JP2008275044A - Fluid bearing device and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluid bearing device capable of an excellent caulking fixation, by improving impact resistance with a simple constitution. <P>SOLUTION: A groove part 20 is formed on an outer peripheral surface of a sleeve opposed to an outer peripheral surface of a thrust plate 12 for blocking up the sleeve having a bearing hole for constituting a fluid bearing device. A caulking part of the sleeve is deformed by caulking. When fixing the thrust plate, the impact resistance and vibration resistance are improved without generating a broken piece and a crack of an outer peripheral surface of the sleeve, and internal stress can be uniformized after caulking, and deformation to the thrust plate is also reduced. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a spindle motor that rotationally drives a disk such as a magnetic disk or an optical disk, and more particularly, to a structure of a fastening part of a sleeve and a thrust plate that constitute a hydrodynamic bearing device, and a manufacturing method thereof. .

  Hard disk drives (hereinafter referred to as HDDs) are becoming popular as storage devices capable of recording and reproducing large amounts of data not only in personal computers but also in various home appliances including audiovisual products. . With the spread of small digital devices such as a small portable music recording / playback device incorporating a HDD and a recording medium for a digital camera, the HDD is required to be further reduced in size and thickness. In addition, miniaturized / thinned HDDs are used for various purposes, and it is necessary to improve the performance of vibration resistance and shock resistance more than ever.

  Since the HDD needs to rotate the disk at high speed and with high accuracy, and requires vibration resistance, impact resistance, and durability (long life), a hydrodynamic bearing device that rotates in a non-contact manner is used. A spindle motor is used.

  The hydrodynamic bearing device used in the spindle motor holds a lubricating fluid therein. When the lubricating fluid leaks, the rotating body and the fixed body are seized, so that the rotation is stopped, and data writing and reading of the HDD cannot be performed. For this reason, it has become important to fasten the lubricating fluid so that the lubricating fluid does not leak from the fastening portion that fastens the components of the hydrodynamic bearing device.

  Various investigations such as a welding method, an adhesive method, a press-fitting method, and a caulking method have been performed on the structure and the fastening method of the fastening portion for fastening each component of the hydrodynamic bearing device. Among them, the caulking method is adopted in many parts because the equipment cost is low and the number of assembly steps is small.

  For example, in the hydrodynamic bearing device 101 shown in FIG. 6, the thrust plate 103 is provided on the inner peripheral side of the caulking portion 102a that protrudes toward the axially outer side (lower direction in the figure) of the sleeve 102 having the bearing hole. Has been placed. Further, an outer peripheral relief portion 104 is formed on the outer peripheral portion of the crimping portion 102a.

A caulking deformation protrusion that occurs when the caulking part 102a is deformed by applying a pressing force (pressing force) to the caulking part 102a in the axial direction (upward direction in the figure) and deforming it to the state of the caulking part 102aa after deformation. The part 102 b projects to the outer peripheral relief part 104. Therefore, the deformation force of the caulking portion 102 a does not affect the dimensional accuracy such as the parallelism of the thrust plate 103. As a result, a technique is disclosed in which the size of the bearing gap formed between the thrust plate 103 and the thrust flange 105 is maintained with high accuracy.
JP 2002-317815 A

  However, as shown in FIG. 6, the outer peripheral surface shape is in a state where tensile stress is concentrated on the outer peripheral surface because the caulking deformation projecting portion 102 b is formed. That is, it can be said that the outer peripheral surface of the crimped portion 102aa after crimping is always pulled. When an external impact / vibration is applied to the caulking portion 102aa in a state where the outer peripheral surface is pulled, the tensile stress on the outer peripheral surface is increased, and breakage / cracking or the like occurs in a fine portion. . The generated fracture portion progresses with time and destroys the caulking portion 102aa, so that the thrust plate 103 cannot be fixed to the sleeve 102, and the lubricating fluid leaks from the bearing gap. It will be.

  Therefore, in order to improve impact resistance and vibration resistance with a simple configuration, the present invention makes it possible to rupture the outer peripheral surface of the sleeve by uniformizing the stress concentration due to caulking at the portion where the sleeve and the thrust plate are caulked and fixed. It is an object of the present invention to provide a method of manufacturing a hydrodynamic bearing device that can be prevented.

In order to solve the above-described conventional problems, a method of manufacturing a hydrodynamic bearing device according to the present invention includes a shaft, a sleeve having a bearing hole into which the shaft is rotatably inserted, an end face of the shaft, and the sleeve. A hydrodynamic bearing device that has a thrust plate for closing the bearing hole, and fixes the thrust plate to the sleeve by a caulking method,
A first step of forming a crimped portion on the closed side of the sleeve; a second step of forming a groove portion on an outer peripheral surface of the crimped portion; and a third step of inserting the thrust plate into the bearing hole of the sleeve. And a fourth step of caulking and fixing the thrust plate by deforming the caulking portion in the inner circumferential direction with the groove portion as a base point.

  The hydrodynamic bearing device of the present invention includes a shaft, a sleeve having a bearing hole into which the shaft is rotatably inserted, a thrust plate facing the end surface of the shaft and closing the bearing hole of the sleeve, And a lubricating fluid interposed in a gap formed by the shaft and the sleeve and the thrust plate, and an outer circumferential surface of an annular caulking portion for caulking and fixing the thrust plate formed on the sleeve Has a surface roughness portion different from the other outer peripheral surface of the sleeve.

  Further, in the hydrodynamic bearing device, the different surface roughness portion is characterized in that it is one half of the surface roughness of the other outer peripheral surface of the sleeve.

  According to the method of manufacturing a hydrodynamic bearing device of the present invention, it becomes possible to suppress the occurrence of fracture and cracking of the outer peripheral surface of the caulking portion of the sleeve by the caulking method, and to prevent leakage of the lubricating fluid from the inside of the hydrodynamic bearing device. Can do. In addition, deformation of the thrust plate constituting the thrust bearing portion can be prevented, and a minute bearing gap that greatly affects the bearing performance can be ensured with high accuracy.

  In addition, since the surface roughness of the outer peripheral surface of the caulking portion is different from that of the other outer peripheral surface of the sleeve (a half), it is possible to visually check the limit at which breakage or cracks occur, so that the change over time It is possible to prevent in advance the breakage of the crimped portion that appears only in

  Below, the form of the fluid dynamic bearing device of the present invention and its manufacturing method is explained in detail with a drawing.

(Embodiment 1)
FIG. 1 shows a cross-sectional view of a spindle motor 1 equipped with a hydrodynamic bearing device 2 manufactured by the manufacturing method of the present invention. First, the configuration of the spindle motor 1 shown in FIG. 1 will be described. In the following description, the vertical direction in FIG. 1 is expressed as “axial direction”, the upward direction as “axially upper side” (axially outer side), and the downward direction as “axially lower side” (axially outer side). These do not limit the mounting direction of the actual hydrodynamic bearing device 2.

  The spindle motor 1 is a device for rotationally driving a recording disk (not shown), and mainly includes a rotating member 4, a stationary member 3, and a hydrodynamic bearing device 2.

  The rotating member 4 mainly has a hub 5 on which a recording disk is mounted and a magnet 6. The hub 5 is formed of, for example, a stainless steel material (for example, martensitic or ferritic stainless steel material such as DHS1), which is an iron-based metal material, and is press-bonded to the shaft 7 or the like. It is integrated with the shaft 7. The hub 5 is integrally formed with a disk mounting portion 5a for mounting a recording disk on the outer periphery.

  The magnet 6 is fixed to the inner peripheral surface of the hub 5 and constitutes a magnetic circuit together with a stator 8 described later. The magnet 6 is made of a magnet material having a high energy product such as neodymium, iron, or a boron resin magnet, and the surface is subjected to an epoxy resin coating, nickel plating, or the like for rust prevention treatment and chipping prevention treatment. .

  A recording disk (not shown) is placed on the disk placing portion 5a, and is pressed downward in the axial direction by a clamper (not shown) fixed to the upper side of the shaft 7 with a screw (not shown). And is sandwiched between the clamper and the disk mounting portion 5a.

  As shown in FIG. 1, the stationary member 3 mainly includes a base 9 and a stator 8 fixed to the base 9, and is formed of an aluminum-based metal material or an iron-based metal material. The stator 8 is fixed to the base 9 and is disposed at a position facing the magnet 6. The stator core 10 of the stator 8 is formed of a silicon steel plate having a thickness of 0.15 to 0.20 mm.

  The base 9 has an annular holding portion 9 a having an opening through which the hydrodynamic bearing device 2 is inserted. The stator 8 is inserted and fixed on the outer peripheral surface of the annular holding portion 9a. Further, a seal 15 is attached to the base 9 so as to close the hydrodynamic bearing device 2 on the lower side in the axial direction of the annular holding portion 9a. The seal 15 is provided to prevent the fluid bearing device from being seen from the outside, and to prevent leakage of contamination from the fluid bearing device 2 to the outside.

  As shown in FIG. 1, the hydrodynamic bearing device 2 is fixed to an opening formed in a substantially central portion of the base 9, and supports the rotating member 4 in a rotatable state with respect to the stationary member 3. The hydrodynamic bearing device 2 is mainly configured to include a shaft 7, a sleeve 11, a thrust plate 12, a thrust flange 13, and a lubricating fluid 14 as a lubricating fluid. Of these, the sleeve 11 and the thrust plate 12 constitute a stationary member, and the shaft 7 and the thrust flange 13 constitute a rotating member.

  The shaft 7 is made of stainless steel that is an iron-based metal material (for example, SUS303 that is austenitic stainless steel, ASK8000 having a higher manganese content than normal austenitic stainless steel, SUS420 that is martensitic stainless steel, etc. ) Or a cylindrical member formed of ceramic or the like and extending in the axial direction, and is rotatably inserted into the bearing hole 11a of the sleeve 11. Specifically, the shaft 7 is disposed so as to be rotatable relative to the inner peripheral side of the bearing hole 11a formed by the sleeve 11 and the thrust plate 12 via a gap.

  And on the axial direction upper side of the shaft 7, in order to attach the hub 5, it has the convex part 7a. The convex portion 7a is fixed to the hub 5 by press fitting, adhesion, laser welding or the like. On the other hand, a thrust flange 13 is fixed to the lower side in the axial direction of the shaft 7 by a method such as press fitting, bonding, or welding. Further, the shaft 7 and the thrust flange 13 may be integrally formed.

  The sleeve 11 is a substantially cylindrical member extending in the axial direction and formed by pure iron, stainless steel, copper alloy, sintered metal, or the like, and is fixed to the annular holding portion 9 a of the base 9.

  The thrust plate 12 is formed of stainless steel (for example, SUS420) or cemented carbide steel (for example, FB10), which is an iron-based metal material, and is substantially circular formed at the lower end of the sleeve 11 in the axial direction. It is fixed by caulking so as to close the opening. The caulking and fixing of the thrust plate 12 will be described later. As a result, a bearing hole 11 a is formed by the sleeve 11 and the thrust plate 12.

  On the surface of the bearing hole 11a, for example, the inner peripheral surface of the sleeve 11, there are two sets of herringbone-shaped radial dynamic pressure generating grooves well known in the art, and for example, the upper surface of the thrust plate 12 (with the thrust flange 13). A spiral-shaped thrust dynamic pressure generating groove is provided on the facing surface.

  The lubricating fluid 14 is filled in a gap formed between the shaft 7 including the radial bearing portion and the thrust bearing portion, the sleeve 11, the thrust flange 13, and the thrust plate 12. As the lubricating fluid 14, for example, low-viscosity ester oil or the like can be used.

  As described above, the hydrodynamic bearing device 2 is a type constituted by two radial dynamic pressure bearings and one thrust dynamic pressure bearing.

  In the spindle motor 1, when the stator 8 is energized, a rotating magnetic field is generated and a rotational force is applied to the magnet 6. As a result, the rotating member 4 can be rotated together with the shaft 7 with the shaft 7 as the center of rotation. When the shaft 7 rotates, a support pressure in the radial direction and the axial direction is generated in each dynamic pressure generating groove. Thereby, the shaft 7 is supported in a non-contact state with respect to the sleeve 11. That is, the rotating member 4 can rotate in a non-contact state with respect to the stationary member 3, thereby realizing a high-precision high-speed rotation of the recording disk.

  The members constituting the spindle motor 1 on which the hydrodynamic bearing device 2 is mounted are fixed (fastened) between the members by various fastening methods such as press-fitting, adhesion, welding, caulking and the like. However, in a spindle motor used for an HDD or the like, in addition to fastening strength, it must be low in gas generation, and must be easily assembled and inexpensive. Therefore, the caulking method is increasingly used to satisfy these items.

In this embodiment, a caulking method is used for fastening the thrust plate 12 and the sleeve 11. A method of fastening the thrust plate 12 and the sleeve 11 using the caulking method will be described in detail with reference to FIGS.
(First step)
First, as shown in FIG. 2A, a crimping portion 11b is formed on the sleeve 11 in order to fix the thrust plate 12 by crimping. The caulking portion 11b is formed by a processing bite when the sleeve 11 is processed into a predetermined shape from a bar material, a blank material or the like. Further, when the sleeve 11 is processed into a predetermined shape from a sintered material or the like, the crimped portion 11b may be formed with a mold or the like. Moreover, the tip shape of the crimping | crimped part 11b which protrudes in the downward direction of FIG.
(Second step)
Next, as illustrated in FIG. 2B, the groove portion 20 is formed by the machining tool 40 on the outer peripheral surface of the crimping portion 11 b. This step may be a separate step from the step of forming the crimped portion 11b, but may be formed within the same step in order to further improve the positional accuracy of the groove portion 20. Further, when the sleeve 11 is a sintered material, it may be formed by a mold. In addition, after the groove portion 20 is formed, a surface treatment such as a plating treatment may be performed on the caulking portion 11 b and the outer peripheral surface of the sleeve 11 including the groove portion 20.
(Third step)
Next, as shown in FIG. 2C, the shaft 7 on which the thrust flange 13 is fixed is inserted into the bearing hole 11a of the sleeve 11, and the thrust is moved along the inner peripheral surface 11c of the caulking portion 11b. Insert the plate 12. Here, the thrust plate 12 may be diametrically press-fitted into the inner peripheral surface 11c of the caulking portion 11b.
(4th step)
Then, as shown in FIG. 3 (a), the caulking portion 11b provided so as to protrude in the shape of a spire in cross section is used in the upward direction (arrow direction) of FIG. A pressing force is applied. The applied pressing force deforms the caulking portion 11b toward the outer peripheral side fixing portion 12a of the thrust plate 12 with the apex 20a of the groove portion 20 as a base point, as shown in FIG.

  The thrust plate 12 is crimped and fixed to the sleeve 11 through the above steps. Here, the state of the crimping portion 11b will be described in more detail with reference to FIG.

  FIG. 4A illustrates the caulking portion 11b before the caulking deformation. When a pressing force is applied to the caulking portion 11b, an internal stress (strain) of the sleeve generated by the pressing force is generated in the upward direction of FIG. A groove portion 20 is formed in the crimped portion 11b, and the internal stress is concentrated on the sleeve 11b in the vicinity of the apex 20a of the groove portion 20. The internal stress is transmitted to the radially outer peripheral surface and the inner peripheral surface direction of the caulking portion 11b in order to make the stress uniform. However, as shown in FIG. 4B, the thrust plate 12 is located on the inner peripheral surface side of the caulking portion 11b, so that internal stress is difficult to transmit, but the caulking portion 11b has an outer peripheral surface. The groove portion 20 is formed so that internal stress can be easily transmitted. As a result, the internal stress of the sleeve generated by the pressing force is transmitted toward the groove 20.

  The internal stress transmitted to the groove portion 20 is transmitted so as to push the groove portion 20 outward in the radial direction, the internal stress is made uniform, and the stress distribution inside the sleeve 11b is stabilized. As a result, as shown in FIG. 4 (c), the absence of the groove 20 prevents the internal stress generated by the pressing force from remaining on the outer peripheral surface of the caulking portion 11b. Occurrence does not occur. In addition, almost no internal stress is transmitted to the outer peripheral surface of the thrust plate 12 constituting the thrust bearing portion located on the inner peripheral surface side of the caulking portion 11b, and the thrust plate 12 is deformed. Therefore, the thrust bearing gap is less likely to be deformed.

  Further, as shown in FIG. 4A, the apex 20a of the groove portion 20 is formed at the same position as the axially outer surface 12b of the thrust plate 12, so that the inside caused by the pressing force of the caulking portion 11b. The stress distribution can be more effectively concentrated on the apex 20 a of the groove portion 20, and the internal stress of the sleeve caused by the pressing force is transmitted toward the groove portion 20. As a result, as described above, the internal stress generated by the pressing force does not remain on the outer peripheral surface of the caulking portion 11b, the breakage and the crack do not occur, and the thrust plate 12 is hardly deformed.

  Further, the amount of warpage of the thrust plate 12 deformed by the caulking method and the mounting strength ratio between the thrust plate 12 and the sleeve 11 were confirmed by experiments. FIG. 5 is data in which the amount of warpage (μm) and the attachment strength ratio (%) of the thrust plate 12 in the hydrodynamic bearing device shown in FIG.

  As shown in FIG. 4A, Do is the diameter of the thrust plate 12, r1 is the thickness of the groove bottom part of the groove part 20 of the caulking part 11b, and r1 is the entire caulking part. Indicates the thickness.

  In FIG. 5, the diameter Do of the thrust plate 12 shown in FIG. 4 (a) is constant, and the thickness shown in r1 shows the evaluation result under a constant condition. Generally, the diameter Do of the thrust plate 12, which is a portion used in the caulking method, is about 4 to 12 mm, and the thickness r1 is about 0.5 to 3.0 mm.

  According to the result of this experiment, it was found that the value of r2 / r1 is one of the important indexes for determining the best shape of the groove 20. Further, as shown in FIG. 5 (a), the warpage amount of the thrust plate 12 does not change much with respect to the numerical value of r2 / r1, but as shown in FIG. 5 (b), the attachment strength ratio is r2 / r1. When the numerical value of 1.5 is 1.5 or less, the strength is small, but when it is 1.5 or more, the strength is suddenly large and a necessary and sufficient strength can be obtained. According to these results, when the value of r2 / r1 is 1.5 or more, a hydrodynamic bearing device can be obtained in which the amount of warpage of the thrust plate 12 after caulking is small and the mounting strength is sufficiently large.

  Note that the best shape of the groove 20 can also be obtained by inverse analysis of an analysis model whose initial state is a shape after crimping.

  Further, as a result of confirming the state of the outer peripheral surface of the crimping portion 11b after the thrust plate 12 is fixed to the sleeve 11 using the caulking method, the surface roughness of the portion A shown in FIG. It turns out that there is a change. Specifically, the portion where the surface roughness of the sleeve outer peripheral surface before crimping was 6.0 μm was changed to 3.0 μm. This seems to be because the surface of the groove part 20 was tensile-deformed by making the internal stress generated by caulking uniform in the groove part 20.

  Due to this change in surface roughness, the gloss of the outer peripheral surface of the sleeve 11 changed, and the change could be confirmed visually. Here, further investigation was made on the change in the surface roughness. Specifically, the pressing force at the time of caulking was changed to check whether the surface roughness after caulking of the outer peripheral surface of the sleeve 11 could be visually confirmed. As a result, what can be visually confirmed was when the surface roughness was changed to half or less of the initial surface roughness. Furthermore, a vibration / impact test and a reliability test were performed on each sample that could be visually confirmed. As a result, when the surface roughness after crimping was 1.0 μm or less, minute cracks (surface breakage) could be confirmed after the reliability test.

  Based on the above results, the surface roughness after caulking is reduced to about half of the surface roughness from the initial state. The occurrence of surface breakage and cracks can be suppressed in advance, and a more reliable hydrodynamic bearing device can be obtained.

  INDUSTRIAL APPLICABILITY The hydrodynamic bearing device and the manufacturing method thereof according to the present invention have the effect that the internal stress generated by caulking is made uniform, and the occurrence of fracture / cracking on the outer peripheral surface of the caulking portion of the sleeve can be prevented. This is useful for a spindle motor or the like that needs to be fastened between members that are less expensive, inexpensive, and capable of withstanding external shocks and vibrations.

Sectional drawing of the hydrodynamic bearing apparatus manufactured by the manufacturing method of the hydrodynamic bearing apparatus of this invention, and a spindle motor using the same (A) A cross-sectional view showing a state in which a crimping portion is formed on the sleeve, (b) a cross-sectional view showing a state in which a groove portion is formed on the outer peripheral surface of the crimping portion, and (c) a state in which the thrust plate is inserted into the bearing hole of the sleeve. Cross section shown (A) Cross-sectional view showing the position where the groove portion of the sleeve is formed, (b) Cross-sectional view showing a state where the sleeve is caulked and secured (A) Detailed cross-sectional view of the groove of the sleeve, (b) Cross-sectional view showing a state in which the sleeve is crimped, (c) Detailed cross-sectional view in which the sleeve is crimped to the thrust plate (A) The figure which shows the thrust plate curvature amount of this invention, (b) Explanatory drawing of thrust plate attachment strength ratio Cross section of conventional hydrodynamic bearing device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Spindle motor 2, 101 Fluid dynamic bearing device 3 Stationary member 4 Rotating member 5 Hub 5a Disk mounting part 6 Magnet 7 Shaft 7a Convex part 8 Stator 9 Base 9a Holding part 10 Stator core 11, 102 Sleeve 11a Bearing hole 11b, 102a, 102aa Caulking portion 11c Inner peripheral surface 12, 103 Thrust plate 13, 105 Thrust flange 14 Lubricating fluid 15 Seal 20, 20b Groove portion 20a Vertex 20c Caulking portion outer peripheral surface 40 after caulking deformation 40 Cutting tool 50 Jig 102b Caulking deformation projecting portion 104 Outer peripheral escape portion

Claims (6)

A shaft,
A sleeve having a bearing hole into which the shaft is rotatably inserted;
A thrust plate facing the end surface of the shaft and closing the bearing hole of the sleeve;
A method of manufacturing a hydrodynamic bearing device for fixing the thrust plate to the sleeve by a caulking method,
A first step of forming a crimped portion on the closed side of the sleeve;
A second step of forming a groove in the outer circumferential surface of the crimped portion;
A third step of inserting the thrust plate into the bearing hole of the sleeve;
A fourth step of caulking and fixing the thrust plate by deforming the caulking portion in an inner circumferential direction with the groove portion as a base point;
A method for manufacturing a hydrodynamic bearing device.   2. The groove portion is formed in the step 2 so that the apex in the radial direction of the groove portion is positioned on the outer side in the axial direction with respect to the back surface of the opposed surface of the shaft of the thrust plate. Manufacturing method of the hydrodynamic bearing device. 3. The method for manufacturing a hydrodynamic bearing device according to claim 1, wherein the groove formed in the second step satisfies Formula (1). 4.
r2 / r1 ≧ 1.5 (1)
r1: Radial length of a portion where the groove is formed r2: Radial length of a portion where the groove is not formed A shaft,
A sleeve having a bearing hole into which the shaft is rotatably inserted;
A thrust plate facing the end face of the shaft and closing the bearing hole of the sleeve;
A lubricating fluid interposed in a gap formed by the shaft and the sleeve and the thrust plate; and an outer circumferential surface of an annular caulking portion for caulking and fixing the thrust plate formed on the sleeve. Has a surface roughness portion different from the other outer peripheral surface of the sleeve.   The hydrodynamic bearing device according to claim 4, wherein the different surface roughness portion is a half of the surface roughness of the other outer peripheral surface of the sleeve. 7. The hydrodynamic bearing device according to claim 5, wherein the different surface roughness portions are located on the outer side in the axial direction with respect to a surface of the thrust plate forming the thrust bearing portion. 8. .