A Fast Prediction Method for Cutting Deformation of Large Thin-Walled Structures Based on Finite Element Analysis

Abstract

This invention discloses a rapid prediction method for machining deformation of large thin-walled structural parts based on finite element analysis. The method obtains the machining trajectory equation, cutting speed, residual stress, cutting temperature under stable cutting conditions, and cutting force components in the workpiece coordinate system {W} during the machining process. In the ABAQUS finite element software, subroutines SIGINI, DFLUX, and DLOAD are written in Fortran programming language to apply the residual stress field, cutting heat, and cutting force. The USDFLD subroutine controls the predefined field and state variables to achieve the "birth and death element" effect, simulating material removal. The established machining deformation prediction model of the large thin-walled structural part is submitted for solution, yielding a deformation contour map of the large thin-walled structural part. This method simultaneously considers the coupling of multiple factors such as residual stress, cutting force, cutting heat, and clamping conditions, providing an important reference and basis for studying machining deformation laws and developing reasonable and effective machining accuracy control optimization strategies.

Description

Technical Field

[0001] This invention relates to the field of machining, and specifically to a method for rapid prediction of cutting deformation of large, complex, thin-walled parts based on finite element analysis. Background Technology

[0002] With the rapid development of my country's aerospace industry, the requirements for the technological level and production capacity of aerospace manufacturing are becoming increasingly stringent. Large thin-walled structural components, due to their compact structure, light weight, and good overall performance, have been widely used in the aerospace field in recent years. However, due to their complex shapes, low stiffness, and long processing cycles, these components are prone to deformation during machining, especially under the combined influence of residual stress, cutting forces, cutting heat, and clamping conditions. This deformation severely affects the dimensional accuracy and mechanical load-bearing capacity of the thin-walled structural components. Therefore, establishing a deformation prediction model during the machining process of large thin-walled structural components is of significant theoretical and practical value for improving their manufacturing quality and accuracy.

[0003] Currently, scholars both domestically and internationally have conducted extensive research on the prediction of cutting deformation of large thin-walled structural components based on finite element technology. Among them, Rai JK used explicit dynamic simulation to establish a three-dimensional finite element model of the thin-walled component, analyzing the influence of factors such as tool geometry parameters, cutting parameters, and machining path on workpiece machining deformation. While explicit dynamic simulation, by defining a damage and failure criterion between the tool and workpiece materials, can accurately predict elastoplastic deformation during the cutting process, it suffers from low solution efficiency and high time cost, limiting its application to predicting local deformation of thin-walled components and failing to predict the overall machining deformation of large thin-walled structures. In response, Chinese patent CN201510234973.6 discloses a finite element method for predicting the machining deformation of large and complex structural components. This invention employs a method of simulating three-dimensional dynamic cutting explicit calculation using multiple continuous static implicit analysis steps. Based on the technology of continuous automatic application and sequential unloading of cutting force loads and the "birth and death element" technology, it proposes a complete structure, full-size finite element simulation prediction method. This method shortens the simulation calculation time, but the loading process of the cutting force is cumbersome and complex, requiring the establishment of a static implicit analysis step for each application of the cutting force load. Predicting the overall machining deformation of large thin-walled structural components requires tens of thousands of static implicit analysis steps, depending on the number of meshes, resulting in cumbersome modeling and high time costs. Furthermore, this method only considers the influence of cutting forces on machining deformation; if cutting heat is also taken into account, continuous application and unloading of heat source loads is necessary, further complicating the modeling process.

[0004] Although there are many research methods for predicting the cutting deformation of thin-walled parts, these methods all have many problems. They show that the dynamic simulation solution is inefficient, and the implicit static simulation modeling process is cumbersome and complex. None of them can achieve rapid prediction of the machining deformation of large thin-walled structural parts. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and, based on finite element simulation technology, provide a rapid prediction method for the cutting deformation of large thin-walled structural parts under the condition of simultaneous coupling of multiple factors such as residual stress, cutting force, cutting heat and clamping conditions. This provides an important reference and basis for studying the law of machining deformation and reasonable and effective machining accuracy control optimization strategies.

[0006] To address the aforementioned technical problems, this invention proposes a rapid prediction method for cutting deformation of large thin-walled structural components based on finite element analysis, comprising the following steps:

[0007] Step 1: Obtain the machining trajectory equation and cutting speed during the cutting process of the large thin-walled structural component; including: establishing a three-dimensional cutting model of the large thin-walled structural component; establishing a workpiece coordinate system {W} with the workpiece center as the origin and a tool coordinate system {D} with the tool center as the origin; fitting the machining trajectory equation under the workpiece coordinate system {W} according to the surface contour of the large thin-walled structural component; and calculating the cutting speed as a function of time based on the machining trajectory equation.

[0008] Step 2: Obtain the residual stress field of the large thin-walled structural component, as well as the cutting temperature and cutting force components in the workpiece coordinate system {W} under stable cutting conditions;

[0009] Step 3: Use ABAQUS finite element software to establish the cutting heat source model of the large thin-walled structural component, apply different heat source loads to the cutting area, submit the analysis, obtain the cutting temperature under different heat source loads, and perform fitting to obtain the fitting analytical expression of heat source load and cutting temperature.

[0010] Step 4: Use ABAQUS finite element software to establish the cutting temperature field model of the large thin-walled structural component. According to the machining trajectory equation in Step 1 and the cutting temperature in Step 2, and based on the fitting analytical expression of heat source load and cutting temperature obtained in Step 3, write the DFLUX subroutine to import the heat source load into the ABAQUS finite element software according to the machining trajectory equation. Apply the cutting heat to the cutting area in the form of a moving heat source in sequence to obtain the temperature field of the large thin-walled structural component as a function of time.

[0011] Step 5: Use ABAQUS finite element software to establish a cutting deformation prediction model for the large thin-walled structural component. Set boundary conditions according to the clamping layout, import the temperature field from Step 4, and write the following subroutine:

[0012] SIGINI subroutine: Imports the residual stress field obtained in step two into the ABAQUS finite element software in analytical form;

[0013] DLOAD subroutine: Based on the machining trajectory equation obtained in step one, the cutting force components in the workpiece coordinate system {W} obtained in step two are applied sequentially to the cutting area in chronological order.

[0014] USDFLD Subroutine: The "birth and death element" technique in ABAQUS finite element software can only be activated at the beginning of an analysis step. Multiple static implicit analysis steps are required to achieve a continuous material removal process. The USDFLD subroutine controls predefined fields to change the material properties of mesh elements and controls state variables to change the mesh element state, simulating the effect of the "birth and death element" technique. It can be activated at the beginning of an incremental step, enabling a continuous material removal process in a single analysis step. The specific process is as follows: Two field variables and two state variables are set in the material properties. When the field variable is "0", the material property is set to the workpiece material; when the field variable is "1", the Young's modulus is set to a range of 0-0.1, and the density is set to a range of 0-10. -15 When the state variable is "0", the unit state is displayed as inactive; when the state variable is "1", the unit state is displayed as active; according to the machining trajectory equation obtained in step one, when the workpiece position reaches the cutting area, the field variable is set to "1" and the state variable is set to "0", thereby simulating the effect of "life and death unit".

[0015] Step 6: Submit the cutting deformation prediction model of the large thin-walled structural component established in Step 5 to the implicit solver for analysis to obtain the deformation cloud map of the large thin-walled structural component.

[0016] Furthermore, in the rapid prediction method for cutting deformation of large thin-walled structural components described in this invention, wherein:

[0017] In step two, the method for obtaining the residual stress of the large thin-walled structural component is to use ABAQUS finite element software to establish a heat treatment simulation model of the blank of the large thin-walled structural component, obtain the residual stress field, and fit it according to the coordinates and the coordinates under the workpiece coordinate system {W}.

[0018] In step two, the method for obtaining the cutting temperature of the large thin-walled structural component under stable cutting conditions is to experimentally measure the cutting temperature of the workpiece under stable cutting conditions at different cutting speeds, and then fit the relationship between the cutting temperature and the cutting speed.

[0019] In step two, the method for obtaining the cutting force components of the large thin-walled structural component under stable cutting conditions in the workpiece coordinate system {W} is to experimentally measure the cutting force components F under the tool coordinate system {D} of the workpiece under stable cutting conditions at different cutting speeds. Dx F Dy F DzThe relationship between the cutting force component and the cutting speed is obtained by fitting; a coordinate transformation matrix P is established between the tool coordinate system {D} and the workpiece coordinate system {W}, and the cutting force component F in the tool coordinate system {D} is transformed by the coordinate transformation matrix P. Dx F Dy F Dz Converted to the cutting force component F in the workpiece coordinate system {W} Wx F Wy F Wz .

[0020] Compared with the prior art, the technical solution provided in this application has the following advantages and positive effects:

[0021] (1) This invention controls the predefined field to change the material properties of the mesh element by controlling the USDFLD subroutine, and controls the state variables to change the state of the mesh element, simulating the effect of the "model change" technique. By setting multiple incremental steps in a single analysis step, a continuous material removal process can be achieved. This overcomes the problem of the cumbersome and complex modeling process when simulating material removal using the "model change" technique in ABAQUS finite element software, greatly reducing modeling time and realizing rapid prediction of the processing deformation of large thin-walled structural parts.

[0022] (2) This invention uses the DFLUX subroutine to realize a moving heat source and simulate the change process of cutting heat during the cutting process, thus obtaining the temperature field of the workpiece during the cutting process. Using a sequential coupling method, the temperature field is imported into the cutting deformation prediction model of large thin-walled structural parts. Residual stress is imported through the SIGINI subroutine, and cutting force is applied sequentially to the cutting area in chronological order through the DLOAD subroutine. This provides a rapid prediction method for the cutting deformation of large thin-walled structural parts that simultaneously considers the coupling of multiple factors such as residual stress, cutting force, and cutting heat, making the simulation results more accurate. The obtained machining deformation model has important guiding value for studying machining deformation laws and developing reasonable and effective machining accuracy control optimization strategies. Attached Figure Description

[0023] Figure 1 This is a flowchart of the method for rapid prediction of cutting deformation of large thin-walled structural parts based on finite element analysis according to the present invention.

[0024] Figure 2 This is a three-dimensional cutting model of a large thin-walled structural component in an embodiment of the present invention;

[0025] Figure 3 This is a residual stress cloud diagram of a large thin-walled structural component in an embodiment of the present invention;

[0026] Figure 4 This is a graph showing the relationship between cutting temperature and cutting speed in an embodiment of the present invention;

[0027] Figure 5 This is a graph showing the relationship between cutting force and cutting speed in an embodiment of the present invention;

[0028] Figure 6 This is a graph showing the relationship between heat source load and cutting temperature in an embodiment of the present invention;

[0029] Figure 7 This is a processing deformation cloud diagram of a large thin-walled structural component according to an embodiment of the present invention; Detailed Implementation

[0030] The design concept and key points of this invention are as follows: For the machining of large thin-walled structural parts, based on finite element simulation technology, and considering the coupling of multiple factors such as residual stress, cutting force, cutting heat, and clamping conditions, the invention aims to achieve rapid prediction of the cutting deformation of these large thin-walled structural parts. This provides important reference and basis for studying machining deformation laws and developing reasonable and effective machining accuracy control optimization strategies. First, the machining trajectory equation and cutting speed during the cutting process of the large thin-walled structural part are obtained, along with the residual stress, cutting temperature under stable cutting conditions, and cutting force components in the workpiece coordinate system {W}. Then, in the ABAQUS finite element software, using the Fortran programming language, the SIGINI, DFLUX, and DLOAD subroutines are written to apply the residual stress field, cutting heat, and cutting force. The USDFLD subroutine controls the predefined field and state variables to achieve the "birth and death element" effect, simulating material removal. Finally, the established cutting deformation prediction model of the large thin-walled structural part is submitted to the implicit solver for analysis, obtaining the deformation cloud map of the large thin-walled structural part.

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. However, this description is only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0032] This embodiment uses, as follows Figure 2 Taking the spherical cap thin-walled shell workpiece 1 as an example of a large thin-walled structural component, a rapid prediction method for the cutting deformation of this workpiece is described, such as... Figure 1 As shown, it includes the following steps:

[0033] Step 1) Establish a three-dimensional cutting model of workpiece 1, such as... Figure 2 As shown, a workpiece coordinate system {W} (i.e., X) is established with the center of the sphere of workpiece 1 as the origin. W Y W Z WWith the contact point between tool 2 and workpiece 1 as the origin, establish tool coordinate system {D} (i.e., X). D Y D Z D Based on the surface profile 3 of workpiece 1, the equation of the machining trajectory 4 in the workpiece coordinate system {W} is obtained by fitting:

[0034]

[0035] In equation (1), X W Y W Z W These are the x, y, and z coordinates in the workpiece coordinate system {W}.

[0036] Step 2) Calculate the cutting speed as a function of time based on the machining trajectory equation:

[0037] v=V(t) (2)

[0038] Step 3) Use ABAQUS finite element software to establish a heat treatment model of workpiece 1 blank, set the analysis step type to "thermo-mechanical coupling", assign material properties, set heat treatment boundary conditions, mesh, and submit the analysis to obtain the residual stress field of workpiece 1 after heat treatment, such as... Figure 3 As shown, a is the equivalent stress cloud diagram of workpiece 1, and b, c, and d are the principal stress cloud diagrams in the x, y, and z directions of workpiece 1 in the workpiece coordinate system, respectively. The principal stresses in the x, y, and z directions in the workpiece coordinate system are fitted according to the x, y, and z coordinates, and the residual stress field is expressed in analytical form:

[0039]

[0040] Where, σ x σ y σ z The principal stresses in the x, y, and z directions of the workpiece coordinate system are respectively.

[0041] Step 4) Measure the cutting temperature of the workpiece under stable cutting conditions using a thermal imager, change the cutting speed to obtain the cutting temperature at different cutting speeds, and fit the relationship between cutting temperature and cutting speed, such as... Figure 4 As shown. Based on the cutting speed calculated in step 2), the cutting temperature as a function of time is obtained:

[0042] T = T(t) (4)

[0043] Step 5) Measure the cutting force component F in the tool coordinate system {D} when the workpiece is in a stable cutting state using a force measuring instrument. Dx F Dy F DzBy changing the cutting speed, the magnitude of the cutting force at different cutting speeds is obtained, and the relationship between the cutting force and the cutting speed is fitted, such as... Figure 5 As shown. Based on the cutting speed calculated in step 2), the cutting force component that varies with time is obtained, including F. Dx F Dy F Dz :

[0044]

[0045] Step 6) Based on the three-dimensional cutting model of workpiece 1 established in Step 1), establish the coordinate transformation matrix P between the tool coordinate system {D} and the workpiece coordinate system {W}:

[0046]

[0047] In equation (6), α = arctan(Y) W / X W ), β = arccos(Z) W ).

[0048] The cutting force component F measured in step 5) as a function of time in the tool coordinate system {D} is... Dx F Dy F Dz Based on the coordinate transformation matrix P, the cutting force F is converted to the workpiece coordinate system {W}. Wx F Wy F Wz :

[0049]

[0050] Step 7) Use ABAQUS finite element software to establish a cutting heat source model of workpiece 1. Set the analysis step type to "heat exchange," assign material properties, mesh, apply heat source load to the cutting area, and submit the analysis to obtain the cutting temperature of the cutting area of ​​workpiece 1. Change the magnitude of the heat source load to obtain the cutting temperature under different heat source loads, and fit the relationship between the cutting temperature and the heat source load, such as... Figure 6 As shown. Based on step 4), the cutting temperature T as a function of time is obtained, and the heat source load as a function of time is obtained:

[0051] Q = q(t) (8)

[0052] Step 8) Use ABAQUS finite element software to establish the cutting temperature field model of workpiece 1, set the analysis step type to "heat exchange", assign material properties, divide the mesh, and set the incremental step size according to the removal time of a single mesh. Based on the machining trajectory equation (1) obtained in step 1) and the heat source load Q that changes with time in step 7), write a DFLUX subroutine to import the heat source load Q into ABAQUS finite element software according to the machining trajectory equation (1), and apply the cutting heat to the cutting area in the form of a moving heat source to obtain the temperature field of workpiece 1 that changes with time.

[0053] Step 9) Use ABAQUS finite element software to establish a cutting deformation prediction model for workpiece 1, set the analysis step type to "implicit static", assign material properties, mesh, set the incremental step size according to the removal time of a single mesh, set boundary conditions according to the clamping layout, and import the temperature field from Step 7. Based on the residual stress analytical formula (3) from Step 3), write the SINGINI subroutine to import the residual stress of workpiece 1; based on the machining trajectory equation (1) from Step 1) and the cutting force F under the workpiece coordinate system {W} that changes with time obtained in Step 6). Wx F Wy F Wz Write a DLOAD subroutine to apply the cutting force to the cutting area in chronological order.

[0054] The "Model Change" technique in ABAQUS finite element software doesn't actually kill elements. Instead, it multiplies the stiffness matrix of the mesh element to be deleted by a tiny reduction factor (1.0e-6) in a specified analysis step, causing its stiffness matrix to become invalid. This results in the mesh element's mass, strain, load, damping, and other properties gradually decreasing linearly until they approach zero. However, this technique can only be activated at the beginning of an analysis step, requiring multiple static implicit analysis steps to achieve a continuous material removal process. For large thin-walled structures, the modeling process becomes extremely cumbersome when the number of meshes to be removed is too large. In this invention, the USDFLD subroutine controls predefined fields to change the material properties of mesh elements and controls state variables to change the state of mesh elements, simulating the effect of the "Model Change" technique. Furthermore, the USDFLD subroutine can be activated at the beginning of an incremental step, allowing for a continuous material removal process by setting multiple incremental steps within a single analysis step, significantly reducing modeling time costs.

[0055] In this embodiment, based on the machining trajectory equation (1) of step 1), a USDFLD subroutine is written to control the predefined field and state variables. By reading the unit node coordinates, it is determined whether the unit satisfies equation (1). When the unit node coordinates satisfy equation (1), the field variable is set to "1" and the state variable is set to "0", that is, the Young's modulus of the workpiece material is set to very small and the unit state is set to inactive, thereby simulating "killing the unit".

[0056] Step 10) Submit the cutting deformation prediction model of workpiece 1 established in step 9) to the implicit solver for analysis to obtain the deformation cloud map of workpiece 1. Figure 7 The simulation results of the machining deformation of workpiece 1 are shown in Figure a. Figure a is the equivalent deformation cloud map of workpiece 1, and Figures b, c, and d are the deformation cloud maps of workpiece 1 in the x, y, and z directions in the workpiece coordinate system, respectively. The maximum deformation of workpiece 1 can be obtained from the machining deformation cloud maps as 1.694 mm, with the maximum deformation occurring approximately 300 mm from the bottom of the workpiece. This embodiment provides a rapid prediction method for the cutting deformation of large thin-walled structural parts that simultaneously considers the coupling of multiple factors such as residual stress, cutting force, cutting heat, and clamping conditions. This method has important reference value for improving machining accuracy and optimizing machining process parameters.

[0057] Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many improvements and changes under the guidance of the present invention without departing from the spirit of the present invention, and these improvements and changes are all within the protection scope of the present invention.

Claims

1. A method for rapid prediction of cutting deformation of large thin-walled structural components based on finite element analysis, characterized in that, Includes the following steps: Step 1: Obtain the machining trajectory equation and cutting speed during the cutting process of large thin-walled structural parts; include A three-dimensional cutting model of the large thin-walled structural component is established. A workpiece coordinate system {W} is established with the workpiece center as the origin and a tool coordinate system {D} is established with the tool center as the origin. The machining trajectory equation under the workpiece coordinate system {W} is obtained by fitting the surface contour of the large thin-walled structural component. The cutting speed as a function of time is calculated based on the machining trajectory equation. Step 2: Obtain the residual stress field of the large thin-walled structural component, as well as the cutting temperature and cutting force components in the workpiece coordinate system {W} under stable cutting conditions; Step 3: Use ABAQUS finite element software to establish the cutting heat source model of the large thin-walled structural component, apply different heat source loads to the cutting area, submit the analysis, obtain the cutting temperature under different heat source loads, and perform fitting. Step 4: Use ABAQUS finite element software to establish the cutting temperature field model of the large thin-walled structural component. According to the machining trajectory equation in Step 1 and the cutting temperature in Step 2, and based on the fitting analytical expression of heat source load and cutting temperature in Step 3, write the DFLUX subroutine to import the heat source load into the ABAQUS finite element software according to the machining trajectory equation. Apply the cutting heat to the cutting area in the form of a moving heat source in sequence to obtain the temperature field of the large thin-walled structural component as a function of time. Step 5: Use ABAQUS finite element software to establish a cutting deformation prediction model for the large thin-walled structural component. Set boundary conditions according to the clamping layout, import the temperature field from Step 4, and write the following subroutine: SIGINI subroutine: Imports the residual stress field obtained in step two into the ABAQUS finite element software in analytical form; DLOAD subroutine: Based on the machining trajectory equation obtained in step one, the cutting force components in the workpiece coordinate system {W} obtained in step two are applied sequentially to the cutting area in chronological order. The USDFLD subroutine simulates the effect of the "birth and death" technique by controlling predefined fields to change the material properties of mesh elements and by controlling state variables to change the state of mesh elements. Its specific process is as follows: The material properties are set with two field variables and two state variables. When the field variable is 0, the material property is set to the workpiece material. When the field variable is 1, the Young's modulus in the material properties is set to a range of 0-0.1, and the density is set to a range of 0-10. -15 When the state variable is 0, the cell status is displayed as inactive; when the state variable is 1, the cell status is displayed as active. Based on the machining trajectory equation obtained in step one, when the workpiece position reaches the cutting area, the field variable is set to 1 and the state variable is set to 0, thereby simulating the "birth and death unit" effect. Step 6: Submit the cutting deformation prediction model of the large thin-walled structural component established in Step 5 to the implicit solver for analysis to obtain the deformation cloud map of the large thin-walled structural component.

2. The method for rapid prediction of cutting deformation of large thin-walled structural components according to claim 1, characterized in that, In step two, the method for obtaining the residual stress of the large thin-walled structural component is to use ABAQUS finite element software to establish a heat treatment simulation model of the large thin-walled structural component blank, obtain the residual stress field, and fit it according to the coordinates under the workpiece coordinate system {W}.

3. The method for rapid prediction of cutting deformation of large thin-walled structural components according to claim 1, characterized in that, In step two, the method for obtaining the cutting temperature of the large thin-walled structural component under stable cutting conditions is to experimentally measure the cutting temperature of the workpiece under stable cutting conditions at different cutting speeds, and then fit the relationship between the cutting temperature and the cutting speed.

4. The method for rapid prediction of cutting deformation of large thin-walled structural components according to claim 1, characterized in that, In step two, the method for obtaining the cutting force of the large thin-walled structural component under stable cutting conditions in the workpiece coordinate system {W} is to experimentally measure the cutting force component F in the tool coordinate system {D} under stable cutting conditions at different cutting speeds. Dx F Dy F Dz The relationship between the cutting force component and the cutting speed is obtained by fitting; a coordinate transformation matrix P is established between the tool coordinate system {D} and the workpiece coordinate system {W}, and the cutting force component F in the tool coordinate system {D} is transformed by the coordinate transformation matrix P. Dx F Dy F Dz Converted to the cutting force component F in the workpiece coordinate system {W} Wx F Wy F Wz .

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