Electron beam melting wire liquid nitrogen cryogenic additive manufacturing method and system

Abstract

The invention belongs to the related technical field of additive manufacturing, and discloses an electron beam melting wire liquid nitrogen copious cooling additive manufacturing method and system.The method comprises the steps that in the electron beam melting printing forming process, liquid nitrogen is sprayed to a molten printing wire under electron beam irradiation, and the liquid nitrogen is sprayed to the molten printing wire; the molten printing wires are subjected to nitridation reaction under the action of electron beams while being subjected to liquid nitrogen cryogenic cooling, so that the crystal structure of a formed part is regulated and controlled, and the mechanical performance is enhanced; and / or liquid nitrogen is sprayed to the printing wire material which begins to be solidified, so that the printing wire material is subjected to liquid nitrogen deep cooling, and the crystal structure of the formed part is regulated and controlled to achieve mechanical property enhancement. Liquid nitrogen is introduced into the electron beam additive manufacturing device for deep cooling, the extruded printing wire is solidified at an extremely high cooling speed after being melted, a large number of homogeneous nucleation sites are formed in a melting area due to the high supercooling degree, the solidification speed is high, a microstructure is customized into uniform and fine equiaxed crystals, the strength and toughness of the material are improved, and the production cost is reduced. The mechanical property is improved.

Description

Technical Field

[0001] This invention belongs to the field of additive manufacturing technology, and more specifically, relates to a method and system for cryogenic additive manufacturing of filaments using electron beam melting and liquid nitrogen. Background Technology

[0002] Electron Beam Freeform Fabrication (EBF) is an additive manufacturing technology that uses an electron beam as a heat source to feed a wire, such as a metal wire, into a molten pool and melt it, depositing it layer by layer to form a part. EBF has become an important technology for manufacturing high-precision metal parts due to its advantages such as high forming speed, a wide selection of printing materials, and broad application scenarios. As a highly efficient metal additive manufacturing technology, EBF uses a high-energy-density electron beam as a heat source to scan, overlap, melt, and solidify the metal wire point by point, line by line, layer by layer, ultimately achieving the precise construction of complex three-dimensional metal structures. It can achieve more efficient near-net-shape forming, more uniform and higher substrate preheating, significantly reducing residual stress inside the material, thereby reducing the risk of material cracking and achieving homogeneous microstructure.

[0003] To further improve the performance of electron beam filament forming, researchers are exploring new technologies and methods. For example, some studies are investigating how to improve electron beam filament forming technology by optimizing the forming path to enhance the mechanical properties and microstructure of materials such as 304 stainless steel. Some studies may also involve changing parameters such as beam intensity, wire feed rate, and substrate feed rate to achieve better forming results and material properties. Furthermore, research is exploring how to manufacture parts with different microstructures and mechanical properties using electron beam filament forming technology, such as controlling the microstructure and mechanical properties of austenitic stainless steel by changing process parameters.

[0004] Existing research on improving electron beam filament forming performance mainly focuses on optimizing conventional process parameters such as beam intensity, wire feed speed, substrate feed speed, and feed path, lacking novel forming performance optimization methods to further enhance mechanical properties. Summary of the Invention

[0005] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a method and system for cryogenic additive manufacturing of electron beam fused filaments using liquid nitrogen. This addresses the problem that current research on improving electron beam fused filament forming performance focuses primarily on optimizing conventional process parameters, lacking novel methods for optimizing forming performance to further enhance mechanical properties.

[0006] To achieve the above objectives, according to one aspect of the present invention, a method for cryogenic additive manufacturing of electron beam-melted filaments using liquid nitrogen is provided, comprising: In the electron beam filament printing process, liquid nitrogen is sprayed onto the molten printing filament under electron beam irradiation, so that the molten printing filament undergoes a nitriding reaction under the action of electron beam while being deeply cooled by liquid nitrogen, in order to regulate the crystal structure of the formed part and enhance its mechanical properties; and / or, liquid nitrogen is sprayed onto the printing filament that has begun to solidify, so that the printing filament undergoes deep cooling by liquid nitrogen, in order to regulate the crystal structure of the formed part and enhance its mechanical properties.

[0007] According to the electron beam melting filament liquid nitrogen cryogenic additive manufacturing method provided by the present invention, the specific method of spraying liquid nitrogen onto the molten printing filament under electron beam irradiation is as follows: During the entire molding process, liquid nitrogen is sprayed onto the molten printing filament under electron beam irradiation while printing; Alternatively, while printing areas requiring performance enhancement, liquid nitrogen can be sprayed onto the molten printing filament under electron beam irradiation.

[0008] According to the electron beam melting filament liquid nitrogen cryogenic additive manufacturing method provided by the present invention, when liquid nitrogen is sprayed onto the molten printing filament under electron beam irradiation, the printing filament is a material capable of undergoing a nitriding reaction with liquid nitrogen.

[0009] According to the electron beam melting filament liquid nitrogen cryogenic additive manufacturing method provided by the present invention, spraying liquid nitrogen onto the printing filament that has begun to solidify specifically involves: When printing areas requiring performance enhancement, liquid nitrogen is sprayed onto the printing filament that has begun to solidify after each at least one pass or at least one layer is printed. Liquid nitrogen can be sprayed onto the solidifying printing filament by controlling the distance between the liquid nitrogen spraying part and the electron beam heating area; or, liquid nitrogen can be sprayed onto the solidifying printing filament by stopping the laying of the printing filament and stopping the electron beam heating, and then spraying liquid nitrogen after a preset interval. According to the electron beam melting filament liquid nitrogen cryogenic additive manufacturing method provided by the present invention, when liquid nitrogen is sprayed onto the molten printing filament under electron beam irradiation or onto the printing filament that has begun to solidify, the flow rate of liquid nitrogen increases with the increase of the thickness of the laid printing filament.

[0010] The electron beam melting filament cryogenic additive manufacturing method according to the present invention further includes: The printed parts are subjected to deep cryogenic treatment by spraying liquid nitrogen, which allows the parts to be deeply cooled by liquid nitrogen in order to regulate the crystal structure of the parts and enhance their mechanical properties.

[0011] The electron beam melting filament cryogenic additive manufacturing method according to the present invention further includes: Different diameter printing filaments are used for printing different parts: the diameter of the printing filament used when printing the surface of the part is smaller than the diameter of the printing filament used when printing the core of the part; a transition diameter of printing filament is used when printing the area between the surface and the core of the part. And / or, the printing scanning strategy uses a zigzag path, with the outer circle speed being lower than the inner circle speed during printing scanning, and the speed decreasing as the diameter of the printing filament increases.

[0012] According to another aspect of the present invention, an electron beam melting filament liquid nitrogen cryogenic additive manufacturing system is provided, comprising an electron beam emitting system, a printing filament feeding system, a molding substrate, a liquid nitrogen rapid cooling system, and a control system. The printing filament feeding system includes a printing nozzle, a filament feeding mechanism, a filament storage chamber, and a mounting bracket. The mounting bracket is fixed to the side of the molding substrate. The filament storage chamber is connected to the mounting bracket and is used to store printing filaments. The filament feeding mechanism is connected to the filament storage chamber and is used to convey printing filaments. The printing nozzle is connected to the filament feeding mechanism and is located above the molding substrate for laying printing filaments on the molding substrate. The filament storage chamber is also connected to a mounting base plate, which is located above the molding base plate. The electron beam emission system is fixed to the mounting base plate and faces the end of the print head. The liquid nitrogen rapid cooling system includes a liquid nitrogen storage bottle, a flow rate control valve, a pipe and a print head connected in sequence. The pipe is fixed by the mounting base plate so that the print head faces the molding base plate. The control system is connected to the electron beam emission system, the printing filament feeding system and the liquid nitrogen rapid cooling system respectively, and is used to control each component to realize the electron beam melting filament liquid nitrogen cryogenic additive manufacturing method described above.

[0013] According to the electron beam melting filament liquid nitrogen cryogenic additive manufacturing system provided by the present invention, the printing filament feeding system is provided in multiple ways, the multiple printing filament feeding systems are arranged around the electron beam emitting system, and the multiple printing filament feeding systems are used to lay up a variety of printing filaments with different sizes and / or materials.

[0014] According to the electron beam melting filament liquid nitrogen cryogenic additive manufacturing system provided by the present invention, the mounting bracket is configured as a telescopic arm structure, so that the height of the printing nozzle and the electron beam emission system is adjustable; and / or, the printing nozzle is rotatably connected to the filament feeding mechanism.

[0015] In summary, compared with the prior art, the electron beam melting filament liquid nitrogen cryogenic additive manufacturing method and system provided by this invention offer the following advantages: 1. A liquid nitrogen deep cooling system was introduced into the electron beam additive manufacturing device. After the extruded printing filament melts, it solidifies at an extremely fast cooling rate. The high supercooling causes a large number of homogeneous nucleation sites to form in the melting zone. The fast solidification rate customizes the microstructure into uniform and fine equiaxed crystals, improves the strength and toughness of the material, and improves its mechanical properties. 2. In the additive manufacturing process, the reaction effect can be flexibly adjusted by controlling the participation rate of liquid nitrogen cryogenics. Specifically, liquid nitrogen cryogenics can be carried out simultaneously when the wire is melting. Under the action of marangoni convection, metal nitrides can be generated in situ inside the molten pool. Liquid nitrogen cryogenics can be carried out when the molten pool begins to solidify, which can play a role in rapid deep cooling and improve its mechanical properties. 3. Introducing liquid nitrogen for deep cooling during filament printing reduces thermal stress caused by temperature gradients, while the condensation stress caused by rapid solidification can be improved by tempering during the bonding of the next layer of printed material, thus playing the role of intrinsic heat treatment. This reduces the risk of deformation and cracking of parts and provides strength assurance for the manufacture of complex multi-material components. 4. In the filament supply system, by matching a set of printing nozzles and filament feeding mechanisms of different diameters, the combined printing of filaments of different sizes can be achieved, so as to better control the balance between efficiency and accuracy in the printing process. When forming the surface of the part, the fine filament feeding system can more accurately approximate the contour of the theoretical model, making the interlayer steps more delicate, thereby obtaining better surface quality and lower roughness, reducing subsequent processing allowance, and the fine grains obtained by faster cooling provide higher hardness and enhance durability. When forming the core of the part, the coarse filament feeding system can effectively improve the forming efficiency, and the coarse grains obtained by slower cooling provide good plasticity to the core of the component, thereby achieving a high-performance design with hard exterior and tough interior. 5. The printing filament supply system achieves a high degree of flexibility and adjustability in the filament supply process. The system is equipped with multiple printing nozzles, filament storage chambers, and corresponding filament guiding mechanisms, enabling the simultaneous processing of multiple types of filaments according to specific needs during manufacturing, and achieving continuous or alternating supply of these filaments. Furthermore, the height-adjustable design of the filament storage chambers and the multi-directional configuration of the filament bundle nuts allow the device to adapt to filaments of different sizes, shapes, and types, as well as electron beam melting requirements at different angles, thereby achieving precise control and efficient manufacturing of multi-material composite components. Attached Figure Description

[0016] Figure 1 This is a system model diagram of an electron beam melting filament with liquid nitrogen cryogenic multi-material composite additive manufacturing device.

[0017] Figure 2 This is a structural model diagram of a device for electron beam melting of filaments and liquid nitrogen cryogenic multi-material composite additive manufacturing.

[0018] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1-Electron beam emission system; 11-Cathode emission system; 12-Electron beam acceleration system; 13-Electron beam focusing system; 2-Printing filament feeding system; 21-Printing nozzle; 22-Filament feeding mechanism; 23-Filament storage chamber; 24-Mechanical telescopic arm; 3-Liquid nitrogen rapid cooling system; 31-Liquid nitrogen storage bottle; 32-Flow rate control valve; 33-Air jet head. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0020] Please see Figure 1 and Figure 2 This embodiment provides a method for cryogenic additive manufacturing of filaments using electron beam melting and liquid nitrogen, the method comprising: In the electron beam filament printing process, liquid nitrogen is sprayed onto the molten printing filament under electron beam irradiation, so that the molten printing filament undergoes a nitriding reaction under the action of electron beam while being deeply cooled by liquid nitrogen, in order to regulate the crystal structure of the formed part and enhance its mechanical properties; and / or, liquid nitrogen is sprayed onto the printing filament that has begun to solidify, so that the printing filament undergoes deep cooling by liquid nitrogen, in order to regulate the crystal structure of the formed part and enhance its mechanical properties.

[0021] This embodiment proposes a rapid cooling process during printing by injecting liquid nitrogen to subject the laid-out printing filament to deep cryogenic cooling. This significantly increases the cooling rate during the forming process. Deep and rapid cooling promotes lattice contraction, inducing the transformation of residual stress generated by extremely high cooling rates during additive manufacturing into uniform compressive stress. It also suppresses the columnar dendritic texture caused by temperature gradients along the forming direction, resulting in fine and uniform equiaxed crystals, eliminating macroscopic anisotropy in mechanical properties and improving material performance. Simultaneously, the deep cryogenic treatment generates significant internal stress within the metal material, causing lattice distortion and generating numerous dislocations within the grains. These dislocations entangle and multiply, increasing the strain energy within the grains. To release this high strain energy, the grains undergo dynamic recrystallization, forming new subgrain boundaries, refining the grains and strengthening them. By controlling the involvement of liquid nitrogen deep cryogenics in the additive manufacturing process, layered heterogeneous structures can also be constructed. The improved microstructure significantly enhances the strength and wear resistance of the formed parts, meeting the requirements for integrated high-strength multi-material components.

[0022] Furthermore, in traditional metal manufacturing, the single temperature gradient of monolithic forming makes it difficult to microscopically control the crystallographic characteristics of materials. However, in metal additive manufacturing, layer-by-layer stacking allows for the creation of differentiated crystal features between adjacent layers. By controlling the timing of liquid nitrogen cryogenic treatment, the cooling rate of the metal material can be controlled, leading to the solidification of grains of different sizes. Additionally, by controlling the degree of liquid nitrogen involvement in the nitriding reaction of molten wire, metal materials with varying in-situ nitride contents can be obtained. Due to the heterogeneity in grain size and metal composition, the resulting differences in physicochemical properties generate back stress when the component deforms under external forces. This back stress helps to coordinate the uniform deformation of adjacent grains, thus achieving heterogeneous strengthening and improving the mechanical properties of the formed component.

[0023] In some embodiments, spraying liquid nitrogen onto the molten printing filament under electron beam irradiation specifically involves: During the entire molding process, liquid nitrogen is sprayed onto the molten printing filament under electron beam irradiation while printing; Alternatively, while printing areas requiring performance enhancement, liquid nitrogen can be sprayed onto the molten printing filament under electron beam irradiation.

[0024] This involves spraying liquid nitrogen into the molten portion of the molten pool under electron beam irradiation during the printing process. By controlling the spray point to overlap with or be near the electron beam irradiation area, liquid nitrogen can be sprayed into a molten printing filament. Liquid nitrogen spraying can continue throughout the entire printing process, enhancing the performance of the formed part from the inside out. In applications with high surface performance requirements, liquid nitrogen can also be sprayed on surface areas during printing, such as the bottom and top layers, and other outer rings, to enhance the areas requiring performance enhancement.

[0025] In some embodiments, spraying liquid nitrogen onto molten filaments not only utilizes the rapid cooling effect of liquid nitrogen but also uses a high-energy electron beam to excite the liquid nitrogen into plasma, allowing it to deeply participate in the material solidification process. This plasma can undergo a nitriding reaction with the material to generate nitrides in situ, serving as heterogeneous nucleation sites for grain refinement and strengthening, and significantly improving hardness and wear resistance. Therefore, when selecting to spray liquid nitrogen onto molten printing filaments irradiated by an electron beam, the printing filaments should be materials capable of undergoing a nitriding reaction with liquid nitrogen, such as titanium alloys.

[0026] In some embodiments, spraying liquid nitrogen into the printing filament that has begun to solidify specifically involves: When printing areas requiring performance enhancement, liquid nitrogen is sprayed onto the printing filament that has begun to solidify after each print pass or layer; for example, when performance enhancement is required on the surface of a part, liquid nitrogen can be sprayed onto the printing filament that has begun to solidify after each print pass or layer.

[0027] Solidification begins when a solid state begins to appear in the material. This is achieved by controlling the distance between the liquid nitrogen injection point and the electron beam heating area to inject liquid nitrogen into the solidifying filament; that is, the liquid nitrogen injection point is positioned at a certain distance from the heating area, ensuring that the injected filament is the material that has begun to solidify. Alternatively, liquid nitrogen can be injected into the solidifying filament after stopping the laying of the printing filament and stopping electron beam heating, followed by a preset time interval. Specifically, after printing at least one pass or at least one layer, laying and electron beam heating can be stopped, and liquid nitrogen can be injected when the material begins to solidify after a preset time interval. Relevant parameters can be obtained through experiments based on specific operating conditions.

[0028] Furthermore, depending on the printing material, a balance can be struck between the increased structural density and strength resulting from rapid cooling and the poor interlayer bonding caused by insufficient preheating temperature due to cooling. Optimal liquid nitrogen jetting process parameters, such as flow rate and time, can be selected to ensure that liquid nitrogen jetting does not affect interlayer bonding. Alternatively, the current layer can be preheated after liquid nitrogen jetting before printing the next layer to guarantee effective interlayer bonding.

[0029] In some embodiments, when liquid nitrogen is sprayed onto molten printing filament under electron beam irradiation or onto printing filament that has begun to solidify, the flow rate of liquid nitrogen increases with the increase of the thickness of the laid printing filament.

[0030] In some embodiments, the electron beam melting filament cryogenic additive manufacturing method further includes: The printed parts are subjected to deep cryogenic treatment by spraying liquid nitrogen, which allows the parts to be deeply cooled by liquid nitrogen in order to regulate the crystal structure of the parts and enhance their mechanical properties.

[0031] In some embodiments, the electron beam melting filament cryogenic additive manufacturing method further includes: Different diameter printing filaments are used for printing different parts: the diameter of the printing filament used when printing the surface of the part is smaller than the diameter of the printing filament used when printing the core of the part; a transition diameter of printing filament is used when printing the area between the surface and the core of the part. And / or, the printing scanning strategy uses a zigzag path, with the outer circle speed being lower than the inner circle speed during printing scanning, and the speed decreasing as the diameter of the printing filament increases.

[0032] In other embodiments, reference is made to... Figure 1 and Figure 2 Furthermore, an electron beam melting filament liquid nitrogen cryogenic additive manufacturing system is provided. This system includes an electron beam emission system 1, a printing filament feeding system 2, a molding substrate, a liquid nitrogen rapid cooling system 3, and a control system. The printing filament feeding system 2 includes a printing nozzle 21, a filament feeding mechanism 22, a filament storage chamber 23, and a mounting bracket. The mounting bracket is fixed to the side of the molding substrate. The filament storage chamber 23 is connected to the mounting bracket and is used to store printing filament. The filament feeding mechanism 22 is connected to the filament storage chamber 23 and is used to convey printing filament. The printing nozzle 21 is connected to the filament feeding mechanism 22 and is located above the molding substrate for laying printing filament on the molding substrate. The filament storage chamber 23 is also connected to a mounting base plate, which is located above the molding base plate. The electron beam emission system 1 is fixed to the mounting base plate and faces the end of the print head 21. The liquid nitrogen rapid cooling system 3 includes a liquid nitrogen storage bottle 31, a flow rate control valve 32, a pipe and a print head connected in sequence. The pipe is fixed by the mounting base plate so that the print head faces the molding base plate. The control system is connected to the electron beam emission system 1, the printing filament feeding system 2 and the liquid nitrogen rapid cooling system 3 respectively, and is used to control each component to realize the electron beam melting filament liquid nitrogen cryogenic additive manufacturing method described above.

[0033] Furthermore, the printing filament feeding system 2 is provided in multiple units, which are arranged around the electron beam emission system 1. These multiple filament feeding systems 2 are used to lay out various printing filaments of different sizes and / or materials. The filament output speed of different filament feeding systems can be flexibly adjusted to print single-material or complex multi-material components according to different usage requirements.

[0034] Furthermore, the mounting bracket is configured as a telescopic arm structure, making the height of the print head 21 and the electron beam emission system 1 adjustable; and / or, the print head 21 is rotatably connected to the filament feeding mechanism 22.

[0035] This embodiment takes into account the increasing demand for multi-material composite components due to the increasing complexity of industrial applications. Traditional electron beam filament manufacturing technology has limitations in terms of multi-material supply and combination. Existing electron beam filament manufacturing equipment can typically only control the supply and melting process of a single metal wire, which limits the ability to manufacture more complex multi-material metal parts. There is a lack of a small, simple wire feeding device that can integrate electron beam filament feeding and extrusion multi-material composite additive manufacturing.

[0036] Based on this, an electron beam melting filament and liquid nitrogen cryogenic multi-material additive manufacturing apparatus is provided. This apparatus includes three sets of multi-material additive manufacturing devices, each consisting of an electron beam emission system 1 and a printing filament feeding system 2. Multiple printing filament feeding systems 2 and liquid nitrogen rapid cooling systems are arranged in a circular pattern around the axis of the electron beam emission system 1. The electron beam emission system 1 includes a cathode emission system 11, an electron beam acceleration system 12, an electron beam focusing system 13, and a power control system, integrated and fixed above the forming chamber. The printing filament feeding system 2 includes a printing nozzle 21, a filament feeding mechanism 22, a filament storage chamber 23, metal filament, a mechanical telescopic arm 24, and a power control system, which delivers the filament to the printing nozzle 21 at a specified speed. The liquid nitrogen rapid cooling system 3 includes a liquid nitrogen storage bottle 31, a flow rate control valve 32, pipes, and a jet nozzle 33, used to control the liquid nitrogen jet flow rate and rapidly cool the printed and solidified material.

[0037] Free electrons generated by the cathode emitting system 11 are accelerated by the electron acceleration system and the accelerating electric field, giving them higher energy. Finally, the electron beam is focused into a fine beam by the focusing system to precisely control the propagation direction and range of the electron beam. The metal wire passes through the wire feeding mechanism 22 in the wire storage chamber 23, where the direction of movement is changed by the wire rollers and the printing height is controlled by the mechanical telescopic arm 24. Finally, it is extruded by the print head 21 and melts under the action of the electron beam to form a molten pool. Liquid nitrogen stored in the liquid nitrogen storage bottle is controlled by the flow rate control valve 32 to open and close the gas flow rate. It is then ejected at the jet nozzle 33 to rapidly cool the printing material.

[0038] More preferably, the printing filament feeding system 2 comprises three sets, each of which can employ different printing methods according to usage requirements to directly process complex multi-material components with varying properties. The filament storage chamber 23 can be height-adjusted via a mechanical telescopic arm 24 at its bottom.

[0039] Application Example 1: Different wire diameters make a single material hard on the outside and tough on the inside. This example describes the use of a single metal filament forming additive manufacturing apparatus, including the following steps: Start the device power supply, preheat the cathode emission system 11 and electron beam acceleration system 12, adjust the position of the mechanical telescopic arm 24 to move the print head 21 above the substrate, and control the print head 21 to maintain a suitable angle with the substrate for printing. Start the motor of the printing filament feeding system 2, and feed the metal filament stored in the filament storage chamber 23 to the printing nozzle 21 through the filament feeding mechanism 22 for extrusion, and control the appropriate filament feeding rate; When the metal wire passes through the print head 21, the electron beam emission system 1 is activated. The free electrons generated by the cathode emission system 11 pass through the electron acceleration system. The accelerating electric field accelerates the electrons, giving them higher energy. Finally, the electron beam is focused into a fine beam by the focusing system, and the metal wire is melted with specific process parameters to print metal parts.

[0040] When printing on the surface, the flow rate control valve 32 of the liquid nitrogen rapid cooling system is opened, allowing the liquid nitrogen stored in the liquid nitrogen storage cylinder to flow through the pipeline to the jet head 33, where it is compressed and ejected to deeply cool the area that has just begun to solidify.

[0041] The formed parts are subjected to cryogenic treatment by spraying liquid nitrogen, which can be combined with laser processing to enhance the surface nitriding treatment.

[0042] The metal wire used is AZ91D magnesium alloy wire. Different wire feeding systems with different diameters are selected for different parts of the component being formed: a 1.0mm diameter wire feeding system is used at the surface of the part; a 1.5mm diameter wire feeding system is used after the surface of the part to print three layers of transition; and a 2.0mm diameter wire feeding system is used at the core of the part. All metal wires are manufactured using a drawing process, suitable for additive manufacturing processes where electron beam melting completes the parts. The suitable process parameters for AZ91D magnesium alloy wire are: accelerating voltage of 60kV, cathode current of 20mA, focusing current of 800mA, scanning strategy using a zigzag path, and different scanning speeds selected for different wire diameters: outer circle speed of 120mm / s and inner circle speed of 160mm / s when forming 1.0mm wire; outer circle speed of 100mm / s and inner circle speed of 140mm / s when forming 1.5mm wire; and outer circle speed of 80mm / s and inner circle speed of 120mm / s when forming 2.0mm wire.

[0043] Furthermore, liquid nitrogen injection is initiated 50ms after the cladding is completed, with an injection angle of 45°. When the deposit thickness is less than 2mm, the flow rate is controlled at 1.5 L / min, and the flow rate increases by 0.5 L / min for every 1mm increase in thickness.

[0044] Application Example 2: The degree of nitriding participation in single materials and the formation of nitrides This example describes the use of a single metal printing filament forming gradient nitrided material conforming additive manufacturing apparatus, including the following steps: Start the device power supply, preheat the cathode emission system 11 and electron beam acceleration system 12, adjust the position of the mechanical telescopic arm 24 to move the print head 21 above the substrate, and control the print head 21 to maintain a suitable angle with the substrate for printing. Start the motor of the printing filament feeding system 2, and feed the metal filament stored in the filament storage chamber 23 to the printing nozzle 21 through the filament feeding mechanism 22 for extrusion, and control the appropriate filament feeding rate; When the metal wire passes through the print head 21, the electron beam emission system 1 is activated. The free electrons generated by the cathode emission system 11 pass through the electron acceleration system. The accelerating electric field accelerates the electrons, giving them higher energy. Finally, the electron beam is focused into a fine beam by the focusing system, and the metal wire is melted with specific process parameters to print metal parts.

[0045] Open the flow rate control valve 32 of the liquid nitrogen rapid cooling system, so that the liquid nitrogen stored in the liquid nitrogen storage cylinder flows through the pipeline to the jet head 33, is compressed and sprayed out, and deeply cools the molten area of ​​the molten pool.

[0046] Liquid nitrogen is sprayed onto the formed parts, and laser processing is performed simultaneously to nitrid the surface.

[0047] The metal wire is TC4 titanium alloy wire, which is made of TC4 metal wire with a diameter of 1.0mm through a drawing process. It is suitable for the additive manufacturing process of parts completed by electron beam melting. The process parameters suitable for TC4 titanium alloy wire are: accelerating voltage of 100kV, cathode current of 30mA, focusing current of 1200mA, scanning strategy using a zigzag path, outer circle speed of 60mm / s, and inner circle speed of 80mm / s.

[0048] Furthermore, the liquid nitrogen injection is synchronized with the laser beam activation. While cooling the molten pool, the high-energy electron beam excites the liquid nitrogen into plasma, which deeply participates in the TC4 solidification process, generating TiN nitrides in situ. This TiN nitride serves as a heterogeneous nucleation site, strengthening the grains and significantly improving hardness and wear resistance. The liquid nitrogen injection angle is 45°, and the flow rate is controlled at 3 L / min when the deposit thickness is less than 2 mm. For every 1 mm increase in thickness, the flow rate increases by 1 L / min.

[0049] Application Example 3: Multi-material forming example This example focuses on three different metal printing filaments: AZ91D magnesium alloy, AlSi10Mg aluminum alloy, and TC4 titanium alloy, all with a diameter of 1 mm, manufactured through a drawing process. The method of using the multi-material composite additive manufacturing apparatus for forming these three different metal printing filaments includes the following steps: Start the device power supply, preheat the cathode emission system 11 and electron beam acceleration system 12, adjust the position of the mechanical telescopic arm 24 to move the print head 21 above the substrate, and control the print head 21 to maintain a suitable angle with the substrate for printing. Start the motor of the printing filament feeding system 2, and feed the metal filament stored in the filament storage chamber 23 to the printing nozzle 21 through the filament feeding mechanism 22 for extrusion, and control the appropriate filament feeding rate; When the metal wire passes through the print head 21, the electron beam emission system 1 is activated. The free electrons generated by the cathode emission system 11 pass through the electron acceleration system. The accelerating electric field accelerates the electrons, giving them higher energy. Finally, the electron beam is focused into a fine beam by the focusing system, and the metal wire is melted with specific process parameters to print metal parts.

[0050] Open the flow rate control valve 32 of the liquid nitrogen rapid cooling system to allow the liquid nitrogen stored in the liquid nitrogen storage cylinder to flow through the pipeline to the jet head 33, where it is compressed and ejected to deeply cool the area that has begun to solidify.

[0051] Following the steps described above, the three sets of different metal wires—AZ91D magnesium alloy, AlSi10Mg aluminum alloy, and TC4 titanium alloy—were printed and formed separately.

[0052] Liquid nitrogen is sprayed onto the formed parts, and laser processing is performed simultaneously to nitrid the surface.

[0053] The electron beam process parameters, wire feeding speed, and liquid nitrogen jet velocity settings for different metal wires are as follows: When the metal wire is AZ91D magnesium alloy wire, the suitable process parameters are: accelerating voltage of 60kV, cathode current of 20mA, focusing current of 800mA, scanning strategy using a zigzag path, outer ring speed of 120mm / s, and inner ring speed of 160mm / s. Liquid nitrogen injection is started 50ms after cladding, with an injection angle of 45°. When the deposit thickness is less than 2mm, the flow rate is controlled at 1.5 L / min, and the flow rate is increased by 0.5 L / min for every 1mm increase in thickness.

[0054] When the metal wire is AlSi10Mg aluminum alloy wire, the suitable process parameters are: accelerating voltage of 70kV, cathode current of 20mA, focusing current of 1000mA, scanning strategy using a zigzag path, outer ring speed of 120mm / s, and inner ring speed of 160mm / s. Liquid nitrogen injection is started 50ms after cladding, with an injection angle of 45°. When the deposit thickness is less than 2mm, the flow rate is controlled at 2.0 L / min, and the flow rate increases by 0.8 L / min for every 1mm increase in thickness.

[0055] When using TC4 titanium alloy wire, the suitable process parameters are: accelerating voltage of 100kV, cathode current of 30mA, focusing current of 1200mA, scanning strategy using a zigzag path, outer ring speed of 60mm / s, and inner ring speed of 80mm / s. Liquid nitrogen spraying starts 50ms after cladding, with a spray angle of 45°. When the deposit thickness is less than 2mm, the flow rate is controlled at 2.6 L / min, increasing by 1.0 L / min for every 1mm increase. The flow rate of liquid nitrogen spraying varies depending on the material; specifically, the spray flow rate is higher for titanium alloy wire than for aluminum alloy wire, which in turn is higher for magnesium alloy wire.

[0056] In summary, this embodiment can process and shape multiple different metal wires simultaneously according to manufacturing requirements, realize the continuous or alternating forming of multiple materials, and perform liquid nitrogen cryogenic treatment and surface nitriding treatment on the corresponding materials.

[0057] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for additive manufacturing of filaments using electron beam melting and liquid nitrogen cryogenic treatment, characterized in that, include: In the electron beam filament printing process, liquid nitrogen is sprayed onto the molten printing filament under electron beam irradiation, so that the molten printing filament undergoes nitriding reaction under the action of electron beam while being deeply cooled by liquid nitrogen, so as to regulate the crystal structure of the formed part and enhance its mechanical properties. And / or, spraying liquid nitrogen into the printing filament that has begun to solidify, causing the printing filament to be subjected to deep cooling by liquid nitrogen, in order to regulate the crystal structure of the molded part and enhance its mechanical properties.

2. The electron beam melting filament cryogenic additive manufacturing method according to claim 1, characterized in that, The specific steps of spraying liquid nitrogen onto molten printing filament under electron beam irradiation are as follows: During the entire molding process, liquid nitrogen is sprayed onto the molten printing filament under electron beam irradiation while printing; Alternatively, while printing areas requiring performance enhancement, liquid nitrogen can be sprayed onto the molten printing filament under electron beam irradiation.

3. The electron beam melting filament cryogenic additive manufacturing method according to claim 1, characterized in that, When liquid nitrogen is sprayed onto a molten printing filament under electron beam irradiation, the printing filament is a material capable of undergoing a nitriding reaction with liquid nitrogen.

4. The electron beam melting filament liquid nitrogen cryogenic additive manufacturing method as described in claim 1, characterized in that, The specific steps involved in spraying liquid nitrogen onto the solidifying printing filament are as follows: When printing areas requiring performance enhancement, liquid nitrogen is sprayed onto the printing filament that has begun to solidify after each at least one pass or at least one layer is printed. Liquid nitrogen can be sprayed onto the solidifying printing filament by controlling the distance between the liquid nitrogen spraying part and the electron beam heating area; or, liquid nitrogen can be sprayed onto the solidifying printing filament by stopping the laying of the printing filament and stopping the electron beam heating, and then spraying liquid nitrogen after a preset interval.

5. The electron beam melting filament liquid nitrogen cryogenic additive manufacturing method as described in claim 1, characterized in that, When liquid nitrogen is sprayed onto molten printing filament under electron beam irradiation or onto printing filament that has begun to solidify, the flow rate of liquid nitrogen increases with the increase of the thickness of the laid printing filament.

6. The electron beam melting filament cryogenic additive manufacturing method according to any one of claims 1-5, characterized in that, Also includes: The printed parts are subjected to deep cryogenic treatment by spraying liquid nitrogen, which allows the parts to be deeply cooled by liquid nitrogen in order to regulate the crystal structure of the parts and enhance their mechanical properties.

7. The electron beam melting filament cryogenic additive manufacturing method according to any one of claims 1-5, characterized in that, Also includes: Different diameter printing filaments are used for printing different parts: the diameter of the printing filament used when printing the surface of the part is smaller than the diameter of the printing filament used when printing the core of the part; a transition diameter of printing filament is used when printing the area between the surface and the core of the part. And / or, the printing scanning strategy uses a zigzag path, with the outer circle speed being lower than the inner circle speed during printing scanning, and the speed decreasing as the diameter of the printing filament increases.

8. A cryogenic additive manufacturing system for electron beam melting of filaments using liquid nitrogen, characterized in that, The system includes an electron beam emission system, a filament feeding system, a molding substrate, a liquid nitrogen rapid cooling system, and a control system. The filament feeding system includes a print head, a filament feeding mechanism, a filament storage chamber, and a mounting bracket. The mounting bracket is fixed to the side of the molding substrate. The filament storage chamber is connected to the mounting bracket and is used to store the filament. The filament feeding mechanism is connected to the filament storage chamber and is used to convey the filament. The print head is connected to the filament feeding mechanism and is located above the molding substrate for laying the filament on the molding substrate. The filament storage chamber is also connected to a mounting base plate, which is located above the molding base plate. The electron beam emission system is fixed to the mounting base plate and faces the end of the print head. The liquid nitrogen rapid cooling system includes a liquid nitrogen storage bottle, a flow rate control valve, a pipe and a print head connected in sequence. The pipe is fixed by the mounting base plate so that the print head faces the molding base plate. The control system is connected to the electron beam emission system, the printing filament feeding system and the liquid nitrogen rapid cooling system respectively, and is used to control each component to realize the electron beam melting filament liquid nitrogen cryogenic additive manufacturing method as described in any one of claims 1-7.

9. The electron beam melting filament liquid nitrogen cryogenic additive manufacturing system as described in claim 8, characterized in that, The printing filament feeding system is provided in multiple ways, and the multiple printing filament feeding systems are arranged around the electron beam emitting system. The multiple printing filament feeding systems are used to lay out various printing filaments of different sizes and / or materials.

10. The electron beam melting filament liquid nitrogen cryogenic additive manufacturing system as described in claim 8, characterized in that, The mounting bracket is configured as a telescopic arm structure, making the height of the print head and the electron beam emission system adjustable; and / or, the print head is rotatably connected to the filament feeding mechanism.

Images