JPH0366529A - Tapping screw tightening method and device thereof - Google Patents

Abstract

PURPOSE:To threadably attach a tapping screw to a thick steel plate even with low screwing torque by threadably attaching a tapping screw at a rotating speed of 1 - 2000 rpm, applying a torsional vibration of 1 - 5000 Hz frequency and 0.1 - 10 deg. angular amplitude. CONSTITUTION:The rotating speed of a DC motor 2 is controlled to be a prescribed rotating speed with a control part 4, and the rotating speed N of a tightening tool, namely, a tapping screw is adjusted to be in the range of 1 - 2000 rpm. Alternating current of 1 - 5000 Hz is generated with a low frequency generator 6, and torsional vibration of frequency (f) is applied on the tapping screw through the tightening tool 1. The alternating current from the low frequency generator 6 is amplified with an amplifier 7 and supplied to the tightening tool 1 in the range of torsional vibration amplitude theta of 0.1 - 10 deg.. Hence, overlapped rotation of the rotating speed N from the DC motor and the torsional vibration having frequency (f) and amplitude theta, is transmitted to the tapping screw and the screw is tightened. Hereby, screwing torque is reduced, and the screw can be threadably attached even to a thick steel plate.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to self-tapping screws, and particularly relates to the technology of tightening self-tapping screws.

[Conventional technology]

A self-tapping screw works like a tap and screws into the other member to be tightened while forming an internal thread in the member.
There is no need to previously form a female thread on the mating side, and tools such as taps are also unnecessary.

Tightening with a self-tapping screw involves applying screw-in torque to the mating member, and in the final stage, applying torque so that the head of the self-tapping screw is crimped onto the member to be tightened. Tightening provides axial force, that is, bonding force.

The tightening torque applied at the end is more than twice the screwing torque in normal tapping screw tightening.

Note that if the material to be tightened is soft, such as plastic or wood, pilot holes are not required, making it possible to reduce the number of man-hours required for each layer and improve the efficiency of assembling various machines. It has the advantage of

[Problem B to be solved by the invention] However, when using, for example, a tapping screw with a cross recess on a steel plate, etc., the conventional tightening method is 211II1.
It can only be used for thin plates of about 1. If it's too thick
If used forcibly on a plate, etc., the screwing torque would become too high and the bottom shape of the female thread would not be formed, and the tightening torque would also become high, causing the cross recess of the screw to collapse. Furthermore, even if a tapping screw having a strong head other than a cross-recessed head is used, there is a risk that the tapping screw itself may be destroyed. Therefore, the tightening torque Tf and screw-in torque must be kept below a certain limit to prevent the cross recess of the screw from collapsing or the tapping screw itself being destroyed. Conventional tightening methods cannot be used on thick steel plates.

By the way, the above-mentioned tightening torque Tf is generally determined by the following equation.

Tf=-d-Ff...--■Where, Ff: Tightening of the screw is the axial force, k: Torque coefficient, d: Nominal diameter of the screw.

Furthermore, the torque coefficient is expressed by the following equation.

In this formula, d2: Effective diameter of the screw, dw: Friction equivalent diameter of the bearing surface, μ
, : Friction coefficient of thread surface, μmll: Fg friction coefficient of bearing surface,
β: Lead angle of the screw.

In the above formula ■, the conventional method of tightening in one direction
μm increases, and the torque coefficient k increases due to its influence. Therefore, if the torque is Tf for the same tightening, the axial force Ff for tightening will be small, and the reliability of the connection will be lacking.

The present invention has been made in view of the above facts, and aims to provide a method and device for tightening tapping screws that can be used for thicker steel plates than before and that improve the bonding force after tightening. The purpose is

[Means to solve the problem]

In order to achieve the above object, the present invention provides a frequency of 1 to 5 for the tapping screw when screwing the tapping screw.
A method is adopted in which a screw rotation speed of 1 to 2000 rpm is applied while applying torsional vibration of 0.000 Hz and an angular amplitude of 0.1 to 10@.

In addition, the tightening device suitable for carrying out the above method includes a DC motor with a tool attached, a low frequency oscillator, and a power amplifier that amplifies the output of the low frequency oscillator. The AC output of the low frequency oscillator is amplified and input to the DC motor, and rotation with torsional vibration is applied to the tapping screw.

[Examples] Examples of the present invention will be described below based on the attached drawings. l is a conventionally used well-known tapping screw tightening tool. Reference numeral 2 denotes a servo motor as a DC motor, and if the tapping screw is right-handed, tightening gives the tool 1 a clockwise rotation of Nrpm as shown by the arrow symbol. 3 is a tacho generator that measures the rotation speed of DC motor 2,
A signal corresponding to the rotation speed is sent to the control section 4. The control section 4 receives this signal, generates a control signal to maintain the desired rotation speed, and sends it to the servo amplifier 5. The servo amplifier 5 is the control unit 4
The controller receives a control signal from the controller, amplifies it and inputs it to the DC motor 2, so that the DC motor 2 reaches the desired rotation speed. Through the above operations, the rotation speed N of the tapping screw is adjusted to a desired value within the range of 1 to 2000 rpm. This rotational speed N is selected as an appropriate value based on the conditions for tightening the tapping screw, such as the diameter of the tapping screw, the material and plate thickness of the mating side, and so on. Below this range, tightening takes a long time and it is difficult to obtain sufficient tightening, and above this range, the tightening speed becomes greater than the vibration speed, and the effect of vibration tightening cannot be expected.

6 is a low frequency oscillator using a resistor and capacitor, 1
Generates ~5000 AC. This oscillation frequency is the frequency of torsional vibration applied to the tapping screw via the tightening tool 1, and is indicated by a small arrow f in the figure. This frequency f is adjustable, and the desired frequency is selected from within the above range of 1 to 5000 Hz, depending on the conditions for tightening the tapping screw, similar to the rotational speed N. Below this range, effective vibration tightening cannot be performed, and above this range, sufficient vibration tightening effects cannot be obtained.

The alternating current from this low frequency oscillator 6 is amplified by the power amplifier 7 to determine the torsion amplitude θ, which is input to the servo amplifier 5. The torsion amplitude θ is in the range of 0.1 to lO@. It is given as follows. Below this range, tightening similar to unidirectional tightening is required, and above this range, reliable vibration tightening effects cannot be obtained.

The servo amplifier 5 superimposes the DC component from the control unit 4 and the AC component from the low frequency oscillator 6 and applies the superimposed signal to the DC motor 2 . Therefore, the DC motor 2 transmits a superimposed rotation of the rotation number N to the tapping screw and the torsional vibration of the vibration θ at the frequency f to the tightening tool l, and transmits the torsional vibration to the tapping screw. Tighten while adding.

With the conventional unidirectional tightening method, when screwing a cross-recessed tapping screw with a nominal diameter of 5 screws into a steel plate of 2 or more holes,
This was extremely difficult as the cross recesses tended to collapse as the screwing torque increased. However, when the tapping screw is tightened while applying torsional vibration using the above device, the value of μ in the above-mentioned formula (■) becomes smaller, and the value of the torque coefficient, which was conventionally about 0.5, becomes Since it decreases to around 0.2, the screwing torque decreases and tightening becomes possible. For example, a steel plate with a thickness of 3.2 mm has a nominal diameter of 5
When tightening a self-tapping screw with a diameter of 1.5 mm, the peak torque of the screw is approximately 25 kgf-c using the conventional unidirectional tightening method.
m, and the cross recess collapsed, but if the torsional vibration type tightening method of the present invention is used, the peak of screwing torque will be reduced to 1/2 or less of 10 kgf-c, making tightening possible. . Furthermore, since the friction coefficient μ of the threaded surface is lowered, seizing during screwing can be prevented. On the other hand, the width of the variation in torque coefficient is also about 1 in the case of unidirectional tightening.
15, which is very small, and the axial force Ff increases during tightening, and there is no variation, and the bonding force is stabilized and improved.

[Effects of the Invention] As explained above, according to the present invention, the friction coefficient μ of the threaded surface decreases and the torque coefficient ratio decreases, so the screwing torque can be significantly lowered than in the case of unidirectional tightening. Tapping screws can now be used on thicker steel plates than before, and the fastening work has become easier. In addition, since the final tightening torque is approximately the same as in the conventional case, the axial force of the tightening increases, and the reliability of the fastening structure can be improved. Furthermore, since the torque coefficient ratio becomes smaller, the frictional force between the tapping screw and the steel plate, etc., decreases.
It is possible to prevent the phenomenon of seizure of screws.

[Brief explanation of drawings]

The figure shows the configuration of the tapping screw tightening device of the present invention. 1... Tool for tightening, 2... DC motor, 6... Low frequency oscillator, 7... Power amplifier. One ↓−?

Claims (2)

[Claims] (1) When screwing the tapping screw, the frequency for the tapping screw is 1 to 5000 Hz, and 0.1 to 1
1 to 2000 while applying torsional vibration with an angular amplitude of 0°.
A tapping screw tightening method characterized by applying a screw rotation speed of rpm. (2) Consists of a DC motor equipped with a tapping screw tightening tool, a low-frequency oscillator, and a power amplifier that amplifies the output of the low-frequency oscillator, and amplifies the AC output of the low-frequency oscillator and inputs it to the DC motor. A tapping screw tightening device characterized in that a rotation with torsional vibration is applied to the tapping screw.