Patent Application
20090317203
The present invention relates to a spiral fluted tap, and more particularly, to a technology of preventing occurrence of chipping or breakage resulted from a biting of chips, especially when a full thread portion is screwed into a threaded bore formed by a chamfer portion.
There has been a kind of a spiral fluted tap, disclosed in for instance Patent Publication 1, which has a threaded portion formed with cutting edges extending along spiral flutes so as to divide or to segmentalize external threads. Screwing the threaded portion into a prepared hole allows the cutting edges to cut or to tap internal threads on an inner circumferential surface of the prepared hole, with discharging chips toward a shank via the spiral flutes.
During such tapping, the chips are discharged via the spiral flutes 104 to an outside of the prepared hole 112. However, when a full thread portion is screwed into a threaded hole 114 formed by a chamfer portion, the chips may be bitten to cause chipping of the cutting edges or breakage of the spiral fluted tap 100. Especially, as the spiral fluted tap dulls due to the use of water-soluble cutting oil and MQL (Minimum Quantity Lubrication) or the like, the chips hardly curled and extended lengthwise reveals an irregular movement. Thus, the chips are easily bitten to cause a remarkable possibility of the chipping of the cutting edges or the breakage of the spiral fluted tap.
On the contrary, Patent Publication 2 proposes a technology of preventing occurrence of chipping of the cutting edges at distal ends i.e., top ends. As shown in
[Patent Publication 1] Japanese Patent Publication 4-75816
[Patent Publication 2] Japanese Patent Publication 10-118844
However, in the spiral fluted tap disclosed in Patent Publication 2, only the radially outward portions (outer diametric portion) positioned outside of the effective diameter are cut away. Therefore, even after such removal, the distal ends of the cutting edges are still sharp to easily bite the chips and to be easily chipped. Thus, the conventional spiral fluted tap was not be necessarily satisfied in an adequate manner.
The present invention has been completed considering with the above situations, and has an object to further effectively prevent occurrence of the chipping of the cutting edges and breakage of the spiral fluted tap resulted from the biting of cutting edges, encountered when screwing a full thread portion into a threaded hole formed by a chamfer portion.
For achieving the above object, a first aspect of the present invention relates to a spiral fluted tap which includes a threaded portion having cutting edges formed along spiral flutes formed to divide external threads, and being screwed into a prepared hole to cut internal threads by the cutting edges on an inner circumferential surface of the prepared hole with discharging chips toward a shank via the spiral flutes.
In the spiral fluted tap, (i) cutting faces of the cutting edges of a shank-side thread portion are formed with chamfers retreating circumferentially toward crests of the threads, and the shank-side thread portion is formed on a full thread portion of the thread portion, except for a chamfer-side thread portion having more than one thread and not more than five threads formed at a distal end contiguous to a chamfer portion and is closer to the shank than the chamfer-side thread portion; and (ii) each of the chamfers has a chamfer height Hmen ranging from 15% to 100% of a thread height Hneji of the full thread portion.
In a second aspect of the present invention, the chamfers are flat planar chamfers or arc R (round)-chamfers.
According to the spiral fluted tap, on the shank-side thread portion of the full thread portion of the threaded portion formed in the area closer to the shank, the cutting edges are formed with the chamfers. The chamfers have the cutting faces each having the chamfer height Hmen fallen within the range of 15% to 100% of the thread height Hneji. This allows the chips to be further easily pushed out toward an outer circumferential area i.e., space along the chamfers, respectively. In addition, the cutting edges can have the increased strength due to formation of the chamfers. This effectively prevents the occurrence of chipping of the cutting edges and breakage of the spiral fluted tap caused by the biting of the chips.
Further, the chamfer-side thread portion, formed on the full thread portion of the threaded portion at the distal end, is contiguous to the chamfer portion, which has an original complete thread configuration with more than one thread and not more than five threads. In addition, the shank-side thread portion formed with the chamfers has an original thread configuration except areas around the cutting edges, respectively. Thus, the entire area of the full thread portion can have the excellent guide action (in lead feed) than that achieved by a structure in which the crests of the threads are cut away in the cylindrical configuration in the areas radially outside the effective diameter. This can tap the internal threads with further increased precision
A spiral fluted tap of the present invention allows chips to be discharged toward a shank. More particularly, the spiral fluted tap is in one style formed cutting edges along right-hand spiral flutes to be rotatably driven clockwise as viewed from the shank to perform cutting work. In the other style, the spiral fluted tap has cutting edges formed along left-hand spiral flutes to be rotatably driven counter-clockwise as viewed from the shank to perform cutting work.
The spiral fluted tap can be made of tool material such as, for instance, high-speed tool steel (high speed steel) or cemented carbide steel or the like and possibly applied with hard coating of TiAlN, TiN, TiCN or the like depending on needs. Further, the spiral fluted tap of the present invention demonstrates excellent advantageous effects particularly when the chips easily extend lengthwise to irregularly move due to dulling of the spiral fluted tag encountered in the tapping with the use of water-soluble oil-based cutting agent, MQL (Minimum Quantity Lubrication) or oil-less dry machining. However, of course, the spiral fluted tap of the present invention can be used for tapping under wet working supplied with lubricating oil-based agent at an adequate feed rate.
If a chamfered-side thread portion, having cutting faces not formed with the chamfer, of a full thread portion has less than one thread, the spiral fluted tap is hardly guided (in lead feed) with increased precision. Meanwhile, if the chamfered-side thread portion has more than five threads, then, the chamfered-side thread portion will easily bite the chips, causing the chipping of the cutting edges or breakage of the spiral fluted tap. Therefore, the chamfered-side thread portion needs to have more than one thread and not more than five (5) threads i.e., five or smaller than five.
A chamfer height Hmen of the chamfer refers to a radial dimension measured based on a distal end (outer circumferential edge) of each cutting edge before the distal ends i.e., radially top ends being chamfered. A thread height Hneji of the full thread portion refers to a radial dimension of a thread between a root and top thereof, and it is particularly represented in terms of “(Tap Outer Diameter−Tap Root Diameter)/2”. If the chamfer height Hmen is less than 15% of the thread height Hneji, the chamfer can not suppress the biting action of the chips, and can not render adequate improved strength of the cutting edges. In contrast, if the chamfer height Hmen exceeds 100% of the thread height Hneji, then, a gap is created between the prepared hole (threaded hole) and the spiral fluted tap with an adverse effect of easily biting the chips. Therefore, the chamfer height Hmen needs to fall in a range between 15% and 100% of the thread height Hneji. The chamfer height Hmen may be fixed i.e., constant in value but may be possibly varied in an axial direction within a predetermined range in a continuous or stepwise manner. Alternatively, the chamfer height Hmen may have differing dimensions different for plural cutting edges, respectively.
Chamfered shapes may have flat planar chamfer, or arc R-chamfer. The flat planar chamfer will be described below in detail with reference to a case wherein each flat planar chamfer has a chamfer angle θ angled with respect to a base line L connecting between a radial distal end i.e., top end (outer circumferential edge) of the cutting edge before the chamfering and a tapping axis O, in a cross section perpendicular to each cutting edge. If the chamfer angle θ is too small, then the chamfer can not render the suppressing action of the biting of the chips, and can improve the strength of the cutting edge by the chamfer. Thus, the chamfer angle θ may preferably be selected to fall in a value of, for instance, 20° or more.
On the contrary, if the chamfer angle θ is too large, then, the spiral fluted tap has a decreased angle between the chamfer and the cutting face, easily catching the chips with increased likelihood. Thus, the chamfer angle θ may preferably be selected to fall in a value of, for instance, 60° or less. Although the chamfer angle θ may have a fixed value, it may be possibly varied within a predetermined range along an axial direction in a continuous or stepwise manner. In an alternative, the chamfer angle θ may have differing dimensions different for plural cutting edges, respectively.
The R-chamfer is formed in a circular arc configuration with a radius being nearly fixed such that the R-chamfer is smoothly connected to the cutting face and the crest of the thread, in a cross section perpendicular to, for instance, the cutting edge. However, the R-chamfer may have a circular arc configuration with the radius of the curvature varying continuously due to a convenience of working.
Threads of the full thread portion may preferably have thread reliefs i.e., reliefs such as eccentric reliefs or the like, respectively. In an alternative, threads of a fixed diametrical dimension with no reliefs can be adopted. That is, it may suffice for the spiral fluted tap of the present invention to have the chamfers formed on the cutting faces of the cutting edges of the shank-side thread portion of the full thread portion, and for the thread reliefs to take a variety of designs including presence/absence of the thread reliefs. For instance, areas of the threads in close proximity to the crests can be cut away into cylindrical configurations.
A flute angle of the spiral flute provided on the threaded portion may preferably be selected to range from approximately, for instance, 15° to 50°. Moreover, the number of teeth of the cutting edges is appropriately varied to have, for instance, about 2 to 6 cutting edges depending on work material to be cut or a tapping size.
Hereunder, embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
A spiral fluted tap 10 includes a shank 12, a neck portion 14 and a threaded portion 16, which are integrally formed on a common axis O in such an order. The threaded portion 16 has external threads formed in groove profiles corresponding to internal threads to be cut, and three spiral flutes 20 formed so to divide the external threads. The threaded portion 16 includes a chamfer portion 22 formed at an axial distal end thereof with threads 18 of the external threads being removed in the axial direction in a tapered shape, and a full thread portion 24 contiguous to the chamfer portion 22 and having the full threads 18. Cutting edges 26 are formed at ridgelines between the threaded portion 16 and the spiral flutes 20.
The spiral flutes 20 are right-hand helixes each of which has a helix angle falling within a range of, for instance, 15° to 50° to lie at a value of approximately, for instance, 40°. In use, the spiral fluted tap 10 is rotatably driven clockwise as viewed from the shank 12 so that a distal end is screwed into, for instance, the prepared hole 112 of the work material 110 shown in
The full thread portion 24 has chamfers i.e., chamfered portions 30. Each of these chamfers 30 is formed on a cutting face i.e., rake face (forming part of each spiral flute 20) of the cutting edge 26 of a shank-side thread portion 24b formed in an area closer to the shank 12, except for a chamfer-side thread portion 24a. The chamfer-side thread portion 24a is formed on the full thread portion 24 in an end portion thereof to be contiguous to the chamfer portion 22 and has more than one threads and not more than five threads. The chamfers 30 are retreated circumferentially (to heel side) toward the crests i.e., outer circumferences of the threads 18. That is, the chamfers 30 are inclined circumferentially (to heel side) as distance from the axis increases.
The chamfer 30 is a flat planar chamfer having a chamfer angle θ, angled with respect to a base line L connecting between the distal end (outer circumferential edge) of the cutting edge 26 prior to the chamfer formation and a tap axis O, which lies in a value of approximately, for instance, 45° within a range of 20° to 60°. The chamfer angle θ is indicated in a cross section perpendicular to the axis O in
In the illustrated embodiment, both the chamfer height Hmen and the chamfer angle θ are set in fixed dimensions at fixed angles over an entire area of the shank-side thread portion 24b. In the illustrated embodiment, further, the spiral fluted tap 10 is made of high-speed tool steel (powdered high-speed steel) with the threaded portion 16 having a hard coating of TiCN. Although each of the threads 18 of the full thread portion 24 in
According to the spiral fluted tap 10 of the present invention, of the full thread portion 24 of the threaded portion 16, the cutting edges 26 of the shank-side thread portion 24b formed in the area closer to the shank 12 are formed with the chamfers 30. The chamfer 30 have the cutting faces each having the chamfer height Hmen fallen within the range of 15% to 100% of the thread height Hneji. This allows the chips to be further easily pushed out toward an outer circumferential area i.e., space along the chamfers 30, respectively. In addition, the cutting edges 26 can have the increased strength thanks to formation of the chamfers 30. This effectively prevents the occurrence of chipping of the cutting edges and breakage of the spiral fluted tap caused by the biting of the chips. Thus, the spiral fluted tap has the increased durability (operating life).
Further, of the full thread portion 24 of the threaded portion 16, the chamfer-side thread portion 24a formed on the full thread portion 24 at the axial distal end thereof is contiguous to the chamfer portion 22, which has an original complete thread configuration with more than one thread and not more than five threads. In addition, the shank-side thread portion 24b formed with the chamfers 30 has an original thread configuration except areas around the cutting edges 26, respectively. Thus, the entire area of the full thread portion 24 can have the more excellent guide actions (in lead feed) than that achieved by a structure in which the crests of the threads are cut away in the cylindrical configuration in the areas radially outside the effective diameter. This can tap the internal threads with further increased precision.
Furthermore, in the present embodiment, the chamfer 30 formed in the flat planar chamfer has the chamfer angle θ falling in a value ranging from 20° to 60°. The chamfer angle θ allows the chamfers 30 to appropriately obtain the suppression action of the biting of the chips, and to improve strength of the cutting edges. Thus, the spiral fluted tap has the increased durability.
While in the illustrated embodiment, the chamfers 30 are formed in the flat planar chamfers, respectively, R-chamfers 32 i.e., round chamfer 32 may be provided as shown in
(Cutting Condition)
Size: M8×1.25
Worked Material: SUS304
Cutting Speed: 8 m/min
Shape of Prepared Hole: Through-hole with φ6.8×25 mm
Effective Length of Threads: 16 mm (two times that of tool diameter)
Cutting Fluid Water-Soluble Cutting Oil
Machine used: Transverse type Machining Center
The test pieces Nos. 1-10 have the same fundamental shapes as that of the spiral fluted tap 10 of the present embodiment. In
All the test pieces Nos. 4-8 represent products of the present invention, each formed with the chamfer-side thread portion 24a having 1.5 threads or four threads, each having the flat chamfers with the chamfer angle θ of 30° or 45° or the R-chamfers formed in the circular arc configurations, and each of the chamfer heights Hmen has value of 20%, 50% and 100% the thread height Hneji, respectively. The test pieces No. 9 represent comparison products, each formed with the chamfer-side thread portion 24a having four threads, each having the chamfers with a chamfer angle θ=45°, and a chamfer height Hmen is too large with a value 1.2 times the thread height Hneji. The test pieces No. 10 represent comparison products, each having a chamfer angle θ=45°, and a chamfer height Hmen is 50% of the thread height Hneji. However, the chamfer-side thread portion 24a has too many number of threads with six threads.
As will be apparent from the test results shown in
Further, one of the comparison products of the test pieces No. 3 is damaged upon tapping 108th holes, and can not improve the durability with the provision of the chamfers 30. Furthermore, ones of the comparison products of the test pieces Nos. 9 and 10 can tap 608 and 705 holes, respectively. Although these test pieces had effects of improving durability at certain degrees, they revealed no remarkable difference as compared to the results of the comparison products of the test pieces No. 2.
In the foregoing, while the present invention has been described above with reference to the accompanying drawings, it is intended that the embodiment described be considered only as illustrative of the present invention and that the present invention may be implemented in various modifications and improvements based on knowledge of those skilled in the art.
In the spiral fluted tap, on the full thread portion of the threaded portion, the cutting edges of the shank-side thread portion formed in the area closer to the shank are formed with the chamfers. The chamfers have the cutting faces each having the chamfer height Hmen fallen within the range of 15% to 100% of the thread height Hneji. This allows the chips to be further easily pushed out toward an outer circumferential area along the chamfers. In addition, the cutting edges can have the increased strength thanks to formation of the chamfers. This effectively prevents the occurrence of chipping of the cutting edges and breakage of the spiral fluted tap caused by the biting of the chips. Thus, the spiral fluted tap can be preferably used for the tapping.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2006/325210 | 12/18/2006 | WO | 00 | 6/16/2009 |
