A milling precision simulation method for updating crystal orientation

Abstract

The present invention discloses a method for accurate milling simulation that updates crystal orientation; the simulation method comprises the following steps: 1. Performing crystal orientation detection on the machined surface of the workpiece before milling to obtain crystal orientation data before milling. 2. Establishing a model and assigning material parameters. 3. Cutting simulation to obtain the crystal orientation of the workpiece after cutting. The crystal orientation is updated during the plastic deformation stage and the damage stage of the cutting simulation. The present invention introduces crystal orientation data into thermodynamic simulation, which can more accurately reflect the microstructure and crystal orientation of the material, and achieve high-precision modeling of thin-walled parts milling, thereby improving the reliability of the simulation results, so that the cutting simulation can more effectively guide the milling process. In addition, in the calculation of crystal orientation distribution, the present invention updates the crystal orientation by calculating the deformation gradient matrix under consideration of deformation, and the computational complexity is low.

Description

Technical Field

[0001] The present invention belongs to the technical field of milling simulation, and in particular relates to a milling precision simulation method for updating crystal orientation. Background Art

[0002] Due to their complex structures and weak rigidity, thin-walled components in aircraft engines often face challenges such as deformation, vibration, and tool wear during milling. Furthermore, their long-term service life in high-speed, high-temperature environments places extremely high demands on their manufacturing performance and processing technology. These factors not only affect machining accuracy but can also lead to part scrap and reduced production efficiency. Therefore, simulation research on the milling of thin-walled aircraft engine components is particularly important. Simulation technology can effectively predict and optimize machining strategies, thereby improving machining quality and efficiency and reducing production costs.

[0003] At present, some scholars are also conducting simulation research in related fields. Patent No.: CN202311382443.7, through the method of smooth particle dynamics, the cutting fluid model constructed as a whole during modeling is divided into discrete micro-particles, thereby realizing the simulation of minimal lubrication processing. The obtained simulation results are closer to the actual processing conditions of minimal lubrication and have guiding significance for real-world processing. Patent No.: CN202211032156.9, a large strain extrusion cutting strip texture prediction method considering the influence of strain rate is proposed. This method establishes an extrusion cutting 2D finite element model through Abaqus software and its Vumat subroutine to obtain the velocity gradient, time increment and temperature change of the material during the extrusion cutting process.

[0004] Most simulation studies are based on homogeneous material models, ignoring the anisotropy exhibited by real materials in different directions. While this approach simplifies the simulation process to some extent, it makes it difficult to predict and analyze changes in the material's crystal orientation and its true behavior. Summary of the Invention

[0005] In response to the above problems, the present invention provides a milling precision simulation method for updating crystal orientation.

[0006] In a first aspect, the present invention provides a method for accurately simulating milling for updating crystal orientation, comprising the following steps:

[0007] Step 1: Perform crystal orientation detection on the machined surface of the workpiece before milling to obtain crystal orientation data before milling.

[0008] Step 2: Establish the model and assign material parameters.

[0009] Step 2-1. Extracting Miller index based on crystal orientation data before milling [ℎ,k,l] T ; h, k, and l are the reciprocals of the orientation components of the sampling point in the X, Y, and Z directions, respectively.

[0010] Step 2-2. Construct the tool model and workpiece model for thermal-mechanical coupled cutting simulation. Mesh the workpiece model so that each mesh node corresponds to a sampling point for crystal orientation detection.

[0011] Step 2-2. Import material parameters of tool model and workpiece model; among them, Miller index [ℎ,k,l] T The density parameter of the workpiece model is added as the initial crystal orientation.

[0012] Step 3: Cutting simulation to obtain the crystal orientation of the workpiece after cutting. During the plastic deformation and damage stages of the cutting simulation, the crystal orientation is updated. The process is as follows:

[0013] Construct the deformation gradient tensor F.

[0014] Perform polar decomposition on the deformation gradient tensor F to obtain the rotation matrix .

[0015]

[0016] in, is the rotation matrix, is a positive definite symmetric tensor.

[0017] Update the crystal orientation after deformation in the current analysis step as follows:

[0018]

[0019] in, Crystal orientation before deformation in the current analysis step.

[0020] Preferably, in step 3, the expression of the deformation gradient tensor F is as follows:

[0021]

[0022] in, 、 are the coordinates of the sampling points before and after deformation, respectively.

[0023] Preferably, after step three is executed, the subsurface deformation of the workpiece under different milling conditions is predicted using the simulated crystal orientation data after milling; and the milling conditions in the actual milling process are selected according to the subsurface deformation.

[0024] Preferably, in step one, the crystal orientation of the processed surface of the workpiece after milling is also detected to obtain the crystal orientation data after milling. After step three is executed, the crystal orientation of the last analysis step before the destruction of each sampling point is taken as the simulated crystal orientation data after milling. The orientation distribution function is calculated for the actual crystal orientation data after milling and the simulated crystal orientation data after milling, and the actual ODF diagram and the simulated ODF diagram are obtained respectively. By comparing the simulated ODF diagram with the actual ODF diagram, the accuracy of the crystal orientation simulation is judged; if the accuracy does not meet the preset requirements, the thermal coupling cutting simulation parameters are adjusted and the simulation is repeated.

[0025] Preferably, the Miller index [ℎ,k,l] T The conversion formula is as follows:

[0026] [ℎ,k,l] T = cos ϕ 1 cos ϕ 2 −sin ϕ 1 sin ϕ 2 cos(Φ) sin ϕ 1 cos ϕ 2 +cos ϕ 1 sin ϕ 2 cos(Φ) sin ϕ 2 sin(Φ)

[0027] in, are the first, second, and third Euler angles of the sampling points respectively.

[0028] Preferably, the process of crystal orientation detection is as follows: the workpiece is cut, roughly ground, finely ground, polished, ultrasonically cleaned, cleaned, and dried in sequence to obtain the piece to be observed, the piece to be observed is tilted in a scanning electron microscope, backscattered electrons are collected, and a detector is used to capture the diffraction pattern.

[0029] Preferably, the specific process of performing cutting simulation in step 3 is as follows:

[0030] Step 3-1. Update principal stresses and shear stress .

[0031] Step 3-2. Yield determination: If the material yields, proceed to step 3-3; otherwise, repeat step 3-1.

[0032] Step 3-3. Calculate the updated plastic stress and update the crystal orientation.

[0033] Step 3-4. Damage determination: If the material is damaged, proceed to step 3-5; otherwise, repeat steps 3-1 to 3-3.

[0034] Steps 3-5. Update the crystal orientation and update the material stress and strain according to the JC damage model until the material is destroyed.

[0035] As a preference, the JC constitutive model and damage model used in the cutting simulation are as follows:

[0036]

[0037] e f =[ D 1 + D 2 exp ( D 3 s ∗ )](1+ D 4 ln e ̇ ∗ )(1+ D 5 T ∗ )

[0038] in, is the material's uniaxial tensile thermo-visco-elastoplastic flow stress, For strain; is the strain rate; is the reference strain rate; is the reference temperature; is the melting temperature of the material; All are preset constants; is the equivalent fracture plastic strain; is the dimensionless plastic strain rate, which is expressed as ; is the dimensionless temperature, and its expression is ; All are preset constants; Ambient temperature for cutting simulation; is the stress triaxiality, and its expression is ; is the spherical stress, is the Mises equivalent stress.

[0039] In a second aspect, the present invention provides a computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the memory stores the computer program; and the processor executes the aforementioned milling precision simulation method for updating crystal orientation.

[0040] In a third aspect, the present invention provides a readable storage medium storing a computer program; when the computer program is executed by a processor, it is used to implement the aforementioned milling precision simulation method for updating crystal orientation.

[0041] The present invention has the beneficial effects:

[0042] 1. The present invention introduces crystal orientation data into thermodynamic simulation, which can more accurately reflect the microstructure and crystal orientation of the material, achieve high-precision modeling of thin-walled parts milling, thereby improving the reliability of simulation results and enabling cutting simulation to more effectively guide milling processing.

[0043] 2. In the calculation of crystal orientation distribution, the present invention updates the crystal orientation by calculating the deformation gradient matrix under deformation, with low computational complexity, providing a scientific basis for optimizing the processing technology and performance of materials.

[0044] 3. The present invention simultaneously considers temperature changes, material anisotropy and damage hardening effects during the simulation process. The multi-factor coupling analysis method can truly reflect the complex behavior of materials during the milling process and provide guidance for actual milling processing.

[0045] 4. The present invention can predict the recrystallization, dislocation, slip and other behaviors of materials under different temperatures and processing conditions, helping to design more reasonable processing technology, improve surface integrity and reduce damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is the overall flow chart of the present invention;

[0047] Figure 2 This is a flow chart of model building and material property parameter assignment in step 2 of the present invention;

[0048] Figure 3 This is a flow chart of the subroutine for simulating workpiece milling in step three of the present invention. DETAILED DESCRIPTION

[0049] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 making creative efforts are within the scope of protection of the present invention.

[0050] A milling precision simulation method for updating crystal orientation includes the following steps:

[0051] Step 1: Crystal orientation testing is performed on the workpiece surface before and after milling, obtaining both pre- and post-milling crystal orientation data. This data includes orientation data for each sampling point in the workpiece and is recorded as EBSD (.ang) data. The specific crystal orientation testing process is as follows: cutting, rough grinding, fine grinding, polishing, ultrasonic cleaning, washing, and drying to obtain the sample to be tested. The sample is tilted in a scanning electron microscope (SEM) to collect backscattered electrons. The diffraction pattern is captured using an EBSD detector with an acquisition step size of 1.2 and a SEM signal intensity of 1 to obtain crystal orientation and coordinate information. EBSD stands for Electron Backscatter Diffraction (EBSD).

[0052] In this embodiment, the workpiece is a GH4169 thin-walled part; a thin-walled part is defined as an annular part with a diameter to maximum thickness ratio greater than 20, or a disc-shaped part with a maximum thickness ratio greater than 6.

[0053] Step 2: Model establishment and material parameter assignment.

[0054] 2.1 EBSD data processing

[0055] First, the pre-milling EBSD data collected in step 1 was denoised to improve the signal-to-noise ratio. The data was then imported into the workstation using the METX tool in MATLAB software. The Euler angles and xy coordinate parameters of each sampling point were extracted, and the Euler angles were then converted to Miller indices using the following formula:

[0056] [ℎ,k,l] T = cos ϕ 1 cos ϕ 2 −sin ϕ 1 sin ϕ 2 cos(Φ) sin ϕ 1 cos ϕ 2 +cos ϕ 1 sin ϕ 2 cos(Φ) sin ϕ 2 sin(Φ)

[0057] in, are the first, second, and third Euler angles respectively; h is the reciprocal of the orientation component of the sampling point in the X direction; k is the reciprocal of the orientation component of the sampling point in the Y direction; and l is the reciprocal of the orientation component of the sampling point in the Z direction.

[0058] 2.2 Constructing tool and workpiece simulation models

[0059] Build a thermal-mechanical coupling cutting simulation model and define the material property interface. Divide the workpiece grid according to the step size and number of sampling points in step 2.1, so that each grid node corresponds to a sampling point, and set the grid type to C3D8. Then perform assembly positioning, create analysis steps and output variables, set the contact constraint between the tool and the workpiece to display dynamic contact, set the motion characteristics of the tool and apply load. After completing the modeling, export the INP file.

[0060] 2.3 Import of material parameters

[0061] First, create an element based on the number of sampling points in step 2.1 and assign cross-sectional properties. Write this to the end of the Element in the INP file. Then, add the density parameter based on the Miller index obtained in step 2.1, import it into the material interface, and write the material property parameters of the tool.

[0062] Step 3: Write and import the subroutine VUMAT to realize cutting simulation.

[0063] In this embodiment, the JC constitutive model and damage model are used to calculate the stress-strain relationship, and then the Miller index of the crystal is updated by the plastic strain tensor. The subroutine is written using a Fortran compiler and imported into the simulation through the VUMAT interface. The JC constitutive model and damage model are as follows:

[0064]

[0065] e f =[ D 1 + D 2 exp ( D 3 s ∗ )](1+ D 4 ln e ̇ ∗ )(1+ D 5 T ∗ )

[0066] in, is the material's uniaxial tensile thermo-visco-elastoplastic flow stress, For strain; is the strain rate; is the reference strain rate; is the reference temperature; is the melting temperature of the material; All are preset constants; is the equivalent fracture plastic strain; is the dimensionless plastic strain rate, which is expressed as ; is the dimensionless temperature, and its expression is ; All are preset constants; Ambient temperature for cutting simulation; is the stress triaxiality, and its expression is ; is the spherical stress, is the Mises equivalent stress.

[0067] like Figure 3 As shown in the figure, the subroutine is used to simulate the parameter changes during the workpiece milling process. The parameters include stress, strain, strain rate, temperature, crystal orientation and energy. The execution process of the subroutine is as follows:

[0068] 3.1 Initial analysis step calculation

[0069] In the initial analysis step, the material is considered to be elastically deformed and the strain increment method is used. According to Hooke's law, the calculation steps are as follows:

[0070] 1) Calculation of Lamé constant

[0071]

[0072] in, is the shear modulus; is the Lamé constant; is the Young's modulus of the material, is the Poisson's ratio of the material.

[0073] 2) Update the stress components. The calculation steps are as follows:

[0074] principal stresses The expression is:

[0075]

[0076] shear stress The expression is:

[0077]

[0078] in, is the strain increment in the principal direction; is the trace of the stress matrix; is the principal stress in the previous analysis step, In the first analysis step, it is the test stress; Updated principal stresses for the current analysis step; is the updated shear stress, i≠j; is the shear stress in the previous analysis step; is the strain increment in the tangential direction.

[0079] 3.2 Yield determination

[0080] 1) Mises stress calculation

[0081]

[0082] in, is the discriminant stress in the current analysis step; is the Mises equivalent stress (i.e., Mises stress); They are the three principal stresses of the material in the current analysis step.

[0083] like , then re-execute step 3.1 and enter the next iteration; if , the material is judged to have entered the yield stage and the process goes to step 3.3.

[0084] 3.3 Plastic update stress calculation:

[0085] After the material is determined to have entered the yield stage, the plastic stress is updated.

[0086] 1) Calculate the stress increment, plastic strain, and plastic strain rate of the mesh nodes in this analysis step.

[0087] 2) Calculate the stress after plastic hardening:

[0088] According to the JC constitutive equation

[0089]

[0090]

[0091]

[0092] in, is the strain rate influencing factor; is the temperature influencing factor; is the temperature calculated in the previous analysis step.

[0093] 3.4 Crystal Orientation Update

[0094] 1) Deformation gradient tensor solution

[0095] In crystal plasticity, the small deformation assumption is used, where the deformation is assumed to be small enough that nonlinear effects can be ignored. This means that both the displacement and strain of the material are assumed to be small, allowing for analysis using linear approximations. However, in impact dynamics, the nonlinear effects of strain and rotation often need to be considered. In this case, the change in crystal orientation depends not only on the magnitude of the strain but also on the plastic behavior of the material. The deformation gradient tensor F can be expressed as:

[0096]

[0097] In the same analysis step, the coordinates of the sampling points before deformation Expressed as , the coordinates after deformation Expressed as . are the three-dimensional coordinate values ​​of the sampling points before deformation; are the three-dimensional coordinate values ​​of the sampling points after deformation.

[0098] 2) Solving the rotation matrix

[0099] Then the deformation gradient tensor F is decomposed into two matrices: the rotation part and the stretching part; the rotation matrix is ​​obtained by polar decomposition. The expression is as follows:

[0100]

[0101] in, is the rotation matrix, is a positive definite symmetric tensor.

[0102] Calculates the crystal orientation after deformation in the current analysis step as follows:

[0103]

[0104] in, is the crystal orientation before deformation in the current analysis step.

[0105] Then the crystal orientation parameters after plastic deformation are derived in the form of intermediate variables.

[0106] 3.5 Damage determination:

[0107] Calculate cumulative plasticity as follows:

[0108]

[0109] in, is the damage initiation strain function, which is a constant at a specific temperature; is the magnitude of the plastic strain rate.

[0110] like , then re-execute steps 3.1 to 3.4 to perform the calculation of the next analysis step; if , the material is judged to be damaged and the process goes to step 3.6.

[0111] 3.6 Damage parameter update:

[0112] Update the material's stress, strain, and crystal orientation based on the JC damage model constructed in step 3. The crystal orientation update process is the same as in step 3.4. When the material begins to fail, the crystal orientation is updated based on the strain before failure.

[0113] Step 4: CP-FEM iterative calculation

[0114] After the code is written, submit the calculation. The crystal orientation at the last analysis step before each sampling point is destroyed is used as the crystal orientation data for the post-milling simulation. During monitoring, check whether the energy change meets the convergence criteria. If not, adjust the incremental step size and recalculate.

[0115] Step 5: MTEX ​​analysis

[0116] First, the intermediate crystal orientation variables calculated in step 3 were imported into the MATLAB workstation. Next, the Miller indices were converted to Euler angles. Using the MTEX ​​tool, the orientation distribution function (ODF) was calculated for the actual milling crystal orientation data obtained in step 1 and the simulated milling crystal orientation data obtained in step 4. This yielded simulated and actual ODF plots, which reveal the statistical characteristics of the grain orientation in the material. The accuracy of the crystal orientation simulation was determined by comparing the simulated and actual ODF plots. If the accuracy did not meet the preset requirements, the constitutive parameters in the JC constitutive model were adjusted and the optimization simulation was repeated.

[0117] Step 6: Use the simulated crystal orientation data after milling to predict the subsurface deformation of the workpiece under different milling conditions, and select the milling conditions that meet the requirements to perform actual milling on the workpiece.

[0118] In this example, the workpiece is a thin-walled GH4169 part. Because milling of thin-walled GH4169 parts can lead to significant deformation and surface damage, previous studies have shown that EBSD can monitor subsurface deformation caused by machining, and that grain size is significantly correlated with the material's fatigue strength. This present invention, through the prediction of crystal orientation, can predict machining-induced deformation and the material's mechanical properties, extending the material's service life and optimizing machining parameters. This reduces material waste and structural defects caused by improper machining, ultimately reducing costs and increasing efficiency.

Claims

1. A milling precision simulation method for updating crystal orientation, characterized by: The following steps are involved: Step 1: Perform crystal orientation detection on the processed surface of the workpiece before milling to obtain crystal orientation data before milling; Step 2: Model establishment and material parameter assignment; Step 2-1. Extracting Miller index based on crystal orientation data before milling ; h, k, and l are the reciprocals of the orientation components of the sampling point in the X, Y, and Z directions, respectively; Step 2-2. Construct a tool model and a workpiece model for thermal-mechanical coupled cutting simulation; mesh the workpiece model so that each mesh node corresponds to a sampling point for crystal orientation detection; Step 2-2. Import material parameters of tool model and workpiece model; among them, Miller index Add the density parameter of the workpiece model as the initial crystal orientation; Step 3: Cutting simulation to obtain the crystal orientation of the workpiece after cutting; during the plastic deformation and damage stages of the cutting simulation, the crystal orientation is updated. The process is as follows: Construct the deformation gradient tensor F; In step 3, the expression of the deformation gradient tensor F is as follows: ； in, 、 are the coordinates of the sampling points before and after deformation respectively; Perform polar decomposition on the deformation gradient tensor F to obtain the rotation matrix ; ； in, is the rotation matrix, is a positive definite symmetric tensor; Update the crystal orientation after deformation in the current analysis step as follows: ； in, The crystal orientation before deformation in the current analysis step; The specific process of cutting simulation in step 3 is as follows: Step 3-1. Update principal stresses and shear stress ; Step 3-2. Yield determination: If the material yields, proceed to step 3-3; otherwise, repeat step 3-1. Step 3-3. Calculate the updated plastic stress and update the crystal orientation; Step 3-4. Damage determination: If the material is damaged, proceed to step 3-5; otherwise, repeat steps 3-1 to 3-3; Steps 3-5. Update the crystal orientation and update the material stress and strain according to the JC damage model until the material is destroyed.

2. The milling precision simulation method for updating crystal orientation according to claim 1, characterized in that: After step three is executed, the subsurface deformation of the workpiece under different milling conditions is predicted using the simulated crystal orientation data after milling; and the milling conditions in the actual milling process are selected based on the subsurface deformation.

3. The milling precision simulation method for updating crystal orientation according to claim 1, characterized in that: In step 1, the crystal orientation of the machined surface of the workpiece after milling is also detected to obtain the crystal orientation data after milling. After step 3 is executed, the crystal orientation of the last analysis step before the destruction of each sampling point is taken as the simulated crystal orientation data after milling. The orientation distribution function is calculated for the actual crystal orientation data after milling and the simulated crystal orientation data after milling, and the actual ODF diagram and the simulated ODF diagram are obtained respectively. The accuracy of the crystal orientation simulation is determined by comparing the simulated ODF diagram with the actual ODF diagram. If the accuracy does not meet the preset requirements, the thermal-mechanical coupling cutting simulation parameters are adjusted and the simulation is repeated.

4. The milling precision simulation method for updating crystal orientation according to claim 1, characterized in that: Miller Index The conversion formula is as follows: ； in, are the first, second, and third Euler angles of the sampling points respectively.

5. The milling precision simulation method for updating crystal orientation according to claim 1, characterized in that: The process of crystal orientation detection is as follows: cutting, rough grinding, fine grinding, polishing, ultrasonic cleaning, cleaning, and drying the workpiece in sequence to obtain the workpiece to be observed, tilting the workpiece to be observed in a scanning electron microscope, collecting backscattered electrons, and using a detector to capture the diffraction pattern.

6. The milling precision simulation method for updating crystal orientation according to claim 1, characterized in that: The JC constitutive model and damage model used in the cutting simulation are as follows: ； ； in, is the material's uniaxial tensile thermo-visco-elastoplastic flow stress, For strain; is the strain rate; is the reference strain rate; is the reference temperature; is the melting temperature of the material; All are preset constants; is the equivalent fracture plastic strain; is the dimensionless plastic strain rate, which is expressed as ; is the dimensionless temperature, and its expression is ; All are preset constants; Ambient temperature for cutting simulation; is the stress triaxiality, and its expression is ; is the spherical stress, is the Mises equivalent stress.

7. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: The memory stores a computer program; the processor executes the milling precision simulation method for updating crystal orientation according to any one of claims 1 to 6.

8. A readable storage medium storing a computer program; characterized in that: When the computer program is executed by a processor, it is used to implement the milling precision simulation method for updating crystal orientation according to any one of claims 1 to 6.

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