U.S. patent application number 12/485385 was filed with the patent office on 2009-11-05 for hydrodynamic bearing member and manufacturing method thereof.
Invention is credited to Makoto HASEGAWA, Hiroyuki KIRIYAMA, Hiroshi NISHIYAMA.
Application Number | 20090271986 12/485385 |
Document ID | / |
Family ID | 37418867 |
Filed Date | 2009-11-05 |
United States Patent
Application |
20090271986 |
Kind Code |
A1 |
NISHIYAMA; Hiroshi ; et
al. |
November 5, 2009 |
HYDRODYNAMIC BEARING MEMBER AND MANUFACTURING METHOD THEREOF
Abstract
The present invention aims to improve the efficiency of a
clamping step for combining a flange with a shaft and to improve
productivity. The shaft and the flange are tentatively combined in
the tentative clamping step. In the tentative clamping step, a
concave part at the end of the shaft is pressurized by a metal mold
such as a ball to be enlarged in an outer circumferential
direction, thereby pressurizing this concave part against the inner
circumference of the flange so as to fix the concave part. The
combined body made by tentatively combining the shaft and the
flange is strongly combined in a proper clamping step. In order to
correct a distortion such as a warpage of the flange that has been
solidly combined by the proper clamping step, sandwiching the
flange by the upper and lower metals, the flange is pressurized and
a flash molding is carried out.
Inventors: |
NISHIYAMA; Hiroshi; (Ehime,
JP) ; KIRIYAMA; Hiroyuki; (Ehime, JP) ;
HASEGAWA; Makoto; (Tottori, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK L.L.P.
1030 15th Street, N.W., Suite 400 East
Washington
DC
20005-1503
US
|
Family ID: |
37418867 |
Appl. No.: |
12/485385 |
Filed: |
June 16, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11404895 |
Apr 17, 2006 |
|
|
|
12485385 |
|
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Current U.S.
Class: |
29/898.02 |
Current CPC
Class: |
F16C 43/02 20130101;
Y10T 29/49639 20150115; F16C 17/045 20130101; F16C 35/02 20130101;
B21K 25/00 20130101; G11B 19/2018 20130101; F16C 2226/78
20130101 |
Class at
Publication: |
29/898.02 |
International
Class: |
F16C 43/00 20060101
F16C043/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 18, 2005 |
JP |
P2005-120224 |
Claims
1-5. (canceled)
6. A manufacturing method of a hydrodynamic bearing member
comprising: a tentative clamping step of inserting a mounting part
of the shaft into a hole of the flange, pressurizing the concave
part of the shaft by a metal mold formed in a certain shape to
enlarge the mounting part, and tentatively combining the flange
with the shaft; a proper clamping step of pressurizing the opposite
faces of the flange by the metal mold while binding the outer
circumference of the flange and making the inner circumferential
part of the hole of the flange to bite into the step part of the
shaft to clamp the flange with the shaft in the flange and the
shaft that were tentatively combined in the tentative clamping
step; and a flash molding step of correcting a distortion of the
flange by pressurizing the opposite faces of the flange; wherein
the hydrodynamic bearing member comprises a shaft having a step
part with a surface that is approximately vertical to a center axis
of a column-shaped member formed at one end of the column-shaped
member, and a mounting part having a diameter larger than the
minimum diameter of the step part and forming a concave part on the
end face; and a flange shaped in a disc having a hole into which
the mounting part of the shaft is inserted.
7. The manufacturing method of the hydrodynamic bearing member
according to claim 6, wherein the front end of the metal mold to
pressurize the concave part is shaped in a ball.
8. The manufacturing method of the hydrodynamic bearing member
according to claim 6, wherein the metal mold pressurizing the
concave part has a plurality of projections, and the projection
enlarges the mounting part to the outer circumferential
direction.
9. The manufacturing method of the hydrodynamic bearing member
according to claim 6, wherein the hydrodynamic bearing member has a
groove mold for forming a dynamic pressure generation groove on the
abutting face of the flange on at least one pressurized face of
each metal mold for pressurizing the opposite faces of the flange
in the proper clamping step.
10. The manufacturing method of the hydrodynamic bearing member
according to claim 6, wherein the concave part disposed on the end
face of the shaft is formed in a cone, a truncated cone or a
column.
11. The manufacturing method of the hydrodynamic bearing member
according to claim 6, wherein the concave part disposed at the end
face of the shaft has an inner diameter that is gradually enlarged
toward the end of the shaft.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a hydrodynamic bearing
member that is used in a motor for rotatably driving a disc
recording medium and a manufacturing method thereof.
[0003] 2. Description of the Related Art
[0004] A hard disc drive (HDD) has an excellent function as a
storage unit that can record and reproduce a large amount of data.
Not only personal computers but also various kinds of home electric
appliances including audio-visual products which have HDD included
therein have been wide spread. A HDD requires rotating a disc at a
high speed and with a high degree of accuracy and also a HDD
requires a decay durability (a longer operating life) that can
stand long use, which is why a spindle motor using a hydrodynamic
bearing member has been used as a motor thereof.
[0005] In recent years, due to development of compact digital
equipment such as a compact portable music record reproduction
apparatus and a recording medium for a digital camera having a HDD
incorporated, HDD are required to be further reduced in size and
thickness. In order to reduce its size and thickness, it is
necessary to reduce the spindle motor for rotatably driving a disc
in size and thickness. A typical conventional example of such a
spindle motor is shown in a sectional view in FIG. 11.
[0006] In FIG. 11, a housing 21 has a cylindrical part 21a at a
center part, and the cylindrical part 21a is provided with a sleeve
22. In a bearing hole 22a of the sleeve 22, a shaft 23 is rotatably
inserted. At the lower end of the shaft 23, a flange 25 is fitted.
An opening of the lower end of the sleeve 22 is sealed by a thrust
support 24. On at least one of the outer circumferential of the
shaft 23 and the inner circumferential face of the bearing hole
22a, a radial dynamic pressure generation groove is disposed. In
addition, on at least one of the opposed faces of the flange 25 and
the thrust support 24, a thrust dynamic pressure generation groove
is disposed. Between the shaft 23 and the sleeve 22 and between the
thrust support 24 and the flange 25, fluid such as oil is loaded so
as to compose a hydrodynamic bearing that is well known in the
art.
[0007] By way of example, the following materials are used as a
material of each part. As the housing 21, an aluminum die cast
material or an iron material is used, and as the sleeve 22, a
material obtained by nickel-plating a brass material (a copper
alloy) is used. As the shaft 23, a stainless steel material (for
example, SUS420J2) is used, and as the flange 25, a stainless steel
material (for example, SUS304) is used. Further, as the thrust
support 24, a stainless steel material (for example, SUS420J2) is
used, and as the hub 27, a stainless steel material (for example,
DHS1) or an aluminum material is used.
[0008] On the upper end portion of the shaft 23, the hub 27 is
fitted. At the center part of the shaft 23, a screw hole 31
disposed in parallel with the axial direction of the shaft 23 is
formed. By screwing a screw (its illustration is herein omitted)
into the screw hole 31 and fixing a clamp member (its illustration
is herein omitted), a magnetic disc or the like to be fitted to a
disc support face 27g at the outer circumferential part of the hub
27 is held. On the inside of the hub 27, a rotor magnet 37 is
provided. A stator core 29 with a coil wounded threaround is fitted
to the housing 21 so as to oppose the rotor magnet 37.
[0009] When the current is applied to the coil wound around the
stator core 29, a magnetic force in a radial direction works
between the stator core 29 and the rotor magnet 37, and then,
receiving a driving force due to this magnetic force, the hub 27,
the shaft 23, and the flange 25 are rotated without contacting the
thrust support 24 and the sleeve 22.
[0010] In order to reduce noise and oscillation, the stator core 29
and the magnet 37 are arranged with the magnetic center position in
each axial direction misaligned so as to generate a magnetic
attraction force in the axial direction. In place of this
structure, arranging a ring-type suction plate in the housing 21
just below a magnet 37 (not illustrated in FIG. 11), the attraction
force in the axial direction may be generated in the hub 27.
[0011] As compared to a hard disk drive incorporated in a common
personal computer, the compact hard disk drive for the
above-described use has many opportunities to turn on and off, and
on each occasion, the motor of the hard disk drive activates and
stops. Upon the activation and the stop of the motor, a force is
added to a connection part between the shaft 23 and the flange 25
in the hydrodynamic bearing incorporated in such a motor. In
addition, high impact may occur when the motor is dropped on a
floor during use. Therefore, it is especially needed to set the
connection intensity of the shaft 23 and the flange 25 sufficiently
high.
[0012] As a conventional method to connect the shaft and the
flange, there is a "press work method" shown in the JP-A No.
2004-204916. According to the press work method, a circular flange
member having a shaft mounting hole at its center and a shaft to be
inserted in the shaft mounting hole have been manufactured as a
component in advance. The shaft and the flange member are connected
in the following respective steps.
Step (1):
[0013] A concave mold (a metal mold) having a hole for inserting a
shaft at its center and having an inner diameter that is slightly
larger than an outer diameter of a flange member is mounted on a
pressing machine, and in the hole of this concave mold, a shaft is
loaded (hereinafter, in place of "load", "set" is used).
Step (2):
[0014] Inserting the end of the shaft in the shaft mounting hole of
the flange member, the flange member is set in the concave mold.
There is a minute gap between the outer circumferential face of the
flange member and the inner circumferential face of the concave
mold, however, the outer circumferential face of the flange member
is bound substantially by the inner circumferential face of the
concave mold. The concave mold moving being opposed to the concave
mold is fitted to the pressing machine so as to add a predetermined
press pressure on the face of the flange member. For example, at
least one of the bottom face of the concave mold and the surface of
a convex mold has a whorl-like groove in order to form the thrust
dynamic pressure generation groove on the opposite surfaces or one
surface of the flange member.
Step (3):
[0015] Operating the pressing machine, the opposite surfaces of the
flange member are sandwiched by the concave mold and the convex
mold to apply pressure thereto (a pressure step). During the
pressure step, the thrust dynamic pressure generation groove is
formed on the opposite surfaces or one surface of the flange
member.
[0016] During this pressure step, the flange member having the
opposite surfaces compressed intends to stretch in the outer
circumferential direction; however, the outer circumferential face
is bound by the concave mold and this makes the flange member
stretch toward the shaft mounting hole. As a result, the diameter
of the shaft mounting hole is decreased (hereinafter, referred to
as a contraction of a diameter) to be fastened by the shaft.
Step (4):
[0017] The shaft whereby the flange member is fixed is detached
from the concave mold.
[0018] The flange member fastened by the shaft has a distortion (a
warpage) generated in the pressure step and the warpage is
corrected in the next step (a correcting step).
Step (5):
[0019] In the correction step, a flange mounted on the shaft is set
between two flat metal molds having flat faces.
Step (6):
[0020] Closing two flat metal molds, the opposite surfaces of the
flange are pressurized to carry out flash molding.
Step (7):
[0021] The flange is detached from the flat metal mold.
[0022] By the steps (1) to (7), the shaft having the flange member
mounted thereon is manufactured. The steps (1) to (4) are referred
to as "a compression molding step", and the steps (5) to (7) are
referred to as "a flash molding step". Further, the shaft having
the flange member mounted thereon will be called "a hydrodynamic
bearing member".
[0023] In the manufacturing step of the conventional hydrodynamic
bearing member, at least steps (1) and (2) are carried out by the
manual operations by a worker. Therefore, a necessary time of the
steps (1) and (2) largely depends on the skill of the worker. In
addition, when the flange member is set in the concave mold in the
step (2), the flange member may not be set accurately. For example,
the edge of the flange member may be set overlapping the edge of
the concave mold. This involves a problem that an expensive concave
mold and convex mold are damaged and they cannot be used if the
concave mold and the convex mold are closed in this state.
[0024] The compression molding steps (1) to (4) and the flash
molding steps (5) to (7) have different working hours (the tact
hour). In other words, normally, the working hours of the
compression molding step is longer. Therefore, both steps cannot
progress in parallel and it is difficult to improve productivity.
As a result, it is difficult to decrease a manufacturing cost
thereof.
SUMMARY OF THE INVENTION
[0025] The present invention has been made taking the foregoing
problems into consideration and an object of which is to provide a
high-grade hydrodynamic bearing member at a low cost and a
manufacturing method thereof.
[0026] A hydrodynamic bearing member according to the present
invention may comprise a shaft having a step part with a surface
that is approximately perpendicular to a center axis of a
column-shaped member formed at one end of the column-shaped member,
and a mounting part having a diameter larger than the minimum
diameter of the step part and forming a concave part on the end
face; and a flange shaped in a disc having a hole into which the
mounting part of the shaft is inserted; wherein one surface of the
flange abuts against the step part of the shaft, and the shaft and
the flange are combined by the clamping processing.
[0027] According to this invention, since one surface of the flange
abuts against the step part of the shaft, the flange is mounted on
the shaft at a correct angle. Since the flange is mounted on the
shaft by the clamping processing, the inner circumferential part of
the hole on the flange bites into the step part of the shaft, and
the shaft and the flange are solidly attached with each other.
[0028] A manufacturing method of a hydrodynamic bearing member
according to the present invention comprises a tentative clamping
step of inserting a mounting part of the shaft into a hole of the
flange, pressurizing the concave part of the shaft by a metal mold
formed in a certain shape to enlarge the mounting part, and
tentatively combining the flange with the shaft; a proper clamping
step of pressurizing the opposite faces of the flange by the metal
mold while binding the outer circumference of the flange and making
the inner circumferential part of the hole of the flange to bite
into the step part of the shaft to clamp the flange with the shaft
in the flange and the shaft that were tentatively combined in the
tentative clamping step; and a flash molding step of correcting a
distortion of the flange by pressurizing the opposite faces of the
flange; wherein the hydrodynamic bearing member comprises a shaft
having a step part with a surface that is approximately vertical to
a center axis of a column-shaped member formed at one end of the
column-shaped member, and a mounting part having a diameter larger
than the minimum diameter of the step part and forming a concave
part on the end face; and a flange shaped in a disc having a hole
into which the mounting part of the shaft is inserted.
[0029] According to this invention, by tentatively attached the
shaft and the flange with each other in a tentative clamping step,
in the following proper clamping step, it becomes very easy to
treat the shaft and the flange in a step of loading the shaft and
the flange in the metal mold for the proper clamping step. The
tentatively clamped shaft and flange are solidly attached in the
proper clamping step. A hydrodynamic bearing device can be
appropriately made by using this hydrodynamic bearing member.
Moreover, a spindle motor can be made appropriately by using this
hydrodynamic bearing device.
[0030] According to the present invention, in the step of
connecting the shaft and the flange, which are component parts of a
hydrodynamic bearing, each other, the shaft and the flange have
been previously made into one unit in the tentative clamping step.
The metal mold in the tentative clamping step is easily composed
and the operation to set the shaft and the flange in the metal mold
is simple. Since the shaft and the flange that are made into one
unit by the tentative clamping can be easily treated, they can be
easily set in a slightly-complex metal mold used in the proper
clamping step. Therefore, it is possible to prevent the shaft and
the flange from being set in the metal mold by mistake and damage
to the metal mold can be prevented. Moreover, by applying the
member to a hydrodynamic bearing, the hydrodynamic bearing with
excellent productivity and high reliability is obtained. In
addition, by applying this hydrodynamic bearing to a spindle motor,
the spindle motor with high reliability is obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a sectional view showing the state that a shaft
and a flange, which are components of a hydrodynamic bearing
member, according to a first embodiment of the present invention
are combined;
[0032] FIG. 2 is a sectional view showing a tentative clamping step
of the shaft and the flange that are combined in FIG. 1;
[0033] FIG. 3 is a sectional view of an upper metal mold and a
lower metal mold for carrying out proper clamping of a tentative
clamping bearing support 10 that was tentatively clamped in a
tentative clamping step;
[0034] FIG. 4 is a sectional view of upper and lower metal molds
showing the state just before the proper clamping step that the
tentative clamping bearing support 10 that is tentatively clamped
is loaded in the lower metal mold shown in FIG. 3;
[0035] FIG. 5 is a sectional view of upper and lower metal molds
showing the proper clamping step;
[0036] FIG. 6 is a sectional view of a bearing member that the
proper clamping step has been completed;
[0037] FIG. 7 is a sectional view of upper and lower metal molds
showing a flash molding step for correcting a warpage of the
flange;
[0038] FIG. 8 is a sectional view of a part of a shaft of a
hydrodynamic bearing member according to a second embodiment of the
present invention;
[0039] FIG. 9 (a) is a perspective view of a front end of the upper
metal mold that is used for the tentative clamping step of the
second embodiment according to the present invention;
[0040] FIG. 9 (b) is a perspective view of a front end of the other
example of the upper metal mold that is used for the tentative
clamping step of the second embodiment according to the present
invention;
[0041] FIG. 10 is a view showing an end face of the shaft that was
tentatively clamped in the second embodiment according to the
present invention; and
[0042] FIG. 11 is a sectional view showing the structure of a
typical spindle motor having the hydrodynamic bearing member.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0043] The preferred embodiments of a hydrodynamic bearing member
and a manufacturing method thereof according to the present
invention will be described below with reference to FIGS. 1 to 9.
The "hydrodynamic bearing member" means a member in which a shaft
serving as a radial bearing and a flange serving as a thrust
bearing which are main components of hydrodynamic bearing have been
combined into one unit.
[0044] The hydrodynamic bearing member according to the first
embodiment of the present invention will be described with
reference to FIGS. 1 to 7.
[0045] FIG. 1 is a partial sectional view of a hydrodynamic bearing
member of the first embodiment showing the state that a shaft 1 and
a flange 5 are combined. The shaft 1 is a column-shaped member
having an annular step part 2 having a face approximately vertical
to a center axis of the shaft 1 is formed at one end 1a, and the
shaft 1 is made of a metal material of a stainless steel such as
SUS420. A mounting part 3 of the shaft 1 is formed in the shape of
a circular cylinder having a face larger than the smallest diameter
of the step part 2 and being parallel to the axial direction (an
arrow a) of the shaft 1. On the center part of the mounting part 3,
for example, a concave part 4 having a section shaped in a cone, a
truncated cone or a mortar is formed. At the lower end of the
shaft, a narrow diameter part 1e is formed.
[0046] The flange 5 is a disc member having a shaft mounting hole 6
for mounting the shaft at the center and the flange 5 is made of a
metal material of a stainless steel such as SUS304. Fit of the
mounting part 3 and the shaft mounting hole 6 may be loose to the
extent that the mounting part 3 can be easily inserted in the shaft
mounting hole 6.
[0047] The manufacturing step of coupling the shaft 1 and the
flange 5 shown in FIG. 1 will be described below with reference to
FIGS. 2 to 7. The manufacturing step of the present embodiment 1 is
composed of (A) a tentative clamping step, (B) a proper clamping
step, and (C) a flash clamping step. The "tentative clamping" means
tentatively coupling the shaft 1 and the flange 5, and this step is
referred to as the "tentative clamping step". The description of a
specific example of the tentative clamping step is as follows. In
the case that a diameter d1 of the mounting part 3 is about 1.9 mm
and a diameter d2 of the concave part 4 is about 1.2 mm, a clamping
metal mold 9 having a ball with a diameter 3 mm or a front end 9a
shaped in a ball is moved in a direction indicated by an arrow 9b
to add a pressure of about 250 kgf.
[0048] The "proper clamping step" is a step of solidly fixing the
shaft 1 and the flange 5. The "flash molding step" is a step of
correcting a distortion such as a warpage of the flange.
[0049] The tentatively clamped shaft 1 and flange 5 are referred to
as "a tentative clamping bearing support 10".
[0050] In FIG. 2, a fixing jig 8 and the clamping metal mold 9 are
mounted on a pressing machine (not illustrated), and in operation,
the clamping metal mold 9 is moved to the direction indicated by
the arrow 9b.
(A) Tentative Clamping Step
[0051] Step (A1): By the manual operation, the shaft 1 is inserted
in a hole 8a of a fixing jig 8 with its end 1a turned up. Step
(A2): The mounting part 3 of the shaft 1 is inserted in the shaft
mounting hole 6 of the flange 5. Step (A3): Operating the pressing
machine, the concave part 4 of the shaft 1 is pressed or struck at
the ball of the clamping metal mold 9 or the front end 9a shaped in
the ball. The diameter of the ball-shaped part of the front end 9a
is preferably large to the extent that the sphere face of this
ball-shaped part contacts the diameter (d2 in FIG. 1) of the upper
face of the concave part 4. As a result, the concave part 4 is
opened outside and in accordance with this, the mounting part 3 is
opened outside. Further, as a result, the mounting part 3 may
compress the inner face of the shaft mounting hole 6 and the shaft
1 is "tentatively clamped" by the flange 5. Step (4a): The
tentatively clamped bearing support 10 is detached from the jig 8
to be kept in a predetermined container.
(B) Proper Clamping Step
[0052] The proper clamping step of the tentatively clamped bearing
support 10 will be described with reference to the sectional views
from FIG. 3 to FIG. 5. FIG. 3 is a side sectional view only showing
a metal mold of a pressing machine (not illustrated) used in the
proper clamping step.
[0053] In the drawing, both of a lower metal mold 11 and an upper
metal mold 12 are mounted on the pressing machine that has been
well known generally, and in press working, for example, the upper
metal mold 12 is moved in the direction indicated by an arrow b to
carry out the press working.
[0054] The lower metal mold 11 has a concave part 11a on the upper
face and has a hole 11b on the center of the concave part 11a. A
depth of the concave part 11a, namely, a height of a side face 11c
is made to be slightly lower than the thickness of the flange 5. On
a bottom face 11d of the concave part 11a, a molding tool for
forming a thrust dynamic pressure generation groove is disposed on
the lower face of the flange 5 in FIG. 1, however, there is a case
that this is not disposed. The diameter of the side face 11c of the
concave part 11a is made to be slightly larger than that of the
flange 5 so that the flange 5 can be easily inserted in the concave
part 11a.
[0055] On a lower face 12a of an upper metal mold 12, a molding
tool for the thrust dynamic pressure generation groove is
disposed.
[0056] FIG. 4 shows the state that the tentatively clamped bearing
support 10 to be processed is set in the lower metal mold 11 by the
manual operation or the automatic loading in a step (B1) of the
proper clamping step. In the drawing, the shaft 1 is inserted in
the hole 11b. A gap is formed between the lower end of the shaft 1
and the bottom face of the hole 11b of the lower metal mold 11, and
this gap is set to be at a larger value than the height of the mold
of the thrust dynamic pressure generation groove formed on the
bottom face 11d of the lower metal mold 11.
[0057] In a step (B2), causing the upper metal mold 12 to decline
as shown in FIG. 5, the upper face of the flange 5 is pressed to
carry out the proper clamping. Thereby, the thrust dynamic pressure
generation groove is formed on the upper and lower faces of the
flange 5 and the flange 5 is crushed to attempt to stretch in a
direction along the face. Since the outer circumference of the
flange 5 is bound by the side face 11c of the concave part 11a of
the lower metal mold 11, the flange 5 cannot stretch to the
direction of the outer circumference. Therefore, the lower end of
the inner circumference of the flange 5 stretches toward a gap 2a
between the step part 2 of the shaft 1 and the flange 5 to bite
into the gap 2a. As a result, the shaft 1 and the flange 5 are
strongly combined. According to this proper clamping step, even if
the face of the step part 2 of the shaft 1 is not at a right angle
to the axis and has some angle errors, by modifying the flange 5
along the metal mold, the right angle of the face of the flange 2
is processed in a desired degree of accuracy by the metal mold.
Therefore, this has an advantage such that a degree of accuracy of
a completed product is not largely affected even if there are some
errors in the size of the component.
[0058] A specific example is set forth as follows. For example, in
the case that a diameter d3 of a small diameter part is about 1.9
mm, a diameter d4 of the concave part 4 is about 1.5 mm, and a
depth d5 of the concave part is 0.6 mm in FIG. 6, a welding force
of the pressing machine is about 4 to 5 tons.
[0059] It is assumed that a combined body made by the shaft 1 and
the flange 5, for which a proper clamping step has been completed,
is referred to as "a proper clamped bearing 10a".
[0060] In a step (B3), the proper clamped bearing 10a is detached
from the lower metal mold 11. FIG. 6 is a partial sectional view of
the completed proper clamped bearing 10a. As shown in the drawing,
the inner circumferential part of the flange 5 throws out at the
step part 2 of the shaft (this may be referred to as a contraction
of a diameter) to bite into the concave part formed on the step
part 2 of an end a of the shaft 1.
(C) Flash Molding Step
[0061] In a step (C1), the proper clamped bearing 10a is set in a
lower metal mold 14 and an upper metal mold 15 mounted on the other
pressing machines shown in FIG. 7.
[0062] In a step (C2), causing the upper metal mold 14 to decline
as shown in FIG. 7 so as to pressurize the flange 5 and sandwich
the flange 5, the flash clamping is carried out so as to correct
the warpage of the flange 5.
[0063] In a step (C3), the proper clamping bearing 10a that was
flash-molded is detached from the lower metal mold 14.
[0064] According to the above-described respective steps, the
completed hydrodynamic bearing member can be obtained.
[0065] According to the manufacturing method of the first
embodiment, it is possible to make the necessary time of the step
(A) from the step (A1) to the step (A3), the necessary time of the
step (B) from the step (B1) to the step (B3), and the necessary
time of the step (C) from the step (C1) to the step (C3) can be
made approximately the same. Therefore, when carrying out the steps
A, B, and C in parallel, "waiting" is not generated so often in the
all manufacturing steps from the step (A) to the step (C) and this
leads to the improvement of a productivity. In addition, by
providing the tentative clamping step, "the tentative clamped
bearing support 10" that was tentatively-clamped can be easily
treated. In the proper clamping step shown in FIGS. 4 to 5, the
tentative clamped bearing support 10 can be normally loaded in the
lower metal mold 11 without fail and there is no fear to damage the
lower metal mold 11 and the upper metal mold 12 due to the error
loading. In the proper clamping state shown in FIG. 4, it becomes
easy to automatically load the tentative clamped bearing support 10
in the lower metal mold 11 by using a part feeder or a robot for an
industry or the like, so that the productivity thereof can be
largely improved. Further, the cost can be largely decreased.
[0066] The hydrodynamic bearing member according to the second
embodiment of the present invention will be described with
reference to FIG. 8 and FIG. 9. In the present embodiment, the
shape of the end of the shaft 18 is different from the shaft 1 of
the embodiment 1. The shape and the structure of the flange are
substantially the same as those of the first embodiment.
[0067] FIG. 8 is a sectional view of the end of the shaft 18
according to the second embodiment. In the drawing, the shaft 18
has a small diameter part 18a and a step part 18b at the right end
of the column-shaped member. A roll off 18d of which diameter is
smaller than that of the small diameter part 18a is formed between
the small diameter part 18a and the step part 18b. At the right end
of the shaft 18, a mounting part 18c of which diameter is larger
than that of the small diameter part 18a is formed. On the right
end face of the shaft 18, a concave part 18e is formed. The side
wall of the concave part 18e has a slope that the diameter thereof
is gradually enlarged from a bottom part diameter d6 to the right
end of the shaft. The size of each part of the shaft 18 according
to the specific example is as follows. The diameter of the shaft 18
is 2.4 mm, the diameter of the small diameter part 18a is 1.5 mm,
the diameter of the mounting part 18c is 1.9 mm, the bottom part
diameter d6 of the concave part 18e is 1.5 mm, and a depth d7 of
the concave part 18e is 0.06 mm. On the center part of the concave
part 18e, a concave part shaped in a cone, a truncated cone or a
column may be formed.
[0068] In the case of tentatively clamping this shaft 18 into the
flange 5, by using clamping metal mold 16 or 19 having three
projections shown in FIG. 9 (a) or FIG. 9 (b), the pressure may be
added to the side wall that is enlarged outside of the concave part
18e or the side wall and the end face.
[0069] FIGS. 9 (a) and 9 (b) are perspective views of the front
ends of the clamping metal molds 16 and 19 that are used in the
tentative clamping step, respectively. In the clamping metal mold
shown in FIG. 9 (a), a flat part 16a approximately in a triangle
shape is formed at the front end, and three angles of the triangle
compose a projection part 16b. FIG. 9 (b) is a perspective view of
the front end of the clamping metal mold 19 according to the other
example. The clamping metal mold 19 shown in FIG. 9 (b) has three
projections 19b shaped in a circular arc at the front end. The
height from an end face 19a of a projection 19b is about 0.5 to 1.0
mm. A diameter d8 of a circle enclosing the outer circumferences of
three projections 16b or three projections 19b is defined to be
larger than the bottom part diameter d6 of the concave part 18e and
be smaller than the diameter of the mounting part 18c. The clamping
metal mold 16 or 19 is turned upside down to be used in place of
the clamping metal mold 9 shown in FIG. 2.
[0070] According to the second embodiment, in place of the clamping
metal mold 9 according to the first embodiment shown in FIG. 2, the
proper clamping will be carried out by using this clamping metal
mold 16. Composing the pressing machine in the same way as FIG. 2
and pressurizing the concave part 18e of the shaft 18 by the
clamping metal mold 16, the mounting part 18c has three parts
pressed by three projection parts 16b of the clamping metal mold 16
which are enlarged to the outer circumferential direction to be
pressed to the inner circumferential face of the flange 5. As a
result, the mounting part 18c of the shaft 18 is fixed at three
positions by the flange 5 and the tentative clamping is carried
out. In the tentative clamping step, the same applies to the
clamping metal mold 19.
[0071] In the tentative clamping step according to the second
embodiment, since three comparatively narrow parts of the mounting
part 18c of the shaft 18 are enlarged to the outer circumferential
direction, the welding force given to the clamping metal mold 16 in
the tentative clamping step may be smaller than that of the first
embodiment. Accordingly, as the pressing machine used for the
tentative clamping step, a compact one can be used. In the shaft 18
shown in FIG. 8, the welding force is about 70 kgf. According to
the second embodiment, the number of the projection parts 16b of
the clamping metal mold 16 is three; however, this number is not
limited to three and it may be smaller than three or larger than
three. In the second embodiment, each step following the tentative
clamping step is the same as the first embodiment. In the proper
clamping step, the inner circumferential part of the flange 5 is
contracted to bite into the roll off 18d of the shaft 18, and then,
the flange 5 is solidly fixed to the shaft 18. FIG. 10 is a plan
view showing the states of the shaft end face and the flange face
after the proper clamping step in the present embodiment. As shown
from the drawing, in the tentative clamping step, a concave part 20
that is formed when pressing the mounting part 18c by the clamping
metal mold 16 or 19 having three projections shown in FIG. 9 (a) or
FIG. 9 (b) can be seen.
[0072] By applying the hydrodynamic bearing member described in the
first and second embodiments to a hydrodynamic bearing and a
spindle motor including it as shown in FIG. 11, the hydrodynamic
bearing device and the spindle motor with high reliability are
provided.
[0073] The present invention is available for the mass production
of the bearing member of the hydrodynamic bearing member.
* * * * *