Path planning method based on milling deformation of irregular trapezoidal frame type thin-walled workpiece

Abstract

The invention provides a path planning method based on milling deformation of an irregular trapezoidal frame type thin-walled workpiece. The path planning method comprises the following steps: determining a plurality of alternative milling feed paths; establishing a model of a to-be-processed workpiece in finite element analysis software, dividing grids, importing a pre-measured temperature field of the to-be-processed workpiece into the model, and performing simulation to obtain an initial residual stress field; for each milling feeding path, the dynamic milling force load, the dynamic milling thermal load and the removed grid units of the advancing points on the path are calculated in real time, so that a simulation result corresponding to each milling feeding path is obtained, and the simulation result comprises a milling machining residual stress field and machining deformation; and according to a simulation result, determining a preferable milling feed path in the plurality of alternative milling feed paths. Thus, the removed grid units are combined with the dynamic load of the moving heat source, and the milling process of the milling cutter can be better simulated.

Description

Technical Field

[0001] This invention relates to the field of machining, and more specifically, to a path planning method based on the deformation of milling thin-walled parts with irregular trapezoidal frames. Background Technology

[0002] Lightweight structures in aerospace applications often manifest as complex thin-walled structural systems, and their precise manufacturing and assembly are the final steps in achieving lightweight goals for aerospace equipment. Currently, new materials are constantly emerging, and the demand for large-size, complex thin-walled structures is increasing. However, the significant contradiction between the inherently low stiffness of large thin-walled structural components and high-performance requirements poses a considerable challenge to my country's existing manufacturing capabilities. Therefore, balancing the functional requirements and manufacturing precision of large-size thin-walled structural components is a crucial aspect of modern aerospace equipment manufacturing.

[0003] Large, multi-frame thin-walled parts are composed of multiple single-frame structures, and the preferred toolpaths differ for single-frame thin-walled parts with different geometric features. Currently, research on the frame shapes of thin-walled parts largely focuses on simple structures such as rectangles and triangles. However, large thin-walled parts, such as rocket panels, contain numerous irregular trapezoidal frame structures, and research on irregular trapezoidal frame shapes is scarce. Furthermore, existing simulation methods largely fail to accurately simulate the milling process. Summary of the Invention

[0004] The present invention aims to at least address the shortcomings and deficiencies of the prior art, and provides a path planning method based on the deformation of milling machining of irregular trapezoidal frame-like thin-walled parts.

[0005] To achieve the above objectives, the technical solution of the present invention provides a path planning method based on the deformation of milling machining of irregular trapezoidal frame-like thin-walled parts, including: Determine multiple alternative milling toolpaths; A model of the workpiece to be processed is established and meshed in the finite element analysis software. The temperature field of the workpiece to be processed is imported into the model in advance, and the initial residual stress field is obtained by simulation. For each milling toolpath, the dynamic milling force load, dynamic milling thermal load, and removed mesh elements at the travel points on the path are calculated in real time to obtain the simulation results corresponding to each milling toolpath. The simulation results include the residual stress field and machining deformation of the milling process. Based on the simulation results, the preferred milling toolpath was determined from multiple alternative milling toolpaths.

[0006] Alternatively, the dynamic milling thermal load is determined in the following way:

[0007] in, Indicates surface heat flux; Indicates thermal conductivity; , and These represent the width of the cutting surface, the height of the cutting surface, and the thickness of the element being cut, respectively. and These represent the milling temperature and the ambient temperature, respectively.

[0008] Optionally, the dynamic milling force is determined in the following way: Based on the cutting force data measured in the experiment, the milling force coefficient is obtained; The dynamic milling force is determined based on the milling force coefficient.

[0009] Optionally, the milling force coefficient is obtained based on the experimentally measured cutting force data, including:

[0010] in, This indicates the feed per tooth. Indicates the number of teeth. Indicates the axial contact angle. Indicates the axial depth of cut. Indicates the axial height of the micro-element cutting edge. This indicates the length of the infinitesimal cutting edge. , , K represents the average triaxial force. tc K rc and K ac K represents the tangential cutting force coefficient, radial cutting force coefficient, and axial cutting force coefficient, respectively. te K re and K ae These represent the tangential, radial, and axial plowing shear force coefficients, respectively.

[0011] Optionally, the dynamic milling force is determined based on the milling force coefficient, including:

[0012] in, , , These represent the cutting forces in the X, Y, and Z directions, respectively.

[0013] Optionally, the removed mesh cells are determined in the following way: Using the projection point of the milling cutter's central axis on the bottom surface as the center, the milling cutter radius as the radius of the bottom circle, and the cutting depth as the height, a cylinder is drawn. The mesh cells inside the cylinder are then identified as the mesh cells to be removed.

[0014] The above technical solution combines the removed mesh cells with the dynamic load of the moving heat source, taking into account the combined effects of the evolution of initial residual stress and thermo-mechanical coupling. Furthermore, the application of the heat source and load, as well as the removal of the cells, adopt a cylindrical shape to better simulate the milling process and accurately determine the optimal milling tool path.

[0015] Additional aspects and advantages of the invention will become apparent in the following description or may be learned by practice of the invention. Attached Figure Description

[0016] Figure 1 This is a flowchart of one embodiment of the present invention; Figure 2 This is a flowchart of a path planning method based on milling deformation of irregular trapezoidal frame-type thin-walled parts in an embodiment of the present invention; Figure 3 This is a schematic diagram of the geometric model of the irregular trapezoidal frame thin-walled component in an embodiment of the present invention; Figure 4 This is a schematic diagram of 12 milling tool paths of three types designed in an embodiment of the present invention; Figure 5 This is a schematic diagram of the initial residual stress field in an embodiment of the present invention; Figure 6 This is a schematic diagram of the birth and death unit removal process in an embodiment of the present invention; Figure 7 This is the cutting force curve obtained by measuring the force using a force gauge in the experiment of this invention embodiment; Figure 8 This is a schematic diagram of the deformation cloud map of the milling simulation of thin-walled parts in an embodiment of the present invention. Detailed Implementation

[0017] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0018] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0019] The following reference Figures 1 to 8 Some embodiments of the present invention are described.

[0020] Reference Figure 1The present invention provides a path planning method based on the deformation of milling machining of irregular trapezoidal frame-like thin-walled parts, including: Step S1: Determine multiple alternative milling toolpaths; Step S2: In the finite element analysis software, a model of the workpiece to be processed is established and meshed. The temperature field of the workpiece to be processed is imported into the model in advance, and the initial residual stress field is obtained by simulation. Step S3: For each milling toolpath, calculate in real time the dynamic milling force load, dynamic milling thermal load, and removed mesh elements at the travel points on the path to obtain the simulation results corresponding to each milling toolpath. The simulation results include the residual stress field and machining deformation of the milling process. Step S4: Based on the simulation results, determine the preferred milling toolpath from multiple alternative milling toolpaths.

[0021] Thus, by combining the removed mesh elements with the dynamic load of the moving heat source, the combined effects of the evolution of initial residual stress and thermo-mechanical coupling are considered. Furthermore, the application of the heat source and load, as well as the removal of elements, are all cylindrical in shape, which better simulates the milling process of the milling cutter.

[0022] Alternatively, the dynamic milling thermal load is determined in the following way:

[0023] in, Indicates surface heat flux; Indicates thermal conductivity; , and These represent the width of the cutting surface, the height of the cutting surface, and the thickness of the element being cut, respectively. and These represent the milling temperature and the ambient temperature, respectively.

[0024] Optionally, the dynamic milling force is determined in the following way: Based on the cutting force data measured in the experiment, the milling force coefficient is obtained; The dynamic milling force is determined based on the milling force coefficient.

[0025] Optionally, the milling force coefficient is obtained based on the experimentally measured cutting force data, including:

[0026] in, This indicates the feed per tooth. Indicates the number of teeth. Indicates the axial contact angle. Indicates the axial depth of cut. Indicates the axial height of the micro-element cutting edge. This indicates the length of the infinitesimal cutting edge. , , K represents the average triaxial force. tc K rc and K ac K represents the tangential cutting force coefficient, radial cutting force coefficient, and axial cutting force coefficient, respectively. te K re and K ae These represent the tangential, radial, and axial plowing shear force coefficients, respectively.

[0027] Optionally, the dynamic milling force is determined based on the milling force coefficient, including:

[0028] in, , , These represent the cutting forces in the X, Y, and Z directions, respectively.

[0029] Optionally, the removed mesh cells are determined in the following way: Using the projection point of the milling cutter's central axis on the bottom surface as the center, the milling cutter radius as the radius of the bottom circle, and the cutting depth as the height, a cylinder is drawn. The mesh cells inside the cylinder are then identified as the mesh cells to be removed. Specific Implementation like Figure 2 As shown, a path planning method based on the deformation of milling in irregular trapezoidal frame-like thin-walled parts specifically includes the following steps: Step 1: Obtain the geometric model and material parameters of the irregular trapezoidal frame thin-walled component; In this embodiment of the invention, it is first necessary to obtain the geometric model of the thin-walled part to be processed, such as... Figure 3 As shown, its material parameters are obtained simultaneously. The geometric model structural dimensions include the thickness of the web and sidewalls, the height and depth of the cavity, the length of the large and small ends, the distance between the two ends, and the slope of both sides; the material parameters include density, Poisson's ratio, and elastic modulus, thermal conductivity, specific heat capacity, coefficient of thermal expansion, and yield stress that vary with temperature.

[0031] Step 2: Design three types of milling toolpath strategies: zigzag toolpath, outward-to-inward zigzag toolpath, and inward-to-outward zigzag toolpath, and further subdivide them into 12 types based on the tool entry or exit position.

[0032] In this embodiment of the invention, the specific 12 tool paths are as follows: Figure 4 As shown.

[0033] Step 3: Establish the geometric model of the thin-walled part in the finite element simulation platform and complete the predefined fields and constraints; In the implementation of this invention, the blank is a metal sheet that has undergone T6 heat treatment. Therefore, the finite element method is used to simulate the T6 heat treatment process to obtain the temperature field that changes over time, which includes three stages: solution treatment (590-620℃), water quenching and artificial aging (150-200℃).

[0034] During the implementation of this invention, such as Figure 5 As shown, when performing finite element simulation of initial residual stress, the mesh of the blank model is first changed to an eight-node linear heat transfer hexahedral element (DC3D8). The ambient temperature is set and heat transfer simulation is performed according to the T6 heat treatment process to obtain the temperature field that changes with time. Then, this temperature field is imported into the blank model with the original element type C3D8T to simulate the initial residual stress field.

[0035] Finally, the processing environment temperature is set in the new blank model, and the above initial residual stress field is imported into its predefined field to complete the application of the initial state.

[0036] In the implementation of this invention, a side edge (clamping plate) with a length of 25mm and a thickness of 2mm is left at the bottom of the model, and three-degree-of-freedom displacement constraints are applied to the side edge, thereby completing the application of clamping constraints for finite element simulation machining.

[0037] As one example, finite element simulation software may include Abaqus, Ansys, etc.

[0038] Step 4: Implement the milling simulation process based on dead and alive cells (removed mesh cells) using Fortran subroutines; In the implementation of this invention, the preparatory work before writing the subroutine is completed. First, two items are added to the material properties: 1. Independent variables; 2. User-defined fields. Among the independent variables, the solution-dependent state variables are set to two. Next, the number of field variables is increased by one for other properties, and the values ​​are multiplied by a very small number (usually 10). -7 ~10 -5 Create a thermo-coupling analysis step.

[0039] Step 5: Use the Usdfld subroutine to implement the cell removal function; In the implementation of this invention, cell removal is the core of the cell birth and death algorithm, and is implemented using the Usdfld subroutine. When a cell is removed, the corresponding cell "FIELD(1) = 1, STATEV(1) = 1" indicates that the cell is "dead"; cells that do not participate in the removal process keep "FIELD(1) = 0, STATEV(1) = 0" indicating that the cell is "alive".

[0040] The removal path for each unit is written according to the toolpath. To simulate the milling process as closely as possible, the model is moved and removed in a cylindrical shape. Figure 6 As shown. The cylinder diameter is the milling cutter diameter, the cylinder height is the milling depth, and the cylinder movement speed is the milling cutter feed rate. The program is written to simulate a milling cutter using a dynamically translating cylinder. It performs element removal operations on all elements inside the cylinder. Specifically, it uses the projection point of the milling cutter's central axis on the bottom surface as the center, the milling cutter radius as the radius of the bottom circle, and the cutting depth as the height to complete the drawing of a cylinder. The 3D coordinates of the part are processed by removing elements inside the cylinder, and the center of the cylinder's bottom surface is translated using the milling cutter's movement. A program example is shown below:

[0041] Step 6: Use the Dflux subroutine to implement the function of applying a moving heat source; In the implementation of this invention, the Dflux subroutine is used for loading a moving heat source. Cutting temperature data is measured experimentally using an infrared thermal imager. Represents surface heat flux; using Indicates thermal conductivity; using , and These represent the cutting surface width, cutting surface height, and thickness of the workpiece, respectively. and Let these represent the milling temperature and the ambient temperature, respectively. The conversion formula between temperature and heat flow is as follows: .

[0042] Write a Dflux subroutine to simulate the heat source based on the calculated heat flow. The shape and trajectory of the moving heat source should be consistent with the shape and trajectory of the cell removal in the Usdfld subroutine.

[0043] Step 7: Use the Dload subroutine to implement the function of applying moving loads; In the implementation of this invention, the Dload subroutine is used to apply the moving load. Cutting force data is measured experimentally using a force gauge, such as... Figure 7 As shown. The milling force coefficient of the tool is obtained based on the milling force coefficient calculation formula, and then... To indicate the feed per tooth, use To indicate the number of teeth, use The axial contact angle is represented by... To indicate the axial depth of cut, use The axial height of the micro-element cutting edge is represented by... The length of the infinitesimal cutting edge is represented by... , , They represent the average triaxial forces, respectively, using K tc , K rc and K ac These represent the tangential cutting force coefficient, radial cutting force coefficient, and axial cutting force coefficient, respectively. K te , K re and K ae These represent the tangential, radial, and axial plowing force coefficients, respectively. The formula for calculating the milling force coefficient is as follows: ; Using the calculated cutting force coefficient, the cutting force curve under given process parameters is obtained according to the cutting force formula. , , These represent the cutting forces in the X, Y, and Z axes, respectively. The formula for calculating the cutting force is as follows: .

[0044] Based on the calculated triaxial cutting force, a Dload subroutine was written to simulate the dynamic load. The shape and trajectory of the dynamic load are consistent with the shape and trajectory of the cell removal in the Usdfld subroutine.

[0045] Step 8: Perform finite element simulation and compare the simulation results; In the implementation of this invention, a job is created in the finite element platform and associated with a pre-written Fortran subroutine. The jobs corresponding to the 12 toolpaths are run separately to obtain the final deformation contour plot results, such as... Figure 8 As shown, the tool path is a zigzag pattern from the outside to the inside, with the small end of the tool cutting at an obtuse angle, resulting in the smallest deformation.

[0046] In this invention embodiment, three categories of 12 toolpath strategies were designed. Accurate simulation of the cylindrical tool path was achieved using Fortran subroutines in a finite element simulation platform. By combining dead and new elements (removed mesh elements), moving heat sources, and dynamic loads, the thermo-mechanical coupling effect and residual stress evolution during milling were simulated. Through simulation analysis of the machining deformation distribution characteristics under different toolpaths, the optimal toolpath with the minimum deformation was obtained. This invention innovatively integrates the evolution of initial residual stress and the thermo-mechanical coupling effect, providing a high-precision deformation prediction and path optimization scheme for machining thin-walled parts of general-shaped single-frame structures.

[0047] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0048] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0049] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0050] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0051] It should be noted that any reference signs placed between parentheses in the claims should not be construed as limiting the claims. The word "comprising" does not exclude the presence of components or steps not listed in the claims. The word "a" or "an" preceding a component does not exclude the presence of a plurality of such components. The invention can be implemented by means of hardware comprising several different components and by means of a suitably programmed computer. In a unit claim enumerating several means, several of these means may be embodied by the same item of hardware. The use of the words first, second, and third, etc., does not indicate any order. These words can be interpreted as names.

Claims

1. A path planning method based on milling deformation of irregular trapezoidal frame-like thin-walled parts, characterized in that, include: Determine multiple alternative milling toolpaths; A model of the workpiece to be processed is established and meshed in the finite element analysis software, and the temperature field of the workpiece to be processed is imported into the model in advance to simulate and obtain the initial residual stress field. For each milling toolpath, the dynamic milling force load, dynamic milling thermal load, and removed mesh elements at the travel points on the path are calculated in real time to obtain the simulation results corresponding to each milling toolpath. The simulation results include the residual stress field and machining deformation of the milling process. Based on the simulation results, the preferred milling toolpath is determined from a plurality of alternative milling toolpaths.

2. The path planning method based on milling deformation of irregular trapezoidal frame-like thin-walled parts according to claim 1, characterized in that, The dynamic milling thermal load is determined in the following way: in, Indicates surface heat flux; Indicates thermal conductivity; , and These represent the width of the cutting surface, the height of the cutting surface, and the thickness of the element being cut, respectively. and These represent the milling temperature and the ambient temperature, respectively.

3. The path planning method based on milling deformation of irregular trapezoidal frame-like thin-walled parts according to claim 1, characterized in that, The dynamic milling force is determined in the following way: Based on the cutting force data measured in the experiment, the milling force coefficient is obtained; The dynamic milling force is determined based on the milling force coefficient.

4. The path planning method based on milling deformation of irregular trapezoidal frame-like thin-walled parts according to claim 3, characterized in that, The milling force coefficient is obtained based on the experimentally measured cutting force data, including: in, This indicates the feed per tooth. Indicates the number of teeth. Indicates the axial contact angle. Indicates the axial depth of cut. Indicates the axial height of the micro-element cutting edge. This indicates the length of the infinitesimal cutting edge. , , K represents the average triaxial force. tc K rc and K ac K represents the tangential cutting force coefficient, radial cutting force coefficient, and axial cutting force coefficient, respectively. te K re and K ae These represent the tangential, radial, and axial plowing shear force coefficients, respectively.

5. The path planning method based on milling deformation of irregular trapezoidal frame-like thin-walled parts according to claim 3, characterized in that, Determining the dynamic milling force based on the milling force coefficient includes: in, , , These represent the cutting forces in the X, Y, and Z directions, respectively.

6. The path planning method based on milling deformation of irregular trapezoidal frame-like thin-walled parts according to claim 1, characterized in that, The removed grid cells are determined in the following way: Using the projection point of the milling cutter's central axis on the bottom surface as the center, the milling cutter radius as the radius of the bottom circle, and the cutting depth as the height, a cylinder is drawn. The mesh cells inside the cylinder with three-dimensional coordinates are determined as the mesh cells to be removed.

Images