JPH061297Y2 - Tap for screw cutting - Google Patents

Description

TECHNICAL FIELD The present invention relates to a tap for thread cutting, and more particularly to a tap capable of cutting a female screw having excellent dimensional accuracy.

2. Description of the Related Art Taps for thread cutting have been widely used as processing tools for forming female threads. Such a tap for thread cutting has a threaded portion provided with a male thread corresponding to the female thread to be formed, and by dividing the thread by a groove formed so as to intersect with the thread of the male thread,
Generally, a cutting edge for cutting the internal thread is formed at one end of the divided thread.

On the other hand, when using such a tap, for example, when tapping a difficult-to-cut material with poor machinability, or when cutting a large-diameter female screw, the thread and the formed female screw There was a problem that the frictional resistance between them became large, welding was caused by cutting heat, and the finished surface of the female screw to be cut was damaged. For this reason, it has been attempted to reduce frictional resistance and cutting heat by using a cutting fluid, and to provide a clearance in a thread of a tap to reduce frictional resistance and improve permeability of the cutting fluid.

That is, in the case of the concentric relief system having a concentric circle shape centered on the axis O of the tap like the screw thread 10 shown in FIG. 7, even if a cutting oil is used, its penetration It is difficult to obtain a sufficient friction reducing effect, but the thread 12 shown in FIG.
Escape angle φ ₁ from the cutting edge 14 to the heel 16
In the case of the eccentric relief method provided with the relief of the cutting oil, the cutting oil easily penetrates between the internal thread machined by the cutting edge 14 and the thread 12, and an excellent friction reducing effect can be obtained. . The alternate long and short dash line in FIG. 9 is an arc centered on the axis O.

Problems to be solved by the invention However, when the relief is provided from the cutting edge to the entire thread in this way, the relief amount in the heel portion becomes excessive and the self-propelled action of screwing the tap in the pitch is sufficiently obtained. There is a problem that the effective diameter of the internal thread becomes large due to excessive cutting of the thread flank particularly near the entrance of the internal thread.

On the other hand, like the screw thread 18 shown in FIG. 9, for example, a part of the cutting edge 20 side is formed into a concentric circle shape centering on the axis O to enhance the self-propelling action of the tap, and the heel 22
A coneccentric relief method is known in which a relief having a clearance angle φ ₂ is provided only on the side portion, but in this case, the permeability of the cutting fluid to the portion on the side of the cutting edge 20 having a concentric circular shape is improved. Unfortunately, the friction reducing effect is halved as compared with the case of the eccentric relief method.

Means for Solving the Problems The present invention has been made to solve the above problems, and the gist thereof is to have a screw portion provided with a male screw corresponding to the female screw to be formed. A thread cutting in which a cutting edge for cutting the female thread is formed at one end of the divided thread by dividing the thread by a groove formed so as to intersect with the thread of the male thread. In the tap for tapping, the cutting side portion of the divided thread is a relief portion having a predetermined clearance angle,
The portion of the thread from the relief portion to the heel is an arc-shaped concentric circle portion passing through the end of the relief portion with the axis of the male screw as the center.

That is, the tap for thread cutting of the present invention, contrary to the concentric relief method, is provided with a relief portion having a clearance angle on the cutting edge side portion of the divided thread,
An arc-shaped concentric circle centered on the axis of the male screw is provided on the heel side portion. In this way, the relief amount of the thread gradually increases from the cutting edge to the end of the relief portion,
Since it is kept constant in the concentric portion from the end to the heel, the relief amount on the heel side is smaller than when the relief amount gradually increases from the cutting edge to the heel as in the eccentric relief method. Become.
Therefore, even in the heel side portion, the self-propelled action of screwing the tap in the pitch according to the rubbing action between the thread and the female screw to be cut can be obtained, and the expansion of the effective diameter of the female screw is reduced to improve the dimensional accuracy. The excellent female thread of is machined.

In addition, since the relief is provided over the entire thread from the cutting edge to the heel, as compared to the case where the relief is provided only on the heel side portion as in the above-described concentric relief system. The effect of reducing the frictional resistance at the time of tapping is large, and the same effect as the eccentric relief method can be obtained.

In addition, in order to effectively prevent expansion of the effective diameter of the internal thread and to effectively reduce frictional resistance, the relief portion is in a range of 1/5 to 1/2 of the land width of the divided thread ridge. The clearance angle of the clearance is 15
It is desirable to be within the range of minutes to 2 degrees.

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

FIG. 1 is a front view showing a tap for thread cutting (hereinafter, simply referred to as tap) 30 according to an embodiment of the present invention.
The drawing is a sectional view taken along line II-II in FIG. This tap 3
Reference numeral 0 is made of high-speed tool steel, and is composed of a threaded portion 32 on the distal end side and a shank portion 34 on the proximal end side, and the threaded portion 32 is provided with a male screw 36 corresponding to a female screw to be formed. In addition, the threaded portion 32 has a thread 38 of the male screw 36.
And the thread 3
8 is composed of a cylindrical complete mountain portion 42 having substantially the same height. The thread portion 38 has a thread 38
Three helical grooves 44 are provided so as to intersect with the screw groove 38, whereby the screw fitting 38 is divided into a plurality of pieces, and a cutting edge 46 for cutting the female screw at one end of the divided thread crest 38.
Are formed.

As is apparent from the enlarged view of FIG. 3, one screw thread 38 divided by the groove 44 has a relief portion 48 provided with a relief angle φ from the cutting edge 46 and a distal end 50 of the relief portion 48. And a concentric circle portion 52 formed in an arc shape around the axis O of the tap 30 as a center. Escape section 4
8 is provided in the range of 1/5 to 1/2 of the land width (center angle) θ of the divided screw thread 38, while the concentric circle portion 52 is the remaining portion, that is, the end 50 to the heel 5.
It is provided in the parts up to 4. Further, the clearance angle φ of the clearance portion 48 is within a range of 15 minutes to 2 degrees, and the clearance amount in the concentric circle portion 52 from the distal end 50 to the heel 54 is a constant amount t. The clearance angle φ is the size at both flanks 56 of the thread 38 shown in the cross-sectional view of FIG. 4, and the clearance angle at the top 58 of the thread 38 is equal to the clearance angle φ. Equivalent angle or clearance angle φ depending on manufacturing conditions
Smaller than zero, and in some cases even zero.
Further, all the divided threads 38 of the screw portion 32 are composed of the above-mentioned escape portion 48 and the concentric circle portion 52.

Further, the threaded portion 32 of the tap 30 is coated with titanium nitride (TiN) over its entire length.

Then, such a tap 30 is attached to a tapping machine or the like, and is fed into the prepared hole of the workpiece from the side of the biting portion 40 while supplying the cutting oil to the biting portion 40,
A female screw is formed on the inner peripheral surface of the prepared hole while cutting is mainly performed by the cutting edge 46 of the bite portion 40. Further, the screw thread 38 of the complete thread portion 42 is screwed into the female thread to be machined formed by the bite portion 40, so that the tap 30 is removed.
It works by screwing it into the pilot hole one pitch at a time.

Here, the thread 38 of the tap 30 of the present embodiment is provided with a relief over the entire area from the cutting edge 46 to the heel 54, so that the relief provided only on the heel 54 side. As compared with the coneccentric relief method, the friction resistance between the internal thread to be machined and the thread 38 becomes smaller, and the cutting fluid is better permeated between them. Therefore, the frictional resistance and the cutting heat at the time of tapping are effectively reduced, and the same reduction effect as that of the eccentric relief method is obtained. In particular, in the present embodiment, since the threaded portion 32 is coated with titanium nitride, the frictional resistance is further reduced, and since titanium nitride is highly stable as a compound, it reacts with the workpiece. There is almost no risk of image sticking.

On the other hand, the relief amount of the screw thread 38 gradually increases from the cutting edge 46 to the end 50 of the relief portion 48, but is maintained at a constant amount t in the concentric circle portion 52 from the end 50 to the heel 54. Compared to the case where the relief amount gradually increases from the cutting edge 46 to the heel 54 as in the eccentric relief method, the relief amount on the heel 54 side portion becomes smaller. Therefore, even in the heel 54 side portion, the self-propelling action of screwing the tap 30 into the prepared hole according to the pitch can be obtained by the rubbing action of the thread 38 and the internal thread to be cut, and the internal thread flank becomes excessive. The expansion of the effective diameter of the internal thread to be cut is reduced, and the internal thread with excellent dimensional accuracy is cut.

Next, in order to clarify the effect of the present invention more specifically,
Taps for thread cutting according to the present invention (Products I, II, III of the present invention)
An example of the results of examining the effective diameter of the internal thread to be machined by tapping with the conventional taps for tapping (comparative products I and II) will be described. The specifications of the tap used, the work material, and the tapping conditions are as follows.

Invented product Material: High speed tool steel SKH53 (JIS-G4403) and M3-2 (ASTM) equivalent [C1.3 Cr4.0 W2.0 Mo10.0 V3.0 (%)] Thread type: Metric Eye screw, nominal M10, pitch 1.5 mm, right-hand thread, effective diameter 9.026 + 0.040 to 0.060 mm back taper 0.040 to 0.025 mm / 25 mm Thread: All threads on the thread part are composed of a relief part and a concentric circle part. The clearance angle of the relief part is 30 minutes (Invention product I), 40 minutes (Invention product II), 1 degree (Invention product III) in the flank of the screw thread. 3 Bited part: 29 angle cone, relief angle 1 degree 50 minutes Groove: Right twist 45 degree Surface treatment: Titanium nitride coating treatment on the whole thread part. Fig. 5 shows the threads of this product I and II. The relief amount of the effective diameter relief measuring device (minimum scale: vertical axis 1 μm, horizontal axis 1 degree)
It is the result measured by.

Comparative product Items other than the screw thread are the same as the product of the present invention. The screw thread has a relief angle of 30 minutes (Comparative product I) and 1 degree (Comparative product II) from the cutting edge to the heel by the eccentric relief method. Work material provided Material: Rolled steel for general structure SS41 (JIS-G3101) Hardness: HRB72-74 Tapping length: 20mm Prepared hole diameter: 8.5mm Tapping condition Device: Horizontal axis NC tapping machine Cutting speed: Peripheral speed 8.8 m / min (280 rpm) Cutting oil: Water-soluble cutting oil (JIS-W Class 1 No. 2) Tap feed: 378 mm / min (using floating tapper) And using the above 5 types of taps for screw cutting, 3 samples made of the work material are tapped with 10 holes each,
Using a machining set screw plug gauge (symbol WP) grade 2 of the metric coarse thread limit gauge (JIS-0251), measure the number of rotations that can be manually screwed into a machined female screw, and then rotate the rotation. Pass / fail was determined by whether the number was two or less. Results are shown in FIG.

FIG. 6 shows only the odd-numbered results of the 10 tapping holes formed in each sample, and shows the number of rotations with a circle. The products I, II, All of the internal threads formed by III are within 0.5 revolutions,
It can be seen that a female screw with excellent dimensional accuracy without expanding the effective diameter can be cut extremely stably. On the other hand, comparative products
Among the internal threads formed by I and II, there are some that exceed the acceptable range, that is, the flanks of the internal threads are excessively cut and the effective diameter expands, and the number of revolutions of the gauge exceeds 2 revolutions. However, the dimensional accuracy is less stable than the product of the present invention.

Although one embodiment of the present invention and the test results have been described in detail above, the present invention can be implemented in other modes.

For example, in the above embodiment, the three-blade tap 30 has been described, but the present invention can be similarly applied to a two-blade tap, a four-blade tap, and the material, surface treatment, and groove thereof. Of course, the shape and the like of 44 can be changed as appropriate.

Further, the range of the clearance 48 of the thread 38 and the clearance angle φ
Is preferably set appropriately within the range described above, and it is also possible to provide the relief on only one of the flanks 56 of the screw thread 38 on the leading side or the trailing side.

Although not illustrated one by one, the present invention can be implemented in variously modified and improved modes based on the knowledge of those skilled in the art without departing from the spirit thereof.

[Brief description of drawings]

FIG. 1 is a front view of a tap for thread cutting which is an embodiment of the present invention. FIG. 2 is a sectional view taken along line II-II in FIG. FIG. 3 is an enlarged view of the threads of FIG. FIG. 4 is an enlarged view showing a cross section of the thread of FIG. Fifth
The figure is a view showing a result of measuring a clearance amount of a thread in a tap for thread cutting according to the present invention. FIG. 6 is a diagram showing the results of measuring with a gauge the dimensional accuracy of the tapping holes obtained by the tap for thread cutting according to the present invention and the tap for conventional thread cutting. FIG. 7 is a sectional view showing a conventional concentric relief type screw thread. FIG. 8 is a sectional view showing a conventional eccentric relief type screw thread. FIG. 9 is a sectional view showing a conventional coneccentric relief type screw thread. 30: Tap for thread cutting 32: Thread part 36: Male thread 38: Thread ridge 44: Groove 46: Cutting edge 48: Relief part 50: End 52: Concentric circle part 54: Heel θ: Land width (center angle) φ: Relief angle

Claims (2)

[Scope of utility model registration request] 1. A threaded portion provided with a male thread corresponding to a female thread to be formed, wherein the thread is divided by a groove formed so as to intersect with the thread of the male thread. In a tap for thread cutting in which a cutting edge for cutting the internal thread is formed at one end of the formed thread, the cutting edge side portion of the divided thread is a relief portion having a predetermined clearance angle. On the other hand, a tap for thread cutting, wherein a portion of the screw thread from the relief portion to the heel is an arc-shaped concentric circle portion passing through an end of the relief portion around the axis of the male screw. 2. The relief portion is provided in a range of 1/5 to 1/2 of a land width of the divided thread, and the relief angle of the relief portion is in a range of 15 minutes to 2 degrees. The tap for thread cutting according to claim 1, which is within the scope of utility model registration.