U.S. patent application number 10/379406 was filed with the patent office on 2003-11-27 for electrolytic machining method and electrolytic machining apparatus.
This patent application is currently assigned to SANKYO SEIKI MFG. CO., LTD.. Invention is credited to Kobayashi, Toshimasa, Usui, Motonori.
Application Number | 20030217931 10/379406 |
Document ID | / |
Family ID | 27800157 |
Filed Date | 2003-11-27 |
United States Patent
Application |
20030217931 |
Kind Code |
A1 |
Usui, Motonori ; et
al. |
November 27, 2003 |
Electrolytic machining method and electrolytic machining
apparatus
Abstract
An electrolytic machining method includes electrolytically
machining a workpiece that is positioned opposite to an electrode
tool while filling an electrolytic solution between the workpiece
and the electrode tool and applying a current across the workpiece
and the electrode tool. The electrolytic machining is performed by
having at least a part of opposing sections of the workpiece and
the electrode tool immersed in the electrolytic solution reserved
in a machining and storing section, while the machining surface of
the workpiece is positioned at a depth of about 5 mm to about 35 mm
from the surface of the electrolytic solution reserved in the
machining and storing section, and by supplying the electrolytic
solution to be filled in a gap at the opposing sections between the
workpiece and the electrode tool.
Inventors: |
Usui, Motonori; (Nagano,
JP) ; Kobayashi, Toshimasa; (Nagano, JP) |
Correspondence
Address: |
HOGAN & HARTSON L.L.P.
500 S. GRAND AVENUE
SUITE 1900
LOS ANGELES
CA
90071-2611
US
|
Assignee: |
SANKYO SEIKI MFG. CO., LTD.
|
Family ID: |
27800157 |
Appl. No.: |
10/379406 |
Filed: |
March 4, 2003 |
Current U.S.
Class: |
205/652 |
Current CPC
Class: |
B23H 3/00 20130101; F16C
33/107 20130101; B23H 9/00 20130101; B23H 7/38 20130101; B23H
2200/10 20130101; F16C 17/045 20130101; F16C 33/14 20130101; B23H
3/04 20130101 |
Class at
Publication: |
205/652 |
International
Class: |
C25F 003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 6, 2002 |
JP |
2002-059817 |
Claims
What is claimed is:
1. An electrolytic machining method for electrolytically machining
a workpiece that is positioned opposite to an electrode tool with
an electrolytic solution filled between the electrode tool and the
workpiece, the method comprising the steps of: immersing at least a
part of an opposing section of the workpiece and the electrode tool
in an electrolytic solution reserved in a machining and storing
section; positioning the opposing section of the workpiece and the
electrode tool at a predetermined depth from a surface of the
electrolytic solution; and supplying the electrolytic solution to
be filled in a gap at the opposing section of the workpiece and the
electrode tool and electrolytically machining a machining surface
of the workpiece.
2. An electrolytic machining method according to claim 1, wherein
the machining surface of the workpiece is positioned at a depth of
about 5 mm to about 35 mm from the surface of the electrolytic
solution retained in the machining and storing section.
3. An electrolytic machining method according to claim 1, wherein
the opposing section of the workpiece and the electrode tool is
completely immersed in the electrolytic solution retained in the
machining and storing section.
4. An electrolytic machining method according to claim 3, wherein
the machining surface of the workpiece is positioned at a depth of
about 5 mm to about 35 mm from the surface of the electrolytic
solution retained in the machining and storing section.
5. An electrolytic machining method according to claim 1, wherein
the opposing section of the workpiece and the electrode tool
includes an end face section of the electrode tool that faces the
machining surface of the workpiece and that is immersed in the
electrolytic solution reserved in the machining and storing
section.
6. An electrolytic machining method according to claim 1, wherein
the workpiece is composed of a material of a shaft member used in a
dynamic pressure bearing device that utilizes a dynamic pressure of
a lubricating fluid, and dynamic pressure generating grooves are
formed as concave sections in the workpiece.
7. An electrolytic machining method according to claim 1, wherein
the workpiece is composed of a material of a bearing member used in
a dynamic pressure bearing device that utilizes a dynamic pressure
of a lubricating fluid, and dynamic pressure generating grooves are
formed as concave sections in the workpiece.
8. An electrolytic machining method according to claim 1, further
comprising the step of adhering a masking member that has
continuous hole patterns formed as through-holes that correspond to
the shapes of the concave sections to the machining surface of the
workpiece.
9. An electrolytic machining method according to claim 8, wherein
the electrolytic solution is supplied to flow in a gap between the
masking member and the electrode tool to allow the electrolytic
solution to enter the continuous hole patterns of the masking
member and an electric current is applied across the workpiece and
the electrode tool to thereby allow an electrolytic machining to
take place.
10. An electrolytic machining method according to claim 1, wherein
the electrolytic solution is a mixed solution containing a
surface-active agent.
11. An electrolytic machining method according to claim 1, further
comprising the step of applying ultrasonic vibration to the
electrolytic solution.
12. An electrolytic machining apparatus comprising: an electrode
tool; a machining and storing section that reserves an electrolytic
solution; and a supporting member that retains at least a part of
the electrode tool immersed in the electrolytic solution and
positions a machining surface of a workpiece at a predetermined
depth from a surface of the electrolytic solution stored in the
machining and storing section.
13. An electrolytic machining apparatus according to claim 12,
wherein the supporting member positions the machining surface of a
workpiece at a depth of about 5 mm to about 35 mm from the surface
of the electrolytic solution retained in the machining and storing
section.
14. An electrolytic machining apparatus according to claim 12,
further comprising a flow control device that controls charging and
discharging of the electrolytic solution in and out of the
machining and storing section to maintain the surface level of the
electrolytic solution in the machining and storing section at a
specified level.
15. An electrolytic machining apparatus according to claim 13,
wherein the workpiece is composed of a material of a shaft member
used in a dynamic pressure bearing device that utilizes a dynamic
pressure of a lubricating fluid.
16. An electrolytic machining apparatus according to claim 13,
wherein the workpiece is composed of a material of a bearing member
used in a dynamic pressure bearing device that utilizes a dynamic
pressure of a lubricating fluid.
17. An electrolytic machining apparatus according to claim 12,
wherein a masking member having continuous through-hole patterns
that correspond to concave sections to be formed on the machining
surface of the workpiece is adhered to the machining surface of the
workpiece.
18. An electrolytic machining apparatus according to claim 12,
wherein the electrolytic solution is a mixed solution containing a
surface-active agent.
19. An electrolytic machining apparatus according to claim 12,
further comprising an ultrasonic vibration generating device that
provides ultrasonic vibration to the electrolytic solution.
20. An electrolytic machining apparatus according to claim 17,
wherein an insulating member is provided on at least the surface
part of the masking member to substantially block energization of
parts other than the continuous hole patterns of the masking
member.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an electrolytic machining
method, in which an electrolytic machining is performed on a
workpiece that is positioned opposite to an electrode tool by
filling an electrolytic solution between the workpiece and the
electrode tool and applying a current across the workpiece and the
electrode tool, a method for fabricating grooves for dynamic
pressure bearings, and dynamic pressure bearing devices
manufactured according to the manufacturing method.
[0003] 2. Related Background Art
[0004] Electrolytic machining is performed by concentrating
electrodissolution on certain parts of a workpiece as required, and
an electrolytic machining apparatus indicated in FIG. 22, for
example, has been known for sometime. In the electrolytic machining
apparatus shown in FIG. 22, a workpiece 4 is placed on a jig 3,
which is mounted on a base 1 via an insulating material 2, and an
electrode tool 5 is placed opposite to the workpiece 4 in close
proximity. The workpiece 4 is connected to the positive side
(+pole) of a power supply for electrolytic machining, which is
omitted from drawings, while the electrode tool 5 is connected to
the negative side (-pole).
[0005] In the meantime, an electrolytic solution 6 collected
externally is supplied by a pump 7, which is a device for supplying
an electrolytic solution, through a filter 8 to a gap between the
electrode tool 5 and the workpiece 4. While the electrolytic
solution 6 is filled between the electrode tool 5 and the workpiece
4, a current is applied across the electrode tool 5 and the
workpiece 4. This causes the workpiece 4 to electrochemically
elute, such that the workpiece 4 is electrolytically machined.
[0006] A feeder 10 is installed on the electrode tool 5. The
electrode tool 5 is fed by the feeder 10 into the workpiece 4 as
the machining on the workpiece 4 progresses, and this allows a
predetermined machining gap (equilibrium gap) between the two to be
maintained, which consequently allows a shape that is an inversion
of the shape of the electrode tool 5 to be formed on the workpiece
4. Gas that is generated by the electrolytic machining is
ventilated outside by a fan 11. In addition, the electrolytic
solution whose temperature rises due to the Joule heat contains
various types of electrolytic products; a used electrolytic
solution 12 is purified by a centrifuge 13 and subsequently
supplied into the gap between the electrode tool 5 and the
workpiece 4 again.
[0007] However, a mass production machining process using such a
general electrolytic machining method entails the following
problems:
[0008] (1) There is a tendency for machining widths of workpieces
to be larger than the widths of electrode tools, and fluctuations
in the machining widths tend to occur.
[0009] (2) When the gap between the electrode tool and the
workpiece is narrowed in order to reduce the fluctuations in
machining widths, various types of particles in the electrolytic
solution such as electrolytic products from the workpieces tend to
cause clogging, which often leads to defective machining.
[0010] (3) Similarly, when the gap between the electrode tool and
the workpiece is made narrower, the flow of the electrolytic
solution is less smooth, which causes deterioration of the
electrolytic solution during machining; this results in deep
machining depth near the supply side of the electrolytic solution
and gradually shallower machining depth towards the drain side;
and
[0011] (4) Some electrolytic solution and/or electrolytic products
tend to adhere to the workpiece.
[0012] When electrolytic machining is used in groove machining of
dynamic pressure generating grooves in a dynamic pressure bearing
device that utilizes the dynamic pressure of a lubricating fluid,
the shapes of the dynamic pressure generating grooves that have a
great impact on the dynamic pressure property cannot be obtained at
the precision required. This not only causes a failure to obtain
favorable dynamic pressure property, but also leads to lower
productivity. Furthermore, when electrolytic products or the
electrolytic solution remain attached to a processed product, they
become chemical debris on certain types of rotating bodies that are
supported by dynamic pressure bearing devices, such as hard disk
drive devices (HDD), and cause the rotating bodies to be
inoperable.
SUMMARY OF THE INVENTION
[0013] In view of the above, the present invention relates to an
electrolytic machining method, as well as a method for
manufacturing dynamic pressure bearing grooves, in which workpieces
can be processed efficiently and with high precision using a simple
structure.
[0014] In order to achieve the objective, in an electrolytic
machining method in accordance with an embodiment of the present
invention, an electrolytic machining is performed by having at
least a part in which a workpiece and an electrode tool oppose each
other is immersed in an electrolytic solution retained in a
machining and storing section, while the machining surface of the
workpiece is positioned at a depth of about 5 mm to about 35 mm
from the surface of the electrolytic solution retained in the
machining and storing section, and by supplying the electrolytic
solution to be filled in a gap between the workpiece and the
electrode tool in the part where they oppose each other.
[0015] According to the electrolytic machining method having such a
structure, due to the fact that the machining surface of the
workpiece is positioned at a depth of about 5 mm or deeper from the
surface of the electrolytic solution retained in the machining and
storing section, there is virtually no amount of air, especially
oxygen, entering the electrolytic solution, which ensures a high
quality electrolytic machining. At the same time, due to the fact
that the machining surface of the workpiece is positioned at a
depth of about 35 mm or less from the surface of the electrolytic
solution retained in the machining and storing section, the
fluidity of the electrolytic solution is maintained favorably,
which allows a smooth elimination of electrolytic products after
the electrolytic machining.
[0016] The material of a shaft member or a bearing member used in a
dynamic pressure bearing device that utilizes the dynamic pressure
of a lubricating fluid may be used as the workpiece described
above. Due to the fact that dynamic pressure generating grooves are
formed as concave sections in the workpiece, the dynamic pressure
generating grooves are machined with especially high precision.
[0017] In one aspect of the present embodiment, a masking member
that has continuous hole patterns formed as through-holes that
correspond to the shapes of concave sections may be adhered to the
machining surface of the workpiece described above. As a result,
the electrolytic solution is supplied to flow in a gap between the
masking member and the electrode tool in order to allow the
electrolytic solution to enter into the continuous hole patterns of
the masking member and thereby allow an electrolytic machining to
take place, and thus the electrolytic solution supplied to the
workpiece flows only within the continuous hole patterns of the
masking member that is adhered to the workpiece. Consequently, even
when the fluidity of the electrolytic solution is improved by
widening the gap between the workpiece and the electrode tool, the
concave sections whose shapes correspond to the continuous hole
patterns of the masking member are formed with greater precision on
the workpiece.
[0018] In one aspect of the present embodiment, a mixed solution
containing a surface-active agent may be used as the electrolytic
solution. As a result, various particles such as electrolytic
products that elute from the workpiece are absorbed by the
surface-active agent within the electrolytic solution, which
ensures a smooth flow of the electrolytic solution.
[0019] In the electrolytic machining method may use an ultrasonic
vibration generating device that provides ultrasonic vibration to
the electrolytic solution. As a result, various particles such as
electrolytic products that elute from the workpiece are made to
flow smoothly due to the ultrasonic vibration provided to the
electrolytic solution.
[0020] An electrolytic machining apparatus in accordance with one
embodiment of the present invention may include a machining and
storing section that retains an electrolytic solution and that
stores at least a part in which a workpiece and an electrode tool
are disposed opposite to each other and immersed in the
electrolytic solution, and a workpiece supporting member that
positions the machining surface of the workpiece at a depth of
about 5 mm to about 35 mm from the surface of the electrolytic
solution retained in the machining and storing section.
[0021] By the electrolytic machining apparatus having such a
structure, due to the fact that the machining surface of the
workpiece is positioned by the workpiece supporting member at a
depth of about 5 mm or deeper from the surface of the electrolytic
solution retained in the machining and storing section, there is
virtually no amount of air, especially oxygen entering the
electrolytic solution, which ensures a high quality electrolytic
machining; at the same time, due to the fact that the machining
surface of the workpiece is positioned by the workpiece supporting
member at a depth of about 35 mm or less from the surface of the
electrolytic solution retained in the machining and storing
section, the fluidity of the electrolytic solution is maintained
favorably, which allows a smooth elimination of electrolytic
products after the electrolytic machining.
[0022] In one aspect of the present embodiment, the material of a
shaft member or a bearing member used in a dynamic pressure bearing
device that utilizes the dynamic pressure of a lubricating fluid
may be used as the workpiece described above. Because dynamic
pressure generating grooves are formed as concave sections in the
workpiece, the dynamic pressure generating grooves are machined
with especially high precision.
[0023] Further, a masking member having continuous hole patterns as
through-holes that correspond to the shapes of concave sections may
be adhered to the machining surface of the workpiece described
above. As a result, the electrolytic solution is supplied to flow
in a gap between the masking member and the electrode tool in order
to allow the electrolytic solution to enter into the continuous
hole patterns of the masking member and thereby allow an
electrolytic machining to take place, and thus the electrolytic
solution supplied to the workpiece flows only within the continuous
hole patterns of the masking member that is adhered to the
workpiece. Consequently, even when the fluidity of the electrolytic
solution is improved by widening the gap between the workpiece and
the electrode tool, the concave sections whose shapes correspond to
the continuous hole patterns of the masking member are formed with
greater precision on the workpiece.
[0024] In one aspect of the present embodiment, a mixed solution
containing a surface-active agent may be used as the electrolytic
solution described above. As a result, various particles such as
electrolytic products that elute from the workpiece are absorbed by
the surface-active agent within the electrolytic solution, which
ensures a smooth flow of the electrolytic solution.
[0025] The electrolytic machining apparatus in accordance with one
aspect of the present embodiment may be provided with an ultrasonic
vibration generating device that provides ultrasonic vibration to
the electrolytic solution. As a result, various particles such as
electrolytic products that elute from the workpiece are made to
flow smoothly due to the ultrasonic vibration provided to the
electrolytic solution.
[0026] Furthermore, in the electrolytic machining apparatus, an
insulating member may be provided on at least the surface part of
the masking member. As a result, energization of parts other than
the continuous hole patterns of the masking member is virtually
completely blocked, which causes the shapes of the concave sections
to be formed with even greater precision.
[0027] Other features and advantages of the invention will be
apparent from the following detailed description, taken in
conjunction with the accompanying drawings that illustrate, by way
of example, various features of embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 schematically shows a front cross-sectional view of
the structure of an electrolytic machining apparatus in accordance
with one embodiment of the present invention.
[0029] FIG. 2 schematically shows a side cross-sectional view of
the electrolytic machining apparatus shown in FIG. 1.
[0030] FIG. 3 shows a plan view of a masking member used in the
electrolytic machining apparatus shown in FIGS. 1 and 2.
[0031] FIG. 4 shows an exterior view illustrating the operating
condition of the electrolytic machining apparatus shown in FIGS. 1
through 3.
[0032] FIG. 5 shows a diagram of one example of energization in the
electrolytic machining apparatus shown in FIGS. 1 through 4.
[0033] FIG. 6 shows a diagram of another example of energization in
the electrolytic machining apparatus shown in FIGS. 1 through
4.
[0034] FIG. 7 shows a line graph showing the relationship between
the immersion positioning depth in an electrolytic solution during
electrolytic machining and the electrolytic machining depth.
[0035] FIG. 8 shows a longitudinal cross-sectional view of an
example of the structure of a hard disk drive (HDD) motor with a
dynamic pressure bearing device manufactured through the
electrolytic machining according to the present invention.
[0036] FIG. 9 shows a bottom view of an example of the structure of
a thrust plate used in the dynamic pressure bearing device shown in
FIG. 8.
[0037] FIG. 10 shows a plan view of an example of the structure of
the thrust plate used in the dynamic pressure bearing device shown
in FIG. 8.
[0038] FIG. 11 shows a longitudinal cross-sectional view of the
thrust plate shown in FIGS. 9 and 10.
[0039] FIG. 12 schematically shows a front cross-sectional view of
the structure of an electrolytic machining apparatus in accordance
with another embodiment of the present invention.
[0040] FIG. 13 schematically shows a side cross-sectional view of
the electrolytic machining apparatus shown in FIG. 12.
[0041] FIG. 14 shows an enlarged cross-sectional view in part of
the electrolytic machining apparatus of FIG. 13 taken along a line
III-III in FIG. 15.
[0042] FIG. 15 shows a plan view of a masking member used in the
electrolytic machining apparatus shown in FIGS. 12, 13 and 14.
[0043] FIG. 16 schematically shows an exterior view illustrating
the operating condition of the electrolytic machining apparatus
shown in FIGS. 12 through 15.
[0044] FIG. 17 schematically shows a front cross-sectional view of
the structure of an electrolytic machining apparatus in accordance
with yet another embodiment of the present invention.
[0045] FIG. 18 schematically shows a side cross-sectional view of
the structure of the electrolytic machining apparatus shown in FIG.
17.
[0046] FIG. 19 shows a front view of a pattern structure on the end
part of an electrode tool used in the electrolytic machining
apparatus shown in FIGS. 17 and 18.
[0047] FIG. 20 shows a cross-sectional view taken along a line
IV-IV in FIG. 19.
[0048] FIG. 21 schematically shows an exterior view illustrating
the operating condition of the electrolytic machining apparatus
shown in FIGS. 17 through 20.
[0049] FIG. 22 schematically shows a side view of one example of a
conventional electrolytic machining apparatus.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0050] Preferred embodiments of the present invention are described
below with reference to the accompanying drawings. First, the
overall structure of a hard disk drive device (HDD) to which the
manufacturing methods according to the present invention are
applied is described.
[0051] FIG. 8 shows an overall view of a shaft-rotation type HDD
spindle motor. The HDD spindle motor may consist of a stator
assembly 10, which is a fixed member, and a rotor assembly 20,
which is a rotating member assembled onto the top of the stator
assembly 10. The stator assembly 10 has a fixed frame 11, which is
screwed to a fixed base, not shown. The fixed frame 11 is formed
with an aluminum material to achieve a lighter weight; on the inner
circumference surface of a ring-shaped bearing holder 12 formed
upright in the generally center part of the fixed frame 11 is a
bearing sleeve 13, which is a fixed bearing member formed in the
shape of a hollow cylinder and joined to the bearing holder 12
through press fit or shrink fit. The bearing sleeve 13 is formed
with a copper material such as phosphor bronze in order to more
easily machine holes with small diameters.
[0052] A stator core 14, which consists of a laminate of
electromagnetic steel plates, is mounted on the outer circumference
mounting surface of the bearing holder 12. A drive coil 15 is wound
on each salient pole section provided on the stator core 14.
[0053] A rotor shaft 21 that composes the rotor assembly 20 is
inserted in a freely rotatable manner in a center hole provided in
the bearing sleeve 13. This means that a dynamic pressure surface
formed on an inner circumference wall section of the bearing sleeve
13 and a dynamic pressure surface formed on an outer circumference
surface of the rotor shaft 21 are positioned opposite to each other
in the radial direction and in close proximity, and radial dynamic
pressure bearing sections RB are formed in a minuscule gap section
between them. More specifically, the dynamic pressure surface on
the bearing sleeve 13 side and the dynamic pressure surface on the
rotor shaft 21 side of each of the radial dynamic pressure bearing
sections RB are positioned opposite to each other in a circular
fashion across a minuscule gap of several .mu.m, and a lubricating
fluid such as lubricating oil, magnetic fluid or air is filled or
present in a continuous manner in the axial direction in a bearing
space formed by the minuscule gap.
[0054] Herringbone-shaped radial dynamic pressure generating
grooves (not shown) are provided on at least one of the dynamic
pressure surfaces of the bearing sleeve 13 and the rotor shaft 21.
For example, the herringbone-shaped radial dynamic pressure
generating grooves may be concavely formed in a ring shape in two
blocks separated in the axial direction. During rotation, a pumping
effect of the radial dynamic pressure generating grooves
pressurizes the lubricating fluid to generate dynamic pressure, and
a rotating hub 22, which is described later, together with the
rotor shaft 21 becomes shaft-supported in a non-contact manner in
the radial direction with the bearing sleeve 13 due to the dynamic
pressure of the lubricating fluid.
[0055] The rotating hub 22 that with the rotor shaft 21 composes
the rotor assembly 20 is a generally cup-shaped member, and a
joining hole 22a provided in the center part of the rotating hub 22
is joined in a unitary fashion with the top end part of the rotor
shaft 21 through press fit or shrink fit. A recording medium such
as a magnetic disk is fixed to the rotating hub 22 with a clamper,
not shown. In other words, the rotating hub 22 has a generally
cylindrical body section 22b, which has a recording medium disk
mounted on its outer circumference section, and a ring-shaped drive
magnet 22c attached towards the bottom on the inner circumference
wall surface of the body section 22b. The ring-shaped drive magnet
22c is positioned in a ring-shaped manner in close proximity to and
opposite to the outer circumference end surface of the stator core
14.
[0056] In the meantime, a disk-shaped thrust plate 23 is fixed by a
plate fixing screw 24 at the bottom end part of the rotor shaft 21,
as shown in FIGS. 9, 10 and 11. The thrust plate 23 is positioned
to be contained within a cylindrically-shaped depressed section 13a
(see FIG. 8), which is concavely formed in the center part of the
bearing sleeve 13 towards the bottom, and a dynamic pressure
surface on the top surface of the thrust plate 23 is positioned
within the depressed section 13a of the bearing sleeve 13 opposite
to a dynamic pressure surface of the bearing sleeve 13 in close
proximity to each other in the axial direction.
[0057] Herringbone-shaped thrust dynamic pressure generating
grooves 23a are formed on the dynamic pressure surface on the top
surface of the thrust plate 23, as shown especially in FIG. 10,
through an electrolytic machining method described later, and a top
thrust dynamic pressure bearing section SBa is formed in the gap
part between the opposing dynamic pressure surfaces of the thrust
plate 23 and the bearing sleeve 13.
[0058] A counter plate 16 is positioned in close proximity to a
dynamic pressure surface on the bottom surface of the thrust plate
23. The counter plate 16 may be a disk-shaped member with a
relatively large diameter. The counter plate 16 is positioned to
close off the opening part at the bottom of the bearing sleeve 13,
and the outer circumference part of the counter plate 16 is fixed
to the bearing sleeve 13.
[0059] Herringbone-shaped thrust dynamic pressure generating
grooves 23b are formed on the dynamic pressure surface on the
bottom surface of the thrust plate 23 as shown especially in FIG. 9
through an electrolytic machining method described later, and a
bottom thrust dynamic pressure bearing section SBb is thereby
formed.
[0060] The two dynamic pressure surfaces of the thrust plate 23 and
the respective opposing dynamic pressure surface of the bearing
sleeve 13 and of the counter plate 16 in close proximity thus form
a set of thrust dynamic pressure bearing sections SBa and SBb that
are positioned adjacent to each other in the axial direction; each
opposing set of dynamic pressure surfaces are positioned opposite
of each other in the axial direction across a minuscule gap of
several micrometers. The lubricating fluid such as oil, magnetic
fluid or air is filled or present in the bearing spaces consisting
of the minuscule gaps in a continuous manner in the axial direction
through a pathway on the outer circumference of the thrust plate
23. During rotation, a pumping effect caused by the thrust dynamic
pressure generating grooves 23a and 23b provided on the thrust
plate 23 pressurizes the lubricating fluid to generate dynamic
pressure; and the dynamic pressure of the lubricating fluid causes
the rotor shaft 21 and the rotating hub 22 to be shaft-supported in
the thrust direction in a floating, non-contact state.
[0061] Next, descriptions are made as to the structure of an
electrolytic machining apparatus used to manufacture the thrust
dynamic pressure generating grooves 23a and 23b on the thrust plate
23 in accordance with an embodiment of the present invention.
[0062] As indicated in FIGS. 1, 2, 3 and 4, a concave section for
mounting a workpiece (i.e., a workpiece mounting concave section)
is provided in the generally center part of a workpiece supporting
jig 32 attached to a main body base section 31. A material
(hereinafter called a thrust plate material) 23' that it to become
the thrust plate 23 is lowered and held horizontally as a workpiece
in the workpiece mounting concave section. The thrust plate
material 23' may be formed from a stainless steel material
according to the present embodiment.
[0063] A masking member 33 made from a thin plate insulating member
is coherently mounted on the top surface of the thrust plate
material 23'. The masking member 33 is a circular member whose
diameter is larger than the outer diameter of the thrust plate
material 23', and the outer circumference edge part of the masking
material 33 is pressed downward and fixed to the workpiece
supporting jig 32 by a cap-shaped member 34.
[0064] Furthermore, as shown in FIG. 3, the masking member 33 has
continuous hole patterns 33a formed as through-holes in shapes that
correspond to the thrust dynamic pressure generating grooves 23a
and 23b. The masking member 33 may preferably have an insulating
material formed at least on its surface part, and thin ceramic
materials or stainless steel plates (SUS) with electrocoating or
ceramic coating, or resin plates, may be used as the masking member
33. The plate thickness of the masking member 33 is approximately
0.05 mm to 0.1 mm.
[0065] In the meantime, immediately above the thrust plate material
23' and the masking member 33 is positioned upright an electrode
tool 35, which consists of a hollow rod-shaped member, in the
generally vertical direction. The electrode tool 35 is fixed to or
held by a main body arm section 36 that extends above the main body
base section 31, and the bottom end part of the electrode tool 35
is positioned to form a gap .delta. of approximately 1 mm, for
example, with the masking member 33 during electrolytic machining.
Furthermore, a negative pole (-pole) of a DC power source with an
output voltage of approximately 5V to 15V, for example, is
connected to the electrode tool 35, while the positive pole (+pole)
of the DC power source is connected to the thrust plate material
23', which is the workpiece.
[0066] In the center part of the electrode tool 35, a solution
pathway 35a is formed as a through-hole in the axial direction, and
an electrolytic solution is delivered by an electrolytic solution
supply device (for example, a pump), not shown, from the top end of
the solution pathway 35a. The electrolytic solution used may be
10-30 wt. % NaNo.sub.2 solution, for example. The electrolytic
solution delivered from the top of the electrode tool 35 travels
through the solution pathway 35a and an exit section provided on
the bottom end and falls onto the masking member 33 and the thrust
plate material 23'. The electrolytic solution supplied to the
center part flows radially outward in radial direction and is
collected in a collection container, not shown. The electrolytic
solution used may also be a 3-10 wt. % KOH, 3-10 wt. % NaOH or 5-15
wt. % Na.sub.2Co.sub.3.
[0067] In the meantime, the electrolytic solution flows while an
appropriate amount thereof is retained within a machining and
storing section 41, which is provided to cover from the outer
circumference side the part where the thrust plate material 23',
which is the workpiece, and the electrode tool 35 are positioned
opposite to each other. The machining and storing section 41 has a
ring-shaped wall section 41a that is formed upright on the top
surface of the cap member 34 of the workpiece supporting jig 32.
The electrolytic solution is retained inside the ring-shaped wall
section 41a to maintain a predetermined solution surface height,
and the part where the thrust plate material 23' and the electrode
tool 35 oppose each other is positioned to be immersed in the
electrolytic solution.
[0068] The machining surface, which is the top surface, of the
thrust plate material 23', which is the workpiece, held by the
workpiece supporting jig 32 is positioned at a depth in the range
of about 5 mm to about 35 mm from the surface of the electrolytic
solution retained in the machining and storing section 41. The
reasons for positioning the machining surface at a depth in the
range of about 5 mm to about 35 mm are described later.
[0069] As the electrolytic solution is allowed to flow in the gap
.delta. between the electrode tool 35 and the masking member 33, as
well as the thrust plate material 23', that are set in the
electrolytic solution, energization takes place across the
electrode tool 35 and the thrust plate material 23'. The
electrolytic solution seeps into the continuous hole patterns 33a
provided in the masking member 33, so that it flows as it comes
into contact with the surfaces of the thrust plate material 23'
that are exposed from the masking member 33. When the parts of the
thrust plate material 23' that are in contact with the electrolytic
solution elute electrochemically, the electrolytic machining of the
thrust plate material 23' takes place.
[0070] A vibrator 37 that constitutes an ultrasonic vibration
generating device is attached at the top most end part of the
electrode tool 35. The vibrator 37 according to the present
embodiment is a horn-type that amplifies vibration amplitude to
about 20-22 .mu.m. By vibrating the electrode tool 35, ultrasonic
vibration is provided to the electrolytic solution.
[0071] In the present embodiment, energization for electrolytic
machining and energization for ultrasonic vibration take place
independently of each other, and the actual mode of energization is
as shown in FIG. 5, where energization Pa for electrolytic
machining and energization Pb for ultrasonic vibration are
generated by rectangular pulse currents that alternate, or as shown
in FIG. 6, where energization Ca with relatively long width for
electrolytic machining and energization Cb for ultrasonic vibration
partially overlap. In either method, particles such as electrolytic
products can be eliminated through ultrasonic vibration while the
electrolytic machining takes place.
[0072] In one aspect, a mixed solution that includes a
surface-active agent is used as the electrolytic solution. The
surface-active agent used in the present embodiment is an
alkylether non-ionic activator, and the amount added is 0.03 vol. %
or more. This addition amount is based on experiment results shown
in table 1.
[0073] Table 1 shows the number of residual metal chips contained
in electrolytic solution after performing an electrolytic machining
for 60 seconds on a work material consisting of a stainless steel
material (SUS 420) with inner diameter of 5.0 mm and thickness of
12 mm, while varying the concentration of the surface-active agent
between 0% and 5%.
1TABLE 1 Number of Residual Metal Chips After Machining SUS 420
Material Concentration/ Machining Time 0%; 60 sec. 0.03%; 60 sec.
0.05%; 60 sec. 1%; 60 sec. 2%; 60 sec. 5%; 60 sec. Average Value
15,425 552 276 0.01 0 0 Maximum Value 24,573 891 828 2 0 0
[0074] It is understood from Table 1 that the number of residual
metal chips is dramatically lowers when the volume ratio of the
surface-active agent is 0.03 vol. % or more compared to when the
concentration is 0 vol. %, which indicates that the surface-active
agent is working effectively. Furthermore, when the volume ratio is
2 vol. % or more, the number of residual metal chips is virtually
zero. On the other hand, increasing the volume ratio of the
surface-active agent to 5 vol. % or more does not change the
property of the machining itself; consequently, the volume ratio
may preferably be set at around 2 vol. %.
[0075] According to the electrolytic machining method for a dynamic
pressure bearing device using the electrolytic machining apparatus
having such a structure, the electrolytic solution supplied to the
thrust plate material 23', which is the workpiece, flows only into
the continuous hole patterns 33a of the masking member 33 that is
adhered to the thrust plate material 23'; consequently, even if the
gap between the electrode tool 35 and the masking member 33, as
well as the thrust plate material 23', is widened to increase the
fluidity of the electrolytic solution, the dynamic pressure
generating grooves 23a and 23b having shapes that correspond to the
continuous hole patterns 33a of the masking member 33 can be formed
with high precision on the thrust plate material 23'.
[0076] According to the present embodiment, the machining surface
of the thrust plate material 23', which is the workpiece, is
positioned at a depth of about 5 mm or deeper from the surface of
the electrolytic solution retained in the machining and storing
section 41. As a result, there is virtually no amount of air,
especially oxygen, that may enter the electrolytic solution, which
ensures a high quality electrolytic machining. At the same time,
the machining surface of the thrust plate material 23', which is
the workpiece, is positioned at a depth of about 35 mm or shallower
from the surface of the electrolytic solution retained in the
machining and storing section 41. As a result, the fluidity of the
electrolytic solution is maintained favorably, which allows a
smooth elimination of electrolytic products after the electrolytic
machining.
[0077] When the relationship between the positioning depth of the
machining surface of the thrust plate material 23', which is the
workpiece, from the surface of the electrolytic solution and the
machining depth achieved through electrolytic machining was
studied, the results were as indicated in table 2 and FIG. 7.
2TABLE 2 Relationship between Immersion Depth in Solution during
Electrolytic Machining and Fluctuations in Electrolysis Depths
Depth (mm) 0.0 1.0 2.0 5.0 9.0 15.0 35.0 55.0 Maximum 13.9 9.1 8.8
9.7 9.3 9.4 9.5 8.7 Value Median Value 11.17 7.57 7.55 7.93 8.10
8.34 8.25 7.44 Minimum 7.8 8.2 6.9 6.7 7.5 7.7 7.6 6.4 Value
[0078] As Table 2 and FIG. 7 make clear, when the machining surface
of the thrust plate material (stainless steel material) 23', which
is the workpiece, is set at a position shallower than point A in
FIG. 7, i.e., 5 mm, there is a tendency for smut (dissolution
residue) to develop from the electrolytic solution in parts that
were electrolytically processed. On the other hand, when the
positioning depth of the machining surface is greater than point B
in FIG. 7, i.e., 35 mm, the machining depth becomes gradually
shallower as a result of voltage drop.
[0079] In contrast to these, when the positioning depth of the
machining surface is set between point A (5 mm) and point B (35 mm)
according to the present invention, the machining depth achieved
through electrolytic machining stabilizes considerably. When the
voltage value, current value and pulse width for implementing
electrolytic machining were changed, the value of the machining
depth did change somewhat with these changes; however, the range in
which stable machining depth can be obtained remained virtually
unchanged in every case, and extremely favorable results were
obtained in the range of 5 mm to 35 mm under various
conditions.
[0080] In the electrolytic machining according to the present
embodiment, the masking member 33 is formed with the insulating
member. As a result, energization of parts other than the
continuous hole patterns 33a of the masking member 33 is virtually
completely blocked, which leads to the shapes of the dynamic
pressure generating grooves 23a and 23b to be formed with even
higher precision.
[0081] Further in the electrolytic machining according to the
present embodiment, due to the fact that a mixed solution that
includes a surface-active agent is used as the electrolytic
solution, various particles such as electrolytic products from the
thrust plate material 23', which is the workpiece, are absorbed by
the surface-active agent within the electrolytic solution, which
ensures a smooth flow of the electrolytic solution.
[0082] In addition, in the electrolytic machining according to the
present embodiment, the ultrasonic vibration generating device 37
that provides ultrasonic vibration to the electrolytic solution is
provided, such that various particles such as electrolytic products
that elute from the workpiece are made to flow smoothly by the
ultrasonic vibration provided to the electrolytic solution.
[0083] According to the present embodiment, energization for
electrolytic machining and energization for ultrasonic vibration
take place independently of each other, and the energization Pa and
Ca for electrolytic machining and energization Pb and Cb for
ultrasonic vibration are alternated or at least partially
overlapped. As a result, energization for electrolytic machining
and energization for ultrasonic vibration can be switched as
necessary depending on the status of the electrolytic machining,
thereby ensuring the best machining condition at all times.
[0084] Next, FIGS. 12, 13, 14, 15 and 16 show another embodiment.
At the center part of a masking member 33 is formed a supply
opening 33a, which allows in an electrolytic solution, as a
through-hole formed in the axial direction. From the supply opening
33a, continuous hole patterns 33b, which include shapes that
correspond to thrust dynamic pressure generating grooves 23a and
23b, are formed to extend radially outward in the radial direction.
Each of the continuous hole patterns 33b is formed as a continuous
hole in the axial direction and is provided to extend further in
the radial direction as shown in FIG. 15 outward of the outer
circumference edge section (indicated by a broken line) of a part
that corresponds to the thrust dynamic pressure generating groove
23a or 23b, which is shaded. At the extended end part outward in
the radial direction of each continuous hole pattern 33b is a
discharge opening 33c, which discharges the electrolytic solution
to the outside.
[0085] Immediately above the masking member 33 is positioned
upright an electrode tool 35, which consists of a hollow rod-shaped
member, in the generally vertical direction and abutting the
masking member 33. The electrode tool 35 is fixed to a main body
arm section 36 that extends above a main body base section 31, and
the bottom end part of the electrode tool 35 is positioned
coherently to the top surface of the masking member 33 to press it
downward in the axial direction.
[0086] The electrolytic solution in accordance with the present
embodiment also flows while an appropriate amount thereof is
retained within a machining and storing section 41, which is
provided to cover the part where a thrust plate material 23', which
is a workpiece, and the electrode tool 35 are positioned opposite
to each other. The flow (charge and discharge) of the electrolytic
solution may be appropriately controlled to maintain the thrust
plate material 23' at an appropriate depth from the surface of the
electrolytic solution. The machining and storing section 41 has a
ring-shaped wall section 41a that is formed upright on the top
surface of a workpiece supporting jig 32; the electrolytic solution
is retained inside the ring-shaped wall section 41a to maintain a
predetermined solution surface height, and the part where the
thrust plate material 23' and the electrode tool 35 oppose each
other is immersed in the electrolytic solution.
[0087] The machining surface, which is the top surface, of the
thrust plate material 23', which is the workpiece, held by the
workpiece supporting jig 32 is positioned at a depth in the range
of about 5 mm to about 35 mm from the surface of the electrolytic
solution retained in the machining and storing section 41.
[0088] The electrolytic solution thus provided to the center part
of the masking member 33 from the electrode tool 35 flows into the
continuous hole patterns 33b provided in the masking member 33 and
comes into contact with the exposed surfaces of the thrust plate
material 23' as it flows in one direction outward in the radial
direction. When energization takes place across the electrode tool
35 and the thrust plate material 23' in this state, the parts of
the thrust plate material 23' that are in contact with the
electrolytic solution elute electrochemically, and the electrolytic
machining of the thrust plate material 23' takes place.
[0089] Since each continuous hole pattern 33b of the masking member
33 is provided to extend in the radial direction to the outer side
of the thrust plate material 23', the electrolytic solution that
flows within each continuous hole pattern 33b further outward in
the radial direction from the outer circumference edge of the
thrust plate material 23' is discharged outside through the
discharge opening 33c, which is provided at the outermost
circumference part of each continuous hole pattern 33b, and is
collected in a collection container not shown, and
re-circulated.
[0090] In the electrolytic machining of a dynamic pressure bearing
device according to the present embodiment, due to the fact that
the continuous hole patterns 33b of the masking member 33 are
extended in the radial direction outward of the outer circumference
edge section of the thrust plate material 23' so that the
electrolytic solution can be discharged from the discharge openings
33c provided at the outer extended end parts of the continuous hole
patterns 33b, the electrolytic solution supplied from the electrode
tool 35 can flow favorably into the continuous hole patterns 33b of
the masking member 33.
[0091] FIGS. 17, 18, and 21 shows still another embodiment. In the
generally center part of a workpiece supporting jig 32 attached to
a main body base section 31, a workpiece mounting concave section
is provided. A material (hereinafter called a thrust plate
material) 23' of a thrust plate 23 is lowered and mounted as a
workpiece into the workpiece mounting concave section. Immediately
above the thrust plate material 23' is positioned upright an
electrode tool 35, which consists of a rod-shaped member, in the
generally vertical direction. The electrode tool 35 is held by a
main body arm section 36 that extends above the main body base
section 31, and the bottom end part of the electrode tool 35 is
positioned to form a gap .delta. with the thrust plate material
23'.
[0092] Convexly formed patterns 35a that are shaped to correspond
to thrust dynamic pressure generating grooves 23a and 23b are
provided at the bottom end surface of the electrode tool 35, as
shown especially in FIGS. 19 and 20. Parts other than the patterns
35a are filled up with an insulator 35b made of resin, so that the
end surface of the electrode tool 35 is a flat surface. The end
surface including the patterns 35a is positioned opposite the
thrust plate material 23'.
[0093] In the meantime, in a gap .delta. between the electrode tool
35 and the thrust plate material 23', which is the workpiece, an
electrolytic solution is supplied to flow in the direction that is
generally orthogonal to the axial direction. The electrolytic
solution is delivered by an electrolytic solution supply device
(e.g., a pump), not shown. The electrolytic solution in the present
embodiment also flows while an appropriate amount thereof is
retained within a machining and storing section 41, which is
provided to cover the part where the thrust plate material 23',
which is the workpiece, and the electrode tool 35 are positioned
opposite to each other. The machining and storing section 41 has a
ring-shaped wall section 41a that is formed upright on the top
surface of a workpiece supporting jig 32; the electrolytic solution
is retained inside the ring-shaped wall section 41a to maintain a
predetermined solution surface height, and the part where the
thrust plate material 23' and the electrode tool 35 oppose each
other is immersed in the electrolytic solution.
[0094] The machining surface, which is the top surface, of the
thrust plate material 23', which is the workpiece, held by the
workpiece supporting jig 32 is positioned at a depth in the range
of about 5 mm to about 35 mm from the surface of the electrolytic
solution retained in the machining and storing section 41.
[0095] According to the present embodiment having such a structure,
even when the electrode tool 35 is placed in close proximity with
the thrust plate material 23', which is the workpiece, ultrasonic
vibration provided to the electrolytic solution causes various
particles such as electrolytic products that elute from the thrust
plate material 23' to flow smoothly, thereby maintaining a
favorable electrolytic machining; as a result, the shapes of the
patterns 35a provided on the electrode tool 35 is formed with high
precision on the thrust plate material 23'.
[0096] The above describes in detail the preferred embodiments of
the present invention, but many modifications can be made without
departing from the subject matter of the present invention.
[0097] For example, stainless steel material is used as the
workpiece (i.e., the thrust plate material 23') in the embodiments
described above, but the present invention can be similarly applied
to copper metals such as phosphor bronze.
[0098] Furthermore, although the embodiments are applications of
the present invention to a dynamic pressure bearing device of a
hard disk drive (HDD) motor, the present invention can be similarly
applied to other types of dynamic pressure bearing devices, as well
as to electrolytic machining methods for various types of
workpieces.
[0099] As described above, in an electrolytic machining method or
an electrolytic machining apparatus in accordance with embodiments
of the present invention, the machining surface of a workpiece is
positioned at a depth of about 5 mm to about 35 mm from the surface
of an electrolytic solution retained in a machining and storing
section to virtually eliminate any amount of air, especially oxygen
that may enter, from the electrolytic solution, and to favorably
maintain the fluidity of the electrolytic solution in order to
smoothly eliminate electrolytic products after electrolytic
machining; consequently, high quality and extremely high precision
electrolytic machining can be achieved easily.
[0100] Furthermore, the material of a shaft member or a bearing
member used in a dynamic pressure bearing device that utilizes the
dynamic pressure of a lubricating fluid may be used as the
workpiece, and dynamic pressure generating grooves are formed as
concave sections in the workpiece in order to achieve high
precision in the machining especially of the dynamic pressure
generating grooves; consequently, dynamic pressure bearing devices
can be manufactured in high quality and with extremely high
precision.
[0101] Moreover, a masking member having as through-holes
continuous hole patterns that correspond to the shapes of concave
sections is adhered to the machining surface of the workpiece. As a
result, the electrolytic solution is supplied to flow in a gap
between the masking member and the electrode tool in order to allow
the electrolytic solution to enter into the continuous hole
patterns of the masking member and thereby allow an electrolytic
machining to take place; and the electrolytic solution is allowed
to flow only within the continuous hole patterns of the masking
member that is adhered to the workpiece in order to easily and with
high precision form on the workpiece the concave sections whose
shapes correspond to the continuous hole patterns; consequently,
high precision electrolytic machining can be performed
inexpensively using a simple structure, which can significantly
improve the practicality of electrolytic machining.
[0102] A mixed solution containing a surface-active agent may be
used as the electrolytic solution in order to ensure a smooth flow
of the electrolytic solution. Consequently, effects described above
can be further enhanced.
[0103] Also, in accordance with the present invention, an
ultrasonic vibration generating device that provides ultrasonic
vibration to the electrolytic solution is provided in order to
allow the electrolytic solution, which contains various particles
such as electrolytic products that elute from the workpiece, to
flow smoothly due to the ultrasonic vibration; consequently,
effects described above can be further enhanced.
[0104] Furthermore, an insulating member is provided on at least
the surface part of the masking member to virtually completely
block energization of parts other than the continuous hole patterns
of the masking member in order to form the shapes of the concave
sections with even greater precision; consequently, effects
described above can be further enhanced.
[0105] While the description above refers to particular embodiments
of the present invention, it will be understood that many
modifications may be made without departing from the spirit
thereof. The accompanying claims are intended to cover such
modifications as would fall within the true scope and spirit of the
present invention.
[0106] The presently disclosed embodiments are therefore to be
considered in all respects as illustrative and not restrictive, the
scope of the invention being indicated by the appended claims,
rather than the foregoing description, and all changes which come
within the meaning and range of equivalency of the claims are
therefore intended to be embraced therein.
* * * * *