A surface forming processing line layout and processing strain calculation method and application
Through finite element model and linear fitting technology, the problem of difficulty in obtaining strain values in complex curvature sheet processing is solved, and the surface expansion and strain values are accurately calculated. It is suitable for different surface shapes, improving the level of processing refinement and intelligence .
Patent Information
- Application Number
- CN202311757548.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-12-20
- Publication Date
- 2024-12-06
- Estimated Expiration
- 2043-12-20
AI Technical Summary
The existing technology cannot effectively and intelligently obtain the strain value in complex curvature sheet processing, which leads to difficulty in determining processing circuit layout and process parameters, and cannot meet the refined needs of complex curvature sheet processing.
By setting the initial machining path, a finite element model of the target surface is constructed, the strain field is calculated, and the strain value on the machining path is obtained using linear fitting. By repeatedly iteratively adjusting until the preset deviation threshold is met, the surface expansion and strain value are realized. Accurate calculation.
It realizes the efficient calculation of the precise processing circuit arrangement and strain value of complex curvature sheets, can adapt to different curved surface shapes, and improves the level of processing refinement and intelligence.
Smart Images
Figure CN117807724B_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field related to complex curvature plate forming, and more specifically, relates to a curved surface forming processing line layout and a processing strain calculation method and application. Background Art
[0002] Curved plates in engineering are usually processed from flat plates. In the complex curvature plate forming process, the layout of the processing line and the determination of the processing parameters are important bases for achieving accurate processing. Therefore, the processing line layout should have the following characteristics: (1) The layout position of the processing line and the strain value to be processed on the processing line should be obtained; (2) The initial flat plate shape required for the forming process should be obtained, and the initial flat plate shape should be able to be processed into the target curved surface shape. The initial flat plate shape can be determined by surface unfolding the target curved plate shape. At the same time, the strain generated during the surface unfolding process can be used to formulate the processing plan.
[0003] At present, the commonly used processing line layout is determined based on manual experience or geometric curvature shape, and it is usually impossible to obtain a direct correspondence between the target shape and the processing parameters. The existing processing line layout and processing strain calculation method cannot meet the requirements of further intelligent and refined processing technology for complex curvature plates. Summary of the invention
[0004] In view of the above defects or improvement needs of the prior art, the present invention provides a curved surface forming processing line layout and a processing strain calculation method and application to solve the problem that strain values cannot be obtained intelligently and finely in the processing technology of complex curvature plates.
[0005] To achieve the above object, according to one aspect of the present invention, a method for arranging a curved surface forming processing line and calculating processing strain is provided, the method comprising the following steps:
[0006] S1 sets an initial processing path, constructs a finite element model of a target surface, sets material properties and material directions on the finite element model, unfolds the target surface on a plane to solve the strain field of each cell on the target surface during the unfolding process, projects the initial processing path on the target surface, and uses the strain field of each cell to solve the required strain value of any point on the initial processing path;
[0007] S2 uses a straight line to fit the initial processing path to obtain a straight processing path, and at the same time, according to the final strain value of any point on the initial processing path, uses a constant function to fit the strain value of any point on the straight processing path, so as to obtain the strain value of any point on the straight processing path;
[0008] S3 applies the strain value of any point on the straight machining path in step S2 to the initial shape to be machined, solves the deformation corresponding to the strain value, uses the deformed shape as the predicted shape, compares the predicted shape with the target surface and calculates the deviation. When the deviation is less than the preset deviation threshold, outputs the current straight machining path and the corresponding strain value. When the deviation is greater than the preset deviation threshold, superimposes the deviation with the target surface to obtain a new surface shape. The new surface shape is used as the new target surface and the initial machining path is kept. Return to step S1 to obtain a new straight machining path and the corresponding strain value until the preset deviation threshold is met.
[0009] Further preferably, in step S1, the initial processing path is set according to an orthogonal grid, a principal curvature line, or a combination of the two.
[0010] Further preferably, in step S1, the material properties are set according to the stiffness matrix of the target surface. For the bending stiffness part, an isotropic material is used. For the in-plane stiffness part, the constitutive tensor of the material is set according to the following relationship:
[0011]
[0012] Among them, the subscripts 1 and 2 represent the 1 and 2 directions of the material coordinate system, the coefficient m should satisfy m>1, typically m=100, and the parameter E t ,E c are the elastic modulus of the material under tension and compression, respectively, and the parameter γ 11 ,γ 22 are the strain values of the material in the 1st and 2nd directions in the material coordinate system, C ···· Represents the components of the constitutive tensor in the 1 and 2 directions of the material coordinate system.
[0013] Further preferably, in step S1, the strain field of each cell on the target surface is calculated according to the steps:
[0014] (1) Calculate the stiffness matrix of each cell;
[0015] (2) Calculate the stiffness matrix of the entire target surface;
[0016] (3) according to the set load and boundary conditions, and in combination with the overall stiffness matrix, obtaining the equation for the displacement of each unit cell node, and solving the displacement of each node;
[0017] (4) Use the displacement of each node to calculate the strain field corresponding to each unit cell.
[0018] Further preferably, in step S1, the strain value of any point on the initial processing path is obtained in the following manner: for any point on the processing path, a plurality of grid units distributed on the processing path according to preset rules are selected in a direction perpendicular to the processing path, and the average value of the strain values of all the selected grid units is calculated, and the average value is used as the initial strain value at the arbitrary point.
[0019] Further preferably, the initial strain value at any point on the initial processing path includes an in-plane strain value and a bending strain value.
[0020] Further preferably, for initial processing paths set in different ways, the final strain value at any point is obtained in different ways.
[0021] Further preferably, for a processing path according to an orthogonal grid line or a principal curvature line, the final strain value at any point is the initial strain value; for a processing path set in a manner combining an orthogonal grid and a principal curvature, the in-plane strain value on the orthogonal grid is used as the final strain value, and the bending strain value on the principal curvature is used as the final strain value.
[0022] According to another aspect of the present invention, a system for arranging a curved surface forming processing line and calculating processing strain is provided, comprising a processor for executing the above-mentioned calculation method.
[0023] According to another aspect of the present invention, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the above-mentioned curved surface forming processing line arrangement and processing strain calculation method are implemented.
[0024] In general, the above technical solutions conceived by the present invention have the following beneficial effects compared with the prior art:
[0025] 1. The present invention calculates the strain field developed from the target surface to the plane, and reversely infers the strain field from the initial plane to the target surface based on the calculated strain field. This method is easy to implement, and can obtain the corresponding developed shape of the target surface while calculating the strain distribution, and obtain the position of the processing line on the initial plane;
[0026] 2. The present invention proposes a processing line arrangement and processing strain calculation method that can be adapted to different curved surface shapes. For different curved surface shapes, curvature lines can be obtained according to the curved surface shapes as processing lines. For particularly complex curved surfaces, grid lines can also be used as processing lines.
[0027] 3. In the material property setting, the present invention adopts a material based on tensile and compressive dual modulus for the in-plane stiffness part. When the material is stretched, the material has a smaller stiffness and is more likely to deform, thereby generating more tensile strain and less shrinkage deformation, making the strain distribution more regular, which is conducive to process implementation;
[0028] 4. The present invention improves the efficiency of strain value calculation. The solution can complete the strain calculation in a single surface unfolding finite element calculation, efficiently obtain the unfolded shape and strain distribution, and extract the strain value on the processing line. BRIEF DESCRIPTION OF THE DRAWINGS
[0029] Figure 1 It is a flow chart of the curved surface forming processing line arrangement and processing strain calculation method constructed according to the preferred embodiment of the present invention;
[0030] Figure 2 is a schematic diagram of a processing line arrangement constructed according to a preferred embodiment of the present invention;
[0031] Figure 3 It is a schematic diagram of the stress-strain relationship of a dual-modulus material constructed according to a preferred embodiment of the present invention. DETAILED DESCRIPTION
[0032] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.
[0033] Curved panel forming processing refers to the process of processing a plate from an initial shape, generally a flat plate, to a specific target shape. This processing process is usually completed by a processing tool moving and loading on the plate along a processing path. Therefore, the processing path and processing tool parameters are important steps to achieve forming processing. According to the target surface shape, the process of determining the initial shape is generally called surface unfolding. The present invention proposes a processing path layout scheme and calculates the processing strain value based on the surface unfolding result, which is used to determine the processing tool parameters.
[0034] like Figure 1 As shown, the specific steps of a curved surface forming processing line layout and processing strain calculation method are as follows:
[0035] S1 obtains the strain value of any point on the processing path
[0036] Step 1: Arrange the machining path
[0037] Arrange the processing path on the board to be processed. The processing path can adopt the following three modes:
[0038] (i) The processing path can be arranged in the form of orthogonal grid lines, which refer to horizontal and vertical lines parallel to the four sides of the rectangular plate.
[0039] (ii) The processing path can also be arranged according to the principal curvature line. The principal curvature line refers to the curve connecting the directions of maximum or minimum curvature at each point on the spatial surface.
[0040] (iii) The processing path can also be arranged in a manner of combining orthogonal grid lines with principal curvature lines, that is, taking some orthogonal grid lines and some principal curvature lines as the processing path. Typically, grid lines parallel to the long side direction and principal curvature lines in the direction of greater curvature are taken.
[0041] Processing passes should be evenly spaced to provide complete coverage of the sheet.
[0042] Step 2: Create a finite element model
[0043] Establish a finite element model of the target surface. The steps to establish a finite element model are the same as those of a general structural static analysis finite element model. Specifically, it can be described as follows: 1. Establish a geometric model to express the shape of the target surface in the program. 2. Divide the grid and discretize the geometric model into a grid. 3. Set unit properties, set the unit type and material parameters of each unit, use plate and shell units, and set the integration method. 4. Set loads and boundary conditions, and deform the target surface shape to the initial shape by applying forced displacement, and no constraints are imposed on the tangent direction of the surface, so it can move freely.
[0044] This step can be performed in a general finite element method or by writing a self-developed program.
[0045] Step 3: Set material parameters
[0046] (1) Set material properties
[0047] Separate the in-plane deformation stiffness and bending deformation stiffness in the stiffness matrix. Specifically:
[0048] For the bending stiffness part, a general isotropic material is used;
[0049] For the in-plane stiffness part, a hypothetical material is used. This hypothetical material model is based on a tensile-compressive dual modulus material. Its main feature is that the material has different stiffness when stretched and compressed. The components of the material's constitutive tensor can be specifically described as follows.
[0050]
[0051] In the above formula, the subscripts 1 and 2 represent the 1 and 2 directions of the material coordinate system, C···· It represents the components of the constitutive tensor in the 1 and 2 directions of the material coordinate system. The coefficient m should satisfy m>1, typically m=100. The parameter E t ,E c Respectively represent the elastic modulus of the material under tension and compression, parameter γ 11 ,γ 22 They represent the strain values of the material in the 1st and 2nd directions in the material coordinate system, and can typically be taken as E c =E,E t =nE, where 0<n<1. The typical value of n is 0.01, and E represents the elastic modulus of the material, and the typical value is the elastic modulus of general steel. At this time, the shrinkage stress generated in the surface development calculation will be much greater than the tensile stress, resulting in more tensile strain.
[0052] (2) Set the material direction
[0053] Different material directions should be set for different processing paths.
[0054] (i) For machining paths that use an orthogonal grid or a combination of an orthogonal grid and principal curvature lines, the direction of the material coordinate system should be along the direction of the orthogonal coordinate system.
[0055] (ii) For the main curvature line processing path, the direction of the material coordinate system should be along the main curvature direction of each point.
[0056] Step 4: Perform finite element calculation on the surface to calculate the strain that will be produced in the material after processing, that is, how much strain needs to be applied from the initial processing surface to the target surface.
[0057] Unfold the target surface onto a plane. The steps of finite element solution are the same as those of general structural static analysis, which can be described as follows: (1) Calculate the unit stiffness matrix; (2) Assemble the overall stiffness matrix; (3) Obtain equations for node displacements based on loads and boundary conditions; Solve the node displacement solutions; (4) Solve the strain field.
[0058] Step 5: Map the calculated strain field to the processing path
[0059] The strain values on the machining path are extracted from the results of the surface unfolding finite element calculation. In the surface unfolding finite element calculation results, at each point on the surface, the strain value contains different strain value components. First, according to the strain value at the cross-section layer integration point, the in-plane strain and bending strain value of each unit are calculated respectively.
[0060] For a set of processing paths, all units in the finite element model are assigned to a processing line nearby. For any point on the processing line, multiple units assigned to this processing line are selected in the direction perpendicular to the processing line, and the average strain of these units is calculated as the initial strain value to be processed at this point, including the in-plane strain value and the bending strain value.
[0061] For different types of machining paths, different strain values are extracted as the final strain values:
[0062] (i) For the orthogonal grid line or principal curvature line processing path, the in-plane strain value and bending strain value on each processing path are extracted respectively.
[0063] (ii) For the processing path combining orthogonal grid lines and principal curvature lines, the in-plane strain values are extracted on the orthogonal grid lines, and the bending strain values are extracted on the principal curvature lines.
[0064] S2 performs engineering processing on machining paths and strain values
[0065] (I) Broken line equivalence of the curvature line of a curve. For complex surfaces, the curvature line is usually in the form of a spatial curve. In order to facilitate processing, it is necessary to use a broken line to equate the curve.
[0066] First, fit the curve with a straight line, specifically:
[0067] The maximum distance between the processing curve and the fitting straight line is calculated. If the distance meets the allowable deviation value, it is considered equivalent. If the distance exceeds the allowable deviation value, the number of polyline segments is increased and refitting is performed until the deviation meets the allowable value. The final fitting polyline is used as the processing path.
[0068] (II) Segmental equivalence of continuously changing strain distribution. The distribution of strain values on the processing path is usually changing. In order to facilitate the determination of processing tool parameters, the continuously changing strain values need to be equivalent to segmented forms.
[0069] For each machining path, the changing strain value is first fitted with a constant function. The maximum deviation between the strain value and the fitting value is calculated; if the deviation meets the allowable value, it is considered equivalent. If the deviation exceeds the allowable value, the number of segments is increased and refitted until the deviation is satisfied. The final fitted piecewise function is used as the strain value of the machining path.
[0070] S3 strain value verification
[0071] The obtained strain is verified by the elastic finite element method. The strain value extracted and processed by engineering is applied as a load to the initial shape. The deformation corresponding to the strain value is calculated by finite element solution as the predicted shape. The predicted shape is compared with the target surface shape:
[0072] (1) If the deviation is less than the specified range, the process ends, and the initial shape corresponding to the target shape, the machining path, and the machining strain value corresponding to the machining path are finally obtained.
[0073] (2) If the deviation is greater than the specified range, the strain value needs to be corrected. The result correction is performed using the inverse deformation iteration method. The inverse deformation iteration method can be described as follows: first, the shape deviation is calculated based on the predicted shape obtained from the strain value and the target shape, and the shape deviation is superimposed on the target shape to obtain a new design shape. Based on the new design shape and keeping the original initial processing path, return to step S1 and recalculate the strain value until the shape deviation meets the deviation requirement.
[0074] like Figure 2 As shown, the processing line layout and the curved surface forming processing process are shown in the figure. The processing tool moves and loads along the processing line in the form of grid lines or curvature lines to process the flat plate into a curved surface shape.
[0075] like Figure 3 The stress-strain relationship of the bimodular material is shown in the figure. The stress-strain relationship of the material is different when it is under tension and compression. t Indicates the elastic modulus of the material under tension, E c Indicates the elastic modulus of the material under pressure, E t <E c The material deforms more easily when it is in tension, resulting in more tensile strain.
[0076] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.
Claims
1. A curved surface forming processing line layout and processing strain calculation method, characterized in that: The method comprises the following steps: S1 sets an initial processing path, constructs a finite element model of a target surface, sets material properties and material directions on the finite element model, unfolds the target surface on a plane to solve the strain field of each cell on the target surface during the unfolding process, projects the initial processing path on the target surface, and uses the strain field of each cell to solve the required strain value of any point on the initial processing path; S2 uses a straight line to fit the initial processing path to obtain a straight processing path, and at the same time, according to the final strain value of any point on the initial processing path, uses a constant function to fit the strain value of any point on the straight processing path, so as to obtain the strain value of any point on the straight processing path; S3 applies the strain value of any point on the straight machining path in step S2 to the initial shape to be machined, solves the deformation corresponding to the strain value, takes the deformed shape as the predicted shape, compares the predicted shape with the target surface and calculates the deviation, when the deviation is less than the preset deviation threshold, outputs the current straight machining path and the corresponding strain value, when the deviation is greater than the preset deviation threshold, superimposes the deviation with the target surface to obtain a new surface shape, takes the new surface shape as the new target surface and keeps the initial machining path unchanged and returns to step S1, solves to obtain a new straight machining path and the corresponding strain value, until the preset deviation threshold is met, thereby obtaining the straight machining path and the corresponding strain value; The processing tool is moved and loaded along the straight processing route and strain value in the form of grid lines or curvature lines to process the flat plate into a curved surface shape.
2. A curved surface forming processing line arrangement and processing strain calculation method as claimed in claim 1, characterized in that: In step S1, the initial processing path is set according to an orthogonal grid, a principal curvature line, or a combination of the two.
3. A curved surface forming processing line arrangement and processing strain calculation method as claimed in claim 1, characterized in that: In step S1, the material properties are set according to the stiffness matrix of the target surface. For the bending stiffness part, an isotropic material is used. For the in-plane stiffness part, the constitutive tensor of the material is set according to the following relationship: Among them, the subscripts 1 and 2 represent the 1 and 2 directions of the material coordinate system, the coefficient m should satisfy m>1, typically m=100, and the parameter E t ,E c are the elastic modulus of the material under tension and compression, respectively, and the parameter γ 11 ,γ 22 are the strain values of the material in the 1st and 2nd directions in the material coordinate system, C .... Represents the components of the constitutive tensor in the 1 and 2 directions of the material coordinate system.
4. A curved surface forming processing line arrangement and processing strain calculation method as claimed in claim 1, characterized in that: In step S1, the strain field of each cell on the target surface is calculated according to the steps: (1) Calculate the stiffness matrix of each cell; (2) Calculate the stiffness matrix of the target surface as a whole; (3) according to the set load and boundary conditions, and in combination with the overall stiffness matrix, obtaining the equation for the displacement of each unit cell node, and solving the displacement of each node; (4) Use the displacement of each node to calculate the strain field corresponding to each unit cell.
5. A curved surface forming processing line arrangement and processing strain calculation method as claimed in claim 1, characterized in that: In step S1, the strain value of any point on the initial processing path is obtained in the following manner: for any point on the processing path, multiple grid units distributed on the processing path according to preset rules are selected in a direction perpendicular to the processing path, and the average value of the strain values of all selected grid units is calculated, and the average value is used as the initial strain value at the arbitrary point.
6. A curved surface forming processing line arrangement and processing strain calculation method as claimed in claim 5, characterized in that: The initial strain value at any point on the initial processing path includes an in-plane strain value and a bending strain value.
7. A curved surface forming processing line arrangement and processing strain calculation method as claimed in claim 6, characterized in that: For initial machining paths set in different ways, the final strain value at any point is obtained in different ways.
8. A curved surface forming processing line arrangement and processing strain calculation method as claimed in claim 7, characterized in that: For machining paths according to orthogonal grid lines or principal curvature lines, the final strain value at any point is the initial strain value; for machining paths set in a combination of orthogonal grids and principal curvatures, the in-plane strain value on the orthogonal grid is taken as the final strain value, and the bending strain value on the principal curvature is taken as the final strain value.
9. A system for arranging curved surface forming processing lines and calculating processing strains, characterized in that: The method comprises a processor configured to execute the calculation method according to any one of claims 1 to 8.
10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the surface forming processing line arrangement and processing strain calculation method described in any one of claims 1 to 8 are implemented.