CN113351891B - Local bonding clamping method for reducing turning deformation of disc plane members - Google Patents

Local bonding clamping method for reducing turning deformation of disc plane members Download PDF

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CN113351891B
CN113351891B CN202110616113.4A CN202110616113A CN113351891B CN 113351891 B CN113351891 B CN 113351891B CN 202110616113 A CN202110616113 A CN 202110616113A CN 113351891 B CN113351891 B CN 113351891B
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bonding
cutting
planar member
unit
plane
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CN113351891A (en
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孙玉文
闫舒洋
孙辉
齐书韬
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Dalian University of Technology
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23B—TURNING; BORING
    • B23B5/00—Turning-machines or devices specially adapted for particular work; Accessories specially adapted therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23B—TURNING; BORING
    • B23B25/00—Accessories or auxiliary equipment for turning-machines
    • B23B25/06—Measuring, gauging, or adjusting equipment on turning-machines for setting-on, feeding, controlling, or monitoring the cutting tools or work
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23Q—DETAILS, COMPONENTS, OR ACCESSORIES FOR MACHINE TOOLS, e.g. ARRANGEMENTS FOR COPYING OR CONTROLLING; MACHINE TOOLS IN GENERAL CHARACTERISED BY THE CONSTRUCTION OF PARTICULAR DETAILS OR COMPONENTS; COMBINATIONS OR ASSOCIATIONS OF METAL-WORKING MACHINES, NOT DIRECTED TO A PARTICULAR RESULT
    • B23Q3/00—Devices holding, supporting, or positioning work or tools, of a kind normally removable from the machine
    • B23Q3/02—Devices holding, supporting, or positioning work or tools, of a kind normally removable from the machine for mounting on a work-table, tool-slide, or analogous part
    • B23Q3/06—Work-clamping means
    • B23Q3/08—Work-clamping means other than mechanically-actuated
    • B23Q3/084—Work-clamping means other than mechanically-actuated using adhesive means

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Milling Processes (AREA)
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Abstract

The invention belongs to the technical field of turning clamping of plane components, and discloses a local bonding clamping method for reducing turning deformation of a disc-type plane component, which comprises the steps of firstly determining the number of bonding points according to a given radius of a dot matrix bonding unit and a stress balance condition of the plane component, and initializing the positions of the bonding points; the method comprises the steps of establishing a multiple-cutting simulation model of a planar member, applying an initial internal stress field, and locally restraining a target member according to a determined bonding point position; on the basis, a non-uniform material removal technology is adopted to determine a removed grid set, and the PV value of the surface shape of the plane member after the processing is finished is submitted to calculation and determined; and finally, optimizing the positions of the bonding points based on a genetic algorithm by taking the minimum processing deformation as a target until the optimal position sequence of the bonding lattice is finally obtained. The invention adopts a local lattice bonding clamping mode, thereby not only reducing the clamping deformation of the plane component, but also effectively reducing the stress deformation caused by the turning process and obviously improving the machining precision of the plane component.

Description

Local bonding clamping method for reducing turning deformation of disc plane members
Technical Field
The invention belongs to the technical field of turning and clamping of planar members, and particularly relates to a local bonding method for reducing machining deformation of disc-type planar members.
Background
The surface shape precision of some disc thin-wall plane components in the fields of information electronics, energy power and the like is often required to be extremely high, but the disc thin-wall plane components are extremely easy to deform under the action of stress due to large diameter-thickness ratio and poor rigidity, so that the difficulty of precision guarantee during turning is extremely high. Although the micro cutting by adopting the ultra-precise single-point diamond lathe can greatly reduce the stress layer of the machine and improve the deformation problem of the thin-wall planar piece under the stress action of the machine, the clamping stress and the internal stress of the component still exist and the whole processing period is completed. The clamping mode not only directly influences the clamping deformation of the component, but also changes the stress release mode in the component processing process, and further influences the stress deformation distribution after the thin-wall planar component is processed.
Currently, a vacuum adsorption clamping method is often adopted to replace a traditional mechanical clamping method, so that the problems of large clamping deformation, easiness in damaging components and the like caused in the clamping process of thin-wall planar components are solved. The vacuum adsorption method firmly presses the component on the surface of the clamp through the pressure difference between the vacuum cavity in the clamp body and the atmosphere, and has the advantage of reliable clamping. However, as the wall thickness of the planar member is reduced, the stress deformation of the member is gradually increased, and the surface shape accuracy is also continuously deteriorated. Under the condition that the surface shape error exists on the clamping surface, although the clamping surface can be forcedly leveled under the action of vacuum adsorption force, the planar member is restrained to be elastically restored after unloading, so that the surface shape error of the clamping surface is restored to the processing surface. At this time, there is a strong correlation between the precision of the machined surface of the planar member and the precision of the clamping surface, and the machining deformation cannot be converged by the turn-over machining mode. In addition, under strong constraints of the adsorption force, the unbalance stress induced by the material removal cannot be released during the processing. After the processing is completed and constraint unloading is completed, the accumulated unbalanced stress is released completely, and the internal stress is rebalanced to generate large stress deformation. At the moment, the clamping deformation and the stress deformation together restrict the machining precision of the thin-wall plane component under the vacuum adsorption clamping condition.
In addition, the bonding method is used in the polishing process of optical elements, mainly to fix a workpiece on a jig to reduce clamping deformation, and generally to bond the positioning surface integrally. The literature 'ultra-thin quartz plate polishing processing cementing holding deformation' (optical precision engineering, 2019, 27 (11): 128-135) explores the influence of an adhesive curing sequence on the clamping deformation of the ultra-thin quartz plate, but does not relate to the optimal selection of the number and the positions of bonding units. At present, the bonding method is not applied in turning, and particularly a local bonding strategy aiming at reducing turning deformation under the action of factors such as internal stress of a part and clamping is not yet seen.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a local bonding clamping method facing the turning process of a planar member, so as to solve the problem of overlarge machining deformation when the planar member of a disc is machined by adopting the existing clamping scheme.
The technical scheme adopted by the invention for solving the problems is as follows:
a local bonding clamping method for reducing turning deformation of disc plane members is characterized in that firstly, the number of bonding points is determined according to a given radius of a dot matrix bonding unit and a stress balance condition of the plane members, and the positions of the bonding points are initialized; the planar member multi-time cutting simulation model is built according to the method, an initial internal stress field is further applied, and the target member is locally restrained according to the determined bonding point position; on the basis, a non-uniform material removal technology is adopted to determine a removed grid set, and the PV value of the surface shape of the plane member after the processing is finished is submitted to calculation and determined; and finally, optimizing the positions of the bonding points based on a genetic algorithm by taking the minimum processing deformation as a target until the optimal position sequence of the bonding lattice is finally obtained.
The invention adopts the following specific steps:
and step one, the plane member is subjected to the combined action of cutting force and gravity in the cutting process. In order to ensure the bonding reliability of the planar member, the bonding force and the bonding torque provided by the bonding wax are required to meet the requirements of the stress balance and the torque balance of the planar member. The shape of the bonding units in the selected local bonding scheme is round, and the radius r of the bonding units is selected to be 2.5-7.5 mm according to the geometric dimension of the plane member. Therefore, the minimum number N of bonding points meeting the balance of the cutting stress in the horizontal direction h The following relationship can be used to determine:
wherein w is the shear strength of the bonding wax, F f For turning feed resistance, f s Is a safety factor.
Different from the horizontal stress condition of the plane member, the stress condition of the plane member in the vertical direction may be slightly different from the different random bed structures. When the processing machine tool is of a front-mounted tool rest structure, the main shaft rotates forward, the main cutting force of the workpiece is opposite to the gravity direction of the workpiece, and the minimum bonding point number N of the cutting stress balance in the vertical direction is met vq The method can be obtained by the following formula:
wherein R is the radius of the disc-like planar member, t is the thickness of the planar member, ρ is the material density of the member, F c The main cutting force is the turning.
When the processing machine tool is of a rear-mounted tool rest structure, the main shaft rotates forward, the main cutting force of the workpiece is the same as the gravity direction of the workpiece, and the minimum bonding point number N of the cutting stress balance in the vertical direction is met vh The method can be obtained by the following formula:
due to N vh Constant greater than N vq Thus selecting N vh The minimum number N of bonding points meeting the stress balance in the vertical direction v Wherein N is v ＝N vh . Further according toAnd (5) primarily selecting the number N of bonding points meeting the stress balance condition of the plane member.
And step two, defining the center of the bottom surface of the workpiece as the origin (0, 0) of the coordinate system under the coordinate system of the machine tool, wherein the Z-direction height is 0 because the bonding unit is positioned on the bottom surface of the workpiece. The bonding point is expressed in polar form as (R i ，θ i ) Wherein 0.ltoreq.R i ≤R-r,0≤θ i And (3) initializing bonding point position combinations. In order to ensure the clamping stability of the workpiece, the circumferential moment generated by the shearing force between the workpiece and the rubber layer needs to satisfy the following conditionsRelationship:
when the circumferential moment of the planar member meets the relation, the bonding position sequence is directly outputOtherwise a new bond point (R n+1 ，θ n+1 ) The bonding points are added to the bonding position sequence and an n=n+1 operation is performed to update the number of bonding points, which is repeated until the equation (4) is established. Setting the maximum number N of bonding points max 1.1 to 1.8 times of the initial selection number of the bonding points, if the number N of the bonding points is larger than a preset number threshold N max And (3) if the condition in the formula (4) is not met, stopping iteration, judging that the bonding point position sequence of the group is unreasonable, reinitializing the bonding point position sequence, and executing the subsequent operation in the step two until the bonding point position combination meeting the clamping stability of the plane component is obtained.
Thirdly, carrying out parameterization modeling on the planar member by applying a Python secondary development technology, completing the setting of simulation parameters such as geometric characteristics, material properties and the like of the planar member in finite element software Abaqus, and locally restraining the planar member to process a positioning surface at the bonding point position sequence determined in the second step. The planar member is divided into a cutting layer and a base layer in the thickness direction, and the cutting layer is locally grid-thinned, wherein the grid type is an eight-node reduced integral hexahedral cell C3D8R. Reconstructing an initial internal stress field after grid refinement based on a shape function interpolation method, and then loading the initial internal stress field into a finite element analysis model.
And step four, since the unbalance stress induced by the material removal is gradually released in the form of deformation of a component in the cutting process, the actual cutting depth of the cutter at each processing position is different although the moving track of the cutter is a straight line parallel to the positioning surface of the workpiece, and the unbalance stress belongs to a non-uniform material removal process. Combining cell death technique according to integration point and deformed grid cellThe relative axial position between the cutting planes determines whether the unit is removed during cutting. Specifically, for the ith cut, the kth cell E in the jth layer of grid k Comprising 8 nodes n kd (d=0, 1 …, 7), the initial axial coordinate corresponding to each node is represented as Ncz kd (d=0, 1 …, 7). Node n at the ith cutting kd The actual Z-direction coordinate of the (C) is the accumulation of the initial axial coordinate of the node and the axial deformation of the node after the (i-1) th cutting. Reading in odb result file generated after i-1 cutting simulation, extracting initial Z-direction coordinate and axial deformation value of corresponding node, and obtaining unit E during i cutting k Actual axial position coordinates Ecz of equivalent integral points k Can be calculated by equation (5).
In the middle ofRepresents the i-1 th cut grid node n kd Is not deformed yet during the first cutting, thus +.>Satisfy equation->
Traversing and calculating the actual axial coordinates of all unit integral points in the jth grid, if the calculated result is higher than the axial height of the ith cutting plane, judging that the unit is killed in the ith cutting process, and storing the unit numbers in the ith cut removed grid setIs a kind of medium. On the contrary, the determination unit "survives" in the ith cut, and stores the unit number thereof in the ith cut non-removed grid set +.>Is a kind of medium. Determining the set of removed units layer by layer according to the above calculation procedure until all grids contained in the ith cut are traversed, and then "killing" the set +.>And submitting calculation to the corresponding grid unit until the ith simulation is completed. Will->The unit numbers in the list are directly stored in the removed unit number set E xc In->The set of unremoved cells contained in the cutting insert will participate in the subsequent simulation operation as part of the material to be removed in the (i+1) th cutting. And step four, the operation is circularly executed until the simulation calculation of the multiple feed cutting is completed.
Step five, after the multiple feed cutting simulation is completed, collecting E xc All units "killed" in each pass cutting simulation were included. Numbering set E of all cells of grid refinement layer x And set E xc Difference set E of (2) xu Representing a refinement layer unremoved set of cells. Traversing set E xc The initial Z-direction coordinates of the unit nodes in the superposition set correspond to the axial deformation of the nodes, and the minimum value of the calculated result represents the lowest point Z of the surface of the planar member after cutting is completed min . Traversing set E xu Calculating the true axial position of the unit nodes in the collection, wherein the maximum value of the result represents the highest point Z of the surface of the planar member after cutting max The surface shape PV value of the planar member can be determined by Z max -Z min And (5) calculating to obtain the product.
And step six, optimizing the position of the local bonding point by adopting a genetic algorithm by taking the minimum surface shape PV value of the planar member after multiple feeding cutting simulation as a target. Setting the maximum iteration number K according to the calculation efficiency requirement max The value range is 200-300 generations, when the iteration number J meets the conditionJ<K max And repeating the second step, the third step, the fourth step and the fifth step, generating a new bonding point position combination and calculating the surface shape PV value of the planar member under the clamping condition. And (3) performing traversal comparison on the generated bonding point position sequence, judging that the bonding sequence has position overlapping if the center distance between the bonding unit i and the bonding unit j meets the condition described by the formula (6), and correcting the surface shape PV value under the unreasonable bonding scheme to be a preset maximum value. And outputting a bonding point position sequence generated by the J-th optimization and a corresponding surface shape PV value, and updating the iteration times according to J=J+1. Number of iterations j=k max And (5) stopping the circulation, and ending the adhesive point position optimization process.
The invention has the beneficial effects that:
the invention provides a local lattice type bonding clamping method for reducing machining deformation, which is oriented to the turning process of a disc type plane member, not only reduces the turning clamping deformation, but also gradually releases unbalanced internal stress induced by material removal in the cutting process, effectively reduces the stress deformation caused by the turning process of the plane member, and improves the machining surface shape precision of the plane member.
Drawings
FIG. 1 is a flow chart for optimizing bonding locations based on minimizing planar member stress deformation.
Fig. 2 is a schematic diagram of the forces exerted on a planar member of the disc type during the cutting process.
Fig. 3 (a) is a schematic view of a cut in consideration of a non-uniform material removal process, and fig. 3 (b) is a schematic view of a node of a single grid cell.
Fig. 4 is a schematic view of the cell states in the j-th layer grid after the i-th cut.
Fig. 5 is a schematic view of the cell states within the overall grid after the planar member cutting simulation is completed.
FIG. 6 is an initial internal stress state of a pure copper planar member at a plate thickness of 2.6 mm.
Fig. 7 is an optimized convergence curve for the PV value of the machined surface of a pure copper planar member.
Fig. 8 is a simulation of the machined surface of a pure copper planar member.
Detailed Description
The following describes specific embodiments of the present invention in detail with reference to the drawings and technical solutions.
A flow chart of a local bonding method facing to the minimization of stress deformation is shown in fig. 1, and the stress deformation of a planar member after the processing is finished is reduced by optimizing the bonding position of the planar member of a disc type, so that the processing surface shape precision of the planar member is improved. The detailed description of the embodiments of the present invention will now be described with reference to the accompanying drawings and specific embodiments, it being understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the invention.
Step one, according to fig. 2, the planar member is subjected to the combined action of cutting force and gravity during the cutting process. In order to ensure the bonding reliability of the planar member, the bonding force and the bonding torque provided by the bonding wax are required to meet the requirements of the stress balance and the torque balance of the planar member. The shape of the bonding units in the selected local bonding scheme is round, and the radius r of the units is selected to be 5mm. Therefore, the minimum number N of bonding points meeting the balance of the cutting stress in the horizontal direction h The following relationship can be used to determine:
wherein w is the shear strength of the bonding wax, F f For turning feed resistance, f s Is a safety factor.
Different from the horizontal stress condition of the plane member, the stress condition of the plane member in the vertical direction may be slightly different from the different random bed structures.
When the processing machine tool is of a front-mounted tool rest structure, the main shaft rotates forward, the main cutting force of the workpiece is opposite to the gravity direction of the workpiece, and the minimum bonding point number N of the cutting stress balance in the vertical direction is met vq The method can be obtained by the following formula:
wherein R is the radius of the disc-like planar member, t is the thickness of the planar member, ρ is the material density of the member, F c The main cutting force is the turning.
When the processing machine tool is of a rear-mounted tool rest structure, the main shaft rotates forward, the main cutting force of the workpiece is the same as the gravity direction of the workpiece, and the minimum bonding point number N of the cutting stress balance in the vertical direction is met vh The method can be obtained by the following formula:
due to N vh Constant greater than N vq Thus selecting N vh The minimum number N of bonding points meeting the stress balance in the vertical direction v Wherein N is v ＝N vh . Further, according to max (N v ，N h ) And (5) primarily selecting the number N of bonding points meeting the stress balance condition of the plane member.
And step two, defining the center of the bottom surface of the workpiece as the origin (0, 0) of the coordinate system under the coordinate system of the machine tool, wherein the Z-direction height is 0 because the bonding unit is positioned on the bottom surface of the workpiece. The bonding point is expressed in polar form as (R i ，θ i ) Wherein 0.ltoreq.R i ≤R-r,0≤θ i And (3) initializing bonding point position combinations. In order to ensure the clamping stability of the workpiece, the circumferential moment generated by the shearing force between the workpiece and the rubber layer needs to satisfy the following relation:
when the circumferential moment of the planar member meets the relation, the bonding position sequence is directly output. Otherwise a new bond point (R n+1 ，θ n+1 ) The bonding points are added to the bonding position sequence and an n=n+1 operation is performed to update the number of bonding points, which is repeated until the equation (4) is established. Setting the maximum number N of bonding points max 1.5 times the number of initial adhesive points, provided that the number N of adhesive points is greater than a predetermined number threshold N max And (3) if the condition in the formula (4) is not met, stopping iteration, judging that the bonding point position sequence of the group is unreasonable, reinitializing the bonding point position sequence, and executing the subsequent operation in the step two until the bonding point position combination meeting the clamping stability of the plane component is obtained.
Thirdly, carrying out parameterization modeling on the planar member by applying a Python secondary development technology, completing the setting of simulation parameters such as geometric characteristics, material properties and the like of the planar member in finite element software Abaqus, and locally restraining the planar member to process a positioning surface at the bonding point position sequence determined in the second step. The planar member is divided into a cutting layer and a base layer in the thickness direction, and the cutting layer is locally grid-thinned, wherein the grid type is an eight-node reduced integral hexahedral cell C3D8R. Reconstructing an initial internal stress field after grid refinement based on a shape function interpolation method, and then loading the initial internal stress field into a finite element analysis model.
Step four, as shown in fig. 3 (a), since the unbalance stress induced by the material removal is gradually released in the form of deformation of the component during the cutting process, the actual cutting depth of the tool at each processing position is not the same although the tool movement path is a straight line parallel to the workpiece positioning surface, which belongs to the non-uniform material removal process. And judging whether the unit is removed in the cutting process according to the axial relative position between the deformed grid unit integral points and the cutting plane by combining the unit death technology. As shown in FIG. 3 (b), for the ith cut, the kth cell E in the jth layer of the grid k Comprising 8 nodes n kd (d=0, 1 …, 7), the initial axial coordinate corresponding to each node is represented as Ncz kd (d=0, 1 …, 7). Node n at the ith cutting kd The actual Z-direction coordinate of the node is the accumulation of the initial axial coordinate of the node and the axial deformation of the node after the i-1 th cutting. Thus reading in odb result text generated after the i-1 th cutting simulationThe element extracts the initial Z-direction coordinate and the axial deformation value of the corresponding node, and then the element E is used for the ith cutting k Actual axial position coordinates Ecz of equivalent integral points k Can be calculated by equation (5).
In the middle ofRepresents the i-1 th cut grid node n kd Axial deformation of the workpiece, since the workpiece is not deformed yet during the first cutting, is +.>Satisfy equation->
Traversing and calculating the actual axial coordinates of all unit integral points in the jth grid, if the calculated result is higher than the axial height of the ith cutting plane, determining that the unit is killed in the ith cutting process, and storing the unit number in the ith cut removed grid set as shown in fig. 4Is a kind of medium. On the contrary, the judging unit "survives" during the ith cutting process, and stores the unit number thereof in the ith cutting non-removed grid set +.>Is a kind of medium. Determining the set of removed units layer by layer according to the above calculation procedure until all grids contained in the ith cut are traversed, and then "killing" the set +.>And submitting calculation to the corresponding grid unit until the ith simulation is completed. Will->The unit numbers in the list are directly stored in the removed unit number set E xc In->The set of unremoved cells contained in the cutting insert will participate in the subsequent simulation operation as part of the material to be removed in the (i+1) th cutting. And step four, the operation is circularly executed until the simulation calculation of the multiple feed cutting is completed.
Step five, after the multiple feed cutting simulation is completed, collecting E xc All units "killed" in each pass cutting simulation were included. Numbering set E of all cells of grid refinement layer x And set E xc Difference set E of (2) xu Representing a refinement layer unremoved set of cells. As shown in fig. 5, the mesh surface generated after the machining simulation is completed and the machining deformation corresponding to the mesh nodes together affect the final machining surface shape of the planar member. Thus traversing set E xc The initial Z-direction coordinates of the unit nodes in the superposition set correspond to the axial deformation of the nodes, and the minimum value of the calculated result represents the lowest point Z of the surface of the planar member after cutting is completed min . Traversing set E xu Calculating the true axial position of the unit nodes in the collection, wherein the maximum value of the result represents the highest point Z of the surface of the planar member after cutting max The surface shape PV value of the planar member can be determined by Z max -Z min And (5) calculating to obtain the product.
And step six, optimizing the position of the bonding unit by adopting a genetic algorithm with the minimum surface shape PV value of the planar member after multiple feeding cutting simulation as a target. Setting the maximum iteration number K max 230, when the iteration number J satisfies the condition J<K max And repeating the second step, the third step, the fourth step and the fifth step, generating a new bonding point position combination and calculating the surface shape PV value of the planar member under the clamping condition. Traversing the newly generated bonding point position sequence, judging that the bonding sequence has position overlapping if the center-to-center distance between the bonding unit i and the bonding unit j meets the condition shown in the formula (6), and adopting the unreasonable bonding schemeThe surface shape PV value of (2) is corrected to a preset maximum value of 500um. And outputting a bonding point position sequence generated by the J-th optimization and a corresponding surface shape PV value, and updating the iteration times J according to J=J+1. Number of iterations j=k max And (5) stopping the circulation, and ending the position optimization process of the bonding unit.
Specifically, taking a pure copper plane disc with a diameter of 200mm and a plate thickness of 2.6mm as an example: wherein, the diamond tool is used for cutting, the cutting depth is 10 mu m each time, and the cutting is continuously carried out for 5 times. The main cutting force of the pure copper plane component under the cutting parameters is lower than 5N, and the feeding resistance is lower than 1N. The density of the pure copper material is 8980kg/m3, and the shearing strength of the bonding wax is 2.314MPa by using a universal tensile testing machine. And combining the simulation parameters, and determining the number of the bonding points to be 17 according to the clamping stability judging model. Fig. 6 shows the initial stress state of a pure copper planar member at a plate thickness of 2.6mm, and fig. 7 shows the optimized convergence curve. Table 1 is the optimized position of the bonding unit under the coordinate system of the machine tool, and fig. 8 is a simulation diagram of the processing surface shape of the pure copper planar member under the bonding clamping condition. The result shows that optimizing the position of the bonding unit is helpful for reducing the processing deformation of the planar member under the bonding clamping condition.
Table 1 optimized bonding location combinations

Claims (1)

1. A local bonding clamping method for reducing turning deformation of disc plane members is characterized in that firstly, the number of bonding points is determined according to a given radius of a dot matrix bonding unit and a stress balance condition of the plane members, and the positions of the bonding points are initialized; the planar member multi-time cutting simulation model is built according to the method, an initial internal stress field is further applied, and the target member is locally restrained according to the determined bonding point position; on the basis, a non-uniform material removal technology is adopted to determine a removed grid set, and the PV value of the surface shape of the plane member after the processing is finished is submitted to calculation and determined; finally, optimizing the positions of the bonding points based on a genetic algorithm by taking the minimum processing deformation as a target until the optimal position sequence of the bonding lattice is finally obtained; the method comprises the following specific steps:
step one, the plane component is subjected to the combined action of cutting force and gravity in the cutting process; in order to ensure the bonding reliability of the planar member, the bonding force and the bonding torque provided by the bonding wax are required to meet the requirements of the stress balance and the torque balance of the planar member; the shape of the bonding units in the selected local bonding scheme is round, and the radius r of the bonding units is selected to be 2.5-7.5 mm according to the geometric dimension of the plane member; therefore, the minimum number N of bonding points meeting the balance of the cutting stress in the horizontal direction h The following relationship is used for the calculation:
wherein w is the shear strength of the bonding wax, F f For turning feed resistance, f s Is a safety coefficient;
different from the horizontal stress condition of the plane member, the stress condition of the plane member in the vertical direction is slightly different from the different random bed structures;
when the processing machine tool is of a front-mounted tool rest structure, the main shaft rotates forward, the main cutting force of the workpiece is opposite to the gravity direction of the workpiece, and the minimum bonding point number N of the cutting stress balance in the vertical direction is met vq The value is obtained from the following equation:
wherein R is the radius of the disc-like planar member, t is the thickness of the planar member, ρ is the material density of the member, F c The main cutting force is the turning;
when the processing machine tool is of a rear-mounted tool rest structure, the main shaft rotates forward, and the workpiece receives the cutting force and the gravity direction of the workpieceThe same minimum number N of bonding points meeting the cutting stress balance in the vertical direction vh The value is obtained from the following equation:
due to N vh Constant greater than N vq Thus selecting N vh The minimum number N of bonding points meeting the stress balance in the vertical direction v Wherein N is v ＝N vh The method comprises the steps of carrying out a first treatment on the surface of the Further, according to max (N v ,N h ) Initially selecting the number N of bonding points meeting the stress balance condition of the plane member;
step two, defining the center of the bottom surface of the workpiece as the origin (0, 0) of the coordinate system under the coordinate system of the machine tool, wherein the Z-direction height is 0 as the bonding unit is positioned on the bottom surface of the workpiece; the bonding point is expressed in polar form as (R i ,θ i ) Wherein 0.ltoreq.R i ≤R-r，0≤θ i Less than or equal to 2 pi, and then initializing bonding point position combinations; in order to ensure the clamping stability of the workpiece, the circumferential moment generated by the shearing force between the workpiece and the rubber layer needs to satisfy the following relation:
when the circumferential moment applied to the planar member meets the above relationship, the bonding position sequence R is directly output 1 ,θ 1 ,R 2 ,θ 2 …R n ,θ n ]The method comprises the steps of carrying out a first treatment on the surface of the Otherwise a new bond point (R n+1 ,θ n+1 ) Adding the bonding points to the bonding position sequence and performing an operation of n=n+1 to update the number of bonding points, and repeating the operation until the formula (4) is established; setting the maximum number N of bonding points max 1.1 to 1.8 times of the initial selection number of the bonding points, if the number N of the bonding points is larger than a preset number threshold N max If the condition of the formula (4) is not satisfied, stopping iteration, judging that the bonding point position sequence of the group is unreasonable, re-initializing the bonding point position sequence, and executingStep two, subsequent operation is carried out until an adhesive point combination meeting the clamping stability of the plane component is obtained;
thirdly, carrying out parameterization modeling on the planar member by applying a Python secondary development technology, completing the setting of geometric characteristics and material attribute simulation parameters of the planar member in finite element software Abaqus, and locally restraining the planar member to process a positioning surface at the bonding point position sequence determined in the second step; dividing the planar member into a cutting layer and a substrate layer along the thickness direction, and carrying out local grid refinement on the cutting layer, wherein the grid type is an eight-node reduced integral hexahedral unit C3D8R; reconstructing an initial internal stress field after grid refinement based on a shape function interpolation method, and then loading the initial internal stress field into a finite element analysis model;
step four, because the unbalance stress induced by material removal is gradually released in the form of component deformation in the cutting process, although the moving track of the cutter is a straight line parallel to the positioning surface of the workpiece, the actual cutting depth of the cutter at each processing position is different, and the non-uniform material removal process is realized; judging whether the unit is removed in the cutting process according to the axial relative position between the integration points of the deformed grid units and the cutting plane by combining the unit death technology; specifically, for the ith cut, the kth cell E in the jth layer of grid k Comprising 8 nodes n kd D=0, 1 …,7, the initial axial coordinate corresponding to each node being indicated as Ncz kd The method comprises the steps of carrying out a first treatment on the surface of the Node n at the ith cutting kd The actual Z-direction coordinate of the node is the accumulation of the initial axial coordinate of the node and the axial deformation of the node after the i-1 th cutting; reading in odb result file generated after i-1 cutting simulation, extracting initial Z-direction coordinate and axial deformation value of corresponding node, and obtaining unit E during i cutting k Actual axial position coordinates Ecz of equivalent integral points k Can be calculated by equation (5):
in the method, in the process of the invention,represents the i-1 th cut grid node n kd I.gtoreq.1, since the workpiece has not yet been deformed during the first cutting, is +.>Satisfy equation->
Traversing and calculating the actual axial coordinates of all unit integral points in the jth grid, if the calculated result is higher than the axial height of the ith cutting plane, judging that the unit is killed in the ith cutting process, and storing the unit numbers in the ith cut removed grid setIn (a) and (b); on the contrary, the determination unit "survives" in the ith cut, and stores the unit number thereof in the ith cut non-removed grid set +.>In (a) and (b); determining the set of removed units layer by layer according to the above calculation procedure until all grids contained in the ith cut are traversed, and then "killing" the set +.>Submitting calculation to the corresponding grid unit until the ith simulation is completed; will->The unit numbers in the list are directly stored in the removed unit number set E xc In->The set of unremoved units contained in the cutting tool is used as the set to be removed in the (i+1) th cutting toolA portion of the material that participates in performing subsequent simulation operations; circularly executing the operation in the step four until the simulation calculation of the multiple feed cutting is completed;
step five, after the multiple feed cutting simulation is completed, collecting E xc All units for killing in each feed cutting simulation are included; numbering set E of all cells of grid refinement layer x And set E xc Difference set E of (2) xu Representing a refinement layer unremoved set of cells; traversing set E xc The initial Z-direction coordinates of the unit nodes in the superposition set correspond to the axial deformation of the nodes, and the minimum value of the calculated result represents the lowest point Z of the surface of the planar member after cutting is completed min The method comprises the steps of carrying out a first treatment on the surface of the Traversing set E xu Calculating the true axial position of the unit nodes in the collection, wherein the maximum value of the result represents the highest point Z of the surface of the planar member after cutting max The surface shape PV value of the planar member passes Z max -Z min Calculating to obtain;
step six, optimizing the position of a local bonding point by adopting a genetic algorithm with the minimum surface shape PV value of the planar member after multiple feeding cutting simulation as a target; setting the maximum iteration number K according to the calculation efficiency requirement max The value range is 200-300 generations, when the iteration times J meet the condition J<K max Repeating the second, third, fourth and fifth steps to generate a new bonding point position sequence and calculate the surface shape PV value of the planar member under the clamping condition; traversing and comparing the generated bonding point position sequences, judging that the bonding sequences have position overlapping if the center distance between the bonding units i and j meets the condition shown in the formula (6), and correcting the surface shape PV value under the unreasonable bonding scheme to be a preset maximum value; outputting a bonding point position sequence generated by the J-th optimization and a corresponding surface shape PV value, and updating iteration times J according to J=J+1; number of iterations j=k max Stopping the circulation and ending the optimization process of the bonding point position;
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