Finite element-based screwed joint screwing method

Abstract

The invention discloses a threaded joint screwing method based on finite elements, which comprises the following steps of: establishing pre-processing files of three parts of threads, sealing surfaces and shoulder surfaces which are different in size and deviation combination, are respectively positioned on an internal threaded joint and an external threaded joint and are matched with each other in batches through a program, submitting finite element calculation in batches, and obtaining post-processing data in batches; and drawing a plurality of screwing curve graphs of different sizes and deviation combinations according to the screwing-in angle and the torque data point calculated according to the post-processing data, respectively obtaining the inflection point torque and the screwing yield torque on each screwing curve graph according to the plurality of screwing curve graphs, and finally synthesizing the torque results of each curve to recommend the optimal screwing torque. According to the Abaqus-based batch finite element pre-treatment and post-treatment method, batch finite element analysis can be performed on various specifications, deviation and load combinations in the research and development stage, or batch finite element evaluation can be performed on the measurement size of a product, so that the performance of the oil casing screwed joint can be comprehensively known.

Description

Technical Field

[0001] This invention relates to a method for determining the tightening torque under a combination of deviations in threaded joints in the field of mechanical design and processing, and more specifically, to a threaded joint tightening method based on the finite element method. Background Technology

[0002] In many fields such as industrial manufacturing, threaded connections are one of the most commonly used connection methods. Although the thread profiles vary slightly, they are all manufactured by rotary cutting on a lathe or rotary rolling on rollers.

[0003] Thread tooth height, pitch, thread diameter, and thread taper inevitably exhibit machining deviations during processing. In practical applications, randomly selected internal and external threaded parts are screwed together, resulting in varying interference fits. In precision applications, to ensure consistent final fit, various machining deviations of the threads are limited to a very narrow range, placing high demands on equipment machining accuracy, measurement accuracy, and production costs. Narrower tolerance zones result in more stable product performance but increase machining difficulty, cost, and yield a lower pass rate under the same machining conditions; conversely, wider tolerance zones lead to less stable product performance but reduce machining difficulty, cost, and yield a higher pass rate under the same machining conditions.

[0004] A threaded connection typically consists of an internally threaded component and a matching externally threaded component. The threaded connection is considered complete only when both components are tightened to the specified torque or length according to operational requirements. An untightened threaded joint can be considered a semi-finished product to some extent. Insufficient or excessive torque, or a length that is too short or too long, will prevent the connection from performing optimally, leading to problems such as loosening, slippage, yielding, and leakage. Incorrect tightening can easily damage the threads.

[0005] Therefore, the dimensions and tolerances of threaded connections are designed, machined, measured, screwed, and their performance are closely related. Furthermore, due to the vast number of thread sizes and specifications required in actual production, the final determination of design dimensions and tolerances often necessitates extensive experimental research.

[0006] For example, one application of threaded joints is in the drilling pipe, tubing, and casing threaded connections during oil and gas exploration and production. Due to variations in formation conditions and oil / gas burial depths at different drilling locations, the tubing string systems composed of casing and tubing differ. Typically, a well's tubing string system consists of surface casing, technical casing, production casing, and tubing, with different types of casing and tubing layered together, gradually penetrating thousands of meters into the target formation. Because well conditions vary greatly globally, there are numerous combinations of casing and tubing dimensions (outer diameter and wall thickness) and materials. Outer diameters range from a minimum of 2-3 / 8 inches (60.32 mm) to a maximum of 20 inches (508 mm), with 19 different outer diameters specified by the API standard alone; each outer diameter has approximately eight different wall thicknesses. Furthermore, based on the yield strength and corrosion resistance of different materials, each size of steel pipe has dozens of different materials. Therefore, the combinations of outer diameter, wall thickness, and materials can reach hundreds or even thousands.

[0007] Because oil casing threaded joints are machined on CNC lathes, especially the diameter, there is a certain machining deviation. The internal and external threads are designed for an interference fit to ensure a certain meshing stress. This interference fit is very sensitive to the amount of interference; often, a deviation of 0.05mm can lead to significant differences. Therefore, before mass production, multiple sets of joints of each size and material need to be machined with extreme deviations for actual threading / unthreading tests, tensile, compression, and combined internal and external pressure tests to ensure safe use. Typically, the largest and smallest thread diameters, thread tapers, and sealing surface diameters are selected and arranged in pairs, resulting in a total of eight sets of extreme deviations. If the joint's structural design is unreasonable, the joint will undergo significant and irreversible plastic deformation at some point during the test, thereby compromising the structural integrity or sealing integrity of the joint.

[0008] In the design and development of tubing casing joints, finite element simulation or physical testing of the joints is required. Physical testing is costly and time-consuming, while finite element simulation, although low-cost, requires a lot of manual work for joint modeling and mesh generation due to the complex geometry of threaded joints. If sufficient finite element analysis is performed, the time spent may even be no less than that spent on physical testing. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the purpose of this invention is to provide a finite element-based threaded joint tightening method, and a batch finite element pre-processing and post-processing method based on Abaqus. This method enables batch finite element analysis of various specifications, deviations, and load combinations during the R&D stage, or batch finite element evaluation of product measurement dimensions, thereby providing a comprehensive understanding of the performance of oil sleeve threaded joints.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A finite element method for screwing threaded joints:

[0012] The program generates pre-processed files in batches, containing three parts—thread, sealing surface, and shoulder surface—located on internal and external threaded joints with different sizes and deviation combinations. These files are then submitted for batch finite element calculations and post-processed data is obtained in batches. Based on the screwing angle and torque data points calculated from the post-processed data, multiple screwing curves with different sizes and deviation combinations are plotted. The inflection point torque and screwing yield torque on each screwing curve are obtained. Finally, the optimal screwing torque is recommended by combining the torque results from all curves.

[0013] Preferably, the batch creation of the preprocessing files specifically includes the following steps:

[0014] S1, use a Python program to obtain the input data and deviation parameters of the threaded connector;

[0015] S2, and based on the input data, deviation parameters and screwing angle, calculate the key node coordinates of the two-dimensional axisymmetric threaded joint section. The key nodes mainly include three parts: thread, sealing surface and shoulder surface.

[0016] S3, through information interaction with Abaqus software, completes the establishment of geometric models, mesh generation, contact definition, boundary load application, and outputs finite element preprocessing analysis files in INP format;

[0017] S4, Increment the screwing angle, repeat steps S1 to S3, loop and batch output INP format finite element preprocessing analysis files;

[0018] S5, change the deviation combination or other input parameters, repeat steps S1 to S4 in a loop and batch output finite element preprocessing analysis files in INP format.

[0019] Preferably, the finite element calculation specifically includes:

[0020] The INP files are submitted one by one to a supercomputing platform with Abaqus installed, and the ODB calculation result files are obtained one by one.

[0021] Preferably, obtaining the post-processed data in batches specifically includes the following steps:

[0022] (1) Select a combination of deviations and open an ODB result file according to the screwing angle;

[0023] (2) Output stress and strain contour plots;

[0024] (3) Select the set of surface nodes for the thread, sealing surface and shoulder surface of this document;

[0025] (4) Sort the sets of thread, sealing surface and shoulder surface nodes according to the spatial distribution of the joint model;

[0026] (5) Calculate the torque based on the contact pressure and spatial coordinates of each node set and integrate it along a linear path;

[0027] (6) The total torque is obtained by integrating the torques of the thread surface, sealing surface and shoulder surface;

[0028] (7) Repeat steps (1) to (6) to obtain the total torque of all screw-in angles of the deviation combination;

[0029] (8) Change the deviation combination and repeat steps (1) to (7) to obtain all the screwing angle torques of all deviation combinations;

[0030] (9) Draw multiple screwing curves with different deviation combinations based on the screwing angle and torque data points.

[0031] Preferably, the post-processing data results are used to judge the quality of the threaded joint design. If the results do not meet the requirements, the design structure is modified, and the steps of batch creating the pre-processing files, the finite element calculation, and batch obtaining the post-processing data are repeated.

[0032] Preferably, in step S1, the input parameters include male connector parameters, female connector parameters, external thread parameters, and internal thread parameters;

[0033] Each input parameter L is considered as the nominal value N_L plus the deviation value D_L, i.e., L = N_L + D_L.

[0034] Preferably, in step S1, the deviation parameters include a combination of the minimum and maximum values ​​of the thread diameter deviation, the minimum and maximum values ​​of the thread taper deviation, the minimum and maximum values ​​of the pitch deviation, and the minimum and maximum values ​​of the tooth height deviation.

[0035] Preferably, in step S2, the coordinates of the key nodes are calculated based on the coordinates of all intersection points of straight lines and arcs of the threaded joint, and then written into Python program code.

[0036] Preferably, in step S3, after the geometric model completes the parameterized construction of four geometric models—male connector body, male connector thread, female connector body, and female connector thread—by calling Abaqus built-in functions, the male connector body is cut off by the male connector thread and the female connector body is cut off by the female connector thread using Boolean functions, thereby generating the male connector component and the female connector component.

[0037] Preferably, in step S3, the mesh division specifically includes:

[0038] The male and female connector components are divided into sections, the threaded sections are separated, and then the local mesh is refined.

[0039] The grid uses a quadrilateral grid.

[0040] Preferably, in step S3, the contact is defined as threaded contact, sealing surface contact, and shoulder surface contact.

[0041] Preferably, in step S3, the boundary load is the plane of symmetry of the fixed internal threaded joint.

[0042] Preferably, in step S5, the replacement deviation combination specifically includes:

[0043] Another combination of minimum and maximum values ​​of thread diameter deviation, thread taper deviation, pitch deviation, and tooth height deviation is used.

[0044] Preferably, the ODB calculation result file includes model data and result data;

[0045] The model data is used to describe the components and component instances in the root assembly;

[0046] The results data are used to describe various analytical results.

[0047] Preferably, in step (6), the total torque is the sum of the thread torque, the sealing surface torque, and the shoulder torque.

[0048] Preferably, the torque of the threaded joint is the sum of the curve integrals of the products of the contact pressure and radius along the thread surface, the sealing surface, and the shoulder surface.

[0049] Preferably, the formula for calculating the line integral is:

[0050] Let the coordinates of two adjacent mesh nodes on the surface of the threaded joint be (x, y ... i ,y i ), (x i+1 ,y i+1 The contact pressures at the two points are p i and p i+1 :

[0051]

[0052] Therefore, the torque of the threaded surface, sealing surface, and shoulder surface is calculated using the same method as the curve integral, except that the curves are for the threaded surface, sealing surface, and shoulder surface, respectively.

[0053] Preferably, in step (9), the horizontal axis of the screwing curve is the screwing angle or the number of screwing turns, and the number of screwing turns is equal to the screwing angle divided by 360 degrees.

[0054] The vertical axis of the screwing curve represents the total torque calculated using finite element analysis.

[0055] Preferably, the torque at the screwing inflection point is the torque value when the shoulders of the internal threaded joint and the external threaded joint just begin to engage.

[0056] Preferably, the tightening torque is located between 70% of the inflection point torque value and 120% of the yield torque value, that is:

[0057] The inflection point torque value divided by 70% ≤ tightening torque ≤ yield torque value divided by 120%.

[0058] Preferably, the optimal tightening torque is the median of the intersection of the tightening torque intervals calculated from each curve.

[0059] The present invention provides a finite element method for threaded joint tightening. All pre-processing and post-processing steps are completed interactively by a pre-written Python program and Abaqus software, requiring no manual intervention. The method evaluates the results of batch finite element calculations, explores the boundaries between the threaded joint design dimensions and tolerances, and thus provides the optimal threaded joint design structure. Attached Figure Description

[0060] Figure 1 This is a schematic diagram of the male connector node in the threaded joint tightening method of the present invention;

[0061] Figure 2 This is a schematic diagram of the female connector node in the threaded connector screwing method of the present invention;

[0062] Figure 3 This is a schematic diagram of the male connector partition in the threaded connector screwing method of the present invention;

[0063] Figure 4 This is a schematic diagram of the female connector partition in the threaded connector screwing method of the present invention;

[0064] Figure 5 This is a schematic diagram of the threaded joint in the threaded joint tightening method of the present invention;

[0065] Figure 6 This is a schematic diagram of the torque curve drawn in an embodiment of the threaded joint tightening method of the present invention. Detailed Implementation

[0066] To better understand the above-mentioned technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0067] This invention provides a threaded joint tightening method based on the finite element method:

[0068] The program generates pre-processed files in batches, containing three parts—thread, sealing surface, and shoulder surface—located on internal and external threaded joints with different sizes and deviation combinations. These files are then submitted for batch finite element calculations and post-processed data is obtained in batches. Based on the screwing angle and torque data points calculated from the post-processed data, multiple screwing curves with different sizes and deviation combinations are plotted. The inflection point torque and screwing yield torque on each screwing curve are obtained. Finally, the optimal screwing torque is recommended by combining the torque results from all curves.

[0069] The preprocessing files and postprocessing data generated above need to consider the mutual fit and coupling relationship of the three parts: the thread, the sealing surface, and the shoulder surface. As the thread is gradually rotated and screwed in, the sealing surface and the shoulder surface will also go from non-contact to contact, until an interference fit is achieved.

[0070] The above-mentioned batch creation of preprocessing files specifically includes the following steps:

[0071] S1 uses a Python program to obtain input data such as threaded joint dimensions, a combination of deviations, material properties, and mesh size.

[0072] S2, and based on the input data, deviation parameters and screwing angle, calculate the key node coordinates of the two-dimensional axisymmetric threaded joint section. The key nodes mainly include three parts: thread, sealing surface and shoulder surface.

[0073] S3 interacts with Abaqus software to complete the establishment of geometric models, mesh generation, contact definition, boundary load application, etc., and outputs finite element preprocessing analysis files in INP format;

[0074] S4, Increment the screwing angle, repeat steps S1 to S3, loop and batch output INP format finite element preprocessing analysis files;

[0075] S5, change the deviation combination or other input parameters, repeat steps S1 to S4 in a loop and batch output finite element preprocessing analysis files in INP format.

[0076] The aforementioned finite element calculation refers to submitting INP files one by one to a supercomputing platform with Abaqus installed, and calculating and obtaining ODB calculation result files one by one.

[0077] The above-mentioned batch acquisition of post-processed data specifically includes the following steps:

[0078] (1) Select a combination of deviations and open an ODB result file according to the screwing angle;

[0079] (2) Output stress and strain contour plots;

[0080] (3) Select the set of surface nodes for the thread, sealing surface and shoulder surface of this document;

[0081] (4) Sort the sets of thread, sealing surface and shoulder surface nodes according to the spatial distribution of the joint model;

[0082] (5) Calculate the torque based on the contact pressure and spatial coordinates of each node set and integrate it along a linear path;

[0083] (6) The total torque is obtained by integrating the torques of the thread surface, sealing surface and shoulder surface;

[0084] (7) Repeat steps (1) to (6) to obtain the total torque of all screw-in angles of the deviation combination;

[0085] (8) Change the deviation combination and repeat steps (1) to (7) to obtain all the screwing angle torques of all deviation combinations;

[0086] (9) Draw multiple screwing curves with different deviation combinations based on the screwing angle and torque data points.

[0087] The above post-processing data results are used to judge the quality of the threaded joint design. If the results do not meet the requirements, the design structure is modified, and the steps of batch creating pre-processing files, finite element calculation, and batch obtaining post-processing data are repeated.

[0088] In step S1 of the above-mentioned batch creation of preprocessing files, the input parameters include male connector parameters, female connector parameters, external thread parameters, and internal thread parameters;

[0089] Each input parameter L is considered as the nominal value N_L plus the deviation value D_L, i.e., L = N_L + D_L.

[0090] The number of actual dimensional parameters depends on the geometric characteristics of the threaded joint, and usually ranges from tens to hundreds. The data is stored in files in formats such as txt, xls, or xml, and is called using pre-written Python code.

[0091] In step S1 of the above-mentioned batch creation of preprocessing files, the deviation parameters include a combination of the minimum and maximum values ​​of thread diameter deviation, thread taper deviation, pitch deviation, and tooth height deviation.

[0092] In step S2 of the above-mentioned batch creation of preprocessing files, the coordinates of key nodes are calculated based on the coordinates of all intersection points of straight lines and arcs according to the geometric relationship of the threaded joint, and written into Python program code, such as... Figure 1 and Figure 2 As shown.

[0093] In step S3 of the above-mentioned batch creation of preprocessing files, the geometric model completes the parameterization construction of four geometric models—male connector body, male connector thread, female connector body, and female connector thread—by calling Abaqus built-in functions. Then, Boolean functions are used to cut off the male connector body by the male connector thread and the female connector body by the female connector thread, thereby generating the male connector component and the female connector component.

[0094] In step S3 of the above-mentioned batch creation of preprocessing files, mesh generation refers to dividing the male and female connector components into sections, separating the threaded segments, and then refining the mesh locally. The mesh should ideally be a quadrilateral mesh, such as... Figures 3 to 5 As shown.

[0095] Among them, such as Figure 5 The diagram shows a key node of one tooth in the thread. The other teeth will be arranged in an array of N teeth upwards and M teeth downwards to form the entire thread.

[0096] In step S3 of the above batch creation of preprocessing files, the contact is defined as thread contact, sealing surface contact, and shoulder surface contact.

[0097] In step S3 of the above-mentioned batch creation of preprocessing files, the boundary load is the symmetry plane of the fixed internal thread joint.

[0098] In actual joint tightening, when fixing the external threaded joint, the relative position (axial and radial) of the torque shoulder of the internal threaded joint on a certain cross-section along the axial direction gradually changes. Since a two-dimensional model is used, it is determined after the model sketch is completed, so a single model cannot simulate the actual tightening process.

[0099] In step S4 of the above-mentioned batch creation of preprocessing files, the entire analysis is set as a loop program. In each loop, the size parameters of the external thread are gradually changed. After the analysis is completed, multiple result files are combined.

[0100] In step S5 of the above-mentioned batch creation of preprocessing files, changing the deviation combination refers to using a combination arrangement of the minimum and maximum values ​​of the thread diameter deviation, the minimum and maximum values ​​of the thread taper deviation, the minimum and maximum values ​​of the pitch deviation, and the minimum and maximum values ​​of the tooth height deviation.

[0101] The ODB calculation result file mentioned above includes model data and result data.

[0102] Model data is used to describe the components and component instances in the root assembly, such as node coordinates, set definitions, and element types.

[0103] The results data are used to describe various analysis results, such as stress, strain, and displacement.

[0104] In step (6) of obtaining post-processing data in batches, the total torque is the sum of the thread torque, the sealing surface torque, and the shoulder torque.

[0105] The torque of the aforementioned threaded joint is the sum of the curve integral of the product of the contact pressure and radius along the thread surface, the sealing surface, and the shoulder surface.

[0106] The formula for calculating the above line integral is:

[0107] Let the coordinates of two adjacent mesh nodes on the surface of the threaded joint be (x, y ... i ,y i ), (x i+1 ,y i+1 The contact pressures at the two points are p i and p i+1 :

[0108]

[0109] Therefore, the torque of the threaded surface, sealing surface, and shoulder surface is calculated using the same method as the curve integral, except that the curves are for the threaded surface, sealing surface, and shoulder surface, respectively.

[0110] In step (9) of obtaining post-processing data in batches, the horizontal axis of the screwing curve is the screwing angle or the number of screwing turns, and the number of screwing turns is equal to the screwing angle divided by 360 degrees.

[0111] The vertical axis of the screwing curve represents the total torque obtained from finite element analysis.

[0112] The torque at the screwing inflection point is the torque value at which the shoulder of the threaded joint yields.

[0113] The tightening torque lies between 70% of the inflection point torque and 120% of the yield torque, i.e.:

[0114] Inflection point torque value divided by 70% ≤ Tightening torque ≤ Yield torque value divided by 120%

[0115] The optimal tightening torque is recommended to be the intersection of the tightening torque ranges calculated from each curve, preferably the median of the intersection.

[0116] Example

[0117] This embodiment uses an airtight threaded joint with an outer diameter of 88.9 mm, a wall thickness of 9.52 mm, and a steel grade of P110 to describe the detailed implementation process of the threaded joint tightening method based on the finite element method of the present invention.

[0118] The dimensional parameters of this threaded connector include, but are not limited to, the following parameters, which can be divided into four categories: male connector parameters, female connector parameters, external thread parameters, and internal thread parameters.

[0119] Male connector parameters: D (outer diameter of pipe body), t (wall thickness), loss_length (upper thread loss length), P_alpha (sealing face angle), P_beta (shoulder face angle), P_gamma (thread angle), P_delta (starting thread chamfer), P_bore_angle (boring angle), P_seal_dia (sealing face diameter), P_cylinder_dia (cylinder diameter), P_bore_dia (boring diameter), P_nose_length (nose length), P_bore_length (boring length), P_seal_length (sealing face length), P_r_shoulder2seal (corner radius), P_r_seal2taper (corner radius), P_r_cylinder2thread (corner radius);

[0120] Female connector parameters: B_W (outer diameter of female connector), B_coupling_length (coupling length), B_seal_dia (diameter of sealing surface), B_cylinder_dia (diameter of cylindrical surface), B_bore_dia (diameter of bore), B_seal_length (length of sealing surface), B_cylinder_length (length of cylindrical surface), B_inside_bevel_dia (diameter of inner chamfer), B_alpha (angle of sealing surface), B_beta (angle of shoulder surface), B_gamma (angle of thread), B_seal2cylinder_angle (angle), B_inside_bevel_angle (angle of inner chamfer), B_r_shoulder2seal (radius of fillet), B_r_seal2face (radius of fillet), B_r_face2cylinder (radius of fillet);

[0121] External thread parameters: P_thread_dia (thread diameter), P_thread_measure (thread measurement length), TPI (number of threads), P_taper (thread taper), P_root_length (root length), P_thread_high (tooth height), P_root_high (root height), P_r_stab_crest (corner radius), P_r_load_crest (corner radius), P_r_load_root (corner radius), P_r_stab_root (corner radius), P_stab_angle (guide surface angle), P_load_angle (load bearing surface angle);

[0122] Internal thread parameters: B_thread_dia (thread diameter), B_thread_measure (thread measurement length), TPI (number of threads), B_taper (thread taper), B_root_length (root length), B_thread_high (tooth height), B_root_high (root height), B_r_stab_crest (corner radius), B_r_load_crest (corner radius), B_r_load_root (corner radius), B_r_stab_root (corner radius), B_stab_angle (guide surface angle), B_load_angle (load surface angle).

[0123] The most important processing and measurement control parameters are shown in Table 1 below:

[0124] Table 1 Main Processing and Measurement Control Parameters

[0125]

[0126] The three sets of control parameters can be combined in pairs to form nine possible extreme deviation combinations as shown in Table 2. In practical applications, these combinations include, but are not limited to, the following deviation combinations, which can be combined arbitrarily as needed.

[0127] Table 2 Deviation Combinations

[0128]

[0129]

[0130] The screw-in angle can be set to: -400°, -300°, -200°, -150°, -100°, -70°, -50°, -30°, -20°, -10°, -5°, 0°, 5°, 10°, 15°, 20°, 25°, 30°, 40°, 50°, etc. The number and value can be increased or decreased as needed. 0° is the angle at which the shoulder just begins to make contact on the drawing. Negative values ​​are for screwing out the thread, and positive values ​​are for screwing in the thread.

[0131] Based on the input parameters, the coordinates of the intersection points of the straight lines and arcs of different geometric cross-section models are calculated. In practical applications, the female connector's geometric cross-section model can be kept constant, while the male connector's geometric cross-section model gradually changes with increasing screw-in angle. Alternatively, the male connector model can be kept constant, while the female connector's model gradually changes with increasing screw-in angle. This embodiment uses the former method.

[0132] like Figure 1 As shown, if the pitch is p and the advance angle is θ, then the axial travel y needs to be added to the ordinate of each node. θ Then it is:

[0133]

[0134] Let the axial length of the measuring point of the male connector thread be L, and the diameter of the measuring point be D. th If the thread taper is T, then after screwing in at an angle θ, the thread diameter D at the measuring point at the axial length L of the thread is... θ Then it is:

[0135]

[0136] The 18×9=162 screwing torque values ​​were calculated one by one, as shown in Table 3 below, and a screwing curve was plotted.

[0137] Table 3

[0138]

[0139]

[0140] According to the threaded joint tightening method of the present invention, the torque curve diagram (e.g.) is plotted. Figure 6 As shown, this reflects the interrelationships of numerous parameters related to the joint, including various design dimensions, deviations, material properties, coefficient of friction, rotation and tightening angle, inflection point torque, recommended tightening torque, and yield torque. According to... Figure 6As shown, the design dimensions, tolerance zones, and recommended tightening torques of threaded joints can be optimized. The calculation process is automated, requiring minimal manual intervention, eliminating the need for expensive physical testing, and minimizing computation time (depending on computer processing power). The analytical calculation report based on this patent can partially or completely replace physical test reports.

[0141] This embodiment is only one implementation case of the present invention patent and does not imply any limitation on the present invention patent. The actual structure of threaded joints varies. Threaded joints may only have a threaded part and no sealing surface or shoulder surface, but they are nothing more than composed of rotating external threads and matching internal threads. The present invention patent is also applicable to threaded joints with different structures and thread tooth profiles.

[0142] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. A threaded joint tightening method based on finite element method, characterized in that: The program generates pre-processing files in batches, containing three parts—thread, sealing surface, and shoulder surface—located on internal and external threaded joints with different sizes and deviation combinations. These files are then submitted for batch finite element calculations and post-processing data is obtained in batches. Based on the screwing angle and torque data points calculated from the post-processing data, multiple screwing curves with different sizes and deviation combinations are plotted. The inflection point torque and screwing yield torque on each screwing curve are obtained. Finally, the optimal screwing torque is recommended by combining the torque results from all curves.

2. The threaded joint tightening method based on finite element method according to claim 1, characterized in that, Specifically, the preprocessing files are created in batches. Includes the following steps: S1, use a Python program to obtain the input data and deviation parameters of the threaded connector; S2, and calculate the key node coordinates of the two-dimensional axisymmetric threaded joint section based on the input data, deviation parameters and screwing angle. The key nodes include three parts: thread, sealing surface and shoulder surface. S3, through information interaction with Abaqus software, completes the establishment of geometric models, mesh generation, contact definition, boundary load application, and outputs finite element preprocessing analysis files in INP format; S4, Increment the screwing angle, repeat steps S1 to S3, loop and batch output INP format finite element preprocessing analysis files; S5, change the deviation combination or other input parameters, repeat steps S1 to S4 in a loop and batch output finite element preprocessing analysis files in INP format.

3. The threaded joint tightening method based on finite element method according to claim 2, characterized in that, The finite element calculation specifically includes: The INP files are submitted one by one to a supercomputing platform with Abaqus installed, and the ODB calculation result files are obtained one by one.

4. The threaded joint tightening method based on finite element method according to claim 3, characterized in that, Obtaining the post-processed data in batches specifically includes the following steps: (1) Select a combination of deviations and open an ODB result file according to the screwing angle; (2) Output stress and strain contour plots; (3) Select the set of surface nodes for the thread, sealing surface and shoulder surface of this document; (4) Sort the sets of thread, sealing surface and shoulder surface nodes according to the spatial distribution of the joint model; (5) Calculate the torque based on the contact pressure and spatial coordinates of each node set and integrate it along a linear path; (6) The total torque is obtained by integrating the torques of the thread surface, sealing surface and shoulder surface; (7) Repeat steps (1) to (6) to obtain the total torque of all screw-in angles of the deviation combination; (8) Change the deviation combination and repeat steps (1) to (7) to obtain all the screwing angle torques of all deviation combinations; (9) Draw multiple screwing curves with different deviation combinations based on the screwing angle and torque data points.

5. The threaded joint tightening method based on finite element method according to claim 4, characterized in that: The post-processing data results are used to judge the quality of the threaded joint design. If the results do not meet the requirements, the design structure is modified, and the steps of batch creating the pre-processing files, the finite element calculation, and batch obtaining the post-processing data are repeated.

6. The threaded joint tightening method based on finite element method according to claim 2, characterized in that: In step S1, the input parameters include male connector parameters, female connector parameters, external thread parameters, and internal thread parameters. Each input parameter L is considered as the nominal value N_L plus the deviation value D_L, i.e., L = N_L + D_L. In step S1, the deviation parameters include a combination of the minimum and maximum values ​​of the thread diameter deviation, the minimum and maximum values ​​of the thread taper deviation, the minimum and maximum values ​​of the pitch deviation, and the minimum and maximum values ​​of the tooth height deviation.

7. The threaded joint tightening method based on finite element method according to claim 2, characterized in that: In step S2, the coordinates of the key nodes are calculated based on the coordinates of all intersections of straight lines and arcs in the geometric relationship of the threaded joint, and then written into Python program code.

8. The threaded joint tightening method based on finite element method according to claim 2, characterized in that: In step S3, the geometric model is parametrically constructed by calling Abaqus built-in functions to create four geometric models: the male connector body, the male connector thread, the female connector body, and the female connector thread. Then, Boolean functions are used to cut off the male connector body from the male connector thread and the female connector body from the female connector thread, thereby generating the male connector component and the female connector component. In step S3, the mesh division specifically includes: The male and female connector components are divided into sections, the threaded sections are separated, and then the local mesh is refined. The grid uses quadrilateral grids. In step S3, the contact is defined as threaded contact, sealing surface contact, and shoulder surface contact. In step S3, the boundary load is the plane of symmetry of the fixed internal threaded joint.

9. The threaded joint tightening method based on finite element method according to claim 2, characterized in that, In step S5, the replacement deviation combination specifically includes: Another combination of minimum and maximum values ​​of thread diameter deviation, thread taper deviation, pitch deviation, and tooth height deviation is used.

10. The threaded joint tightening method based on finite element method according to claim 3, characterized in that: The ODB calculation result file includes model data and result data; The model data is used to describe the components and component instances in the root assembly; The results data are used to describe various analytical results.

11. The threaded joint tightening method based on finite element method according to claim 4, characterized in that, In step (6), the total torque is the sum of the thread torque, the sealing surface torque, and the shoulder torque. The torque of the threaded joint is the sum of the curve integral of the product of the contact pressure and radius along the thread surface, the sealing surface, and the shoulder surface.

12. The threaded joint tightening method based on finite element method according to claim 11, characterized in that, The formula for calculating the line integral is as follows: Let the coordinates of two adjacent mesh nodes on the surface of the threaded joint be (x, y ... i ,y i ), (x i +1,y i +1), the contact pressures at the two points are respectively p i and p i+1 :

13. The threaded joint tightening method based on finite element method according to claim 4, characterized in that: In step (9), the horizontal axis of the screwing curve is the screwing angle or the number of screwing turns, and the number of screwing turns is equal to the screwing angle divided by 360 degrees. The vertical axis of the screwing curve represents the total torque calculated using finite element analysis.

14. The threaded joint tightening method based on finite element method according to claim 1, characterized in that: The torque at the screwing inflection point is the torque value when the shoulders of the internal threaded joint and the external threaded joint just begin to engage.

15. The threaded joint tightening method based on finite element method according to claim 1, characterized in that, The tightening torque is located between 70% of the inflection point torque value and 120% of the yield torque value, that is: The inflection point torque value divided by 70% ≤ tightening torque ≤ yield torque value divided by 120%.

16. The threaded joint tightening method based on finite element method according to claim 15, characterized in that: The optimal tightening torque is recommended to be the median of the intersection of the tightening torque ranges calculated from each curve.

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