JP7724251B2 - Spiral Tap - Google Patents

Description

The present invention relates to a spiral tap.

Cutting taps are known as tools for forming internal threads in workpieces. Cutting taps are screwed into the workpiece while rotating, forming the internal thread while collecting chips generated by the cutting process in multiple grooves on the outer surface of the body. The shape and discharge direction of the chips generated by cutting taps vary depending on the direction and shape of the grooves. For example, spiral taps with helical flutes are known (Patent Documents 1 and 2). Due to the characteristic chip discharge direction of spiral taps, spiral taps are primarily used as taps for machining internal threads into blind holes.

International Publication No. 2008-136123 Japanese Utility Model Application Laid-Open Publication No. 5-12042

In general, spiral taps generate multiple chips according to the number of threads in the chamfer. These chips curl according to the shape of the corresponding spiral flutes and are discharged in a continuous line toward the shank. In other words, the chips form a series of spirally curled lines. Depending on the shape of the chips, multiple chips generated within the same spiral flute or adjacent spiral flutes may become entangled, the chips may become entangled in the spiral tap or the workpiece, or the chips may become caught between the threads formed by machining and the threads of the spiral tap, potentially damaging the spiral tap and the threads formed in the workpiece. Therefore, it may be necessary to remove the chips as needed to prevent them from becoming entangled with each other or with the spiral tap or the workpiece.

In particular, according to tests conducted by the inventors, when machining large-diameter internal threads, such as M20, or internal threads with a thread length more than twice the nominal diameter, long, continuous chips are generated in proportion to the thread length, making the above-mentioned problems more likely to occur. In order to perform stable, continuous machining using spiral taps, it is important to solve the above-mentioned problems caused by chips.

As a method for preventing chip jamming, the spiral tap described in Patent Document 1 is equipped with a tapered section that tapers from a full thread section consisting of 1 to 5 threads toward the shank, reducing the diameter as it approaches the shank. This prevents chips generated by the chamfer from getting jammed in the spiral flute. However, when drilling deep holes where the drilling depth is nearly twice the nominal diameter, even if the problem of chip jamming is solved, the spiral flute's ability to discharge chips is reduced, and the problem of chips not being properly discharged and becoming entangled in the spiral tap remains.

On the other hand, the spiral tap described in Patent Document 2 has a guide portion for discharging chips between the male thread portion and the shank portion. By approximating the outer diameter of the guide portion to the dimensions of the pilot hole in the workpiece, the discharged chips are guided to be discharged through the spiral flutes of the guide portion. This solves the problems of chips becoming entangled in the spiral tap and chips discharged from adjacent spiral flutes becoming entangled with each other. However, because chip shapes can vary depending on the type of workpiece and cutting conditions, the guide portion, which approximates the dimensions of the pilot hole in the workpiece, is inserted too deeply relative to the reference surface of the workpiece, which can result in multiple chips generated within the same spiral flute becoming entangled, or chips easily becoming caught between the formed threads and the spiral tap's threads.

The objective of the present invention is to provide a spiral tap that enables stable chip discharge.

One aspect of the present invention provides a spiral tap comprising: a male thread portion consisting of a chamfer portion and a full-thread portion; a tapered portion in which the threads continuing from the male thread portion are tapered rearward from the rear end of the male thread portion; a cylindrical guide portion disposed between the tapered portion and the shank and having a larger diameter than the shank; and a plurality of helical grooves arranged in a spiral pattern along the axial direction so as to divide the male thread portion. When the reference dimension of the outer diameter of the full-thread portion is D and the pitch of the male thread portion is P, the outer diameter of the guide portion is D-1.5P, and the slope angle of the tapered portion is within the range of 10 to 15 degrees.

The overall length of the male thread portion may be 1.2D or less. The male thread portion may be M18 or greater. At least the male thread portion may be subjected to a coating treatment, oxidation treatment, or nitriding treatment, and the helix angle of the spiral flute relative to the axis of the spiral tap may be within the range of 40 to 48 degrees.

The aspects of the present invention have the common effect of providing a spiral tap that allows for stable chip discharge.

FIG. 1 is a side view of a spiral tap according to an embodiment of the present invention. FIG. 2 is a schematic diagram of the spiral tap of FIG. FIG. 3 is an end view of the male thread portion side of the spiral tap of FIG. FIG. 4 is a cross-sectional view showing machining using a spiral tap. FIG. 5 is a photograph of the spiral tap according to the first embodiment of the present invention and chips generated during internal thread machining using the spiral tap. FIG. 6 is a photograph of a spiral tap according to a second embodiment of the present invention and chips generated during internal thread machining using the spiral tap. FIG. 7 is a photograph of a spiral tap according to a comparative example of the present invention and chips generated by internal thread machining using the same.

Embodiments of the present invention will be described in detail below with reference to the drawings. Corresponding components are designated by common reference symbols throughout the drawings.

Figure 1 is a side view of a spiral tap 1 according to an embodiment of the present invention, Figure 2 is a schematic diagram of the spiral tap 1 of Figure 1, and Figure 3 is an end view of the male thread portion 2 side of the spiral tap 1 of Figure 1.

The spiral tap 1 has a male thread portion 2 consisting of a chamfer portion 3 and a fully threaded portion 4 with a complete thread shape; a tapered portion 5 in which the threads continuing from the male thread portion 2 are tapered rearward from the rear end of the male thread portion 2; a cylindrical guide portion 7 disposed between the tapered portion 5 and the shank 6 and having a larger diameter than the shank 6; and four helical flutes 8 (Figure 3) disposed equally spaced around the axis C along the axis C so as to divide the male thread portion 2. The helical flutes 8 are disposed between the tapered portion 5 and the shank 6 and extend to a neck 9 whose diameter is slightly smaller than that of the shank 6. In this specification, the male thread portion 2 side in the axial direction of the spiral tap 1 is defined as the "front" side, and the shank 6 opposite the male thread portion 2 is defined as the "rear" side.

The spiral flutes 8 of the spiral tap 1 are right-handed and extend beyond the guide portion 7 toward the shank 6. A cutting edge is provided along each of the spiral flutes 8. At least the external thread portion 2 of the spiral tap 1 has been subjected to a surface treatment such as a coating treatment with TiCN or the like, an oxidation treatment, or a nitriding treatment.

When the slope angle of the tapered portion 5 relative to the axis C of the tapered portion 5 is θ, the reference dimension of the outer diameter of the full thread portion 4 is D, and the pitch of the male thread portion 2 is P, the outer diameter of the guide portion 7 is preferably D-1.5P. In this case, the slope angle θ of the tapered portion 5 is preferably within the range of 10 to 15 degrees. The overall length of the male thread portion 2 is preferably 1.2D or less. The male thread portion 2 is preferably M18 or greater, and more preferably M24 or less.

Figure 4 is a cross-sectional view showing machining using the spiral tap 1. A pilot hole 101 is provided in the surface of the workpiece 100. The spiral tap 1 is threaded into the pilot hole 101 from the tip side, cutting the inner surface of the pilot hole 101 and forming a female thread 102. Chips G generated by the cutting process pass through the helical flute 8 and reach the vicinity of the opening of the pilot hole 101, and are discharged radially from the opening of the pilot hole 101 toward the shank 6. The chips G are formed into a series of spirally curled lines.

In the spiral tap 1, a predetermined gap is formed between the tapered portion 5 and the formed internal thread 102. Therefore, when the full thread portion 4 passes over the internal thread 102 formed by the chamfer 3 and the tapered portion 5 is then screwed in, the predetermined gap prevents chips from getting caught. This prevents chipping, increased cutting torque, and breakage due to chipping, further improving the durability of the spiral tap 1. In addition, because the base of the tapered portion 5 after the threads have been removed is the same as the base of the complete thread shape of the full thread portion 4, the full thread portion 4 and tapered portion 5 provide excellent guiding (lead feed) and enable the internal thread to be cut with high machining precision.

A predetermined gap is also formed between the guide portion 7, located behind the tapered portion 5, and the formed internal thread 102. The guide portion 7 guides chips into the spiral flutes 8 so that they are discharged in a fixed direction, reducing the risk of chips getting caught between the workpiece 100 and the spiral tap 1. Furthermore, because chips are discharged in a fixed direction using the spiral flutes 8 formed in the guide portion 7 as a passage, they are prevented from becoming entangled with the spiral tap 1, specifically the shank 6, and chips discharged from different spiral flutes 8 are prevented from becoming entangled with each other, allowing for stable chip discharge.

The helix angle of the spiral flutes 8 relative to the axis C of the spiral tap 1 is preferably within the range of 40 to 48 degrees. If the external thread portion is subjected to a surface treatment such as coating, oxidation, or nitriding, the wear resistance of the spiral tap is improved, but the high lubricity makes the chips more likely to elongate, increasing their length. This makes the chips more likely to become entangled with the spiral tap or the workpiece. Therefore, in the spiral tap 1 according to an embodiment of the present invention, the helix angle of the spiral flutes 8 is set within the above-mentioned range, thereby adjusting the shape of the chips to achieve a curl diameter appropriate for cutting performance. As a result, entanglement of discharged chips with the spiral tap 1 and entanglement of chips discharged from different spiral flutes 8 are suppressed, enabling stable chip discharge.

Figure 5 is a photograph of a spiral tap 1 according to a first embodiment of the present invention and chips generated when it is used to machine an internal thread. Figure 6 is a photograph of a spiral tap 1 according to a second embodiment of the present invention and chips generated when it is used to machine an internal thread. Figure 7 is a photograph of a spiral tap according to a comparative example to the present invention and chips generated when it is used to machine an internal thread. Figure 7(A) is the first comparative example, Figure 7(B) is the second comparative example, and Figure 7(C) is the third comparative example.

The spiral taps in each example and comparative example are all M20 x 2.5 spiral taps, with the length of the male thread portion being 20 mm, the outer diameter of the shank 6 being 15.0 mm, and the outer diameter of the neck 9 being 14.5 mm.

The workpiece was S50C, and the spiral tap 1 was set on a vertical machining center. The machining conditions were a cutting speed of 10 m/min, a machining depth of 47.5 mm, and a water-soluble cutting fluid diluted 20 times. The machining depth was set so that the thread length of the internal thread was 2D, where D is the reference dimension of the outer diameter of the fully threaded portion 4 of the spiral tap 1.

As shown in the left diagram of Figure 5, the spiral tap 1 according to the first embodiment has a tapered portion 5 with a slope angle of 12.5 degrees and a guide portion 7 with an outer diameter of 16.3 mm. That is, as mentioned above, the outer diameter of the guide portion 7 is preferably D-1.5P, and this value was set based on the dimensions of the M20 x 2.5 spiral tap. When the spiral tap 1 according to the first embodiment was used, no chipping, increased cutting torque, or breakage of the spiral tap 1 due to chipping was observed, and the chips were discharged smoothly. Furthermore, as shown in the right diagram of Figure 5, the curl diameter of the chips was approximately uniform, and the length of each chip was also approximately uniform.

As shown in the left diagram of Figure 6, the spiral tap 1 according to the second embodiment differs from the spiral tap 1 according to the first embodiment in that the slope angle of the tapered portion 5 is 15 degrees. When the spiral tap 1 according to the second embodiment was used, no chipping, increased cutting torque, or breakage of the spiral tap 1 due to chipping was observed, and the chips were discharged smoothly. Furthermore, as shown in the right diagram of Figure 6, the curl diameter of the chips was approximately uniform, and the length of each chip was also approximately uniform.

As shown in the left diagram of Figure 7(A), the spiral tap according to the first comparative example differs from the spiral tap 1 according to the first embodiment in that the slope angle of the tapered portion is 30 degrees. When the spiral tap according to the first comparative example was used, chips became trapped and were not properly discharged. A slight increase in cutting torque was also observed. However, no chipping or breakage of the spiral tap 1 due to trapping was observed. As shown in the right diagram of Figure 7(A), the chips did not curl completely and were broken into small pieces.

As shown in the left diagram of Figure 7(B), the spiral tap according to the second comparative example has a tapered portion with a slope angle of 5 degrees. Furthermore, because the slope angle of the tapered portion is small, no guide portion is essentially provided. When the spiral tap according to the second comparative example was used, chips became trapped and the cutting torque increased. However, the chips were discharged relatively well. Furthermore, no chipping or breakage of the spiral tap 1 due to trapping was observed. As shown in the right diagram of Figure 7(B), the curl diameter of the chips was relatively uniform, but there was some variation in length.

As shown in the left diagram of Figure 7(C), the spiral tap of the third comparative example has a tapered portion with a slope angle of 15 degrees, but differs from the spiral tap 1 of the first embodiment in that it does not have a guide portion. When the spiral tap of the third comparative example was used, chips became trapped and were not properly discharged. In addition, a slight increase in cutting torque was observed, and it was confirmed that the chips became tangled around the spiral tap. As shown in the right diagram of Figure 7(C), the chips did not curl completely and were broken into small pieces.

As a result, the spiral tap 1 enables stable chip discharge and prevents chip tangles during continuous machining.

1 Spiral tap 2 Male thread portion 3 Chamfer portion 4 Full thread portion 5 Tapered portion 6 Shank 7 Guide portion 8 Helical flute 9 Neck

Claims (4)

a tapered portion in which the threads continuing from the male thread portion are tapered rearward from the rear end of the male thread portion; a cylindrical guide portion provided between the tapered portion and the shank and having a larger diameter than the shank; and a plurality of helical grooves provided spirally along the axial direction so as to divide the male thread portion,
When the reference dimension of the outer diameter of the fully threaded portion is D and the pitch of the male thread portion is P, the outer diameter of the guide portion is D-1.5P,
The spiral tap is characterized in that the slope angle of the tapered portion is within a range of 10 to 15 degrees. The spiral tap according to claim 1, wherein the overall length of the male thread portion is 1.2D or less. The spiral tap according to claim 1 or 2, wherein the external thread portion is M18 or larger. The spiral tap according to claim 1 or 2, wherein at least the male thread portion has been subjected to a coating treatment, oxidation treatment, or nitriding treatment, and the helix angle of the spiral flute relative to the axis of the spiral tap is within the range of 40 to 48 degrees.