Metal droplet spraying additive manufacturing system and method

Abstract

The invention relates to the technical field of additive manufacturing, in particular to a molten metal drop spraying additive manufacturing system and method.The core structure of the system is a multi-pole electric arc melting-molten metal drop spraying integrated composite sprayer, and continuous feeding metal wires are efficiently smelted through double-bypass MIG electric arcs; the pulse heating power generated by the central plasma arc in a high-frequency state is adjusted, and the molten metal is driven to be sprayed out from a nozzle below the spray head in cooperation with air pressure, so that jet deposition with stable and adjustable molten drop size and frequency is realized. According to the composite nozzle structure, a first-stage structure for achieving efficient metal smelting is composed of a center plasma arc-double-bypass MIG composite multi-pole arc and a feeding welding wire, and a second-stage structure for achieving metal rectification-injection is composed of a small funnel-shaped buffer cavity and a tail end nozzle. The system has the characteristics of small size, easiness in carrying, high integration, wide application range and the like.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology, and in particular to a metal droplet jet additive manufacturing system and method. Background Technology

[0002] Metal droplet jet deposition additive manufacturing technology, as a novel direct energy deposition manufacturing process, has advantages such as low heat input and easy control of stress deformation, and has important application value in the structurally complex, precision and performance-required components of major equipment. Using metal microdroplets as the basic forming unit, three-dimensional structures are rapidly manufactured by "stacking" them point by point and layer by layer according to the shape characteristics of the parts. However, in the actual application of existing metal droplet jet deposition technology, the following problems often exist: (1) Existing processes mostly use electromagnetic coil induction heating to fix the initial volume of bulk metal, the melting-deposition efficiency is obviously low, and the forming size is limited; (2) The driving force of the droplet jet process is limited, and it does not have the function of fine control, so it cannot achieve complete on-demand supply; (3) The equipment structure is complex, the volume is large, and it is not easy to integrate, making it difficult to meet the applicability of robots in flexible manufacturing. Summary of the Invention

[0003] The purpose of this invention is to provide a metal droplet jet additive manufacturing system and method that can solve the above-mentioned technical problems.

[0004] This invention provides a metal droplet jet additive manufacturing system, comprising a composite nozzle device, a welding power module, and a shielding gas supply unit. The composite nozzle device integrates a central high-frequency plasma welding torch, a bypass MIG welding torch, a wire feeding mechanism, and a water-cooled copper torch. The welding power module includes a GMA power supply and an adjustable high-frequency power supply. The tungsten electrode of the central high-frequency plasma welding torch is connected to the negative terminal of the GMA power supply. Two bypass MIG welding torches are provided, each with an independent wire feeding mechanism. The welding wire is connected to the positive terminal of the GMA power supply, and the tungsten electrode and the welding wire form a MIG arc. A buffer chamber and a buffer rectifier-jet nozzle are sequentially provided below the end of the welding wire. The water-cooled copper torch has an integrated circulating water cooling channel and is connected to the positive terminal of the adjustable high-frequency power supply. The negative terminal of the adjustable high-frequency power supply is connected to the tungsten electrode, and the water-cooled copper torch and the tungsten electrode form a plasma arc. The shielding gas supply unit has three independent gas paths, corresponding to melting protection, jet driving, and jet protection, respectively.

[0005] The wire feeding mechanism can be adapted to metal welding wires with a diameter of 1.2 mm or larger, and the wire feeding speed can be dynamically adjusted according to the melting efficiency.

[0006] Preferably, the buffer chamber has a funnel-shaped structure, with the top receiving molten droplets and the bottom connected to the buffer rectification-jet nozzle to form a molten metal rectification-jet channel. The rectification-jet nozzle is made of graphite material, which combines the characteristics of high temperature resistance and non-thermal conductivity.

[0007] Preferably, the first gas path of the protective gas supply unit is connected to the melting area of ​​the composite nozzle device, the second gas path is connected to the funnel-shaped buffer chamber, and the third gas path surrounds the outlet of the buffer rectifier-jet nozzle. The flow rate and pressure of the three gas paths can be adjusted independently.

[0008] Preferably, the first air passage is provided with a constraint nozzle.

[0009] Preferably, the cross-section of the constrained nozzle gradually decreases along the airflow direction.

[0010] Preferably, the circulating water cooling channel of the water-cooled copper is connected to an external cooling system to quickly absorb the radiant and conductive heat generated by the multi-pole electric arc, thus preventing the component from overheating.

[0011] Preferably, the composite nozzle device is encased in an aluminum alloy shell.

[0012] Preferably, the high-frequency plasma welding torch has an operating current frequency >100kHz and a melting efficiency >300mm during operation. 3 / s.

[0013] The present invention also provides a metal droplet jet additive manufacturing method, based on the above-described system implementation, comprising the following steps: Based on the characteristics of the metal material to be processed, set the current parameters of the central high-frequency plasma welding gun and the dual-bypass MIG welding gun, the wire feeding speed of the wire feeding mechanism, the flow rate and pressure of the three shielding gases, adjust the distance between the composite nozzle device and the additive worktable, and place the substrate on the additive worktable. When the welding power module is started, the central high-frequency plasma welding torch and the water-cooled copper generate a plasma arc, and the dual-bypass MIG welding torch and the tungsten electrode generate a dual-path MIG arc. The wire feeding mechanism feeds the wire, which melts under the high temperature of the multi-pole arc to form droplets. The droplets accumulate in the buffer chamber to form a molten metal pool under the assistance of gravity, MIG arc force and the first path of shielding gas. The central high-frequency plasma welding torch outputs a high-frequency pulsed arc force, which excites the molten pool in the oscillating buffer chamber. At the same time, the second shielding gas is introduced into the buffer chamber, which works with the arc force to drive the molten metal through the buffer rectifier-jet nozzle to form a jet. The third shielding gas wraps the jet droplets, and the additive worktable moves along the path. The droplets are deposited layer by layer to complete the additive manufacturing.

[0014] Preferably, the metal material to be processed includes conventional deposited metals such as 5B06 aluminum alloy. The pressure parameters of the second protective gas are adjusted according to the viscosity difference after the material is melted. The substrate material is also 5B06 aluminum alloy.

[0015] In addition, the pulse amplitude and frequency of the high-frequency electric arc force can be flexibly adjusted, and in conjunction with the gas pressure inside the cavity, the droplet jet can be controlled as needed. The third protective gas continuously envelops the droplets during the jet process, preventing the droplets from oxidizing upon contact with air.

[0016] Beneficial effects: The multi-stage electric arc high-efficiency melting-stable spray integrated composite nozzle of the present invention can realize the efficient and stable on-demand spraying of metal droplets under the combined drive of controlled plasma arc and gas pressure and its jet control mechanism. By adjusting the controllable high-frequency electric arc force and the gas pressure in the cavity, the effect of controllable and stable jet deposition of metal droplets is obtained. The device has the characteristics of compact structure, high efficiency and easy integration. Attached Figure Description

[0017] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the composite nozzle device in this invention; Figure 2 This is a schematic diagram of the overall structure of the metal droplet jet additive manufacturing system of the present invention; Figure 3 This is a schematic diagram of the additive manufacturing process of a metal droplet jet additive manufacturing system.

[0019] Explanation of reference numerals in the attached drawings: 1-Tungsten electrode, 2-Constraint nozzle, 3-Shell, 4-Conductive nozzle, 5-Wire feeding mechanism, 6-Water-cooled copper, 7-End cap, 8-Buffer rectifier-jet nozzle, 9-Welding wire, 1001-GMA power supply, 1002-Adjustable high-frequency power supply, 1101-First gas path, 1102-Second gas path, 1103-Third gas path, 12-Substrate, 13-Buffer cavity; Figure 3 In the diagram: Fair represents the pressure of the shielding gas on the buffer molten pool under internal pressure, and Farc represents the plasma arc force exerted by the plasma welding torch on the buffer molten pool. Detailed Implementation

[0020] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0022] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the stated features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. Furthermore, the terms "installed," "connected," and "linked" should be interpreted broadly; for example, they may refer to a fixed connection, a detachable connection, or an integral connection; they may refer to a mechanical connection or an electrical connection; they may refer to a direct connection or an indirect connection through an intermediate medium; and they may refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0023] Example A metal droplet jet additive manufacturing system includes a composite nozzle device, a welding power module, and a shielding gas supply unit, such as... Figure 1-2 As shown in the figure (only the key parts of the central high-frequency plasma welding gun and the bypass MIG welding gun are retained, such as the tungsten electrode 1 of the central high-frequency plasma welding gun and the conductive nozzle 4 of the bypass MIG welding gun. The conductive nozzle directly connects the wire feeding mechanism and the welding area, and is a key node for current and wire transmission), the composite nozzle device has a built-in central high-frequency plasma welding gun, bypass MIG welding gun, wire feeding mechanism 5 and water-cooled copper 6. The welding power module includes a GMA power supply 1001 and an adjustable high-frequency power supply 1002. The tungsten electrode 1 of the central high-frequency plasma welding gun is connected to the negative terminal of the GMA power supply 1001. There are two bypass MIG welding guns, each with an independent wire feeding mechanism. The welding wire 9 is connected to the positive terminal of the GMA power supply 1001. The tungsten electrode 1 and the welding wire 9 form a MIG arc. Below the end of the welding wire 9, there is a buffer chamber 13 and a buffer rectification-jet nozzle 8. The buffer chamber 13 has a funnel-shaped structure. Its top receives molten droplets, and its bottom is connected to the buffer rectification-jet nozzle 8 to form a molten metal rectification-jet channel.

[0024] The water-cooled copper 6 has a built-in circulating water cooling channel and is connected to the positive terminal of the adjustable high-frequency power supply 1002. The negative terminal of the adjustable high-frequency power supply 1002 is connected to the tungsten electrode 1. The water-cooled copper 6 and the tungsten electrode 1 form a plasma arc. The protective gas supply unit has three independent gas paths, corresponding to melting protection, jet drive, and jet protection, respectively. Figure 2 As shown, the first gas path 1101 of the protective gas supply unit is connected to the melting area of ​​the composite nozzle device, the second gas path 1102 is connected to the funnel-shaped buffer chamber 13, and the third gas path 1103 surrounds the outlet of the buffer rectifier-jet nozzle 8. The flow rate and pressure of the three gas paths can be adjusted independently. A constraint nozzle 2 is provided in the first gas path 1101. The cross-section of the constraint nozzle 2 gradually decreases along the airflow direction. The narrowing design of the constraint nozzle 2 can accelerate the airflow, causing it to be ejected in a high-speed, directional manner to form a stable gas column. The high-speed airflow can, on the one hand, "encircle" the electric arc to prevent it from spreading and maintain the straightness and stability of the electric arc, and on the other hand, complete the protection of the melting process.

[0025] The wire feeding mechanism 5 can be adapted to metal welding wires with a diameter of 1.2mm and above, and the wire feeding speed can be dynamically adjusted according to the melting efficiency; the circulating water cooling channel of the water-cooled copper 6 is connected to the external cooling system to quickly absorb the radiant heat and conductive heat generated by the multi-pole electric arc and avoid overheating of the components; the composite nozzle device is wrapped with an aluminum alloy shell 3, and the top of the entire composite nozzle device is also equipped with an end cap 7.

[0026] The system is characterized by its small size, easy installation, high integration, and wide range of applications. It can be easily installed on the end effector of industrial robots. During operation, it achieves efficient metal melting and stable jet deposition of metal droplets by real-time control of the high-frequency plasma arc and coordinated with air pressure drive.

[0027] Working principle: The system's "dual bypass wires" refer to two independently fed metal welding wires (driven by the wire feeding mechanism of the dual bypass MIG welding torch). One end of each of these two welding wires is connected to the positive terminal of the MIG welding power source (GMA power source), while the other end is continuously fed into the composite nozzle device (eventually approaching the tungsten electrode of the central plasma welding torch).

[0028] The formation of a MIG arc requires a complete circuit of "electrode (welding wire) - arc - negative target". This invention cleverly reuses the tungsten electrode of the central plasma welding torch as the negative target, allowing a MIG arc to be formed directly between the dual bypass wire and the tungsten electrode, instead of the traditional MIG welding method of "the welding wire forming an arc with the substrate (workpiece)". The specific circuit and arc formation logic are as follows: Circuit closure: The double bypass wire is connected to the positive terminal of the MIG power supply, and the tungsten electrode of the central plasma welding torch is connected to the negative terminal of the welding power supply (simultaneously meeting the power supply requirements of the plasma arc and the MIG arc); when the welding wire is fed to a distance close enough to the tungsten electrode (usually a few millimeters, meeting the conditions for the arc to break down the air), a voltage difference is formed between the positive and negative electrodes, breaking down the air and generating an arc.

[0029] Arc type determination: Since the "consuming electrode" of this arc is a double bypass wire (the welding wire itself will be melted by the arc heat) and the "protective medium" is the shielding gas built into the system (the first shielding gas to prevent the arc from contacting the air), it fully meets the definition of a MIG arc. Therefore, the arc between the "wire (positive electrode) and the tungsten electrode (negative electrode)" is essentially a MIG arc, and because there are two welding wires, it will form a "dual parallel MIG arc".

[0030] The core function of the MIG arc is to "generate high temperature." In this invention, the "MIG arc between the central plasma welding torch and the dual bypass wires" directly melts the dual bypass wires through arc heat, completing the core melting step. The specific process consists of two steps: Step 1: Arc heating: The MIG arc between the dual-bypass wire and the tungsten electrode can quickly heat the end of the welding wire to above the melting point; Step 2: Wire melting and droplet formation: Under the continuous action of arc heat, the end of the welding wire gradually melts to form a liquid metal droplet. As the welding wire is continuously fed (the wire feeding mechanism continuously pushes it), the droplet will detach from the end of the welding wire. After detachment, the droplet is directly sprayed into the funnel-shaped buffer cavity below with the assistance of arc force, gravity and shielding gas flow, accumulating molten metal for subsequent "jet deposition".

[0031] Special attention should be paid to the fact that the "MIG arc generated by the central plasma welding torch and the dual bypass wires" is part of the "multi-electrode arc synergistic melting" of this invention (the other part is the "plasma arc generated by the tungsten electrode and water-cooled copper"). The core advantage of this design is to improve melting efficiency and stability. Compared to traditional "single-wire MIG welding", the "dual-path MIG arc" formed by dual-bypass wires can melt two welding wires at the same time, doubling the melting rate; The tungsten electrode of the central plasma welding torch serves as the "fixed negative electrode target" of the MIG arc. Compared with the traditional MIG welding method where "the welding wire and the moving substrate form an arc", it can avoid the influence of substrate position fluctuations on arc stability, ensuring that the energy output of the MIG arc is more concentrated and the welding wire melts more uniformly (with better consistency in droplet size).

[0032] In summary: "The tungsten electrode of the central plasma welding torch serves as the negative electrode of the MIG arc, while the dual bypass wires serve as the positive electrode (consuming electrode) of the MIG arc. When energized, they form a dual-path MIG arc. The high temperature of the arc directly melts the two feed welding wires, generating molten metal droplets that are then fed into the buffer chamber. This process is the efficient melting of the dual bypass wires through the MIG arc." "Droplet transfer" refers to the process where "after the dual-bypass wire is melted by the MIG arc, the liquid metal droplet detaches from the end of the wire and moves towards the buffer chamber." In traditional processes, droplet transfer relies solely on the MIG arc force and gravity, which can easily lead to problems such as "droplets sticking to the end of the wire (not detaching)" and "droplets being too large (clogging the nozzle)." In this invention, the plasma arc generated by the "tungsten electrode-water-cooled copper" directly enhances the droplet transfer effect through two methods: Although the dual-bypass wire is melted by the MIG arc to form droplets, if the droplets come into contact with low-temperature components or the heat dissipates too quickly before detaching from the end of the wire, "local solidification" may occur, causing the droplets to stick to the wire (and unable to detach naturally).

[0033] The plasma arc generated by the "tungsten electrode-water-cooled copper" has a high-temperature arc column that wraps around the end area of ​​the double bypass wire, which is equivalent to providing "continuous auxiliary heating" for the droplet. This ensures that the droplet always maintains a low-viscosity liquid state (does not solidify or clump), greatly reducing the "physical resistance" for the droplet to detach from the end of the wire, and making the droplet transition more naturally.

[0034] In addition, the molten pool in the oscillation buffer cavity is excited in situ by the high-frequency plasma arc force, and the gas pressure in the cavity works together to drive the molten pool metal to form a stable jet in the confined nozzle flow channel.

[0035] The system's functions are divided into "primary smelting" and "secondary rectification-jetting": The core task of primary smelting is to "efficiently melt metal wires, generate qualified liquid droplets, and stably transport them to the buffer chamber to accumulate and form a uniform molten metal pool" (to prepare "raw material reserves" for subsequent secondary spraying). The plasma arc of the "tungsten electrode-water-cooled copper" ensures, through the dual effects of "auxiliary heating + arc force," that: The dual-bypass filaments can melt continuously and without interruption (without sticking or jamming). The molten droplets can quickly and stably detach from the filament and enter the buffer cavity; The molten droplets entering the buffer chamber can continuously accumulate, eventually forming a metal pool with "sufficient volume and uniform viscosity". At this point, the goal of "first-stage melting" is fully achieved, providing a stable "raw material base" for the subsequent "second-stage rectification-jetting" (driven by plasma arc pulse force and gas pressure to propel the molten pool jet).

[0036] The invention also provides a metal droplet jet additive manufacturing method, based on the above-described system, comprising the following steps: Based on the characteristics of the metal material to be processed, set the current parameters of the central high-frequency plasma welding gun and the dual-bypass MIG welding gun, the wire feeding speed of the wire feeding mechanism, the flow rate and pressure of the three shielding gases, adjust the distance between the composite nozzle device and the additive worktable, and place the substrate on the additive worktable. When the welding power module is started, the central high-frequency plasma welding torch and the water-cooled copper generate a plasma arc, and the dual-bypass MIG welding torch and the tungsten electrode generate a dual-path MIG arc. The wire feeding mechanism feeds the wire, which melts under the high temperature of the multi-pole arc to form droplets. The droplets accumulate in the buffer chamber to form a molten metal pool under the assistance of gravity, MIG arc force and the first path of shielding gas. The central high-frequency plasma welding torch outputs a high-frequency pulsed arc force, which excites the molten pool in the oscillating buffer chamber. At the same time, the second shielding gas is introduced into the buffer chamber, which works with the arc force to drive the molten metal through the buffer rectifier-jet nozzle to form a jet. The third shielding gas wraps the jet droplets, and the additive worktable moves along the path. The droplets are deposited layer by layer to complete the additive manufacturing.

[0037] The metal materials to be processed include conventional deposited metals such as 5B06 aluminum alloy. The pressure parameters of the second protective gas are adjusted according to the viscosity difference after the material is melted.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A metal droplet jet additive manufacturing system, characterized in that, The system includes a composite nozzle assembly, a welding power module, and a shielding gas supply unit. The composite nozzle assembly incorporates a central high-frequency plasma welding torch, a bypass MIG welding torch, a wire feeding mechanism, and a water-cooled copper torch. The welding power module includes a GMA power supply and an adjustable high-frequency power supply. The tungsten electrode of the central high-frequency plasma welding torch is connected to the negative terminal of the GMA power supply. Two bypass MIG welding torches are provided, each with an independent wire feeding mechanism. The welding wire is connected to the positive terminal of the GMA power supply, and the tungsten electrode and welding wire form a MIG arc. A buffer chamber and a buffer rectifier-jet nozzle are sequentially located below the end of the welding wire. The water-cooled copper torch has a built-in circulating water cooling channel and is connected to the positive terminal of the adjustable high-frequency power supply. The negative terminal of the adjustable high-frequency power supply is connected to the tungsten electrode, and the water-cooled copper torch and the tungsten electrode form a plasma arc. The shielding gas supply unit has three independent gas paths, corresponding to melting protection, jet drive, and jet protection, respectively.

2. The metal droplet jet additive manufacturing system according to claim 1, characterized in that, The buffer chamber has a funnel-shaped structure, with its top receiving molten droplets and its bottom connected to a buffer rectification-jet nozzle to form a molten metal rectification-jet channel.

3. The metal droplet jet additive manufacturing system according to claim 2, characterized in that, The first gas path of the protective gas supply unit is connected to the melting area of ​​the composite nozzle device, the second gas path is connected to the funnel-shaped buffer chamber, and the third gas path surrounds the outlet of the buffer rectifier-jet nozzle.

4. The metal droplet jet additive manufacturing system according to claim 3, characterized in that, The first air passage is equipped with a constraint nozzle.

5. The metal droplet jet additive manufacturing system according to claim 4, characterized in that, The cross-section of the constrained nozzle gradually decreases along the airflow direction.

6. The metal droplet jet additive manufacturing system according to claim 1, characterized in that, The circulating water cooling channel of the water-cooled copper is connected to the external cooling system to quickly absorb the radiant and conductive heat generated by the multi-pole electric arc, thus preventing the component from overheating.

7. The metal droplet jet additive manufacturing system according to claim 1, characterized in that, The composite nozzle device is encased in an aluminum alloy shell.

8. The metal droplet jet additive manufacturing system according to claim 1, characterized in that, The operating current frequency of the high-frequency plasma welding torch is >100kHz.

9. A method for metal droplet spraying additive manufacturing, characterized in that, The system implementation based on any one of claims 1-8 includes the following steps: Based on the characteristics of the metal material to be processed, set the current parameters of the central high-frequency plasma welding gun and the dual-bypass MIG welding gun, the wire feeding speed of the wire feeding mechanism, the flow rate and pressure of the three shielding gases, and adjust the distance between the composite nozzle device and the additive worktable. When the welding power module is started, the central high-frequency plasma welding torch and the water-cooled copper generate a plasma arc, and the dual-bypass MIG welding torch and the tungsten electrode generate a dual-path MIG arc. The wire feeding mechanism feeds the wire, which melts under the high temperature of the multi-pole arc to form droplets. The droplets accumulate in the buffer chamber to form a molten metal pool under the assistance of gravity, MIG arc force and the first path of shielding gas. The central high-frequency plasma welding torch outputs a high-frequency pulsed arc force, which excites the molten pool in the oscillating buffer chamber. At the same time, the second shielding gas is introduced into the buffer chamber, which works with the arc force to drive the molten metal through the buffer rectifier-jet nozzle to form a jet. The third shielding gas wraps the jet droplets, and the additive worktable moves along the path. The droplets are deposited layer by layer to complete the additive manufacturing.

10. The metal droplet jet additive manufacturing method according to claim 9, characterized in that, The metal material to be processed includes 5B06 aluminum alloy.

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