Microgravity metal fuse wire additive melt directional transfer and liquid bridge transition maintaining device and method

Abstract

The invention provides a microgravity metal fuse wire additive melt directional transfer and liquid bridge transition maintaining device and method. A forming substrate is installed on a multi-axis motion platform; the multi-axis motion platform customizes a three-dimensional motion track path according to three-dimensional data in additive manufacturing; the two current clamps are respectively fixed between the metal wire and the forming substrate, a current path is formed between the metal wire and the forming substrate through a direct-current power supply, and an ampere meter is connected in series in the current path; the electromagnetic coil is arranged in the circumferential direction of the metal wire, and the magnetic conductive bars are connected with the electromagnetic coil and distributed at the symmetrical positions of the two sides of the end of the metal wire. The AC power supply provides an alternating electric field for the electromagnetic coil; the wire feeding mechanism and the driving motor feed the metal wire to the action range of the light spot emitted by the laser source quantitatively at a constant speed; the laser acts on the forming substrate, and a liquid molten pool is formed on the forming substrate; the metal wire and the forming substrate form a liquid bridge connection mode through the liquid melt. The air hole defect of the component can be reduced.

Description

Technical Field

[0001] The present invention relates to the field of laser additive manufacturing in a space microgravity environment, and in particular to a device and method for directional transfer of a metal fuse additive melt and liquid bridge transition. Background Art

[0002] Metal fused filament additive manufacturing under microgravity is one of the most effective ways to manufacture in situ in space. -2 g~10 -5 g, the flow behavior caused by gravity almost disappears. Therefore, the flow behavior of fluids in a microgravity environment is very different from that in a ground environment. In the fused wire additive manufacturing process, the way in which the metal wire enters the substrate molten pool is one of the key factors affecting the formability, and directly determines the surface morphology and mechanical properties of the formed part. In the ground fused wire additive manufacturing process, the transition between the wire and the molten pool is mainly liquid bridge transition and droplet transition. When the filler metal wire transitions to the molten pool in the form of molten droplets, the stability of the process is strongly disturbed, resulting in poor forming quality; in addition, the surface tension of the molten droplets becomes the main driving force for the transfer of droplets under the condition of no gravity constraint. Droplets without gravity constraints may crawl back along the wire, and thus cannot be transported to the molten pool in a directional manner. Furthermore, the crawling of droplets along the wire will block the wire feeding nozzle, resulting in forming failure. In the liquid bridge transition mode, melting occurs within a very small distance range at the end of the wire, and the metal wire can continuously enter the molten pool through the melt. In addition, in the liquid bridge transition mode, the process of the melt entering the molten pool will not produce additional impact on the molten pool, ensuring the stability of the molten pool and the forming process. Therefore, how to maintain the liquid bridge transition mode between the metal wire and the molten pool and maintain the stability of the liquid bridge in the fused filament additive process under a microgravity environment is a key factor in determining the success and quality of the forming.

[0003] Porosity defects are inevitable inside additively manufactured components due to gas entrapment or gas precipitation that cannot be discharged from the molten pool in time during the manufacturing process. However, in a microgravity environment, since the fluid is not constrained by gravity, the gas inside the molten pool stays in the melt and cannot be easily discharged. Porosity defects are one of the most common defects in additively manufactured components. Porosity can cause stress concentration and a sharp drop in component performance. Summary of the invention

[0004] In order to solve the above-mentioned technical problems faced in the manufacture of fused metal additive in a microgravity environment, the present invention provides a microgravity metal fused additive melt directional transfer and liquid bridge transition maintenance device and method, which utilizes the recoil pressure generated by metal vapor, the pre-pressure between the metal wire and the forming substrate, and the dynamic wire feeding method to effectively promote the directional transport of the metal melt to the molten pool under the condition of no gravity constraint. At the same time, the electromagnetic force and Lorentz force generated by the alternating magnetic field and the constant electric field are utilized to form an electromagnetic stirring effect inside the molten pool, effectively discharge the gas in the molten pool during the process, reduce the porosity defects of the component, and further promote the uniformity of the solidification structure and the refinement of the grains.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] The microgravity metal fuse additive melt directional transfer and liquid bridge transition holding device includes a multi-axis motion platform, a forming substrate, an industrial control system, a laser source, a metal wire reel, a wire feeding mechanism and a driving motor, an insulating sleeve, a coaxial wire feeding and air feeding pipe, a metal wire angle adjustment structure, a metal wire pressing mechanism, an air pipe heating device, a DC power supply, a current clamp, an ammeter, a protective gas, a precision gas flow meter, an electromagnetic coil, a magnetic head, an electromagnetic coil fixing frame, and an AC power supply; the forming substrate is installed on the multi-axis motion platform; the multi-axis motion platform customizes the three-dimensional motion trajectory path according to the three-dimensional data in additive manufacturing; two current clamps are respectively fixed on the metal wire and the forming substrate, and a current path is formed between the metal wire and the forming substrate through a DC power supply, and at the same time An ammeter is connected in series in the current path; an electromagnetic coil is arranged circumferentially of the metal wire, and a magnetic rod is connected to the electromagnetic coil and distributed at symmetrical positions on both sides of the end of the metal wire, and the electromagnetic coil is fixedly connected to the coaxial wire feeding and air feeding pipe through an electromagnetic coil fixing frame; an AC power supply provides an alternating electric field for the electromagnetic coil, thereby generating an alternating magnetic field near the end of the metal wire; a wire feeding mechanism and a driving motor quantitatively and constantly send the metal wire to the action range of the light spot emitted by the laser source; the laser emitted by the laser source acts within the end range of the metal wire to form a liquid melt at the end of the metal wire; at the same time, the laser acts on a forming substrate to form a liquid molten pool on the forming substrate; the metal wire and the forming substrate form a liquid bridge connection mode through the liquid melt.

[0007] Furthermore, during operation, the laser source and the metal wire are fixed.

[0008] Furthermore, a protective gas is blown coaxially with the metal wire.

[0009] Furthermore, the shielding gas is an inert gas, which is ejected through a precision gas flow meter and a coaxial wire feeding gas tube; the coaxial wire feeding gas tube is heated by a gas tube heating device, and the coaxial wire feeding gas tube transfers heat to the metal wire and the shielding gas by heat conduction, thereby achieving heating of the shielding gas and the metal wire.

[0010] Furthermore, the metal wire is a stainless steel wire, an aluminum alloy wire, a titanium alloy wire, a flux-cored welding wire, a high / medium entropy alloy, an amorphous alloy wire or a metal composite material wire.

[0011] Furthermore, the metal wire angle adjustment structure adjusts the angle between the metal wire and the horizontal direction, and the angle range is 0-60°.

[0012] Furthermore, the end of the metal wire is kept in contact with the forming substrate, and a pre-compression force is applied between the end of the metal wire and the forming substrate by the metal wire pressing mechanism to ensure good contact between the end of the metal wire and the forming substrate.

[0013] Furthermore, the industrial control system detects through an ammeter whether a closed current path is formed between the forming substrate and the metal wire; when the current of the ammeter is 0A, it indicates that the liquid bridge between the metal wire and the forming substrate is disconnected; in the working state of the liquid bridge being disconnected, the industrial control system increases the wire feeding length through the wire feeding mechanism and the driving motor; when there is a closed circuit in the path, the industrial control system adjusts the wire feeding speed to the normal process to keep the forming substrate and the metal wire in a stable liquid bridge connection.

[0014] The present invention also provides a microgravity metal fuse additive melt directional transfer and liquid bridge transition maintenance method, comprising the following steps:

[0015] Step S1, adjusting the relative position of the laser source and the metal wire and the initial processing position of the forming substrate, forming a pre-pressure between the forming substrate and the metal wire through the metal wire pressing mechanism, and ensuring good contact between the metal wire and the forming substrate;

[0016] Step S2, slicing the data according to the three-dimensional model to be constructed, and ensuring that the wire-feeding metal wire is always parallel to the forming direction and kept at the front end of the forming direction through a multi-axis motion platform; ensuring that the metal wire is in contact with the forming substrate;

[0017] Step S3, sequentially starting the protective gas, laser source, DC power supply, AC power supply, wire feeding mechanism and driving motor, after the metal wire contacts the forming substrate, a current path is generated between the metal wire and the forming substrate, the current is used as a control signal, and additive processing is started according to the slice data of the three-dimensional model;

[0018] Step S4, during the processing, the industrial control system detects the current generated between the metal wire and the forming substrate. When the current is 0, the dynamic wire feeding amount program is started, and the metal liquid bridge between the metal wire and the forming substrate is connected by increasing the wire feeding amount; when the current value is restored, the dynamic wire feeding amount program is adjusted to a normal wire feeding amount process, so that a stable liquid bridge connection is maintained between the metal wire and the forming substrate;

[0019] Step S5, after the current layer processing is completed, the wire feeding mechanism and the driving motor, the DC power supply, the laser source and the shielding gas are turned off in sequence; at the same time, the metal wire pressing mechanism moves upward to release the pre-pressure between the metal wire and the forming substrate, and the multi-axis motion platform moves the forming substrate to the initial position of the next trajectory;

[0020] Step S6, repeating steps S1, S2, S3, S4 and S5 until the entire three-dimensional component is processed.

[0021] Furthermore, the flow rate of the protective gas is 0L / min~25L / min; the laser source is used to output pulsed laser or continuous laser, its maximum output power is 4000W, the pulse frequency is 10Hz~1000HZ, the laser pulse width is 2~50ms, and its scanning speed is 50mm / min~2000mm / min; the maximum output current of the DC power supply is 400A.

[0022] Beneficial effects:

[0023] 1. The energy source of the present invention adopts a laser source. By adjusting the relative position of the laser source and the metal wire and the initial processing position of the forming substrate, the end metal wire and the forming substrate are melted at the same time, and the recoil steam pressure generated by the instantaneous high energy is used to promote the directional transfer of the liquid melt generated by the melting of the end of the metal wire to the molten pool.

[0024] 2. The present invention uses the current of the closed circuit between the metal wire and the forming substrate as the control signal and adopts a closed-loop control method to dynamically adjust the wire feeding speed and length to ensure the stability of the liquid bridge formed between the metal wire and the molten pool.

[0025] 3. The present invention applies a forming pre-compression force between the end of the metal wire and the forming substrate, and the pre-compression force ensures a good combination between the liquid melt at the end of the metal wire and the forming substrate.

[0026] 4. The present invention forms an alternating magnetic field around the molten pool, and under the action of the electric field and the magnetic field, electromagnetic force and Lorentz force are formed inside the molten pool, forming dynamic stirring of the molten pool, accelerating the floating of bubbles in the molten pool, thereby solving the problem of bubble overflow in the molten pool under microgravity, greatly reducing the internal pore defects of metal additive manufacturing components under microgravity, and improving the performance and printing quality of the formed parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of a microgravity metal fuse additive melt directional transfer and liquid bridge transition holding device of the present invention.

[0028] Among them, the accompanying drawings are marked as: multi-axis motion platform 1, forming substrate 2, industrial control system 3, laser source 4, metal wire 5, metal wire reel 6, wire feeding mechanism and driving motor 7, insulating sleeve 8, coaxial wire feeding and air feeding pipe 9, metal wire angle adjustment structure 10, metal wire pressing mechanism 11, air pipe heating device 12, DC power supply 13, current clamp 14, ammeter 15, protective gas 16, precision gas flow meter 17, electromagnetic coil 18, magnetic head 19, electromagnetic coil fixing frame 20, AC power supply 21, liquid melt 22. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0030] like Figure 1 As shown, the microgravity metal fuse additive melt directional transfer and liquid bridge transition holding device of the present invention includes a multi-axis motion platform 1, a forming substrate 2, an industrial control system 3, a laser source 4, a metal wire 5, a metal wire reel 6, a wire feeding mechanism and a driving motor 7, an insulating sleeve 8, a coaxial wire feeding and air feeding pipe 9, a metal wire angle adjustment structure 10, a metal wire pressing mechanism 11, an air pipe heating device 12, a DC power supply 13, an electric current clamp 14, an ammeter 15, a protective gas 16, a precision gas flow meter 17, an electromagnetic coil 18, a magnetic head 19, an electromagnetic coil fixing frame 20, and an AC power supply 21.

[0031] The forming substrate 2 is mounted on the multi-axis motion platform 1, and the multi-degree-of-freedom motion of the forming substrate 2 in space is realized by the multi-axis motion platform 1. The multi-axis motion platform 1 customizes the three-dimensional motion trajectory path according to the three-dimensional data in additive manufacturing. The laser source 4 is fixed above the forming substrate 2, so that the light beam emitted by the laser source 4 can irradiate the upper surface of the forming substrate 2, and the energy accumulation of the laser source 4 on the forming substrate 2 can form a liquid metal molten pool within the action range of the laser spot. The metal wire 5, the wire feeding mechanism and the driving motor 7 and the coaxial wire feeding and air feeding pipe 9 are installed on the side of the laser source 4 through the metal wire angle adjustment structure 10. The wire feeding mechanism and the driving motor 7 can drive the metal wire 5 to be transmitted to the action range of the laser source 4 through the coaxial wire feeding and air feeding pipe 9, and contact the forming substrate 2. The metal wire reel 6 is fixedly mounted at the inlet end of the metal wire 5 of the wire feeding mechanism and the driving motor 7, and the metal wire reel 6 is used to provide a continuous supply of the metal wire 5 for the present invention.

[0032] There are two current clamps 14, one of which is fixed on the forming substrate 2, and the other current clamp is kept in contact with the metal wire 5 through the contact sheet, and a current path is formed between the metal wire 5 and the forming substrate 2 through the DC power supply 13, and an ammeter 15 is connected in series in the current path. An insulating sleeve 8 is coaxially installed between the inside of the coaxial wire feeding and air feeding pipe 9 and the metal wire 5. The function of the insulating sleeve 8 is to insulate the electric field generated by the DC power supply 13 from the metal wire angle adjustment structure 10, the metal wire pressing mechanism 11, the air pipe heating device 12, the electromagnetic coil fixing frame 20 and other components.

[0033] The electromagnetic coil 18 is arranged circumferentially of the metal wire 5, and the magnetic rod 19 is connected to the electromagnetic coil 18 and distributed at symmetrical positions on both sides of the end of the metal wire 5. The electromagnetic coil 18 is fixedly connected to the coaxial wire feeding and air feeding pipe 9 through the electromagnetic coil fixing frame 20. The AC power supply 21 provides an alternating electric field to the electromagnetic coil 18, thereby generating an alternating magnetic field near the end of the metal wire 5.

[0034] The present invention can realize additive manufacturing of metal fuses in a microgravity environment. During the additive manufacturing process, the laser source 4 and the metal wire 5 are fixed, and multi-degree-of-freedom movement in space is achieved through the multi-axis motion platform 1.

[0035] The present invention is designed to blow a shielding gas 16 coaxially with the metal wire 5. The shielding gas 16 has two main functions: (1) the shielding gas coaxially blown with the metal wire 5 can cover the liquid metal molten pool on the forming substrate 2 to prevent the liquid metal molten pool from being oxidized; (2) the shielding gas coaxially blown with the metal wire 5 generates a thrust along the wire axis on the end liquid melt 22 of the metal wire 5, thereby promoting the directional transfer of the end liquid melt 22 to the liquid metal molten pool on the forming substrate 2, and reducing the problem of the end liquid melt 22 creeping back along the wire.

[0036] Preferably, the shielding gas 16 is an inert gas, and a precision gas flow meter 17 is installed on the airflow path between the shielding gas 16 and the coaxial wire feeding air supply pipe 9, and the shielding gas 16 is coaxially ejected through the precision gas flow meter 17 and the coaxial wire feeding air supply pipe 9.

[0037] The gas pipe heating device 12 is installed on the coaxial wire feeding gas pipe 9. The gas pipe heating device 12 can heat the coaxial wire feeding gas pipe 9. When the shielding gas 16 and the metal wire 5 pass through the heated coaxial wire feeding gas pipe 9, the temperature rises; the gas pipe heating device 12 can be used to heat the shielding gas 16 and the metal wire 5. Heating the shielding gas 16 can reduce the convection cooling effect of the shielding gas 16 on the liquid metal molten pool formed on the forming substrate 2, avoiding the low temperature of the molten pool, resulting in discontinuous fuse and reduced laser energy utilization; heating the metal wire 5 can increase the temperature of the wire at a certain position away from the end of the metal wire, thereby reducing the temperature gradient of the solid metal wire 5 and the liquid melt 22 at the end of the metal wire, thereby reducing the surface tension on the end liquid melt 22 creeping back along the wire.

[0038] Preferably, the metal wire 5 includes but is not limited to stainless steel wire, aluminum alloy wire, titanium alloy wire, flux cored welding wire, high / medium entropy alloy, amorphous alloy wire and metal composite wire. The angle between the metal wire 5 and the horizontal direction is adjusted by the metal wire angle adjustment structure 10, preferably, the angle range is 0-60°. The metal wire 5 can be quantitatively and constantly delivered to the action range of the light spot emitted by the laser source 4 by the wire feeding mechanism and the driving motor 7.

[0039] Preferably, the wire feeding mechanism and the drive motor 7 can realize quantitative adjustment of the wire feeding speed. In the present invention, the end of the metal wire 5 is kept in contact with the forming substrate 2. The metal wire clamping mechanism 11 is installed above the coaxial wire feeding and air feeding pipe 9, and a pre-compression force is applied between the end of the metal wire 5 and the forming substrate 2 by the metal wire clamping mechanism 11 to ensure good contact between the end of the metal wire 5 and the forming substrate 2. Preferably, the wire feeding mechanism and the drive motor 7 are used to realize metal wire feeding with a wire diameter of 0.1mm~10mm.

[0040] Preferably, the laser emitted by the laser source 4 acts within the end range of the metal wire 5, forming a liquid melt 22 at the end of the metal wire 5; at the same time, the laser acts on the forming substrate 2, and a liquid molten pool can be formed on the forming substrate 2. The metal wire 5 and the forming substrate 2 form a liquid bridge connection mode through the liquid melt 22.

[0041] Preferably, the industrial control system 3 can detect whether a closed current path is formed between the forming substrate 2 and the metal wire 5 through the ammeter 15. When the current of the ammeter 15 is 0A, it means that the liquid bridge between the metal wire 5 and the forming substrate 2 is disconnected. In the working state where the liquid bridge is disconnected, the industrial control system 3 increases the wire feeding length through the wire feeding mechanism and the driving motor 7, so that the forming substrate 2 and the metal wire 5 maintain a stable liquid bridge connection.

[0042] The present invention also provides a microgravity metal fuse additive melt directional transfer and liquid bridge transition maintenance method, comprising the following steps:

[0043] Step S1, manufacturing preparation: adjusting the relative position of the laser and the metal wire 5 and the initial processing position of the forming substrate 2, forming a pre-pressure between the forming substrate 2 and the metal wire 5 through the metal wire pressing mechanism 11, and ensuring good contact between the metal wire 5 and the forming substrate 2;

[0044] Step S2, data preparation: data slicing is performed according to the three-dimensional model to be constructed, and the multi-axis motion platform 1 is used to ensure that the wire 5 is always parallel to the forming direction and is kept at the front end of the forming direction; the metal wire 5 is ensured to be in contact with the forming substrate 2;

[0045] Step S3, start processing: start the shielding gas 16, the laser source 4, the DC power supply 13, the AC power supply 21, the wire feeding mechanism and the driving motor 7 in sequence, after the metal wire 5 contacts the forming substrate 2, a current path is generated between the metal wire 5 and the forming substrate 2, and the current formation is used as a control signal, that is, the processing starts after the current is formed, thereby starting the additive processing according to the slice data of the three-dimensional model;

[0046] Step S4, monitoring during processing: during the processing, the industrial control system 3 detects the current generated between the metal wire 5 and the forming substrate 2. When the current is 0, the dynamic wire feeding amount program is started, and the metal liquid bridge between the metal wire and the forming substrate is connected by increasing the wire feeding amount; when the current value is restored, the dynamic wire feeding amount program is adjusted to the normal wire feeding amount process, so that the metal wire and the forming substrate maintain a stable liquid bridge connection;

[0047] Step S5, the processing of the current layer is finished: after the processing of the current layer is finished, the wire feeding mechanism and the driving motor 7, the DC power supply 13, the laser source 4 and the shielding gas 16 are turned off in sequence; at the same time, the metal wire material pressing mechanism 11 will move upward to release the pre-pressure between the metal wire material 5 and the forming substrate 2, and the multi-axis motion platform 1 will move the forming substrate 2 to the initial position of the next track;

[0048] Step S6, repeating steps S1, S2, S3, S4 and S5 until the entire three-dimensional component is processed.

[0049] Preferably, the flow rate of the protective gas 16 is 0 L / min to 25 L / min.

[0050] Preferably, the laser source 4 is used to output pulsed laser or continuous laser, with a maximum output power of 4000W, a pulse frequency of 10Hz~1000HZ, a laser pulse width of 2~50ms, and a scanning speed of 50mm / min~2000mm / min; the maximum output current of the DC power supply 13 is 400A.

Claims

1. Microgravity metal fuse additive melt directional transfer and liquid bridge transition holding device, characterized in that: It includes a multi-axis motion platform, a forming substrate, an industrial control system, a laser source, a metal wire reel, a wire feeding mechanism and a driving motor, an insulating sleeve, a coaxial wire feeding and air feeding pipe, a metal wire angle adjustment structure, a metal wire pressing mechanism, an air pipe heating device, a DC power supply, an electric current clamp, an ammeter, a protective gas, a precision gas flow meter, an electromagnetic coil, a magnetic head, an electromagnetic coil fixing bracket, and an AC power supply; the forming substrate is installed on the multi-axis motion platform; the multi-axis motion platform customizes the three-dimensional motion trajectory path according to the three-dimensional data in additive manufacturing; Two current clamps are fixed on the metal wire and the forming substrate respectively, and a current path is formed between the metal wire and the forming substrate through a direct current power supply, and an ammeter is connected in series in the current path; an electromagnetic coil is arranged circumferentially of the metal wire, and a magnetic rod is connected to the electromagnetic coil and distributed at symmetrical positions on both sides of the end of the metal wire, and the electromagnetic coil is fixedly connected to the coaxial wire feeding and air feeding pipe through an electromagnetic coil fixing frame; the alternating current power supply provides an alternating electric field for the electromagnetic coil, thereby generating an alternating magnetic field near the end of the metal wire; the wire feeding mechanism and the driving motor quantitatively and constantly send the metal wire to the action range of the light spot emitted by the laser source; the laser emitted by the laser source acts within the end range of the metal wire to form a liquid melt at the end of the metal wire; at the same time, the laser acts on the forming substrate to form a liquid molten pool on the forming substrate; the metal wire and the forming substrate form a liquid bridge connection mode through the liquid melt.

2. The microgravity metal fuse additive melt directional transfer and liquid bridge transition holding device according to claim 1 is characterized in that: During operation, the laser source and the metal wire are stationary.

3. The microgravity metal fuse additive melt directional transfer and liquid bridge transition holding device according to claim 1, characterized in that: Blow the protective gas coaxially with the metal wire.

4. The microgravity metal fuse additive melt directional transfer and liquid bridge transition holding device according to claim 1, characterized in that: The shielding gas is an inert gas, which is ejected through a precision gas flow meter and a coaxial wire feeding and air feeding pipe. The coaxial wire feeding and air feeding pipe is heated by a gas pipe heating device, and the coaxial wire feeding and air feeding pipe transfers heat to the metal wire and the shielding gas by heat conduction, thereby heating the shielding gas and the metal wire.

5. The microgravity metal fuse additive melt directional transfer and liquid bridge transition holding device according to claim 1, characterized in that: The metal wire is a stainless steel wire, an aluminum alloy wire, a titanium alloy wire, a flux-cored welding wire, a high / medium entropy alloy, an amorphous alloy wire or a metal composite material wire.

6. The microgravity metal fuse additive melt directional transfer and liquid bridge transition holding device according to claim 1, characterized in that: The metal wire angle adjustment structure adjusts the angle between the metal wire and the horizontal direction, and the angle range is 0~60°.

7. The microgravity metal fuse additive melt directional transfer and liquid bridge transition holding device according to claim 1, characterized in that: The end of the metal wire is kept in contact with the forming substrate, and a pre-compression force is applied between the end of the metal wire and the forming substrate by the metal wire pressing mechanism to ensure good contact between the end of the metal wire and the forming substrate.

8. The microgravity metal fuse additive melt directional transfer and liquid bridge transition holding device according to claim 1, characterized in that: The industrial control system detects whether a closed current path is formed between the forming substrate and the metal wire through an ammeter; when the current of the ammeter is 0A, it means that the liquid bridge between the metal wire and the forming substrate is disconnected; in the working state of the liquid bridge being disconnected, the industrial control system increases the wire feeding length through the wire feeding mechanism and the driving motor; When a closed circuit exists in the passage, the industrial control system adjusts the wire feeding speed to the normal process to keep the forming substrate and the metal wire in a stable liquid bridge connection.

9. A method for directional transfer of metal fuse additive melt and liquid bridge transition maintenance in microgravity, characterized in that: The steps include: Step S1, adjusting the relative position of the laser source and the metal wire and the initial processing position of the forming substrate, forming a pre-pressure between the forming substrate and the metal wire through the metal wire pressing mechanism, and ensuring good contact between the metal wire and the forming substrate; Step S2, slicing the data according to the three-dimensional model to be constructed, and ensuring that the wire-feeding metal wire is always parallel to the forming direction and kept at the front end of the forming direction through a multi-axis motion platform; ensuring that the metal wire is in contact with the forming substrate; Step S3, sequentially starting the protective gas, laser source, DC power supply, AC power supply, wire feeding mechanism and driving motor, after the metal wire contacts the forming substrate, a current path is generated between the metal wire and the forming substrate, the current is used as a control signal, and additive processing is started according to the slice data of the three-dimensional model; Step S4, during the processing, the industrial control system detects the current generated between the metal wire and the forming substrate. When the current is 0, the dynamic wire feeding amount program is started, and the metal liquid bridge between the metal wire and the forming substrate is connected by increasing the wire feeding amount; when the current value is restored, the dynamic wire feeding amount program is adjusted to a normal wire feeding amount process, so that a stable liquid bridge connection is maintained between the metal wire and the forming substrate; Step S5, after the current layer processing is completed, the wire feeding mechanism and the driving motor, the DC power supply, the laser source and the shielding gas are turned off in sequence; at the same time, the metal wire pressing mechanism moves upward to release the pre-pressure between the metal wire and the forming substrate, and the multi-axis motion platform moves the forming substrate to the initial position of the next trajectory; Step S6, repeating steps S1, S2, S3, S4 and S5 until the entire three-dimensional component is processed.

10. A microgravity metal fuse additive melt directional transfer and liquid bridge transition maintenance method according to claim 9, characterized in that: The flow rate of the protective gas is 0L / min~25L / min; the laser source is used to output pulsed laser or continuous laser, its maximum output power is 4000W, the pulse frequency is 10Hz~1000HZ, the laser pulse width is 2~50ms, and the scanning speed is 50mm / min~2000mm / min; the maximum output current of the DC power supply is 400A.

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