AU2019351468A1 - Drilling tip and drill bit - Google Patents

Abstract

The present invention comprises: a tip body 2 composed of a cemented carbide and having a trailing end section 2A that forms a cylindrical or disk shape centered on the tip center line C, and a leading end 2B; and a hard layer 3 composed of a polycrystalline diamond sintered body covering the leading end section 2B. The leading end section 2B of the tip body 2 has: a protruding section 2a in which the outer surface forms a protruding arc shape in a cross-section along the tip center line C; and a recess section 2b forming a recessed arc shape contacting the protruding section 2a. The diameter D (mm) of the trailing end section 2A is in the range of 8-20 mm, the ratio r1/D of the radius r1 (mm) of the protruding section 2a to the diameter D (mm) is in the range of 0.1-0.65, the ratio r2/D of the radius r2 (mm) of the recessed section 2b to the diameter D is in the range of 0.05-3, and the angle θ (º) between the tip center line C and the straight line L connecting the contact point F between the protruding section 2a and the recessed section 2b and the center Q of the protruding section 2a is in the range of 20-90º.

Description

DESCRIPTION TITLE OF INVENTION DRILLING TIP AND DRILL BIT TECHNICAL FIELD

[0001]

The present invention relates to a drilling tip, in which a distal end portion of a

tip main body made of a cemented carbide is coated with a hard layer made of a

polycrystalline diamond sintered body and which is attached to a distal end portion of a

bit main body of a drill bit to perform drilling, and the drill bit in which such a drilling tip

is attached to the distal end portion of the bit main body.

Priority is claimed on Japanese Patent Application No. 2018-184791, filed

September 28, 2018, and Japanese Patent Application No. 2019-175936, filed September

26, 2019, the contents of which are incorporated herein by reference.

BACKGROUND ART

[0002]

Although such a drilling tip, in which a distal end portion of a tip main body

made of a cemented carbide is coated with a hard layer made of a polycrystalline

diamond sintered body, is manufactured by integrally sintering the cemented carbide of

the tip main body and the polycrystalline diamond sintered body of the hard layer, due to

a difference in a thermal expansion coefficient between the cemented carbide and the

polycrystalline diamond sintered body, residual stress occurs near an interface

therebetween when sintering. In a case where this residual stress is high, the drilling tip

attached to a drill bit used in striking excavation has problems in which cracks are generated in the hard layer due to impact during drilling and the life of the drill bit is shortened.

[0003]

Therefore, techniques, in which the residual stress of a hard layer made of such a

polycrystalline diamond sintered body after sintering is relaxed, are described in Patent

Documents 1 to 3. Among these, a technique, in which an intermediate layer having an

inclined composition is interposed between an outermost layer of the hard layer and a tip

main body, is described in Patent Document 1. In addition, a technique, in which

residual stress is relaxed by defining an intermediate layer thickness of the type of a

material according to a purpose in view of a difference in a thermal expansion coefficient

of a polycrystalline diamond sintered body, is described in Patent Document 2. Further,

a technique, in which the life of a drilling tip is extended as the thickness of the hard

layer is secured so that a tip main body is not exposed even after an outer peripheral

polishing step required when attaching the drilling tip to a drill bit, by controlling the

shape of the tip main body, is described in Patent Document 3.

[Citation List]

[Patent Literature]

[0004]

[Patent Document 1]

United States Patent No. 6315065

[Patent Document 2]

United States Patent No. 8857541

[Patent Document 3]

Japanese Unexamined Patent Application, First Application, No. 2016-135983

SUMMARY OF INVENTION TECHNICAL PROBLEM

[0005]

However, as described in Patent Documents I and 2, in the intermediate layer

interposed between the outermost layer of the hard layer and the tip main body, the

thickness of the outermost layer which is hardest in the hard layer cannot be secured even

if residual stress is relaxed. In a case of being used in drilling the ground made of hard

rock, the progress of wear of the hard layer is faster, and the tip main body made of a

cemented carbide is likely to be exposed at an early stage, thereby shortening the life of

the drill bit.

[0006]

In addition, in the drilling tip described in Patent Document 3, the thickness is

secured as described above on a posterior end side of the hard layer by forming a

columnar or disk-shaped intermediate portion having an outer diameter smaller than a

posterior end portion between the posterior end portion and a distal end portion of the tip

main body. However, in this case, since an angled corner part is formed between a

distal end surface of the posterior end portion of the tip main body and an outer

peripheral surface of the intermediate portion, there is a tendency in which stress is likely

to be concentrated on this corner part.

[0007]

Herein, in the drilling tip described in Patent Document 3, the outer diameter of

the intermediate portion further decreases in a case where the hard layer is made thicker

in order to further extend the life. Thus, when an excessive load is present during

drilling, with the corner part where stress is likely to be concentrated as a origin, cracks

are likely to be generated in an interface of the intermediate portion between the tip main body made of a cemented carbide and the hard layer made of a polycrystalline diamond sintered body on the outer periphery. Due to the destruction of the hard layer caused by the cracks, there is a possibility that the life of the drill bit is shortened.

[0008]

The present invention is devised under such circumstances, and an object thereof

is to provide a long-life drilling tip, in which a distal end portion of a tip main body made

of a cemented carbide is coated with a hard layer made of a polycrystalline diamond

sintered body, the drilling tip allowing the prevention of generation of cracks in the hard

layer by relaxing the residual stress of an interface between the tip main body and the

hard layer, and improvement of impact resistance and wear resistance, and to provide a

drill bit, to which such a drilling tip is attached and which has long life and can perform

efficient drilling.

SOLUTION TO PROBLEM

[0009]

According to an aspect of the present invention, in order to solve the problems

and achieve such an object, there is provided a drilling tip that is attached to a distal end

portion of a drill bit to perform drilling. The drilling tip includes a tip main body that

has a posterior end portion having a columnar or disk shape centered on a tip center line

and a distal end portion having an outer diameter from the tip center line, which

gradually decreases from the posterior end portion toward a distal end side, and is made

of a cemented carbide and a hard layer that coats the distal end portion of the tip main

body and is made of a polycrystalline diamond sintered body. The distal end portion of

the tip main body has a convex portion having a convex arc shape of which a surface is

convex toward the distal end side in a cross section taken along the tip center line, and a concave portion having a concave arc shape in a cross section taken along the tip center line, of which a surface tangents to a convex arc in the cross section of the convex portion and which extends to an outer peripheral side as going toward a posterior end side of the tip main body. A diameter D (mm) of the posterior end portion of the tip main body is within a range of 8 (mm) to 20 (mm). With respect to the diameter D

(mm) of the posterior end portion of the tip main body, a ratio rl/D of a radius rI(mm)

of the convex arc of the convex portion in the cross section is within a range of 0.1 to

0.65, and a ratio r2/D of a radius r2 (mm) of a concave arc of the concave portion in the

cross section is within a range of 0.05 to 3.0. An angle 0 () formed by a straight line

that connects a point which the convex portion tangents to the concave portion and a

center of the convex arc of the convex portion to each other with respect to the tip center

line in the cross section is within a range of 20 () to 90(°).

[0010]

In addition, according to another aspect of the present invention, there is

provided a drill bit including such a drilling tip that is attached to a distal end portion of a

bit main body. A fitting hole is formed in the distal end portion of the bit main body.

The drilling tip is attached such that the posterior end portion of the tip main body is

buried in the fitting hole.

[0011]

In the drilling tip having the configuration, the distal end portion of the tip main

body has the convex portion having the convex arc shape of which the surface is convex

toward the distal end side in the cross section taken along the tip center line and the

concave portion having the concave arc shape in the cross section taken along the tip

center line, of which the surface tangents to the convex arc in the cross section of the

convex portion and which extends to the outer peripheral side toward the posterior end side of the tip main body. Since corner parts intersecting with an angle are not formed, residual stress generated by sintering can be relaxed, and such corner parts do not serve as origins of cracks in the hard layer.

[0012]

Herein, if the diameter D (mm) of the posterior end portion of the tip main body

is smaller than 8 (mm), the residual stress of an interface between the hard layer and the

tip main body can be relaxed, but an impact load acting on the tip main body per unit

area increases in a case of being used in drilling under a higher impact load condition.

Therefore, damage caused by the fracture origin in the tip main body is likely to occur,

and there is a possibility that the life of the drill bit is shortened. On the other hand,

when the diameter D (mm) of the posterior end portion of the tip main body is larger than

(mm), the volume of the hard layer is large with respect to the area of the tip main

body in contact with the hard layer, residual stress that occurs at the interface between the

hard layer and the tip main body cannot be relaxed, and thus there is a possibility that

cracks are generated after sintering.

[0013]

With respect to the diameter D (mm) of the posterior end portion of the tip main

body which is within a range of 8 (mm) to 20 (mm), the ratio rl/D of the radius rl (mm)

of the convex arc of the convex portion in the cross section is within a range of 0.1 to

0.65, and the ratio r2/D of the radius r2 (mm) of the concave arc of the concave portion

in the cross section is within a range of 0.05 to 3.0. The angle 0 (0) formed by the

straight line that connects the point which the convex portion tangents to the concave

portion and the center of the convex arc of the convex portion to each other with respect

to the tip center line in the cross section is within a range of 20 (°) to 90 (). Therefore,

the residual stress of the interface between the hard layer and the tip main body can be more reliably relaxed, and it is possible to extend the life by securing a sufficient thickness for the hard layer. The cross section taken along the tip center line may be a cross section taken along the tip center line in a range where a distance from the tip center line is 0.1 (mm) or less.

The hard layer is not particularly limited, but Vickers hardness of 4,000 HV or

more and a thickness of 1.1 mm or more and 3.0 mm or less are preferable. Herein, the

hard layer means a polycrystalline diamond sintered body portion, and in a case where a

polycrystalline diamond sintered body layer is configured by two or more layers having

different compositions, a layer positioned at an outermost periphery is the hard layer. In

addition, the Vickers hardness of the hard layer is not limited to an upper limit, but the

value of what can be industrially manufactured is 8,000 HV or less.

The Vickers hardness was measured at ten points under a load of 5 kg, and the

average value is set as the Vickers hardness of the hard layer. The thickness of the hard

layer is defined as a value obtained by acquiring an observation image along the tip

center line C with the use of an optical microscope in a tip cross section which is cut

along the tip center line and measuring.

[0014]

That is, when the ratio rl/D is less than 0.1, the radius of the convex portion is

excessively small compared to the thickness of the hard layer, and the curvature of the

convex portion is large. Thus, residual stress is likely to be concentrated particularly at

a distal end portion of the convex portion, and there is a possibility that cracks are likely

to be generated in the hard layer. On the other hand, conversely, when the ratio rl/D

exceeds 0.65, the thickness of the hard layer is small at an outer peripheral portion of the

convex portion. The wear of the outer peripheral portion of the convex portion during

drilling progresses early compared to the distal end portion so that the convex portion of the tip main body made of a cemented carbide is likely to be exposed. Thus, there is a possibility that the life of the drill bit is shortened.

[0015]

In addition, when the ratio r2/D is less than 0.05, the radius of the concave

portion is excessively small compared to the thickness of the hard layer as well, and the

curvature of the concave portion is large. Thus, residual stress is likely to be

concentrated at the concave portion, and there is a possibility that cracks are generated in

the hard layer. On the other hand, when the ratio r2/D exceeds 3.0, the thickness of the

hard layer is small at the concave portion. The wear of the hard layer coating the

concave portion at a side surface of the drilling tip during drilling progresses early

compared to the convex portion so that the tip main body made of a cemented carbide is

likely to be exposed. Thus, there is a possibility that the life of the drill bit is shortened.

[0016]

Further, when the angle 0 (°) formed by the straight line that connects the point

the convex portion tangents to the concave portion and the center of the convex arc of the

convex portion to each other with respect to the tip center line in the cross section is less

than 20 (°), the thickness of the hard layer, which is on the outer peripheral portion, is

small compared to the distal end portion of the convex portion, and the wear of the hard

layer during drilling of the outer peripheral portion of the convex portion progresses early

compared to the distal end portion so that the tip main body is likely to be exposed.

Thus, there is a possibility that the life of the drill bit is shortened. On the other hand,

when the angle 0 () formed by the straight line that connects the point the convex

portion tangents to the concave portion and the center of the convex arc of the convex

portion to each other with respect to the tip center line in the cross section exceeds 90(°),

the radius r2 of the concave portion is small so that the curvature is large, and residual stress is likely to be concentrated in the vicinity of the tangent point to the convex portion, thereby creating a possibility of becoming a origin of fracture of the hard layer when an impact load acts.

[0017]

In a case where the diameter D (mm) of the posterior end portion of the tip main

body is within a range of 14 (mm) to 20 (mm) in particular, the ratio rl/D of the radius rl

(mm) of the convex arc of the convex portion in the cross section with respect to the

diameter D (mm) of the posterior end portion of the tip main body may be within a range

of 0.18 to 0.45.

[0018]

A connecting portion having a convex arc shape of which a surface is convex in

a cross section taken along the tip center line may be provided between the posterior end

portion of the tip main body and the concave portion. Accordingly, residual stress

generated by sintering can be more relaxed. In a case of providing such a connecting

portion of which a cross section has a convex arc shape, it is desirable that a ratio r3/D of

a radius r3 (mm) of a convex arc of the connecting portion in the cross section with

respect to the diameter D (mm) of the posterior end portion of the tip main body is within

a range of 0.05 to 0.2.

[0019]

That is, when the ratio r3/D of the radius r3 (mm) of the convex arc in the cross

section of the connecting portion with respect to the diameter D (mm) is less than 0.05,

the radius of the connecting portion is excessively small, and the curvature is large.

Thus, residual stress generated by sintering or stress caused by a drilling load is likely to

be concentrated, and there is a possibility that an effect of preventing cracks in the hard

layer is lost. On the other hand, when the ratio r3/D exceeds 0.2, the thickness of the hard layer is small on the posterior end side of the connecting portion. The progress of wear of the hard layer during drilling is fast so that the tip main body is likely to be exposed. Thus, there is a possibility that the life of the drill bit is shortened.

[0020]

In the drilling tip, the hard layer may be configured to have a multi-layer

structure including a plurality of diamond sintered body layers having diamond particle

contents different from each other. In this configuration, a diamond particle content and

a layer thickness can be adjusted in each diamond sintered body layer configuring the

hard layer. With this adjustment, it is also possible to reduce residual stress generated

by sintering while maintaining the hardness of the outermost surface layer of the hard

layer. For example, in a case of a structure having at least two or more layers, it is

desirable to have a configuration where a diamond particle content in an outermost

surface layer is 65 vol% or more and 95 vol% or less and a diamond particle content in a

layer between the outermost surface layer and a cemented carbide is less than 60 vol%.

In a case of a three-layer structure, a configuration where a diamond particle content in a

layer in contact with an outermost surface layer is less than 60 vol% and more than 35

vol%, a diamond particle content in a layer in contact with a cemented carbide is 50 vol%

or less and 20 vol% or more, and a diamond particle content in each layer from the

outermost surface layer to the cemented carbide decreases is preferable to reduce residual

stress generated by sintering.

ADVANTAGEOUS EFFECTS OF INVENTION

[0021]

As described above, in the drilling tip and the drill bit of the present invention,

residual stress generated by sintering can be relaxed, the exposure of the tip main body caused by the wear of the hard layer during drilling can be prevented, and it is possible to perform efficient drilling by improving impact resistance and wear resistance and extending the life of the drilling tip and the life of the drill bit.

BRIEF DESCRIPTION OF DRAWINGS

[0022]

Fig. 1 is a cross-sectional view illustrating a first embodiment of a drilling tip of

the present invention, taken along a tip center line.

Fig. 2 is a cross-sectional view illustrating one embodiment of a drill bit of the

present invention, in which the drilling tip of the embodiment illustrated in Fig. I is

attached to a distal end portion of a bit main body, taken along an axial line of the bit

main body.

Fig. 3 is a cross-sectional view illustrating a second embodiment of the drilling

tip of the present invention, taken along the tip center line.

Fig. 4 is a cross-sectional view illustrating a third embodiment of the drilling tip

of the present invention, taken along the tip center line.

Fig. 5 is a cross-sectional view illustrating a fourth embodiment of the drilling

tip of the present invention, taken along the tip center line.

Fig. 6 is a cross-sectional view illustrating a fifth embodiment of the drilling tip

of the present invention, taken along the tip center line.

DESCRIPTION OF EMBODIMENTS

[0023]

Fig. 1 is a cross-sectional view illustrating a first embodiment of a drilling tip of

the present invention (drilling tip of Example I in an example to be described later), and

Fig. 2 is a cross-sectional view illustrating an embodiment of a drill bit of the present

invention to which the drilling tip of the embodiment is attached. A drilling tip 1 of the

present embodiment includes a tip main body 2 that is formed integrally with a columnar

or disk-shaped posterior end portion 2A centered on a tip center line C and a distal end

portion 2B, whose outer diameter from the tip center line C gradually decreases from the

posterior end portion 2A toward a distal end side, and is made of a cemented carbide and

a hard layer 3 that coats a surface of the distal end portion 2B of the tip main body 2 and

is made of a polycrystalline diamond sintered body having hardness higher than the tip

main body 2.

[0024]

As illustrated in Fig. 1, the distal end portion 2B of the tip main body 2 has a

convex portion 2a having a convex arc shape of which a surface is convex toward the

distal end side in a cross section taken along the tip center line C and a concave portion

2b having a concave arc shape in the cross section also taken along the tip center line C,

of which a surface tangents to the convex arc of the cross section of the convex portion

2a at a tangent point P and which extends to an outer peripheral side as going toward a

posterior end side of the tip main body 2. In the present embodiment, the surface of the

convex portion 2a is formed in a convex spherical shape having a center on the tip center

line C, and the surface of the concave portion 2b in the cross section intersects an outer

peripheral surface of the posterior end portion 2A of the tip main body 2 at an obtuse

angle.

[0025]

In addition, a diameter D (mm) of the posterior end portion 2A of the tip main

body 2 is within a range of 8 (mm) to 20 (mm), and is 9 (mm) in the present

embodiment. A ratio rl/D of a radius r1 (mm) of the convex are of the convex portion

2a in the cross section taken along the tip center line C with respect to the diameter D

(mm) of the posterior end portion 2A of the tip main body 2 is within a range of 0.1 to

0.65, and a ratio r2/D of a radius r2 (mm)of the concave are of the concave portion 2b in

the cross section with respect to the diameter D is within a range of 0.05 to 3.0.

[0026]

Herein, in the present embodiment in which the diameter D (mm) of the

posterior end portion 2A of the tip main body 2 is 9 (mm), the radius r1 (mm) of the

convex portion 2a is 3 (mm), and the ratio rl/D is 0.33. In addition, the radius r2 (mm)

of the concave portion 2b is 4 (mm), and the ratio r2/D is 0.44. The cross section taken

along the tip center line C described above may be a cross section taken along the tip

center line C in a range where a distance from the tip center line C is within 0.1 (mm).

[0027]

Further, an angle 0 () formed by a straight line L that connects the tangent point

P which the convex portion 2a tangents to the concave portion 2b and a center Q of the

convex arc of the convex portion 2a to each other with the tip center line C in the cross

section also taken along the tip center line C is within the range of 20 (°) to 90 (°). In

the present embodiment, the angle 0 () is 70(°).

[0028]

The hard layer 3 is a single layer in the present embodiment. Aposteriorend

portion 3A of the hard layer 3, which is connected to the distal end side of the posterior

end portion 2A of the tip main body 2, has an outer peripheral surface that has a

cylindrical surface shape centered on the tip center line C having the diameter D (mm)

equal to the posterior end portion 2A of the tip main body 2. A surface of a distal end

portion 3B of the hard layer 3 has a convex hemispherical surface shape, which is

smoothly connected to the outer peripheral surface of the posterior end portion 3A and is centered on the center Q. That is, the drilling tip I of the present embodiment is a so called button tip. In addition, the thickness of the hard layer 3 is made substantially uniform at least on the distal end side of the tangent point P.

[0029]

The drill bit having a distal end portion to which such a drilling tip 1 is attached

has a bit main body 11 that is formed of a steel material and is formed in a substantially

bottomed cylindrical shape centered on an axial line 0 as illustrated in Fig. 2. A

bottomed portion is the distal end portion (upper portion in Fig. 2), and the drilling tip I

is attached to the distal end portion. In addition, a female screw portion 12 is formed in

an inner periphery of a cylindrical posterior end portion (lower portion in Fig. 2). As a

drill rod connected to a drill device is screwed into the female screw portion 12 and a

striking force and an impelling force toward a distal end side in an axial line 0 direction

and a rotating force about the axial line 0 are transmitted, the drilling tip 1 crushes a

bedrock to form a borehole.

[0030]

The distal end portion of the bit main body 11 has an outer diameter slightly

larger than the posterior end portion, a plurality of discharge flutes 13 extending parallel

to the axial line 0 are formed at a distance from each other in a circumferential direction

in an outer periphery of the distal end portion, and crushed debris generated by the

drilling tip I crushing the bedrock is discharged to the posterior end side through the

discharge flutes 13. In addition, a blow hole 14 is formed along the axial line 0 from a

bottom surface of the female screw portion 12 of the bottomed bit main body 11, the

blow hole 14 obliquely branches at the distal end portion of the bit main body 11 so that

an opening is formed in a distal end surface of the bit main body 11, and a fluid such as

compressed air supplied via the drill rod is ejected to facilitate the discharge of crushed debris.

[0031]

Further, the distal end surface of the bit main body 11 includes a circular face

surface 15 that is on an inner peripheral side perpendicular to the axial line 0 and is

centered on the axial line 0 and a gauge surface 16 that is positioned on an outer

periphery of the face surface 15 and has a conical base surface shape toward the posterior

end side as going toward the outer peripheral side. The blow hole 14 is opened in the

face surface 15, and a distal end of the discharge flute 13 is opened on the outer

peripheral side of the gauge surface 16. In addition, a plurality of fitting holes 17 each

having a circular cross section are formed in the face surface 15 and the gauge surface 16

to be perpendicular to the face surface 15 and the gauge surface 16 such that each of

opening portions of the blow hole 14 and the discharge flutes 13 is avoided.

[0032]

The drilling tip is fixed, that is, buried and attached to such fitting holes 17 by

being tightly fitted through press-fitting and shrink-fitting or being brazed in a state

where the posterior end portion 2A of the tip main body 2 is buried as illustrated in Fig.

2. Further, the distal end portion of the drilling tip I coated with the hard layer 3

protrudes from the face surface 15 and the gauge surface 16 to crush the bedrock by the

striking force, the impelling force, and the rotating force, which are described above.

[0033]

In the drilling tip 1 that is attached to the bit main body 11 of the drill bit in this

manner and has the configuration, the distal end portion 2B of the tip main body 2 has

the convex portion 2a having the convex arc shape of which the surface is convex toward

the distal end side in the cross section taken along the tip center line C and the concave

portion 2b having the concave arc shape in the cross section also taken along the tip center line C, of which the surface tangents to the convex arc in the cross section of the convex portion 2a and which extends to the outer peripheral side toward the posterior end side of the tip main body 2. That is, since corner parts intersecting at an angle are not formed at an interface between the tip main body 2 and the hard layer 3 unlike the drilling tip described in Patent Document 3, residual stress generated by sintering can be relaxed, and cracks are not generated in the hard layer 3 with such corner parts as a origin thereof.

[0034]

Herein, if the diameter D (mm) of the posterior end portion 2A of the tip main

body 2 is smaller than 8 (mm), the residual stress of the interface between the hard layer

3 and the tip main body 2 can be relaxed, but an impact load acting on the tip main body

2 per unit area increases in a case of being used in drilling under a higher impact load

condition. Therefore, damage caused by the origin in the tip main body 2 is likely to

occur, and there is a possibility that the life of the drill bit is shortened. On the other

hand, when the diameter D (mm) of the posterior end portion 2A of the tip main body 2

is larger than 20 (mm), the volume of the hard layer 3 is large with respect to the area of

the tip main body 2 in contact with the hard layer 3, residual stress that occurs at the

interface between the hard layer 3 and the tip main body 2 cannot be relaxed, and thus

there is a possibility that cracks are generated after sintering.

[0035]

In the drilling tip 1 having the configuration, with respect to the diameter D

(mm) of the posterior end portion 2A of the tip main body 2, which is within a range of 8

(mm) to 20 (mm), the ratio rl/D of the radius r1 (mm) of the convex arc of the convex

portion 2a in the cross section is within a range of 0.1 to 0.65, and the ratio r2/D of the

radius r2 (mm) of the concave arc of the concave portion 2b in the cross section is within a range of 0.05 to 3.0. The angle 0 (°) formed by the straight line L that connects the tangent point P which the convex portion 2a tangents to the concave portion 2b and the center Q of the convex arc of the convex portion 2a to each other with the tip center line

C in the cross section taken along the tip center line C is within a range of 20 (°) to 90

(0). For this reason, residual stress at the interface between the hard layer 3 and the tip

main body 2 can be more reliably relaxed, and it is possible to extend the life by securing

a sufficient thickness for the hard layer 3.

[0036]

When the ratio rl/D is less than 0.1, the radius rIof the convex portion 2a is

excessively small compared to the thickness of the hard layer 3, and the curvature of the

convex portion 2a is large. Thus, residual stress is likely to be concentrated at a distal

end portion of the convex portion 2a, and there is a possibility that cracks are likely to be

generated in the hard layer 3. On the other hand, conversely, when the ratio rl/D

exceeds 0.65, the thickness of the hard layer 3 is small at an outer peripheral portion of

the convex portion 2a. The wear of the hard layer 3 at the outer peripheral portion of

the convex portion 2a during drilling progresses early compared to the distal end portion

so that the convex portion 2a of the tip main body 2 made of a cemented carbide is likely

to be exposed. Thus, there is a possibility that the life of the drill bit is shortened.

[0037]

In addition, when the ratio r2/D is less than 0.05, the radius r2 of the concave

portion 2b is excessively small compared to the thickness of the hard layer 3 as well, and

the curvature of the concave portion 2b is large. Thus, residual stress is likely to be

concentrated at the concave portion 2b, and there is a possibility that cracks are generated

in the hard layer 3. On the other hand, when the ratio r2/D exceeds 3.0, the thickness of

the hard layer 3 is small at the concave portion 2b. The wear of the hard layer 3 coating the concave portion 2b at a side surface of the drilling tipI during drilling progresses early compared to the convex portion 2a so that the tip main body 2 made of a cemented carbide is likely to be exposed. Thus, there is a possibility that the life of the drill bit is shortened.

[0038]

Further, when the angle 0 () formed by the straight line L that connects the

tangent point P which the convex portion 2a tangents to the concave portion 2b and the

center Q of the convex arc of the convex portion 2a to each other with the tip center line

C in the cross section is less than 20 (°), the thickness of the hard layer 3 which is on the

outer peripheral portion is small compared to the distal end portion of the convex portion

2a, and the wear of the hard layer 3 during drilling of the outer peripheral portion of the

convex portion 2a progresses early compared to the distal end portion so that the tip main

body 2 is likely to be exposed. Thus, there is a possibility that the life of the drill bit is

shortened. On the other hand, when the angle 0 (°) formed by the straight line L with

respect to the tip center line C in the cross section exceeds 90 (), the radius r2 of the

concave portion 2b is small so that the curvature is large, and residual stress is likely to

be concentrated in the vicinity of the tangent point P with the convex portion 2a, thereby

creating a possibility of becoming a fracture origin of the hard layer 3 when an impact

load acts.

[0039]

Next, Fig. 3 is a cross-sectional view illustrating a second embodiment of the

drilling tip I of the present invention (drilling tip of Example 2 in the example to be

described later). Starting with the second embodiment illustrated in Fig. 3, even in third

to fifth embodiments of the drilling tip 1 of the present invention illustrated in Figs. 4 to

6, portions common to the drilling tip 1 of the first embodiment illustrated in Fig. 1 will be assigned with the same reference signs as in Fig. 1, and a description thereof will be omitted. In the drilling tip 1 of the second embodiment, the diameter D (mm) of the posterior end portion 2A of the tip main body 2 is 13 (mm), the radius r1 of the convex portion 2a of the distal end portion 2B of the tip main body 2 is 4.5 (mm), the ratio rl/D is 0.35, the radius r2 (mm) of the concave portion 2b is 6 (im),the ratio r2/D is 0.46, and the angle 0 (°) formed by the straight line L with respect to the tip center line C is 70

(0).

[0040]

In addition, in the drilling tip (drilling tip of Example 10 in the example to be

described later) I of the third embodiment illustrated in Fig. 4, the diameter D (mm) of

the posterior end portion 2A of the tip main body 2 is 16 (mm), the radius r1 of the

convex portion 2a of the distal end portion 2B of the tip main body 2 is 5 (mm), the ratio

rl/D is 0.31, the radius r2 (mm) of the concave portion 2b is 7.5 (mm), the ratio r2/D is

0.47, and the angle 0 (°) formed by the straight line L with respect to the tip center line C

is 70()

[0041]

Further, in the drilling tip (drilling tip of Example 11 in the example to be

described later) 1 of the fourth embodiment illustrated in Fig. 5, the diameter D (mm) of

the posterior end portion 2A of the tip main body 2 is 18 (mm), the radius r1 of the

convex portion 2a of the distal end portion 2B of the tip main body 2 is 5.5 (mm), the

ratio rl/D is 0.3, the radius r2 (mm) of the concave portion 2b is 9 (mm), the ratio r2/D is

0.5, and the angle 0 () formed by the straight line L with respect to the tip center line C

is 70 (0).

[0042]

In a case where the diameter D (mm) of the posterior end portion 2A of the tip main body 2 is within a range of 14 (mm) to 20 (mm) as in the third and fourth embodiments, the ratio rl/D of the radius r1 (mm) of the convex arc of the convex portion 2a in the cross section taken along the tip center line C with respect to the diameter D (mm) of the posterior end portion 2A of the tip main body 2 may be within a range of 0.18 to 0.45 as described above. Accordingly, also in the drilling tip 1 in which the diameter D (mm) of the posterior end portion 2A of the tip main body 2 is relatively large, the exposure of the tip main body 2 caused by wear can be suppressed while more reliably relaxing residual stress.

[0043]

In addition, the drilling tip (drilling tip of Example 6 in the example to be

described later) 1 of the fifth embodiment illustrated in Fig. 6 has, between the posterior

end portion 2A of the tip main body 2 and the concave portion 2b of the distal end

portion 2B, a connecting portion 2c having a convex arc shape of which a surface is

convex in the cross section taken along the tip center line C. Herein, the diameter D

(mm) of the posterior end portion 2A of the tip main body 2 of the fifth embodiment is 13

(mm) as in the second embodiment, the radius r1 of the convex portion 2a of the distal

end portion 2B of the tip main body 2 is 3.25 (mm), the ratio rl/D is 0.25, the radius r2

(mm) of the concave portion 2b is 7.8 (mm), the ratio r2/D is 0.6, and the angle (0)

formed by the straight line L with respect to the tip center line C is 60()

[0044]

Further, in the fifth embodiment, a ratio r3/D of a radius r3 (nmn) of the convex

arc of the connecting portion 2c in the cross section taken along the tip center line C with

respect to the diameter D (mm) of the posterior end portion 2A of the tip main body 2 is

within a range of 0.05 to 0.2. In the present embodiment, the radius r3 (mm) is 1.3

(mm), and accordingly the ratio r3/D of the radius r3 with respect to the diameter D (mm) is 0.1.

[0045]

In such a drilling tip 1 of the fifth embodiment, the residual stress of the

interface between the tip main body 2 and the hard layer 3 at the connecting portion 2c

can be more relaxed. When the ratio r3/D of the radius r3 (nm) of the convex arc in the

cross section of the connecting portion 2c with respect to the diameter D (mm) of the

posterior end portion 2A of the tip main body 2 is less than 0.05, the radius r3 of the

connecting portion 2c is excessively small, and there is a possibility that an effect of

relaxing the residual stress generated by sintering is lost. When the ratio r3/D exceeds

0.2, the thickness of the hard layer 3 on the posterior end side of the connecting portion

2c is small so that the tip main body 2 is likely to be exposed. Thus, it is desirable for

the ratio r3/D to be within a range of 0.05 to 0.2 as described above.

EXAMPLES

[0046]

Next, an effect of the present invention will be demonstrated by giving examples

of the drilling tip of the present invention. In the present example, based on the

embodiment, each of a plurality of fifteen types of the drilling tips 1, in which the

diameter D (mm) of the posterior end portion 2A of the tip main body 2 is within a range

of 8 (mm) to 20 (mm), the ratio ri/D of the radius r1 (mm) of the convex arc of the

convex portion 2a in the cross section taken along the tip center line C with respect to the

diameter D (mm) of the posterior end portion 2A of the tip main body 2 is within a range

of 0.1 to 0.65, the ratio r2/D of the radius r2 (mm) of the concave arc of the concave

portion 2b in the cross section with respect to the diameter D (mm) is within a range of

0.05 to 3.0, the angle 0 (°) formed by the straight line L with respect to the tip center line in the cross section is within a range of 20 (°) to 90 (°), was manufactured one by one.

In any drilling tip 1, a hard layer having the Vickers hardness of 4,000 HV or

more and a thickness along the tip center line C of 1.1 mm or more and 3.0 mm or less

was formed at the distal end portion of the tip main body 2 made of a cemented carbide.

[0047]

Among these, four types of the drilling tips I each had, between the posterior

end portion 2A of the tip main body 2 and the concave portion 2b of the distal end

portion 2B, the connecting portion 2c having a convex arc shape of which a surface is

convex in the cross section taken along the tip center line C as in the fifth embodiment.

The ratio r3/D of the radius r3 (mm) of the convex arc of the connecting portion 2c in the

cross section with respect to the diameter D (mm) of the posterior end portion of the tip

main body was within a range of 0.05 to 0.2.

In addition, one type of the drilling tip 1 (Example 14) had a three-layer

structure hard layer in which diamond particle contents are different from each other.

Among the three hard layers, an outermost hard layer was a hard layer having the Vickers

hardness of 4,000 HV or more and a thickness along the tip center line C of 1.2 mm.

The two layers between the outermost hard layer and cemented carbide were layers

having the Vickers hardness of 2,800 HV or less and a total thickness along the tip center

line C of 1.2 mm.

As Examples 1 to 15, these are shown in Table I together with the diameter D

(mm), the ratio rl/D, the angle 0 (0), the ratio r2/D, and the ratio r3/D, if the connecting

portion 2c is included.

[0048]

In addition, each of a plurality of eight types of the drilling tips 1, in which the

diameter D (mm) of the posterior end portion 2A of the tip main body 2 is within a range of 8 (mm) to 20 (mm) but any one of the ratio rl/D, the ratio r2/D, and the angle 0 (°) is out of the range of the embodiment, was manufactured one by one as a comparative example with respect to Examples 1 to 15. Among these, three types of the drilling tips

I each had, between the posterior end portion 2A of the tip main body 2 and the concave

portion 2b of the distal end portion 2B, the connecting portion 2c that has a convex arc

shape of which a surface is convex in the cross section taken along the tip center line C.

As Comparative Examples I to 8, these are shown in Table 2 together with the diameter

D (mm), the ratio rl/D, the angle 0 (°), the ratio r2/D, and the ratio r3/D, if the

connecting portion 2c is included.

[0049]

The radius r I(mm) of the convex portion 2a, the radius r2 (mm) of the concave

portion 2b, and the angle 0 (°) of the drilling tip I of each of Examples 1 to 15 and

Comparative Examples 1to 8 were measured by cutting the drilling tip I along the tip

center line C within a radius of 0.1 (mm) from the tip center line C with an electrical

discharge machine and determining the position of the interface through image analysis

based on a difference in color between a cemented carbide and a polycrystalline diamond

sintered body. In addition, the center Q of the convex arc of the convex portion 2a was

positioned on a line, which passes through the apex of the convex portion 2a in the distal

end portion 2B of the tip main body 2 in a case where the cross section went through

image analysis in such a manner and bisects the posterior end portion 2A in a radial

direction.

[0050]

Next, the impact resistance performance of each of the plurality of drilling tips I

of Examples 1 to 15 and Comparative Examples 1 to 8 manufactured in such a manner

was measured using a drop weight type impact tester. In the drop weight type impact test, the drilling tip I was fixed in a state where the distal end portion 2B of the tip main body 2 was faced upward, and impact was added by dropping a weight made of a cemented carbide along the tip center line C from immediately above the drilling tip 1.

Impact energy (J) given to the drilling tip I was controlled by making the mass of the

weight constant and changing the dropping height.

[0051]

In addition, after adding impact by dropping the weight, the surface of the hard

layer 3 of the drilling tip I was observed with a stereomicroscope. In a case where

damage to the hard layer 3 was found, energy to which the impact was added was set as

energy (J) that had led to the damage. Energy generated by dropping the weight was set

to 10 (J) at the start of the test, and in a case where no damage was found in the hard

layer 3, the tested ones, among the plurality of drilling tips 1, were replaced with untested

ones. Then, a test of adding energy increased by 10 (J) was repeated until damage was

found, and the energy (J) that had led to the damage was measured. The results are

shown for Examples 1 to 15 and Comparative Examples 1 to 8 in Tables 1 and 2.

[0052]

[Table 1]

Example D (mm) rl/D 0 (0) r2/D r3/D Energyledto destruction [J] 1 9 0.33 70 0.44 - 140 2 13 0.35 70 0.46 - 160 3 13 0.10 20 1.50 - 80 4 13 0.30 40 0.30 - 110 5 13 0.65 35 1.50 - 70 6 13 0.25 60 0.60 0.10 150 7 13 0.55 55 0.05 - 110 8 13 0.33 90 0.50 0.20 140 9 13 0.35 70 3.00 0.10 130

10 16 0.31 70 0.47 - 150 11 18 0.30 70 0.50 - 150 12 18 0.18 70 0.90 0.05 130 13 18 0.45 60 0.60 - 120 14 18 0.30 70 0.46 - 120 15 20 0.30 70 0.48 - 100

[0053]

[Table 2]

Comparative D (mm) rl/D 0(°) r2/D r3/D Energy led to Example destruction[J]

1 9 1.10 20 1.00 - 30

2 13 0.40 100 0.45 - 40 3 13 0.03 40 0.80 0.20 30 4 13 0.40 60 4.00 - 30 5 13 0.33 85 0.02 0.10 40 6 18 0.40 5 1.40 0.10 30 7 16 1.30 20 0.46 - 30 8 18 0.05 30 0.75 - 30

[0054]

From the results of Tables 1 and 2, first, in the drilling tip 1 of each of

Comparative Examples Ito 8, in which any one of the diameter D (mm), the ratio rl/D,

the angle 0 (°), and the ratio r2/D is out of the range of the embodiment, it has turned out

that energy (J) that has led to the destruction is 40 (J) or less, and the impact resistance is

poor.

[0055]

On the other hand, in the drilling tip 1 of each of Examples 1 to 15 in which all

of the diameter D (mm), the ratio rl/D, the angle 0 (), and the ratio r2/D are within the

respective ranges of the embodiment, even in Example 5 in which energy (J) that has led

to destruction is smallest, 70 (J) could be obtained which is approximately two times the

impact resistance of Comparative Examples I to 8, and in Example 2 in which energy (J) that has led to destruction is largest, 160 (J) could be obtained which is approximately four or more times the impact resistance of Comparative Examples 1 to 8.

INDUSTRIAL APPLICABILITY

[0056]

As described above, in the drilling tip and the drill bit of the present invention,

residual stress during sintering can be relaxed, the exposure of the tip main body caused

by the wear of the hard layer during drilling can be prevented, and it is possible to

perform efficient drilling by improving impact resistance and wear resistance and

extending the life of the drilling tip and the life of the drill bit.

REFERENCE SIGNS LIST

[0057]

1 Drilling Tip

2 Tip main body

2a Posterior end portion of tip main body 2

2b Distal end portion of tip main body 2

2a Convex portion

2b Concave portion

2c Connecting portion

3 Hard layer

I IBit main body

C Tip center line

O Axial line of bit main body 11

D Diameter of posterior end portion 2A of tip main body 2 rl Radius of convex arc of convex portion 2a in cross section taken along tip centerline C r2 Radius of concave arc of concave portion 2b in cross section taken along tip center line C r3 Radius of convex arc of connecting portion 2c in cross section taken along tip center line C

P Point which convex portion 2a tangents to concave portion 2b in cross section

taken along tip center line C

Q Center of convex arc of convex portion 2a in cross section taken along tip

center line C

L Straight line that connects tangent point P and center Q to each other

o Angle formed by straight line L with respect to tip center line C in cross section taken along tip center line C

Claims (6)

1. What is claimed is:

   [Claim 1]

   A drilling tip that is attached to a distal end portion of a drill bit to perform

   drilling, the drilling tip comprising:

   a tip main body that has a posterior end portion having a columnar or disk shape

   centered on a tip center line and a distal end portion having an outer diameter from the tip

   center line, which gradually decreases from the posterior end portion toward a distal end

   side, and is made of a cemented carbide; and

   a hard layer that coats the distal end portion of the tip main body and is made of

   a polycrystalline diamond sintered body,

   wherein the distal end portion of the tip main body has a convex portion having

   a convex are shape of which a surface is convex toward the distal end side in a cross

   section taken along the tip center line, and a concave portion having a concave are shape

   in a cross section taken along the tip center line, of which a surface tangents to a convex

   are in the cross section of the convex portion and which extends to an outer peripheral

   side as going toward a posterior end side of the tipmain body,

   a diameter D (mm) of the posterior end portion of the tip main body is within a

   range of 8 (mm) to 20 (mm),

   with respect to the diameter D (mm) of the posterior end portion of the tip main

   body, a ratio rl/D of a radius rl (mm)of the convex are of the convex portion in the cross

   section is within a range of 0.1 to 0.65, and a ratio r2/D of a radius r2 (mm) of a concave

   are of the concave portion in the cross section is within a range of 0.05 to 3.0, and

   an angle 0 (°) formed by a straight line that connects a point which the convex

   portion tangents to the concave portion and a center of the convex are of the convex portion to each other with respect to the tip center line in the cross section is within a range of 20 (°) to 90(°)
2. [Claim 2]

   The drilling tip according to Claim 1,

   wherein the diameter D (mm) of the posterior end portion of the tip main body is

   14 (mm) to 20 (mm), and

   the ratio rl/D of the radius r1 (mm) of the convex arc of the convex portion in

   the cross section with respect to the diameter D (mm) of the posterior end portion of the

   tip main body is within a range of 0.18 to 0.45.
3. [Claim 3]

   The drilling tip according to Claim 1 or 2,

   wherein a connecting portion having a convex arc shape of which a surface is

   convex in a cross section taken along the tip center line is provided between the posterior

   end portion of the tip main body and the concave portion, and

   a ratio r3/D of a radius r3 (mm) of a convex arc of the connecting portion in the

   cross section with respect to the diameter D (mm) of the posterior end portion of the tip

   main body is within a range of 0.05 to 0.2.
4. [Claim 4]

   The drilling tip according to any one of Claims 1 to 3,

   wherein an outermost surface layer of the hard layer has Vickers hardness of

   4,000 HV or more, and the hard layer has a thickness of 1.1 mm or more and 3.0 mm or

   less.
5. [Claim 5]

   The drilling tip according to any one of Claims I to 4,

   wherein the hard layer has a multi-layer structure including a plurality of

   diamond sintered body layers having diamond particle contents different from each other.
6. [Claim 6]

   A drill bit comprising the drilling tip according to any one of Claims I to 5 that

   is attached to a distal end portion of a bit main body,

   wherein a fitting hole is formed in the distal end portion of the bit main body,

   and

   the drilling tip is attached such that the posterior end portion of the tip main

   body is buried in the fitting hole.