.

[0052] Optionally, during the process of moving synchronously with the laser beam in step S4, the process further comprises: monitoring and adjusting the vertical distance between the end surface of the multi-stage microwave screening device 22 and the surface of the melt pool 100 in real time, so as to keep it within the near-field coupling range of 1mm to 5mm, so as to ensure that the microwave energy is coupled to the melt pool 100 in the form of evanescent wave and prevent the energy from diverging in the far field transmission.

[0053] In the process of synchronous movement, the vertical distance between the end of the screening device and the surface of the molten pool 100 is monitored in real time by a distance sensor (such as a capacitive or laser displacement sensor), and is strictly locked in the range of 1mm to 5mm (i.e. near-field coupling zone) by the Z-direction actuator in the linkage movement mechanism. The evanescent wave decays exponentially with distance, and strict control of the near distance is the key to achieving efficient energy injection. The embodiment can ensure coupling efficiency, while also avoiding diffraction divergence of microwaves in far-field transmission, ensuring energy concentration.

[0054] Optionally, a microwave-assisted quality verification step is also included: the microwave assistance is turned off in the first half of the process and turned on in the second half, forming a contrast region on one workpiece; the grain refinement degree and microhardness improvement effect are verified by nanoindentation matrix testing and electron backscatter diffraction (EBSD) analysis of the regions on both sides of the interface, and the microwave power parameters for the next batch are optimized accordingly.

[0055] In the first trial production, the "half-way switching" method is used: the microwave is not turned on in the first half and is turned on in the second half. After forming, a slice is cut at the interface, the hardness distribution is measured using a nanoindenter, and the grain orientation and size are analyzed using EBSD. The comparison data are used to reverse correct the microwave power parameters for the next batch. The embodiment provides a fast and homologous comparison process verification method, eliminating batch-to-batch error interference; and establishes a closed-loop optimization logic between material micro-performance and microwave macro-parameters.

[0056] The preparation for additive manufacturing is as follows: Before formally entering the layer-by-layer accumulation process, detailed data model processing and path planning are required. This process begins with importing and analyzing the three-dimensional digital model of the part to be formed, and using slicing software to discretize it along the height direction to generate a series of two-dimensional cross-sectional profile data. Based on this cross-sectional information, the system will plan the scanning path of the laser beam and the moving trajectory of the microwave beam generated synchronously to ensure that the two can achieve precise trajectory coincidence and linkage control in subsequent processing.

[0057] At the same time, the formation of the forming environment and the preparation of the material must be completed. This includes strict drying and screening treatment of the selected metal powder to ensure that the flowability and sphericity of the powder meet the process requirements; at the same time, the forming cavity is evacuated and filled with inert protective gas (such as argon or nitrogen), and the oxygen content is controlled below the preset safety threshold to prevent oxidation of the metal at high temperatures. In addition, the substrate on which the processing is performed also needs to be leveled and preheated to reduce the accumulation of thermal stress at the beginning of the forming.

[0058] The most core step is the synergistic setting of the dual-energy field process parameters. In this stage, not only the laser processing parameters (such as laser power, scanning speed, spot diameter and overlap rate) need to be determined, but also the key microwave control parameters need to be set for the microwave auxiliary system. This includes adjusting the output frequency and power of the microwave generating system 20, and according to the preset size of the molten pool 100, by adjusting the relative position or parameters of the wave-transparent focusing layer 221 and the special-shaped hollow metal structure layer 222, the focusing scale and beam shape of the microwave beam are accurately set. Through the coupling matching of these parameters, the optimal ratio of laser energy density and microwave energy injection amount is established, which lays the foundation for the subsequent realization of the combined processing mode of "laser melting and microwave steady-state temperature control".

[0059] The processing cycle of additive manufacturing performs the process of layer-by-layer accumulation as follows: Firstly, the powder laying / sending step: for the powder bed type process, the system will lay a layer of uniform metal powder on the substrate or the formed layer; if it is a directional energy deposition type process, the metal powder will be sent into the processing area through the nozzle.

[0060] Next is the key step of microwave screening and focusing (step S2). This step is performed by the microwave generating system 20 outputting a microwave beam. The microwave beam will pass through a wave-transparent focusing layer 221 (such as a Fresnel lens) for preliminary aggregation, which is equivalent to primary energy convergence. Subsequently, the microwave beam passes through a special-shaped hollow metal structure layer 222, which functions to spatially constrain, locally screen and shape the beam, and the goal is to accurately focus the action range of the microwave beam to a scale matching the preset molten pool 100 size. During the focusing process, the excess microwave is fully absorbed by the wave-absorbing cutoff layer 223, which effectively prevents these stray microwaves from causing secondary thermal effects on the surrounding area, ensuring directional concentration of energy.

[0061] Then is the energy coupling and directional application (step S3) stage. 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, the screened microwave beam is accurately applied to the liquid molten pool 100 and the solid-liquid interface region around it, realizing the synergistic coupling of the two kinds of energy.

[0062] Finally, dynamic synchronous scanning (step S4). The linkage moving mechanism accurately controls the screened microwave beam and the laser beam to keep them moving synchronously on the entire scanning path. The entire system will perform layer-by-layer accumulation according to the preset scanning path until the part is finally formed.

[0063] The real-time monitoring and dual-closed-loop regulation process of additive manufacturing occurs in parallel with the processing cycle, which is as follows: In the dynamic process of layer-by-layer accumulation, the system is equipped with multi-dimensional real-time monitoring. Using coaxial or paraxial sensor groups (such as high-speed infrared thermal imager, color temperature detector, and high-resolution CCD camera) integrated in the optical path, the processing area is continuously captured at nanosecond level. The core objects of monitoring focus on the topographic features of the center of the molten pool 100 (including the area, aspect ratio, and spatter of the molten pool 100) and the thermal field distribution of the solid-liquid interface region (including temperature gradient and cooling rate). These sensors convert the collected optical and thermal signals into digital signals in real time and feed them back to the central processing unit for data fusion analysis.

[0064] Based on the monitoring data, the system runs a set of precise double-closed-loop feedback control strategy. The first heavy closed loop is for 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 will adjust the laser power and scanning speed in real time according to the PID algorithm to ensure that the melting quality of the metal powder remains stable. The second heavy closed loop is specifically for the microwave auxiliary 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 form of the microwave beam. This control is not simply heating, but through the microwave to the periphery of the molten pool 100 for compensatory or smooth energy injection, actively intervening in the heat conduction during solidification.

[0065] Through this double-energy field coordinated closed-loop control, "steady-state thermal management" of the processing process is achieved. The dynamic intervention of microwave energy effectively reduces the severe thermal shock caused by rapid heating and cooling of the laser, significantly reducing the residual stress in the forming process. The system can correct process deviations within milliseconds according to real-time feedback, ensuring that each layer of the cladding layer is solidified in the best temperature field environment, effectively suppressing the generation of micro defects such as cracks and pores, and ensuring the consistency and reliability of the organization and performance of the final formed components.

[0066] In some embodiments, there is a specific time phase difference between the microwave pulse and the laser pulse. The laser pulse melts the metal first, and the microwave pulse is triggered with a delay, specifically acting on the solidification stage of the molten pool 100. Using microwave vibration to break the growing dendrites, promote the formation of equiaxed crystals, rather than simply heating.

[0067] This embodiment is mainly applied to the manufacture of aero-engine blade with strict requirements on grain morphology. Unlike continuous wave heating, this scheme adopts time-domain pulse synergistic process. The control system sets the microwave generator to pulse mode and phase-locks it with the laser pulse signal. Specifically, the trigger time of the microwave pulse is set to lag behind the laser pulse (e.g. lag 2-5 ms). When the laser pulse just goes out, the molten pool 100 enters the rapid cooling crystallization stage, and the microwave pulse intervenes accurately. The high-intensity microwave electromagnetic field is used to transiently "electromagnetic jolt" the paste zone, break the dendrite tip that is growing in direction, inhibit the formation of coarse columnar crystals, and promote the nucleation and growth of fine equiaxed crystals. This precise timing avoids inputting too much energy during the laser heating stage, resulting in an excessively large molten pool 100, and at the same time, plays the non-thermal effect of microwave in the key window period of solidification, realizing the regulation of microstructure.

[0068] In some embodiments, during single-layer printing, the microwave frequency is controlled to be periodically and rapidly switched between high frequency (e.g. 25 GHz) and low frequency (e.g. 2.45 GHz). High-frequency microwaves heat the surface of the molten pool 100 with small skin depth to reduce surface tension (smooth the surface); low-frequency microwaves heat the bottom of the molten pool 100 with large penetration depth to promote substrate bonding. Layered and accurate regulation of the full depth of the molten pool 100 is achieved.

[0069] In some embodiments, the control system reads the three-dimensional slice data of the part and identifies feature areas with poor heat dissipation conditions (e.g. overhanging structures, sharp corners). Before the laser head reaches the area, the microwave power is reduced or the microwave frequency is changed in advance, realizing heat field pre-compensation based on geometric features.

[0070] This embodiment is suitable for printing precision parts with complex geometric features such as overhanging structures, thin-walled sharp corners, etc. In order to overcome the hysteresis of traditional feedback control, this scheme introduces a feedforward control mechanism based on thermal history. Before printing starts, the control system reads the three-dimensional slice data of the part in advance, and identifies the "thermal node" areas (such as overhanging beams and sharp corner edges) with poor heat dissipation conditions through thermal simulation algorithm. Before the laser head moves to these specific areas, the control system generates instructions in advance to actively reduce the output power of the microwave or increase the microwave frequency (reduce the penetration depth). This "pre-judgment" adjustment offsets the local heat accumulation caused by the geometric shape, preventing overheating collapse or warping deformation at the thin-walled part. At the same time, the system combines with the acoustic emission sensor to monitor the molten pool 100 state, and once the abnormal "bursting sound" signal (indicating pore generation) is detected, the microwave parameters are immediately fine-tuned for suppression, realizing the dual protection of "feedforward preset and feedback correction".

[0071] In some embodiments, the plasma light intensity fluctuation above the molten pool 100 or the acoustic emission signal inside the molten pool 100 is monitored. When a characteristic signal representing "gas pore collapse" or "gas pore burst" is detected, the microwave stirring power is instantaneously enhanced to stabilize the molten pool 100 fluctuation by using strong electromagnetic force.

[0072] In some embodiments, for high laser reflectivity materials such as copper and aluminum, the preheating effect of microwave conductance loss on the surface of metal powder is used to increase the resistivity of the material, thereby significantly increasing its absorption rate of laser energy, solving the problem of difficult printing of high-reflectivity materials.

[0073] This embodiment is specifically designed to solve the problem of additive manufacturing of high laser reflectivity materials such as pure copper and aluminum alloys. It is well known that the absorption rate of copper powder at cold state to infrared laser is extremely low, which leads to difficulty in melting. This scheme uses the preheating effect of microwave conductance loss on the surface of metal powder to solve the problem. Before laser scanning, high-frequency microwaves (such as 25 GHz) output by a multi-stage screening device are used to pre-cover the powder area to be scanned. The microwave energy rapidly raises the surface temperature of the metal powder, and by using the physical property that the resistivity of metal increases with temperature, the absorption rate of copper powder to subsequent laser energy is significantly increased. This "microwave-assisted absorption" method enables pure copper, which originally requires extremely high laser power to melt, to form a stable molten pool 100 under conventional laser power, and through the continuous assistance of microwaves, the density and conductivity of the copper part are greatly improved, expanding the application of the device in the field of electronic component manufacturing.

[0074] In some embodiments, in the printing of dissimilar materials (such as ceramic reinforced metal matrix composites), the selective heating of different materials by microwaves, such as the heating of ceramic particles by microwaves, compensates for the deficiency of laser in heating only the metal matrix, improves the wettability of ceramic particles and metal matrix, and solves the problem of weak interfacial bonding.

[0075] The embodiments of the present disclosure also provide a dynamic microwave-assisted laser metal additive manufacturing device, which is applied to the above-mentioned method and comprises: an additive manufacturing host 10 configured with a laser generating system for providing a laser beam heat source and controlling the layer-by-layer deposition of metal materials to form a liquid molten pool 100 in 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 arranged at the end of the microwave transmission path, configured to spatially constrain and directionally screen the microwave beam, and focus the action range of the microwave beam to a scale matching the size of the liquid molten pool 100; a linkage moving 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 real-time regulating and controlling the output power and output frequency of the microwave generating system 20 according to a preset double-closed-loop control strategy.

[0076] The embodiment constructs an integrated additive manufacturing hardware system. The device main body 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 pool 100. On this basis, the system integrates a microwave generating system 20 that generates microwave energy with adjustable frequency and power. The key is that a multi-stage microwave screening device 22 is installed at the end of the microwave transmission path, and is physically bound next to the laser head through a linkage moving mechanism (such as a follow-up robot arm or a rigid connection bracket). When the laser head moves and prints according to the path, the microwave screening device moves synchronously, and always accurately projects the millimeter-level microwave beam after focusing and screening on the current liquid pool 100. At the same time, the control system acts as the "brain" and dynamically adjusts the output parameters of the microwave in real time by receiving the pool 100 temperature data.

[0077] Optionally, the multi-stage microwave screening device 22 includes, from top to bottom along the microwave transmission direction: a wave-transparent focusing layer 221 made of wave-transparent material and configured to concentrate the divergent microwave beam towards the central axis; a special-shaped hollow metal structure layer 222 made of conductive metal material and having a sub-wavelength scale hollow pattern on the surface and configured to perform localized screening and beam shaping on the microwave; and a wave-absorbing cutoff layer 223 made of dielectric loss material and configured to intercept and absorb excess microwaves outside the screening range to prevent secondary thermal effects on the solidified and formed area.

[0078] The multi-stage microwave screening device 22 adopts a layered structure design similar to a "sandwich" or a "funnel", which includes, from top to bottom along the microwave propagation direction: the wave-transparent focusing layer 221 located at the uppermost layer, using high-transmissivity quartz glass or alumina ceramic to preliminarily converge the divergent microwave beam from the waveguide transmission towards the central axis; the special-shaped hollow metal structure layer 222 located at the middle core layer, which is a conductive metal plate (such as copper or silver) processed with a specific sub-wavelength pattern, and uses the small hole coupling principle to forcibly screen the microwave; and the wave-absorbing cutoff layer 223 located at the lowermost layer or periphery, which uses dielectric loss material to absorb the diffraction side lobes outside the main beam like an "diaphragm". The embodiment shapes the electromagnetic wave like an optical lens, eliminates stray waves, and prevents edge energy from causing sparks in the non-pool 100 area of the workpiece.

[0079] In some embodiments, the multi-stage microwave screening device 22 is internally provided with a circulating cooling flow channel, and the cooling medium is non-polar cooling oil with good wave-transparent property, which not only cools the device, but also does not interfere with the transmission and focusing of the microwave. In this way, the problem of frequency drift caused by the deformation of the special-shaped metal layer due to long-term high-temperature radiation and metal spatter environment can be effectively avoided, since the distance between the microwave screening device and the pool 100 is only 1-5 mm. For example, a micro-flow channel cooling system is integrated inside the wave-transparent focusing layer 221 (ceramic / glass) or the special-shaped metal layer.

[0080] The embodiment aims to solve the problem of heat stability and anti-pollution of the microwave screening device in the near-field distance (1-5 mm) under long-term work. In the structural design of the multi-stage microwave screening device 22, the wave-transparent focusing layer 221 (such as alumina ceramic) and the special-shaped hollow metal structure layer 222 are integrated with a micro-channel cooling system inside. The cooling medium is selected to be a non-polar cooling oil (such as fluorinated liquid) with excellent wave-transparent property. Under the premise of not absorbing microwave energy, the heat generated by the radiation and microwave loss of the molten pool 100 is taken away through circulating flow, preventing the aperture from deforming and frequency drifting due to thermal expansion of the metal layer. In addition, the lower surface of the wave-absorbing truncation layer 223 at the bottom of the device is integrated with a ring-shaped air knife structure. The air knife is connected with the protective gas path of the additive manufacturing main machine 10 and sprays high-speed laminar gas downward. This gas flow not only strengthens the oxidation protection of the molten pool 100, but more importantly, forms an "air curtain barrier" that uses aerodynamic principles to forcibly blow the metal splashes and dust generated by the molten pool 100 away from the screening hole area, preventing the sub-wavelength aperture from being blocked, thereby ensuring the stability and life of the device during long-time continuous printing.

[0081] Optionally, the multi-stage microwave screening device 22 adopts a modular design, and the special-shaped hollow metal structure layer 222 is configured as a detachable and replaceable plug-in structure; the device is equipped with plug-in structures of special-shaped hollow metal structure layers 222 of different aperture sizes or different hollow patterns (such as ring-shaped, diamond-shaped, and multi-point hole type) to adapt to the additive manufacturing process requirements of different laser spot sizes or different material properties.

[0082] The multi-stage microwave screening device 22 adopts a modular card slot design, and the special-shaped hollow metal structure layer 222 in the middle is made into a plug-in structure that can be quickly detached. The operator can take out the corresponding plug-in structure (such as ring-shaped hole, diamond-shaped hole, etc.) from the accessory library according to the laser spot size (such as 0.5 mm or 2 mm) or material type of the current printing task and insert it into the device. A multi-stage microwave screening device 22 can adapt to different process requirements of additive manufacturing scenes without replacing the entire microwave head, reducing equipment costs.

[0083] Optionally, the external shell of the multi-stage microwave screening device 22 is in the shape of an inverted cone or a funnel, and its cross-sectional area gradually decreases along the microwave transmission direction; the wave-transparent focusing layer 221, the special-shaped hollow metal structure layer 222, and the wave-absorbing truncation layer 223 are coaxially arranged along the axis of the conical structure in sequence to physically adapt to the focusing path of the microwave beam from centimeter level to millimeter level.

[0084] The outer shell of the multi-stage microwave screening device 22 is designed as an inverted cone or funnel. Its cross-sectional area gradually decreases along the direction of microwave transmission (from the microwave source end to the end of the molten pool 100). The three internal layers (focusing layer, metal layer, and cutoff layer) are coaxially distributed along the central axis of the cone structure. The structure conforms to the physical path of the narrowing of the microwave beam focus, reducing the reflection loss of the microwave inside the device. In addition, the inverted cone design minimizes the size of the device at the end, facilitating installation next to the compact laser processing head and reducing interference with other components.

[0085] In some embodiments, additive manufacturing requires inert gas protection, and the screening device close to the molten pool 100 may block the protective gas flow and be easily clogged by splashes. Therefore, the lower surface of the wave-absorbing cutoff layer 223 of the multi-stage microwave screening device 22 is provided with an annular gas flow nozzle for forming a high-speed gas curtain, which on the one hand protects the molten pool 100 from oxidation and on the other hand uses aerodynamic force to blow away metal splashes to prevent sub-wavelength aperture clogging. Exemplarily, the inverted cone structure of the screening device is designed as part of a coaxial gas nozzle, or a gas curtain structure is added at the bottom of the device.

[0086] Optionally, the geometric cross-section of the wave-transparent focusing layer 221 is a Fresnel lens structure, configured to concentrate the incident microwave to the central axis by phase modulation.

[0087] The geometric cross-section of the wave-transparent focusing layer 221 is not a ordinary flat plate, but is processed into a Fresnel lens structure, i.e. the surface is engraved with a series of concentric ring-shaped grooves. By modulating the phase of the microwave by different ring bands, the incident plane wave or divergent wave converges to the focal point after passing through the lens. Compared with traditional thick and heavy dielectric lenses, the Fresnel structure is thinner and lighter, which is beneficial to follow the high-speed movement of the laser head; effectively improves the microwave energy density reaching the surface of the special-shaped metal layer, and improves the screening efficiency.

[0088] In some embodiments, if a curved surface part is printed, a fixed focal length may cause a decrease in coupling efficiency. This embodiment utilizes the refractive index change of the electrically controlled liquid crystal unit to real-time fine-tune the focal point depth of the microwave beam without moving the mechanical structure, to adapt to the slight changes in Z-axis height when printing complex curved surface parts. Exemplarily, a liquid crystal phased array or a deformable liquid lens is introduced above the wave-transparent focusing layer 221 (Fresnel lens).

[0089] Optionally, the distance between the special-shaped hollow metal structure layer 222 and the surface of the molten pool 100 is configured to be within the near-field coupling range of the microwave, to enhance the energy density of the microwave on the surface of the molten pool 100 by using the evanescent wave effect.

[0090] Optionally, the shaped hollow metal structure layer 222 adopts any one of the following structural forms: a ring fence structure composed of a plurality of concentric metal rings or ring-shaped slits, for generating a ring-shaped microwave field with low central energy and high peripheral energy; a diamond fence structure composed of a periodically arranged diamond metal mesh, for filtering out low-frequency microwaves; a multi-point hole structure composed of an array of circular through holes, for splitting and limiting the microwave beam in the dot array area.

[0091] For different metallurgical defects, three types of plug-ins with specific functions are provided: the ring fence type center is a solid metal disc, and the periphery is a ring-shaped slit. Microwaves can only penetrate from the periphery, forming a "hollow" beam; the diamond fence type is similar to a metal mesh, with mesh size designed as a cutoff frequency filter; the multi-point hole type is an array of small round holes.

[0092] The "high periphery and low center" microwave field generated by the ring structure (energy complementation) perfectly compensates for the Gaussian thermal distribution of the laser "high center and low periphery", flattening the temperature gradient. The diamond structure (frequency control depth) filters out low-frequency waves with excessive penetration, allowing only specific high-frequency waves to pass through, accurately controlling the heating depth (skin depth) of microwaves in the molten pool 100. The multi-point structure (discrete action) disperses energy in multiple tiny points, suitable for uniformization processing when large-area cladding is applied.

[0093] Optionally, the wave-absorbing cutoff layer 223 is arranged at the periphery or lower part of the shaped hollow metal structure layer 222, surrounding the output path of the microwave beam in a ring shape; the wave-absorbing cutoff layer 223 is made of silicon carbide doped ceramic or ferrite composite material, configured to convert microwave energy that does not pass through the screening aperture into heat energy and dissipate it, to form a clear microwave beam edge.

[0094] The wave-absorbing cutoff layer 223 is arranged at the lower edge of the shaped metal layer, surrounding the output port in a ring shape. The material is selected from silicon carbide doped ceramic or ferrite composite material. When microwaves diffract through the shaped holes, the side lobe energy that spreads outward will be quickly converted into heat energy and dissipated by this layer. In this way, the output microwave beam edge is clear and sharp, without tailing, eliminating the risk of stray microwave causing tip discharge (sparking) at the sharp corners of the formed part.

[0095] Optionally, the microwave generating system 20 adopts a solid-state microwave source 21, which includes a voltage-controlled oscillator (VCO) and a phase-locked loop (PLL) synthesizer, configured to realize millisecond-level real-time adjustment of the output frequency within the preset bandwidth through digital control.

[0096] The microwave generating system 20 abandons the traditional magnetron and adopts a solid-state microwave source 21. The core circuit includes a voltage-controlled oscillator (VCO) and a phase-locked loop (PLL) synthesizer. The control system sends a digital signal, which can achieve millisecond-level frequency switching within a preset bandwidth (such as 1-25 GHz); it can adjust the frequency extremely quickly to cope with the 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 realizing fine frequency selection heating.

[0097] Optionally, it further comprises an external infrared temperature measuring instrument for obtaining macro temperature distribution data of the surface of the molten pool 100; and an internal optical fiber temperature sensor for obtaining transient temperature data of the center of the molten pool 100; wherein the external infrared temperature measuring instrument and the internal optical fiber temperature sensor are electrically connected with the control system, and the control system calculates the average temperature and temperature uniformity index of the molten pool 100 through the feedback data of the external infrared temperature measuring instrument and the internal optical fiber temperature sensor, so as to adjust the power and frequency of the microwave generating system 20.

[0098] The device of the embodiment integrates two sets of temperature measuring systems: the external infrared temperature measuring instrument is installed on the side to shoot the overall thermal image (macro data) of the molten pool 100 and the heat affected zone; the internal optical fiber temperature sensor is integrated in the laser head to coaxially monitor the highest temperature point (transient data) of the center of the molten pool 100; the control system simultaneously collects the data of the two, calculates the "average temperature" and "temperature uniformity (such as the temperature difference between the center and the edge)", and respectively adjusts the power (power ring) and frequency (frequency ring) of the microwave; both the whole and the part are observed, and the data is more comprehensive; the decoupling control of "temperature equalization" and "temperature control" is realized, and the consistency of the forming quality is significantly improved.

[0099] Optionally, the linkage moving mechanism is connected with the control system, and is used for maintaining 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.

[0100] The linkage moving mechanism is equipped with a high-precision Z-axis adjustment function (or is preset fixed during installation). During the processing, the vertical distance between the end emission surface of the multi-stage microwave screening device 22 and the surface of the liquid molten pool 100 is strictly controlled to be maintained between 1 mm and 5 mm; this distance is within the near-field coupling range of the microwave wavelength. Only in the extremely close distance, the evanescent wave excited by the sub-wavelength aperture can be coupled into the molten pool 100. If the distance is too far, the energy will be sharply attenuated or diverged.

[0101] Optionally, the linkage moving mechanism is configured to install the multi-stage microwave screening device 22 at a preset inclined angle on one side of the laser processing head; the inclined angle is configured to make the central axis of the focused microwave beam intersect with the central axis of the laser beam at the surface of the liquid molten pool 100, so as to realize the fixed-point coupling of the microwave and the laser.

[0102] The linkage moving mechanism installs the multi-stage microwave screening device 22 at a preset inclined angle on the side of the laser head (non-coaxial wrapping). The inclined angle is adjusted so that the central axis of the focused microwave beam and the central axis of the laser beam accurately intersect at the surface of the liquid molten pool 100. In this way, the "double beam integration" is realized, ensuring that the microwave energy always covers the laser molten pool 100. In addition, the lateral inclined installation avoids shielding the vertically incident laser light path, and the structure is simpler to realize.

[0103] Optionally, a microwave parameter matching database is integrated inside the control system; the database stores the correspondence between the thermal physical properties of different materials, laser power parameters, and the best microwave frequency, the best screening aperture, and the best action distance; the control system is configured to call the matching control parameters from the database according to the input material and laser parameters before processing, and prompt the operator to replace the corresponding special-shaped perforated metal structure layer 222 insert.

[0104] The control system has a built-in microwave parameter matching database. The library stores a large amount of experimental data corresponding to different materials (such as titanium alloy, aluminum alloy), different laser powers, and the required best microwave frequency, best screening aperture shape, and best action distance. Before processing, the user inputs the material and laser parameters, and the system automatically calls the best solution and prompts the user on the screen: "Please replace the ring-shaped insert, aperture 1.5mm". This embodiment simplifies the complex multi-parameter control, and the operator does not need to have deep knowledge of microwaves to use it. In addition, it reduces human error and ensures the stability of the processing effect of different batches.

[0105] Optionally, the control system is configured with a specific non-uniformity adjustment module; the module is configured to calculate the difference between the center temperature and the surface temperature of the molten pool 100 in real time, and when the difference exceeds a preset threshold, a frequency adjustment instruction is generated through a PI control algorithm (proportional-integral control) to drive the voltage-controlled oscillator of the microwave generating system 20 to change frequency to adjust the skin depth of the microwave in the molten pool 100.

[0106] The control system has a specific algorithm module embedded. It calculates 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 (e.g. 50°C), the PI (proportional-integral) control algorithm intervenes to generate a frequency adjustment instruction to drive the VCO to change the microwave frequency. The change in frequency causes a change in the skin depth of the microwave in the metal molten pool 100, thereby correcting the temperature distribution. It can dynamically eliminate hot spots or cold spots in the molten pool 100, preventing element burning due to local overheating or incomplete fusion due to local overcooling.

[0107] In the embodiment of additive manufacturing applied to hot crack sensitive materials such as nickel-based superalloy or titanium alloy, the key to the cooperation between the additive manufacturing host 10 and the microwave generating system 20 in device configuration is the use of a special-shaped metal insert with a ring fence structure in the multi-stage microwave screening device 22. The center of the insert is a solid metal disc, and the periphery is a ring-shaped wave-transparent gap.

[0108] During processing, the laser beam irradiates the metal powder, forming a high-energy Gaussian distribution thermal field with a sharp drop in energy at the edge in the center of the molten pool 100. This large temperature difference is usually the main cause of cracking. At this time, the microwave beam is screened by the ring fence after preliminary aggregation by the wave-transparent focusing layer 221. The central part of the microwave is blocked, and only the peripheral microwave is transmitted, forming a hollow ring-shaped microwave thermal field. The linkage movement mechanism controls the coaxial synchronous movement of the ring-shaped microwave field and the laser spot, accurately heating the solid-liquid interface area around the molten pool 100. This "low in the center and high around" microwave field and "high in the center and low around" laser field perfectly complement each other in space, reshaping the temperature field in the molten pool 100 from a sharp peak to a flat top. In this way, the temperature gradient inside the molten pool 100 is significantly reduced, and the generation of residual stress is inhibited from the root cause, effectively eliminating the micro-crack defects inside the formed part.

[0109] In the embodiment for printing scenarios of large layer thickness accumulation or heterogeneous metal gradient materials, the aim is to solve the unmelted defect and strengthen the bonding force in the Z-axis direction. In this embodiment, the multi-stage microwave screening device 22 uses an insert with a diamond fence structure, and the diamond grid size is designed to a specific cutoff wavelength, used as a high-pass filter to filter out interfering low-frequency noise.

[0110] During processing, the real-time control system calculates the required microwave penetration depth according to the thickness of the current printing layer (for example, increased from the conventional 30 μm to 60 μm). The system dynamically reduces the microwave frequency (for example, adjusted to a low frequency within the allowed bandwidth) by driving the voltage-controlled oscillator (VCO) in the solid-state microwave source 21. The physical property of large skin depth of long-wavelength microwaves enables the microwave energy to penetrate the surface molten pool 100 and directly act on the remelted area at the bottom of the molten pool 100 and the previous solidified layer. The diamond fence ensures the pure transmission of microwaves of a specific frequency band during this process, achieving precise energy deposition in the depth direction. This deep heating effect promotes the metallurgical bonding between the current layer and the substrate, effectively eliminating the unmelted defects during thick layer printing.

[0111] In the embodiment for the manufacture of aerospace components with extremely high porosity requirements or aluminum alloy materials prone to porosity, the core of the device is to adopt a multi-point hole type structure of the screening insert, the aperture of which is designed to be sub-wavelength scale (for example, 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 in the near-field coupling range of 1 mm to 5 mm through the linkage moving mechanism.

[0112] In the process of laser moving following the microwave beam, the microwave excites high-intensity evanescent waves at the exit through the sub-wavelength small hole. This high-frequency electromagnetic field breaks through the diffraction limit and directly couples into the liquid molten pool 100, inducing the metal atoms to produce intense high-frequency vibration, i.e., non-thermal dynamic effect. This oscillation at the microscopic level is similar to the vibration of concrete pouring, which can destroy the surface tension of micro-bubbles in the melt and accelerate the bubbles to float out. This embodiment can significantly reduce the porosity of the formed part, and the atomic vibration promotes the breaking and proliferation of crystal nuclei, so that the final metallographic structure presents fine equiaxed crystals instead of coarse columnar crystals.

[0113] In the embodiment suitable for printing parts with complex geometry and severe changes in heat dissipation conditions (such as blades with overhanging structures or thin walls), the device integrates an external infrared thermal imager and an internal optical fiber sensor, which are respectively used to monitor the macroscopic thermal field distribution and the transient temperature of the center of the molten pool 100.

[0114] The control system runs a double closed-loop strategy: when printing to the thin-walled sharp corner or other poor heat dissipation areas, the infrared thermal imager detects that the average temperature of the molten pool 100 abnormally rises, and the power control loop (PID algorithm) immediately intervenes to automatically reduce the microwave output power to prevent overheating collapse; when printing to large-area solid regions, if the optical fiber sensor and the infrared data show that the temperature difference between the center and the edge exceeds the threshold, the frequency control loop (PI algorithm) intervenes to adjust the microwave frequency to change the standing wave distribution and forcibly improve the edge heating efficiency. This intelligent intervention throughout the process realizes the decoupling control of "uniform temperature" and "temperature control", ensuring the consistency of the grain structure and mechanical properties of different parts of the complex part.

[0115] The dynamic microwave-assisted laser metal additive manufacturing method and device provided by the embodiment of the present disclosure aim to overcome the problems of lack of localization, poor thermal field control, and insufficient microscopic dynamic intervention in the prior art. By highly coordinating the microwave energy field and the laser thermal field in space, time, and control, the embodiment realizes directional, quantitative, dynamic, and special-shaped energy application and regulation of the additive manufacturing liquid molten pool 100 and the solid-liquid interface region, thereby significantly improving the quality and performance of the formed part.

[0116] In terms of spatial localization and thermal field compensation, by setting up a multi-stage microwave screening device 22, the originally divergent microwave beams are focused, screened and beam-shaped, successfully confining the action range of microwave energy from centimeter or decimeter level environmental space to a millimeter level area matching the size of the laser molten pool 100. More importantly, by adopting a special-shaped hollow metal structure layer 222 such as a ring fence structure, the scheme can reshape the microwave energy into a ring-shaped beam, concentrating its energy on the solid-liquid transition area around the molten pool 100. This "high in the four corners and low in the center" microwave field and the inherent "high in the center and low in the four corners" Gaussian thermal field complement each other in space, effectively flattening the temperature gradient inside the molten pool 100, significantly reducing residual thermal stress from the root, and thus greatly inhibiting the generation of micro-cracks and macro-deformation, solving the core quality problem in additive manufacturing.

[0117] In terms of micro-dynamics intervention and metallurgical bonding, after the screened microwave beams are applied to the liquid molten pool 100, the high-frequency vibration (non-thermal dynamic effect) of charged particles and atoms in the molten pool caused by the microwave electromagnetic field greatly accelerates the rapid mutual solubility and diffusion migration of metal elements at the solid-liquid interface, promotes the metallurgical bonding strength between layers, and is particularly important for the formation of dissimilar materials or gradient functional materials. At the same time, this high-frequency vibration effect is equivalent to "electromagnetic vibration" of the liquid metal, effectively destroying the surface tension of the micro-bubbles, accelerating the bubble floating out, and thus significantly reducing the porosity of the formed part (improving the density). In addition, the microwave-assisted oscillation effect also helps to break the growing coarse dendrites, promote the nucleation and growth of fine equiaxed crystals, and according to the Hall-Petch effect, the yield strength and overall mechanical properties of the material are significantly improved.

[0118] In terms of process control and intelligent adaptation, a double-closed-loop control strategy based on temperature feedback is 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 uniformity / depth control). By monitoring the molten pool 100 temperature and thermal field distribution (such as infrared thermal imaging or optical fiber sensing) in real time, 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 the embodiment to quickly respond to local thermal accumulation differences caused by changes in scanning path, geometry (such as thin-walled, sharp corners) in the additive manufacturing process, ensuring the stability of the molten pool 100 state and the robustness of the processing process, thereby ensuring the uniform consistency of the forming quality of complex structural parts.

[0119] The dynamic microwave auxiliary method and device provided by the embodiment compensate for the inherent defects of the laser from the thermal field angle, and improve the metallurgical defects from the microscopic dynamics angle, compared with the overall or static heating of the prior art, and have the effects of simple method, accurate control, high forming quality and superior material performance.

[0120] The above description and drawings sufficiently illustrate the embodiments of the present disclosure to enable one skilled in the art to practice them. Other embodiments can include structural and other changes. The embodiments are merely representative of the possible variations. Individual components and functions are optional unless explicitly required, and the order of operations can be varied. Parts and features of some embodiments can be included in or replace parts and features of other embodiments. The embodiments of the present disclosure are not limited to the structures that have been described above and shown in the drawings, and various modifications and changes can be made without departing from the scope thereof. The scope of the present disclosure is limited only by the appended claims, and the above-described embodiments should be regarded as exemplary and non-limiting.

Claims

1. A method of dynamic microwave assisted based laser metal additive manufacturing characterized in that, The method comprises the following steps: S1: determining the process parameters of laser additive manufacturing, and determining the preset molten pool size based on the process parameters; S2: controlling the laser beam to act on the metal material to form a liquid molten pool, and simultaneously using a multi-stage microwave screening device to spatially constrain and screen the microwave beam, so that the action range of the microwave beam is focused to a size matching the preset molten pool size; S3: directionally applying the screened microwave beam to the liquid molten pool and the solid-liquid interface region; S4: controlling the screened microwave beam to move synchronously with the laser beam, and cooperating with the laser beam to perform layer-by-layer accumulation of the material to complete the part forming.

2. The method of claim 1, wherein, The directional application mode of the microwave in step S3 comprises: adjusting the spatial distribution of the microwave energy by the multi-stage microwave screening device, so that the distribution of the microwave energy on the surface of the molten pool is low in the center and high around; the energy characteristics of the microwave energy distribution state and the laser heat source are complementary in space to compensate for the energy difference of the laser heat source, so as to form a flat-top temperature field distribution in the molten pool to reduce the temperature gradient of the molten pool.

3. The method of claim 1, wherein, The directional application of the screened microwave beam to the liquid molten pool and the solid-liquid interface region comprises: exciting the near-field coupling effect of the microwave by the sub-wavelength aperture structure in the multi-stage microwave screening device, so as to constrain and concentrate the microwave energy field on the solid-liquid interface region of the molten pool; by the non-thermal dynamic effect of the high-frequency microwave electromagnetic field on the metal atoms in the molten pool, inducing high-frequency vibration of the atoms, thereby reducing the diffusion barrier at the solid-liquid interface of the molten pool, accelerating the migration and mutual solubility of alloy elements, and driving the bubbles in the molten pool to escape to eliminate pore defects.

4. The method of claim 1, wherein, The directional application of the screened microwave beam to the liquid molten pool and the solid-liquid interface region adopts a double closed-loop real-time control strategy, comprising: 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, to control the overall heat input of the molten pool; a frequency control loop, which adjusts the microwave frequency in real time according to the temperature difference between the center and the edge of the molten pool or the temperature distribution uniformity, to change the penetration depth and energy distribution uniformity of the microwave in the molten pool.

5. The method of claim 1, wherein, In step S1, the preset molten pool size is determined, comprising: based on the thermal physical properties of the material to be processed, calculating the molten pool size and shape under different laser parameters by finite element simulation, and presetting the initial frequency and action range of the microwave according to the simulation results.

6. The method of claim 1, wherein, Controlling the screened microwave beam to move synchronously with the laser beam comprises: controlling the multi-stage microwave screening device and the laser beam to move synchronously, and the vertical distance between the end exit surface of the multi-stage microwave screening device and the surface of the molten pool is within the near-field coupling range of the microwave, so as to realize energy coupling by evanescent waves.

7. A dynamic microwave assisted laser metal additive manufacturing apparatus for use in the method of any one of claims 1 to 6, characterized in that, comprising: an additive manufacturing host configured with a laser generating system for providing a laser beam heat source and controlling layer-by-layer deposition of the metal material to form a liquid molten pool during the forming process; a microwave generating system for generating a microwave beam with adjustable frequency and power; a multi-stage microwave screening device connected to the microwave generating system, arranged at the end of the microwave transmission path, and configured to spatially constrain and directionally screen the microwave beam, so as to focus the action range of the microwave beam to a size matching the size of the liquid molten pool; A linkage moving mechanism is used to drive the multi-stage microwave screening device to move synchronously with the laser beam; A control system is used to receive the temperature feedback data of the molten pool and to adjust the output power and frequency of the microwave generating system in real time according to a preset double closed-loop control strategy.

8. The apparatus of claim 7, wherein, The multi-stage microwave screening device comprises, from top to bottom along the microwave transmission direction: A wave-transparent focusing layer made of wave-transparent material is configured to concentrate the divergent microwave beam towards the central axis; A special-shaped hollow metal structure layer made of conductive metal material is provided with a sub-wavelength scale hollow pattern on the surface and is configured to perform localized screening and beam shaping on the microwave; A wave-absorbing cutting layer made of dielectric loss material is configured to intercept and absorb the excess microwave outside the screening range to prevent secondary thermal influence on the solidified and formed area.

9. The apparatus of claim 8, wherein, The special-shaped hollow metal structure layer adopts any one of the following structural forms: A ring fence type structure composed of a plurality of concentric metal rings or ring-shaped slits is used to generate a ring-shaped microwave field with low central energy and high peripheral energy; A diamond fence type structure composed of periodically arranged diamond metal grids is used to filter out low-frequency microwaves; A multi-point hole type structure composed of an array of circular through holes is used to divide and limit the microwave beam within the dot matrix area.

10. The apparatus of claim 7, wherein: The microwave generating system adopts a solid-state microwave source which includes a voltage-controlled oscillator and a phase-locked loop synthesizer and is configured to realize millisecond-level real-time adjustment of the output frequency within a preset bandwidth through digital control.

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