Laser ablated titanium alloy numerical simulation method based on plasma shielding effect

Abstract

The invention relates to the technical field of laser micromachining, in particular to a laser ablation titanium alloy numerical simulation method based on a plasma shielding effect. In order to solve the problems that the precision and efficiency of an existing laser processing and manufacturing micro-nano structure are low, the plasma shielding effect is not fully considered in a simulation model and the like, two-dimensional and three-dimensional models are constructed by means of COMSOL Multiphysics software. According to the model, the plasma shielding effect is fully considered, a laser energy transfer equation is corrected, and the molten pool behavior and surface topography forming process is simulated by combining mass, momentum and energy conservation equations. A laser ablation process is accurately simulated by setting a heat source and boundary conditions, applying a level set method, considering various effects and calculating plasma related parameters. And inputting different laser parameters to simulate and analyze the influence on the groove morphology, and comparing an experiment with a simulation result to correct the model. Simulation precision is improved, laser processing parameters can be optimized, cost is reduced, universality is high, theoretical guidance can be provided for laser processing of various metal materials, and the laser processing technology is promoted to be developed in multiple fields.

Description

Technical Field

[0001] The present invention relates to the technical field of laser micromachining, and in particular to a laser ablation numerical simulation method that fully considers the plasma shielding effect, and the application of the method in accurately predicting the surface morphology of titanium alloys. Background Art

[0002] In the development of laser processing technology, the physical processes involved in the interaction between lasers and metal materials are extremely complex, covering multiple key links such as heat conduction, melting, gasification, and plasma formation. How to accurately predict the surface morphology of materials after laser ablation and optimize laser processing parameters has always been a core problem in research in this field. When manufacturing micro-nano structures, traditional laser processing technology lacks precise control of the processing process, which makes it difficult to improve processing accuracy and greatly limits processing efficiency.

[0003] At present, although research on laser ablation has achieved certain results, most simulation models still have obvious defects in predicting the surface morphology after laser ablation. Some studies did not fully consider the plasma shielding effect in the modeling process, which resulted in a large deviation between the simulation results and the actual processing conditions. In fact, during the laser ablation process, the plasma will absorb and scatter the laser energy, seriously affecting the efficiency of the laser energy reaching the target surface, and thus having a crucial impact on the formation of the surface morphology. In addition, the existing simulation methods often simplify or ignore some key factors when dealing with multi-physical field coupling problems, resulting in the simulation results being unable to truly and accurately reflect the full picture of the actual processing process.

[0004] Taking TC4 titanium alloy as an example, it has been widely used in high-end fields such as aerospace and automobile manufacturing due to its excellent properties such as high strength, good corrosion resistance and high temperature stability. However, the low thermal conductivity of TC4 titanium alloy causes a large heat-affected zone during laser processing, which undoubtedly further increases the difficulty of accurately controlling the processing process. In summary, the development of a numerical simulation method that can comprehensively and accurately simulate the laser ablation process, especially fully considering the plasma shielding effect, is of great significance to improving the efficiency of laser processing. Summary of the invention

[0005] The present invention is committed to providing an innovative numerical simulation method for laser ablation that takes into account the plasma shielding effect. By constructing a high-precision model, this method can accurately predict the dynamic evolution of the surface morphology during laser ablation of titanium alloys, and deeply analyze the influence mechanism of laser parameters on groove morphology, thereby providing a solid theoretical basis for the optimization of laser processing parameters, and ultimately achieving a significant improvement in laser processing accuracy and efficiency.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A numerical simulation method for laser ablation of titanium alloy based on plasma shielding effect comprises the following steps:

[0008] Step 1: Create a laser ablation model

[0009] The fluid flow module and heat transfer module of COMSOL Multiphysics software are used to construct two-dimensional and three-dimensional laser ablation models. In the process of model construction, the plasma shielding effect is fully considered and the laser energy transfer equation is reasonably modified. The level set method is introduced to accurately track the evolution of the solid-liquid-gas interface. At the same time, the mass conservation equation, momentum conservation equation and energy conservation equation are combined to fully simulate the dynamic behavior of the molten pool and the formation process of the surface morphology.

[0010] Solving the control equations: Strictly follow the three conservation equations of fluid mechanics, namely the mass conservation equation, momentum conservation equation and energy conservation equation. Combined with the thermophysical parameters of TC4 titanium alloy (such as liquidus temperature, solidus temperature, vaporization temperature, solidus density, liquidus density, etc.), these equations are accurately solved. In the momentum conservation equation, its generalized source term covers multiple factors such as surface tension, recoil pressure, thermal buoyancy and mushy zone resistance, so as to fully consider the various forces acting on the material during laser processing.

[0011] Setting heat source and boundary conditions: Based on the characteristic that laser energy follows Gaussian distribution, the laser heat source expression is accurately set to accurately describe the distribution of laser energy on the material surface. When setting the model boundary conditions, the thermal convection and thermal radiation phenomena caused by heat conduction between the laser and the target are fully considered. The level set method is used to capture the dynamic changes of the solid-liquid-gas two-phase interface, and the velocity source term and level set source term are cleverly added to the continuity equation and the level set transport equation. At the same time, the Marangoni effect is fully considered and effectively coupled to achieve a more accurate simulation of the melt pool flow and surface morphology evolution.

[0012] Considering the plasma shielding effect: In view of the phenomenon that the gasified material forms plasma and absorbs and shields the subsequent laser energy during nanosecond laser processing, the particle number density in the plasma is calculated using the Saha-Eggert equation, and the inverse bremsstrahlung absorption effect is fully considered to obtain the absorption coefficient of the laser-induced plasma, and finally accurately determine the laser energy reaching the target surface.

[0013] It should be noted that there are certain assumptions and simplifications in the construction of this model. For example, when calculating the plasma shielding effect, the Saha-Eggert equation is used to calculate the particle number density in the plasma. This equation is based on certain thermodynamic equilibrium assumptions and may have certain deviations in the non-equilibrium plasma environment of actual laser processing. In addition, when considering processes such as heat conduction, convection and radiation, some complex microscopic mechanisms are simplified, which may have a certain impact on the accuracy of the model. However, under the current research conditions, these assumptions and simplifications can effectively simulate the laser ablation process within an acceptable error range.

[0014] Step 2: Simulate surface morphology evolution and analyze the influence of laser parameters

[0015] Using the established model, different combinations of laser parameters (such as wavelength, pulse width, laser power, repetition frequency, spot radius, scanning speed, etc.) are input to simulate the entire process of laser ablation of titanium alloy. During the simulation process, the evolution of the surface morphology of the target area is closely observed, and the influence of different laser parameters on the groove morphology (such as key indicators such as depth, width, and height of the recast layer) is deeply analyzed. By systematically changing the laser parameters, the intrinsic relationship between them and the groove morphology is comprehensively studied, providing rich data support for the subsequent optimization of laser processing parameters.

[0016] Table 1 Laser processing parameters

[0017]

[0018] Step 3: Model Validation

[0019] Carry out targeted experiments to obtain the microstructure and size parameters of titanium alloy pits under different laser parameters (such as accurate measurement of pit depth, width, recast layer height, etc.). Compare the simulation results with the experimental data in detail to verify the accuracy of the model. Once a deviation between the simulation results and the experimental data is found, analyze the cause of the deviation in depth, which may involve the rationality of the model assumptions, the accuracy of the parameter settings, etc. According to the analysis results, modify the model in a targeted manner, such as adjusting the model parameters, improving the model algorithm, etc., to continuously improve the prediction accuracy of the model.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) Improved simulation accuracy: The laser ablation model constructed by the present invention fully considers the plasma shielding effect and can more accurately simulate the transmission and absorption process of laser energy in plasma compared with traditional models. By comparing and verifying with experimental results, the model simulation results show good consistency with the actual processing conditions, providing strong support for the precise control of the laser processing process.

[0022] (2) Optimizing laser processing parameters: With the help of the simulation method of the present invention, the influence of different laser parameters on the groove morphology can be quickly and comprehensively analyzed. Before actual laser processing, the simulation results can be used to optimize the laser processing parameters according to specific processing requirements, effectively reducing the number of experimental trial and error, significantly improving processing efficiency, and reducing production costs.

[0023] (3) Expanding the scope of application: This numerical simulation method is not only applicable to the laser processing simulation of TC4 titanium alloy, but also has wide versatility and can be extended to the laser processing of other metal materials. By flexibly adjusting the material parameters in the model, it can provide reliable theoretical guidance for the laser processing of different materials, and effectively promote the application and innovative development of laser processing technology in more fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is an execution flow chart of a numerical simulation method for laser ablation of titanium alloy based on plasma shielding effect provided by the present invention;

[0025] Figure 2 It is a schematic diagram of a laser ablation multi-physics field coupling model of a numerical simulation method for laser ablation of titanium alloy based on plasma shielding effect provided by the present invention;

[0026] Figure 3 It is a two-dimensional model ablation result of a numerical simulation method for laser ablation of titanium alloy based on plasma shielding effect provided by the present invention;

[0027] Figure 4 It is a three-dimensional model ablation result of a numerical simulation method for laser ablation of titanium alloy based on plasma shielding effect provided by the present invention;

[0028] Figure 5 It is a laser ablation groove morphology profile diagram of a numerical simulation method for laser ablation of titanium alloy based on plasma shielding effect provided by the present invention;

[0029] Figure 6 The present invention provides a comparison between the experimental dimensions and simulation results of a numerical simulation method for laser ablation of titanium alloy based on the plasma shielding effect. DETAILED DESCRIPTION

[0030] In order to more fully understand the content of the present invention, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific examples. The examples listed are only used to illustrate the core idea of ​​the present invention and do not constitute any limitation to its scope.

[0031] The present invention is further described in detail below with reference to the accompanying drawings and embodiments:

[0032] Step 1. Without affecting the accuracy of the ablation results, make the following reasonable assumptions: the ablated target is uniform and isotropic in microstructure and physical properties; the temperature gradient in the direction perpendicular to the target is much greater than that in the direction parallel to the target, so it can be described by a one-dimensional heat conduction equation; the thermophysical parameters of the target remain constant when the phase state remains unchanged; the reflectivity of the target surface to the laser is a fixed constant; the laser pulse has a Gaussian distribution in time; the generated plasma plume is regarded as an inviscid compressible fluid that satisfies the ideal gas law; and the plasma is in local thermal equilibrium.

[0033] Step 2, set the equations followed by the model and solve them: Set the three major conservation equations of fluid mechanics followed by the model, namely the mass conservation equation, momentum conservation equation and energy conservation equation. These equations are solved in combination with the thermophysical parameters of TC4 titanium alloy. The generalized source term in the momentum conservation equation includes factors such as surface tension, recoil pressure, thermal buoyancy and mushy zone resistance, so as to fully consider the various forces acting on the material during laser processing.

[0034] The mass conservation equation:

[0035]

[0036] Where ρ represents the density of the material and u represents the velocity vector of the fluid

[0037] Momentum conservation equation:

[0038]

[0039] Where P 1 It's pressure, I m is the unit matrix, μ is the dynamic viscosity, g is the gravitational acceleration; F 0 is the generalized source term of the momentum equation, including the surface tension f s , recoil pressure P r , thermal buoyancy f v and the mushy zone resistance f D .

[0040] Energy conservation equation:

[0041]

[0042] Among them C p is the specific heat capacity of the solid-liquid mixture, k is the thermal conductivity, and S is the temperature source term.

[0043] Step 3: Set the laser heat source and boundary conditions: The laser energy follows a Gaussian distribution. According to this distribution, the laser heat source expression is set to accurately describe the distribution of laser energy on the material surface. The physical field interaction process between the laser and the target material is referenced. Figure 2 shown.

[0044] The Gaussian laser heat source is expressed as:

[0045]

[0046] Where τ is the laser pulse width, f is the frequency, R 0 is the reflection coefficient of the target surface, P is the average output power of the laser, t 0 is the time corresponding to the maximum pulse energy, r is the laser spot radius, and g(t) is the periodic working section function.

[0047] The thermal convection and thermal radiation caused by heat conduction between the laser and the target are considered, and the boundary conditions of the model are set. The level set method is used to capture the changes in the solid-liquid-gas two-phase interface, and velocity source terms and level set source terms are added to the continuity equation and level set transport equation. The Marangoni effect is considered and coupled to more accurately simulate the molten pool flow and surface morphology evolution.

[0048] The level set equation is expressed as:

[0049]

[0050] in, is the gas-liquid interface level set function, according to Different calculation regions are divided by the distance from 0.5: Defining the solid-liquid phase region Gas phase area u is the interface velocity vector, is the liquid mass flow rate, ρ v and ρ l represent the density of the gaseous and liquid states of the material, respectively. Indicates about The delta function, γ is the initialization parameter of the convection transport equation, ε Is is the interface thickness.

[0051] Step 4, consider the plasma shielding effect: During nanosecond laser processing, the vaporized material will form plasma, which has an absorption and shielding effect on the subsequent laser energy. The particle number density in the plasma is calculated by the Saha-Eggert equation, and the absorption coefficient of the laser-induced plasma is obtained by considering the inverse bremsstrahlung absorption, thereby determining the laser energy that finally reaches the target surface.

[0052] The absorption number of the laser-induced plasma:

[0053]

[0054] Among them, n 1 、n 2are the number densities of first-order ions and second-order ions, n e is the electron number density, e is the electron charge, n 1 +4n 2 is the charge of the ion, λ is the laser wavelength, and c is the speed of light.

[0055] Due to the influence of plasma shielding, the laser energy that finally reaches the target surface can be expressed as:

[0056]

[0057] Step 5, set model parameters and calculate: set laser processing parameters, including laser wavelength, pulse width, average power, repetition frequency, spot diameter, etc. These parameters are optimized according to actual processing requirements and material properties; mesh the model, and use finer meshes in key areas (such as laser action area and molten pool boundary) to accurately capture the changes in physical quantities; set parameters such as initial temperature, pressure and liquid phase velocity. The physical parameters involved in the model are shown in Table 2. , clarify the boundary conditions of the target area and gas area to ensure that the model can accurately reflect the actual processing situation; set the time step, and use the PARDISO parameter solver to calculate the control equations and boundary fluxes to ensure the stability and accuracy of the calculation.

[0058] Table 2 TC4 physical parameters

[0059]

[0060] Step 6, study the influence of different parameters on surface morphology: systematically change the laser parameters (such as laser power, repetition frequency, scanning speed, etc.), and perform simulation calculations again. Make an in-depth comparison of the simulation results under different parameters, and comprehensively analyze the influence of laser parameters on groove morphology (such as depth, width, height of recast layer, etc.). For example, study in detail the specific changes in groove depth and width when laser power increases, as well as the comprehensive influence mechanism of repetition frequency and scanning speed on groove morphology.

[0061] Step 7, simulation calculation and result processing: perform simulation calculation based on the established model and post-process the simulation results. Use a two-dimensional geometric model to simulate the evolution of the surface morphology of the pits of TC4 titanium alloy after laser ablation (refer to Figure 3 As shown in Figure 2), a three-dimensional model was constructed to study the effect of different laser parameters on the size of the processed groove morphology (reference Figure 4 shown).

[0062] Step 8, experimental verification of simulation results: In order to verify the accuracy of the simulation results, a groove laser processing experiment is subsequently performed to verify the results. Figure 5For the actual processing of the groove morphology map, the depth, width and recast layer height of the groove are obtained by precise measurement. According to the analysis results, the model is modified in a targeted manner. For example, the meshing accuracy is adjusted, the coefficients in the control equation are modified, and the plasma-related calculation method is improved to continuously improve the prediction accuracy of the model. After the laser engraving machine is processed, the sample is randomly measured for 5 times to obtain the average value. It is found that under the same experimental parameters, the experimental groove depth h1 and groove width d are consistent with the simulation size ((denoted by H' 1 , D' are the pit depth and width without considering the plasma shielding model)) The relative errors are less than 5%, indicating that the model has good accuracy (reference Figure 6 shown).

[0063] 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 the same. Although the present invention has been described in detail with reference to the above embodiments, a person skilled in the art can still modify or make equivalent substitutions to the specific implementation schemes of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are within the scope of protection of the claims of the present invention to be approved.

Claims

1. A numerical simulation method for laser ablation of titanium alloy based on plasma shielding effect, characterized in that: The following steps are involved: Step 1, establish a laser ablation model: Use the fluid flow module and heat transfer module of COMSOL Multiphysics software to construct two-dimensional and three-dimensional laser ablation models. Consider the plasma shielding effect to modify the laser energy transfer equation, and introduce the level set method to track the evolution of the solid-liquid-gas interface. Combine the mass, momentum and energy conservation equations to simulate the dynamic behavior of the molten pool and the surface morphology formation process. The mass conservation equation, momentum conservation equation and energy conservation equation are used to accurately describe the physical changes of materials during laser processing, provide a theoretical basis for simulation, and ensure that the model can accurately reflect the material, momentum and energy transfer in actual processing. Step 2: Based on the established model, input different combinations of laser parameters (such as wavelength, pulse width, laser power, repetition frequency, spot radius, scanning speed, etc.) to simulate the entire process of laser ablation of titanium alloy. During the simulation process, the evolution of the surface morphology of the target area is closely observed, and the influence of different laser parameters on the groove morphology (such as key indicators such as depth, width, and recast layer height) is deeply analyzed. By systematically adjusting the laser parameters, the intrinsic relationship between them and the groove morphology is comprehensively explored, providing detailed data support for subsequent laser processing parameter optimization. Step 3: Carry out targeted experiments to obtain the microstructure and dimensional parameters of titanium alloy pits and grooves under different laser parameters (such as accurate measurement of pit depth, width, recast layer height, etc.). The simulation results are carefully compared with the experimental data to verify the accuracy of the model. If a deviation is found between the simulation results and the experimental data, the cause of the deviation needs to be analyzed in depth, which may involve the rationality of the model assumptions, the accuracy of the parameter settings, etc. According to the analysis results, the model is modified in a targeted manner, such as adjusting the model parameters, improving the model algorithm, etc., to continuously improve the prediction accuracy of the model.

2. The numerical simulation method for laser ablation of titanium alloy based on plasma shielding effect according to claim 1 is characterized in that: In the step of establishing the laser ablation model: The mass conservation equation: Where ρ represents the density of the material and u represents the velocity vector of the fluid Momentum conservation equation: Where P1 is the pressure, I m is the identity matrix, μ is the dynamic viscosity, and g is the gravitational acceleration; F0 is the generalized source term of the momentum equation, including the surface tension f s , recoil pressure P r , thermal buoyancy f v and the mushy zone resistance f D . Energy conservation equation: Among them C p is the specific heat capacity of the solid-liquid mixture, k is the thermal conductivity, and S is the temperature source term. Set the laser heat source and boundary conditions: The laser energy follows a Gaussian distribution. According to this distribution, the laser heat source expression is set to accurately describe the distribution of laser energy on the material surface. The laser heat source expression is: Where τ is the laser pulse width, f is the frequency, R0 is the reflection coefficient of the target surface, P is the average output power of the laser, t0 is the time corresponding to the maximum pulse energy, r is the laser spot radius, and g(t) is the periodic working section function. This expression is used to describe the distribution of laser energy on the material surface. When setting the model boundary conditions, the heat convection and heat radiation caused by heat conduction between the laser and the target are considered. The level set method is used to capture the changes in the solid-liquid-gas two-phase interface, and the velocity source term and the level set source term are added to the continuity equation and the level set transport equation. The velocity source term is used to accurately simulate the fluid flow, and the level set source term is used to accurately track the interface evolution. By considering the Marangoni effect and coupling, the melt pool flow and surface morphology evolution can be more accurately simulated.

3. The numerical simulation method for laser ablation of titanium alloy based on plasma shielding effect according to claim 1 is characterized in that: In the level set method, the solid-liquid-gas interface is expressed by an implicit function Definition, gas phase region Solid-liquid phase region The interface transport equation satisfies: Where u is the interface velocity vector, is the liquid mass flow rate, ρ v and ρ l represent the density of the gaseous and liquid states of the material, respectively. Indicates about The delta function, γ is the initialization parameter of the convection transport equation, ε Is is the interface thickness.

4. The numerical simulation method for laser ablation of titanium alloy based on plasma shielding effect according to claim 1, characterized in that: In the step of establishing the laser ablation model, the particle number density in the plasma is calculated by the Saha-Eggert equation, the absorption coefficient of the laser-induced plasma is obtained by considering the inverse bremsstrahlung absorption, and the laser energy that finally reaches the target surface is determined; wherein the absorption number calculation formula of the laser-induced plasma is: Among them, n1 and n2 are the number densities of first-order and second-order ions, respectively, and n e is the electron number density, e is the electron charge, n1+4n2 is the charge of the ion, λ is the laser wavelength, and c is the speed of light. Due to the influence of plasma shielding, the laser energy that finally reaches the target surface can be expressed as:

5. The numerical simulation method for laser ablation of titanium alloy based on plasma shielding effect according to claim 1, characterized in that: In the step of simulating the evolution of surface morphology and analyzing the influence of laser parameters, the laser parameters include laser wavelength, pulse width, laser power, repetition frequency, spot radius, and scanning speed.

6. The application of the numerical simulation method for laser ablation of titanium alloy based on plasma shielding effect in optimizing laser processing parameters according to claim 1 is characterized in that: The simulation method is used to predict the morphology of the titanium alloy surface after ablation under different laser parameters, and the laser processing parameters are optimized according to the prediction results to improve the accuracy and efficiency of laser processing.

7. An application of the numerical simulation method for laser ablation of titanium alloy based on plasma shielding effect as claimed in any one of claims 1 to 6 in laser processing simulation of other metal materials, characterized in that: By adjusting the material parameters in the model, the simulation method is applied to the laser processing simulation of other metal materials, providing theoretical guidance for the laser processing of other metal materials.

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