U.S. patent application number 12/149553 was filed with the patent office on 2008-12-18 for chamfering apparatus, a grinding wheel, and a chamfering method.
This patent application is currently assigned to FUJI ELECTRIC DEVICE TECHNOLOGY. Invention is credited to Norihiko Nakajima, Shinichiro Nishimaki, Yoshihiko Tanaka.
Application Number | 20080311827 12/149553 |
Document ID | / |
Family ID | 40132780 |
Filed Date | 2008-12-18 |
United States Patent
Application |
20080311827 |
Kind Code |
A1 |
Tanaka; Yoshihiko ; et
al. |
December 18, 2008 |
Chamfering apparatus, a grinding wheel, and a chamfering method
Abstract
A chamfering apparatus for chamfering an outer periphery of a
disk-shaped substrate includes a grinding member having a circular
hole inside thereof, wherein the hole has a diameter larger than an
outer diameter of the substrate. An inner periphery of the grinding
member forming the hole is a grinding surface and grinds the outer
periphery of the substrate.
Inventors: |
Tanaka; Yoshihiko; (Nagano,
JP) ; Nakajima; Norihiko; (Nagano, JP) ;
Nishimaki; Shinichiro; (Nagano, JP) |
Correspondence
Address: |
KANESAKA BERNER AND PARTNERS LLP
1700 DIAGONAL RD, SUITE 310
ALEXANDRIA
VA
22314-2848
US
|
Assignee: |
FUJI ELECTRIC DEVICE
TECHNOLOGY
Tokyo
JP
|
Family ID: |
40132780 |
Appl. No.: |
12/149553 |
Filed: |
May 5, 2008 |
Current U.S.
Class: |
451/44 ; 451/258;
451/541 |
Current CPC
Class: |
B24B 9/065 20130101;
B24B 9/08 20130101 |
Class at
Publication: |
451/44 ; 451/258;
451/541 |
International
Class: |
B24B 1/00 20060101
B24B001/00; B24B 9/08 20060101 B24B009/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 14, 2007 |
JP |
2007-157603 |
Claims
1. A chamfering apparatus for chamfering an outer periphery of a
disk-shaped substrate, comprising: a grinding member having a
circular hole inside thereof, the hole having a diameter larger
than an outer diameter of the substrate to receive the substrate
therein, and a grinding surface at an inner periphery thereof to
chamfer the outer periphery of the substrate.
2. A chamfering apparatus according to claim 1, wherein said
grinding member includes, as the grinding surface, a recess
provided along the inner periphery and having an upper machining
plane and a lower machining plane with a vertical plane
therebetween, the upper and lower machining planes being arranged
obliquely with respect to the substrate to form upper and lower
peripheral edges of the substrate, respectively.
3. A chamfering apparatus according to claim 1, further comprising:
a base member provided inside the hole for placing the substrate
thereon and rotating the substrate, and a pressing member provided
inside the hole for sandwiching the substrate between the pressing
member and the base member.
4. A chamfering apparatus according to claim 3, further comprising
grooves provided on the base member, and suction holes provided in
the grooves and adapted to be connected to a suction pump for
applying a negative pressure to the substrate to firmly attract the
substrate to the base member.
5. A chamfering apparatus according to claim 4, further comprising
first means for rotating the base member in one direction, and
second means for rotating the grinding member in a direction
opposite to the one direction.
6. A grinder for grinding a disk-shaped substrate to chamfer an
outer periphery of the substrate, wherein the grinder has an
annular shape with a hole therein, said hole having a diameter
larger than an outer diameter of the substrate and being defined by
an inner periphery, said inner periphery having a recess extending
along the same to serve as a grinding surface contacting the
substrate.
7. A grinder according to claim 6, wherein said grinding surface
comprises an upper machining plane and a lower machining plane with
a vertical plane therebetween, provided in the recess, the upper
and lower machining planes being arranged obliquely with respect to
the substrate so that the upper and lower machining planes contact
an upper and lower peripheral edges of the substrate for
chamfering, respectively.
8. A method of chamfering an outer periphery of a disk-shaped
substrate, comprising: preparing a grinding member having a
circular hole inside thereof, the hole having a diameter larger
than an outer diameter of the substrate and being defined by an
inner periphery, arranging the substrate in the hole to contact the
inner periphery of the grinding member to chamfer the substrate,
and rotating the grinding member and the substrate.
9. A method of chamfering according to claim 8, wherein the
grinding member has a groove with a grinding surface to chamfer the
substrate.
10. A method of chamfering according to claim 8, wherein said
grinding member is rotated in one direction, and the substrate
disposed on a base member is rotated in a direction opposite to the
one direction.
Description
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
[0001] The present invention relates to a chamfering apparatus, a
grinding wheel, and a chamfering method for a glass substrate of a
hard disk used with a magnetic head of a magneto resistance type or
a giant magneto resistance type.
[0002] In a process of manufacturing a glass disk for a glass
substrate of a magnetic recording medium (a hard disk) mounted on
various types of magnetic recording apparatuses, chamfer machining
is generally done on circular edges at the outer periphery of the
glass substrate obtained by press molding, for example. Through the
chamfering process at an outer periphery of the glass disk, the
circular edges at the outer periphery are chamfered to have an
inclination by removing the edges. The chamfering is conducted on
the glass disk because the glass disk having a keen edge at the
outer periphery is dangerous and mechanically fragile to chip
readily. Regarding chamfer machining on a glass disk, Patent
Document 1 (Japanese Unexamined Patent Application Publication No.
H11-198012), for example, discloses a chamfering apparatus and a
chamfering method. The Patent Document 1 shows that the chamfer
apparatus and method disclosed therein alleviate the load and shock
generated in the chamfer process by setting the circumferential
speed of the glass disk and the circumferential speed of the
grinding wheel within respective appropriate ranges. Also, Patent
Document 1 shows that a good chamfered surface can be attained by
making the rotating direction of the grinding wheel and the
rotating direction of the glass disk be the same.
[0003] In the apparatus and method of chamfering a glass disk
disclosed in Patent Document 1, chamfering is conducted by making
the outer periphery of the grinding wheel having a disk shape in
contact with the outer periphery of the glass disk. FIG. 4 shows an
arrangement in a chamfering process in which the outer periphery of
the disk-shaped grinding wheel is made contact with the outer
periphery of the glass disk. For chamfering the outer periphery of
the glass disk 101, generally, the outer periphery of the rotating
disk-shaped grinding wheel 102 is made into contact with the
circular edge at the periphery of the rotating glass disk 101.
Grinding fluid is supplied at a contact point, and the grinding
wheel is pressed against the glass disk to grind the circular edge.
The glass disk 101 is mounted on a base and chucked. The glass disk
on the base rotates together with rotation of the base.
[0004] Some of commonly used glass substrates have an outer
diameter of about 65 mm. In the course of chamfering on such a
glass substrate, a grinding wheel with an outer diameter of about
160 mm is employed. Rotation speed of the grinding wheel is
generally set in the range from 2,000 to 2,500 rpm for the chamfer
machining. Depending on conditions in the chamfering process,
so-called chipping, any broken chips (pieces or fragments)
generated on the glass disk, may occur.
[0005] In the chamfer machining conducted by means of the outer
periphery of the grinding wheel, the surface area at the contact
point between the glass disk and the grinding wheel is relatively
small. Consequently, the pressure acting on the outer periphery of
the glass disk is high, which causes large load on the glass disk.
At locations where the disk receives large load, chips may occur.
In addition, some micro cracks may occur, thereby decreasing
strength of the substrate.
[0006] In order to avoid this chipping, it can be considered to
control a cutting speed in the chamfering process low and conduct
careful machining. However, such a way of chamfering suppresses a
high-speed fabrication of the glass substrate.
[0007] Moreover, the chamfer machining using the outer periphery of
the grinding wheel causes a collision between the glass disk and
the grinding wheel at the moment of contact therebetween. The glass
disk is held on a rotatable base in the chamfer machining. A
positioning of the glass disk, however, unavoidably accompanies
some errors with respect to the predetermined location on the base.
This causes an oscillation of the glass disk during the chamfer
machining and frequent, quick collisions in proportion to the
rotational speed of the grinding wheel. In the event of collision,
the pressure on the glass disk from the grinding wheel rises
abruptly. Repeating such collisions many times, the load on the
glass disk further increases and the glass substrate tends to
generate the chips.
[0008] In view of the above situation, it is an object of the
present invention to provide a chamfering apparatus, a grinding
wheel, and a chamfering method in which an occurrence of chipping
is suppressed and the time for manufacturing a substrate is
shortened.
[0009] Further objects and advantages of the invention will be
apparent from the following description of the invention.
SUMMARY OF THE INVENTION
[0010] A chamfering apparatus of the invention that chamfers
circular edges at an outer periphery of a disk-shaped substrate
comprises a grinding member having a circular hole inside thereof,
the hole having a diameter larger than an outer diameter of the
substrate. An inner peripheral surface of the grinding member
forming the hole serves as a grinding surface that comes in contact
with the circular edges of the substrate and grinds the circular
edges.
[0011] In the chamfer machining using this chamfering apparatus,
the center of curvature of the outer periphery of the substrate and
the center of curvature of the inner periphery of the grinding
member locate in the same side with respect to the contact point.
That is, the outer peripheral surface of the substrate and the
inner peripheral surface of the grinding member have respective
curved surfaces that are curved towards the same direction. As a
result, the surface area of the contact point between the substrate
and the grinding member is relatively large due to a microscopic
elastic deformation during the chamfer machining. Further, a
pulling angle or rake angle of the substrate material by the
grinding member is smaller in the chamfering apparatus of the
invention, which has the centers of curvature of both of the
substrate and the grinding member in the same direction, than in
the conventional apparatus of FIG. 4, which has the centers of
curvature in the opposite directions. Therefore, the load on the
substrate is diffused, and generation of chips and micro cracks is
suppressed. Since the load on the substrate is reduced, the chips
and micro cracks are scarcely generated even at a raised cutting
speed for the substrate. Hence, it has become able to raise cutting
speed in the chamfer machining yet suppressing the occurrence of
chipping. A higher cutting speed in the chamfer machining shortens
the time for a chamfer step, and the time for manufacturing a
substrate.
[0012] The grinding member of the invention chamfers the circular
edges at the periphery of the disk-shaped substrate in which the
grinding member comes in contact with the circular edges at an
outer periphery of the substrate and grinds the circular edges to
chamfer the substrate, and has a hole with a diameter larger than a
diameter of the substrate inside the grinding member. The inner
periphery of the grinding member around the hole serves as a
grinding surface that comes in contact with the circular edges of
the substrate and grinds the circular edges.
[0013] In a chamfering method according to the invention, the
chamfering apparatus chamfers circular edges at the outer periphery
of the disk-shaped substrate using the grinding member having the
hole with the diameter larger than that of the substrate inside the
grinding member. The chamfering is carried out by making the
grinding member in contact with the circular edges of the substrate
at the inner peripheral surface of the grinding member and grinding
the circular edges of the substrate.
[0014] The present invention suppresses the occurrence of chipping
and provides a substrate with an improved quality. In addition, the
invention shortens the time for manufacturing the substrate and
enhances productivity thereof.
[0015] Now, some preferred embodiments according to the invention
will be described with reference to accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a plan view of a chamfering apparatus according to
an embodiment of the invention;
[0017] FIG. 2 is a sectional view taken along line 2-2 in the
chamfering apparatus of FIG. 1;
[0018] FIGS. 3(a), 3(b), and 3(c) illustrate the contact point
between a glass substrate and an inner periphery of the grinding
wheel; and
[0019] FIG. 4 is a plan view of a chamfering apparatus of prior
art.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] FIG. 1 is a schematic plan view of a chamfering apparatus
for a glass substrate of one embodiment according to the present
invention. FIG. 2 is a sectional view taken along the line 2-2 in
FIG. 1.
[0021] The chamfering apparatus 1 of this embodiment comprises a
grinding wheel 2, which is a grinding member having a machining
surface at the inner peripheral surface thereof, and a base 3 for
attaching a work piece, which is a glass substrate 4 to be
chamfered.
[0022] The grinding wheel 2 is a disk having a grinding wheel hole
formed in the central region thereof. A machining surface is formed
at the inner peripheral surface 6 of the grinding hole, the surface
6 forming the grinding wheel hole. The outer diameter of the
grinding wheel 2 in this embodiment is 160 mm and the diameter of
the inner peripheral surface 6 of the grinding wheel is 100 mm, the
surface 6 forming the grinding wheel hole in the central region of
the grinding wheel. The inner peripheral surface 6 of the grinding
wheel is of a diameter larger than the outer diameter of the glass
substrate 4, allowing the glass substrate 4 to be arranged inside
the grinding wheel hole. A recess 9 is formed in the inner
peripheral surface 6 of the grinding wheel 2 so that the glass
substrate 4 comes in contact obliquely in the chamfering process.
The recess 9 has a bottom plane 9a, an upper machining plane 9b,
and a lower machining plane 9c. The bottom plane 9a is
perpendicular to the record plane of the glass substrate 4 in which
information is written. (The record plane is parallel to the
horizontal plane in this embodiment, for example.) The upper
machining plane 9b and the lower machining plane 9c become in
contact with the upper and lower circular edges, respectively, of
the glass substrate 4 obliquely with respect to the record plane.
The inner peripheral surface 6 forming the grinding wheel hole in
the grinding wheel 2 serves as a grinding surface that becomes in
contact with the circular edges of the glass substrate 4 and grinds
them. In the grinding wheel 2 of this embodiment, grinding
particles of diamond are held on the surface of the grinding wheel
having the grinding wheel hole and then an electroless plating of
nickel is plated on the surface to fix the grinding particles of
diamond on the grinding wheel. Roughness of the surface is of a
grain size #325. The material for the grinding wheel is not limited
to that of this embodiment described above, but other appropriate
materials can be used.
[0023] The glass substrate 4 is preliminarily formed to a disk
configuration by press molding, for example, and a central part is
removed by coring process, for example, to form a toroidal shape.
The glass substrate 4 has a glass substrate hole, and the inner
periphery 7 of the glass substrate forms a glass substrate hole.
The glass substrate 4 in this embodiment has an outer diameter of
65 mm and a circular glass substrate hole with an outer diameter of
20 mm formed by the inner periphery of the glass substrate. The
glass substrate obtained in the press molding step remains having
an outer peripheral shape that is almost the same as the shape of
the die used in the press molding step, leaving circular edges at
the outer periphery. Accordingly, the chamfering process is
generally conducted to eliminate the circular edges on the glass
substrate.
[0024] The base 3 is a support member to mount and support the
glass substrate 4, so that the glass substrate 4 is chucked and
fixed on the base 3. The chucking of the glass substrate 4 is
carried out by pushing the glass substrate 4 down onto the base 3
with a pressing member 5 and by suction from bottom with the base
3. The pressing member 5 is formed in a hollow cylinder
configuration and pushes the glass substrate 4 from above on the
region from a radius of about 25 mm to a radius of 30 mm towards
the base 3. The suction of the glass substrate 4 with the base 3 is
carried out by drawing through a negative pressure set up in
grooves 8 formed on the support surface of the base 3. The base 3
has three concentric grooves 8 that have a suction hole,
respectively (not shown in the figure). The suction holes are
connected to a tank (not shown in the figure) at the negative
pressure through inside of the base 3. The tank is connected to a
suction pump and a motor to drive the pump, which create the
negative pressure in the tank preliminarily. This system produces
the negative pressure in the grooves 8 to attract the glass
substrate 4. Thus, the glass substrate 4 is fixed on the base 3 by
pushing down onto the base 3 and attracting from bottom. The base 3
rotates with the glass substrate 4 chucked thereon to rotate the
glass substrate 4 on the base 3.
[0025] Description has been made for a method for chucking the
glass substrate 4 in this embodiment in which the glass substrate 4
is pushed down from above onto the base and yet attracted from
bottom to the base. However, the method for chucking the glass
substrate on the base 3 is not limited to the above-described
method but other methods can be applied.
[0026] Next, a process for chamfering the glass substrate 4 with
the grinding wheel 2 is described as follows.
[0027] A chamfering apparatus 1 of this embodiment allows disposing
a glass substrate 4 inside the grinding wheel hole. The inner
peripheral surface 6 forming the grinding wheel hole in the
grinding wheel serves as a grinding surface that becomes in contact
with the circular edges of the glass substrate to grind them.
First, in the chamfering process, the glass substrate 4 is fixed
and chucked on the base 3. After chucking the glass substrate 4,
the base 3 with the glass substrate disposed thereon is rotated to
rotate the glass substrate 4. The glass substrate 4 rotates
together with the base 3 at a rotating speed in a range of 30 to
240 rpm. The grinding wheel 2 surrounding the glass substrate 4
rotates in the reversed direction to the rotation direction of the
glass substrate as indicated by the arrows in FIG. 1. The grinding
wheel 2 is set to rotate at a rotating speed of about 2,000 to
2,500 rpm.
[0028] In this embodiment, the glass substrate 4 is disposed inside
the grinding wheel hole formed by the inner peripheral surface 6 of
the grinding wheel 2 and chamfered at the contact point between the
glass substrate 4 and the grinding wheel 2. Thus, the glass
substrate 4 comes in contact with the grinding wheel at the inner
peripheral surface 6 of the grinding wheel 2. Hence, the center of
curvature of the outer periphery of the glass substrate 4 and the
center of curvature of the inner periphery of the grinding wheel 2
locate at the same side with respect to the contact point. The
outer periphery of the glass substrate 4 and the grinding wheel 2
also have curved surfaces facing the same direction. In these
conditions of the embodiment, the contact surface area at the
contact point between the grinding wheel 2 and the glass substrate
4 in the actual chamfering process is larger than that in a case in
which chamfering is done by the outer peripheral surface of a
grinding wheel as in the prior art. According to the pure geometry,
the contact would occur at a single point similar to the case of
chamfering at the outer peripheral surface of the grinding wheel in
the prior art. Actually, however, the contact surface area in the
process of chamfering the glass substrate 4 by the grinding wheel 2
is larger in the configuration of the invention. As a result, the
pressing force per unit area acting between the glass substrate 4
and the grinding wheel 2 is reduced, thereby keeping the load on
the glass substrate 4 at a relatively low level in the chamfering
process.
[0029] The following describes the process to become contact and
depart from the contact between the glass substrate 4 and the
grinding wheel 2. FIGS. 3(a), 3(b), and 3(c) are enlarged views for
illustrating the contact point between the glass substrate 4 and
the grinding wheel 2. The structures other than the glass substrate
4 and the grinding wheel 2 are eliminated in FIGS. 3(a), 3(b), and
3(c) to simplify the illustration. FIG. 3(a) is a sectional view
illustrating a state before the contact of the glass substrate 4 to
the grinding wheel 2. As shown in FIG. 3(a), the glass substrate 4
is not chamfered yet and the outer periphery is in a configuration
as-formed in the press molding step, with the circular edges
remaining. From this state, the glass substrate 4 and the grinding
wheel 2 are pushed against each other to chamfer the substrate.
[0030] Then, as shown in FIG. 3(b), the glass substrate 4 enters
into the recess 9 of the inner peripheral surface of the grinding
wheel 2, in which the circular edges of the glass substrate 4 come
in contact with the upper machining plane 9b and the lower
machining plane 9c that are parts of the recess 9. Since the upper
machining plane 9b and the lower machining plane 9c of the recess 9
are oblique to the recording surface of the glass substrate 4, the
upper and lower machining planes 9b and 9c come into contact with
the circular edges obliquely, allowing to chamfer the edges. Thus,
the upper and lower machining planes 9b and 9c, which are portions
of the inner peripheral surface 6 of the grinding wheel, come into
contact with the circular edges of the glass substrate 4 serving as
grinding planes. After completion of the chamfer machining, the
glass substrate 4 is separated from the grinding wheel 2 as shown
in FIG. 3(c).
[0031] The contacting step in the chamfering process in this
embodiment is performed gently between the glass substrate 4 and
the inner peripheral surface 6 of the grinding wheel 2. The
grinding place 10 in FIG. 1 refers to a plane at which chamfer
machining is carried out by pushing the glass substrate 4 to the
grinding wheel 2. The grinding place 10, which is a contact point
between the glass substrate 4 and the grinding wheel 2, has a
certain finite area, because the glass substrate 4 and the inner
peripheral surface 6 have curved surfaces bending towards the same
direction. Even if the glass substrate begins to contact on the
inner peripheral surface 6 with a small misalignment with respect
to the grinding place 10, during the course of movement of each
contact point from each starting point of the edges towards the
grinding point 10 accompanying an increase in contact area, the
pressure between the glass substrate 4 and the grinding wheel 2
gradually increases. When the contact point between the glass
substrate 4 and the grinding wheel 2 meets the grinding point 10, a
chamfer machining process proceeds there. At the end of the
chamfering process, the contact point between the glass substrate 4
and the grinding wheel 2 moves, decreasing the contact area, to the
position at which the glass substrate 4 and the inner peripheral
surface 6 of the grinding wheel 2 depart from the grinding place
10. Finally, the glass substrate 4 and the grinding wheel 2 become
apart. During the departing process, the pressure acting between
the two members gradually decreases.
[0032] When the glass substrate 4 comes into contact with inner
peripheral surface 6 of the grinding wheel at a correct position
without misalignment with respect to the grinding place 10, the
contact area between the glass substrate 4 and the inner peripheral
surface 6 of the grinding wheel gradually increases from the start
of contact by a mutual pushing force, forming the grinding place
10. Since the grinding point 10 has a certain finite area, during
the course from the start of the contact between the glass
substrate 4 and the inner peripheral surface 6 of the grinding
wheel to the formation of the grinding place 10, the pressure
between the two members gradually increases. When the glass
substrate 4 moves away from the inner peripheral surface 6 of the
grinding wheel at the correct position without misalignment with
respect to the grinding place 10, the contact area between the two
members gradually shrinks and the pressure between them gradually
decreases, and finally, the glass substrate 4 and the inner
peripheral surface 6 of the grinding wheel become apart. Thus, the
process of the contact and departure between the glass substrate 4
and the grinding wheel 2 proceeds with gentle increase and decrease
of the pressure between the two members. Therefore, an abrupt
change of the load on the glass substrate 4 from the grinding wheel
2 is avoided.
[0033] Since the load on the glass substrate 4 is reduced and the
abrupt change of the load is avoided in the chamfering process as
described above, a chipping scarcely occurs with a chamfering
apparatus 1 and a grinding wheel 2 of the invention. Consequently,
the chipping hardly occurs even when the rotating speed of the base
3 is raised to increase the rotating speed of the glass substrate 4
and the pushing force of the glass substrate onto the inner
peripheral surface 6 of the grinding wheel is increased. As a
result, the cutting speed in the chamfering process can be
raised.
[0034] The cutting speed in the chamfer machining of this
embodiment is set at about 10 mm/min. Since the cutting speed set
in the conventional chamfer machining, in which the glass substrate
is made in contact with the outer peripheral surface of the
grinding wheel, is in the range from 0.1 to 0.5 mm/min, the chamfer
machining is performed at a significantly higher speed in the
embodiment than in the prior art technology. Therefore, the time
for chamfering process is shortened.
[0035] When the glass substrate 4 is chucked on the base 3, it is
still difficult in the embodiment of the present invention to
exactly match the rotation center of the base 3 and the center of
the glass substrate 4. It is very likely to generate some
misalignment between the two centers. When there is a misalignment
between the centers, the glass substrate 4 rotates with a lateral
oscillation relative to the base 3 and comes into contact with the
grinding wheel every time the glass substrate 4 rotates in the
early stage of the chamfer process. Thus, collisions between the
glass substrate 4 and the grinding wheel 2 are repeated.
[0036] Nevertheless, after the chamfer machining has proceeded
passing over such misalignment between the center of the glass
substrate 4 and the rotation center of the base 3 that caused the
lateral oscillation, the oscillation relative to the grinding wheel
2 ceases and the glass substrate 4 continues in contact with the
grinding wheel 2. Since the chipping scarcely occurs in an
embodiment of the invention, the cutting speed of the glass
substrate 4 by the grinding wheel 2 can be increased in the chamfer
machining. At an elevated cutting speed, the chamfer machining
proceeds rather quickly passing over the extent due to the
misalignment. Hence, the repeated collision of the glass substrate
against the grinding wheel can be reduced, suppressing the
occurrence of chipping. Since the oscillation of the glass
substrate 4 relative to the grinding wheel 2 is reduced, the
occurrence of chipping can be further alleviated. As a result, the
cutting speed of the glass substrate 4 by the grinding wheel 2 can
be further increased.
[0037] The following describes experimental results demonstrating a
decrease in the chip generation in the chamfer apparatus according
to the embodiment of the invention. Table 1 shows rates of
occurrence of the chipping at various rotating speeds when compared
between the chamfering at the inner peripheral surface of a
grinding wheel according to the present invention and the
chamfering at the outer peripheral surface of a grinding wheel
according to a prior art.
TABLE-US-00001 TABLE 1 Rotating speed 240 120 60 30 of the base 3
(rpm) Rate of occurrence of 100 100 90 70 chipping (%) in
chamfering of a prior art Rate of occurrence of 10 5 0 0 chipping
(%) in chamfering of the invention
[0038] Conditions in the experiments are as follows.
[0039] In the chamfering at the inner peripheral surface of the
grinding wheel according to the invention, the glass substrate had
an outer diameter of about 65 mm, and had a circular hole with a
diameter of 20 mm in the central region of the substrate. The
grinding wheel, used in the chamfer machining at the inner
peripheral surface thereof according to the invention, had an outer
diameter of 160 mm and had a hole with a diameter of 100 mm in the
central region of the grinding wheel, the hole being formed by the
inner peripheral surface of the grinding wheel. In the grinding
wheel used in the experiments, as in the embodiment described
above, grinding particles of diamond were fixed on the surface of
the grinding wheel having a hole and electroless nickel plating was
plated thereon to fix the grinding particles of diamond on the
grinding wheel surface. The roughness of the surface was of a grain
size of #325.
[0040] In these experiments, for chamfering at the inner periphery
of a grinding wheel according to the invention, the chamfering
apparatus of the embodiment example as described above was used.
For chamfering at the outer periphery of a grinding wheel according
to a prior art, a grinding wheel used in the experiments had an
outer diameter of 160 mm, had no grinding wheel hole, and had a
machining surface at the outer periphery. Glass substrates used in
the experiments are the same as in the chamfering in the
above-described embodiment example.
[0041] The experiments were executed only for the purpose of
studying a trend of chip generation. Therefore, the grinding wheel
was held stationary and not rotated. The rotating glass substrate
was made in contact at various rotating speed with the held
grinding wheel. The glass substrate was observed after the
chamfering to inspect the occurrence of chipping. The observation
on the glass substrate was carried out by an optical microscope
that was capable of measuring the size of the generated chips. The
occurrence of chip generation was defined by the observation of
chips having the size larger than 200 .mu.m. When the glass
substrate was made in contact with the grinding wheel, the center
of the glass substrate was positioned with an eccentricity of 50
.mu.m with respect to the center of rotation of the base. The
cutting speed in the chamfer machining was set at 10 mm/min in
these experiments.
[0042] As shown in Table 1, the chamfer machining at the outer
peripheral surface of the grinding wheel according to the prior art
resulted in the chip generation with high rates over the whole
rotating speed rages of 30 to 240 rpm. At the rotating speeds of
120 rpm and 240 rpm, in particular, the chipping occurred at the
rate of 100%. In contrast, the chamfer machining at the inner
peripheral surface of the grinding wheel according to the invention
demonstrated generally low rates of chip generation. At the
rotating speeds of 30 rpm and 60 rpm, in particular, no chip was
generated, that is, the rate of occurrence of chipping was
zero.
[0043] Thus, the chamfering according to the invention, in which
the contact between the glass substrate and the grinding wheel
takes place at the inner peripheral surface of the grinding wheel,
showed much lower rates of the occurrence of the chipping than the
chamfering in the prior art, in which the contact between the glass
substrate and the grinding wheel takes place at the outer
peripheral surface of the grinding wheel. Hence, a high quality of
a glass substrate after chamfer machining is obtained. Since the
chipping scarcely occur at a high rotating speed of the base in the
chamfering process of the invention, in which the contact between
the glass substrate and the grinding wheel takes place at the inner
peripheral surface of the grinding wheel, it is possible to raise
the rotating speed of the base and increase the mutual pushing
force between the glass substrate and the grinding wheel.
Consequently, the cutting speed can be raised to shorten the time
for the chamfering process.
[0044] Sizes and configuration of the glass substrate and the
grinding wheel are not limited to those of the embodiment examples.
Rather, every element constituting a substrate and a chamfering
apparatus can have any other size and configuration as long as the
chamfer machining is carried out at the inner peripheral surface of
the grinding wheel.
[0045] The disclosure of Japanese Patent Application No.
2007-157603, filed on Jun. 14, 2007, is incorporated in the
application.
[0046] While the invention has been explained with reference to the
specific embodiments of the invention, the explanation is
illustrative and the invention is limited only by the appended
claims.
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