Simulation method for molten pool characteristics of different vacuum contact materials

Abstract

The invention discloses a method for simulating molten pool characteristics of different vacuum contact materials, which comprises the following steps of: establishing a geometric model of a vacuum circuit breaker contact, and setting initial conditions and boundary conditions; solving a temperature field and a flow field of the model by using a finite difference method to obtain distribution of the temperature field and the flow field so as to obtain a temperature gradient change condition and a flow field volume fraction change condition, and solving a solid-liquid phase change proportion of the contact material to obtain a phase change speed; material parameters of different contact materials are set, molten pool characteristics under the different material parameters are obtained, fusion welding resistance of the different contact materials is analyzed, and an optimal scheme of the contact materials is preliminarily screened out; trace elements of different types and different contents are added into the contact material, the molten pool characteristics and the fusion welding resistance of the contact material after the trace elements are added are compared, and the contact material element proportion with the optimal fusion welding resistance is obtained; according to the method, the contact material and the element ratio with the optimal fusion welding resistance under high voltage can be obtained, the cost can be reduced, the development period can be shortened, and resource waste can be reduced.

Description

Technical Field

[0001] The invention relates to the technical field of material simulation, and in particular to a method for simulating molten pool characteristics of different vacuum contact materials. Background Art

[0002] As an important component to ensure the normal operation of the circuit breaker, the reliability of the vacuum circuit breaker directly determines the reliability of the circuit breaker, so there are strict standards and requirements for the ablation resistance of the contact. During the circuit breaker opening process, an arc will be generated. There are two main aspects of the arc ablation on the contact material: one is the thermal effect of the arc causing the evaporation and sublimation of the metal liquid; the other is the force of the arc causing the splashing of metal droplets. The arc inputs energy to the contact system, causing the contact temperature to rise, melt and form a molten pool. After the liquid metal in the molten pool solidifies, it causes contact welding. Different contact materials have different anti-welding properties. Selecting contact materials with good anti-welding properties can improve the overall performance of the vacuum circuit breaker. As the voltage increases, the temperature generated by the arc is also constantly increasing. The anti-welding performance of existing contact materials under high voltage is not ideal. It is necessary to find contact materials that can withstand higher temperatures and have better anti-welding performance. Contact materials are mostly mixtures of several metals. During the research process, a lot of time is required to select and proportion metals. At the same time, when using metals for experiments, a lot of research costs will be spent. It is impossible to cover all possibilities. The contact materials obtained by comparing the anti-welding performance are only local optimal. Summary of the invention

[0003] The present invention provides a method for simulating molten pool characteristics of different vacuum contact materials, so as to overcome the technical problems of high cost, long time consumption and failure to obtain contact materials with good anti-welding characteristics under high voltage in the process of researching contact materials.

[0004] In order to achieve the above object, the technical solution of the present invention is:

[0005] A method for simulating molten pool characteristics of different vacuum contact materials, comprising:

[0006] S1: Establish the geometric model of the vacuum circuit breaker contact and set the initial conditions and boundary conditions;

[0007] S2: using the finite difference method under the initial conditions and boundary conditions to solve the change states of the temperature field and flow field of the geometric model of the vacuum circuit breaker contact, to obtain the temperature field distribution and the flow field distribution, to obtain the temperature gradient change according to the temperature field distribution, and to obtain the flow field volume fraction change according to the flow field distribution;

[0008] S3: according to the volume fraction change of the flow field, solving the solid-liquid phase change ratio of different contact materials from the time when the contact material starts to melt to the time when it is completely melted, and obtaining the phase change speed;

[0009] S4: setting material parameters of different contact materials, obtaining molten pool characteristics under different material parameters, and analyzing the anti-welding performance of different contact materials according to the molten pool characteristics, phase change speed and temperature gradient changes, and preliminarily screening out the preferred scheme of contact materials;

[0010] S5: adding trace elements of different types and contents to the contact material selected in S4, comparing the molten pool characteristics and anti-welding performance of the contact material after adding the trace elements, and obtaining the element ratio of the contact material with the best anti-welding performance.

[0011] Further, S2 uses a finite difference method under the initial conditions and boundary conditions to solve the change state of the temperature field and flow field of the geometric model of the vacuum circuit breaker contact, obtains the temperature field distribution and the flow field distribution, obtains the temperature gradient change according to the temperature field distribution, and obtains the flow field volume fraction change according to the flow field distribution, including:

[0012] S21. Assumptions for the calculation of the geometric model of the vacuum circuit breaker contact:

[0013] The contact metal and the sub-vacuum environment above are regarded as fluids, the gas in the sub-vacuum environment is regarded as a compressible Newtonian fluid, and the contact metal material is regarded as an incompressible Newtonian fluid, which is consistent with the theory of fluid dynamics.

[0014] The flow of liquid metal in the metal region is smooth, and adjacent fluid layers flow in an orderly manner with each other, and the flow deformation of the molten material of the metal is treated as laminar flow;

[0015] The process of arc ablation contact forming molten pool is regarded as thermodynamic equilibrium state;

[0016] S22. Solve the temperature field and flow field of the geometric model of the vacuum circuit breaker contact under the initial conditions and boundary conditions:

[0017] S221, setting the input heat source position and heat source power, and determining the initial heat source distribution on the molten pool surface according to the heat source position and the heat source power;

[0018] S222, setting the initial time and time step for solving the temperature field and flow field;

[0019] S223, using the time stepping method to simulate each time step according to the set time step, in each time step, according to the set boundary conditions, initial conditions and initial heat source distribution, the temperature and fluid change state in the molten pool are obtained, and the temperature and fluid change state are iteratively solved by the finite difference method to obtain the temperature field and flow field distribution. The finite difference method is shown in formula (1).

[0020]

[0021] Among them, h is the function value to be solved, that is, the temperature value distribution of a certain point in the temperature field or the volume value of a certain point in the flow field. All temperature values ​​and all volume values ​​constitute the distribution of the temperature field and the distribution of the flow field; i and j represent the indexes of the spatial discrete points on the grid, corresponding to the horizontal and vertical coordinates respectively; t is a certain time corresponding to the temperature change of the temperature field, or a certain time variable corresponding to the volume change of the flow field; Δt is the time interval of the temperature change of the temperature field or the time interval of the volume change of the flow field; Δx is the interval of the temperature solution of the temperature field or the volume change of the flow field in the horizontal direction; Δy is the interval of the temperature field or flow field solution function in the vertical direction; a is the transmission coefficient; b is the error coefficient;

[0022] S224. According to the Level-Set method, the solid-liquid change of the contact material is tracked, and the phase change process is defined by the energy conservation equation, the mass conservation equation and the momentum conservation equation to obtain the numerical simulation results of the solid-liquid distribution. The energy conservation equation, the mass conservation equation and the momentum conservation equation are shown in formulas (2), (3) and (4).

[0023]

[0024] Where T is the surface temperature of the molten pool, t is the time, ρ is the density, c p is the specific heat capacity, λ is the thermal conductivity, S arc and Q vap represent the arc energy and the energy lost by evaporation, respectively. is the velocity vector, p is the pressure, I is the unit matrix, μ is the dynamic viscosity, (.) T is the transposed matrix, Indicates that the temperature is below the melting temperature T melting The Darcy damping force that counteracts the velocity is is the acceleration due to gravity, β l is the volume expansion coefficient of the liquid, φ is the Level-Set function, γ is the surface tension coefficient, is the surface normal vector, κ is the curvature, and δ(φ) is the delta function of the Level-Set value;

[0025] The variable φ is introduced to define the phase change process of the contact material. The Level-Set equation is shown in formula (5):

[0026]

[0027] Among them, γ ls is the transition distance, ε ls is the speed of reinitialization;

[0028] At the solid-liquid interface, the φ variable gradually changes from 0 to 1, that is, the material gradually changes from the solid phase to the liquid phase. Solve the φ variable, and the value of the φ variable is the numerical simulation result of the solid-liquid distribution;

[0029] S225. In combination with the flow field distribution and numerical simulation results, the shapes of the metal in the molten pool after melting, splashing and solidification are analyzed to determine the degree of solid-liquid phase change, and then the volume fraction changes of solid and liquid in the flow field are obtained; according to the temperature distribution in the temperature field, the temperature gradient changes extending from the surface of the molten pool to the inside of the molten pool in the temperature field are obtained.

[0030] Furthermore, the initial conditions include but are not limited to initial temperature, pressure, heat flux and density; the boundary conditions include but are not limited to velocity, flow rate, pressure of the fluid at the inlet and outlet, fixed temperature on the boundary, and adiabatic boundary conditions.

[0031] Further, S3 solves the solid-liquid phase change ratio of different contact materials from the time when the contact material starts to melt to the time when it is completely melted according to the volume fraction change of the flow field, and obtains the phase change speed, including:

[0032] S31, initializing the calculation domain by using a hybrid initialization method; the calculation domain is the area to be solved in the flow field;

[0033] S32, determine the volume fraction in the calculation domain as n, set the phase volume fractions corresponding to the solid phase and the liquid phase in the calculation domain to V and nV respectively, solve the ratio of the solid-liquid phase change of the contact material from the beginning of melting to the complete melting of the contact material, and calculate the phase change speed. The calculation formula is shown in formula (6):

[0034]

[0035] Wherein, v is the phase change rate, Δt is the time interval, and V% represents the ratio of the volume fraction change of the solid phase gradually turning into the liquid phase over time.

[0036] Further, S4 sets material parameters of different contact materials, wherein the material parameters include but are not limited to density, thermal conductivity, electrical conductivity, dynamic viscosity, melting point, boiling point, molar mass and constant-pressure heat capacity of the contact material.

[0037] Furthermore, the molten pool characteristics under different material parameters are obtained, and the anti-welding performance of different contact materials is analyzed according to the molten pool characteristics, the speed of phase change and the change of temperature gradient, and the preferred scheme of contact materials is preliminarily screened out, including:

[0038] S41. Changing different contact materials, setting material parameters of different contact materials, and changing input parameters, wherein the input parameters include but are not limited to arc current, voltage, energy, and input frequency, to obtain molten pool parameters under different input parameters, i.e., molten pool characteristics; the molten pool parameters include but are not limited to temperature, depth, and width, and drawing molten pool characteristic curves under different contact materials with different contact materials as the abscissa and width or depth as the ordinate;

[0039] S42. Solve the fusion welding force according to the characteristics of the molten pool, and measure its anti-fusion welding performance through the fusion welding force. The fusion welding cross-sectional area is shown in formula (7).

[0040] S=σkπR 2 (7)

[0041] Where S is the cross-sectional area of ​​the weld, σ is the weld strength, k is a constant less than 1, and R is the radius of the weld pool;

[0042] The welding force is shown in formula (8):

[0043] F=K*S*T (8)

[0044] Where F is the welding force, K is a constant related to material properties, melting state and current density, and T represents the temperature of the molten pool surface;

[0045] S43. Compare the welding force, phase change speed and temperature gradient changes of different contact materials, and preliminarily screen out the optimal solution for the contact material.

[0046] Further, S5 adds trace elements of different types and contents to the contact material selected in S4, compares the molten pool characteristics and anti-welding performance of the contact material after adding the trace elements, and obtains the element ratio of the contact material with the best anti-welding performance, including:

[0047] S51, adding different trace elements to the contact material selected in S4, adjusting the content of the trace elements, and analyzing the influence of adding different trace elements on the characteristics of the molten pool;

[0048] S52. Calculate the welding force of the contact material with different trace elements added, draw the welding force distribution curve, compare the anti-welding performance of the materials with different trace elements added and the trace element contents, and obtain the trace elements with the best anti-welding performance and the element ratio of the contact material and the trace elements.

[0049] Beneficial effect: The present invention provides a method for simulating the molten pool characteristics of different vacuum contact materials. By establishing a geometric model of a vacuum circuit breaker contact, the model is solved to obtain changes in the temperature field and flow field distribution parameters of the model in the molten pool, the time evolution of the temperature distribution, the volume change of the flow field distribution, and then the molten pool characteristics of the contact material are obtained. Different contact materials are replaced to obtain the molten pool characteristics of different materials. The main contact material with better anti-welding performance is first selected, and then different trace elements are added to the selected contact material and the content is changed. The effect of adding different contents of trace elements on the anti-welding performance of the contact can be determined, and the contact material and element ratio with the best anti-welding performance under high voltage are obtained, which helps to reduce costs, shorten development cycles, and reduce waste of resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0051] Figure 1 A method flow chart of a method for simulating molten pool characteristics of different vacuum contact materials according to the present invention;

[0052] Figure 2 It is a schematic diagram of a two-dimensional model of contact molten pool simulation of the present invention;

[0053] Figure 3 It is a schematic diagram of the contact temperature field simulation effect of the present invention;

[0054] Figure 4 This is a schematic diagram of the contact fluid field simulation effect of the present invention;

[0055] Figure 5 This is an actual display diagram of the experimental molten pool of the present invention. DETAILED DESCRIPTION

[0056] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0057] This embodiment provides a method for simulating the molten pool characteristics of different vacuum contact materials, such as Figure 1 As shown, including:

[0058] S1: Establish the geometric model of the vacuum circuit breaker contact and set the initial conditions and boundary conditions;

[0059] S2: using the finite difference method under the initial conditions and boundary conditions to solve the change states of the temperature field and flow field of the geometric model of the vacuum circuit breaker contact, to obtain the temperature field distribution and the flow field distribution, to obtain the temperature gradient change according to the temperature field distribution, and to obtain the flow field volume fraction change according to the flow field distribution;

[0060] S3: according to the volume fraction change of the flow field, solving the solid-liquid phase change ratio of different contact materials from the time when the contact material starts to melt to the time when it is completely melted, and obtaining the phase change speed;

[0061] S4: setting material parameters of different contact materials, obtaining molten pool characteristics under different material parameters, and analyzing the anti-welding performance of different contact materials according to the molten pool characteristics, phase change speed and temperature gradient changes, and preliminarily screening out the preferred scheme of contact materials;

[0062] S5: adding trace elements of different types and contents to the contact material selected in S4, comparing the molten pool characteristics and anti-welding performance of the contact material after adding the trace elements, and obtaining the element ratio of the contact material with the best anti-welding performance.

[0063] Specifically, firstly, a geometric model of the vacuum circuit breaker contact is established, initial conditions and boundary conditions are set, and a simulation model is constructed, which can save resources, and the setting conditions provide restriction conditions for the calculation of subsequent simulation models; secondly, the finite difference method is used under the initial conditions and boundary conditions to solve the change state of the temperature field and flow field of the model, and the temperature field distribution and flow field distribution are obtained, and the temperature gradient change is obtained according to the temperature field distribution, and the flow field volume fraction change is obtained according to the flow field distribution. Making assumptions can reduce the complexity of simulation, improve calculation efficiency, ignore some minor factors, and improve the feasibility of the model. The finite difference method can obtain accurate results and provide data support for subsequent steps; according to the change of the volume fraction of the flow field, the solid-liquid phase change ratio of different contact materials from the time when the contact material begins to melt to the time when it is completely melted is solved, and the speed of the phase change is obtained. , calculate the speed of phase change, and it can be seen how fast the molten pool forms under different materials and different initial conditions. The slower the phase change, the slower the molten pool forms, which means that the material's anti-welding performance is better; set the material parameters of different contact materials, obtain the molten pool characteristics under different material parameters, and analyze the anti-welding performance of different contact materials according to the molten pool characteristics, the speed of phase change and the change of temperature gradient, preliminarily screen out the preferred scheme of the contact material, select different contact materials for comparison, and make preliminary optimization of the anti-welding performance of the contact material, provide the main material for obtaining the best material ratio, and reduce the melting rate under high voltage; finally, add different types and contents of trace elements to the contact material, compare the molten pool characteristics and anti-welding performance of the contact material after adding trace elements, and obtain the element ratio of the contact material with the best anti-welding performance, which can make the contact material have better anti-welding performance.

[0064] In a specific embodiment, the scheme for establishing the geometric model of the vacuum circuit breaker contact and setting the initial conditions and boundary conditions is:

[0065] S11. Obtain material parameters from material databases, data provided by material manufacturers, and literature, obtain geometric information from laboratory projects, integrate the information obtained from different data sources into a unified data structure, input it into the modeling software, and then use computer modeling software to create a calculation area, that is, a two-dimensional geometric model of the contact, and simulate the two-dimensional model such as Figure 2 As shown;

[0066] S12. Use the mesh generation tool to divide the two-dimensional geometric model into finite element meshes, and refine the meshes of the heat source boundary, the contact center area, that is, the center position of the contact shape, and the center area of ​​the fluid in the upper part of the contact. In this scheme, the calculation domain uses a free triangle network, the maximum unit of the central calculation area is less than 0.05, the maximum unit of the remaining area is less than 0.1, and the number of meshes is greater than 15,000. Figure 2 As shown in the grid diagram;

[0067] S13. Reasonably simplify the contact structure of the vacuum circuit breaker, simplify the contact geometry and ignore the groove state of the contact surface; simplify the bottom handle of the contact to a state without a handle;

[0068] S14. Set initial conditions and boundary conditions. The initial conditions include but are not limited to initial temperature, pressure, heat flux and density; the boundary conditions include but are not limited to velocity, flow rate, pressure of the fluid at the inlet and outlet, fixed temperature on the boundary, and adiabatic boundary conditions.

[0069] In this scheme, the geometric model is constructed first, and then the model is meshed. For the parts that require more accurate results, such as the contact surface and the molten pool area, mesh processing is performed to make the calculation results more accurate;

[0070] In this scheme, COMSOL software is used as simulation software, which can perform modeling and simulation of multi-physical fields. Using COMSOL software for simulation integrates most calculation methods and can accurately calculate the parameters and changes required for contact material simulation.

[0071] In a specific embodiment, the finite difference method is used under the initial conditions and boundary conditions to solve the change states of the temperature field and flow field of the geometric model of the vacuum circuit breaker contact, to obtain the temperature field distribution and the flow field distribution, and the scheme for obtaining the temperature gradient change according to the temperature field distribution and the flow field volume fraction change according to the flow field distribution is:

[0072] S21. Assumptions for the calculation of the geometric model of the vacuum circuit breaker contact:

[0073] The contact metal and the sub-vacuum environment above are regarded as fluids, the gas in the sub-vacuum environment is regarded as a compressible Newtonian fluid, and the contact metal material is regarded as an incompressible Newtonian fluid, which is consistent with the theory of fluid dynamics.

[0074] The flow of liquid metal in the metal region is smooth, and adjacent fluid layers flow in an orderly manner with each other, and the flow deformation of the molten material of the metal is treated as laminar flow;

[0075] The process of arc ablation contact forming molten pool is regarded as thermodynamic equilibrium state;

[0076] S22. Solve the temperature field and flow field of the geometric model of the vacuum circuit breaker contact under the initial conditions and boundary conditions:

[0077] S221. Set the input heat source position and heat source power, and determine the initial heat source distribution on the molten pool surface according to the heat source position and the heat source power:

[0078] The heat source distribution of the input heat source position and power size is determined according to the Gaussian heat source formula, as shown in formula (9):

[0079]

[0080] Where Q is the energy input power; c is the characteristic radius of heat flux distribution; x is the abscissa of the heat source position; ζ is the ordinate of the heat source position; the energy beam is distributed as a rectangular shape;

[0081] S222, setting the initial time and time step for solving the temperature field and flow field;

[0082] S223, using the time stepping method to simulate each time step according to the set time step, in each time step, according to the set boundary conditions and initial conditions, the temperature and fluid change state in the molten pool are obtained in the rectangular heat source distribution area on the surface of the molten pool, and the temperature and fluid change states are iteratively solved by the finite difference method to obtain the temperature field and flow field distribution. The finite difference method is shown in formula (10).

[0083]

[0084] Among them, h is the solved function value, that is, the temperature value distribution of a certain point in the temperature field or the volume value of a certain point in the flow field. All temperature values ​​and all volume values ​​constitute the distribution of the temperature field and the distribution of the flow field; i and j represent the indexes of the spatial discrete points on the grid, corresponding to the horizontal and vertical coordinates respectively; t is a certain time corresponding to the temperature change of the temperature field or the volume change of the flow field; Δt is the time interval of the temperature change of the temperature field or the time interval of the volume change of the flow field; Δx is the interval of the temperature solved by the temperature field or the volume change solved by the flow field in the horizontal direction; Δy is the interval of the temperature field or flow field solution function in the vertical direction; a is the transmission coefficient; b is the error coefficient; the simulation of the temperature field and the flow field is as follows Figure 3 and Figure 4 As shown;

[0085] S224. According to the Level-Set method, the solid-liquid change of the contact material is tracked, and the phase change process is defined by the energy conservation equation, the mass conservation equation and the momentum conservation equation to obtain the numerical simulation results of the solid-liquid distribution. The energy conservation equation, the mass conservation equation and the momentum conservation equation are shown in formulas (11), (12) and (13).

[0086]

[0087] Where T is the surface temperature of the molten pool, t is the time, ρ is the density, c p is the specific heat capacity, λ is the thermal conductivity, S arc and Q vaprepresent the arc energy and the energy lost by evaporation, respectively. is the velocity vector, p is the pressure, I is the unit matrix, μ is the dynamic viscosity, (.) T is the transposed matrix, Indicates that the temperature is below the melting temperature T melting The Darcy damping force that counteracts the velocity is is the acceleration due to gravity, β l is the volume expansion coefficient of the liquid, φ is the Level-Set function, γ is the surface tension coefficient, is the surface normal vector, κ is the curvature, and δ(φ) is the delta function of the Level-Set value;

[0088] The variable φ is introduced to define the phase change process of the contact material. The Level-Set equation is shown in formula (14):

[0089]

[0090] Among them, γ ls is the transition distance, ε ls is the speed of reinitialization;

[0091] At the solid-liquid interface, the φ variable gradually changes from 0 to 1, that is, the material gradually changes from the solid phase to the liquid phase. Solve the φ variable, and the value of the φ variable is the numerical simulation result of the solid-liquid distribution;

[0092] S225, combining the flow field distribution and the numerical simulation results, analyzing the shape of the metal in the molten pool after melting, splashing and solidification, and determining the degree of solid-liquid phase change. The more the metal melts into liquid and splashes outward and then solidifies, the greater the degree of phase change;

[0093] Then, the changes in the volume fractions of solids and liquids in the flow field are obtained. With the increase of time and temperature, the volume fraction of solids gradually decreases, while the volume fraction of liquids gradually increases.

[0094] According to the temperature distribution in the temperature field, the temperature gradient change extending from the molten pool surface to the inside of the molten pool in the temperature field is obtained. The temperature on the molten pool surface is the highest, and the temperature decreases as it extends outward into the inside of the molten pool.

[0095] The smaller the degree of phase change and the slower the temperature change, the better the anti-welding performance of the contact material.

[0096] In this scheme, making assumptions can reduce the complexity of simulation, improve computational efficiency, ignore some minor factors, and improve the feasibility of the model. The finite difference method is a commonly used method for solving boundary conditions and initial conditions. The finite difference method used in this scheme can obtain accurate results. The Level set method has the advantages of implicitly tracking the motion interface, automatically processing topological deformation, eliminating the need for complex and cumbersome interface reconstruction technology, and having a large number of available interpolation formats. It is widely used in the field of two-phase flow numerical simulation. The Level set method can well simulate the solid-liquid phase change and determine the accurate changes in the solid-liquid situation.

[0097] In a specific embodiment, according to the volume fraction change of the flow field, the solid-liquid phase change ratio of different contact materials from the time when the contact material starts to melt to the time when it is completely melted is solved, and the solution for obtaining the phase change speed is:

[0098] S31, initializing the calculation domain by using a hybrid initialization method; the calculation domain is the area to be solved in the flow field;

[0099] S32, determine the volume fraction in the calculation domain as n, set the phase volume fractions corresponding to the solid phase and the liquid phase in the calculation domain to V and nV respectively, solve the ratio of the solid-liquid phase change of the contact material from the beginning of melting to the complete melting of the contact material and calculate the phase change speed, the calculation formula is shown in formula (15),

[0100]

[0101] Wherein, v is the phase change rate, Δt is the time interval, and V% represents the ratio of the volume fraction change of the solid gradually turning into the liquid over time.

[0102] In this scheme, the volume fraction in the calculation domain is set to 2, and the volume fractions corresponding to the solid phase and the liquid phase are both set to 1. When the volume fraction of the solid phase changes from 1 to 0.9, it means that the solid phase changes by 0.1, and the proportion of the volume fraction change is 10%.

[0103] In this scheme, by calculating the speed of phase change, we can see how fast the molten pool forms under different materials and different initial conditions. The slower the phase change, the slower the molten pool forms, which means that the material has better anti-welding performance.

[0104] In a specific embodiment, material parameters of different contact materials are set, molten pool characteristics under different material parameters are obtained, and the anti-welding performance of different contact materials is analyzed according to the molten pool characteristics, the speed of phase change and the change of temperature gradient. The preferred scheme of the contact material is preliminarily screened out as follows:

[0105] S41. Change different materials and set material parameters of different contact materials, wherein the material parameters include but are not limited to density, thermal conductivity, electrical conductivity, dynamic viscosity, melting point, boiling point, molar mass and constant pressure heat capacity of the contact material; change input parameters, wherein the input parameters include but are not limited to arc current, voltage, energy and input frequency, and obtain molten pool parameters under different input parameters, i.e., molten pool characteristics; the molten pool parameters include but are not limited to temperature, depth and width, and draw molten pool characteristic curves under different contact materials with different contact materials as the horizontal coordinate and width or depth as the vertical coordinate;

[0106] S42. Solve the welding force according to the characteristics of the molten pool, and measure its anti-welding performance by the welding force. The welding cross-sectional area is shown in formula (16).

[0107] S=σkπR 2 (16)

[0108] Where S is the cross-sectional area of ​​the weld, σ is the weld strength, k is a constant less than 1, R is the radius of the weld pool, and the horizontal and vertical coordinates of the weld pool curve are

[0109] The welding force is shown in formula (17):

[0110] F=K*S*T (17)

[0111] In the formula, F is the welding force, K is a constant related to material properties, melting state and current density, and T represents the temperature of the molten pool surface;

[0112] S43. Compare the welding force, phase change speed and temperature gradient of different contact materials to perform preliminary contact material optimization:

[0113] The smaller the welding force, the slower the phase change speed and the smaller the temperature gradient change, that is, the more stable the temperature value change, the better the anti-welding performance of the contact material. The welding force, phase change speed and temperature gradient change of different contact materials are compared to preliminarily screen out the preferred solution for the contact material.

[0114] In this scheme, different contact materials are selected for comparison. By selecting different contact materials for comparison, the preferred scheme of contact materials can be preliminarily screened out, the main material is provided for obtaining the best material ratio, and the melting rate is reduced under high voltage.

[0115] In a specific embodiment, different types and contents of trace elements are added to the contact material selected in S4, and the molten pool characteristics and anti-welding performance of the contact material after adding the trace elements are compared. The solution for obtaining the element ratio of the contact material with the best anti-welding performance is:

[0116] S51, adding different trace elements to the contact material selected in S4, adjusting the content of the trace elements, and analyzing the influence of adding different trace elements on the characteristics of the molten pool;

[0117] S52, calculating the welding force of the contact material with different trace elements added, drawing the welding force distribution curve, comparing the anti-welding performance of the contact material with different trace elements added and the trace element content, and obtaining the trace element with the best anti-welding performance and the element ratio of the contact material and the trace element;

[0118] S53. Verify the correctness of data through data query and comparison to reflect new material parameters, geometric information or research results in real time.

[0119] In this solution, trace elements are added to the contact material to make the material's anti-welding performance more superior.

[0120] In this scheme, it is assumed that CuCr is the selected contact material and Te is the selected trace element. Te elements with contents of 0.005%, 0.01%, 0.1% and 0.3% are added to the CuCr contact material respectively, and the effect of adding different contents of Te elements on the molten pool characteristics is analyzed. The molten pool diagram of the experiment is shown in FIG. Figure 5 As shown, the results show that the contact has the best anti-fusion welding performance between 0.1-0.3, the molten pool width and depth, that is, the area is smaller, the fusion welding force is smaller, and the anti-fusion welding performance is better.

[0121] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for simulating the molten pool characteristics of different vacuum contact materials, characterized in that: include: S1: Establish the geometric model of the vacuum circuit breaker contact and set the initial conditions and boundary conditions; S2: using the finite difference method under the initial conditions and boundary conditions to solve the change states of the temperature field and flow field of the geometric model of the vacuum circuit breaker contact, to obtain the temperature field distribution and the flow field distribution, to obtain the temperature gradient change according to the temperature field distribution, and to obtain the flow field volume fraction change according to the flow field distribution; S3: according to the volume fraction change of the flow field, solving the solid-liquid phase change ratio of different contact materials from the time when the contact material starts to melt to the time when it is completely melted, and obtaining the phase change speed; S4: setting material parameters of different contact materials, obtaining molten pool characteristics under different material parameters, and analyzing the anti-welding performance of different contact materials according to the molten pool characteristics, phase change speed and temperature gradient changes, and preliminarily screening out the preferred scheme of contact materials; S5: adding trace elements of different types and contents to the contact material selected in S4, comparing the molten pool characteristics and anti-welding performance of the contact material after adding the trace elements, and obtaining the element ratio of the contact material with the best anti-welding performance.

2. The method for simulating molten pool characteristics of different vacuum contact materials according to claim 1, characterized in that: S2 uses a finite difference method under the initial conditions and boundary conditions to solve the temperature field and flow field change states of the vacuum circuit breaker contact geometric model to obtain temperature field distribution and flow field distribution, obtains temperature gradient change according to the temperature field distribution, and obtains flow field volume fraction change according to the flow field distribution, including: S21. Assumptions are made for the calculation of the geometric model of the vacuum circuit breaker contact: The contact metal and the sub-vacuum environment above are regarded as fluids, the gas in the sub-vacuum environment is regarded as a compressible Newtonian fluid, and the contact metal material is regarded as an incompressible Newtonian fluid, which is consistent with the theory of fluid dynamics. The flow of liquid metal in the metal region is smooth, and adjacent fluid layers flow in an orderly manner with each other, and the flow deformation of the molten material of the metal is treated as laminar flow; The process of arc ablation contact forming molten pool is regarded as thermodynamic equilibrium state; S22. Solve the temperature field and flow field of the geometric model of the vacuum circuit breaker contact under the initial conditions and boundary conditions: S221, setting the heat source position and heat source power to be input, and determining the initial heat source distribution on the molten pool surface according to the heat source position and the heat source power; S222, setting the initial time and time step for solving the temperature field and flow field; S223, using the time stepping method to simulate each time step according to the set time step, in each time step, according to the set boundary conditions, initial conditions and initial heat source distribution, the temperature and fluid change state in the molten pool are obtained, and the temperature and fluid change state are iteratively solved by the finite difference method to obtain the temperature field and flow field distribution. The finite difference method is shown in formula (1). Among them, h is the function value to be solved, that is, the temperature value distribution of a certain point in the temperature field or the volume value of a certain point in the flow field. All temperature values ​​and all volume values ​​constitute the distribution of the temperature field and the distribution of the flow field; i and j represent the indexes of the spatial discrete points on the grid, corresponding to the horizontal and vertical coordinates respectively; t is a certain time corresponding to the temperature change of the temperature field, or a certain time variable corresponding to the volume change of the flow field; Δt is the time interval of the temperature change of the temperature field or the time interval of the volume change of the flow field; Δx is the interval of the temperature solution of the temperature field or the volume change of the flow field in the horizontal direction; Δy is the interval of the temperature field or flow field solution function in the vertical direction; a is the transmission coefficient; b is the error coefficient; S224. According to the Level-Set method, the solid-liquid change of the contact material is tracked, and the phase change process is defined by the energy conservation equation, the mass conservation equation and the momentum conservation equation to obtain the numerical simulation results of the solid-liquid distribution. The energy conservation equation, the mass conservation equation and the momentum conservation equation are shown in formulas (2), (3) and (4). Where T is the surface temperature of the molten pool, t is the time, ρ is the density, c p is the specific heat capacity, λ is the thermal conductivity, S arc and Q vap represent the arc energy and the energy lost by evaporation, respectively. is the velocity vector, p is the pressure, I is the unit matrix, μ is the dynamic viscosity, (.) T is the transposed matrix, Indicates that the temperature is below the melting temperature T melting The Darcy damping force that counteracts the velocity is is the acceleration due to gravity, β l is the volume expansion coefficient of the liquid, φ is the Level-Set function, γ is the surface tension coefficient, is the surface normal vector, κ is the curvature, and δ(φ) is the delta function of the Level-Set value; The variable φ is introduced to define the phase change process of the contact material. The Level-Set equation is shown in formula (5): Among them, γ ls is the transition distance, ε ls is the speed of reinitialization; At the solid-liquid interface, the φ variable gradually changes from 0 to 1, that is, the material gradually changes from the solid phase to the liquid phase. Solve the φ variable, and the value of the φ variable is the numerical simulation result of the solid-liquid distribution; S225. In combination with the flow field distribution and numerical simulation results, the shapes of the metal in the molten pool after melting, splashing and solidification are analyzed to determine the degree of solid-liquid phase change, and then the volume fraction changes of solid and liquid in the flow field are obtained; according to the temperature distribution in the temperature field, the temperature gradient changes extending from the surface of the molten pool to the inside of the molten pool in the temperature field are obtained.

3. The method for simulating molten pool characteristics of different vacuum contact materials according to claim 2, characterized in that: The initial conditions include but are not limited to initial temperature, pressure, heat flux and density; the boundary conditions include but are not limited to velocity, flow rate, pressure of the fluid at the inlet and outlet, fixed temperature on the boundary, and adiabatic boundary conditions.

4. The method for simulating molten pool characteristics of different vacuum contact materials according to claim 1, characterized in that: S3 solves the solid-liquid phase change ratio of different contact materials from the time when the contact material starts to melt to the time when it is completely melted according to the volume fraction change of the flow field, and obtains the phase change speed, including: S31, initializing the calculation domain by using a hybrid initialization method; the calculation domain is the area to be solved in the flow field; S32, determine the volume fraction in the calculation domain as n, set the phase volume fractions corresponding to the solid phase and the liquid phase in the calculation domain to V and nV respectively, solve the ratio of the solid-liquid phase change of the contact material from the beginning of melting to the complete melting of the contact material, and calculate the phase change speed. The calculation formula is shown in formula (6): Wherein, v is the phase change rate, Δt is the time interval, and V% represents the ratio of the volume fraction change of the solid phase gradually turning into the liquid phase over time.

5. The method for simulating molten pool characteristics of different vacuum contact materials according to claim 1, characterized in that: S4 sets material parameters of different contact materials, wherein the material parameters include but are not limited to density, thermal conductivity, electrical conductivity, dynamic viscosity, melting point, boiling point, molar mass and constant-pressure heat capacity of the contact material.

6. The method for simulating molten pool characteristics of different vacuum contact materials according to claim 4, characterized in that: Obtain the molten pool characteristics under different material parameters, and analyze the anti-welding performance of different contact materials according to the molten pool characteristics, phase change speed and temperature gradient changes, and preliminarily screen out the optimal scheme of contact materials, including: S41. Changing different contact materials, setting material parameters of different contact materials, and changing input parameters, wherein the input parameters include but are not limited to arc current, voltage, energy, and input frequency, to obtain molten pool parameters under different input parameters, i.e., molten pool characteristics; the molten pool parameters include but are not limited to temperature, depth, and width, and drawing molten pool characteristic curves under different contact materials with different contact materials as the abscissa and width or depth as the ordinate; S42. Solve the fusion welding force according to the characteristics of the molten pool, and measure its anti-fusion welding performance through the fusion welding force. The fusion welding cross-sectional area is shown in formula (7). S=σkπR 2 (7) Where S is the cross-sectional area of ​​the weld, σ is the weld strength, k is a constant less than 1, and R is the radius of the weld pool; The welding force is shown in formula (8): F=K*S*T (8) In the formula, F is the welding force, K is a constant related to material properties, melting state and current density, and T represents the temperature of the molten pool surface; S43. Compare the welding force, phase change speed and temperature gradient changes of different contact materials, and preliminarily screen out the optimal solution for contact materials.

7. The method for simulating molten pool characteristics of different vacuum contact materials according to claim 1, characterized in that: S5 adds trace elements of different types and contents to the contact material selected in S4, compares the molten pool characteristics and anti-welding performance of the contact material after adding the trace elements, and obtains the element ratio of the contact material with the best anti-welding performance, including: S51, adding different trace elements to the contact material selected in S4, adjusting the content of the trace elements, and analyzing the influence of adding different trace elements on the characteristics of the molten pool; S52. Calculate the welding force of the contact material with different trace elements added, draw the welding force distribution curve, compare the anti-welding performance of the materials with different trace elements added and the trace element contents, and obtain the trace elements with the best anti-welding performance and the element ratio of the contact material and the trace elements.

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