SLB thread contour precision finite element model generation method

Abstract

The invention discloses an SLB thread contour precision finite element model generation method, which is used for generating SLB thread contour precision finite element models under various standard and non-standard size parameters by circularly calling contour expressions of common meter thread contours and parallel thread contours for multiple times, and lays a theoretical technical foundation for finite element calculation of SLB threads. According to the method, researchers can efficiently generate the precise finite element model of the SLB thread with high precision, key node information does not need to be manually calculated, the research threshold of the SLB nut finite element is reduced, and theoretical and technical bases are provided for subsequent researchers to carry out local stress analysis and other simulation researches on the SLB nut finite element.

Description

Technical Field

[0001] This invention belongs to the field of precision finite element technology for bolts, specifically relating to the design of a method for generating a precision finite element model of SLB thread profile. Background Technology

[0002] Currently, in the field of precision finite element analysis of bolts, domestic and international research is mainly focused on the study of standard metric threads. For the performance research of special anti-loosening threads such as Step Lock threads (SLB threads), due to limitations in finite element model technology and the lack of relevant research on SLB thread profile formulas in domestic and international literature, the precise finite element calculation of SLB threads has not yet been studied. Summary of the Invention

[0003] The purpose of this invention is to solve the problem that existing SLB thread profiles cannot be generated due to the lack of corresponding contour formulas, and to propose a method for generating precise finite element models of SLB thread profiles.

[0004] The technical solution of this invention is: a method for generating a precise finite element model of an SLB thread profile, comprising the following steps: S1. Obtain the bolt physical parameters of the SLB thread and the finite element three-dimensional node information before transformation.

[0005] S2. Construct the profile equations for the metric thread profile and the parallel thread profile based on the bolt's physical parameters.

[0006] S3. Convert the finite element 3D node information before transformation to Cartesian coordinates to cylindrical coordinates within the range of 0~2πrad to obtain the original mesh node cylindrical coordinate data.

[0007] S4. Set the initial value of the phase value θ of the SLB thread to 0 rad.

[0008] S5. Determine whether the phase value θ reaches the metric thread profile phase. If yes, proceed to step S6; otherwise, proceed to step S7.

[0009] S6. Perform a profile offset operation on the nodes at the external thread in the original grid node cylindrical coordinate data according to the profile equation of the metric thread profile.

[0010] S7. Determine whether the phase value θ reaches the parallel thread profile phase. If yes, proceed to step S8; otherwise, proceed to step S9.

[0011] S8. Perform a profile offset operation on the nodes at the external thread in the original mesh node cylindrical coordinate data according to the profile equation of the parallel thread profile.

[0012] S9. Determine whether θ>2π is true. If yes, proceed to step S10. Otherwise, increase the value of phase θ by Δθ and return to step S5.

[0013] S10. Perform transition processing on the nodes at the spiral tail in the original mesh node cylindrical coordinate data after the contour offset operation to obtain the updated node cylindrical coordinates.

[0014] S11. Convert the updated node cylindrical coordinates to Cartesian coordinates, keep the node numbers unchanged, replace the finite element 3D node information before the transformation, and output the SLB thread profile precision finite element model.

[0015] Furthermore, the bolt physical parameters in step S1 include thread type, nominal diameter, pitch, equivalent diameter of bearing surface, number of pitches drawn, pitch division and circumferential division, number of dense grid layers, and thread direction.

[0016] Furthermore, the finite element 3D node information before transformation in step S1 is the finite element node information of the untransformed thread with a dense mesh in inp format.

[0017] Furthermore, the specific contour equation for the metric thread profile constructed in step S2 is as follows: in , and These are the coordinates along the three axes of a cylindrical coordinate system. This represents the radial distance from the point to the Z-axis. Indicates the phase value of a point. Indicates the height of the point. Indicates the nominal diameter of the bolt. This represents the tooth height of the original triangle of the thread. Indicates the pitch. Indicates the radius of the tooth base arc. , , and These are the four phase values ​​corresponding to the inflection point of the thread profile.

[0018] Furthermore, the specific contour equation of the parallel thread profile constructed in step S2 is as follows: in and Let be the coordinates on the two axes of the cylindrical coordinate system. This represents the radial distance from the point to the Z-axis. Indicates the height of the point. Indicates the nominal diameter of the bolt. Indicates the helix angle of the thread. This represents the tooth height of the original triangle of the thread. Indicates the pitch. This indicates the radius of the tooth base arc.

[0019] Furthermore, step S6 includes the following sub-steps: S6-1. Select the multi-layer dense mesh nodes in the original mesh node cylindrical coordinate data that require contour offset operation at the external thread.

[0020] S6-2. Based on the profile equation of the metric thread profile, perform a profile offset operation on the outermost dense grid nodes of the external thread.

[0021] S6-3. Keep the position of the innermost dense mesh node at the external thread unchanged, and perform a positional distribution operation on the multi-layer dense mesh nodes between the innermost and outermost dense meshes at the external thread.

[0022] Furthermore, step S8 includes the following sub-steps: S8-1 Select the multi-layer dense mesh nodes in the original mesh node cylindrical coordinate data that require contour offset operation at the external thread.

[0023] S8-2. Based on the profile equation of the parallel thread profile, perform a profile offset operation on the outermost dense grid nodes at the external thread.

[0024] S8-3. Keep the position of the innermost dense mesh node at the external thread unchanged, and perform a positional distribution operation on the multi-layer dense mesh nodes between the innermost and outermost dense meshes at the external thread.

[0025] Furthermore, the formula for calculating Δθ is: in It represents fractions in the perimeter.

[0026] Furthermore, step S10 includes the following sub-steps: S10-1 Select multi-layer dense mesh nodes in the original mesh node cylindrical coordinate data after the contour offset operation that require transition processing at the spiral tail.

[0027] S10-2. Based on the profile equation of the metric thread profile, define an offset coefficient along the Z-axis direction to perform a profile offset operation on the outermost dense grid nodes at the thread tail, so that the offset of the nodes gradually decreases to 0 as the Z coordinate value increases.

[0028] S10-3. Keep the position of the innermost dense grid node at the screw tail unchanged, and perform a positional distribution operation on the multi-layer dense grid nodes between the innermost and outermost dense grids at the screw tail.

[0029] The beneficial effects of this invention are: (1) This invention proposes a method for generating SLB threads by alternating and cyclically using metric thread profile and parallel thread profile equations. This method can quickly generate SLB thread profiles and is a necessary condition and prerequisite for finite element research on the anti-loosening performance of SLB threads. In addition, SLB threads are divided into different parameter models such as 8+8 and 16+16 according to the different numbers of alternating arrangement of the two types of threads (8+8 means that there are 8 segments of ordinary metric thread and 8 segments of parallel thread in one thread). Using the method of this invention, SLB threads with n+n parameters can be generated, and the degree of freedom in parameter selection far exceeds that of existing theories.

[0030] (2) This invention can obtain SLB thread precision finite element models under various parameters with high efficiency, high accuracy and large quantity under fully automatic calculation. It breaks through the technical difficulties of bolt precision finite element theory and advances the complex contour mesh drawing work from being completely impossible to draw based on the original theory to pure algorithm drawing after inputting the calculation contour formula. It lays the technical foundation for the subsequent research and improvement of stress distribution and anti-loosening performance of SLB thread contour with n+n parameters. Attached Figure Description

[0031] Figure 1 The diagram shown is a flowchart of a method for generating a precise finite element model of an SLB thread profile according to an embodiment of the present invention.

[0032] Figure 2 The diagram shown is a schematic diagram of the SLB thread structure provided in an embodiment of the present invention.

[0033] Figure 3 The figure shown is a schematic diagram of a finite element model of a bolt with a dense mesh and untransformed thread provided in an embodiment of the present invention.

[0034] Figure 4 The diagram shown is a schematic diagram of the relationship between the SLB thread profile and the phase value θ provided in an embodiment of the present invention.

[0035] Figure 5 The figure shown is a schematic diagram of a complete SLB thread profile precision finite element model provided in an embodiment of the present invention. Detailed Implementation

[0036] Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be understood that the embodiments shown and described in the drawings are merely exemplary and are intended to illustrate the principles and spirit of the invention, and are not intended to limit the scope of the invention.

[0037] This invention provides a method for generating a precise finite element model of an SLB thread profile, such as... Figure 1 As shown, it includes the following steps S1~S11: S1. Obtain the bolt physical parameters of the SLB thread and the finite element three-dimensional node information before transformation.

[0038] The structural principle of SLB threads is as follows: Figure 2 As shown, the structure of an SLB thread can be simply described as an alternating arrangement of standard metric threads and parallel threads. When a standard nut is screwed into an SLB bolt, due to the special profile of the SLB bolt thread, the standard triangular thread of the nut undergoes plastic deformation and conforms to the "stepped" profile of the bolt. At this point, the "steps" in the thread—the parallel thread portion—play an anti-loosening role, preventing the bolt from loosening. Figure 2 middle This indicates the helix angle of the thread; it is 30° for metric threads and 0° for parallel threads. This indicates the axial force of the bolt. Bolt represents the bolt, and Nut represents the nut.

[0039] In this embodiment of the invention, the physical parameters of the bolt include thread type, nominal diameter, pitch, equivalent diameter of the bearing surface, number of plotted pitches, pitch division and circumferential division, number of dense grid layers, and thread direction.

[0040] In this embodiment of the invention, the finite element three-dimensional node information before transformation is the finite element node information of the untransformed thread with a dense mesh in inp format, such as... Figure 3 As shown.

[0041] S2. Construct the profile equations for the metric thread profile and the parallel thread profile based on the bolt's physical parameters.

[0042] In this embodiment of the invention, the profile equation of the metric thread profile is specifically as follows: The specific contour equation for the parallel thread profile is as follows: in , and Let be the coordinates in the three axes (r-axis, θ-axis, and Z-axis) of the cylindrical coordinate system. This represents the radial distance from the point to the Z-axis. Indicates the phase value of a point. Indicates the height of the point. Indicates the nominal diameter of the bolt. Indicates the helix angle of the thread. This represents the tooth height of the original triangle of the thread. Indicates the pitch. Indicates the radius of the tooth base arc. , , and The four phase values ​​corresponding to the inflection point of the thread profile are as follows: In the metric thread profile, the phase values ​​are: , , , .

[0043] S3. Convert the finite element 3D node information before transformation to Cartesian coordinates to cylindrical coordinates within the range of 0~2πrad to obtain the original mesh node cylindrical coordinate data.

[0044] S4. Set the initial value of the phase value θ of the SLB thread to 0 rad.

[0045] The profile of the SLB thread is related to the nodal phase value θ, such as Figure 4 The diagram shows the relationship between the SLB thread profile and the phase value θ. The profile formula used for node offset is different for different phase values ​​θ.

[0046] S5. Determine whether the phase value θ reaches the metric thread profile phase. If yes, proceed to step S6; otherwise, proceed to step S7.

[0047] S6. Perform a profile offset operation on the nodes at the external thread in the original grid node cylindrical coordinate data according to the profile equation of the metric thread profile.

[0048] Step S6 includes the following sub-steps S6-1 to S6-3: S6-1. Select the multi-layer dense mesh nodes in the original mesh node cylindrical coordinate data that require contour offset operation at the external thread.

[0049] S6-2. Based on the profile equation of the metric thread profile, perform a profile offset operation on the outermost dense grid nodes of the external thread.

[0050] S6-3. Keep the position of the innermost dense mesh node at the external thread unchanged, and perform a positional distribution operation on the multi-layer dense mesh nodes between the innermost and outermost dense meshes at the external thread.

[0051] S7. Determine whether the phase value θ reaches the parallel thread profile phase. If yes, proceed to step S8; otherwise, proceed to step S9.

[0052] S8. Perform a profile offset operation on the nodes at the external thread in the original mesh node cylindrical coordinate data according to the profile equation of the parallel thread profile.

[0053] Step S8 includes the following sub-steps S8-1 to S8-3: S8-1 Select the multi-layer dense mesh nodes in the original mesh node cylindrical coordinate data that require contour offset operation at the external thread.

[0054] S8-2. Based on the profile equation of the parallel thread profile, perform a profile offset operation on the outermost dense grid nodes at the external thread.

[0055] S8-3. Keep the position of the innermost dense mesh node at the external thread unchanged, and perform a positional distribution operation on the multi-layer dense mesh nodes between the innermost and outermost dense meshes at the external thread.

[0056] S9. Determine whether θ>2π is true. If yes, proceed to step S10. Otherwise, increase the value of phase θ by Δθ and return to step S5.

[0057] In this embodiment of the invention, the formula for calculating Δθ is: in It represents fractions in the perimeter.

[0058] S10. Perform transition processing on the nodes at the spiral tail in the original mesh node cylindrical coordinate data after the contour offset operation to obtain the updated node cylindrical coordinates.

[0059] Step S10 includes the following sub-steps S10-1 to S10-3: S10-1 Select multi-layer dense mesh nodes in the original mesh node cylindrical coordinate data after the contour offset operation that require transition processing at the spiral tail.

[0060] S10-2. Based on the profile equation of the metric thread profile, define an offset coefficient along the Z-axis direction to perform a profile offset operation on the outermost dense grid nodes at the thread tail, so that the offset of the nodes gradually decreases to 0 as the Z coordinate value increases.

[0061] S10-3. Keep the position of the innermost dense grid node at the screw tail unchanged, and perform a positional distribution operation on the multi-layer dense grid nodes between the innermost and outermost dense grids at the screw tail.

[0062] S11. Using a general coordinate transformation method, the updated node cylindrical coordinates are converted to Cartesian coordinates while keeping the node number unchanged. The updated node coordinates are written into the finite element mesh node file before the transformation, replacing the finite element 3D node information before the transformation. The output is the SLB thread profile precision finite element model, i.e., the SLB thread finite element model mesh node file in inp format.

[0063] Figure 5 (a) and Figure 5 (b) Schematic diagrams from different angles of the precise finite element model of the SLB thread profile generated using the method of the present invention. Figure 5 (c) Different colors are used to show the distribution of parallel threads and metric threads in the SLB profile.

[0064] In this embodiment of the invention, the contour expressions of ordinary metric thread profile and parallel thread profile are repeatedly called in a loop to generate a precise finite element model of SLB thread profile under various standard and non-standard dimensional parameters, thus laying a theoretical and technical foundation for the finite element calculation of SLB threads.

[0065] In this embodiment of the invention, the dense mesh is processed by node offset. Different contour formulas are called according to the phase angle θ to calculate the node offset, so that the SLB thread can be generated without a dedicated contour formula.

[0066] In this embodiment of the invention, since the tail portion of the SLB bolt receives less attention, the tail portion is treated using a standard metric thread tail instead of the same algorithm used for the thread portion, which reduces the amount of computation and improves the bolt generation efficiency.

[0067] In this embodiment of the invention, the thread profile mesh is generated by deforming the dense mesh in the undeformed bolt model into a thread profile through node offset. The node offset operation only affects the shape of the dense mesh and does not change the original mechanical parameters in the input bolt model.

[0068] In this embodiment of the invention, the outermost mesh is kept unchanged, the innermost mesh is fitted to the contour, and then the intermediate layer nodes are uniformly offset. The advantage of this method is that the number of dense mesh layers can be set arbitrarily without modifying the method itself, and it has strong applicability.

[0069] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. A method for generating a precise finite element model of an SLB thread profile, characterized in that, Includes the following steps: S1. Obtain the bolt physical parameters of the SLB thread and the finite element three-dimensional node information before transformation; S2. Construct the profile equations of metric thread profile and parallel thread profile based on the bolt physical parameters; S3. Convert the finite element 3D node information before transformation to Cartesian coordinates to cylindrical coordinates within the range of 0~2πrad to obtain the original mesh node cylindrical coordinate data. S4. Set the initial value of the phase value θ of the SLB thread to 0 rad; S5. Determine whether the phase value θ reaches the metric thread profile phase. If yes, proceed to step S6; otherwise, proceed to step S7. S6. Perform a profile offset operation on the nodes at the external thread in the original grid node cylindrical coordinate data according to the profile equation of the metric thread profile. S7. Determine whether the phase value θ reaches the parallel thread profile phase. If yes, proceed to step S8; otherwise, proceed to step S9. S8. Perform a profile offset operation on the nodes at the external thread in the original mesh node cylindrical coordinate data according to the profile equation of the parallel thread profile. S9. Determine whether θ>2π is true. If yes, proceed to step S10. Otherwise, increase the value of phase θ by Δθ and return to step S5. S10. Perform transition processing on the nodes at the helical tail in the original mesh node cylindrical coordinate data after the contour offset operation to obtain the updated node cylindrical coordinates. S11. Convert the updated node cylindrical coordinates to Cartesian coordinates, keep the node numbers unchanged, replace the finite element 3D node information before the transformation, and output the SLB thread profile precision finite element model.

2. The method for generating a precise finite element model of an SLB thread profile according to claim 1, characterized in that, The bolt physical parameters in step S1 include thread type, nominal diameter, pitch, equivalent diameter of bearing surface, number of pitches drawn, pitch division and circumferential division, number of dense grid layers, and thread direction.

3. The method for generating a precise finite element model of an SLB thread profile according to claim 1, characterized in that, In step S1, the finite element three-dimensional node information before transformation is the finite element node information of the untransformed thread with a dense mesh in inp format.

4. The method for generating a precise finite element model of an SLB thread profile according to claim 1, characterized in that, The specific contour equation for the metric thread profile constructed in step S2 is as follows: in , and These are the coordinates along the three axes of a cylindrical coordinate system. This represents the radial distance from the point to the Z-axis. Indicates the phase value of a point. Indicates the height of the point. Indicates the nominal diameter of the bolt. This represents the tooth height of the original triangle of the thread. Indicates the pitch. Indicates the radius of the tooth base arc. , , and These are the four phase values ​​corresponding to the inflection point of the thread profile.

5. The method for generating a precise finite element model of an SLB thread profile according to claim 1, characterized in that, The specific contour equation of the parallel thread profile constructed in step S2 is as follows: in and Let be the coordinates on the two axes of the cylindrical coordinate system. This represents the radial distance from the point to the Z-axis. Indicates the height of the point. Indicates the nominal diameter of the bolt. Indicates the helix angle of the thread. This represents the tooth height of the original triangle of the thread. Indicates the pitch. This indicates the radius of the tooth base arc.

6. The method for generating a precise finite element model of an SLB thread profile according to claim 1, characterized in that, Step S6 includes the following sub-steps: S6-1. Select the multi-layer dense mesh nodes in the original mesh node cylindrical coordinate data that require contour offset operation at the external thread; S6-2. Perform profile offset operation on the outermost dense grid nodes of the external thread according to the profile equation of the metric thread profile. S6-3. Keep the position of the innermost dense mesh node at the external thread unchanged, and perform a positional distribution operation on the multi-layer dense mesh nodes between the innermost and outermost dense meshes at the external thread.

7. The method for generating a precise finite element model of an SLB thread profile according to claim 1, characterized in that, Step S8 includes the following sub-steps: S8-1. Select the multi-layer dense mesh nodes in the original mesh node cylindrical coordinate data that require contour offset operation at the external thread; S8-2. Perform profile offset operation on the outermost dense grid nodes at the external thread according to the profile equation of the parallel thread profile. S8-3. Keep the position of the innermost dense mesh node at the external thread unchanged, and perform a positional distribution operation on the multi-layer dense mesh nodes between the innermost and outermost dense meshes at the external thread.

8. The method for generating a precise finite element model of an SLB thread profile according to claim 1, characterized in that, The formula for calculating Δθ in step S9 is: in It represents fractions in the perimeter.

9. The method for generating a precise finite element model of an SLB thread profile according to claim 1, characterized in that, Step S10 includes the following sub-steps: S10-1 Select multi-layer dense grid nodes in the original grid node cylindrical coordinate data after the contour offset operation that require transition processing at the spiral tail. S10-2. Based on the profile equation of the metric thread profile, define an offset coefficient along the Z-axis direction to perform profile offset operation on the outermost dense grid nodes at the thread tail, so that the offset of the nodes gradually decreases to 0 as the Z coordinate value increases. S10-3. Keep the position of the innermost dense grid node at the screw tail unchanged, and perform a positional distribution operation on the multi-layer dense grid nodes between the innermost and outermost dense grids at the screw tail.

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