JP2002205212A - Drill - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve drill rigidity and to provide excellent cutting quality. SOLUTION: One chip discharge groove 12 is formed in a blade tip part 11. A cutting blade 14 is formed such that it protrudes to the tip of the cutting tip part 11 toward an outer peripheral end 14A. In a second escape surface 13A, a distance (a) in the direction of a rotary axis O between a point A positioned on the most tip side and a point B positioned on the most base end side in the direction of the rotary axis O is set to a range of 0.1D<=a<=1.0D. A second escape angle is set to at least 5 deg. and third escape angle is set to at least 10 deg.. A core thickness ratio is set to at least 50% and up to 80%. A maximum outside diameter D of a blade edge part 11 is set to up to 1 mm and a ratio L/D between an effective blade length L and a maximum outside diameter D is set to at least 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drill used for drilling a work material. For example, a drill having a small diameter and a deep hole is drilled in a work material such as a printed circuit board, minute metal parts, or plastic. To a small drill used to do

[0002]

2. Description of the Related Art Generally, a small drill has an extremely small hole to be drilled. For example, a small-diameter rod-shaped cutting edge having a diameter of about 0.05 to 3.175 mm is provided at the front end of the drill body, and at the rear end. A relatively large-diameter shank portion for gripping the drill body on the rotating shaft of the machine tool is provided integrally with the cutting edge portion or connected by brazing or interference fitting. The material of the cutting edge portion is usually a cemented carbide, and the shank portion is made of a cemented carbide or a steel material such as steel.

An example of such a small drill is disclosed in Japanese Patent Application Laid-Open No. 5-253718. This small drill is characterized in that the cutting edge is provided with two chips discharge grooves, and the cutting edge formed at the tip of the cutting edge has a fishtail shape. Here, the fish tail shape is defined as a ridge line portion between a rake face and a tip flank, which is a tip side area of a wall face in the drill rotation direction of the two chip discharge grooves.
The two cutting blades project toward the distal end of the cutting edge as they move toward the outer peripheral side, and are formed so as to be inclined such that the outer peripheral end of each cutting edge is positioned at the most distal end of the cutting edge. As the name implies, it is shaped like a fish fin (ie, the tip angle of the cutting edge is greater than 180 °).

[0004] When drilling a work material using a small drill having this fish-tail shaped cutting edge, the cutting edge bites into the work material in order from the cutting edge located on the outer peripheral side of the cutting edge portion having a high peripheral speed. Thus, the effect of preventing the generation of burrs at the time of drilling by exhibiting excellent sharpness is extremely high, and a high-quality machined hole can be obtained.

[0005]

By the way, these days,
To increase drilling efficiency, increase the feed rate,
The number of layers of the work material to be stacked and processed is increased (that is, the holes are deepened), and the diameter of the holes to be processed is reduced by increasing the wiring density. There is an increasing number of small-diameter deep hole processings in which the hole diameter is small and the ratio between the hole depth and the hole diameter is large. However, when a small drill having a fishtail-shaped cutting edge as described above is used in such small-diameter deep hole processing, the core thickness becomes thin due to the two chip discharge grooves at the cutting edge. As a result, the drill stiffness is reduced, and the blade tip is broken or the hole is bent. In particular, the diameter of the hole to be drilled is 1 mm or less,
At present, a small drill having a fishtail-shaped cutting edge cannot be practically used in small-diameter deep-hole processing in which the ratio between the hole depth and the hole diameter is 5 or more.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide a drill that maintains high rigidity of a drill, has high hole position accuracy, and has excellent sharpness.

[0007]

Means for Solving the Problems To solve the above problems,
In order to achieve such an object, according to the present invention, a chip discharge groove that is twisted around a rotation axis from a tip of the blade portion toward a base end side is formed on a peripheral surface of the blade edge portion, and rotation of the chip discharge groove is performed. In a drill in which a tip side region of a wall surface facing in the direction is a rake face and a cutting edge is formed at an intersection ridge line portion between the rake face and the tip flank, a chip discharge groove formed on a peripheral surface of the cutting edge portion has a shape of 1. The cutting edge is formed so that the cutting edge protrudes toward the distal end side of the cutting edge portion toward the outer peripheral side thereof, and the outer peripheral end of the cutting edge is positioned at the most distal end side of the cutting edge portion. It is characterized by being. With such a configuration, since there is only one chip discharge groove provided in the cutting edge portion, the core thickness is larger than that of a drill in which the cutting edge portion has two chip discharge grooves, and high drill rigidity is obtained. Obtainable. Furthermore, the cutting edge formed at the tip of the cutting edge protrudes toward the tip of the cutting edge as it goes toward the outer peripheral side. The cutting edge located on the outer peripheral side of the portion will bite into the work material in order, and good sharpness can be obtained.

[0008] Further, the tip flank constitutes the tip flank, and in the second flank where the cutting blade extends, the point located at the most distal side and the most proximal side of the cutting edge in the direction along the rotation axis. The distance a in the rotation axis direction from the point to be set is set in a range of 0.1D ≦ a ≦ 1.0D with respect to the maximum outer diameter D of the cutting edge portion. With such a configuration,
The cutting edge is made to protrude sufficiently toward the distal end as it goes toward the outer peripheral side, so that the effect of obtaining good sharpness can be obtained, and the thickness near the distal end of the cutting edge is sufficiently secured to maintain high rigidity. Can be. Here, the distance a is 0.1D
If it is smaller, the entire length of the cutting edge will simultaneously bite into the work material during drilling of the work material and a good sharpness will not be obtained. The thickness in the vicinity of the tip becomes thin, and there is a possibility that bending of the hole or chipping of the tip of the cutting edge due to a decrease in rigidity may occur.

The tip flank is constituted by a plurality of flank surfaces, and the second flank angle of the second flank surface formed by the cutting blade is at least 5 ° and is continuous with the second flank surface. The third flank has a third flank angle of 10 ° or more. With such a configuration, the clearance angle of the flank of the tip is set to be sufficiently large, and when drilling the work material, the flank of the tip may come into contact with the work material and cause a problem. There is no. Here, if the second clearance angle is smaller than 5 ° or the third clearance angle is smaller than 10 °, there is a possibility that the flank of the leading end contacts the work material.

A ratio d / D (hereinafter referred to as a core thickness ratio) of a diameter d of a maximum circle inscribed in a cross section of the cutting edge to a maximum outer diameter D of the cutting edge is 50%. ≦ d /
D is set in a range of 80% or less.
With such a configuration, the core thickness of the cutting edge portion can be sufficiently ensured, the rigidity of the drill can be kept high, and the space for the chip discharge groove can be sufficiently ensured to obtain good chip dischargeability. . Here, if the core thickness ratio d / D is less than 50%, the core thickness of the cutting edge portion becomes thin, and it becomes impossible to maintain sufficient drill rigidity, while the core thickness ratio d / D is more than 80%. If it is large, the space of the chip discharge groove becomes too small, and there is a possibility that chip clogging may occur.

The maximum outer diameter D of the cutting edge is 1 mm or less, and the ratio L / D of the effective cutting length L of the cutting edge to the maximum outer diameter D of the cutting edge is 5 or more. I do. By adopting such a configuration, the present invention can be effectively used particularly when drilling a hole having a small diameter and a deep hole that requires drill rigidity to secure the hole position accuracy.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a side view of a cutting edge of the small drill according to the first embodiment of the present invention, FIG. 2 is an enlarged side view of a main part of the cutting edge of the small drill, FIG. 5 is a view in the direction of the arrow Y in FIG. 2, FIG. 5 is a front end view of the cutting edge of the small drill, and FIG. 6 is a sectional view taken along line ZZ in FIG.

A small drill 1 according to a first embodiment of the present invention.
Reference numeral 0 denotes a blade edge portion 11 and a shank portion.
As shown in FIG. 1, reference numeral 1 denotes a straight type having the same outer diameter D from the distal end to the proximal end. That is, the outer diameter D of the cutting edge 11 is set to the maximum outer diameter D.

The blade tip 11 is provided with a single chip discharge groove 12 which is helically twisted about the rotation axis O at a constant torsion angle from the tip end to the base end, and is opened on the outer peripheral surface. I have. The chip discharge groove 12 has a constant groove depth and a constant groove width, and thereby has the diameter d of the largest circle inscribed in the cross section of the cutting edge portion 11 (so-called core thickness d of the cutting edge portion 11).
Is constant from the distal end to the proximal end of the cutting edge 11.

As shown in FIGS. 1 to 4, the tip side region of the wall surface of the chip discharge groove 12 facing the rotation direction T of the small drill 10 is a rake face 12 A, and the rake face 12 A and the tip of the cutting edge 11 are provided. Cutting edge 1 at the intersection ridgeline with flank 13
4 are formed. The tip flank 13 has a second flank 13A located immediately behind the cutting edge 14 in the rotational direction T, and a third flank 13B connected to the second flank 13A and located rearward in the rotational direction T. It is composed of two flat surfaces.

Further, the second flank 13A and the rake face 12
The cutting edge 14 formed at the intersection ridge line with A is formed so as to protrude toward the distal end side as it goes toward the outer peripheral side, and accordingly the second flank 13A is inclined with respect to the rotation axis O. Is formed. For this reason, the tip portion of the cutting edge portion 11 has a shape as if the cutting edge portion 11 is cut obliquely, the wall thickness becomes thinner toward the tip side, and the outer peripheral end 14A of the cutting blade 14 is It is located on the most distal side.

Here, the second flank 1 on which the cutting blade 14 extends.
3A, the point A located at the most distal end side in the direction along the rotation axis O (that is, the outer peripheral end 14A of the cutting blade 14, in this embodiment, the second flank 13A and the rake face 12).
A and the outer peripheral surface (a margin 15 described later) of the cutting edge portion 11) and a point B (the second flank 13A and the third flank 13B in the present embodiment) located closest to the base end. 13C is the outer peripheral surface of the cutting edge portion 11 (margin 1).
Of the two points that intersect with 5), the distance a in the direction of the rotation axis O with respect to the point located at a position near the front side in the rotation direction T of the chip discharge groove 12) is relative to the maximum outer diameter D of the cutting edge portion 11. , 0.1D
≦ a ≦ 1.0D, and in the first embodiment, for example, a = 0.7D. Further, as shown in FIG. 6, the second clearance angle α of the second flank 13A is set to 5 ° or more, and the third clearance angle β of the third flank 13B is set to 10 ° or more. In the first embodiment, for example, α = 15 ° and β = 40 °.

As shown in FIG. 5, the outer peripheral surface of the cutting edge portion 11 except for the chip discharge groove 12 is defined by a margin 15, which contacts the inner wall surface of the machined hole when drilling a work material. And has a function of obtaining the straightness of the drill, and is formed in a spiral shape by being twisted toward the rear side in the rotation direction T of the small drill 10 from the tip end of the cutting edge portion 11 toward the base end side like the chip discharge groove 12. And is formed over the entire effective blade length L of the blade edge portion 11.

The maximum outer diameter D of the cutting edge 11 (in the first embodiment, the rotation axis O
, The diameter of an imaginary circle having a margin 15 as an arc) is 1 mm or less, and the effective blade length L of the blade edge portion 11
The cutting edge portion 11 is formed such that the ratio L / D between the cutting edge 11 and the maximum outer diameter D is 5 or more.

Further, as can be seen from the top view of the cutting edge portion 11 in FIG. 5, the diameter d of the largest circle inscribed in the cross section of the cutting edge portion 11 (so-called core thickness d of the cutting edge portion 11) is determined. The ratio d / D (core thickness ratio d / D) with respect to the maximum outer diameter D is set in a range of 50% ≦ d / D ≦ 80%. Here, in the first embodiment, as can be seen from FIG. 5, the circle inscribed in the margin 15 and the chip discharge groove 12 has the maximum outer diameter d, and the core thickness ratio d / D is, for example, 60%. And is constant from the distal end to the proximal end of the cutting edge 11.

The small drill 10 constructed as described above.
Since the number of the chip discharge grooves 12 provided in the cutting edge portion 11 is only one, the core thickness of the cutting edge portion 11 can be sufficiently secured, and compared with a small drill provided with two chip discharge grooves. And the drill stiffness is overwhelmingly high. For this reason,
Even when the feed speed of the small drill 10 is increased or the number of layers of the work material is increased (deepening of the processing hole) during drilling of the work material, bending of the hole or breakage of the cutting edge 11 may occur. Not
High efficiency drilling can be performed.

Further, since the cutting blade 14 is formed so as to protrude toward the tip end of the cutting edge 11 as it goes toward its outer peripheral end 14A, the peripheral speed is reduced when drilling a work material. The cutting edge 14 on the high outer peripheral side bites into the work material sequentially, so that excellent sharpness can be obtained. Accordingly, it is possible to prevent burrs from being generated in the work material, and it is possible to form a high quality machined hole.

Further, a tip flank 13 is formed, and a cutting blade 14 is formed.
In the second flank 13A where the material extends, a point A located at the most distal end side of the cutting edge portion 11 (the outer peripheral end 14A of the cutting blade 14) and a point B located at the most proximal side in the direction along the rotation axis O. Is set in the range of 0.1D ≦ a ≦ 1.0D with respect to the maximum outer diameter D of the cutting edge portion, so that the cutting edge 14 is moved to its outer peripheral end 14A. , It is possible to obtain excellent sharpness by protruding sufficiently toward the front end side, and to secure sufficient rigidity by sufficiently securing the thickness near the front end of the blade edge portion 11. here,
When the distance a is smaller than 0.1D, when drilling a work material,
When the entire length of the cutting edge 14 simultaneously bites into the work material, good sharpness cannot be obtained. On the other hand, when the distance a is greater than 1.0 D, the wall thickness near the tip of the cutting edge becomes thin, and the rigidity increases. There is a possibility that bending of the hole or chipping of the tip of the cutting edge due to the drop may occur.

The tip flank 13 is composed of two flank surfaces (second flank 13A, third flank 13B), and the second flank 13A has a second flank angle α of 5 ° or more and three flank. Since the third clearance angle β of the third flank 13B is set to a sufficient clearance angle of 10 ° or more, the leading flank 13 contacts the work material when drilling the work material. There is no such thing as. Here, if the second clearance angle α is smaller than 5 ° or the third clearance angle β is smaller than 10 °, there is a possibility that the tip flank 13 comes into contact with the work material.

Further, in the small drill 10 according to the first embodiment, the maximum outer diameter D of the cutting edge 11 is 1 mm or less, and the ratio L / D of the maximum outer diameter D of the cutting edge 11 to the effective blade length L is 5. As described above, an excellent effect is obtained particularly when drilling a hole having a small diameter and a deep hole in which drill rigidity is strongly required.

Further, since the core thickness ratio d / D is set within the range of 50% ≦ d / D ≦ 80% over the entire length of the cutting edge portion 11, a sufficient core thickness of the cutting edge portion 11 is ensured. Done,
The drill rigidity can be kept high, and the space in which the chip discharge groove 12 is formed is not narrowed more than necessary, so that the chip discharge performance is not deteriorated. Here, the core thickness ratio d / D is 5
If it is less than 0%, the core thickness of the cutting edge portion 11 becomes thin, and it becomes impossible to maintain sufficient drill rigidity. On the other hand, if the core thickness ratio d / D is more than 80%, the chip discharge performance deteriorates. Chip clogging may occur. Further, in order to further ensure the above-described effects, the core thickness ratio d / D is preferably set in a range of 60% ≦ d / D ≦ 80%.

In the first embodiment, the cutting edge 1
Although the straight type small drill in which the outer diameter D of 1 is constant from the distal end to the proximal end has been described, the present invention is not limited to this, and as the outer diameter of the cutting edge 11 goes from the distal end toward the proximal end side, A small drill having a back taper that becomes gradually smaller may be used. In this case, the cutting edge 1
The outer diameter of the tip side portion of 1 is the maximum outer diameter D.

Further, the present invention is not limited to the straight type small drill 10 as in the first embodiment described above.
An undercut type drill in which only one end portion is enlarged by one step may be used. A small drill in such a case will be described as a second embodiment of the present invention. The second embodiment differs from the first embodiment only in the shape of the cutting edge 11, and the same parts as those in the above-described first embodiment are denoted by the same reference numerals and description thereof is omitted.

FIG. 7 is an enlarged side view of a main part of a cutting edge of a small drill according to a second embodiment of the present invention. As shown in FIG. 7, the small drill 20 according to the second embodiment
However, the first cutting edge portion 11A located at the tip portion thereof, and the second cutting edge portion 11B located on the rear end side of the first cutting edge portion 11A and having an outer diameter smaller than the outer diameter D of the first cutting edge portion 11A. It is an undercut type as configured. At this time, the outer diameter D of the first cutting edge 11A becomes the maximum outer diameter D of the cutting edge 11, and the margin 15 for rubbing the inner wall surface of the machining hole is formed only on the outer peripheral surface of the first cutting edge 11A. Become.

The length b where the first cutting edge 11A is formed, that is, the length b (the second flank 13A) of the enlarged diameter portion of the cutting edge 11 along the rotation axis O direction.
, The length b in the direction of the rotation axis O from the point B located on the most proximal side of the cutting edge 11 in the direction along the rotation axis O to the connection portion between the first cutting edge 11A and the second cutting edge 11B. ) Is formed to be larger than 0.5D with respect to the maximum outer diameter D of the cutting edge portion 11.

The small drill 20 according to the second embodiment of the undercut type as described above has the same effect as the small drill 10 according to the first embodiment described above. By forming the second cutting edge portion 11B whose outer diameter is reduced by one step in the side portion, the drill 15 loses some drill rigidity, but the area of the margin 15 that contacts the inner wall surface of the machined hole is reduced. hand,
It is possible to further improve the accuracy of the inner wall surface of the processing hole. Here, the length b where the first cutting edge 11A is formed
However, if it is smaller than 0.5D, the area of the margin 15 that contacts the inner wall surface of the machined hole is excessively reduced, so that the straightness of the drill cannot be obtained and the hole is bent.

In this embodiment, the cutting edge 11
The outer peripheral surface excluding the chip discharge groove 12 is constituted only by the margin 15, but is not limited thereto.
As shown in FIG. 8, the outer peripheral surface of the cutting edge portion 11 excluding the chip discharge groove 12 is located behind the margin 15 and the margin 15 in the drill rotation direction T, and has a constant second cutting depth c. The surface 16 may be used. Further, the outer peripheral surface of the cutting edge portion 11 excluding the chip discharge groove 12 is constituted by a margin 15 and a second cutting surface 16, and the margin 15 may be divided into, for example, two by the second cutting surface 16. .

Further, in the present embodiment, the tip flank 13 is constituted by two flank (second flank 13A, third flank 13B), but is not limited to this. It may be constituted by one flank or three or more flank. Here, in the case where the tip flank 13 is constituted by only one flank, that is, the tip flank 13 is the second flank 13A.
In the case where it is constituted only by the cutting edge portion 1A in the direction along the rotation axis O on the second flank 13A,
The point B located at the most proximal side of 1 is a point on the intersection ridge line between the second flank 13A and the outer peripheral surface (the margin 15 or the second cutting surface 16) of the cutting edge portion 11.

In the present embodiment, the core thickness ratio d
/ D is constant from the distal end to the proximal end of the cutting edge portion 11, but is not limited to this, and the core thickness ratio d / D is gradually increased from the distal end of the cutting edge portion 11 toward the proximal end side. You may make it larger.

In this embodiment, the rotation axis O
The torsion angle of the chip discharge groove 12 twisted around
Although the torsion angle is constant from the distal end to the proximal end, the torsion angle may be continuously changed from the distal end toward the proximal end.

Further, in this embodiment, the maximum outer diameter D of the blade tip is 1 mm or less, and the effective blade length L and the maximum outer diameter D
A small drill having a ratio L / D of 5 or more has been described. However, without being limited to this range, a drill having a larger maximum outer diameter D or a drill having an L / D smaller than 5 is used. Also, by applying the present invention, the effects as described above can be obtained.

[0037]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A small drill according to an embodiment of the present invention is shown in FIGS.
The drilling test was performed on the work material using small drills having various configurations (Comparative Examples 1 to 6 and a conventional example).

In Examples 1 to 11 and Comparative Examples 1 to 6, a single chip discharge groove 12 is formed in the cutting edge 11 at a constant twist angle from the tip to the base end of the cutting edge 11. In Examples 1 to 11, the core thickness ratio d / D of the cutting edge 11 and the cutting edge 1
4 is the point A (the outer peripheral end 14A of the cutting edge 14) located at the most distal side in the direction along the rotation axis O of the distal flank 13 (second flank 13A) where the material is extended, and is located the most proximal The distance a from the point B in the direction of the rotation axis O is within the range of the present invention (50% ≦
d / D ≦ 80%, 0.1D ≦ a ≦ 1.0D), and Comparative Examples 1 and 6 have the core thickness ratio d / D, and Comparative Examples 2 to 5 have the distance a. Are out of the range.

Further, in the conventional example, two chip discharge grooves are formed in the cutting edge portion, and the cutting edge formed at the tip of the cutting edge portion has a fishtail shape (Japanese Patent Laid-Open No. 5-253718). Of a small drill as disclosed in Japanese Unexamined Patent Publication (Kokai) No) Small drill as described above (Examples 1-1
Table 1 shows the test conditions and results of the drilling test performed using Comparative Examples 1 to 6 and Conventional Examples).

[0040]

[Table 1]

The examples 1 to 11, the comparative examples 1 to 6, and the conventional example are commonly of a straight type in which the outer diameter D of the cutting edge 11 is a constant 0.3 mm from the tip to the base end of the cutting edge 11. , The effective blade length L is 5 mm (L / D = 16.
7) Furthermore, the torsion angle of the chip discharge groove 12 is
The angle from the front end to the base end is 40 °. Also,
The tip angle of the cutting blade in the conventional example is 230 ° (fishtail angle is 130 °).

A small drill having such a configuration (Examples 1 to 4)
11, using Comparative Examples 1 to 6 and a conventional example), a substrate (a double-sided BT resin double-sided plate having a thickness of 0.1 mm) laminated on a substrate to be a work material (LE400 having a thickness of 0.2 mm)
And a bottom plate (a bakelite resin plate having a thickness of 1.6 mm), and a drilling test was performed. The number of rotations of the drill is 12,500
0 min ^-1 (rpm), feed rate is 20 μm / rev.
The maximum surface roughness of the inner wall of the machined hole was measured for every 00 holes, and the number of machined holes (life) that could be drilled while maintaining the maximum surface roughness within 10 μm was measured. Furthermore, the average hole position accuracy of 100 holes drilled immediately before the end of the life (the average value of the deviation of each hole position from the target position) was measured.

As shown in Table 1, in Examples 1 to 11 which are examples of the present invention, the number of processed holes all takes a value of 6100 or more, and the average hole position accuracy becomes a value within 43 μm. As a result, many holes could be drilled while maintaining good inner wall surface accuracy of the machined hole without generating burrs and the like, and the result that the average hole position accuracy was good due to high drill rigidity was obtained.

In Comparative Example 1 in which the core thickness ratio d / D is set to 45%, which is smaller than the range of the present invention,
The number of processing holes was 6000, and many holes could be drilled while maintaining good inner wall surface accuracy. However, since the core thickness ratio d / D was as small as 45%, straightness of the drill was obtained due to insufficient rigidity. Bending occurred, the average hole position accuracy was 72 μm, and the result was that the hole position accuracy was poor as compared with Examples 1 to 11 as an example of the present invention.

Further, although the core thickness ratio d / D is set within the range of the present invention, the distances a are both set to 0.05 D, which is smaller than the range of the present invention.
As for the average hole position accuracy, good values of 32 μm and 31 μm were obtained, but since the distance a was as small as 0.05 D, the cutting edge 1
Due to the lack of sharpness of No. 4, burrs were generated on the work material and the inner wall surface accuracy could not be maintained satisfactorily, and the number of drilled holes was 3800, 3
The value was as low as 200, and the result that the inner wall surface roughness was inferior to Examples 1 to 11 as an example of the present invention was obtained.

Although the core thickness ratio d / D is set within the range of the present invention, the comparative example 3 in which the distance a is set to be larger than the range of the present invention is 1.2 D, Is 62
Although a good value of 00 was obtained, since the distance a was as large as 1.2D, the thickness of the tip portion of the blade edge portion was reduced, and the rigidity could not be kept high. The accuracy is as low as 74 μm, and the distance a is 1.
In Comparative Example 5 which is set to be larger than 3D, the rigidity of the tip of the cutting edge becomes smaller, chipping occurs at the tip of the cutting edge, the inner wall surface of the machining hole becomes rough, and the number of machining holes is 29.
It was a low value of 00.

In Comparative Example 6 where the core thickness ratio d / D is set to 85%, which is larger than the range of the present invention,
Very good rigidity and average hole position accuracy of 25 μm were obtained. However, since the core thickness ratio d / D was very large at 85%, it was necessary to secure sufficient space for the chip discharge groove 12. However, the result was that chip clogging occurred, the inner wall surface roughness was reduced, and the number of machined holes remained as low as 2300.

Further, in the conventional example having two chip discharge grooves and a fishtail-shaped cutting edge, the number of machining holes is one.
At the point of 100, the cutting edge 11 was broken, and the result was that the drill stiffness was far inferior to those of Examples 1 to 11 according to an example of the present invention.

As described above, Examples 1 to 1 according to the present invention were used.
1 has a larger number of holes while maintaining the inner wall surface accuracy of the processed hole better than Comparative Examples 1 to 6 and the conventional example in which the core thickness ratio d / D and the distance a are out of the range of the present invention. Can pierce,
Moreover, the result that the hole position accuracy was good was obtained.

[0050]

As described above, according to the drill of the present invention, since there is only one chip discharge groove provided in the cutting edge, high drill rigidity can be obtained without reducing the core thickness, and the Position accuracy can be improved. In addition, high drill stiffness can be obtained, so that it can respond to higher drill feed speeds when drilling work materials and increase the number of stacked work materials, achieving high efficiency machining. can do. Furthermore, since the cutting edge is protruded toward the front end side toward the outer peripheral side so as to bite into the work material from the outer peripheral side cutting edge having a high peripheral speed, good sharpness is obtained, and The accuracy of the inner wall surface can be improved.

Further, the tip flank constitutes a tip flank, and in the second flank on which the cutting blade extends, a point located at the most distal side and a point located at the most proximal side of the cutting edge in the direction along the rotation axis. Is set in the range of 0.1D ≦ a ≦ 1.0D with respect to the maximum outer diameter D of the blade edge portion, so that the cutting blade moves toward the outer peripheral side thereof. Accordingly, the tip portion is sufficiently protruded to the tip side to obtain excellent sharpness, and the thickness of the tip portion of the cutting edge portion is made thinner than necessary, whereby there is no possibility that the rigidity is reduced or the tip portion of the cutting edge is chipped.

The flank of the tip is constituted by a plurality of flank surfaces, the second flank angle is 5 ° or more, and the third flank angle is 1 °.
When the angle is 0 ° or more, the clearance angle of the flank of the tip is set to be sufficiently large, and there is no problem that the flank of the tip contacts the workpiece when drilling the workpiece.

Further, when the core thickness ratio d / D is 50% ≦ d / D
By setting the range of ≦ 80%, the core thickness of the cutting edge portion can be sufficiently secured, the drill rigidity can be kept high, and the space in which the chip discharge groove is formed is ensured, so that the chip discharge property can be secured. Can be obtained.

Further, the maximum outer diameter D of the cutting edge is 1 mm or less,
And the ratio L / D of the maximum outer diameter D of the blade tip to the effective blade length L is 5
According to the features described above, the present invention can be effectively used when drilling a hole having a small diameter and a deep hole, which requires particularly high drill rigidity.

[Brief description of the drawings]

FIG. 1 is a side view of a cutting edge portion of a small drill according to a first embodiment of the present invention.

FIG. 2 is an enlarged side view of a main part of a cutting edge of the small drill according to the first embodiment of the present invention.

FIG. 3 is a view as seen in the direction of arrow X in FIG. 2;

FIG. 4 is a view in the direction of the arrow Y in FIG. 2;

FIG. 5 is a front end view of the cutting edge of the small drill according to the first embodiment of the present invention.

FIG. 6 is a sectional view taken along line ZZ in FIG. 5;

FIG. 7 is an enlarged side view of a main part of a cutting edge of a small drill according to a second embodiment of the present invention.

FIG. 8 is an explanatory view showing a distal end surface of a cutting edge portion of the small drill according to the embodiment of the present invention.

[Explanation of symbols]

 10, 20 Small drill 11 Blade edge 12 Chip discharge groove 12A Rake surface 13 Tip flank 13A Secondary flank 13B Third flank 14 Cutting edge 14A Outer peripheral edge 15 Margin a Distance in the rotation axis direction between point AB d Edge Outer diameter of the largest circle inscribed in the section of A Rotational direction α Secondary clearance angle β Third clearance angle

Claims (5)

[Claims] 1. A chip discharge groove which is twisted around a rotation axis from a tip end of the cutting edge portion toward a base end side is formed on a peripheral surface of the cutting edge portion, and a tip side region of a wall surface of the chip discharging groove which faces in a rotation direction is formed. In a drill having a rake face and a cutting edge formed at an intersection ridge line between the rake face and the tip flank, there is only one chip discharge groove formed on a peripheral surface of the cutting edge, and the cutting edge is A drill that protrudes toward the distal end of the cutting edge portion toward the outer peripheral side thereof so that the outer peripheral end of the cutting edge is located at the most distal end side of the cutting edge portion. 2. A tip flank constituting the tip flank, wherein a second flank on which the cutting blade extends is located at the most distal side and the most proximal side of the cutting edge in a direction along a rotation axis. The distance a in the rotation axis direction from the point to be set is set in a range of 0.1D ≦ a ≦ 1.0D with respect to the maximum outer diameter D of the cutting edge portion. Drill. 3. The tip flank is constituted by a plurality of flank faces, and a second flank angle of a second flank face extended by the cutting edge is 5 ° or more, and is connected to the second flank face. 3. The drill according to claim 1, wherein the third flank has a third flank angle of 10 [deg.] Or more. 4. The ratio d of the diameter d of the largest circle inscribed in the cross section of the cutting edge to the maximum outer diameter D of the cutting edge
4. The drill according to claim 1, wherein / D is set in a range of 50% ≦ d / D ≦ 80%. 5. The method according to claim 1, wherein a maximum outer diameter D of the cutting edge is 1 mm or less, and a ratio L / D between an effective blade length L of the cutting edge and a maximum outer diameter D of the cutting edge is 5 or more. The drill according to any one of claims 1 to 4, wherein the drill is used.