Method for establishing laser etching metal model considering short pulse laser shock peening

Abstract

The application relates to a laser etching metal model establishment method considering short pulse laser shock peening, which comprises the following steps: establishing a physical field of a laser etching part by coupling thermal ablation and molten pool dynamics; introducing a shock wave pressure model and a material constitutive model into the physical field of the laser etching part to establish a multi-physical field transient model; performing multi-objective optimization on the multi-physical field transient model, and replacing model parameters in an original model with optimized model parameters; and realizing synchronous and high-precision simulation of laser shock peening effect in a short pulse laser etching metal surface micro groove process by establishing a multi-physical field transient model coupling ablation and shock wave effects; the method overcomes the limitation that traditional simulation separates "shape control processing" and "performance strengthening" from each other; not only deepens the understanding of the internal strengthening mechanism in the laser etching process, but also provides an efficient digital design and prediction tool for realizing integrated process optimization of micro groove high-quality shape control and base fatigue performance improvement.

Description

Technical Field

[0001] This invention relates to the field of laser processing technology, and more specifically to a method for establishing a laser-etched metal model considering short-pulse laser shock enhancement. Background Technology

[0002] Currently, known simulation methods for short-pulse laser processing, such as nanosecond pulse laser processing, are mainly divided into two categories: one is the laser etching finite element model, which focuses on predicting the microgroove morphology. This type of model pays attention to the thermal ablation and removal process of the material, but generally ignores the laser shock wave effect that accompanies the etching process; the other is the laser shock strengthening simulation, which focuses on improving the fatigue performance of metals. This type of model focuses on analyzing the residual compressive stress introduced by the shock wave, but its research object is an independent post-processing process, separated from the etching process. However, the above-mentioned existing technologies artificially separate laser etching from the shock strengthening effect, making it impossible for existing simulation methods to accurately predict and reveal the strengthening effect of the laser shock wave on the substrate material while laser etching microgrooves. Therefore, it is difficult to guide the integrated control of high-quality microgroove shape control and substrate fatigue performance improvement. Summary of the Invention

[0003] The purpose of this invention is to provide a method for establishing a laser-etched metal model that takes into account short-pulse laser shock enhancement, thereby solving the problems in the existing short-pulse laser processing simulation methods, which separate the control of etching morphology from the shock enhancement effect and fail to reflect the synergistic coupling mechanism of "processing" and "enhancing" in the interaction between laser and material.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a method for establishing a laser-etched metal model considering short-pulse laser shock enhancement, comprising:

[0005] The physical field of the laser etching section is established by coupling thermal ablation and molten pool dynamics;

[0006] A shock wave pressure model and a material constitutive model are introduced into the physical field of the laser etching section to establish a multiphysics transient model; and

[0007] The multiphysics transient model is optimized using multiple objectives, and the optimized model parameters replace the model parameters in the original model.

[0008] Preferably, a geometric model is constructed based on the nanosecond pulsed laser processing capability and the overall size of the etched microgroove array. Based on the principles of energy conservation, mass conservation, and momentum conservation, heat transfer, flow, and phase transition processes are coupled, and the heat transfer and stress conditions within the molten pool are considered to establish governing equations. These governing equations are then applied to COMSOL to construct the physical field of the laser-etched portion. The governing equations include:

[0009] mass conservation equation:

[0010] ;

[0011] in, Represents the fluid velocity vector;

[0012] Energy conservation equation:

[0013] ;

[0014] Where T represents the target temperature, t represents time, k represents thermal conductivity, and ρ represents the density of the molten metal. Indicates the direction of heat flow, and S represents the temperature source term. Indicates the equivalent specific heat capacity;

[0015] Momentum conservation equation:

[0016] ;

[0017] Where μ represents dynamic viscosity, Let p represent the identity matrix and p represent the molten pool pressure. This represents the generalized source term of force.

[0018] Preferably, the laser heat flux Q for establishing the etched microgroove array is:

[0019] ;

[0020] ;

[0021] In the formula, v is the scanning speed. The length of the microgroove The distance between the centerlines of adjacent microgrooves. The source is a transient Gaussian laser heat source, where x and y are spatial coordinates. For pulse period, This represents the pulse width.

[0022] Preferably, the transient Gaussian laser heat source for:

[0023] ;

[0024] In the formula, Where P is the absorptivity of the material and P is the laser power. The laser pulse repetition frequency, The radius of the light spot is... This represents the displacement along the length of the microgroove. This represents the displacement along the width of the microgroove.

[0025] Preferably, a shock wave pressure model is introduced based on the physical field of the laser etching part, and a material constitutive model is considered. The shock wave pressure model and the material constitutive model are added to the COMCOL solid mechanics physical field to establish a multi-physics transient model.

[0026] Preferably, within each pulse cycle, the shock wave pressure of the shock wave... for:

[0027] ;

[0028] In the formula, The peak value of the shock wave is obtained by uncoated laser shock enhancement.

[0029] Preferably, the modified Johnson-Cook model is used to characterize the high strain rate dynamic plastic deformation of the metal target under laser shock wave, and the constitutive equation is constructed as follows:

[0030] ;

[0031] In the formula, The yield stress of the material, The initial yield stress, Where n is the strength coefficient and n is the hardening exponent. Where C is the equivalent plastic strain and C is the strain rate hardening coefficient, For equivalent plastic strain rate, For reference strain rate, For ambient temperature, is the melting temperature, and m is the temperature index.

[0032] Preferably, the multiphysics transient model uses a moving mesh method to describe and track the motion of the molten pool interface; and an ultrafine mesh is used in the laser etching region, with the ultrafine mesh unit size being 0.005-0.5μm; while a coarse mesh is used in the region far from the polishing region, with the coarse mesh unit size being 3-8μm.

[0033] Preferably, multi-objective optimization of the multiphysics transient model includes:

[0034] Determine the parameters of the model to be corrected and the laser etching parameters;

[0035] The model parameters to be corrected and the etching parameters are used as experimental design factors to conduct response surface simulation experiments and obtain the response surface model of the simulated groove depth and residual compressive stress.

[0036] Multi-objective optimization was carried out with the goal of minimizing the relative error between the calculated and experimental values ​​of the response surface model for trench depth and residual compressive stress, in order to obtain the optimal model parameters;

[0037] Replace the model parameters in the original model with the optimal model parameters.

[0038] Preferably, after designing the response surface simulation test, the depth of each simulated groove and the residual compressive stress are calculated. Response surface analysis is performed with the simulated groove depth and the residual compressive stress as the targets. Factors with a significance level P value greater than 0.05 are removed to obtain the response surface models of the simulated groove depth and the residual compressive stress.

[0039] Beneficial Effects: This invention establishes a multi-physics transient model coupling ablation and shock wave effects, achieving synchronous and high-precision simulation of the laser shock strengthening effect during short-pulse laser etching of microgrooves on metal surfaces. It overcomes the limitations of traditional simulations that separate "shape control" from "performance enhancement," accurately revealing the synergistic control mechanism of laser parameters on microgroove morphology and substrate residual stress field. This not only deepens the understanding of the intrinsic strengthening mechanism during laser etching but also provides an efficient digital design and prediction tool for integrated process optimization to achieve high-quality microgroove shape control and substrate fatigue performance improvement. This has significant engineering value for overcoming the technical bottleneck of integrated drag reduction and fatigue resistance manufacturing of key components in high-end equipment, significantly shortening process development cycles, and reducing experimental costs. Attached Figure Description

[0040] Figure 1 The flowchart of the method for establishing a laser-etched metal model with short-pulse laser shock enhancement is shown in this invention.

[0041] Figure 2 This is a flowchart of the multiphysics coupled finite element model correction method based on the response surface methodology of this invention. Detailed Implementation

[0042] To make the objectives and advantages of this invention clearer, the invention will be specifically described below with reference to embodiments. It should be understood that the following text is merely used to describe one or more specific embodiments of the invention and does not strictly limit the scope of protection specifically claimed by the invention.

[0043] Example: Reference Figure 1 As shown, the method for establishing a laser-etched metal model considering short-pulse laser shock enhancement includes:

[0044] S1: Establish the physical field of the laser etching section by coupling thermal ablation and molten pool dynamics;

[0045] S11. Construct a cuboid geometric model in COMSOL. Based on the nanosecond pulse laser processing capability and the overall size of the etched microgroove array, determine the length, width, and height of the geometric model to ensure that the etching process of the microgroove array can be simulated.

[0046] In one specific embodiment, TC4 titanium alloy is selected, and its thermal conductivity, density, specific heat capacity, melting point, vaporization temperature, Young's modulus, Poisson's ratio, Johnson-Cook model parameters and other parameters are set to complete the creation of the geometric model of TC4 titanium alloy target material.

[0047] S12. Based on the principles of energy conservation, mass conservation, and momentum conservation, and coupling heat transfer, flow, and phase change processes, considering the heat transfer and stress conditions within the molten pool, a governing equation is established. This governing equation is then applied to COMSOL to construct the physical field of the laser etching section. The governing equation includes the mass conservation equation, energy conservation equation, and momentum conservation equation.

[0048] For the mass conservation equation: assuming the liquid phase in the molten pool is an incompressible fluid, the mass conservation equation describing the melt flow during nanosecond pulsed laser etching is:

[0049] ;

[0050] In the formula, Represents the fluid velocity vector;

[0051] For the energy conservation equation, this embodiment takes into account the effects of gas-liquid convection, solid-liquid-gas heat transfer, evaporative heat flux, and radiative heat loss. Therefore, the energy conservation equation describing the fluid temperature change during nanosecond pulsed laser etching is:

[0052] ;

[0053] In the formula, T represents the target temperature, t represents time, and k represents thermal conductivity. This indicates the density of the molten metal. Indicates the direction of heat flow, and S represents the temperature source term. Indicates the equivalent specific heat capacity;

[0054] In this embodiment, the effect of latent heat of fusion is considered. Represented as:

[0055] ;

[0056] In the formula, Indicates latent heat of fusion. Indicates the liquid volume fraction. Indicates specific heat capacity;

[0057] Liquid phase volume fraction is :

[0058] ;

[0059] In the formula, Indicates the solidus temperature. This indicates the liquidus temperature.

[0060] For the momentum conservation equation, this embodiment considers the drag force, surface tension of the molten liquid phase, buoyancy, and vapor back pressure to describe the momentum conservation equation for melt flow during nanosecond pulsed laser etching:

[0061] ;

[0062] In the formula, Indicates dynamic viscosity. Let p represent the identity matrix and p represent the molten pool pressure. This represents the generalized source term of force.

[0063] Laser heat flux is applied to the upper surface of the model, while air convection, surface radiation heat transfer to the atmosphere, and evaporation loss occur simultaneously. The heat transfer equation is as follows:

[0064] ;

[0065] In the formula, Q represents the absorptivity of the material, and Q represents the laser heat flux. Represents evaporative heat flux. The emissivity of the metal target is represented by h, and the convective heat transfer coefficient is represented by h. Indicates ambient temperature. This represents the Stefan-Boltzmann constant.

[0066] For a microslot array, the laser is in the off state during the scanning section between the microslots, therefore the laser heat flux Q:

[0067] ;

[0068] In the formula, v is the scanning speed. The length of the microgroove This represents the centerline distance between adjacent microgrooves.

[0069] The energy of a pulsed laser spot exhibits a Gaussian distribution and is effective only during the pulse duration; for the remainder of the pulse period, the light intensity is zero, and its heat flux is zero. :

[0070] ;

[0071] In the formula, For pulse period, The pulse width;

[0072] In this embodiment, a transient Gaussian laser heat source considering spatial and temporal distribution is presented. :

[0073] ;

[0074] In the formula, P is the laser power. The laser pulse repetition frequency, The radius of the light spot is... This represents the displacement along the length of the microgroove. This represents the displacement along the width of the microgroove.

[0075] Displacement along the length of the microgroove : ;

[0076] Displacement in the width direction of the microgroove : ;

[0077] In this embodiment, for the four vertical surfaces of the constructed geometric model, both air convection and surface radiation heat transfer to the atmosphere occur simultaneously. The heat transfer equation is as follows:

[0078] ;

[0079] The bottom surface of the geometric model serves as an adiabatic surface, and its heat transfer equation is:

[0080] ;

[0081] Evaporative heat flux :

[0082] ;

[0083] ;

[0084] In the formula, Indicates the material removal rate. Indicates latent heat of vaporization. denoted by , m represents the reverse diffusion coefficient, R represents the molar mass, and R represents the gas constant.

[0085] Saturated vapor pressure :

[0086] ;

[0087] In the formula, Indicates standard atmospheric pressure. Indicates the vaporization temperature.

[0088] Among them, the metal vapor recoil pressure generated by the nanosecond pulsed laser acting on the upper surface of the geometric model :

[0089] ;

[0090] For nanosecond pulsed laser etching of a molten pool, considering liquid gravity and thermal buoyancy, the volume force is obtained. :

[0091] ;

[0092] In the formula, g represents the acceleration due to gravity. Indicates the coefficient of thermal expansion. Indicates the melting temperature.

[0093] The geometric model is defined with the upper surface as a free-deformable surface and the other surfaces as non-slip walls. Considering the Marangoni effect, the upper surface material melts after being heated by a nanosecond pulsed laser, and the stress at the top of the molten pool is mainly surface tension. :

[0094] ;

[0095] The normal component of surface tension is capillary force, which is caused by the change in spatial curvature of the free surface, resulting in a normal flow velocity on the surface of the molten pool. Represented as:

[0096] ;

[0097] In the formula, κ represents the surface curvature, and γ represents the surface tension coefficient. This represents the normal vector of the freeform surface.

[0098] The tangential component of surface tension, thermocapillary force, is generated by the temperature gradient and causes the fluid interface to slide along the tangential direction.

[0099] ;

[0100] In the formula, This represents the normal vector of the freeform surface.

[0101] During the nanosecond pulsed laser treatment, the titanium alloy gradually transforms from a solid phase to a liquid phase, resulting in a mushy region where the two phases coexist. This region acts as a barrier to the liquid phase, similar to the resistance of a porous medium, hindering liquid flow and causing momentum dissipation, i.e., Darcy drag. :

[0102] ;

[0103] In the formula, C c denoted by , b represents a constant for the pasty region, and in this embodiment, b is taken as 0.001.

[0104] S2. Introduce a shock wave pressure model and a material constitutive model into the physical field of the laser etching section to establish a multi-physics transient model;

[0105] Nanosecond pulsed laser etching of TC4 titanium alloy was performed under a water film. The material surface was uncoated, and the constraint layer was pure water. The peak pressure of the uncoated laser-induced shock wave acting on the surface of the geometric model was then determined. :

[0106] ;

[0107] In the formula, The energy conversion efficiency coefficient. The reduced acoustic impedance of the material and the constraint layer. This represents the laser power density.

[0108] Compressed acoustic impedance :

[0109] ;

[0110] In the formula, The acoustic impedance of the material, The acoustic impedance of pure water.

[0111] Laser power density :

[0112] ;

[0113] The shock wave pressure of the plasma shock wave during each pulse cycle :

[0114] ;

[0115] For the entire geometric model, the modified Johnson-Cook model is used to reflect the high strain rate dynamic plastic deformation of the TC4 titanium alloy target under the action of nanosecond pulsed laser shock wave. Its constitutive equation is:

[0116] ;

[0117] In the formula, The yield stress of the material, The initial yield stress, Where n is the strength coefficient and n is the hardening exponent. Where C is the equivalent plastic strain and C is the strain rate hardening coefficient, For equivalent plastic strain rate, For reference strain rate, For ambient temperature, is the melting temperature, and m is the temperature index.

[0118] TC4 titanium alloy melts and vaporizes under nanosecond pulsed laser irradiation, and the morphology of local regions in the model changes due to fluid flow. The moving mesh method, combining the Eulerian and Lagrangian methods, can effectively simulate the internal flow of the melt and handle large deformation flows. Therefore, the moving mesh method is chosen to describe and track the motion of the molten pool interface, and its governing equations are:

[0119] ;

[0120] In the formula, represents the mesh movement rate, and u represents the molten material flow rate.

[0121] In this embodiment, considering both computational accuracy and efficiency, an adaptive mesh generation technique is used to optimize the mesh in order to improve the computational accuracy and efficiency of nanosecond pulse laser etching of TC4 titanium alloy.

[0122] In a preferred embodiment, an ultrafine mesh with a unit size of 0.005-0.5 μm is used in the laser etching area, and a coarse mesh with a unit size of 3-8 μm is used in the area away from the polishing area.

[0123] S3. Perform multi-objective optimization on the multiphysics transient model, and replace the original model parameters with the optimized model parameters. (Refer to...) Figure 2 As shown;

[0124] S31. Based on the multiphysics transient model finally established in S2, investigate the influence of model parameters such as material absorptivity, emissivity, thermal convection coefficient, specific heat, and thermal conductivity on the simulated groove depth and residual compressive stress. Determine the model parameters to be corrected based on the significance of the influence. Also, determine the laser etching parameters, such as laser power, pulse frequency, and scanning speed, based on the adjustable parameters of the nanosecond pulsed laser processing equipment used in the experiment.

[0125] S32. Using the model parameters to be corrected and the etching parameters as experimental design factors, conduct response surface simulation experiments. Calculate the simulated groove depth and residual compressive stress according to the experimental scheme. Perform response surface analysis with simulated groove depth and residual compressive stress as targets. After removing factors with a significance level P value greater than 0.05, obtain the response surface models for simulated groove depth and residual compressive stress respectively.

[0126] S33. Based on the response surface model of simulated groove depth and residual compressive stress, the groove depth and residual compressive stress corresponding to each etching parameter in the experimental scheme are solved respectively, and compared with the actual groove depth and residual compressive stress measured by the corresponding nanosecond pulse laser etching experiment. The relative error is solved, and the minimum relative error is used as the optimization target to carry out multi-objective optimization. After parameter optimization, the optimal model parameters are obtained. After replacing the model parameters in the original finite element model, the model is corrected, and the high-precision three-dimensional transient laser etching multiphysics transient model of TC4 titanium alloy considering the nanosecond pulse laser shock strengthening effect is established.

[0127] The embodiments of the present invention have been described in detail above with reference to the examples. However, the present invention is not limited to the above embodiments. For those skilled in the art, after learning the contents described in the present invention, several equivalent changes and substitutions can be made without departing from the principle of the present invention. These equivalent changes and substitutions should also be considered to fall within the protection scope of the present invention.

Claims

1. A method for establishing a laser-etched metal model considering short-pulse laser shock enhancement, characterized in that: include: The physical field of the laser etching section is established by coupling thermal ablation and molten pool dynamics; A shock wave pressure model and a material constitutive model are introduced into the physical field of the laser etching section to establish a multiphysics transient model; and The multiphysics transient model is optimized for multiple objectives, and the optimized model parameters replace the model parameters in the original model. Within each pulse cycle, the shock wave pressure of the shock wave for: ； In the formula, The peak value of the shock wave pressure for uncoated laser-strengthened shock waves; The modified Johnson-Cook model is used to characterize the high strain rate dynamic plastic deformation of the metal target under laser shock wave irradiation, and the constitutive equation is constructed as follows: ； In the formula, The yield stress of the material, The initial yield stress, Where n is the strength coefficient and n is the hardening exponent. Where C is the equivalent plastic strain and C is the strain rate hardening coefficient, For equivalent plastic strain rate, For reference strain rate, For ambient temperature, is the melting temperature, and m is the temperature index.

2. The method for establishing a laser-etched metal model considering short-pulse laser shock enhancement according to claim 1, characterized in that: A geometric model is constructed based on the nanosecond pulsed laser processing capability and the overall size of the etched microgroove array. Based on the principles of energy conservation, mass conservation, and momentum conservation, heat transfer, flow, and phase transition processes are coupled, and considering the heat transfer and stress conditions within the molten pool, governing equations are established. These governing equations are then applied to COMSOL to construct the physical field of the laser etching section. The governing equations include: mass conservation equation: ； in, Represents the fluid velocity vector; Energy conservation equation: ； Where T represents the target temperature, t represents time, k represents thermal conductivity, and ρ represents the density of the molten metal. Indicates the direction of heat flow, and S represents the temperature source term. Indicates the equivalent specific heat capacity; Momentum conservation equation: ； Where μ represents dynamic viscosity, Let p represent the identity matrix and p represent the molten pool pressure. This represents the generalized source term of force.

3. The method for establishing a laser-etched metal model considering short-pulse laser shock enhancement according to claim 2, characterized in that: The laser heat flux Q for establishing the etched microgroove array is: ； ； In the formula, v is the scanning speed. The length of the microgroove The distance between the centerlines of adjacent microgrooves. The source is a transient Gaussian laser heat source, where x and y are spatial coordinates. For pulse period, This represents the pulse width.

4. The method for establishing a laser-etched metal model considering short-pulse laser shock enhancement according to claim 3, characterized in that: The transient Gaussian laser heat source for: ； In the formula, Where P is the absorptivity of the material and P is the laser power. The laser pulse repetition frequency, The radius of the light spot is... This represents the displacement along the length of the microgroove. This represents the displacement along the width of the microgroove.

5. The method for establishing a laser-etched metal model considering short-pulse laser shock enhancement according to claim 4, characterized in that: A shock wave pressure model is introduced based on the physical field of the laser etching part, and a material constitutive model is considered. The shock wave pressure model and the material constitutive model are added to the COMCOL solid mechanics physical field to establish a multi-physics transient model.

6. The method for establishing a laser-etched metal model considering short-pulse laser shock enhancement according to claim 1, characterized in that: The multiphysics transient model employs a moving mesh method to describe and track the motion of the molten pool interface; and uses an ultrafine mesh in the laser etching region, with the ultrafine mesh unit size being 0.005-0.5μm; and uses a coarse mesh in the region far from the polishing region, with the coarse mesh unit size being 3-8μm.

7. The method for establishing a laser-etched metal model considering short-pulse laser shock enhancement according to claim 1, characterized in that: Multi-objective optimization of the multiphysics transient model includes: Determine the parameters of the model to be corrected and the laser etching parameters; The model parameters to be corrected and the etching parameters are used as experimental design factors to conduct response surface simulation experiments and obtain the response surface model of the simulated groove depth and residual compressive stress. Multi-objective optimization was carried out with the goal of minimizing the relative error between the calculated and experimental values ​​of the response surface model for trench depth and residual compressive stress, in order to obtain the optimal model parameters; Replace the model parameters in the original model with the optimal model parameters.

8. The method for establishing a laser-etched metal model considering short-pulse laser shock enhancement according to claim 7, characterized in that: After designing the response surface simulation test, the depth of each simulated groove and the residual compressive stress were calculated. Response surface analysis was performed with the simulated groove depth and the residual compressive stress as the targets. Factors with a significance level P value greater than 0.05 were removed, and the response surface models of the simulated groove depth and the residual compressive stress were obtained respectively.

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