阅读说明：本技术 一种模拟微重力下金属微滴追击熔合过程实时捕获系统 (Real-time capturing system for simulating metal droplet chasing fusion process under microgravity ) 是由 齐乐华 王熠晨 罗俊 夏宇翔 李贺军 于 2021-07-06 设计创作，主要内容包括：本发明提供了一种模拟微重力下金属微滴追击熔合过程实时捕获系统,解决现有落管技术无法完成微重力环境下的金属微滴熔合试验不足之处。一种模拟微重力下金属微滴追击熔合过程实时捕获系统包括管体、主体支撑架、微重力微滴追击熔合模块、微重力微滴追击熔合实时捕捉模块、图像处理模块、收集模块以及抽真空与惰性气体补充模块；管体通过主体支撑架竖直固定,其和抽真空与惰性气体补充模块连接,以在管体内营造惰性气体环境,微重力微滴追击熔合模块、微重力微滴追击熔合实时捕捉模块以及收集模块沿管体高度方向自上而下依次设置。(The invention provides a real-time capturing system for simulating a metal droplet chasing fusion process under microgravity, which solves the defect that the existing pipe falling technology cannot complete a metal droplet fusion test under a microgravity environment. A real-time capturing system for simulating a metal droplet chasing fusion process under microgravity comprises a pipe body, a main body supporting frame, a microgravity droplet chasing fusion module, a microgravity droplet chasing fusion real-time capturing module, an image processing module, a collecting module and a vacuumizing and inert gas supplementing module; the pipe body is vertically fixed through the main body supporting frame and is connected with the vacuumizing and inert gas supplementing module to create an inert gas environment in the pipe body, and the microgravity droplet chasing fusion module, the microgravity droplet chasing fusion real-time capturing module and the collecting module are sequentially arranged from top to bottom in the height direction of the pipe body.)

1. A real-time capture system for simulating the metal droplet chasing fusion process under microgravity is characterized in that: the micro-gravity droplet chasing fusion device comprises a pipe body, a main body support frame, a micro-gravity droplet chasing fusion module, a micro-gravity droplet chasing fusion real-time capturing module, an image processing module, a collecting module and a vacuumizing and inert gas supplementing module;

the tube body is vertically fixed through the main body support frame and is connected with the vacuumizing and inert gas supplementing module so as to create an inert gas environment in the tube body;

the microgravity droplet chasing fusion module, the microgravity droplet chasing fusion real-time capturing module and the collecting module are sequentially arranged from top to bottom along the height direction of the pipe body;

the microgravity droplet chasing and fusing module comprises a control unit, a uniform metal droplet spraying unit and a solidified metal droplet releasing unit, wherein the uniform metal droplet spraying unit and the solidified metal droplet releasing unit are arranged in the pipe body from top to bottom;

the uniform metal droplet ejection unit is used for generating molten metal droplets; the solidified metal droplet release unit is used for accommodating, preheating and releasing the solidified metal droplets, and the release points of the solidified metal droplets and the spraying points of the uniform metal droplet spraying unit are positioned on the same vertical line; the height of the solidified metal droplet release unit in the pipe body is adjustable, and the control unit is used for adjusting the opening sequence of the uniform metal droplet injection unit and the solidified metal droplet release unit;

the microgravity droplet chasing fusion real-time capturing module comprises a high-speed CCD camera, a light source, an adjusting camera support frame and a transparent observation window, wherein the high-speed CCD camera, the light source and the adjusting camera support frame are arranged outside the tube body, and the transparent observation window is arranged on the fusion section of the tube body; the high-speed CCD camera and the light source are oppositely arranged on the main body support frame outside the transparent observation window through adjusting the camera shooting support frame, and the heights of the high-speed CCD camera and the light source are both adjustable;

the image processing module is used for processing the image shot by the microgravity droplet chasing fusion real-time capturing module in real time;

the collection module is located within the tube for collecting the fused sample.

2. The system of claim 1, wherein the system is configured to simulate a metal droplet chasing fusion process under microgravity, and comprises:

the uniform metal droplet jetting unit comprises an excitation component, a crucible, a heating component and a nozzle; the crucible is used for containing metal raw materials, and the lower end of the crucible is provided with the nozzle which is used for ejecting molten metal droplets; the heating assembly is used for heating the crucible to enable the metal raw material to be in a molten state; the excitation assembly is used for generating a driving force and providing an initial speed for the molten metal droplets sprayed out of the nozzle;

the initial distance between the solidified metal droplet release unit and the uniform metal droplet ejection unit is L₀The sliding block is connected with a guide rail with the length of b on the inner wall of the pipe body, so that the interval between every two adjacent guide rails can be realized (L)₀，L₀+ b) freely adjustable, solidified metal droplet discharge unit comprising an electrically powered component and a heating component; the heating assembly comprises a heat conduction base block and a heating pipe, and the heating pipe is used for heating the heat conduction base block; the heat-conducting base block is composed of a first base block and a second base block which are symmetrically arranged, when the first base block and the second base block are folded, the middle part of the heat-conducting base block penetrates along the vertical direction to form a deep hole, the deep hole comprises a cylindrical section and a conical section which are communicated with each other from top to bottom, the diameters of the bottom surfaces of the cylindrical section and the conical section are equal, and the deep hole can store and heat the solidified metal microdroplets; releasing the solidified metal droplets in the deep hole when the first base block and the second base block are separated; the electric component is used for realizing the folding and the separation of the first base block and the second base block.

3. The system of claim 2, wherein the system is configured to simulate a metal droplet chasing fusion process under microgravity, and comprises:

the electric assembly comprises a power element and power arms positioned on two opposite sides of the power element;

the two power arms are respectively connected with the first base block and the second base block through the heat insulation plates, and the first base block and the second base block are driven to fold and separate under the action of the power element;

the opposite wall surfaces of the first base block and the second base block are coated with coatings for preventing molten metal from adhering, and the depth of a deep hole formed when the first base block and the second base block are folded is not less than 10 mm.

4. The system of claim 3, wherein the system is configured to simulate a metal droplet chasing fusion process under microgravity, and comprises:

the control unit comprises a signal generator, an injection unit signal wire and a release unit signal wire; the signal generator sends two paths of signals, the uniform metal droplet spraying unit and the solidified metal droplet releasing unit are controlled by the spraying unit signal line and the releasing unit signal line respectively, and the sequence and the interval time of the two paths of signals sent by the signal generator can be set.

5. The system for simulating the metal droplet chasing fusion process in real time according to any one of claims 1 to 4, wherein:

the vacuumizing and inert gas supplementing module comprises a vacuum pump, a test atmosphere source, a pressure release valve, a first gas path pipeline and a second gas path pipeline;

the first air path pipeline is connected with the vacuum pump and the pipe body and used for vacuumizing, and a pneumatic pipeline valve and an air pressure gauge of the vacuum pump are arranged on the first air path pipeline;

the second gas path pipeline is connected with the test atmosphere source and the pipe body, is used for filling inert gas into the pipe body, and is provided with a gas flow controller;

the pressure relief valve is installed on the pipe body, and the air pressure in the pipe body is ensured to be constant at the normal pressure level.

6. The system of claim 5, wherein the system is configured to simulate a metal droplet chasing fusion process under microgravity, and comprises:

the collecting module comprises a beaker, a beaker supporting frame and a collecting section pipe body with a bypass;

the beaker supporting frame is arranged on the pipe body and is in sealing connection with the bypass of the collecting section pipe body;

the beaker is fixed on the beaker supporting frame, and silicone oil is contained in the beaker.

7. The system of claim 6, wherein the system is configured to simulate a metal droplet chasing fusion process under microgravity, and comprises:

the hoisting module is used for disassembling the pipe body; the hoisting module comprises a portal frame and a hoist.

8. A method for image capture using a real-time capture system for simulating the process of metal droplet chasing fusion under microgravity according to any one of claims 1 to 7, comprising the steps of:

1) preparation before fusion test

1.1) putting metal raw materials into a uniform metal droplet jetting unit of a microgravity droplet chasing fusion module, and assembling all the modules in place after sealing;

1.2) starting a vacuumizing and inert gas supplementing module, vacuumizing the tube body and filling inert gas to normal pressure;

1.3) heating the metal raw material in the uniform metal droplet jetting unit to melt the metal raw material;

2) measuring initial velocity of molten metal droplet ejection

Starting a microgravity droplet chasing fusion module, carrying out image analysis on the first n photos of the molten metal droplets during ejection by adopting a microgravity droplet chasing fusion real-time capturing module, and calculating the diameter of the molten metal droplets and the initial speed during ejection;

3) combining the diameter of the molten metal droplets measured in the step 2) and the initial speed of the molten metal droplets during ejection, and calculating the falling speed and displacement of the molten metal droplets and the solidified metal droplets in the atmosphere of normal-pressure inert gas;

4) determining the time interval between the molten metal droplet injection and the solidified metal droplet release and the fusion position corresponding to fusion by combining the falling speed and the displacement obtained in the step 3);

5) setting and adjusting the opening time of the uniform metal droplet jetting unit and the solidified metal droplet releasing unit in the control unit according to the time interval and the fusing position obtained in the step 4), and adjusting the microgravity droplet chasing fusing real-time capturing module to a height position corresponding to the fusing position;

6) a fusion test was performed and the fusion image was captured in real time.

9. The method of claim 8, further comprising:

in step 3), the specific calculation process is as follows:

according to the newton's equation of resistance, the gas drag experienced by the droplets during their fall is:

wherein, C_DIs the drag coefficient, p_gIs the gas density, v_dIn order to determine the drop velocity of the droplets,is the droplet cross-sectional area, D is the droplet diameter;

drag coefficient C_DCan be given by empirical formulas:

wherein R is_e＝ρ_gDv_d/μ_gReynolds number of the droplet, μ_gIs the kinetic viscosity of the gas;

the kinetic equation for the droplet drop process is:

wherein v is_dThe drop velocity of the droplet, g₀As acceleration of gravity, ρ_dIs the density of the droplets; for molten metal droplets, the ejection velocity is v₁(t₁) The falling speed of the solidified metal droplet is v₂(t₂) (ii) a Path X of molten metal droplets from nozzle to fusion₁The path X along which the droplets of solidified metal fall from the release to the fusion₂。

10. The method of claim 9, further comprising:

in step 4), the specific calculation process is as follows:

defining the time t from the ejection of the molten metal droplet to the fusion₁The time from the release of the solidified metal droplet to the fusion is t₂Wherein, t₁<t₂Time interval Δ t ═ t₂-t₁，

L is defined as the actual height difference between the uniform metal droplet ejection unit and the solidified metal droplet discharge unit, L₀<L<L₀+b；

The conditions to be met by fusion are as follows:

(X₂+L)-X₁<D

t₁<t₂

t is obtained by calculation₁，t₂Then, the time difference Δ t required for fusing is determined as t₂-t₁And a fusion position L + X₂。

Technical Field

The invention relates to the technical field of space metal droplet 3D printing, in particular to a real-time capturing system for simulating a metal droplet chasing fusion process under microgravity.

Background

The uniform metal droplet jet printing technology generates uniform metal droplets through a droplet jet, and simultaneously controls the movement of a three-dimensional substrate, so that the metal droplets are precisely deposited at specific positions and are fused and solidified mutually, and are 'piled up' point by point layer by layer, thereby realizing the rapid printing of a complex three-dimensional structure; the method has the advantages of no need of expensive high-power energy sources and special equipment, no need of specially-made metal raw materials, controllable size of metal droplets and the like, and is a better solution for realizing the space on-orbit metal 3D printing.

However, how the fusion effect of the metal droplets in the microgravity environment (collision fusion of the molten droplets and the solidified droplets) is good, whether the fused tissue has good performance, determines whether the technology can be applied in space. Since it is not practical to directly perform expensive on-orbit verification tests, the foundation simulation microgravity test becomes a necessary choice.

Therefore, it is necessary to develop a device that can simulate the fusion of metal droplets in a microgravity environment on the ground and realize the image capture of the droplets during fusion. On one hand, the early-stage experience of metal droplet fusion under the microgravity environment can be accumulated; on the other hand, a ground simulation basis is provided for the long-term theoretical research of metal droplet fusion under the space environment.

The pipe falling technology simultaneously simulates microgravity, high vacuum and no container of a space environment, and is one of the most comprehensive ground space simulation technologies. Chinese patent CN107589145A discloses a microgravity solidification device for metal droplets, which integrates microgravity and liquid quenching, and combines free falling of metal droplets in a tube with subsequent liquid quenching and extreme cooling, thereby realizing rapid solidification of large-size millimeter-scale droplets in a shorter tube body under the action of microgravity. Similarly, the same patents US2002255348a1, JPWO2003095719a1 and AU2002255348B8 are also available.

However, the existing pipe dropping technology is mostly used for preparing super-normal solidification materials with spatial characteristics on the ground. For scientific problems such as the metal droplet fusion process and the dynamic behavior thereof under microgravity, a test device and a feasible image capturing method are also lacked.

Disclosure of Invention

The invention aims to solve the defect that the existing pipe falling technology cannot complete a metal droplet fusion test in a microgravity environment, and provides a real-time capturing system for simulating the metal droplet chasing fusion process under the microgravity.

In order to achieve the purpose, the technical solution provided by the invention is as follows:

a real-time capturing system for simulating the metal droplet chasing fusion process under microgravity is characterized in that: the micro-gravity droplet chasing fusion device comprises a pipe body, a main body support frame, a micro-gravity droplet chasing fusion module, a micro-gravity droplet chasing fusion real-time capturing module, an image processing module, a collecting module and a vacuumizing and inert gas supplementing module;

the tube body is vertically fixed through the main body support frame and is connected with the vacuumizing and inert gas supplementing module so as to create an inert gas environment in the tube body and ensure that uniform metal droplets can be smoothly sprayed and molten metal droplets are not oxidized; wherein the pipe body is made of 304 stainless steel materials, and the height is not less than 3 m;

the microgravity droplet chasing fusion module, the microgravity droplet chasing fusion real-time capturing module and the collecting module are sequentially arranged from top to bottom along the height direction of the pipe body;

the microgravity droplet chasing and fusing module comprises a control unit, a uniform metal droplet spraying unit and a solidified metal droplet releasing unit, wherein the uniform metal droplet spraying unit and the solidified metal droplet releasing unit are arranged in the pipe body from top to bottom;

the uniform metal droplet ejection unit is used for generating molten metal droplets as a fusion test raw material; the solidified metal droplet release unit is used for accommodating, preheating and releasing the solidified metal droplets and used as a fusion test target material, and the release point of the solidified metal droplet release unit and the spray point of the uniform metal droplet spray unit are positioned on the same vertical line so as to enable the falling tracks of the solidified metal droplets and the molten metal droplets to be superposed and ensure the occurrence of microgravity fusion in space; the height of the solidified metal droplet release unit in the pipe body is adjustable so as to simulate microgravity fusion of metal droplets under different flight distances, namely, the falling distance of the molten metal droplets when fusion occurs is changed, and therefore the collision speed is changed; the control unit is used for adjusting the starting sequence of the uniform metal droplet jetting unit and the solidified metal droplet release unit so as to coordinate the movement of the solidified metal droplets and the movement of the molten metal droplets and ensure the occurrence of microgravity fusion in terms of time;

the microgravity droplet chasing fusion real-time capturing module comprises a high-speed CCD camera, a light source, an adjusting camera support frame and a transparent observation window (a quartz glass window can be adopted) which are arranged outside the tube body, and the transparent observation window is arranged on the fusion section of the tube body; the high-speed CCD camera and the light source are oppositely arranged on the main body support frame outside the transparent observation window through adjusting the camera shooting support frame, the heights of the high-speed CCD camera and the light source are both adjustable, the heights of the high-speed CCD camera and the light source are adjusted to be calculated fusion positions, the dynamic process of the metal micro-droplets during fusion is recorded in real time, and shooting data are sent to the image processing module;

the image processing module is used for processing the image shot by the microgravity droplet chasing fusion real-time capturing module in real time;

the collection module is located within the tube for collecting the fused sample.

Further, the uniform metal droplet ejection unit comprises an excitation assembly, a crucible, a heating assembly, and a nozzle; the crucible is used for containing metal raw materials, and the lower end of the crucible is provided with the nozzle which is used for ejecting molten metal droplets; the heating assembly is used for heating the crucible to enable the metal raw material to be in a molten state; the excitation assembly is used for generating a driving force and providing an initial speed for the molten metal droplets sprayed out of the nozzle;

the solidified metal droplet discharging unit and the uniform metal droplet ejecting unitThe initial spacing of the elements being L₀The sliding block is connected with a guide rail with the length of b on the inner wall of the pipe body, so that the interval between every two adjacent guide rails can be realized (L)₀，L₀+ b) freely adjustable, solidified metal droplet discharge unit comprising an electrically powered component and a heating component; the heating assembly comprises a heat conduction base block and a heating pipe, and the heating pipe is used for heating the heat conduction base block; the heat-conducting base block is composed of a first base block and a second base block which are symmetrically arranged, when the first base block and the second base block are folded, the middle part of the heat-conducting base block penetrates along the vertical direction to form a deep hole, the deep hole comprises a cylindrical section and a conical section which are communicated with each other from top to bottom, the diameters of the bottom surfaces of the cylindrical section and the conical section are equal, and the deep hole can store and heat the solidified metal microdroplets; releasing the solidified metal droplets in the deep hole when the first base block and the second base block are separated; the electric component is used for realizing the folding and the separation of the first base block and the second base block.

Further, the electric assembly comprises a power element and power arms positioned on two opposite sides of the power element; the two power arms are respectively connected with the first base block and the second base block through the heat insulation plates, and the first base block and the second base block are driven to fold and separate under the action of the power element;

due to heat loss, in order to ensure that the preheating temperature of the heat-conducting base block fluctuates within plus or minus 5 ℃ of a set value, the heating assembly further comprises a thermocouple for measuring the temperature of the heat-conducting block, and after the temperature of the thermocouple heat-conducting base block is returned, a temperature controller in the control unit can adjust the heating condition of the heating pipe according to the signal;

in order to avoid the molten metal from adhering to the wall surface of the deep hole, the opposite wall surfaces of the first base block and the second base block are coated with coatings for preventing the molten metal from adhering, and the depth of the deep hole formed when the first base block and the second base block are folded is not less than 10mm, so that the droplets are prevented from falling off the deep hole after bouncing on the wall surface.

Further, the control unit includes a signal generator, an ejection unit signal line, and a release unit signal line; the signal generator sends two paths of signals, the uniform metal droplet spraying unit and the solidified metal droplet releasing unit are controlled by the spraying unit signal line and the releasing unit signal line respectively, and the sequence and the interval time of the two paths of signals sent by the signal generator can be set.

Further, the vacuumizing and inert gas supplementing module comprises a vacuum pump, a test atmosphere source, a pressure release valve, a first gas path pipeline and a second gas path pipeline; the first air path pipeline is connected with the vacuum pump and the pipe body and used for vacuumizing, and a pneumatic pipeline valve and an air pressure gauge of the vacuum pump are arranged on the first air path pipeline; the second gas path pipeline is connected with the test atmosphere source and the pipe body, is used for filling inert gas into the pipe body, and is provided with a gas flow controller; the pressure relief valve is installed on the pipe body, and the air pressure in the pipe body is ensured to be constant at the normal pressure level. In terms of overall layout, the evacuation and inert gas replenishment module is preferably connected to the bottom end of the tube.

Further, the collecting module comprises a beaker, a beaker supporting frame and a collecting section pipe body with a bypass; the beaker supporting frame is arranged on the tube body and is in sealing connection with the bypass of the tube body of the collecting section so as to prevent air leakage during vacuum pumping and can be taken out after the experiment is finished; the beaker is fixed on the beaker supporting frame, silicon oil is contained in the beaker and used for buffering collision of a fused sample in the falling process and reducing collision deformation, the silicon oil can ensure smooth vacuumizing and backward invariability of dropping of the fused liquid, and other solutions with the same functions as the silicon oil can be replaced. Wherein, the beaker is made of stainless steel.

The device further comprises a hoisting module for disassembling the pipe body, and the hoisting module is positioned at the topmost part of the pipe falling platform; the hoisting module comprises a portal frame and a hoist.

Meanwhile, the invention provides a method for capturing images by adopting the real-time capturing system for simulating the metal droplet chasing fusion process under microgravity, which is characterized by comprising the following steps of:

1) preparation before fusion test

1.1) putting metal raw materials into a uniform metal droplet jetting unit of a microgravity droplet chasing fusion module, and assembling all the modules in place after sealing;

1.2) starting the vacuumizing and inert gas supplementing module, vacuumizing the tube body and filling inert gas to normal pressure, specifically vacuumizing to 10%^-3pa, filling inert gas to normal pressure, and opening a pressure release valve;

1.3) heating the metal raw material in the uniform metal droplet jetting unit to melt the metal raw material;

2) measuring initial velocity of molten metal droplet ejection

Starting a microgravity droplet chasing fusion module, carrying out image analysis on the first n photos (namely three photos) of the molten metal droplets during ejection by adopting the microgravity droplet chasing fusion real-time capturing module, and calculating the diameter and the initial speed of the molten metal droplets during ejection;

3) combining the diameter of the molten metal droplets measured in the step 2) and the initial speed of the molten metal droplets during ejection, and calculating the falling speed and displacement of the molten metal droplets and the solidified metal droplets in the atmosphere of normal-pressure inert gas;

4) determining the time interval between the molten metal droplet injection and the solidified metal droplet release and the fusion position corresponding to fusion by combining the falling speed and the displacement obtained in the step 3);

5) setting and adjusting the opening time of the uniform metal droplet jetting unit and the opening time of the solidified metal droplet releasing unit in the control unit according to the time interval and the fusing position obtained in the step 4), and adjusting the microgravity droplet chasing fusing real-time capturing module to a height position corresponding to the fusing position;

6) a fusion test was performed and a fusion image was captured.

Further, in step 3), the specific calculation process is as follows:

according to the newton's equation of resistance, the gas drag experienced by the droplets during their fall is:

wherein, C_DIs the drag coefficient, p_gIs the gas density, v_dIn order to determine the drop velocity of the droplets,is the droplet cross-sectional area, D is the droplet diameter;

drag coefficient C_DCan be given by empirical formulas:

wherein R is_e＝ρ_gDv_d/μ_gReynolds number of the droplet, μ_gIs the kinetic viscosity of the gas;

the kinetic equation for the droplet drop process is:

wherein v is_dTo the velocity of the falling droplet, g₀Is the acceleration of gravity (about 9.8 m/s)²),ρ_dFor droplet density, the velocity of ejection is v for molten metal droplets₁(t₁) The falling speed of the solidified metal droplet is v₂(t₂) (ii) a Path X of molten metal droplets from nozzle to fusion₁The path X along which the droplets of solidified metal fall from the release to the fusion₂。

Further, in step 4), the specific calculation process is as follows:

defining the time t from the ejection of the molten metal droplet to the fusion₁The time from the release of the solidified metal droplet to the fusion is t₂Since the present invention is a case where the solidified metal droplet is released and then the molten metal droplet is ejected to realize the chase, t is₁<t₂Time interval Δ t ═ t₂-t₁，

Thus, the phase difference delta theta between two signals of the control unit is determined to be 2 pi f delta t, wherein f is 1 Hz;

l is defined as the actual height difference between the uniform metal droplet ejection unit and the solidified metal droplet discharge unit, L₀<L<L₀+b；

The conditions to be met by fusion are as follows:

(X₂+L)-X₁<D

t₁<t₂

t is obtained by calculation₁，t₂Then, the time difference Δ t required for fusing is determined as t₂-t₁And a fusion position L + X₂(from the nozzle).

The invention has the advantages that:

1. the capture system not only can simulate the fusion behavior between molten droplets and condensed droplets in the space microgravity environment on the ground, but also can record the dynamic process of the metal droplets during fusion in real time, and has the characteristics of high vacuum degree and higher microgravity level. The system is easy to operate, can repeatedly carry out experiments, and definitely influences the action mechanism of two main factors (the temperature difference between the melting microdroplets and the solidifying microdroplets and the collision speed between the microdroplets under microgravity) of the microdroplet fusion effect by analyzing the microstructure and the micromechanical property of a fusion sample, so as to explore the optimal parameter range of the droplet fusion under the microgravity.

2. The capturing method can approximately estimate the position of the molten metal droplet when the molten metal droplet is fused, can realize the capturing and collecting of the pursuit fusion process of the molten droplet and the solidified droplet under multiple groups of collision speed parameters through the high-speed CCD camera, researches the spreading-oscillation-solidification kinetic behavior in the droplet fusion process under microgravity, and discloses the influence mechanism of the microgravity on the droplet fusion by combining the microscopic analysis result of a fusion sample, thereby providing guidance for the fusion problem among the droplets in space 3D printing.

3. The invention is specially provided with a solidified metal droplet release unit for accommodating, preheating and releasing the solidified metal droplets, and the solidified metal droplet release unit is matched with the uniform metal droplet injection unit and the control unit, so that the controlled fusion of the metal droplets under the microgravity condition can be realized, fused droplet samples under different collision speeds and different temperatures can be obtained, and image data of the fusion process can be acquired (by means of an image acquisition module), thereby laying a foundation for the microgravity fusion behavior research of the metal droplets and even the 3D printing of space metal. Although it is not difficult in principle to realize microgravity fusion of two droplets, the application is to solve the problem of precision as well as the problem of how to make two droplets with tiny sizes collide at a predetermined position, and at the same time, the observation is convenient and is used for basic research.

4. The invention can adjust the distance between the solidified metal droplet release unit and the uniform metal droplet ejection unit, and change the height difference of the initial positions of the two droplets, thereby changing the falling distance of the droplets before pursuing fusion, further changing the collision speed when the droplets meet, and being used for exploring the optimal speed condition of fusion. In addition, the release point of the solidified metal droplet release unit and the spraying point of the uniform metal droplet spraying unit are ensured to be positioned on the same vertical line, so that the motion tracks of the two droplets are accurately superposed, and the accurate collision of the submillimeter-level droplets is realized by using a low-cost and simple structure.

5. The solidified metal droplet release unit comprises an electric heating tube and a thermocouple, can preheat the solidified metal droplet under the control of the control unit temperature controller, realizes fusion under different temperature conditions, and can be used for exploring the optimal temperature condition of fusion.

6. The control unit can adjust the time of jetting the molten metal droplets and releasing the solidified metal droplets, and is matched with the adjustment of the distance between the solidified metal droplet releasing unit and the uniform metal droplet jetting unit to coordinate the movement of the solidified metal droplets and the molten metal droplets, so that microgravity fusion at a preset position is realized, on one hand, the acquisition of image data is facilitated, and a decisive evidence can be provided for the fusion under the microgravity condition; on the other hand, the convenient control of the fusion parameters also enables systematic testing in groups to explore the optimal conditions for microgravity fusion.

Drawings

FIG. 1 is a schematic diagram of the overall structure of a real-time capturing system for simulating the metal droplet chasing fusion process under microgravity according to the present invention;

FIG. 2 is a schematic view of the initial position of a microgravity droplet chasing fusion module of the present invention;

FIG. 3 is a schematic view of the micro-gravity droplet chasing fusing module of the present invention after adjusting its height;

FIG. 4 is a schematic diagram of a microgravity droplet chasing fusion real-time capture module according to the present invention;

FIG. 5 is a schematic structural view of a collection module according to the present invention;

FIG. 6 is a first schematic structural diagram of the air path control end according to the present invention;

FIG. 7 is a second schematic structural diagram of the air path control end according to the present invention;

FIG. 8 is a schematic structural view of a uniform metal droplet ejection unit according to the present invention;

FIG. 9 is a side view of a solidified metal droplet discharge unit of an embodiment of the invention;

FIG. 10 is a top view of a solidified metal droplet discharge unit of an embodiment of the invention;

FIG. 11 is a cross-sectional view of a solidified metal droplet discharge unit in accordance with an embodiment of the invention;

FIG. 12 is an isometric view of a solidified metal droplet discharge unit of an embodiment of the invention;

FIG. 13 shows the theoretical point of fusion under an argon atmosphere with microgravity of 500 μm aluminum drops in the present invention;

the reference numbers are as follows:

1-a pipe body; 2-a main body support frame; 3-microgravity droplet chasing fusion device; 4-microgravity droplet chasing fusion real-time capture module; 5-an image processing module; 6-a collection module; 7-a vacuum pump; 8-a source of test atmosphere; 9-gas circuit control end; 10-a portal frame; 11-hoisting a hoist; 12-a homogeneous metal droplet ejection unit; 13-a solidified metal droplet release unit; 14-a control unit; 15-a guide rail; 16-a transparent observation window; 17-high speed CCD camera; 18-a light source; 19-adjusting the camera support frame; 20-beaker; 21-silicone oil; 22-beaker support; 23-a collecting section pipe body with a bypass; 24-a first conduit; 25-vacuum pump pneumatic line valve; 26-a barometer; 27-a gas flow controller; 28-pressure relief valve; 29-a second conduit; 31-a vibration exciting assembly; 32-ejection-unit signal lines; 33-a heating assembly; 34-a crucible; 35-a nozzle; 36-release unit signal line; 37-an electrically powered component; 38-a heat insulation plate; 39-thermocouple; 40-bolt; 41-electric heating tubes; 42-deep holes; 43-a thermally conductive base block; 44-a signal generator; 45-a first base block; 46-a second base block; 47-a power element; 48-power arm.

Detailed Description

The invention is described in further detail below with reference to the following figures and specific examples:

as shown in fig. 1-12, a system for simulating the process of metal droplet chasing fusion under microgravity includes a tube, a main body support, a microgravity droplet chasing fusion module, a microgravity droplet chasing fusion real-time capturing module, an image processing module, a collecting module, a vacuum and inert gas supplementing module, and a hoisting module.

The tube body is made of 304 stainless steel materials, the height of the tube body is not less than 3 m, enough falling time is provided, microgravity solidification is completed, and the tube body is vertically fixed through the main body supporting frame; the bottom end of the tube body is connected with a vacuumizing and inert gas supplementing module so as to create an inert gas environment in the tube body.

The vacuumizing and inert gas supplementing module comprises a vacuum pump, a test atmosphere source, a pressure release valve and a gas path control end; the gas circuit control end comprises two parts: firstly, connecting a vacuum pump with a bottom pipe body, and mainly used for vacuumizing; the device comprises a first gas path pipeline, a vacuum pump pneumatic pipeline valve and a barometer, wherein the vacuum pump pneumatic pipeline valve and the barometer are positioned on the gas path pipeline; a first gas path pipeline and a second gas path pipeline. Connecting the bottom tube body with a test atmosphere source, and inflating the tube body; comprises a second gas path pipeline and a gas flow controller arranged on the second gas path pipeline. The pressure relief valve is arranged on the pipe body to ensure that the air pressure in the pipe body is constant at the normal pressure level.

The microgravity droplet chasing fusion module, the microgravity droplet chasing fusion real-time capturing module and the collecting module are all positioned on the pipe body connected with the vacuumizing and inert gas supplementing module along the pipe body, and are sequentially arranged from top to bottom in the height direction.

The microgravity droplet chasing fusion module comprises a control unit, a uniform metal droplet spraying unit and a solidified metal droplet releasing unit, wherein the uniform metal droplet spraying unit and the solidified metal droplet releasing unit are arranged in the pipe body from top to bottom; the uniform metal droplet jetting unit is used for generating molten metal droplets serving as fusion test raw materials and comprises an excitation component, a crucible, a heating component and a nozzle; the crucible is used for containing metal raw materials, the lower end of the crucible is provided with the nozzle, and the nozzle is used for ejecting molten metal droplets; the heating assembly is used for heating the crucible to enable the metal raw material to be in a molten state; the excitation assembly is used for generating a driving force to provide an initial velocity for the molten metal droplets ejected from the nozzle. The vibration excitation assembly receives a signal sent by the control unit, pulse pressure is generated according to needs to extrude molten liquid in the cavity, the molten liquid is forced to flow downwards to form a liquid column, more molten liquid flows out under the action of pressure and surface tension in the cavity, the liquid column is extended to gradually form an approximate sphere shape, and after the pressure in the cavity is reduced, the speed of fluid at the outlet of the nozzle is smaller than that of the fluid which flows out in advance, so that the liquid column is necked and is broken into single molten drops; the stability of the jet is related to the size of the excitation driving force, the size of the nozzle, the oxygen content in the environment and the like. In the embodiment, the parameters of the excitation driving force are determined by the amplitude and the pulse width of the applied pulse signal, the commonly used amplitude is about 1-7V, and the pulse width is about 100-800 mu s; the diameter of the nozzle is generally about 300 to 600 μm; the oxygen content in the environment is generally required to be less than 20 ppm.

The solidified metal droplet release unit is used for accommodating, preheating (the preheating temperature range is generally 200-550 ℃) and releasing the solidified metal droplets, and the solidified metal droplet release unit is used as a fusion test target material and comprises an electric component and a heating component; the heating assembly comprises a heat conduction base block, a heating pipe and a thermocouple, the heating pipe is used for heating the heat conduction base block, the thermocouple is used for measuring the temperature of the heat conduction block, a temperature controller can be introduced into a control unit for controlling the heating assembly, the heating pipe and the thermocouple are connected to the temperature controller, the heating temperature is set on the temperature controller for controlling, the temperature controller is arranged outside a drop pipe and is connected with a part in the drop pipe through a vacuum electrode on the pipe wall, the temperature controller utilizes a feedback signal of the thermocouple to enable the heating pipe to work again in real time to raise the temperature, and the fluctuation of the preheating temperature is ensured to be out of plus or minus 5 ℃; the heat-conducting base block is composed of a first base block and a second base block which are symmetrically arranged, when the first base block and the second base block are folded, the middle part of the heat-conducting base block penetrates along the vertical direction to form a deep hole, the deep hole comprises a cylindrical section and a conical section which are communicated with each other from top to bottom, the diameters of the bottom surfaces of the cylindrical section and the conical section are equal, and the deep hole can store and heat the solidified metal microdroplets; releasing the solidified metal droplets in the deep hole when the first base block and the second base block are separated; the electric assembly comprises a power element and power arms positioned on two opposite sides of the power element; the two power arms are respectively connected with the first base block and the second base block through the heat insulation plates (through bolts), and the first base block and the second base block are driven to fold and separate under the action of the power element.

The release point of the solidified metal droplet release unit and the spray point of the uniform metal droplet spray unit are positioned on the same vertical line, so that the falling tracks of the solidified metal droplet and the molten metal droplet are superposed, and the microgravity fusion is ensured to occur in space; the initial distance between the solidified metal droplet release unit and the uniform metal droplet ejection unit is L₀The sliding block is connected with the guide rail with the length of b on the inner wall of the pipe body, so that the interval (L) between every two adjacent guide rails can be realized₀，L₀+ b) to simulate microgravity fusion of the metal droplets at different flight distances, i.e. to change the falling distance of the molten metal droplets when fusion occurs, thereby changing the collision speed, the distance between the ejection position and the release position being in the range of 50mm to 150 mm. In the embodiment, the experiment cost and the experiment space are considered, the current position adjustment is still stopped in manual adjustment, and the adjusted position is sealed in the pipe body.

The control unit can adjust the starting sequence of the uniform metal droplet injection unit and the solidified metal droplet release unit so as to coordinate the movement of the solidified metal droplets and the molten metal droplets and ensure the occurrence of microgravity fusion in terms of time; it includes signal generator, injection unit signal line and release unit signal line; the signal generator sends two paths of signals, the uniform metal droplet spraying unit and the solidified metal droplet releasing unit are controlled by the spraying unit signal line and the releasing unit signal line respectively, and the sequence and the interval time of the two paths of signals sent by the signal generator can be set. Since the molten metal droplet is ejected at a high speed, the solidified metal droplet ejection unit is preferably activated to eject the solidified metal droplet in order to prevent the solidified metal droplet from being caught by the molten metal droplet before being ejected. By adopting a simulated microgravity micro-molten drop fusion capturing method, the time difference and the fusion position corresponding to the fusion of the drops under microgravity can be determined. The obtained time difference is set in the control unit, and the capturing of the simulated microgravity micro molten drop fusion process is realized by matching with the microgravity micro droplet chasing fusion real-time capturing module.

The microgravity droplet chasing fusion real-time capturing module comprises a high-speed CCD camera, a light source, an adjusting camera support frame and a transparent observation window (a quartz glass window can be adopted) which are arranged outside the tube body, and the transparent observation window is arranged on the fusion section of the tube body; the high-speed CCD camera and the light source are arranged on the main body supporting frame outside the transparent observation window relatively by adjusting the camera shooting supporting frame, the heights of the high-speed CCD camera and the light source are adjustable, the heights of the high-speed CCD camera and the light source are adjusted to be the calculated fusion position, the dynamic process of the metal micro-drops during fusion is recorded in real time, and the shooting data are sent to the image processing module. The image processing module is used for processing the image shot by the microgravity droplet chasing fusion real-time capturing module in real time.

The collecting module is positioned in the tube body and used for collecting the fusion sample and comprises a beaker, a beaker support frame and a collecting section tube body with a bypass; the beaker supporting frame is arranged on the tube body, is in sealing connection with the bypass of the tube body of the collection section and can be taken out after the experiment is finished; the beaker is fixed on the beaker supporting frame, and silicone oil is contained in the beaker, so that the impact of the fused sample in the falling process is buffered, the impact deformation is reduced, and the analysis result is influenced. Wherein, the beaker is made of stainless steel.

The hoisting module is positioned at the topmost part of the pipe dropping platform and comprises a portal frame and a hoisting block for disassembling the pipe body.

Meanwhile, the invention provides an image capturing method by adopting the real-time capturing system for the metal droplet chasing fusion process under the simulated microgravity, which comprises the following steps:

1) preparation before fusion test

1.1) putting metal raw materials into a uniform metal droplet jetting unit of a microgravity droplet chasing fusion module, and assembling all the modules in place after sealing;

1.2) starting the vacuumizing and inert gas supplementing module, vacuumizing the tube body and filling inert gas to normal pressure, specifically vacuumizing to 10^-3pa, filling inert gas to normal pressure, and opening a pressure release valve;

1.3) heating the metal raw material in the uniform metal droplet jetting unit to melt the metal raw material;

2) measuring initial velocity of molten metal droplet ejection

Starting a microgravity droplet chasing fusion module, carrying out image analysis on the first n photos (namely three photos) of the molten metal droplets during ejection by adopting the microgravity droplet chasing fusion real-time capturing module, and calculating the diameter and the initial speed of the molten metal droplets during ejection;

3) combining the diameter of the molten metal droplets measured in the step 2) and the initial speed of the molten metal droplets during ejection, and calculating the falling speed and displacement of the molten metal droplets and the solidified metal droplets in the normal-pressure argon environment;

according to the newton's equation of resistance, the gas drag experienced by the droplets during their fall is:

wherein, C_DIs the drag coefficient, p_gIs the gas density, v_dIn order to determine the drop velocity of the droplets,is the droplet cross-sectional area, D is the droplet diameter;

drag coefficient C_DCan be given by empirical formulas:

wherein R is_e＝ρ_gDv_d/μ_gReynolds number of the droplet, μ_gIs the kinetic viscosity of the gas;

the kinetic equation for the droplet drop process is:

wherein v is_dTo the velocity of the falling droplet, g₀Is the acceleration of gravity (about 9.8 m/s)²),ρ_dIs the drop density. For molten metal droplets, the ejection velocity is v₁(t₁) The falling speed of the solidified metal droplet is v₂(t₂) (ii) a Path X of molten metal droplets from nozzle to fusion₁The path X along which the droplets of solidified metal fall from the release to the fusion₂；

4) Determining the time interval between the molten metal droplet injection and the solidified metal droplet release and the fusion position corresponding to fusion by combining the falling speed and the displacement obtained in the step 3);

defining the time t from the ejection of the molten metal droplet to the fusion₁The time from the release of the solidified metal droplet to the fusion is t₂Since the present invention is a case where the solidified metal droplet is released and then the molten metal droplet is ejected to realize the chase, t is₁<t₂Time interval Δ t ═ t₂-t₁，

Thus, the phase difference delta theta between two signals of the control unit is determined to be 2 pi f delta t, wherein f is 1 Hz;

l is defined as the actual height difference between the uniform metal droplet ejection unit and the solidified metal droplet discharge unit, L₀<L<L₀+b；

The conditions to be met by fusion are as follows:

(X₂+L)-X₁<D

t₁<t₂

t is obtained by calculation₁，t₂Then, the time difference Δ t required for fusing is determined as t₂-t₁And a fusion position L + X₂(from the nozzle).

5) Setting and adjusting the opening time of the uniform metal droplet injection unit and the opening time of the solidified metal droplet release unit in the control unit according to the time interval and the fusion position obtained in the step 4), and adjusting a high-speed CCD camera and a light source of the microgravity droplet chasing fusion real-time capturing module to a height position corresponding to the fusion position;

6) a fusion test was performed and the fusion image was captured in real time.

In this example, the metal source material was aluminum, argon atmosphere, L₀0.005m, b 0.05m, and a pitch adjusting range (0.005, 0.055), the initial velocity of molten aluminum droplets ejected from the nozzle was determined to be 1m/s after a plurality of measurements, and the diameter D of the aluminum droplets was 500. mu.m. Fusion positions corresponding to different L and different delta t are obtained, and as shown in fig. 13, if other inert gases are filled, physical parameters of the used gases need to be substituted when liquid drop falling kinetic formula calculation and subsequent fusion position, delay time and other parameters are determined.

By adopting the method for capturing the microgravity droplet fusion process in real time, the visual experimental study on the fusion process of metal droplets of different types, different diameters and different collision speeds can be realized under the atmosphere of normal-pressure inert gas. The method is simple to operate and high in reliability, can be used for most basic research experiments related to the liquid drops, and the research result of the method is of great significance to the 3D printing of the space metal based on the liquid drops.

While the invention has been described with reference to specific embodiments, the invention is not limited thereto, and various equivalent modifications or substitutions can be easily made by those skilled in the art within the technical scope of the present disclosure.