JP2012031969A - Hub integrated shaft for fluid dynamic pressure bearing device, and method for manufacturing the same - Google Patents

Abstract

Provided is a hub integrated shaft capable of sufficiently increasing the dimensional accuracy even when the hub portion is thinned.
A forming member 30 integrally having a shaft portion 21 and a hub portion 22 is formed by plastic processing of a plate member, and at least an outer peripheral surface 21b of the shaft portion 21 and a rotating body of the hub portion 22 of the forming member 30 are formed. The mounting surface (upper end surface 22c1 of the flange 22c) is ground.
[Selection] Figure 7

Description

  The present invention relates to a hub integrated shaft used in a fluid dynamic bearing device and a manufacturing method thereof.

  The fluid dynamic pressure bearing device supports a shaft member so as to be relatively rotatable by a dynamic pressure action of lubricating oil generated in a radial bearing gap between an inner peripheral surface of the bearing member and an outer peripheral surface of the shaft member. Since the fluid dynamic bearing device has excellent rotational accuracy and quietness, for example, for spindle motors of various disk drive devices (such as HDD magnetic disk drive devices and CD-ROM optical disk drive devices), laser beams, etc. It is suitably used for a polygon scanner motor of a printer (LBP) or a color wheel motor of a projector.

  For example, Patent Document 1 discloses a fluid dynamic bearing device assembled in a spindle motor of an HDD. This fluid dynamic pressure bearing device includes a shaft member 2, a bearing sleeve 8 in which the shaft member 2 is inserted on the inner periphery, and a disk hub 3 fixed to the outer periphery of the upper end of the shaft member 2. A disk D as a medium is mounted. When the shaft member 2 rotates, the pressure of the oil film generated in the radial bearing gap between the outer peripheral surface of the shaft member 2 and the inner peripheral surface of the bearing sleeve 8 is increased, and this dynamic pressure action causes the shaft member 2 and the disk hub 3 to move. , And the disk D are integrally supported by rotation.

JP 2009-299836 A Japanese Patent Laid-Open No. 6-261489

  In recent years, information devices such as notebook personal computers have been made thinner and lighter, and the demand for thinner and lighter HDD spindle motors incorporated therein has been increasing. In order to meet this demand, in a fluid dynamic bearing device for a spindle motor of an HDD, it is considered to reduce the thickness of a disk hub on which a magnetic disk is mounted. However, when the disk hub is thinned, the following problems arise.

  First, since the fastening area between the shaft member and the disk hub is reduced by reducing the thickness of the disk hub, the fastening strength of the two may be reduced. For example, if an adhesive is applied to the fastening portion, the fastening strength can be increased. In this case, the material cost of the adhesive is increased, and the manufacturing cost is increased due to the need for the step of applying the adhesive.

  Secondly, since the fitting area between the shaft member and the disk hub is reduced by reducing the thickness of the disk hub, the assembling accuracy of the both decreases. As a result, the surface accuracy (runout accuracy, etc.) of the disk mounting surface with respect to the outer peripheral surface of the shaft member is lowered, and there is a possibility that the rotation accuracy of the disk is lowered, and consequently the disk reading accuracy of the HDD is lowered.

  Thirdly, the processing amount of the blank material increases due to the thinning of the disk hub. For example, when the disk hub is formed by turning, a large amount of chips are generated because the amount of cutting from the blank material increases. When the amount of cutting is large as described above, the material cost increases, and the tool is heavily consumed, resulting in an increase in the cost of the tool. Moreover, since the processing time per product becomes long, it is necessary to prepare a large number of turning machines in order to manufacture in a predetermined cycle, which requires a large-scale capital investment.

  For example, in Patent Document 2, a blank material (slag) having a predetermined length is cut from a round bar, and after the upsetting process and the punching process are performed on the blank material, the hub and the shaft portion are integrally manufactured by forging extrusion. How to do is shown. In this way, if the disk hub and the shaft member are integrally formed, the fastening strength between them can be increased as compared with the case where they are fixed after being formed separately. Further, by forming the integrated hub and shaft part by forging, a large amount of chips are not generated unlike turning, and the yield of the material can be increased.

  However, in Patent Document 2, a cylindrical blank material is plastically processed to form a hub integrated shaft. Therefore, the amount of deformation from the slag to the product is large, and it is difficult to obtain a desired dimensional accuracy. In particular, when the hub is thinned as described above, the amount of deformation from the blank material is further increased, and the rigidity of the hub is reduced, making it more difficult to increase the dimensional accuracy of the hub integrated shaft. For this reason, the dimensional accuracy required for the HDD spindle motor, in particular, the surface accuracy of the disk mounting surface with respect to the outer peripheral surface of the shaft member, cannot be obtained, and the rotational accuracy of the disk may be reduced.

  The above-mentioned problem, that is, the problem of dimensional accuracy when the hub is thinned, is not limited to the HDD spindle motor. For example, the same applies to a fluid dynamic pressure bearing device incorporated in a polygon scanner motor or a color wheel motor. To occur. However, the fluid dynamic pressure bearing device for the spindle motor of the HDD has a strong demand for weight reduction and thinning as described above, and the required rotational accuracy of the disk is high. To do.

  The problem to be solved by the present invention is to provide a hub integrated shaft capable of sufficiently increasing the dimensional accuracy even when the hub is thinned, and particularly to obtain a hub integrated shaft suitable for a spindle motor of an HDD. is there.

  In order to solve the above problems, the present invention provides a shaft portion whose outer peripheral surface faces a radial bearing gap filled with a lubricating fluid, and a rotating body mounting surface that projects from the shaft portion to the outer diameter and is orthogonal to the axial direction. A hub-integrated shaft for a fluid dynamic pressure bearing device, which is integrally provided with a hub portion having a shaft portion, and an outer peripheral surface of the shaft portion and a hub among the shaped members in which the shaft portion and the hub portion are integrally formed by plastic processing of a plate material Provided is a hub-integrated shaft having a grinding finish on the rotating body mounting surface of the part.

  As described above, the hub integrated shaft of the present invention is formed by using a shaped material in which the shaft portion and the hub portion are integrally formed by plastic working of a plate material. By integrally forming the hub part and the shaft part in this way, the fastening strength between the two can be increased as described above, so that even when the hub part is thinned, the hub part and the shaft part are firmly fixed (integrated). can do. In addition, by forming the base material from a plate material, the amount of deformation due to plastic working can be suppressed even when the hub portion is thinned, so that the dimensional accuracy of the base material can be increased.

  Of the raw material thus obtained, a grinding finish is applied to a portion that requires particularly high accuracy. Specifically, the outer peripheral surface of the shaft part facing the radial bearing gap and the rotating body mounting surface on which the rotating body is mounted are ground. As a result, the rotational accuracy of the rotating body is enhanced, so that the rotational accuracy of the rotating body (disk) required for a fluid dynamic bearing device for an HDD spindle motor, for example, can be satisfied.

  Since the outer peripheral surface of the shaft portion faces the radial bearing gap, it is necessary to process with particularly excellent surface accuracy. Therefore, if the hub portion is first ground and then the outer peripheral surface of the shaft portion is ground based on this highly accurate ground surface, the surface accuracy of the outer peripheral surface of the shaft portion can be further improved.

  Moreover, even if the outer peripheral surface of the shaft portion and the rotating body mounting surface of the hub portion are processed with excellent dimensional accuracy, if the relative positional accuracy (for example, runout accuracy) is not sufficient, the rotational accuracy of the rotating body There is a risk that it cannot be raised sufficiently. Therefore, as described above, if the outer peripheral surface of the shaft part is ground with reference to the rotating body mounting surface of the hub part that has been ground, the runout accuracy of the rotating body mounting surface with respect to the outer peripheral surface of the shaft part can be improved. Can do. In addition, when grinding the outer peripheral surface of the hub portion, in addition to the rotating body mounting surface, if the outer peripheral surface of the hub portion that has been ground is used as a reference, the outer peripheral surface of the shaft portion and the hub portion The degree of coaxiality can be increased. The definition of runout accuracy and coaxiality is based on JIS B 0021: 1998.

  The deflection accuracy of the rotating body mounting surface with respect to the outer peripheral surface of the shaft portion is preferably 5 μm or less, for example. The flatness of the rotating body mounting surface is preferably set to 1 μm or less, for example.

  Since the outer peripheral surface of the shaft portion may slide in contact with the inner peripheral surface of the bearing member facing through the radial bearing gap, high wear resistance is required. Therefore, it is preferable to increase the wear resistance by subjecting the outer peripheral surface of the shaft portion to surface hardening treatment or coating treatment. In this case, if surface hardening treatment or coating treatment is performed on the outer peripheral surface of the shaft portion to increase wear resistance, and grinding finish is applied to this surface, wrinkles due to grinding can be suppressed. Further, if grinding is performed on the outer peripheral surface of the shaft portion and then this surface is subjected to a coating treatment, the wrinkles by grinding can be covered with the coating.

  As described above, high wear resistance is required for the outer peripheral surface of the shaft portion. Moreover, since it is necessary to maintain a shape for a long time in the state which mounted the rotary body, the hub part requires high intensity | strength. From these points, the hub integrated shaft is preferably formed of stainless steel. However, since stainless steel is generally poor in formability, in order to form a shaped material integrally having a hub part and a shaft part from a plate material as described above, a ferritic series having relatively excellent formability among stainless steels. It is preferable to use stainless steel. Furthermore, it is preferable to add 0.05% or more of Ti to ferritic stainless steel because ductility can be improved.

  For example, the hub portion may have a shape including a disk portion extending from the shaft portion to the outer diameter, a cylindrical portion extending from the disk portion in the axial direction, and a flange portion extending from the cylindrical portion to the outer diameter. According to the hub integrated shaft described above, even when the hub portion is thin, specifically, when the axial thickness of the disc portion of the hub portion is 20% or less of the axial dimension of the shaft portion. However, it can be formed with excellent dimensional accuracy.

  Since the hub integrated shaft as described above can sufficiently increase the dimensional accuracy even when the hub portion is thinned, it can be suitably used particularly for an HDD spindle motor.

  The hub is integrated with the hub integrated shaft, the bearing member in which the shaft portion of the hub integrated shaft is inserted into the inner periphery, and the fluid film generated in the radial bearing gap between the outer peripheral surface of the shaft portion and the inner peripheral surface of the bearing member. A fluid dynamic pressure bearing device including a radial bearing portion that rotatably supports a shaft can reduce the size in the axial direction and can have excellent rotational accuracy.

  As described above, the hub-integrated shaft of the present invention can be formed into a thin, lightweight, and high-dimensional accuracy shaped material by plastic processing of the plate material. Furthermore, the precision of these surfaces can be raised especially by giving grinding finishing to the outer peripheral surface of the axial part of a molding material, and the rotary body mounting surface of a hub part.

It is sectional drawing which shows the spindle motor of HDD. It is sectional drawing of the fluid dynamic pressure bearing apparatus provided with the hub integrated shaft which is integrated in the said spindle motor and concerns on embodiment of this invention. It is sectional drawing of the bearing sleeve of the said fluid dynamic pressure bearing apparatus. It is a top view of the housing of the said fluid dynamic pressure bearing apparatus. (A)-(e) is sectional drawing which shows the process of plastically processing a board | plate material and shape | molding the raw material which has a shaft part and a hub part integrally. It is sectional drawing which shows a mode that grinding finishing is performed to the hub part of a base material. It is sectional drawing which shows a mode that a grinding finish is given to the axial part of an original shape material. It is sectional drawing of the fluid dynamic pressure bearing apparatus provided with the hub integrated shaft which concerns on other embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a spindle motor used in, for example, a 2.5-inch HDD disk drive device. This spindle motor includes a fluid dynamic pressure bearing device 1 that rotatably supports a hub integrated shaft 9 according to an embodiment of the present invention, a bracket 6 to which the fluid dynamic pressure bearing device 1 is attached, and a radial gap. And a stator magnet 4 and a rotor magnet 5 which are opposed to each other. The stator coil 4 is attached to the bracket 6, and the rotor magnet 5 is attached to the hub integrated shaft 9 via the yoke 10. The hub integrated shaft 9 holds a predetermined number of disks D (one in the illustrated example) as a rotating body. When the stator coil 4 is energized, the rotor magnet 5 is rotated by electromagnetic force between the stator coil 4 and the rotor magnet 5, whereby the hub integrated shaft 9 and the disk D are rotated together.

  As shown in FIG. 2, the fluid dynamic bearing device 1 includes a hub integrated shaft 9 having a shaft portion 2 and a hub portion 3, and a bearing member that rotatably supports the hub integrated shaft 9. In the present embodiment, the bearing member includes a bearing sleeve 8 in which the shaft portion 2 of the hub integrated shaft 9 is inserted on the inner periphery, and a bottomed cylindrical housing 7 that holds the bearing sleeve 8 on the inner periphery. A retaining member 11 is provided at the lower end of the shaft portion 2. In the following, for convenience of explanation, the opening side of the housing 7 in the axial direction is the upper side and the closing side is the lower side.

  The hub integrated shaft 9 is made of metal, for example, iron-based metal, particularly stainless steel. Since stainless steel generally has poor ductility, it is preferable to use a ferritic material (for example, SUS430) that is relatively rich in ductility among stainless steels. Moreover, in order to improve ductility, it is preferable to make content of C of stainless steel 0.2% or less, and it is preferable to mix | blend Ti 0.05% or more by weight ratio with stainless steel for the same purpose. In addition, the hub integrated shaft 9 can be formed of, for example, general structural steel, aluminum alloy, titanium alloy, or the like.

  The shaft portion 2 is provided at the axis of the hub integrated shaft 9 and has an outer diameter of about 2 to 4 mm. The shaft portion 2 has a straight cylindrical outer peripheral surface 2a having no irregularities and an axial hole 2b provided in the shaft center. In the present embodiment, the axial hole 2b penetrates the shaft portion 2 in the axial direction, and a thread groove is formed on the inner peripheral surface thereof. A retaining member 11 is provided at the lower end of the shaft portion 2. The retaining member 11 includes a disk portion 11a that protrudes from the lower end portion of the shaft portion 2 to the outer diameter, and a male screw portion 11b that extends upward from the axis of the disk portion 11a. The male screw portion 11 b is screwed to the lower end of the axial hole 2 b of the shaft portion 2. The disk portion 11 a is arranged between the lower end surface 8 b of the bearing sleeve 8 and the upper end surface 7 b 1 of the bottom portion 7 b of the housing 7 in the axial direction. The disk portion 11a of the retaining member 11 and the lower end surface 8b of the bearing sleeve 8 are engaged in the axial direction, so that the shaft portion 2 is prevented from being detached from the bearing sleeve 8.

  The outer peripheral surface 2a of the shaft portion 2 is subjected to surface hardening treatment or coating treatment, or both. Examples of the surface hardening treatment include surface hardening treatment such as vacuum quenching, vacuum carburizing treatment, vacuum nitriding treatment, gas soft nitriding treatment, or ion nitriding treatment. Examples of the coating process include a coating process using electroless Ni plating, DLC, TiN, TiAlN, or TiC. When the hub integrated shaft 9 is formed of stainless steel, if the C content is 0.2% or less as described above, the hardening process by quenching becomes difficult, so surface effect treatment other than vacuum quenching, or A coating treatment is preferably performed. The surface treatment and the coating treatment may be performed not only on the outer peripheral surface 2a of the shaft portion 2, but also on other regions, for example, the lower end surface 3a1 of the disk portion 3a of the hub portion 3 facing the thrust bearing gap. Alternatively, if the wear resistance of the outer peripheral surface 2a of the shaft portion 2 is sufficient, the surface effect treatment or the coating treatment may be omitted.

  The hub portion 3 includes a rotating body mounting surface (disk mounting surface 3d in the present embodiment) that extends from the upper end of the shaft portion 2 to the outer diameter and is orthogonal to the axial direction. The hub portion 3 of the present embodiment includes a disc portion 3a that covers the opening of the housing 7, a cylindrical portion 3b that extends downward in the axial direction from the outer peripheral portion of the disc portion 3a, and a further outer diameter from the lower end portion of the cylindrical portion 3b. The disc mounting surface 3d is formed on the upper end surface of the flange portion 3c. A disk fitting surface 3e is formed on the outer peripheral surface of the cylindrical portion 3b. The disc D is fitted on the outer periphery of the disc fitting surface 3e and placed on the disc mounting surface 3d. In this state, the upper surface of the disc D is pressed by the clamper (not shown) and pressed onto the disc mounting surface 3d. The disk D is held by the hub portion 3. In addition, the upper part of the axial direction hole 2b of the axial part 2 functions as a screw hole for fixing a clamper.

  As will be described in detail later, the hub-integrated shaft 9 is formed by forming a shape material integrally having the shaft portion 2 and the hub portion 3 by plastic working of a metal plate material, and grinding a predetermined portion of the shape material. It is formed by. In the present embodiment, the outer peripheral surface 2a of the shaft portion 2 facing the radial bearing gap filled with lubricating oil and the lower end surface 3a1 of the disk portion 3a of the hub portion 3 facing the thrust bearing gap filled with lubricating oil. Then, the disc mounting surface 3d and the disc fitting surface 3e of the hub portion 3 are ground. The outer peripheral surface 2a of the shaft portion 2 and the lower end surface 3a1 of the disc portion 3a are ground with reference to the ground finish surface (the disc mounting surface 3d and the disc fitting surface 3e) of the hub portion 3. As a result, the deflection accuracy of the disc mounting surface 3d with respect to the outer peripheral surface 2a of the shaft portion 2 is set to 5 μm or less, and the coaxiality of the disc fitting surface 3e with respect to the outer peripheral surface 2a of the shaft portion 2 is set to 5 μm or less. In other words, if the dimensional accuracy of the disc mounting surface 3d and the disc fitting surface 3e with respect to the outer peripheral surface 2a of the shaft portion 2 is within the above range, the outer peripheral surface 2a of the shaft portion 2 is connected to the disc mounting surface 3d and the disc fitting surface. It can be estimated that the ground surface 3e is ground.

  The bearing sleeve 8 is formed of a metal material in a cylindrical shape, and in this embodiment, is formed of, for example, a sintered metal containing copper as a main component. For example, as shown in FIG. 3, herringbone-shaped dynamic pressure grooves 8 a 1 and 8 a 2 are formed on the inner peripheral surface 8 a of the bearing sleeve 8 in two regions separated in the axial direction. A region indicated by hatching in the figure is a hill formed between the dynamic pressure grooves 8a1 and 8a2, and is one step higher than the dynamic pressure grooves 8a1 and 8a2 (that is, protrudes toward the inner diameter). In the illustrated example, the upper dynamic pressure groove 8a1 is formed asymmetrically in the axial direction. Specifically, the axial dimension X1 of the region above the axial center part m is the axial dimension X2 of the lower region. (X1> X2). The lower dynamic pressure groove 8a2 is formed symmetrically in the axial direction. An axial groove 8d1 is formed over the entire length in the axial direction on the outer peripheral surface 8d of the bearing sleeve 8. For example, three axial grooves 8d1 are equally arranged in the circumferential direction.

  The housing 7 is formed by, for example, resin injection molding, and is formed in a bottomed cylindrical shape integrally having a side portion 7a and a bottom portion 7b as shown in FIG. The outer peripheral surface 8d of the bearing sleeve 8 is fixed to the cylindrical inner peripheral surface 7a1 of the side portion 7a by gap bonding, press-fitting, press-fitting with an adhesive interposed therebetween, or the like. On the upper end surface 7a2 of the side portion 7a of the housing 7, for example, a region in which a plurality of dynamic pressure grooves 7a20 are arranged in a spiral shape is formed as shown in FIG. At the upper end of the outer periphery of the side portion 7a of the housing 7, as shown in FIG. 2, a tapered seal surface 7a3 that gradually increases in diameter upward is formed. This tapered seal surface 7a3 forms an annular seal space S whose radial dimension is gradually reduced upward with respect to the inner peripheral surface 3b1 of the cylindrical portion 3b of the hub portion 3. The seal space S communicates with the outer diameter side of the thrust bearing gap of the thrust bearing portion T when the hub integrated shaft 9 rotates. The capillary force of the seal space S prevents the lubricating oil filled in the housing 7 from leaking out.

  By filling the space inside the housing 7 including the internal pores of the bearing sleeve 8 with the hub integrated shaft 9, the bearing sleeve 8, the housing 7, and the retaining member 11 assembled as described above, The fluid dynamic bearing device 1 shown in FIG. 2 is completed. At this time, the oil level of the lubricating oil is held inside the seal space S.

  When the hub integrated shaft 9 rotates, a radial bearing gap is formed between the inner peripheral surface 8 a of the bearing sleeve 8 and the outer peripheral surface 2 a of the shaft portion 2. Then, the pressure of the lubricating oil filled in the radial bearing gap is increased by the dynamic pressure grooves 8a1 and 8a2, and the radial bearing that supports the hub integrated shaft 9 rotatably in the radial direction by this pressure (dynamic pressure action). Portions R1 and R2 are configured.

  At the same time, a thrust bearing gap is formed between the lower end surface 3 a 1 of the disk portion 3 a of the hub portion 3 and the upper end surface 7 a 2 of the side portion 7 a of the housing 7. Then, the pressure of the lubricating oil filled in the thrust bearing gap is increased by the dynamic pressure groove 7a20, and the thrust bearing portion T for supporting the hub integrated shaft 9 rotatably in the thrust direction in a non-contact manner by this pressure (dynamic pressure action). Is configured.

  At this time, the axial groove 8d1 formed in the outer peripheral surface 8d of the bearing sleeve 8 forms a communication path through which lubricating oil can flow. This communication path can prevent a local negative pressure from being generated in the lubricating oil filled in the housing 7. In particular, in the present embodiment, as shown in FIG. 3, the upper dynamic pressure groove 8a1 formed in the inner peripheral surface 8a of the bearing sleeve 8 is formed in an axially asymmetric shape, so that the rotation of the hub integrated shaft 9 is performed. Along with this, the lubricating oil in the radial bearing gap is pushed downward, and the lubricating oil circulates through the communication path, thereby reliably preventing the generation of local negative pressure.

  Hereinafter, a method for manufacturing the hub integrated shaft 9 will be described.

  The hub-integrated shaft 9 is formed by molding a plate material to form a shaped material integrally having the shaft portion 2 and the hub portion 3, and a grinding finish for grinding a predetermined portion of the shaped material. It is formed through a process.

(1) Shaped Material Forming Process In the shaped material forming process, first, as shown in FIG. 5 (a), a metal (for example, ferritic stainless steel containing 0.5% or more of Ti) plate material 20 is prepared. To do. For example, in the case of the hub integrated shaft 9 for the spindle motor of the 2.5 inch HDD as in this embodiment, the thickness of the plate material is about 1 mm.

  And as shown in FIG.5 (b), the axial center of the board | plate material 20 is protruded below by cold plastic working (deep drawing process), and the axial part 21 is shape | molded. At this time, an axial hole 21 a is formed in the shaft center of the shaft portion 21 in order to push the shaft portion 21 to protrude by a mold (not shown).

  Next, as shown in FIG.5 (c), the hub part 22 is shape | molded around the axial part 21 by cold plastic working (press work). Specifically, a disk part 22a extending from the shaft part 21 to the outer diameter, a cylindrical part 22b extending downward from the outer diameter end of the disk part 22a, and a flange part 22c extending from the lower end of the cylindrical part 22b to the outer diameter are formed. Is done. At this time, an annular recess (relief portion) 22c10 is simultaneously formed at the inner diameter end of the upper end surface 22c1 of the flange portion 22c.

  Thereafter, as shown in FIG. 5 (d), the tip end portion (lower end portion) of the shaft portion 21 is cut off and the axial hole 21 a is opened at the lower end of the shaft portion 21. At the same time, a thread groove is formed on the inner peripheral surface of the axial hole 21 a of the shaft portion 21.

  Finally, as shown in FIG. 5 (e), the flange portion 22 c of the hub portion 22 and the plate material 20 are separated, and the base material 30 having the shaft portion 21 and the hub portion 22 is separated from the plate material 20.

  By forming the base material 30 from the plate material 20 in this way, the thickness of the base material 30 is approximately uniform. Specifically, the radial thickness of the shaft portion 21, the axial thickness of the disk portion 22a of the hub portion 22, the radial thickness of the cylindrical portion 22b, and the axial thickness of the flange portion 22c. However, it is almost uniform. Specifically, the thickness of the portion (the shaft portion 21 and the cylindrical portion 22b) that is squeezed by the plastic processing and extends in the axial direction is the thickness of the surface (the disk portion 22a and the flange portion 22c) in the direction orthogonal to the axial direction. Is slightly thinner. For example, when the base material 30 is formed using the plate material 20 of about 1 mm, the thickness of the disk portion 22a and the flange portion 22c is about 0.8 mm, whereas the thickness of the shaft portion 21 and the cylindrical portion 22b. Is about 0.5 mm. That is, in the present embodiment, the amount of change in thickness when the base material 30 is obtained from the plate material 20 is 50% or less. Thus, since the deformation amount from the plate material 20 is relatively small, the base material 30 can be plastically processed with high accuracy.

(2) Grinding finishing process Grinding finishing is performed on a predetermined portion of the shaped material 30 formed as described above. In the grinding finishing process shown in FIG. 6 and FIG. 7, the machining is performed with the axial direction of the shaped material 30 being horizontal, and the same name as above is given to each part of the shaped material 30. Yes.

  First, a grinding finish is applied to a predetermined portion of the hub portion 22 of the raw material 30. Specifically, as shown in FIG. 6, rotation centers 41 and 42 are attached to the axial holes 21 a of the shaft portion 21 of the shaped material 30 to rotatably support the shaped material 30, and the hub portion 22. The lower end surface 22c2 of the collar portion 22c is supported by the backing plate 43. Then, the backing plate 43 is rotationally driven to rotate the base material 30 around the shaft portion 21, and the angular grindstone 44 is brought into contact with the base material 30 in this state. Specifically, the angular grindstone 44 is made up of the upper end surface 22c1 (corresponding to the disc mounting surface) of the flange portion 22c, the outer peripheral surface 22b1 (corresponding to the disc fitting surface) of the cylindrical portion 22b, and the outer periphery of the upper end surface 22a1 of the disc portion 22a. At the same time, these surfaces are ground simultaneously. At this time, since the escape portion 22c10 is provided at the inner diameter end of the upper end surface 22c1 of the flange portion 22c, the angular grindstone 44 can be brought into close contact with the upper end surface 22c1 of the flange portion 22c and the outer peripheral surface 22b1 of the cylindrical portion 22b. .

  Next, as shown in FIG. 7, the outer peripheral surface 21 b of the shaft portion 21 and the lower end surface 22 a 2 of the disc portion 22 a of the hub portion 22 with reference to the ground finish surface of the hub portion 22 (shown by a dotted line in the drawing). The outer peripheral portion (region facing the thrust bearing gap) is ground. For example, the outer peripheral portion of the upper end surface 22 a 1 of the disk portion 22 a of the hub portion 22 is attracted and supported by the magnet chuck 51, and the outer peripheral surface 22 b 1 of the cylindrical portion 22 b is slidably supported by the shoe 52. In this state, the magnet chuck 51 is rotationally driven to rotate the shaped member 30 around the shaft portion 21 so that the grindstone 53 is brought into contact with the outer peripheral surface 21b of the shaft portion 21 and the lower end surface 22a2 of the disk portion 22a. The grindstone 54 is brought into contact with the outer peripheral portion of the steel plate, and these surfaces are ground.

  Thus, by grinding the outer peripheral surface 21b of the shaft portion 21 with reference to the ground finish surface of the hub portion 22 processed with high accuracy, this surface can be processed with high accuracy. In particular, by grinding the outer peripheral surface 21b of the shaft portion 21 with reference to the upper end surface 22c1 of the flange portion 22c corresponding to the disk mounting surface 3d, the relative surface accuracy (for example, runout accuracy) of these surfaces is high. Can be set to In the present embodiment, when the outer peripheral surface 21b of the shaft portion 21 is ground, the upper end surface 22c1 of the flange portion 22c is not directly supported, but the outer peripheral portion of the upper end surface 22a1 of the disk portion 22a is supported by the magnet chuck 51. (See FIG. 7). Since the outer peripheral portion of the upper end surface 22a1 of the disk portion 22a and the upper end surface 22c1 of the flange portion 22c are ground simultaneously, the parallelism of these surfaces is set with extremely high accuracy. Therefore, as shown in FIG. 7, by supporting the outer peripheral portion of the upper end surface 22a1 of the disk portion 22a with the magnet chuck 51, the upper end surface 22c1 of the flange portion 22c can be indirectly used as a reference. Of course, if possible, the upper end surface 22c1 of the flange 22c may be attracted and supported by the magnet chuck 51, and this surface may be directly used as a reference.

  Further, since the outer peripheral surface 22b1 of the cylindrical portion 22b corresponding to the disc fitting surface 3e is supported by the shoe 52, the outer peripheral surface 21b of the shaft portion 21 can be ground on the basis of this surface. Relative surface accuracy (for example, coaxiality) can be set with high accuracy.

  As described above, the hub integrated shaft 9 (see FIG. 2) having the shaft portion 2 and the hub portion 3 is formed by performing grinding finishing on a predetermined portion of the shaped member 30. The outer peripheral surface 2a of the shaft portion 2 of the hub integrated shaft 9 is subjected to surface hardening treatment or coating treatment as necessary. Note that if surface hardening treatment or coating treatment is performed prior to the above-described grinding finishing step, wrinkles due to grinding can be suppressed. Moreover, if a coating process is performed after said grinding finishing process, the grinding | polishing wrinkles can be covered with a coating. Further, both surface hardening treatment and coating treatment may be performed. For example, after the surface hardening treatment is performed on the outer peripheral surface 2a of the shaft portion 2, the above-described grinding finishing process is performed, and further this surface is coated. Also good.

  The present invention is not limited to the above embodiment. Hereinafter, although other embodiment of this invention is described, the same code | symbol is attached | subjected to the location which has the same function as said embodiment, and duplication description is abbreviate | omitted.

  In the above embodiment, as shown in FIGS. 6 and 7, the disk mounting surface (the upper end surface 22c1 of the flange portion 22c) of the hub portion 22 and the disk fitting surface (the outer peripheral surface 22b1 of the cylindrical portion 22b) of the shaped member 30. ), And the outer peripheral surface 21b of the shaft portion 21 is ground with reference to these surfaces. However, the present invention is not limited to this. For example, the outer peripheral surface 21b of the shaft portion 21 may be ground with reference to only the disk mounting surface that has been ground.

  The configuration of the fluid dynamic bearing device 1 is not limited to the above. For example, the fluid dynamic bearing device 1 shown in FIG. 8 is the same as the above embodiment in that the lower end of the axial hole 2b provided in the shaft portion 2 is closed and the retaining portion at the lower end of the shaft portion 2 is omitted. Different. Thus, by omitting the retaining portion at the lower end of the shaft portion 2, the axial dimension of the fluid dynamic bearing device 1 is reduced, and the spindle motor can be further reduced in thickness. In this embodiment, the retaining member 11 is provided outside the housing 7. Specifically, an annular retaining member 11 is fixed to the lower end of the cylindrical portion 3 b of the hub portion 3. The retaining member 11 is engaged with a shoulder surface 7a4 provided below the tapered seal surface 7a3 of the housing 7 in the axial direction, so that the shaft portion 2 is prevented from being detached from the bearing sleeve 8.

  In the above-described embodiment, the lower end surface 3a1 of the disk portion 3a of the hub portion 3 faces the thrust bearing gap. However, the surface may not face the thrust bearing gap. In this case, the grinding finish of the lower end surface 3a1 of the hub portion 3 may be omitted.

  In the above embodiment, the seal space S is formed between the outer peripheral surface of the housing 7 and the inner peripheral surface 3b1 of the hub portion 3, but the location of the seal space S is not limited to this. For example, although not shown, a seal member can be fixed to the upper end portion of the inner peripheral surface of the housing, and a seal space can be formed between the inner peripheral surface of the seal member and the outer peripheral surface of the shaft portion.

  In the above embodiment, the lubricating fluid is a lubricating oil. However, the present invention is not limited to this. For example, a fluid such as a magnetic fluid or air can be used.

  In the above embodiment, an example in which the hub integrated shaft 9 according to the present invention is incorporated in a fluid dynamic bearing device for an HDD spindle motor is shown, but the present invention is not limited to this. For example, the hub integrated shaft of the present invention can be applied to a fluid dynamic pressure bearing device for a polygon scanner motor or a fluid dynamic pressure bearing device for a color wheel motor.

DESCRIPTION OF SYMBOLS 1 Fluid dynamic pressure bearing apparatus 2 Shaft part 2a Outer peripheral surface 2b Axial hole 3 Hub part 3a Disk part 3b Cylindrical part 3c Eaves part 3d Disk mounting surface 3e Disk fitting surface 4 Stator coil 5 Rotor magnet 6 Bracket 7 Housing 8 Bearing sleeve 9 Hub integrated shaft 10 Yoke 11 Retaining member 20 Plate material 21 Shaft portion 22 Hub portion 22a Disk portion 22b Cylindrical portion 22c Ridge portion 30 Material 31 Shaft portion 32 Hub portion 41 Rotating center 43 Backing plate 44 Angular whetstone 51 Magnet chuck 52 Shoe 53 Grinding wheel 54 Grinding wheel D Disc R1, R2 Radial bearing part S Seal space T Thrust bearing part

Claims (16)

Fluid dynamic pressure with an outer peripheral surface integrally provided with a shaft portion facing a radial bearing gap filled with a lubricating fluid and a hub portion having a rotating body mounting surface that projects from the shaft portion to the outer diameter and is orthogonal to the axial direction A hub integrated shaft for a bearing device,
A hub-integrated shaft in which at least the outer peripheral surface of the shaft portion and the rotating body mounting surface of the hub portion are ground and finished out of the shaped material in which the shaft portion and the hub portion are integrally formed by plastic processing of the plate material.   The hub integrated shaft according to claim 1, wherein the outer peripheral surface of the shaft portion is subjected to grinding finish with reference to the rotating body mounting surface of the hub portion subjected to grinding finish.   The outer peripheral surface of the hub portion is also ground and the outer peripheral surface of the shaft portion is ground with reference to the outer peripheral surface of the hub portion and the rotating body mounting surface subjected to the grinding finish. Hub integrated shaft.   The hub integrated shaft according to any one of claims 1 to 3, wherein a deflection accuracy of the rotating body mounting surface with respect to the outer peripheral surface of the shaft portion is 5 µm or less.   The hub integrated shaft according to any one of claims 1 to 4, wherein the flatness of the rotating body mounting surface is 1 µm or less.   The hub-integrated shaft according to any one of claims 1 to 5, wherein the outer peripheral surface of the shaft portion is subjected to surface hardening treatment or coating treatment.   The hub integrated shaft according to claim 6, wherein the outer peripheral surface of the shaft portion that has been subjected to surface hardening treatment or coating treatment is ground.   The hub-integrated shaft according to claim 6, wherein the outer peripheral surface of the shaft portion that has been ground is coated.   The hub integrated shaft according to any one of claims 1 to 8, wherein the hub integrated shaft is formed of a ferritic stainless steel containing 0.05% or more of Ti.   The hub according to any one of claims 1 to 9, wherein the hub portion includes a disk portion extending from the shaft portion to the outer diameter, a cylindrical portion extending from the disk portion in the axial direction, and a flange portion extending from the cylindrical portion to the outer diameter. Integral shaft.   The hub-integrated shaft according to claim 10, wherein the axial thickness of the disk portion of the hub portion is 20% or less of the axial dimension of the shaft portion.   The hub integrated shaft according to any one of claims 1 to 11, which is used for a spindle motor of an HDD.   The hub integrated shaft according to any one of claims 1 to 12, a bearing member in which a shaft portion of the hub integrated shaft is inserted into an inner periphery, and a radial between an outer peripheral surface of the shaft portion and an inner peripheral surface of the bearing member A fluid dynamic bearing device including a radial bearing portion that rotatably supports a hub integrated shaft by a fluid film generated in a bearing gap. Fluid dynamic pressure with an outer peripheral surface integrally provided with a shaft portion facing a radial bearing gap filled with a lubricating fluid and a hub portion having a rotating body mounting surface that projects from the shaft portion to the outer diameter and is orthogonal to the axial direction A method for manufacturing a hub integrated shaft for a bearing device, comprising:
A step of forming a shaped material integrally having a shaft portion and a hub portion by plastic processing of a plate material; a step of grinding the outer peripheral surface of the shaft portion of the shaped material and the rotating body mounting surface of the hub portion; A method of manufacturing a hub-integrated shaft.   The method for manufacturing a hub-integrated shaft according to claim 14, wherein after the grinding body is finished on the rotating body mounting surface of the hub portion, the outer peripheral surface of the shaft portion is ground with reference to the rotating body mounting surface.   The hub integrated shaft manufacturing method according to claim 14, wherein after grinding is applied to the rotating body mounting surface and the outer peripheral surface of the hub portion, the outer peripheral surface of the shaft portion is subjected to grinding finishing before mounting the rotating body and the outer peripheral surface as a reference. .

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