Thread-forming tap

Abstract

A thread-forming tap 10 has a thread part 14 including: a complete thread part 24; and a chamfer part 22 which is provided contiguous to the complete thread part 24 and which tapers towards the tip. A plurality of lobe parts 18 are provided on the thread part 14 in the circumferential direction. Each of the lobe parts 18 includes a pressing section 18a, a crest section 18b, and a relief section 18c. In the pressing section 18a of each lobe part 18, a mountain shape 28a in a cross-section including an axis-C direction of the thread-forming tap 10 changes in the circumferential direction, so that the contact manner of the lobe part 18 with a working material improves, and cooling performance is improved. As a result of these, a highly durable thread-forming tap 10 can be provided.

Description

Forming Tap

[0001] The present invention relates to a thread forming tap, and more particularly to a thread forming tap that is less abrasive and has improved durability.

[0002] A thread forming tap is known, which has a thread portion including a full thread portion and a chamfer portion that is continuous with the full thread portion and that tapers toward the tip, and in which multiple lobes are provided at equal circumferential intervals on the thread portion (see Patent Document 1). This type of thread forming tap is screwed into a pilot hole in a workpiece from the chamfer side, and the multiple lobes bite into the surface layer of the inner wall of the pilot hole, causing plastic deformation, thereby forming a female thread. This prevents chips from being discharged, eliminating problems such as chip clogging and chip wrapping. It also enables high-strength female threads to be machined with reduced dimensional accuracy. Furthermore, it simplifies the process of removing chips from the machined female thread.

[0003] Japanese Patent No. 6420515 Japanese Patent Laid-Open No. 2001-252827 Japanese Patent Laid-Open No. 2004-001103

[0004] However, because the lobes of such thread forming taps contact the workpiece at a predetermined angle, chipping and wear are likely to occur, which can shorten tool life. In response to this, Patent Document 1 reduces the load torque by gradually changing the shape of the working teeth at the chamfering portion. Patent Document 2 improves tool life by forming the valley depth of the chamfering portion to be equal and constant to the valley depth of the parallel thread portion of the fully threaded portion. In addition, Patent Document 3 reduces thread forming resistance in areas where chipping is likely to occur by making the crest cut height of the chamfering portion greater than the crest cut height of the parallel thread portion of the fully threaded portion. The technologies of Patent Documents 1 to 3 all define the thread shape and gradient to change in the axial direction.

[0005] The present invention has been made in light of the above circumstances, and its object is to provide a thread forming tap that reduces the load on the crest portion of the lobe when plastically processing an internal thread, thereby improving durability.

[0006] In order to achieve this object, the features of the thread forming tap according to the first invention are as follows: (a) a thread portion including a full thread portion and a chamfer portion that is continuous with the full thread portion and whose diameter decreases toward the tip, and wherein the thread portion is provided with a plurality of lobes in the circumferential direction; (b) each of the lobes includes a pressing portion, a crest portion, and a relief portion in the circumferential direction within one lobe; and (c) the shape of the crest in a cross section including the axis of the thread forming tap changes in the circumferential direction at least in one of the pressing portion and the relief portion of each of the lobes.

[0007] The thread forming tap according to the first aspect of the present invention has a thread portion including a full thread portion and a chamfer portion that is continuous with the full thread portion and that decreases in diameter toward the tip, and the thread portion is provided with a plurality of lobes in the circumferential direction, each of the lobes including a pressing portion, a crest portion, and a relief portion, and the thread shape in a cross section including the axis of the thread forming tap varies in the circumferential direction in at least one of the pressing portion and the relief portion, making it possible to give each thread a shape that increases rigidity and also improves the contact mode of the lobes with the workpiece. Furthermore, cooling performance is improved, and as a result, a highly durable thread forming tap can be provided.

[0008] A second aspect of the present invention is the thread forming tap of the first aspect, characterized in that the crest shape of each of the lobes varies in the circumferential direction at the pressing portion, which further improves the contact state of the lobes with the workpiece and also improves cooling performance, thereby providing a thread forming tap with high durability.

[0009] The third invention is characterized in that, in the thread forming tap of either the first or second invention, the root diameter relief amount in the thread portion is smaller than the crest diameter relief amount. This prevents the roots from removing part of the cross-sectional shape of the tap and reducing its cross-sectional area, thereby increasing the rigidity and breakage strength of the tap. Furthermore, the flow of lubricating / cooling oil (coolant) is less likely to be obstructed by the roots, allowing it to flow more easily to the machining point, improving cooling performance. As a result, a highly durable thread forming tap can be provided.

[0010] A fourth invention is the thread forming tap of either the first or second invention, characterized in that the amount of crest diameter relief in the thread portion is greater than the amount of intermediate diameter relief, which further improves the contact state of the lobe with the workpiece and also improves cooling performance, thereby making it possible to provide a thread forming tap with high durability.

[0011] 1 is a front view illustrating the configuration of a thread forming tap according to one embodiment of the present invention;

[0023] FIG. 1 is a cross-sectional view showing a portion of the thread forming tap of FIG. 1 cut along a plane including the axis C;

[0024] FIG. 2 is a view illustrating the cross-sectional shape of the threads at the lobe portion of the thread forming tap of FIG. 1;

[0025] FIG. 3 is a view defining the range of change in the thread shape at the thread portion;

[0026] FIG. 4 is a view illustrating the change in the thread shape at the lobe portion of the thread forming tap of a comparative example;

[0027] FIG. 5 is a view illustrating the relationship between the change in thread shape and a rectangular shape in the thread forming tap of the comparative example;

[0028] FIG. 6 is a photograph illustrating the unused state of the thread forming tap of this embodiment and the thread forming tap of the comparative example;

[0029] FIG. 7 is a diagram illustrating the results of a comparative tapping durability test conducted on the thread forming tap of this embodiment and the thread forming tap of the comparative example;

[0029] FIG. 8 is a photograph illustrating the side view of the thread forming tap of this embodiment and the thread forming tap of the comparative example after the comparative tapping durability test;

[0029] FIG. 9 is an enlarged view showing the wear modes of the lobe portion of the thread forming tap of this embodiment and the lobe portion of the thread forming tap of the comparative example;

[0029] FIG. 10 is a view illustrating the cross-sectional shape of the threads at the lobe portion of a thread forming tap according to another embodiment of the present invention, and corresponds to FIG. 3.

[0023] Fig. 1 is a view illustrating the cross-sectional shape of the threads at the lobe portions of a thread forming tap according to yet another embodiment of the present invention, and is a view corresponding to Fig. 3.

[0024] Fig. 1 is a view illustrating the cross-sectional shape of the threads at the lobe portions of a thread forming tap according to yet another embodiment of the present invention, and is a view corresponding to Fig. 3.

[0025] Fig. 1 is a view illustrating the cross-sectional shape of the threads at the lobe portions of a thread forming tap according to yet another embodiment of the present invention, and is a view corresponding to Fig. 3.

[0026] Fig. 1 is a view illustrating the cross-sectional shape of the threads at the lobe portions of a thread forming tap according to yet another embodiment of the present invention, and is a view corresponding to Fig. 3.

[0027] Fig. 1 is a view illustrating the cross-sectional shape of the threads at the lobe portions of a thread forming tap according to yet another embodiment of the present invention, and is a view corresponding to Fig. 3.

[0012] Preferably, the thread has a substantially polygonal cross section when viewed axially, with radially protruding margins at positions corresponding to the vertices of the polygon, and relief portions having a smaller diameter than the margins provided between the margins. For example, the thread has a substantially square cross section when viewed axially, with radially protruding margins at positions corresponding to the four vertices of the square. That is, four radially protruding margins may be provided in the circumferential direction. However, the thread may have a substantially triangular cross section when viewed axially, with three radially protruding margins in the circumferential direction. Alternatively, the thread may have five or more radially protruding margins in the circumferential direction. Alternatively, the thread may have a substantially elliptical cross section with two radially protruding margins at the ends of the major axis.

[0013] In the thread forming tap, an oil groove is preferably formed on the outer periphery of the thread, approximately parallel to the axis, for supplying oil to the processing part during tapping with the thread forming tap. This oil groove is preferably formed in a thread forming tap with a relatively large diameter, but does not necessarily have to be provided in a thread forming tap with a relatively small diameter.

[0014] The thread forming tap is preferably configured to include a cylindrical shank portion and a thread portion provided coaxially with the shank portion at the tip side of the shank portion. The thread portion is preferably formed integrally with the shank portion, but may also be provided detachably, so that the thread portion is attached to the shank portion when tapping with the thread forming tap. The thread forming tap is preferably used with the shank portion attached to a tapping machine.

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. For the sake of convenience, the drawings used in the following description do not necessarily depict the dimensional proportions of the various components.

[0016] Embodiments of the present invention will be described in detail below with reference to the drawings. Fig. 1 is a front view illustrating the configuration of a thread forming tap 10 according to one embodiment of the present invention, and Fig. 2 is a cross-sectional view (cross-sectional view taken along line II-II in Fig. 1 ) of a portion of the thread forming tap 10 cut along a plane including the axis C. As shown in these figures, the thread forming tap 10 of this embodiment is configured to include a cylindrical shank portion 12 and a thread portion 14 integrally formed at the tip of the shank portion 12 and coaxially with the shank portion 12 (on the common axis C). A thread (external thread) 16 corresponding to the internal thread to be machined (the internal thread to be machined by the thread forming tap 10) is formed on the outer periphery of the thread portion 14. The thread portion 14 is preferably formed integrally with the shank portion 12, but may also be configured to be detachable from the shank portion 12. In this embodiment, when the thread forming tap 10 is used to form an internal thread, the thread portion 14 is fixed integrally to the tip end of the shank portion 12.

[0017] The thread 16 is formed in the shape of an external thread along a helix corresponding to a specified lead angle, with radially protruding lobes 18 provided at equal intervals in the circumferential direction. These lobes 18 correspond to the portions that bite into the pilot hole (surface portion) of a workpiece when a female thread is machined with the thread forming tap 10. In other words, the lobes 18 correspond to the action sites that plastically deform the pilot hole of the workpiece when a female thread is machined with the thread forming tap 10, and are protruding portions (lobes, lands) that protrude radially to match the shape of the female thread to be machined.

[0018] The lobe portion 18 includes a chamfer portion 18a, a crest portion 18b, and a relief portion 18c. The pressing portion 18a and the relief portion 18c have smaller diameters than the crest portion 18b. The lobe portion 18 is formed on the male thread in the circumferential direction, and therefore the crest portion 18b, the relief portion 18c having a smaller diameter than the crest portion 18b, and the pressing portion 18a are arranged in this order. As shown in FIG. 2 , for example, the thread 16 has a substantially rectangular cross section (view cross section) when viewed from the direction of the axis C. The crest portions 18b are provided at positions corresponding to the four vertices of the rectangular shape, protruding in the radial direction, and the relief portions 18c and the pressing portions 18a having smaller diameters than the lobe portions 18 are provided between the crest portions 18b.

[0019] As shown in FIG. 1 , the thread portion 14 is configured to include a chamfering portion 22 formed in a tapered shape with a diameter that gradually decreases toward the tip (the diameter becomes smaller toward the tip), and a full thread portion 24 formed in a columnar (cylindrical) shape with a substantially constant diameter. The chamfering portion 22 is a portion that, when machining an internal thread with the thread forming tap 10, bites into the surface layer of a pilot hole in a workpiece and plastically deforms that surface layer to form the internal thread, and corresponds to the configuration of several threads (e.g., 2 to 8 threads) from the tip side of the thread 16. The full thread portion 24, when machining an internal thread with the thread forming tap 10, finishes the surface of the internal thread formed by the chamfering portion 22 and improves the self-guiding properties of the thread portion 14. The full thread portion 24 has a shape that substantially matches the shape of the internal thread to be machined with the thread forming tap 10. Although not specifically described in this embodiment, the threaded portion 14 may have one or more oil grooves formed in the direction of the axis C. Alternatively, an oil hole may be provided.

[0020] With the thread forming tap 10 configured as described above, the lobe portions 18 of the threads 16 bite into the surface layer of a pilot hole formed in a workpiece, thereby forming (forming) a female thread through plastic deformation of the surface layer. For example, the thread forming tap 10 is attached to a tapping machine by its shank portion 12, and the shank portion 12 is rotated, for example, clockwise as viewed from the shank 12, while being fed axially with respect to a pilot hole into which a female thread is to be formed, so that the thread portion 14 provided on the tip side of the shank portion 12 is screwed into the pilot hole. As a result, the pressing portions 18a of the lobe portions 18 on the chamfering portion 22 bite into the surface layer (inner peripheral surface) of the pilot hole and plastically deform the surface layer, thereby rolling-forming a female thread, and the surface of the formed female thread is finished by the full thread portion 24, forming the target female thread in the pilot hole. Machining using such a thread forming tap 10 is well suited to forming internal threads in materials with excellent malleability, and has the advantage of being able to form highly accurate internal threads without producing chips, but on the other hand, a relatively large torque is applied to the thread forming tap 10 when forming the internal thread.

[0021] 3A and 3B are diagrams illustrating the cross-sectional shape (thread shape) of the thread at the lobe portion 18. Fig. 3A illustrates the change in cross-sectional shape at each of the pressing portion 18a, crest portion 18b, and relief portion 18c, which are continuous around the circumference of the tap. Fig. 3B illustrates cross sections 28a, 28b, and 28c of the pressing portion 18a, crest portion 18b, and relief portion 18c, respectively, in a plane including the axis C (axis) of the tap. In Fig. 3B, a dashed line is drawn at a position corresponding to the root diameter of the crest portion 18b, showing the relative positional relationship of the cross sections 28a, 28b, and 28c of the pressing portion 18a, crest portion 18b, and relief portion 18c in the radial direction from the axis C of the tap. In Fig. 3A, the ridge line extending from the pressing portion 18a through the crest portion 18b to the relief portion 18c is indicated by a solid line.

[0022] 3(a) and 3(b), in the thread forming tap 10 of this embodiment, the root diameter of the thread 16 of the tap does not change, and in one lobe portion 18, the height from the root portion 26 of the thread 16 increases at the pressing portion 18a toward the crest portion 18b. Furthermore, in the relief portion 18c, the height from the root diameter of the thread 16 decreases as the distance from the crest portion 18b increases. Thus, in each lobe 18, the thread shape 28 in the pressing portion 18a in a cross section including the axial direction C of the thread forming tap 10 changes in the circumferential direction. Furthermore, in the relief portion 18c, the thread shape 28 also changes in the circumferential direction.

[0023] FIG. 4 is a diagram defining the range of change in the mountain shape 28. FIG. 4 shows the mountain shape 28 in a cross section including the axis C of the thread forming tap 10 at the crest 18b of the lobe portion 18. A rectangular shape 30 surrounding the mountain shape of the crest 18b shown in FIG. 4 is defined as the upper limit (maximum area) of the range of change in the mountain shape 28. An upper side 30a and a lower side 30b of the rectangular shape 30 are parallel to the axis C of the thread forming tap 10. Furthermore, the upper side 30a is defined as the position of the crest of the crest 18b, and the lower side 30b is defined as the position of the lower of the two valleys 26 located on either side of the crest 18b, in other words, the valley closer to the axis C. Furthermore, the horizontal length w of the rectangular shape 30 in FIG. 4 , in other words, the length of the upper and lower sides 30 a and 30 b, which is also the distance between the left side, i.e., the side 30 c on the chamfer 22 side, and the right side, i.e., the side 30 d on the full thread side, corresponds to the pitch of the thread lead of the thread 16. Here, the left and right sides 30 c and 30 d are respectively located at the centers of the valleys 26 on both sides of the thread 16 in the direction of the axis C. While the above definitions relate to the crest 18 b, for the pressing portion 18 a and the relief portion 18 c, the upper and lower sides 30 a and 30 b are based on the crests in a cross section including the respective axes. However, the distance between the upper and lower sides is assumed to be equal to the distance between the upper and lower sides of the crest 18 b. Therefore, the deformation ranges of the pressing portion 18 a and relief portion 18 c have the same area as the crest 18 b, and only the position of the deformation range moves depending on the crest height.

[0024] As described above, in this embodiment, the root diameter does not change in one lobe portion 18, while the height from the root diameter of the thread 16 in the pressing portion 18a increases toward the crest portion 18b, and the height from the root diameter of the thread 16 in the relief portion 18c decreases as the distance from the crest portion 18b increases. Therefore, the ridge shape 28a in the pressing portion 18a and the ridge shape 28c in the relief portion 18c each change continuously in the circumferential direction. The maximum size of the changing ridge shapes 28a and 28b is the ridge shape 28b at the crest portion 18b in the lobe portion 18. Therefore, the change in the ridge shapes 28a, 28c in the pressing portion 18a and the relief portion 18c occurs within the range of the rectangular shape 30 defined based on the cross-sectional shape 28b of the crest portion 18b. The change in the mountain shapes 28a, 28c referred to here is intended to be continuous, and does not include discontinuous shape changes such as the mountain disappearing locally due to oil grooves provided in the tap.

[0025] Fig. 5 is a diagram illustrating the change in the crest shape 66 of the lobe portion 68 in the thread forming tap 60 of the comparative example, and corresponds to Fig. 3 described above. Similar to Fig. 3, Fig. 5(a) illustrates the change in the cross-sectional shape of each of the pressing portion 68a, crest portion 68b, and relief portion 68c, which are continuous around the periphery of the tap, and Fig. 5(b) is a cross-sectional view of each of the pressing portion 68a, crest portion 68b, and relief portion 68c, taken along a plane including the axis C of the tap. Note that, similar to Fig. 3(b), a dashed line is drawn in Fig. 5(b) at a position corresponding to the valley diameter of the crest portion 18b, indicating the relative positional relationship of the cross sections 28a, 28b, and 28c of the pressing portion 18a, crest portion 18b, and relief portion 18c in the radial direction from the axis C of the tap. In the thread forming tap 60 of this comparative example, the recessed portion is formed by making the root diameter smaller than that of the crest portion 68b in the portion other than the crest portion 68b of the lobe portion 68. Meanwhile, the difference between the crest diameter and the root diameter is set to approximately the same value in the pressing portion 68a, the crest portion 68b, and the recessed portion 68c.

[0026] 6 and 7 are diagrams illustrating the relationship between the changes in the ridge shapes 26, 66 and the rectangular shape 30 in the thread forming tap 10 of this embodiment and the thread forming tap 60 of the comparative example, respectively. FIG. 6(b) is a diagram illustrating the changes in the ridge shape 66 of the thread forming tap 60 of the comparative example, and corresponds to FIG. 5(b). FIG. 6(a) is a cross-sectional view perpendicular to the axis of the tap 60, showing an enlarged view of one lobe. FIG. 6(a) shows the positions of the ridge shapes 66a, 66b, and 66c shown in FIG. 6(b) on the tap 60. FIG. 7(b) is a diagram illustrating the changes in the ridge shape 26 of the thread forming tap 10 of this embodiment, and corresponds to FIG. 3(b). FIG. 7(a) is a cross-sectional view perpendicular to the axis of the tap 10, showing an enlarged view of one lobe. FIG. 7(a) shows the positions of the ridge shapes 28a, 28b, and 28c shown in FIG. 7(b) on the tap 10. In addition, the black parts in FIGS. 6(b) and 7(b) indicate parts that are outside the range of the definition of shape change.

[0027] 6 and 7 , the crest diameter is the diameter of an imaginary cylinder that is in contact with the crest of the tap's thread and is coaxial with the tap axis in the crest cross section including the axis; the intermediate diameter is the diameter of an imaginary cylinder that is in contact with the tap axis and has the width of the thread groove equal to the width of the thread in the crest cross section including the axis; and the root diameter is the diameter of an imaginary cylinder that is in contact with the root of the tap and is coaxial with the tap axis in the crest cross section including the axis. The crest diameter is indicated by a dashed line, the intermediate diameter by a dotted line, and the root diameter by a dashed-dotted line. Furthermore, a rectangular shape 30 corresponding to the ridge shapes of the crests 18b and 68b is indicated by a rectangle with two-dot chain lines. In the thread forming tap 60 of the comparative example, as shown in FIG. 6( b), the ridge shape 66 does not change within the rectangular shape 30 before and after the crest 68b. In the thread forming tap 10 of this embodiment, as shown in FIG. 7( b), the ridge shape 28 changes within the rectangular shape 30 before and after the crest 18b.

[0028] Figure 8 is a photograph showing the thread forming tap 10 of this example and the thread forming tap 60 of the comparative example when not in use. Figure 8(a) is a side view of the thread forming tap 60 of the comparative example, and Figure 8(b) is a side view of the thread forming tap 10 of this example. Figure 8(c) is an oblique photograph of the tip of the thread forming tap 60 of the comparative example, and Figure 8(d) is an oblique photograph of the tip of the thread forming tap 10 of this example.

[0029] Next, the results of a durability test of the thread forming tap 10 of this embodiment conducted by the inventors of the present invention will be described.

[0030] 9 is a diagram showing the results of a comparative tapping durability test conducted on a common workpiece material for the thread forming tap 10 of this embodiment and the thread forming tap 60 of the comparative example. In this test, tapping was performed under the following test conditions for each of the thread forming tap 10 of this embodiment and the thread forming tap 60 of the comparative example, and the formed internal threads were checked with a plug gauge. A test was conducted to compare the number of holes drilled by each sample before the plug gauge could no longer pass through (GP-OUT). This test was conducted twice for each of the thread forming taps 10 and 60.

[0031] [Test conditions] Machining material: Carbon steel S50C (JIS) Machining speed: 10 m / min Hole depth: 12 mm Pilot hole diameter: 5.54 mm Pilot hole shape: Through hole Machine used: Vertical machining center Oil: Water-soluble oil Size: M6 x 1 (4 lobes)

[0032] As shown in Figure 9, the thread forming tap 60 of the comparative example wore out after approximately 1,400 holes and approximately 2,800 holes, respectively, and the internal thread gauged out. With the thread forming tap 10 of this example, one of the taps wore out after approximately 4,000 holes, and the internal thread gauged out, but the other tap showed no wear even after more than 4,000 holes, and was still capable of further machining. As such, it can be seen that the wear resistance of the thread forming tap 10 of this example is significantly improved. The tool base material of the thread forming tap 10 of this example is molten HSS (High Speed ​​Steel) with a hardness of 64 HRC, while the tool base material of the thread forming tap 60 of the comparative example is powdered HSS (High Speed ​​Steel) with a hardness of 67 HRC.

[0033] Figure 10 is a photograph showing the side view of the thread forming tap 10 of this example and the thread forming tap 60 of the comparative example when the above-mentioned tapping durability comparison test was conducted. Figure 10(a) shows the side view of the thread forming tap 60 of the comparative example after drilling 1,400 holes. As indicated by the arrow in Figure 10(a), the wear of the lobe portion 68 is significant, and the endurance limit has been reached. Figure 10(b) shows the side view of the thread forming tap 10 of this example after drilling 2,800 holes. No wear of the lobe portion 18 is observed.

[0034] FIG. 11 shows enlarged views of the wear patterns at 4,000 and 1,400 holes, respectively, for the lobe portion 18 of the thread forming tap 10 of this embodiment, which has a larger change in crest diameter than the change in intermediate diameter, and the lobe portion 68 of the comparative thread forming tap 60. FIG. 11( a) shows the lobe portion 68 of the comparative thread forming tap 60. Wear is concentrated at the crests, with particularly severe wear observed at the crests of the lobes near the full crest of the chamfer. FIG. 11( b) shows the lobe portion 18 of the thread forming tap 10 of this embodiment. Scratch marks are not concentrated at the crests but are dispersed over a wide area of ​​the flank surface. It can be seen that the contact mode of the pressing portion with the workpiece has been improved, and the load is dispersed rather than concentrated at the crests of the lobes.

[0035] The thread forming tap 10 of this embodiment has a thread portion 14 including a full thread portion 24 and a chamfer portion 22 that is continuous with the full thread portion 24 and whose diameter decreases toward the tip, and the thread portion 14 is provided with a plurality of lobe portions 18 in the circumferential direction, and each of the lobe portions 18 includes a pressing portion 18a, a crest portion 18b, and a relief portion 18c, and in each of the lobe portions 18, the thread shape 28a in the pressing portion 18a in a cross section including the axial C direction of the thread forming tap 10 changes in the circumferential direction, thereby improving the rigidity of the thread and suppressing vibration during machining. In addition, cooling performance is improved, and as a result, a highly durable thread forming tap 10 can be provided.

[0036] Furthermore, with the thread forming tap 10 of this embodiment, the ridge shape 28c of each of the lobe portions 18 changes in the circumferential direction at the relief portion 18c, so that a sufficient amount of relief can be secured while preventing any loss of thread rigidity, and cooling performance is improved, resulting in a highly durable thread forming tap 10.

[0037] Furthermore, with the thread forming tap 10 of this embodiment, the amount of crest diameter relief in the thread portion 14 is greater than the amount of root diameter relief, so the infiltration of lubricating / cooling oil (coolant) is not impeded, improving cooling performance, and as a result, a highly durable thread forming tap 10 can be provided.

[0038] Furthermore, with the thread forming tap 10 of this embodiment, the amount of outer diameter relief in the thread portion 14 is greater than the amount of intermediate diameter relief, which further improves the contact state of the lobe with the workpiece and also improves cooling performance, making it possible to provide a thread forming tap 10 with high durability.

[0039] Next, another embodiment of the present invention will be described. In the following description, parts common to the embodiments will be given the same reference numerals and the description thereof will be omitted.

[0040] Figure 12 illustrates a cross-sectional shape 98 of a lobe portion 88 in another embodiment of the present invention, corresponding to Figure 3 in the first embodiment. Figure 12(a) illustrates the change in cross-sectional shape at each of the pressing portion 88a, crest portion 88b, and relief portion 88c, which are continuous around the periphery of the tap, and Figure 12(b) illustrates cross sections 98a, 98b, and 98c of the pressing portion 88a, crest portion 88b, and relief portion 88c, respectively, taken along a plane including the tap axis C. As in Figure 3(b), Figure 12(b) also illustrates a dashed line at a position corresponding to the root diameter of the crest portion 88b, indicating the relative positional relationship of the cross sections 98a, 98b, and 98c of the pressing portion 88a, crest portion 88b, and relief portion 88c in the radial direction from the tap axis C.

[0041] 12, in the lobe portion 88 of this embodiment, the angle of the peak of the triangular mountain shape 98 does not change, but the amount of protrusion from the position corresponding to the valley diameter increases as the mountain shape 98a in the pressing portion 88a approaches the peak 88b, and also decreases as the mountain shape 98c in the relief portion 88c moves away from the peak 88b. In other words, the amount of protrusion of the triangular shape is greatest at the peak 88b.

[0042] The thread forming tap 10 having the lobe portion 118 of this embodiment also provides the same effects as those of the previous embodiment.

[0043] Figure 13 illustrates a cross-sectional shape 128 of a lobe portion 118 in another embodiment of the present invention, corresponding to Figure 3 in the first embodiment. Figure 13(a) illustrates the change in cross-sectional shape at each of a pressing portion 128a, a crest portion 128b, and a relief portion 128c, which are continuous around the periphery of the tap. Figure 13(b) illustrates cross-sectional views of each of the pressing portion 128a, the crest portion 128b, and the relief portion 128c, taken along a plane including the tap axis C. As in Figure 3(b), Figure 13(b) also illustrates a dashed line at a position corresponding to the root diameter of the crest portion 118b, showing the relative positional relationship of the cross sections 128a, 128b, and 128c at each of the pressing portion 118a, the crest portion 118b, and the relief portion 118c in the radial direction from the tap axis C.

[0044] 13, in the lobe portion 118 of this embodiment, the angle of the peak of the triangular mountain shape 128 changes, so that the mountain shape 128a in the pressing portion 118a changes as it approaches the peak 118b, and the mountain shape 128c in the relief portion 128c also changes as it moves away from the peak 118b. In other words, the peak 118b has the sharpest angle.

[0045] The thread forming tap 10 having the lobe portion 118 of this embodiment also provides the same effects as those of the previous embodiment.

[0046] Figure 14 illustrates a cross-sectional shape 228 of a lobe portion 218 in another embodiment of the present invention, corresponding to Figure 3 in the first embodiment. Figure 14(a) illustrates the change in cross-sectional shape at each of a pressing portion 228a, a crest portion 228b, and a relief portion 228c, which are continuous around the periphery of the tap. Figure 14(b) illustrates cross-sectional views of each of the pressing portion 228a, the crest portion 228b, and the relief portion 228c, taken along a plane including the tap axis C. As in Figure 3(b), Figure 14(b) also illustrates the relative positional relationship of the cross sections 228a, 228b, and 228c at each of the pressing portion 218a, the crest portion 218b, and the relief portion 118c in the radial direction from the tap axis C.

[0047] 14, in the lobe portion 218 of this embodiment, the peak of the generally triangular mountain shape 228 is curved, and the radius of curvature changes, so that the mountain shape 228a in the pressing portion 218a changes toward the peak 218b, and the mountain shape 228c in the relief portion 228c also changes as it moves away from the peak 218b. In other words, the peak 218b has the smallest radius of curvature.

[0048] The thread forming tap 10 having the lobe portion 218 of this embodiment also provides the same effects as those of the previously described embodiments.

[0049] Figure 15 illustrates a cross-sectional shape 328 of a lobe portion 318 in another embodiment of the present invention, corresponding to Figure 3 in the first embodiment. Figure 15(a) illustrates the change in cross-sectional shape at each of a pressing portion 328a, a crest portion 328b, and a relief portion 328c, which are continuous around the tap periphery, and Figure 15(b) illustrates cross-sectional views of each of the pressing portion 328a, the crest portion 328b, and the relief portion 328c, taken along a plane including the tap axis C. As in Figure 3(b), Figure 15(b) also illustrates a dashed line at a position corresponding to the root diameter of the crest portion 318b, showing the relative positional relationship of the cross-sections 328a, 328b, and 328c of the pressing portion 318a, the crest portion 318b, and the relief portion 318c in the radial direction from the tap axis C.

[0050] 15, in the lobe portion 318 of this embodiment, the amount of removal varies in the mountain shape 328, which has a trapezoidal shape with the apex removed from a triangular shape. As a result, the mountain shape 328a in the pressing portion 318a changes as it approaches the peak 318b, and the mountain shape 328c in the relief portion 328c also changes as it moves away from the peak 318b. In other words, the amount of removal is smallest at the peak 318b. Note that the term "removed" here is used to describe the trapezoidal shape and does not refer to the manufacturing method.

[0051] The thread forming tap 10 having the lobe portion 318 of this embodiment also provides the same effects as those of the previously described embodiments.

[0052] Figure 16 illustrates a cross-sectional shape 428 of a lobe portion 418 in another embodiment of the present invention, corresponding to Figure 3 in the first embodiment. Figure 16(a) illustrates the change in cross-sectional shape at each of a pressing portion 428a, a crest portion 428b, and a relief portion 428c, which are continuous around the periphery of the tap. Figure 16(b) illustrates cross-sectional views of the pressing portion 428a, the crest portion 428b, and the relief portion 428c, taken along a plane including the tap axis C. As in Figure 3(b), Figure 16(b) also illustrates a dashed line at a position corresponding to the root diameter of the crest portion 418b, showing the relative positional relationship of the cross sections 428a, 428b, and 428c at each of the pressing portion 418a, the crest portion 418b, and the relief portion 418c in the radial direction from the tap axis C.

[0053] As shown in Fig. 16, in the lobe portion 418 of this embodiment, the change in the mountain shape 428a at the pressing portion 418a is different from the change in the mountain shape 428c at the relief portion 418c. The change in the mountain shape 428a at the pressing portion 418a is similar to that in the embodiment shown in Fig. 13, where the angle of the peak of the triangular mountain shape 428a changes and becomes the sharpest at the peak 418b. The change in the mountain shape 428c at the relief portion 418c is similar to that in the embodiment shown in Fig. 14, where the peak of the approximately triangular mountain shape 428 is curved, and the radius of curvature changes. Specifically, the radius of curvature, which is smallest at the peak 418b, increases as the distance from the peak 418b increases in the relief portion 428c, whereby the mountain shape 428c at the relief portion 428c changes.

[0054] The thread forming tap 10 having the lobe portion 418 of this embodiment also provides the same effects as those of the previously described embodiments.

[0055] In this embodiment, the change in the angled shape 428a in the pressing portion 418a corresponds to the embodiment shown in Fig. 14, and the change in the angled shape 428c in the relief portion 418c corresponds to the embodiment shown in Fig. 15, but this is not limiting. In other words, as long as the change in the angled shape 428a in the pressing portion 418a and the change in the angled shape 428c in the relief portion 418c are different from each other, the combination is not limited.

[0056] Figure 17 illustrates a cross-sectional shape 528 of a lobe portion 518 in another embodiment of the present invention, corresponding to Figure 3 in the first embodiment. Figure 17(a) illustrates the changes in cross-sectional shapes 528a, 528b, and 528c at the pressing portion 518a, crest portion 518b, and relief portion 518c, respectively, which are continuous around the tap. Figure 17(b) illustrates cross-sectional views of the pressing portion 518a, crest portion 518b, and relief portion 518c, taken along a plane including the tap axis C. As in Figure 3(b), Figure 17(b) also illustrates the relative positional relationship of the cross-sections 528a, 528b, and 528c at the pressing portion 518a, crest portion 518b, and relief portion 518c in the radial direction from the tap axis C.

[0057] As shown in Fig. 17, in the lobe portion 518 of this embodiment, the change in the mountain shape 528a at the pressing portion 518a is different from the change in the mountain shape 528c at the relief portion 518c, as in the embodiment shown in Fig. 16. That is, the change in the mountain shape 528a at the pressing portion 518a is similar to the embodiment shown in Fig. 13, where the angle of the peak of the triangular mountain shape 528a changes, changing to the sharpest angle at the peak 518b. The change in the mountain shape 528c at the relief portion 518c is similar to the embodiment shown in Fig. 15, where the peak of the approximately triangular mountain shape 528 is curved, and the radius of curvature changes. Specifically, the radius of curvature, which is smallest at the peak 518b, increases as the distance from the peak 518b increases in the relief portion 528c, whereby the mountain shape 528c at the relief portion 528c changes. Furthermore, in the lobe portion 418 shown in Fig. 16 , the apex of the mountain shape 428 is located near the center in the left-right direction of Fig. 16( b ) from the pressing portion 418 a through the peak portion 418 b to the relief portion 418 c, whereas in the lobe portion 518 shown in Fig. 17 , the apex of the mountain shape 528 is off-center to one side. Specifically, in the example of Fig. 17 , in the pressing portion 518 a, the apex of the triangular shape 528 a is located closer to the left in Fig. 17( b ), while in the peak portion 518 b, the apex of the triangular shape 528 b is located closer to the right in Fig. 17( b ). Furthermore, in the relief portion 518 c, the apex of the triangular shape 528 c is again located closer to the left in Fig. 17( b ). In this way, from the pressing portion 518a through the peak portion 518b to the relief portion 518c, the apex of the triangular shape 528 moves to the opposite side through the center of the triangular shape 528 in the left-right direction in Figure 17(b) (in other words, the axial direction of the tap).

[0058] The thread forming tap 10 having the lobe portion 518 of this embodiment also provides the same effects as those of the previously described embodiments.

[0059] Although the embodiments of the present invention have been described in detail above with reference to the drawings, this is merely one embodiment, and the present invention can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art.

[0060] For example, in the above-described Examples 1 and 2, the relief amount of the root diameter was set to 0, but this is not limited to this, and it may be changed under the condition that it is smaller than the relief amount of the crest diameter and / or smaller than the relief amount of the intermediate diameter in the thread portion 14. Doing so can contribute to the construction of a highly durable thread forming tap.

[0061] Furthermore, while in the above-described first to seventh embodiments, the triangular shapes are symmetrical, this is not limiting. For example, as shown in the embodiment of Figure 7, the triangular shapes may be asymmetrical, with the apex leaning to one side in the axial direction C of the tap 10, such as the chevron shape 528a at the pressing portion 518a, the chevron shape 528b at the crest portion 518b, and the chevron shape 528c at the relief portion 518c. In this way, it is possible to machine, for example, an internal thread corresponding to a buttress thread.

[0062] The thread forming tap of the present invention is used to form a female thread by screwing it into a pilot hole in a workpiece from the chamfer side, with the protrusion biting into the surface layer of the inner wall of the pilot hole and causing plastic deformation. Various configurations are possible, such as a drill or reamer for machining the pilot hole being integrally provided at the tip of the tap, or an internal diameter finishing blade or pressure lobe for finishing the internal diameter of the female thread being integrally provided.

[0063] It is desirable for the thread forming tap to be provided in three or more rows at equal intervals around the axis so that multiple protrusions are continuous and parallel to the axis, but various configurations are possible, such as the protrusions in each row being continuous in a twisted spiral around the axis, or being provided at unequal intervals around the axis.If necessary, an oil groove or the like for supplying cutting oil may be provided in the axial direction so as to divide the male thread.

[0064] Since forming taps do not generate cutting chips, they can be used to tap blind holes and through holes well to form internal threads. According to the present invention, even when forming internal threads under conditions that are likely to cause welding, such as high-speed machining or the use of low-lubricating oils (such as water-soluble lubricants), friction torque and heat generation are reduced without compromising the durability of the protruding portion, thereby suppressing welding and improving tool life. However, it is of course also possible to perform forming at a low speed or using lubricants with relatively high lubricating properties, such as water-insoluble lubricants.

[0065] The present invention relates to the shape of the protruding portion of the male thread, and the manufacturing method thereof is not particularly limited, and the present invention can also be applied when the male thread of a thread forming tap is formed using a manufacturing technique other than a grinding wheel.

[0066] The forming tap of the present invention is not limited to the above-mentioned base material, but is made of tool materials such as cemented carbide, ceramics, etc. Furthermore, if necessary, it can be coated with a hard film such as a compound film of TiN, TiCN, TiAlN, CrN, etc., a DLC (Diamond Like Carbon) film, a diamond film, etc., or can be subjected to a water vapor treatment, nitriding treatment, etc.

[0067] 10: Forming tap 12: Shank portion 14: Thread portion 16: Thread 18: Lobe portion 18a: Pressing portion 18b: Crest portion 18c: Relief portion 22: Chamfer portion 24: Full thread portion 26: Root portion 28: Thread shape 28a: Thread shape (of pressing portion) 28b: Thread shape (of crest portion) 28c: Thread shape (of relief portion) 30: Upper limit of the range of change of the thread shape (rectangular shape) 30a: Upper side 30b: Lower side 30c: Left side 30d: Right side

Claims

1. A threaded tap having a threaded portion including a full thread portion and a chamfer portion that is continuous with the full thread portion and that reduces in diameter toward the tip, and wherein the threaded portion has a plurality of lobes provided in the circumferential direction, wherein each of the lobes includes a pressing portion, a crest portion, and a relief portion in the circumferential direction, and wherein the shape of the crest in a cross section including the axis of the threaded tap changes in the circumferential direction at least in one of the pressing portion and the relief portion.

2. The thread forming tap according to claim 1, wherein the mountain shape of each of the lobes changes in the circumferential direction at the pressing portion.

3. The thread forming tap according to claim 1 or 2, wherein the amount of root diameter relief in the thread portion is smaller than the amount of crest diameter relief.

4. The thread forming tap according to claim 1 or 2, wherein the amount of crest diameter relief in said thread portion is greater than the amount of intermediate diameter relief.

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