JP2008298234A - Method for manufacturing shaft member for fluid bearing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a shaft member for a fluid bearing device, which sufficiently improves processing accuracy of an outer periphery, and restrains dispersion of outer periphery accuracy per product. <P>SOLUTION: In this manufacturing method, angular grinding processing (first grinding processing) using both end faces 11b, 12b as references is applied to an outer peripheral face 11a of a shaft raw material 10 to improve accuracy of the outer peripheral face 11a, and then, coreless grinding processing (second grinding processing) using the outer peripheral face 11a as a reference is applied to both of the end faces 11b, 12b. Thereby, compared to conventional width grinding processing, face accuracy of both of the end faces 11b, 12b is improved, and dispersion of the end face accuracy per product is restrained. When finish grinding processing (third grinding processing) is applied to the outer peripheral face 11a using the end faces 11b, 12b as a references, processing accuracy of the outer peripheral face 11a is sufficiently improved, and dispersion per product is be restrained. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a shaft member used in a hydrodynamic bearing device.

  Due to its high rotational accuracy and quietness, the hydrodynamic bearing device is an information device, for example, a magnetic disk drive device such as HDD, an optical disk drive device such as CD-ROM, CD-R / RW, DVD-ROM / RAM, MD, MO, etc. Suitable for small motors such as fan motors used for spindle motors such as magneto-optical disk drive devices, etc., polygon scanner motors for laser beam printers (LBP), color wheels for projectors, cooling fans for electrical equipment, etc. It can be used.

  For example, Patent Document 1 discloses a method for manufacturing a shaft member for a hydrodynamic bearing device whose outer peripheral surface faces a radial bearing gap. In this manufacturing method, (1) a shaft material having a flange portion is formed by forging, (2) both end surfaces of the shaft material are ground by width grinding, and (3) The outer peripheral surface is ground into a predetermined shape. (4) Further, the outer peripheral surface is subjected to finish grinding with reference to both end surfaces.

JP 2006-77861 A

  By the way, with the recent improvement in performance of information equipment, the hydrodynamic bearing device as described above is required to further improve rotational accuracy and runout accuracy. Further, since the outer peripheral surface of the shaft member as described above faces the radial bearing gap, the processing accuracy is directly related to the gap width of the radial bearing gap, that is, the bearing performance. At this time, if there is a large variation in the accuracy of the outer peripheral surface for each manufactured shaft member, the bearing performance varies, which may increase the proportion of defective products for which the predetermined bearing performance cannot be obtained. Accordingly, it is required to suppress variations in processing accuracy for each product, particularly processing accuracy on the outer peripheral surface.

  In the shaft member manufacturing method disclosed in Patent Document 1 described above, final finish grinding is performed on the outer peripheral surface with reference to both end surfaces of the shaft material that has been subjected to width grinding. Although the end face accuracy can be increased to some extent by such width grinding, it is difficult to achieve higher accuracy. Therefore, the end surface itself of the product itself is not processed with sufficient accuracy to meet the above requirements, and by processing the outer peripheral surface with reference to such an end surface, processing such as perpendicularity to the outer peripheral surface of the end surface and runout accuracy, etc. There is a risk that the accuracy cannot be increased sufficiently. In addition, variation in end surface accuracy for each product cannot be sufficiently suppressed, and variation in outer surface accuracy for each product may occur.

  Then, an object of this invention is to provide the manufacturing method of the shaft member for hydrodynamic bearing apparatuses which can fully raise the processing precision of an outer peripheral surface, and can suppress the variation in the outer peripheral surface precision for every product.

  In order to achieve the above object, the present invention provides a method for manufacturing a shaft member for a hydrodynamic bearing device having an outer peripheral surface facing a radial bearing gap, wherein the outer peripheral surface of the shaft material is based on both end surfaces. After the first grinding process is performed, the second grinding process is performed on both end faces of the shaft material with reference to the outer peripheral face, and the third grinding process is performed on the outer peripheral face with reference to the both end faces. To do.

  Thus, in the manufacturing method of the present invention, the accuracy of the outer peripheral surface is improved by performing the first grinding process on the outer peripheral surface of the shaft material with reference to the both end surfaces, and then the outer peripheral surface is used as the reference for both end surfaces. The second grinding process is performed. Thereby, compared with the conventional width grinding process, the surface accuracy of both end faces is increased, and variations between products are suppressed. When the third grinding process is performed on the outer peripheral surface with this end surface as a reference, the squareness and runout accuracy of the outer peripheral surface with respect to the end surface can be sufficiently increased, and variations in each product can be suppressed.

  This second grinding process can be performed by, for example, coreless grinding. Coreless grinding is an advantageous processing method in that the end face can be finished with high accuracy in a short time.

  In addition, if preliminary grinding is performed on both end faces of the shaft material before performing the first grinding, the first grinding can be performed with improved end face accuracy. It is possible to further increase the processing accuracy of both end surfaces which are the basis of the grinding process.

  With this manufacturing method, for example, a shaft member integrally having a flange portion at the shaft end can be manufactured. In this case, a flange portion is provided at the end portion of the shaft material, and a second grinding process is performed on the end surface of the flange portion.

  As described above, according to the method for manufacturing a shaft member for a hydrodynamic bearing device of the present invention, the squareness and runout accuracy with respect to the end surface of the outer peripheral surface can be sufficiently increased, and variations in the outer peripheral surface accuracy of each product can be suppressed. .

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

  FIG. 2 is for information equipment incorporating a fluid dynamic bearing device (dynamic pressure bearing device) 1 having a fluid dynamic bearing device shaft member 2 (hereinafter simply referred to as a shaft member 2) manufactured by the manufacturing method according to the present invention. 1 shows a conceptual example of a configuration of a spindle motor. This spindle motor for information equipment is used in a disk drive device such as an HDD, and includes a hydrodynamic bearing device 1 that rotatably supports a shaft member 2 in a non-contact manner, a disk hub 3 attached to the shaft member 2, For example, a stator coil 4 and a rotor magnet 5 which are opposed to each other via a gap in the radial direction, and a bracket 6 are provided. The stator coil 4 is attached to the outer periphery of the bracket 6, and the rotor magnet 5 is attached to the inner periphery of the disk hub 3. The bracket 6 has the hydrodynamic bearing device 1 mounted on the inner periphery thereof. The disk hub 3 holds one or more disks D such as magnetic disks on the outer periphery thereof. In this spindle motor for information equipment, when the stator coil 4 is energized, the rotor magnet 5 is rotated by the magnetic force between the stator coil 4 and the rotor magnet 5, and accordingly, the disk hub 3 and the shaft member 2 are integrated. Rotate.

  FIG. 3 shows the hydrodynamic bearing device 1. The hydrodynamic bearing device 1 mainly includes a housing 7 having a bottom 7 b at one end, a bearing sleeve 8 fixed to the inner periphery of the housing 7, and a shaft member 2 inserted into the inner periphery of the bearing sleeve 8. Configured as a part. For convenience of explanation, the following description will be made with the bottom 7b side of the housing 7 as the lower side and the side opposite the bottom 7b as the upper side.

  In the hydrodynamic bearing device 1, the shaft member 2 is rotated in the radial direction between radial bearing surfaces 23 a and 23 b formed on the outer peripheral surface of the shaft portion 21 of the shaft member 2 and the inner peripheral surface 8 a of the bearing sleeve 8. Radial bearing portions R1 and R2 that are freely contactlessly supported are formed. Further, a thrust bearing surface 22b formed between the thrust bearing surface 22a formed on the upper end surface of the flange portion 22 of the shaft member 2 and the lower end surface 8b of the bearing sleeve 8, and a thrust bearing surface 22b formed on the lower end surface of the flange portion 22. Between the upper end surface 7b1 of the bottom 7b of the housing 7, thrust bearing portions T1 and T2 for supporting the shaft member 2 in a non-contact manner so as to be rotatable in the thrust direction are formed.

  For example, as shown in FIG. 1, the shaft member 2 formed by the manufacturing method according to the present invention has a T-shaped cross section integrally including a shaft portion 21 and a flange portion 22 provided at the lower end of the shaft portion 21. On the outer periphery of the shaft portion 21, smooth cylindrical radial bearing surfaces 23a and 23b facing the radial bearing gap are formed at two locations separated in the axial direction. The radial bearing surfaces 23 a and 23 b face radial bearing gaps formed when the shaft member 2 is incorporated into the fluid dynamic bearing device 1. Above one of the radial bearing surfaces 23a, a tapered surface 24 that gradually decreases in diameter toward the tip of the shaft is formed adjacently, and a cylindrical surface 25 that serves as a mounting portion of the disk hub 3 described later is further formed thereabove. ing. Between the two radial bearing surfaces 23a, 23b, between the other radial bearing surface 23b and the flange portion 22 and between the tapered surface 24 and the cylindrical surface 25, annular nuisance portions 26, 27, 28 are respectively provided. Is formed.

  Smooth flat thrust bearing surfaces 22 a and 22 b are formed on both end surfaces of the flange portion 22, and the thrust bearing surfaces 22 a and 22 b are formed when the shaft member 2 is assembled into the hydrodynamic bearing device 1. Facing the thrust bearing gap.

  As shown in FIG. 3, the housing 7 is composed of, for example, a side portion 7a formed in a cylindrical shape with a resin material, and a bottom portion 7b located on one end side of the side portion 7a and formed with a metal material, for example. Yes. The resin material of the side portion 7a is, for example, an amorphous resin such as polysulfone (PSF), polyethersulfone (PES), polyphenylsulfone (PPSU), polyetherimide (PEI), or the like as a crystalline resin, or liquid crystal. A polymer (LCP), polyether ether ketone (PEEK), polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), or the like can be used. The type of filler to be filled in the resin is not particularly limited. For example, as the filler, fibrous filler such as glass fiber, whisker-like filler such as potassium titanate, and scaly filler such as mica. A fibrous or powdery conductive filler such as carbon fiber, carbon black, graphite, carbon nanomaterial, or metal powder can be used. These fillers may be used alone or in combination of two or more.

  In this embodiment, the bottom portion 7b is formed as a separate body from the side portion 7a, and is retrofitted to the lower inner periphery of the side portion 7a. In the partial annular region of the upper end surface 7b1 of the bottom portion 7b, for example, a spiral dynamic pressure groove is formed as a dynamic pressure generating portion, although illustration is omitted. The bottom portion 7b is not limited to this, and can be integrally molded with the side portion 7a and a resin material, for example. At that time, the dynamic pressure groove provided in the upper end surface 7b1 can be molded simultaneously with the injection molding of the housing 7 composed of the side portion 7a and the bottom portion 7b, thereby eliminating the trouble of separately forming the dynamic pressure groove in the bottom portion 7b. It can be omitted.

  The bearing sleeve 8 is formed in a cylindrical shape with a porous body made of sintered metal, in particular, a sintered metal porous body mainly composed of copper, and is fixed at a predetermined position on the inner peripheral surface 7 c of the housing 7. The

  A dynamic pressure groove as a dynamic pressure generating portion is formed on the entire inner surface 8a of the bearing sleeve 8 or a partial cylindrical surface region. In this embodiment, for example, as shown in FIG. 4, herringbone-shaped dynamic pressure grooves 8 a 1 and 8 a 2 are formed at two locations in the axial direction. The upper dynamic pressure groove 8a1 is formed to be axially asymmetric with respect to the annular smooth portion formed in the axially intermediate portion, and the axial dimension X1 of the upper region from the annular smooth portion is the axial dimension of the lower region. It is larger than X2 (X1> X2).

  For example, a spiral-shaped dynamic pressure groove is formed on the entire lower surface 8b of the bearing sleeve 8 or a partial annular region as a dynamic pressure generating portion, although illustration is omitted.

  On the outer peripheral surface 8d of the bearing sleeve 8, axial grooves 8d1 are formed at a plurality of locations (for example, three locations) in the circumferential direction. Further, a radial groove 8c1 is formed on the upper end surface 8c of the bearing sleeve 8 at a position communicating with the axial groove 8d1 of the outer peripheral surface 8d.

  The seal member 9 is formed in a ring shape from, for example, a soft metal material such as brass, another metal material, or a resin material, and is fixed to the inner periphery of the upper portion of the side portion 7a of the housing 7 by means such as press fitting or adhesion. In this embodiment, the inner peripheral surface 9 a of the seal member 9 is formed in a cylindrical shape, and the lower end surface 9 b of the seal member 9 is in contact with the upper end surface 8 c of the bearing sleeve 8.

  Between the taper surface 24 of the shaft portion 21 and the inner peripheral surface 9a of the seal member 9 facing the taper surface 24, an annular seal whose radial dimension gradually increases from the bottom 7b side of the housing 7 upward. A space S is formed. In the hydrodynamic bearing device 1 (see FIG. 3) after completion of assembly, the oil level is within the range of the seal space S.

  In the dynamic pressure bearing device 1 configured as described above, when the shaft member 2 is rotated, the formation regions (two upper and lower portions) of the dynamic pressure grooves 8a1 and 8a2 on the inner periphery of the bearing sleeve 8 are opposed to these regions, respectively. The dynamic pressure of the lubricating oil is generated in the radial bearing gap between the radial bearing surfaces 23a and 23b of the shaft portion 21, and the shaft portion 21 of the shaft member 2 is supported in a non-contact manner so as to be rotatable in the radial direction. The portions that support the shaft member 2 in a non-contact manner so as to be rotatable in the radial direction are conceptually referred to as a first radial bearing portion R1 and a second radial bearing portion R2. The first thrust between the dynamic pressure groove region formed on the lower end surface 8b of the bearing sleeve 8 and the thrust bearing surface 22a on the upper side (shaft side) of the flange portion 22 facing the dynamic pressure groove region. The second thrust bearing between the bearing clearance and the dynamic pressure groove region formed in the upper end surface 7b1 of the bottom portion 7b and the thrust bearing surface 22b on the lower side (on the opposite shaft side) of the flange portion 22 facing this surface. The dynamic pressure of the lubricating oil is generated in the gap, and the flange portion 22 of the shaft member 2 is supported in a non-contact manner so as to be rotatable in both thrust directions. The portions that support the shaft member 2 in a non-contact manner so as to be rotatable in the thrust direction are conceptually referred to as a first thrust bearing portion T1 and a second thrust bearing portion T2, respectively.

  As shown in FIG. 3, the axial groove 8d1 formed on the outer peripheral surface 8d of the bearing sleeve 8 and the radial groove 8c1 formed on the upper end surface 8c allow the upper end of the radial bearing gap and the first thrust bearing gap to be The outer diameter end is communicated. Thereby, the pressure balance in the internal space of the bearing device can be properly maintained. Furthermore, in this embodiment, as shown in FIG. 4, the dynamic pressure groove 8a1 of the inner peripheral surface 8a of the bearing sleeve 8 is axially asymmetric with respect to the annular smooth portion formed in the axially intermediate portion, specifically The axial dimension X1 of the upper region from the annular smooth portion is larger than the axial dimension X2 of the lower region (X1> X2). For this reason, when the shaft member 2 rotates, the pulling force (pumping force) of the lubricating oil by the dynamic pressure groove 8a1 is relatively larger in the upper region than in the lower region. Due to the differential pressure of the pulling force, the lubricating oil filled in the radial bearing gap flows downward, flows in the first thrust bearing gap → the axial groove 8d1 → the radial groove 8c1, and returns to the radial bearing gap again. Thus, by forcibly circulating the lubricating oil in the radial bearing gap, it is possible to more effectively prevent the generation of a local negative pressure in the internal space of the bearing device. When there is no need to force the lubricating oil to flow through the radial bearing gap as described above, the shape of the dynamic pressure groove 8a1 may be formed symmetrically with respect to the annular smooth portion.

  Hereinafter, an embodiment of a method for manufacturing the shaft member 2 according to the present invention, in particular, a surface grinding method for the shaft member 2 will be described.

  First, a metal material such as stainless steel as a material of the shaft member 2 to be formed is processed by an arbitrary method such as forging or turning, and the shaft portion 11 and the flange portion 12 are integrally provided as shown in FIG. A shaft material 10 having a T-shaped cross section is formed. In the example shown in FIG. 5, the outer peripheral surface 11 a of the shaft portion 11 has a shape having a large-diameter outer peripheral surface 13, a tapered surface 14, and a small-diameter outer peripheral surface 15. The shape of the shaft portion 11 is not limited thereto, and for example, it can be a cylindrical surface having a uniform diameter over the entire length of the outer peripheral surface 11a.

  On the surface of the shaft blank 10 thus formed, (1) width grinding (preliminary grinding), (2) angular grinding (first grinding), and (3) coreless grinding (second grinding) ) And (4) Finish grinding (third grinding) is performed. Hereinafter, details of these grinding steps will be described.

(1) Width grinding (preliminary grinding)
Both end surfaces of the shaft blank 10, that is, the shaft end surface 11b and the opposite shaft end surface 12b (see FIG. 5) of the flange portion 12 are ground with reference to the large-diameter outer peripheral surface 13 of the shaft outer peripheral surface 11a. For example, as shown in FIGS. 6 and 7, a grinding device 40 used in this grinding process includes a carrier 41 that holds a plurality of shaft materials 10 as workpieces, and a shaft end face 11 b of the shaft material 10 held by the carriers 41. And a pair of grindstones 42 and 42 for grinding the opposite end surface 12b of the flange portion 12.

  A plurality of notches 43 are provided at equal circumferential circumferential pitches in a partial circumferential region of the outer peripheral edge of the carrier 41 (see FIG. 6A). The shaft material 10 is accommodated in the notch 43 in a state in which the straightened surface 13 is in angular contact with the inner surface 43a of the notch 43 (see FIG. 6B). The large-diameter outer peripheral surface 13 of the shaft material 10 protrudes slightly from the outer peripheral surface of the carrier 41, and the protruding portion (large-diameter outer peripheral surface 13) of the shaft material 10 is restrained from the outer diameter side on the outer diameter side of the carrier. In this manner, the belt 44 is stretched. A pair of grindstones 42 and 42 are coaxially arranged at predetermined intervals on both ends in the axial direction of the carrier 41 of the shaft material 10 accommodated in the notch 43 so that the end surfaces (grinding surfaces) thereof face each other.

  As the carrier 41 rotates, the shaft material 10 is sequentially put into the notch 43 from a fixed position. The thrown shaft material 10 traverses from the outer diameter end to the inner diameter end on the end faces of the rotating grindstones 42 and 42 in a state where the dropping from the notch 43 is restrained by the belt 44. Accordingly, both end faces of the shaft material 10, that is, the shaft end face 11 b and the opposite end face 12 b of the flange section 12 are ground by the end faces of the grindstones 42 and 42. At the same time, the axial width (the entire length including the flange portion 12) of the shaft material 10 is finished to a predetermined dimension.

(2) Angular grinding (first grinding)
Next, the outer peripheral surface 10b of the shaft material 10 and the shaft portion side end surface 12a of the flange portion 12 are ground (angular) with reference to both end surfaces 11b and 12b of the shaft material subjected to the width grinding (preliminary grinding). Grinding). For example, as shown in FIG. 8, the grinding device 50 used in this grinding process plunges the outer peripheral surface 11 a of the shaft material 10 with the grindstone 53 while pressing the backing plate 54 and the pressure plate 55 against both end surfaces of the shaft material 10. It is to be ground. At this time, the large-diameter outer peripheral surface 13 of the shaft material 10 is rotatably supported by the shoe 52.

  The grindstone 53 is a general-purpose grindstone provided with a grinding surface 56 corresponding to the outer peripheral surface shape of the shaft member 2 as a finished product. The grinding surface 56 includes a cylindrical grinding portion 56a that grinds the outer peripheral surface 11a over the entire axial length of the shaft portion 11 and the outer peripheral surface 12c of the flange portion 12, and a surface grinding portion 56b that grinds the shaft portion side end surface 12a of the flange portion 12. And. In the illustrated grindstone 53, as the cylindrical grinding portion 56a, the portions 56a1 and 56a2 for grinding the regions corresponding to the radial bearing surfaces 23a and 23b of the shaft member 2, the portion 56a3 for grinding the region corresponding to the tapered surface 24, and the cylindrical surface 25, a portion 56 a 4 for grinding the region corresponding to 25, portions 56 a 5 to 56 a 7 for grinding each of the portions 26 to 28, and a portion 56 a 8 for grinding the outer peripheral surface 12 c of the flange portion 12.

  The grinding process in the grinding apparatus 50 having the above-described configuration is performed according to the following procedure. First, with the shaft material 10 and the grindstone 53 rotated, the grindstone 53 is fed in an oblique direction (in the direction of arrow 1 in the figure), and the surface grinding portion of the grindstone 53 is placed on the shaft portion side end surface 12a of the flange portion 12 of the shaft material 10. 56b is pressed and the axial part side end surface 12a is mainly ground. Thereby, the shaft part side end surface 12a in the flange part 22 of the shaft member 2 is ground. Next, the grindstone 53 is fed in a direction orthogonal to the rotational axis of the shaft blank 10 (in the direction of arrow 2 in the figure), and the grindstone 53 is placed on the outer circumferential surface 11 a of the shaft portion 11 and the outer circumferential surface 12 c of the flange portion 12. The cylindrical grinding portion 56a is pressed to grind the surfaces 11a and 12c. Thereby, out of the outer peripheral surface of the shaft portion 21 of the shaft member 2, the regions 13 a and 13 b corresponding to the radial bearing surfaces 23 a and 23 b of the shaft material 10, the tapered surface 24, the region 15 corresponding to the cylindrical surface 25, and the flange portion 22. The outer peripheral surface 22c is ground, and further each of the pussies 26 to 28 are formed. In the grinding, for example, as shown in FIG. 8, it is preferable to perform grinding while measuring the remaining grinding allowance with a measurement gauge 57. Thus, the outer peripheral surface of the shaft material 10 and the like can be processed with high accuracy by performing the angular grinding process on the basis of the both end faces 11b and 12b whose accuracy has been increased by the immediately preceding width grinding process.

(3) Coreless grinding (second grinding)
Next, the both end surfaces 11b and 12b of the shaft blank 10 are ground with reference to the outer peripheral surface ground by the above-described angular grinding (first grinding). As shown in FIG. 9, the grinding device 60 used here performs so-called two-roll one-shoe type coreless grinding. Specifically, the two driving rolls 61 and 62 and the shoe 63 support the shaft portion 11 of the shaft material 10 from the outer periphery with three-point contact, while the driving rolls 61 and 62 are in the direction indicated by the arrow a in FIG. To rotate the shaft blank 10 in the direction indicated by the arrow b. In this state, while the end surface 11b of the shaft portion 11 is supported by the pressure plate 65, the grindstone 64 is pressed against the end surface 12b opposite to the shaft portion of the flange portion 12 and is ground. The outer peripheral surface 11a of the shaft portion 11 serving as a reference surface for the centerless grinding has a high cylindricity because the angular grinding is performed. Therefore, this surface can be finished with high accuracy by grinding the opposite end surface 12b of the flange portion 12 on the basis of this surface. In particular, by grinding the non-shaft side end surface 12b of the flange portion 12 by coreless grinding, due to the characteristics of the coreless grinding, the straight surface of the nonshaft side end surface 12b of the flange portion 12 with respect to the outer peripheral surface 11a serving as the reference surface is obtained. Angle and runout accuracy can be increased. In the same manner as described above, the end surface 11b of the shaft portion 11 is ground by a centerless grinding process using the outer peripheral surface 11a as a reference.

(4) Finish grinding (third grinding)
Areas 13a and 13b corresponding to the radial bearing surfaces 23a and 23b of the shaft member 2 and the cylindrical surface 25 with reference to both end faces 12b and 11b of the shaft blank 10 subjected to the centerless grinding process (second grinding process). , 15 is subjected to final finish grinding. A grinding apparatus 70 used for this grinding is a cylindrical grinder shown in FIG. 10, and plunge-grinds with a grindstone 73 while rotating the shaft material 10 held between the backing plate 74 and the pressure plate 75. At this time, the shaft material 10 is rotatably supported by the shoe 72. The grinding surface 73a of the grindstone 73 includes a first cylindrical grinding portion 73a1 for grinding the regions 13a and 13b corresponding to the radial bearing surfaces 23a and 23b, and a second cylindrical grinding portion for grinding the region 15 corresponding to the cylindrical surface 25. 73a2.

  In the grinding device 70 having the above-described configuration, the regions 13a, 13b, and 15 corresponding to the radial bearing surfaces 23a and 23b and the cylindrical surface 25 are formed by bringing the rotating grindstone 73 into contact with the outer peripheral surface of the shaft blank 10 from the outside in the radial direction. Each is ground to finish these areas to final surface accuracy. At this time, since both end surfaces 12b and 11b of the shaft blank 10 serving as the reference surface are subjected to the centerless grinding, these surfaces have high flatness, squareness, runout accuracy, and the like. Accordingly, by finishing grinding the outer peripheral surface of the shaft member 2, particularly the radial bearing surfaces 23a and 23b, with reference to this surface, the processing accuracy of these surfaces can be increased and the variation in accuracy of each product can be suppressed. Can do. In this embodiment, both the region corresponding to the radial bearing surfaces 23a and 23b and the region corresponding to the cylindrical surface 25 are finish-ground, but grinding of the region corresponding to the cylindrical surface 25 can be omitted. .

  After passing through the grinding process as described above, the shaft member 2 shown in FIG. 1 is completed by performing heat treatment or cleaning treatment as necessary.

  As described above, in the method for manufacturing a shaft member for a hydrodynamic bearing device according to the present invention, it becomes a reference surface for final finish grinding (third grinding) applied to the radial bearing surfaces 23a and 23b on the outer peripheral surface. The both ends 11b and 12b of the shaft blank 10 are subjected to coreless grinding (second grinding) in advance. Further, an angular grinding process (first grinding process) is performed in advance on the outer peripheral surface 11a of the shaft blank 10 which is a reference surface for the coreless grinding process. In this way, it is possible to improve the accuracy of the final finish grinding process by pre-grinding the surface that will be the reference surface for the next process in advance, and to improve the accuracy of the outer peripheral surface grinding for each product. Can be suppressed.

  Further, by performing grinding processing (preliminary grinding processing) on both end faces of the shaft blank 10 which is the reference surface of this processing at the first stage of the first grinding processing, the accuracy of the final finish grinding processing is further improved. be able to.

  In the above description, in the angular grinding process shown in FIG. 8, the cylindrical grinding of the outer peripheral surface 10 b of the shaft material 10 and the surface grinding of the shaft portion side end surface 12 a of the flange portion 12 are performed by the common grindstone 53. However, it is also possible to perform both in separate steps using separate whetstones.

  Moreover, in the above description, although the case where the pussies 26-28 of the shaft member 2 were formed by the angular grinding process shown in FIG. 8 was illustrated, these stubs 26-28 are the shaft raw material 10 shown in FIG. It can also be formed in advance. In this case, in particular, the angular portion (see FIG. 8) of the flange portion 12 is formed by forming the corner portion 27 between the shaft portion 21 and the flange portion 22 in an inclined shape as shown in FIG. It can be made to function as relief of the grindstone 53 at the time of grinding the shaft part side end surface 12a and the shaft part outer peripheral surface 11a simultaneously.

  Moreover, although the radial bearing surfaces 23a and 23b and the thrust bearing surfaces 22a and 22b of the shaft member 2 are all smooth surfaces without dynamic pressure grooves in the above embodiment, the dynamic pressure is applied to these bearing surfaces. Grooves can also be formed. In this case, the radial dynamic pressure groove can be formed by rolling or forging before the angular grinding process shown in FIG. 8, and the thrust dynamic pressure groove can be formed by pressing or forging.

  Moreover, in the above embodiment, as the dynamic pressure bearings constituting the radial bearing portions R1 and R2 and the thrust bearing portions T1 and T2, for example, a dynamic pressure generating portion including a herringbone shape or a spiral shape dynamic pressure groove is used. Although the bearing is illustrated, the configuration of the dynamic pressure generating unit is not limited to this. For example, multi-arc bearings, step bearings, taper bearings, taper / flat bearings can be used as the radial bearing portions R1, R2, and step bearings, wave bearings, etc. are used as the thrust bearing portions T1, T2. You can also.

  Moreover, in the above embodiment, radial bearing part R1, R2 is provided in the axial direction apart, However, You may provide these continuously in an axial direction. Alternatively, only one of the radial bearing portions R1 and R2 may be provided.

  Moreover, although the case where the dynamic pressure is forcibly generated in the lubricating oil in the radial bearing gap by the dynamic pressure generating portion is shown in the above embodiment, the outer peripheral surface of the shaft member 2 and the inner peripheral surface of the bearing sleeve 8 are shown. It is also possible to constitute a so-called perfect circle bearing in which all 8a are cylindrical surfaces.

  Moreover, in the above embodiment, the inside of the hydrodynamic bearing device 1 is filled, and the radial bearing gap between the bearing sleeve 8 and the shaft member 2 and the thrust between the bearing sleeve 8 and the housing 7 and the shaft member 2 are filled. Although the lubricating oil is exemplified as the fluid that causes the dynamic pressure action in the bearing gap, it is not particularly limited to this fluid. A fluid capable of generating a dynamic pressure action in each bearing gap having the dynamic pressure grooves, for example, a gas such as air, or a fluid lubricant such as a magnetic fluid may be used.

  In addition, the hydrodynamic bearing device having the shaft member according to the manufacturing method of the present invention is not limited to the spindle motor used for the disk drive device such as the HDD as described above, but is a high-speed rotation such as a spindle motor for driving the magneto-optical disk of the optical disk. It can also be suitably used as a fan motor for rotating shaft support in a small motor for information equipment used below, a polygon scanner motor of a laser beam printer, or a cooling fan for electrical equipment.

It is a side view of a shaft member. It is sectional drawing of the spindle motor for information equipment incorporating the dynamic pressure bearing apparatus. It is a longitudinal cross-sectional view of a fluid dynamic bearing device. It is a longitudinal cross-sectional view of a bearing sleeve. It is a side view of the shaft raw material shape | molded by the forging process. (A) is a top view which shows an example of the grinding apparatus which concerns on the width grinding process of a shaft raw material, (b) is an enlarged view of the notch periphery of the carrier holding a shaft raw material. It is a partial cross section side view which shows an example of the grinding device which concerns on the said width grinding process (preliminary grinding process). It is a side view which shows an example of the grinding device which concerns on the angular grinding process (1st grinding process) of a shaft raw material. It is a side view which shows an example of the grinding device which concerns on the coreless grinding process (2nd grinding process) of a shaft raw material. It is a side view which shows an example of the grinding device which concerns on the grinding finishing process (3rd grinding process) of a shaft raw material. It is an expanded sectional view of the corner | angular part periphery of the axial part and flange part of a shaft member.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Dynamic pressure bearing apparatus 2 Shaft member 21 for fluid dynamic bearing apparatuses Shaft part 22 Flange part 22a, 22b Thrust bearing surface 23a, 23b Radial bearing surface 7 Housing 8 Bearing sleeve 9 Seal member 10 Shaft material 11 Shaft part 11a Outer surface 11b Shaft part End surface 12 Flange portion 12a Shaft side end surface 12b Countershaft side end surface 40, 50, 60, 70 Grinding device D Disc R1, R2 Radial bearing portion T1, T2 Thrust bearing portion S Seal space

Claims (5)

A method for manufacturing a shaft member for a hydrodynamic bearing device with an outer peripheral surface facing a radial bearing gap,
After the first grinding process is performed on the outer peripheral surface of the shaft material with reference to both end surfaces, the second grinding process is performed on the both end surfaces of the shaft material with reference to the outer peripheral surface. A method for manufacturing a shaft member for a hydrodynamic bearing device, characterized in that a third grinding process is performed on the surface.   The method for manufacturing a shaft member for a hydrodynamic bearing device according to claim 1, wherein the second grinding is centerless grinding.   The method of manufacturing a shaft member for a hydrodynamic bearing device according to claim 1, wherein the first grinding process is performed on the outer peripheral surface after the both end surfaces of the shaft material are preliminarily ground.   The method of manufacturing a shaft member for a hydrodynamic bearing device according to claim 1, wherein a flange portion is integrally provided at an end portion of the shaft material, and the second grinding process is performed on an end surface of the flange portion.   A shaft member for a hydrodynamic bearing device manufactured by the method according to claim 1.

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