Milling precision simulation method for updating crystal orientation

Abstract

The invention discloses a precise milling simulation method for updating crystal orientation. The simulation method comprises the following steps of: 1, performing crystal orientation detection on a processed surface of a workpiece before milling to obtain crystal orientation data before milling; 2, establishing a model and endowing material parameters; and thirdly, cutting simulation is conducted, and the crystal orientation of the cut workpiece is obtained. And in the plastic deformation stage and the damage stage of cutting simulation, the crystal orientation is updated. According to the method, crystal orientation data are introduced into thermodynamic simulation, the microstructure and crystal orientation of a material can be reflected more accurately, high-precision modeling of milling of the thin-walled workpiece is achieved, and therefore the reliability of a simulation result is improved, and milling can be guided more effectively through cutting simulation. Besides, in the aspect of crystal orientation distribution calculation, under the condition that deformation is considered, crystal orientation is updated by calculating a deformation gradient matrix, and the calculation complexity is low.

Description

Technical Field

[0001] The 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] The thin-walled parts of aircraft engines often face challenges such as deformation, vibration and tool wear during milling due to their complex structure and weak rigidity. However, due to their long-term service in high-speed and high-temperature environments, they place extremely high demands on their manufacturing performance and processing technology. These factors not only affect the processing accuracy, but may also lead to the scrapping of parts and reduced production efficiency. Therefore, it is particularly important to carry out simulation research on the milling of thin-walled parts of aircraft engines. Through simulation technology, it is possible to effectively predict and optimize processing strategies, thereby improving processing 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, which has guiding significance for actual 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 of actual materials in different directions. Although this method simplifies the simulation process to a certain extent, it is difficult to predict and analyze the changes in the crystal orientation and the actual behavior of the material. Summary of the invention

[0005] In view of 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 milling precision simulation method for updating crystal orientation, which comprises the following steps: Step 1: Perform crystal orientation detection on the processed surface of the workpiece before milling to obtain crystal orientation data before milling.

[0007] Step 2: Establish the model and assign material parameters.

[0008] Step 2-1. Extract 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.

[0009] Step 2-2. Construct a tool model and a workpiece model for thermal-mechanical coupling cutting simulation. Grid the workpiece model so that each grid node corresponds to a sampling point for crystal orientation detection.

[0010] Step 2-2. Import material parameters of tool model and workpiece model; Miller index [ℎ,k,l] T The density parameters of the workpiece model are added as the initial crystal orientation.

[0011] Step 3: Cutting simulation to obtain the crystal orientation of the workpiece after cutting. In the plastic deformation stage and damage stage of cutting simulation, the crystal orientation is updated. The process is as follows:

[0012] Construct the deformation gradient tensor F.

[0013] Perform polar decomposition on the deformation gradient tensor F to obtain the rotation matrix .

[0014] in, is the rotation matrix, is a positive definite symmetric tensor.

[0015] Update the crystal orientation after deformation in the current analysis step as follows: in, Crystal orientation before deformation in the current analysis step.

[0016] Preferably, 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.

[0017] Preferably, after step three is executed, the sub-surface 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 sub-surface deformation.

[0018] Preferably, in step one, the crystal orientation of the processed surface of the workpiece after milling is 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-mechanical coupling cutting simulation parameters are adjusted and the simulation is performed again.

[0019] Preferably, the Miller index [ℎ,k,l] T The conversion formula is as follows: [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) in, are the first, second, and third Euler angles of the sampling points respectively.

[0020] 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 a 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 a diffraction pattern.

[0021] Preferably, the specific process of performing cutting simulation in step 3 is as follows: Step 3-1. Update principal stresses and shear stress .

[0022] Step 3-2. Yield determination; if the material yields, proceed to step 3-3; otherwise, repeat step 3-1.

[0023] Step 3-3. Calculate the updated plastic stress and update the crystal orientation.

[0024] Step 3-4. Damage determination; if the material is damaged, proceed to step 3-5; otherwise, repeat steps 3-1 to 3-3.

[0025] Step 3-5. Update the crystal orientation and update the material stress and strain according to the JC damage model until the material is damaged.

[0026] As a preference, the JC constitutive model and damage model used in the cutting simulation are as follows: e f =[ D 1 + D 2 exp ( D 3 s ∗ )](1+ D 4 ln e ̇ ∗ )(1+ D 5 T ∗ ) in, is the uniaxial tensile thermo-viscous elastic-plastic flow stress of the material, 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.

[0027] In a second aspect, the present invention provides a computer device, which includes 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 the crystal orientation.

[0028] 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.

[0029] The present invention has the beneficial effects: 1. The present invention introduces crystal orientation data into thermodynamic simulation, which can more accurately reflect the microstructure and crystal orientation of the material, realize 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.

[0030] 2. In the calculation of crystal orientation distribution, the present invention updates the crystal orientation by calculating the deformation gradient matrix under deformation, and the calculation complexity is low, which provides a scientific basis for optimizing the processing technology and performance of the material.

[0031] 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.

[0032] 4. The present invention can predict the recrystallization, dislocation, slip and other behaviors of materials under different temperatures and processing conditions, help design more reasonable processing technology, improve surface integrity and reduce damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is the overall flow chart of the present invention; Figure 2 A flowchart of model building and material property parameter assignment in step 2 of the present invention; Figure 3 This is a subroutine flow chart for simulating workpiece milling in step three of the present invention. DETAILED DESCRIPTION

[0034] 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.

[0035] A milling precision simulation method for updating crystal orientation includes the following steps: Step 1: Perform crystal orientation detection on the processed surface of the workpiece before and after milling, and obtain the crystal orientation data before milling and after milling respectively; the crystal orientation data includes the orientation data of each sampling point in the workpiece, which is recorded in the form of EBSD (.ang) data. The specific detection process of crystal orientation detection is as follows: cutting, rough grinding, fine grinding, polishing, ultrasonic cleaning, cleaning, and drying to obtain the observed piece of the material to be tested, tilt the sample in a scanning electron microscope (SEM) to collect backscattered electrons, and use an EBSD detector to capture the diffraction pattern. Set the acquisition step size to 1.2, the scanning electron microscope signal intensity to 1, and obtain the crystal orientation and coordinate information. EBSD is Electron BackScatter Diffraction.

[0036] 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.

[0037] Step 2: Model establishment and material parameter assignment.

[0038] 2.1 EBSD data processing First, the EBSD data collected before milling in step 1 is denoised to improve the signal-to-noise ratio. Then it is imported into the workstation through the METX tool in the MATLAB software, and the Euler angle and xy coordinate parameters of each sampling point are extracted. Then, the Euler angle and Miller index are converted. The conversion formula is as follows:

[0039] [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) 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; l is the reciprocal of the orientation component of the sampling point in the Z direction.

[0040] 2.2 Constructing tool and workpiece simulation models Construct 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 loads. After completing the modeling, export the INP file.

[0041] 2.3 Import of material parameters First, create elements and assign cross-sectional properties according to the number of sampling points in 2.1, and write them to the back of the INP file Element. Then, add density parameters according to the Miller index obtained in step 2.1, import them to the material interface, and write the material property parameters of the tool.

[0042] Step 3: Write and import the subroutine VUMAT to realize cutting simulation.

[0043] In this embodiment, the JC constitutive model and the 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 by the Fortran compiler and imported into the simulation through the VUMAT interface. The JC constitutive model and the damage model are as follows: e f =[ D 1 + D 2 exp ( D 3 s ∗ )](1+ D 4 ln e ̇ ∗ )(1+ D 5 T ∗ ) in, is the uniaxial tensile thermo-viscous elastic-plastic flow stress of the material, 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.

[0044] 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:

[0045] 3.1 Initial analysis step calculation 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: 1) Calculation of Lamé constant 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.

[0046] 2) Update the stress components. The calculation steps are as follows: Principal stress The expression is: Shear stress The expression is: 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.

[0047] 3.2 Yield determination 1) Mises stress calculation 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.

[0048] 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.

[0049] 3.3 Plastic update stress calculation: After determining that the material has entered the yield stage, the plastic stress is updated.

[0050] 1) Calculate the stress increment, plastic strain, and plastic strain rate of the mesh nodes in this analysis step.

[0051] 2) Calculate the stress after plastic hardening: According to the JC constitutive equation in, is the strain rate influencing factor; is the temperature influence factor; is the temperature calculated in the previous analysis step.

[0052] 3.4 Crystal orientation update 1) Deformation gradient tensor solution In crystal plasticity, the small deformation assumption is used, and the deformation is considered to be small enough that the nonlinear effect can be ignored. That is, it is assumed that the displacement and strain of the material are small, so that linear approximation can be used for analysis. However, in impact dynamics, it is often necessary to consider the nonlinear effects of strain and rotation. In this case, the orientation change of the crystal 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:

[0053] In the same analysis step, the coordinates of the sampling points before deformation Expressed as , the coordinates after deformation Expressed as . They are the three-dimensional coordinate values ​​of the sampling points before deformation; They are the three-dimensional coordinate values ​​of the sampling points after deformation.

[0054] 2) Solving the rotation matrix 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: in, is the rotation matrix, is a positive definite symmetric tensor.

[0055] Calculates the crystal orientation after deformation in the current analysis step as follows: in, is the crystal orientation before deformation in the current analysis step.

[0056] Then the crystal orientation parameters after plastic deformation are derived in the form of intermediate variables.

[0057] 3.5 Damage determination: Calculate the cumulative plasticity as follows: in, is the damage initiation strain function, which is a constant at a specific temperature; is the magnitude of the plastic strain rate.

[0058] 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 go to step 3.6.

[0059] 3.6 Damage parameter update: Update the stress, strain and crystal orientation of the material according to the JC damage model constructed in step 3; the update process of the crystal orientation is consistent with step 3.4. When the material begins to fail, the crystal orientation is updated with the strain before failure.

[0060] Step 4: CP-FEM Iterative Calculation After the code is written, submit the calculation, and use the crystal orientation of the last analysis step before each sampling point is destroyed as the crystal orientation data for simulation after milling. Check whether the energy change meets the convergence condition in the monitoring. If not, adjust the size of the incremental step and recalculate.

[0061] Step 5: MTEX ​​analysis First, the crystal orientation intermediate variables calculated in step 3 are imported into the MATLAB workstation. Next, the Miller index and Euler angle are converted. Using the MTEX ​​tool, the orientation distribution function (ODF) is calculated for the actual crystal orientation data after milling obtained in step 1 and the simulated crystal orientation data after milling obtained in step 4, respectively, to obtain the simulated ODF diagram and the actual ODF diagram used to reveal the statistical characteristics of the grain orientation in the material. 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 constitutive parameters in the JC constitutive model are adjusted and the optimization simulation is re-performed.

[0062] Step 6: Use the simulated crystal orientation data after milling to predict the sub-surface deformation of the workpiece under different milling conditions, and select the milling conditions that meet the requirements to perform actual milling on the workpiece.

[0063] In this embodiment, the workpiece is a GH4169 thin-walled part; because the GH4169 thin-walled part has problems such as large deformation and surface damage during milling, existing studies have shown that EBSD research can observe the sub-surface deformation caused by processing, and the grain size also has a significant relationship with the fatigue strength of the material. The present invention can predict the deformation caused by processing and the mechanical properties of the material through the prediction of crystal orientation, extend the service life of the material, optimize the processing parameters, thereby reducing material waste and structural defects caused by improper processing, and achieving the effect of reducing costs and increasing efficiency.

Claims

1. A milling precision simulation method for updating crystal orientation, characterized in that: 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. Extract 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 coupling 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; 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; in the plastic deformation stage and damage stage of the cutting simulation, the crystal orientation is updated. The process is as follows: Construct the deformation gradient tensor F; 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, Crystal orientation before deformation in the current analysis step.

2. The milling precision simulation method for updating crystal orientation according to claim 1, characterized in that: 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.

3. The milling precision simulation method for updating crystal orientation according to claim 1, characterized in that: After step 3 is executed, the sub-surface 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 sub-surface deformation.

4. The method for accurate milling simulation of updating crystal orientation according to claim 1, characterized in that: In step 1, 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 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 performed again.

5. The method for accurate milling simulation 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.

6. 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.

7. The milling precision simulation method for updating crystal orientation according to claim 1, characterized in that: 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; Step 3-5. Update the crystal orientation and update the stress and strain of the material according to the JC damage model until the material is damaged.

8. 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 uniaxial tensile thermo-viscous elastic-plastic flow stress of the material, 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.

9. 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 as described in any one of claims 1-8.

10. 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 as described in any one of claims 1 to 8.

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