U.S. patent application number 13/687039 was filed with the patent office on 2013-05-30 for saw blade and method for multiple sawing of rare earth magnet.
This patent application is currently assigned to SHIN-ETSU CHEMICAL CO., LTD.. The applicant listed for this patent is SHIN-ETSU CHEMICAL CO., LTD.. Invention is credited to Koji Sato, Yasunori Uraki.
Application Number | 20130137343 13/687039 |
Document ID | / |
Family ID | 47257626 |
Filed Date | 2013-05-30 |
United States Patent
Application |
20130137343 |
Kind Code |
A1 |
Sato; Koji ; et al. |
May 30, 2013 |
SAW BLADE AND METHOD FOR MULTIPLE SAWING OF RARE EARTH MAGNET
Abstract
A multiple blade assembly comprising a plurality of spaced apart
saw blades mounted on a rotating shaft is used for sawing a rare
earth magnet block into multiple pieces by rotating the plurality
of saw blades. The saw blade comprises a core in the form of a thin
doughnut disk and a peripheral cutting part on an outer peripheral
rim of the core. The cutting part is made of a composition
comprising an abrasive, a resin binder, and a lubricant.
Inventors: |
Sato; Koji; (Tokyo, JP)
; Uraki; Yasunori; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SHIN-ETSU CHEMICAL CO., LTD.; |
Tokyo |
|
JP |
|
|
Assignee: |
SHIN-ETSU CHEMICAL CO.,
LTD.
Tokyo
JP
|
Family ID: |
47257626 |
Appl. No.: |
13/687039 |
Filed: |
November 28, 2012 |
Current U.S.
Class: |
451/28 ;
451/541 |
Current CPC
Class: |
B24B 1/00 20130101; B24D
3/346 20130101; B28D 5/029 20130101; B24D 5/12 20130101 |
Class at
Publication: |
451/28 ;
451/541 |
International
Class: |
B24D 5/12 20060101
B24D005/12; B24B 1/00 20060101 B24B001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 28, 2011 |
JP |
2011-259157 |
Claims
1. In connection with a multiple blade assembly comprising a
plurality of saw blades coaxially mounted on a rotating shaft at
axially spaced apart positions, which is used for sawing a rare
earth magnet block into multiple pieces by rotating the plurality
of saw blades, the saw blade comprising a core in the form of a
thin disk or thin doughnut disk and a peripheral cutting part on an
outer peripheral rim of the core, the cutting part being made of a
composition comprising an abrasive, a resin binder, and a lubricant
for reducing the friction between the cutting part and the magnet
block during the sawing operation.
2. The saw blade of claim 1 wherein the lubricant is selected from
the group consisting of boron nitride, carbon, molybdenum
disulfide, tungsten disulfide, graphite fluoride, and
polytetrafluoroethylene, and mixtures thereof.
3. The saw blade of claim 1 wherein the lubricant is in particulate
form having a particle size in the range of 1 to 200 .mu.m.
4. The saw blade of claim 1 wherein the cutting part is made of a
composition comprising 10 to 40% by weight of diamond and/or CBN as
the abrasive, 20 to 60% by weight of a matrix selected from the
group consisting of SiC having a particle size of 1 to 100
SiO.sub.2 having a particle size of 1 to 100 .mu.m, Al.sub.2O.sub.3
having a particle size of 1 to 100 .mu.m, WC having a particle size
of 0.1 to 50 .mu.m, Fe, Ni and Cu having a particle size of 1 to
200 .mu.m, and mixtures thereof, 10 to 50% by weight of a
thermosetting resin as the binder, and 1 to 50% by weight of the
lubricant.
5. A method for sawing a rare earth magnet block into multiple
pieces, comprising the steps of providing a multiple blade assembly
comprising a plurality of saw blades coaxially mounted on a
rotating shaft at axially spaced apart positions, each saw blade
being as set forth in claim 1, and rotating the plurality of saw
blades.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This non-provisional application claims priority under 35
U.S.C. .sctn.119(a) on Patent Application No. 2011-259157 filed in
Japan on Nov. 28, 2011, the entire contents of which are hereby
incorporated by reference.
TECHNICAL FIELD
[0002] This invention generally relates to a method for sawing a
magnet block into multiple pieces. More particularly, it relates to
a saw blade for use in sawing a rare earth magnet block into
multiple pieces.
BACKGROUND ART
[0003] Systems for manufacturing commercial products of rare earth
magnet include a single part system wherein a part of substantially
the same shape as the product is produced at the stage of press
molding, and a multiple part system wherein once a large block is
molded, it is divided into a plurality of parts by machining. The
single part system includes press molding, sintering or heat
treating, and finishing steps. A molded part, a sintered or heat
treated part, and a finished part (or product) are substantially
identical in shape and size. Insofar as normal sintering is
performed, a sintered part of near net shape is obtained, and the
load of the finishing step is relatively low. However, when it is
desired to manufacture parts of small size or parts having a
reduced thickness in magnetization direction, the sequence of press
molding and sintering is difficult to form sintered parts of normal
shape, leading to a lowering of manufacturing yield, and at worst,
such parts cannot be formed.
[0004] In contrast, the multiple part system eliminates the
above-mentioned problems and allows press molding and sintering or
heat treating steps to be performed with high productivity and
versatility. It now becomes the mainstream of rare earth magnet
manufacture. In the multiple part system, a molded block and a
sintered or heat treated block are substantially identical in shape
and size, but the subsequent finishing step requires cutting or
sawing. It is the key for manufacture of finished parts how to saw
the block in the most efficient and least wasteful manner.
[0005] Tools for cutting rare earth magnet blocks include two
types, a diamond grinding wheel inner-diameter (ID) blade having
diamond grits bonded to an inner periphery of a thin
doughnut-shaped disk, and a diamond grinding wheel outer-diameter
(OD) blade having diamond grits bonded to an outer periphery of a
thin disk as a core. Nowadays the sawing technology using OD blades
becomes the mainstream, especially from the aspect of productivity.
The sawing technology using ID blades is low in productivity
because of a single blade cutting mode. In the case of OD blade,
multiple cutting is possible. FIG. 1 illustrates an exemplary
multiple blade assembly 1 comprising a plurality of saw blades 11
coaxially mounted on a rotating shaft (not shown) alternately with
spacers 12, each blade 11 comprising a core 11b in the form of a
thin doughnut disk and a cutting part or abrasive grain layer 11a
on an outer peripheral rim of the core 11b. This multiple blade
assembly 1 is capable of multiple sawing, that is, cutting a block
into a multiplicity of parts at a time.
[0006] For the manufacture of OD abrasive blades, diamond grains
are generally bonded by three typical binding systems including
resin bonding with resin binders, metal bonding with metal binders,
and electroplating. These abrasive blades are often used in sawing
of rare earth magnet blocks.
[0007] When sawing abrasive blades are used to machine a rare earth
magnet block of certain size into a multiplicity of parts, the
relationship of the cutting part (axial) width of the saw blade is
crucially correlated to the material yield of the workpiece (magnet
block). It is important to maximize a material yield and
productivity by using a cutting part with a minimal width,
machining at a high accuracy to minimize a machining allowance and
reduce chips, and increasing the number of parts available.
[0008] In order to form a cutting part with a minimal width (or
thinner cutting part) from the standpoint of material yield, the
abrasive wheel core must be thin. In the case of OD blade 11 shown
in FIG. 1, its core lib is usually made of steel materials from the
standpoints of material cost and mechanical strength. Of these
steel materials, alloy tool steels classified as SK, SKS, SKD, SKT,
and SKH according to the JIS standards are often used in commercial
practice. However, in an attempt to saw a hard material such as
rare earth magnet by a thin OD blade, the prior art core of alloy
tool steel is short in mechanical strength and becomes deformed or
bowed during sawing operation, losing dimensional accuracy.
[0009] One solution to this problem is a cutoff wheel for use with
rare earth magnet alloys comprising a core of cemented carbide to
which high hardness abrasive grains such as diamond and CBN are
bonded with a binding system such as resin bonding, metal bonding
or electroplating, as described in JP-A H10-175172. Use of cemented
carbide as the core material mitigates buckling deformation by
stresses during machining, ensuring that rare earth magnet is sawed
at a high accuracy. However, if a high frictional resistance is
exerted between the cutting part and the magnet during sawing of
the magnet, high accuracy machining is not expected. In particular,
if substantial friction occurs between the side surface of the
cutting part (not directly contributing to grinding operation) and
the magnet, the grinding resistance is enhanced. Then, even if the
cemented carbide core is used, chipping and/or bowing can occur,
adversely affecting the machined state.
[0010] One solution to the above problem is to add a lubricant such
as fatty acid to grinding fluid or coolant. However, since the
space between the saw blade and the workpiece or rare earth magnet
is extremely narrow, it is difficult to effectively supply the
coolant between the saw blade and the magnet.
CITATION LIST
[0011] Patent Document 1: JP-A H10-175172
DISCLOSURE OF INVENTION
[0012] An object of the invention is to provide a saw blade in the
form of a resinoid wheel, which is used in multiple sawing of a
rare earth magnet block into multiple pieces, which reduces the
sawing resistance between the saw blade and the magnet block, and
which ensures sawing at a high accuracy and high speed even if the
saw blade is thinner than the conventional blades. Another object
is to provide a method for sawing a rare earth magnet block into
multiple pieces.
[0013] The invention pertains to a multiple blade assembly
comprising a plurality of saw blades coaxially mounted on a
rotating shaft at axially spaced apart positions. The multiple
blade assembly is used for sawing a rare earth magnet block into
multiple pieces by rotating the plurality of saw blades. The saw
blade has a core in the form of a thin disk or thin doughnut disk
and a peripheral cutting part on an outer peripheral rim of the
core. The inventors have developed a saw blade in the form of a
resinoid wheel having a cutting part made of a composition
comprising a component or lubricant for reducing the friction
between the cutting part and the magnet block during the sawing
operation. When the magnet block is sawed by the saw blades, the
sawing operation experiences a reduced cutting resistance, and
achieves an equivalent yield and accuracy compared with the prior
art even if thinner saw blades are used.
[0014] The invention generally pertains to a multiple blade
assembly comprising a plurality of saw blades coaxially mounted on
a rotating shaft at axially spaced apart positions, which is used
for sawing a rare earth magnet block into multiple pieces by
rotating the plurality of saw blades. In one aspect, the invention
provides the saw blade comprising a core in the form of a thin disk
or thin doughnut disk and a peripheral cutting part on an outer
peripheral rim of the core, the cutting part being made of a
composition comprising an abrasive, a resin binder, and a lubricant
for reducing the friction between the cutting part and the magnet
block during the sawing operation.
[0015] In a preferred embodiment, the lubricant is selected from
the group consisting of boron nitride, carbon, molybdenum
disulfide, tungsten disulfide, graphite fluoride, and
polytetrafluoroethylene, and mixtures thereof. Also preferably, the
lubricant is in particulate form having a particle size in the
range of 1 to 200 .mu.m.
[0016] Typically, the cutting part is made of a composition
comprising 10 to 40% by weight of diamond and/or CBN as the
abrasive; 20 to 60% by weight of a matrix selected from the group
consisting of SiC having a particle size of 1 to 100 .mu.m,
SiO.sub.2 having a particle size of 1 to 100 .mu.m, Al.sub.2O.sub.3
having a particle size of 1 to 100 .mu.m, WC having a particle size
of 0.1 to 50 .mu.m, Fe, Ni and Cu having a particle size of 1 to
200 .mu.m, and mixtures thereof; 10 to 50% by weight of a
thermosetting resin as the binder; and 1 to 50% by weight of the
lubricant.
[0017] In another aspect, the invention provides a method for
sawing a rare earth magnet block into multiple pieces, comprising
the steps of providing a multiple blade assembly comprising a
plurality of the above-defined saw blades coaxially mounted on a
rotating shaft at axially spaced apart positions, and rotating the
plurality of saw blades.
ADVANTAGEOUS EFFECTS OF INVENTION
[0018] The saw blades in the form of a resinoid wheel are used in
multiple sawing of a rare earth magnet block into multiple pieces.
As compared with the prior art, the saw blade reduces the cutting
resistance, improves the sawing accuracy, and ensures sawing at a
high accuracy and high speed even if the saw blade is thinner than
the conventional blades. The blade is of great worth in the
industry.
BRIEF DESCRIPTION OF DRAWINGS
[0019] FIG. 1 illustrates a multiple blade assembly in one
embodiment of the invention, FIG. 1a being a perspective view and
FIG. 1b being a cross-sectional view.
[0020] FIG. 2 is an enlarged cross-sectional view of a peripheral
portion of the saw blade.
DESCRIPTION OF EMBODIMENTS
[0021] The term "axial" refers to the axis of a rotating shaft and
"radial" refers to a circular blade in an assembly. The width of
the cutting part corresponds to an axial size in this sense.
[0022] A multiple blade assembly is constructed by coaxially
mounting a plurality of saw blades on a rotating shaft at axially
spaced apart positions (as shown in FIG. 1). The multiple blade
assembly is operated by rotating the plurality of saw blades for
thereby sawing a rare earth magnet block into a multiplicity of
pieces at the same time. The saw blade 23 in the form of a resinoid
wheel according to the invention is shown in FIG. 2 as comprising a
core 21 in the form of a thin disk or thin doughnut disk and a
peripheral cutting part 22 on an outer peripheral rim of the core
21. The cutting part 22 is made of a composition comprising an
abrasive 24, a resin binder, and a lubricant for reducing the
friction between the cutting part and the workpiece (or magnet
block) during the sawing operation.
[0023] Examples of the lubricant used herein include boron nitride,
carbon (including graphite and amorphous carbon), molybdenum
disulfide, tungsten disulfide, graphite fluoride, and
polytetrafluoroethylene (PTFE), which may be used alone or in
admixture of two or more. Although the conventional sawing
operation is difficult to reduce the friction between the cutting
part side surface and the workpiece by providing a coolant supply
for lubrication, the inclusion of the lubricant within the cutting
part is effective for reducing the friction between the cutting
part side surface and the workpiece, thereby preventing the cutting
edge from axial runout during the sawing operation. This allows the
cutting part to transmit its grinding force only in a radial
direction and ensures high-accuracy sawing operation even with the
saw blade using a thin core with a low deflective strength.
[0024] If a smaller amount of the lubricant is used, the effect of
reducing friction on the side surface is reduced. A larger amount
of the lubricant used has the problem that since the lubricant
lacks the strength of a structural matrix, not only the strength of
the cutting part of the blade is reduced, but also the frictional
force of the grinding surface is reduced, resulting in a degraded
grinding rate. The lubricant should preferably be used in an amount
of 1 to 50% by weight of the composition of which the cutting part
is made. As to the preferred amount of each species (% by weight
based on the composition), boron nitride is 1 to 40% by weight,
carbon (including graphite and amorphous carbon) is 1 to 40% by
weight, molybdenum disulfide is 1 to 40% by weight, tungsten
disulfide is 5 to 50% by weight, graphite fluoride is 5 to 40% by
weight, and PTFE is 5 to 40% by weight. More preferably, boron
nitride is 5 to 30% by weight, carbon (including graphite and
amorphous carbon) is 5 to 30% by weight, molybdenum disulfide is 5
to 30% by weight, tungsten disulfide is 10 to 40% by weight,
graphite fluoride is 10 to 30% by weight, and PTFE is 10 to 30% by
weight. When a mixture of two or more lubricants is used, the total
amount should preferably be in the range of 1 to 50% by weight,
more preferably 5 to 40% by weight.
[0025] The lubricant is typically available in particulate form.
Since the cutting part has a width of 0.2 to 2 mm, a particle size
in excess of 0.2 mm (200 .mu.m) is inadequate. Too fine particles
have an increased volume, detracting from the strength of the
cutting part. The lubricant preferably has a particle size of 1 to
200 .mu.m, more preferably 10 to 150 .mu.m.
[0026] In addition to the lubricant, the composition of which the
cutting part is made contains abrasive grains, a resin binder, and
a structural matrix. Preferred examples of the matrix include SiC
having a particle size of 1 to 100 .mu.m, SiO.sub.2 having a
particle size of 1 to 100 .mu.m, Al.sub.2O.sub.3 having a particle
size of 1 to 100 .mu.m, WC having a particle size of 0.1 to 50
.mu.m, Fe, Ni and Cu having a particle size of 1 to 200 .mu.m,
which may be used alone or in admixture of two or more. The role of
the matrix is to increase the strength of the cutting part, prevent
the cutting part from deforming in a direction perpendicular to the
feed direction of the saw blade during the sawing operation,
prevent the cutting edge from axial runout during the sawing
operation, allows the saw blade to transmit its grinding force only
in a radial direction, and ensures high-accuracy sawing operation
even with the saw blade using a thin core with a low deflective
strength. The matrix is available in particulate form. Too fine
particles have an increased volume, failing to provide the cutting
part with strength. If the particle size is large, only one
particle is present per width of the cutting part, also leading to
a reduced strength. Thus the matrix preferably has a particle size
in the above range. More preferably, the particle size of SiC is 2
to 50 .mu.m, SiO.sub.2 is 2 to 50 .mu.m, Al.sub.2O.sub.3 is 2 to 50
.mu.m, WC is 1 to 30 .mu.m, and Fe, Ni and Cu is 10 to 150
.mu.m.
[0027] The matrix should preferably be used in an amount of 20 to
60% by weight, more preferably 25 to 50% by weight of the
composition. Outside the range, a smaller amount of the matrix may
be less effective whereas a larger amount may detract from the
strength of the cutting part.
[0028] The abrasive grains may be any well-known abrasives,
preferably diamond and CBN. The abrasive grains preferably have a
particle size of 10 to 200 .mu.m, more preferably 50 to 200 .mu.m.
A particle size in excess of 200 .mu.m may exceed the width of the
cutting part whereas a smaller particle size may interfere with
grinding efficiency, sawing speed, and productivity. The abrasive
should preferably be used in an amount of 20 to 60% by weight, more
preferably 20 to 40% by weight of the composition. Outside the
range, a smaller amount of the abrasive may lead to a lower
grinding rate whereas a larger amount may detract from the strength
of the cutting part.
[0029] The binder has a function of binding diamond or CBN, the
lubricant and the matrix together to high strength so that a
cutting part having a high stiffness despite thinness may be
formed. Thermosetting resins are preferred as the binder. Inter
alia, phenolic resins, formaldehyde resins and urea resins are more
preferred. Phenol formaldehyde resins obtained by condensation of
phenol and formaldehyde are most preferred since they have
excellent heat resistance and water resistance and can tightly bind
the abrasive and matrix. Melamine resins prepared from melamine and
formaldehyde are also favorable. The binder should preferably be
used in an amount of 10 to 50% by weight of the composition.
Outside the range, a smaller amount of the binder may be weak in
binding the other components whereas a larger amount of the binder
indicates smaller amounts of the other components, leading to
shortage of strength, grinding rate and lubrication.
[0030] The core supporting the cutting part is preferably made of
cemented carbide. Any of the cemented carbides described in Patent
Document 1 may be used.
[0031] The workpiece which is intended herein to saw is a rare
earth magnet block. The rare earth magnet as the workpiece is not
particularly limited. Suitable rare earth magnets include sintered
rare earth magnets of R--Fe--B systems wherein R is at least one
rare earth element inclusive of yttrium.
[0032] Suitable sintered rare earth magnets of R--Fe--B systems are
those magnets containing, in weight percent, 5 to 40% of R, 50 to
90% of Fe, and 0.2 to 8% of B, and optionally one or more additive
elements selected from C, Al, Si, Ti, V, Cr, Mn, Co, Ni, Cu, Zn,
Ga, Zr, Nb, Mo, Ag, Sn, Hf, Ta, and W, for the purpose of improving
magnetic properties and corrosion resistance. The amounts of
additive elements added are conventional, for example, up to 30 wt
% of Co, and up to 8 wt % of the other elements. The additive
elements, if added in extra amounts, rather adversely affect
magnetic properties.
[0033] Suitable sintered rare earth magnets of R--Fe--B systems may
be prepared, for example, by weighing source metal materials,
melting, casting into an alloy ingot, finely dividing the alloy
into particles with an average particle size of 1 to 20 .mu.m,
sintered R--Fe--B magnet powder, compacting the powder in a
magnetic field, sintering the compact at 1,000 to 1,200.degree. C.
for 0.5 to 5 hours, and heat treating at 400 to 1,000.degree.
C.
[0034] When the rare earth magnet block is sawed into a
multiplicity of pieces by the multiple blade assembly of saw
blades, any well-known procedures may be employed.
EXAMPLE
[0035] Examples and Comparative Examples are given below for
further illustrating the invention although the invention is not
limited thereto.
Example 1
[0036] OD blades were fabricated by providing a doughnut-shaped
disk core of cemented carbide (consisting of WC 90 wt %/Co 10 wt %)
having an outer diameter 120 mm, inner diameter 40 mm, and
thickness 0.3 mm, and heat pressing a composition to an outer
peripheral rim of the core to form a resinoid grinding wheel
section or cutting part. The composition contained 10 wt % of
graphite having a particle size of 5 to 30 .mu.m as the lubricant,
40 wt % of #800 SiC (GC powder) as the matrix, 25 wt % of a phenol
formaldehyde resin as the binder, and 25 wt % of synthetic diamond
grains having an average particle size of 150 .mu.m. Subsequent
finish work completed OD blades (or sawing abrasive blades). The
axial extension of the cutting part from the core was 0.05 mm on
each side, that is, the cutting part had a width of 0.4 mm (in the
thickness direction of the core). The radial extension or length of
the cutting part is 2.5 mm, that is, the blade had an outer
diameter of 125 mm.
[0037] Using the OD blades, a sawing test was carried out on a
workpiece which was a sintered Nd--Fe--B magnet block. A multiple
blade assembly was constructed as shown in FIG. 1 by coaxially
mounting 41 OD blades on a shaft at an axial spacing of 2.1 mm,
with spacers interposed therebetween. The spacers each had an outer
diameter 85 mm, inner diameter 40 mm, and thickness 2.1 mm. The
multiple blade assembly was designed so that the magnet block was
cut into magnet strips having a thickness of 2.0 mm.
[0038] Using the multiple blade assembly consisting of 41 OD blades
and 40 spacers alternately mounted on the shaft, the sintered
Nd--Fe--B magnet block was sawed. The sintered Nd--Fe--B magnet
block had a length 101 mm, width 30 mm and height 17 mm and had
been polished on all six surfaces at an accuracy of .+-.0.05 mm by
a vertical double-disk polishing tool. By the multiple blade
assembly, the magnet block was longitudinally divided into a
multiplicity of magnet strips of 2.0 mm thick. Specifically, one
magnet block was cut into 40 magnet strips.
[0039] The sawing operation was carried out while supplying 30
L/min of a grinding fluid or coolant from the feed nozzle, rotating
the OD blades at 7,000 rpm (circumferential speed of 46 m/sec), and
feeding the multiple blade assembly at a speed of 20 mm/min.
[0040] After magnet strips were cut using the OD blades constructed
as above, they were measured for thickness between the machined
surfaces at the center by a micrometer. The strips were rated
"passed" if the measured thickness was within a cut size tolerance
of 2.0.+-.0.05 mm. If the measured thickness was outside the
tolerance, the multiple blade assembly was tailored by adjusting
the thickness of spacers, so that the measured thickness might fall
within the tolerance. If the spacer adjustment was repeated more
than two times for the same OD blades, these OD blades were judged
as having lost stability and replaced by new OD blades. Under these
conditions, 1000 magnet blocks were sawed. The evaluation results
of the sawed state are shown in Table 1.
Comparative Example 1
[0041] A sintered rare earth magnet block was sawed by the same
procedure as in Example 1 except that the cutting part composition
was changed. In this way, 1000 magnet blocks were sawed, and the
sawed state was evaluated. The evaluation results are also shown in
Table 1.
[0042] The composition of the cutting part in Comparative Example 1
contained 45 wt % of #800 SiC (GC powder) as the matrix, 30 wt % of
the phenol formaldehyde resin as the binder, and 25 wt % of
synthetic diamond grains having an average particle size of 150
.mu.m.
TABLE-US-00001 TABLE 1 After sawing of After sawing of After sawing
of After sawing of After sawing of Number of 200 blocks 400 blocks
600 blocks 800 blocks 1000 blocks strips A B A B A B A B A B
Example 1 40 0 0 0 0 0 0 0 0 0 0 Comparative 40 10 0 16 2 25 7 39
18 69 27 Example 1 A: number of spacer adjustments B: number of OD
blade replacements
[0043] As seen from Table 1, the multiple sawing method of the
invention maintains consistent dimensional accuracy for products
over a long term despite the reduced blade thickness and is
successful in reducing the number of spacer adjustments and the
number of OD blade replacements. Then an increase in productivity
is attained.
Examples 2 to 10 and Comparative Example 2
[0044] OD blades were fabricated by providing a doughnut-shaped
disk core of cemented carbide (consisting of WC 90 wt %/Co 10 wt %)
having an outer diameter 95 mm, inner diameter 40 mm, and thickness
0.3 mm, and heat pressing a composition shown in Table 2 to an
outer peripheral rim of the core to form a cutting part. The axial
extension of the cutting part from the core was 0.025 mm on each
side, that is, the cutting part had a width of 0.35 mm (in the
thickness direction of the core). The radial extension or length of
the cutting part is 2.5 mm, that is, the blade had an outer
diameter of 100 mm.
[0045] Using the OD blades, a sawing test was carried out on a
workpiece which was a sintered Nd--Fe--B magnet block. A multiple
blade assembly was constructed as shown in FIG. 1 by coaxially
mounting 38 OD blades on a shaft at an axial spacing of 1.05 mm,
with spacers interposed therebetween. The spacers each had an outer
diameter 70 mm, inner diameter 40 mm, and thickness 1.05 mm. The
multiple blade assembly was designed so that the magnet block was
cut into magnet strips having a thickness of 1.0 mm.
[0046] The multiple blade assembly consisting of 38 OD blades and
37 spacers alternately mounted on the shaft was set relative to the
sintered Nd--Fe--B magnet block such that the lowermost end of the
blades was 2 mm below the bottom surface of the magnet block. The
sintered Nd--Fe--B magnet block had a length 50 mm, width 30 mm and
height 12 mm and had been polished on all six surfaces at an
accuracy of .+-.0.05 mm by a vertical double-disk polishing tool.
By the multiple blade assembly, the magnet block was longitudinally
divided into a multiplicity of magnet strips of 1.0 mm thick.
Specifically, one magnet block was cut into 37 magnet strips.
[0047] The sawing operation was carried out while supplying 30
L/min of a grinding fluid or coolant from the feed nozzle, rotating
the OD blades at 7,000 rpm (circumferential speed of 37 m/sec), and
feeding the multiple blade assembly at a speed of 20 mm/min.
[0048] Using each of the OD blades of Examples 2 to 10 and
Comparative Example 2, 1000 magnet blocks were sawed. The magnet
strips were measured for thickness between the machined surfaces at
the center by a micrometer. Provided that the cut size tolerance
was 1.0.+-.0.075 mm, a process capability index (Cpk) of measured
thickness was computed. The results are shown in Table 2.
TABLE-US-00002 TABLE 2 Comparative Example Example Composition (wt
%) 2 3 4 5 6 7 8 9 10 2 Lubricant BN, 10 .mu.m 5 5 Graphite, 10
.mu.m 3 7 Graphite, 100 .mu.m 3 3 Amorphous carbon, 30 .mu.m 3
Molybdenum disulfide, 50 .mu.m 5 5 10 Molybdenum disulfide, 150
.mu.m 7 Tungsten disulfide, 5 .mu.m 10 Graphite fluoride, 50 .mu.m
3 PTFE, 100 .mu.m 2 Matrix GC powder, 10 .mu.m 30 40 25 37 SiO2, 90
.mu.m 40 5 10 Al2O3, 80 .mu.m 10 5 WC, 1 .mu.m 5 10 35 15 Fe, 15
.mu.m 10 Ni, 10 .mu.m 10 Cu, 10 .mu.m 30 30 30 Abrasive Synthetic
diamond, 80 .mu.m 15 10 30 23 24 23 Synthetic diamond, 150 .mu.m 20
25 22 25 CBN, 100 .mu.m 25 Binder Phenolic resin 35 24 30 25 30 35
35 Melamine resin 30 31 35 Cpk 0.67 0.89 0.91 0.71 0.65 0.95 0.93
0.87 0.91 0.52
[0049] As seen from Table 2, the saw blades comprising the
lubricant ensures high-accuracy sawing operation even when they are
as thin as 0.35 mm. The number of cut strips is increased.
[0050] Japanese Patent Application No. 2011-259157 is incorporated
herein by reference.
[0051] Although some preferred embodiments have been described,
many modifications and variations may be made thereto in light of
the above teachings. It is therefore to be understood that the
invention may be practiced otherwise than as specifically described
without departing from the scope of the appended claims.
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