JP2001009637A - Machining method for female screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce force required for machining, to smooth a screw surface, and to improve tensile strength by performing a part of screw machining by cutting machining, and performing the remainder by rolling machining. SOLUTION: A spiral groove 12 is machined in a prepared hole of a nut blank by cutting by using a cutting tool. A quantity of the cutting machining is decided as K=0.54 by using an expression D2'=D2-(D-D1)×K. Where, D2 is an effective diameter of a female screw 21, D2' is an effective diameter of the cutting machining, D is a major diameter of the female screw 21, D1 is an inner diameter of the female screw 21, and K=0.25 to 0.80 is realized. Here, the effective diameter D2' of the cutting means an effective diameter of a virtual female screw 13 in assuming that the spiral groove 12 forms a part of a trough of the virtual female screw 13. Thus, in machining the spiral groove 12, the female screw 21 having an effective diameter D2, the major diameter D and an inner diameter D1 is rolled with the spiral groove 12 as a guide by using a rolling tap.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of machining a female screw, and more particularly to a method suitable for machining a female screw of a nut.

[0002]

2. Description of the Related Art When manufacturing a nut, it is necessary to form a nut into a nut shape by forging or the like, and then process a female screw to be screwed with a male screw of a bolt on an inner surface of a prepared hole of the nut. Normal,
There are a rolling method and a cutting method in the processing of the female screw. When the female screw is processed by the rolling method, a nut having an extremely smooth thread surface can be manufactured.

[0003]

However, since the rolling method requires a larger working force than the cutting method, the nut actually formed by the rolling method is a nut made of a thin plate of approximately 5 mm or less. In the case of a nut having a standard larger than the nut of ISOM14 (nut height 11 mm), it is difficult to industrially produce the nut by the rolling method, and a smooth screw surface is not obtained.

[0004] In view of the above problems, it is an object of the present invention to provide a method of machining a female screw which can obtain a smooth thread surface with a small machining force.

[0005]

Therefore, in the method of machining a female screw according to the present invention, when machining a female screw on the inner surface of a prepared hole, the valley of the female screw to be formed is smaller in groove width than the pitch of the female screw to be formed. A helical groove shallower than that is cut at the pitch of the female screw to be formed, and the helical groove is used as a guide to form the ridges and valleys of the specified female screw.

One of the features of the present invention is that a part of the threading is performed by cutting, and the rest is performed by rolling. As a result, less force is required for processing than when all are rolled, and since an appropriate amount of rolling is performed, the thread surface is smoother than when performing cutting. Since the thread surface is plastically worked by rolling, the strength can be improved.

[0007] According to the experiments of the present inventors, it has been found that it is better to perform the cutting by the machining amount determined by the following equation. D2 '= D2-(D-D1) x K where D2' is the effective diameter of the cutting process, D2 is the effective diameter of the internal thread, D is the diameter of the root of the internal thread, D1 is the internal diameter of the internal thread, and K =
0.25 to 0.80. The effective diameter D2 of the internal thread is defined as the diameter of a virtual cylinder (or cone) such that when the pitch is P, the groove width of the thread is equal to the width of the thread, but for a metric thread, D2 = D -0.64951
It may be calculated by 9P. The effective diameter of the cutting means the effective diameter of the internal thread when it is assumed that the spiral groove forms a part of the root of the internal thread.

The reason why K is set to 0.25 to 0.80 is as follows. That is, when the value of K is less than 0.25, the amount of rolled processing increases, and thus the thread falls down. On the other hand, when the value of K exceeds 0.80, a bulge is formed near the thread valley. It is because.

The processing method of the present invention can be applied to the processing of any internal thread, but when applied to the processing of the internal thread of a nut, the effect is great. The type of steel to be processed by the screw processing method of the present invention is not limited.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to specific examples shown in the drawings. FIG. 1 schematically shows a preferred embodiment of a method for processing a screw according to the present invention. When a female screw of a nut is machined by the method of the present embodiment, as shown in FIG. 1A, a nut blank 10 having a pilot hole 11 is manufactured by an ordinary method.

Next, as shown in FIG. 1B, a spiral groove 12 is formed in the prepared hole 11 of the nut material 10 by cutting using a cutting tool. The amount of cutting was determined using the following equation, with K = 0.54. D2 '= D2-(D-D1) x K where D2 is the effective diameter of the internal thread, D2' is the effective diameter of the cutting process, D is the diameter of the root of the internal thread, D1 is the internal diameter of the internal thread, and K =
0.25 to 0.80.

Here, the effective diameter D2 'of the cutting process is shown in FIG.
As shown in (a), when it is assumed that the spiral groove 12 constitutes a part of the valley of the virtual female screw 13, it means the effective diameter of the virtual female screw 13.

When the spiral groove 12 is processed in this way,
As shown in FIG. 1C, the effective diameter D2, the valley diameter D, and the inner diameter D1 are formed by using a rolling tap and using the spiral groove 12 as a guide, as shown in FIG. 2B. Is rolled. The shape of the obtained female screw 21 is shown in FIG. 3, and it can be seen that a standard screw shape is obtained.

On the other hand, a female screw was machined in the same manner as in this example, with K = 0.18 and K = 1.00. FIG. 4 shows the shape of the screw when K = 0.18, and FIG. 5 shows the shape of the screw when K = 1.00. In the case of K = 0.18, the rolling amount is small, and it can be seen that a step is formed at the root of the screw and the shape is defective. In addition, when K = 1.00, the amount of rolling is too large, and it can be seen that ridges are formed on the threads of the screw, resulting in a defective shape.

Further, SUS304 is used as a material,
4mm, height 11mm, pilot hole 14.05mm, effective diameter 1
A 4.7 mm ISOM16 nut internal thread was machined according to the method of the invention and the comparative method. That is, in consideration of the build-up after rolling, a blank nut having an inner diameter of 14.7 mm is cut by changing the effective diameter of a cutting screw from 0 to 1.00, and then rolled with a rolling tap. processed. The screw shape, thread surface smoothness and tensile strength of the obtained screw were examined. The thread surface smoothness was determined by dividing the tightening torque by 1000 kgf · cm by the value of axial force × bolt diameter at that time. Table 1 shows the results.

[0016]

[Table 1]

From Table 1, it can be seen that when a screw is processed by the method of the present invention, a nut having a good thread shape, excellent thread surface smoothness, and high tensile strength can be produced.

[Brief description of the drawings]

FIG. 1 is a view schematically showing a preferred embodiment of a thread processing method according to the present invention.

FIG. 2 is a diagram for explaining the embodiment.

FIG. 3 is a view showing an example of a screw shape obtained in the embodiment.

FIG. 4 is a view showing one example of a thread shape obtained by a thread processing method of a comparative example.

FIG. 5 is a view showing an example of a screw shape obtained by a screw processing method of another comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Nut base material 11 Prepared hole 12 Spiral groove 20 Nut 21 Female screw

Claims (3)

[Claims] When machining a female screw on the inner surface of a prepared hole, a spiral groove having a groove width smaller than the pitch of the female screw to be formed and shallower than a valley of the female screw to be formed is cut at a pitch of the female screw to be formed. A method of machining a female screw, comprising: forming a thread and rolling a specified female screw ridge and valley using the spiral groove as a guide. 2. The cutting process is performed as follows: D2 ′ = D2− (D−D1) × K (where D2 ′ is the effective diameter of the cutting process, D2 is the effective diameter of the female screw, D is the diameter of the root of the female screw, D1 Is the internal diameter of the internal thread, K =
0.25 to 0.80. 2. The method for processing a female screw according to claim 1, wherein the processing is performed by an amount determined by (1). 3. The method according to claim 1, wherein the female thread of the nut is processed.