Multi-material additive manufacturing method and device

Abstract

The invention specifically discloses a multi-material additive manufacturing method and device in the field of additive manufacturing, and the method comprises the following steps: S1, three-dimensional model processing and path planning: obtaining a three-dimensional model of a to-be-formed workpiece, and carrying out material composition partition design according to preset function requirements of different regions of the workpiece, generating spatial distribution information containing at least two material components; through the integrated coaxial printing head, dynamic mixing of materials and application of stress waves are accurately synchronized in time and space. In the material mixing stage, the micro-flow field dynamic mixer realizes the primary homogenization or gradient of the material at the micron / nano scale. At the moment of deposition and solidification, high-frequency micro-amplitude stress waves intervene immediately, the effect of the high-frequency micro-amplitude stress waves is cooperated with energy deposition, on one hand, diffusion and uniform distribution of different material components in a molten pool are further promoted through cavitation and acoustic streaming effects, and an interface barrier is broken;

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology, and more particularly to a method and apparatus for multi-material additive manufacturing. Background Technology

[0002] Additive manufacturing (3D printing) technology has been widely used in aerospace, biomedicine, automotive and other fields due to its unique advantages in manufacturing complex geometric components. Among them, multi-material additive manufacturing technology can distribute materials with different properties on demand within a component, realizing the integrated integration of materials, structure and function. It is an ideal way to manufacture high-performance graded functional parts, multifunctional components and biomimetic structures, and represents an important development direction in this field.

[0003] However, existing multi-material additive manufacturing technologies still face a series of key technical challenges in practical applications, which restrict the reliability and application boundaries of the fabricated components. First, the low interfacial bonding strength between heterogeneous materials is a core bottleneck. When two materials with vastly different physical and chemical properties (such as metal and ceramic, or different metal alloys) meet during the printing process, due to mismatches in thermal expansion coefficients, crystal structures, etc., problems such as thermal stress concentration, insufficient atomic diffusion, oxide film obstruction, and weak bonding easily occur at the interface. This makes the interface a weak point in mechanical properties, prone to cracking or peeling (see the problem described in claim 1). Existing technologies often improve the interface through heat treatment after printing, but the effect is limited and may affect the overall structure.

[0004] Secondly, the gradient transition between material composition and properties is discontinuous and imprecise. Existing printheads based on multiple powder feeders or coaxial filament feeders, while capable of material switching or simple parallel flow, struggle to achieve uniform mixing or precise gradient changes of material composition according to a preset function at the microscopic scale. Materials are often distributed in discrete layers or strips rather than a truly continuous gradual change in composition, leading to abrupt performance changes and stress concentration (the "continuous gradient transition" problem sought to be addressed in claim 3). Current dynamic mixing technologies suffer from low mixing efficiency and poor performance in high-viscosity, immiscible systems.

[0005] Furthermore, the manufacturing process lacks the ability to actively control the molten pool dynamics, solidification behavior, and internal defects in situ. Traditional methods mainly rely on preset process parameters, making it difficult to intervene and correct problems such as porosity, incomplete fusion, coarse grains, and residual stress generated during the printing process in real time. Although some studies have attempted to introduce external energy fields such as ultrasonic vibration and mechanical shock, these are mostly applied globally or as post-processing, resulting in dispersed energy and a lack of specificity. They cannot precisely intervene in the microscopic physicochemical processes at specific locations (such as the molten pool and interface) within the "golden time window" of material deposition and solidification (see the precise control sought to be achieved in claims 2, 4, and 7).

[0006] Finally, existing technologies lack effective online monitoring and closed-loop control strategies. Multi-material additive manufacturing is a complex dynamic process with strong coupling of multiple parameters, and relying solely on offline simulation and preset parameters is insufficient to guarantee stability and repeatability. There is an urgent need for an in-situ feedback control mechanism that can perceive the molten pool state, interface bonding quality, and internal defect information in real time, and dynamically adjust process parameters accordingly (as described in claim 8, an intelligent control requirement).

[0007] Therefore, there is an urgent need in this field for an innovative method and apparatus that can simultaneously achieve precise mixing, deposition and active control of microstructure of materials during the manufacturing process, and possess intelligent process adaptability, so as to fundamentally improve the interface bonding quality, structural integrity and performance reliability of multi-material components. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of existing technologies by proposing a multi-material additive manufacturing method and apparatus.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A multi-material additive manufacturing method includes the following steps: S1. 3D Model Processing and Path Planning: Obtain the 3D model of the workpiece to be formed, design the material composition partitions according to the preset functional requirements of different areas of the workpiece, and generate spatial distribution information containing at least two material components; based on the spatial distribution information, slice and layer the 3D model, and plan the multi-material printing path for each printing layer. The printing path includes delivery instructions, dynamic mixing instructions and energy application instructions for different material components. S2. Material Supply and Dynamic Mixing: According to the printing path of the current printing layer, at least two basic material powders or filaments are synchronously fed into an integrated coaxial printhead at a preset ratio and conveying rate through an independently controllable feeding module; when the material is conveyed into the mixing chamber inside the printhead or is about to leave the outlet area of ​​the printhead, a built-in micro-flow field dynamic mixer is activated according to the dynamic mixing command to perform instantaneous, high-intensity physical agitation and turbulent mixing of the converged multiple materials to form an intermediate material flow with gradient components or uniform composites; S3. In-situ Stress Wave Control and Energy Deposition: While the intermediate material flow is deposited onto the surface of the printed substrate or the formed layer, a coaxial integrated energy source is activated to apply focused energy to the deposition point according to the energy application command, causing the material to melt or sinter; characterized in that, during the initial stage and the continuous process of material melting or sintering, a non-destructive high-frequency micro-amplitude stress wave is simultaneously applied to the deposition point and the adjacent formed material area, and the frequency, amplitude and duration of the stress wave are adjusted in real time according to the material composition, interface state and thermal history of the current point; S4. Stress Feedback and Process Closed-Loop Control: Through a stress wave monitoring module integrated on the printhead side, stress wave signals returned from the deposition point or acoustic emission signals induced by them are collected in real time, and real-time feedback information reflecting the melt pool flow field state, the tightness of interface bonding, and the generation of internal micro-defects is calculated; the real-time feedback information is compared with the expected state information generated based on the material model and process database to generate process compensation instructions; S5. Multi-parameter dynamic collaborative adjustment: Based on the process compensation command, in the subsequent printing process, at least one of the following process parameters is adjusted in real time and collaboratively: the conveying rate of each basic material by the feeding module to change the material ratio, the mixing intensity and mode of the microflow field dynamic mixer, the power and scanning speed of the energy source, and the waveform parameters of the applied stress wave, so as to realize the in-situ active control of the material microstructure, interface diffusion behavior and internal residual stress. S6. Layer-by-layer cyclic manufacturing: Repeat steps S2 to S5 until all printing layers are completed, ultimately obtaining a multi-material functional gradient component with composition, structure, and properties that vary according to the design space.

[0010] Preferably, in steps S3 and S4, the high-frequency micro-amplitude stress wave is generated by an ultrasonic transducer module integrated in the printhead, with a frequency range of 20kHz to 1MHz and an amplitude of nanometer to micrometer. The application of the stress wave and the energy deposition are precisely synchronized in time and space, and the application focus and the energy deposition focus have an adjustable relative positional relationship in three-dimensional space. The relative positional relationship is dynamically adjusted according to the characteristics of the current deposited material to achieve differentiated disturbance to different regions of the molten pool (such as the leading edge, wake, and center), or to refine the grains of the heat-affected zone that has solidified but is still at a high temperature.

[0011] Preferably, the base material mentioned in step S2 includes at least two materials that differ in physical or chemical properties. The materials are selected from at least two of the following: metal alloy powder, ceramic powder, polymer filaments, or metal-based composite powder. The dynamic mixing command controls the microfluidic dynamic mixer to continuously or stepwise adjust the mixing intensity within a single printing path according to the preset material composition gradient change function in the spatial distribution information. This ensures that the intermediate material flow output from the printhead has a uniform composition in the radial direction, but its composition changes continuously with the printing position in the axial direction, thereby achieving a continuous gradient transition of material composition within the single deposition trajectory.

[0012] Preferably, the ultrasonic transducer module includes at least two independently controlled piezoelectric ceramic arrays, capable of generating stress waves with different vibration modes (such as longitudinal vibration, bending vibration, and torsional vibration), and capable of synthesizing complex stress wave fields. When printing the heterogeneous material interface region, the ultrasonic transducer module is controlled to generate a high-frequency shear stress wave perpendicular to the interface. This shear stress wave can promote the interdiffusion of atoms on both sides of the interface, break the oxide film barrier, and agitate the melt at the interface to increase heterogeneous nucleation sites, thereby forming a nanoscale diffusion composite layer with graded composition, metallurgical bonding, and controllable thickness at the heterogeneous interface of the multi-material functionally graded component.

[0013] Preferably, the microfluidic dynamic mixer described in step S2 is a valveless active mixer that uses piezoelectric drive or micro-electromagnetic drive to drive a micro-disturbance body to perform high-frequency (frequency greater than 100Hz) reciprocating linear motion, rotational motion, or chaotic motion within the mixing chamber. The dynamic mixing command includes precise control of the motion frequency, amplitude, and trajectory pattern of the micro-disturbance body to adapt to the mixing requirements of material combinations with different viscosities and particle sizes, ensuring that even immiscible metal-ceramic systems can achieve uniform particle-level dispersion within a very short chamber residence time.

[0014] Preferably, in the path planning of step S1, a special stress wave-assisted path strategy is planned for special geometric feature areas with sharp inner corners, thin walls, or overhanging structures: when printing in such areas, one or more pure stress wave scanning paths are added on the basis of the conventional energy scanning path. That is, without delivering new material or applying the main melting energy, the print head is controlled to move along a specific path and a specially modulated stress wave is applied to perform local stress relaxation, micro-plastic deformation, or microstructure adjustment on the existing material in the area, so as to reduce the residual stress concentration in the feature area and prevent deformation or cracking.

[0015] Preferably, the energy source in step S3 is a laser, an electron beam, or an electric arc. The stress wave and the energy beam are further coupled and controlled by a composite energy field: by modulating the power waveform of the energy beam (such as the frequency and duty cycle of a pulsed laser) and the waveform of the stress wave, a specific phase difference or frequency correlation is generated between the two. For example, the peak of the stress wave is periodically made to coincide with the peak power of the pulsed laser. By utilizing the instantaneous thermo-coupling effect, strong acoustic flow and cavitation effects are excited in the molten pool, which deeply purifies the molten pool and breaks the columnar crystals, thereby obtaining a uniform and fine equiaxed crystal structure inside the multi-material functionally graded component.

[0016] Preferably, the real-time feedback information mentioned in step S4 includes the characteristic oscillation frequency of the molten pool, the propagation attenuation coefficient of stress waves in the material, and the spectral characteristics of the interface reflection signal; the generation of the process compensation command adopts an intelligent controller based on a machine learning model, which takes the real-time feedback information, current process parameters, and material partitioning information as input, and the adjustment amount of the process parameters to be adjusted mentioned in step S5 as output; the intelligent controller performs offline training and online learning on the "process parameters-feedback signal-final performance" data collected in the historical printing process to achieve adaptive optimization and intelligent feedforward compensation for complex multi-material additive manufacturing processes.

[0017] An additive manufacturing apparatus, comprising: The main control system is used to perform 3D model processing, path planning, and generate control commands for each unit. A multi-channel feeding system, comprising at least two independently controllable feeding modules, for storing and precisely conveying different base materials; An integrated coaxial printhead integrates the following components: a microfluidic dynamic mixing chamber connected to the outlet of each feeding module; a microfluidic dynamic mixer located in the mixing chamber or at the outlet; an energy beam emitter for applying focused energy to the deposited material; an ultrasonic transducer module for generating high-frequency micro-amplitude stress waves; and a stress wave monitoring sensor for real-time acquisition of stress wave feedback signals. A motion system is used to drive the integrated coaxial printhead and the printing substrate to move relative to each other in order to complete the three-dimensional scanning and forming. The main control system is electrically connected to the multi-channel feeding system, the micro-flow field dynamic mixer, the energy beam emitter, the ultrasonic transducer module, the stress wave monitoring sensor, and the motion system to form a closed-loop control circuit. It can adjust the feeding, mixing, energy application, and stress wave parameters in real time according to the feedback signals from the monitoring sensors.

[0018] The beneficial effects of this invention are as follows: (1) This invention does not simply superimpose two technologies, but rather uses an integrated coaxial printhead to precisely synchronize the dynamic mixing of materials and the application of stress waves in time and space. During the material mixing stage, the microfluidic dynamic mixer achieves the initial homogenization or gradient of materials at the micrometer / nanometer scale. At the instant of deposition and solidification, high-frequency micro-amplitude stress waves are immediately introduced, and their effect is synergistic with energy deposition. On the one hand, through cavitation and acoustic flow effects, it further promotes the diffusion and uniform distribution of different material components in the molten pool, breaking the interface barrier; on the other hand, the energy of the stress wave is precisely applied to the forming interface and molten pool, promoting atomic diffusion, refining grains, and relaxing thermal stress in real time. This synergistic mechanism of "initial homogenization in mixing + active optimization in solidification" significantly enhances the metallurgical bonding strength of heterogeneous materials physically, realizing true integrated control of composition-structure-performance, and solving the core problems of weak interface bonding and discontinuous gradient in the background technology. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the steps of the multi-material additive manufacturing method and apparatus proposed in this invention. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0021] Reference Figure 1 The additive manufacturing method for multi-materials includes the following steps: S1. 3D Model Processing and Path Planning: Obtain the 3D model of the workpiece to be formed, design the material composition partitions according to the preset functional requirements of different areas of the workpiece, and generate spatial distribution information containing at least two material components; based on the spatial distribution information, slice and layer the 3D model, and plan the multi-material printing path for each printing layer. The printing path includes delivery instructions, dynamic mixing instructions and energy application instructions for different material components. S2. Material Supply and Dynamic Mixing: According to the printing path of the current printing layer, at least two basic material powders or filaments are synchronously fed into an integrated coaxial printhead at a preset ratio and conveying rate through an independently controllable feeding module; when the material is conveyed into the mixing chamber inside the printhead or is about to leave the outlet area of ​​the printhead, a built-in micro-flow field dynamic mixer is activated according to the dynamic mixing command to perform instantaneous, high-intensity physical agitation and turbulent mixing of the converged multiple materials to form an intermediate material flow with gradient components or uniform composites; S3. In-situ Stress Wave Control and Energy Deposition: While the intermediate material flow is deposited onto the surface of the printed substrate or the formed layer, a coaxial integrated energy source is activated to apply focused energy to the deposition point according to the energy application command, causing the material to melt or sinter; characterized in that, during the initial stage and the continuous process of material melting or sintering, a non-destructive high-frequency micro-amplitude stress wave is simultaneously applied to the deposition point and the adjacent formed material area, and the frequency, amplitude and duration of the stress wave are adjusted in real time according to the material composition, interface state and thermal history of the current point; S4. Stress Feedback and Process Closed-Loop Control: Through a stress wave monitoring module integrated on the printhead side, stress wave signals returned from the deposition point or acoustic emission signals induced by them are collected in real time, and real-time feedback information reflecting the melt pool flow field state, the tightness of interface bonding, and the generation of internal micro-defects is calculated; the real-time feedback information is compared with the expected state information generated based on the material model and process database to generate process compensation instructions; S5. Multi-parameter dynamic collaborative adjustment: Based on the process compensation command, in the subsequent printing process, at least one of the following process parameters is adjusted in real time and collaboratively: the conveying rate of each basic material by the feeding module to change the material ratio, the mixing intensity and mode of the microflow field dynamic mixer, the power and scanning speed of the energy source, and the waveform parameters of the applied stress wave, so as to realize the in-situ active control of the material microstructure, interface diffusion behavior and internal residual stress. S6. Layer-by-layer cyclic manufacturing: Repeat steps S2 to S5 until all printing layers are completed, ultimately obtaining a multi-material functional gradient component with composition, structure, and properties that vary according to the design space.

[0022] In this specific embodiment, the present invention creatively uses stress waves as both an "actuator" and a "sensor".

[0023] As an actuator, its parameters can be adjusted in real time to cope with different materials and working conditions.

[0024] As a sensor, by analyzing the feedback stress wave signal, it can obtain key state information such as the flow state of the molten pool, the tightness of the interface bonding, and the initiation of micro-defects in situ and without damage, which is difficult to achieve with traditional optical or thermal imaging monitoring.

[0025] Based on this feedback information, the system adjusts the feeding ratio, mixing intensity, energy input and stress wave parameters in real time and in a coordinated manner through the intelligent controller, forming a complete "perception-decision-execution" closed loop.

[0026] This enables the manufacturing process to adapt to complex multi-material systems and geometries, significantly improving the stability, repeatability, and yield of the process, and achieving a leap from "experience-driven, open-loop control" to "data-driven, closed-loop intelligence".

[0027] Preferably, in steps S3 and S4, the high-frequency micro-amplitude stress wave is generated by an ultrasonic transducer module integrated in the printhead, with a frequency range of 20kHz to 1MHz and an amplitude of nanometer to micrometer. The application of the stress wave and the energy deposition are precisely synchronized in time and space, and the application focus and the energy deposition focus have an adjustable relative positional relationship in three-dimensional space. The relative positional relationship is dynamically adjusted according to the characteristics of the current deposited material to achieve differentiated disturbance to different regions of the molten pool (such as the leading edge, wake, and center), or to refine the grains of the heat-affected zone that has solidified but is still at a high temperature.

[0028] Preferably, the base material mentioned in step S2 includes at least two materials that differ in physical or chemical properties. The materials are selected from at least two of the following: metal alloy powder, ceramic powder, polymer filaments, or metal-based composite powder. The dynamic mixing command controls the microfluidic dynamic mixer to continuously or stepwise adjust the mixing intensity within a single printing path according to the preset material composition gradient change function in the spatial distribution information. This ensures that the intermediate material flow output from the printhead has a uniform composition in the radial direction, but its composition changes continuously with the printing position in the axial direction, thereby achieving a continuous gradient transition of material composition within the single deposition trajectory.

[0029] Preferably, the ultrasonic transducer module includes at least two independently controlled piezoelectric ceramic arrays, capable of generating stress waves with different vibration modes (such as longitudinal vibration, bending vibration, and torsional vibration), and capable of synthesizing complex stress wave fields. When printing the heterogeneous material interface region, the ultrasonic transducer module is controlled to generate a high-frequency shear stress wave perpendicular to the interface. This shear stress wave can promote the interdiffusion of atoms on both sides of the interface, break the oxide film barrier, and agitate the melt at the interface to increase heterogeneous nucleation sites, thereby forming a nanoscale diffusion composite layer with graded composition, metallurgical bonding, and controllable thickness at the heterogeneous interface of the multi-material functionally graded component.

[0030] Preferably, the microfluidic dynamic mixer described in step S2 is a valveless active mixer that uses piezoelectric drive or micro-electromagnetic drive to drive a micro-disturbance body to perform high-frequency (frequency greater than 100Hz) reciprocating linear motion, rotational motion, or chaotic motion within the mixing chamber. The dynamic mixing command includes precise control of the motion frequency, amplitude, and trajectory pattern of the micro-disturbance body to adapt to the mixing requirements of material combinations with different viscosities and particle sizes, ensuring that even immiscible metal-ceramic systems can achieve uniform particle-level dispersion within a very short chamber residence time.

[0031] Preferably, in the path planning of step S1, a special stress wave-assisted path strategy is planned for special geometric feature areas with sharp inner corners, thin walls, or overhanging structures: when printing in such areas, one or more pure stress wave scanning paths are added on the basis of the conventional energy scanning path. That is, without delivering new material or applying the main melting energy, the print head is controlled to move along a specific path and a specially modulated stress wave is applied to perform local stress relaxation, micro-plastic deformation, or microstructure adjustment on the existing material in the area, so as to reduce the residual stress concentration in the feature area and prevent deformation or cracking.

[0032] Preferably, the energy source in step S3 is a laser, an electron beam, or an electric arc. The stress wave and the energy beam are further coupled and controlled by a composite energy field: by modulating the power waveform of the energy beam (such as the frequency and duty cycle of a pulsed laser) and the waveform of the stress wave, a specific phase difference or frequency correlation is generated between the two. For example, the peak of the stress wave is periodically made to coincide with the peak power of the pulsed laser. By utilizing the instantaneous thermo-coupling effect, strong acoustic flow and cavitation effects are excited in the molten pool, which deeply purifies the molten pool and breaks the columnar crystals, thereby obtaining a uniform and fine equiaxed crystal structure inside the multi-material functionally graded component.

[0033] Preferably, the real-time feedback information mentioned in step S4 includes the characteristic oscillation frequency of the molten pool, the propagation attenuation coefficient of stress waves in the material, and the spectral characteristics of the interface reflection signal; the generation of the process compensation command adopts an intelligent controller based on a machine learning model, which takes the real-time feedback information, current process parameters, and material partitioning information as input, and the adjustment amount of the process parameters to be adjusted mentioned in step S5 as output; the intelligent controller performs offline training and online learning on the "process parameters-feedback signal-final performance" data collected in the historical printing process to achieve adaptive optimization and intelligent feedforward compensation for complex multi-material additive manufacturing processes.

[0034] In this specific embodiment, the component prepared by the present invention achieves breakthrough improvements in both microscopic and macroscopic properties. Specifically: Excellent interface performance: A nanoscale diffusion composite layer can be formed at the interface of heterogeneous materials, and the interfacial bonding strength can approach the strength of the weaker parent material, which greatly reduces the risk of interface failure.

[0035] Fine and uniform microstructure: The combined energy field coupling of stress wave and energy beam effectively breaks columnar crystals and promotes the formation of equiaxed crystals, resulting in a fine and uniform microstructure for the entire component, especially in the interface area, thereby improving its mechanical properties.

[0036] Extremely low internal defects and residual stress: Real-time application of stress waves can effectively suppress defects such as porosity and lack of fusion, and actively release stress concentration in characteristic areas through special path strategies, thereby significantly reducing the residual stress level of components and fundamentally improving dimensional stability and fatigue performance.

[0037] These effects together ensure that the resulting multi-material functionally graded components have highly reliable performance and broader application prospects.

[0038] An additive manufacturing apparatus, comprising: The main control system is used to perform 3D model processing, path planning, and generate control commands for each unit. A multi-channel feeding system, comprising at least two independently controllable feeding modules, for storing and precisely conveying different base materials; An integrated coaxial printhead integrates the following components: a microfluidic dynamic mixing chamber connected to the outlet of each feeding module; a microfluidic dynamic mixer located in the mixing chamber or at the outlet; an energy beam emitter for applying focused energy to the deposited material; an ultrasonic transducer module for generating high-frequency micro-amplitude stress waves; and a stress wave monitoring sensor for real-time acquisition of stress wave feedback signals. A motion system is used to drive the integrated coaxial printhead and the printing substrate to move relative to each other in order to complete the three-dimensional scanning and forming. The main control system is electrically connected to the multi-channel feeding system, the micro-flow field dynamic mixer, the energy beam emitter, the ultrasonic transducer module, the stress wave monitoring sensor, and the motion system to form a closed-loop control circuit. It can adjust the feeding, mixing, energy application, and stress wave parameters in real time according to the feedback signals from the monitoring sensors.

[0039] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A multi-material additive manufacturing method, characterized in that, Includes the following steps: S1. 3D Model Processing and Path Planning: Obtain the 3D model of the workpiece to be formed, design the material composition partitions according to the preset functional requirements of different areas of the workpiece, and generate spatial distribution information containing at least two material components; based on the spatial distribution information, slice and layer the 3D model, and plan the multi-material printing path for each printing layer. The printing path includes delivery instructions, dynamic mixing instructions and energy application instructions for different material components. S2. Material Supply and Dynamic Mixing: According to the printing path of the current printing layer, at least two basic material powders or filaments are synchronously fed into an integrated coaxial printhead at a preset ratio and conveying rate through an independently controllable feeding module; when the material is conveyed into the mixing chamber inside the printhead or is about to leave the outlet area of ​​the printhead, a built-in micro-flow field dynamic mixer is activated according to the dynamic mixing command to perform instantaneous, high-intensity physical agitation and turbulent mixing of the converged multiple materials to form an intermediate material flow with gradient components or uniform composites; S3. In-situ Stress Wave Control and Energy Deposition: While the intermediate material flow is deposited onto the surface of the printed substrate or the formed layer, a coaxial integrated energy source is activated to apply focused energy to the deposition point according to the energy application command, causing the material to melt or sinter; characterized in that, during the initial stage and the continuous process of material melting or sintering, a non-destructive high-frequency micro-amplitude stress wave is simultaneously applied to the deposition point and the adjacent formed material area, and the frequency, amplitude and duration of the stress wave are adjusted in real time according to the material composition, interface state and thermal history of the current point; S4. Stress Feedback and Process Closed-Loop Control: Through a stress wave monitoring module integrated on the printhead side, stress wave signals returned from the deposition point or acoustic emission signals induced by them are collected in real time, and real-time feedback information reflecting the melt pool flow field state, the tightness of interface bonding, and the generation of internal micro-defects is calculated; the real-time feedback information is compared with the expected state information generated based on the material model and process database to generate process compensation instructions; S5. Multi-parameter dynamic collaborative adjustment: Based on the process compensation command, in the subsequent printing process, at least one of the following process parameters is adjusted in real time and collaboratively: the conveying rate of each basic material by the feeding module to change the material ratio, the mixing intensity and mode of the microflow field dynamic mixer, the power and scanning speed of the energy source, and the waveform parameters of the applied stress wave, so as to realize the in-situ active control of the material microstructure, interface diffusion behavior and internal residual stress. S6. Layer-by-layer cyclic manufacturing: Repeat steps S2 to S5 until all printing layers are completed, ultimately obtaining a multi-material functional gradient component with composition, structure, and properties that vary according to the design space.

2. The multi-material additive manufacturing method according to claim 1, characterized in that, In steps S3 and S4, the high-frequency micro-amplitude stress wave is generated by an ultrasonic transducer module integrated in the printhead, with a frequency range of 20kHz to 1MHz and an amplitude of nanometer to micrometer. The application of the stress wave and the energy deposition are precisely synchronized in time and space, and the application focus and the energy deposition focus have an adjustable relative positional relationship in three-dimensional space. The relative positional relationship is dynamically adjusted according to the characteristics of the current deposited material to achieve differentiated disturbance to different regions of the molten pool (such as the leading edge, wake, and center), or to refine the grains of the heat-affected zone that has solidified but is still at a high temperature.

3. The multi-material additive manufacturing method according to claim 1 or 2, characterized in that, The base material mentioned in step S2 includes at least two materials that differ in physical or chemical properties. The materials are selected from at least two of the following: metal alloy powder, ceramic powder, polymer filament, or metal matrix composite powder. The dynamic mixing command controls the microfluidic dynamic mixer to continuously or stepwise adjust the mixing intensity within a single printing path according to the preset material composition gradient change function in the spatial distribution information. This makes the intermediate material flow output from the printhead have a uniform composition in the radial direction, but the composition changes continuously with the printing position in the axial direction, thereby achieving a continuous gradient transition of material composition within the single deposition trajectory.

4. The multi-material additive manufacturing method according to claim 2, characterized in that, The ultrasonic transducer module includes at least two independently controlled piezoelectric ceramic arrays, capable of generating stress waves with different vibration modes (such as longitudinal vibration, bending vibration, and torsional vibration), and synthesizing complex stress wave fields. When printing the interface region of heterogeneous materials, the ultrasonic transducer module is controlled to generate a high-frequency shear stress wave perpendicular to the interface. This shear stress wave can promote the interdiffusion of atoms on both sides of the interface, break the oxide film barrier, and agitate the melt at the interface to increase heterogeneous nucleation sites, thereby forming a nanoscale diffusion composite layer with graded composition, metallurgical bonding, and controllable thickness at the heterogeneous interface of the multi-material functionally graded component.

5. The multi-material additive manufacturing method according to claim 1, characterized in that, The microfluidic dynamic mixer described in step S2 is a valveless active mixer that uses piezoelectric drive or micro-electromagnetic drive to drive a micro-disturbance body to perform high-frequency (frequency greater than 100Hz) reciprocating linear motion, rotational motion, or chaotic motion within the mixing chamber. The dynamic mixing command includes precise control of the motion frequency, amplitude, and trajectory mode of the micro-disturbance body to adapt to the mixing requirements of material combinations with different viscosities and particle sizes, ensuring that even immiscible metal-ceramic systems can achieve uniform particle-level dispersion within a very short residence time in the chamber.

6. The multi-material additive manufacturing method according to claim 1, characterized in that, In the path planning of step S1, a special stress wave-assisted path strategy is planned for special geometric feature areas with sharp inner corners, thin walls, or overhanging structures: when printing in such areas, one or more pure stress wave scanning paths are added on the basis of the conventional energy scanning path. That is, without delivering new material or applying the main melting energy, the print head is controlled to move along a specific path and a specially modulated stress wave is applied to perform local stress relaxation, micro-plastic deformation, or microstructure adjustment on the existing material in the area, so as to reduce the residual stress concentration in the feature area and prevent deformation or cracking.

7. The multi-material additive manufacturing method according to claim 1, characterized in that, The energy source mentioned in step S3 is a laser, an electron beam, or an electric arc. The stress wave and the energy beam are also coupled and controlled by a composite energy field: by modulating the power waveform of the energy beam (such as the frequency and duty cycle of the pulsed laser) and the waveform of the stress wave, a specific phase difference or frequency correlation is generated between the two. For example, the peak of the stress wave is periodically made to coincide with the peak power of the pulsed laser. By utilizing the instantaneous thermo-coupling effect, strong acoustic flow and cavitation effects are excited in the molten pool, which deeply purifies the molten pool and breaks the columnar crystals, thereby obtaining a uniform and fine equiaxed crystal structure inside the multi-material functionally graded component.

8. The multi-material additive manufacturing method according to claim 1, characterized in that, The real-time feedback information mentioned in step S4 includes the characteristic oscillation frequency of the molten pool, the propagation attenuation coefficient of stress waves in the material, and the spectral characteristics of the interface reflection signal; the process compensation command is generated using an intelligent controller based on a machine learning model, which takes the real-time feedback information, current process parameters, and material partitioning information as inputs, and takes the adjustment amount of the process parameters to be adjusted mentioned in step S5 as the output. The intelligent controller performs offline training and online learning using "process parameters-feedback signals-final performance" data collected during historical printing processes, enabling adaptive optimization and intelligent feedforward compensation for complex multi-material additive manufacturing processes.

9. An additive manufacturing apparatus for implementing the method according to any one of claims 1-8, characterized in that, include: The main control system is used to perform 3D model processing, path planning, and generate control commands for each unit. A multi-channel feeding system, comprising at least two independently controllable feeding modules, for storing and precisely conveying different base materials; An integrated coaxial printhead integrates the following components: a microfluidic dynamic mixing chamber connected to the outlet of each feeding module; a microfluidic dynamic mixer located in the mixing chamber or at the outlet; an energy beam emitter for applying focused energy to the deposited material; an ultrasonic transducer module for generating high-frequency micro-amplitude stress waves; and a stress wave monitoring sensor for real-time acquisition of stress wave feedback signals. A motion system is used to drive the integrated coaxial printhead and the printing substrate to move relative to each other in order to complete the three-dimensional scanning and forming. The main control system is electrically connected to the multi-channel feeding system, the micro-flow field dynamic mixer, the energy beam emitter, the ultrasonic transducer module, the stress wave monitoring sensor, and the motion system to form a closed-loop control circuit. It can adjust the feeding, mixing, energy application, and stress wave parameters in real time according to the feedback signals from the monitoring sensors.

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