A device and method for spraying high-melting-point metal droplets on demand using water hammer effect

Abstract

The present invention discloses a device for spraying high-melting-point metal droplets on demand by using the water hammer effect, comprising a crucible, an electromagnetic induction heating system, a nozzle and a nozzle driving system. The crucible is filled with high-melting-point metal and has a small hole at the bottom. The electromagnetic induction heating system is used to heat and melt the metal and keep the temperature of the molten metal above the melting point. The top of the nozzle is connected to the nozzle driving system, and the bottom extends into the crucible and passes through the small hole, and the small hole and the nozzle are in clearance fit. The upper side wall of the nozzle is provided with a vent hole connected to the atmosphere, the lower side wall is provided with a liquid inlet hole, and the bottom end is provided with a spray hole. The nozzle driving system is used to drive the nozzle to achieve sub-millimeter reciprocating movement along its axial direction. The water hammer pressure generated by the molten metal itself in the nozzle serves as the spraying power of the molten metal. It only needs to apply a small reciprocating displacement along its axial direction to the nozzle to realize the spraying of any high-temperature molten metal on demand, and the whole device has high working reliability.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal additive manufacturing and injection molding, and specifically relates to a device and method for on-demand injection of high-melting-point metal droplets using a water hammer effect. Background Art

[0002] Metal additive manufacturing technology is a technology that manufactures objects by adding materials layer by layer. With the continuous development of metal additive manufacturing technology, droplet injection metal additive manufacturing technology has become another mainstream direction besides laser additive manufacturing. At present, there are three main technical schools of droplet injection metal additive manufacturing technology: binder injection, metal nanoparticle injection and metal droplet injection.

[0003] Binder jetting metal additive manufacturing is a process of alternately jetting binder and spreading powder to bond metal powders into shape; the bonded three-dimensional components are then placed in a high-temperature furnace for degreasing and sintering to increase their density. Metal nanoparticle jetting metal additive manufacturing technology is to print metal nanoparticle ink, and after the ink evaporates, the formed three-dimensional structure is sintered into shape. However, both methods require post-processing processes such as sintering, which increases the complexity of the process and cannot guarantee the density of the formed parts.

[0004] At present, there are two main methods for droplet jetting additive manufacturing: continuous flow droplet jetting and on-demand droplet jetting. The jetting methods mainly include piston extrusion, pneumatic pulse, electromagnetic pulse and other droplet on-demand jetting methods. The above three methods use piezoelectric ceramics (or other actuators), high-pressure gas and electromagnetic coils as actuators to generate an instantaneous pressure pulse in a relatively closed liquid storage chamber, so that high-temperature liquid metal is ejected from the nozzle to form droplets.

[0005] The piston extrusion droplet injection technology uses the piston to quickly press down to generate a pressure pulse at the nozzle hole to achieve on-demand injection of the droplet. The high-pressure gas pulse droplet injection technology requires the use of a closed crucible, with a nozzle at the bottom of the crucible and two gas paths at the top; one of which is connected to the high-pressure source through the intake valve, and the other is connected to the atmosphere through the exhaust valve. When the exhaust valve is closed and the intake valve is opened, a positive air pressure pulse can be formed in the closed crucible to achieve droplet injection. After that, the intake valve is closed and the exhaust valve is opened at the same time to connect the crucible to the atmosphere, and the droplet injection can be stopped. This technology can achieve droplet injection of metals with higher melting points, but the injection frequency is low due to the switch of the valve involved. The electromagnetic pulse droplet injection technology uses an electromagnetic coil to induce eddy currents in the molten metal in the crucible, or directly applies a large current through an external circuit, and uses the Lorentz force of the magnetic field on the current to generate a pressure pulse in the crucible to achieve droplet injection.

[0006] The actuators and drive mechanisms required for the above three injection methods are generally large in size, making it difficult to integrate multiple independent nozzles into one nozzle with high density, so current commercial droplet injection additive manufacturing equipment usually only uses one nozzle; on the other hand, the actuators and drive mechanisms have a relatively complex structure as a whole, and the reliability of the entire mechanism is not high, especially for high-melting-point metals with a melting point of more than 1000 degrees Celsius. The working reliability is even lower, and it is difficult to meet the stable and efficient injection requirements of high-melting-point metals.

[0007] Based on the above problems, the present invention proposes a method for on-demand injection of high-melting-point metal droplets using the water hammer effect. The injection principle is completely different from the above-mentioned piston extrusion, pneumatic pulse and electromagnetic pulse droplet injection principles. It does not require complex actuating elements and driving mechanisms, nor does it require a relatively closed crucible. It can stably and efficiently achieve on-demand injection of high-melting-point metal droplets and arrayed droplet injection of multiple nozzles in a crucible. Summary of the invention

[0008] In view of the above problems existing in the prior art, the present invention proposes a device and method for on-demand injection of high-melting-point metal droplets using the water hammer effect, which has a reasonable design, solves the shortcomings of the prior art and has good effects.

[0009] In order to achieve the above-mentioned invention objective 1, the following technical solution is adopted:

[0010] A device for spraying high-melting-point metal droplets on demand using the water hammer effect, comprising a crucible, an electromagnetic induction heating system, a nozzle and a nozzle driving system, wherein the crucible contains high-melting-point metal and has a small hole at the bottom; the electromagnetic induction heating system is arranged on the periphery of the crucible and is used to heat and melt the metal and keep the temperature of the molten metal above the melting point; the top end of the nozzle is connected to the nozzle driving system, and the bottom end extends into the crucible and passes through the small hole, and the small hole and the nozzle are in clearance fit; the upper side wall of the nozzle is provided with an air vent connected to the atmosphere, the lower side wall is provided with a liquid inlet hole, and the bottom inner cavity is in a truncated cone shape and has a spray hole; the nozzle driving system is used to drive the nozzle to achieve sub-millimeter reciprocating movement along its axial direction.

[0011] Furthermore, the gap between the nozzle and the small hole is several tens of micrometers, and the upper limit of the gap size is that the molten metal does not leak when it is stationary and in the process of spraying.

[0012] Furthermore, the diameter of the nozzle hole is several hundred microns, the liquid inlet hole is immersed in the molten metal, and the molten metal enters the nozzle through the liquid inlet hole, so that the liquid level in the nozzle is consistent with the liquid level in the crucible.

[0013] Furthermore, the electromagnetic induction heating system comprises a heating coil and a power supply, and the heating coil is wound around the periphery of the crucible.

[0014] Furthermore, the nozzle driving system adopts a reciprocating pneumatic tool or a solenoid valve driving device or any device that can drive the nozzle to achieve sub-millimeter reciprocating displacement.

[0015] Furthermore, the number of the nozzles in the crucible is one or more. When the number of the nozzles is multiple, the nozzle driving system controls the movement of each nozzle independently or controls multiple nozzles simultaneously.

[0016] In order to achieve the above-mentioned purpose 2 of the invention, the following technical solution is adopted:

[0017] A method for on-demand injection of high-melting-point metal droplets using the water hammer effect, using the above-mentioned on-demand injection device for high-melting-point metal droplets using the water hammer effect, firstly, the nozzle driving system drives the nozzle to move downward from its initial position, that is, its upper limit position, during the rapid downward movement of the nozzle, there is a relative movement at the liquid-solid interface between the molten metal in the nozzle and the nozzle wall, and the wall exerts a downward shear force on the molten metal, causing it to produce a downward acceleration; since the molten metal has a large inertia, its downward movement speed will be much smaller than the movement speed of the nozzle, and the liquid level of the molten metal in the nozzle remains basically stationary; since the volume of the molten metal in the nozzle remains unchanged, the downward movement of the nozzle will cause the molten metal at the nozzle hole to move upward relative to the nozzle, and some gas will enter the bottom of the nozzle, causing the molten metal to form a concave or convex liquid surface in the conical area at the bottom of the nozzle;

[0018] After the nozzle moves downward until it reaches the lower limit position, the nozzle drive system starts to drive the nozzle upward. At this time, the molten metal in the nozzle has a downward speed and collides with the cone surface at the bottom of the nozzle. Due to the water hammer effect, a large pressure pulse is generated at the nozzle hole, thereby ejecting the molten metal from the nozzle hole; the nozzle continues to move upward under the drive of the drive system and returns to its initial position, that is, the upper limit position. Each time the nozzle moves back and forth, a molten droplet is ejected.

[0019] Furthermore, the displacement of the nozzle changes with time in a sinusoidal or triangular pattern, the limit position includes an upper limit position and a lower limit position, and the distance between the upper and lower limit positions is based on the standard of being able to achieve stable droplet injection.

[0020] Furthermore, the speed v of the nozzle upward movement and the distance h between the nozzle hole and the liquid inlet hole are adjusted according to actual needs; the larger the h and v, the greater the water hammer pressure generated, the greater the speed of the sprayed metal droplets, the longer the jet time, and the larger the volume of the sprayed droplets.

[0021] Beneficial technical effects brought by the present invention:

[0022] (1) The water hammer pressure generated by the molten metal itself in the nozzle of the present invention serves as the ejection power of the molten metal. It is only necessary to apply a small reciprocating displacement along the axial direction of the nozzle to realize the on-demand ejection of any high-temperature molten metal. This is technically easy to realize and the working reliability of the entire device is high.

[0023] (2) The velocity and volume of the molten metal spray can be quantitatively controlled by the speed of the nozzle displacement and the mass of the molten metal in the tube, and the volume of the sprayed molten droplets is consistent.

[0024] (3) A single crucible can be used to achieve multi-nozzle injection, so that the injection efficiency is doubled according to the number of nozzles.

[0025] (4) Instead of using a crucible, the nozzle can be directly used as a heating container, making the nozzle structure more compact and the working reliability higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic structural diagram of the on-demand injection device for high melting point metal droplets in the present invention;

[0027] Figure 2 is a graph showing the nozzle displacement and the pressure in the nozzle hole changing with time in the present invention;

[0028] Among them, (a) shows that the nozzle displacement changes with time in a sinusoidal manner, and (b) shows that the nozzle displacement changes with time in a triangular manner;

[0029] Figure 3 It is a schematic diagram of jet printing using a single crucible and multiple nozzles in the present invention;

[0030] Figure 4 It is a schematic diagram of a device in which a nozzle is directly used as a heating container in the present invention;

[0031] Figure 5 It is a schematic diagram of high melting point metal droplet injection in the present invention;

[0032] Among them, (a) means that the inner wall of the nozzle can be wetted by the molten metal; (b) means that the inner wall of the nozzle cannot be wetted by the molten metal;

[0033] Among them, 1-crucible; 2-nozzle; 3-nozzle driving system; 4-heating coil; 5-molten metal; 6-air vent; 7-liquid inlet; 8-nozzle; 9-metal droplet; 10-moving platform; 11-printing workpiece; 12-wire feeding mechanism; 13-wire feeding and air inlet; 14-graphite sleeve; 15-metal wire; DETAILED DESCRIPTION

[0034] The specific implementation of the present invention is further described below in conjunction with specific embodiments:

[0035] A device for spraying high melting point metal droplets on demand using the water hammer effect, such as Figure 1 As shown, it includes a crucible 1, an electromagnetic induction heating system, a nozzle 2 and a nozzle driving system 3;

[0036] The crucible 1 contains a high melting point metal, and a small hole slightly larger than the outer diameter of the nozzle 2 is opened at the bottom of the crucible; the electromagnetic induction heating system includes a heating coil 4 and a power supply, and the heating coil 4 is wound around the periphery of the crucible 1 to heat and melt the metal and keep the temperature of the molten metal 5 above the melting point;

[0037] The nozzle 2 is a slender column structure, the top of which is connected to the nozzle drive system 3, and the bottom of which extends into the crucible 1 and passes through a small hole. The small hole and the nozzle 2 are in clearance fit, and the gap between the two is several tens of microns. The upper limit of the gap size is that the molten metal 5 does not leak during the static and spraying process; the upper side wall of the nozzle 2 is provided with a vent 6 connected to the atmosphere, and the lower side wall is provided with a liquid inlet 7. The inner cavity of the nozzle 2 is cylindrical as a whole, and the bottom end thereof is in a truncated cone shape and provided with a nozzle 8. The diameter of the nozzle 8 is several hundred microns. The liquid inlet 7 is immersed in the molten metal 5. The molten metal 5 enters the nozzle 2 through the liquid inlet 7, so that the liquid level in the nozzle 2 is consistent with the liquid level in the crucible 1;

[0038] The nozzle drive system 3 uses a reciprocating pneumatic tool, a solenoid valve drive device or any device capable of driving the nozzle to achieve sub-millimeter reciprocating displacement, which is used to drive the nozzle 2 to achieve sub-millimeter precision reciprocating displacement along its axial direction. The precision displacement includes first moving the nozzle 2 toward the bottom at a specific speed for a specific distance in the axial direction, and then moving the same distance in the reverse direction at a specific speed to return to its initial position.

[0039] In order to reduce the vibration impact of the nozzle drive system 3 and reduce the noise during printing, the displacement of the nozzle 2 changes sinusoidally with time, such as Figure 2 (a), but with a linear displacement over time, as Figure 2 As shown in (b), as well as other displacement forms, the same ejection effect can be produced.

[0040] The number of the nozzles 2 in the crucible 1 is one or more, such as Figure 3 As shown, by inserting multiple nozzles 2 into a crucible 1, multiple nozzle holes 8 can be integrated. The nozzle drive system 3 controls the movement of each nozzle independently or controls multiple nozzles simultaneously, so that multi-nozzle printing can be achieved, and the injection efficiency is doubled according to the number of nozzle holes;

[0041] The high-melting-point metal droplet on-demand injection device can also directly use the nozzle 2 as a heating container to melt the high-melting-point metal wire 15, forming a liquid column of a certain height at the bottom of the nozzle 2, such as Figure 4As shown, the top of the nozzle 2 is connected to the nozzle drive system 3, the bottom is in a truncated cone shape, and a nozzle hole 8 is opened. The upper part of the nozzle 2 is provided with a wire feeding and air inlet hole 13, and the outside of the nozzle 2 is provided with a graphite sleeve 14, and the outside of the graphite sleeve 14 is wound with a heating coil 4. The high melting point metal wire 15 passes through the wire feeding and air inlet hole 13 through the wire feeding mechanism 12 and enters the nozzle 2. Under the heating action of the heating coil 4, it becomes molten metal 5. The nozzle drive system 3 applies vibration of a specific frequency and amplitude to the nozzle, so that the molten metal 5 can be sprayed on demand. This device eliminates the crucible, which not only makes the overall structure of the nozzle more compact, but also avoids the relative movement between the nozzle components (nozzle and crucible), and improves the reliability of the system. However, since the amount of liquid metal that can be stored in the nozzle 2 is limited, it is difficult to control the temperature and liquid level of the molten metal.

[0042] A method for on-demand injection of high-melting-point metal droplets using the water hammer effect, using the above-mentioned on-demand injection device for high-melting-point metal droplets using the water hammer effect, firstly, the nozzle driving system drives the nozzle to move downward from its initial position 0, that is, its upper limit position, during the rapid downward movement of the nozzle, there is a relative movement at the liquid-solid interface between the molten metal in the nozzle and the nozzle wall, and the wall exerts a downward shear force on the molten metal, causing it to generate a downward acceleration; since the molten metal has a large inertia, its downward movement speed will be much smaller than the movement speed of the nozzle, and the liquid level of the molten metal in the nozzle remains basically motionless; since the volume of the molten metal in the nozzle remains unchanged, the downward movement of the nozzle will cause the molten metal at the nozzle hole to move upward relative to the nozzle;

[0043] For molten metal that can wet the inner wall of the nozzle, the bottom of the molten metal in the nozzle will form a Figure 5 The concave liquid surface shown in (a) is usually about 3 times the downward displacement of the nozzle. If the inner wall of the nozzle cannot be wetted by the molten metal, the liquid surface at the nozzle hole will remain convex, such as Figure 5 (b) shows that the displacement of the molten metal surface relative to the nozzle hole and the effect of its overall injection are basically consistent with the wettable situation;

[0044] At time T3, the nozzle moves down to the lower limit position 3, and the nozzle drive system starts to drive the nozzle upward. At this time, the molten metal in the nozzle has a downward speed (the downward speed is caused by the shear force on it during the downward movement of the nozzle), and collides with the cone surface at the bottom end of the nozzle (the collision time is between T4 and T5). Due to the water hammer effect, a large pressure pulse is generated at the nozzle hole, thereby ejecting the molten metal droplet 9 from the nozzle hole; at time T6, the nozzle drive system drives the nozzle back to the initial position 0, and the nozzle moves back and forth once to generate a molten droplet injection.

[0045] The limit positions include an upper limit position and a lower limit position, and the distance between the upper limit position and the lower limit position is based on the standard of achieving stable droplet ejection.

[0046] Adjust the speed v of the upward movement of the nozzle 2 and the distance h between the nozzle hole 8 and the liquid inlet hole 7 according to actual needs; the larger the h and v are (the larger the mass of the molten metal in the nozzle, and the larger the corresponding kinetic energy), the greater the water hammer pressure generated, the greater the speed of the sprayed metal droplets, the longer the jet time, and the larger the volume of the sprayed droplets.

[0047] Example 1: Using graphite crucible and stainless steel nozzle to realize the additive manufacturing of molten droplet jetting of metal tin

[0048] The devices used are Figure 1 As shown, a mobile platform 10 is placed under the device, which uses a graphite crucible, and uses high-frequency induction heating to melt the metal tin and keep its temperature above the melting point by 80 degrees Celsius; stainless steel is used as the nozzle, the nozzle has an outer diameter of 3mm, an inner diameter of 2mm, a nozzle semi-cone angle of 20°, and a nozzle size of 300 microns; during the printing process, the height of the liquid column is maintained at 30mm; a reciprocating pneumatic tool is used as the nozzle drive system. In this embodiment, the reciprocating pneumatic tool is a pneumatic ultrasonic grinder with a reciprocating motion frequency of 1500 Hz and a maximum displacement of 200 microns. The jet length of a single injection is about 3700 microns, the droplet volume of a single injection is about 200 nanoliters, and the printing efficiency is 1080 milliliters per hour. During the printing process, the entire injection system only moves upward in the Z direction, and the mobile platform 10 moves two-dimensionally in the XY plane, and finally a printed workpiece 11 is obtained.

[0049] Example 2: Using graphite crucible and ceramic nozzle to realize droplet jetting additive manufacturing of metal aluminum

[0050] Since high-temperature aluminum liquid is very easy to oxidize and clog the nozzle, the entire printing system is placed in an inert gas environment provided by a glove box during the printing process to avoid oxidation of the high-temperature aluminum liquid. Figure 1As shown, a mobile platform 10 is placed under the device, which uses a graphite crucible, and uses high-frequency induction heating to melt the metal aluminum and keep its temperature 100 degrees Celsius above the melting point; alumina ceramic material is used as the nozzle, the nozzle has an outer diameter of 3mm, an inner diameter of 2mm, a nozzle semi-cone angle of 20°, and a nozzle size of 600 microns; during the printing process, the height of the liquid column is maintained at 30mm; a reciprocating pneumatic tool is used as the nozzle drive system, the reciprocating frequency is 600 Hz, and the maximum displacement is 300 microns. The jet length of a single injection is about 3000 microns, the droplet volume of a single injection is about 300 nanoliters, and the printing efficiency is 648 milliliters per hour. During the printing process, the entire injection system only moves upward in the Z direction, and the mobile platform 10 moves two-dimensionally in the XY plane, and finally a printed workpiece 11 is obtained.

[0051] Example 3: Using a ceramic nozzle as a nozzle and a heating container to realize droplet jetting additive manufacturing of metal iron

[0052] In order to avoid oxidation of high-temperature molten iron, an argon gas pipeline is used to provide a local inert gas environment at the nozzle. Figure 4 As shown, a mobile platform 10 is placed under the device, and a nozzle made of aluminum oxide ceramic is used as the nozzle, with an outer diameter of 6 mm, an inner diameter of 4 mm, a nozzle semi-cone angle of 20°, and a nozzle size of 600 microns; in order to improve the heating efficiency, a layer of graphite sleeve is coated on the ceramic nozzle; a wire with a diameter of 2 mm is fed into the nozzle through the wire feeding hole by a wire feeding mechanism 12, and the metal wire is melted by high-frequency induction heating and its temperature is maintained at 150 degrees Celsius above the melting point; during the printing process, the height of the metal liquid column is maintained at 30 mm;

[0053] This embodiment uses a solenoid valve drive device as the nozzle drive system, uses a mac solenoid valve, fixes the nozzle on the valve core, sets the valve core reciprocating frequency to 500 Hz, and the maximum displacement to 400 microns. The jet length of a single injection is about 3000 microns, the droplet volume of a single injection is about 300 nanoliters, and the printing efficiency is 540 milliliters per hour. During the printing process, the entire injection system only moves upward in the Z direction, and the mobile platform 10 performs two-dimensional movement in the XY plane, and finally obtains the printed workpiece 11.

[0054] The present invention utilizes the water hammer pressure generated by the relative movement between the high-temperature molten metal in the nozzle and the nozzle as the injection power, and can stably, efficiently and reliably realize the on-demand injection of high-melting-point metal droplets, thereby realizing high-melting-point metal additive manufacturing based on droplet injection. The present invention only needs to apply a small reciprocating displacement along its axial direction to the nozzle to realize the on-demand injection of any high-temperature molten metal. The injection process is simple to operate and easy to control. The entire system has high working reliability and is technically easy to implement. The speed and injection volume of the molten metal injection can be quantitatively controlled by using the nozzle diameter, the speed of the nozzle displacement and the mass of the molten metal in the tube. The injection speed can be adjusted in the range of several meters per second to tens of meters per second, and the single injection volume can be adjusted in the range of picoliters to nanoliters. The injection speed and injection volume have a large adjustable range.

[0055] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A high melting point metal droplet on-demand injection device utilizing water hammer effect, characterized in that: It comprises a crucible, an electromagnetic induction heating system, a nozzle and a nozzle driving system. The crucible contains a high melting point metal and has a small hole at the bottom. The electromagnetic induction heating system is arranged on the periphery of the crucible and is used to heat and melt the metal and keep the temperature of the molten metal above the melting point. The top end of the nozzle is connected to the nozzle driving system, and the bottom end extends into the crucible and passes through the small hole, and the small hole and the nozzle are in clearance fit. The upper side wall of the nozzle is provided with an air vent connected to the atmosphere, the lower side wall is provided with a liquid inlet hole, and the inner cavity at the bottom is in a truncated cone shape and has a nozzle hole. The nozzle driving system is used to drive the nozzle to achieve sub-millimeter reciprocating movement along its axial direction.

2. The high melting point metal droplet on-demand injection device using the water hammer effect according to claim 1 is characterized in that: The upper limit of the gap size between the nozzle and the small hole is that the molten metal does not leak when it is stationary and in the spraying process.

3. The high melting point metal droplet on-demand injection device using water hammer effect according to claim 1, characterized in that: The liquid inlet hole is immersed in the molten metal, and the molten metal enters the interior of the nozzle through the liquid inlet hole, so that the liquid level in the nozzle is consistent with the liquid level in the crucible.

4. The high melting point metal droplet on-demand injection device using water hammer effect according to claim 1, characterized in that: The electromagnetic induction heating system comprises a heating coil and a power supply, wherein the heating coil is wound around the periphery of the crucible.

5. The high melting point metal droplet on-demand injection device using water hammer effect according to claim 1, characterized in that: The nozzle driving system adopts a reciprocating pneumatic tool, a solenoid valve driving device or any other device that can drive the nozzle to achieve sub-millimeter reciprocating displacement.

6. The high melting point metal droplet on-demand injection device utilizing the water hammer effect according to claim 1, characterized in that: The number of the nozzles in the crucible is one or more. When the number of the nozzles is multiple, the nozzle driving system controls the movement of each nozzle independently or controls multiple nozzles simultaneously.

7. A method for on-demand injection of high-melting-point metal droplets using water hammer effect, characterized in that: A high-melting-point metal droplet on-demand injection device utilizing the water hammer effect as described in any one of claims 1 to 6 is used. First, the nozzle drive system drives the nozzle to move downward from its initial position, i.e., the upper limit position. During the rapid downward movement of the nozzle, there is a relative movement at the liquid-solid interface between the molten metal in the nozzle and the nozzle wall. The wall exerts a downward shear force on the molten metal, causing it to generate a downward acceleration. Since the molten metal has a large inertia, its downward movement speed will be much smaller than the movement speed of the nozzle, and the liquid level of the molten metal in the nozzle remains basically stationary. Since the volume of the molten metal in the nozzle remains unchanged, the downward movement of the nozzle will cause the molten metal at the nozzle hole to move upward relative to the nozzle, and some gas will enter the bottom of the nozzle, causing the molten metal to form a concave or convex liquid surface in the conical area at the bottom of the nozzle. After the nozzle moves downward until it reaches the lower limit position, the nozzle drive system starts to drive the nozzle upward. At this time, the molten metal in the nozzle has a downward speed and collides with the cone surface at the bottom of the nozzle. Due to the water hammer effect, a large pressure pulse is generated at the nozzle hole, thereby ejecting the molten metal from the nozzle hole; the nozzle continues to move upward under the drive of the drive system and returns to its initial position, that is, the upper limit position. Each time the nozzle moves back and forth, a molten droplet is ejected.

8. The method for on-demand injection of high-melting-point metal droplets using water hammer effect according to claim 7, characterized in that: The displacement of the nozzle changes with time in a sinusoidal or triangular pattern, and the distance between the upper and lower limit positions is based on the standard of being able to achieve stable droplet injection.

9. The method for on-demand injection of high-melting-point metal droplets using water hammer effect according to claim 7, characterized in that: Adjust the speed v of the nozzle upward movement and the distance h between the nozzle hole and the liquid inlet hole according to actual needs; the larger the h and v, the greater the water hammer pressure generated, the greater the speed of the sprayed metal droplets, the longer the jet time, and the larger the volume of the sprayed droplets.

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