JPH0710467B2 - Round chamfering method of thread rolling round die - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of rounding chamfering a thread of a chamfered portion of a thread rolling round die, and more particularly to a method of efficiently chamfering with high accuracy. .

2. Description of the Related Art Although bolts used in automobiles, aircraft, high-rise buildings, huge structures, etc. are required to have high fatigue strength, weak points of such bolts are indicated by a circle in FIG. It is the base end part of the screw. This is the part where the end of the thread rolling round die is pressed and rolled, and as shown in FIG. 3, the root 10 of the screw becomes rectangular and stress concentration is likely to occur at the corners. Is. That is, as shown in FIG. 4, a thread rolling round die is generally provided with a thread 12 on an outer peripheral surface thereof and an end portion 14 thereof.
As shown in FIG. 5, the thread 12 is chamfered so that the height of the thread 12 is tapered toward the end surface 16, and the top 18 of the thread 12 at that portion is rectangular. This is because.

On the other hand, the cross-sectional shape of the screw thread in the chamfered portion is a circular arc shape in contact with the crest and the left and right flanks in the portion where the thread height is relatively high, and in the portion where the thread height is low There is proposed a thread rolling round die having an arc shape which is in contact with the arcs of the valley bottoms on both sides. FIG. 6 shows an example thereof, and the screw thread 20 has an arc shape in contact with the left and right flanks, and the screw thread 22 has an arc shape in contact with the arcs of the valley bottoms on both sides. According to such a thread rolling round die, as shown in FIG. 7, the roots 24 and 26 of the thread to be rolled have a smooth arc shape, so that stress concentration is prevented and fatigue strength is improved. improves. Such a thread rolling round die is described, for example, in Japanese Utility Model Publication No. 48-76236.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, such a thread rolling round die has no suitable processing method because the circular arc shape of the screw thread in the chamfered portion gradually changes as the screw advances, and relies exclusively on manual work. However, the processing accuracy is low, and the productivity and economy are extremely poor. Note that this is not necessarily limited to the case where the cross-sectional shape of the screw thread forms an arc shape in contact with the crest and the left and right flanks or valley bottoms as described above, and the cross-sectional shape gradually changes as the screw advances. This is also the case when processing threads.

The present invention has been made in view of the above circumstances, and an object of the present invention is to efficiently machine a thread whose cross-sectional shape gradually changes as the screw advances as described above with high accuracy. To do.

Means for Solving the Problems To achieve the above object, the present invention provides a screw having a chamfered portion in which a thread is provided on an outer peripheral surface and the height of the thread gradually decreases toward an end surface. A method for rounding chamfering a thread of a chamfered portion in a rolled round die, wherein (a) a cross-sectional shape is a shape in which a ridge and a valley are opposite to those of a thread to be formed by performing the rounded chamfering. Then, a step of preparing a rotary tool having a reverse thread whose pitch and lead angle are equal to those of the thread rolling round die on the outer peripheral surface, and (b) the outer peripheral surface of the rotary tool and the thread rolling Pressing the chamfered portion of the round die, and at least one of them is forcibly rotated while supplying the abrasive grains to the contacting portion so as to rotate relative to each other.

Instead of supplying the abrasive grains, it is also possible to use a fixed abrasive tool as the rotary tool.

Further, the cross-sectional shape of the screw thread to be formed by performing the rounded chamfer is preferably an arc shape that is in contact with the crest and the left and right flanta or the arc of the valley bottom, but the rounded shape of other shapes It is also possible to chamfer.

That is, the method of the present invention, the cross-sectional shape is a shape opposite to the thread to be formed, the pitch and the lead angle is the reverse thread equal to the thread of the thread rolling round die on the outer peripheral surface. Using the provided rotary tool, while pressing its outer peripheral surface against the chamfering of the thread rolling round die, while supplying abrasive grains to the contact portion to rotate relative to each other, the thread rolling round by the brittle fracture action by the abrasive grains The surface layer portion of the chamfered portion of the die is removed corresponding to the outer peripheral surface shape of the rotary tool. This is because when an indentation is made on the surface of the chamfered part by pressing abrasive grains, a plastic deformation region is created around it and a shallow work-affected layer is formed by repeating this, and eventually micro-cracks are formed and the altered layer is crushed and removed. This removal processing amount is proportional to the pressing pressure of the abrasive grains and the number of pressings, that is, the pressing pressure between the rotary tool and the thread rolling round die and the number of rotations of the thread rolling round die. Further, the processing efficiency depends on the rotation speed of the thread rolling round die.

It is desirable that the pitch and the lead angle of the reversing screw thread are completely the same as the screw thread of the thread rolling round die, but they may be slightly different. In that case,
In order to reduce the processing error, it is desirable to periodically reverse the direction of relative rotation.

As described above, the rounded chamfering method of the present invention comprises rounded chamfering by machining using a rotary tool,
The processing accuracy and the production efficiency are remarkably improved as compared with the conventional case where the processing is performed manually.

Further, if a fixed abrasive tool with abrasive grains fixed on the outer peripheral surface is used as the rotary tool, it is not necessary to supply the abrasive grains to the contact portion with the thread rolling round die, and the abrasive grains can be reliably threaded. Since it can be pressed against a round die, the number of effective abrasive grains is increased and the processing efficiency is further improved.

Embodiment Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

In FIG. 1, 30a and 30b are a pair of thread-rolled round dies for rounded chamfering, and 32 is a rotary tool for rounded chamfering. Screw rolling round die
30a, 30b have exactly the same configuration, the outer peripheral surface is provided with screw threads 34a, 34b corresponding to the male screw to be rolled, and its end portions 36a, 36b are not shown,
As in the case of FIG. 5, chamfering is performed beforehand so that the heights of the threads 34a, 34b taper down toward the end surfaces 38a, 38b. The ends 36a, 36b correspond to chamfered portions in which the heights of the threads 34a, 34b gradually decrease as the screw advances.

Further, the rotary tool 32 is made of a material harder than the thread rolling round dies 30a, 30b, and at one end thereof, a screw thread whose cross-sectional shape is round chamfered, specifically, the above-mentioned. As shown in FIG. 6, it has an arc shape in contact with the crest and the left and right flanks at a portion where the thread height is relatively high, and at the portion where the thread height is low, the crest and the valley bottoms on both sides are formed. A reversing screw thread 40 having a shape in which peaks and valleys are reversed is provided for a screw thread having an arc shape in contact with an arc.
The reverse thread 40 is a reverse thread to the thread 34a, 34b of the thread rolling round die 30a, 30b, and its pitch and lead angle are equal to the thread 34a, 34b. In this illustration, the rotary tool 32
Is provided with a single reverse thread 40, and the thread rolling round dies 30a, 30b are provided with a single thread or a plurality of threads 34a, 34b depending on the diameter dimension thereof. That is,
In order to equalize the pitch and the lead angle, the ratio of the number of thread threads to the diameter dimension should be equal to each other. In addition, although not shown in the drawings, center holes are provided on both ends of the rotary tool 32 on the axis thereof.

When performing round chamfering processing on the end portions 36a, 36b using the rotary tool 32, first, the rotary tool 32 is supported by a pair of centers so that the rotary tool 32 is rotatable about its axis, and the rotary tool is Thread rolling round dies 30a and 30b are arranged on the opposite sides of 32 and parallel to the axis of the rotary tool. In that state, those thread rolling round dies 30a, 30
b is pressed against the rotary tool 32 by the pressing pressure P, and the end portions 36a, 3
The threads 34a, 34b in 6b are engaged with the reverse thread 40. After that, while supplying the working fluid 42 containing abrasive grains to those contact portions, by forcibly rotating one of the thread rolling round dies 30a, the rotary tool 32 and the other thread rolling round die 30b are rotated together. Let Silicon carbide, fused alumina, or the like is used as the abrasive grains.

As a result, the abrasive grains in the working fluid 42 are pressed against the ends 36a, 36b of the thread rolling round dies 30a, 30b, and an indentation is formed on the surface thereof, and a plastic deformation region is generated around the indentation. . Abrasive grains are repeatedly pressed against the ends 36a, 36b as the thread rolling round die 30a rotates, so that a brittle work-affected layer is formed on the surface, and eventually microcracks occur and the altered layer is crushed and removed. To be done. Then, by repeating such crushing, the threads 34a, 3 at the end portions 36a, 36b are
The shape of 4b is the same as the valley of the reverse thread 40, that is, the arc shape is in contact with the crest and the left and right flanks or the arc of the valley bottom. The removal processing amount at this time is proportional to the pressing pressure P and the number of times the abrasive grains are pressed, that is, the rotation speed of the thread rolling round die 30a, and the processing efficiency depends on the rotation speed.

According to such a rounded chamfering method, it is sufficient to press the thread rolling round dies 30a, 30b against the rotary tool 32 and relatively rotate them while supplying the working fluid 42, so that it is processed by the mining work. Compared with the case, the production efficiency is significantly improved, and the round chamfering process can be performed with high accuracy.

By the way, using the following thread rolling round die, rotary tool, and working fluid, the rotation speed of the thread rolling round die is 400 rpm, pressing pressure P
When round chamfering was performed with 1 kg, it was possible to process in 40 minutes, and in that case the finished surface roughness was Rmax of 2.
It was 8 μm.

Thread rolling round die M10 × 1.5 For thread processing, Material: SKD11, Hardness: HRC61, Outer diameter: 16
2.6mm, width: 60mm, screw thread: 18, thread diameter: 54mm, 4 with respect to shaft center
Chamfering with 5 ° inclination Rotary tool Material: SKH57, Hardness: HRC66, Outer diameter: 46 mm, Reverse screw thread: 5 threads, Round chamfer with 30 ° inclination to the axis Working fluid: Silicon carbide 180 Mesh, oil agent: # 200 machine oil 1
+ Seed oil 1, mixing ratio: Abrasive grains 40% by weight Above, one embodiment of the present invention has been described in detail with reference to the drawings, but the present invention can be implemented in other modes.

For example, in the above embodiment, the thread rolling round dies 30a, 30b, and the rotary tool 32 are relatively rotated while supplying the working fluid 42 containing the abrasive grains, but the outer peripheral surface of the rotary tool 32 has abrasive grains. It is also possible to use a fixed-abrasive tool to which is fixed.

Further, regarding the material and diameter of the rotary tool 32, the number of threads of the reverse thread 40, etc., the material of the thread rolling round die 30a, 30b and the thread 34a, 34b.
Can be appropriately set based on the pitch, the lead angle, and the like. The cross-sectional shape of the reverse thread 40 and the material and size of the abrasive grains can be changed as appropriate.

Further, in the above embodiment, a pair of thread rolling round dies 30a, 30b
Is pressed against the rotary tool 32 for rounded chamfering at the same time, but it is also possible to machine one by one or machine three or more thread rolling round dies at the same time.

Further, in the above embodiment, the thread rolling round die 30a is forcibly rotated, but the rotating tool 32 may be forcibly rotated, or the thread rolling round die 30a, 30b, and the rotating tool 32 are all forcibly rotated. It does not matter if you rotate it.

Although not illustrated one by one, the present invention can be implemented in various modified and improved modes based on the knowledge of those skilled in the art.

[Brief description of drawings]

FIG. 1 is a front view showing a state in which a thread rolling round die is subjected to round chamfering processing according to the round chamfering method according to the present invention. FIG. 2 is a front view of the bolt. FIG. 3 is an enlarged cross-sectional view of the part marked with a circle in FIG. FIG. 4 is a sectional view of a conventional thread rolling round die. FIG. 5 is an enlarged sectional view of a chamfered portion in the thread rolling round die of FIG. FIG. 6 is an enlarged cross-sectional view of a chamfered portion having a rounded chamfer. FIG. 7 is an enlarged sectional view of a portion rolled by the chamfered portion of FIG. 30a, 30b: Thread rolling round die 32: Rotary tool, 34a, 34b: Thread 36a, 36b: End (chamfer) 38a, 38b: End, 40: Reverse thread 42: Working fluid (abrasive)

Claims (3)

[Claims] 1. A thread rolling round die having a screw thread on the outer peripheral surface and having a chamfered portion in which the height of the screw thread gradually decreases toward the end surface, and the screw thread of the chamfered portion has a rounded shape. A method of chamfering, wherein the cross-sectional shape is a shape in which the ridges and valleys are reversed from the threads to be formed by applying the rounded chamfer, and the pitch and lead angle are the same as the threads of the thread rolling round die. A step of preparing a rotary tool having equal outer threads on the outer peripheral surface, pressing the outer peripheral surface of the rotary tool and the chamfered portion of the thread rolling round die, and supplying abrasive grains to the contact portion. And at least one of them is forcibly rotated for relative rotation, and a round chamfering method for a thread rolling round die. 2. The thread rolling round according to claim 1, wherein, instead of supplying the abrasive grains, a fixed abrasive tool is used as the rotary tool. Round chamfering method for dice. 3. The cross-sectional shape of the screw thread to be formed by applying the rounded chamfer is an arc shape that is in contact with the crest and the left and right flanks or the arc of the valley bottom. Rounded chamfering method for thread rolling round dies.