Drop tube metal microdroplet deposition device and method for simulating space environment

Abstract

The invention discloses a drop tube metal microdroplet deposition device and method for simulating a space environment. The device comprises a drop tube; a metal microdroplet nozzle is mounted at the top of the drop tube, a composite substrate is arranged below the metal microdroplet nozzle, a replaceable tested substrate is arranged in the middle of the composite substrate, and two ends of the composite substrate are matched with a release mechanism arranged on the inner wall of the drop tube; a transparent window is arranged on the side wall of the drop tube below the composite substrate, and an image collecting device is arranged on one side of the window; when the metal liquid drops of the experimental metal material start to fall off from the metal micro-drop spray head, controlling the release mechanism to release the composite substrate after a preset time; the metal liquid drops and the composite substrate are pursued and contacted in a weightlessness falling state, are captured and recorded by the image acquisition device through the window, and then are transmitted to the upper computer for subsequent analysis. The technical problem that in the prior art, the contact solidification process of the metal liquid drops and the substrate in the space microgravity environment cannot be truly simulated on the ground is solved.

Description

Technical Field

[0001] This invention belongs to the field of ground simulation technology for space manufacturing, specifically relating to a droplet metal deposition device and method for simulating the space environment. It is used to study the deposition behavior and final solidification morphology of metal droplets under microgravity environment on the ground, thereby providing a basis for on-orbit 3D printing of metal droplets in space. Background Technology

[0002] Uniform metal droplet jetting technology is considered to have potential applications in future on-orbit metal 3D printing in space due to its low energy consumption and high material utilization. This technology generates uniformly sized metal droplets using a droplet generator and controls their precise deposition, fusion, and solidification on a substrate, thus "stacking" layers together to form three-dimensional components. However, to reliably apply this technology to the microgravity environment of space, it is essential to first deeply understand the influence of microgravity on the deposition behavior of metal droplets on Earth. In this process, the dynamic behavior of the metal droplets at the moment of contact with the substrate, the spreading process, and the final solidification morphology directly determine the forming accuracy and mechanical properties of the printed parts.

[0003] In a microgravity environment, the effects of gravity are significantly reduced, making the dominant factors such as interfacial tension, wettability, and solidification kinetics between droplets and substrates more prominent. The contact characteristics between metal droplets and substrates, especially their dynamic spreading behavior and final solidification angle, differ significantly from those under normal gravity conditions on Earth. Therefore, accurately acquiring data on the contact characteristics of metal droplets under microgravity is crucial for predicting and optimizing space printing processes. However, conducting direct on-orbit experiments is extremely costly and limited in opportunities, making the development of reliable ground-based simulation methods an inevitable choice.

[0004] Currently, ground-based methods for studying the solidification behavior of liquid metal droplets mainly fall into two categories: one is to characterize the macroscopic morphology of the solidified sample and measure the solidification angle; the other is to use high-speed photography to record the dynamic process of droplet collision, spreading, and solidification. (See references) Contact line arrest in solidifying spreading drops, (2017) However, existing ground-based experimental devices have a fundamental limitation: they cannot eliminate the influence of gravity on both the droplet and the substrate. This makes the contact conditions between the droplet and the substrate fundamentally different from the real situation in space where both are in a state of weightlessness.

[0005] To circumvent the difficulties of microgravity experiments, some researchers have attempted to use a scaled-down model method, employing small droplets (e.g., 10 μm) under conventional terrestrial gravity to simulate the behavior of large droplets (e.g., 1 mm) under microgravity. However, this method is only effective for non-solidifying fluids. For metal droplets, the cooling and solidification rate is closely related to the droplet size (the cooling rate is approximately inversely proportional to the square of the droplet radius, i.e., ...). Size differences will lead to completely different solidification paths and microstructures, so scaled-down models cannot accurately reflect the solidification characteristics of molten metal droplets under microgravity.

[0006] In summary, existing technologies lack a comprehensive experimental device capable of simulating the contact between molten metal droplets and a substrate under microgravity conditions on the ground, and simultaneously conducting dynamic observation of the contact process and static characterization of the solidified sample. Summary of the Invention

[0007] The purpose of this invention is to provide a droplet metal microdroplet deposition device and method that simulates the space environment, in order to solve the technical problem that the existing technology cannot realistically simulate the contact and solidification process of metal droplets with a substrate under the microgravity environment of space on the ground.

[0008] To achieve the above objectives, the present invention employs the following technical solution: A droplet deposition device for metal microparticles in a simulated space environment includes a droplet tube; a metal microparticle nozzle is mounted on the top of the droplet tube, a composite substrate is disposed below the metal microparticle nozzle, a replaceable test substrate is disposed in the middle of the composite substrate, and both ends of the composite substrate cooperate with release mechanisms disposed on the inner wall of the droplet tube; a transparent window is disposed on the side wall of the droplet tube below the composite substrate, and an image acquisition device is disposed on one side of the window; when the metal droplets of the experimental metal material begin to fall from the metal microparticle nozzle, the release mechanism is controlled to release the composite substrate after a preset time; the metal droplets and the composite substrate chase and contact each other under weightless falling conditions, and the image acquisition device captures and records the data through the window and transmits it to a host computer for subsequent analysis.

[0009] Furthermore, the release mechanism includes a set of electromagnets symmetrically arranged on the inner wall of the drop tube and a set of guide rods; wherein, the guide rods have an L-shaped structure, with the shorter end fixed to the inner wall of the drop tube and the longer end pointing downwards from the drop tube and parallel to the axis of the drop tube.

[0010] Furthermore, the two ends of the composite substrate are adsorption end blocks that cooperate with electromagnets, and the adsorption end blocks are provided with guide holes that cooperate with the guide rod; the middle part of the composite substrate is a replaceable test substrate, and the test substrate is mechanically connected to the adsorption end blocks at both ends. In the release mechanism, the longer end of a set of guide rods passes through the guide holes of the adsorbable end blocks at both ends of the composite substrate, and then an electromagnet is used to adsorb the adsorbable end blocks to fix the position of the composite substrate; the electromagnet is controlled by the host computer.

[0011] Furthermore, a crucible is installed inside the metal droplet nozzle for filling the experimental metal material; the crucible is induction heated by an induction heating chamber to melt the experimental metal material; a pulse generator is installed inside the host computer, which is connected to the piezoelectric ceramic inside the metal droplet nozzle; the pulse generator generates pulses through a preset timing program, and the vibration of the piezoelectric ceramic disperses the molten metal into uniform droplets; then, under the pressure of the back pressure gas path, the metal droplets are ejected from the metal droplet nozzle; the initial velocity of the metal droplets is controlled by adjusting the pressure.

[0012] Furthermore, the environmental control system includes a first inert gas source, an overpressure relief valve, and a vacuum pump unit, wherein: The first inert gas source is connected to the inside of the drop pipe through the first pipeline, and a first gas flow meter and a third vacuum valve are installed on the first pipeline; the vacuum pump unit is connected to the inside of the drop pipe through the second pipeline, and a first vacuum valve is installed on the second pipeline; the overpressure relief valve is connected to the inside of the drop pipe through the third pipeline.

[0013] Furthermore, a cooling circulating water circuit provides cooling protection for the piezoelectric ceramic inside the metal microdroplet nozzle; one end of the back pressure gas circuit is connected to the interior of the metal microdroplet nozzle, and the other end is connected to a second inert gas source; a second gas flow meter and a second vacuum valve are also installed on the back pressure gas circuit.

[0014] Furthermore, a first transition door that can be opened and closed is installed on the side wall above the drop tube. After opening the first transition door, the composite substrate can be disassembled and replaced. A second transition door that can be opened and closed is installed on the side wall below the drop tube. After opening the first transition door, the composite substrate can be recovered and the bottom buffer material inside the drop tube can be replaced.

[0015] A method for depositing metal microdroplets in a drop tube to simulate a space environment includes: Step 1: Install the test substrate on the composite substrate, then insert the composite substrate into the drop tube, pass the guide rod in the release mechanism through the guide holes at both ends of the composite substrate, and use an electromagnet to firmly attract the composite substrate; fill the experimental metal material into the crucible of the metal microdroplet nozzle, and install and fix the metal microdroplet nozzle on the top of the drop tube. Step 2: Close the first transition chamber door, the second transition chamber door, the second vacuum valve, and the third vacuum valve. Then, turn on the vacuum pump unit and the first vacuum valve to evacuate the inside of the drop tube to the preset level. After that, turn off the vacuum pump unit and the first vacuum valve, open the third vacuum valve, and fill the tube with inert gas through the first inert gas source until the overpressure release valve detects that the inside of the drop tube has reached positive pressure and the oxygen content has stably dropped below the preset concentration. Then, turn off the first inert gas source and the three vacuum valves. Step 3: Activate the cooling circulation system and induction heating chamber to melt the experimental metal material inside the metal droplet nozzle; then, activate the second vacuum valve and adjust the back pressure gas path to the specified pressure through the second inert gas source; at this time, the host computer executes the preset timing program, controls the piezoelectric ceramic to vibrate through the trigger pulse generator to disperse the molten metal into uniform droplets, causing the nozzle to generate metal droplets, and controls the release mechanism to release the composite substrate after a preset time; the entire process of dynamic contact, spreading and solidification of the metal droplets and the composite substrate is captured and recorded in real time through an image acquisition device and a viewing window, and the image data is transmitted to the host computer.

[0016] Furthermore, the method for determining the preset time is as follows: First, a microgravity overlapping motion model is established for the device, and its contact criterion is constrained by both geometric relationships and the droplet falling dynamics equation; the initial velocity of the metal droplet and the distance parameters between the composite substrate and the metal droplet nozzle are determined. Secondly, the total mechanical / electrical response time from the issuance of the control command from the host computer to the actual ejection of the metal droplets and the actual release of the composite substrate was measured. Finally, the response time is compensated into the microgravity overlapping motion model, and the initial velocity and distance parameters are input to obtain a preset time; this means that after the metal droplets are ejected, the release mechanism is triggered after the preset time to release the composite substrate.

[0017] Furthermore, after the experiment, the composite substrate with metal droplets adhering to it fell onto the buffer material at the bottom of the drop tube and was recovered through the second transition chamber door. Subsequently, the recovered composite substrate was subjected to macroscopic morphological characterization, solidification angle measurement and microstructure analysis to obtain its final solidification morphology.

[0018] Compared with the prior art, the present invention has the following technical features: 1. Through synergistic release technology, the chasing and contact conditions between metal droplets and heterogeneous substrates under microgravity were realistically reproduced.

[0019] 2. It integrates two methods: high-speed camera dynamic observation and static characterization of solidified samples, enabling a comprehensive study of the complete laws from dynamic processes to final morphology.

[0020] 3. The type, size, collision speed, substrate material, and roughness of the metal droplets can all be flexibly adjusted, making it widely applicable.

[0021] 4. The entire process is highly automated, and the data is quantifiable and the experiments are reproducible. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall structure of the device of the present invention; Figure 2 This is a flowchart of the experimental operation steps in an embodiment of the present invention; Figure 3 This is a schematic diagram of the microgravity deposition process of metal droplets in an embodiment of the present invention.

[0023] Explanation of reference numerals in the attached drawings: 1. Metal microdroplet nozzle; 2. Electromagnet; 3. Composite substrate; 4. Pulse generator; 5. Host computer; 6. Induction heating box; 7. Cooling circulation system; 8. Viewing window; 9. Image acquisition device; 10. Light source; 11. Vacuum pump group; 12-1 First inert gas source; 12-2 Second inert gas source; 13-1 First vacuum valve; 13-2 Second vacuum valve; 13-3 Third vacuum valve; 14. Overpressure relief valve; 15. Buffer material; 16-1 First gas flow meter; 16-2 Second gas flow meter; 17-1 First transition chamber door; 17-2 Second transition chamber door; 18. Guide rod. Detailed Implementation

[0024] See Figure 1 This invention provides a droplet deposition device for metal microparticles in a simulated space environment, comprising a droplet tube; a metal microparticle nozzle 1 is mounted on the top of the droplet tube, a composite substrate 3 is disposed below the metal microparticle nozzle 1, a replaceable test substrate is disposed in the middle of the composite substrate 3, and both ends of the composite substrate 3 cooperate with release mechanisms disposed on the inner wall of the droplet tube; a transparent window 8 is disposed on the side wall of the droplet tube below the composite substrate 3, and an image acquisition device 9 is disposed on one side of the window 8; when the metal droplets of the experimental metal material begin to fall from the metal microparticle nozzle 1, the release mechanism is controlled to release the composite substrate 3 after a preset time; the metal droplets and the composite substrate 3 chase and contact each other in a weightless falling state, and the image acquisition device 9 captures and records the data through the window and transmits it to the host computer 5 for subsequent analysis. The specific design process of this invention will be further described in detail below with reference to the accompanying drawings.

[0025] 1. Main body.

[0026] The main body of the present invention includes a drop tube, which may be a tubular component made of stainless steel and has a closed structure; the lower end of the drop tube is fixed to the base, and a buffer material 15 is provided at the bottom inside the drop tube for receiving the composite substrate 3 with metal droplets adhering to it.

[0027] A metal micro-droplet nozzle 1 is installed at the top of the drop tube. The release mechanism below the metal micro-droplet nozzle 1 includes a set of electromagnets 2 symmetrically arranged on the inner wall of the drop tube and a set of guide rods 18. The guide rods 18 are L-shaped, with the shorter end fixed to the inner wall of the drop tube and the longer end pointing downwards and parallel to the axis of the drop tube.

[0028] The viewing window 8 is located in the lower middle part of the side wall of the drop tube, below the composite substrate 3; the axial range of the viewing window 8 should be set according to the actual calculation results and observation requirements; the material of the viewing window 8 can be high-pressure resistant glass. One side of the viewing window 8 is the image acquisition device 9, which is a high-speed camera in this embodiment; the other side of the viewing window 8 is the light source 10, thereby providing a clear and bright field of view for the image acquisition device 9 during the acquisition process.

[0029] 2. Composite substrate.

[0030] The composite substrate 3 has two adsorption end blocks at both ends that cooperate with the electromagnet 2. These end blocks can be made of low-carbon steel, for example. The adsorption end blocks have guide holes that cooperate with the guide rod 18. The middle part of the composite substrate 3 is a replaceable test substrate, which is the substrate on which the metal droplet deposition characteristics to be studied are to be set. It can be set according to actual needs, such as aluminum alloy, tin-lead alloy, etc. The test substrate is mechanically connected to the adsorption end blocks at both ends. In one possible implementation, the adsorption end blocks and the test substrate are connected by bolts.

[0031] During the installation of the composite substrate 3, the longer end of a set of guide rods 18 in the release mechanism is passed through the guide holes of the adsorbable end blocks at both ends of the composite substrate 3. Then, the adsorbable end blocks are adsorbed by the electromagnet 2 to fix the position of the composite substrate 3. When the electromagnet 2 is de-energized, the composite substrate 3 is unrestrained and falls freely. The cooperation between the guide rods 18 and the guide holes allows it to remain horizontal during the fall.

[0032] The switching on and off of the electromagnet 2 is controlled by the host computer 5 through port two.

[0033] 3. Metal microdroplet nozzle.

[0034] The piezoelectric ceramic metal droplet nozzle 1 contains a crucible for filling with experimental metal materials. The metal droplet nozzle 1 is induction heated by an induction heating box 6 to melt the experimental metal materials. The host computer 5 contains a pulse generator 4, which is connected to the piezoelectric ceramic inside the metal droplet nozzle 1 via port 1. The pulse generator 4 generates pulses according to a preset timing program, using the vibration of the piezoelectric ceramic to disperse the molten metal into uniform droplets. Then, under the pressure of the back pressure gas path, the metal droplets are ejected from the metal droplet nozzle 1. The initial velocity of the metal droplets can be controlled by adjusting the pressure.

[0035] The device is also equipped with a cooling circulation system 7, which provides cooling protection for the piezoelectric ceramic inside the metal microdroplet nozzle 1 through a cooling circulation water path; in addition, one end of the back pressure gas path is connected to the inside of the metal microdroplet nozzle 1, and the other end is connected to the second inert gas source 12-2; a second gas flow meter 16-2 and a second vacuum valve 13-2 are also installed on the back pressure gas path.

[0036] 4. Environmental control system.

[0037] The environmental control system in this scheme includes a first inert gas source 12-1, an overpressure relief valve 14, and a vacuum pump unit 11, wherein: The first inert gas source 12-1 is connected to the inside of the drop pipe through the first pipeline, and the first gas flow meter 16-1 and the third vacuum valve 13-3 are installed on the first pipeline; the vacuum pump group 11 is connected to the inside of the drop pipe through the second pipeline, and the first vacuum valve 13-1 is installed on the second pipeline; the overpressure relief valve 14 is connected to the inside of the drop pipe through the third pipeline.

[0038] 5. Assembly / disassembly mechanism.

[0039] A first transition door 17-1 that can be opened and closed is installed on the side wall above the drop tube. After opening the first transition door 17-1, the composite substrate 3 can be disassembled and replaced. A second transition door 17-2 that can be opened and closed is installed on the side wall below the drop tube. After opening the first transition door 17-1, the composite substrate 3 can be recovered and the cushioning material 15 can be replaced.

[0040] Based on the above technical solution, the present invention further provides a method for depositing metal microdroplets in a tube to simulate a space environment, comprising the following steps: The first phase is preparation and installation.

[0041] First, the test substrate is installed on the composite substrate 3. Then, the composite substrate 3 is loaded into the drop tube through the first transition chamber 17-1. The guide rod 18 in the release mechanism passes through the guide holes at both ends of the composite substrate 3, and the composite substrate 3 is firmly attracted by the electromagnet 2. The experimental metal material is filled into the crucible of the metal microdroplet nozzle 1, and the metal microdroplet nozzle 1 is installed and fixed on the top of the drop tube.

[0042] The second stage is environmental control.

[0043] To ensure that molten metal droplets are generated and deposited in a clean, inert atmosphere, the drop tube needs to be evacuated and purged. The first transition chamber door 17-1, the second transition chamber door 17-2, the second vacuum valve 13-2, and the third vacuum valve 13-3 are closed. Then, the vacuum pump unit 11 and the first vacuum valve 13-1 are turned on to evacuate the inside of the drop tube to a vacuum level of 10. - The pressure is on the order of ³ Pa. Subsequently, the vacuum pump group 11 and the first vacuum valve 13-1 are shut off, and the third vacuum valve 13-3 is opened. Inert gas is introduced into the pipe through the first inert gas source 12-1. A gas washing strategy of first flushing with a large flow rate and then maintaining with a small flow rate is adopted until the overpressure release valve 14 detects that the inside of the pipe reaches a slightly positive pressure and the oxygen content is stably reduced to below 30 ppm (usually about 40 minutes) to meet the requirements of metal droplet ejection. After that, the first inert gas source 12-1 and the three vacuum valves 13-3 are shut off.

[0044] The third stage involves experimental execution and dynamic observation.

[0045] The cooling circulation system 7 and the induction heating box 6 are activated to melt the experimental metal material inside the metal droplet nozzle 1. Then, the second vacuum valve 13-2 is opened, and the back pressure gas path is adjusted to a specified pressure (0.6~1.2 kPa) via the second inert gas source 12-2. At this time, the host computer 5 executes a preset timing program, triggering the pulse generator 4 and using port one to control the vibration of the piezoelectric ceramic to disperse the molten metal into uniform droplets, causing the nozzle 1 to generate metal droplets. After a preset time, the composite substrate 3 is released via port two through the release mechanism. This aims to precisely control the release timing of the metal droplets and the substrate, utilizing the brief microgravity environment provided during the descent to achieve contact between the two under "weightless conditions." The entire process of dynamic contact, spreading, and solidification is recorded in real-time by the image acquisition device 9 and the viewing window 8, and the image data is transmitted to the host computer 5. The initial velocity of the metal droplets can be controlled by adjusting the pressure of the back pressure gas path.

[0046] The method for determining the preset time is as follows: First, a microgravity overlap motion model is established for the device, and its contact criterion is based on geometric relationships and the droplet falling dynamics equations. Heat transfer of micro-droplet during free fall in drop tube , (2018) Joint constraints; determine the initial velocity of the metal droplets and the distance parameters between the composite substrate 3 and the metal microdroplet nozzle 1.

[0047] Secondly, the total mechanical / electrical response time from the issuance of the control command from the host computer 5 to the actual ejection of the metal droplets and the actual release of the composite substrate 3 was measured.

[0048] Finally, the response time is compensated into the microgravity overlapping motion model, and the initial velocity and distance parameters are input to obtain an accurate timing delay as the preset time; wherein the preset time means that after the metal droplet is ejected, the release mechanism is triggered after the preset time to release the composite substrate 3.

[0049] The fourth stage involves sample recovery and static analysis.

[0050] After the experiment, the composite substrate 3 with metal droplets adhering to it falls onto the buffer material 15 at the bottom of the drop tube and can be recovered through the second transition chamber door 17-2. Subsequently, the recovered composite substrate 3 is subjected to macroscopic morphological characterization, solidification angle measurement and microstructure analysis to obtain its final solidification morphology.

[0051] Example: This embodiment focuses on the deposition of tin-lead eutectic alloy (Sn-37Pb) on a 6061 aluminum alloy substrate.

[0052] I. Specific configuration and parameters of the device.

[0053] Main structure: The drop tube is made of 304 stainless steel, with an inner diameter of 180 mm, a wall thickness of 8 mm, and a total height of 2.5 m. It can provide an effective microgravity time window of about 0.71 seconds in the 8 viewing windows.

[0054] Guiding mechanism: Two high-strength stainless steel guide rods 18 with a diameter of 4 mm and a parallelism error of ≤0.1 mm / m are vertically installed inside the tube.

[0055] The composite substrate 3 has a total size of 60 mm (length) × 20 mm (width). The adsorption end blocks on both sides are made of low carbon steel, and each adsorption end block is 20 mm long. The center of each adsorption end block is machined with a guide hole with a diameter of 5 mm, which forms a sliding fit with the guide rod 18 with a single-sided gap of about 1 mm. The test substrate is made of 6061 aluminum alloy substrate with a size of 20 mm × 20 mm × 10 mm (thickness) and the surface is polished to a roughness Ra of 0.4 μm.

[0056] Microdroplet injection and temperature control system: The induction heating coil is made of 5 turns of 5 mm copper tube (inner diameter ~24 mm, height ~50 mm), driven by a 10 kW induction heating box 6, which can heat 30 grams of tin-lead alloy to 280°C in 2 minutes.

[0057] The metal microdroplet nozzle 1 is equipped with a dedicated cooling system 7 (3P, model JZ-3000) to ensure that the temperature of the core components is below 20°C during continuous operation.

[0058] Electromagnets 2 are symmetrically mounted on the tube wall, with an adsorption surface width of 30 mm, and are used to firmly adsorb the composite substrate 3 before the experiment.

[0059] II. Step-by-step experimental procedure and core operations.

[0060] The composite substrate 3 is inserted through the first transition chamber 17-1, and its guide hole is fitted into the guide rod 18 and fixed by electromagnet 2; 30 grams of tin-lead alloy is filled into the crucible of the metal microdroplet nozzle 1; after completion, the first transition chamber 17-1 and the second transition chamber 17-2 are sealed.

[0061] Vacuuming: Start vacuum pump unit 11 and first vacuum valve 13-1 to evacuate the inside of the drop pipe to a high vacuum (≤5.0×10). - ³ Pa).

[0062] Gas washing: Close the first vacuum valve 13-1 and the second vacuum valve 13-2, and introduce high-purity argon gas (purity >99.999%, first inert gas source 12-1).

[0063] After flushing with a high flow rate of 25 kgf / cm² (approximately 2.45 MPa) for 2 minutes, the pressure was reduced to 5 kgf / cm² (approximately 0.49 MPa). A slight positive pressure (+1.0 kPa) was maintained in the pipe through the high-pressure relief valve 14, and the gas was continuously flushed for 40 minutes until the oxygen content was stabilized below 30 ppm.

[0064] III. Implementation and dynamic monitoring of core processes.

[0065] This step, which integrates pre-set processes, model calculations, and systematic error correction, is crucial to the success of the experiment.

[0066] Preset process parameters: To achieve uniform tin-lead droplets with a diameter of ~1 mm, the injection parameters are set as follows: nozzle diameter 400 μm, back pressure 2.0 kPa (second inert gas source 12-2), drive pulse width 1800 μs, and voltage 3.257 V. Under these conditions, the initial droplet velocity... V 0 is approximately 0.11 m / s.

[0067] Final parameters: In this embodiment, the distance between the composite substrate 3 and the metal droplet nozzle 1 is used when establishing the microgravity overlapping motion model. S =58mm, response time is 66 ms; the calculated final preset time (timing delay) is =171 ms.

[0068] Execution and Recording: =171 ms input control program; after the alloy melts and is held at a certain temperature for 10 minutes, the cooling and back pressure (2.0 kPa) are turned on in sequence; the program is executed, and at the same time the high-speed camera (10000 fps) is started to record the whole process through window 8.

[0069] IV. Sample recovery and effect verification.

[0070] After the experiment, the composite substrate 3 with deposited tin-lead alloy was recovered under an inert atmosphere. Image analysis software determined the solidification angle obtained in this experiment to be 61.0°. For direct comparison, under the same droplet material (tin-lead alloy), similar substrate (aluminum alloy), and collision velocity (Weber number), the typical solidification angle value in conventional gravity ground experiments is approximately 52.9°. The result of this experiment is consistent with the trend of a larger solidification angle under microgravity. Therefore, this device successfully achieved the ground simulation target.

[0071] V. Key Methods and Extended Applications

[0072] System calibration method: For new metallic material systems, it is recommended to follow the principle of "process calibration first, then system correction": Process optimization: Conduct 3-5 spraying experiments under constant gravity to determine the optimal process parameters for producing stable and uniform droplets.

[0073] Response retest: After changing the materials, the response time under this process needs to be retested.

[0074] Parameter update: Substitute the new material properties and measured response time into the aforementioned microgravity overlapping motion model to generate a new time delay. This is to ensure the reliability of the first pulse.

[0075] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A droplet deposition device for metal microdroplets in a simulated space environment, characterized in that, The system includes a drop tube; a metal microdroplet nozzle (1) is installed at the top of the drop tube, a composite substrate (3) is provided below the metal microdroplet nozzle (1), a replaceable test substrate is provided in the middle of the composite substrate (3), and the two ends of the composite substrate (3) are engaged with a release mechanism provided on the inner wall of the drop tube; a transparent window (8) is provided on the side wall of the drop tube below the composite substrate (3), and an image acquisition device (9) is provided on one side of the window (8); when the metal droplets of the experimental metal material start to fall from the metal microdroplet nozzle (1), the release mechanism is controlled to release the composite substrate (3) after a preset time; the metal droplets and the composite substrate (3) chase and contact each other in a weightless falling state, and the image acquisition device (9) captures and records the data through the window and transmits it to the host computer (5) for subsequent analysis.

2. The droplet metal microdroplet deposition device simulating a space environment according to claim 1, characterized in that, The release mechanism includes a set of electromagnets (2) symmetrically arranged on the inner wall of the drop tube and a set of guide rods (18); wherein, the guide rod (18) is an L-shaped structure, with the shorter end fixed to the inner wall of the drop tube and the longer end pointing downwards from the drop tube and parallel to the axis of the drop tube.

3. The droplet metal microdroplet deposition device simulating a space environment according to claim 1, characterized in that, The composite substrate (3) has two ends that are adsorbable end blocks that cooperate with the electromagnet (2), and the adsorbable end blocks are provided with guide holes that cooperate with the guide rod (18); the middle part of the composite substrate (3) is a replaceable test substrate, and the test substrate is mechanically connected to the adsorbable end blocks at both ends. The longer end of a set of guide rods (18) in the release mechanism passes through the guide holes of the adsorbable end blocks at both ends of the composite substrate (3), and then the adsorbable end blocks are adsorbed by an electromagnet (2) to fix the position of the composite substrate (3); the electromagnet (2) is controlled by the host computer (5).

4. The droplet metal microdroplet deposition device simulating a space environment according to claim 1, characterized in that, A crucible is provided inside the metal droplet nozzle (1) for filling experimental metal materials; the metal droplet nozzle (1) is induction heated by the induction heating box (6) to melt the experimental metal materials; a pulse generator (4) is provided inside the host computer (5), and the pulse generator (4) is connected to the piezoelectric ceramic inside the metal droplet nozzle (1); the pulse generator (4) generates pulses through a preset timing program, and uses the vibration of the piezoelectric ceramic to disperse the molten metal into uniform droplets; then, under the pressure of the back pressure gas path, the metal droplets are ejected from the metal droplet nozzle (1); the initial velocity of the metal droplets is controlled by adjusting the pressure.

5. The droplet metal microdroplet deposition device simulating a space environment according to claim 1, characterized in that, The environmental control system includes a first inert gas source (12-1), an overpressure relief valve (14), and a vacuum pump unit (11), wherein: The first inert gas source (12-1) is connected to the inside of the drop pipe through the first pipeline. The first gas flow meter (16-1) and the third vacuum valve (13-3) are installed on the first pipeline. The vacuum pump group (11) is connected to the inside of the drop pipe through the second pipeline. The first vacuum valve (13-1) is installed on the second pipeline. The overpressure relief valve (14) is connected to the inside of the drop pipe through the third pipeline.

6. The drop-tube metal microdroplet deposition device simulating a space environment according to claim 1, characterized in that, The piezoelectric ceramic inside the metal microdroplet nozzle (1) is cooled and protected by a cooling circulating water circuit; one end of the back pressure gas circuit is connected to the inside of the metal microdroplet nozzle (1), and the other end is connected to the second inert gas source (12-2); a second gas flow meter (16-2) and a second vacuum valve (13-2) are also provided on the back pressure gas circuit.

7. The droplet metal microdroplet deposition device for simulating a space environment according to claim 1, characterized in that, A first transition door (17-1) that can be opened and closed is installed on the side wall above the drop tube. After opening the first transition door (17-1), the composite substrate (3) can be disassembled and replaced. A second transition door (17-2) that can be opened and closed is installed on the side wall below the drop tube. After opening the first transition door (17-1), the composite substrate (3) can be recovered and the bottom buffer material (15) inside the drop tube can be replaced.

8. A method for depositing metal microdroplets in a drop tube to simulate a space environment, characterized in that, include: Step 1: Install the test substrate on the composite substrate (3), then insert the composite substrate (3) into the drop tube, pass the guide rod (18) in the release mechanism through the guide holes at both ends of the composite substrate (3), and use the electromagnet (2) to firmly adsorb the composite substrate (3); fill the experimental metal material into the crucible of the metal microdroplet nozzle (1), and install and fix the metal microdroplet nozzle (1) on the top of the drop tube; Step 2: Close the first transition chamber door (17-1), the second transition chamber door (17-2), the second vacuum valve (13-2), and the third vacuum valve (13-3). Then turn on the vacuum pump group (11) and the first vacuum valve (13-1) to evacuate the inside of the drop tube to the preset level. Then turn off the vacuum pump group (11) and the first vacuum valve (13-1), open the third vacuum valve (13-3), and fill the tube with inert gas through the first inert gas source (12-1) until the overpressure release valve (14) detects that the inside of the drop tube has reached positive pressure and the oxygen content has stably dropped below the preset concentration. Then turn off the first inert gas source (12-1) and the three vacuum valves (13-3). Step 3: Turn on the cooling circulation system (7) and the induction heating box (6) to melt the experimental metal material in the metal droplet nozzle (1); then, turn on the vacuum valve (13-2) and adjust the back pressure gas path to the specified pressure through the second inert gas source (12-2); at this time, the host computer (5) executes the preset timing program, controls the piezoelectric ceramic vibration through the trigger pulse generator (4) to disperse the molten metal into uniform droplets, so that the nozzle (1) generates metal droplets, and controls the release mechanism to release the composite substrate (3) after a preset time; the entire process of dynamic contact, spreading and solidification of the metal droplets and the composite substrate (3) is recorded in real time by the image acquisition device (9) and the viewing window (8), and the image data is transmitted to the host computer (5).

9. The method for depositing metal microdroplets in a simulated space environment according to claim 8, characterized in that, The method for determining the preset time is as follows: First, a microgravity overlapping motion model is established for the device, and its contact criterion is constrained by the geometric relationship and the droplet falling dynamics equation; the initial velocity of the metal droplet and the distance parameters between the composite substrate (3) and the metal droplet nozzle (1) are determined. Secondly, the total mechanical / electrical response time from the issuance of the control command from the host computer (5) to the actual ejection of the metal droplets and the actual release of the composite substrate (3) was measured. Finally, the response time is compensated into the microgravity overlapping motion model, and the initial velocity and distance parameters are input to obtain the preset time; It indicates that after the metal droplets are ejected, the release mechanism is triggered after a preset time to release the composite substrate (3).

10. The method for depositing metal microdroplets in a simulated space environment according to claim 8, characterized in that, After the experiment, the composite substrate (3) with metal droplets adhering to it fell onto the buffer material (15) at the bottom of the drop tube and was recovered through the second transition chamber door (17-2). Subsequently, the recovered composite substrate (3) was subjected to macroscopic morphological characterization, solidification angle measurement and microstructure analysis to obtain its final solidification morphology.

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