Feeding path simulation and optimization method for milling of thin-wall structure with complex shape

Abstract

The invention belongs to the technical field of machining, and particularly relates to a feeding path simulation and optimization method for milling of a thin-wall structure in a complex shape. The method comprises the steps that a feeding path scheme is obtained, and a tool moving track is generated; constructing a milled workpiece model, determining a grid size according to the milling parameters, and performing grid division on the milled workpiece model; dispersing the cutter moving track into a plurality of cutter feeding track points of the cutter, wherein the cutter feeding track points are in one-to-one correspondence with the grid units of the milled workpiece model; determining a milled unit set in the milled workpiece model according to a relative position relationship between the feeding track point and a grid unit of the milled workpiece model; the milling force is applied to the milled unit set, and workpiece deformation data and residual stress data are obtained; and repeating the steps 1-5 to obtain workpiece deformation data and residual stress data corresponding to different feeding path schemes, and screening out the feeding path scheme meeting the requirements 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 a thin-walled structure with a complex shape. Background Art

[0002] Thin-walled structural parts have the characteristics of large volume, poor local stiffness, and high material removal rate. Therefore, large overall machining deformation occurs after the workpiece is processed. The main reason is the release and redistribution of residual stress in the blank caused by the high material removal rate. In addition to being affected by the initial residual stress, milling force and clamping device, the machining deformation of the workpiece is also significantly affected by the tool path. The tool path is a unique process in the milling process of thin-walled structures. Specifically, it refers to the trajectory setting of the tool movement during the machining process. Due to the existence 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 will affect the workpiece machining deformation from three aspects: the order of residual stress release, the order of milling stress application, and the order of change in the rigidity of the workpiece structure. It is an important factor affecting the workpiece machining deformation. In finite element simulation, the deformation simulation of different tool paths can generally be achieved through two methods: three-dimensional dynamic finite element method and life and death unit technology. However, the efficiency of the first method is low and it is difficult to achieve milling deformation simulation of large thin-walled structures. Therefore, the second method is more common. However, in the life and death unit technology, the selection of milling paths is generally achieved through unit numbering. Although this method can realize the tool path simulation of simple flat-type workpieces, it relies on the meshing rules of specific finite element software, has low versatility, and is less applicable to the milling of workpieces with complex surface shapes.

[0004] In summary, it is difficult for existing finite element methods to achieve fast and accurate calculation of 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 lack of a preferred evaluation method for the milling path 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 defects of the prior art. Summary of the invention

[0006] The purpose of the present application is to provide a tool path simulation and optimization method for milling a thin-walled structure with a complex shape, 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 a thin-walled structure with a complex shape, comprising:

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

[0010] Step 2: construct a model of the workpiece to be milled, determine a grid size according to milling parameters, and mesh the model of the workpiece to be milled according to the grid size;

[0011] Step 3, discretizing the tool movement trajectory into a plurality of tool path trajectory points, wherein the tool path trajectory points correspond one-to-one to the grid units 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 milled unit set 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 model of the workpiece 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 model of the workpiece to be milled is divided into hexahedral grids according to the determined grid sizes in the depth direction, the width direction, and the advancing 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 moves forward, 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 according to a relative position relationship between the tool path point and the grid unit of the milled workpiece model includes:

[0025] Calculate the distance d between the tool path point and the centroid of the grid unit 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 a set of milled units.

[0031] In at least one embodiment of the present application, determining whether to put the grid unit into the set of milled units by a point envelope method includes:

[0032] S41, obtaining eight vertex coordinates of the grid unit, and constructing 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 point into the plane equation to calculate a second determination 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 volume force according to the distance the milling cutter advances;

[0043] Through 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 the tool path scheme that meets the requirements is 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 the present application determines the set of grid cells that need to be removed during the tool path process 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 based on the workpiece deformation data and residual stress data. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 It is a tool path simulation flow chart for milling a thin-walled structure with a complex shape according to an embodiment of the present application;

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

[0054] Figure 3 It is a schematic diagram of a tool path scheme of an implementation method of the present application;

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

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

[0057] Figure 6 It is a schematic diagram of the relative position determination of the tool path points discretization and the grid units in 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 scheme and advantages of the implementation of this application clearer, the technical scheme in the embodiment of this application will be described in more detail below in conjunction with the drawings in the embodiment 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 them. 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 construed 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 the present application, it should be understood that the terms "center", "longitudinal", "lateral", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present 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, and therefore should not be understood as limiting the scope of protection of the present 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 according to 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 model of the workpiece to be milled according to the grid size;

[0065] Step 3: discretize the tool movement trajectory into a number of tool path trajectory points, and the tool path trajectory points correspond one-to-one to the grid cells of the milling 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: applying the 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 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 residual stress data.

[0069] The tool path simulation and optimization method for milling thin-walled structures of complex shapes in this application, first, in step 1, the tool path scheme in the actual processing process is obtained, including: horizontal sequential milling, vertical sequential milling, horizontal S-shaped milling, vertical S-shaped milling, spiral milling from outside to inside, and spiral milling from inside to outside. Through CAD / CAM software, the tool movement trajectory is determined in combination with the tool path parameters to obtain the tool movement trajectory equation.

[0070] The tool path simulation and optimization method for milling a thin-walled structure with a complex shape in the present 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 model of the workpiece to be milled 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 as 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 moves forward, 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, the width direction, and the advancing 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 number of tool path points according to the milling cutter advance distance. The continuous tool movement trajectory is discretized into a number of tool position coordinate points, which correspond one-to-one to the grid units of the milled workpiece model.

[0078] The tool path simulation and optimization method for milling a thin-walled structure of a complex shape of the present application, in step 4, determines the set of milled units in the milled workpiece model according to the relative position relationship between the tool path point and the grid unit 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 unit 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 a 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 centroid coordinates of the grid unit are extracted. According to the relationship between the distance from the tool trajectory point to the centroid of the grid unit and the diagonal length of the grid unit, it is judged whether the grid unit should be placed in the set of milled units. If the judgment result cannot be obtained by this method, the point envelope method is used to further judge the relative position relationship between the tool trajectory point and the grid unit. According to the grid unit coordinates and the tool trajectory point coordinates, the position of the selected grid unit is judged to judge whether the tool trajectory point is in 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 envelope 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, obtaining eight vertex coordinates of the grid unit, and constructing 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 point into the plane equation to calculate a second determination 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 unit corresponding to the tool path point into a unit set, its content includes all the model information such as the geometric data, material model, unit type, etc. of the finite element model.

[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 that is not on plane 1 among the eight vertices (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 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), (x_8,y_8,z_8) be the coordinates of points de, f, g, 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 respectively:

[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, point Q is on plane 1; if co_1>0, point Q and point e are on the same side of plane 1; if co_1<0, 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, then stop the calculation, put the grid unit into the set, and judge the next grid unit; if point Q and point e are on the same side of plane 1, repeat the above steps, calculate the relationship between point Q and the remaining planes 2, 3, 4, 5, 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 unit, renumber it, and put it into the set of units to be removed. If the above conditions are not met, the tool path point is outside the grid unit, as shown in the figure Q' point.

[0115] The tool path simulation and optimization method for milling a thin-walled structure with a complex shape 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 the milling force based on the milling parameters;

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

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

[0119] Traverse all mesh units in the milling unit set to simulate the milling process and obtain 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 unit removal. The load, mass, strain and specific heat of the removed unit tend to zero. The milling force at this position is unloaded, and the milling force is applied to the next mesh unit to be milled. This is repeated until all mesh units to be milled are removed, thus simulating the milling process.

[0125] In step six, the technical indicators of different tool path solutions are calculated based on the workpiece deformation data and residual stress data, and the tool path solution that meets the requirements is screened out based on the technical indicators, and the technical indicators 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 influence 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 a specific embodiment of the present application, a 7050 aluminum alloy plate is subjected to structural milling tool path simulation and optimization. A simulation model is constructed with the help of the domestic SABER finite element simulation platform. The point envelope method is used to determine the set of milled units. The unit stiffness reduction method is used to simulate the removal process of workpiece material during processing. The script file is used to implement simulation parameters and plan the tool path, simulate milling deformation, evaluate the deformation amount, and 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, combine the model parameters to calculate the tool movement trajectory, and obtain the tool trajectory 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 division 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 milling cutter forward direction is equal to the milling cutter forward distance 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 workpiece being milled and the distance d of the milling cutter advance w , the continuous tool movement trajectory is discretized into several tool movement trajectory position coordinate points, so that they 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 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 mesh 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 in a certain grid unit of the finite element model of the milled workpiece, and the corresponding grid unit is selected and put 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 node number corresponding to each unit is after the unit type. 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 units stored in the above file, the milling force is applied to the mesh units in feed steps. The milling force is applied to the unit set corresponding to the analysis step in the form of volume force.

[0150] The mesh unit that has been milled off is found in the total stiffness matrix by the finite element software, and the stiffness matrix of the corresponding unit 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 unit tend to zero. In order to reduce the numerical oscillation, the reduction coefficient can be gradually changed. When the mesh unit is removed, the load at the corresponding position is unloaded.

[0151] Traverse all the mesh units in the milling unit set until all the mesh units 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 structural deformation under different tool paths, and compare the maximum machining deformation, average machining deformation and residual stress after machining under different tool paths. This embodiment finally selects the tool path scheme of spiral milling from outside to inside as the best scheme.

[0153] The tool path simulation and optimization method for milling thin-walled structures with complex shapes of the present application can realize the tool path simulation and optimization for milling complex thin-walled structures. It does not rely on the meshing rules of specific finite element software, has high versatility, and is highly applicable to the milling of workpieces with complex surface shapes. Through tool path simulation technology, a method for segmenting and discretizing structural units and tool paths can be performed according to 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 best tool path can be selected.

[0154] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope 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: construct a model of the workpiece to be milled, determine a grid size according to milling parameters, and mesh the model of the workpiece to be milled according to the grid size; Step 3, discretizing the tool movement trajectory into a plurality of tool path trajectory points, wherein the tool path trajectory points correspond one-to-one to the grid units 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; Step 5: applying a milling force to the milled unit set 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, characterized in that: In step 2, a model of a workpiece to be milled is constructed, a mesh size is determined according to milling parameters, and the model of the workpiece to be milled is meshed according to the mesh 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 model of the workpiece to be milled is divided into hexahedral grids according to the determined grid sizes in the depth direction, the width direction, and the advancing 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 moves forward, 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 thin-walled structure with a complex shape according to claim 4, characterized in that: 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.

6. The tool path simulation and optimization method for milling a complex-shaped thin-walled structure according to claim 5, characterized in that: In step 4, according to the relative position relationship between the tool path point and the grid unit of the milled workpiece model, a set of milled units in the milled workpiece model is determined, including: Calculate the distance d between the tool path point and the centroid of the grid unit 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 a set of milled units.

7. The tool path simulation and optimization method for milling a thin-walled structure with a complex shape according to claim 6, 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, obtaining eight vertex coordinates of the grid unit, and constructing 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 point into the plane equation to calculate a second determination 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.

8. The tool path simulation and optimization method for milling a complex-shaped thin-walled structure according to claim 7, characterized in that: In step five, a milling force is applied to the milled unit set 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 volume force according to the distance the milling cutter advances; 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.

9. The tool path simulation and optimization method for milling a thin-walled structure with a complex shape according to claim 8, 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.

10. The tool path simulation and optimization method for milling a thin-walled structure with a complex shape according to claim 9, characterized in that: In step six, the technical indicators of different tool path solutions are calculated based on the workpiece deformation data and residual stress data, and the tool path solution 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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