Mechanical seal dynamic pressure tank laser ablation numerical simulation method considering evaporation effect and plasma shielding effect

Abstract

The invention relates to the technical field of mechanical seal laser processing, and discloses a mechanical seal dynamic pressure groove laser ablation numerical simulation method considering an evaporation effect and a plasma shielding effect. The method comprises the following steps of: establishing a geometric model of dynamic pressure groove laser processing by using COMSOL Multiphysics software, setting thermophysical performance parameters of a processing material, determining heat loss generated by evaporation in an evaporation effect and a plasma absorption coefficient in a plasma shielding effect, setting boundary conditions of the geometric model, performing grid division on the geometric model, performing mobile grid setting, and performing dynamic pressure groove laser processing. And numerical simulation and post-processing are completed. According to the method, the evaporation effect and the plasma shielding effect are considered, a three-dimensional simulation model for dynamic pressure groove laser machining is constructed, groove depth values under different process parameters can be effectively predicted, guidance is provided for laser precision machining of mechanical seal dynamic pressure grooves, and reference and theoretical guidance can be provided for laser precision machining of various microgrooves.

Description

Technical Field

[0001] The invention relates to the technical field of mechanical seal laser processing, and in particular to a numerical simulation method for laser ablation of a mechanical seal dynamic pressure groove taking into account evaporation effect and plasma shielding effect. Background Art

[0002] When a high-energy laser beam irradiates a material, the material is instantly vaporized. After the vapor group formed absorbs the laser energy, the internal temperature will continue to rise, causing some vapor particles to ionize and form plasma. The plasma continues to absorb the energy of the laser beam during the outward diffusion process, thereby reducing the laser energy density reaching the laser action surface, which will significantly reduce the efficiency and quality of laser processing. Professor Zhang Duanming's team at Huazhong University of Science and Technology has conducted a comprehensive and in-depth study on the plasma shielding effect and evaporation effect in laser pulse deposition technology. After years of research, a complete set of physical models has been established, and the influence mechanism of evaporation effect, plasma shielding effect and dynamic absorption effect of materials on laser ablation has been revealed. The law of change of material temperature and ablation depth during laser ablation of materials has been obtained, which is a guiding research discussion in the field of laser ablation plasma research in China. In 2017, Cai Song et al. conducted a numerical simulation study on the process of pulsed laser dressing of bronze diamond grinding wheels, considering factors such as evaporation, plasma, and pulsed laser heat accumulation effect. In addition, some scholars have calculated the transmission phenomenon of solid and liquid regions during laser ablation by solving the mass conservation equation, momentum conservation equation and energy conservation equation at the same time, studied the influence of material vaporization, recoil pressure generated by plasma expansion and temperature-dependent surface tension on ablation morphology, and explored the recasting behavior of molten fluid and the formation mechanism of "hump" morphology during laser ablation of materials. In 2009, Samant et al. conducted research on laser drilling of silicon carbide ceramics and established a comprehensive theoretical model that takes into account the thermal effect of material decomposition, recoil pressure caused by evaporation, surface tension caused by temperature gradient and surface cooling caused by evaporation. The model can predict the energy and time required to drill through materials of any depth. In 2012, Vora et al. used COMSOL Multiphysics software to develop a one-dimensional single-pulse laser processing computational model, using the level set method to track the interface between the liquid-solid phase and the gas-liquid phase. The model was used to analyze the influence of laser energy density, recoil pressure, surface tension and other factors on the temperature field, molten fluid velocity, crater size and surface morphology. The results showed that the material loss caused by laser ablation increased the pit depth, while the strong velocity gradient generated by the recoil pressure increased the liquid accumulation. Both effects increased the overall surface roughness. Subsequently, in 2013 and 2015, Vora further expanded the one-dimensional single-pulse laser processing computational model to a one-dimensional multi-pulse laser processing computational model and a three-dimensional laser processing computational model.

[0003] Mechanical seal rings are generally made of hard and wear-resistant materials such as silicon carbide (SiC) or tungsten carbide (WC). Currently, laser processing technology (laser marking method) is generally used to open fluid dynamic pressure grooves on such hard materials. Laser technology involves multiple branches of physics, such as laser physics, plasma physics, thermodynamics, explosion mechanics, etc. The process of laser ablation of materials will produce complex physical phenomena such as melting, evaporation, plasma generation and expansion. These phenomena play an important role in the laser ablation process. Therefore, these factors need to be considered in the research on laser processing of dynamic pressure grooves. The role of these factors is not considered in the existing technology. Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] In view of the deficiencies in the prior art, the present invention provides a numerical simulation method for laser ablation of dynamic pressure grooves in mechanical seals taking into account evaporation effect and plasma shielding effect, which can effectively predict the groove depth value under different process parameters and solve the above technical problems.

[0006] (II) Technical solution

[0007] To achieve the above purpose, the present invention provides the following technical solution: a numerical simulation method for laser ablation of dynamic pressure grooves of mechanical seals considering evaporation effect and plasma shielding effect, comprising the following steps:

[0008] S1. Use COMSOL Multiphysics software to establish the geometric model of dynamic pressure groove laser processing;

[0009] S2. Set the thermophysical performance parameters of the processed material, including length l0, width w0, height h0, and density ρ, specific heat c, thermal conductivity k, melting point T of the model material m , boiling point T v , latent heat of vaporization L v , Absorption rate A s wait;

[0010] S3. Determine the heat loss Q generated by evaporation in the evaporation effect v and the plasma absorption coefficient α in the plasma shielding effect pl ;

[0011] S4, setting boundary conditions, wherein the heat source is loaded on the surface of the geometric model in the form of heat flux;

[0012] S5. After the boundary conditions are set, meshing is performed, specifically, the maximum cell size is 6 μm, the minimum cell size is 0.225 μm, the maximum cell growth rate is 1.35, the curvature factor is 0.3, and the narrow area resolution is 0.85;

[0013] S6. Setting the upper boundary grid speed of the laser energy;

[0014] S7. Perform simulation calculation and post-processing.

[0015] As a preferred technical solution of the present invention, the heat loss Q generated by evaporation in the evaporation effect in step S3 is v The specific expression is as follows:

[0016] Q v =L v m v

[0017] Among them, Q v Indicates the heat loss caused by evaporation in the evaporation effect, L v represents the latent heat of vaporization of the material, m v It represents the rate of change of steam particles, and its specific expression is as follows:

[0018]

[0019] Among them, m v represents the rate of change of steam particles, p represents the saturated vapor pressure, k b represents the Boltzmann constant, T s represents the surface temperature of the material, m represents the particle mass, β r represents the diffusion coefficient.

[0020] As a preferred technical solution of the present invention, the specific expression of the saturated vapor pressure p is as follows:

[0021]

[0022] Where p(T) represents the saturated vapor pressure at temperature T, p amb represents standard atmospheric pressure, exp represents an exponential function with a natural constant as the base, m represents the mass of the particle, and k b represents the Boltzmann constant, T s Indicates the surface temperature of the material, T v Indicates the boiling point of a material.

[0023] As a preferred technical solution of the present invention, the plasma absorption coefficient α in the plasma shielding effect in step S3 is pl The photoionization absorption coefficient α PI and the inverse bremsstrahlung absorption coefficient α IB Composition, where the inverse bremsstrahlung absorption coefficient α IB The expression is as follows:

[0024]

[0025] Among them, n i represents the plasma particle density, T p represents the plasma temperature, exp represents an exponential function with a natural constant as the base, h, v, n e , Z represent Planck constant, laser frequency, plasma electron density, and atomic number, respectively.

[0026] As a preferred technical solution of the present invention, the boundary condition in step S4 includes the heat flux of the upper boundary, which is expressed as follows:

[0027]

[0028] Among them, A s represents the absorptivity of the material, ρ represents the density of the material, exp represents the exponential function with the natural constant as the base, I0 represents the laser peak power, x and y represent the horizontal and vertical coordinates respectively, S(T) represents the step function, H represents the plasma linearity perpendicular to the material, r0 represents the focal plane laser spot radius, x m and m It indicates the moving position of the light spot during the calculation process. Its specific expression is as follows:

[0029]

[0030] Among them, ν scan represents the scanning speed, x0 and y0 represent the initial positions of the light spot, mod(t, t1) represents the modulo function, t1 represents the time required to process a filling line, t represents the time, S represents the filling spacing, and p1(t) represents the function that controls the movement of the light spot along the filling direction.

[0031] Compared with the prior art, the present invention provides a numerical simulation method for laser ablation of dynamic pressure grooves of mechanical seals taking into account evaporation effect and plasma shielding effect, which has the following beneficial effects:

[0032] The present invention constructs a three-dimensional simulation model for laser processing of mechanical seal dynamic pressure grooves taking into account evaporation effect and plasma shielding effect. Through numerical simulation, the groove depth value under different process parameters can be effectively predicted, providing guidance for the laser precision processing of mechanical seal dynamic pressure grooves, and can also provide reference and theoretical guidance for the laser precision processing of various micro grooves. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic diagram showing the process flow of the present invention;

[0034] Figure 2 A schematic diagram showing the plasma linear variation rule during the isothermal expansion stage of the present invention;

[0035] Figure 3A schematic diagram showing the step function S(T) of the present invention. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only 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.

[0037] See also Figure 1 - Figure 3 , a numerical simulation method for laser ablation of dynamic pressure grooves of mechanical seals considering evaporation effect and plasma shielding effect, comprising the following steps:

[0038] S1. Use COMSOL Multiphysics software to establish the geometric model of dynamic pressure groove laser processing;

[0039] S2. Set the thermophysical performance parameters of the processed material, including length l0, width w0, height h0, and density ρ, specific heat c, thermal conductivity k, melting point T of the model material m , boiling point T v , latent heat of vaporization L v , Absorption rate A s ;

[0040] The length of the laser ablation model is set to l0 = 150 μm, the height h0 = 20 μm, and the width w0 = 150 μm. The material used in the simulation of the present invention is silicon carbide, and the thermal physical parameters of the silicon carbide material are: density ρ = 3200 kg / m 3 , specific heat capacity c = 1300 j / (kg·K), thermal conductivity k = 370 W / (m·K), melting point T m =2445K, boiling point T v =3103K, latent heat of vaporization L v =530Kj / mol, absorption rate A s =0.8;

[0041] S3. Determine the heat loss Q generated by evaporation in the evaporation effect v and the plasma absorption coefficient α in the plasma shielding effect pl ;

[0042] In order to obtain the heat loss Q caused by evaporation v and the plasma absorption coefficient α of the plasma shielding effect pl Set the laser power P = 15.03W and the scanning speed v scan =432.19 mm·s -1, filling spacing S = 15μm, repetition frequency v = 30kHz. Then the heat loss caused by evaporation is Q v :

[0043] Q v =L v m v

[0044] Among them, Q v Indicates the heat loss caused by evaporation in the evaporation effect, L v represents the latent heat of vaporization of the material, m v It represents the rate of change of steam particles, and its specific expression is as follows:

[0045]

[0046] Among them, m v represents the rate of change of steam particles, p represents the saturated vapor pressure, k b represents the Boltzmann constant, T s represents the surface temperature of the material, m represents the particle mass, β r represents the diffusion coefficient, and the laser peak power

[0047] The specific expression of saturated vapor pressure p is as follows:

[0048]

[0049] Where p(T) represents the saturated vapor pressure at temperature T, p amb represents standard atmospheric pressure, exp represents an exponential function with a natural constant as the base, m represents the mass of the particle, and k b represents the Boltzmann constant, T s Indicates the surface temperature of the material, T v Indicates the boiling point of a material;

[0050] Plasma absorption coefficient α pl It can be expressed as α pl =α IB+ α PI , where the inverse bremsstrahlung absorption coefficient α IB :

[0051]

[0052] Among them, n i represents the plasma particle density, T p represents the plasma temperature, exp represents an exponential function with a natural constant as the base, h, v, n e , Z represent Planck constant, laser frequency, plasma electron density, and atomic number, respectively.

[0053] Plasma particle density n i Range is 10 19 ~10 21 / cm 3， Plasma temperature T P The range is 10000~50000K. The photoionization absorption coefficient α PI The typical value is 10 -21 m -2 .

[0054] S4, setting boundary conditions, wherein the heat source is loaded on the surface of the geometric model in the form of heat flux;

[0055] Based on the above evaporation effect and plasma shielding effect, the boundary conditions of the model are set, and the initial value of the model is: T| t＝0 =293K, the heat flux on the upper boundary is:

[0056]

[0057] Among them, A s represents the absorptivity of the material, ρ represents the density of the material, exp represents the exponential function with the natural constant as the base, I0 represents the laser peak power, x and y represent the horizontal and vertical coordinates respectively, S(T) represents the step function, H represents the plasma linearity perpendicular to the material, r0 represents the focal plane laser spot radius, x m and m It indicates the moving position of the light spot during the calculation process. Its specific expression is as follows:

[0058]

[0059] Among them, v scan represents the scanning speed, x0 and y0 represent the initial positions of the light spot, mod(t, t1) represents the modulus function, t1 represents the time required to process a filling line, t represents the time, S represents the filling spacing, and p1(t) represents the function that controls the movement of the light spot along the filling direction;

[0060] p1(t) piecewise function value

[0061] Starting Finish value 0 <![CDATA[t1]]> 0 <![CDATA[t1]]> <![CDATA[2t1]]> 1 <![CDATA[2t1]]> <![CDATA[3t1]]> 2 <![CDATA[3t1]]> <![CDATA[4t1]]> 3 <![CDATA[4t1]]> <![CDATA[5t1]]> 4 <![CDATA[5t1]]> <![CDATA[6t1]]> 5 <![CDATA[6t1]]> <![CDATA[7t1]]> 6

[0062] S5. After the boundary conditions are set, meshing is performed, specifically, the maximum cell size is 6 μm, the minimum cell size is 0.225 μm, the maximum cell growth rate is 1.35, the curvature factor is 0.3, and the narrow area resolution is 0.85;

[0063] S6. Setting the upper boundary grid speed of the laser energy;

[0064] Since the depth of the laser heat penetration layer is shallow, the laser energy has no effect on the lower boundary, so the normal grid displacement at the lower boundary is also zero. When the laser acts on the material surface, the surface material is vaporized and removed, and the grid velocity v at the upper boundary is g It can be expressed as:

[0065]

[0066] In the formula, q a is the heat flux absorbed by the material; ρ is the density of the material; L v is the latent heat of evaporation of the material.

[0067] S7. Perform simulation calculation and post-processing.

[0068] The above steps complete the numerical simulation of laser ablation of the dynamic pressure groove of the mechanical seal considering the evaporation effect and plasma shielding effect. The simulation results are: pulse time t = 5.33x10 -4 The groove depth after s is 7.13μm. The experimental value of the dynamic pressure groove depth measurement under the same process parameters is 7.28μm, and its relative error is only 2.06%, indicating that the model has good accuracy.

[0069] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A numerical simulation method for laser ablation of dynamic pressure grooves of mechanical seals considering evaporation effect and plasma shielding effect, characterized in that: The following steps are involved: S1. Use COMSOL Multiphysics software to establish the geometric model of dynamic pressure groove laser processing; S2. Set the thermophysical performance parameters of the processed material, including length l0, width w0, height h0, and density ρ, specific heat c, thermal conductivity k, melting point T of the model material m , boiling point Tv, latent heat of vaporization L v , Absorption rate A s wait; S3. Determine the heat loss Q generated by evaporation in the evaporation effect v and the plasma absorption coefficient α in the plasma shielding effect pl ; S4, setting boundary conditions, wherein the heat source is loaded on the surface of the geometric model in the form of heat flux; S5. After the boundary conditions are set, meshing is performed, specifically, the maximum cell size is 6 μm, the minimum cell size is 0.225 μm, the maximum cell growth rate is 1.35, the curvature factor is 0.3, and the narrow area resolution is 0.85; S6. Setting the upper boundary grid speed of the laser energy; S7. Perform simulation calculation and post-processing.

2. According to claim 1, a numerical simulation method for laser ablation of a mechanical seal dynamic pressure groove taking into account evaporation effect and plasma shielding effect, characterized in that: The heat loss Q generated by evaporation in the evaporation effect in step S3 v The specific expression is as follows: Q v =L v m v Among them, Q v Indicates the heat loss caused by evaporation in the evaporation effect, L v represents the latent heat of vaporization of the material, m v It represents the rate of change of steam particles, and its specific expression is as follows: Among them, m v represents the rate of change of steam particles, p represents the saturated vapor pressure, k b represents the Boltzmann constant, T s represents the surface temperature of the material, m represents the particle mass, β r represents the diffusion coefficient.

3. The numerical simulation method for laser ablation of dynamic pressure grooves of mechanical seals considering evaporation effect and plasma shielding effect according to claim 2, characterized in that: The specific expression of the saturated vapor pressure p is as follows: Where p(T) represents the saturated vapor pressure at temperature T, pam b represents standard atmospheric pressure, exp represents an exponential function with a natural constant as the base, m represents the mass of the particle, and k b represents the Boltzmann constant, T s Indicates the surface temperature of the material, T v Indicates the boiling point of a material.

4. The numerical simulation method for laser ablation of dynamic pressure grooves of mechanical seals considering evaporation effect and plasma shielding effect according to claim 1, characterized in that: The plasma absorption coefficient α in the plasma shielding effect in step S3 pl The photoionization absorption coefficient α PI and the inverse bremsstrahlung absorption coefficient α IB Composition, where the inverse bremsstrahlung absorption coefficient α IB The expression is as follows: Among them, n i represents the plasma particle density, T p represents the plasma temperature, exp represents an exponential function with a natural constant as the base, h, v, n e , Z represent Planck constant, laser frequency, plasma electron density, and atomic number, respectively.

5. The numerical simulation method for laser ablation of dynamic pressure grooves of mechanical seals considering evaporation effect and plasma shielding effect according to claim 4, characterized in that: The boundary condition in step S4 includes the heat flux of the upper boundary, which is expressed as follows: Among them, A s represents the absorptivity of the material, ρ represents the density of the material, exp represents the exponential function with the natural constant as the base, I0 represents the laser peak power, x and y represent the horizontal and vertical coordinates respectively, S(T) represents the step function, H represents the plasma linearity perpendicular to the material, r0 represents the focal plane laser spot radius, x m and m Indicates the moving position of the light spot during the calculation process, and its specific expression is as follows: Among them, v scan represents the scanning speed, x0 and y0 represent the initial positions of the light spot, mod(t, t1) represents the modulus function, t1 represents the time required to process a filling line, t represents the time, S represents the filling spacing, and p1(t) represents the function that controls the movement of the light spot along the filling direction.

Images