JP2619628B2 - Bolt tightening method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a bolt (or nut) tightening method for tightening a bolt (or nut) at a value close to an elastic limit.

(Prior art) Conventional bolt tightening methods include, for example,
There is a constant torque tightening method described in JP-A-58272.

This fastening method is a method in which a constant torque is applied in order to tighten the bolt within the elastic limit. However, this conventional method has a drawback that the fastening axial force greatly varies due to a change in the friction coefficient of the bolt.

In order to solve such a drawback, a rotation angle tightening method as shown in FIG. 5 and a seating point angle tightening method as shown in FIG. 6 have already been invented.

In Fig. 5, the horizontal axis indicates the bolt tightening torque, and the vertical axis indicates the tightening axial force, and the M10 pitch 1 bolt is fixed torque (2.5 kg.m) + constant angle method (75 degrees). FIG. 6 is a characteristic diagram of a tightened state in which the tightening is controlled. FIG. 6 shows the bolt tightening torque on the horizontal axis, and the tightening axial force on the vertical axis. FIG. 6 is a characteristic diagram of a tightened state where the tightening is controlled at (115 degrees), and the circles in FIGS. 5 and 6 indicate actual measurement (plot) points.

As shown in FIG. 5, the former rotation angle tightening method is affected by the friction coefficient μ up to the first starting point of the snag torque. Low bolts had the problem of entering the yield zone.

On the other hand, the latter seating point angle tightening method (see FIG. 6) has the advantage of stabilizing the tightening axial force P without the influence of snag torque, but in particular, for bolts having a high friction coefficient μ,
As is clear from FIG. 6, the angle from the seating point to the yield was reduced, and the fastening axial force P had a problem of a relatively low value.

(Problems to be Solved by the Invention) According to the present invention, the variation in tightening axial force can be significantly improved as compared with the conventional torque method, and the average axial force can be increased as compared with the rotation angle method. It is possible to stably obtain the tightening axial force within the range where the bolt does not yield, and to tighten the bolt at a value close to the yield range, especially making full use of the capacity of each bolt, An object of the present invention is to provide a bolt tightening method capable of increasing a bolt axial force.

(Means for Solving the Problems) The present invention provides a first step of obtaining a torque rate corresponding to a friction coefficient of a screw during tightening of a bolt, and a second step of calculating a theoretical seating point from the torque rate. A third step of calculating a theoretical tightening angle from the theoretical seating point to the elastic limit point based on the tightening coefficient, and a fourth step of performing angle tightening based on the calculation result. The method is characterized in that it is a bolt tightening method provided.

(Effect of the Invention) According to the present invention, in the first step, the torque rate (the ratio of the tightening torque to the tightening angle, in other words, the torque rate) corresponding to the friction coefficient of the screw during the tightening of the bolt. In the second step, a theoretical seating point is calculated from this torque rate, and then in the third step, tightening is performed in the second step. The theoretical tightening angle from the above theoretical seating point to the elastic limit point is calculated based on the coefficient, and then, in the fourth step, the angle is tightened based on the above calculation result, so that the friction coefficient of the bolt is reduced. Even if it fluctuates, it always follows the elastic limit line,
In addition, tightening can be performed at a value close to the yield range, and there is an effect that the tightening axial force can be stabilized at a high value.
In other words, there is an effect that the axial limit force of the bolt can be increased by making full use of the elastic limit of each bolt, in other words, the bolt capacity can be fully utilized.

Embodiment An embodiment of the present invention will be described below in detail with reference to the drawings.

First, the theory of the fastening method will be described with reference to FIGS.

Fig. 4 shows the case where the horizontal axis indicates the tightening torque, and the vertical axis indicates the tightening axial force, and the tightening control of the connecting rod bolt of MIO x pitch 1 is performed from the seating point to near the elastic limit using the method of the present invention. In the characteristic diagram of, the generated axial force was measured using a strain gauge-attached load cell. 4 indicate actual measurement (plot) points.

When tightening the bolt, the higher the friction coefficient μ of the screw portion, the lower the axial force P at which the yield occurs. This is because torsion stress acts on the bolt together with tensile stress, and this torsional stress τ is expressed by the following equation.

T: Tightening torque. d ₁ : valley diameter d ₂ : effective diameter. P: Tightening axial force μ: Friction coefficient. β: Lead angle of screw From the above formula, it is clear that the higher the friction coefficient μ of the bolt, the greater the torsional stress τ, and yielding occurs with a lower tightening axial force P, and this tightening axial force P Is proportional to the angle θ, the smaller the friction coefficient μ of the screw portion is, the smaller the angle of entering the yield zone from the seating point becomes.

That is, within the elastic range limit of the bolt and at a high axial force P
In order to obtain the optimum value, it is optimal to control the tightening angle according to the friction coefficient μ.

Since the above-mentioned friction coefficient μ and the torque rate have a correspondence relationship, this torque rate is determined during the tightening of the bolt.

That is, the torque rate of the bolt A in FIG. 3 can be obtained from both the tightening torque T ₂ -T ₁ and the tightening angle θ ₂ -θ _{1 in the} middle of the tightening by the following equation.

A bolt torque rate = (T ₂ -T ₁ ) / (θ ₂ −
θ ₁ ) Similarly, the tightening torque T _{2 in the} middle of tightening the bolt B shown in FIG.
From both −T ₁ and the tightening angle θ _{2 ′} −θ _{1 ′} , the torque rate can be obtained by the following equation.

B bolt torque rate = (T ₂ −T ₁ ) / (θ _{2 ′} −θ
_{1 '} ) The theoretical seating point θ is obtained from the torque gradient of each characteristic shown in FIG.
₀ calculated, theoretical additional-turning angle .theta.A from the theoretical seating point theta ₀ to elastic limit point P _1, P ₂ of each bolt, then calculates the .theta.B, this theory additional-turning angle .theta.A, performs angle tightening based on .theta.B .

The theoretical tightening angles θA and θB can be obtained by the following equations.

However, K ₁ = 360 · Fy / · (1 / Kt + 1 / Kc) K ₁ is the tightening coefficient R is the torque rate of bolts A and B Fy is the bolt yield point p is the pitch Kt is the spring constant of the bolt Kc is the tightening The body spring constant d ₂ is the effective screw diameter K ₃ is the coefficient of friction and torque rate correspondence d ₁ is the thread root diameter α is the half angle of the thread β is the screw lead angle Note that the tightening coefficient K ₁ is the bolt size and tightening by a factor determined by the spring constant of the biasing member, when initially previously obtained experimentally, K ₁ can be easily set.

Therefore, the above-described theoretical tightening angles θA and θB can be approximately obtained from the following equations.

θA = term determined by the torque rate of K / A volts θB = term determined by the torque rate of K / B volts where K is a tightening coefficient.

In FIG. 3, δ ₁ indicates the amount of plastic elongation of the A bolt, and δ ₂ indicates the amount of plastic elongation of the B bolt. These are expressed by the following equations.

δ ₁ = θ / 360 · p δ ₂ = θ / 360 · p where θ is a tightening angle (rotation angle) and p is a thread pitch. FIG. 1 is a block diagram of a control device used for a bolt tightening method. A DC motor 3 is disposed on the transducer 1 via a reduction gear device 2, and an angle encoder 4 for encoding the current tightening angle is provided on one side of the DC motor 3.
The output of the torque transducer 1 is amplified by the preamplifier AMP.

The DC nut runner 5 includes a DC motor 3, a reduction gear device 2,
Transducer 1, Angle encoder 4, Preamplifier AM
It is composed of P.

On the other hand, the first torque setting device 6 for setting the seating torque T ₀
And a second torque setting device 7 for setting a torque rate detection start torque T ₁ and a third torque setting device 8 for setting a torque rate detection end torque T ₂ . 8 to the first comparator 9 and the second
A comparator 10, a third comparator 11, and a first analog switch 12, a second analog switch 13, and a third analog switch 14 are connected to a control circuit 15 via each of them.

Further, the above-described torque transducer 1 is connected to the other input terminals of the above-described comparators 9, 10, and 11 and a fourth analog switch 17 via a line 16, while the control circuit 15 is connected to a servo amplifier 18 via a line 16. The DC motor 3 described above.

Further, a first angle gate 20 and a second angle gate 21 are connected to the above-mentioned angle encoder 4 via a line 19, and an output stage of one of the first angle gates 20 outputs an increased angle output via a first counter 22. Circuit 23 and the other second angle gate
An output stage 21 is connected to a tightening angle output circuit 25 via a second counter 24.

The increased torque output circuit 26 connected to the output side of the fourth analog switch 17 and the increased angle output circuit
And 23 are connected to a computing unit 29 via respective lines 27 and 28, and the computing unit 29 controls the torque rate dT / dθ and the theoretical seating point θ.
₀ and the theoretical tightening angles θA, θB (see FIG. 3).

Furthermore, the theoretical tightening angle output circuit 30 connected to the output stage of the arithmetic unit 29 and the tightening angle output circuit 25 are connected to the comparator 33 via the respective lines 31 and 32. .

In addition, the above-described control circuit 15 and each element 17, 18, 20, 21, 22, 29, 33
Are connected to each other via lines 34-41.

Next, a bolt tightening method (a tightening method up to an elastic limit point) will be described with reference to a flowchart of FIG.

In a first step 51, the nutrunner 5 is started,
The first torque setter 6 above in the second step 52 follows to set the seating torque T _0.

The start signal of the nut runner 5 is applied to the control circuit 15 via a signal line (not shown). The control circuit 15 receiving the nut runner start signal drives the servo amplifier 18 in the next third step 53 and , The next fourth
In step 54, the DC motor 3 is driven.

The bolt is tightened via the reduction gear device 2 by the driving of the DC motor 3 described above.

Next, in fifth step 55, the first comparator 9 is consistent with the current and the tightening torque, seating torque T ₀ to a preset first torque setter 6 from the torque transducer 1, to determine the discrepancies, with current tightening When the torque reaches the seating torque T ₀ , the first analog switch 12 is turned on in the next sixth step 56 according to the coincidence output of the first comparator 9 described above.

By applying the analog switch ON signal to the servo amplifier 18 via the control circuit 15, the servo amplifier 18 stops the nut runner 5 in the next seventh step 57.

Next, in the eighth step 58, the nut runner 5 is rotated again, and in the next ninth step 59, the second torque setting device 7 sets the torque rate detection start torque T ₁ (see FIG. 3).

By re-driving the nut runner 5 described above, the current tightening torque from the torch clamp juicer 1 is reduced by the second comparator 10.
In the next tenth step 60, the second comparator 10 compares the current tightening torque with the second torque setting device 7
In agreement with the torque rate detection start torque T ₁ which is set in advance, it determines a mismatch, when with the current tightening torque has reached the torque rate detection start torque T _1, the second comparator 10 described above
The second analog switch 13 is turned on in the next eleventh step 61 by the coincidence output of.

This analog switch ON signal is applied to the control circuit 15, and the control circuit 15 turns on the fourth analog switch 17 in the next twelfth step 62, and takes the increased torque signal into the increased torque output circuit 26 at the next stage.

In the next thirteenth step 63, the control circuit 15 opens the first angle gate 20 and takes in the increased angle signal from the angle encoder 4 into the increased angle output circuit 23 via the first counter 22.

Then sets the torque rate detection completion torque T ₂ by the third torque setter 8 at the 14th step 64.

Third Konpareta 11 at the 15 step 65 then the determination torque with current tightening, consistent with the torque rate detection end torque T ₂ set in advance by the third torque setter 8 described above, the discrepancy from the torque transducer 1 and, when the torque for the current tightening has reached the torque rate detection end torque T _2, the third described above
The next 16th step 66 according to the match output of the comparator 11
To turn on the third analog switch 14.

The analog switch ON signal is applied to the control circuit 15, and the control circuit 15 turns off both the fourth analog switch 17 and the first angle gate 20 in the next seventeenth step 67.

Then, in the 18th step 68, the increasing torque signal T ₂ -T ₁ from calculator 29 increases the torque output circuit 26, increasing angle output circuit
The torque rate dT / d is based on both the increasing angle signal from 23, for example, θ ₂ -θ _{1 in} the case of A volt in FIG.
θ = (T ₂ −T ₁ ) / (θ ₂ −θ ₁ ) and the theoretical seating point θ
₀ and a theoretical tightening angle (the angle θA in the case of the bolt A in FIG. 3) are calculated (first, second and third steps).

Next, in a nineteenth step 69, the theoretical tightening angle θA as a result of the above calculation is taken in as a set value of the theoretical tightening angle output circuit 30, and in a twentieth step 70, the control circuit 15 sets the second angle gate 21 to Turn ON.

When the second angle gate 21 is turned on, the current tightening angle signal from the angle encoder 4 is taken into the tightening angle output circuit 25 via the second counter 24.

Next, in a 21st step 71, the comparator 33 determines whether the theoretical tightening angle θA as the set value from the theoretical tightening angle output circuit 30 matches the current tightening angle from the tightening angle output circuit 25. and, when the current additional-turning angle reaches a theoretical additional-turning angle θA above, upon reaching the elastic limit point P ₁ in other words, the above-mentioned comparator
The coincidence output of 33 is fed back to the control circuit 15, and in the next 22nd step 72, the control circuit 15 stops the DC motor 3 and the nut runner 5, ends the bolt tightening, and turns off the second angle gate 21. To end the series of processing (fourth step).

As described above, in the first step, the torque rate corresponding to the friction coefficient of the screw during the tightening of the bolt, that is, (T ₂ −T ₁ ) / (θ ₂ ) in the case of the A bolt in FIG. −θ
₁ ) In the case of B volts, (T ₂ −T ₁ ) / (θ _{2 ′} −θ
_{1 ')} is obtained, in a second step, as well as calculating the theoretical seating point theta ₀ from the torque rate, the three step, the elastic limit point from the theoretical seating point theta ₀ of based on with this tightening factor P ₁ , P ₂
Since the theoretical tightening angles θA and θB up to the above are calculated and the angle tightening is performed in the fourth step based on the result of this calculation, the yield range shown in FIG. And a value close to the yield range can be tightened, and there is an effect that the tightening axial force can be stabilized at a high value. In other words, there is an effect that the axial limit force of the bolt can be increased by making full use of the elastic limit of each bolt, in other words, the bolt capacity can be fully utilized. Fig. 4 shows the horizontal axis with bolts
FIG. 10 is a tightening state characteristic diagram in which a bolt having an M10 pitch of 1 is controlled to be fastened from a seating point to near an elastic limit by a method of the present embodiment by taking a tightening axial force on a vertical axis.

The tightening method also enables plastic area tightening in which the bolt is tightened beyond the yield point, and the plastic elongation δ ₁ , δ ₂ during plastic tightening (see FIG. 3) should be controlled to be constant. Can be.

That is, in the first step, a torque rate corresponding to the friction coefficient of the screw is determined during the tightening of the bolt,
In the second step, the theoretical seating point is calculated from the above-described torque rate, and in the next step, the theoretical tightening angle corresponding to the amount of plastic elongation at the time of the plastic area tightening is calculated, and the plastic area tightening exceeding the elastic limit is performed. By doing so, it is possible to tighten the plastic region beyond the yield point, and at this time, the amount of plastic elongation can be controlled to be constant.

As a result, the inspection of the plastic elongation during mass production becomes easy, and the reusability can be improved and a predetermined axial force can be easily secured.

The above-mentioned tightening method can also be applied to the fixed torque + angle method tightening in the nut rotation angle method. By controlling the tightening angle from the constant torque by the torque rate, the same effect as the seating angle method can be obtained. be able to.

[Brief description of the drawings]

The drawings show an embodiment of the present invention. FIG. 1 is a block diagram of a control device used for a bolt tightening method. FIG. 2 is a flowchart showing a bolt tightening method. FIG. 4 is a characteristic diagram showing a bolt tightening state by a seating point theoretical tightening angle control method, and FIG. 5 is a bolt tightening state by a conventional torque method and a constant torque + angle method. FIG. 6 is a characteristic diagram showing a bolt tightened state by the conventional seating point angle tightening method. 29 …… Calculator

Claims (1)

(57) [Claims] A first step of obtaining a torque rate corresponding to a friction coefficient of a screw during tightening of a bolt; a second step of calculating a theoretical seating point from the torque rate; A bolt tightening method, comprising: a third step of calculating a theoretical tightening angle from the theoretical seating point to the elastic limit point based on the above; and a fourth step of performing angle tightening based on the calculation result.