On-demand metal jet spray forming method based on forced vibration

Abstract

The invention discloses an on-demand metal jet spray forming method based on forced vibration, which belongs to the technical field of 3D printing, and comprises the following steps: step 1, calculating the resonant frequency fn of a molten metal liquid column in a spray pipe; 2, determining the excitation frequency f of the forced vibration system; 3, an excitation signal with the frequency of f is input into the forced vibration system, and the forced vibration system drives the spray pipe to conduct forced vibration in the axial direction; the forced vibration of the spray pipe comprises an unstable vibration starting stage and a stable stage, and after the vibration of the spray pipe enters the stable stage, a stable metal droplet jet flow with the frequency of f is generated; and 4, after the stable metal droplet jet flow is obtained, the bottom plate is made to move in a three-dimensional mode, metal deposition is conducted through the metal droplet jet flow, and forming of the metal component is completed. The spraying frequency can reach tens of thousands of hertz, and the manufacturing efficiency of molten drop spraying type metal additive manufacturing can be greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of 3D printing, and in particular relates to an on-demand metal jet injection forming method based on forced vibration. Background Art

[0002] Metal additive manufacturing technology is a rapid prototyping technology that manufactures three-dimensional metal components by adding materials layer by layer. The current mainstream metal additive manufacturing technologies mainly include laser selective sintering technology characterized by powder laying, electron beam selective sintering technology, laser near-net shaping technology characterized by powder feeding, and laser fuse technology and arc additive manufacturing technology characterized by wire feeding. The above technologies all use high-energy beams as heat sources. During the manufacturing process, there are extremely high temperature gradients in the materials, which can easily cause problems such as stress concentration. In addition, the equipment cost is relatively high, which to a certain extent limits the promotion and application of such methods.

[0003] The droplet jetting metal additive manufacturing technology uses metal wire or even metal block as raw material, melts it, and then sprays it out from the nozzle in the form of micro droplets as needed, spraying point by point, line by line, and layer by layer to complete the injection molding of three-dimensional metal components. In this type of technology, the temperature gradient of the material is relatively low and the equipment is relatively simple, so it has a broad development prospect.

[0004] At present, there are two main types of droplet jetting metal additive manufacturing technologies: continuous flow droplet jetting and on-demand droplet jetting. Continuous flow droplet jetting usually uses gas back pressure to eject molten metal from the nozzle, and breaks it into discrete metal droplets through natural fracture or external disturbance. Although continuous flow jetting is more efficient, additional devices are required to deflect and collect useless droplets, resulting in low material utilization and complex jetting structure. In addition, due to the hysteresis of gas pressure drive, the start and stop of droplet jetting usually takes hundreds of milliseconds or even longer. During the start and stop process, the droplet jetting is extremely unstable, which limits the application of this jetting form in the field of additive manufacturing. On-demand jetting can accurately control the number of ejected droplets and the jetting frequency, and can realize the ejection of a single droplet without start and stop time. Therefore, it has been more widely used in the field of metal additive manufacturing.

[0005] According to the different driving modes, the on-demand injection technology of molten droplets can be divided into several types, such as pneumatic, electromagnetic, and mechanical impact. Limited by the hysteresis of air pressure control, the maximum injection frequency of pneumatic on-demand injection is usually only tens of hertz, and the uniformity of the ejected molten droplets is poor. Electromagnetic molten droplet injection technology uses the Lorentz force generated inside the molten metal to eject the molten metal from the nozzle. The MetalJet system using electrodes can achieve a maximum droplet injection frequency of 2000Hz. The principle of mechanical impact molten droplet injection technology is similar to that of piezoelectric dispensing valves. It usually uses piezoelectric ceramics through a displacement amplification mechanism to drive the striker that matches the nozzle; through the rapid reciprocating motion of the striker, a pulse pressure is generated at the nozzle to form a molten droplet injection. Since the residual vibration of the mechanical structure after each excitation lasts for a long time (milliseconds to sub-milliseconds), the maximum on-demand injection frequency of mechanical impact molten droplets usually does not exceed 1000Hz.

[0006] In summary, although the continuous flow droplet injection technology is very efficient, its start-stop phases are time-consuming and the injection is unstable. The control ability of the droplet injection is weak, and it is difficult to manufacture components with complex shapes. Although the on-demand droplet injection technology has a strong control ability over the droplet injection, its injection frequency is usually low.

[0007] In order to ensure the ability to spray droplets while increasing the spray frequency of droplets, the present invention proposes an on-demand metal jet injection forming method based on forced vibration. The forced vibration system drives the nozzle to perform high-frequency forced vibration in the axial direction, so that the molten metal in the nozzle can be ejected from the nozzle hole at the same frequency, and the spray process of the droplets is highly repeatable. Compared with the continuous flow droplet injection technology, the start and stop process of the present invention is extremely short, which greatly improves the control ability of droplet injection; compared with the current on-demand droplet injection frequency of up to 2000Hz, the injection frequency of the present invention can reach tens of thousands of hertz, which is an order of magnitude higher, and can greatly improve the manufacturing efficiency of droplet injection metal additive manufacturing. Summary of the invention

[0008] The purpose of the present invention is to overcome the above-mentioned deficiencies of the prior art and to provide an on-demand metal jet injection forming method based on forced vibration.

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

[0010] A forced vibration-based on-demand metal jet forming method is implemented by a jet injection device, the jet injection device 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 bottom plate located at the bottom of the nozzle for receiving a metal molten droplet jet;

[0011] The forming method comprises the following steps:

[0012] Step 1: Calculate the resonant frequency f of the molten metal column in 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; h is the height of the molten metal column, which is the vertical distance from the central axis of the liquid inlet hole on the side wall of the nozzle to 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, inputting an excitation signal with a frequency of f into the forced vibration system, the forced vibration system drives the nozzle to vibrate in the axial direction, and each cycle of the nozzle vibration will drive the molten metal inside to produce a spray; the forced vibration of the nozzle includes an unstable start-up stage and a stable stage, and when the vibration of the nozzle enters the stable stage, a stable metal droplet jet with a frequency of f is generated;

[0016] Step 4, after obtaining a stable metal droplet jet, the bottom plate is moved in three dimensions, and the metal droplet jet is used to perform metal deposition to complete the forming of the metal component.

[0017] Preferably, the nozzle extends downward into the crucible, a through hole is provided at the bottom of the crucible, the bottom end of the nozzle is a tapered nozzle hole and passes through the crucible through the through hole, and a liquid inlet hole is provided on the side wall of the nozzle located inside the crucible;

[0018] A heating system is arranged outside the crucible;

[0019] A wire feeding system for feeding metal wire into the crucible is arranged on one side of the nozzle.

[0020] Preferably, a high-temperature cotton sleeved on a nozzle is arranged in the through hole of the crucible.

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

[0022] Preferably, 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 hole of the nozzle.

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

[0024] The beneficial effects of the present 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, so that the molten metal in the nozzle can be ejected from the nozzle hole at the same frequency, and the molten droplet injection process is highly repeatable; compared with the continuous flow molten droplet injection technology, the start and stop process of the present invention is extremely short, which greatly improves the control ability of the molten droplet injection; compared with the current on-demand molten droplet injection frequency of up to 2000 Hz, the injection frequency of the present invention can reach tens of thousands of hertz, which can greatly improve the manufacturing efficiency of molten droplet injection metal additive manufacturing; in addition, the molten droplet injection frequency can be adjusted between several hundred 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 higher droplet injection frequency. The high droplet injection frequency can continuously input heat into the molten pool during the metal injection forming process, which can cause partial remelting of the previously printed layer, so that the current printed layer and the previously printed layer have a good metallurgical bond, thereby ensuring the mechanical properties of the printed metal component. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The drawings in the specification, which constitute a part of the present application, are used to provide further understanding of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0028] Figure 1 It is a schematic flow chart of the on-demand metal jet spray forming method based on forced vibration of the present invention;

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

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

[0031] Figure 4 It is a schematic structural diagram of the jet injection device in the present 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-bottom plate, 10-metal component, 11-high temperature cotton, 12-fastening nut, 13-gauze. DETAILED DESCRIPTION

[0034] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0035] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0036] In the present invention, the directions or positional relationships indicated by terms such as "upper", "lower", "bottom", "top", etc. are based on the directions or positional relationships shown in the accompanying drawings. They are relational words determined only for the convenience of describing the structural relationships of the various parts or elements of the present invention. They do not specifically refer to any part or element in the present invention and cannot be understood as limitations on the present invention.

[0037] In the present invention, terms such as "connected" and "connection" should be understood in a broad sense, indicating that the connection can be fixed, integral or detachable; it can be directly connected or indirectly connected through an intermediate medium. Relevant scientific research or technical personnel in this field can determine the specific meaning of the above terms in the present invention according to specific circumstances, and they should not be understood as limiting the present invention.

[0038] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0039] Embodiment 1:

[0040] like Figure 1 As shown, a method for on-demand metal jet forming based on forced vibration is implemented by a jet injection device, the jet injection device includes a nozzle 2, a forced vibration system 1 located at the top of the nozzle 2 for driving the nozzle 2 to perform axial forced vibration, and a bottom plate 9 located at the bottom of the nozzle 2 for receiving the molten metal jet. In the present application, the forced vibration system 1 is any mechanical system that can generate high-frequency forced vibration, and the excitation source of the forced vibration can be any driving device that can quickly make the mechanical system enter a forced vibration state, such as a piezoelectric ceramic stack and an electromagnetic valve;

[0041] The forming method comprises the following steps:

[0042] Step 1: Calculate the resonant frequency f of the molten metal column in nozzle 2 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; 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 the nozzle 2 and the bottom of the 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, input an excitation signal with a frequency of f to the forced vibration system 1, and the forced vibration system 1 drives the nozzle 2 to perform forced vibration along the axial direction. Each vibration cycle of the nozzle 2 will drive the molten metal inside to produce a spray; the forced vibration of the nozzle 2 includes an unstable start-up stage and a stable stage. After the vibration of the nozzle 2 enters the stable stage, a stable metal droplet jet with a frequency of f is generated; the displacement time curve of the forced vibration system 1 driving the nozzle 2 to perform forced vibration is as shown in Figure 2 As shown in FIG. 1 , the vibration of the nozzle 2 is not stable in the initial vibration stage, and becomes stable after entering the stable vibration stage; the metal droplet jet injection is shown in FIG. Figure 3 As shown, the ejection process is unstable in the initial vibration stage, and after the vibration enters the stable stage, a stable molten metal jet with a frequency of f is generated;

[0046] Step 4, after obtaining a stable metal droplet jet, the bottom plate 9 is moved in three dimensions, and the metal droplet jet is used to perform metal deposition to complete the forming of the metal component 10.

[0047] The method of the present application can achieve a metal droplet jetting frequency range of several hundred to tens of thousands of hertz, and the maximum efficiency of metal jet forming can be achieved is cm 3 / S level.

[0048] Specifically, Figure 4 As shown, the nozzle 2 extends downward into the crucible 3, a through hole is formed at the bottom of the crucible 3, the bottom end of the nozzle 2 is a tapered nozzle hole and passes through the crucible 3 through the through hole, and a liquid inlet hole 201 is formed on the side wall of the nozzle 2 located inside the crucible 3;

[0049] A heating system 4 is arranged outside the crucible 3;

[0050] A wire feeding system 5 for feeding the metal wire into the crucible 3 is disposed on one side of the nozzle 2. 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 sleeved on the nozzle 2 is arranged in the through hole of the crucible 3 to prevent the molten metal 7 from leaking out from the lower part of the crucible 3 .

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

[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 hole of the nozzle 2, which is used to deliver the 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 to prevent oxidation.

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

[0055] Embodiment 2:

[0056] The forced vibration system 1 uses a piezoelectric ceramic stack as an excitation source, and amplifies the nano-scale deformation of the piezoelectric ceramic stack through a displacement amplification mechanism and transmits it to the nozzle 2. The nozzle 2 is a thin-walled pure titanium tube, and a ceramic nozzle is connected to the bottom of the nozzle. The diameter of the nozzle is 400 microns, and the central axis of the liquid inlet hole 201 is 40 mm away from the bottom of the nozzle 2. The metal wire is aluminum alloy.

[0057] Using the forming method in Example 1:

[0058] Calculate the first-order resonant frequency f1 of the molten metal column in nozzle 2, is 12500Hz;

[0059] The excitation frequency f of the forced vibration system 1 is 2000 Hz, satisfying the condition 100 Hz < 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 can make the nozzle 2 enter the stable forced vibration stage from the start-up stage within 8ms. In the stable vibration stage, the amplitude of the nozzle 2 is about 15 microns, the injection frequency of the metal droplets is consistent with the excitation frequency, the average injection speed of the metal droplets is 6.5m / s, the volume of a single metal droplet is 91.9nL, and the injection forming efficiency is 0.18cm 3 / s.

[0061] When the bottom plate 9 moves in the horizontal plane, the relative movement speed between the nozzle 2 and the bottom plate 9 is 0.025 m / s, and the wall thickness of the thin-walled structure printed in a single pass is about 2 mm. The metallurgical bonding between adjacent layers is good, and there is no significant anisotropy in the mechanical properties of the printed components.

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

[0063] Embodiment 3:

[0064] The forced vibration system 1 uses a piezoelectric ceramic stack as an excitation source, and amplifies the nano-scale deformation of the piezoelectric ceramic stack through a displacement amplification mechanism and transmits it to the nozzle 2. The nozzle 2 is a thin-walled pure titanium tube, and a ceramic nozzle is connected to the bottom of the nozzle. The diameter of the nozzle is 400 microns, and the central axis of the liquid inlet hole 201 is 40 mm away from the bottom of the nozzle 2. The metal wire is aluminum alloy.

[0065] The forming method in Example 1 is adopted:

[0066] Calculate the first-order resonant frequency f1 of the molten metal column in nozzle 2, is 12500Hz;

[0067] The excitation frequency f of the forced vibration system 1 is 12500 Hz, satisfying 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 can make the nozzle 2 enter the stable forced vibration stage from the start-up stage within 6ms. In the stable vibration stage, the amplitude of the nozzle 2 is about 8 microns, the injection frequency of the metal droplets is consistent with the excitation frequency, the average injection speed of the metal droplets is 7m / s, the volume of a single metal droplet is 113.1nL, and the injection forming efficiency is 1.41cm 3 / s.

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

[0070] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not a limitation of 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 on the basis of the technical solution of the present invention without creative work are still within the protection scope of the present invention.

Claims

1. A method for on-demand metal jet forming based on forced vibration, which is implemented by a jet injection device, wherein the jet injection device comprises a nozzle, a forced vibration system located at the top of the nozzle for driving the nozzle to perform axial forced vibration, and a bottom plate located at the bottom of the nozzle for receiving the metal droplet jet; characterized in that: The forming method comprises the following steps: Step 1: Calculate the resonant frequency f of the molten metal column in 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; h is the height of the molten metal column, which is the vertical distance from the central axis of the liquid inlet hole on the side wall of the nozzle to 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, inputting an excitation signal with a frequency of f into the forced vibration system, the forced vibration system drives the nozzle to vibrate in the axial direction, and each cycle of the nozzle vibration will drive the molten metal inside to produce a spray; the forced vibration of the nozzle includes an unstable start-up stage and a stable stage, and when the vibration of the nozzle enters the stable stage, a stable metal droplet jet with a frequency of f is generated; Step 4, after obtaining a stable metal droplet jet, the bottom plate is moved in three dimensions, and the metal droplet jet is used to perform metal deposition to complete the forming of the metal component.

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

3. The on-demand metal jet spray forming method based on forced vibration according to claim 2, characterized in that: A high-temperature cotton sleeved on the nozzle is arranged in the through hole of the crucible.

4. The on-demand metal jet spray forming method based on forced vibration according to claim 3, characterized in that: A fastening nut for supporting the high-temperature cotton is arranged at the lower end of the nozzle.

5. The on-demand metal jet spray forming method based on forced vibration according to claim 2, characterized in that: An inert gas delivery pipe is arranged 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 spray hole of the spray pipe.

6. The on-demand metal jet spray forming method based on forced vibration according to claim 5, characterized in that: A gauze is arranged between the through hole wall surface of the bottom of the crucible and the outer wall of the nozzle, and the gauze is located between the inert gas delivery pipe and the nozzle hole.

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