A method for generating a generalized thread precision finite element model

Abstract

The application discloses a method for generating a general screw thread precision finite element model, comprising the following steps: S1: acquiring basic physical parameters and finite element grid node data of a bolt, and performing coordinate conversion; S2: judging whether to generate an external thread contour, if yes, entering step S3, otherwise, entering step S4; S3: performing contour offset operation on the thread finite element grid node, and entering step S4; S4: judging whether to generate an internal thread contour, if yes, entering step S5, otherwise, entering step S6; S5: performing contour offset operation on the nut finite element grid node, and entering step S6; S6: converting the cylindrical coordinates of the finite element grid node data into Cartesian coordinates, and replacing the original finite element grid node data with the finite element grid node data after the contour offset operation. The application can efficiently and accurately obtain various screw thread precision finite element models in a large quantity without manual calculation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of thread finite element model, and particularly relates to a method for generating a general thread precision finite element model. BACKGROUND

[0002] In the field of bolt precision finite element research, due to technical limitations, the research progress is relatively slow, and at present, the research on the precision finite element model at home and abroad is basically focused on the research on standard metric threads. Research on non-standard thread profiles is beneficial to improve the performance of thread fastening, anti-loosening and the like, but there is no relevant research on the general profile formula of the non-standard thread profile in the current domestic and foreign literature. The lack of advanced theory leads to no one to study the method for generating a general thread precision finite element model. SUMMARY

[0003] The purpose of the application is to solve the problem that the non-standard thread has no corresponding profile formula, resulting in the inability to generate a precision finite element model, and a method for generating a general thread precision finite element model is proposed.

[0004] The technical scheme of the application is that a method for generating a general thread precision finite element model comprises the following steps:

[0005] S1: Obtain the basic physical parameters of the bolt and the finite element grid node data, and convert the Cartesian coordinates of the finite element grid node data to cylindrical coordinates, wherein the finite element grid node data comprises thread finite element grid nodes and nut finite element grid nodes;

[0006] S2: Determine whether to generate an external thread profile according to the basic physical parameters of the bolt, if yes, go to step S3, otherwise go to step S4;

[0007] S3: Perform profile offset operation on the thread finite element grid nodes, and go to step S4;

[0008] S4: Determine whether to generate an internal thread profile according to the basic physical parameters of the bolt, if yes, go to step S5, otherwise go to step S6;

[0009] S5: Perform profile offset operation on the nut finite element grid nodes, and go to step S6;

[0010] S6: Convert the cylindrical coordinates of the finite element grid node data to Cartesian coordinates, replace the original finite element grid node data with the finite element grid node data after the profile offset operation, and obtain a general thread precision finite element model.

[0011] Further, in step S1, the basic physical parameters of the bolt include bolt physical parameters, profile segmentation points and bolt finite element grid node information; wherein the bolt physical parameters include nominal diameter Threaded pitch Threaded pitch fraction N P Number of dense grid layers n m Threaded direction, tooth angle Top cutting amount Bottom cutting amount Thread original triangle height H Calculated diameter External thread root radius 、 Internal thread nominal diameter D Internal thread pitch diameter D 2and internal thread root radius ; finite element grid node information includes bolt head, bolt rod, nut, whether to generate external thread and whether to generate internal thread; profile segmentation points include first profile segmentation point Second profile segmentation point Third profile segmentation point And fourth profile segmentation point .

[0012] Further, the calculation formulas of the first profile segmentation point Second profile segmentation point Third profile segmentation point And fourth profile segmentation point are as follows:

[0013]

[0014]

[0015]

[0016]

[0017] Wherein, The bottom cutting amount is represented by b, The tooth angle is represented by a, The top cutting amount is represented by t, H The thread original triangle height is represented by h.

[0018] Further, step S3 includes the following sub-steps:

[0019] S31: Obtain the column coordinates of the threaded finite element grid nodes, and take the threaded finite element grid nodes with the r Axis coordinate value in To As a multi-layer dense grid node, wherein, , Indicates the number of dense grid layers. d Indicates the nominal diameter. Indicates the height of the dense grid layer. Indicates the pitch as a fraction. P Indicates the thread intercept;

[0020] S32: Perform contour offset operation on the outermost node of the multi-layer dense mesh node, and perform position uniform distribution operation on the multi-layer dense mesh nodes between the outermost node and the innermost node.

[0021] S33: The cylindrical coordinates after the position distribution operation. z The axis coordinate values ​​are in arrive The multi-layered dense mesh nodes within are used as spiral tail dense mesh nodes, where, Indicates the number of pitches to be drawn;

[0022] S34: Set the offset coefficient, use the offset coefficient to perform a contour offset operation on the outermost node of the spiral tail dense mesh node so that the offset of the spiral tail dense mesh node is 0, and perform a position uniform distribution operation on the spiral tail dense mesh nodes between the outermost node and the innermost node.

[0023] Furthermore, in step S32, the calculation formula for the contour offset operation is as follows:

[0024]

[0025] in, Indicates the coordinates of the external thread column. θ Representing cylindrical coordinates θ Data for the independent variables of the coordinate axes, d Indicates the nominal diameter. Indicates the calculated diameter. z Representing cylindrical coordinates z Data for the independent variables of the coordinate axes, This indicates the root radius of the external thread. Indicates the thread intercept. Indicates the tooth angle. Indicates the segmentation point of the first contour. Indicates the segmentation point of the second contour. Indicates the segmentation point of the third contour. Indicates the segmentation point of the fourth contour;

[0026] In step S32, the specific method for performing the position distribution operation is as follows: the multi-layer dense grid nodes between the outermost node and the innermost node are evenly divided at intervals.

[0027] Furthermore, step S5 includes the following sub-steps:

[0028] S51: Obtain the cylindrical coordinates of the finite element mesh nodes of the nut, and convert the cylindrical coordinates to... r The axis coordinate values ​​are in arrive The finite element mesh nodes within the nut are used as multi-layer dense mesh nodes for the nut. Indicates the number of dense grid layers. Indicates the height of the dense grid layer. d Indicates the nominal diameter;

[0029] S52: Perform a contour offset operation on the innermost node of the multi-layer dense mesh node of the nut, and perform a position uniform distribution operation on the multi-layer dense mesh nodes between the outermost node and the innermost node.

[0030] Furthermore, in step S52, the calculation formula for the contour offset operation is as follows:

[0031]

[0032] in, Indicates the coordinates of the internal thread cylinder. P Indicates the thread intercept. Representing cylindrical coordinates Data for the independent variables of the coordinate axes, d Indicates the nominal diameter. D Indicates the nominal diameter of the internal thread. Indicates the pitch diameter of the internal thread. Indicates the radius of the internal thread root. z Representing cylindrical coordinates z Data for the independent variables of the coordinate axes, Indicates the tooth angle. Indicates the segmentation point of the first contour. Indicates the segmentation point of the second contour. Indicates the segmentation point of the third contour. This indicates the segment point of the fourth contour.

[0033] The beneficial effects of this invention are:

[0034] (1) The generalized thread profile theory proposed in this invention can not only quickly generate various standard profiles that conform to the generalized profile definition, such as existing standard metric thread profiles, aerospace MJ thread profiles, American unified UN thread profiles, and German standard thread profiles, but also provides a way to generate various non-standard thread profiles. This invention is a major advancement in the existing theory of bolt precision finite element research, achieving a breakthrough from only being able to generate finite element models of ordinary metric threads to being able to quickly generate finite element models of various standard and non-standard threads, and realizing stepless adjustment of thread profile parameters.

[0035] (2) The application can efficiently and accurately obtain various thread precision finite element models in large quantities without manual calculation. The professional and complex mesh drawing work is improved from manual calculation of key node information and program assisted offset mesh to pure algorithm drawing after inputting the contour, which lays a technical foundation for subsequent improvement of the bolt contour. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 A flowchart of a method for generating a generalized thread precision finite element model is provided for the embodiments of the application;

[0037] Figure 2 A structure and parameter diagram of a generalized thread contour is provided;

[0038] Figure 3 A schematic diagram of position uniform operation on the mesh between the innermost layer and the outermost layer is provided;

[0039] Figure 4 A schematic diagram of dense mesh transformation into external thread mesh is provided;

[0040] Figure 5 A schematic diagram of a generalized thread contour precision finite element model is provided. DETAILED DESCRIPTION

[0041] The embodiments of the application will be further described below with reference to the accompanying drawings.

[0042] As shown in Figure 1 , the application provides a method for generating a generalized thread precision finite element model, comprising the following steps:

[0043] S1: Obtain the basic physical parameters and finite element mesh node data of the bolt, and convert the Cartesian coordinates of the finite element mesh node data to cylindrical coordinates, wherein the finite element mesh node data includes thread finite element mesh nodes and nut finite element mesh nodes;

[0044] S2: Determine whether to generate an external thread contour according to the basic physical parameters of the bolt, if yes, go to step S3, otherwise go to step S4;

[0045] S3: Perform contour offset operation on the thread finite element mesh nodes, and go to step S4;

[0046] S4: Determine whether to generate an internal thread contour according to the basic physical parameters of the bolt, if yes, go to step S5, otherwise go to step S6;

[0047] S5: Perform contour offset operation on the nut finite element mesh nodes, and go to step S6;

[0048] S6: Convert the cylindrical coordinates of the finite element mesh node data to Cartesian coordinates, replace the original finite element mesh node data with the finite element mesh node data after the profile offset operation, and obtain the generalized screw thread precision finite element model.

[0049] Before describing the computer program flow, the definition of the generalized thread profile needs to be proposed first. The structural definition of the generalized thread profile is as follows Figure 2 As shown, the details are that the thread root circle is tangent to the thread flank; the thread top is flat; and the original triangle is an isosceles triangle. By changing the thread angle , the top cutting amount , and the bottom cutting amount three variables, various non-standard threads can be generated.

[0050] The definition is based on the structures of the current standard metric thread profile, the aviation MJ thread profile, the unified UN thread profile, and the German standard thread profile. The structural features of all the above threads are extracted and extended, and finally the definition is obtained. All the above-mentioned standard thread profiles belong to the specific structure generated by the generalized thread profile at the thread angle , the top cutting amount , and the bottom cutting amount taking specific values.

[0051] In the embodiment of the present application, in step S1, the basic physical parameters of the bolt include bolt physical parameters, profile segmentation points, and bolt finite element mesh node information; wherein the bolt physical parameters include nominal diameter d , thread intercept P , pitch fraction N P , dense grid layers n m , thread rotation direction (right-handed, left-handed), thread angle , top cutting amount , bottom cutting amount , thread original triangle height H, calculation diameter , thread root radius of external thread , nominal diameter D of internal thread, pitch diameter D2 of internal thread, and thread root radius of internal thread ; the finite element mesh node information includes bolt head, bolt rod, nut, whether to generate external thread, and whether to generate internal thread; the profile segmentation points include first profile segmentation point , second profile segmentation point , third profile segmentation point , and fourth profile segmentation point .

[0052] In the embodiment of the present application, the first profile segmentation point θ1. Second contour segmentation point θ 2. Third contour segmentation point θ 3 and the fourth contour segmentation point θ The formulas for calculating 4 are as follows:

[0053]

[0054]

[0055]

[0056]

[0057] in, h root Indicates the amount of material removed from the bottom. α Indicates the tooth angle. h top Indicates the amount of material removed at the top. H This indicates the original triangle height of the thread.

[0058] In this embodiment of the invention, step S3 includes the following sub-steps:

[0059] S31: Obtain the cylindrical coordinates of the thread finite element mesh nodes, and convert the cylindrical coordinates to... r The axis coordinate values ​​are in arrive The internal thread finite element mesh nodes are used as multi-layer dense mesh nodes, where, , n m Indicates the number of dense grid layers. d Indicates the nominal diameter. Indicates the height of the dense grid layer. N P Indicates the pitch as a fraction. P Indicates the thread intercept;

[0060] S32: Perform contour offset operation on the outermost node of the multi-layer dense mesh node, and perform position uniform distribution operation on the multi-layer dense mesh nodes between the outermost node and the innermost node.

[0061] S33: The cylindrical coordinates after the position distribution operation. z The axis coordinate values ​​are in arrive The multi-layered dense mesh nodes within are used as spiral tail dense mesh nodes, where... n p Indicates the number of pitches to be drawn;

[0062] S34: Set the offset coefficient, use the offset coefficient to perform a contour offset operation on the outermost node of the spiral tail dense mesh node so that the offset of the spiral tail dense mesh node is 0, and perform a position uniform distribution operation on the spiral tail dense mesh nodes between the outermost node and the innermost node.

[0063] In this embodiment of the invention, the multi-layer dense mesh nodes between the innermost and outermost meshes are arranged as follows: Figure 3 The method shown performs a layer-by-layer distribution operation, dividing all nodes between the innermost and outermost nodes in each layer into equal intervals. ( , , Indicates the number is i The cylindrical coordinates of the nodes, , Indicates the innermost node r Coordinate values (representing the r-coordinate value of the radius of the outermost node), thus generating a value like... Figure 4 The finite element mesh of the thread profile is shown.

[0064] In this embodiment of the invention, the calculation formula for performing the contour offset operation in step S32 is as follows:

[0065]

[0066] in, Indicates the coordinates of the external thread column. θ Representing cylindrical coordinates θ Data for the independent variables of the coordinate axes, d Indicates the nominal diameter. Indicates the calculated diameter. z Representing cylindrical coordinates z Data for the independent variables of the coordinate axes, This indicates the root radius of the external thread. P Indicates the thread intercept. α Indicates the tooth angle. Indicates the segmentation point of the first contour. Indicates the segmentation point of the second contour. Indicates the segmentation point of the third contour. This represents the fourth profile segment point; when the thread direction is right-handed, the angle variable is... θ When the thread direction is left-handed, it is necessary to... θ Replace with ;

[0067] In step S32, the specific method for performing the position distribution operation is as follows: the multi-layer dense grid nodes between the outermost node and the innermost node are evenly divided at intervals.

[0068] In this embodiment of the invention, step S5 includes the following sub-steps:

[0069] S51: Obtain the cylindrical coordinates of the finite element mesh nodes of the nut, and convert the cylindrical coordinates to... r The axis coordinate values ​​are in arrive The finite element mesh nodes within the nut are used as multi-layer dense mesh nodes for the nut. Indicates the number of dense grid layers. Indicates the height of the dense grid layer. d Indicates the nominal diameter;

[0070] S52: Perform a contour offset operation on the innermost node of the multi-layer dense mesh node of the nut, and perform a position uniform distribution operation on the multi-layer dense mesh nodes between the outermost node and the innermost node.

[0071] In this embodiment of the invention, the calculation formula for the contour offset operation in step S52 is as follows:

[0072]

[0073] in, Indicates the coordinates of the internal thread cylinder. P Indicates the thread intercept. θ Representing cylindrical coordinates θ Data for the independent variables of the coordinate axes, d Indicates the nominal diameter. D Indicates the nominal diameter of the internal thread. D 2 indicates the pitch diameter of the internal thread. Indicates the radius of the internal thread root. z Representing cylindrical coordinates z Data for the independent variables of the coordinate axes, α Indicates the tooth angle. Indicates the segmentation point of the first contour. Indicates the segmentation point of the second contour. Indicates the segmentation point of the third contour. The fourth profile segment point is represented by the angle variable when the thread direction is right-handed. θ When the thread direction is left-handed, it is necessary to... θ Replace with .

[0074] In this embodiment of the invention, the mesh node index values ​​are kept unchanged, and the updated node coordinates are written to and replace the original finite element mesh node file, resulting in the following: Figure 5 The complete generalized thread profile precision finite element model is shown.

[0075] The working principle and process of the present application are as follows: (1) the present application proposes the definition of a generalized thread profile, and deduces the profile formula and profile segmentation point expression of the generalized thread profile. Based on the definition and expression, by changing the thread angle α , the top cutting amount h top and the bottom cutting amount h root three variables, the standard metric thread profile, the aviation MJ thread profile, the unified UN thread profile and the German standard thread profile and other types of standard thread profiles conforming to the definition can be generated, and the profile parameters of various non-standard thread profiles can be infinitely adjusted. (2) The generation mode of the thread profile grid is divided into two parts: importing the undeformed bolt model and deforming the dense grid into the thread profile. The grid deformation operation only offsets the dense grid to the set thread profile grid, and does not affect any physical parameters of the input model itself. (3) The thread profile grid is divided into three regions: external thread, thread tail and internal thread. The operations of the three regions are independent, respectively generated and do not interfere with each other. Only part of the operation can be called to generate a bolt or a nut alone. (4) The grid of the thread tail part is contracted inward along the Z-axis positive direction on the basis of the general profile formula of the external thread, until it fits the light pole area, forming a smooth thread tail transition similar to the machining mark of the tool withdrawal groove. This transition mode makes the thread finite element model more consistent with the real physical model, which is beneficial to improve the accuracy of finite element calculation. (5) The position uniform distribution operation is used to uniformly distribute the grid between the innermost layer and the outermost layer of each layer, so as to obtain a regular and beautiful internal thread grid. The regular internal thread grid can greatly reduce the convergence difficulty of finite element model calculation and improve the calculation efficiency.

[0076] The beneficial effects of the present application are as follows:

[0077] (1) The generalized thread profile theory proposed by the present application can not only quickly generate the existing standard metric thread profile, aviation MJ thread profile, unified UN thread profile and German standard thread profile and other types of standard profiles conforming to the definition of the generalized profile, but also provides a way to generate various non-standard thread profiles. The present application is a major progress in the field of existing bolt precision finite element research, which has achieved a breakthrough from being able to generate only ordinary metric screw finite element model to being able to quickly generate various standard thread and non-standard thread finite element models, and realizes the infinite adjustment of thread profile parameters.

[0078] (2) The present application can efficiently and accurately obtain various thread precision finite element models in large quantities without manual calculation. The professional and complex grid drawing work is improved from manual calculation of key node information and program assisted grid offset to algorithm drawing after inputting the profile, which lays a technical foundation for subsequent improvement of bolt profile.

[0079] Those skilled in the art will appreciate that the embodiments described herein are presented for purposes of illustration and understanding of the principles of the application and should not be construed as limiting the scope of the application to such specifically outlined embodiments and examples. Various other specific embodiments and examples not described herein will be apparent to those skilled in the art in view of the teachings provided herein. The scope of the application should be determined from the claims.

Claims

1. A method for generating a generalized precision finite element model of a thread, characterized in that, Includes the following steps: S1: Obtain the basic physical parameters and finite element mesh node data of the bolt, and transform the Cartesian coordinates of the finite element mesh node data to cylindrical coordinates. The finite element mesh node data includes thread finite element mesh nodes and nut finite element mesh nodes. In step S1, the basic physical parameters of the bolt include bolt physical parameters, profile segmentation points, and bolt finite element mesh node information. The contour segmentation points include the first contour segmentation point. Second contour segmentation points Third contour segmentation point and the fourth contour segment point The first contour segmentation point Second contour segmentation points Third contour segmentation point and the fourth contour segment point The calculation formulas are as follows: in, Indicates the amount of material removed from the bottom. Indicates the tooth angle. Indicates the amount of material removed at the top. This represents the original triangle height of the thread. Indicates the thread intercept; S2: Determine whether to generate an external thread profile based on the basic physical parameters of the bolt. If yes, proceed to step S3; otherwise, proceed to step S4. S3: Perform a profile offset operation on the thread finite element mesh nodes, and proceed to step S4; the calculation formula for the profile offset operation is: in, Indicates the coordinates of the external thread column. Representing cylindrical coordinates Data for the independent variables of the coordinate axes, Indicates the nominal diameter. Indicates the calculated diameter. Representing cylindrical coordinates Data for the independent variables of the coordinate axes, This indicates the root radius of the external thread. Indicates the thread intercept. Indicates the tooth angle. Indicates the segmentation point of the first contour. Indicates the segmentation point of the second contour. Indicates the segmentation point of the third contour. Indicates the segmentation point of the fourth contour; S4: Determine whether to generate an internal thread profile based on the basic physical parameters of the bolt. If yes, proceed to step S5; otherwise, proceed to step S6. S5: Perform a profile offset operation on the finite element mesh nodes of the nut, and proceed to step S6; the calculation formula for the profile offset operation is: in, Indicates the coordinates of the internal thread cylinder. Indicates the thread intercept. Representing cylindrical coordinates Data for the independent variables of the coordinate axes, Indicates the nominal diameter. Indicates the nominal diameter of the internal thread. Indicates the pitch diameter of the internal thread. Indicates the radius of the internal thread root. Representing cylindrical coordinates Data for the independent variables of the coordinate axes, Indicates the tooth angle. Indicates the segmentation point of the first contour. Indicates the segmentation point of the second contour. Indicates the segmentation point of the third contour. Indicates the segmentation point of the fourth contour; S6: Convert the cylindrical coordinates of the finite element mesh node data to Cartesian coordinates, and replace the original finite element mesh node data with the finite element mesh node data after the profile offset operation to obtain a generalized thread precision finite element model.

2. The method for generating a generalized precision finite element model of a thread according to claim 1, characterized in that, The physical parameters of the bolt include the nominal diameter. Thread intercept fractions such as pitch Number of dense grid layers Thread direction, thread angle Top cutting amount Bottom cutting amount Original triangle height of the thread Calculate the diameter External thread root radius Nominal diameter of internal thread Internal thread pitch diameter and the radius of the root of the internal thread The finite element mesh node information includes bolt head, bolt shank, nut, whether external threads are generated, and whether internal threads are generated.

3. The method for generating a generalized precision finite element model of a thread according to claim 1, characterized in that, Step S3 includes the following sub-steps: S31: Obtain the cylindrical coordinates of the thread finite element mesh nodes, and convert the cylindrical coordinates to... The axis coordinate values ​​are in arrive The internal thread finite element mesh nodes are used as multi-layer dense mesh nodes, where, , Indicates the number of dense grid layers. Indicates the nominal diameter. Indicates the height of the dense grid layer. Indicates the pitch as a fraction. Indicates the thread intercept; S32: Perform contour offset operation on the outermost node of the multi-layer dense mesh node, and perform position uniform distribution operation on the multi-layer dense mesh nodes between the outermost node and the innermost node. S33: The cylindrical coordinates after the position distribution operation. The axis coordinate values ​​are in arrive The multi-layered dense mesh nodes within are used as spiral tail dense mesh nodes, where... Indicates the number of pitches to be drawn; S34: Set the offset coefficient, use the offset coefficient to perform a contour offset operation on the outermost node of the spiral tail dense mesh node so that the offset of the spiral tail dense mesh node is 0, and perform a position uniform distribution operation on the spiral tail dense mesh nodes between the outermost node and the innermost node.

4. The method for generating a generalized precision finite element model of a thread according to claim 3, characterized in that, In step S32, the specific method for performing the position distribution operation is as follows: the multi-layer dense grid nodes between the outermost node and the innermost node are evenly divided at intervals.

5. The method for generating a generalized precision finite element model of a thread according to claim 1, characterized in that, Step S5 includes the following sub-steps: S51: Obtain the cylindrical coordinates of the finite element mesh nodes of the nut, and convert the cylindrical coordinates to... The axis coordinate values ​​are in arrive The finite element mesh nodes within the nut are used as multi-layer dense mesh nodes for the nut. Indicates the number of dense grid layers. Indicates the height of the dense grid layer. Indicates the nominal diameter; S52: Perform a contour offset operation on the innermost node of the multi-layer dense mesh node of the nut, and perform a position uniform distribution operation on the multi-layer dense mesh nodes between the outermost node and the innermost node.

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