JPH0457681A - Fastening method for screw member - Google Patents

Abstract

PURPOSE:To hold a fastening axial force in the specific zone of the elastic limit vicinity without being effected by the change of friction coefficients while under fastening and to stabilize the fastening axial force, by fastening with chasing the angle difference in a torque rate on the way of fastening and virtual torque rate for a screw member from the fastening completion time. CONSTITUTION:A torque rate RT1 on the way of fastening is found on the correlation chart of a fastening angle and fastening torque. A logical seating point is then calculated from this torque rate RT1 and a virtual torque rate RT2 is found from the fastening angle and torque values of the logical seating point and fastening completion time. Moreover, the angle difference thetaalpha in the torque rate RT1 of on the way of fastening at the specific fastening torque time of on the way of fastening and the virtual torque rate RT2 is found and the screw member is subjected to chase-fastening by a nut runner l from this angle difference fastening completion time.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a tightening method for tightening a screw member such as a bolt to near its elastic limit.

(Prior Art) Conventionally, the following methods have been known as methods for tightening screw members of this type.

■ Torque method in which a screw member is tightened to a predetermined torque (see Japanese Patent Publication No. 60-14675, etc.).

■ Angle method in which a screw member is tightened by a preset rotation angle (see Japanese Patent Publication No. 61-5857, etc.).

■ During the tightening of a screw member, determine the torque rate, which is the ratio of the increase in tightening torque to the increase in tightening rotation angle, determine the theoretical seating point from this torque rate, and then proceed from the seating point until a predetermined angle is reached. Method of tightening (Unexamined Japanese Patent Publication No. 6
2-102978, etc.).

(Problem to be Solved by the Invention) However, in the above torque method (①), the friction coefficient is greatly affected by the friction coefficient that occurs between the screw member and the member to be screwed into which the screw member is screwed. There is a problem in that the tightening axial force varies greatly due to the difference in . Also, ■
Even with the angle method, the friction coefficient affects up to the seating torque, which is the starting point of the rotation angle. Therefore, if the seating torque is high, trying to obtain a high tightening axial force will result in a low friction coefficient. There is a possibility that it will enter the yield zone. Furthermore, in the method (2), the tightening axial force is more stable than in the torque method, but when considering the yielding of the screw member, there remains the problem that the tightening axial force must be stabilized at a low level.

Therefore, the present applicant has previously proposed a tightening method that can always secure a tightening axial force near the elastic limit without being affected by the friction coefficient (Japanese Patent Application No. 1-32027). and drawings). In other words, the proposed tightening method achieves the elastic limit tightening of the threaded member when the coefficient of friction occurring between the threaded member and the member to which the threaded member is threaded has a maximum value and a minimum value. Find the difference from the tightening axial force that occurs at each time, find the seating torque corresponding to the axial force difference that is approximately equal to the tightening axial force difference, and then use the torque method to tighten the above-mentioned screw member until the seating torque is obtained. After tightening, it is tightened at a predetermined angle using the angle method.

However, due to the shape of the screw member or the member to be screwed, the coefficient of friction may change during the tightening process. For such things, the above-mentioned proposed tightening method cannot be sufficiently effective. That is, the fifth
As shown in the figure, the lower the friction coefficient μ, the higher the yield zone Z increases, so the friction coefficient μa at the set torque (at the time of tightening to the seating torque Tx using the torque method) This is because if the friction coefficient μb at the end of tightening is lower than that at the end of tightening, even if the tightening is performed at a predetermined angle θ1 from the set torque, the predetermined region A near the elastic limit will not be reached, resulting in insufficient tightening.

The present invention has been made in view of the above points, and its purpose is to improve the tightening method proposed above so as to improve elasticity without being affected by changes in the coefficient of friction during tightening. This makes it possible to stabilize the tightening axial force in a predetermined range near the limit.

(Means and operations for solving the problem) In order to achieve the above object, the solving means of the present invention provides a method for tightening a screw member, in which the screw member and the member to be screwed are connected to each other. When the friction coefficient that occurs between the two is the maximum value and the minimum value, calculate the difference from the tightening axial force that occurs when the screw member is tightened to its elastic limit, and calculate the axial force difference that is approximately equal to the tightening axial force difference. After determining the corresponding seating torque and tightening the screw member by the torque method until the seating torque is obtained,
It is assumed that the angle method is used to tighten at a predetermined angle.

Then, on the correlation diagram between tightening angle and tightening torque,
Determine the torque rate during tightening, calculate the theoretical seating point from the torque rate, determine the virtual torque rate from the theoretical seating point and the tightening angle and tightening torque value at the end of tightening, and then , the angular difference between the torque rate during tightening and the virtual torque rate at a predetermined tightening torque during tightening is determined. Then, the screw member is additionally tightened from the time point when this angular differential tightening is completed.

Next, the theory of the present invention will be explained with reference to FIG. Incidentally, FIG. 6 is a correlation diagram between the tightening angle and the tightening torque in the case where the friction coefficient changes during the tightening of the screw member.

During tightening, the torque rate RTI is determined by measuring the tightening angle between two points (two points of torque Tl and T2) where the tightening torque is a predetermined amount, and a straight line representing the slope of this torque rate RTI is obtained. The theoretical seating point (the point of tightening angle θ0) is calculated as the intersection of and the horizontal axis. Further, a virtual torque rate RT2 is determined from the theoretical seating point, the fastening angle at the end of tightening, and the tightening torque value.

Here, there is no change in the friction coefficient during tightening, and R
If it exhibits the characteristics of T2, it is tightened to point A on the RT2 straight line at the initial torque T1, and tightened at a predetermined angle θ1 from point A using the angle method. Therefore, if the friction coefficient changes during tightening, the above initial torque 1
If the angle difference θα between the torque rate RT1 during tightening at 1 o'clock and the virtual Dorkley) RT2 is additionally tightened from the end of tightening, the same tightening axial force as when tightening from point A at a predetermined angle θ1 can be obtained. and reaches a predetermined region A near the elastic limit shown in FIG.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 3 shows the overall configuration of a bolt tightening device used in the bolt tightening method according to the present invention.

In FIG. 3, 1 is a nut runner, and the nut runner 1 includes a socket 2 that fits into a bolt head, a motor 3 that rotationally drives the socket 2 via a main shaft (not shown), and a main shaft. It includes a torque transducer 4 that detects torque, and an angle encoder 5 that detects the rotation angle of the main shaft.

6 is a CPU that controls the operation of the nut runner 1.

Further, 11 and 12 are first and second torque setting devices that perform torque setting based on the seating torque Tx calculated by the CPU 6, and in the case of this embodiment, the torque Tl of the first torque setting device 11 is The torque T2 of the second torque setting device 12 is set to the same value as the seating torque Tx.
1 (that is, seating torque Tx) by a predetermined amount. Comparators 13 and 14 compare the tightening torque detected by the torque transducer 4 with the set torques Tl and T2 set by the corresponding torque setters 11 and 12. and when both match, the corresponding torque game) 1
A signal is sent to the CPU 6 via 5.16.

Furthermore, 17 is a peak torque memory that receives the signal from the torque transducer 4 and stores the peak torque Ts as the fastening torque at the time of completion of tightening, and the peak torque Ts stored in the memory 17 is , is appropriately input to the CPU 6 as the information. 18 and 19 are the minimum value μsin and maximum value μWa of the friction coefficient of the bolt, respectively.
Friction coefficient setting devices 21 to 23 for setting X are first to third angle gates 2 which receive control signals from the CPU 6 and send rotation angle signals detected by the angle encoder 5 to the CPU 6, respectively.
4 is a servo amplifier that transmits the output from the CPU 6 to the motor 3 of the nut runner 1.

Next, a method for tightening bolts using the bolt tightening device described above will be explained with reference to flowcharts shown in FIGS. 1 and 2.

FIG. 2 shows a flowchart for calculating the bolt seating torque Tx, which is performed prior to bolt tightening.

In this flow, after inputting the minimum value μ■1n and maximum value μ■aX of the friction coefficient specific to the bolt to be tightened from the friction coefficient setter 18.19 to the CPU 6 (step SL), the CPU 6 calculates the seating torque Tx. (Step S2).

Here, as shown in FIG. 4, the minimum value μsi of the friction coefficient
Friction coefficient line Gl representing n and maximum value μmaX.

If the coefficient representing the slope of G2 is 2 for Kl, the above friction coefficient line Gl, G2 is F-Kl ・T...(1)
F- to 2 ・T...
It is expressed as (2).

Therefore, the tightening axial force difference ΔF at the elastic limit tightening is determined from both the above equations and the functional equation expressing the elastic limit based on elastic theory.
Based on this, the tightening axial force difference ΔF- corresponding to the seating torque Tx that is equal to this can be derived from the following formula.

Fl −Kl ・T ... (
1) 2 φT to -F2-
・C2)', °, ΔF--Fl-F2-TX-(KL-2) Therefore, the optimal seating torque Tx at ΔF-ΔF' can be found as Tx-ΔF/(Kl-2) .

The seating torque Tx obtained in this way is
The output signal is sent to the first and second torque setting devices 11.12, and used for torque setting in each torque setting device 11.12 (step S3).

After the calculation of the seating torque Tx as described above is completed, the first
Bolts are tightened according to the flow shown in the figure.

That is, first, in step S11, the CPU 6 starts the servo amplifier 24 in response to an external nut runner start signal.
The motor 3 of the nut runner 1 is rotated via the nut runner 1 to start tightening the bolts. After waiting for the tightening torque T detected by the torque transducer 4 to match the set torque TI set by the first torque setting device 11 in step S12, the first and second angle gates are Turn on 21.22.

Subsequently, while continuing the tightening in step SL4, in step S15 the tightening torque T and the set torque T2 set by the second torque setting device 12 match, and in step S16, the first angle gate 21 is adjusted. Turn off. Then, in step S17, the O of the first angle gate 21 is
The tightening angle Δθ during the N period (that is, the period from when the tightening torque T changes from the set torque T1 to the set torque T2) is determined, and the RTI during tightening is determined using the following formula (see FIG. 6).

RTI - (T2 - Tl )/Δθ Subsequently, while continuing tightening in step 5lli, in step S19 the reading angle pulse of the second angle gate 22 is changed to the angle θ1 (sixth
(see figure). Then, in step S20, the servo amplifier 24 is operated to temporarily stop bolt tightening. Further, the peak torque Ts from the torque transducer 4 (the fastening torque at the current moment, that is, the moment when the tightening is temporarily stopped (hereinafter referred to as the tightening end point)) Ts is read.

Thereafter, in step 821, a virtual torque rate RT2 at the time of completion of tightening is determined. In FIG. 6, this virtual torque relay RT2 has a torque rate R during tightening.
The point where the straight line representing the slope of TI intersects with the horizontal axis is the theoretical seating point θ
0, and this is a straight line connecting this theoretical seating point θ0 and a point B corresponding to the tightening end point on the torque rate curve, and is expressed by the following equation.

RT2-Ts /θ2-Ts/(θl +TI /RTI) and the torque rate RTI during tightening mentioned above and the virtual torque rate) R
Compare T2 and find that they are approximately equal (RTI = RT2
) Sometimes, just finish tightening.

On the other hand, when the torque rate RTI during tightening is larger than the virtual torque rate RT2 (RTI > RT2), in step 521, the torque rate RTI during tightening at the time when the set torque TI is reached is further compared with the virtual torque rate RTI. An angular difference θα with the torque rate RT2 is determined. This angular difference θα is calculated using the following formula.

Subsequently, in step S22, the third angle gate 23 is turned on, and in step 52g, bolt tightening is started and additional tightening is performed from the time when the tightening of the angle difference θα is completed. Then, in step S24, the tightening is finished after waiting for the additional tightening to be completed.

Therefore, when tightening a bolt using this method, if the friction coefficient μ does not change during tightening (that is, when the torque rate RTI during tightening is approximately equal to the virtual torque rate RT2 at the end of tightening) The fourth
As shown in the figure, the friction coefficient has a maximum value μlaX and a minimum value μ
The bolt is tightened by the torque method until the seating torque Tx corresponding to the axial force difference ΔF' equal to the tightening axial force difference ΔF at the time of elastic limit tightening in the case of sin is obtained, and then,
By tightening at a predetermined angle θ1 using the angle method, the tightening axial force F can always be maintained in a predetermined region A near the elastic limit without being affected by the friction coefficient.

In addition, in the case where the friction coefficient μ changes during tightening (that is, when the torque rate RTI during tightening is larger than the virtual torque rate RT2 at the end of tightening), the set torque TL (that is, seating torque Tx) The tightening axial force F is reduced to a predetermined range near the elastic limit by additional tightening from the point at which the dividing line is marked, which corresponds to the angular difference θα between the torque rate RTI during tightening and the virtual torque rate RT2 at the time when A can be secured and its stability can be achieved.

(Effects of the Invention) As described above, according to the method for tightening a screw member of the present invention, the angular difference between the torque rate during tightening and the virtual torque rate is applied to the screw member from the time of completion of tightening. This makes it possible to maintain the tightening axial force within a predetermined range near the elastic limit without being affected by changes in the coefficient of friction during tightening, thereby making it possible to stabilize the tightening axial force. be.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, and FIG. 1 is a flowchart of a bolt tightening method, FIG. 2 is a flowchart of calculating the bolt seating torque X, and FIG. 3 is a flowchart of a bolt tightening method. FIG. 4 is an overall configuration diagram of the bolt tightening device used, and is a diagram showing how to determine the seating torque in the bolt tightening method. Figure 5 is a correlation diagram between tightening torque and tightening axial force in the case where the coefficient of friction changes during tightening of a screw member, and Figure 6 is a diagram showing the relationship between the tightening torque and the tightening axial force in the case where the coefficient of friction changes during the tightening of the screw member. It is a correlation diagram between and tightening torque. 1... Natsu runner 4... Torque transducer 5... Angle encoder 13.14... Comparator 15.16... Torque gate 21-23... Angle gate Dragon 1 Shikai 5L U-Ro Figure 2 Figure 2] Figure

Claims (1)

[Claims] (1) Tightening that occurs when the threaded member is tightened to its elastic limit when the coefficient of friction that occurs between the threaded member and the member to which the threaded member is threaded is the maximum value and the minimum value, respectively. After determining the difference from the axial force, determining the seating torque corresponding to the axial force difference that is approximately equal to the tightening axial force difference, and tightening the screw member by the torque method until the seating torque is obtained,
This is a tightening method that uses the angle method to tighten at a predetermined angle, and the torque rate during tightening is determined on the correlation diagram between the tightening angle and tightening torque, and the theoretical seating point is calculated from this torque rate. , find a virtual torque rate from the theoretical seating point and the tightening angle and tightening torque values at the end of tightening, and further calculate the torque rate during tightening and the virtual torque rate at the specified tightening torque during tightening. A method for tightening a screw member, characterized in that the angle difference between the torque rate and the torque rate is determined, and the screw member is additionally tightened from the point at which tightening is completed based on this angle difference.