Tightening method of threaded fastener

Abstract

The invention provides a screwing method for a threaded fastener. The screwing method comprises the steps that the target torque T0 of the threaded fastener is obtained; n sub-torques are sequentially set from small to large according to the target torque T0; sequentially tightening the threaded fastener to a sub-torque T1, a sub-torque T2,..., a sub-torque Tn by using a tightening tool; after the threaded fastener is tightened to each sub-torque, at least one time of back-screwing is included, during back-screwing, the torque of the tightening tool is set to be a back-screwing standard torque, and the back-screwing standard torque is 60%-80% of the sub-torque before back-screwing; when back-screwing is completed and the threaded fastener is not loosened, the threaded fastener is tightened to the next torque of the sub-torque before back-screwing; the threaded fastener is tightened to a target torque T0 using a tightening tool. The method has the advantages that the whole tightening process is divided into several stages, the influence caused by manual tightening operation is reduced, the torque dispersion is small, the compensation torque value of the next stage is increased through reverse back-screwing, and the influence of the lead angle and the embedding damage amount between a clamping piece and a fastener is eliminated.

Description

Technical Field

[0001] The invention relates to the technical field of fasteners, and in particular to a method for tightening a threaded fastener. Background Art

[0002] In the automobile test laboratory, due to the limitation of on-site conditions, it is inconvenient to perform mechanized operation for bolt tightening. The assembly and bolt tightening of many test vehicles and parts can only be completed manually by testers, who only rely on their experience and the torque value set on the torque wrench used to judge and tighten the state. Due to the differences in tightening methods and skills and experience of each person, the axial preload of the bolts is often dispersed, which affects the assembly quality of parts and even affects the performance test results such as vehicle reliability. For automobile testing and trial production, the correctness of fastener installation directly affects the use status of parts and further affects the test results and trial production conclusions. Therefore, it is particularly important to reduce the dispersion of fastener installation torque and reduce the difference between the final installation torque and the target torque. Summary of the invention

[0003] In order to solve at least one of the above technical problems, the present invention provides a method for tightening a threaded fastener, which adopts a torque tightening method that combines segmentation and back-tightening to reduce the impact of manual tightening operations and reduce the impact of the thread lead angle and the embedding loss of the contact surface between the clamp and the fastener.

[0004] The present invention solves the technical problem by adopting the following technical solution:

[0005] A method for tightening a threaded fastener comprises the following steps:

[0006] Step S1, obtaining a target torque T0 of a threaded fastener;

[0007] Step S2, according to the target torque T0, n sub-torques T1, T2, ..., Tn are set in order from small to large, each sub-torque is smaller than the target torque, wherein n is an integer and n≥2;

[0008] Step S3, use a tightening tool to tighten the threaded fastener to sub-torque T1, sub-torque T2, ..., sub-torque Tn in sequence; after the threaded fastener is tightened to each sub-torque, at least one back-tightening is included, during which the torque of the tightening tool is set to the back-tightening standard torque, and the back-tightening standard torque is 60%-80% of the sub-torque before back-tightening; when the back-tightening is completed and the threaded fastener is not loose, the threaded fastener is tightened to the next torque of the sub-torque before back-tightening;

[0009] Step S4: Use a tightening tool to tighten the threaded fastener to a target torque T0.

[0010] Furthermore, the method further comprises: when re-tightening, if the threaded fastener becomes loose, replacing the threaded fastener with a new one and re-performing step S3.

[0011] Further, when a tightening tool is used to tighten a threaded fastener to a sub-torque Ti, the tightening tool maintains the sub-torque Ti for time ti, where i=1, 2, ..., n; and / or, when a tightening tool is used to tighten a threaded fastener to a target torque T0, the tightening tool maintains the target torque T0 for time t0; preferably, the time ti for the tightening tool to maintain the sub-torque Ti and the time t0 for maintaining the target torque T0 are 1-5s, so as to release the elastic strain of the bolt at each stage and reduce attenuation.

[0012] Furthermore, according to the target torque T0, 1-4 sub-torques are set in sequence from small to large.

[0013] Furthermore, according to the target torque T0, the sub-torque T1 and the sub-torque T2 are set in order from small to large, and the tightening process is divided into three stages, which is beneficial to the operability of applying each torque stage.

[0014] Further, step S3 includes the following steps:

[0015] Step S3.1, tightening the threaded fastener to a sub-torque T1, and the tightening tool maintains the sub-torque T1 for a time t1;

[0016] Step S3.2, back-tighten the threaded fastener, and set the torque of the tightening tool to the back-tightening standard torque T1′, and the back-tightening standard torque T1′ is 60%-80% of the sub-torque T1;

[0017] Step S3.3, determine whether the threaded fastener is loose, if the threaded fastener is not loose, execute step S3.4, if the threaded fastener is loose, replace it with a new one, and return to step S3.1;

[0018] Step S3.4, tightening the threaded fastener to a sub-torque T2, and the tightening tool maintains the sub-torque for a time t2;

[0019] Step S3.5, back-tighten the threaded fastener, and set the torque of the tightening tool to the back-tightening standard torque T2′, and the back-tightening standard torque T2′ is 60%-80% of the sub-torque T2;

[0020] Step S3.6, determine whether the threaded fastener is loose. If the threaded fastener is not loose, execute step S4. If the threaded fastener is loose, replace it with a new one and return to step S3.1.

[0021] Furthermore, the sub-torque T1 is 40%-50% of the target torque T0, and the sub-torque T2 is 70%-80% of the target torque T0.

[0022] Furthermore, the standard torque for back-tightening is 65%-72% of the torque before back-tightening.

[0023] Furthermore, when tightening multiple threaded fasteners, first execute steps S3.1-S3.3 to tighten each threaded fastener to sub-torque T1 and back-tighten, then execute steps S3.4-S3.6 to tighten each threaded fastener to sub-torque T2 and back-tighten, and then execute step S4 to tighten each threaded fastener to target torque T0.

[0024] Furthermore, the tightening tool includes a torque digital display wrench, which applies torque accurately with small discreteness.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The entire tightening process is divided into several stages, and the target torque is divided into several sub-torques. Tightening is performed step by step, which reduces the impact of manual tightening operations. The gap between the actual tightening torque and the target torque is small, and the torque discreteness is small.

[0027] (2) Reverse tightening can increase the compensation torque value of the next stage, thereby eliminating the influence of the thread lead angle and the amount of embedded damage between the clamp and the fastener.

[0028] (3) Improve the surface roughness and flatness of the connected surfaces, thereby changing the friction coefficient; prevent the occurrence of "false torque" caused by manufacturing reasons or surface cleaning. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to better understand the above and other purposes, features, advantages and functions of the present invention, reference may be made to the embodiments shown in the accompanying drawings. The same reference numerals in the accompanying drawings refer to the same components. It should be understood by those skilled in the art that the accompanying drawings are intended to schematically illustrate the preferred embodiments of the present invention and have no limiting effect on the scope of the present invention, and the components in the drawings are not drawn to scale.

[0030] Figure 1 The present invention is a flowchart of a method for tightening a threaded fastener.

[0031] Figure 2 The following are the measured torque distribution diagrams of bolts tightened using a digital torque wrench and a torque meter respectively.

[0032] Figure 3 The flowchart of one embodiment of the present invention is shown in FIG.

[0033] Figure 4 This is a torque curve diagram of an embodiment of the present invention.

[0034] Figure 5This is the measured torque curve of the bolt when it is loosened during the first stage of tightening.

[0035] Figure 6 This is the measured torque curve of the bolt when it loosens during the second stage of tightening.

[0036] Figure 7 The measured torque distribution diagram of bolts tightened using four torque tightening methods. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the exemplary embodiments of the present invention are described below in conjunction with the accompanying drawings, including various details of the embodiments of the present invention to facilitate understanding, which should be considered as merely exemplary. Therefore, it should be recognized by those of ordinary skill in the art that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present disclosure. Similarly, for the sake of clarity and conciseness, the description of well-known functions and structures is omitted in the following description.

[0038] In the description of the present invention, it should be noted that the term "including" and its variations represent open inclusion, that is, "including but not limited to". The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance. The term "and / or" when used to list two or more items means that any one of the listed items can be used, or any combination of two or more of the listed items can be used. In addition, in the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0039] There are four main tightening methods for threaded fasteners: torque method, torque angle method, yield point control method and elongation control method. However, all of them have limitations and applicable scenarios, and rely heavily on personnel experience and the accuracy of special tightening equipment. In particular, human operation will lead to large torque discreteness and errors.

[0040] (1) Torque method: The torque method is the most commonly used manual tightening method. The manual tightening operation is simple. It is a control method that directly tightens within the elastic range of the material using the linear relationship between the tightening torque and the axial preload. The target torque value is set by the torque wrench, and the threaded fastener is directly tightened to the target torque value. The fasteners tightened by this method can be repeatedly disassembled and assembled without the need to replace new threaded fasteners. However, since the axial preload obtained by manual operation has a large discreteness, the main factors affecting the tightening quality are the following five points: the difference in manual tightening operation; the material, processing accuracy and surface quality of the threaded fastener; the perpendicularity between the thread centerline and the fastening connection surface; the surface quality and flatness of the connected parts; the error in thread lubrication, tightening speed and thread diameter.

[0041] (2) Torque angle method: The torque angle method is also a commonly used manual tightening method. It comprehensively utilizes the effects of tightening torque and angle on axial preload. It first tightens to the initial torque, allowing the threaded fastener to pass through the elastic range, and then twists to the specified angle to allow the threaded fastener to enter the yield area and reach the yield point, thereby obtaining the required axial preload, making full use of the material strength of the threaded fastener to achieve the purpose of high-precision axial force control. The fasteners tightened by this method are usually parts that require a large torque, such as chassis parts. New threaded fasteners need to be replaced every time they are disassembled and assembled. It has the advantages of large axial preload, small discreteness, and high reliability. The main factors affecting its tightening quality are the following four points: the torque and angle of the manual tightening operation cannot be accurately guaranteed; thread processing accuracy; elastic modulus of the threaded fastener material; hardness of the threaded fastener material.

[0042] (3) Yield point control method: The yield point control method uses the relationship between tightening torque and rotation angle to monitor whether the threaded fastener has reached the yield point by calculating the change in torque slope in real time. When the slope of the torque-rotation angle curve is judged to have dropped significantly, tightening is stopped. The accuracy of the axial preload is determined by the yield limit of the threaded fastener material. A larger axial preload can be obtained more accurately. The preload is concentrated near the average value, has a very small discreteness, and is not affected by the elastic modulus of the operator, threaded fastener, and fastened component. After the connected component is disassembled, a new threaded fastener needs to be replaced. This method requires a computer system to assist in monitoring and judgment (instead of human operation), the tightening system is complex, and the tightening cost is high.

[0043] (4) Elongation control method: The elongation control method uses measuring instruments to monitor the changes in the axial elongation of threaded fasteners during the tightening process, or uses ultrasonic and other measuring methods to monitor the axial deformation of threaded fasteners. The axial preload is controlled by controlling the axial elongation of the threaded fasteners. This is also the most accurate and reliable tightening method currently. However, the measuring device of this method is complex and it is difficult to easily install and measure on a vehicle assembly with a complex structure. In addition, the equipment is expensive, the operation is complicated, and the tightening cost is high.

[0044] Considering the limitations of the laboratory and trial production operations, the characteristics of metal materials and the cost, the tightening method of the present invention adopts a torque method to control the tightening process of the threaded fastener by torque.

[0045] The present invention provides a method for tightening a threaded fastener, such as Figure 1 As shown, the following steps are included:

[0046] Step S1, obtaining a target torque T0 of a threaded fastener;

[0047] Step S2, according to the target torque T0, n sub-torques T1, T2, ..., Tn are set in order from small to large, each sub-torque is smaller than the target torque, wherein n is an integer and n≥2;

[0048] Step S3, use a tightening tool to tighten the threaded fastener to sub-torque T1, sub-torque T2, ..., sub-torque Tn in sequence; after the threaded fastener is tightened to each sub-torque, at least one back-tightening is included, during which the torque of the tightening tool is set to the back-tightening standard torque, and the back-tightening standard torque is 60%-80% of the sub-torque before back-tightening; when the back-tightening is completed and the threaded fastener is not loose, the threaded fastener is tightened to the next torque of the sub-torque before back-tightening;

[0049] Step S4: Use a tightening tool to tighten the threaded fastener to a target torque T0.

[0050] In step S1, the target torque T0 for tightening the threaded fastener can be obtained according to the threaded fastener drawing or according to the specification of the threaded fastener. In step S2, n sub-torques are set in sequence from small to large, and the tightening process of the threaded fastener can be divided into n+1 stages. Step S3 tightens the threaded fastener step by step according to each torque, reducing the impact of the manual tightening operation, and can avoid or improve many adverse factors of the torque tightening method, such as improving the surface roughness and flatness of the connected surface, thereby changing the friction coefficient, and preventing the "false torque" phenomenon caused by manufacturing reasons or surface cleaning, so that the actual tightening torque is small from the target torque, and the torque discreteness is small. Step 3 After tightening the threaded fastener to the sub-torque, it is re-tightened, that is, the threaded fastener is reversely loosened. When re-tightening between each sub-torque, the next torque of the sub-torque before re-tightening is the next sub-torque; after tightening the threaded fastener to the sub-torque Tn and then completing the re-tightening, when the threaded fastener is not loose, the next torque is the target torque T0. The reverse back-tightening operation can increase the compensation torque value of the next stage, thereby eliminating the influence of the embedded damage between the clamp and the fastener, making the actual tightening torque closer to the target torque, reducing the discreteness of the preload force, and ensuring the quality of part assembly.

[0051] Preferably, in step 3, when the tightening tool is used to tighten the threaded fastener to the sub-torque Ti, the tightening tool can maintain the sub-torque Ti time ti, where i=1, 2, ..., n. And / or, in step 4, when the tightening tool is used to tighten the threaded fastener to the target torque T0, the tightening tool maintains the target torque T0 time t0. In this way, the elastic strain of the bolt at each stage can be released and the attenuation can be reduced. Preferably, the time ti for the tightening tool to maintain the sub-torque Ti and the time t0 for maintaining the target torque T0 are 1-5s, and the holding time includes 1s, 1.5s, 2s, 2.5s, 3s, 3.5s, 4s, 4.5s, 5s, etc.

[0052] It is understandable that the tightening method of the threaded fastener of the present invention can be applied to threaded fasteners such as bolts, nuts, and screws. For the convenience of description, the tightening method is described below by taking bolts as an example.

[0053] In order to reduce the impact of the accuracy of the tightening equipment, it is necessary to select more accurate manual tightening tools. Considering factors such as ease of operation and tightening costs, the current laboratory can only tighten bolts through manual operation. Usually, the laboratory has two types of tightening equipment: digital torque wrenches and handheld torque meters. Digital torque wrenches can display the specific value of torque in real time, while handheld torque meters can record the angle and torque curve of the entire tightening process through a computer.

[0054] The operating accuracy of the two devices was compared by taking a bolt with a standard torque of 50N∙m as an example. The same experienced tester used the two devices to torque the bolt to 50N∙m, and then measured the stable torque of the bolt after the bolt was left to stand for 30 minutes. 1000 samples were randomly collected from the same batch of bolts, and the sample data were rounded off according to the rounding method. Statistical analysis was performed. The comparison between the torque digital wrench and the torque measuring instrument is shown in Table 1 and Figure 2 As shown, Figure 2 The distribution histogram and distribution curve of the measured torque of bolts tightened using two tightening tools are shown.

[0055] Table 1 Comparison of tightening tools

[0056]

[0057] From the comparison results, it can be seen that the results of the digital torque wrench are more accurate and have a smaller discreteness than those of the torque meter. Although the torque meter can record the angle-torque curve, the sampling frequency is low, and a torque value is collected every 1° rotation, resulting in some torque values ​​not being collected, thereby increasing the error of manual reading of data. Therefore, preferably, the tightening tool uses a digital torque wrench.

[0058] The basic requirement of bolt connection is to ensure that the bolt and the connected parts do not experience axial elongation, shear fracture, fatigue fracture, loosening of preload force, crushing of connected parts, etc. during preload and use. The essence of various tightening methods is to ensure that the bolt has sufficient axial preload force.

[0059] The relationship between the axial preload and the tightening torque is as shown in formula (1):

[0060] (1)

[0061] Where Mc is the tightening torque, P is the axial preload, d is the thread diameter, d1 is the thread pitch diameter, f is the friction coefficient between threads, α is the thread lead angle, β is the tooth profile half angle, f1 is the friction coefficient between the nut and the gasket, D is the nut support surface diameter, d k is the gasket hole diameter.

[0062] It can be seen from formula (1) that the axial preload is proportional to the tightening torque. The axial preload coefficient is mainly related to the thread lead angle α of the bolt and the nut, the friction coefficient f between the threads, and the friction coefficient f1 between the nut and the washer. When tightening the bolt, the torque applied by the external force to the bolt is mainly used to resist the friction force and the thread lead angle. When the bolt is tightened to the sub-torque and then re-tightened, the re-tightening torque must be lower than the sub-torque before re-tightening. Therefore, in step S3, when re-tightening, the torque of the tightening tool is set to the re-tightening standard torque, and the re-tightening standard torque is set to 60%-80% of the sub-torque before re-tightening. Preferably, the re-tightening standard torque is 65%-72% of the sub-torque before re-tightening. For example, after tightening the bolt to a sub-torque of Ti, the bolt is re-tightened. The standard torque for re-tightening can be set to Ti*60%, Ti*62%, Ti*65%, Ti*66%, Ti*67%, Ti*68%, Ti*69%, Ti*70%, Ti*71%, Ti*72%, Ti*73%, Ti*74%, Ti*75%, Ti*80%, etc. During re-tightening, if the torque wrench makes a "click" sound, it indicates that the applied torque reaches the standard torque for re-tightening, and it can be determined that the bolt is not loose, and a larger torque needs to be applied to loosen the bolt; if the torque wrench does not make a "click" sound, it indicates that the applied torque cannot reach the standard torque for re-tightening, and it can be determined that the bolt is loose. At this time, it can even be seen that the bolt is loosened.

[0063] The relationship between the axial preload and the tightening angle is as shown in formula (2):

[0064] (2)

[0065] Where θ is the tightening angle, p is the thread pitch, P is the axial preload, K b is the bolt stiffness, K p is the stiffness of the connected parts.

[0066] It can be seen from formula (2) that the axial preload is proportional to the tightening angle. During the operation, when the torque wrench makes a "click" sound to remind you that it is tightened in place, you should stop applying torque in time, otherwise the applied torque will increase, causing the actual tightening torque to exceed the target value.

[0067] In one embodiment of the present invention, the method further includes: when re-tightening, if the threaded fastener becomes loose, a new threaded fastener is replaced, and step S3 is re-executed. When two parts are connected by bolts in the laboratory or trial production, the surface state of the bolt is destroyed during the tightening process. If the loose bolts are continued to be used to connect the two parts, the constraint conditions of the parts cannot meet the requirements. In order to make the connection between the parts reliable and ensure the reliability of the test results, it is necessary to ensure that the state of the bolts meets the requirements. Therefore, when re-tightening, if the threaded fastener becomes loose, a new threaded fastener is replaced, and the segmented tightening operation of step S3 is re-executed. It can be understood that when the bolt and nut are used in combination, when tightening the bolt, if the bolt becomes loose when re-tightening, a new bolt is replaced, and when tightening the bolt and then tightening the nut, if the nut becomes loose when re-tightening, a new bolt and nut are replaced.

[0068] In one embodiment of the present invention, according to the target torque T0, 1-4 sub-torques are set in order from small to large. Preferably, according to the target torque T0, sub-torques T1 and sub-torques T2 are set in order from small to large, that is, the tightening process is divided into three stages. If there are too few segments (2 stages), the overall holding time is too short, which is not conducive to the final torque being close to the target torque; if there are too many segments (4-5 stages), the torque value required to be increased in the latter stage is small relative to the previous stage, and the operator only needs to turn a small angle to reach the next torque value when applying torque, which is not conducive to the operability of each stage of torque application, and it is easy to over-tighten, and the speed will be too fast at the end of the torque application, and the consistency will be worse, resulting in increased discreteness. Preferably, sub-torque T1 is 40%-50% of the target torque T0, and sub-torque T2 is 70%-80% of the target torque T0. For example, sub-torque T1 can be set to T0*40%, T0*45%, T0*50%, etc., and sub-torque T2 can be set to T0*70%, T0*75%, T0*80%, etc.

[0069] In one embodiment of the present invention, when the tightening process is divided into three stages, such as Figure 3As shown, step S3 includes step S3.1-step S3.6. In step S3.1, the bolt is tightened in the first stage. At this time, the torque of the torque wrench is set to sub-torque T1, and the bolt is tightened to sub-torque T1, T1=T0*50%, and sub-torque T1 is maintained for about 5s. In step S3.2, the bolt is re-tightened. At this time, the torque of the torque wrench is set to the re-tightening standard torque T1′, and the re-tightening standard torque T1′=T1*70%=T0*50%*70%. In step S3.3, after re-tightening the bolt, determine whether the bolt is loose. If the bolt is not loose, continue to execute step S3.4. If the bolt is loose, replace it with a new bolt, return to step S3.1, and re-perform the segmented tightening operation. In step S3.4, the bolt is tightened in the second stage. At this time, the torque of the torque wrench is set to sub-torque T2, and the bolt is tightened to sub-torque T2, T2=T0*70%, and the sub-torque T2 is maintained for about 5s. In step S3.5, the bolt is re-tightened. At this time, the torque of the torque wrench is set to the re-tightening standard torque T2′, and the re-tightening standard torque T2′=T2*70%=T0*70%*70%. In step S3.6, after the bolt is re-tightened, it is determined whether the bolt is loose. If the bolt is not loose, step S4 is executed to perform the third stage tightening and tighten the bolt to the target torque T0; if the bolt is loose, a new bolt is replaced, and the process returns to step S3.1 to re-perform the segmented tightening operation. In this embodiment, when the bolt does not loosen in the first stage and the second stage, the measured torque curve of the bolt is as follows: Figure 4 As shown in the figure, the torque of the bolt increases in a step-like manner to the target torque T0. If the bolt is loosened during the first stage of tightening, the measured torque curve of the bolt is as follows: Figure 5 As shown in the figure, the torque of the bolt increases to the first sub-torque T1 and then decreases. If the bolt is loosened during the second stage of tightening, the measured torque curve of the bolt is as follows: Figure 6 As shown, the torque of the bolt increases in a step-like manner to the second sub-torque T2 and then decreases.

[0070] The segmented torque tightening method (segmented + back-tightening) of the present invention takes into account the main influencing factors of the torque tightening method and the characteristics of metal materials, and proposes from the perspective of the operating process of the torque tightening method that the entire tightening process is divided into several stages, and the target torque is divided into several sub-torques, which are tightened step by step, thereby reducing the impact of manual tightening operations and increasing the compensation torque value of the next stage, thereby eliminating the impact of the thread lead angle and the amount of embedded damage between the clamp and the fastener, so that the actual tightening torque is closer to the target torque.

[0071] Common manual torque tightening methods include one-time torque tightening method and reverse torque tightening method. One-time torque tightening method is to use a torque digital wrench to tighten the bolt to the target torque at one time, and reverse torque tightening method is to use a torque digital wrench to first tighten the bolt to the target torque, then rotate it a few degrees in the direction of loosening the bolt, and then tighten it to the target torque in the tightening direction. The current tightening status of manual tightening of bolts is: when performing bolt tightening operations, the operator is not deliberately required to tighten to the target torque at one time. The operator will unconsciously pause or turn his hand during tightening, which unconsciously alternates between the one-time torque tightening method and the segmented torque tightening method. The operation is random and the consistency of the tightening quality is poor.

[0072] The segmented torque tightening method of the present invention is compared with the tightening status quo, the one-time torque tightening method and the reverse torque tightening method. The comparative test is carried out by taking a bolt with a standard torque of 50N∙m as an example. The same experienced tester uses a torque digital wrench to tighten the bolts using the four methods respectively. The segmented torque tightening method adopts a three-stage torque tightening method. The tightened bolt is left to stand for 30 minutes before measuring the stable torque of the bolt. Each tightening method uses the same batch of bolts to randomly collect 1000 samples, rounds the sample data according to the rounding method, and performs statistical analysis. The measured torque comparison of the bolts tightened by the four methods is shown in Table 2 and Figure 7 As shown, Figure 7 The distribution bar graph and distribution curve of the measured torque of the bolts tightened using the four methods are shown respectively.

[0073] Table 2 Comparison of four torque tightening methods

[0074]

[0075] From the statistical results, it can be seen that the segmented torque tightening method has the highest accuracy and the smallest discreteness, while the results of the one-time torque tightening method and the reverse torque tightening method are similar and the distribution curve trend is similar. The test result accuracy of the tightening status is higher than that of the one-time tightening method, but lower than that of the segmented torque tightening method. When the segmented torque tightening method is used to tighten the bolts, the actual tightening torque is closer to the target torque, and the tightening effect is better.

[0076] When parts are connected by bolts, multiple bolts are generally set for connection. Each bolt is located at the same operating angle or at different operating angles. For example, some bolts can be tightened when the vehicle is placed on the ground, and some bolts need to be tightened after the vehicle is lifted. When each threaded fastener is located at the same operating angle, when tightening multiple threaded fasteners, first perform steps 3.1-3.3 to tighten each threaded fastener to sub-torque T1 and back-tighten, then perform steps 3.4-3.6 to tighten each threaded fastener to sub-torque T2 and back-tighten, and then perform step 4 to tighten each threaded fastener to target torque T0, thereby completing the tightening of each threaded fastener at the same operating angle. After completing the tightening operation of each threaded fastener at one operating angle, use the segmented tightening method to tighten each threaded fastener at another operating angle, thereby improving the tightening effect and the convenience of operation.

[0077] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for tightening a threaded fastener, characterized in that: The following steps are involved: Step S1, obtaining a target torque T0 of a threaded fastener; Step S2, according to the target torque T0, n sub-torques T1, T2, ..., Tn are set in order from small to large, each sub-torque is smaller than the target torque, wherein n is an integer and n≥2; Step S3, use a tightening tool to tighten the threaded fastener to sub-torque T1, sub-torque T2, ..., sub-torque Tn in sequence; after the threaded fastener is tightened to each sub-torque, at least one back-tightening is included, during which the torque of the tightening tool is set to the back-tightening standard torque, and the back-tightening standard torque is 60%-80% of the sub-torque before back-tightening; when the back-tightening is completed and the threaded fastener is not loose, the threaded fastener is tightened to the next torque of the sub-torque before back-tightening; Step S4: Use a tightening tool to tighten the threaded fastener to a target torque T0.

2. The method for tightening a threaded fastener according to claim 1, characterized in that: The method further includes: when re-tightening, if the threaded fastener becomes loose, replacing the threaded fastener with a new one and re-performing step S3.

3. The method for tightening a threaded fastener according to claim 1, characterized in that: When a tightening tool is used to tighten a threaded fastener to a sub-torque Ti, the tightening tool maintains the sub-torque Ti for time ti, where i=1, 2, ..., n; and / or, when a tightening tool is used to tighten a threaded fastener to a target torque T0, the tightening tool maintains the target torque T0 for time t0; preferably, the time ti for the tightening tool to maintain the sub-torque Ti and the time t0 for maintaining the target torque T0 are 1-5s.

4. The method for tightening a threaded fastener according to claim 1, characterized in that: According to the target torque T0, 1-4 sub-torques are set in order from small to large.

5. The method for tightening a threaded fastener according to any one of claims 1 to 4, characterized in that: According to the target torque T0, the sub-torque T1 and the sub-torque T2 are set in order from small to large.

6. The method for tightening a threaded fastener according to claim 5, characterized in that: Step S3 includes the following steps: Step S3.1, tightening the threaded fastener to a sub-torque T1, and the tightening tool maintains the sub-torque T1 for a time t1; Step S3.2, back-tighten the threaded fastener, and set the torque of the tightening tool to the back-tightening standard torque T1′, and the back-tightening standard torque T1′ is 60%-80% of the sub-torque T1; Step S3.3, determine whether the threaded fastener is loose, if the threaded fastener is not loose, execute step S3.4, if the threaded fastener is loose, replace it with a new one, and return to step S3.1; Step S3.4, tightening the threaded fastener to a sub-torque T2, and the tightening tool maintains the sub-torque for a time t2; Step S3.5, back-tighten the threaded fastener, and set the torque of the tightening tool to the back-tightening standard torque T2′, and the back-tightening standard torque T2′ is 60%-80% of the sub-torque T2; Step S3.6, determine whether the threaded fastener is loose. If the threaded fastener is not loose, execute step S4. If the threaded fastener is loose, replace it with a new one and return to step S3.

1.

7. The method for tightening a threaded fastener according to claim 6, characterized in that: Sub-torque T1 is 40%-50% of the target torque T0, and sub-torque T2 is 70%-80% of the target torque T0.

8. The method for tightening a threaded fastener according to claim 6, characterized in that: The standard torque for back-tightening is 65%-72% of the torque before back-tightening.

9. The method for tightening a threaded fastener according to claim 5, characterized in that: When tightening multiple threaded fasteners, first perform steps S3.1-S3.3 to tighten each threaded fastener to sub-torque T1 and back-tighten, then perform steps S3.4-S3.6 to tighten each threaded fastener to sub-torque T2 and back-tighten, and then perform step S4 to tighten each threaded fastener to target torque T0.

10. The method for tightening a threaded fastener according to claim 1, characterized in that: Tightening tools include digital torque wrenches.

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