A method for on-demand metal jet injection forming based on forced vibration

Abstract

This invention discloses an on-demand metal jet forming method based on forced vibration, belonging to the field of 3D printing technology, including the following steps: Step 1, calculating the resonant frequency f of the molten metal column in the nozzle. n Step 2: Determine the excitation frequency f of the forced vibration system; Step 3: Input an excitation signal with frequency f into the forced vibration system, which drives the nozzle to vibrate axially; The forced vibration of the nozzle includes an unstable start-up stage and a stable stage. After the nozzle vibration enters the stable stage, a stable metal droplet jet with frequency f is generated; Step 4: After obtaining the stable metal droplet jet, the base plate is subjected to three-dimensional motion, and metal deposition is performed using the metal droplet jet to complete the forming of the metal component. The spraying frequency of this invention can reach tens of thousands of hertz, which can greatly improve the manufacturing efficiency of droplet-spraying metal additive manufacturing.

Description

Technical Field

[0001] This invention belongs to the field of 3D printing technology, specifically relating to an on-demand metal jet forming method based on forced vibration. Background Technology

[0002] Metal additive manufacturing is a rapid prototyping technology that creates three-dimensional metal components by adding materials layer by layer. Currently, the mainstream metal additive manufacturing technologies include laser selective sintering (SSC) and electron beam selective sintering (EBSS), characterized by powder spreading; laser near-net-shape forming, characterized by powder feeding; and laser wire melting and arc additive manufacturing, characterized by wire feeding. All of these technologies use high-energy beams as heat sources, resulting in extremely high temperature gradients within the material during manufacturing, which can easily lead to stress concentration and other problems. Furthermore, the high cost of the equipment limits the widespread application of these methods.

[0003] Molten droplet jetting metal additive manufacturing technology uses metal wires or even metal blocks as raw materials. After melting, the materials are ejected as micro-droplets from nozzles on demand, completing the jetting of three-dimensional metal components point by point, line by line, and layer by layer. This type of technology has a relatively low temperature gradient for the material and relatively simple equipment, thus it has broad development prospects.

[0004] Current droplet-jetting metal additive manufacturing technologies mainly include continuous-flow droplet jetting and on-demand droplet jetting. Continuous-flow droplet jetting typically uses gas back pressure to eject molten metal from a nozzle, which then breaks into discrete metal droplets through natural fracture or external disturbance. While continuous-flow jetting is highly efficient, it requires additional equipment to deflect and collect unwanted droplets, resulting in low material utilization and a complex jetting structure. Furthermore, due to the hysteresis of gas pressure drive, the start-up and shutdown of droplet jetting typically require hundreds of milliseconds or even longer, during which the droplet jetting is highly unstable, limiting its application in additive manufacturing. On-demand jetting, on the other hand, allows for precise control of the number and frequency of jetted droplets, enabling the jetting of individual droplets without start-up or shutdown time, thus gaining wider application in metal additive manufacturing.

[0005] Depending on the driving method, on-demand droplet ejection technology can be divided into several types, including pneumatic, electromagnetic, and mechanical impact. Due to the lag in air pressure control, the highest ejection frequency of pneumatic on-demand ejection is typically only tens of hertz, and the uniformity of the ejected droplets is poor. Electromagnetic droplet ejection technology utilizes the Lorentz force generated inside the molten metal to eject the molten metal from the nozzle. The MetalJet system using electrodes can achieve a droplet ejection frequency of up to 2000 Hz. Mechanical impact droplet ejection technology works similarly to piezoelectric dispensing valves. It typically uses piezoelectric ceramics to drive a striker that cooperates with the nozzle through a displacement amplification mechanism; the rapid reciprocating motion of the striker generates pulse pressure at the nozzle, forming a droplet ejection. Because the residual vibration of the mechanical structure after each excitation lasts for a long time (milliseconds to sub-milliseconds), the highest on-demand droplet ejection frequency of mechanical impact is usually no more than 1000 Hz.

[0006] In summary, while continuous flow droplet jetting technology is highly efficient, its start-up and shutdown phases are time-consuming and the jetting is unstable, resulting in weak control over droplet jetting and making it difficult to manufacture components with complex shapes. On the other hand, while on-demand droplet jetting technology has strong control over droplet jetting, its jetting frequency is usually low.

[0007] To ensure droplet ejection capability while increasing the ejection frequency, this invention proposes an on-demand metal jet ejection forming method based on forced vibration. By driving the nozzle to perform high-frequency forced vibration in the axial direction through a forced vibration system, the molten metal inside the nozzle is ejected from the nozzle orifice at the same frequency, and the droplet ejection process is highly repeatable. Compared to continuous flow droplet ejection technology, the start-up and shutdown process of this invention is extremely short, greatly improving the control capability of droplet ejection. Compared to the current maximum droplet ejection frequency of 2000Hz for on-demand droplet ejection, the ejection frequency of this invention can reach tens of thousands of hertz, an order of magnitude increase, which can significantly improve the manufacturing efficiency of droplet ejection metal additive manufacturing. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art and provide an on-demand metal jet spraying forming method based on forced vibration.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A method for on-demand metal jet forming based on forced vibration is implemented using a jet jetting device, which includes a nozzle, a forced vibration system located at the top of the nozzle for driving the nozzle to perform axial forced vibration, and a base plate located at the bottom of the nozzle for receiving the molten metal droplet jet.

[0011] The forming method includes the following steps:

[0012] Step 1: Calculate the resonant frequency f of the molten metal column inside the nozzle. n The formula is Where n is the resonance order, which is a positive integer; c is the speed of sound in the molten metal; and h is the height of the molten metal column, which is the vertical distance between the center axis of the liquid inlet hole on the side wall of the nozzle and the bottom of the nozzle.

[0013] Step 2, determine the excitation frequency f of the forced vibration system, where f satisfies the following requirements:

[0014] 100Hz < f < 0.2f1 or 0.95f n <f < 1.05f n ;

[0015] Step 3: Input an excitation signal with frequency f into the forced vibration system. The forced vibration system drives the nozzle to vibrate axially. Each cycle of the nozzle vibration will cause the molten metal inside to be ejected once. The forced vibration of the nozzle includes an unstable start-up stage and a stable stage. After the vibration of the nozzle enters the stable stage, a stable molten metal droplet jet with frequency f is generated.

[0016] Step 4: After obtaining a stable metal droplet jet, the base plate is subjected to three-dimensional motion, and metal is deposited using the metal droplet jet to complete the forming of the metal component.

[0017] Preferably, the nozzle extends downward into the crucible, the bottom of the crucible has a through hole, the bottom end of the nozzle is a tapered nozzle that passes through the through hole and exits the crucible, and the nozzle has a liquid inlet hole on the side wall inside the crucible.

[0018] A heating system is provided on the outside of the crucible;

[0019] A wire feeding system is provided on one side of the nozzle to feed the metal wire into the crucible.

[0020] Preferably, a high-temperature cotton ball fitted onto the nozzle is placed inside the through hole of the crucible.

[0021] Preferably, the lower end of the nozzle is provided with a fastening nut for supporting the high-temperature cotton.

[0022] Preferably, an inert gas delivery pipe is provided on the side wall of the crucible, one end of which is connected to an inert gas supply system, and the other end of which extends to the upper part of the nozzle orifice of the nozzle.

[0023] Preferably, a mesh is provided between the through hole wall at the bottom of the crucible and the outer wall of the nozzle, and the mesh is located between the inert gas delivery pipe and the nozzle.

[0024] The beneficial effects of this invention are:

[0025] (1) The forming method of the present invention drives the nozzle to perform high-frequency forced vibration in the axial direction through a forced vibration system, which can make the molten metal in the nozzle ejected from the nozzle at the same frequency, and the ejection process of the molten droplets is highly repeatable. Compared with the continuous flow molten droplet ejection technology, the start-up and stop process of the present invention is extremely short, which greatly improves the control capability of molten droplet ejection. Compared with the current on-demand molten droplet ejection frequency of up to 2000Hz, the ejection frequency of the present invention can reach tens of thousands of hertz, which can greatly improve the manufacturing efficiency of molten droplet ejection metal additive manufacturing. In addition, the ejection frequency of the molten droplets can be adjusted between hundreds of hertz and tens of thousands of hertz to meet the needs of different occasions.

[0026] (2) The forming method of the present invention can achieve a high droplet spraying frequency. The high droplet spraying frequency can continuously input heat into the molten pool during the metal spraying forming process, which can cause partial remelting of the previous printed layer, so that the current printed layer and the previous printed layer can form a good metallurgical bond, ensuring the mechanical properties of the printed metal component. Attached Figure Description

[0027] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an undue limitation of this application.

[0028] Figure 1 This is a schematic flowchart of the on-demand metal jet forming method based on forced vibration of the present invention.

[0029] Figure 2 This is a displacement-time curve of the forced vibration system driving the nozzle to perform forced vibration in this invention;

[0030] Figure 3 This is a schematic diagram of the metal droplet jet injection of the present invention;

[0031] Figure 4 This is a schematic diagram of the jet injection device in this invention;

[0032] in:

[0033] 1-Forced vibration system, 2-Nozzle, 201-Liquid inlet, 3-Crucible, 4-Heating system, 5-Wire feeding system, 6-Inert gas delivery pipe, 7-Molten metal, 8-Metal droplet jet, 9-Base plate, 10-Metal component, 11-High temperature cotton, 12-Fasting nut, 13-Wool mesh. Detailed Implementation

[0034] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0035] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0036] In this invention, terms such as "upper," "lower," "bottom," and "top" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are merely relational terms determined for the convenience of describing the structural relationship of the various components or elements of this invention, and do not specifically refer to any component or element in this invention, and should not be construed as limiting this invention.

[0037] In this invention, terms such as "connected" and "linked" should be interpreted broadly, indicating a fixed connection, an integral connection, or a detachable connection; a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can determine the specific meaning of these terms in this invention based on the specific circumstances, and they should not be construed as limitations on the invention.

[0038] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0039] Example 1:

[0040] like Figure 1 As shown, an on-demand metal jet forming method based on forced vibration is implemented using a jet jetting device. The jet jetting device includes a nozzle 2, a forced vibration system 1 located at the top of the nozzle 2 to drive the nozzle 2 to perform axial forced vibration, and a base plate 9 located at the bottom of the nozzle 2 to receive the molten metal jet. In this application, the forced vibration system 1 can be any mechanical system that can generate high-frequency forced vibration, and the excitation source of forced vibration can be any driving device that can enable the mechanical system to quickly enter the forced vibration state, such as a piezoelectric ceramic stack or a solenoid valve.

[0041] The forming method includes the following steps:

[0042] Step 1: Calculate the resonant frequency f of the molten metal column inside nozzle 2. n The formula is Where n is the resonance order, which is a positive integer; c is the sound velocity in the molten metal; h is the height of the molten metal column, which is the vertical distance between the central axis of the liquid inlet hole 201 on the side wall of nozzle 2 and the bottom of nozzle 2.

[0043] Step 2, determine the excitation frequency f of the forced vibration system 1, where f satisfies the following requirements:

[0044] 100Hz < f < 0.2f1 or 0.95f n <f < 1.05f n ;

[0045] Step 3: An excitation signal with frequency f is input to the forced vibration system 1. The forced vibration system 1 drives the nozzle 2 to vibrate axially. Each cycle of the nozzle 2's vibration causes the molten metal inside to be ejected once. The forced vibration of the nozzle 2 includes an unstable start-up phase and a stable phase. After the vibration of the nozzle 2 enters the stable phase, a stable jet of molten metal droplets with frequency f is generated. The displacement-time curve of the forced vibration system 1 driving the nozzle 2 to perform forced vibration is shown in the figure. Figure 2 As shown, the vibration of nozzle 2 is not stable during the initial vibration stage, but becomes stable after entering the stable vibration stage; the schematic diagram of metal droplet jet injection is shown below. Figure 3 As shown, the injection process is unstable during the initial vibration stage. After the vibration enters the stable stage, a stable jet of molten metal with a frequency of f is generated.

[0046] Step 4: After obtaining a stable metal droplet jet, the base plate 9 is subjected to three-dimensional motion, and metal is deposited using the metal droplet jet to complete the forming of the metal component 10.

[0047] The method described in this application can achieve metal droplet ejection frequencies ranging from several hundred to tens of thousands of hertz, and the highest achievable efficiency for metal spray forming is cm. 3 On the order of / S.

[0048] Specifically, such as Figure 4 As shown, the nozzle 2 extends downward into the crucible 3. The bottom of the crucible 3 has a through hole. The bottom end of the nozzle 2 is a tapered nozzle that passes through the through hole and exits the crucible 3. The nozzle 2 has a liquid inlet hole 201 on the side wall inside the crucible 3.

[0049] A heating system 4 is provided on the outside of the crucible 3;

[0050] A wire feeding system 5 is provided on one side of the nozzle 2 to feed the metal wire into the crucible 3. The wire feeding system 5 feeds the metal wire into the crucible 3. The heating system 4 is used to melt the metal wire in the crucible 3 into molten metal 7 and keep it within a set temperature range.

[0051] Specifically, a high-temperature cotton 11 fitted onto the nozzle 2 is provided inside the through hole of the crucible 3 to prevent molten metal 7 from leaking out from the bottom of the crucible 3.

[0052] Specifically, the lower end of the nozzle 2 is provided with a fastening nut 12 for supporting the high-temperature cotton 11.

[0053] Specifically, an inert gas delivery pipe 6 is provided on the side wall of the crucible 3. One end of the inert gas delivery pipe 6 is connected to the inert gas supply system, and the other end of the inert gas delivery pipe 6 extends to the upper part of the nozzle orifice of the nozzle 2. It is used to deliver inert protective gas to the lower part of the nozzle 2 through the inert gas delivery pipe 6, so that the metal droplet jet 8 ejected from the nozzle 2 is in an inert protective gas environment and is protected from oxidation.

[0054] Specifically, a mesh 13 is provided between the through-hole wall at the bottom of the crucible 3 and the outer wall of the nozzle 2, and the mesh 13 is located between the inert gas delivery pipe 6 and the nozzle. The mesh 13 is used to make the flow of the protective gas uniform and to prevent the airflow from affecting the movement of the molten metal droplet jet 8.

[0055] Example 2:

[0056] The forced vibration system 1 uses a piezoelectric ceramic stack as the excitation source. The nanoscale deformation of the piezoelectric ceramic stack is amplified and transmitted to the nozzle 2 through a displacement amplification mechanism. The nozzle 2 is a thin-walled pure titanium tube with a ceramic nozzle connected to its lower part. The nozzle diameter is 400 micrometers, and the distance from the central axis of the liquid inlet 201 to the bottom of the nozzle 2 is 40 mm. The metal wire is made of aluminum alloy.

[0057] The forming method described in Example 1 is used:

[0058] Calculate the first resonant frequency f1 of the molten metal column inside nozzle 2. 12500Hz;

[0059] The excitation frequency f of the forced vibration system 1 is 2000Hz, which satisfies the condition 100Hz<f<0.2f1;

[0060] Applying a sinusoidal excitation signal with an amplitude of 10V and a frequency of 2000Hz to the forced vibration system 1 causes the nozzle 2 to transition from the initial vibration stage to a stable forced vibration stage within 8ms. During the stable vibration stage, the amplitude of the nozzle 2 is approximately 15 micrometers, the ejection frequency of the molten metal droplets matches the excitation frequency, the average ejection velocity of the molten metal droplets is 6.5 m / s, the volume of a single molten metal droplet is 91.9 nL, and the ejection formation efficiency is 0.18 cm⁻¹. 3 / s.

[0061] When the base plate 9 moves in the horizontal plane, and the relative speed between the nozzle 2 and the base plate 9 is 0.025 m / s, the wall thickness of the thin-walled structure printed in a single pass is approximately 2 mm. The metallurgical bonding between adjacent layers is good, and the mechanical properties of the printed components do not exhibit significant anisotropy.

[0062] In this embodiment, other waveforms such as positive half-wave, trapezoidal wave, and triangular wave can also be used to drive the piezoelectric ceramic stack, as long as the nozzle 2 can quickly enter a stable forced vibration state.

[0063] Example 3:

[0064] The forced vibration system 1 uses a piezoelectric ceramic stack as the excitation source. The nanoscale deformation of the piezoelectric ceramic stack is amplified and transmitted to the nozzle 2 through a displacement amplification mechanism. The nozzle 2 is a thin-walled pure titanium tube with a ceramic nozzle connected to its lower part. The nozzle diameter is 400 micrometers, and the distance from the central axis of the liquid inlet 201 to the bottom of the nozzle 2 is 40 mm. The metal wire is made of aluminum alloy.

[0065] The forming method described in Example 1 is used:

[0066] Calculate the first resonant frequency f1 of the molten metal column inside nozzle 2. 12500Hz;

[0067] The excitation frequency f of the forced vibration system 1 is 12500Hz, which satisfies the condition 0.95f1 < f < 1.05f1;

[0068] Applying a sinusoidal excitation signal with an amplitude of 6V and a frequency of 12500Hz to the forced vibration system 1 causes the nozzle 2 to transition from the initial vibration stage to a stable forced vibration stage within 6ms. During the stable vibration stage, the amplitude of the nozzle 2 is approximately 8 micrometers, the ejection frequency of the molten metal droplets matches the excitation frequency, the average ejection velocity of the molten metal droplets is 7 m / s, the volume of a single molten metal droplet is 113.1 nL, and the ejection forming efficiency is 1.41 cm⁻¹. 3 / s.

[0069] Similarly, an excitation frequency close to the second-order resonant frequency f2 = 37500Hz of the molten metal column can be used to achieve a higher droplet ejection frequency and forming efficiency.

[0070] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, they are not intended to limit the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for on-demand metal jet forming based on forced vibration, implemented using a jet jetting device, the jet jetting device comprising a nozzle, a forced vibration system located at the top of the nozzle for driving axial forced vibration of the nozzle, and a base plate located at the bottom of the nozzle for receiving the molten metal droplet jet; characterized in that, The forming method includes the following steps: Step 1: Calculate the resonant frequency f of the molten metal column inside the nozzle. n The formula is Where n is the resonance order, which is a positive integer; c is the speed of sound in the molten metal; and h is the height of the molten metal column, which is the vertical distance between the center axis of the liquid inlet hole on the side wall of the nozzle and the bottom of the nozzle. Step 2, determine the excitation frequency f of the forced vibration system, where f satisfies the following requirements: 100Hz < f < 0.2f1 or 0.95f n <f < 1.05f n ; Step 3: Input an excitation signal with frequency f into the forced vibration system. The forced vibration system drives the nozzle to vibrate axially. Each cycle of the nozzle vibration will cause the molten metal inside to be ejected once. The forced vibration of the nozzle includes an unstable start-up stage and a stable stage. After the vibration of the nozzle enters the stable stage, a stable molten metal droplet jet with frequency f is generated. Step 4: After obtaining a stable metal droplet jet, the base plate is subjected to three-dimensional motion, and metal is deposited using the metal droplet jet to complete the forming of the metal component.

2. The on-demand metal jet forming method based on forced vibration as described in claim 1, characterized in that, The nozzle extends downward into the crucible, the bottom of the crucible has a through hole, the bottom end of the nozzle is a tapered nozzle and passes through the through hole out of the crucible, and the nozzle has a liquid inlet hole on the side wall inside the crucible. A heating system is provided on the outside of the crucible; A wire feeding system is provided on one side of the nozzle to feed the metal wire into the crucible.

3. The on-demand metal jet forming method based on forced vibration as described in claim 2, characterized in that, The crucible has a through hole fitted with high-temperature cotton that is sleeved on the nozzle.

4. The on-demand metal jet spraying forming method based on forced vibration as described in claim 3, characterized in that, The lower end of the nozzle is provided with a fastening nut for supporting the high-temperature cotton.

5. The on-demand metal jet forming method based on forced vibration as described in claim 2, characterized in that, An inert gas delivery pipe is provided on the side wall of the crucible. One end of the inert gas delivery pipe is connected to the inert gas supply system, and the other end of the inert gas delivery pipe extends to the upper part of the nozzle orifice of the nozzle.

6. The on-demand metal jet spraying forming method based on forced vibration as described in claim 5, characterized in that, A mesh is provided between the through hole wall at the bottom of the crucible and the outer wall of the nozzle, and the mesh is located between the inert gas delivery pipe and the nozzle.

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