U.S. patent application number 13/176455 was filed with the patent office on 2011-10-27 for surface-covered cubic boron nitride sintered body tool and method of manufacturing the same.
This patent application is currently assigned to Sumitomo Electric Hardmetal Corp.. Invention is credited to Tomohiro Fukaya, Satoru Kukino, Katsumi Okamura.
Application Number | 20110262700 13/176455 |
Document ID | / |
Family ID | 35241491 |
Filed Date | 2011-10-27 |
United States Patent
Application |
20110262700 |
Kind Code |
A1 |
Okamura; Katsumi ; et
al. |
October 27, 2011 |
SURFACE-COVERED CUBIC BORON NITRIDE SINTERED BODY TOOL AND METHOD
OF MANUFACTURING THE SAME
Abstract
A surface-covered CBN sintered body tool includes a base
material formed with a cubic boron nitride (CBN) sintered body and
a surface covering film covering a surface of the base material,
and has a nega-land exposing the CBN sintered body in at least a
portion thereof and a flank having the surface covering film formed
thereon. With this, the surface-covered CBN sintered body tool
having high defect resistance and wear resistance can be provided.
The surface covering film preferably includes a nitride or a
carbonitride of a compound including at least one element selected
from the group consisting of Ti, Cr, Zr, and V and at least one
element selected from the group consisting of Al, Si and B, or a
nitride or a carbonitride of Ti.
Inventors: |
Okamura; Katsumi;
(Itami-shi, JP) ; Kukino; Satoru; (Itami-shi,
JP) ; Fukaya; Tomohiro; (Itami-shi, JP) |
Assignee: |
Sumitomo Electric Hardmetal
Corp.
Hyogo
JP
|
Family ID: |
35241491 |
Appl. No.: |
13/176455 |
Filed: |
July 5, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11579138 |
Oct 30, 2006 |
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PCT/JP2005/003295 |
Feb 28, 2005 |
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13176455 |
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Current U.S.
Class: |
428/143 ;
427/289; 428/141; 428/192 |
Current CPC
Class: |
Y10T 428/24372 20150115;
C04B 41/5068 20130101; C04B 41/87 20130101; C04B 41/5068 20130101;
B23P 15/28 20130101; Y10T 428/24355 20150115; B23B 2224/32
20130101; C04B 41/5061 20130101; C04B 41/5062 20130101; C04B
41/5063 20130101; C04B 35/5831 20130101; C04B 41/5061 20130101;
C04B 41/4529 20130101; C04B 41/5066 20130101; C04B 41/4529
20130101; C04B 41/4529 20130101; C04B 41/4529 20130101; C04B
41/5063 20130101; C04B 41/5068 20130101; C04B 41/009 20130101; C04B
41/009 20130101; C04B 41/5068 20130101; B23B 2200/283 20130101;
Y10T 428/24777 20150115; C04B 41/5068 20130101; C04B 41/5063
20130101; B23B 2228/10 20130101; C04B 41/5063 20130101; B23B
2224/36 20130101; C04B 41/5057 20130101; C04B 41/4529 20130101;
Y10T 407/27 20150115; B23B 27/141 20130101 |
Class at
Publication: |
428/143 ;
427/289; 428/141; 428/192 |
International
Class: |
B32B 3/02 20060101
B32B003/02; B32B 9/04 20060101 B32B009/04; B32B 33/00 20060101
B32B033/00; B05D 3/12 20060101 B05D003/12 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 30, 2004 |
JP |
2004-136816 (P) |
Claims
1. A surface-covered cubic boron nitride sintered body tool,
comprising: a base material formed with a cubic boron nitride
sintered body; and a surface covering film covering a surface of
the base material; wherein a nega-land exposing the cubic boron
nitride sintered body in at least a portion thereof associated with
a cutting cross section and a flank having the surface covering
film are formed.
2. (canceled)
3. The surface-covered cubic boron nitride sintered body tool
according to claim 1, wherein the cubic boron nitride sintered body
is exposed in a whole portion of the nega-land.
4. The surface-covered cubic boron nitride sintered body tool
according to claim 3, wherein the nega-land has a width W of
0.05-0.2 mm.
5. The surface-covered cubic boron nitride sintered body tool
according to claim 1, wherein arithmetic mean surface roughness Ra
of a portion of the nega-land exposing the cubic boron nitride
sintered body is expressed as
0.3.ltoreq.Ra(min)/Ra(max).ltoreq.0.8, where Ra(min) represents
surface roughness in a direction parallel to a grinding direction
of a grinder and Ra(max) represents surface roughness in a
direction perpendicular to the grinding direction of the
grinder.
6. The surface-covered cubic boron nitride sintered body tool
according to claim 1, wherein the surface covering film includes a
nitride or a carbonitride of a compound including at least one
element selected from the group consisting of Ti, Cr, Zr, and V and
at least one element selected from the group consisting of Al, Si
and B, or a nitride or a carbonitride of Ti.
7. (canceled)
8. The surface-covered cubic boron nitride sintered body tool
according to claim 6, wherein arithmetic mean surface roughness Ra
of a portion of the nega-land exposing the cubic boron nitride
sintered body is expressed as 0.3 Ra(min)/Ra(max) 0.8, where
Ra(min) represents surface roughness in a direction parallel to a
grinding direction of a grinder and Ra(max) represents surface
roughness in a direction perpendicular to the grinding direction of
the grinder.
9. The surface-covered cubic boron nitride sintered body tool
according to claim 6, wherein the cubic boron nitride sintered body
is exposed in a whole portion of the nega-land.
10. The surface-covered cubic boron nitride sintered body tool
according to claim 9, wherein the nega-land has a width W of
0.05-0.2 mm.
11. A surface-covered cubic boron nitride sintered body tool,
comprising: a base material formed with a cubic boron nitride
sintered body; and a surface covering film covering a surface of
the base material; wherein a nega-land exposing the cubic boron
nitride sintered body in at least a portion thereof associated with
a cutting cross section and a flank having the surface covering
film are formed, and a cubic boron nitride particle in said cubic
boron nitride sintered body exposed contains at least one of Ti,
Cr, Zr, V, and Ar at a depth of at least 0.05 .mu.m from a surface
of the cubic boron nitride particle with a total content of at most
an amount of an unavoidable impurity.
12. The surface-covered cubic boron nitride sintered body tool
according to claim 11, wherein the surface covering film includes a
nitride or a carbonitride of a compound including at least one
element selected from the group consisting of Ti, Cr, Zr, and V and
at least one element selected from the group consisting of Al, Si
and B, or a nitride or a carbonitride of Ti.
13. (canceled)
14. The surface-covered cubic boron nitride sintered body tool
according to claim 12, wherein arithmetic mean surface roughness Ra
of a portion of the nega-land exposing the cubic boron nitride
sintered body is expressed as 0.3 Ra(min)/Ra(max) 0.8, where
Ra(min) represents surface roughness in a direction parallel to a
grinding direction of a grinder and Ra(max) represents surface
roughness in a direction perpendicular to the grinding direction of
the grinder.
15. The surface-covered cubic boron nitride sintered body tool
according to claim 12, wherein the cubic boron nitride sintered
body is exposed in a whole portion of the nega-land.
16. The surface-covered cubic boron nitride sintered body tool
according to claim 15, wherein the nega-land has a width W of
0.05-0.2 mm.
17. (canceled)
18. The surface-covered cubic boron nitride sintered body tool
according to claim 11, wherein the cubic boron nitride sintered
body is exposed in a whole portion of the nega-land.
19. The surface-covered cubic boron nitride sintered body tool
according to claim 18, wherein the nega-land has a width W of
0.05-0.2 mm.
20. The surface-covered cubic boron nitride sintered body tool
according to claim 11, wherein arithmetic mean surface roughness Ra
of a portion of the nega-land exposing the cubic boron nitride
sintered body is expressed as
0.3.ltoreq.Ra(min)/Ra(max).ltoreq.0.8, where Ra(min) represents
surface roughness in a direction parallel to a grinding direction
of a grinder and Ra(max) represents surface roughness in a
direction perpendicular to the grinding direction of the
grinder.
21. A method of manufacturing a surface-covered cubic boron nitride
sintered body tool, comprising the steps of: forming a surface
covering film with a PVD method on a surface of a tool material
having a cutting edge portion of a cubic boron nitride sintered
body, said surface covering film includes a nitride or a
carbonitride of a compound including at least one element selected
from the group consisting of Ti, Cr, Zr, and V and at least one
element selected from the group consisting of Al, Si and B, or a
nitride or a carbonitride of Ti; and forming a nega-land to expose
the cubic boron nitride sintered body in at least a portion thereof
associated with a cutting cross section.
22. The method according to claim 21, further comprising the step
of honing at least a portion of a periphery of the nega-land after
the step of forming said nega-land.
Description
TECHNICAL FIELD
[0001] The present invention relates to an improvement in a
material for a tool which has, as a base material, a sintered body
including cubic boron nitride as a main component and has a surface
covered with a thin film.
BACKGROUND ART
[0002] Cubic boron nitride (hereafter abbreviated as "CBN") is a
material having high hardness after diamond and low reactivity with
metals, and therefore, a sintered body thereof is used for a tool
for cutting a heat resistant alloy or quenched steel. Even for the
CBN sintered body having such high hardness, a surface covering
film is formed thereon to prevent wear of an edge portion.
[0003] Patent Document 1 discloses a hard film-covered very high
temperature and high pressure sintered body characterized in that
peak intensity from a specific crystal surface of a surface
covering film (coating) on a CBN sintered body during X-ray
diffraction has a specific relation. In this technique, it is
proposed to process a cutting edge with beveling or into a honed
shape such as an R shape to prevent nicking or chipping. It is also
disclosed that when a thickness of the coating decreases toward a
cutting edge ridgeline portion, properties regarding peeling of the
coating and minute chipping of the cutting edge are improved.
[0004] Patent Document 1: Japanese Patent Laying-Open No.
2002-3284
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0005] With the technique disclosed in Patent Document 1, however,
especially when the tool is used for interrupted cutting, a crack
is generated with an intermittent impact on the coating formed with
ceramics which has lower strength and toughness than the CBN
sintered body. When the cutting is continued, the crack propagates
to the CBN sintered body as a base material, because the base
material and coating are strongly joined together. Moreover, it
turned out that the crack further propagates to cause chipping of
the CBN sintered body and life of the tool is thus ended.
[0006] Accordingly, a main object of the present invention is to
provide a surface-covered CBN sintered body tool which can suppress
cracking and chipping of a nega-land (a portion formed by beveling
a cutting edge ridgeline along a cutting edge with a substantially
uniform width in order to strengthen an edge portion of a tool) to
decrease wear of a flank even in a situation of interrupted cutting
of a high hardness material such as quenched steel, and to provide
a method of manufacturing the same.
Means for Solving the Problems
[0007] The present invention is a surface-covered cubic boron
nitride sintered body tool (a surface-covered CBN sintered body
tool) which includes a base material formed with a cubic boron
nitride (CBN) sintered body and a surface covering film covering a
surface of the base material, and in which a nega-land exposing the
cubic boron nitride sintered body in at least a portion thereof and
a flank having the surface covering film are formed.
[0008] Herein, a CBN particle in the CBN sintered body exposed
preferably contains at least one of Ti, Cr, Zr, V, and Ar at a
depth of at least 0.05 .mu.m from a surface of the CBN particle
with a content of at most an amount of an unavoidable impurity.
[0009] The surface covering film in the present invention
preferably includes a nitride or a carbonitride of a compound
including at least one element selected from the group consisting
of Ti, Cr, Zr, and V and at least one element selected from the
group consisting of Al, Si and B, or a nitride or a carbonitride of
Ti.
[0010] In addition, in the surface-covered CBN sintered body tool
of the present invention, it is preferable that (1) the CBN
sintered body be exposed in a whole portion of the nega-land, or
(2) the CBN sintered body be exposed in at least a portion of the
nega-land associated with a cutting cross section.
[0011] In the surface-covered CBN sintered body tool of the present
invention, the nega-land preferably has a width W of 0.05-0.2
mm.
[0012] In the surface-covered CBN sintered body tool of the present
invention, arithmetic mean surface roughness Ra of a portion of the
nega-land exposing the CBN sintered body is preferably expressed as
0.3.ltoreq.Ra(min)/Ra(max).ltoreq.0.8, where Ra(min) represents
surface roughness in a direction parallel to a grinding direction
of a grinder and Ra(max) represents surface roughness in a
direction perpendicular to the grinding direction of the
grinder.
[0013] The present invention also provides a method of
manufacturing a surface-covered CBN sintered body tool which
includes the steps of: forming a surface covering film with a PVD
method on a surface of a tool material having a cutting edge
portion of a CBN sintered body, which surface covering film
includes a nitride or a carbonitride of a compound including at
least one element selected from the group consisting of Ti, Cr, Zr,
and V and at least one element selected from the group consisting
of Al, Si and B, or a nitride or a carbonitride of Ti; and forming
a nega-land to expose the CBN sintered body in at least a portion
thereof.
[0014] The method of manufacturing a surface-covered CBN sintered
body tool of the present invention preferably further includes the
step of honing at least a portion of a periphery of the nega-land
after the step of forming the nega-land.
EFFECTS OF THE INVENTION
[0015] With the present invention including a construction in which
the CBN sintered body as the base material is exposed in at least a
portion of the nega-land, a surface-covered CBN sintered body tool
can be attained which avoids cracking of a surface covering film of
a nega-land which occurs in a conventional tool and suppresses
chipping, and has high defect resistance and wear resistance. The
surface-covered CBN sintered body tool as such can be suitably used
particularly for a purpose in which defect resistance of the tool
is required, such as interrupted cutting of quenched steel.
[0016] In addition, though the present invention includes a
construction in which the surface covering film is formed on the
flank, since a work material does not initially strike the flank at
biting of the edge portion during the interrupted cutting, a crack
is not easily generated on the flank even when the surface covering
film is formed thereon, and wear of the flank is suppressed with
the surface covering film without decreasing life of the tool,
which can attain a long-life tool. It is to be noted that, though a
phenomenon in which a crack is not easily generated on the surface
covering film of the flank in the tool of the present invention is
markedly observed especially in the interrupted cutting, a similar
effect is also obtained in continuous cutting.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a cross-sectional view of a surface-covered CBN
sintered body tool according to the present invention.
[0018] FIG. 2 is a perspective view of a tool material used in the
tool of the present invention.
[0019] FIG. 3A shows a step of preparing the tool material in
manufacturing of the surface-covered CBN sintered body tool of the
present invention.
[0020] FIG. 3B shows a step of forming a surface covering film in
manufacturing of the surface-covered CBN sintered body tool of the
present invention.
[0021] FIG. 3C shows a step of forming a nega-land in manufacturing
of the surface-covered CBN sintered body tool of the present
invention.
DESCRIPTION OF THE REFERENCE CHARACTERS
[0022] 1 surface-covered CBN sintered body tool; 2 base material; 3
surface covering film; 4 nega-land; 5 flank; 6 base; 7 notch
portion; 40 tool material; and W width of nega-land.
BEST MODES FOR CARRYING OUT THE INVENTION
[0023] Embodiments of the present invention will now be described
in the following.
[0024] FIG. 1 is a schematic cross-sectional view of a
surface-covered CBN sintered body tool 1 as a preferred example of
the present invention. Surface-covered CBN sintered body tool 1 of
the present invention includes a base material 2 formed with a CBN
sintered body and a surface covering film 3 covering a surface of
base material 2, and has a basic construction in which a nega-land
4 exposing the CBN sintered body in at least a portion thereof and
a flank 5 having surface covering film 3 are formed.
[0025] Surface-covered CBN sintered body tool 1 of the present
invention may be constructed such that base material 2 is attached
to a base 6 to use base material 2 as a cutting edge portion, or
may be formed with base material 2 in whole. When base material 2
is attached to base 6, a resulting structure may be of a one-layer
type in which only base material 2 is attached, or may be of a
two-layer type in which base material 2 and a cemented carbide are
attached. FIG. 1 exemplarily shows the one-layer type
surface-covered CBN sintered body tool 1 formed by attaching merely
base material 2 to base 6.
[0026] Base 6 is formed with a cemented carbide such as a WC--Co
alloy. A shape of base 6 is generally selected as appropriate with
a tool model number without specific limitation. In the example
shown in FIG. 1, the base has a tabular shape having a quadrate
cross section and a corner thereof is notched to form a shape
allowing attachment of base material 2 (in FIG. 1, it is notched in
a shape of a triangular prism having a base surface of a right
triangle) to form a notch portion 7.
[0027] Base material 2 in the present invention can be realized in
a conventionally known appropriate shape such as a triangular prism
or a quadrangular prism, which shape is not specifically limited.
FIG. 1 shows an example in which base material 2 is formed in a
triangular prism shape having a base surface of a right triangle
and is attached to notch portion 7 of base 6 described above.
[0028] As the CBN sintered body forming base material 2 in the
present invention, a sintered body including 30-90 volume % of CBN
powder and a remaining portion of a bonding material is preferably
used. The bonding material of the remaining portion preferably
includes at least one substance selected from the group consisting
of nitrides, carbides, borides, and oxides of elements of 4a, 5a
and 6a groups of the periodic system and solid solutions thereof,
an aluminum compound and an unavoidable impurity. The aluminum
compound described here is, for example, an oxide, a boride or a
nitride of aluminum. Though various CBN sintered bodies other than
that described above are also known, the above-described base
material is suitable for cutting quenched steel.
[0029] Base material 2 in the present invention has a surface on
which surface covering film 3 is formed such that the CBN sintered
body is exposed in a portion thereof. Herein, a CBN particle in the
CBN sintered body exposed preferably contains at least one of Ti,
Cr, Zr, V, and Ar at a depth of at least 0.05 .mu.m from a surface
of the CBN particle with a content of at most an amount of the
unavoidable impurity. The "unavoidable impurity" means an impurity
remaining in a manufacturing process of the CBN particle as raw
material powder, and an amount thereof is at most 0.1 weight %.
That is, the content of the element of "at most an amount of the
unavoidable impurity" means that a composition equivalent to that
of an original CBN particle is maintained. When at least two of Ti,
Cr, Zr, V, and Ar are included at a depth of at most 0.05 .mu.m
from a surface of the CBN sintered body, a total amount thereof is
at most the amount of the unavoidable impurity. It is to be noted
that, the element defined here is not Ti or Zr included as a
bonding phase of the CBN sintered body, but the element included in
the CBN particle itself, which is a hard phase of the CBN sintered
body.
[0030] The inventors have examined various causes of chipping and
have found the following fact. When the surface covering film is
formed with a PVD method on the CBN sintered body as the base
material, cleaning of the base material such as ion bombardment is
generally performed to increase adhesion between the surface
covering film and the base material to improve a cutting property.
As a result of detailed analysis and experiments as to the
surface-covered CBN sintered body tool, however, the inventors have
found a detrimental effect of the cleaning. That is, when the ion
bombardment is performed, for example, an affected layer is formed
in a surface layer portion of the CBN sintered body with
implantation of a metal ion such as Ti or Cr or an Ar ion used in
this process into the base material. It turned out that the
affected layer became an origin of chipping or the like even when a
thin surface covering film was formed. On the other hand, in a tool
having the nega-land but not having the surface covering film,
though cracking or chipping does not frequently occur on a
nega-land surface, it appeared that wear of the flank is
substantially advanced.
[0031] Each element Ti, Cr, Zr, V, or Ar is used in the ion
bombardment and, in the base material subjected to this process,
the element usually exists in the CBN particle located in the
surface layer portion (a portion of a depth of at most 5 .mu.m from
the surface) of the CBN sintered body in an amount larger than the
amount of the unavoidable impurity to form the affected layer. In
the present invention, the CBN particle in the exposed CBN sintered
body preferably contains at least one of Ti, Cr, Zr, V, and Ar at a
depth of at least 0.05 .mu.m from a surface of the CBN particle
with a content of at most the amount of the unavoidable impurity so
that the affected layer is substantially not formed. With this, the
chipping or defect originating from the affected layer can be
suppressed to attain a longer life. The wording "substantially not
formed" indicates that, even when at least one of Ti, Cr, Zr, V,
and Ar is contained at a depth of at least 0.05 .mu.m from the
surface of the CBN particle, a content thereof is at most the
amount of the unavoidable impurity and the chipping resulting from
advanced cracking originating from the affected layer does not
occur. Whether the content of at least one of Ti, Cr, Zr, V, and Ar
at a depth of at least 0.05 .mu.m from the surface of the CBN
particle is at most the amount of the unavoidable impurity or not
can be checked by an analysis using, for example, an EDS (Energy
Dispersive Spectrometer).
[0032] Though surface covering film 3 formed on base material 2 in
the present invention is not specifically limited and can be formed
with any conventionally known appropriate material to form a hard
film highly resistant to wear, peeling and chipping, since the
surface-covered CBN sintered body tool suitable for cutting of
quenched steel can be realized, the surface covering film
preferably includes a nitride or a carbonitride of a compound
including at least one element selected from the group consisting
of Ti, Cr, Zr, and V and at least one element selected from the
group consisting of Al, Si and B, or a nitride or a carbonitride of
Ti.
[0033] As "a nitride or a carbonitride of a compound including at
least one element selected from the group consisting of Ti, Cr, Zr,
and V and at least one element selected from the group consisting
of Al, Si and B", TiAlN, TiSiAlCN, VZrAlN, CrAlN, CrAlCN, CrCN,
CrBN, or the like can be specifically listed. In addition, "a
nitride or a carbonitride of Ti" indicates TiN or TiCN. Among
these, TiAlN, TiSiAlCN, CrAlCN, or TiCN, which is highly resistant
to wear, is preferred.
[0034] Whether "a nitride or a carbonitride of a compound including
at least one element selected from the group consisting of Ti, Cr,
Zr, and V and at least one element selected from the group
consisting of Al, Si and B" or "a nitride or a carbonitride of Ti"
is included in surface covering film 3 in the surface-covered CBN
sintered body tool of the present invention or not can be checked
by an analysis using, for example, an XRD (X-Ray
Diffractometer).
[0035] Though a thickness of surface covering film 3 in the present
invention is not specifically limited, it is preferably 0.1-5 .mu.m
and, more preferably, 0.5-2 .mu.m. It is because, a sufficient
effect of forming surface covering film 3 may not be obtained with
the thickness of surface covering film 3 less than 0.1 .mu.m, while
chipping may occur in surface covering film 3 during formation of
nega-land 4 when the thickness of surface covering film 3 is larger
than 5 .mu.m.
[0036] Base material 2 in the present invention has a corner
beveled to form nega-land 4. One of important points of the present
invention is that nega-land 4 has a construction to expose the CBN
sintered body, which is base material 2, in at least a portion
thereof. With this, the surface-covered CBN sintered body tool can
be attained which avoids cracking of the surface covering film of
the nega-land which occurs in a conventional tool and suppresses
chipping, and has high defect resistance and wear resistance. The
surface-covered CBN sintered body tool as such can be suitably used
particularly for a purpose in which defect resistance of the tool
is required, such as interrupted cutting of quenched steel.
[0037] Though nega-land 4 in the present invention may expose the
CBN sintered body, which is base material 2, in at least a portion
thereof, in a preferred example, the CBN sintered body is exposed
in a whole portion thereof. It is advantageous to expose the CBN
sintered body in the whole portion of nega-land 4 because
generation of cracks in the nega-land can be suppressed in various
cutting conditions, and it is also advantageous in terms of a
manufacturing cost.
[0038] In addition, nega-land 4 may be realized in the present
invention so as to expose the CBN sintered body in at least a
portion associated with a cutting cross section. Since a portion of
nega-land 4 other than that associated with the cutting cross
section is not directly involved in cutting, surface covering film
3 may be formed thereon. The "cutting cross section" described here
indicates a cross-sectional shape of a portion of a tool which
contacts with a work material, which shape is determined with a
shape of the tool as well as a depth of cut and a feed rate.
[0039] Nega-land 4 in the surface-covered CBN sintered body tool of
the present invention has a width W of preferably 0.05-0.2 mm and,
more preferably, 0.1-0.15 mm. When width W of nega-land 4 is less
than 0.05 mm, the cutting cross section extends beyond a nega-land
portion in many situations, though it depends on a cutting
condition, and thus a sufficient effect of the present invention
may not be obtained. When width W is larger than 0.2 mm, on the
other hand, a volume of removal for forming the nega-land is
increased and thus the manufacturing cost may be increased. It is
to be noted that, width W of nega-land 4 represents, in a cross
section shown in FIG. 1, a projected length on a face 1 of a
distance from an edge 10 of intersection of an inclined surface of
nega-land 4 and flank 5 to an edge 12 of intersection of the
inclined surface of nega-land 4 and face 1.
[0040] In the present invention, width W of nega-land 4 is also
closely related to a cutting condition. In turning, for example, a
feed rate per one rotation is preferably made smaller than width W
of nega-land 4. A work material strikes nega-land 4 of the tool,
and a chip generated curls on face 1 and is removed. In the
surface-covered CBN sintered body tool of the present invention,
since surface covering film 3 is not formed on nega-land 4 on which
the work material strikes as described above, chipping due to
cracking does not occur and stable long-term cutting is
enabled.
[0041] In the surface-covered CBN sintered body tool of the present
invention, surface roughness of the nega-land portion exposing the
CBN sintered body also relates to a cutting property. Arithmetic
mean surface roughness Ra of the nega-land portion exposing the CBN
sintered body is preferably expressed as
0.3.ltoreq.Ra(min)/Ra(max).ltoreq.0.8, where Ra(min) represents
surface roughness in a direction parallel to a grinding direction
of a grinder and Ra(max) represents surface roughness in a
direction perpendicular to the grinding direction of the grinder.
It is to be noted that, the aforementioned arithmetic mean surface
roughness Ra is that of JIS. Ra(min)/Ra(max) is dependent on a
particle size of the grinder used to grind the nega-land.
Ra(min)/Ra(max) tends to decrease when the particle size becomes
larger and increase when it becomes smaller. When honing is
performed on the nega-land surface using a rotating brush and
diamond grains, for example, since minute abrasive lines are
randomly arranged, Ra(min)/Ra(max) becomes approximately 1. When
Ra(min)/Ra(max) is less than 0.3, projections and depressions of
the abrasive lines become excessively large, which may become
origin of chipping. Since high residual stress of compression is
applied within a range of 0.3.ltoreq.Ra(min)/Ra(max).ltoreq.0.8,
propagation of a crack is suppressed with high effectiveness. When
Ra(min)/Ra(max) is larger than 0.8, residual stress of tensility is
applied and therefore the crack may be easily propagated.
[0042] Another important point in surface-covered CBN sintered body
tool 1 of the present invention is that flank 5 has surface
covering film 3. That is, since the work material does not
initially strike the flank at biting of an edge portion during the
interrupted cutting, a crack is not easily generated on the flank
even when the surface covering film is formed thereon, and wear of
the flank is suppressed with the surface covering film without
decreasing life of the tool, which can attain a long-life tool. It
is to be noted that, though a phenomenon in which the crack is not
easily generated on the surface covering film of the flank in the
tool of the present invention is markedly observed especially in
the interrupted cutting, a similar effect is also obtained in
continuous cutting.
[0043] The present invention also provides a method of
manufacturing the surface-covered CBN sintered body tool of the
present invention as described above. FIG. 2 is a perspective view
schematically showing a tool material 40 used in the method of the
present invention. FIGS. 3A-3C are cross-sectional views of
successive steps of the method of the present invention. It is to
be noted that, FIG. 3A is a cross-sectional view taken along the
section line III-III in FIG. 2. The method of manufacturing the
surface-covered CBN sintered body tool according to the present
invention includes the step of forming a surface covering film with
a PVD method on a surface of a tool material having a cutting edge
portion of a CBN sintered body, which surface covering film
includes a nitride or a carbonitride of a compound including at
least one element selected from the group consisting of Ti, Cr, Zr,
and V and at least one element selected from the group consisting
of Al, Si and B, or a nitride or a carbonitride of Ti, and the step
of forming a nega-land to expose the CBN sintered body in at least
a portion thereof. The method of the present invention will now be
described in a step-by-step manner.
[0044] In the method of the present invention, first, tool material
40 is prepared (FIG. 3A). One type of tool material 40 (FIG. 2) is
formed by attaching base material 2 formed with the CBN sintered
body with brazing, for example, to notch portion 7 formed in
advance on base 6 formed with a cemented carbide, while another
type is formed with the CBN sintered body in whole. The type formed
by attaching base material 2 to base 6 is further divided into a
one-layer type in which base material 2 is formed with the CBN
sintered body alone, and a two-layer type including two layers of
the CBN sintered body and the cemented carbide. Any of the
aforementioned types can be used as tool material 40 in the present
invention. FIGS. 2 and 3 show tool material 40 into which base
material 2 formed with one layer of the CBN sintered body is
integrated with brazing in a pair of diagonal positions of base 6
made of a cemented carbide.
[0045] Then, surface covering film 3 is formed on a surface of tool
material 40 with the PVD method. As shown in FIG. 3B, surface
covering film 3 is formed on a whole surface of tool material 40
including a surface of base material 2 besides a surface of base 6.
Naturally, surface covering film 3 is also formed on flank 5 and
face 1.
[0046] The method of the present invention is characterized in
that, surface covering film 3 formed includes a nitride or a
carbonitride of a compound including at least one element selected
from the group consisting of Ti, Cr, Zr, and V and at least one
element selected from the group consisting of Al, Si and B, or a
nitride or a carbonitride of Ti. Details of the material for
forming surface covering film 3 are as described above.
[0047] Then, as shown in FIG. 3C, a corner of base material 2 as a
cutting edge portion in tool material 40 is processed to form an
inclined surface to form nega-land 4. This processing is performed
with a strength to allow partial removal of the CBN sintered body,
and is not a grinding process only to grind the surface covering
film. The tool of the present invention can be manufactured with an
economical speed by grinding with a diamond grinder or the like.
With this processing for the nega-land, edges 10 and 12 are formed
on tool material 40 in respective portions of intersection of flank
5 and nega-land 4 and intersection of nega-land 4 and face 1. As a
result, the surface-covered CBN sintered body tool can be obtained
in which at least a portion of nega-land 4 (a whole portion of
nega-land 4 in a situation shown in FIG. 3C) does not have surface
covering film 3 and exposes the CBN sintered body which is base
material 2, while surface covering film 3 is formed on flank 5 and
face 1.
[0048] For exposing the CBN sintered body in at least a portion of
nega-land 4, one may form the nega-land in the tool material
beforehand, mask the nega-land surface to avoid covering of the
nega-land surface, and then form the surface covering film. It is,
however, difficult to industrially mask a tool having a
three-dimensional complex shape with accurately distinguishing the
nega-land surface from the flank. In the method of the present
invention, the CBN sintered body is exposed in at least a portion
of nega-land 4 by forming surface covering film 3 on the whole tool
material 40 and then forming the nega-land. With this, a reliable,
accurate and economically advantageous method of manufacturing a
surface-covered CBN sintered body tool can be provided. The method
of the present invention also has an advantage that the affected
layer can be easily removed.
[0049] The method of manufacturing the surface-covered CBN sintered
body tool of the present invention preferably further includes the
step of honing at least a portion of a periphery of the nega-land
after the step of forming the nega-land. The honing step is
performed in order to smoothly link portions of intersection of the
nega-land and flank and intersection of the nega-land and face with
curves. Smooth linkage of such portions of intersection of these
surfaces can suppress occurrence of chipping due to intermittent
shock and hard particles during cutting. That is, in the method of
the present invention, only the periphery of the nega-land (edges
10 and 12 and proximal regions thereof) is further honed for
rounding as shown in FIG. 1 to enable suppression of chipping of
the surface covering film in the periphery.
[0050] More specifically, the honing step can be performed by
applying a rotating brush and diamond grains or the like around the
edges. With this, surface covering film 3 is mainly removed from
the periphery of the nega-land, while a portion of base material 2
is hardly removed.
[0051] Though the present invention is described in more detail in
the following with experimental examples, the present invention is
not limited thereto.
Experimental Example 1
[0052] Bonding material powder was obtained by mixing TiN and
aluminum in a ratio of 80:20 by weight using a pot made of a
cemented carbide and a ball. Then, the bonding material was mixed
with CBN powder having an average particle diameter of 1 .mu.m in a
ratio of 35:65 by volume, and the resulting mixture was packed into
a container made of Mo and was sintered in a pressure of 55 kb (5.6
GPa) at a temperature of 1450.degree. C. for 20 minutes. When
analyzed with an XRD (X-Ray Diffractometer), a sintered body
included aluminum compounds which were probably aluminum nitride,
aluminum oxide and aluminum boride. The sintered body was cut with
electric discharge machining or a diamond grinder for use as a tip
for a cutting tool. In this experimental example, a tool material
for a completed product of model No. SNGN120408 was produced.
[0053] Next, a method of forming the surface covering film is
described. In this experimental example, the surface covering film
was formed on the tool material by ion plating with vacuum arc
discharge. A target was made in the same composition as that of
metal components of the covering film, and Ti-50 at % Al, Cr-50 at
% Al, V-45 at % Al-10 at % Zr, Ti and Cr-5 at % B, Ti-45 at % Al-10
at % Si, or the like was used. Herein, "at %" represents atomic %.
A film formation device was first depressurized to a degree of
vacuum of 1.33.times.10.sup.-3 Pa (10.sup.-5 torr), and an Ar gas
was introduced to perform cleaning with ion bombardment using an Ar
ion and a metal ion forming the target with application of a bias
voltage of -1000 V to the tip in an atmosphere of 1.33 Pa
(10.sup.-2 torr).
[0054] Then, the tip was heated to 500.degree. C., the Ar gas was
exhausted and then an N.sub.2 gas was introduced as a reaction gas,
and a voltage of -120 V was applied to the tip for covering with
evaporation and ionization of the target with an arc current of 100
A by the vacuum arc discharge. A pressure was set to 1.33 Pa
(10.sup.-2 torr) and a thickness of the film was controlled with a
covering time. After a surface of the tool material was covered as
such, the nega-land was formed to produce a sample.
[0055] Table 1 shows a manufacturing condition and a film
characteristic for each sample. When the covering film included C
(carbon) in addition to N (nitrogen) as in sample No. 3 in Table 1,
CH.sub.4 in addition to N.sub.2 was used as the reaction gas.
Ratios of N and C in the covering film can be adjusted by
controlling ratios of flow rates of N.sub.2 and CH.sub.4. A crystal
system of the covering film was a cubic crystal structure.
TABLE-US-00001 TABLE 1 Film Thickness (.mu.m) Y Sample Processing
Film X (Nega- No. Steps Material (Flank) land) Y/X 1 Example
C.fwdarw.N.fwdarw.H TiAlN 1.0 0 0 2 Example C.fwdarw.N TiAlN 1.2 0
0 3 Example C.fwdarw.N.fwdarw.H TiCN 1.0 0 0 4 Example
C.fwdarw.N.fwdarw.H TiN 1.5 0 0 5 Example C.fwdarw.N TiN 1.4 0 0 6
Comparative N.fwdarw.H.fwdarw.C TiAlN 1.1 1.2 1.1 Example 7
Comparative N.fwdarw.C.fwdarw.H TiAlN 0.9 0.5 0.56 Example 8
Comparative N.fwdarw.C.fwdarw.H TiAlN 1.0 0.2 0.2 Example 9
Comparative N.fwdarw.H -- 0 0 0 Example 10 Example
N.fwdarw.C.fwdarw.N.fwdarw.H TiAlN 1.0 0 0 11 Example
C.fwdarw.N.fwdarw.H TiSiAlCN 1.0 0 0 12 Example C.fwdarw.N.fwdarw.H
CrAlCN 1.0 0 0 13 Example C.fwdarw.N.fwdarw.H VZrAlN 1.0 0 0 14
Example C.fwdarw.N.fwdarw.H CrBN 1.0 0 0 (In Table 1, characters C,
N and H in a column "Processing Steps" have the following meanings.
C: surface covering, N: nega-land formation, and H: honing.)
[0056] Processing steps of each sample will now be described
referring to Table 1. Sample Nos. 1, 3, 4, and 1-14, which are
examples, were honed after the nega-land formation. Each of samples
of comparative examples (sample Nos. 6-8) was similarly produced by
first forming the nega-land on the tool material and then
performing the steps of surface covering and honing, as shown in
Table 1. Sample No. 9 was produced by the nega-land formation and
honing without the surface covering. In each step of nega-land
formation, the nega-land having an angle of 25.degree. and a width
of 0.2 mm was formed by grinding. In this experimental example, the
nega-land was formed using a diamond grinder having a grain of a
particle size of 800 meshes.
[0057] In each of sample Nos. 1-5 and 10-14, which are examples,
the surface covering film on the nega-land was removed. For sample
No. 10, the nega-land having an angle of 25.degree. and a width of
0.19 mm was formed by grinding before the covering step, a TiAlN
film of 1.0 .mu.m was formed on the flank and the face, and then
the nega-land having an angle of 25.degree. and a width of 0.2 mm
was formed by grinding, which was followed by honing. For each of
sample Nos. 1-5 and 11-14, on the other hand, the nega-land having
the angle of 25.degree. and width of 0.2 mm was formed by grinding
after the covering step. Each of sample Nos. 1, 3, 4, and 6-14,
which was subjected to the honing step, had an arc-like honed shape
with a curvature of 0.02 mm. For each of sample Nos. 6-8 as
comparative examples, the nega-land having the angle of 25.degree.
and width of 0.2 mm was formed by grinding.
[0058] Table 1 also shows thicknesses of the surface covering film
measured on the flank and nega-land. The film thickness on the
nega-land was zero in each example of sample Nos. 1-5, 10-14 since
the nega-land was formed after the covering step. In each
comparative example of sample Nos. 6-8, the surface covering film
was also formed on the nega-land.
[0059] (Cutting Test 1)
[0060] Evaluation of each sample was made by cutting for 30 minutes
a work material having four U-shaped grooves in a longitudinal
direction with the tip described in Table 1. Results are shown in
Table 2. As the work material, SCR420H (JIS) of quenched steel
having a hardness adjusted to 58-62 HRC was used. A condition of a
cutting test was as follows.
[0061] Work material: SCR420H (a work material having four U-shaped
grooves in a longitudinal direction)
[0062] Cutting condition: Cutting speed V=120 mm/min. [0063] Feed
rate f=0.1 mm/rev. [0064] Depth of cut d=0.15 mm [0065] Wet,
Cutting time 30 min. [0066] Tool model No. SNGN120408
TABLE-US-00002 [0066] TABLE 2 Flank Surface Wear Roughness Sample
No. (mm) Rz (.mu.m) State of Damage Evaluation 1 Example 0.085 2.7
Normal Wear Outstanding 2 Example 0.078 4.5 0.01 mm Minute Good
Chipping 3 Example 0.081 3.2 Normal Wear Outstanding 4 Example
0.135 1.9 Normal Wear Outstanding 5 Example 0.129 3.8 0.01 mm
Minute Good Chipping 6 Comparative -- -- 0.5 mm Defect
Unsatisfactory Example in 6.2 min 7 Comparative -- -- 0.5 mm Defect
Unsatisfactory Example in 6.3 min 8 Comparative -- -- 0.6 mm Defect
Unsatisfactory Example in 8.2 min 9 Comparative 0.217 3.8 Large
Wear, Satisfactory Example 0.06 mm Chipping 10 Example 0.084 2.8
0.05 mm Minute Good Chipping 11 Example 0.075 3.0 Normal Wear
Outstanding 12 Example 0.074 3.1 Normal Wear Outstanding 13 Example
0.09 1.4 Normal Wear Outstanding 14 Example 0.095 1.2 Normal Wear
Outstanding
[0067] As shown in Table 2, each of sample Nos. 1-5 and 10-14,
which are examples, had a life of at least 30 minutes. Among these,
in each of sample Nos. 1, 3, 4 and 11-14, a state of damage of the
tool was normal wear since it was honed. As a result, it can be
said that processing of the work material with a small surface
roughness Rz and thus a good surface condition was enabled. For
sample No. 2 or 5 which was not honed, minute chipping was observed
and surface roughness Rz of the work material was larger than that
with a honed sample. Therefore, the honed sample can be considered
superior.
[0068] In sample Nos. 6-8, which were comparative examples formed
by the surface covering after the nega-land formation, defects were
produced after cutting times of 6.2, 6.3 and 8.2 minutes,
respectively. It can be seen from Table 1 that the smaller a value
Y/X is, the longer a time required to produce the defect becomes.
In sample No. 9 of the comparative example, wear became larger as
the cutting time extended and the chipping occurred after cutting
for 30 minutes. When the wear of the flank increases, a cutting
resistance increases and chipping easily occurs, which means that
the life of the sample is nearly ended.
[0069] Sample Nos. 1-5 and 11-14 of the examples could attain
longer life than sample No. 10 of the example though they had
similar shapes of edge portions and the surface covering films
similarly removed from the nega-lands. A surface of each nega-land
of the CBN sintered body base material after removal of the surface
covering film was analyzed with an EDS (Energy Dispersive
Spectrometer). As a result, while existence of the element used for
cleaning by ion bombardment such as Ti, Cr, Zr, V or Ar was
recognized in a central portion of a CBN particle of sample No. 10,
Ti, Cr, Zr, V or Ar was not detected in sample Nos. 1-5 and 11-14.
As a result of a detailed analysis of damaged portions of the edge
portions after cutting, it became obvious that, in each of sample
Nos. 1-5 and 11-14 which had a larger removal amount during
grinding as compared with sample No. 10, the affected layer
generated in an interface between the surface covering film and the
CBN sintered body could be completely removed, and therefore
generation of the crack to be an origin of the chipping or defect
could be suppressed.
[0070] Though the tools of sample Nos. 1-5 and 11-14 are superior
from a viewpoint of increased defect resistance, these tools
require large removal amounts, which increase costs of manual
formation of the nega-lands. When a method of forming the nega-land
as performed for sample No. 10 is employed, on the other hand,
since a first stage of the nega-land formation can be performed
with a commercially available automatic peripheral grinding
machine, the removal amount of manual formation of the nega-land
after the surface covering can be decreased, which is advantageous
in terms of the cost.
[0071] (Cutting Test 2)
[0072] Cutting tests were performed using the surface-covered CBN
sintered body tool of model No. SNGN120408 produced in example 1
and the like. A round bar of SCR420H was used as a work material. A
condition of continuous cutting was as follows. Results are shown
in Table 3.
[0073] Work material: SCR420H round bar (outside diameter
turned)
[0074] Cutting condition: Cutting speed V=150 mm/min. [0075] Feed
rate f=0.1 mm/rev. [0076] Depth of cut d=0.1 mm [0077] Dry, Cutting
time 50 min.
TABLE-US-00003 [0077] TABLE 3 Flank Surface Wear Roughness Sample
No. (mm) Rz (.mu.m) State of Damage Evaluation 1 Example 0.102 2.5
Normal Wear Outstanding 2 Example 0.095 3.9 Minute Chipping Good 3
Example 0.11 3 Normal Wear Outstanding 4 Example 0.21 1.8 Normal
Wear Outstanding 5 Example 0.195 2.9 Minute Chipping Good 6
Comparative 0.115 5.2 Minute Peeling Satisfactory Example 7
Comparative 0.12 4.9 Minute Peeling Satisfactory Example 8
Comparative 0.1 4.7 Minute Peeling Satisfactory Example 9
Comparative 0.253 5.7 Large Wear Unsatisfactory Example
[0078] Surface roughness Rz of the work material was smaller and a
fine finished surface could be obtained in the example as compared
with the comparative example. In particular, the honed sample had
the state of damage of normal wear and could attain a better
finished surface as compared with sample No. 2 or 5 which was not
honed. It is to be noted that, the "minute peeling" described in a
column of the state of damage in Table 3 means that the film in a
minute region came unstuck and the CBN sintered body was exposed.
In this situation, a step is formed in a cutting edge ridgeline
portion, which step is transferred to a surface of the work
material and thus the surface roughness of the work material is
deteriorated.
INDUSTRIAL APPLICABILITY
[0079] The surface-covered CBN sintered body tool of the present
invention has high wear resistance, a low possibility of chipping
and a long life. In addition, a desirable surface roughness of a
suitable work material could be obtained. Therefore, the
surface-covered CBN sintered body tool of the present invention can
be utilized for interrupted or continuous cutting of quenched steel
or the like.
* * * * *