Indirect electric arc additive manufacturing method based on plasma coaxial wire feeding and application

Abstract

The invention discloses an indirect electric arc additive manufacturing method based on plasma coaxial wire feeding and application, and belongs to the crossing field of additive manufacturing and welding technologies. A positive electrode of a plasma arc welding power supply is connected with a water-cooling copper nozzle of a plasma welding gun, and a negative electrode of the plasma arc welding power supply is connected with a hollow tungsten electrode of the plasma welding gun; the welding wire is coaxially sent out through the hollow tungsten electrode, and an indirect electric arc between the hollow tungsten electrode and the water-cooling copper nozzle forms an annular electric arc shape to surround the welding wire; arc energy acts on the welding wire in an annular mode through annular distribution of indirect arcs, more than 60% of energy acts on the welding wire to be melted, and heat input of base metal is reduced by 40%-60%. According to the method, the problem of heat input of base metal in the material increasing process is fundamentally solved, heat input is finely regulated and controlled, a heat affected zone is controlled within an extremely small range, and the excellent initial microstructure and mechanical properties of the base metal are completely reserved, so that the process can better meet the manufacturing requirements of high-end equipment.

Description

Technical Field

[0001] The present invention belongs to the cross - field of additive manufacturing and welding technology, and particularly relates to an indirect arc additive manufacturing method and application based on plasma coaxial wire feeding. Background Art

[0002] Additive manufacturing has currently become a research hotspot in the field of mechanical science. In various fields, parts and structural components formed by composite of dissimilar materials are gradually becoming research hot - spot issues. The development and application of composite structures face the technical bottleneck of additive manufacturing of dissimilar metals. There are significant differences in the chemical composition and thermal - physical properties of different metals, and the metallurgical compatibility of some materials is poor. If the heat input is too large, a large number of intermetallic compounds will be generated at the interface, deteriorating the mechanical properties of the structure. The above - mentioned problems directly affect the stacking dimensional accuracy, microstructure, and mechanical properties of dissimilar - metal composite components. Therefore, the key common problem faced by the current additive manufacturing technology of dissimilar metals is shape and property control, that is, how to control and optimize the forming accuracy and mechanical properties while controlling the interface heat and fusion.

[0003] Currently, several indirect additive manufacturing process methods have been introduced at home and abroad, such as double - wire indirect arc alternating bypass welding, laser double - wire indirect arc welding, and three - wire indirect arc welding, etc. The double - filler - wire process can not only improve the cladding efficiency during additive manufacturing, but also directly prepare heterogeneous composite complex components by feeding two kinds of wire materials. Abe et al. from the University of Yamanashi in Japan, based on the gas - metal arc welding system, melted two heterogeneous wire materials simultaneously to conduct an additive test of two wire materials in a single component, manufacturing high - performance components with different surface and internal structures; the indirect arc method realized a new welding arc distribution scheme, that is, a separate adjustment mechanism for heat input and metal cladding. By adopting the form of gas - metal arc indirect arc and laser indirect arc, high - efficiency metal cladding and a smaller welding heat input are obtained. The arc not only preheats the workpiece and melts the welding wire, but also affects the droplet transfer form, realizing the high - efficiency and high - quality additive manufacturing process of existing equipment.

[0004] Traditional melting - based additive manufacturing processes face many bottlenecks. On the one hand, in common direct - arc additive manufacturing means, when melting the welding wire to build the material layer, a large amount of heat will be transferred to the base metal, resulting in an excessive depth of the heat - affected zone of the base metal. This not only changes the original microstructure morphology of the base metal, promotes abnormal grain growth, reduces the key mechanical properties such as the strength and toughness of the base metal itself, but also may cause residual stress concentration, increasing the risk of component deformation and cracking, greatly limiting the application of additive manufacturing in high - end fields with strict requirements for precision and performance, such as the repair of aero - engine blades and the customization of high - performance medical devices.

[0005] On the other hand, from the perspective of energy utilization and welding wire melting, the traditional process cannot efficiently focus on the welding wire due to the dispersion of arc energy, resulting in uneven melting of the welding wire and slow rate. This not only slows down the overall additive manufacturing progress, but also causes a large amount of energy to be wasted on unnecessary heating of the base material, raising production costs and making it difficult to meet the demands of large-scale, high-efficiency and high-quality industrial additive manufacturing.

[0006] The present invention utilizes the indirect arc formed between the tungsten electrode and the welding wire in the plasma arc to melt the welding wire for additive manufacturing, which is an innovative technology suitable for many industries with high requirements on component precision, performance and manufacturing efficiency, such as shipbuilding, aerospace, electronics, automobiles, medical equipment, etc. Summary of the invention

[0007] The purpose of the present invention is to focus on the field of indirect arc additive manufacturing and to develop cutting-edge technology for additive manufacturing by generating an indirect arc between a tungsten electrode and a welding wire to melt the welding wire.

[0008] The present invention provides an indirect arc additive manufacturing method based on plasma coaxial wire feeding, wherein the positive electrode of a plasma arc welding power supply is connected to a water-cooled copper nozzle of a plasma welding gun, and the negative electrode of the plasma arc power supply is connected to a hollow tungsten electrode of the plasma welding gun; the welding wire is coaxially fed through the hollow tungsten electrode, and the indirect arc between the hollow tungsten electrode and the water-cooled copper nozzle forms a ring-shaped arc shape, surrounding the welding wire; the ring-shaped distribution of the indirect arc enables the arc energy to act on the welding wire in a "ring-shaped" manner.

[0009] Furthermore, the hollow tungsten pole is divided into two parts, the upper part is a hollow cylinder, and the lower part is a hollow cone.

[0010] Further, the following steps are included:

[0011] Step 1: Connect the additive system, connect the positive pole of the plasma arc welding power supply to the water-cooled copper nozzle of the plasma welding gun, and connect the negative pole of the plasma arc welding power supply 1 to the hollow tungsten electrode of the plasma welding gun; the welding wire is fed into the hollow tungsten electrode by the wire feeder through the wire feed wheel, and extends to the position of the indirect arc welding torch;

[0012] Step 2: During additive manufacturing, start the plasma arc welding power supply, wire feeder, cooling water and shielding gas of the water-cooled copper nozzle at the same time; adjust the plasma current to 40-200A; melt the welding wire through the indirect arc formed between the copper nozzle and the hollow tungsten electrode to carry out the additive manufacturing process.

[0013] Furthermore, the ion gas and the shielding gas are both argon gas; the shielding gas flow rate is 10 to 20 L / min; the ion gas flow rate is 1 to 3 L / min.

[0014] Furthermore, the moving speed of the plasma welding gun is 4 to 10 mm / s; the wire feeding speed of the wire feeder is 3 to 15 m / min.

[0015] Further, the diameter of the welding wire is 1.0 - 2.0 mm; the distance between the bottom of the hollow tungsten electrode and the substrate is 6 - 8 mm.

[0016] Further, the plasma arc power source 1 is selected as a PAW welding power source.

[0017] Further, the heat input of the base material of the method is reduced by 40% - 60%, the additive manufacturing efficiency is increased by 60% - 80%, and the additive manufacturing time is shortened by 25% - 40%.

[0018] Further, the heat input H of the base material BM is:

[0019]

[0020] where η BM is the heat efficiency acting on the base material and the molten pool, η BM takes a value of 0.2 - 0.4; E is the arc voltage; I is the arc current; v is the moving speed of the ion welding torch during the additive manufacturing process.

[0021] The present invention provides an application of an indirect arc additive manufacturing method based on coaxial wire feeding of plasma, which is applied to the additive manufacturing of high-temperature nickel-based alloys.

[0022] The beneficial effects of the present invention are as follows:

[0023] (1) The method of the present invention innovates the indirect arc architecture, successfully realizes the "shunt" of heat, and more than 60% of the arc energy acts precisely on the melting of the welding wire, and the heat input of the base material is sharply reduced by 40% - 60% compared with the traditional plasma arc additive manufacturing process.

[0024] (2) The energy conduction link of the method of the present invention is combined with intelligent power control, and the absorption rate of the arc energy by the welding wire soars, and the melting efficiency is increased by 30% - 50% compared with the past. In the additive manufacturing project of mass-producing complex metal parts, the manufacturing time is shortened by 25% - 40%, and the unit energy consumption is reduced by 20% - 30%, with remarkable economic benefits.

[0025] (3) The stable and controllable indirect arc of the method of the present invention ensures that the molten droplets of the welding wire are transferred in an almost ideal state, and the welds stacked layer by layer are flat, smooth and the structure is dense. The alloy manufactured by this method is detected by flaw detection, and the internal defect density is reduced by 70% - 90%, and the overall strength of the component is increased by 15% - 25%. Description of the Drawings

[0026] Figure 1 It is a schematic diagram of the working principle of plasma indirect arc additive manufacturing;

[0027] Figure 2Macrograph and surface forming diagram of the additive sample manufactured by plasma indirect arc in Example 1;

[0028] Figure 3 Macrograph and surface forming diagram of the additive sample manufactured by plasma direct arc in Comparative Example 1.

[0029] Reference numerals: 1, plasma arc welding power source; 2, wire feeding wheel; 3, welding wire; 4, hollow tungsten electrode; 5, water-cooled copper nozzle; 6, cooling water inlet; 7, compression nozzle; 8, shielding gas; 9, shielding gas hood; 10, ion gas; 11, cooling water outlet; 12, indirect arc; 13, wire feeder. Detailed implementation manners

[0030] The present invention will be further described below with reference to the accompanying drawings.

[0031] The present invention discloses an indirect arc additive manufacturing system based on plasma coaxial wire feeding, including a plasma arc welding power source 1, a wire feeding wheel 2, a welding wire 3, a hollow tungsten electrode 4, a water-cooled copper nozzle 5, a cooling water inlet 6, a compression nozzle 7, a shielding gas 8, a shielding gas hood 9, an ion gas 10, a cooling water outlet 11, an indirect arc 12, and a wire feeder 13; one end of the welding wire 3 is located in the wire feeder 13, and the other end of the welding wire 3 is inserted into the hollow tungsten electrode 4 and fixed in position by the wire feeding wheel 2; the hollow tungsten electrode 4 is located in the shielding gas hood 9, the upper half of the hollow tungsten electrode 4 is a hollow cylinder, and the lower half of the hollow tungsten electrode 4 is a hollow cone; the water-cooled copper nozzle 5 is located outside the hollow tungsten electrode 4, and the ion gas 10 is introduced between the water-cooled copper nozzle 5 and the hollow tungsten electrode 4; a compression nozzle 7 and a shielding gas hood 9 are sequentially arranged outside the water-cooled copper nozzle 5, and the shielding gas is introduced between the compression nozzle 7 and the shielding gas hood 9.

[0032] Plasma coaxial wire feeding system: The welding wire 3 is coaxially fed out through the hollow tungsten electrode 4, and an annular arc shape is formed by the indirect arc between the hollow tungsten electrode 4 and the water-cooled copper nozzle 5. The hollow tungsten electrode 4 is designed as a hollow cylinder (upper half) and a hollow cone (lower half) to ensure the coaxiality of the welding wire 3 and the hollow tungsten electrode 4, and the arc is annularly distributed between the hollow tungsten electrode 4 and the water-cooled copper nozzle 5.

[0033] Indirect arc structure: The positive electrode of the plasma arc welding power source 1 is connected to the water-cooled copper nozzle 5, and the negative electrode is connected to the hollow tungsten electrode 4. An indirect arc (not conducting with the substrate) is formed between the water-cooled copper nozzle 5 and the hollow tungsten electrode 4, surrounding the welding wire. This annular arc further restricts the arc shape through the synergistic effect of the compression nozzle 7 and the ion gas 10, making the energy act concentratedly on the welding wire.

[0034] Since the indirect arc has relatively high heat, in order to ensure the structural stability of the gun body during the additive process, a water-cooled copper nozzle 5 is used to connect the positive electrode of the plasma arc welding power source 1. Utilizing the characteristics of copper, which has good electrical and thermal conductivity, a cooling water passage is designed to prevent it from melting due to excessive temperature, ensuring the adaptability and stability of the additive process.

[0035] The present invention also discloses an additive manufacturing method for an indirect arc additive system based on plasma coaxial wire feeding, including:

[0036] Step 1: Perform pre-welding pretreatment on the workpiece, including cleaning oil stains, grinding the oxide layer, preparing a groove, and selecting a suitable welding wire according to the relevant requirements of the additive component. Then connect the equipment and devices;

[0037] Step 2: According to the process requirements, select a suitable aperture of the hollow tungsten electrode 4 to avoid direct contact between the tungsten electrode and the welding wire, ensure that the axis of the welding wire is basically perpendicular to the workpiece, and control the distance between the hollow tungsten electrode and the workpiece as well as the length of the dry extension of the welding wire;

[0038] Step 3: Start the PAW welding power source and set the plasma current, ion gas flow rate, shielding gas flow rate, wire feeding speed, and travel speed according to the welding process;

[0039] Step 4: Ignite the plasma arc to form an indirect arc that does not conduct with the substrate between the water-cooled copper nozzle 5 and the hollow tungsten electrode 4. The welding wire 3 is coaxially fed through the hollow tungsten electrode 4, and stable droplet transfer is formed under the action of the plasma arc and cladded on the substrate to achieve additive manufacturing on the substrate.

[0040] Using the above additive manufacturing method, the heat input to the base material is reduced by 40% - 60%. According to the heat input formula:

[0041]

[0042] where η BM is the thermal efficiency acting on the base material and the molten pool, approximately 0.2 - 0.4 (because most of the total energy is used for the welding wire and the remaining part is transferred to the base material), E is the arc voltage, I is the arc current, and v is the deposition speed during the additive process. Compared with the traditional plasma arc additive, the thermal efficiency is significantly reduced (the PAW thermal efficiency is about 0.7 - 0.9), resulting in a 40% - 60% reduction in the heat input to the base material.

[0043] Using the above additive manufacturing method, compared with the traditional direct arc additive process of plasma coaxial wire feeding, the additive manufacturing time is shortened by 25% - 40%, and the additive efficiency is increased by 60% - 75%.

[0044] Additive efficiency ε:

[0045] ε = ηρAv

[0046] Among them, η is the wire melting efficiency, ρ is the density of the wire material, A is the cross-sectional area of the wire, and v is the wire feeding speed.

[0047] The relationship between the direct arc additive manufacturing efficiency ε and the indirect arc additive manufacturing efficiency ε of the traditional process can be expressed as: j as follows:

[0048]

[0049] Among them, in indirect arc additive manufacturing, the efficiency factor η j is affected by process parameters such as the inner diameter of the compression nozzle, the flow rate of the shielding gas, and the spatial position between the tungsten electrode and the wire. The indirect arc forms a more concentrated arc column through the compression nozzle and gas shielding. The inner diameter size of the compression nozzle and the ion gas flow rate affect the j value of η. The smaller the inner diameter size, the higher the value of the ion gas flow rate η j ; the distance between the wire and the tungsten electrode also affects the j value of η. The smaller the distance between the wire and the tungsten electrode, the higher the j value of η, but it will also affect the droplet transfer form at the same time. Usually, spray transfer can reduce spatter and non-melting. It is necessary to adjust the spatial position to ensure a good transfer form to obtain high-quality additive components; the value of η is 0.3 - 0.5; the j value of η is 0.65 - 0.85;

[0050]

[0051] Among them, t is the direct arc additive manufacturing time of the traditional process; t j is the indirect arc additive manufacturing time.

[0052] Example 1

[0053] An indirect arc additive manufacturing method based on plasma coaxial wire feeding in this example includes the following steps:

[0054] Step 1: Perform pre-welding pretreatment on the AH36 steel plate workpiece, including cleaning oil stains, grinding the oxide layer, and opening a groove. The wire selected is a C276 nickel wire with a diameter of 1.2 mm.

[0055] Step 2: According to the process requirements, select the appropriate inner diameter of the hollow tungsten electrode 4 to avoid direct contact between the tungsten electrode and the wire, ensure that the axis of the wire 3 is basically perpendicular to the workpiece, and control the distance between the hollow tungsten electrode 4 and the workpiece and the length of the wire dry elongation;

[0056] Step 3: Connect the additive manufacturing system; the positive pole of the plasma arc power supply 1 is connected to the water-cooled copper nozzle 5 of the plasma welding torch, and the negative pole of the plasma arc power supply 1 is connected to the hollow tungsten electrode 4 of the plasma welding torch; the wire 3 is sent into the hollow tungsten electrode 4 by the wire feeder 13 through the wire feeding wheel 2 and extends to the position of the indirect arc welding torch.

[0057] Step 4: Start the PAW welding power source and adjust the parameters: plasma current 150 A, wire feeding speed 450 cm / min, travel speed 6 mm / s, ion gas flow rate 1.5 L / min, shielding gas flow rate 15 L / min, arc length 6 mm.

[0058] Step 5: Ignite the plasma arc to form an indirect arc that does not conduct with the substrate between the water-cooled copper nozzle 5 and the hollow tungsten electrode 4. The welding wire 3 is coaxially fed out through the hollow tungsten electrode 4 and forms stable droplet transfer under the action of the plasma arc and is cladded on the substrate, realizing additive manufacturing on the substrate. The forming of the indirect arc is as Figure 2 shown.

[0059] Comparative Example 1

[0060] The difference from Example 1 is that in Step 3, the additive manufacturing system is connected; the positive pole of the plasma arc power source 1 is connected to the substrate, and the negative pole of the plasma arc power source 1 is connected to the hollow tungsten electrode 4 of the plasma welding torch; the welding wire 3 is fed into the inside of the hollow tungsten electrode 4 by the wire feeder 13 through the wire feeding wheel 2 and extends to the position of the indirect arc torch. The conditions of the remaining steps are the same; in Comparative Example 1, a direct arc is formed for the additive manufacturing of nickel-based alloys. The forming of the direct arc is as Figure 3 shown.

[0061] In the Hastelloy C276 coating formed by plasma arc additive manufacturing in Comparative Example 1, the microstructure shows a cellular structure with distinct dendrites, as shown in Figure 3 b and Figure 3 b1. The characteristics of the cellular structure are slender cells with an average width of about 20 - 30 μm, indicating a relatively slow cooling rate. This cooling rate is caused by the typically higher heat input of the plasma arc, which results in a larger molten pool and a longer high-temperature residence time. In the Hastelloy C276 coating prepared by plasma indirect arc in Example 1, the microstructure transforms into a finer cellular structure without prominent dendrites, as shown in Figure 2 b and Figure 2 b1. Compared with the plasma arc additive manufacturing sample in Comparative Example 1, the cells are smaller and more equiaxed, reflecting a higher cooling rate due to the reduced heat input. The plasma indirect arc additive manufacturing process minimizes the heat input, shortens the high-temperature residence time of the molten pool, and suppresses dendrite formation and solute segregation. This results in a more uniform microstructure, reduces inter-dendritic segregation, and decreases the possibility of forming a second phase.

[0062] In summary, the annular distribution of the indirect arc in the present invention enables the arc energy to act on the welding wire in an "annular" manner, with more than 60% of the energy concentrated on the melting of the welding wire rather than directly transferred to the base material. This shunt mechanism is achieved through the collaborative optimization of the equipment structure (hollow tungsten electrode, compression nozzle) and process parameters (current, gas flow rate), significantly reducing the heat input to the base material while improving the energy utilization rate. The present invention fundamentally reduces the heat input problem of the base material metal during the additive manufacturing process, finely regulates the heat input, controls the heat affected zone within a very small range, and completely retains the excellent initial microstructure and mechanical properties of the base material, enabling this process to better meet the manufacturing requirements of high-end equipment. By optimizing the welding energy flow direction and constructing an "energy high-speed channel" from the power supply to the welding wire through optimized design, the arc energy is promoted to be transmitted to the welding wire almost directionally, comprehensively improving the melting speed, stability, and uniformity of the welding wire, thereby significantly shortening the additive manufacturing cycle and optimizing the efficiency of additive manufacturing.

[0063] As described above, based on the content of the solutions given in combination with the accompanying drawings and embodiments, similar technical solutions can be derived. Any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention without departing from the technical solutions of the present invention still fall within the scope of the technical solutions of the present invention.

Claims

1. An indirect arc additive manufacturing method based on plasma coaxial wire feeding, characterized in that, The positive electrode of the plasma arc welding power source (1) is connected to the water-cooled copper nozzle (5) of the plasma welding torch, and the negative electrode of the plasma arc welding power source (1) is connected to the hollow tungsten electrode (4) of the plasma welding torch; the welding wire (3) is sent out coaxially through the hollow tungsten electrode (4), and an indirect arc between the hollow tungsten electrode (4) and the water-cooled copper nozzle (5) forms an annular arc shape surrounding the welding wire (3); the annular distribution of the indirect arc enables the arc energy to act on the welding wire (3) in an "annular" manner.

2. The indirect arc additive manufacturing method based on plasma coaxial wire feeding according to claim 1, wherein The hollow tungsten electrode (4) is divided into upper and lower parts. The upper part is a hollow cylinder, and the lower part is a hollow cone.

3. The indirect arc additive manufacturing method based on plasma coaxial wire feeding according to claim 1, characterized in that It includes the following steps: Step 1: Connect the additive manufacturing system. The positive electrode of the plasma arc welding power source (1) is connected to the water-cooled copper nozzle (5) of the plasma welding torch, and the negative electrode of the plasma arc welding power source (1) is connected to the hollow tungsten electrode (4) of the plasma welding torch; the welding wire (3) is fed into the interior of the hollow tungsten electrode (4) by the wire feeder (13) through the wire feeding wheel (2) and extends to the position of the indirect arc welding torch. Step 2: During additive manufacturing, simultaneously start the plasma arc welding power source (1), the wire feeder 13, the cooling water and the shielding gas of the water-cooled copper nozzle (5); adjust the plasma current to 40 - 200 A; melt the welding wire through the indirect arc formed between the water-cooled copper nozzle (5) and the hollow tungsten electrode (4) to carry out the process of additive manufacturing.

4. The indirect arc additive manufacturing method based on plasma coaxial wire feeding according to claim 3, wherein, Both the ion gas and the shielding gas are argon; the gas flow rate of the shielding gas is 10 - 20 L / min; the gas flow rate of the ion gas is 1 - 3 L / min.

5. The indirect arc additive manufacturing method based on plasma coaxial wire feeding according to claim 3, characterized in that The moving speed of the plasma welding torch is 4 - 10 mm / s; the wire feeding speed of the wire feeder (13) is 3 - 15 m / min.

6. The indirect arc additive manufacturing method based on plasma coaxial wire feeding according to claim 3, characterized in that, The diameter of the welding wire is 1.0 - 2.0 mm.

7. The indirect arc additive manufacturing method based on plasma coaxial wire feeding according to claim 3, wherein The plasma arc welding power source (1) selects a PAW welding power source.

8. The indirect arc additive manufacturing method based on plasma coaxial wire feeding according to claim 3, characterized in that, For this method, the heat input to the base material is reduced by 40% - 60%, the additive manufacturing efficiency is increased by 60% - 80%, and the additive manufacturing time is shortened by 25% - 40%.

9. The indirect arc additive manufacturing method based on plasma coaxial wire feeding according to claim 1, characterized in that, The heat input H of the base material BM is as follows: Among them, η BM is the thermal efficiency acting on the base material and the molten pool, η BM ranges from 0.2 to 0.4; E is the arc voltage; I is the arc current; v is the moving speed of the ion welding torch during the additive manufacturing process.

10. Application of the indirect arc additive manufacturing method based on plasma coaxial wire feeding as described in claim 1, characterized in that, It is applied to the additive manufacturing of high-temperature nickel-based alloys.

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