Powder feeding nozzle structure for droplet composite electric arc additive manufacturing and optimization method

Abstract

The invention belongs to the field of additive manufacturing, and discloses a powder feeding nozzle structure for droplet composite arc additive manufacturing and an optimization method.The optimization method comprises the steps that a powder feeding nozzle is designed to be of a scaling structure, and a three-dimensional model of the internal structure of the powder feeding nozzle is established; based on relevant parameters of the three-dimensional model, a gas-solid two-phase motion theoretical model is established in combination with the physical environment of powder and air in the actual manufacturing process; a gas-solid two-phase motion theoretical model is adopted to solve the three-dimensional model subjected to structured grid division processing, and a gas-solid coupling simulation result is obtained; based on an analysis result of a gas-solid coupling simulation result, taking a particle distribution standard and a particle feeding rate as optimization targets to obtain an optimal scaling structure; by the adoption of the method, the particle feeding rate can be remarkably increased, the particle distribution uniformity can be ensured, the morphology of a deposition layer is effectively improved, the pore defect is reduced, and the requirement of the molten drop composite arc additive manufacturing technology for the particle distribution uniformity is met.

Description

Technical Field

[0001] The present invention belongs to the technical field of additive manufacturing, and in particular relates to a powder feeding nozzle structure and an optimization method for droplet composite arc additive manufacturing. Background Art

[0002] The droplet composite arc additive manufacturing technology uses independently generated droplets as additive materials and arc as the main heat source. It can independently regulate material addition and arc heat input, and realize efficient and high-quality additive manufacturing of metal materials including aluminum, copper and nickel-based high-temperature alloys. Compared with traditional arc fuse additive manufacturing technology, it breaks the inherent wire-arc strong coupling characteristics, has the advantages of low cost, high efficiency and high process stability, and shows great potential in efficient and high-quality additive manufacturing of medium and large components.

[0003] At present, the particle-reinforced metal matrix composites manufactured by droplet composite arc additive manufacturing still have problems such as uneven particle distribution, obvious pore defects and low strength of the reinforcement phase / matrix interface, which greatly limits the improvement of the microstructure and mechanical properties of the composite materials. Therefore, ensuring the uniform distribution of particles entering the molten pool during additive manufacturing has become a key issue that needs to be solved urgently.

[0004] The powder feeder nozzle is one of the most critical equipment for transporting powder particles into the molten pool. Improving its internal structure can promote the uniform distribution of powder particles during the forming process. However, the improvement effects in the reported related devices are limited, and there is a lack of corresponding data support for experimental verification and optimization of the powder feeder nozzle structure.

[0005] Chinese patent publication number CN101942656 B provides a nozzle device and a method for uniform powder distribution thereof. The patent inlays a number of steel balls that are staggered and evenly distributed on the outer wall of the nozzle core. The powder collides with the steel balls and rebounds in different directions. The powder is gradually evenly distributed in the powder channel and discharged along the powder outlet to achieve uniform powder delivery. However, this method has a long powder delivery time, a low powder utilization rate, and insufficient adaptability between the steel ball diameter and the powder particle size, which has limited effect on the uniformity control of powder in the additive manufacturing process. Summary of the invention

[0006] The present invention provides a powder feeding nozzle structure and optimization method for droplet composite arc additive manufacturing, so as to solve the technical problems that the structure of the conventional powder feeding nozzle used in the droplet composite arc additive manufacturing process cannot ensure a good particle feeding rate and the particles fed are unevenly distributed, which greatly affects the mechanical properties and wear resistance of the composite material.

[0007] In order to achieve the above object, the present invention adopts the following technical contents: A method for optimizing a powder feeding nozzle structure for droplet composite arc additive manufacturing, comprising: The powder delivery nozzle is designed as a scaled structure, and a three-dimensional model of the internal structure of the powder delivery nozzle is established; Based on the relevant parameters of the three-dimensional model and the physical environment of powder and air in the actual manufacturing process, a theoretical model of gas-solid two-phase movement is established; The gas-solid two-phase motion theoretical model is used to solve the three-dimensional model after structured grid division to obtain the gas-solid coupling simulation results; Based on the analysis of the gas-solid coupling simulation results, the optimal scaling structure was obtained by taking the particle distribution standard and the particle feeding rate as the optimization objectives.

[0008] Furthermore, the powder feeding nozzle adopts a three-level scaling structure, and the three-dimensional model of the internal structure of the powder feeding nozzle has three key structural parameters: a first-level scaling ratio, a second-level scaling ratio, and an outlet angle.

[0009] Furthermore, the first-stage scaling ratio is defined as the ratio of the maximum diameter to the minimum diameter of the head; the second-stage scaling ratio is defined as the ratio of the maximum diameter to the minimum diameter of the middle; and the outlet angle is defined as the angle of the cone at the particle outlet.

[0010] Furthermore, the gas-solid two-phase motion theoretical model includes a gas phase control equation and a particle motion equation; The process of establishing the gas phase control equation is as follows: After the powder delivery nozzle model is established, the air inside it is regarded as an ideal gas and the gas gap is ignored. On the basis of considering the drag force and gravity, the continuity equation, momentum conservation equation and turbulence equation are derived: Continuity equation:

[0011] Momentum conservation equation:

[0012] in:

[0013]

[0014] In the formula, ρ is the gas density; g is the acceleration due to gravity; , is the positive direction of the coordinate axis; , The gas speed is , Directional weight; is the gas pressure; is the interaction term between fluid and solid; is the air viscosity coefficient; is the turbulent viscosity coefficient; is the Kronecker number; is an empirical constant; k represents turbulent kinetic energy; The gas phase flows faster in the nozzle, and its actual flow state is turbulent, so the standard k-ε model is established: Among them, the k equation is the turbulent kinetic energy equation; the ε equation is the turbulent dissipation equation, specifically: k equation:

[0015] Epsilon equation:

[0016] in:

[0017]

[0018]

[0019] Where: The turbulent kinetic energy generation phase caused by the movement of the particle phase; is the dissipation rate generation term caused by particle phase motion; is the drag coefficient; , are the velocity fluctuations of gas and particles respectively; is the velocity of the gas; is the velocity of the particle; , , , , are experimental constants respectively; Turbulent kinetic energy generated for laminar velocity gradients; Fluctuations generated by diffusion in compressible turbulence transitions; The volume of the particles required in the experiment accounts for a small proportion of the gas volume, so its volume fraction is ignored; according to Newton's second law, the motion formula of a single spherical solid particle under the action of gas is as follows: g

[0020] in:

[0021]

[0022] Where: mp is the particle mass; is the resistance of the fluid to the particles; is the force generated by the collision between particles; is the volume of a single particle; is the pressure gradient; is the angular velocity of rotation; is the comprehensive torque acting on the particle; is the inertia term; is the drag coefficient; is the Reynolds number.

[0023] Furthermore, before using the gas-solid two-phase motion theoretical model to solve the three-dimensional model processed by structured meshing, the diameter of the powder feeding nozzle, generation rate, initial velocity of particles, gravity and total simulation time are set in EDEM; at the same time, the fluid in the flow channel, velocity inlet, initial velocity and pressure outlet are set in Fluent.

[0024] Furthermore, the three-dimensional model of the powder delivery nozzle is input into ICEM, and structured mesh processing is performed on the three-dimensional model, and the mesh quality is at least 0.35.

[0025] Furthermore, the molten pool is equivalent to a cylinder with a preset diameter. By setting cylindrical areas with different diameters and preset heights at a preset distance from the powder feeding nozzle outlet in EDEM, the mass distribution of the particles before entering the molten pool is simulated, thereby obtaining different gas-solid coupling simulation results.

[0026] Furthermore, the analysis process of the gas-solid coupling simulation results is as follows: Based on the gas-solid coupling simulation results, the particle mass in the cylindrical area with different diameters is counted; Subtract the mass of particles in two adjacent cylindrical regions to obtain the mass distribution of particles in circular regions with different diameters; then divide by the corresponding volume to obtain the mass distribution of particles in multiple regions; The average value is solved according to the mass distribution of multiple areas, and then the standard deviation of the particle mass distribution is obtained. The particle mass distribution standard deviation is used to characterize the uniformity of powder feeding by the powder feeding nozzle; the particle feeding rate is equal to the ratio of the particle mass in the relevant area to the total mass.

[0027] Furthermore, the scaling structure corresponding to the smallest particle mass distribution standard deviation and the highest particle feeding rate is output as the optimal scaling structure.

[0028] A powder feeding nozzle structure for droplet composite arc additive manufacturing is designed using the above optimization method.

[0029] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides an optimization method for a powder feeding nozzle structure for droplet composite arc additive manufacturing. The optimization method designs the powder feeding nozzle as a scaling structure and establishes a three-dimensional model of the internal structure of the powder feeding nozzle; based on relevant parameters of the three-dimensional model and in combination with the physical environment of powder and air in the actual manufacturing process, a gas-solid two-phase motion theoretical model is established; the gas-solid two-phase motion theoretical model is used to solve the three-dimensional model after structured grid division to obtain a gas-solid coupling simulation result; based on the analysis results of the gas-solid coupling simulation results, the particle distribution standard and the particle feeding rate are used as optimization targets to obtain the optimal scaling structure; the use of this method can significantly improve the particle feeding rate and ensure the uniformity of the particle distribution, thereby effectively improving the morphology of the deposited layer, reducing pore defects, and meeting the requirements of the droplet composite arc additive manufacturing technology for the uniformity of particle distribution.

[0030] Preferably, in the present invention, the powder feeding nozzle is designed as a three-level scaling structure, and the three-dimensional model of the internal structure of the powder feeding nozzle has three key structural parameters: the first-level scaling ratio, the second-level scaling ratio and the outlet angle, which can more accurately control the shape and size of the powder feeding nozzle, thereby further optimizing the particle feeding rate and distribution uniformity.

[0031] Preferably, in the present invention, the specific definitions of the first-stage scaling ratio, the second-stage scaling ratio and the outlet angle are clarified, which provides clear guidance for the parametric design and optimization of the powder feeding nozzle structure and helps to achieve more accurate powder feeding control.

[0032] Preferably, in the present invention, a gas-solid two-phase motion theoretical model including the gas phase control equation and the particle motion equation is established. This model can more accurately describe the motion state of gas and particles during the powder feeding process, and provides a solid theoretical basis for subsequent simulation and optimization.

[0033] Preferably, in the present invention, by setting the relevant parameters of the powder delivery nozzle and the flow channel in EDEM and Fluent, necessary initial conditions and boundary conditions are provided for subsequent simulation calculations, thereby ensuring the accuracy and reliability of the simulation results.

[0034] Preferably, in the present invention, by adopting structured grid division to process the three-dimensional model of the powder feeding nozzle and ensuring that the grid quality is at least 0.35, the accuracy and efficiency of the simulation calculation can be improved, providing strong support for subsequent optimization work.

[0035] Preferably, in the present invention, by treating the molten pool as equivalent to a cylinder of a preset diameter and setting cylindrical areas of different diameters and preset heights to simulate the mass distribution of particles before entering the molten pool, the powder feeding effect of the powder feeding nozzle can be evaluated more accurately, providing a strong basis for optimizing the powder feeding nozzle structure.

[0036] Preferably, in the present invention, by counting the particle masses in cylindrical regions of different diameters and calculating the particle mass distribution and the particle mass distribution standard deviation in multiple regions, the powder feeding uniformity of the powder feeding nozzle can be quantitatively evaluated, providing a clear optimization target for optimizing the powder feeding nozzle structure.

[0037] Preferably, in the present invention, by taking the minimum standard deviation of particle mass distribution and the maximum particle feeding rate as optimization goals, it can be ensured that the powder feeding nozzle structure has the best powder feeding effect after optimization, thereby improving the quality and performance of the deposited layer.

[0038] The present invention also provides a powder feeding nozzle structure for molten droplet composite arc additive manufacturing, which is designed based on the above-mentioned optimization method for the powder feeding nozzle structure for molten droplet composite arc additive manufacturing. The powder feeding nozzle structure has a good scaling structure, which can significantly improve the particle feeding rate and distribution uniformity, thereby improving the morphology and performance of the deposited layer, and can meet the requirements of the molten droplet composite arc additive manufacturing technology for particle distribution uniformity; the powder feeding nozzle structure is of great significance for improving the overall level and application effect of the molten droplet composite arc additive manufacturing technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A schematic diagram of the principle of the droplet composite arc additive manufacturing process provided by an embodiment of the present invention; Figure 2 A schematic diagram of the structure of a powder delivery nozzle provided in an embodiment of the present invention; Figure 3 A statistical area set in EDEM provided in an embodiment of the present invention; Figure 4 Five areas divided for analyzing powder feeding uniformity provided in an embodiment of the present invention; Figure 5 The effects of different structural parameters on powder feeding characteristics provided by the embodiments of the present invention; wherein (a) is the first-stage scaling ratio; (b) is the second-stage scaling ratio; (c) is the outlet angle; Figure 6 A schematic diagram of particle blockage caused by the 3-3-10° structural parameter provided in an embodiment of the present invention; Figure 7 A distribution diagram of the particle distribution range relative to the molten pool position under structural parameters of different outlet angles provided in an embodiment of the present invention; Figure 8 The internal gas phase pressure, velocity cloud map and particle velocity distribution map under the 2.4-3-8° structural parameters provided by the embodiment of the present invention; wherein (a) is the gas phase pressure cloud map; (b) is the gas phase velocity cloud map; (c) is the particle velocity distribution in EDEM; Fig. 9Trajectories of six particles randomly counted in an embodiment of the present invention; wherein (a), (b), (c), (d), (e) and (f) correspond to the trajectory of one particle respectively; Fig.10 A physical diagram of the 2.4-3-10° structural parameters used in the experimental verification provided in the embodiment of the present invention; Fig.11 The particle aggregation range at different outlet distances provided by the embodiment of the present invention; Fig.12 for Fig.11 Linear fitting of the middle outlet distance and particle collection range; Fig.13 A flow chart of a method for optimizing a powder feeding nozzle structure for droplet composite arc additive manufacturing provided in an embodiment of the present invention.

[0040] Reference numerals: 1. Substrate; 2. Particle-reinforced metal matrix composite deposition layer; 3. Molten pool; 4. Electric arc; 5. Powder feeding nozzle; 6. Powder feeding tube; 7. Arc welding torch; 8. Metal melt; 9. Crucible; 10. Induction heating coil; 11. Heating sleeve; 12. Nozzle; 13. Metal jet; 14. Metal droplet; 15. Powder beam. DETAILED DESCRIPTION

[0041] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail in the following specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0042] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0043] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] Example 1 As mentioned in the background technology, in the current droplet composite arc additive manufacturing process, due to the use of a conventional powder feeding nozzle structure, a good particle feeding rate cannot be guaranteed and the particle distribution is uneven, which greatly affects the mechanical properties and wear resistance of the composite material.

[0045] In order to solve the above problems, this embodiment provides a method for optimizing the powder feeding nozzle structure for droplet composite arc additive manufacturing. By adopting this preferred method, the problem of uneven distribution of particles in the matrix in the droplet composite arc additive manufacturing process can be solved.

[0046] like Fig.13 As shown, this embodiment provides a method for optimizing the powder feeding nozzle structure for droplet composite arc additive manufacturing, and the steps are as follows: The powder delivery nozzle is designed as a scaled structure, and a three-dimensional model of the internal structure of the powder delivery nozzle is established; Based on the relevant parameters of the three-dimensional model and the physical environment of powder and air in the actual manufacturing process, a theoretical model of gas-solid two-phase movement is established; The gas-solid two-phase motion theoretical model is used to solve the three-dimensional model after structured grid division to obtain the gas-solid coupling simulation results; Based on the analysis of the gas-solid coupling simulation results, the optimal scaling structure was obtained by taking the particle distribution standard and the particle feeding rate as the optimization objectives.

[0047] It can be seen that this optimization method designs the powder feeding nozzle as a scaling structure and establishes a three-dimensional model of the internal structure of the powder feeding nozzle; based on the relevant parameters of the three-dimensional model and combined with the physical environment of powder and air in the actual manufacturing process, a gas-solid two-phase motion theoretical model is established; the gas-solid two-phase motion theoretical model is used to solve the three-dimensional model after structured meshing to obtain the gas-solid coupling simulation result; based on the analysis results of the gas-solid coupling simulation results, the particle distribution standard and particle feeding rate are used as optimization targets to obtain the optimal scaling structure; the use of this method can significantly improve the particle feeding rate and ensure the uniformity of particle distribution, thereby effectively improving the morphology of the deposited layer, reducing pore defects, and meeting the requirements of the droplet composite arc additive manufacturing technology for particle distribution uniformity.

[0048] Example 2 like Figure 1 As shown, this embodiment is further improved and optimized on the basis of embodiment 1, and provides another method for optimizing the powder feeding nozzle structure for droplet composite arc additive manufacturing, and the specific steps are as follows: S1: Based on the special working conditions inside the powder delivery nozzle, the powder delivery nozzle is designed as a scaled structure, and a three-dimensional model of the internal structure of the powder delivery nozzle is established; S2: Based on the three-dimensional model of the powder delivery nozzle obtained in step S1 and combined with the physical environment of powder and air in the actual manufacturing process, a mathematical theoretical model of gas-solid two-phase motion is established; S3: Based on the size of the three-dimensional model established in step S1, combined with information such as powder characteristics, powder feeding speed and powder feeding conditions in the actual manufacturing process, boundary conditions and solution settings are set in EDEM and Fluent; S4: Import the three-dimensional model obtained in step S1 into ICEM for structured meshing, combine the gas-solid two-phase motion mathematical theoretical model obtained in step S2 and the boundary conditions and solution settings set in step S3, and import the mesh file into EDEM and Fluent for solution; S5: Based on the gas-solid coupling simulation results obtained in step S4, the powder feeding uniformity and particle feeding rate are analyzed to reveal the influence mechanism of the nozzle scaling structure on the powder feeding characteristics; S6: According to the analysis conclusion obtained in step S5, the particle distribution standard and the particle feeding rate are used as optimization indicators to determine the optimal scaling structure, and experimentally verify the powder feeding nozzle structure.

[0049] The technical solution of this embodiment is further explained below in conjunction with the accompanying drawings: Figure 1 This is a process schematic diagram of the molten droplet composite arc additive manufacturing system carried by this embodiment, which is mainly composed of a molten droplet generation system, an inert atmosphere glove box, a three-dimensional motion unit, a GTA (Gas Tungsten Arc) heat source, a particle reinforcement phase implantation unit, and a corresponding process control unit. The following components are specifically included: a substrate 1, a particle-reinforced metal matrix composite deposition layer 2, a molten pool 3, an arc 4, a powder feeding nozzle 5, a powder feeding tube 6, an arc welding torch 7, a metal melt 8, a crucible 9, an induction heating coil 10, a heating sleeve 11, a nozzle 12, a metal jet 13, a metal droplet 14, and a powder beam 15. In the process of molten droplet composite arc additive manufacturing, the GTA welding gun is tilted and arranged below the molten droplet generation system to form a molten pool on the substrate or the previous deposition layer. The droplet generation system uses induction heating to melt the metal material in the crucible. Under the action of continuously applied gas pressure, the melt in the crucible generates a columnar jet through the orifice at the end of the nozzle. Under the action of surface tension, gravity and environmental disturbances, the columnar jet will disperse into metal droplets and fall vertically and orderly into the molten pool. At the same time, the particle reinforcement phase is accurately delivered to the second half of the molten pool in the form of airborne powder through the powder feeding nozzle. With the relative movement between the arc and the substrate, the molten pool undergoes a rapid solidification process, and the particle reinforcement phase can be evenly dispersed in the metal matrix to form a particle-reinforced metal matrix composite material, which is gradually accumulated into the final target component in a layer-by-layer / channel-by-channel deposition method.

[0050] S1: Powder nozzle structure design This embodiment uses a powder feeding nozzle with a three-stage scaling structure to improve the distribution of particles when entering the molten pool. Combining the idea of ​​parametric modeling, three key structural parameters, the first-stage scaling ratio, the second-stage scaling ratio and the outlet angle, are determined. The first-stage scaling ratio is defined as the ratio of the maximum diameter to the minimum diameter of the head; the second-stage scaling ratio is defined as the ratio of the maximum diameter to the minimum diameter in the middle; the outlet angle is defined as the angle of the cone at the particle outlet. In addition, the smallest diameter in the powder feeding nozzle is 1 mm, the diameter at the particle inlet is 1.6 mm, the diameter at the outlet is 4 mm, and the total length of the powder feeding nozzle is 7 mm; the flow field area in the simulation device uses a cylinder with a diameter of 15 mm and a height of 60 mm, such as Figure 2 In this embodiment, 11 groups of simulation experiments were conducted to explore the influence of structural parameters on powder feeding characteristics, as shown in Table 1.

[0051] Table 1 Powder delivery nozzle structure under different parameters

[0052] S2-1: Establishment of gas phase control equation After the powder delivery nozzle model is established, the air inside it is regarded as an ideal gas and the gas gap is ignored. On the basis of considering the drag force and gravity, the continuity equation, momentum conservation equation and turbulence equation are derived: Continuity equation:

[0053] Momentum conservation equation:

[0054] in:

[0055]

[0056] In the formula, ρ is the gas density, , is the positive direction of the coordinate axis; , The gas speed is , Directional weight; is the gas pressure; g is the acceleration due to gravity; is the interaction term between fluid and solid; is the air viscosity coefficient; is the turbulent viscosity coefficient; is the Kronecker number; is an empirical constant; k represents turbulent kinetic energy; The gas phase flows faster in the nozzle, and its actual flow state is turbulent, so the standard k-ε model is established. k is the turbulent kinetic energy equation, and ε is the turbulent dissipation equation, specifically: k equation:

[0057] Epsilon equation:

[0058] in:

[0059]

[0060]

[0061] Where: It is the turbulent kinetic energy generated by the laminar velocity gradient; Fluctuations generated by diffusion in compressible turbulence transitions; The turbulent kinetic energy generation phase caused by the movement of the particle phase; is the dissipation rate generation term caused by particle phase motion; is the drag coefficient; , are the velocity fluctuations of gas and particles respectively; is the velocity of the gas; is the velocity of the particle; , , , , are experimental constants respectively; The WC particles used in the experiment of this embodiment are spherical. Therefore, the solid particles are set to be spherical in EDEM. The properties of the WC particles are shown in Table 2.

[0062] Table 2 shows the properties of WC particles.

[0063] The volume of the particles required in the experiment accounts for a small proportion of the gas volume, so its volume fraction can be ignored. According to Newton's second law, the motion formula of a single spherical solid particle under the action of gas is as follows: g

[0064] in:

[0065]

[0066] Where: m p is the particle mass; Make the fluid resist the particles; is the force generated by the collision between particles; is the volume of a single particle; is the pressure gradient; is the angular velocity of rotation; is the comprehensive torque acting on the particle; is the inertia term; is the drag coefficient; is the Reynolds number.

[0067] S3: Boundary Conditions and Solution Setup Parameter settings in EDEM: The particle material is set to WC particles, and its basic properties are shown in Table 2. The nozzle material is set to titanium alloy. The particle factory position is set to the powder nozzle inlet plane, its diameter is 1.6 mm, the generation rate is 0.628 g / s, and the particle initial velocity is 10 m / s. The gravity is set in the environment, and it is saved every 0.0005s, for a total of 100 times, and the total simulation time is 0.05 s. Parameter settings in Fluent: The fluid in the flow channel is set to argon, the inlet is the velocity inlet, the initial velocity is 20m / s, and the outlet is set to the pressure outlet.

[0068] S4: Obtaining gas-solid coupling simulation results Import the established three-dimensional model of the powder feeding nozzle into ICEM for structured meshing to ensure that the mesh quality is above 0.35. Import the mesh file into EDEM and Fluent for solution. By analyzing the morphology of the deposited layer, it was found that the layer width was approximately 9 mm, and it was inferred that the actual shape of the molten pool was approximately an ellipse with a large diameter of 9 mm. For the convenience of statistics, the molten pool is equivalent to a cylinder with a diameter of 9 mm. By setting cylindrical areas of different diameters and a height of 2 mm at 30 mm from the outlet of the powder feeding nozzle in EDEM, the mass distribution of the particles before entering the molten pool is simulated, as shown in the figure. Figure 3 The statistical results are shown in Table 3.

[0069] Table 3 shows the particle mass in the cylindrical area with different diameters

[0070] S5-1: Analysis of powder feeding uniformity and particle feeding rate Table 3 summarizes the mass of particles in cylindrical regions with different diameters. Subtracting the mass of particles in two adjacent cylindrical regions can obtain the mass distribution of particles in circular regions with different diameters. Dividing it by the corresponding volume can characterize the mass distribution of particles in these five regions. Figure 4As shown. In order to more intuitively show the powder feeding uniformity, the calculated mass distribution of the five areas is averaged and the standard deviation is obtained. The smaller the standard deviation, the closer the particle distribution of the five areas, and the better the powder feeding uniformity of the powder feeding nozzle. The particle feeding rate is defined as the ratio of the mass of the particles in a cylindrical area with a diameter of 9 mm (the approximate shape of the molten pool) to the total mass. This embodiment uses the two indicators of particle distribution standard deviation and particle feeding rate to comprehensively describe the powder feeding characteristics of the powder feeding nozzle under different structures.

[0071] As shown in Table 1, experiments 1# to 4# explored the effect of the first-stage scaling ratio on the powder feeding characteristics. Experiments 2#, 5# to 7# explored the effect of the second-stage scaling ratio on the powder feeding characteristics; experiments 4#, 8# to 11# explored the effect of the outlet angle on the powder feeding characteristics. The results are as follows: Figure 5 As shown. Figure 5 It can be seen from a that with the increase of the first-stage scaling ratio, the particle distribution standard deviation fluctuates, but generally shows a decreasing trend, but the particle feeding rate does not fluctuate greatly with the change of the first-stage scaling ratio. This means that increasing the first-stage scaling ratio within a certain range can reduce the particle distribution standard deviation without changing the particle feeding rate, and achieve uniform distribution of particles; Figure 5 As can be seen from Figure b, as the second-stage scaling ratio increases from 2 to 3, the standard deviation of the particle distribution decreases significantly, from 3.8 to 2.6, and the particle distribution uniformity is greatly improved, but the particle feeding rate remains basically unchanged. This shows that when the second-stage scaling ratio increases within a certain range, the powder feeding uniformity of the powder feeding nozzle can be effectively improved without affecting the particle feeding rate.

[0072] Figure 6 It is the simulation result under the 3-3-10° structure. It can be found that the particles are not ejected from the powder delivery nozzle outlet, but gather in the middle area of ​​the powder delivery nozzle to cause blockage. When the scaling ratio is too large, the curvature of the wall will also become larger, and the particles will collide with the wall and rebound, causing the particle speed to reverse. Therefore, too large a scaling ratio may also cause particle blockage. The scaling ratios adopted in this embodiment are all less than 3.

[0073] Figure 5 c shows the influence of the outlet angle on the powder feeding characteristics. It can be seen that as the outlet angle increases from 6° to 11°, the particle feeding rate decreases significantly from 80% to around 60%, indicating that the outlet angle is the decisive factor affecting the particle feeding rate. When the particle distribution standard deviation is smaller, the particles are more dispersed, and it becomes more difficult for the particles to be concentrated in the molten pool area, resulting in a decrease in the particle feeding rate. However, from Figure 5 It can be seen from Figure c that as the particle feeding rate decreases, the particle distribution standard deviation first decreases and then increases. Combining the analysis of the outlet angle and the relative position of the molten pool, as shown in Figure 5, Figure 7As shown, when the outlet angle is about 10°, its divergence and particle feeding rate should be better. However, the experimental results show that when the outlet angle is 8°, the standard deviation of the particle distribution is the smallest, and the particle feeding rate is also higher. This is because the distribution of particles is roughly normally distributed along the radial direction, which means that there are more particles distributed in the middle area, and the fewer particles are distributed toward the periphery. By appropriately shrinking the outlet angle, the particles that originally diverged to the periphery of the molten pool can be concentrated in areas with less particle distribution. This not only reduces the differences in particle distribution in different areas, but also increases the particle feeding rate. Combining the particle distribution standard deviation and the particle feeding rate, this embodiment derives that the powder feeding nozzle with a 2.4-3-8° structure is optimal, with a particle distribution standard deviation of 2.03 and a particle feeding rate of 72.98%.

[0074] S5-2: Investigate the mechanism of the influence of nozzle scaling structure on powder feeding characteristics In order to analyze the influence mechanism of the scaling structure on the powder feeding characteristics, this embodiment takes the 2.4-3-8° structure as an example, and obtains the pressure cloud map and velocity cloud map of the gas phase flow field inside the powder feeding nozzle in Fluent, as shown in FIG. Figure 8 a, 8b. The pressure distribution in the powder nozzle shows a decreasing trend from the inlet to the outlet. This pressure difference is a necessary condition for gas flow. In addition, in the contraction section of the powder nozzle, as its cross-sectional area decreases, the static pressure presents a negative pressure state, and the gas flow rate gradually increases in this section; in the diffusion section of the powder nozzle, as the cross-sectional area increases, the static pressure value gradually increases, resulting in a decrease in the gas phase flow rate, which is consistent with the state of the fluid in the powder nozzle under actual working conditions. Figure 8 b shows that the air flow velocity at the throat of the powder feeding nozzle varies greatly, with the maximum speed reaching 55 m / s, and then the pressure drops rapidly to about 20 m / s. This change is conducive to destroying the original trajectory of the particles and improving their distribution uniformity.

[0075] Figure 8 c is the velocity distribution result of the particles in EDEM, which shows that the velocity of the particles does not change significantly during the entire transportation process, and the overall velocity of the particles is concentrated in the range of 9-11 m / s. In order to further reveal the influence mechanism of the scaling structure on the powder feeding characteristics, the trajectories of 6 particles were randomly counted, such as Fig. 9 shown. Fig. 9 The trajectories of particles a and b are approximately a straight line, which just enters the center of the molten pool. Fig. 9 The trajectories of the four particles c, d, e, and f have all changed, which indicates that the dispersion of the particles in the scaling structure is high. Therefore, this embodiment believes that the dispersion of the particles mainly comes from the collision with the wall, thereby changing the direction of their velocity; the effect of improving the distribution uniformity of the particles by only relying on the change of the airflow is not obvious.

[0076] S6: Experimental verification of powder nozzle structure.

[0077] In this embodiment, the particle distribution standard deviation and particle feeding rate are used as optimization indicators, and the optimal scaling structure is determined to be 2.4-3-8°, which verifies the powder feeding characteristics of the processed 2.4-3-10° powder feeding nozzle. Fig.10 shown.

[0078] In order to verify the powder feeding characteristics under this structure, this embodiment counted the particle convergence range (R) at a distance S from the powder feeding nozzle outlet. The schematic diagram and experimental results are shown in Fig.11 As shown, and a straight line is used for fitting, such as Fig.12 As shown. The expression is:

[0079] The R obtained by fitting 2 The value is 0.99673, indicating that the fitting effect is good. The slope of the straight line shows that the actual particle distribution range is approximately a conical area with an angle of 12.97°, which is larger than the particle outlet angle (10°) used in modeling. This shows that the particles will continue to diverge in the process of leaving the powder feeding nozzle and entering the molten pool. The reason is that when leaving the powder feeding nozzle, if the speed angle of the particles is greater than the outlet angle used in modeling, the particles will continue to move in the original direction, causing them to appear outside the designed range. This also confirms that even if the outlet angle is set to 8°, the particle feeding rate cannot reach 100%, but is 72.98% statistically calculated by the present invention.

[0080] This embodiment provides a method for optimizing the powder feeding nozzle structure for droplet composite arc additive manufacturing, which has the following advantages: First, the present invention designs powder delivery nozzle models with different structural parameters, and adopts the numerical simulation method of gas-solid two-phase flow to better restore the particle movement in the powder delivery nozzle during pneumatic transportation; Second, the present invention explores the influence of the scaling structure of the powder feeding nozzle on the powder feeding characteristics and determines the main reason for particle divergence; Third, the present invention uses the particle distribution standard deviation and the particle feeding rate as optimization indicators to obtain the optimal structure of the powder feeding nozzle, and experimentally verifies the powder feeding nozzle structure. Ultimately, the powder feeding nozzle structure and optimization method can meet the requirements of droplet composite arc additive manufacturing technology for particle distribution uniformity. The above embodiment is only one of the implementation methods that can realize the technical solution of the present invention. The scope of protection claimed by the present invention is not limited only to this embodiment, but also includes changes, replacements and other implementation methods that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed by the present invention.

Claims

1. A method for optimizing the powder feeding nozzle structure for droplet composite arc additive manufacturing, characterized in that: include: The powder delivery nozzle is designed as a scaled structure, and a three-dimensional model of the internal structure of the powder delivery nozzle is established; Based on the relevant parameters of the three-dimensional model and the physical environment of powder and air in the actual manufacturing process, a theoretical model of gas-solid two-phase movement is established; The gas-solid two-phase motion theoretical model is used to solve the three-dimensional model after structured grid division to obtain the gas-solid coupling simulation results; Based on the analysis of the gas-solid coupling simulation results, the optimal scaling structure was obtained by taking the particle distribution standard and the particle feeding rate as the optimization objectives.

2. The method for optimizing the powder feeding nozzle structure for droplet composite arc additive manufacturing according to claim 1, characterized in that: The powder delivery nozzle adopts a three-level scaling structure, and the three-dimensional model of the internal structure of the powder delivery nozzle has three key structural parameters: a first-level scaling ratio, a second-level scaling ratio, and an outlet angle.

3. The method for optimizing the powder feeding nozzle structure for droplet composite arc additive manufacturing according to claim 2, characterized in that: The first-stage scaling ratio is defined as the ratio of the maximum diameter to the minimum diameter of the head; the second-stage scaling ratio is defined as the ratio of the maximum diameter to the minimum diameter of the middle; and the outlet angle is defined as the angle of the cone at the particle outlet.

4. The method for optimizing the powder feeding nozzle structure for droplet composite arc additive manufacturing according to claim 1, characterized in that: The gas-solid two-phase motion theoretical model includes a gas phase control equation and a particle motion equation; The process of establishing the gas phase control equation is as follows: After the powder delivery nozzle model is established, the air inside it is regarded as an ideal gas and the gas gap is ignored. On the basis of considering the drag force and gravity, the continuity equation, momentum conservation equation and turbulence equation are derived: Continuity equation: Momentum conservation equation: in: In the formula, ρ is the gas density; g is the acceleration due to gravity; , is the positive direction of the coordinate axis; , The gas speed is , Directional weight; is the gas pressure; is the interaction term between fluid and solid; is the air viscosity coefficient; is the turbulent viscosity coefficient; is the Kronecker number; is an empirical constant; k represents turbulent kinetic energy; The gas phase flows faster in the nozzle, and its actual flow state is turbulent, so the standard k-ε model is established: Among them, the k equation is the turbulent kinetic energy equation; the ε equation is the turbulent dissipation equation, specifically: k equation: Epsilon equation: in: Where: The turbulent kinetic energy generation phase caused by the movement of the particle phase; is the dissipation rate generation term caused by particle phase motion; is the drag coefficient; , are the velocity fluctuations of gas and particles respectively; is the velocity of the gas; is the velocity of the particle; , , , , are experimental constants respectively; Turbulent kinetic energy generated for laminar velocity gradients; Fluctuations generated by diffusion in compressible turbulent transitions; The volume of the particles required in the experiment accounts for a small proportion of the gas volume, so its volume fraction is ignored; according to Newton's second law, the motion formula of a single spherical solid particle under the action of gas is as follows: g in: Where: m p is the particle mass; is the resistance of the fluid to the particles; is the force generated by the collision between particles; is the volume of a single particle; is the pressure gradient; is the angular velocity of rotation; is the comprehensive torque acting on the particle; is the inertia term; is the drag coefficient; is the Reynolds number.

5. The method for optimizing the powder feeding nozzle structure for droplet composite arc additive manufacturing according to claim 1, characterized in that: Before using the gas-solid two-phase motion theoretical model to solve the three-dimensional model processed by structured meshing, the diameter of the powder feeding nozzle, generation rate, initial particle velocity, gravity and total simulation time are set in EDEM; at the same time, the fluid in the flow channel, velocity inlet, initial velocity and pressure outlet are set in Fluent.

6. The method for optimizing the powder feeding nozzle structure for droplet composite arc additive manufacturing according to claim 1, characterized in that: The 3D model of the powder delivery nozzle is input into ICEM, and the 3D model is structured meshed with a mesh quality of at least 0.

35.

7. The method for optimizing the powder feeding nozzle structure for droplet composite arc additive manufacturing according to claim 1, characterized in that: The molten pool is equivalent to a cylinder with a preset diameter. By setting cylindrical areas with different diameters and preset heights at a preset distance from the powder feeding nozzle outlet in EDEM, the mass distribution of particles before entering the molten pool is simulated to obtain different gas-solid coupling simulation results.

8. The method for optimizing the powder feeding nozzle structure for droplet composite arc additive manufacturing according to claim 1, characterized in that: The analysis process of the gas-solid coupling simulation results is as follows: Based on the gas-solid coupling simulation results, the particle mass in the cylindrical area with different diameters is counted; Subtract the mass of particles in two adjacent cylindrical regions to obtain the mass distribution of particles in circular regions with different diameters; then divide by the corresponding volume to obtain the mass distribution of particles in multiple regions; The average value is solved according to the mass distribution of multiple areas, and then the standard deviation of the particle mass distribution is obtained. The particle mass distribution standard deviation is used to characterize the uniformity of powder feeding by the powder feeding nozzle; the particle feeding rate is equal to the ratio of the particle mass in the relevant area to the total mass.

9. The method for optimizing the powder feeding nozzle structure for droplet composite arc additive manufacturing according to claim 1, characterized in that: The scaling structure corresponding to the smallest particle mass distribution standard deviation and the highest particle feeding rate is output as the optimal scaling structure.

10. A powder feeding nozzle structure for droplet composite arc additive manufacturing, characterized in that: The optimization method according to any one of claims 1 to 9 is used for design.

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