U.S. patent application number 13/733388 was filed with the patent office on 2013-07-11 for dressing and manufacture of outer blade cutting wheel.
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 Harukazu Maegawa, Masanobu Shimao, Takaharu Yamaguchi.
Application Number | 20130174493 13/733388 |
Document ID | / |
Family ID | 47721967 |
Filed Date | 2013-07-11 |
United States Patent
Application |
20130174493 |
Kind Code |
A1 |
Maegawa; Harukazu ; et
al. |
July 11, 2013 |
DRESSING AND MANUFACTURE OF OUTER BLADE CUTTING WHEEL
Abstract
An outer blade cutting wheel (1) comprising a base and a blade
section (11) of metal or alloy-bonded abrasive grains is dressed by
clamping the cutting wheel between a pair of circular jigs (2) such
that the blade section (11) projects beyond the jigs, immersing the
cutting wheel in an electropolishing liquid, positioning counter
electrodes (4, 5, 6) relative to the blade section, and effecting
electropolishing for thereby removing part of the metal or alloy
bond and chips received in chip pockets until abrasive grains are
exposed on the blade section surface.
Inventors: |
Maegawa; Harukazu;
(Echizen-shi, JP) ; Yamaguchi; Takaharu;
(Echizen-shi, JP) ; Shimao; Masanobu;
(Echizen-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Shin-Etsu Chemical Co., Ltd.; |
Tokyo |
|
JP |
|
|
Assignee: |
SHIN-ETSU CHEMICAL CO.,
LTD.
Tokyo
JP
|
Family ID: |
47721967 |
Appl. No.: |
13/733388 |
Filed: |
January 3, 2013 |
Current U.S.
Class: |
51/295 ; 205/110;
205/666 |
Current CPC
Class: |
B24B 53/001 20130101;
C23C 18/1603 20130101; C23C 18/1651 20130101; C25D 5/006 20130101;
B23H 9/00 20130101; B24D 3/00 20130101; C25D 3/12 20130101; C25D
5/10 20130101; C25D 17/06 20130101; C25F 7/00 20130101; C23C
18/1662 20130101; C23C 18/36 20130101; B24D 5/12 20130101; C25D
17/12 20130101; C25D 5/14 20130101; C25F 3/22 20130101; B23H 7/02
20130101; C25D 15/00 20130101; B24D 18/0018 20130101; C25D 5/02
20130101 |
Class at
Publication: |
51/295 ; 205/666;
205/110 |
International
Class: |
B24D 18/00 20060101
B24D018/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 6, 2012 |
JP |
2012-001250 |
Claims
1. A method for dressing an outer blade cutting wheel comprising a
base in the form of an annular thin disc of cemented carbide having
an outer periphery and a blade section formed on the outer
periphery of the base, the blade section being an abrasive layer
comprising abrasive grains and a metal or alloy for bonding the
grains to each other and to the base, said method comprising the
steps of: clamping the outer blade cutting wheel between a pair of
circular jigs to hold the cutting wheel such that the opposed
surfaces of the cutting wheel are covered over a predetermined
range with the jigs and the blade section projects beyond the outer
edge of the circular jigs, immersing the cutting wheel clamped
between the jigs in an electropolishing liquid in an
electropolishing tank, providing an electrode which is spaced apart
from and encloses the outer circumference of the blade section and
a pair of electrodes which are opposed to and spaced apart from the
side surfaces of the blade section, as counter electrodes, and
conducting electricity between the cutting wheel and the counter
electrodes for electrolytically dissolving away part of the metal
or alloy between abrasive grains and chips received in chip pockets
in the blade section surface until abrasive grains are partially
raised from the blade section surface.
2. The dressing method of claim 1 wherein the counter electrodes
include a cage electrode which is spaced apart from and encloses
the outer circumference of the blade section and a pair of annular
electrodes which are opposed to and spaced apart from the side
surfaces of the blade section.
3. The dressing method of claim 1 wherein the abrasive grains in
the blade section are diamond and/or CBN grains, and the metal or
alloy for bonding the grains to each other and to the base is
formed by electroplating or electroless plating.
4. The dressing method of claim 1 wherein of the metal or alloy for
bonding the grains to each other and to the base, the bonding metal
is selected from Ni and Cu, and the bonding alloy is selected from
the group consisting of Ni--Fe, Ni--Mn, Ni--P, Ni--Co and Ni--Sn
alloys.
5. The dressing method of claim 1 wherein the blade section further
comprises a metal or alloy infiltrated into voids between abrasive
grains or between abrasive grains and the base.
6. The dressing method of claim 5 wherein the infiltrating metal is
Sn and/or Pb, and the infiltrating alloy is selected from the group
consisting of Sn--Ag--Cu, Sn--Ag, Sn--Cu, Sn--Zn and Sn--Pb alloys
and mixtures thereof.
7. A method for manufacturing an outer blade cutting wheel
comprising a base in the form of an annular thin disc of cemented
carbide having an outer periphery and a blade section formed on the
outer periphery of the base, said method comprising the steps of:
effecting electroplating or electroless plating on the base having
abrasive grains retained on its outer periphery in a plating bath,
to deposit a metal or alloy for bonding the abrasive grains to each
other and to the base, for thereby forming an abrasive layer
composed of the abrasive grains and the metal or alloy, the
abrasive layer constituting the blade section, tailoring the
protrusion, thickness and outer diameter of the abrasive layer by
wire electrical discharge machining and/or a grinding wheel, and
dressing the cutting wheel by the method of claim 1, using the
plating bath in the electroplating or electroless plating step as
an electropolishing liquid, for thereby electrolytically dissolving
away part of the metal or alloy between abrasive grains and chips
received in chip pockets in the blade section surface until
abrasive grains are partially raised from the blade section
surface.
8. The method of claim 7 wherein the abrasive grains are diamond
and/or CBN grains.
9. The method of claim 7 wherein of the metal or alloy for bonding
the grains to each other and to the base, the bonding metal is
selected from Ni and Cu, and the bonding alloy is selected from the
group consisting of Ni--Fe, Ni--Mn, Ni--P, Ni--Co and Ni--Sn
alloys.
10. The method of claim 7, comprising, after the step of
electroplating or electroless plating to form an abrasive layer
composed of abrasive grains and the metal or alloy, the step of
effecting further electroplating or electroless plating to form a
plating cover for enhancing the bond strength between abrasive
grains and between abrasive grains and the base.
11. The method of claim 7, comprising, after the step of
electroplating or electroless plating to form an abrasive layer
composed of abrasive grains and the metal or alloy, the step of
infiltrating a molten metal and/or alloy into voids between
abrasive grains or between abrasive grains and the base and
solidifying the metal and/or alloy therein.
12. The method of claim 11 wherein the infiltrating metal is Sn
and/or Pb, and the infiltrating alloy is selected from the group
consisting of Sn--Ag--Cu, Sn--Ag, Sn--Cu, Sn--Zn and Sn--Pb alloys
and mixtures thereof.
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. 2012-001250 filed in
Japan on Jan. 6, 2012, the entire contents of which are hereby
incorporated by reference.
TECHNICAL FIELD
[0002] This invention relates to a method for dressing an
outer-diameter blade cutting wheel comprising a base in the form of
an annular thin disc of cemented carbide and a blade section formed
on the outer periphery of the base, the blade section being an
abrasive layer comprising abrasive grains and a metal or alloy bond
for bonding the grains to each other and to the base.
BACKGROUND ART
[0003] For cutting of rare earth permanent magnets (sintered
magnets), the sawing method using outer-diameter blade cutting
wheels is well known. By virtue of many advantages including an
inexpensive cutting wheel, an acceptable cutting allowance on use
of hard-metal blades, a high dimensional accuracy of workpieces, a
relatively high machining speed, and a mass scale of manufacture,
the outer blade cutting-off technique is widely employed in cutting
of rare earth sintered magnets.
[0004] Patent Documents 1 to 3 disclose outer blade cutting wheels
for use in cutting of rare earth permanent magnets. The known
cutting wheel comprises a cemented carbide base and a blade section
having diamond or CBN abrasive grains bonded to the outer periphery
of the base by metal or alloy plating, typically nickel
plating.
[0005] The outer blade cutting wheel is typically manufactured by
providing a base in the form of an annular thin disc of cemented
carbide, distributing diamond or CBN abrasive grains on the outer
periphery of the base, and electroplating or electroless plating a
metal or alloy to deposit a metal or alloy bond for bonding
abrasive grains together or to the base to form an abrasive layer
composed of abrasive grains and the metal or alloy bond. The
abrasive layer constitutes a blade section. After the blade section
is formed, the abrasive layer constituting the blade section is
shaped and dressed to expose abrasive grains outside. As the
cutting edge wears on use after the preparation, a dressing
treatment like that at the end of preparation is taken at an
appropriate time interval in order to restore the cutting edge.
[0006] The dressing treatment may be generally carried out by wire
electrical discharge machining (EDM), or by using a dresser in the
form of a grinding wheel of diamond, CBN, SiC or alumina grains,
and grinding the surface of the abrasive layer to remove clogging
chips or scrape the bonding material for thereby exposing new
abrasive grains.
[0007] Whether or not the dressing treatment is satisfactory
largely affects the cutting performance after preparation or after
restoration, for example, leaving cutting marks on the cut surface
or causing a difference in cutting accuracy. It is desired to have
a method for dressing an outer blade cutting wheel which is capable
of sufficient dressing to ensure that chips received in chip
pockets in the blade section are shed and part of the bonding
material is removed to expose new abrasive grains, for thereby
improving the performance of the outer blade cutting wheel.
CITATION LIST
[0008] Patent Document 1: JP-A H09-174441 [0009] Patent Document 2:
JP-A H10-175171 [0010] Patent Document 3: JP-A H10-175172 [0011]
Patent Document 4: JP-A S63-216627 [0012] Patent Document 5: JP-A
H05-005605
DISCLOSURE OF INVENTION
[0013] The invention pertains to an outer blade cutting wheel
comprising a base in the form of an annular thin disc of cemented
carbide and a blade section formed on an outer periphery of the
base, the blade section being an abrasive layer comprising abrasive
grains and a metal or alloy bond for bonding the grains to each
other and to the base. An object of the invention is to provide a
method for dressing the outer blade cutting wheel in a satisfactory
and efficient manner so that the cutting wheel as dressed is ready
for effective cutoff operation. Another object is to provide a
method for manufacturing such an outer blade cutting wheel using
the dressing method.
[0014] In conjunction with an outer blade cutting wheel comprising
a base in the form of an annular thin disc of cemented carbide and
a blade section formed on an outer periphery of the base, the blade
section being an abrasive layer comprising abrasive grains and a
metal or alloy bond for bonding the grains to each other and to the
base, the inventors have found that in dressing of the blade
section of the outer blade cutting wheel, if part of the bond and
chips received in chip pockets are dissolved away by
electropolishing, then abrasive grains are effectively exposed and
chip pockets are formed, achieving satisfactory truing.
[0015] Continuing further investigations on the efficient dressing
of the blade section by electropolishing, the inventors have found
that very efficient and consistent electropolishing is ensured by
clamping the outer blade cutting wheel between a pair of circular
jigs to hold the cutting wheel such that the opposed surfaces of
the cutting wheel are covered over a predetermined range with the
jigs and the blade section projects beyond the outer edge of the
circular jigs, immersing the cutting wheel clamped between the jigs
in an electropolishing liquid in an electropolishing tank,
providing an electrode which is spaced apart from and encloses the
outer circumference of the blade section and a pair of electrodes
which are opposed to and spaced apart from the side surfaces of the
blade section, as counter electrodes, and conducting electricity to
the cutting wheel via the circular jigs and the counter electrodes.
That is, efficient and satisfactory dressing operation is possible.
It has also been found that in case electroplating or electroless
plating is effected on the base having abrasive grains retained on
its outer periphery in a plating bath, to deposit a metal or alloy
bond for forming the blade section, the plating bath in the
electroplating or electroless plating step may be used as the
electropolishing liquid after the blade section is shaped or
tailored by wire electrical discharge machining (EDM) and/or a
grinding wheel.
[0016] Accordingly, in one aspect, the invention provides a method
for dressing an outer blade cutting wheel comprising a base in the
form of an annular thin disc of cemented carbide having an outer
periphery and a blade section formed on the outer periphery of the
base, the blade section being an abrasive layer comprising abrasive
grains and a metal or alloy for bonding the grains to each other
and to the base, the method comprising the steps of:
[0017] clamping the outer blade cutting wheel between a pair of
circular jigs to hold the cutting wheel such that the opposed
surfaces of the cutting wheel are covered over a predetermined
range with the jigs and the blade section projects beyond the outer
edge of the circular jigs,
[0018] immersing the cutting wheel clamped between the jigs in an
electropolishing liquid in an electropolishing tank,
[0019] providing an electrode which is spaced apart from and
encloses the outer circumference of the blade section and a pair of
electrodes which are opposed to and spaced apart from the side
surfaces of the blade section, as counter electrodes, and
[0020] conducting electricity between the cutting wheel and the
counter electrodes for electrolytically dissolving away part of the
metal or alloy between abrasive grains and chips received in chip
pockets in the blade section surface until abrasive grains are
partially raised from the blade section surface.
[0021] In a preferred embodiment, the counter electrodes include a
cage electrode which is spaced apart from and encloses the outer
circumference of the blade section and a pair of annular electrodes
which are opposed to and spaced apart from the side surfaces of the
blade section.
[0022] In a preferred embodiment, the abrasive grains in the blade
section are diamond and/or CBN grains, and the metal or alloy for
bonding the grains to each other and to the base is formed by
electroplating or electroless plating. In a preferred embodiment,
the bonding metal is selected from Ni and Cu, and the bonding alloy
is selected from Ni--Fe, Ni--Mn, Ni--P, Ni--Co and Ni--Sn
alloys.
[0023] In a preferred embodiment, the blade section further
comprises a metal or alloy infiltrated into voids between abrasive
grains or between abrasive grains and the base. More preferably,
the infiltrating metal is Sn and/or Pb, and the infiltrating alloy
is selected from Sn--Ag--Cu, Sn--Ag, Sn--Cu, Sn--Zn and Sn--Pb
alloys and mixtures thereof.
[0024] In another aspect, the invention provides a method for
manufacturing an outer blade cutting wheel comprising a base in the
form of an annular thin disc of cemented carbide having an outer
periphery and a blade section formed on the outer periphery of the
base, the method comprising the steps of:
[0025] effecting electroplating or electroless plating on the base
having abrasive grains retained on its outer periphery in a plating
bath, to deposit a metal or alloy for bonding the abrasive grains
to each other and to the base, for thereby forming an abrasive
layer composed of the abrasive grains and the metal or alloy, the
abrasive layer constituting the blade section,
[0026] tailoring the protrusion, thickness and outer diameter of
the abrasive layer by wire electrical discharge machining and/or a
grinding wheel, and
[0027] dressing the cutting wheel by the dressing method defined
above, using the plating bath in the electroplating or electroless
plating step as an electropolishing liquid, for thereby
electrolytically dissolving away part of the metal or alloy between
abrasive grains and chips received in chip pockets in the blade
section surface until abrasive grains are partially raised from the
blade section surface.
[0028] In a preferred embodiment, the abrasive grains are diamond
and/or CBN grains.
[0029] In a preferred embodiment, the bonding metal is selected
from Ni and Cu, and the bonding alloy is selected from Ni--Fe,
Ni--Mn, Ni--P, Ni--Co and Ni--Sn alloys.
[0030] The manufacturing method may comprise, after the step of
electroplating or electroless plating to form an abrasive layer
composed of abrasive grains and the metal or alloy, the step of
effecting further electroplating or electroless plating to form a
plating cover for enhancing the bond strength between abrasive
grains and between abrasive grains and the base; or the step of
infiltrating a molten metal and/or alloy into voids between
abrasive grains or between abrasive grains and the base and
solidifying the metal and/or alloy therein. Preferably the
infiltrating metal is Sn and/or Pb, and the infiltrating alloy is
selected from Sn--Ag--Cu, Sn--Ag, Sn--Cu, Sn--Zn and Sn--Pb alloys
and mixtures thereof.
ADVANTAGEOUS EFFECTS OF INVENTION
[0031] The inventive method for dressing an outer blade cutting
wheel comprising a cemented carbide base and a blade section
composed of abrasive grains and a metal or alloy bond on the outer
periphery of the base ensures efficient and satisfactory dressing
of the blade section. A high-performance outer blade cutting wheel
can be manufactured in an efficient and consistent manner.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 schematically illustrates exemplary circular jigs
used in the dressing method of the invention.
[0033] FIG. 2 schematically illustrates an outer blade cutting
wheel held between the jigs, FIG. 2A showing an overall assembly,
FIG. 2B showing an outer periphery portion in one situation, and
FIG. 2C showing an outer periphery portion in another
situation.
[0034] FIG. 3 is a schematic perspective view of an
electropolishing or plating tank used in the dressing or
manufacturing method.
[0035] FIG. 4 is a schematic perspective view of one exemplary cage
electrode used as the counter electrode (during electropolishing)
or anode (during plating) in the dressing or manufacturing
method.
[0036] FIG. 5 is a schematic perspective view of a pair of annular
electrodes used as the counter electrode in the dressing
method.
[0037] FIG. 6 is a schematic enlarged view showing the blade
section of the cutting wheel relative to the counter electrodes in
the dressing method.
[0038] FIG. 7 is a micrograph under optical stereomicroscope,
showing the side surface of a blade section of an outer blade
cutting wheel in Example 1.
[0039] FIG. 8 is a micrograph under optical stereomicroscope,
showing the side surface of a blade section of an outer blade
cutting wheel in Comparative Example 1.
[0040] FIG. 9 is a micrograph showing the surface of a rare earth
permanent magnet piece cut by the outer blade cutting wheel, FIGS.
9A and 9B corresponding to Examples 1 and 2, respectively.
[0041] FIG. 10 is a micrograph showing the surface of a rare earth
permanent magnet piece cut by the outer blade cutting wheel, FIGS.
10A and 10B corresponding to Comparative Examples 1 and 2,
respectively.
[0042] FIG. 11 is a graph comparing the dimensional accuracy of
rare earth permanent magnet pieces cut by the outer blade cutting
wheels of Examples 1, 2 and Comparative Examples 1, 2.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0043] It is noted that since the disc has a center and an outer
circumference, the terms "radial" and "axial" are used relative to
the center of the disc. And so, the thickness is an axial
dimension, and the height is a radial dimension. Likewise the term
"outer" or the like is used relative to the center of the disc.
[0044] As used herein, the term "electropolishing" refers to
electrolytic polishing.
[0045] The invention pertains to an outer blade cutting wheel
comprising a base in the form of an annular thin disc of cemented
carbide and a blade section formed on the outer periphery of the
base, the blade section being an abrasive layer comprising abrasive
grains and a metal or alloy for bonding the grains to each other
and to the base. One embodiment of the invention is a method for
dressing the blade section of the outer blade cutting wheel by
electropolishing. The outer blade cutting wheel is held by clamping
it between a pair of circular jigs and immersed in an
electropolishing liquid in an electropolishing tank, where
electropolishing is carried out.
[0046] The outer blade cutting wheel is held by clamping the
cutting wheel between a pair of circular jigs such that the opposed
surfaces of the cutting wheel are covered over a predetermined
range with the jigs and the blade section projects beyond the outer
edge of the circular jigs. FIG. 1 shows a pair of circular jigs 2,
2 for clamping an outer blade cutting wheel 1 therebetween.
[0047] In FIG. 1, circular jigs 2, 2 are shown as discs having a
screw insertion bore (not shown) at the center. The circular jigs 2
are made of a dielectric material including engineering plastics or
ceramics such as alumina and have an outer diameter smaller than
the outer diameter of the cutting wheel 1 to be dressed.
Retainer/electrode plates 21, 21 are mounted in central recesses of
the circular jigs 2, 2. The electrode plates 21, 21 are in
electrical contact with a conductive support or rod 22 via power
feed pieces 23, 23 so that electricity may be conducted from the
support 22 to the electrode plates 21, 21. It is noted that the
portions of these electricity conducting members which come in
contact with the electropolishing liquid in the electropolishing
tank are coated with a dielectric material such as silicone. A
washer 24 is interposed between the upper jig 2 and the support 22,
and another washer 24 is interposed between the lower jig 2 and an
end block 25.
[0048] The cutting wheel 1 is placed between the circular jigs 2
and 2 as shown in FIG. 1. A screw portion projecting from the
support 22 and a screw portion projecting from the end block 25 are
threadably engaged into internally threaded bores (not shown) in
power feed pieces 23, 23 for fastening the circular jigs 2, 2 via
the washers 24, 24 as shown in FIG. 2A. Then the circular jigs 2, 2
hold the cutting wheel 1 as clamped therebetween.
[0049] Since the retainer/electrode plates 21, 21 are in contact
with the base of the cutting wheel 1 under an appropriate pressure,
electricity may be conducted from the support 22 to the electrode
plates 21, 21 via the power feed pieces 23, 23 whereby electric
current may flow to the cutting wheel 1. Also, since the circular
jigs 2, 2 have a smaller outer diameter than the cutting wheel 1,
the opposed surfaces of the cutting wheel are covered over a
predetermined range with the jigs and the blade section 11 on the
outer periphery of the cutting wheel 1 projects beyond the outer
edge of the circular jigs 2, 2 as best shown in FIG. 2B. The
(radial) projection "p" of the blade section 11 beyond the jigs 2,
2 should preferably be set equal to or greater than the thickness
(or axial distance) of the blade section 11 to ensure that the
blade section 11 projects beyond the outer edge of circular jigs 2,
2.
[0050] The cutting wheel 1 clamped between the circular jigs 2, 2
is immersed in an electropolishing liquid in an electropolishing
tank. An electrode which is spaced apart from and encloses the
outer circumference of the blade section 11 and a pair of
electrodes which are opposed to and spaced apart from the side
surfaces of the blade section are provided as counter electrodes.
With this setting, electropolishing is carried out.
[0051] The electropolishing tank used herein may be similar to the
electroplating bath used in forming the blade section by
electroplating. One exemplary electropolishing tank is a box-shaped
tank 3 equipped with an electric heater 31 for heating the bath and
piping 32 for circulating the bath as shown in FIG. 3.
Alternatively, the electropolishing tank may be an electroless
plating bath used in forming the blade section by electroless
plating, in which the counter electrodes are disposed.
[0052] Also the electrode which encloses the outer circumference of
the blade section 11 at a certain spacing and serves as one counter
electrode may be similar to the anode used in electroplating the
blade section. One exemplary electrode is a cylindrical cage
electrode 4 consisting of two large and small cylindrical frames 41
and 42 which each consists of a pair of rings and several columns
connecting the rings and which are concentrically telescoped and
linked by ties, as shown in FIG. 4.
[0053] The pair of electrodes which are opposed to the side
surfaces of the blade section 11 at a certain spacing and which
also serve as counter electrodes may be, for example, annular
electrodes 5, 6 as shown in FIG. 5. A lower annular electrode 5 is
to be disposed below the cutting wheel 1 (near the bottom of the
electropolishing tank 3) and consists of an annular frame and an
annular metal mesh 51 disposed inside the annular frame. An upper
annular electrode 6 is to be disposed above the cutting wheel 1 and
consists of an annular frame and an annular metal mesh 61 disposed
inside the annular frame. Four upright suspenders 62 each having a
hook at the top are attached to the annular frame of the upper
electrode 6. The upper annular electrode 6 is positioned above the
cutting wheel 1, with the hooks of suspenders 62 engaged with the
upper periphery of the cage electrode 4.
[0054] These counter electrodes 4, 5, 6 are composed of frames and
meshes which are all formed of electroconductive metal material
such as titanium, austenite stainless steel or nickel. Of these,
titanium is most preferred for lightweight and corrosion
resistance.
[0055] The cutting wheel 1 held by the circular jigs 2, 2 is
received in the electropolishing tank 3, and the cage electrode 4
and annular electrodes 5, 6 are mounted in place. These members are
positioned in such relationship, as shown in FIG. 6, that the cage
electrode 4 encloses the circumference of the blade section 11 on
the outer periphery of the base 12 (or cutting wheel 1) at a
certain spacing, and the pair of annular electrodes 5, 6 are
opposed to the side surfaces of the blade section 11 at a certain
spacing. Electric current is conducted from support 22 to cutting
wheel 1 via power feed pieces 23 and electrode plates 21.
Electricity is also conducted to the cage electrode 4 and annular
electrodes 5, 6 as the counter electrode. Then the surface of blade
section 11 of cutting wheel 1 is electrolytically polished.
[0056] The electropolishing liquid used in electropolishing may be
selected from well-known electropolishing liquids, depending on the
metal or alloy bond in the blade section 11. Typically an
electropolishing liquid which readily dissolves away the metal or
alloy bond is used. Also electrolytic conditions may be determined
as appropriate in accordance with the type of bond and the degree
of dressing. In an example where a single metal such as by nickel
plating is used as the bond, an electropolishing liquid having the
same composition as the nickel plating bath used for that nickel
plating may be used. Specifically, a nickel plating bath containing
240 to 380 g/L of nickel sulfate, 40 to 90 g/L of nickel chloride,
and 40 to 60 g/L of boric acid or a nickel sulfamate plating bath
containing 450 to 650 g/L of nickel sulfamate, 5 to 15 g/L of
nickel chloride, and 30 to 40 g/L of boric acid may be used as the
electropolishing liquid. In the former example where the nickel
plating bath is used as the electropolishing liquid,
electropolishing may be effected at a current density of 1 to 10
A/dm.sup.2. In the latter example where the nickel sulfamate
plating bath is used, electropolishing may be effected at a current
density of 3 to 10 A/dm.sup.2.
[0057] Alternatively, an electroless nickel plating bath used in
nickel deposition by electroless plating may be used as the
electropolishing liquid. Specifically, an electroless nickel
plating bath containing 20 to 25 g/L of nickel sulfate, 20 to 25
g/L of sodium hypophosphite, 5 to 10 g/L of sodium acetate, and 5
to 10 g/L of sodium citrate may be used as the electropolishing
liquid. In this example, electropolishing may be effected at a
current density of 0.3 to 1.0 A/dm.sup.2.
[0058] As alluded to above, the outer blade cutting wheel subject
to the dressing method of the invention is one comprising a base in
the form of an annular thin disc of cemented carbide and a blade
section formed on the outer periphery of the base, the blade
section being an abrasive layer comprising abrasive grains and a
metal or alloy bond for bonding the grains to each other and to the
base.
[0059] The abrasive grains and the metal or alloy bond used herein
are not particularly limited. Examples of the abrasive grains
include diamond grains, cubic boron nitride (CBN) grains, alumina
grains, alumina based grains, SiC grains, and SiC based grains. Of
these, diamond grains and/or CBN grains are preferred. The bonding
metal or alloy is preferably a single metal or alloy to be
deposited by electroplating or electroless plating though not
limited thereto. More particularly, the metal is preferably
selected from Ni and Cu. The alloy is preferably selected from
Ni--Fe, Ni--Mn, Ni--P, Ni--Co and Ni--Sn alloys.
[0060] It is also acceptable that a metal or alloy infiltrates into
microscopic voids between abrasive grains or between abrasive
grains and the base. The infiltrating metal may be either one or
both of Sn and Pb. The infiltrating alloy may be selected from
Sn--Ag--Cu, Sn--Ag, Sn--Cu, Sn--Zn, and Sn--Pb alloys, for example,
or a mixture thereof.
[0061] The dressing method of the invention is, of course,
advantageously used in the dressing treatment of dressing a (worn)
outer blade cutting wheel with a blunt cutting edge to restore a
fresh cutting edge. Since the electroplating bath or electroless
plating bath used in forming the blade section can be used as the
electropolishing liquid, the dressing method of the invention may
also be advantageously used in the dressing step of a process of
manufacturing an outer blade cutting wheel by electroplating or
electroless plating to deposit a metal or alloy bond around
abrasive grains to form a blade section, tailoring the blade
section, and dressing the blade section.
[0062] Namely, another embodiment of the invention is a method for
manufacturing an outer blade cutting wheel comprising a base in the
form of an annular thin disc of cemented carbide having an outer
periphery and a blade section formed on the outer periphery of the
base, the method comprising the steps of effecting electroplating
or electroless plating on the base having abrasive grains retained
on its outer periphery in a plating bath, to deposit a metal or
alloy for bonding the abrasive grains to each other and to the
base, for thereby forming an abrasive layer composed of the
abrasive grains and the metal or alloy, the abrasive layer
constituting the blade section; tailoring the protrusion, thickness
and outer diameter of the abrasive layer by wire electrical
discharge machining and/or a grinding wheel; and dressing the
cutting wheel by the dressing method of one embodiment, using the
plating bath in the electroplating or electroless plating step as
an electropolishing liquid. As used herein the term "protrusion" of
the abrasive layer is a height of the abrasive layer as measured
from the base surface in an axial direction of the base.
[0063] When electroplating or electroless plating is effected to
deposit a metal or alloy on the base to form an abrasive layer
serving as the blade section, the same jigs as the circular jigs
used in the above dressing method may be used in the electroplating
or electroless plating. In this case, however, the outer diameter
of circular jigs 2, 2 is larger than the base 12, as shown in FIG.
2C, to define a space between outer peripheral portions of the jigs
2, 2, which is filled with abrasive grains. With abrasive grains
held in the space, plating is carried out whereby the plating metal
or alloy bonds abrasive grains together and to the base. The radial
distance "d" of the space for receiving abrasive grains may be
determined as appropriate, depending on the size of the blade
section 11 to be formed there. The metal or alloy to be deposited
by electroplating or electroless plating is as exemplified
above.
[0064] The means for holding abrasive grains in the space between
the outer peripheral portions of circular jigs 2, 2 may be magnetic
attraction, for example. Magnetic holding may be achieved by
previously coating abrasive grains with a magnetic material, and
attaching permanent magnets to circular jigs 2, 2, for thereby
holding the abrasive grains in the space by the magnetic attractive
force.
[0065] In carrying out electroplating, a plating bath similar to
the bath shown in FIG. 3 may be used. In the case of
electroplating, the cage electrode 4 is used as the anode rather
than the counter electrode, and a pair of annular electrodes 5, 6
are unnecessary. In the case of dressing by electropolishing, this
plating bath may be used as the electropolishing bath without a
substantial modification except that a pair of annular electrodes
5, 6 are positioned and used as the counter electrode along with
the cage electrode 4.
[0066] Once the abrasive layer composed of abrasive grains and the
metal or alloy bond is formed by electroplating or electroless
plating, additional electroplating or electroless plating may be
carried out to form a plating cover for enhancing the bond strength
between abrasive grains and between abrasive grains and the base.
This cover plating may be carried out in the same manner as the
previous electroplating or electroless plating. The only difference
is that the outer diameter of the circular jigs 2, 2 is smaller
than the cutting wheel so that the blade section 11 in the form of
the abrasive layer projects beyond the outer edge of the jigs 2, 2
as shown in FIG. 2B. Then cover plating is applied to the abrasive
layer.
[0067] Alternatively, once the abrasive layer composed of abrasive
grains and the metal or alloy bond is formed by electroplating or
electroless plating, a molten metal and/or alloy may be infiltrated
into voids between abrasive grains and between abrasive grains and
the base and solidified there. More particularly, in the outer
blade cutting wheel having the blade section formed by bonding
abrasive grains to the base via electroplating or electroless
plating, since the abrasive grains used have a certain particle
size, the abrasive grains are bonded such that contacts between
grains and between grains and the base are only local. Voids are
left between abrasive grains and between abrasive grains and the
base. The electroplating or electroless plating is impossible to
fully fill these voids with the plating metal or alloy. As a
result, the blade section still contains voids in communication
with its surface even after the plating. If such voids are filled
with a metal or alloy, then the bond strength is improved and
eventually a higher machining accuracy is available. The
infiltrating metal or alloy preferably has a melting point of up to
350.degree. C. while examples of the metal or alloy are the same as
mentioned above.
[0068] The metal or alloy may be infiltrated into the abrasive
layer or blade section, for example, by working the metal or alloy
into a wire with a diameter of 0.1 to 2.0 mm, preferably 0.8 to 1.5
mm, particles, or a thin-film ring of the same shape and size as
the blade section having a thickness of 0.05 to 1.5 mm, resting the
wire, particles or ring on the blade section, heating the blade
section on a heater such as a hot plate or in an oven to a
temperature above the melting point, holding the temperature for
letting the molten metal or alloy infiltrate into the blade
section, and thereafter slowly cooling to room temperature.
Alternatively, infiltration is carried out by placing the outer
blade cutting wheel in a lower mold half with a clearance near the
blade section, charging the mold half with a weighed amount of
metal or alloy, mating an upper mold half with the lower mold half,
heating the mated mold while applying a certain pressure across the
mold, for letting the molten metal or alloy infiltrate into the
blade section. Thereafter the mold is cooled, the pressure is then
released, and the wheel is taken out of the mold. The cooling step
following heating should be slow so as to avoid any residual
strains.
[0069] Before the metal or alloy is rested on the abrasive layer or
blade section, for example, a commercially available solder flux
containing chlorine or fluorine may be applied to the blade section
for the purpose of improving the wettability of the blade section
or retaining the metal or alloy to the blade section.
[0070] After the abrasive layer or blade section is formed on the
outer periphery of the base as mentioned above and before the
dressing by the inventive method is applied to the blade section,
the protrusion, thickness and outer diameter of the blade section
are tailored by wire electrical discharge machining (EDM) or by
grinding and polishing with a grinding wheel of aluminum oxide,
silicon carbide or diamond. At this point, the blade section at the
edge may be chamfered (beveled or rounded) to a degree of at least
C0.1 or R0.1, though depending on the thickness of the blade
section, because such chamfering is effective for reducing cut
marks on the cut surface or mitigating chipping of a magnet piece
at the edge. Thereafter, the blade section is subjected to dressing
by the inventive method.
EXAMPLE
[0071] Examples are given below by way of illustration and not by
way of limitation.
Example 1
[0072] A cemented carbide base in the form of an annular thin disc
having an inner diameter of 60 mm and an outer diameter of 133 mm
was held by clamping it between a pair of circular jigs as shown in
FIGS. 1, 2A and 2B. The circular jigs had an outer diameter which
was 2 mm smaller than the outer diameter of the base so that the
outer edge of the base projected 1 mm beyond the outer
circumference of the jigs. Electroplating was carried out in a
nickel electroplating bath #1, defined below, to deposit an
undercoat. The base was then held by clamping it between a pair of
circular jigs 2, 2 as shown in FIGS. 1, 2A and 2C. The circular
jigs 2, 2 had an outer diameter which was 2 mm larger than the
outer diameter of the base. Permanent magnet segments were built in
the outer peripheral portions of the jigs. The space defined
between the outer peripheral portions of the jigs (FIG. 2C) was
filled with 0.8 g of diamond abrasive grains pre-coated with a
magnetic material (nickel) and having an average particle size of
130 .mu.m. The diamond grains were held within the space by the
magnetic force. The assembly was immersed in a nickel
electroplating bath #2, defined below, in an electroplating tank 3
as shown in FIG. 3. Electroplating was carried out to deposit
nickel to bond abrasive grains together and to the base, thereby
bonding abrasive grains to the outer periphery of the base to form
an abrasive layer. At this point, the cage electrode 4 served as an
anode.
[0073] Next the base was held by clamping it between a pair of
circular jigs as shown in FIGS. 1, 2A and 2B. The circular jigs had
an outer diameter which was 2 mm smaller than the outer diameter of
the abrasive layer-baring base so that the abrasive layer on the
outer periphery of the base projected beyond the outer
circumference of the jigs. Electroplating was carried out in a
nickel sulfamate electroplating bath, defined below, in an
electroplating tank 3 shown in FIG. 3 to deposit a plating cover
for enhancing the bond strength between abrasive grains and between
abrasive grains and the base. The abrasive layer thus obtained was
ground using two grinding wheels, WA and GC grinding wheels,
thereby tailoring the protrusion and thickness of the abrasive
layer so that the abrasive layer had a protrusion of 50 .mu.m. The
abrasive layer was further ground to an outer diameter of 135 mm by
wire EDM, completing the blade section.
[0074] Next, the base having the blade section formed was held by
clamping it between a pair of circular jigs as shown in FIGS. 1, 2A
and 2B. The circular jigs had an outer diameter which was 2 mm
smaller than the outer diameter of the blade section-baring base so
that the blade section projected beyond the outer circumference of
the jigs. The blade section was dressed by electropolishing using
the nickel electroplating bath #2 (used in the previous
electroplating) as the electropolishing liquid, completing an outer
blade cutting wheel. At this point, the plating tank 3 of FIG. 3
used in the previous electroplating was used as the
electropolishing tank, and annular electrodes 5, 6 as shown in FIG.
5 were positioned as shown in FIG. 6. With the annular electrodes
5, 6 and cage electrode 4 set as the counter electrode, and the
base as the anode, electropolishing was carried out.
TABLE-US-00001 Nickel electroplating bath #1 (undercoat plating)
Composition NiCl.sub.2--6H.sub.2O 55 g/L NiSO.sub.4--6H.sub.2O 370
g/L Boric acid 45 g/L Plating conditions Bath temperature
50-55.degree. C. Constant current 0.5 A/dm.sup.2 Conduction time 60
min
TABLE-US-00002 Nickel electroplating bath #2 Composition
NiCl.sub.2--6H.sub.2O 70 g/L NiSO.sub.4--6H.sub.2O 370 g/L Boric
acid 45 g/L Plating conditions Bath temperature 50-55.degree. C.
Constant current 0.2 A/dm.sup.2 Conduction time 150 min
TABLE-US-00003 Nickel sulfamate plating bath Composition Ni
(NH.sub.2SO.sub.3).sub.2--4H.sub.2O 600 g/L NiCl.sub.2--6H.sub.2O
10 g/L Boric acid 35 g/L Plating conditions Bath temperature
60-65.degree. C. Constant current 0.5 A/dm.sup.2 Conduction time 60
min
[0075] The side surface of the blade section of the resulting outer
blade cutting wheel was observed under an optical stereomicroscope,
with the micrograph shown in FIG. 7. It is evident that abrasive
grains were fully exposed (or raised) and definite chip pockets
were defined between abrasive grains.
[0076] Using the outer blade cutting wheel, a rare earth permanent
magnet block (Nd--Fe--B magnet) was cutoff machined into magnet
pieces under the following conditions.
TABLE-US-00004 OD cutting wheel operating conditions Rotational
speed 6000 rpm Feed speed 400 mm/min Depth of cut 1 mm/pass
FIG. 9A is a photograph showing the cut surface of a cut magnet
piece. It is evident from FIG. 9A that the cut surface was smooth
and free of cutting marks. Using the outer blade cutting wheel,
four magnet pieces of 2 mm thick were sawed. The maximum difference
in thickness between opposite cut surfaces of each piece was
measured for evaluating the dimensional accuracy of cutting. The
results are plotted in the graph of FIG. 11. As is evident from
FIG. 11, the four magnet pieces had a dramatically improved
dimensional accuracy as demonstrated by a maximum thickness
difference of around 0.025 .mu.m. It is demonstrated that the outer
blade cutting wheel is improved in machining accuracy.
Comparative Example 1
[0077] An outer blade cutting wheel was manufactured as in Example
1 except that the electropolishing was omitted, and instead, the
dressing was achieved by the grinding with grinding wheels and the
machining by wire EDM. The protrusion, thickness and outer diameter
of the abrasive layer were tailored (protrusion 50 .mu.m) by
grinding with grinding wheels, and the outer diameter was tailored
by wire EDM.
[0078] The side surface of the blade section of the outer blade
cutting wheel was observed under an optical stereomicroscope, with
the micrograph shown in FIG. 8. Few abrasive grains were exposed on
the side surface and no definite chip pockets were seen.
[0079] Using the outer blade cutting wheel, a rare earth permanent
magnet block (Nd--Fe--B magnet) was cutoff machined into magnet
pieces under the same conditions as in Example 1. FIG. 10A is a
photograph showing the cut surface of a cut magnet piece. It is
evident from FIG. 10A that many cutting marks were seen and the cut
surface was unacceptable. Using the outer blade cutting wheel, four
magnet pieces were sawed as in Example 1 for evaluating the
dimensional accuracy of cutting. The maximum thickness difference
is plotted in the graph of FIG. 11. As is evident from FIG. 11, the
four magnet pieces were inferior in dimensional accuracy as
demonstrated by a maximum thickness difference in far excess of
0.05 .mu.m. Therefore, the outer blade cutting wheel is inferior in
machining accuracy to Example 1.
Example 2
[0080] An outer blade cutting wheel was manufactured as in Example
1 except that the cover plating was omitted, and instead, a Sn--Pb
alloy was infiltrated into the abrasive layer or blade section.
Infiltration of Sn--Pb alloy was carried out by resting the blade
section-baring base on a hot plate at 230.degree. C., heating the
base for 5 minutes, melting a wire of Sn--Pb alloy having a
diameter of 8 mm using a soldering iron at 230.degree. C., applying
the molten alloy to the hot blade section on the base, letting the
alloy infiltrate, and allowing the blade section to cool down.
[0081] Using the outer blade cutting wheel, a rare earth permanent
magnet block (Nd--Fe--B magnet) was cutoff machined into magnet
pieces under the same conditions as in Example 1. FIG. 9B is a
photograph showing the cut surface of a cut magnet piece. It is
evident from FIG. 9B that the cut surface was smooth and free of
cutting marks. Using the outer blade cutting wheel, four magnet
pieces were sawed as in Example 1 for evaluating the dimensional
accuracy of cutting. The maximum thickness difference is plotted in
the graph of FIG. 11. As is evident from FIG. 11, the four magnet
pieces had a dramatically improved dimensional accuracy as
demonstrated by a maximum thickness difference of around 0.025
.mu.m. It is demonstrated that the outer blade cutting wheel is
improved in machining accuracy.
Comparative Example 2
[0082] An outer blade cutting wheel was manufactured as in Example
2 except that the electropolishing was omitted, and instead, the
dressing was achieved by the grinding with grinding wheels and the
machining by wire EDM. The protrusion, thickness and outer diameter
of the abrasive layer were tailored (protrusion 50 .mu.m) by
grinding with grinding wheels, and the outer diameter was tailored
by wire EDM.
[0083] Using the outer blade cutting wheel, a rare earth permanent
magnet block (Nd--Fe--B magnet) was cutoff machined into magnet
pieces under the same conditions as in Example 1.
[0084] FIG. 10B is a photograph showing the cut surface of a cut
magnet piece. It is evident from FIG. 10B that many cutting marks
were seen and the cut surface was unacceptable. Using the outer
blade cutting wheel, four magnet pieces were sawed as in Example 1
for evaluating the dimensional accuracy of cutting. The maximum
thickness difference is plotted in the graph of FIG. 11. As is
evident from FIG. 11, the four magnet pieces were inferior in
dimensional accuracy as demonstrated by a maximum thickness
difference in far excess of 0.1 .mu.m, with one piece showing a
remarkable thickness variation in excess of 0.2 .mu.m. Therefore,
the outer blade cutting wheel is inferior in machining accuracy to
Example 2.
[0085] Japanese Patent Application No. 2012-001250 is incorporated
herein by reference.
[0086] 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.
* * * * *