A multi-objective optimization method for the layout of oil pad screws in a large and heavy-loaded hydrostatic turntable

Abstract

The present invention provides a multi-objective optimization method for the layout of oil pad screws on the support rail of a large heavy-duty liquid hydrostatic turntable. The oil pad is connected to the turntable base through a number of screws. First, a single fan-shaped oil film oil pad and a 1 / 16 base are subjected to fluid-solid coupling simulation analysis through ANSYS software to obtain the overall deformation of the oil pad oil cover, the deformation of the oil pad edge and the equivalent stress data of the oil pad. The minimum value of the above three data is used as the multi-objective function, and the screw spacing angle and screw radius of each circle are used as optimization parameters. A multi-group experimental design with five factors and five levels is established. The influence of each optimization parameter on the objective function is obtained based on the response surface method. Finally, the optimal solution of the screw layout is obtained according to the experimental design table and the multi-objective optimization model, and through the genetic algorithm. The method provided by the present invention is to further improve the screw layout between the oil pad and the turntable base, reduce the influence of the deformation of the oil pad surface on the thickness of the supporting oil film, thereby improving the static performance such as the stiffness and bearing capacity of the hydrostatic oil film, and provide a reasonable basis for the research on the oil pad and oil film of a large heavy-duty liquid hydrostatic turntable.

Description

Technical Field

[0001] The invention relates to the technical field of large-scale heavy-loaded hydrostatic turntable support oil pads and hydrostatic oil film design, and in particular to a multi-objective optimization method for the layout of oil pad screws for a large-scale heavy-loaded hydrostatic turntable. Background Art

[0002] Large CNC machine tools play a vital role in the manufacturing industry and are widely used in important fields such as national defense, military industry, and aerospace. They also promote the development of machine tools towards high processing precision and high load-bearing. As an important component of heavy-duty machine tools, the hydrostatic turntable can effectively ensure the stable operation of the machine tool worktable. The hydrostatic oil film support has become an important support form. It has the advantages of good load-bearing performance, high rigidity, low-speed non-creep, low friction, and good stability. With the upgrading of technology and the improvement of the performance requirements of processed parts, there are more stringent requirements for the performance of the hydrostatic oil film of the heavy-duty machine tool turntable. The various properties of the oil pad and the oil film have an important influence on the load-bearing and processing capacity of the machine tool. Therefore, the research on high-precision, large-load, high-rigidity, and small-deformation hydrostatic guides and oil film supports has become a hot topic in the industry. Summary of the invention

[0003] The present invention provides a multi-objective optimization method for the layout of oil pad screws of a large heavy-loaded liquid hydrostatic turntable. The method can effectively reduce the force deformation on the oil pad surface caused by the pressure distribution of the oil film and the pre-tightening force of the bolts after the fan-shaped oil pad is connected to the turntable base by a number of screws. When the overall deformation of the oil pad surface is large and the deformation of the edge of the oil outlet is large, the deformation will directly affect the oil film thickness in the pressure-bearing area of ​​the hydrostatic oil film, thereby causing a reduction in the bearing capacity and stiffness of the oil film. The method can effectively reduce the above-mentioned deformation and improve the bearing performance of the hydrostatic turntable oil film by optimizing the layout of the oil pad screws.

[0004] To achieve the above object, the technical solution of the present invention is as follows:

[0005] A multi-objective optimization method for the layout of oil pad screws of a large heavy-loaded hydrostatic turntable, characterized by comprising the following steps:

[0006] S1: According to the original layout, the fluid and solid three-dimensional models of the fan-shaped oil film, fan-shaped oil pad and turntable base are established and imported into the ANSYS fluid-solid coupling module to perform finite element modeling on the three parts;

[0007] S2: Perform fluid meshing and finite element simulation on the fan-shaped oil film part in FLUENT module;

[0008] S3: Use the static analysis module to mesh the oil pad and turntable base, set material properties, constraints and preload, and select the coupling surface for fluid-solid coupling simulation;

[0009] S4: Post-process the fluid-structure coupling simulation results and extract the overall deformation of the oil cover, the edge deformation of the oil pad, and the equivalent stress data of the oil pad;

[0010] S5: Establish a mathematical model of multi-objective optimization function;

[0011] S6: Based on the response surface module of DESIGN-EXPERT software, a combination test plan table is established according to the mathematical model of multi-objective optimization function;

[0012] S7: Use the response surface analysis model to generate the surface diagram of the interaction of the four parameters on the three objective functions;

[0013] S8: According to the horizontal test design data, the screw layout parameters are optimized by using a multi-objective genetic algorithm in MATLAB to obtain the optimal solution of the screw layout parameters;

[0014] S9: Repeat the above steps to perform the same analysis steps on the other two circles of guide rail oil pads. The innermost circle main guide rail oil pad adopts 1 / 14 model, and the auxiliary guide rail oil pad adopts 1 / 24 model analysis;

[0015] S10: After optimization, the optimal layout of the oil pad screws is obtained, which provides a theoretical basis for the layout of the oil pad screws.

[0016] In the step S1, since the structures of the oil pads in each circle are completely consistent and one oil film corresponds to one oil pad, which are relatively independent, a 1 / 16 three-dimensional model of the second circle of main rail oil pads is used for simulation calculation.

[0017] In the steps S1 and S3, the mesh density of the fluid domain is greater than that of the solid domain, and the mesh is encrypted at the locations of the oil pad coupling surface and the screw holes in the solid domain.

[0018] In the solid domain simulation in step S3, it is necessary to define two sections of the 1 / 16 turntable base as frictionless contact surfaces, the bottom bolt hole positions as fixed constraints, apply gravity acceleration g, use beam elements to simulate screws and insert preload.

[0019] The multi-objective optimization function mathematical model in step S5 is based on the deformation of the oil cover caused by the fluid pressure and the screw preload on the oil pad surface. , Deformation of the oil outlet edge Equivalent stress of oil pad are three objective functions, with the screw spacing angle of each circle on the oil pad and the first screw radius and the third screw radius To optimize the parameters, its mathematical form is:

[0020] ;

[0021] ;

[0022] in, α is the angle of the fan-shaped oil pad, which is a fixed value; is the number of screws per circle on a single oil pad, Depend on Decide; It is the radius of the second circle of screws on a single oil pad and is a constant value.

[0023] In step S6, the five-factor five-level table is constructed by the CentralCompositeDesign module according to the constraint conditions and generates 31 sets of central composite experimental design schemes.

[0024] In step S7, factors with insignificant effects need to be removed according to the variance analysis results.

[0025] In step S8, the importance of the three objective functions needs to be ranked: , avoiding conflicts between objective functions. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is an overall diagram of the 4.5m static pressure turntable base and the oil pad connected by screws of the present invention;

[0027] Figure 2 This is an exploded view of the assembly of a single sector-shaped oil film, oil pad, and 1 / 16 base model of the second circle main guide rail of the present invention; Figure 3 This is a schematic diagram of a single fan-shaped oil pad of the second main guide rail of the present invention;

[0028] Figure 4 This is a schematic diagram of the layout parameters of a single fan-shaped oil pad screw of the second circle main guide rail of the present invention;

[0029] Figure 5 This is an exploded view of the assembly of a single sector-shaped oil film, oil pad, and 1 / 14 base model of the first circle main guide rail of the present invention; Figure 6 It is an exploded view of the assembly of a single sector-shaped oil film, oil pad, and 1 / 24 base model of the auxiliary guide rail of the present invention;

[0030] In the figure: 1 is a fan-shaped oil film, 2 is a fan-shaped oil pad, 3 is a turntable base, 4 is an oil pad oil inlet pipeline, 5 is a screw hole, 6 is an oil cover, and 7 is an oil pad edge. DETAILED DESCRIPTION

[0031] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0032] A multi-objective optimization method for the layout of oil pad screws for a large heavy-loaded hydrostatic turntable includes the following steps:

[0033] 1. According to the original layout, the fluid and solid three-dimensional models of the fan-shaped oil film, fan-shaped oil pad and turntable base are established and imported into the ANSYS fluid-solid coupling module to perform finite element modeling on the three parts;

[0034] 4.5m large hydrostatic base and oil pad guide rail as a whole Figure 1 As shown in the figure, the structure of the base and the fan-shaped oil pad is simplified, and unnecessary chamfers and other irrelevant bolt holes are removed. Since the structures of each circle of oil pads are completely consistent and one oil film corresponds to one oil pad, they are relatively independent. Therefore, the 1 / 16 3D model of the second circle of main rail oil pads is imported into ANSYS Workbench, and the FSI (Fluid Flow-Static Structural) module is selected for analysis. The 1 / 16 model is shown in the figure. Figure 2 shown.

[0035] 2. Perform fluid meshing and finite element simulation on the fan-shaped oil film part in the FLUENT module;

[0036] A single sector oil film 1 is divided into hexahedral grids, and the 50μm film part is layered and refined. The overall grid of the fluid domain is more precise than the solid domain, and the boundary conditions are named: pressure inlet, pressure outlet, oil pad fluid-solid coupling surface, and core shaft fluid-solid coupling surface. Use double precision mode to enter FLUENT, select VG46 hydraulic oil, and its dynamic viscosity ,density , the Reynolds number is calculated according to formula (1) and the laminar flow model is used for simulation analysis.

[0037] (1)

[0038] 3. Use the static analysis module to mesh the oil pad and turntable base, set material properties, constraints and preload, and select the coupling surface for fluid-solid coupling simulation;

[0039] For example Figure 2The fan-shaped oil pad 2 and the turntable base part 3 shown in the figure are divided into two solid domains using tetrahedral meshes. The overall mesh size is larger than the fluid domain size, but the mesh of the oil pad fluid-solid coupling surface and the screw position needs to be encrypted; the oil pad and base material are HT300, and its density , elastic modulus , Poisson's ratio Define the two sections of the 1 / 16 turntable base as frictionless contact surfaces, the bolt hole positions on the bottom surface as fixed constraints, and apply gravity acceleration g , use beam elements to simulate the screws and insert the preload, select the fluid-solid coupling surface between the fluid domain and the solid domain and import the oil film pressure for simulation calculation. The solid conservation equation in this step is obtained from Newton's second law, as shown in formula (2):

[0040] (2)

[0041] in, Solid density, Solid domain acceleration vector, Cauchy stress tensor, Volume force vector. The most basic conservation principle is followed when coupling data between the fluid domain and the solid domain, as shown in formula (3):

[0042] (3)

[0043] in, τ is stress, d is the displacement, q is the heat flow, T is the temperature, subscript f For fluid, s It is solid.

[0044] 4. Post-process the fluid-solid coupling simulation results and extract the overall deformation of the oil cover, the edge deformation of the oil pad, and the equivalent stress data of the oil pad.

[0045] From the fluid-solid coupling simulation results of step 3, the overall deformation data δsurface of the oil cover 5 of the fan-shaped oil pad is extracted, as shown in Equation 4; the deformation data δoutlet of the edge of the oil pad, i.e. the hydraulic oil outlet 7, affects the outflow resistance of the hydrostatic oil film hydraulic oil and directly affects its bearing performance; the equivalent stress data of the oil pad after applying load and preload is F .

[0046] (4)

[0047] 5. Establish a mathematical model of multi-objective optimization function

[0048] The oil cover deformation caused by the fluid pressure and screw preload on the oil pad surface , Deformation of the oil outlet edge Equivalent stress of oil pad are three objective functions, with the screw spacing angle of each circle on the oil pad and the first screw radius and the third screw radius To optimize the parameters, the screw layout parameters such as Figure 4 As shown, its mathematical form is:

[0049] ;

[0050] ;

[0051] in, is the angle of the fan-shaped oil pad, which is a fixed value; is the number of screws per circle on a single oil pad, Depend on Decide; It is the radius of the second circle of screws on a single oil pad and is a constant value.

[0052] 6. Based on the response surface module of DESIGN-EXPERT software, a combined test plan table is established according to the mathematical model of multi-objective optimization function. Based on the CentralComposite in the ResponseSurface module of DESIGN-EXPERT software

[0053] Design module, a mathematical model with five factors, five levels and three dependent variables is constructed according to the constraints, and 31 sets of central combination test schemes are generated as shown in Table 1. The parameter combinations designed according to the test scheme in Table 1 are simulated and calculated by the ANSYS fluid-structure coupling module to obtain the oil pad and oil cover deformation of each screw layout parameter combination. Deformation of oil outlet edge and equivalent stress F and fill in the test plan table accordingly. For specific steps, see 1-4.

[0054] Table 1 Combination test plan

[0055] Serial number 1 / ° 2 / ° 3 / ° 1 / mm 3 / mm 1 13.5 13.5 13.5 1570 1810 2 9 9 9 1560 1820 3 22.5 13.5 13.5 1570 1810 4 13.5 13.5 13.5 1570 1790 5 9 9 9 1580 1800 6 18 9 9 1560 1800 7 4.5 13.5 13.5 1570 1810 8 13.5 13.5 13.5 1550 1810 9 13.5 13.5 13.5 1570 1810 10 18 9 18 1560 1820 11 13.5 4.5 13.5 1570 1810 12 13.5 22.5 13.5 1570 1810 13 13.5 13.5 22.5 1570 1810 14 13.5 13.5 13.5 1570 1830 15 18 18 18 1560 1800 16 18 18 18 1580 1820 17 18 9 9 1580 1820

[0056] 18 9 18 9 1580 1820 19 18 9 18 1580 1800 20 18 18 9 1580 1800 21 18 18 9 1560 1820 22 9 9 18 1560 1800 23 13.5 13.5 13.5 1590 1810 24 13.5 13.5 13.5 1570 1810 25 9 18 18 1560 1820 26 9 18 18 1580 1800 27 13.5 13.5 13.5 1570 1810 28 13.5 13.5 13.5 1570 1810 29 9 9 18 1580 1820 30 9 18 9 1560 1800 31 13.5 13.5 4.5 1570 1810

[0057] 7. Use the response surface analysis model to generate the interaction diagram of the four parameters on the three objective functions. According to the results of variance analysis, remove the factors with insignificant influence, and obtain the response surface of the interactive influence of two factors on the objective function among the five factors. The relationship between the three dependent variables and the five independent variables is obtained by surface analysis.

[0058] 8. Sort the importance of the three objective functions: According to the data of the horizontal test shown in Table 1, the layout parameters of the oil pad screws are optimized by using a multi-objective genetic algorithm through MATLAB. and The optimal solution of .

[0059] The deformation of the edge of the oil pad directly affects the outlet size of the 50μm thick oil film hydraulic oil. If the deformation of the edge of the oil pad becomes larger, the hydraulic oil outlet range becomes larger, the liquid resistance becomes smaller, the pressure holding performance of the oil film decreases, the oil chamber pressure decreases, and the bearing capacity decreases. Therefore, the deformation of the edge of the oil pad is regarded as the most important influence.

[0060] 9. Repeat the above steps to analyze the other two rail oil pads. The innermost rail oil pad uses a 1 / 14 model. Figure 5 As shown, the auxiliary rail oil pad adopts 1 / 24 model analysis, such as Figure 6 As shown;

[0061] 10. After optimization, the optimal layout of the oil pad screws is obtained, which provides a theoretical basis for the layout of the oil pad screws.

Claims

1. A multi-objective optimization method for the layout of oil pad screws for a large heavy-loaded hydrostatic turntable, characterized in that: The following steps are involved: S1: According to the original layout, the fluid and solid 3D models of the fan-shaped oil film, fan-shaped oil pad and turntable base are established and imported into the ANSYS fluid-solid coupling module to perform finite element modeling on the three parts; S2: Perform fluid meshing and finite element simulation on the fan-shaped oil film part in the FLUENT module; S3: Use the static analysis module to mesh the oil pad and turntable base, set material properties, constraints and preload, and select the coupling surface for fluid-solid coupling simulation; S4: Post-process the fluid-structure coupling simulation results and extract the overall deformation of the oil cover, the edge deformation of the oil pad, and the equivalent stress data of the oil pad; S5: Establish a mathematical model of multi-objective optimization function; The oil cover deformation caused by the fluid pressure and screw preload on the oil pad surface , Deformation of the oil outlet edge Equivalent stress of oil pad are three objective functions, with the screw spacing angle of each circle on the oil pad and the first screw radius and the third screw radius To optimize the parameters, the mathematical form is: ； ； in, α is the angle of the fan-shaped oil pad, which is a fixed value; is the number of screws per circle on a single oil pad, Depend on Decide; The radius of the second screw circle on a single oil pad is a fixed value; S6: Based on the response surface module of DESIGN-EXPERT software, a combination test plan table is established according to the mathematical model of multi-objective optimization function; S7: Using the response surface analysis model, generate R 1 , R 3、 θ 1、 θ 2、 θ 3 Parameters for oil cover deformation , Deformation of the oil outlet edge Equivalent stress of oil pad Interaction surface plot of the three objective functions; S8: According to the horizontal test design data, the screw layout parameters are optimized using a multi-objective genetic algorithm through MATLAB to obtain the optimal solution of the screw layout parameters; S9: Repeat the above steps to perform the same analysis steps on the other two circles of guide rail oil pads. The main guide rail oil pad of the innermost circle adopts a 1 / 14 model, and the auxiliary guide rail oil pad adopts a 1 / 24 model for analysis; S10: After optimization, the optimal layout of the oil pad screws is obtained, which provides a theoretical basis for the layout of the oil pad screws.

2. The multi-objective optimization method for the layout of oil pad screws for a large heavy-loaded hydrostatic turntable according to claim 1 is characterized by: In the step S1, since the structures of the oil pads in each circle are completely consistent and one oil film corresponds to one oil pad, which are relatively independent, a 1 / 16 three-dimensional model of the second circle of main rail oil pads is used for simulation calculation.

3. The multi-objective optimization method for the layout of oil pad screws for a large heavy-loaded hydrostatic turntable according to claim 1 is characterized in that: In the steps S1 and S3, the mesh density of the fluid domain is greater than that of the solid domain, and the mesh is encrypted at the locations of the oil pad coupling surface and the screw holes in the solid domain.

4. The multi-objective optimization method for the layout of oil pad screws for a large heavy-loaded hydrostatic turntable according to claim 1 is characterized in that: In the solid domain simulation in step S3, it is necessary to define the two sections of the 1 / 16 turntable base as frictionless contact surfaces, the bottom bolt hole positions as fixed constraints, apply gravity acceleration g, use beam elements to simulate screws and insert preload.

5. The multi-objective optimization method for the layout of oil pad screws for a large heavy-loaded hydrostatic turntable according to claim 1 is characterized in that: In step S6, the five-factor five-level table is constructed by the CentralCompositeDesign module according to the constraint conditions and generates 31 sets of central composite experimental design schemes.

6. The multi-objective optimization method for the layout of oil pad screws for a large heavy-loaded hydrostatic turntable according to claim 1 is characterized by: In step S7, factors that have no significant impact on the objective function need to be removed according to the variance analysis results.

7. The multi-objective optimization method for the layout of oil pad screws for a large heavy-loaded hydrostatic turntable according to claim 1 is characterized in that: In step S8, the importance of the three objective functions needs to be ranked: , avoiding conflicts between objective functions.

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