A design method for magnetically controlled hollow tungsten pole full-area negative pressure arc

Abstract

The present invention belongs to the technical field of hollow tungsten electrode welding technology. The present invention discloses a design method for magnetron hollow tungsten electrode negative pressure arc welding, including: calculating the arc shape of the hollow tungsten electrode; calculating the hollow tungsten electrode arc under an externally applied longitudinal magnetic field; studying the influence law of the externally applied magnetic field on the arc temperature, pressure, velocity, and current density by changing the initial conditions and boundary conditions of the hollow tungsten electrode arc, and then obtaining the dominant effect on the arc physical characteristics and the change law of the workpiece surface pressure under different parameters; through the above steps, it has the advantages of a more uniform and stable molten pool and a more realistic numerical simulation result, providing a complete new idea for numerical simulation and facilitating subsequent personnel to continue the research on negative pressure arc.

Description

Technical Field

[0001] The present invention relates to the technical fields of negative-pressure arc welding technology and negative-pressure arc additive manufacturing technology. More specifically, the present invention relates to a design method for a magnetron hollow tungsten electrode full-domain negative-pressure arc. Background Art

[0002] A negative-pressure arc refers to a state where the arc pressure is negative at a conventional horizontal standard position, forming a reverse pressure gradient with increasing pressure from the center to the periphery in the arc, causing the arc temperature distribution to decrease uniformly and rapidly in the central region, thereby enhancing the technological characteristics of the arc, improving the physical properties and energy distribution of the traditional positive-pressure arc, effectively regulating the adverse effects of the positive-pressure arc, and improving the additive manufacturing efficiency, forming accuracy, and quality. Negative-pressure arc welding refers to a welding position at the horizontal welding position, which is also a common standard position for arc additive manufacturing. Relative to the welding molten pool, the welding arc pressure is negative, that is, the arc negative pressure (attraction force), and the arc has an attracting (adsorbing) effect, which is called a negative-pressure arc. To distinguish it from conventional positive-pressure arc welding, it is newly defined as negative-pressure arc welding. Negative-pressure arc welding is generated by an externally applied longitudinal magnetic field to control the arc welding method, so it is defined as magnetron negative-pressure arc welding to distinguish it from conventional magnetron positive-pressure arc welding. Obviously, there is a fundamental difference between negative-pressure arc welding and hollow tungsten electrode "micro-negative-pressure" arc welding because the "overall arc pressure in the hollow tungsten electrode 'micro-negative-pressure' arc welding is still positive, only the local area has a lower pressure than the conventional arc", still having the characteristics of a positive-pressure arc, not the full-domain negative-pressure characteristic, and completely belonging to the scientific and technological category of positive-pressure arc welding, not belonging to the true negative-pressure arc welding and negative-pressure arc additive manufacturing technology system. Compared with the conventional solid tungsten electrode arc, the arc pressure of the hollow tungsten electrode decreases, and the energy distribution and thermal output of the hollow tungsten electrode arc both change, decreasing with the reduction of the local pressure. The characteristics and regulation of the hollow tungsten electrode arc have flexibility and have the development potential for applying the hollow tungsten electrode to coaxial wire feeding arc welding, arc-laser hybrid welding, surface surfacing, and arc additive manufacturing fields. The inner hole of the hollow tungsten electrode is in a "micro-negative-pressure" state, reducing the pressure value in the arc region and having characteristics different from the conventional arc. However, the welding arc of the hollow tungsten electrode is still a positive-pressure welding arc, only the arc pressure is lower than the conventional arc, and no arc negative pressure is generated, still showing the working mechanism of positive-pressure arc welding. By using the magnetic field control method, it is very convenient to promote various arc characteristics of the GTAW welding arc from positive pressure to negative pressure and from positive pressure gradient to negative pressure gradient, and it can realize the flexible regulation of the arc additive manufacturing (or welding) technology. At present, the external field technology provides diversified control means and technical references for the negative-pressure arc welding technology, and can innovatively construct the magnetron hollow tungsten electrode full-domain negative-pressure arc welding technology and the magnetron hollow tungsten electrode full-domain negative-pressure arc additive manufacturing technology.

[0003] Through means such as experimental observation, numerical simulation, and theoretical analysis, the formation mechanism, ionization process, and energy transfer characteristics of the negative-pressure arc can be revealed, providing a scientific basis for optimizing and applying negative-pressure arc welding and additive manufacturing. For the design method of the negative-pressure arc, the process of using experiments to measure its laws and design its characteristics is very complex and unsatisfactory. Therefore, numerical simulation is used for auxiliary design. However, so far, there is no economical, effective, and reliable design method for the magnetron hollow tungsten electrode full-domain negative-pressure arc to promote the development and engineering application of negative-pressure arc welding technology and negative-pressure arc additive manufacturing technology.

[0004] In view of this, the present invention proposes a design method for a magnetron hollow tungsten electrode full-domain negative-pressure arc to solve the above problems. Summary of the Invention

[0005] To overcome the above-mentioned defects of the prior art, an embodiment of the present invention provides a design method for a magnetron hollow tungsten electrode full-domain negative-pressure arc.

[0006] To achieve the above object, the present invention provides the following technical solution: A design method for a magnetron hollow tungsten electrode full-domain negative-pressure arc, characterized by comprising the following steps:

[0007] Step 1: Calculate the arc shape of the hollow tungsten electrode; the said Step 1 includes the following steps:

[0008] (1) Establish the mass conservation equation and momentum conservation equation under the negative-pressure arc to determine the velocity and pressure distribution of the arc plasma:

[0009]

[0010] In the formula, ρ is the density; v is the velocity vector; P is the pressure; μ is the viscosity; I is the unit matrix; F is the momentum source term;

[0011] Solve the arc temperature T according to the energy conservation equation:

[0012]

[0013] In the formula, k is the thermal conductivity; T is the temperature; Cp is the specific heat capacity; Q is the source term of the energy conservation equation;

[0014] Calculate the electric potential and magnetic vector potential distribution according to the current continuity equation and Ohm's law:

[0015]

[0016] In the formula, V is the electric potential, A is the magnetic vector potential, and σ is the conductivity;

[0017] Obtain the current density J and magnetic induction intensity B according to V and A:

[0018]

[0019] The arc energy source term consists of three parts: Joule heat, electron enthalpy transfer, and arc radiation loss:

[0020]

[0021] where \(K_B\) is the Boltzmann constant; \(e\) is the electron charge; \(T\) is the temperature field of the arc shape; \(Q\) is the heat source term; \(Q\) rad is the arc radiation loss;

[0022] According to the self-induced magnetic field strength \(B\) of the arc, the current density \(J\), and the momentum conservation equation, solve the momentum source term in the momentum conservation equation:

[0023] \(F = J\times B\)

[0024] (2) Define the initial process parameters of the hollow tungsten electrode arc, the thermal physical properties of the material, and the boundary conditions;

[0025] (3) Obtain the physical characteristics of the hollow tungsten electrode arc according to the temperature field \(T\), pressure \(p\), velocity \(v\), and current density \(J\) of the arc shape;

[0026] Step 2: Calculate the hollow tungsten electrode arc under an externally applied longitudinal magnetic field; the said Step 2 includes the following steps:

[0027] (1) Add an externally applied electromagnetic force by changing the momentum source term:

[0028] \(F = J\times (B + B\) 0 )

[0029] where \(B\) 0 is the magnetic induction intensity of the externally applied longitudinal magnetic field;

[0030] (2) Study the influence of the externally applied longitudinal magnetic field on the arc temperature, pressure, velocity, and current density according to the changes in the physical characteristics of the arc under the externally applied magnetic field, and then obtain the change laws of the arc pressure and the negative pressure on the workpiece surface under the externally applied magnetic field;

[0031] Step 3: By comparing the calculation results with the experimental results under the same conditions, verify whether the calculation results are consistent with the experimental results under the same conditions. If they are consistent, proceed to the next step; otherwise, return to Step 1, adjust the model or boundary conditions or initial conditions, and repeat the cycle of re-modeling and numerical simulation calculations until the calculation results are consistent with the experimental results under the same conditions, and complete the verification of the model accuracy; fix the model, change other conditions or parameters, and solve the arc results under various conditions and situations.

[0032] Step 4: Study the influence law of the external magnetic field on the arc temperature, pressure, velocity, and current density by changing other conditions or parameters of the hollow tungsten electrode arc; then obtain, analyze, and summarize the dominant effect on the arc physical characteristics and the change law of the workpiece surface pressure under different parameters; complete the design of the magnetron hollow tungsten electrode global negative-pressure arc.

[0033] In a magnetron hollow tungsten electrode global negative-pressure arc design method of the present invention, when there is no air extraction and only the external magnetic field changes, the existence of the hollow cavity of the tungsten electrode promotes the generation of the arc plasma reflux. The externally applied longitudinal magnetic field always reduces the surface pressure of the workpiece welded by the hollow tungsten electrode arc and forms a negative pressure on the workpiece surface, realizing the construction of the magnetron hollow tungsten electrode negative-pressure arc.

[0034] In a magnetron hollow tungsten electrode global negative-pressure arc design method of the present invention, when the air extraction pressure and the external magnetic field change, when the air extraction pressure is close to -20 kPa, the pressure change value is small when the magnetic induction intensity is less than 0.03 T. When the magnetic induction intensity is greater than 0.04 T, the pressure drops rapidly. When the magnetic induction intensity is less than 0.03 T, the air extraction pressure plays a major role in the arc center pressure. When the magnetic induction intensity is greater than 0.04 T, the external magnetic field plays a major role in the arc center pressure.

[0035] The technical effects and advantages of a magnetron hollow tungsten electrode global negative-pressure arc design method of the present invention: By numerically simulating and simulating magnetic field control and changing the air extraction pressure, controlling the surface temperature of the workpiece, making the molten pool more uniform and stable. By adding the method of volume force to load the external electromagnetic force to realize the control of the external magnetic field on the arc, and adding the method of cathode and anode heat source boundary conditions to realize the simulation of the cathode and anode sheath regions, making the numerical simulation results more in line with the actual situation, providing a new idea for the complete numerical simulation-assisted negative-pressure arc design, which is beneficial to the development of negative-pressure arc welding technology and negative-pressure arc additive manufacturing technology.

[0036] The present invention is applicable to negative-pressure arc welding technology, or negative-pressure arc additive manufacturing technology, or negative-pressure arc-laser coaxial hybrid welding technology, or negative-pressure arc-laser off-axis hybrid welding technology, or negative-pressure arc-laser hybrid cladding technology, or negative-pressure arc-laser hybrid additive manufacturing technology, or negative-pressure arc-high energy beam hybrid welding technology, or negative-pressure arc-high energy beam hybrid cladding technology, or negative-pressure arc-high energy beam hybrid additive manufacturing technology. Brief Description of the Drawings

[0037] Figure 1 It is a flow schematic diagram of the present invention;

[0038] Figure 2 It is a geometric model diagram of the hollow tungsten electrode of the present invention;

[0039] Figure 3It is the negative pressure arc pressure diagram of a hollow tungsten electrode under the sole action of an external magnetic field in the present invention;

[0040] Figure 4 It is the design parameter diagram of a hollow tungsten electrode negative pressure arc under the combined action of air extraction and an external magnetic field in the present invention. Specific implementation manners

[0041] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0042] Embodiment 1

[0043] Please refer to Figure 1 As shown, a method for designing a magnetron hollow tungsten electrode global negative pressure arc in this embodiment includes:

[0044] A method for designing a magnetron hollow tungsten electrode global negative pressure arc, characterized by including the following steps:

[0045] Step 1: Calculate the arc shape of the hollow tungsten electrode; the said Step 1 includes the following steps:

[0046] (1) Establish the mass conservation equation and momentum conservation equation under the negative pressure arc to determine the velocity and pressure distribution of the arc plasma:

[0047]

[0048] In the formula, ρ is the density; v is the velocity vector; P is the pressure; μ is the viscosity; I is the unit matrix; F is the momentum source term;

[0049] Solve for the arc temperature T according to the energy conservation equation:

[0050]

[0051] In the formula, k is the heat conduction coefficient; T is the temperature; Cp is the specific heat capacity; Q is the source term of the energy conservation equation;

[0052] Calculate the electric potential and magnetic vector potential distribution according to the current continuity equation and Ohm's law:

[0053]

[0054] In the formula, V is the electric potential, A is the magnetic vector potential, and σ is the conductivity;

[0055] Obtain the current density J and magnetic induction intensity B according to V and A:

[0056]

[0057] The arc energy source term consists of three parts: Joule heat, electron enthalpy transfer, and arc radiation loss:

[0058]

[0059] where \(K_B\) is the Boltzmann constant; \(e\) is the electron charge; \(T\) is the temperature field of the arc shape; \(Q\) is the heat source term; \(Q\) rad is the arc radiation loss;

[0060] According to the self-induced magnetic field strength \(B\) of the arc, the current density \(J\), and the momentum conservation equation, solve the momentum source term in the momentum conservation equation:

[0061] \(F = J\times B\)

[0062] (2) Define the initial process parameters of the hollow tungsten electrode arc, the material thermophysical properties parameters, and the boundary conditions;

[0063] (3) Obtain the physical characteristics of the hollow tungsten electrode arc according to the temperature field \(T\), pressure \(p\), velocity \(v\), and current density \(J\) of the arc shape;

[0064] Step 2: Calculate the hollow tungsten electrode arc under an externally applied longitudinal magnetic field; the said Step 2 includes the following steps:

[0065] (1) Add an externally applied electromagnetic force by changing the momentum source term:

[0066] \(F = J\times (B + B\) 0 )

[0067] where \(B\) 0 is the magnetic induction intensity of the externally applied longitudinal magnetic field;

[0068] (2) Study the influence of the externally applied longitudinal magnetic field on the arc temperature, pressure, velocity, and current density according to the changes in the physical characteristics of the arc under the externally applied magnetic field, and then obtain the change laws of the arc pressure and the negative pressure on the workpiece surface under the externally applied magnetic field.

[0069] Step 3: Compare the calculation results with the experimental results under the same conditions to verify whether the calculation results are consistent with the experimental results under the same conditions. If they are consistent, proceed to the next step; otherwise, return to Step 1, adjust the model or boundary conditions or initial conditions, and re-perform the cycle process of modeling and numerical simulation calculation until the calculation results are consistent with the experimental results under the same conditions, and complete the verification of the model accuracy; fix the model, change other conditions or parameters, and solve the arc results under multiple conditions and situations.

[0070] Step 4: Study the influence rules of the applied magnetic field on the arc temperature, pressure, velocity, and current density by changing other conditions or parameters of the hollow tungsten electrode arc; then obtain, analyze, and summarize the dominant effects on the arc physical characteristics and the variation rules of the workpiece surface pressure under different parameters; complete the design of the magnetically controlled hollow tungsten electrode global negative pressure arc.

[0071] Preferably, step 1 includes the following steps:

[0072] (1) Construct a welding arc geometric model according to the actual torch geometric dimensions;

[0073] (2) Mesh the welding arc geometric model; the meshing process includes:

[0074] Define the mesh size: Use free quadrilateral meshes and adjust the distribution; complete the meshing through mapping and sweeping operations.

[0075] (3) Verify the model and calculation results;

[0076] (4) Change the conditions and solve the negative pressure arc characteristics under multiple conditions or scenarios.

[0077] Preferably, step 1 further includes the following steps:

[0078] (1) Load the initial conditions of the negative pressure arc model;

[0079] (2) Define the boundary conditions of the welding arc model; the boundary conditions include:

[0080] Current density input:

[0081]

[0082] Protective gas flow rate:

[0083]

[0084] Cathode boundary condition:

[0085]

[0086] J e =J r [(|J·n|-J r )>0]+|J·n|[(|J·n|-J r )<0]

[0087] J i =|J·n|-J e

[0088]

[0089] Anode boundary condition:

[0090]

[0091] wherein, |J i |V i is the cathode ion heat, and is the electron heat for cooling; is the surface work function; V i is the ionization potential of argon; A r is the Richardson constant, is the effective work function of the cathode, e is the elementary charge, k b is the Boltzmann constant.

[0092] Preferably, the step 2 includes the following steps:

[0093] (1) Reload the momentum source term of the negative pressure arc model;

[0094] (2) Perform parametric scanning by changing the magnetic induction intensity;

[0095] Preferably, the step 3 includes the following steps:

[0096] (1) Redefine the boundary condition of the welding arc model;

[0097] (2) Perform parametric scanning by changing the boundary condition;

[0098] (3) Reload the momentum source term of the negative pressure arc model;

[0099] Preferably, the existence of the pumping pressure changes the flow mode of the arc plasma. As the pumping pressure decreases, part of the recirculating plasma flows along the axis from the workpiece to the hollow cavity. When the pumping pressure is -12 kPa, the arc plasma is completely composed of recirculating plasma, which will make the welding more stable.

[0100] As the pumping pressure decreases, the workpiece surface pressure does not always show a downward trend. When the impact force of the arc plasma on the workpiece surface takes effect, the workpiece center pressure decreases with the decrease of the pumping pressure. When the arc plasma flow is completely composed of recirculation, the impact force does not play a major role. At this time, the arc contraction caused by the decrease of the pumping pressure increases the workpiece center pressure, which is convenient to be controlled simultaneously with the external magnetic field to achieve a better welding effect.

[0101] Example 2

[0102] Please refer to Figure 2As shown in the figure, it is the geometric model diagram of the hollow tungsten electrode negative pressure arc of the present invention. According to the geometric model, boundary conditions and initial conditions are set in the numerical simulation to establish a mathematical model of the magnetron hollow tungsten electrode negative pressure arc. For the parts not described in detail in this embodiment, refer to the description content of Embodiment 1. A design method for the magnetron hollow tungsten electrode global negative pressure arc is provided. The method includes: when only the external magnetic field acts on the hollow tungsten electrode negative pressure arc welding, the hollow tungsten electrode does not exhaust air and is in a natural state. The tungsten electrode radius of the negative pressure arc at the center of the hollow tungsten electrode is 1.6 mm, the hollow cavity radius is 0.5 mm, the arc length is 3 mm, the welding current is 80 A, when the magnetic induction intensity is 0 - 0.05 T, the extraction pressure is 0 kPa, the shielding gas is 99.99% argon, and the shielding gas flow rate is 20 - 30 L / min.

[0103] As Figure 3As shown in the figure, it is the negative pressure arc pressure diagram of a hollow tungsten electrode under the sole action of an external magnetic field in the present invention. From the free arc state with an external longitudinal magnetic field of 0 to the calculation results of the magnetron arc temperature field, velocity field, and pressure field when the external longitudinal magnetic field is 0.05 T, it can be seen that the peak arc temperature appears below the tungsten electrode. Under the action of the external longitudinal magnetic field, the arc near the tungsten electrode contracts, and the arc near the workpiece expands outward. There are two low-temperature regions in the magnetron state: there is a "low-temperature region" in the arc temperature near the workpiece, and there is also a "low-temperature region" in the arc temperature below the hollow cavity of the tungsten electrode. The peak arc temperature rises with the increase of the external magnetic field strength. When the external magnetic field strength is 0.01 T, a backflow plasma is generated at the arc center, and at the same time, the pressure formed at the arc center is greater than 0 Pa, forming an upward flow in the hollow cavity. Compared with the backflow phenomenon that occurs when the external magnetic field strength of a solid tungsten electrode arc is 0.02 T, the existence of the hollow cavity of the tungsten electrode promotes the generation of plasma backflow. When the external magnetic field strength is 0.02 T, the plasma flows from the hollow cavity of the tungsten electrode to the arc center, and a negative pressure has been formed below the tungsten electrode. As the external magnetic field strength is further increased, the arc plasma flow velocity changes from being concentrated below the tungsten electrode to being concentrated on both sides of the axis. With the increase of the external magnetic field strength, the rotation speed of the arc plasma near the tungsten electrode continuously increases, causing the pressure at the arc center to continuously decrease. When the external magnetic field strength is 0.01 T, the peak arc pressure appears at the workpiece. When the external magnetic field strength is 0.02 T, a negative pressure concentration region appears at the arc center. As the magnetic induction intensity continuously rises, the negative pressure region continuously expands and finally forms a negative pressure on the workpiece surface, realizing the design of a negative pressure arc. Due to the existence of the hollow tungsten electrode, when the external magnetic field strength is 0 - 0.01 T, the pressure distribution on the workpiece surface is a Gaussian distribution; when the external magnetic field strength is 0.02 T, the pressure on the workpiece surface does not show a Gaussian distribution nor a bimodal distribution; when the external magnetic field strength is greater than 0.03 T, the pressure on the workpiece surface is a bimodal distribution, and the peak pressure appears at the bimodal positions. When the external magnetic field strength is 0.01 T, a backflow plasma appears in the arc, but a bimodal distribution is not formed on the workpiece surface, and the impact of the arc plasma on the workpiece surface is reduced, and the pressure at the workpiece center continuously decreases. In summary, without gas extraction, when only the external magnetic field changes, the existence of the hollow cavity of the tungsten electrode promotes the generation of arc plasma backflow. The external longitudinal magnetic field always reduces the pressure on the workpiece surface of the hollow tungsten electrode arc and forms a negative pressure on the workpiece surface, realizing the construction of a magnetron hollow tungsten electrode negative pressure arc.

[0104] Example 3

[0105] Please refer to Figure 4 As shown in the figure, for the parts not described in detail in this embodiment, refer to the description content of Embodiment 1. A method for designing a magnetron hollow tungsten electrode global negative pressure arc is provided. The method includes: The simultaneous action of the pumping pressure and the external magnetic field on the hollow tungsten electrode negative pressure arc welding is more abundant and flexible than the single external magnetic field control means, and the arc characteristics are more stable and effective.

[0106] As shown Figure 4 in the figure is a design parameter diagram of a hollow tungsten electrode negative pressure arc under the combined action of air extraction and an external magnetic field in the present invention. For the negative pressure arc in the center of the hollow tungsten electrode, the tungsten electrode radius is 1.6 mm, the hollow cavity radius is 0.5 mm, the arc length is 3 mm, the welding current is 80 A, when the magnetic induction intensity is 0 - 0.05 T, the air extraction pressure ranges from 0 kPa to -20 kPa, the shielding gas is 99.99% argon, and the shielding gas flow rate is 20 - 30 L / min. The pressure change caused by reducing the air extraction pressure is less than the pressure change value caused by increasing the magnetic induction intensity. The influence of the external magnetic field on the central pressure of the workpiece is greater than that of the air extraction pressure. When the air extraction pressure is close to -20 kPa, the pressure change value is smaller when the magnetic induction intensity is less than 0.03 T, and when the magnetic induction intensity is greater than 0.04 T, the pressure drops rapidly. When the magnetic induction intensity is less than 0.03 T, the air extraction pressure plays a major role in the central pressure of the arc. When the magnetic induction intensity is greater than 0.04 T, the external magnetic field plays a major role in the central pressure of the arc.

[0107] Example 4

[0108] For the parts not described in detail in this example, refer to the description in Example 1. A design method for a magnetron hollow tungsten electrode global negative pressure arc is provided. The method includes: a welding current of 80 A, an arc length of 3 mm, protected by 100% pure argon, and the central pressure of the arc without an external magnetic field and air extraction pressure is 61.5 Pa. When the external magnetic field acts alone on the hollow tungsten electrode arc, a negative pressure is formed at a magnetic induction intensity of 0.025 T.

[0109] Example 5

[0110] For the parts not described in detail in this example, refer to the description in Example 1. A design method for a magnetron hollow tungsten electrode global negative pressure arc is provided. The method includes: a welding current of 80 A, an arc length of 3 mm, protected by 100% pure argon. Under the action of a weak air extraction pressure (-1 kPa to -3 kPa), when the external magnetic field acts on the hollow tungsten electrode arc, a negative pressure is formed between 0.0225 T and 0.0245 T. This is lower than the 0.025 T required when the external magnetic field acts alone on the hollow tungsten electrode arc. The weak air extraction pressure can promote the formation of negative pressure.

[0111] Example 6

[0112] For the parts not described in detail in this embodiment, refer to the description in Embodiment 1. A design method for a magnetically controlled hollow tungsten electrode global negative pressure arc is provided. The method includes: a welding current of 80 A, an arc length of 3 mm, 100% pure argon gas protection. Under the action of a strong pumping pressure (-4 kPa to -20 kPa), when an external magnetic field acts on the hollow tungsten electrode arc, a negative pressure is formed between 0.0259 T and 0.036 T. This is an increase compared to the 0.025 T required when the external magnetic field acts on the hollow tungsten electrode arc alone. The strong pumping pressure has an inhibitory effect on the formation of negative pressure.

[0113] 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 preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for designing a magnetically controlled hollow tungsten pole global negative pressure arc, characterized in that: include: Follow these steps: Step 1: Calculate the hollow tungsten electrode arc shape; Step 1 comprises the following steps: (1) Establish the mass conservation equation and momentum conservation equation under negative pressure arc to determine the velocity and pressure distribution of arc plasma: Where ρ is density; v is velocity vector; P is pressure; μ is viscosity; I is the unit matrix; F is momentum source term; Solve the arc temperature T according to the energy conservation equation: In the formula, k is the thermal conductivity; T is the temperature; Cp is the specific heat capacity; Q is the source term of the energy conservation equation; The electric potential and magnetic vector potential distribution are calculated based on the current continuity equation and Ohm's law: Where V is the electric potential, A is the magnetic vector potential, and σ is the conductivity; According to V and A, the current density J and magnetic induction intensity B are obtained: The arc energy source term consists of three parts: Joule heat, electron enthalpy transfer and arc radiation loss: Where k b is the Boltzmann constant; E is the electron charge; T is the temperature field of the arc shape; q is the heat source term; Q rad is the arc radiation loss; According to the arc self-induced magnetic field intensity B, current density J and momentum conservation equation, the momentum source term in the momentum conservation equation is solved: F=J×B (2) Define the initial process parameters of the hollow tungsten arc, material thermophysical parameters, and boundary conditions; (3) Obtain the physical characteristics of the hollow tungsten electrode arc based on the temperature field T, pressure p, velocity v and current density J of the arc morphology; Step 2: Calculate the hollow tungsten pole arc under an applied longitudinal magnetic field; Step 2 comprises the following steps: (1) Add external electromagnetic force by changing the momentum source term: F=J×(B+B0) Wherein, B0 is the magnetic induction intensity of the external longitudinal magnetic field; (2) Based on the changes in the physical characteristics of the arc under the external magnetic field, the influence of the external longitudinal magnetic field on the arc temperature, pressure, velocity and current density is studied, and then the changing law of the arc pressure and the negative pressure on the workpiece surface under the external magnetic field is obtained; Step 3: By comparing the calculated results with the experimental results under the same conditions, verify whether the calculated results are consistent with the experimental results under the same conditions. If they are consistent, proceed to the next step; otherwise, return to step 1, adjust the model or boundary conditions or initial conditions, and repeat the cycle of modeling and numerical simulation calculation until the calculated results are consistent with the experimental results under the same conditions, completing the model accuracy verification; fix the model, change other conditions or parameters, and solve the arc results under various conditions and situations; Step 4: Study the influence of the external magnetic field on the arc temperature, pressure, speed and current density by changing other conditions or parameters of the hollow tungsten pole arc; then obtain and analyze the dominant role of the arc physical characteristics and the change law of the workpiece surface pressure under different parameters; complete the design of the magnetically controlled hollow tungsten pole full-domain negative pressure arc; The step 1 also includes the following steps: (1) Initial conditions of negative pressure arc model; (2) Define the boundary conditions of the welding arc model; including the current density input: The step 2 further comprises the following steps: (1) Reload the momentum source term of the negative pressure arc model; (2) Performing parametric scanning by changing the magnetic induction intensity; When the exhaust pressure and the external magnetic field change, when the exhaust pressure is close to -20kPa, the pressure change value is small when the magnetic induction intensity is less than 0.03T, and the pressure drops rapidly when the magnetic induction intensity is greater than 0.04T. When the magnetic induction intensity is less than 0.03T, the exhaust pressure plays a major role in the pressure at the center of the arc, and when the magnetic induction intensity is greater than 0.04T, the external magnetic field plays a major role in the pressure at the center of the arc. The existence of exhaust pressure changes the flow pattern of arc plasma. As the exhaust pressure decreases, part of the reflux plasma flows along the axis from the workpiece to the hollow cavity. When the exhaust pressure is -12 kPa, the arc plasma is completely composed of reflux plasma, which will make the welding more stable.

2. A method for designing a magnetically controlled hollow tungsten pole full-range negative pressure arc according to claim 1, characterized in that: The step 1 comprises the following steps: (1) Construct a welding arc geometry model based on the actual welding gun geometry; (2) Meshing the welding arc geometry model; the meshing process includes: Define the mesh size: use free quadrilateral mesh and adjust the distribution; complete meshing through mapping and sweeping operations; (3) Verification of models and calculation results; (4) Change the conditions and solve the negative pressure arc characteristics under various conditions or situations.

3. A method for designing a magnetically controlled hollow tungsten pole global negative pressure arc according to claim 1, characterized in that: The step 3 comprises the following steps: (1) Redefine the boundary conditions of the welding arc model; (2) Perform parametric sweeps by changing boundary conditions; (3) Reload the momentum source term of the negative pressure arc model.

4. A method for designing a magnetically controlled hollow tungsten pole full-range negative pressure arc according to claim 1, characterized in that: When there is no exhaust and only the external magnetic field changes, the existence of the tungsten pole hollow cavity promotes the generation of arc plasma reflux. The external longitudinal magnetic field will always reduce the surface pressure of the hollow tungsten pole arc welding workpiece and form a negative pressure on the workpiece surface, thus realizing the construction of a magnetically controlled hollow tungsten pole negative pressure arc.

5. The method for designing a magnetically controlled hollow tungsten pole full-range negative pressure arc according to claim 1, characterized in that: Applicable to negative pressure arc welding technology, or negative pressure arc additive manufacturing technology, or negative pressure arc-laser coaxial composite welding technology, or negative pressure arc-laser paraxial composite welding technology, or negative pressure arc-laser composite cladding technology, or negative pressure arc-laser composite additive manufacturing technology, or negative pressure arc-high energy beam composite welding technology, or negative pressure arc-high energy beam composite cladding technology, or negative pressure arc-high energy beam composite additive manufacturing technology.

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