JP2004358644A - Bolt fastening method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize elastic region fastening with high accuracy and good manufacturing efficiency by avoiding fastening in a plastic region after an yield point with a raised risk of delay breakage. <P>SOLUTION: This method has a first stage for detecting sample data comprising a fastening angle and a fastening torque by sample fastening set to a condition identical to a manufacturing condition in a main fastening step, a second stage for estimating an axial force corresponding to an arbitrary fastening torque from a ratio of a fastening torque at the yield point and a yield point axial force as a bolt characteristic and fetching a fastening angle required for a target axial force, and a third stage for fastening bolts using a fastening angle fetched in the second stage as an index fastening angle in the main fastening step. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to management of axial force at the time of bolt fastening.
[0002]
[Prior art]
Tightening with bolts is characterized in that it can be tightened by adjusting the tightening force, that is, the axial force, and is easily disassembled. Typical fastening methods include a torque method, an angle method, and a torque gradient method.
[0003]
The torque method is a method of managing the axial force using the tightening torque as an index by utilizing the fact that the tightening torque is proportional to the axial force until the bolt yields. Since this torque method can be performed with relatively simple tools and operations, it is the most widely used fastening method. However, the tightening torque does not become the axial force as it is, but is consumed by the friction on the bolt surface and the nut seat surface. Even if the tightening torque is fixed, the obtained axial force is the friction coefficient of the bolt surface. Depends heavily on Since a coating film applied to an object to be fastened also has a large effect on friction on the seat surface, high-accuracy axial force management cannot be expected simply by using the tightening torque as an index.
[0004]
The angle method is a method of tightening up to a certain index tightening torque by a torque method (this area is referred to as a snag point), and then managing the axial force using the tightening angle of the bolt and nut as an index. Although the tightening accuracy is much better than the above-mentioned torque method, since the tightening is performed by the torque method up to the snag point, it is also affected by the friction coefficient. As a prior art which solves this problem, there is, for example, one disclosed in Japanese Patent Application Laid-Open No. 63-74577. In this gazette, based on data of the actually measured tightening torque and tightening angle, the data is linearly approximated to obtain an angle at which the torque value becomes 0, and the angle value converges to a fixed position to determine the seating point. It is disclosed that the angle method is performed using this seating point as a tightening start point. Although it is possible to control the axial force with high accuracy according to this method, there are many bolting points, such as the fastening of the disc and rim in an assembled wheel for vehicles, and products that tighten more than two bolts at a time In this case, if this management method is used for each bolt, the production efficiency is low, and the apparatus becomes large.
[0005]
The torque gradient method is a method of detecting an increase in the tightening torque with respect to the tightening angle and managing the axial force using the torque gradient. For example, there are those disclosed in JP-A-61-142081 and JP-A-7-290370. Since the yield point is detected from the change in the torque gradient and the fastening is stopped, the fastening is performed in the plastic region. Tightening in the plastic region by the torque gradient method is highly accurate, and it can be said that the strength of the bolt is effectively used. However, when the strength exceeds the yield point, tightening in a plastic region where the strength of the metal sharply drops has a problem in reusing bolts. In the case of high-strength bolts, the axial force increases and delayed fracture (static fatigue) ), The durability of the product becomes questionable.
[0006]
[Problems to be solved by the invention]
The problem to be solved by the present invention is to avoid plastic zone tightening after the yield point where the risk of delayed fracture increases, and to realize elastic zone tightening with high accuracy and high production efficiency. Further, in the assembled wheel for vehicles, about 30 bolts for fastening the rim and the disc are arranged on the same circumference, but the wheels are distorted due to stress during running of the vehicle. There is a need to equalize the forces and to respond to this.
[0007]
[Means for Solving the Problems]
The bolt fastening method according to claim 1 includes a first stage for detecting sample data consisting of a fastening angle and a fastening torque by test fastening set under the same conditions as the production conditions in the actual fastening process. The yield point is calculated from the detected sample data, the axial force corresponding to any tightening torque is estimated from the ratio of the tightening torque at the yield point to the axial force at the yield point, which is the bolt characteristic, and the target axial force is calculated. It has a second step of acquiring a required tightening angle, and a third step of performing bolt fastening using the tightening angle acquired in the second step as an index fastening angle in the actual fastening step.
[0008]
The production conditions of the fastening process are conditions that affect the fastening torque in bolt fastening, such as painting applied to the workpiece, material or shape of the workpiece, types of bolts or nuts, and the like. The test fastening is performed before the actual production, and attempts to collect sample data assuming bolt fastening in the actual production by adjusting the production conditions. The sample data consists of the tightening torque for each minute tightening angle interval. The shorter the sampling period of these values, the more data can be collected, but the tightening speed at the test fastening is limited to actual production. The tightening speed should be assumed assuming the tightening speed, and the sampling cycle is desirably determined without decreasing the tightening speed. For the yield point axial force, which is a bolt characteristic, the yield point axial force of the bolt itself may be measured in advance, or experimental data provided by a bolt manufacturer may be used. Estimating the axial force can be done by comparing the tightening torque with the tightening torque in a graph as shown in Fig. 1 to appeal the axial force curve to the visual effect to make it easier for the tester to understand. There is no sex. Using the ratio between the tightening torque at the yield point and the axial force at the yield point to calculate the tightening angle at the target axial force back from the target axial force, it means estimating the axial force. I have. This utilizes the fact that the tightening torque and the axial force are in a proportional relationship as shown in FIG.
[0009]
By collecting sample data in this test fastening, it is possible to simulate the fastening in actual production. For example, when the paint applied to the workpiece is changed, the friction coefficient related to the bolt fastening also changes, which affects the fastening angle at the snag point, which is the starting point of the fastening angle. ΘS2 _-S1 shown in FIG. 3 indicates the deviation of the snug point in the angle method due to the change in the coefficient of friction due to the change of the paint. In the angle method in which the index tightening angle is tightened with the snug point as a starting point, this shift is directly connected to the shift in the tightening at the time of completion of the tightening (θ _E in the drawing). Test fastening is performed when there is such a change in production conditions, and is adjusted to the same conditions as the fastening process in the actual production, so that the deviation of the snag point is eliminated and the fastening in the fastening process in the actual production is performed. The relationship between the attachment angle and the estimated axial force is simulated by the relationship between the tightening angle in test fastening and the estimated axial force. By the test fastening, it is possible to obtain the adjusted tightening angle for tightening with the target axial force, so the work in the actual fastening process is the same as the work in the normal angle method, a simple work and high Axial force can be controlled with precision.
[0010]
In the bolt fastening method according to claim 2, in the bolt fastening method according to claim 1, the method of calculating the yield point is such that a part of the sample data of the tightening torque is linearized by a least square method, and a constant is calculated from the straight line. It is characterized in that it is regarded as a yield point when the distance deviates.
[0011]
As shown in FIG. 4, when the bolt seat surface or the nut seat surface is seated, the tightening angle and the tightening torque show a substantially proportional relationship. However, the linearization of the sample data of the tightening torque by the least squares method is as follows. This means that the sample data of the portion having a substantially proportional relationship is linearized. The point in time at which the predetermined distance is deviated means the point in time at which the torque deviates by more than a predetermined torque from the straight line as shown in the figure.
[0012]
In the analysis of sample data, the yield point is calculated by using a computer to perform a numerical calculation process using the least squares method. To improve.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described step by step with reference to the drawings.
[0014]
[First Stage: Data Sampling] First, test fastening is performed in accordance with production conditions (members to be fastened, bolt members, nut members, and coating applied to each of them) in the actual fastening process. In test fastening, tighten the bolt at least until it exceeds the yield point. FIG. 5 is a configuration diagram showing a system for taking in sample data from the nut runner 1 as an assembling machine to the personal computer 8 when detecting sample data in the test conclusion. The nut runner 1 for fastening a bolt includes a torque transducer 2 for detecting a tightening torque and an angle pulse encoder 3 for detecting a tightening angle. The output of the tightening torque detected by the torque transducer 2 is A / D converted by the A / D converter 4 and is taken into the internal memory of the sequencer 6. On the other hand, the pulse output of the tightening angle detected by the angle pulse encoder 3 is measured as rotation angle information via a high-speed counter block 5 for controlling a high-speed signal, and is taken into an internal memory of the sequencer 6. Thus, the tightening torque for each tightening angle is stored in the internal memory of the sequencer 6. The sample data stored in the internal memory of the sequencer 6 is transmitted from the sequencer 6 to the personal computer 8 via an RS232C communication according to a command from the personal computer 8.
[0015]
FIG. 6 shows a user interface output screen of software used when the sample data stored in the internal memory of the sequencer 6 is taken into the personal computer 8. This software is programmed with EXCEL-VBA, which is also a common macro language between applications of Microsoft Corporation, for storing sample data in a sheet of Microsoft EXCEL. When the PLC_DC button 11 in the figure is pressed, a PLC communication dialog form 12 for communicating with the sequencer 6 is activated. A tightening torque serving as a trigger for starting the measurement is input to the measurement start torque input field 13 on this form, and the measurement preparation button 14 is pressed. Since the data is ready to be sampled, the nut runner 1 is activated to bolt the object to be fastened, and when one fastening is completed, the measurement stop button 15 is pressed. The measured sample data is moved from the internal memory of the sequencer 6 to the EXCEL sheet by pressing the data reception set button 16. When the test conclusion sample data is required a plurality of times, this is repeated from the point where the measurement preparation button 14 is pressed.
[0016]
[Second Stage: Sample Data Analysis / Axial Force Estimation] Since the stage of data sampling by the conclusion of the test has been completed, the process proceeds to the stage of analyzing using this sample data. FIG. 7 is a user interface output screen of software (also programmed by EXCEL-VBA) for analyzing data captured on an EXCEL sheet. The software has a tightening torque curve graphing function activated by pressing the graph button 21, a yield point calculation / axial force estimation function activated by pressing the yield point button 22, and a snag button 23 pressed. And an optimal snag torque calculating function started by the above.
[0017]
The tightening torque curve graphing function extracts sample data from the snug torque designated in the snag torque input field 24 and graphs the tightening torque curve plot area 25 with the horizontal axis as the tightening angle and the vertical axis as the tightening torque. . The tester can check the state of the tightening torque for each tightening angle as a graph, which makes it easier to understand.
[0018]
Regarding the yield point calculation / axial force estimation function, the index tightening angle from the snug point is measured in the set tightening angle input field 26 and the tightening yield axial force data input field 27 is measured in advance before the yield point button 22 is pressed. In the approximate value allowable error input box 28, the allowable range of the deviation error from the straight line of the least squares approximation method serving as the reference for calculating the yield point is set in the yield point axial force of the bolt member. When the yield point calculation / axial force estimation function is started, the data points from the snag torque of the sample data are analyzed, the yield point is calculated, and the tightening at the yield point is output to the yield tightening angle output column 29 and the yield torque output column 30. Outputs attachment angle and tightening torque. As shown in FIG. 8, the method of calculating the yield point in this embodiment is based on the tightening torque at the next 15 tightening angles by the least squares approximation method from the tightening torque data points 41 at the 15 consecutive minute tightening angles. The torque is predicted, and if the actually measured tightening torque falls below the tightening torque predicted value 42 five times consecutively beyond the value set in the approximate value allowable error input box 28, it is determined that a yield has occurred. The mechanism is such that the tightening torque immediately before starting to drop consecutively is calculated as the yield point. After the yield point is calculated, the yield point tightening torque output in the yield torque output field 30 and the yield point axial force of the bolt member input in the fastening yield axial force data input field 27 are compared, and the tightening is set based on the ratio. The axial force is estimated from the tightening torque at the tightening angle set in the angle input field 26 and output to the completed estimated axial force output field 31. By repeating this analysis at different set tightening angles, it becomes possible to obtain an index tightening angle for achieving the target axial force.
[0019]
The optimum snag torque calculating function is to detect a snag torque with a small deviation of the axial force by performing a simulation while changing the snag torque from the sample data. When the target axial force is input in the target axial force input column 32 and the snag button 23 is pressed, the axial force deviation curve is graphed in the axial force deviation plot area 33, and the snag torque having a small deviation is easily visually observed by the tester. It becomes possible to detect. This function is intended to further enhance the effect of the present invention, and does not need to be particularly implemented.
[0020]
[Third stage: actual fastening] The index tightening angle obtained in the second stage is used in the fastening process in the actual production. Tighten the index tightening angle from the snug torque. If the snug torque having a small axial force deviation is also simulated in the second stage, the snug torque may be used for actual fastening.
[0021]
【The invention's effect】
As described above, the bolt fastening method according to the present invention can perform more accurate axial force management by analyzing data simulated under production conditions for actual fastening. Further, since the bolt axial force is estimated, various conditions such as snag torque and tightening angle for obtaining a desired tightening force can be obtained. Since the actual fastening is a fastening by a simple angle method, speedy bolt fastening can be performed with a relatively simple tool. Further, by using the angle method, it is possible to set the axial force in the elastic region while avoiding the tightening in the plastic region where there is a risk of delayed fracture. Further, in the assembled wheel for vehicles, it is required to equalize the axial force of the bolts for fastening the rim and the disk, but the bolt fastening method in the present invention is extremely effective.
[Brief description of the drawings]
FIG. 1 is a graph showing a tightening torque curve and an axial force curve with respect to a tightening angle.
FIG. 2 is a graph showing a relationship between a tightening torque and an axial force.
FIG. 3 is a graph showing a deviation in tightening by an angle method due to a change in a coefficient of friction.
FIG. 4 is an image diagram for calculating a yield point from a tightening angle and a tightening torque by a least squares approximation method.
FIG. 5 is a configuration diagram showing a system when detecting sample data in test conclusion.
FIG. 6 is a diagram showing a user interface output screen of software used when taking sample data into a personal computer.
FIG. 7 is a view showing a user interface output screen of software for analyzing sample data.
FIG. 8 is a diagram showing a tightening torque prediction method by the least squares approximation method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Nut runner 2 Torque transducer 3 Angle pulse encoder 4 A / D converter 5 High-speed counter block 6 Sequencer 7 Communication board 8 Personal computer 11 PLC_DC button 12 PLC communication dialog form 12
13 Measurement start torque input field 14 Measurement preparation button 15 Measurement stop button 16 Data reception set button 21 Graph button 22 Yield point button 23 Snag button 24 Snag torque input field 25 Tightening torque curve plot area 26 Setting tightening angle input field 27 Tightening axis Force data input field 28 Approximate value allowable error input field 29 Yield tightening angle output field 30 Yield torque output field 31 Completion estimated axial force output field 32 Target axial force input field 33 Axial force deviation plot area 41 Tightening torque data point 42 Tightening Predicted torque value

Claims (2)

The first stage in which sample data consisting of the tightening angle and the tightening torque is detected by test fastening set to the same conditions as the production conditions in the actual fastening process, and the yield point is calculated from the sample data detected in the first stage. A second method of estimating an axial force corresponding to an arbitrary tightening torque from a ratio of a tightening torque at a yield point and an axial force at a yield point, which is a bolt characteristic, and obtaining a tightening angle required for a target axial force. A bolt fastening method comprising: a stage; and a third stage in which bolt fastening is performed using the fastening angle acquired in the second stage as an index fastening angle in the actual fastening process. The method for calculating a yield point according to claim 1, wherein a part of the sample data of the tightening torque is linearized by a least squares method, and the yield point is regarded as a yield point when a certain distance is deviated from the straight line. Bolt fastening method.

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