JP4896429B2 - Bearing, bearing device, motor, and bearing manufacturing method - Google Patents

Description

  The present invention relates to a bearing having a bearing surface formed by electroforming and a manufacturing method thereof.

  Sliding bearings (hereinafter simply referred to as “bearings”) are widely used in applications that support relative rotation, sliding, or sliding rotation with a shaft member. In this type of bearing, since the bearing surface accuracy greatly affects the bearing performance, various proposals have been conventionally made in order to obtain good bearing surface accuracy.

For example, JP 2003-56552 A and JP 2003-56569 A propose a bearing (electroformed bearing) in which an electroformed part is insert-molded in order to improve bearing surface accuracy. In both the inventions described in both publications, unnecessary portions of the master shaft are masked to form a cylindrical electroformed portion which is an electroformed shell other than the mask portion, and injection molding is performed on the outer periphery of the electroformed portion. After the resin is filled by molding the bearing, the bearing is separated from the master shaft.
JP 2003-56552 A JP 2003-56569 A

  By the way, when an electroformed part is shape | molded cylindrically, it is thought that the residual stress of a diameter expansion direction acts on the internal structure of the electroformed part after shaping | molding. On the other hand, since the cylindrical resin mold portion tends to shrink as it solidifies, the outer peripheral surface of the electroformed portion and the inner peripheral surface of the resin mold portion are opposite to each other after the resin molding of the electroformed portion. Pressed against. In addition, the inner peripheral surface of the electroformed part is a smooth surface that follows the outer peripheral surface of the master shaft, but the outer peripheral surface of the electroformed part is generally rough, so that the surface irregularities of the electroformed part are uneven after resin molding. Resin enters and produces an anchor effect. By these combined actions, a strong fixing force can be obtained between the electroformed part and the resin mold part.

  However, with the current structure, it is difficult to secure a further fixing force, which restricts the expansion of application of bearings.

  An object of this invention is to provide the bearing which fixed the electroformed part and the mold part more firmly, and its manufacturing method.

In order to solve the above-mentioned problems, the bearing of the present invention comprises a bearing surface formed by a surface on the metal deposition start side on the inner peripheral surface of the electroformed part, and the electroformed part is molded by injection molding. A flange is formed by plastic deformation at least one of the axial ends of the electroformed part, the axial length L2 of the electroformed part before plastic deformation of the flange, and the axis of the electroformed part after plastic deformation The length L1 in the direction satisfies the relationship 0 <A / L1 ≦ 0.5 (where A = L2−L1) .

  Due to the characteristics of electroforming, the surface of the master shaft is accurately transferred to the bearing surface made of the electroformed part, and the surface accuracy follows the surface accuracy of the master shaft. Therefore, if the surface accuracy of the master shaft is increased, high bearing surface accuracy can be obtained, and the rotation accuracy and sliding accuracy of the bearing can be dramatically increased as compared with existing products.

  In particular, when an electroformed part having a flange is molded with resin or metal (insert molding), the flange is integral with the electroformed part and the mold part that is in close contact with the flange is prevented from coming off or rotating. A high fixing force can be obtained between the cast part and the mold part. In particular, by making the outer peripheral surface of the flange non-circular, it is possible to obtain an even higher anti-rotation effect. The flange includes those extending in the direction perpendicular to the axis (see FIG. 5) and those extending in the oblique direction of the axis (see FIG. 8).

The flange of the electroformed part is formed by plastically deforming the electroformed part. For example, if the end surface of the electroformed part that is in close contact with the outer periphery of the master shaft is pressed in the axial direction, the pressed part cannot be deformed to the inner diameter side that is in close contact with the master shaft. Plastic deformation to the outer diameter side makes it possible to easily form an outward flange. In this way, when the flange is formed by plastic deformation, if the applied pressure acting on the electroformed part is too large, the inner peripheral surface of the electroformed part in close contact with the master shaft may be peeled off from the outer peripheral surface of the master shaft due to the impact at that time. There is. In order to prevent such a situation, it is desirable to set the change in the axial length of the electroformed part before and after plastic deformation within 50% of the axial length of the electroformed part after plastic deformation. That is, the axial length of the electroformed part before plastic deformation of the flange is L2, the axial length of the electroformed part after plastic deformation is L1, and L1 and L2 are 0 <A / L1 ≦ 0.5. (However, A = L2-L1) is satisfied.

  If the flange formed by plastic deformation is formed at one end portion or both end portions of the electroformed portion, the influence of the plastic deformation is less likely to reach the central portion in the axial direction of the bearing surface. Therefore, it is possible to avoid a decrease in bearing surface accuracy at the axial center portion of the bearing surface which is important for bearing function.

In particular, when molding the electroformed part by injection molding, if the electroformed part is partially plastically deformed by clamping the mold, the bearing is formed by injecting resin or metal into the cavity as it is after the flange is formed. Insert molding can be performed, and a bearing can be manufactured at low cost without requiring special processing for forming the flange. In addition, since the outer peripheral surface of the plastically deformed flange is normally non-circular, a flange having the non-circular outer peripheral surface can be formed without any additional process.

  It is possible to provide a bearing device having high bearing performance and durability by inserting a shaft member into the inner periphery of the bearing described above. As the shaft member, in addition to using the master shaft used at the time of forming the electroformed part, a member different from the master shaft can also be used. A motor having this bearing device is characterized by good rotational accuracy and high durability.

  According to the present invention, since the retaining or rotation prevention is performed between the electroformed part and the mold part, the fixing force between the electroformed part and the mold part can be further increased.

  A first embodiment of the present invention will be described with reference to FIGS.

  The bearing 5 of the present invention shown in FIG. 1 includes a step of masking a required portion of the master shaft 2 (see FIG. 3) and a step of forming an electroformed shaft 1 by performing electroforming on a non-mask portion (see FIG. 4). The electroformed shaft 4 is manufactured through a process of molding the electroformed portion 4 of the electroformed shaft 1 with a resin or the like (see FIGS. 6 and 7) and a step of separating the electroformed portion 4 and the master shaft 2.

  In the following description, the “rotating bearing” means the bearing 5 for supporting the relative rotation with the shaft, regardless of whether the bearing 5 is on the rotating side or the fixed side. . The “sliding bearing” means the bearing 5 for supporting the relative linear motion between the shafts, and it does not matter whether the bearing 5 is the moving side or the fixed side. The “rotating and sliding bearing” has the functions of the two bearings, and means the bearing 5 for supporting both the rotational motion and the linear motion between the shafts.

  The master shaft 2 is made of a conductive material, for example, hardened stainless steel, and is manufactured as a straight shaft having a circular cross section. Of course, the material is not limited to stainless steel, but it has a mechanical function such as rigidity, slidability, heat resistance, chemical resistance, workability and separability of the electroformed part 4, and so on. A material and a heat treatment method suitable for the characteristics required above are selected. Even non-metallic materials such as ceramics can be used by conducting a conductive treatment (for example, by forming a conductive metal film on the surface). The surface of the master shaft 2 is preferably subjected to a surface treatment for reducing the frictional force with the electroformed part 4, for example, a fluorine-based resin coating.

  In addition to the hollow shaft, the master shaft 2 may be a solid shaft in which a hollow shaft or a hollow portion is filled with resin. In the rotation bearing, the cross section of the master shaft is basically circular, but in the case of the sliding bearing, the cross section can be arbitrarily shaped. It can also be a perfect circle shape. In a sliding bearing, the cross-sectional shape of the master shaft 2 is basically constant in the axial direction. However, a rotating bearing or a rotating / sliding bearing does not have a constant cross-sectional shape over the entire length of the shaft. May take the form.

  Since the accuracy of the outer peripheral surface of the master shaft 2 directly affects the accuracy of the bearing gap described later, the surface accuracy that is important for bearing functions such as roundness, cylindricity, and surface roughness must be finished in advance. There is. For example, in a bearing for rotation, since roundness is important from the viewpoint of avoiding contact with the bearing surface, it is desirable to increase the roundness of the outer peripheral surface of the master shaft 2 as much as possible. As a result of verification by the present inventors, when the roundness of the outer peripheral surface of the master shaft 2 is finished to 80% or less of the average width (radial dimension) of a bearing gap described later, contact with the bearing surface is prevented. It was found that good rotation accuracy can be obtained. Therefore, for example, when the average width of the bearing gap is set to 2 μm, it is desirable that the outer peripheral surface of the master shaft is finished to a roundness of 1.6 μm or less.

  As shown in FIG. 3, masking is performed on the outer peripheral surface of the master shaft 2 except for a portion where the electroformed portion 4 is to be formed. As the covering material 3 for masking, an existing product having non-conductivity and corrosion resistance against the electrolyte solution is selectively used.

  The electroforming process is performed by immersing the master shaft 2 in an electrolyte solution containing metal ions such as Ni and Cu, and energizing the electrolyte solution to deposit a target metal on the surface of the master shaft 2. If necessary, the electrolyte solution may contain a sliding material such as carbon or a stress relaxation material such as saccharin. The type of electrodeposited metal is appropriately selected according to physical properties and chemical properties such as hardness and fatigue strength required for the bearing surface of the bearing. If the thickness of the electroformed part 4 is too thick, the peelability from the master shaft 2 is reduced, and if it is too thin, the durability of the bearing surface is reduced. The optimum thickness is set accordingly. For example, in a rotating bearing having a shaft diameter of 1 mm to 6 mm, the thickness is preferably 10 μm to 200 μm.

  Through the above steps, as shown in FIG. 4, the electroformed shaft 1 in which the cylindrical electroformed portion 4 is attached to a partial region of the outer periphery of the master shaft 2 is manufactured. When the covering material 3 for masking is thin, both ends of the electroformed part 4 protrude toward the covering material 3 side, and a tapered chamfered part 4a may be formed on the inner peripheral surface.

  The electroformed shaft 1 is transferred to the molding process shown in FIGS. 6 and 7, and insert molding is performed using the electroformed portion 4 and the master shaft 2 as insert parts.

  In this molding step, the electroformed shaft 1 is supplied into the mold composed of the upper mold 6 and the lower mold 7 with its axial direction parallel to the mold clamping direction (the vertical direction in the drawing) as shown in FIG. The The lower die 7 is formed with a positioning hole 9 adapted to the outer diameter of the master shaft 2, and the lower end of the electroformed shaft 1 transferred from the previous process is inserted into the positioning hole 9 to position the electroformed shaft 1. Made. In this positioning state, the lower end surface of the electroformed part 4 of the electroformed shaft 1 is engaged with the molding surface of the lower mold 7, and the upper end of the electroformed part 4 is the parting line P.D. L. Rather than the other mold (upper mold 6 in this embodiment). The depth L3 of the positioning hole 9 is larger than the distance L4 between the lower end of the master shaft 2 and the lower end of the electroformed part 4 (L3> L4). Therefore, in the state before mold clamping, The end face floats from the bottom of the positioning hole 9. By adjusting the flying height, the plastic deformation amount of the flange formed at the lower end of the electroformed portion 4 can be changed.

  A guide hole 10 is formed in the upper mold 6 coaxially with the positioning hole 9. The depth L5 of the guide hole 10 is sufficient as long as the upper end of the master shaft 2 does not abut against the bottom of the guide hole 10 during mold clamping shown in FIG. 7 (note that the lower end of the master shaft 2 is a positioning hole). It hits the bottom of 9).

  In the above mold, when the movable mold (upper mold 6 in this embodiment) is brought close to the fixed mold (lower mold 7 in the present embodiment) and clamped, the upper end of the master shaft 2 is first brought into the guide hole 10. The master shaft 2 is centered by being inserted, and the upper end surface of the electroformed part 4 comes into contact with the molding surface of the upper mold 6. When the upper die 6 is further approached, the entire electroformed shaft 1 is pushed downward, and the lower end portion of the electroformed portion 4 that is in contact with the molding surface of the lower die 7 and the electroforming that is in contact with the molding surface of the upper die 6. The upper ends of the parts 4 are plastically deformed to the outer diameter side, and flanges 11 (see FIG. 5) are formed at both ends in the axial direction of the electroformed part 4 as shown in FIG. It is also possible to form the flange 11 only at one axial end of the electroformed part 4 by changing the mold structure.

  After completion of the mold clamping, a resin material is injected into the cavity 8 through the spool 12, the runner 13, and the gate 14, and insert molding is performed. As the resin material, for example, a highly functional crystalline polymer such as a liquid crystal polymer (LCP), a polyphenylene sulfide (PPS) resin, a polyacetal resin, and a polyamide resin can be used. Of course, these are merely examples, and a resin material suitable for the application and use environment of the bearing can be selected from various existing resin materials. You may add various fillers, such as a reinforcement (regardless of forms, such as a fiber form and a powder form) and a lubricant, as needed.

  After the mold opening, the molded product removed from the mold has a structure in which the master shaft 2, the electroformed part 4, and the mold part 15 are integrated as shown in FIG. The molded product is then transferred to a separation step and separated into a bearing 5 composed of an electroformed part 4 and a mold part 15 and a master shaft 2. In this separation step, for example, an impact is applied to the master shaft 2 and the mold portion 15, or the electroformed portion 4 and the master shaft 2 are heated (may be cooled), and a difference in thermal expansion is generated between them. Is done by. Since the residual stress in the diameter expansion direction in the electroformed metal structure is released by these operations, the inner diameter of the electroformed portion 4 is increased, and the radial dimension between the outer diameter of the master shaft 2 is 1 μm to several A minute gap of about 10 μm is formed. Since this minute gap functions as a bearing gap, a bearing 5 (see FIG. 1) that supports the master shaft 2 so as to be relatively rotatable or slidable by the integrated electroformed portion 4 and mold portion 15 is configured. Is done. In the bearing 5, the inner peripheral surface of the electroformed part 4 functions as a bearing surface 4 b that supports relative rotation or sliding of the master shaft 2.

  This bearing gap is characterized by a very small clearance and high precision due to the characteristics of electroforming. Therefore, by using the master shaft 2 as a shaft member as it is and inserting it into the inner periphery of the bearing 5, it is possible to provide a bearing device having high rotational accuracy or slidability. In addition, it is not always necessary to use the master shaft 2 as a shaft member, and a bearing device can be configured by replacing it with a shaft member separately manufactured with the same degree of accuracy as the master shaft. In this case, once the master shaft is manufactured, it can be repeatedly used, so that the manufacturing cost of the master shaft 2 can be suppressed and the cost of the bearing device can be further reduced.

  In addition to using this bearing device without lubrication, it can also be used by supplying a lubricant such as oil into the bearing gap.

  As described above, in the present invention, since the flange 11 is formed in the electroformed part 4 and the electroformed part 4 is insert-molded in a form including the flange 11, the electroformed part 4 and further the mold part 15 are formed. It is prevented from coming off in between, and is further prevented from rotating. Therefore, it is possible to increase the fixing force between the electroformed part 4 and the mold part 15 and provide a highly reliable bearing having excellent durability. In particular, when the flange 11 is formed by plastic deformation of the electroformed part 4 as in the embodiment shown in FIGS. 6 and 7, the shape of the outer peripheral surface 16 has random irregularities as shown in FIG. Since it has a non-circular shape, a high detent effect is obtained. In FIG. 1, the irregularities on the outer peripheral surface 16 are exaggerated for easy understanding.

  In order to obtain a sufficient retaining effect and further a detent effect, it is necessary to ensure high adhesion between the resin and the flange 11. When the molding shrinkage rate of the resin is too low, the adhesion of the resin to the flange 11 is lowered, and the above effect becomes insufficient. As a result of verification by the present inventors, if the resin material has a molding shrinkage of 0.02% or more, a sufficient effect can be obtained as a stopper and a rotation stopper. On the other hand, if the molding shrinkage is too high, the residual stress becomes excessive, and there is a concern about the dimensional change of the solidified molded product. Therefore, it is desirable that the molding shrinkage of the resin material to be used is 2.0% or less.

  By the way, as described above, when the flange 11 is formed by plastic deformation, if the pressure applied from the mold acting on the electroformed part 4 is too large, the electroformed part 4 in close contact with the master shaft 2 due to the impact at that time. There is a possibility that the inner peripheral surface of the master shaft 2 is peeled off from the outer peripheral surface of the master shaft 2. When the electroformed part 4 is peeled off, the diameter of the electroformed part 4 is enlarged at that moment and a gap is formed between the electroformed part 4 and the master shaft 2. There is a possibility that the diameter of the surface is randomly reduced and the accuracy of the bearing surface 4b is lowered. In order to prevent such a situation, it is necessary to try to prevent peeling of the electroformed part 4 from the master shaft 2 before injection molding. This can be achieved by managing the upper limit of the plastic deformation amount of the electroformed part 4. Conceivable.

  From this viewpoint, the length in the axial direction of the electroformed part 4 (shown by a solid line in FIG. 5) after plastic deformation is L1, and the electroformed part 4 (shown by a broken line in FIG. 5) before plastic deformation. When the axial length is L2, the change in the axial length A = L2-L1 of the electroformed part 4 is within 50% of the axial length L1 of the electroformed part 4 after plastic deformation (desirably Is within 20%), it has been found that peeling of the electroformed part 4 before injection molding due to plastic deformation can be prevented. On the other hand, when A = 0, the flange 11 cannot be formed. Therefore,

0 <A / L1 ≦ 0.5
It is desirable to determine L1 and L2 so as to satisfy the above.

  In the above description, the case where the flange 11 is formed by plastic deformation is illustrated, but the flange 11 can also be formed by a method other than plastic deformation. For example, as shown in FIG. 8, if the master shaft 2 is formed in a stepped shaft shape, when the master shaft 2 is immersed in an electrolytic solution in the electroforming process, generally, the corner portion 2 a of the master shaft 2 has another plane portion. Since the amount of metal particles deposited is larger than that of the above, depending on the electroforming conditions, an inclined flange 11 as shown in the figure can be formed at the corner 2a after the end of electroforming. Accordingly, if the electroformed part including the flange 11 is thereafter molded by injection molding (indicated by a two-dot chain line), it is possible to obtain the same effect as retaining or rotating.

  In the above description, the case where the electroformed part 4 is molded with a resin material has been described. However, the present invention is not limited to resin, and metal injection molding, for example, low melting point metal such as magnesium alloy or aluminum alloy is injected and electroformed. The part 4 can also be molded. In this case, a bearing that is superior in terms of strength, heat resistance, conductivity, and the like can be obtained as compared with the case of using a resin.

  Next, the bearing device described above is applied to support the rotating shaft of the motor 21, and one embodiment thereof will be described with reference to FIG.

  The motor 21 in the illustrated example is a spindle motor used in a disk drive device such as an HDD. The bearing device of the motor 21 includes a radial bearing portion R that supports the shaft member 22 rotatably in the radial direction, and a thrust bearing portion T that supports the shaft member 22 rotatably in the thrust direction. The radial bearing portion R is configured by inserting the shaft member 22 into the inner periphery of the bearing 5, and the thrust bearing T is a thrust plate 23 in which the convex spherical shaft end of the shaft member 22 faces the end surface of the bearing 5. It is configured by supporting in contact. As described in the above description, the bearing 5 is formed by molding the electroformed part 4 by injection molding, and flanges 11 are formed at both ends of the electroformed part 4 in the axial direction. In addition to the bearing device, the motor 21 includes a rotor (disk hub) 24 on which a shaft member is mounted, and a stator coil 25 and a rotor magnet 26 that are opposed to each other with a gap in the radial direction, for example. The stator coil 25 is attached to the outer periphery of the bracket 27, and the rotor magnet 26 is attached to the inner periphery of the disk hub 24. The disk hub 24 holds one or more magnetic disks D.

  When the stator coil 25 is energized, the rotor magnet 26 is rotated by the electromagnetic force between the stator coil 25 and the rotor magnet 26, whereby the disk hub 24 and the shaft member 22 are rotated together.

  As the shaft member 22 of the motor 21, not only the master shaft 2 but also another member replaced with the master shaft 2 can be used. FIG. 9 illustrates the case where the thrust bearing portion T is constituted by a pivot bearing. In addition to this, the shaft member 22 is supported in a non-contact manner in the thrust direction by dynamic pressure generating means such as a dynamic pressure groove. A hydrodynamic bearing can also be used.

  The bearing device of the present invention is not limited to the above examples, and can be widely applied to support a rotating shaft of a motor. Since this bearing device has a high-precision bearing gap (radial bearing gap) in the radial bearing portion R as described above, information that requires high rotational accuracy, such as a spindle motor for driving a magnetic disk such as the HDD described above. It is particularly suitable for supporting a rotating shaft in a small motor for equipment, for example, a spindle motor for driving a magneto-optical disk of an optical disk or a polygon scanner motor of a laser beam printer.

It is a perspective view of the bearing of this invention. It is a perspective view of the master axis | shaft which shows the manufacturing process of the electroformed axis | shaft of this invention. It is a perspective view which shows the state which masked the master axis | shaft of FIG. It is a perspective view of the electroformed shaft of the present invention. It is sectional drawing of the resin bearing of the state provided with the master axis | shaft of this invention. It is a schematic diagram explaining the state which attached the electroformed shaft to the injection mold. It is a schematic diagram explaining formation of a flange with an injection mold. It is sectional drawing which shows other embodiment of the bearing of this invention. It is a schematic diagram which shows the motor structure of Embodiment 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electroformed shaft 2 Master shaft 2a Corner | angular part 3 Coating | covering material 4 Electroformed part 4a Chamfered part 4b Bearing surface 5 Bearing 6 Upper mold 7 Lower mold 8 Cavity 9 Positioning hole 10 Guide hole 11 Flange 12 Spool 13 Runner 14 Gate 15 Mold part 16 outer peripheral surface 21 motor 22 shaft member 23 thrust plate 24 rotor (disc hub)
25 Stator coil 26 Rotor magnet 27 Bracket R Radial bearing part T Thrust bearing part

Claims (7)

The inner peripheral surface of the electroformed part is provided with a bearing surface formed by a surface on the metal deposition start side , and the electroformed part is molded by injection molding, and at least at both axial ends of the electroformed part On the other hand, a flange is formed by plastic deformation, and the axial length L2 of the electroformed part before plastic deformation of the flange and the axial length L1 of the electroformed part after plastic deformation are 0 <A / L1. ≦ 0.5 (where A = L2−L1) .
  The bearing according to claim 1, wherein an outer peripheral surface of the flange has a non-circular shape. A bearing device comprising the bearing according to claim 1 and a shaft member inserted in an inner periphery of the bearing. The bearing device according to claim 3 , wherein the shaft member is a master shaft used during molding of the electroformed part. The bearing device according to claim 3 , wherein the shaft member is a separate member from the master shaft used when forming the electroformed part. Motor comprising a bearing device according to any one of claims 3-5.   Manufacturing a bearing characterized by forming a flange in the electroformed part by plastically deforming the electroformed part by clamping the mold when the electroformed part forming the bearing surface is molded by injection molding Method.

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