A method for simulating and optimizing a milling path of a complex shape thin-walled structure

Abstract

The application belongs to the technical field of machining, and particularly relates to a milling path simulation and optimization method for a complex shape thin-wall structure. The method comprises the following steps: obtaining a milling path scheme, generating a tool movement track; constructing a milled workpiece model, determining a grid size according to milling parameters, and performing grid division on the milled workpiece model; discretizing the tool movement track into a plurality of tool milling track points, and one-to-one corresponding the tool milling track points with the grid units of the milled workpiece model; determining a milled unit set in the milled workpiece model according to the relative position relationship between the tool milling track points and the grid units of the milled workpiece model; applying a milling force to the milled unit set to obtain workpiece deformation data and residual stress data; repeating steps 1 to 5 to obtain workpiece deformation data and residual stress data corresponding to different milling path schemes, and screening a required milling path scheme according to the workpiece deformation data and the residual stress data.

Description

Technical Field

[0001] The present application belongs to the field of mechanical processing technology, and in particular relates to a tool path simulation and optimization method for milling thin-walled structures with complex shapes. Background Art

[0002] Thin-walled structural components are characterized by large volume, poor local stiffness, and high material removal rates. Consequently, significant overall deformation occurs after machining. This is primarily due to the release and redistribution of residual stress in the blank caused by the high material removal rate. In addition to being influenced by initial residual stress, milling forces, and the clamping device, workpiece deformation is also significantly affected by the tool path. The tool path is a unique process in the milling process of thin-walled structures and specifically refers to the trajectory of tool movement during machining. Due to the phenomenon of stress propagation, the distribution and magnitude of residual stress on the workpiece surface during milling are closely related to the tool path.

[0003] The tool path affects workpiece deformation during machining through three key factors: the order in which residual stress is released, the order in which milling stress is applied, and the order in which the workpiece's structural rigidity changes. This is a significant factor affecting workpiece deformation during machining. In finite element simulation, deformation simulation for different tool paths can generally be achieved using two methods: the three-dimensional dynamic finite element method and the birth-and-death cell technique. However, the first method is less efficient and makes it difficult to simulate milling deformation of large, thin-walled structures. Therefore, the second method is more common. In birth-and-death cell techniques, the milling path is generally selected by cell numbering. While this method can simulate the tool path process for simple, flat workpieces, it relies on the meshing rules of specific finite element software, resulting in low versatility and poor applicability for milling workpieces with complex surface shapes.

[0004] In summary, existing finite element methods make it difficult to quickly and accurately calculate the milling deformation of large and complex structures. General finite element software cannot perform three-dimensional dynamic milling simulation according to complex CNC machining tool paths. These two reasons have led to the current lack of an optimal evaluation method for the milling paths of complex thin-walled structures.

[0005] Therefore, it is desired to have a technical solution to overcome or at least alleviate at least one of the above-mentioned deficiencies of the prior art. Summary of the Invention

[0006] The purpose of this application is to provide a tool path simulation and optimization method for milling thin-walled structures with complex shapes, so as to solve at least one problem existing in the prior art.

[0007] The technical solution of this application is:

[0008] A tool path simulation and optimization method for milling complex thin-walled structures includes:

[0009] Step 1: Obtain a tool path plan and generate a tool movement trajectory according to the tool path plan;

[0010] Step 2: constructing a model of the workpiece to be milled, determining a grid size according to milling parameters, and meshing the workpiece model according to the grid size;

[0011] Step 3: discretize the tool movement trajectory into a plurality of tool path points, wherein the tool path points correspond one-to-one to the grid cells of the milled workpiece model;

[0012] Step 4: determining a set of milled units in the milled workpiece model according to the relative position relationship between the tool path points and the grid units of the milled workpiece model;

[0013] Step 5: applying a milling force to the set of milled units to obtain workpiece deformation data and residual stress data;

[0014] Step 6: Repeat steps 1 to 5 to obtain workpiece deformation data and residual stress data corresponding to different tool path schemes, and select a tool path scheme that meets the requirements based on the workpiece deformation data and the residual stress data.

[0015] In at least one embodiment of the present application, in step one, the tool path scheme includes: transverse sequential milling, longitudinal sequential milling, transverse S-shaped milling, longitudinal S-shaped milling, spiral milling from outside to inside, and spiral milling from inside to outside.

[0016] In at least one embodiment of the present application, in step 2, constructing a model of a workpiece to be milled, determining a grid size according to milling parameters, and meshing the workpiece model to be milled according to the grid size includes:

[0017] Construct a model of the workpiece to be milled;

[0018] The milling depth is used as the grid size in the depth direction, the milling width is used as the grid size in the width direction, and the milling cutter advance distance is used as the grid size in the milling cutter advance direction;

[0019] The milled workpiece model is divided into hexahedral grids according to the determined grid sizes in the depth direction, the width direction, and the forward direction of the milling cutter.

[0020] In at least one embodiment of the present application, the milling cutter advance distance is:

[0021]

[0022] Among them, d w is the distance the milling cutter advances, R is the radius of the milling cutter, a eis the milling width.

[0023] In at least one embodiment of the present application, in step three, the tool movement trajectory is discretized into a plurality of tool movement trajectory points according to the advance distance of the milling cutter.

[0024] In at least one embodiment of the present application, in step 4, determining a set of milled units in the milled workpiece model based on a relative positional relationship between the tool path points and the grid units of the milled workpiece model includes:

[0025] Calculate the distance d between the tool path point and the centroid of the grid cell p ;

[0026] Calculate the diagonal length of the grid cells, including the maximum diagonal length Max(E w )、Minimum diagonal length Min(E w );

[0027] If the distance is greater than the maximum diagonal length: d p >Max(E w ), then remove the grid unit;

[0028] If the distance is less than half the length of the minimum diagonal: d p <Min(E w ) / 2, then put the grid unit into the set of milled units;

[0029] If the distance is greater than half of the minimum diagonal length and less than the maximum diagonal length: Min(E w ) / 2 <d p <Max(E w ), then the point envelope method is used to determine whether to put the grid unit into the set of milled units;

[0030] According to the above method, all tool path points and grid units are traversed to obtain the set of milled units.

[0031] In at least one embodiment of the present application, determining whether to place the mesh unit into the set of milled units by a point surface envelopment method includes:

[0032] S41. Obtain the coordinates of eight vertices of the grid unit and construct plane equations of six planes of the grid unit;

[0033] S42, selecting a plane of the grid unit and any vertex that is not on the plane;

[0034] S43, substituting the coordinates of the vertex into the plane equation to calculate a first determination value;

[0035] S44, substituting the coordinates of the tool path points into the plane equation to calculate a second judgment value;

[0036] S45, calculating the product of the first determination value and the second determination value;

[0037] If it is equal to 0, the grid cell is placed into the set of milled cells;

[0038] If it is less than 0, the grid cell will be removed;

[0039] If it is greater than 0, select another plane of the grid unit and any vertex that is not on the plane, and return to step S43 until the six planes of the grid unit are traversed, and the calculated product of the first judgment value and the second judgment value is greater than 0, then the grid unit is placed in the milling unit set.

[0040] In at least one embodiment of the present application, in step five, applying a milling force to the set of milled units to obtain workpiece deformation data and residual stress data includes:

[0041] calculating a milling force according to the milling parameters;

[0042] Applying a milling force to the set of milled units in the form of a body force according to the advancement distance of the milling cutter;

[0043] By using the element stiffness reduction method, the mesh elements that have been milled are removed and the milling force is unloaded;

[0044] All mesh units in the milled unit set are traversed to simulate the milling process and obtain workpiece deformation data and residual stress data.

[0045] In at least one embodiment of the present application, the milling force is:

[0046]

[0047] F i ∈(F x , F y , F z )

[0048] Among them, F i is the milling force, is the milling force coefficient, n is the milling speed, a p is the milling depth, is the exponential coefficient corresponding to the milling speed n, is the milling depth a p The corresponding exponential coefficient is, The distance d that the milling cutter advances w The corresponding exponential coefficient is, is the exponential coefficient corresponding to the milling cutter radius R.

[0049] In at least one embodiment of the present application, in step six, technical indicators of different tool path schemes are calculated based on the workpiece deformation data and residual stress data, and tool path schemes that meet the requirements are screened out based on the technical indicators, and the technical indicators include maximum machining deformation, average machining deformation and / or residual stress.

[0050] The invention has at least the following beneficial technical effects:

[0051] The tool path simulation and optimization method for milling complex-shaped thin-walled structures in this application determines the set of grid cells that need to be removed during the tool path based on discrete tool trajectory points and grid cell node information. On this basis, the finite element method and unit stiffness reduction technology are used to simulate the thin-walled structure milling process. Finally, the optimal tool path solution is obtained by screening based on the workpiece deformation data and residual stress data. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is a flow chart of tool path simulation for milling thin-walled structures of complex shapes according to one embodiment of the present application;

[0053] Figure 2 This is a flow chart of tool path optimization for milling thin-walled structures with complex shapes according to one embodiment of the present application;

[0054] Figure 3 This is a schematic diagram of a tool path scheme according to an embodiment of the present application;

[0055] Figure 4 This is a schematic diagram of mesh division of a milled workpiece model according to one embodiment of the present application;

[0056] Figure 5 This is a schematic diagram of the relative positions of discrete tool path points and grid units in one embodiment of the present application;

[0057] Figure 6 This is a schematic diagram of discretization of tool path points and relative position determination of grid units according to one embodiment of the present application;

[0058] Figure 7 It is a schematic diagram of the finite element simulation results of a milled workpiece model according to one embodiment of the present application. DETAILED DESCRIPTION

[0059] In order to make the purpose, technical solutions and advantages of the implementation of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below in conjunction with the drawings in the embodiments of this application. In the drawings, the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The described embodiments are part of the embodiments of this application, not all of the embodiments. The embodiments described below with reference to the drawings are exemplary and are intended to be used to explain this application, and should not be understood as limitations on this application. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. The embodiments of this application are described in detail below in conjunction with the drawings.

[0060] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be understood as limiting the scope of protection of this application.

[0061] The following is combined with Figures 1 to 7 This application is described in further detail.

[0062] This application provides a tool path simulation and optimization method for milling thin-walled structures with complex shapes, such as Figure 1-2 As shown, the following steps are included:

[0063] Step 1: Obtain a tool path plan and generate a tool movement trajectory based on the tool path plan;

[0064] Step 2: construct a model of the workpiece to be milled, determine the grid size according to the milling parameters, and mesh the workpiece model according to the grid size;

[0065] Step 3: Discretize the tool movement trajectory into a number of tool path points, and the tool path points correspond one-to-one to the grid cells of the milled workpiece model;

[0066] Step 4: determining a set of milled units in the milled workpiece model according to the relative position relationship between the tool path points and the grid units of the milled workpiece model;

[0067] Step 5: Apply milling force to the set of milled units to obtain workpiece deformation data and residual stress data;

[0068] Step 6: Repeat steps 1 to 5 to obtain the workpiece deformation data and residual stress data corresponding to different tool path schemes, and select the tool path scheme that meets the requirements based on the workpiece deformation data and residual stress data.

[0069] The tool path simulation and optimization method for milling complex thin-walled structures in this application begins with step 1, where the tool path schemes used in the actual machining process are obtained, including: horizontal sequential milling, vertical sequential milling, horizontal S-shaped milling, vertical S-shaped milling, outside-to-inward spiral milling, and inside-to-outward spiral milling. Using CAD / CAM software, the tool path parameters are combined to determine the tool movement trajectory and obtain the tool movement trajectory equation.

[0070] The tool path simulation and optimization method for milling thin-walled structures of complex shapes in this application, in step 2, constructs a model of the workpiece to be milled, determines the grid size according to the milling parameters, and meshes the workpiece model according to the grid size, specifically including:

[0071] Obtain the workpiece to be milled and build a model of the workpiece to be milled;

[0072] The grid size is determined according to the milling parameters. The milling parameters include tool parameters and milling processing parameters. The specific method of determining the grid size is: p As the grid size in the depth direction, the milling width a e As the grid size in the width direction, advance the milling cutter by a distance d w The mesh size in the direction of the milling cutter's advance;

[0073] In order to save calculation time, the feed step grid division strategy is adopted to simplify the material removal process. The main idea is to complete the material removal amount of multiple single tooth feeds as one analysis step in the finite element simulation. The grid size along the milling cutter forward direction is equal to the milling cutter forward distance d of each feed step. w Or its factor, the distance the milling cutter advances d w The specific calculation formula is:

[0074]

[0075] Among them, d w is the distance the milling cutter advances, R is the radius of the milling cutter, a e is the milling width.

[0076] Finally, the model of the workpiece to be milled is divided into hexahedral meshes according to the determined mesh sizes in the depth direction, width direction, and forward direction of the milling cutter, thereby dividing the workpiece to be milled into a finite element model composed of hexahedral meshes.

[0077] In a preferred embodiment of the present application, in step 3, the tool movement trajectory is discretized into a plurality of tool path points according to the distance the milling cutter advances. The continuous tool movement trajectory is discretized into a plurality of tool position coordinate points, which correspond one-to-one to the grid cells of the milled workpiece model.

[0078] The tool path simulation and optimization method for milling a complex-shaped thin-walled structure of the present application, in step 4, determines the set of milled units in the milled workpiece model based on the relative position relationship between the tool path points and the grid units of the milled workpiece model, including the following steps:

[0079] Calculate the distance d between the tool path point and the centroid of the grid cell p ;

[0080] Calculate the diagonal length of the grid cells, including the maximum diagonal length Max(E w )、Minimum diagonal length Min(E w );

[0081] If the distance is greater than the maximum diagonal length: d p >Max(E w ), then remove the grid unit;

[0082] If the distance is less than half the length of the minimum diagonal: d p <Min(E w ) / 2, then put the grid unit into the set of milled units;

[0083] If the distance is greater than half of the minimum diagonal length and less than the maximum diagonal length: Min(E w ) / 2 <d p <Max(E w ), then the point envelope method is used to determine whether to put the grid unit into the set of milled units;

[0084] According to the above method, all tool path points and grid units are traversed to obtain the set of milled units.

[0085] The relationship between the tool movement trajectory and the unit grid is converted into the relative position relationship between the tool trajectory point and the unit grid. By writing a script program, the center of mass coordinates of the grid unit are extracted. Based on the relationship between the distance from the tool trajectory point to the center of mass of the grid unit and the diagonal length of the grid unit, it is determined whether the grid unit should be placed in the set of milled units. If the judgment result cannot be obtained through this method, the point envelope method is used to further determine the relative position relationship between the tool trajectory point and the grid unit. Based on the grid unit coordinates and the tool trajectory point coordinates, the position of the selected grid unit is determined to determine whether the tool trajectory point is within a grid unit of the finite element model of the milling workpiece. The corresponding grid unit is selected and placed in the set of milled units.

[0086] The point surface envelopment method is used to determine whether to put the mesh unit into the set of milled units. The specific process is as follows:

[0087] S41. Obtain the coordinates of eight vertices of the grid unit and construct plane equations of six planes of the grid unit;

[0088] S42, selecting a plane of the grid unit and any vertex that is not on the plane;

[0089] S43, substituting the coordinates of the vertex into the plane equation to calculate a first determination value;

[0090] S44, substituting the coordinates of the tool path points into the plane equation to calculate a second judgment value;

[0091] S45, calculating the product of the first determination value and the second determination value;

[0092] If it is equal to 0, the grid cell is placed into the set of milled cells;

[0093] If it is less than 0, the grid cell will be removed;

[0094] If it is greater than 0, select another plane of the grid unit and any vertex that is not on the plane, and return to step S43 until the six planes of the grid unit are traversed, and the calculated product of the first judgment value and the second judgment value is greater than 0, then the grid unit is placed in the milling unit set.

[0095] In three-dimensional space, construct a plane equation and substitute the coordinates of the tool path point into the plane equation; if the point is on the plane, the result is zero; when the point is on the upper and lower (or left and right) sides of the plane, the result has the opposite sign, that is, one side is greater than zero (less than zero) and the other side is less than zero (greater than zero). Determine the relationship between the tool path point and the six planes of the grid unit. If the tool path point is inside a grid unit, number the grid unit and place it in the set of units that need to be milled. If the tool path point is outside the grid unit, select other units that meet Min (E w ) / 2 <d p <Max(E w ) conditions until all mesh cells that need to be milled are screened out, such as Figure 4 In order to realize the mesh units corresponding to the tool path points into a unit set, its content includes all the model information such as the geometric data of the finite element model, material model, unit type, etc.

[0096] The specific calculation process of the point envelope method is as follows:

[0097] like Figure 5 As shown, first, the plane equations of the six planes of the hexahedron can be constructed from the eight vertex coordinates of the hexahedral mesh unit (the eight node coordinates of the mesh unit in the finite element simulation model) (for the convenience of expression, the six planes are numbered here, and then the positional relationship between the coordinate points of the tool path points and the planes of the hexahedron is determined). Taking plane 1 as an example, it can be seen from the figure that the four vertices a, b, c, and d are on the plane, while the four vertices e, f, g, and h are not on the plane. Now select any vertex among the eight vertices that is not on plane 1 (any point among e, f, g, and h), and substitute the coordinates of the vertex into the plane equation of plane 1 (the equation of plane 1 can be obtained from the coordinates of points a, b, c, and d). At the same time, the coordinate value of the given coordinate point Q is also substituted into the plane equation of plane 1. From the above properties of the positional relationship between planes and points, it can be seen that if point Q and point e (or f, g, h) are on the same side of plane 1, the two substituted values ​​have the same sign. If the substituted values ​​have different signs, the two points are on different sides of plane 1.

[0098] Assume that the equation of element plane 1 is:

[0099] A_1*x+B_1*y+C_1*z+D_1=0

[0100] in,

[0101] A_1=y_1*z_2-y_1*z_3-y_1*z_1+y_2*z_3+y_3*z_1-y_3*z_2

[0102] B_1=x_1*z_2+x_1*z_3+x_2*z_1-x_2*z_3-x_3*z_1+x_3*z_2

[0103] C_1=x_1*y_2-x_1*y_3+x_2*y_1+x_2*y_3+x_3*y_1-x_3*y_2

[0104] D_1=x_1*y_2*z_3-x_1*y_3*z_2-x_2*y_1*z_3+x_2*y_3*z_1+

[0105] x_3*y_1*z_2-x_3*y_2*z_1

[0106] Among them, (x_1, y_1, z_1), (x_2, y_2, z_2), and (x_3, y_3, z_3) are the coordinates of vertices a, b, and c respectively;

[0107] Let (x_4,y_4,z_4), (x_5,y_5,z_5), (x_6,y_6,z_6), (x_7,y_7,z_7), and (x_8,y_8,z_8) be the coordinates of points de, f, g, and h respectively, and let the coordinates of point Q be (x_0,y_0,z_0).

[0108] Substitute the coordinates of points Q and e into the equation of plane 1:

[0109] de_1=A_1*x_0+B_1*y_0+C_1*z_1+D_1

[0110] de_2=A_1*x_5+B_1*y_5+C_1*z_5+D_1

[0111] calculate:

[0112] co_1=de_1*de_2

[0113] If co_1=0, then point Q is on plane 1; if co_1>0, then point Q and point e are on the same side of plane 1; if co_1<0, then point Q and point e are on different sides of plane 1.

[0114] Based on the previous step, if co_1 = 0, then point Q is on plane 1. The calculation stops, the grid cell is added to the set, and the next grid cell is determined. If point Q and point e are on the same side of plane 1, the above steps are repeated to calculate the relationship between point Q and the remaining planes 2, 3, 4, 5, and 6. If co_i (i = 2, 3, 4, 5, 6, 7, 8) are all greater than 0, then the tool path point is inside the grid cell, renumbered, and added to the set of cells to be removed. If the above conditions do not hold, the tool path point is outside the grid cell, as shown at point Q'.

[0115] The tool path simulation and optimization method for milling a complex-shaped thin-walled structure of the present application, in step 5, applies a milling force to the set of milled units to obtain workpiece deformation data and residual stress data, including:

[0116] Calculate milling forces based on milling parameters;

[0117] Applying milling force to the set of milled units in the form of body force according to the advance distance of the milling cutter;

[0118] By using the element stiffness reduction method, the mesh elements that have been milled are removed and the milling force is unloaded;

[0119] Traverse all the mesh units in the milling unit set to simulate the milling process and obtain the workpiece deformation data and residual stress data.

[0120] The milling force is:

[0121]

[0122] F i ∈(F x , F y , F z )

[0123] Among them, F i is the milling force, is the milling force coefficient determined by the processing material and milling conditions, n is the milling speed, a p is the milling depth, is the exponential coefficient corresponding to the milling speed n, is the milling depth a p The corresponding exponential coefficient is, The distance d that the milling cutter advances w The corresponding exponential coefficient is, is the exponential coefficient corresponding to the milling cutter radius R.

[0124] The milling parameters in the milling force formula are determined based on the milling test. The milling force is applied to the unit set corresponding to the analysis step in the form of volume force according to the calculation step and gradually applied to the mesh units that need to be removed. According to the milling parameters, the unit stiffness is multiplied by the minimum amount (10e -6 ) to achieve the effect of element removal. The load, mass, strain, and specific heat of the removed element all approach zero. The milling force at this location is unloaded, and the milling force is applied to the next mesh element to be milled. This process is repeated until all mesh elements to be milled are removed, thus simulating the milling process.

[0125] In step six, the technical indicators of different tool path schemes are calculated based on the workpiece deformation data and residual stress data, and the tool path scheme that meets the requirements is screened out based on the technical indicators, which include maximum machining deformation, average machining deformation and / or residual stress.

[0126] Complete the finite element analysis of structural deformation under different tool path schemes, evaluate the impact of the tool path on the maximum machining deformation, average machining deformation and residual stress of the milled workpiece, and select the optimal tool path scheme through comparison.

[0127] In one specific embodiment of this application, a tool path for structural milling of a 7050 aluminum alloy plate was simulated and optimized using the domestically produced SABER finite element simulation platform. A simulation model was constructed using the point envelope method to determine the set of milled elements, and the element stiffness reduction method was used to simulate the material removal process during machining. A script file was used to implement simulation parameters and plan the tool path. Milling deformation was simulated, and the deformation was evaluated based on the magnitude of the deformation to optimize the tool path.

[0128] The specific steps are as follows:

[0129] A. Determine the optimal tool path plan. First, analyze the sequential tool path plan. Use CAD software such as UG and combine the model parameters to calculate the tool movement trajectory and obtain the tool path equation file (*.CLS).

[0130] B. Construct the model of the workpiece to be milled and perform finite element mesh discretization. It is necessary to determine the mesh unit size of the model based on the tool parameters and milling processing parameters. The mesh size in the depth direction is equal to the milling depth a. p =2mm, the grid size in the width direction is equal to the milling width a e =2mm; the mesh size in the direction of the milling cutter's advance is equal to the distance the milling cutter advances d w , the milling cutter radius R is 4mm, and the milling cutter advance distance for each feed step can be calculated as

[0131] C. According to the mesh size of the finite element model of the milled workpiece and the milling cutter advance distance d w , the continuous tool movement trajectory is discretized into several tool movement trajectory position coordinate points, which correspond one-to-one with the grid units of the milling workpiece model. The discrete tool movement trajectory points are stored in the finite element software in node format. The specific form of the node information storage format is:

[0132] GRID,3,,8.5,0.,6.5,,456

[0133] GRID,5,,8.5.0.5,6.5,,2456

[0134] GRID,7,,0.,0.5,6.5,,2456

[0135] GRID,9,,0.,0.,4.34,,456

[0136] GRID,11,,8.5,0.,4.34,,456

[0137] The first column after GRID is the node number. Since the simulation analysis model in this embodiment is a three-dimensional model, the coordinate value of the node in the three-dimensional space is after the node number.

[0138] D. Calculate the diagonal length of the grid unit. The grid unit in this embodiment is a regular cuboid, so the calculation of Min(E w )=Max(E w )=4.46mm, make a preliminary judgment on the relative position of the grid unit and the tool path point. If the distance d p Greater than the maximum diagonal length d of the unit p >Max(E w )=4.46mm, then skip this unit and proceed to the next step of calculation; when the relative distance d between the grid unit and the tool path point p <Min(E w ) / 2=2.23mm, the grid unit is included in the set of milled units.

[0139] When the relative distance d between the grid unit and the tool path point p >Min(E w ) / 2=2.23mm and d p <Max(E w )=4.46mm, the point envelope method is used to determine whether the tool path point is within a grid unit of the finite element model of the milled workpiece, and the corresponding grid unit is selected and placed into the milled unit set.

[0140] In order to put the grid cells corresponding to the coordinate points on the tool movement trajectory into a set of milled cells, the storage format of the cell information stored in the file is:

[0141] CHEX8.1,200,11.13,15,0.3.6,ABC

[0142] +BC,7,1

[0143] CHEX8, 2, 200, 23, 25, 27, 21, 11, 13, ABE

[0144] +BE, 15, 9

[0145] CHEX8.3.200,35,37,39,33,23,25,ABG

[0146] +BG, 27, 21

[0147] Since the simulation analysis involves a large number of operations on grid units, the unit type is followed by the node number corresponding to each unit. Since the unit type set for the simulation model analysis is CHEX8, which is a hexahedral unit, each hexahedral unit has 8 nodes, each unit number is followed by eight corresponding node numbers.

[0148] E. Determine the milling parameters in the milling force formula based on the milling test, and calculate the milling force as F x =160N, F y =180N, F z =90N.

[0149] By accessing the milled elements stored in the above file, the milling force is applied to the mesh elements in the feed step. The milling force is applied to the element set corresponding to the analysis step in the form of volume force.

[0150] The mesh elements that are milled out are found in the total stiffness matrix by the finite element software, and the stiffness matrix of the corresponding element is multiplied by the reduction coefficient. In this embodiment, the reduction coefficient is taken as 10e -6 , the load, mass, strain, and specific heat of the removed mesh element all tend to zero. To reduce numerical oscillations, the reduction coefficient can be gradually changed. When a mesh element is removed, the load at the corresponding position is unloaded.

[0151] Traverse all the grid cells in the milling unit set until all the grid cells in the milling set are eliminated, and calculate the workpiece machining deformation under the tool path as follows: Figure 7 shown.

[0152] Repeat the above steps to complete the finite element analysis of the structural deformation under different tool paths, and compare the maximum machining deformation, average machining deformation and residual stress under different tool paths. In this embodiment, the tool path scheme of spiral milling from outside to inside is finally selected as the best scheme.

[0153] The tool path simulation and optimization method for milling complex thin-walled structures disclosed in this application can simulate and optimize the tool path process for milling complex thin-walled structures. It does not rely on the meshing rules of specific finite element software, is highly versatile, and is highly applicable to milling workpieces with complex surface shapes. Through tool path simulation technology, a method for segmenting and discretizing structural units and tool paths can be performed based on milling tools and process parameters, so that the tool path process can be represented by removing finite element units, shortening the calculation time of milling deformation. Through the tool path optimization method, the milling deformation and residual internal stress of different tool paths can be quickly evaluated, and the optimal tool path can be selected.

[0154] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A tool path simulation and optimization method for milling thin-walled structures with complex shapes, characterized in that: include: Step 1: Obtain a tool path plan and generate a tool movement trajectory according to the tool path plan; Step 2: constructing a model of the workpiece to be milled, determining a grid size according to milling parameters, and meshing the workpiece model according to the grid size; Step 3: discretize the tool movement trajectory into a plurality of tool path points, wherein the tool path points correspond one-to-one to the grid cells of the milled workpiece model; Step 4: determining a set of milled units in the milled workpiece model according to the relative position relationship between the tool path points and the grid units of the milled workpiece model, including: Calculate the distance d between the tool path point and the centroid of the grid cell p ; Calculate the diagonal length of the grid cells, including the maximum diagonal length Max(E w )、Minimum diagonal length Min(E w ); If the distance is greater than the maximum diagonal length: d p >Max(E w ), then remove the grid unit; If the distance is less than half the length of the minimum diagonal: d p <Min(E w ) / 2, then put the grid unit into the set of milled units; If the distance is greater than half of the minimum diagonal length and less than the maximum diagonal length: Min(E w ) / 2 <d p <Max(E w ), then the point envelope method is used to determine whether to put the grid unit into the set of milled units; According to the above method, all tool path points and grid units are traversed to obtain the set of milled units; Step 5: applying a milling force to the set of milled units to obtain workpiece deformation data and residual stress data; Step 6: Repeat steps 1 to 5 to obtain workpiece deformation data and residual stress data corresponding to different tool path schemes, and select a tool path scheme that meets the requirements based on the workpiece deformation data and the residual stress data.

2. The tool path simulation and optimization method for milling a complex-shaped thin-walled structure according to claim 1 is characterized in that: In step 1, the tool path scheme includes: transverse sequential milling, longitudinal sequential milling, transverse S-shaped milling, longitudinal S-shaped milling, spiral milling from outside to inside, and spiral milling from inside to outside.

3. The tool path simulation and optimization method for milling a complex-shaped thin-walled structure according to claim 2 is characterized in that: In step 2, a model of the workpiece to be milled is constructed, a grid size is determined according to milling parameters, and the model of the workpiece to be milled is meshed according to the grid size, including: Construct a model of the workpiece to be milled; The milling depth is used as the grid size in the depth direction, the milling width is used as the grid size in the width direction, and the milling cutter advance distance is used as the grid size in the milling cutter advance direction; The milled workpiece model is divided into hexahedral grids according to the determined grid sizes in the depth direction, the width direction, and the forward direction of the milling cutter.

4. The tool path simulation and optimization method for milling a complex-shaped thin-walled structure according to claim 3 is characterized in that: The milling cutter advance distance is: Among them, d w is the distance the milling cutter advances, R is the radius of the milling cutter, a e is the milling width.

5. The tool path simulation and optimization method for milling a complex-shaped thin-walled structure according to claim 4 is characterized in that: In step three, the tool movement trajectory is discretized into a number of tool movement trajectory points according to the advance distance of the milling cutter.

6. The tool path simulation and optimization method for milling a complex-shaped thin-walled structure according to claim 5 is characterized in that: The point envelope method is used to determine whether to put the mesh unit into the set of milled units, including: S41. Obtain the coordinates of eight vertices of the grid unit and construct plane equations of six planes of the grid unit; S42, selecting a plane of the grid unit and any vertex that is not on the plane; S43, substituting the coordinates of the vertex into the plane equation to calculate a first determination value; S44, substituting the coordinates of the tool path points into the plane equation to calculate a second judgment value; S45, calculating the product of the first determination value and the second determination value; If it is equal to 0, the grid cell is placed into the set of milled cells; If it is less than 0, the grid cell will be removed; If it is greater than 0, select another plane of the grid unit and any vertex that is not on the plane, and return to step S43 until the six planes of the grid unit are traversed, and the calculated product of the first judgment value and the second judgment value is greater than 0, then the grid unit is placed in the milling unit set.

7. The tool path simulation and optimization method for milling a complex-shaped thin-walled structure according to claim 6 is characterized in that: In step five, a milling force is applied to the set of milled units to obtain workpiece deformation data and residual stress data, including: calculating a milling force according to the milling parameters; Applying a milling force to the set of milled units in the form of a body force according to the advancement distance of the milling cutter; By using the element stiffness reduction method, the mesh elements that have been milled are removed and the milling force is unloaded; All mesh units in the milled unit set are traversed to simulate the milling process and obtain workpiece deformation data and residual stress data.

8. The tool path simulation and optimization method for milling a complex-shaped thin-walled structure according to claim 7, characterized in that: The milling force is: F i ∈(F x ,F y ,F z ) Among them, F i is the milling force, is the milling force coefficient, n is the milling speed, a p is the milling depth, is the exponential coefficient corresponding to the milling speed n, is the milling depth a p The corresponding exponential coefficient is, The distance d that the milling cutter advances w The corresponding exponential coefficient is, is the exponential coefficient corresponding to the milling cutter radius R.

9. The tool path simulation and optimization method for milling a complex-shaped thin-walled structure according to claim 8, characterized in that: In step six, the technical indicators of different tool path schemes are calculated based on the workpiece deformation data and residual stress data, and the tool path scheme that meets the requirements is screened out based on the technical indicators, wherein the technical indicators include maximum machining deformation, average machining deformation and / or residual stress.

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