Air suction device of L-PBF printer sintering chamber

Abstract

The invention discloses an air suction device of an L-PBF printer sintering chamber, and relates to the technical field of L-PBF printers, and the air suction device comprises an air return block which is arranged on the inner side wall of a gas outlet close to the bottom of the sintering chamber in the vertical direction; an air return flow channel is formed in the air return block in the vertical direction in a penetrating mode and comprises an upper flow channel and a lower flow channel which communicate with each other, the longitudinal section of the upper flow channel is a right trapezoid with the upper bottom larger than the lower bottom, and the width of the lower flow channel is gradually narrowed from top to bottom; an outlet of the lower runner is communicated with an air return cover of the sintering chamber in a penetrating manner; and the rotating cylinder is rotationally arranged above the air return block through a driving device. Turbulent flow generated when airflow blowing towards the galvanometer and airflow blowing towards the workbench converge in front of the air return cover is eliminated, and a flow field above the workbench is optimized, so that the efficiency of removing splashed metal particles by the airflow is improved, meanwhile, the efficiency of cleaning the galvanometer by the airflow above is improved, and finally, the quality of printed products is improved.

Description

Technical Field

[0001] This invention relates to the field of L-PBF printer technology, and in particular to an air suction device for the sintering chamber of an L-PBF printer. Background Technology

[0002] In practical production applications, L-PBF (Laser Powder Bed Fusion) printers generate a large number of metal particles during printing. These particles adhere to the workpiece surface, causing poor surface quality and even creating porosity, thus affecting its mechanical properties. These metal particles are mainly formed by the instantaneous melting of metal powder by the laser, generating metal vapor and plasma. The recoil pressure causes surrounding powder or droplets in the molten pool to sputter, forming splashed metal particles. Therefore, most research focuses on analyzing and improving the internal flow field of the sintering chamber to remove splashed metal particles.

[0003] Currently, most L-PBF printer sintering chamber designs primarily focus on optimizing the flow field through uniform airflow distribution. This is mainly achieved by optimizing the structure of the gas inlet, allowing the airflow from the upper and lower sides of the sintering chamber to exit simultaneously from a single return hood outlet. However, the convergence of the upper and lower airflows affects the uniformity and velocity of the lower airflow, thus weakening the ability of the airflow above the worktable to remove splashed metal particles, resulting in poorer print quality. Summary of the Invention

[0004] Based on the deficiencies of the existing technology, the present invention provides an air suction device for the sintering chamber of an L-PBF printer, which solves the problem that the convergence of the upper and lower airflows in the sintering chamber of the existing L-PBF printer affects the uniformity and speed of the lower airflow, thus weakening the ability of the airflow above the worktable to remove splashed metal particles and causing a deterioration in the quality of printed products.

[0005] The present invention adopts the following technical solution: This invention provides an air suction device for the sintering chamber of an L-PBF printer, comprising: The return air block is vertically arranged on the inner wall of the gas outlet near the bottom of the sintering chamber. The top and bottom of the return air block have the same length, and the width of the top is greater than the width of the bottom. The return air block has a vertically penetrating return air channel inside, which includes an upper channel and a lower channel. The longitudinal section of the upper channel is a right trapezoid with the upper base larger than the lower base, and the width of the lower channel gradually narrows from top to bottom. The outlet of the lower channel is connected to the return air hood of the sintering chamber. A rotating cylinder is mounted above the return air block by a drive device; the rotation direction of the rotating cylinder should be such that the linear velocity direction of the upper apex of the rotating cylinder is opposite to the direction of the airflow coming from the upper airflow entering the first gas inlet of the sintering chamber.

[0006] Preferably, the length of the rotating cylinder is greater than the length of the first gas inlet.

[0007] Preferably, the driving device includes: Two fixed plates are fixedly installed at both ends of the top of the return air block, and the rotating cylinder is rotatably installed between the two fixed plates through the transmission shafts at both ends; A fixing box is fixedly disposed on the outside of one of the fixing plates; The electric motor is located inside the fixed box, and its output end is connected to the drive shaft via a coupling.

[0008] Preferably, the distance between the return air block and the top plate of the sintering chamber is greater than the width of the first gas inlet.

[0009] Preferably, a gap is left between the top of the rotating cylinder and the top plate of the sintering chamber.

[0010] Preferably, the longitudinal section of the return air hood is a quarter circle, with the two right-angled sides corresponding to the second gas inlet and the airflow outlet of the sintering chamber, respectively, and the circular side corresponding to the return air channel that runs through and connects.

[0011] Compared with the prior art, the above-mentioned at least one technical solution adopted by the present invention can achieve the following beneficial effects: This invention features a return air channel and a rotating cylinder on the inner wall of the rear plate of the sintering chamber. When the airflow from above contacts the rotating cylinder, its velocity is significantly reduced because the airflow direction is opposite to the upward movement direction of the rotating cylinder, making it easier for the airflow to be drawn into the return air channel. A portion of the intercepted gas rotates downwards with the rotating cylinder and flows into the return air channel. The rotating cylinder creates a pressure difference between the inside and outside of the return air channel, further promoting the intake of the airflow from above. This invention eliminates the turbulence generated by the convergence of airflow directed towards the galvanometer (upper airflow) and airflow directed towards the worktable (lower airflow) in front of the return air hood, optimizing the flow field above the worktable. This improves the efficiency of airflow in removing splashed metal particles and simultaneously enhances the efficiency of the upper airflow in cleaning the galvanometer, ultimately improving the quality of the printed products. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a structural diagram of an air suction device for the sintering chamber of an L-PBF printer according to the present invention; Figure 2 This is a front view of the return air duct device of the present invention; Figure 3 This is an isometric view of the relative position of the return air duct device of the present invention in the sintering chamber; Figure 4 This is a cross-sectional view of the return air duct device of the present invention; Figure 5 This is the original model of the sintering chamber flow domain in this invention; Figure 6 This is a diagram of the return air duct-Magnus cylinder cooperative structure of the present invention; Figure 7 This is an overall diagram showing the location of the monitoring points in this invention; Figure 8 This is a side sectional view of the monitoring point location according to the present invention; Figure 9 This is a top sectional view showing the location of the monitoring points in this invention; Figure 10 This is a front sectional view of the monitoring point location according to the present invention; Figure 11 This is a graph showing the velocity statistics of the monitoring points for the grid-independent verification of the present invention. Figure 12 This is a vector diagram of the velocity in the middle plane of the sintering chamber in the original model of the present invention; Figure 13 This is a streamline diagram of the original model of the present invention, starting from the inlet above the sintering chamber; Figure 14 This is a vector diagram of the surface velocity near the powder bed in the original model of this invention; Figure 15 This is a streamline diagram of the original model of the present invention, starting from the inlet below the sintering chamber; Figure 16 This is a vector diagram of the velocity in the middle plane of the sintering chamber in the improved model of the present invention; Figure 17 This is a streamline diagram (side view) of the improved model of the present invention, starting from the upper inlet of the sintering chamber. Figure 18 This is a streamline diagram (top view) of the improved model of the present invention, starting from the inlet above the sintering chamber. Figure 19 This is a velocity vector diagram near the Magnus cylinder of the present invention; Figure 20 This is a streamline diagram near the Magnus cylinder of the present invention; Figure 21 This is a vector diagram of the sintering chamber velocity above the powder bed in this invention. Figure 22 This is a streamline diagram of the sintering chamber above the powder bed according to the present invention.

[0014] In the diagram: 1-Top plate, 2-Bottom plate, 3-Front plate, 4-Rear plate, 5-Left plate, 6-Right plate, 7-Galvanometer, 8-Worktable, 9-First gas inlet, 10-Second gas inlet, 11-Gas outlet, 12-Return air hood, 13-Return air block, 14-Rotating cylinder, 15-Upper flow channel, 16-Lower flow channel, 17-Fixed plate, 18-Fixed box, 19-Motor. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] The air intake principle of the sintering chamber in a traditional L-PBF printer: The sintering chamber includes a top plate 1, a bottom plate 2, a front plate 3, a rear plate 4, a left plate 5, and a right plate 6. A galvanometer 7 is mounted on the top plate 1 for laser emission. A worktable 8 is mounted on the bottom plate 2 for metal printing. The upper half of the front plate 3 has a first gas inlet 9, and the lower half has a second gas inlet 10. A gas outlet 11 is located at the end of the bottom plate 2 near the rear plate 4. A return air hood 12 is located on top of the gas outlet 11, with an inlet and an outlet, the outlet communicating with the gas outlet 11. The upper airflow enters through the first gas inlet 9 and blows towards the galvanometer. The lower airflow enters through the second gas inlet 10 and blows towards the worktable. Both the upper and lower airflows are drawn into the return air hood inlet and then drawn out by a negative pressure pump from the return air hood outlet.

[0017] This invention provides an air intake device for the sintering chamber of an L-PBF printer based on the Magnus effect, referring to... Figures 1-4 The design method breaks away from the traditional approach of relying solely on the return air hood at the bottom of the sintering chamber for air extraction. Instead, it adopts a sintering chamber extraction design that adds an air intake channel that blows air towards the galvanometer. This design is simple, reasonable, easy to install and use, and has high extraction efficiency.

[0018] Specifically, it includes a return air block 13 and a rotating cylinder 14. The return air block 13 is vertically positioned on the inner wall of the gas outlet 11 near the bottom of the sintering chamber, i.e., on the inner wall of the rear plate 4. The top and bottom of the return air block 13 have the same length, and the width of the top is greater than the width of the bottom. A return air channel is vertically oriented through the interior of the return air block 13. The return air channel includes an upper channel 15 and a lower channel 16. The longitudinal section of the upper channel 15 is a right-angled trapezoid. The back plate corresponding to the height of the right-angled trapezoid is in close contact with the rear plate 4 of the sintering chamber. The upper base of the right-angled trapezoid (i.e., the inlet end of the upper channel 15) is connected to the wall-mounted channel portion of the return air channel, ensuring that the airflow above the sintering chamber can be drawn into the return air channel. The inlet end of the lower channel 16 is connected to the outlet end of the upper channel 15. The width of the lower channel 16 gradually narrows from top to bottom, and the outlet end of the lower channel 16 is connected to the top of the return air hood 12.

[0019] A rotating cylinder 14 is rotatably mounted above the upper flow channel 15. Two fixed plates 17 are symmetrically arranged on the inner wall of the rear plate 4. The rotating cylinder 14 is rotatably mounted between the two fixed plates 17 via a drive shaft. A fixed box 18 is provided on the outer side of one fixed plate 17, and a motor 19 is located inside the fixed box 18. The motor 19 is connected to the drive shaft via a coupling, driving the rotating cylinder 14 to rotate. Drive shafts are located at both ends of the rotating cylinder 14 and are connected to the motor 19 via couplings to achieve cylinder rotation. Due to the Magnus effect, the rotating cylinder 14 creates a pressure difference inside and outside the return air flow channel, causing the airflow above the sintering chamber to be drawn into the return air flow channel. The bottom of the return air flow channel is connected to the top of the return air hood 12, allowing the gas in the return air flow channel to merge with the gas on the lower side of the sintering chamber before being drawn out from the outlet pipe. The rotation direction of the rotating cylinder should be such that the linear velocity direction of the upper apex of the rotating cylinder is opposite to the direction of the incoming airflow from the first gas inlet.

[0020] The rotating cylinder 14 is directly driven by the motor 19 through a coupling. The rotating cylinder 14 has transmission shafts at both ends, and bearings are installed on the transmission shafts at both ends. The return air hood is a structure with openings in three directions. The longitudinal section is a quarter circle. The two right-angled sides correspond to the airflow inlet below the sintering chamber and the total airflow outlet, respectively. The circular side corresponds to the gas inlet of the return air channel.

[0021] This invention eliminates the turbulence generated by the convergence of airflow towards the galvanometer (upper airflow) and airflow towards the worktable (lower airflow) in front of the return air hood, optimizing the flow field above the worktable. This improves the efficiency of airflow in removing splashed metal particles and also enhances the efficiency of the upper airflow in cleaning the galvanometer. Furthermore, an innovative roller-type suction device design at the intake of the airflow channel utilizes the Magnus effect to create a pressure difference from the outside to the inside of the channel, improving the intake efficiency. This optimizes the flow field within the sintering chamber, reducing metal particles adhering to the product. Ultimately, this leads to improved printed product quality.

[0022] The pressure value and distribution in the low-pressure region at the bottom of the Magnus cylinder significantly affect the air intake effect of the return air duct. The flow field around the Magnus cylinder can be simplified to an incompressible, two-dimensional, steady, irrotational, and inviscid flow with circulation around the Magnus cylinder (when the Magnus cylinder reaches a critical rotational speed, the wake vortex is completely eliminated, and the wake reaches a steady state). This flow field is composed of parallel flow (along... x The velocity potential function of the parallel flow around the cylinder without circulation (in the forward direction) and the counterclockwise point vortex flow (which simplifies the effect of the Magnus cylinder in causing the surrounding fluid to rotate as a point vortex plus a cylinder) are superimposed. According to this superposition principle, the velocity potential function of the parallel flow around the cylinder without circulation and the velocity potential function of the point vortex flow are superimposed to obtain the composite velocity potential function of the two-dimensional irrotational flow with circulation around the Magnus cylinder.

[0023] Velocity potential function and stream function for two-dimensional flow: (1); (2); In the formula, Let be the velocity potential function. For the incoming flow velocity, Given the radius of the cylinder of revolution, the flow field is described using polar coordinates with the center of the cylinder as the origin. Points in the flow field are represented by polar coordinates. express, For stream functions, x and y The flow field is described using a Cartesian coordinate system (with the origin at the center of the circle).

[0024] Velocity potential function and stream function of point vortex flow: (3); (4); In the formula, The vortex ring quantity is a point vortex.

[0025] The composite velocity potential function of a two-dimensional irrotational flow with circulation around a Magnus cylinder: (5); Similarly, by superimposing the stream function of the parallel flow around a cylinder without circulation in a two-dimensional flow and the stream function of the point vortex flow, we obtain the composite stream function of the two-dimensional irrotational flow with circulation around a cylinder: (6); From the velocity potential function, the velocity distribution function of the flow field is obtained as follows: (7); (8); In the formula, The radial velocity along the polar coordinate system, This represents the tangential velocity along the polar coordinate system.

[0026] For the surface of the Magnus cylinder, i.e. , The constant indicates that the circumference of the Magnus cylinder surface itself is a streamline; it meets the requirements of ideal fluid flowing in close contact with the cylinder surface. Based on the velocity distribution function in the flow field, the velocity distribution on the Magnus cylinder surface can be obtained as follows: (9); (Γ>0)(10); The pressure distribution on the surface of the Magnus cylinder can be derived from Bernoulli's equation. Substituting the velocity distribution on the surface of the Magnus cylinder into Bernoulli's equation, we can obtain the pressure distribution along the streamline of the Magnus cylinder as follows: (12); In the formula, p This refers to the pressure in the low-pressure region below the surface of the cylinder. For environmental pressure, The density is the gas density.

[0027] The above is a mathematical model of the flow field around a cylinder with circulation derived from potential flow theory. The mathematical model for measuring the air intake capacity of the Magnus cylinder is similar in principle to the above model, except that it has an additional boundary condition, namely... , ω is the angular velocity of the cylinder.

[0028] It is the difference between the ambient pressure and the pressure in the low-pressure area below the cylindrical surface, as shown in formula (13): (13); This formula is used to measure the pressure in the low-pressure region below the surface of a cylinder compared to the ambient pressure. It only generates suction on the surrounding airflow when the value is less than 0.

[0029] Integrating the streamlines on the surface of the Magnus cylinder yields: (14); Because the Magnus cylindrical flow mathematical model has one more boundary condition than the two-dimensional incompressible irrotational flow mathematical model of a cylindrical body with circulation (the cylinder is a rotating cylinder, the surface has a streamline, and the velocity on the streamline is...). There is one more restriction, namely .

[0030] <0 o'clock The range is the boundary range of the low-pressure region below the Magnus cylinder in contact with the cylinder, as shown in formula (15): (15); In the formula, This refers to the boundary area where the low-pressure region below the Magnus cylinder contacts the cylinder.

[0031] The purpose of determining the distribution range of the low-pressure region on the cylindrical surface is to provide a basis for later proof. , It is positively correlated with the range of the double integral at the bottom of the Magnus cylinder.

[0032] As can be seen from the above equation (13), the size of the low-pressure region on the surface of the Magnus cylinder is negatively correlated with the incoming flow velocity and also with the radius of the Magnus cylinder. angular velocity of rotation Positively correlated with fluid density It's irrelevant. Because of the low-pressure area below the cylinder. <0, therefore And because .so hour Finding the minimum value, which is the lowest pressure point in the low-pressure region on the lower surface of the Magnus cylinder, we obtain the formula for the minimum pressure on the lower surface of the Magnus cylinder:

[0033] (16); Directly Substituting into (13) yields the minimum pressure across the entire flow field.

[0034] According to formula (16), the absolute value of the minimum pressure on the lower surface of the Magnus cylinder is related to the inflow velocity. ,density Magnus cylinder radius All showed a positive correlation.

[0035] Formula (17) is the formula for the pressure coefficient in a steady inviscid flow field: (17); In the formula, This is the pressure coefficient.

[0036] This formula is used to determine the pressure distribution function across the entire flow field.

[0037] From formulas (7) and (8), we can obtain As shown in equation (18): (18); We can obtain the following from the pressure coefficient formula (17): (19); The pressure distribution across the entire flow field is obtained from the pressure coefficient formula (17), as shown in formula (20): (20); The pressure distribution function in the flow field is obtained from the pressure coefficient.

[0038] From formula (20), the minimum pressure in the entire flow field at the surface of the Magnus cylinder can be obtained. , Place.

[0039] <0 is the pressure description formula (21) for the region below the Magnus cylinder where the pressure is lower than the incoming flow pressure: (twenty one); This formula is used to measure the pressure in the low-pressure region below the surface of a cylinder compared to the ambient pressure. = It only generates suction on the surrounding airflow when the value is less than 0.

[0040] To better describe the strength of the suction force exerted on the airflow by the low-pressure region generated by the Magnus cylinder, Integrating over the region <0, we obtain formula (22): (twenty two); right Integrating the region <0 to measure the Magnus cylinder's suction capacity.

[0041] Equation (22) can accurately describe the suction force of the low-pressure region generated by the Magnus cylinder on the airflow above the sintering chamber, but it is difficult to obtain an analytical solution for equation (22). To prove the relationship between the suction force of the low-pressure region generated by the Magnus cylinder on the airflow and these parameters, we will now use: (twenty three); This formula proves The function has a monotonically increasing trend on r, Magnus cylinder surface The pressure is lowest at that point, and as r The pressure gradually increases.

[0042] Analysis of formula (23) yields the following results right r The partial derivatives are greater than or equal to 0.

[0043] make <0 The range is used to demonstrate that the range of the low-pressure region on the lower surface of Magnus is positively correlated with the range of the low-pressure region in the lower part of the Magnus cylinder: ; In the formula, a for , , .

[0044] This formula is used to obtain the pressure distribution function of the flow field where the value is less than... hour The range of , which is also the range of the double integral.

[0045] Solving for: (twenty four); (25); In the formula, This refers to the range of angles in the flow field below the ambient pressure.

[0046] Under the inviscid assumption, negative pressure regions are generated on both the upper and lower sides of the Magnus cylinder, but the negative pressure region generated at the bottom of the cylinder is larger, and the cylinder's air intake capacity depends only on the low-pressure region at the bottom of the cylinder (in the turbulence model simulation, a low-pressure region is not actually generated above the Magnus cylinder, so the air intake capacity is only related to the low-pressure region at the bottom).

[0047] in The region is located below the cylinder and is the low-pressure area beneath the Magnus cylinder. The range, because , The low-pressure area below the Magnus cylinder Scope and k Positively correlated (through the analysis of...) (This is proven by differentiation), therefore and Positively correlated, that is Follow It increases as it grows.

[0048] It is now proven that with Increase It increases accordingly: (26); Proof with Increase The function decreases overall, meaning it satisfies the definition of the derivative, therefore for Find the partial derivative.

[0049] Analysis of the formula shows that >0, but it should be noted that this condition must be met for it to be valid. Proved; It is now proven that with Increase It increases accordingly: (27); With The same logic applies to finding partial derivatives.

[0050] Analysis of the formula shows that >0, thus proven; Based on the above The derivative is greater than 0. The lowest value is The range of points obtained varies. and Positive correlation >0 and >0 In summary, the absolute value of the double integral and , Positive correlation.

[0051] And because of the radius of the Magnus cylinder angular velocity of rotation The radius of the Magnus cylinder is positively correlated with the range of the double integral in the low-pressure region below the Magnus cylinder and also positively correlated with the maximum value of the absolute value of the original expression. angular velocity of rotation and A positive correlation can be obtained from the mathematical model of the inviscid steady flow field in the Magnus cylinder; the suction capacity of the Magnus cylinder is related to the radius of the Magnus cylinder. angular velocity of rotation Positive correlation.

[0052] simulation.

[0053] Construction of the sintering chamber watershed for AM252 type L-PBF equipment.

[0054] Based on the actual dimensions of the sintering chamber of the AM252 L-PBF equipment, a geometric model was created using SolidWorks, such as... Figure 5 As shown, key components affecting airflow and particle movement, such as the sintering chamber, upper and lower airflow inlets and outlets, powder bed, and laser galvanometer, are retained, while irrelevant structures such as bolts and non-critical fillets are simplified to reduce computational load while ensuring simulation accuracy.

[0055] Coordinate system definition: The origin (0,0,0) is set at the center of the powder bed, the X-axis is the width direction of the sintering chamber, the Y-axis is vertically upward and perpendicular to the powder bed, and the Z-axis is the length direction of the sintering chamber. The geometric parameters of each key component are shown in Table 1.

[0056] Table 1 Specific Parameters Based on the flow field defects revealed by the original sintering chamber simulation, the structure was improved, such as... Figure 6As shown, the original structure, with its dual-inlet, single-outlet layout, resulted in mutual interference between the upper and lower airflows. The upper airflow, after impacting the backplate, was deflected and spiraled down to the powder bed, severely affecting particle removal. To address this, a return air duct was installed on the backplate of the sintering chamber to effectively separate the two airflows. Its narrow width prevents interference with laser processing. A Magnus cylinder and drive motor were installed at the top to enhance suction capacity. The bottom, located directly above the gas outlet, guides metal particles to the front baffle of the return air duct for collection. The structure is easy to disassemble and assemble, facilitating regular cleaning.

[0057] The key geometric parameters of the return air duct and the Magnus cylinder are shown in Table 2.

[0058] Table 2 Key geometric parameters of the return air duct and Magnus cylinder Reference Figure 6 The rotating Magnus cylinder generates a uniform and stable low-pressure zone at the inlet of the return air duct. This low-pressure zone, located at the inlet of the return air duct, increases the air intake of the return air duct and makes the airflow above the sintering chamber uniform and stable, increasing the flow velocity and allowing more splashed metal particles to enter the return air duct for collection, reducing the adhesion rate of particles on the sintering chamber wall. The airflow entering the return air duct is separated from the airflow below the sintering chamber, thereby reducing the influence of the airflow above the sintering chamber on the airflow below. At the same time, the direction of the return air duct is the same as the direction of the gas outlet of the sintering chamber and perpendicular to the airflow direction on the worktable surface, which can improve the exhaust efficiency of the sintering chamber outlet.

[0059] Grid division.

[0060] To balance computational accuracy and efficiency, a tetrahedral mesh was used to divide the sintering chamber model. Local meshing was performed on key areas that significantly affect airflow and particle movement, such as the laser scanning area, airflow inlet, exhaust outlet, powder bed surface, and around the Magnus cylinder, to ensure the accuracy of local flow field simulation.

[0061] To verify the independence of the mesh, refer to Figures 7-10 Nine monitoring points (A1-C) were set up at 23 mm and 253 mm above the powder bed. The monitoring points (A1-C3) located 23 mm above the powder bed focus on the local flow rate in the process-sensitive area, while the monitoring point (A1-C3) located 253 mm above the powder bed focuses on the flow rate in the process-sensitive area. -C The study focuses on the velocity changes in the low-velocity zone in the middle of the sintering chamber to reflect the development of the airflow within the sintering chamber. The distance between adjacent monitoring points is 89 mm, and the airflow velocity at 18 monitoring points is used as the verification indicator.

[0062] Calculations were performed on three schemes with different numbers of mesh elements: coarse mesh (5,136,962 elements), medium mesh (10,949,282 elements), and fine mesh (17,649,520 elements). Because the sintering chamber inlet structure is fan-shaped, the flow velocities at points A2, B2, and C2 in the middle of the bottom of the sintering chamber are significantly higher, while at point A... -C The flow velocity is relatively low because it is located in the turbulent zone of the sintering chamber, where the airflow velocity from the inlet decreases and the flow becomes dispersed. The velocity deviation between the medium and fine grids is less than 1%. Therefore, a medium grid scheme is used in this invention.

[0063] Reference Figure 11 The verification results show that when the coarse mesh is improved to a fine mesh, the maximum velocity difference is less than 1%, indicating that the coarse mesh scheme (5,136,962 elements) can meet the requirements of simulation accuracy and computational efficiency. Finally, the coarse mesh was used for subsequent simulations.

[0064] Fluid control equations.

[0065] This invention uses ANSYS Fluent as the numerical simulation platform. This software incorporates a mature Discrete Phase Model (DPM) and advanced dynamic mesh technology, effectively simulating the complex motion of metal spatter particles within the sintering chamber while capturing the low-pressure intake zone formed by the rotation of the Magnus cylinder. The protective gas (argon) in the sintering chamber is considered an incompressible Newtonian fluid, and its flow behavior is described by the continuity equation and the Reynolds-averaged Navier-Stokes (RANS) equations. The standard k-ε turbulence model is used to close the Reynolds stress term. This model is widely used in engineering turbulence simulation, exhibiting good computational stability and accuracy, and is suitable for the complex turbulent flow in the sintering chamber studied in this invention (the sintering chamber flow field is dominated by moderate-intensity turbulence, and the k-ε model can effectively capture airflow disturbances and vortex structures).

[0066] Mass conservation equation (continuity equation): ; Momentum conservation equation (Reynolds-averaged Navier–Stokes equation): ; In the formula, For gas density, For time-averaged velocity components, For pressure, For dynamic viscosity, This is the acceleration due to gravity.

[0067] Standard k-ε turbulence model equations: Turbulent kinetic energy k equation: ; Equation for dissipation rate ε: ; Eddy viscosity coefficient: ; The model constants are taken as standard values: , , , ;in This is the turbulent kinetic energy generation term produced by the average velocity gradient.

[0068] Discrete phase model.

[0069] The splashed metal particles are considered as discrete phases. The DPM model is used to track the particle trajectory. The particle material is titanium alloy (Ti-6Al-4V). Based on the actual working conditions of L-PBF forming, two typical particle sizes are selected: 0.2 mm (large particle size) and 0.05 mm (small particle size) to simulate the removal effect of particles of different sizes.

[0070] The particle motion follows the control equations and settings as follows: Particle force balance (orbit equations): ; Relative Reynolds number: ; Drag coefficient (standard spherical particle): The corresponding calculation formula is selected according to the relative Reynolds number range, which is suitable for simulating the motion of small particles with low Reynolds number.

[0071] Particle emission setup: A UDF (Unified Device Function) was used to control the movement of the particle emission sources, simulating the sweeping process of a laser across a powder bed. Parameters such as emission direction, number of emission sources, distance between emission sources, movement mode, and emission speed were set according to existing literature; the emission flow rate was set to 1×10⁻². 0 The value of kg / s was set by this invention based on the principle of tracer particles, aiming to simulate the splashing trajectory with tracer particles and avoid calculation divergence caused by excessive particle concentration. Each group of emission sources has five emission directions (vertical, 45° angle between the y-axis and the positive / negative x-axis, and 45° angle between the y-axis and the positive / negative z-axis). Each group has five single emission sources with a spacing of 89 mm. The emission velocities are 5 m / s and 10 m / s, moving linearly within the powder bed at the same direction and speed. The emission sources return at their original speed immediately after reaching the powder bed boundary. Simulations of both the same and opposite directions of laser sweeping and airflow are set according to existing literature.

[0072] Coupling method: The particle volume fraction is less than 1%, and the collision between particles is ignored. The continuous phase and the discrete phase are coupled in one direction (the airflow affects the particle motion, and the particle's influence on the airflow is negligible). This conforms to the principle of engineering simplification and will not affect the rationality of the core conclusions.

[0073] Boundary conditions and simulation parameters.

[0074] The fluid medium is argon gas, at room temperature (300 K), with a density of 1.6228 kg / m³ and a dynamic viscosity of mu = 2.125e-0.5 kg / (m*s) (at room temperature (300 K)). The upper and lower inlets of the sintering chamber are velocity inlets with a flow velocity of 5 m / s. The DPM boundary condition of the front plate of the return air channel is set to trap (capturing particles and simulating particle recovery). The DPM boundary condition of the inlet section of the return air hood at the sintering chamber outlet is set to escape (statistically escaping particles). The DPM boundary condition of the sintering chamber wall is set to trap. The DPM boundary condition at the powder bed is set to reflect (simulating the particle emission surface).

[0075] The Magnus cylinder rotation was handled using a sliding mesh method (to avoid negative volume errors in the moving mesh), with a rotation speed of 100 rad / s, a rotation center of (0, 0.362, -0.1575), and a rotation axis direction of (1, 0, 0). The total number of computation steps was 2400, with a time step of 0.001 s. The computation results were output every 100 steps, and the convergence process was monitored in real time.

[0076] Results and Analysis.

[0077] Simulation results of the original sintering chamber flow field show that it has significant flow defects, mainly manifested in the following four aspects: Reference Figure 12 and Figure 13 Interference between upper and lower airflows: The airflow above the sintering chamber is deflected after hitting the back plate and flows downward along the positive z-axis, opposite to the direction of the airflow at the lower inlet, forming obvious turbulence, which leads to overall flow field disorder and affects the directional removal of particles.

[0078] Reference Figure 14 and Figure 15 Uneven flow velocity on the powder bed surface: Due to the use of a grid to divert the flow at the lower inlet of the sintering chamber, some of the airflow impacts the grid and returns, forming vortices inside the inlet structure. This causes the flow velocity on the powder bed surface to exhibit a distribution characteristic of "high in the middle and low on both sides". The flow velocity at point B2 (center) is 1.575 m / s, while the flow velocities at points B1 and B3 (both sides) are 0.225 m / s and 0.246 m / s, respectively. The average difference is 1.34 m / s, which is not conducive to the uniform removal of splashed particles near the powder bed.

[0079] Inlet vortex energy loss: Due to the presence of the grille at the lower inlet, the airflow area is suddenly reduced, generating symmetrical vortices, resulting in airflow energy loss and reducing the inlet flow utilization efficiency.

[0080] Turbulent flow field near the laser galvanometer: The airflow velocity is uneven near the galvanometer, and the airflow is deflected after reaching the back plate, generating large-scale turbulence on both sides of the yz plane, covering the entire sintering chamber, causing particles to be blown to the wall for deposition or suspended for a long time.

[0081] Improved solution: Return airflow channel - smooth Magnus cylinder cooperative structure.

[0082] Reference Figures 16-18 The generation of turbulence in the flow field is reduced and the airflow is more rationally guided: The Magnus cylindrical air intake device effectively widens the airflow width upstream of the sintering chamber and guides most of the airflow directly into the return air channel through directional guidance, thereby reducing the generation of turbulence in the sintering chamber from the source and improving the overall stability of the flow field. The interference between the upper and lower airflows is reduced, and the stability of the flow field is improved: the airflow below the sintering chamber is deflected after encountering the front baffle, forming an upward trajectory along the surface of the baffle; at the same time, part of the airflow entering from the upper region is guided downward after hitting the baffle. The two opposing airflows converge in the middle of the sintering chamber, and their opposing momentum cancels each other out, effectively reducing their interference and further stabilizing the flow field.

[0083] Reference Figure 19 and Figure 20 The airflow distribution exhibits differentiated characteristics: as can be seen from the velocity vector diagram, the airflow above the sintering chamber is affected by the wall-attached flow generated by the rotating cylinder, and can smoothly enter the flow channel below the cylinder to achieve the air intake effect.

[0084] Reference Figure 21 and Figure 22 The uniformity of the powder bed flow field is significantly improved: Comparing the simulation results of the original model and the model with the flow guiding device, it can be seen that the airflow thickness above the powder bed is greater and the flow is more uniform; the flow velocity at point B2 in the sintering chamber powder bed is 1.347 m / s, the flow velocity at point B1 is 0.216 m / s, and the flow velocity at point B3 is 0.233 m / s. The average difference between the flow velocities at points B1 and B3 is 1.1225 m / s, which is lower than the average value of the original model, further verifying the improvement in the uniformity of the flow field.

[0085] Statistical analysis of the trajectory of splashed metal particles.

[0086] Table 3 Statistical Analysis Large-diameter particles, due to their greater momentum, are less affected by airflow. Their trajectory distribution and changes show significant differences under different operating conditions. Referring to Table 3, the specific statistical analysis for each operating condition is as follows: (a) Original sintering chamber operating conditions.

[0087] The original sintering chamber flow field had significant defects, resulting in low particle removal efficiency. Under this condition, 79.74% of large-diameter particles adhered to the sintering chamber wall, with no particles escaping from the sintering chamber outlet, and 8.2% remaining suspended inside the sintering chamber. Due to the large momentum of the particles, they easily adhered to the sintering chamber wall, significantly negatively impacting equipment contamination and L-PBF forming quality, failing to meet forming quality requirements.

[0088] (ii) Working condition of return air channel-smooth Magnus cylinder cooperative structure.

[0089] This synergistic structure significantly optimizes the removal and recovery of large-diameter particles. Compared with the original operating conditions, the wall adhesion rate decreased from 79.74% to 62.89%, a reduction of 16.85%; the suspension rate in the sintering chamber decreased from 8.20% to 4.18%, a reduction of 4.02%, reducing the number of particles trapped in the sintering chamber and minimizing the impact of metal particle mist on laser operation; simultaneously, 19.56% of the particles were effectively collected by the front plate of the return air duct, achieving directional capture and recovery of splashed particles.

[0090] Statistical analysis of the trajectory of small-diameter particles (0.05 mm) at a launch velocity of 5 m / s.

[0091] Small-diameter particles have low momentum and are greatly affected by airflow disturbances, easily forming suspended particle fog and attenuating laser energy. The core of the variation in their trajectory distribution under different operating conditions is the fluctuation of suspension rate, escape rate, and wall adhesion rate. Specific statistical analysis for each operating condition is as follows: (a) Original sintering chamber operating conditions.

[0092] Defects in the original sintering chamber flow field also resulted in poor removal of small-diameter particles. Under these conditions, 54.84% of the particles adhered to the wall surface, 33.73% were suspended in the chamber, with a suspension time of 0.866 s, and 11.44% of the particles escaped from the outlet. Due to their small size and low momentum, small-diameter particles easily aggregate to form a mist of suspended metal particles, which in turn attenuates the sintering laser energy and affects the forming quality.

[0093] (ii) Working condition of return air channel-smooth Magnus cylinder cooperative structure.

[0094] This collaborative structure offers some optimization for the removal of small-diameter particles, but limitations remain. Compared to the original operating conditions, the wall adhesion rate decreased from 54.84% to 50.76%, a reduction of 4.08%; 9.05% of the particles were collected by the front plate of the return air duct; the average particle residence time decreased from 0.866 s to 0.486 s, reducing the particle suspension time in the sintering chamber; the suspension rate in the sintering chamber decreased from 33.73% to 24.29%, a reduction of 9.44%, minimizing the impact of metal particle fog on the laser; and 15.89% of the particles escaped at the sintering chamber outlet, an improvement of 4.45% compared to the original sintering chamber model.

[0095] Statistical analysis of the trajectory of small-diameter particles (0.05 mm) at an emission velocity of 10 m / s.

[0096] Small-diameter particles have low mass and are greatly affected by the plume near the molten pool, generating splashed metal particles that are difficult to remove. Specific statistical analysis for each working condition is as follows: (a) Original sintering chamber operating conditions.

[0097] Under these conditions, 53.64% of the particles adhered to the wall surface, 35.76% were suspended in the chamber, with a suspension time of 0.791 s, and 10.6% of the particles escaped from the outlet. Due to the small size and high velocity of the small-diameter particles, they splashed in the sintering chamber and were difficult to collect, resulting in more particles remaining in the sintering chamber.

[0098] (ii) Working condition of return air channel-smooth Magnus cylinder cooperative structure.

[0099] Compared with the original operating conditions, the wall adhesion rate decreased from 53.64% to 45.51%, a decrease of 8.13%, which significantly reduced the adhesion rate of the sintering chamber wall; 10.71% of the particles were collected by the front plate of the return air channel; the average particle residence time decreased from 0.791 s to 0.609 s, which reduced the suspension time of particles in the sintering chamber; the suspension rate in the sintering chamber decreased from 35.76% to 31.69%, a decrease of 4.07%, which reduced the impact of metal particle fog on the laser; 12.1% of the particles escaped at the sintering chamber outlet, which was 1.5% higher than the original sintering chamber model, but the difference was small and there was still considerable room for improvement.

[0100] The upper airflow inlet of the sintering chamber is located at the front end of the Magnus cylinder. Therefore, the low-pressure zone generated by the Magnus cylinder directly affects the flow state of the airflow above the sintering chamber. The function of the airflow above the sintering chamber is to remove metal particles near the galvanometer. The uniform low-pressure zone generated by the Magnus cylinder increases the airflow velocity and maintains airflow uniformity, reduces turbulent dissipation, and enhances the airflow removal effect. Increasing the cylinder radius... angular velocity of rotation It can improve the suction capacity of the Magnus cylinder device and the air removal effect of the airflow above the sintering chamber, and increase the flow rate of the airflow above the sintering chamber into the return air channel, thereby avoiding mutual interference between the airflows above and below the sintering chamber and affecting the metal particle removal rate.

[0101] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0102] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A suction device for the sintering chamber of an L-PBF printer, characterized in that, include: The return air block (13) is vertically arranged on the inner wall of the gas outlet (11) near the bottom of the sintering chamber. The top and bottom of the return air block (13) have the same length, and the width of the top is greater than the width of the bottom. The return air block (13) has a return air channel extending vertically through its interior. The return air channel includes an upper channel (15) and a lower channel (16) that are connected. The longitudinal section of the upper channel (15) is a right trapezoid with the upper base larger than the lower base. The width of the lower channel (16) gradually narrows from top to bottom. The outlet of the lower channel (16) is connected to the return air hood (12) of the sintering chamber. The rotating cylinder (14) is rotated and positioned above the return air block (13) by a drive device; the rotation direction of the rotating cylinder (14) should be such that the direction of the linear velocity of the top of the rotating cylinder (14) is opposite to the direction of the airflow coming from the first gas inlet (9) of the sintering chamber.

2. The air suction device for the sintering chamber of an L-PBF printer as described in claim 1, characterized in that, The length of the rotating cylinder (14) is greater than the length of the first gas inlet (9).

3. The air suction device for the sintering chamber of an L-PBF printer as described in claim 1, characterized in that, The driving device includes: Two fixed plates (17) are fixedly installed at both ends of the top of the return air block (13), and the rotating cylinder (14) is rotatably installed between the two fixed plates (17) through the transmission shafts provided at both ends; A fixing box (18) is fixedly disposed on the outside of a fixing plate (17); The electric motor (19) is located inside the fixed box (18), and its output end is connected to the drive shaft via a coupling.

4. The air suction device for the sintering chamber of an L-PBF printer as described in claim 1, characterized in that, The distance between the return air block (13) and the top plate (1) of the sintering chamber is greater than the width of the first gas inlet (9).

5. The air suction device for the sintering chamber of an L-PBF printer as described in claim 1, characterized in that, A gap is left between the top of the rotating cylinder (14) and the top plate (1) of the sintering chamber.

6. The air suction device for the sintering chamber of an L-PBF printer as described in claim 1, characterized in that, The return air hood (12) has a longitudinal section of a quarter circle, with two right-angled sides corresponding to the second gas inlet (10) and the air outlet (11) of the sintering chamber, respectively, and the circular side corresponding to the return air channel that runs through it.

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