Two-dimensional electric spark machining gap microbubble simulation method

Abstract

The invention is suitable for the field of bubble dynamics, and provides a simulation method for microbubbles in a minimum area for electric spark machining, and the method comprises the following steps: selecting a proper spatial dimension, a physical field and a research mode in simulation software; establishing a simplified electric spark machining gap microbubble geometric model; physical property parameters, material parameters, boundary conditions and a solution algorithm are set; establishing an electric spark machining gap microbubble grid model; initialization operation is carried out, calculation conditions are set, iterative calculation is carried out, and an electric spark machining gap flow field is obtained; post-processing the calculation result to obtain the motion of bubbles in the flow field of the electric spark machining gap and various parameters of the flow field; according to the content of the invention, the movement of the electric spark gap flow field and the microbubbles thereof can be researched more efficiently and cheaply.

Description

Technical Field

[0001] The invention belongs to the field of bubble dynamics, and in particular relates to a two-dimensional electric spark gap microbubble simulation method. Background Art

[0002] Electrodischarge machining (EDM) is a precision machining method that uses electric pulse discharge to generate high temperatures on the workpiece surface, thereby removing material. During this process, bubbles form, expand, and contract within the extremely small machining gap, pulsating in a process called pulsation. This promotes fluid movement within the gap, thereby facilitating the removal of electroerosion products from the inter-electrode gap and improving machining efficiency. Furthermore, because the discharge process during EDM lasts for a very short time, the bubbles generated during breakdown are only a few micrometers long. Furthermore, the internal pressure during bubble formation is extremely high, reaching thousands of atmospheres, and the pulsation process is also extremely brief, only a few microseconds. This makes it difficult to accurately measure the motion of bubbles and fluid within the flow field using instruments. Currently, traditional simulation methods, such as the volume of fluid (VOF) model, can only address the flow field distribution in the EDM gap and have failed to provide in-depth and detailed research on the expansion and contraction behavior of microbubbles. Furthermore, simulation methods for bubble dynamics have primarily focused on underwater explosions. While the bubble generation process is similar, the bubble environment is typically near a wall or in an open space, and the volume is relatively large, making it difficult to simulate the microbubble generation within the extremely small gaps required for EDM. However, in some inventions involving microbubbles, the bubble pressure is usually very low, with almost no pulsation of bubble expansion and contraction. Furthermore, the bubble has little relevance to EDM, making it difficult to reflect the dynamic changes in bubbles during EDM. Therefore, there is a lack of simulation methods for microbubbles in EDM gaps.

[0003] The present invention proposes a two-dimensional EDM gap microbubble simulation method based on the COMSOL Multiphysics platform, which can dynamically track the expansion and contraction process of microbubbles and analyze the influence of microbubbles on the EDM gap flow field. Summary of the Invention

[0004] The purpose of the embodiments of the present invention is to provide a two-dimensional electric spark microbubble simulation method, aiming to solve the problems existing in the prior art identified in the background technology.

[0005] The technical solutions of the present invention are as follows:

[0006] A two-dimensional electric spark gap microbubble simulation method, characterized in that the method comprises the following steps performed in sequence:

[0007] S1. Create a two-dimensional electrode-workpiece gap flow field model in COMSOL Multiphysics. Select the "Multiphase Flow - Level Set" physics interface and the transient study mode to implement interface tracking.

[0008] S2. Establish a two-dimensional geometric model of microbubbles in the EDM gap in the geometry section;

[0009] S3, setting physical property parameters, setting material parameters, setting boundary conditions and setting solution algorithm;

[0010] S4, meshing the two-dimensional geometric model of microbubbles in the EDM gap to obtain a mesh model of microbubbles in the EDM gap;

[0011] S5. Perform initialization operations, set calculation conditions, perform iterative calculations, and obtain the microbubble flow field in the EDM gap;

[0012] S6. Post-process the calculation results such as the volume fraction of the fluid, the pressure and velocity of the flow field, etc.

[0013] Preferably, in step S2, a simplified EDM gap model is established based on a common EDM gap, where the width of the gap is 20 μm. The initial radius and pressure of the bubble are dynamically calculated based on the energy of a single discharge during EDM, and simplified to an ideal circular region with a radius of 0.2-1 μm, with the bubble located between the electrode and the workpiece.

[0014] Preferably, in step S3, the upper boundary of the rectangular region is set as a pressure outlet with a pressure of 1 standard atmosphere, and the remaining portion is set as a wetted wall. Based on the composition, size, and internal pressure of the bubbles generated during EDM, the material within the bubbles is set to hydrogen, and the initial pressure is set to 500-3000 standard atmospheres. Because the internal pressure of bubbles is extremely high during their generation, their dynamic expansion and contraction are extremely dramatic, leading to dramatic changes in both temperature and pressure. Therefore, the density of hydrogen is a function of both pressure and temperature, and its dynamic viscosity is also a function of both pressure and temperature. The density formula entered in COMSOL is pA*0.002016 / R_const[K*mol / J] / T, where pA is pressure, T is temperature, and R_const is the molar mass of hydrogen. The dynamic viscosity formula is 2.14524642E-6+2.54245E-8*T^1-1.0235587E-11*T^2+2.80895021E-15*T^3. The working fluid is kerosene, with a density of 0.739 g / ml and a dynamic viscosity of 1.92 mPa·s. Since hydrogen has a small effect on the surface tension, which is determined by the properties of kerosene, the surface tension between the air bubble and the liquid is set to 0.0728 N / m.

[0015] Preferably, in step S3, the basic assumptions for the model solution include: the gas within the bubble is a compressible fluid, the working fluid is an incompressible fluid, the entire flow field is set to turbulent, the turbulence model is the k-ω model, the wall function is the standard wall function, gravity is included, and the direction of gravity is the negative direction of the y-axis. The initial velocity of the calculation area is 0 m / s.

[0016] Preferably, in step S4, the specific method for mesh refinement is as follows: the computational domain is divided into free triangle meshes, the mesh cell size is set to ultrafine, the mesh is calibrated to fluid dynamics, and the mesh inside and around the bubble is subjected to non-uniform refinement based on the bubble expansion trend to achieve early fitting of boundary layer changes. The resulting mesh has a maximum cell size of 1.95 μm and a minimum cell size of 0.0225 μm, a cell count of 13149, and an average mesh quality of 0.9119.

[0017] Preferably, in step S5, taking into account the bubble pulsation time and the accuracy of the calculation, the initial time step is set to 0.001 μs, the total time is set to 1 μs, and the step size adopted by the solver is free.

[0018] Preferably, in step S6, by expanding the "Results" list, a cloud map of flow field velocity, bubble volume fraction, and contour map of flow field pressure can be obtained. After post-processing, the maximum expanded diameter of the bubble, the periodic pulsation frequency of the bubble, and the expansion process of the bubble in the processing fluid can be obtained.

[0019] An embodiment of the present invention provides a controllable and repeatable simulation method for the random fusion of multiple adjacent bubbles in an EDM gap. This method can dynamically track the expansion and contraction of microbubbles and analyze their impact on the flow field in the EDM gap. This simulation method can be used to analyze and study the fusion process of bubbles during EDM and their impact on the flow field and chip removal, enriching the theoretical framework of EDM gap flow fields. Using simulation methods to study bubbles and flow fields in EDM gaps can significantly reduce experimental costs and improve experimental efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a flow chart of a method for simulating microbubbles in a gap of two-dimensional electrospark machining according to an embodiment of the present invention;

[0021] Figure 2 is a geometric model of microbubble flow field in a two-dimensional EDM gap in an embodiment of the present invention;

[0022] Figure 3 is a mesh model of microbubble flow field in a two-dimensional EDM gap in an embodiment of the present invention;

[0023] Figure 4is a time series diagram of the expansion and contraction process of a bubble in an embodiment of the present invention;

[0024] Figure 5 is a graph showing the change in bubble volume over time in an embodiment of the present invention;

[0025] Figure 6 1. A flow field velocity cloud map and a pressure contour map in accordance with an embodiment of the present invention;

[0026] Figure 7 is a graph showing bubble pulsation boundaries and flow field velocity in an embodiment of the present invention;

[0027] Figure 8 is a diagram showing the effect of bubbles with different initial pressures on the flow field in an embodiment of the present invention;

[0028] Figure 9 Graph showing the effect of bubbles of different initial sizes on the flow field in an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The specific implementation of the present invention is described in detail below with reference to specific embodiments.

[0030] This embodiment provides a two-dimensional electrospark machining gap micro-bubble pulsation simulation method, such as Figure 1 As shown, the method specifically includes the following steps:

[0031] S1. Select the two-dimensional space dimension in the COMSOL software, and select the multiphase flow, level set, and turbulent k-ω model in the fluid flow physics interface. The equation of the model is:

[0032]

[0033] In the study options, we choose to include transient behavior like initialization. The model also contains the following coupled equations:

[0034] Momentum equation:

[0035]

[0036] Continuity equation:

[0037]

[0038] S2. Establish a regional model of the EDM gap range in the geometric component. Establish a circular area with a radius of 0.5 μm as the geometric model of the EDM gap microbubbles. The location of the bubbles is between the electrode and the workpiece, such as Figure 2 shown.

[0039] Step S3: Select compressible flow in the compressible options of the laminar flow physics field and check Include gravity. Create an initial value for the bubble and set the pressure to 1000 atmospheres based on the energy released by a single discharge during EDM. Set the bubble to hydrogen and the rest to kerosene. Set the surface tension to 0.0728 N / m. Set the lower right endpoint of the rectangular area as the laminar pressure constraint point. When the temperature T is less than 2000 K, the gas viscosity can be calculated using the Satterland formula:

[0040]

[0041] Step S4: In the mesh component, select the free triangle mesh as the mesh type, the mesh density as refined, and calibrate the mesh to fluid dynamics. The EDM gap microbubble mesh model is as follows: Figure 3 shown.

[0042] Step S5: Initialize the model. In the transient study settings, set the step size to 0.0001 μs and the total time to 1 μs. Then, perform iterative calculations on the model.

[0043] Step S6: Post-process the solution results to obtain the two-dimensional EDM gap bubble pulsation flow field.

[0044] By post-processing the volume fraction of fluid 1 in the result, the process diagram of bubble pulsation can be obtained, such as Figure 4 At the same time, the curve of the bubble volume changing with time is shown as Figure 5 shown.

[0045] By post-processing the velocity and pressure in the results, we can obtain the velocity cloud map and pressure contour map of the bubble pulsation flow field in the two-dimensional EDM gap, such as Figure 6 As shown. The bubble pulsation velocity can be obtained by the Rayleigh-Plesset equation:

[0046]

[0047] Where: p b is the pressure inside the bubble. Ignoring the influence of condensable gas, the pressure of non-condensable gas inside the bubble approximately satisfies the adiabatic state equation, that is:

[0048]

[0049] Where: R0 is the initial radius of the bubble, and λ is the adiabatic index.

[0050] By establishing a data set of gas and liquid boundaries, the velocity difference between the bubble boundary and the flow field can be compared, such as Figure 7 shown.

[0051] By changing the initial pressure of the bubble, the influence of bubble pulsation on the flow field under different pressures can be obtained, such as Figure 8 shown.

[0052] By changing the initial size of the bubble, the influence of bubble pulsation of different sizes on the flow field can be obtained, such as Figure 9 shown.

[0053] This paper proposes a controllable and repeatable simulation method for microbubbles within extremely small gaps during EDM. This method can be used to analyze bubble generation, expansion and contraction, and their impact on flow field states during EDM. This method enriches the theoretical framework of flow fields in EDM gaps and provides a theoretical basis and simulation support for optimizing EDM processes. Using simulation methods to study bubbles and flow fields in EDM gaps can significantly reduce experimental costs and improve experimental efficiency.

[0054] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A two-dimensional electric spark gap microbubble simulation method, characterized by: The method comprises the following steps performed in sequence: S1. Create a 2D electrode-workpiece gap flow model in COMSOL Multiphysics. Select the Multiphase Flow - Level Set physics interface and the transient study mode to implement interface tracking. S2. Establish a two-dimensional geometric model of microbubbles in the EDM gap in the geometry section; S3, setting physical property parameters, setting material parameters, setting boundary conditions and setting solution algorithm; S4, meshing the two-dimensional geometric model of microbubbles in the EDM gap to obtain a mesh model of microbubbles in the EDM gap; S5. Perform initialization operations, set calculation conditions, perform iterative calculations, and obtain the microbubble flow field in the EDM gap; S6. Post-process the calculation results such as the volume fraction of the fluid, the pressure and velocity of the flow field, etc.

2. The two-dimensional electric spark gap microbubble simulation method according to claim 1, characterized in that: In step S2, an EDM gap model is established through simplification based on a common EDM gap, and the width of the gap is 20 μm. The initial radius and pressure of the bubble are dynamically calculated based on the single discharge energy during EDM, and simplified to an ideal circular area with a radius of 0.2-1μm. The bubble is located between the electrode and the workpiece.

3. The two-dimensional electric spark gap microbubble simulation method according to claim 1, characterized in that: In step S3, the upper boundary of the EDM gap model is set as a pressure outlet with a pressure of 1 standard atmosphere, and the remaining boundary is set as a wetted wall. Based on the composition, size, and internal pressure of the bubbles generated during EDM, the material within the bubbles is set to hydrogen, and the initial pressure is set to 500-3000 standard atmospheres. Because the internal pressure of bubbles is extremely high during their generation, their dynamic expansion and contraction are extremely dramatic, leading to dramatic changes in both temperature and pressure. Therefore, the density of hydrogen is a function of both pressure and temperature, and its dynamic viscosity is also a function of both pressure and temperature. The density formula entered in COMSOL is pA*0.002016 / R_const[K*mol / J] / T, where pA is pressure, T is temperature, and R_const is the molar mass of hydrogen. The dynamic viscosity formula is 2.14524642E-6+2.54245E-8*T^1-1.0235587E-11*T^2+2.80895021E-15*T^3. The working fluid is kerosene, with a density of 0.739 g / ml and a dynamic viscosity of 1.92 mPa·s. Since hydrogen has a small effect on the surface tension, which is determined by the properties of kerosene, the surface tension between the air bubble and the liquid is set to 0.0728 N / m.

4. The two-dimensional electric spark gap microbubble simulation method according to claim 1, characterized in that: In step S3, the basic assumptions for the model solution include: the gas within the bubble is compressible, the working fluid is incompressible, the entire flow field is set to turbulent, the k-ω turbulence model is the k-ω model, the wall function is the standard wall function, gravity is included, and the direction of gravity is the negative y-axis. The initial velocity in the calculation area is 0 m / s.

5. The two-dimensional electric spark bubble microbubble simulation method according to claim 1, characterized in that: In step S4, the specific method for mesh refinement is as follows: the computational domain is divided into free triangle meshes, the mesh cell size is set to ultrafine, the mesh is calibrated to fluid dynamics, and the mesh inside and around the bubble is refined non-uniformly based on the bubble expansion trend to achieve early fitting of boundary layer changes. The resulting mesh has a maximum cell size of 1.95 μm and a minimum cell size of 0.0225 μm, a total of 13,149 cells, and an average mesh quality of 0.9119.

6. The two-dimensional electric spark bubble and micro bubble simulation method according to claim 1, characterized in that: In step S5, taking into account the bubble pulsation time and the accuracy of the calculation, the initial time step is set to 0.001 μs, the total time is set to 1 μs, and the step size adopted by the solver is free.

7. The two-dimensional electric spark bubble and micro bubble simulation method according to claim 1, characterized in that: In step S6, expanding the "Results" list reveals contour plots of flow field velocity and bubble volume fraction, as well as contour plots of flow field pressure. Post-processing reveals the maximum bubble expansion diameter, periodic bubble pulsation frequency, and the bubble expansion process in the machining fluid.

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