Numerical simulation method for laser processing of mechanical seal dynamic pressure groove

Abstract

The invention relates to the technical field of mechanical seal laser precision machining, and discloses a numerical simulation method for laser machining of a mechanical seal dynamic pressure groove, a fluid flowing module and a heat transfer module of COMSOL Multiphysics software are used for analyzing the laser machining process of the dynamic pressure groove, a geometric model of the laser machining process of the dynamic pressure groove is established, and a mechanical seal dynamic pressure groove is obtained. Physical property parameters required by materials are set, boundary conditions of a geometric model are set based on a fluid flow and heat and mass transfer control equation, grid division is conducted on a computational domain based on the established geometric model, and simulation is conducted. According to the method, based on a fluid dynamics equation and a level set equation, a three-dimensional model of the moving heat source machining dynamic pressure groove is established, the ablation process of the laser machining dynamic pressure groove is simulated, the forming and evolution process of the dynamic pressure groove is described, the groove depth and the groove bottom surface roughness are accurately predicted, and the dynamic pressure groove machining accuracy is improved. The laser processing mechanism can be disclosed, and laser precision processing of the dynamic pressure groove can be guided.

Description

Technical Field

[0001] The invention relates to the technical field of mechanical seal laser precision processing, in particular to a numerical simulation method for laser processing of a mechanical seal dynamic pressure groove. Background Art

[0002] Precision machining of dynamic pressure grooves of mechanical seals plays an important role in ensuring the stable operation of mechanical seals. At present, laser machining technology is the most commonly used machining method for dynamic pressure grooves. However, during the laser machining of dynamic pressure grooves, the phenomenon of multiple physical changes such as melting and gasification coupling each other leads to unclear machining mechanism. Simulating the laser machining process of dynamic pressure grooves helps to clarify the laser machining mechanism and predict the groove depth and groove bottom surface roughness after machining, which is of great significance for realizing or guiding the precision machining of dynamic pressure grooves.

[0003] Laser processing is a non-contact processing technology that is suitable for small-area processing through focused pulses. It has the characteristics of transient high-energy injection, can process high-hardness, brittleness and high-melting-point materials, and will not cause tool wear. It is widely used in the precision forming of difficult-to-cut materials. However, the mechanism of interaction between pulsed laser and materials is complex, which seriously affects the stability and quality of laser processing. In recent years, many researchers have carried out a lot of research on the interaction mechanism between laser and materials. In order to explore the ablation characteristics and material removal mechanism of diamond in picosecond laser processing, Wang Hui, Wen Qiuling and others conducted experimental research on picosecond laser processing microgrooves on CVD single crystal diamond. Wu Dongjiang and others studied the morphological change law of the ablation groove on the surface of RB-SiC by changing the laser energy density and the effective pulse number, and determined the removal mechanism of RB-SiC processed by femtosecond laser. The above studies are all experimental studies on the laser processing mechanism. Although the specific ablation morphology after processing can be intuitively observed, the experimental cost is high. When the multi-pulse laser interacts with the material, the high-energy laser beam removes the material instantly. In the laser processing experiment, the process is difficult to be observed. Summary of the invention

[0004] 1. Technical issues to be solved

[0005] In view of the deficiencies in the prior art, the present invention provides a numerical simulation method for laser processing of a dynamic pressure groove of a mechanical seal, which has the advantages of predicting the groove depth and the surface roughness of the groove bottom, and solves the above-mentioned technical problems.

[0006] (II) Technical solution

[0007] To achieve the above object, the present invention provides the following technical solution: a numerical simulation method for laser processing of a dynamic pressure groove of a mechanical seal, comprising the following steps:

[0008] S1. Analyze the laser processing dynamic pressure groove process using the fluid flow module and heat transfer module of COMSOL Multiphysics software;

[0009] S2. Establishing the geometric model of the laser processing dynamic pressure groove process, including air domain and solid domain;

[0010] S3, setting the physical property parameters required by the material for the air domain and the solid domain respectively, including laser process parameters, laser beam parameters, and physical property parameters of the solid workpiece material;

[0011] S4. Setting boundary conditions of the geometric model based on the control equations of fluid flow, heat transfer and mass transfer. The control equations include level set equations, mass conservation equations, momentum conservation equations, energy conservation equations and laser heat source model;

[0012] S5. Meshing the computational domain based on the established geometric model;

[0013] S6. Perform simulation calculations and post-process the simulation results.

[0014] As a preferred technical solution of the present invention, the level set equation is expressed as follows:

[0015]

[0016] Where φ represents the level set function, represents the partial derivative with respect to time t, represents a vector operator, represents the evaporation rate, u represents the velocity vector, ε h represents the boundary layer thickness, ρ v and ρ l Respectively represent the density of the gaseous and liquid states of the material, δ(φ) represents the delta function about φ, γ a Indicates the function initialization value, represents the vector operator of the level set function, represents the absolute value of the level set function vector operator;

[0017] The mass conservation equation is expressed as follows:

[0018]

[0019] Among them, δ(φ) represents the delta function with respect to φ, represents the evaporation rate, u represents the velocity vector, represents a vector operator, n represents the normal direction of the gas-liquid interface, represents velocity divergence;

[0020] The momentum conservation equation is expressed as follows:

[0021]

[0022] Among them, T, ρ, μ, P a Respectively represent the temperature, density, dynamic viscosity and pressure of the material. represents a vector operator, I, β, T m , k represent the unit matrix, the thermal expansion coefficient of the material, the melting temperature of the material, and the thermal conductivity of the material, respectively. σ and y represent the surface tension coefficient and the ordinate, respectively. δ(φ) represents the delta function about φ. represents the partial derivative of the surface tension coefficient with respect to the temperature of the material, represents the partial derivative of the material temperature with respect to the horizontal coordinate x, u represents the velocity vector, g represents the gravitational acceleration vector, represents the partial derivative of the velocity vector u with respect to time, n represents the normal direction of the gas-liquid interface, P r Indicates recoil pressure;

[0023] The energy conservation equation is expressed as follows:

[0024]

[0025] Among them, r 0 , τ, and f represent the laser spot radius, pulse width, and repetition frequency during laser processing, respectively. 0 represents the surface emissivity, k b , L v 、h c 、T 0 They represent the Boltzmann constant, evaporation rate, latent heat of vaporization, heat transfer coefficient, initial temperature, and A. s represents the absorption rate of the material to the laser energy, g(t) represents the laser pulse time function, x and y represent the horizontal and vertical coordinates respectively, P represents the laser power, C p represents the specific heat capacity of the material, and exp represents an exponential function with a natural constant as the base;

[0026] The laser heat source model expression is as follows:

[0027]

[0028] Where Q(x,y,t) represents the moving heat source that changes with time, R represents the reflectivity of the material, f represents the repetition frequency, τ represents the pulse width, and r 0 represents the spot radius, exp represents the exponential function with a natural constant as the base, x and y represent the horizontal and vertical coordinates respectively, and g(t) represents the laser pulse time function.

[0029] As a preferred technical solution of the present invention, the laser pulse time function g(t) is expressed as follows:

[0030]

[0031] Wherein, t represents time, τ represents pulse width, and f represents repetition frequency.

[0032] As a preferred technical solution of the present invention, the shape of the dynamic pressure groove includes any one of a rectangular groove, a triangular groove, a spiral groove, a T-shaped groove, a U-shaped groove, a herringbone groove, a straight groove, and an arc groove.

[0033] As a preferred technical solution of the present invention, the laser process parameters include laser power, repetition frequency, scanning speed, number of markings, and filling spacing, and the laser beam parameters include pulse width and spot radius.

[0034] Compared with the prior art, the present invention provides a numerical simulation method for laser processing of dynamic pressure grooves of mechanical seals, which has the following beneficial effects:

[0035] The present invention establishes a three-dimensional model of dynamic pressure groove processed by moving heat source based on fluid dynamics equations and level set equations, simulates the ablation process of laser processed dynamic pressure groove, effectively describes the formation and evolution process of the dynamic pressure groove, and accurately predicts the groove depth and groove bottom surface roughness, which is helpful to reveal the laser processing mechanism and guide the laser precision processing of the dynamic pressure groove, and has the characteristics of low experimental cost and easy observation of the laser ablation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a flow chart of the present invention;

[0037] Figure 2 This is a schematic diagram of a three-dimensional model of a laser-processed dynamic pressure groove according to the present invention;

[0038] Figure 3 A schematic diagram of meshing a three-dimensional model according to the present invention;

[0039] Figure 4 This is a schematic diagram of the third filling line marked by the laser beam of the present invention;

[0040] Figure 5 This is a two-dimensional topography diagram of the groove depth actually processed by the present invention. DETAILED DESCRIPTION

[0041] 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.

[0042] See also Figure 1 - Figure 5 , a numerical simulation method for laser processing of a dynamic pressure groove of a mechanical seal, comprising the following steps:

[0043] S1. Analyze the laser processing dynamic pressure groove process using the fluid flow module and heat transfer module of COMSOL Multiphysics software;

[0044] The shape of the dynamic pressure groove includes any one of a rectangular groove, a triangular groove, a spiral groove, a T-shaped groove, a U-shaped groove, a herringbone groove, a straight groove, and an arc groove;

[0045] For the fluid flow module, the two-phase flow module should be selected; for the level set module, the heat transfer module should be selected; for the two-phase flow module, the laminar flow module should be selected;

[0046] S2. Establish a geometric model of the laser processing dynamic pressure groove process, including air domain and solid domain. The solid domain is a solid workpiece. The material of the solid workpiece is not limited, including silicon carbide, tungsten carbide, stainless steel, etc.;

[0047] S3, setting the physical property parameters required by the material for the air domain and the solid domain respectively, including laser process parameters, laser beam parameters, and physical property parameters of the solid workpiece material;

[0048] The laser process parameters include laser power, repetition frequency, scanning speed, marking times, and filling spacing, and the laser beam parameters include pulse width and spot radius;

[0049] S4. Setting boundary conditions of the geometric model based on the control equations of fluid flow, heat transfer and mass transfer. The control equations include level set equations, mass conservation equations, momentum conservation equations, energy conservation equations and laser heat source model;

[0050] The level set equation expression is as follows:

[0051]

[0052] Where φ represents the level set function, represents the partial derivative with respect to time t, represents a vector operator, represents the evaporation rate, u represents the velocity vector, ε hrepresents the boundary layer thickness, ρ v and ρ l Respectively represent the density of the gaseous and liquid states of the material, δ(φ) represents the delta function about φ, γ a Indicates the function initialization value, represents the vector operator of the level set function, Represents the absolute value of the level set function vector operator; the value of the liquid region (including solid and solid-liquid mixed region) is 0, the value of the gas region is 1, the value at the gas / liquid interface is defined as 0.5, and φ smoothly transitions between 0 and 1;

[0053] The mass conservation equation is expressed as follows:

[0054]

[0055] Among them, δ(φ) represents the delta function with respect to φ, represents the evaporation rate, u represents the velocity vector, represents a vector operator, n represents the normal direction of the gas-liquid interface, represents velocity divergence;

[0056] The momentum conservation equation is expressed as follows:

[0057]

[0058] Among them, T, ρ, μ, P a Respectively represent the temperature, density, dynamic viscosity and pressure of the material. represents a vector operator, I, β, T m Respectively represent the unit matrix, the thermal expansion coefficient of the material, and the melting temperature of the material. σ and y represent the surface tension coefficient and the ordinate, respectively. δ(φ) represents the delta function about φ. represents the partial derivative of the surface tension coefficient with respect to the temperature of the material, represents the partial derivative of the material temperature with respect to the horizontal coordinate x, u represents the velocity vector, g represents the gravitational acceleration vector, represents the partial derivative of the velocity vector u with respect to time, n represents the normal direction of the gas-liquid interface, P r Indicates recoil pressure;

[0059] The energy conservation equation is expressed as follows:

[0060]

[0061] Among them, r 0 , τ, f represent the spot radius, pulse width, and repetition frequency respectively, ε 0 represents the surface emissivity, k b , Lv 、h c 、T 0 They represent the Boltzmann constant, evaporation rate, latent heat of vaporization, heat transfer coefficient, initial temperature, and A. s represents the absorption rate of the material to the laser energy, g(t) represents the laser pulse time function, x and y represent the horizontal and vertical coordinates respectively, P represents the laser power, C p represents the specific heat capacity of the material, and exp represents an exponential function with a natural constant as the base;

[0062] The laser heat source model expression is as follows:

[0063]

[0064] Where Q(x,y,t) represents the moving heat source that changes with time, R represents the reflectivity of the material, f represents the repetition frequency, τ represents the pulse width, and r 0 represents the spot radius, exp represents the exponential function with the natural constant as the base, x and y represent the horizontal and vertical coordinates respectively, and g(t) represents the laser pulse time function;

[0065] S5. Based on the established geometric model, the computational domain is divided into finite element meshes, and the finite element mesh is a free tetrahedral mesh;

[0066] S6. Perform simulation calculations and post-process the simulation results.

[0067] The specific implementation parameters are as follows: select the fluid flow and heat transfer module in the simulation software, further select the two-phase flow and level set-laminar flow options in the fluid flow module; and further select the fluid heat transfer option in the fluid heat transfer module.

[0068] Figure 2 Schematic diagram of the 3D model of the laser-processed dynamic pressure groove. The total model size is 160μm long, 80μm wide, and 100μm high, of which the solid workpiece area is 160μm×80μm×20μm and the air area is 160μm×80μm×80μm.

[0069] Table 1 shows the process parameters used for laser processing of dynamic pressure grooves, and Table 2 shows the physical properties of silicon carbide workpieces. The laser beam parameters are pulse width of 110ns, operating wavelength of 1064nm, and spot radius of 25μm.

[0070] According to the boundary conditions set by the control equation, the position of the light spot during the marking process can be expressed as:

[0071]

[0072] x m ,y mare the coordinates of the light spot on the x and y axes respectively; 0 ,y 0 are the coordinates of the initial position of the light spot;

[0073] Table 1

[0074]

[0075] Table 2

[0076]

[0077]

[0078] Figure 3 The figure is a schematic diagram of meshing a three-dimensional model. The geometric model established by the present invention uses free tetrahedral mesh units for meshing. In order to balance the calculation efficiency and the accuracy of the calculation results, a coarser mesh unit type is used in the air domain, and a finer mesh unit type is used in the solid domain. When the laser beam acts on the filling line, the temperature and deformation of the material on the filling line and the surrounding area are large. A finer mesh should be used, and the boundary mesh should be set in layers at the filling line. The specific mesh size is shown in Table 3;

[0079] Table 3

[0080]

[0081] Figure 4 The figure is a schematic diagram of the laser beam marking the third filling line. In order to improve the calculation efficiency, three filling lines are marked under the premise of ensuring the accuracy of the calculation results. It can be seen from the figure that the groove bottom contour is relatively uniform after the third filling line is marked, and the influence of heat accumulation on the ablation depth is basically stable. Therefore, the data after the third filling line is marked is selected to represent the groove depth and groove bottom surface roughness of the dynamic pressure groove after laser processing. Through the calculation of the simulation data, it can be obtained that the groove depth result h g =0.77μm, roughness Ra=0.60μm.

[0082] In order to verify the accuracy of the simulation results, the dynamic pressure groove laser processing experiment was carried out. Figure 5 This is the actual two-dimensional topography of the groove depth. After being processed by the laser engraving machine, the surface roughness profile shape measuring machine randomly measured 3 times to get the average value: the experimental groove depth h ge is 0.803μm, and the relative error of the groove depth is ε s (h ge ) is 4.36%, the experimental roughness Ra is 0.587μm, and the relative error of roughness ε s (Ra) is only 2.32%, indicating that the model has good accuracy.

[0083] 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 processing of dynamic pressure grooves of mechanical seals, characterized in that: The following steps are involved: S1. Analyze the laser processing dynamic pressure groove process using the fluid flow module and heat transfer module of COMSOL Multiphysics software; S2. Establishing the geometric model of the laser processing dynamic pressure groove process, including air domain and solid domain; S3, setting the physical property parameters required by the material for the air domain and the solid domain respectively, including laser process parameters, laser beam parameters, and physical property parameters of the solid workpiece material; S4. Setting boundary conditions of the geometric model based on the control equations of fluid flow, heat transfer and mass transfer. The control equations include level set equations, mass conservation equations, momentum conservation equations, energy conservation equations and laser heat source model; S5. Meshing the computational domain based on the established geometric model; S6. Perform simulation calculations and post-process the simulation results.

2. The numerical simulation method for laser processing of dynamic pressure groove of mechanical seal according to claim 1 is characterized in that: The level set equation expression is as follows: Where φ represents the level set function, represents the partial derivative with respect to time t, represents a vector operator, represents the evaporation rate, u represents the velocity vector, ε h represents the boundary layer thickness, ρ v and ρ l Respectively represent the density of the gaseous and liquid states of the material, δ(φ) represents the delta function about φ, γ a Indicates the function initialization value, represents the vector operator of the level set function, represents the absolute value of the level set function vector operator; The mass conservation equation is expressed as follows: Among them, δ(φ) represents the delta function with respect to φ, represents the evaporation rate, u represents the velocity vector, represents a vector operator, n represents the normal direction of the gas-liquid interface, represents velocity divergence; The momentum conservation equation is expressed as follows: Among them, T, ρ, μ, P a Respectively represent the temperature, density, dynamic viscosity and pressure of the material. represents a vector operator, I, β, T m Respectively represent the unit matrix, the thermal expansion coefficient of the material, and the melting temperature of the material. σ and y represent the surface tension coefficient and the ordinate, respectively. δ(φ) represents the delta function about φ. represents the partial derivative of the surface tension coefficient with respect to the temperature of the material, represents the partial derivative of the material temperature with respect to the horizontal coordinate x, u represents the velocity vector, g represents the gravitational acceleration vector, represents the partial derivative of the velocity vector u with respect to time, n represents the normal direction of the gas-liquid interface, P r Indicates recoil pressure; The energy conservation equation is expressed as follows: Among them, r0, τ, and f represent the laser spot radius, pulse width, and repetition frequency during laser processing, ε0 represents the surface emissivity, and k b , L v 、h c , T0 represent the Boltzmann constant, evaporation rate, material vaporization latent heat, heat transfer coefficient, initial temperature, A s represents the absorption rate of the material to the laser energy, g(t) represents the laser pulse time function, x and y represent the horizontal and vertical coordinates respectively, P represents the laser power, C p represents the specific heat capacity of the material, and exp represents an exponential function with a natural constant as the base; The laser heat source model expression is as follows: Among them, Q(x,y,t) represents the moving heat source that changes with time, R represents the reflectivity of the material, f is the repetition frequency, τ represents the pulse width, r0 is the spot radius, exp represents the exponential function with natural constants as the base, x and y represent the horizontal and vertical coordinates respectively, and g(t) represents the laser pulse time function.

3. The numerical simulation method for laser processing of dynamic pressure groove of mechanical seal according to claim 2 is characterized in that: The laser pulse time function g(t) is expressed as follows: Among them, t represents time, τ represents pulse width, and f represents repetition frequency.

4. The numerical simulation method for laser processing of dynamic pressure groove of mechanical seal according to claim 1, characterized in that: The shape of the dynamic pressure groove includes any one of a rectangular groove, a triangular groove, a spiral groove, a T-shaped groove, a U-shaped groove, a herringbone groove, a straight groove, and an arc groove.

5. The numerical simulation method for laser processing of dynamic pressure groove of mechanical seal according to claim 1, characterized in that: The laser process parameters include laser power, repetition frequency, scanning speed, number of markings, and filling spacing; the laser beam parameters include pulse width and spot radius.

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