Method for accurately controlling pre-tightening force of bolt during multiple times of assembly based on overload tightening

Abstract

The invention discloses a method for accurately controlling pre-tightening force of multiple bolt assembling based on overload tightening, and belongs to the technical field of mechanical engineering. The method comprises the following steps: simulating a pre-tightening force application process on a finite element model of a threaded connection structure by utilizing an overload tightening method to obtain a displacement angle-pre-tightening force calibration curve of the whole process of the overload tightening method; carrying out analogue simulation under a vibration working condition on the finite element model of the threaded connection structure which is simulated by utilizing the overload tightening method; and after the simulation result under the vibration working condition meets the requirement, the actual bolt and nut are assembled according to the obtained displacement angle-pretightening force calibration curve in the whole process of the overload tightening method, and axial pretightening force control is achieved. According to the method, the limitation in the prior art is effectively overcome, the reliability and repeatability of the bolt connection structure under the condition of multiple times of assembly are remarkably improved, an operable simulation foundation and technical means are provided for high-precision mechanical assembly, and the problem that in the prior art, a threaded connection structure is poor in anti-loosening performance is solved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of mechanical engineering, and particularly relates to a bolt multi-assembly pre-tightening force accurate control method based on overload tightening. BACKGROUND

[0002] In the prior art, the pre-tightening force control method of high-strength bolts mainly relies on torque method, torque-angle method, yield point method or tensioning method and the like. These methods are all achieved by assembling the bolt-nut to form a target pre-tightening force.

[0003] Specifically, the torque method is essentially to indirectly control the pre-tightening force by controlling the tightening torque, according to the formula T=KxFxd, wherein T is the applied torque, F is the pre-tightening force, d is the nominal diameter of the bolt, and K is the torque coefficient (affected by the friction of the thread and the bearing surface), so as to make the bolt axially elongated, thereby generating a tensile force to achieve the design pre-tightening force; the torque-angle method is to apply an initial torque on the basis of the initial torque, apply a fitting torque to make the contact surface fit, and then rotate the nut or bolt according to the set additional angle tightening, the elastic and plastic deformation of the bolt in the actual tightening process makes the pre-tightening force closer to the target value; the yield point method utilizes the yield characteristics of the bolt material, and forms plastic stretching through the super-yield state, so as to achieve the purpose of controlling the pre-tightening force. According to the geometric relationship, the axial elongation is approximately ΔL= / (2π) (single thread pitch =p), and the pre-tightening force can be estimated by the equivalent axial stiffness F≈k eq ΔL; the yield point method takes the material yield as the control benchmark, and the target pre-tightening force is usually F target ≈ασyA s (σ y is the yield strength, A s is the stress section, and α is the specification coefficient), and the tightening is performed until the yield characteristics (inflection point / slope significantly decreases) of the torque-angle curve appear or the specified plasticity index is reached, so as to obtain a high and consistent F; the tensioning method uses a hydraulic stretcher to directly apply an axial force to the bolt and lock it in the stretched state, or estimates the pre-tightening force F≈(EA s / L g )ΔL (E is the elastic modulus, L g is the effective clamping length, and A s is the stress section) after measuring the bolt elongation ΔL.

[0004] Although the prior art can achieve the target preload to some extent, there are still some limitations. First, in high-vibration environment, repeated assembly or complex structure conditions, these methods are difficult to guarantee the stability of the preload and the anti-loose performance, especially in large-scale bolt group or non-standard bolt. The traditional method pays more attention to the final preload, but ignores the stress evolution, plastic springback and friction distribution in the process of bolt-nut assembly, resulting in deviation between theoretical calculation and actual engineering assembly state.

[0005] In summary, the torque method is affected by the friction dispersion, and the preload is dispersed; the torque-angle method is affected by the fitting point judgment and stiffness tolerance, and the angle-elongation conversion has errors; the yield point method has good consistency, but at the cost of controlled yield, and the reusability and service life are limited; the tensioning method has high precision, but requires high equipment and space, and the load-locking conversion is prone to relaxation. The above methods are generally difficult to simultaneously consider "complete gap elimination, friction stabilization and initial load suppression". SUMMARY

[0006] In view of the shortcomings of the prior art, the present application provides a bolt multi-assembly preload accurate control method based on overload tightening. By establishing a complete assembly model based on finite elements, introducing a dynamic iterative solution and cumulative error correction mechanism, the bolt preload can be accurately predicted, applied and controlled during repeated assembly simulation, thereby effectively overcoming the limitations of the prior art, significantly improving the reliability and repeatability of the bolt connection structure under multiple assembly conditions, and providing an operable simulation basis and technical means for high-precision mechanical assembly, to solve the poor anti-loose performance of the threaded connection structure in the prior art.

[0007] The technical scheme of the present application is as follows:

[0008] On the one hand, the present application provides a bolt multi-assembly preload accurate control method based on overload tightening, comprising the following steps:

[0009] Determine the geometric parameters of the threaded connection structure and construct a finite element model of the threaded connection structure;

[0010] Simulate the process of preload application on the finite element model of the threaded connection structure using the overload tightening method, and obtain the displacement angle-preload calibration curve of the entire process of the overload tightening method; the overload tightening method includes three stages, namely, applying an overload preload to the bolt beyond the target preload, then unloading the preload, and finally applying the target preload to the bolt again;

[0011] Simulate the finite element model of the threaded connection structure after simulation using the overload tightening method under vibration conditions;

[0012] After the simulation result under the vibration working condition meets the requirement, the displacement angle-pre-tightening force calibration curve of the whole process of the overload tightening method is obtained to assemble the actual bolt and nut, axial pre-tightening force control is realized, if not, the displacement angle-pre-tightening force calibration curve of the whole process of the overload tightening method is obtained again.

[0013] Further, the determining the geometric parameters of the threaded connection structure and constructing the finite element model of the threaded connection structure specifically comprises:

[0014] A1: constructing a geometric model of the threaded connection structure according to the geometric parameters of the threaded connection structure; the threaded connection structure comprises a bolt, a nut, an upper compressed piece and a lower compressed piece;

[0015] A2: setting material parameters for the geometric model of the threaded connection structure;

[0016] A3: dividing the geometric model of the threaded connection structure into finite element grids to obtain the finite element model of the threaded connection structure.

[0017] Further, the simulating the process of pre-tightening force application on the finite element model of the threaded connection structure by the overload tightening method to obtain the displacement angle-pre-tightening force calibration curve of the whole process of the overload tightening method specifically comprises:

[0018] B1: first setting a reference point in the finite element model of the bolt connection structure and coupling it with the node on the outer surface of the nut in the finite element model of the bolt connection structure for controlling the rotational loading of the nut; the reference point is set on the central axis of the bolt and the nut;

[0019] B2: defining the rotational freedom of the reference point around the Z axis as a control variable of the applied load, so that the control of the rotation angle of the nut is realized by applying an angular displacement on the rotational freedom, thereby indirectly applying the axial pre-tightening force of the bolt; the direction of the Z axis is the direction of the axial pre-tightening force;

[0020] B3: determining the target pre-tightening force and the overload pre-tightening force according to the bolt specification;

[0021] B4: setting the initial loading value of the displacement angle of the rotational freedom of the reference point around the Z axis to realize the equivalent loading of the initial tightening process, then performing simulation analysis, reading the axial pre-tightening force of the bolt corresponding to the reference point to obtain the axial pre-tightening force of the bolt under different displacement angles;

[0022] B5: gradually increase the load value of the displacement angle of the reference point rotating around the Z-axis and perform simulation analysis until the axial pretightening force reaches the overload pretightening force, so that the external thread of the bolt gradually contacts the internal thread of the nut and enters the yield state in a local area to form a plastic zone, realizing the overloading tightening of the nut to the bolt, combining the axial pretightening force of the bolt under different displacement angles obtained in this simulation process with the axial pretightening force of the bolt under different displacement angles obtained in B4 to form a displacement angle-pretightening force calibration curve in the first assembly state;

[0023] B6: taking the load value of the displacement angle corresponding to the overload pretightening force as negative as the displacement angle of the reference point rotating around the Z-axis in this simulation simulation, performing simulation simulation, thereby realizing the reverse tightening process simulation after reversing the loading direction, and the axial pretightening force of the bolt is returned to 0kN, so that the threaded connection structure is completely unloaded;

[0024] B7: tightening process of applying target pretightening force to the bolt again after simulation unloading, obtaining a displacement angle-pretightening force calibration curve in a repeated assembly state;

[0025] Specifically: gradually increase the load value of the displacement angle of the reference point rotating around the Z-axis and perform simulation analysis until the axial pretightening force reaches the target pretightening force, integrate the axial pretightening force of the bolt under different displacement angles obtained in this simulation process to obtain a displacement angle-pretightening force calibration curve in a repeated assembly state;

[0026] B8: combining the displacement angle-pretightening force calibration curve in the first assembly state and the displacement angle-pretightening force calibration curve in the repeated assembly state as the displacement angle-pretightening force calibration curve of the entire process of the overloading tightening method.

[0027] Further, the simulation results include the contact state, stress distribution and plastic deformation of each circle of the thread.

[0028] Further, after the simulation results under the vibration working condition meet the requirements, the actual bolt and nut are assembled according to the obtained displacement angle-pretightening force calibration curve of the entire process of the overloading tightening method to realize axial pretightening force control, specifically including:

[0029] C1: determining the displacement angle corresponding to the overload pretightening force according to the displacement angle-pretightening force calibration curve in the first assembly state, so that the nut is rotated in the forward direction until the angle measured by the angle measuring tool reaches the displacement angle corresponding to the overload pretightening force;

[0030] C2: control the nut to rotate in the reverse direction to return the axial pretightening force of the bolt to 0kN, so that the threaded connection structure is completely unloaded;

[0031] C3: According to the displacement angle-pre-tightening force calibration curve under the repeated assembly state, the displacement angle corresponding to the target pre-tightening force is determined, the nut is rotated in the positive direction, and the angle measured by the angle measuring tool is kept until the angle reaches the displacement angle corresponding to the target pre-tightening force.

[0032] In a second aspect, the present application provides an electronic device, comprising: one or more processors, and a memory for storing instructions, when the instructions are executed by the one or more processors, the one or more processors execute the bolt pre-tightening force accurate control method based on overload tightening.

[0033] In a third aspect, the present application provides a computer readable storage medium, which stores executable instructions, when the instructions are executed, the processor executes the bolt pre-tightening force accurate control method based on overload tightening.

[0034] In a fourth aspect, the present application provides a computer program product, comprising a computer program or instructions, when the computer program or instructions are executed by a processor, the bolt pre-tightening force accurate control method based on overload tightening is realized.

[0035] Compared with the prior art, the beneficial effects of the present application are:

[0036] (1) Enhance the anti-loose ability

[0037] By first overloading and tightening, the bolt is locally yielded, and then unloaded to the target pre-tightening force, which eliminates the gap between the bolt and the nut, improves the contact friction force, and significantly enhances the anti-loose performance of the bolt connection, especially suitable for high-vibration or repeated assembly working conditions. The plastic deformation generated in the initial overload stage still remains in the bolt after unloading and target pre-tightening force loading, so that the bolt maintains a certain residual stress, improves the connection stiffness and structural stability, and is beneficial to prolong the service life of the bolt.

[0038] (3) Improve the pre-tightening force calibration accuracy and the consistency of repeated assembly

[0039] The present application can realize dynamic correction and re-calibration of the pre-tightening force in the repeated assembly scene by establishing the accurate correspondence between the nut rotation angle and the bolt pre-tightening force in the finite element simulation environment. By applying angular displacement control of the Z-axis rotation degree of freedom (UR3) to the reference point (RP), the nut loading process can be accurately quantified, and the accuracy of pre-tightening force calculation and the reproducibility under repeated assembly conditions are significantly improved.

[0040] (4) Solve the problem of nonlinear error caused by material yield

[0041] When the threaded pair is stressed beyond the material yield limit, the bolt produces plastic tensile, causing the angle-pre-tightening force relationship to deviate from linearity. The present application re-establishes the pre-tightening force-angle relationship of the bolt after yielding by calibrating in the yield stage and the second calibration after yielding, realizes the accurate correction of the nonlinear characteristics after plastic deformation, and avoids the problem of pre-tightening force misalignment in the repeated assembly process.

[0042] (5) Realize the visualization and quantitative control of the whole bolt assembly process

[0043] Through the dynamic tracking of the UR3 loading state in the finite element simulation, the axial force, stress distribution and threaded pair contact state of the bolt can be obtained in real time, the visualization monitoring and quantitative analysis of the whole assembly process are realized, and an intuitive basis is provided for the pre-tightening process parameter optimization.

[0044] (6) Establish the mechanical response model under the repeated assembly scene

[0045] The present application constructs a complete finite element model including a bolt, a nut and a connected part, and considers the factors such as nonlinear contact, material yield, friction slip and the like, so that the stress and deformation evolution law of each component under the repeated assembly condition can be accurately reflected, and basic data support is provided for subsequent multiple assembly simulation and fatigue life prediction.

[0046] (7) Reduce the experimental cost and improve the engineering popularization value

[0047] Compared with the traditional pre-tightening force calibration method relying on experiment determination, the present application completes the pre-tightening force calibration process based on finite element simulation, reduces a large amount of physical test and sample consumption, and greatly reduces the engineering cost. At the same time, the simulation result can be directly used to guide the actual assembly process, and has high popularization and engineering application value.

[0048] (8) Provide an extensible pre-tightening force control framework

[0049] The finite element calibration idea proposed in the present application is not only suitable for ordinary bolt connection, but also can be extended to self-locking nut, overload tightening method, temperature coupling loading and other complex assembly scenes. The method system has good universality and expansibility, and provides a unified simulation analysis framework for subsequent research on pre-tightening force control under different materials and different loading paths. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1 The flow chart of the bolt multiple assembly pre-tightening force accurate control method based on overload tightening in the embodiment of the present application is shown;

[0051] Figure 2 The threaded connection structure, bolt and nut schematic diagram in the embodiment of the present application is shown;

[0052] Wherein, (a) is a schematic diagram of a threaded connection structure; (b) is a schematic diagram of a bolt; (c) is a schematic diagram of a nut;

[0053] Figure 3 Fig. 1 is a finite element mesh and a cross-sectional view of a threaded connection structure in an embodiment of the present application;

[0054] Fig. 1 is a finite element mesh and a cross-sectional view of a threaded connection structure in an embodiment of the present application;

[0055] Figure 4 Fig. 2 is a schematic diagram of an assembly mechanism of an overload loading tightening method in an embodiment of the present application;

[0056] Figure 5 Fig. 3 is a displacement angle-pre-tightening force calibration curve diagram of a first calibration in an embodiment of the present application;

[0057] Figure 6 Fig. 4 is a displacement angle-pre-tightening force calibration curve diagram of a second calibration in an embodiment of the present application;

[0058] Figure 7 Fig. 5 is a pre-tightening force decay diagram of different tightening processes under transverse vibration in an embodiment of the present application. DETAILED DESCRIPTION

[0059] The present application will be described in detail below with reference to the accompanying drawings and embodiments.

[0060] Embodiment 1:

[0061] A bolt multi-assembly pre-tightening force accurate control method based on overload tightening, as shown in Fig. 1, comprises the following steps: Figure 1

[0062] Step 1: Determine the geometric parameters of the threaded connection structure and construct a finite element model of the threaded connection structure;

[0063] Step 1.1: Construct a geometric model of the threaded connection structure according to the geometric parameters of the threaded connection structure;

[0064] A typical threaded connection structure is shown in Fig. 1(a), which includes a bolt, a nut, an upper compressed part and a lower compressed part, wherein the specific size of the bolt and the nut conforms to the relevant provisions of national standards GB / T5782-2016 and GB / T41-2000. In this embodiment, the bolt and the nut are as shown in Figs. 1(b) and 1(c). Figure 2 Figure 2 Figure 2 ​​​(c) as shown, the specifications of which are M10x1.5, wherein A=6.4mm, B=24mm, L=50mm, D=10mm, S=15.7mm, E=18.1mm, M=8.25mm, H1=H2=9mm, the length of the bolt tail protrusion is 2mm, the diameter of the through hole is designed to be 11.6, which meets the national standard GBT5277-1985, and the specific values are shown in Table 1.

[0065] Table 1 Geometric parameters of M10 thread;

[0066]

[0067] Step 1.2: Setting material parameters for the geometric model of the threaded connection structure;

[0068] The material parameters in the embodiment are as shown in Table 2. Figure 2

[0069] Table 2 Material parameters;

[0070]

[0071] Step 1.3: Dividing the finite element grid for the geometric model of the threaded connection structure to obtain the finite element model of the threaded connection structure;

[0072] The solid element type used in the finite element modeling is SOLID185; based on the threaded grid division method first proposed by FUKUOKA, the shape of the thread is considered, and the finite element modeling is performed on the bolt, the nut, the upper compressed part and the lower compressed part, and all the grids in the finite element model are divided into hexahedrons. Figure 3 The finite element model of the threaded connection structure established by HYPERMESH includes the bolt, the nut and the upper compressed part. In the lateral vibration test, the lateral force is applied to the upper compressed part, so the upper compressed part is also called the movable part, and the lower compressed part is fixed. In order to simplify, the lower compressed part in the Figure 2 is ignored in modeling, and this simplification is also adopted by other scholars.

[0073] There are two pairs of contact interfaces in the finite element model of the threaded connection structure: the first contact interface is the contact interface between the bolt and the nut, wherein the outer surface of the bolt is the master surface and the inner surface of the nut is the slave surface; the second contact interface is the contact interface between the nut and the compressed part, wherein the lower surface of the nut is the master surface and the upper surface of the compressed part is the slave surface; the master surface and the slave surface are respectively meshed by CONTA173 elements and TARGE170 elements;

[0074] In order to ensure the solution accuracy of the finite element results, the density of the finite element grid is tested, and the number of the finite element grid is finally determined to be about 160000. ​

[0075] Step 2: simulate the process of pre-tightening force application on the finite element model of the threaded connection structure by using the overload tightening method to obtain the displacement angle-pre-tightening force calibration curve of the entire process of the overload tightening method; the overload tightening method as shown in the figure includes three stages, which are to apply an overload pre-tightening force to the bolt beyond the target pre-tightening force, then unload the pre-tightening force, and finally apply the target pre-tightening force to the bolt again; Figure 4

[0076] Specifically, the following steps are included:

[0077] Step 2.1: first set a reference point (RP) in the finite element model of the bolted connection structure and couple it with the nodes on the outer surface of the nut in the finite element model of the bolted connection structure for controlling the rotational loading of the nut; the reference point (RP) is set on the central axis of the bolt and the nut;

[0078] Step 2.2: define the rotational freedom (UR3) of the reference point (RP) around the Z-axis as a control variable for applying a load, so that by applying an angular displacement on this rotational freedom, the rotational angle of the nut can be accurately controlled, thereby indirectly applying the axial pre-tightening force of the bolt; the direction of the Z-axis is the direction of the axial pre-tightening force;

[0079] Step 2.3: determine the target pre-tightening force and the overload pre-tightening force according to the bolt specification;

[0080] In this embodiment, the final target pre-tightening force is selected as 28kN (75% of the maximum pre-tightening force) as a typical working condition, the overload pre-tightening force in the tightening stage of the general overload tightening is 90% of the maximum pre-tightening force, and the maximum pre-tightening force can be determined by the overload ratio. In this embodiment, the overload pre-tightening force is set to 33KN (90% of the maximum pre-tightening force), and the entire loading and simulation process is displayed;

[0081] Step 2.4: set the initial loading value of the displacement angle of the rotational freedom (UR3) of the reference point (RP) around the Z-axis to realize the equivalent loading of the initial tightening process, then perform simulation analysis, read the axial pre-tightening force of the bolt corresponding to the reference point, and obtain the axial pre-tightening force of the bolt under different displacement angles;

[0082] In this embodiment, the initial loading value is set to -0.5 radians; the loading amplitude curve (Amplitude) corresponding to the displacement angle is kept at the default setting, i.e. the loading curve does not need to be modified additionally; the axial pre-tightening force is the sum of the reaction forces of each node on the bottom surface of the bolt head; the axial pre-tightening force is generated by the pre-tightening force unit method;

[0083] ​Step 2.5: gradually increase the loading value of the displacement angle of the reference point (RP) around the Z-axis rotation degree of freedom (UR3) and perform simulation analysis until the axial pretightening force reaches the overload pretightening force, so that the external thread of the bolt gradually contacts the internal thread of the nut and enters the yield state in a local area to form a plastic zone, and the nut realizes overload tightening of the bolt, the axial pretightening force of the bolt under different displacement angles obtained in this simulation process is combined with the axial pretightening force of the bolt under different displacement angles obtained in step 2.4 to form a displacement angle-pretightening force calibration curve in the first assembly state, as shown in Figure 5

[0084] In order to expand the analysis range and improve the representativeness of the calibration result in the embodiment, the loading value of the displacement angle of the reference point (RP) around the Z-axis rotation degree of freedom (UR3) is adjusted from-0.5 radian to-1 radian or-1.2 radian, and the stress distribution of the bolt, the thread pair contact state and the change of the axial pretightening force under the condition of a larger displacement angle can be observed; in addition, the corresponding data of the displacement angle and the pretightening force can be extracted by analyzing the results in the first calibration process of the previous loading case with convergence difficulty or simulation failure, and the displacement angle-pretightening force calibration curve is further enriched, which provides a reference for the finite element calibration under the subsequent repeated assembly condition; in the above manner, the bolt pretightening force calibration based on the Z-axis rotation degree of freedom (UR3) displacement angle loading (the first calibration) is realized in the finite element simulation environment, which provides basic data and calculation basis for accurate control in the subsequent repeated assembly process.

[0085] Step 2.6: in order to realize the consistency of the yield loading and unloading path, the loading value of the displacement angle corresponding to the overload pretightening force is taken as negative as the displacement angle of the reference point (RP) around the Z-axis rotation degree of freedom (UR3) in this simulation simulation, so as to realize the simulation of the back-off process after the direction of loading is reversed, and the axial pretightening force of the bolt is returned to 0kN, so that the threaded connection structure is completely unloaded, and the plastic hysteresis effect formed in the early stage is still retained in the bolt (back-off stage).

[0086] Through the method, the mechanical response of the bolt in the back-off stage after plastic deformation can be accurately captured, and then reliable control basis is provided for realizing the re-calibration of the second rotation angle-pretightening force relationship after yield and the finite element simulation under the repeated assembly state.

[0087] Step 2.7: after the simulation unloading, the tightening process of applying the target pretightening force to the bolt is performed again to obtain the displacement angle-pretightening force calibration curve under the repeated assembly state.

[0088] ​In the repeated assembly process of bolt connection, the load transfer of the contact area of the threaded pair often exceeds the yield limit of the material, resulting in plastic tensile deformation of the bolt after initial tightening, so that the effective length of the bolt and the threaded engagement state are irreversibly changed. This change directly leads to the relationship between the displacement angle and the axial pretightening force no longer maintaining linearity, but showing obvious nonlinear characteristics. If the load is applied according to the displacement angle-pretightening force calibration curve obtained in the first calibration after the material yields, even if the nut is rotated to the same angle, the axial pretightening force generated by the bolt cannot be restored to the target value, and is usually significantly lower than the design pretightening force. Therefore, after the bolt experiences plastic deformation, a second calibration is needed to reestablish the corresponding relationship between the nut displacement angle and the axial pretightening force of the bolt to ensure the loading accuracy in the repeated assembly simulation.

[0089] Specifically: gradually increase the loading value of the displacement angle of the reference point (RP) around the Z-axis rotation degree of freedom (UR3) and perform simulation analysis until the axial pretightening force reaches the target pretightening force, integrate the axial pretightening force of the bolt at different displacement angles obtained in this simulation process to obtain the displacement angle-pretightening force calibration curve in the repeated assembly state, as shown in Figure 6

[0090] Step 2.8: combine the displacement angle-pretightening force calibration curve in the first assembly state and the displacement angle-pretightening force calibration curve in the repeated assembly state as the displacement angle-pretightening force calibration curve of the entire process of the overload tightening method;

[0091] Step 3: perform simulation and analysis of the finite element model of the threaded connection structure simulated by the overload tightening method under vibration conditions, and when the simulation results meet the requirements, execute step 4, otherwise re-execute step 2;

[0092] The simulation results include the contact state, stress distribution and plastic deformation of each circle of the thread, which are key responses and serve as a benchmark for subsequent vibration condition analysis and engineering applications;

[0093] The simulation and analysis under the vibration condition is specifically: a periodic lateral force is applied on the outer circular surface of the compressed part. Since the vibration frequency of the actual test is relatively low (<12.5 Hz), the lateral vibration is assumed to be a quasi-static process in the present application, and this assumption is also adopted by other scholars. Other boundary conditions include: The bolt head surface is fully constrained; ② the bottom surface of the compressed part is constrained in the X, Y and Z directions of rotation, the Y and D directions of translation, only the X direction of parallel displacement is retained, and the X direction is the vibration displacement direction, and the Y direction is the vertical direction of the same horizontal plane;

[0094] ​Step 4: according to the displacement angle-preload calibration curve of the whole process of the overloading tightening method obtained, the actual bolt and nut are assembled to realize axial preload control;

[0095] Step 4.1: according to the displacement angle-preload calibration curve in the first assembly state, the displacement angle corresponding to the overloading preload is determined, the nut is rotated in the positive direction, and the angle measured by the angle measuring tool is measured until the angle measured by the angle measuring tool reaches the displacement angle corresponding to the overloading preload;

[0096] Step 4.2: control the nut to rotate in the reverse direction, and the bolt axial preload is returned to 0kN, so that the threaded connection structure is completely unloaded;

[0097] Step 4.3: according to the displacement angle-preload calibration curve in the repeated assembly state, the displacement angle corresponding to the target preload is determined, the nut is rotated in the positive direction, and the angle measured by the angle measuring tool is measured until the angle measured by the angle measuring tool reaches the displacement angle corresponding to the target preload and is kept, at this time, the threaded connection structure is in an elastic stress state, but the residual plastic deformation reserved in the bolt body can enhance the contact stiffness and the anti-loose ability;

[0098] The overloading tightening method provided by the application is based on the traditional torque method or torque-angle method, a controllable overloading loading higher than the target preload is introduced in a stage, and then the tightening is performed to the target preload after unloading, the geometric state and stress state of the bolt and the contact interface are adjusted through the controllable elastic-plastic loading-unloading process, so that the preload control precision and long-term stability are improved.

[0099] For single-threaded connection, the axial displacement amount of the nut relative to the bolt and the angle increment can be approximately represented as:

[0100] (1) ;

[0101] Under the small deformation assumption, the bolt and the clamped part can be equivalent to a series elastic system in the axial direction, the equivalent axial stiffness is denoted as , and the axial preload and the axial displacement amount satisfy:

[0102] (2) ;

[0103] Therefore, there is a one-to-one function relationship F(θ) between the axial preload and the angle. In the completely elastic region, F(θ) approximately increases linearly and monotonously. In the overloading tightening stage, the axial preload is increased to η times (η>1) of the target preload F t , denoted as:

[0104] (3) ;​

[0105] wherein, is the overloading pretension force;

[0106] During the loading process, the clearance between the threaded pair and the bearing surface is gradually eliminated, the actual contact area increases, the clamped part and the bolt bearing surface have obvious embedded deformation, the equivalent stress of the bolt shank and the first circle of thread root can reach or slightly exceed the yield strength, and the local area enters the elastic-plastic state. At this time, the equivalent axial stiffness k eq Changes relative to the initial assembly stage, and the F(θ) curve gradually transitions from approximately linear to elastic-plastic.

[0107] After completing the overloading, the nut is reversed to unload, and the axial pretension force gradually decreases until it approaches zero or a specified small value. During the unloading process, the stress in the elastic region returns along the original linear path, and the plastic region produces stress return and retains residual plastic strain. At the end of unloading, a specific residual stress field and residual deformation state is formed inside the bolted structure: the bolt shank has a certain plastic tensile, the clamped part and the bearing surface maintain a high actual contact area, and the threaded engagement state is more stable than the initial assembly.

[0108] On this basis, it is tightened again to the target pretension force F t At this time, since the gap and the main embedded deformation have been completed in the overloading stage, the pretension force-rotation relationship in the second loading process is: the nonlinear section is significantly shortened, the equivalent axial stiffness k eq is increased and the change range is reduced, and the slope of the F(θ) curve near the target pretension force is more stable. For the same batch of bolt connections, the rotation angle interval corresponding to the target pretension force tends to converge, making the axial pretension force more easily controlled by the rotation angle to achieve accurate reproduction.

[0109] Under multiple disassembly and repeated tightening conditions, the bolt and the contact interface may still produce limited additional plastic deformation, but its increment is significantly smaller than that in the initial overloading stage. By calibrating the F(θ) relationship under each assembly state, the corrected rotation angle corresponding to the target pretension force under different assembly times can be obtained, and the pretension force can be predicted and controlled throughout the life cycle of multiple tightening.

[0110] Based on the above, the precise tightening based on overloading can be determined, which has obvious advantages compared to traditional methods based on only single elastic tightening or simple torque-rotation control in the following aspects:

[0111] (1) The controlled overloading process makes the thread engagement length, contact area and interface indentation deformation stable, and the pre-tightening force is mainly determined by the equivalent axial stiffness and rotation angle in the second tightening process, which reduces the sensitivity to the random fluctuation of the contact friction coefficient. The F(θ) curves of the bolts in the same batch are more consistent near the target pre-tightening force, thereby significantly reducing the pre-tightening force dispersion and improving the stress consistency of the multi-bolt connection.

[0112] (2) The main evolution of the indentation deformation and micro contact topography is completed in the overloading process, and the additional indentation and initial relaxation amplitude under the target pre-tightening force and service load are significantly reduced. The existence of residual compressive stress is beneficial to inhibit the early relaxation and the development of partial fatigue damage, so that the pre-tightening force attenuation rate under vibration and cyclic load conditions is reduced, and the long-term pre-tightening force retention capability is improved.

[0113] (3) Through the geometric relationship and equivalent stiffness model, combined with finite element analysis or experimental calibration, the complete F(θ) curve can be obtained in the overloading tightening, unloading and re-tightening stages. For the bolt connection that has experienced overloading treatment, the rotation angle control parameter corresponding to the target pre-tightening force can be established for different assembly times. Compared with using only the empirical torque value or single rotation angle control, this method can maintain the pre-tightening force control precision under multiple disassembly conditions, and is particularly suitable for structures with strict requirements for repeated assembly consistency.

[0114] (4) The overloading tightening method explicitly expresses the pre-tightening force control process as a rotation angle-pre-tightening force relationship, and the F(θ) curve under different overloading coefficients, material parameters and structure forms can be predicted and optimized through the finite element model. This relationship can be directly embedded in the control strategy of the torque-rotation angle tightening machine, servo tightening system and other numerical control equipment, realizing the parameterized control and digital management of the pre-tightening process, and providing a unified initial pre-tightening force boundary condition for vibration, anti-loose and fatigue life analysis.

[0115] (5) The process path of first tightening-unloading-reloading can complete the first two steps of pre-treatment in the factory manufacturing stage, i.e. only the rotation angle needs to be loaded to the target pre-tightening force at the assembly site, so that the indentation setting and residual stress establishment are moved to the manufacturing link. By observing and measuring the pre-tightening force evolution, bolt axial elongation and thread engagement form during the overloading tightening and unloading process in the manufacturing stage, the system data of bolt effective length change, thread load distribution and local deformation characteristics under different working conditions can be obtained. These data can provide quantitative basis and optimization direction for the parameter design of special thread structures such as variable pitch bolts, and improve the coordination degree between bolt geometric design and overloading tightening process.

[0116] The anti-loose effect of the method of the present application is compared with that of other existing technologies, as shown in Figure 7

[0117] ​The pre-tightening force decay curves of the threaded connection structures assembled by common tightening and overload tightening method are analyzed under the same target pre-tightening force and transverse vibration. Firstly, the pre-tightening force of the two working conditions has a larger decay in the first vibration cycle, and the decay of working condition one is larger. Then, it enters the slow decay stage, and the initial drop of the overload back-off curve is significantly smaller, and it transitions to the approximate linear low slope section faster. The pre-tightening force decay process conforms to the typical pre-tightening force decay curve. Secondly, in terms of unit cycle decay slope K in the steady state stage, the overload back-off is always smaller than the single loading, and the curve is smoother. Finally, the pre-tightening force retention rate at the end of the test or at the same cycle count, the overload back-off is higher than the single loading throughout.

[0118] The local yielding introduced in the overload phase and the pitch difference make the multi-turn thread form a stable cooperative load under the target pre-tightening force, reducing the unloading amplitude of the leading edge layer and the micro-slip in the cycle, thus showing smaller initial relaxation, lower long-term decay slope and higher final value retention rate under vibration. The overload back-off is superior to the single loading tightening method in terms of initial anti-relaxation and long-term pre-tightening retention, which is direct evidence of its stronger pre-tightening force retention ability.

[0119] Embodiment 2

[0120] The embodiment provides an electronic device, comprising: one or more processors, and a memory for storing instructions that, when executed by the one or more processors, cause the one or more processors to perform the method for accurate control of pre-tightening force of bolt multi-assembly based on overload tightening.

[0121] The electronic device can be a mobile phone, computer, tablet computer or the like, comprising a memory and a processor, and the memory stores a computer program which, when executed by the processor, implements the method for accurate control of pre-tightening force of bolt multi-assembly based on overload tightening as described in the embodiments. It can be understood that the electronic device can further comprise an input / output (I / O) interface and a communication component.

[0122] The processor is configured to execute all or part of the steps of the method for accurate control of pre-tightening force of bolt multi-assembly based on overload tightening as described in the above embodiments. The memory is configured to store various types of data, which can include, for example, instructions of any application program or method in the electronic device, and application program related data.

[0123] The processor can be an Application Specific Integrated Cricuit (ASIC), a Digital Signal Processor (DSP), a Programmable Logic Device (PLD), a Field Programmable Gate Array (FPGA), a controller, a microcontroller, a microprocessor, or other electronic elements, which are used to execute the bolt multi-assembly pre-tightening force accurate control method based on overload tightening described in the above embodiments.

[0124] Embodiment 3

[0125] The embodiment provides a computer readable storage medium, which stores executable instructions. When the instructions are executed, if a software function unit is implemented and sold or used as an independent product, the instructions can be stored in one computer readable storage medium.

[0126] The computer software product is stored in a storage medium, and includes a plurality of instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the bolt multi-assembly pre-tightening force accurate control method based on overload tightening described in various embodiments of the present application.

[0127] The aforementioned storage media include: flash memory, hard disks, multimedia cards, card-type memory (e.g., SD (Secure Digital Memory Card) or DX (Memory Data Register, MDR) memory), random access memory (RAM), static random-access memory (SRAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), programmable read-only memory (PROM), magnetic storage, disks, optical discs, servers, APP (Application) app stores, and other media capable of storing program verification codes. These media store computer programs, and when executed by a processor, they can implement the various steps of the aforementioned method for precise control of preload force in multiple bolt assembly based on overload tightening.

[0128] Example 4:

[0129] This embodiment proposes a computer program product, including a computer program or instructions, which, when executed by a processor, implements the aforementioned method for precise control of preload force in multiple assembly of bolts based on overload tightening.

[0130] Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or part of the technical solution, can be embodied in the form of a computer program product.

[0131] The various embodiments in this application are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0132] The scope of protection of this application is not limited to the embodiments described above. Obviously, those skilled in the art can make various modifications and variations to this disclosure without departing from the scope and spirit of this disclosure. If such modifications and variations fall within the scope of this disclosure and its equivalents, then the intent of this disclosure also includes these modifications and variations.

Claims

1. A method for precise control of preload force in multiple bolt assembly based on overload tightening, characterized in that, Includes the following steps: Determine the geometric parameters of the threaded connection structure and construct the finite element model of the threaded connection structure; The overload tightening method is used to simulate the preload application process on the finite element model of the threaded connection structure, and the displacement angle-preload calibration curve of the entire process of the overload tightening method is obtained. The overload tightening method includes three stages: applying an overload preload to the bolt beyond the target preload, then unloading the preload, and finally applying the target preload to the bolt again. The finite element model of the threaded connection structure simulated by the overload tightening method is simulated under vibration conditions. After the simulation results under vibration conditions meet the requirements, the actual bolts and nuts are assembled according to the displacement angle-preload calibration curve of the entire overload tightening method to achieve axial preload control. If the requirements are not met, the displacement angle-preload calibration curve of the entire overload tightening method is re-obtained.

2. The method for precise control of preload force in multiple bolt assembly based on overload tightening according to claim 1, characterized in that, The determination of the geometric parameters of the threaded connection structure and the construction of the finite element model of the threaded connection structure specifically include: A1: Construct a geometric model of the threaded connection structure based on its geometric parameters; the threaded connection structure includes a bolt, a nut, an upper clamping member, and a lower clamping member; A2: Set material parameters for the geometric model of the threaded connection structure; A3: Divide the geometric model of the threaded connection structure into a finite element mesh to obtain the finite element model of the threaded connection structure.

3. The method for precise control of preload force in multiple bolt assembly based on overload tightening according to claim 1, characterized in that, The process of applying preload using the overload tightening method on the finite element model of the threaded connection structure is simulated to obtain the displacement angle-preload calibration curve for the entire overload tightening process, specifically including: B1: First, a reference point is set in the finite element model of the bolted connection structure and coupled with the node on the outer surface of the nut in the finite element model of the bolted connection structure to control the rotational loading of the nut; the reference point is set on the central axis of the bolt and the nut. B2: Define the rotational degree of freedom of the reference point about the Z-axis as the control variable for applying the load, so that by applying angular displacement on this rotational degree of freedom, the rotation angle of the nut can be controlled, thereby indirectly applying the axial preload of the bolt; the Z-axis direction is the direction of the axial preload. B3: Determine the target preload and overload preload based on the bolt specifications; B4: Set the initial loading value of the displacement angle of the reference point about the Z-axis rotation degree of freedom to realize the equivalent loading of the initial tightening process, and then perform simulation analysis to read the axial preload of the bolt corresponding to the reference point and obtain the axial preload of the bolt under different displacement angles. B5: Gradually increase the loading value of the displacement angle of the reference point about the Z-axis rotation degree of freedom and perform simulation analysis until the axial preload reaches the overload preload, so that the external thread of the bolt and the internal thread of the nut gradually contact each other and enter the yield state in a local area, forming a plastic zone, so that the nut can overload the bolt. Combine the axial preload of the bolt under different displacement angles obtained in this simulation with the axial preload of the bolt under different displacement angles obtained in B4 to form the displacement angle-preload calibration curve in the first assembly state. B6: The loading value of the displacement angle corresponding to the overload preload is negative and used as the displacement angle of the reference point about the Z-axis rotation degree of freedom in this simulation. The simulation is carried out to realize the simulation of the tightening process after the loading direction is reversed. The axial preload of the bolt is reduced to 0kN, so that the threaded connection structure is completely unloaded. B7: Perform a simulated unloading and then apply the target preload to the bolt again during the tightening process to obtain the displacement angle-preload calibration curve under repeated assembly conditions; Specifically: Gradually increase the loading value of the displacement angle of the reference point about the Z-axis rotation degree of freedom and perform simulation analysis until the axial preload reaches the target preload. Integrate the axial preload of the bolts under different displacement angles obtained in this simulation to obtain the displacement angle-preload calibration curve under repeated assembly conditions. B8: Combine the displacement angle-preload calibration curve under the first assembly state and the displacement angle-preload calibration curve under the repeated assembly state to form the displacement angle-preload calibration curve for the entire process of the overload tightening method.

4. The method for precise control of preload force in multiple bolt assembly based on overload tightening according to claim 1, characterized in that, The simulation results include the contact state, stress distribution, and plastic deformation of each thread turn.

5. The method for precise control of preload force in multiple bolt assembly based on overload tightening according to claim 1, characterized in that, After the simulation results under the vibration condition meet the requirements, the actual bolts and nuts are assembled according to the displacement angle-preload calibration curve of the entire overload tightening process to achieve axial preload control, specifically including: C1: Based on the displacement angle-preload calibration curve in the first assembly state, determine the displacement angle corresponding to the overload preload, and rotate the nut in the positive direction until the angle measured by the angle measuring tool reaches the displacement angle corresponding to the overload preload. C2: Control the nut to rotate in the opposite direction, return the axial preload of the bolt to 0kN, and completely unload the threaded connection structure; C3: Based on the displacement angle-preload calibration curve under repeated assembly conditions, determine the displacement angle corresponding to the target preload, rotate the nut in the positive direction until the angle measured by the angle measuring tool reaches the displacement angle corresponding to the target preload, and then hold it.

6. An electronic device, characterized in that, include: One or more processors, and a memory for storing instructions that, when executed by the one or more processors, cause the one or more processors to perform the method for precise control of preload force in multiple assembly of bolts based on overload tightening, as described in any one of claims 1-5.

7. A computer-readable storage medium, characterized in that, It stores executable instructions that, when executed, cause the processor to perform the method for precise control of preload in multiple assembly of bolts based on overload tightening, as described in any one of claims 1-5.

8. A computer program product, characterized in that, Includes a computer program or instructions that, when executed by a processor, implement the method for precise control of preload force in multiple assembly of bolts based on overload tightening, as described in any one of claims 1-5.

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