JP2002195265A - Manufacturing method of thrust plate used for fluid bearing unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a thrust plate used for a fluid bearing unit capable of effectively mass-producing a thrust plate having superior dimensional accuracy of a through-hole at low cost. SOLUTION: The thrust plate used for the fluid bearing unit is comprised of core metal 70 fitted in the through-hole 51 of a blank 50 of the thrust plate, an upper and lower dies 80 and 90 in which the upper and lower dies are fitted in both end portions of the core metal 70 so as to put the blank between the dies and a groove pattern generating hydrodynamic pressure is respectively formed in an opposing face to both end faces of the blank 50, and an outer cylinder 100 leading movement of the blank 50 and the upper and lower dies 80 and 90 in an axial direction by fitting on an outer periphery of the blank 50 and the upper and lower dies 80 and 90. The groove generating hydrodynamic pressure is engraved in the end faces of the blank in proportion to the groove pattern by pressing in a state in which a whole surface for both end faces and inner and outer peripheral faces of the blank 50 is tightly closed while the upper and lower dies 80 and 90 are relatively moved to an axial direction. Thus, the thrust plate used for the fluid bearing as a final product is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to information equipment,
The present invention relates to a method for manufacturing a thrust plate of a hydrodynamic bearing device incorporated in a video device, an office machine, etc.
The present invention relates to a method for manufacturing a thrust plate suitable for a hydrodynamic bearing device to be incorporated in an HDD, a fan motor, or the like.

[0002]

2. Description of the Related Art As a conventional hydrodynamic bearing device, for example, the one shown in FIG. 7 is known. In this hydrodynamic bearing device, a hub 2 is concentrically fixed to an upper end of a rotating shaft 1, and a rotor (magnet portion) 3 is attached to an inner peripheral portion of the hub 2. The rotating shaft 1 is fitted into a sleeve 5 fitted to the cylindrical portion 4a of the base 4 with a predetermined gap therebetween, and a stator 6 is attached to the outer peripheral portion of the cylindrical portion 4a so as to face the rotor 3. . Grooves (not shown) for generating dynamic pressure are provided on the inner peripheral surface of the sleeve 5 and / or the outer peripheral surface of the rotating shaft 1, and are formed by the outer peripheral surface of the rotating shaft 1 and the inner peripheral surface of the sleeve 5. It constitutes a radial dynamic pressure bearing.

A flat thrust plate 9 is fixed to the lower end of the rotating shaft 1.
The upper end of the sleeve 5 is opposed to the lower end of the sleeve 5. Grooves 10 for generating dynamic pressure are provided on the upper end surface of the thrust plate 9 to constitute a thrust fluid bearing. Lubricants such as grease are sealed in bearing clearances of the radial dynamic pressure bearing and the thrust fluid bearing.

By the way, the thrust fluid bearing in which one end surface of the flat thrust plate is used as a bearing surface moves to a hardened and hardened stainless steel surface (surface hardness Hv of 500 to 600). It has been manufactured by printing a groove pattern for pressure generation with a corrosion-resistant ink and chemically etching the uncoated surface. In this case, the non-bearing surface and the outer peripheral surface on the opposite side (lower end surface side) of the thrust plate blank, for which processing accuracy is not particularly required, are not coated to prevent corrosion, and the entire thrust plate blank is immersed in a corrosive liquid and etched. Was.

[0005]

However, in the above-mentioned etching process, a groove for generating a dynamic pressure is formed at both ends by forming a through hole at a center portion to be a fitting surface with a shaft or a guiding surface. When applying to the manufacturing process of a thrust plate, it is necessary to apply a corrosion-resistant coating such as a coating of corrosion-resistant paint or corrosion-resistant ink to the inner peripheral surface of the through hole that requires dimensional accuracy, and the productivity is significantly reduced. There has been a problem that manufacturing costs have risen.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to provide a method of manufacturing a thrust plate for a hydrodynamic bearing device, which can improve productivity and reduce manufacturing costs. And

[0007]

In order to achieve the above object, a method of manufacturing a thrust plate for a hydrodynamic bearing device according to the present invention has a through hole at a central portion and grooves for generating dynamic pressure at both end surfaces. In the manufacturing method of the engraved thrust plate for a hydrodynamic bearing device, a metal core fitted into a through hole of a thrust plate blank is fitted to both ends of the metal core so as to sandwich the thrust plate blank, A pair of upper and lower dies each having a groove pattern for generating dynamic pressure formed on a surface facing both end surfaces of the thrust plate blank,
An outer cylinder fitted to the outer peripheral surface of the thrust plate blank and the upper and lower molds to guide the axial movement of the thrust plate blank and the upper and lower molds, and relatively moving the pair of upper and lower molds in the axial direction. By pressing both end surfaces and the entire inner and outer peripheral surfaces of the thrust plate blank in a sealed state, grooves for dynamic pressure generation according to the groove pattern are formed on both end surfaces of the thrust plate blank. Features.

In this case, the depth of the groove for generating dynamic pressure is 15 μm.
m or less is preferable. Also, as the core metal, the outer diameter is coaxial and the diameter is gradually changed in the axial direction, the diameter of the tip is smaller than the diameter of the through hole of the thrust plate blank, and the center part is the same as the through hole of the thrust plate blank. It is preferable to use one having a clearance of ± 2 μm and a base end having substantially the same diameter as the hole diameter of the lower die.

[0009] Further, as a method of removing the outer cylinder and the core after the thrust plate is manufactured by engraving a groove for generating dynamic pressure in the thrust plate blank, the upper die and the lower die sandwich the thrust plate at first. Remove the core metal and then remove the outer cylinder, or remove the core metal and outer cylinder simultaneously while holding the thrust plate between the upper and lower molds, or use the upper and lower molds It is preferable to first remove the outer cylinder and then remove the metal core while sandwiching the thrust plate.

Further, after the thrust plate is manufactured by the above manufacturing method, it is preferable that the bearing surface is pressed (spanned) by a press machine using a flat mold.
Further, in the above manufacturing method, it is preferable that the distance L from the lower end face of the thrust plate blank to the end face on the base end side of the metal core is not less than the outer diameter dimension (2R) of the thrust plate blank.

Further, it is preferable that the groove pattern for generating dynamic pressure provided on the end surfaces of the upper and lower dies is formed by ion etching. Further, it is preferable that the surface hardness of the thrust plate manufactured by the above manufacturing method is substantially equal to or lower than the surface hardness of a mating member constituting the thrust fluid bearing.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory view for explaining a method of manufacturing a thrust plate for a hydrodynamic bearing device according to an embodiment of the present invention, showing a state in which a thrust plate blank is inserted into a metal core, and FIG. 2 is a thrust plate blank. FIG. 3 is an enlarged view of a cored bar, and FIG. 4 is a view for explaining the relationship between the outer diameter 2R of the thrust plate blank and the insertion length L of the base end of the cored bar into the lower mold. Explanatory diagram,
FIG. 5 is an explanatory cross-sectional view for explaining a hydrodynamic bearing device provided with a thrust plate obtained by the manufacturing method of the present invention, and FIG. 6 shows a thrust plate for a hydrodynamic bearing device according to another embodiment of the present invention. It is an explanatory view for explaining a manufacturing method.

First, for convenience of description, a hydrodynamic bearing device provided with a thrust plate obtained by the manufacturing method of the present invention will be described with reference to FIG.
Is a rotating shaft, and a hub 21 is concentrically fixed to the upper end of the rotating shaft 20, and a rotor (magnet portion) 22 is attached to an inner peripheral portion of the hub 21. The rotation shaft 20 is the base 2
3 is fitted into the sleeve 24 fitted to the bottomed cylindrical portion 23a with a predetermined gap, and a stator 24a is attached to the outer peripheral portion of the bottomed cylindrical portion 23a so as to face the rotor 22.

The inner peripheral surface of the sleeve 24 and / or the rotating shaft 2
A groove (not shown) for generating dynamic pressure is provided on the outer peripheral surface of the sleeve 0, and the outer peripheral surface of the rotary shaft 20 and the inner peripheral surface of the sleeve 24 constitute a radial dynamic pressure bearing. In FIG. 5, reference numeral 25 denotes an air vent hole. A thrust plate 30 is fixed to a lower end of the rotating shaft 20 via a bolt 40. The thrust plate 30 has a through hole 31 serving as a fitting surface and a guide surface in the center, and grooves (not shown) for generating dynamic pressure are formed on both upper and lower end surfaces. A thrust fluid bearing is configured to face the end face and the lower end face faces the bottom of the bottomed cylindrical portion 23a. Lubricants such as oil and grease are sealed in the bearing clearances of the radial dynamic pressure bearing and the thrust fluid bearing.

Here, in this embodiment, the thrust plate 30 is manufactured as follows. First,
With reference to FIGS. 1 to 3, the coining device will be described. The coining device includes a metal core 70 fitted into a through hole 51 of a thrust plate 50 (hereinafter, referred to as a thrust plate blank) 50 before molding. The thrust plate blank 50 was fitted to both ends of the metal core 70 so as to sandwich the thrust plate blank 50, and for example, a herringbone-shaped groove pattern for generating dynamic pressure was formed on the surface facing the upper and lower end surfaces of the thrust plate blank 50. A pair of upper and lower dies 80, 90
And the thrust plate blank 50 and the upper and lower dies 80, 9
0 thrust plate blank 50
And an outer cylinder 1 for guiding the axial movement of the upper and lower dies 80, 90
00.

Referring to FIG. 3, the metal core 70 has an upper die guide 71, a molded portion 72, and a lower die guide 73 formed in order from the distal end to the base end. Upper guide 7
Numeral 1 is for guiding the thrust plate blank 50 to the forming part 72, and its outer diameter is smaller by 10 to 20 μm than the outer diameter of the forming part 72.

The forming portion 72 is provided with a thrust plate blank 5
This is for forming an inner diameter of 0, which is the same as the completed inner diameter of the through hole 31 at the product level. Upper guide 7
It is preferable that the step portion at the boundary between 1 and the forming portion 72 be connected smoothly so that the thrust plate blank 50 can be inserted smoothly. By preparing a number of metal cores having different outer diameters of the molded portion 72, the through holes 3
Thrust plates with different dimensions can be manufactured.

The lower die guide portion 73 is supported by the lower die 90 to maintain concentricity with the lower die 90.
The clearance with the hole diameter is set to φ3 μm or less.
The upper die guide part 71, the forming part 72, and the lower die guide part 73 are formed coaxially, and the whole core 70 can be moved in the axial direction during coining. In this embodiment, as shown in FIG. 2, the lower die guide portion 73 of the core 70 is fitted to the lower die 90, and the proximal end surface (lower end surface) of the core 70.
Is attached to the base 101, or in a state where the base 101 has a slight gap between the base end face of the metal core 70 and the base 101, the thrust plate blank 50 is formed by the molding portion 72.
It is at the position where coining of the inner diameter is completed. In addition, when inserting the thrust plate blank 50, the upper end surface of the lower die 90 is raised near the upper die guide portion 71 of the core metal 70 by a spring or the like, and the thrust plate blank 50 is sandwiched between the upper die 80 and the lower die 90. When the insertion is performed while maintaining the perpendicularity with the metal core 70, the perpendicularity of the inner diameter of the through hole after coining (the perpendicularity between the internal diameter and the end face) can be increased.

Upper and lower dies 80 and 90, outer cylinder 100 and core metal 7
As the material of No. 0, quenched bearing steel, die steel, high-speed steel, carbide and the like are suitable, but in order to improve dimensional accuracy, carbide having little elastic deformation is preferable. In particular, as the material of the guide core 70 in which the influence of bending at the time of pressing becomes a problem, a carbide having a small elastic deformation is suitable. The thrust plate blank 50 can be formed into an annular shape on a lathe and then used to remove burrs by magnetic polishing or lap finished. Further, the through hole 51 of the thrust plate blank 50 is formed by core metal molding. The accuracy is set to ± 2 μm of the outer diameter of the portion 72.

The material of the thrust plate blank 50 is
To prevent the thrust plate from sliding with the mating member (in this embodiment, the lower end surface of the sleeve and the bottom of the bottomed cylindrical portion) and prevent the mating member from being damaged and worn, A material whose surface hardness is substantially the same as or lower than the surface hardness of the mating member, for example, a copper alloy or stainless steel having an Hv of 400 or less, preferably a plastic workability of 300 or less is suitable. Other materials for the thrust plate blank 50 include sintered metal, sintered oil-impregnated metal, and other soft metals.

In the case where a copper alloy or stainless steel is used as a mating member that slides with the thrust plate, the thrust plate slides when the hydrodynamic bearing device is started and stopped so that the bearing surface slides easily with the mating member and is hardly damaged. The surface hardness of the blank 50 is preferably substantially the same as or lower than the surface hardness of the mating member. In addition, even when a combination of copper alloy or stainless steel (so-called gold) is used for both the thrust plate and the mating member, if the combination of the material components is different, the durability at the time of starting and stopping the fluid bearing device even if the hardness is almost the same is obtained. It was confirmed by experiments and the like that it was not impaired. Instead of using a material having high hardness for the mating member, the surface may be plated with nickel or coated with a DLC film or the like to improve the surface hardness.

The groove patterns for generating the dynamic pressure provided in the upper and lower dies 80 and 90 are preferably formed by ion etching. By doing so, it is possible to obtain the upper and lower dies 80 and 90 having a groove pattern with a groove bottom roughness of 2 μm or less and excellent dimensional accuracy without unevenness, and durability for starting and stopping required for a hydrodynamic bearing device. Thrust plates excellent in quality can be mass-produced at low cost.

Further, in order to further improve the roughness of the groove bottom of the upper and lower dies 80 and 90, if necessary, lapping is performed using an abrasive so long as the shape is not impaired. Can be. In addition, as a result of trying a method of machining the groove pattern of the upper and lower dies 80 and 90 by milling, the roughness of the groove bottom is better than that of the chemical etching, but unevenness tends to remain on the groove bottom due to the repeated movement of the cutting edge. And the outer diameter of the thrust plate blank 50 is 10
When it is applied to the processing of less than mm, it has been confirmed that the processing of a fine groove pattern becomes difficult due to the narrow groove width, and the dimensional accuracy is inferior to the ion etching processing.

Incidentally, a force is applied to the metal core 70 by plastic deformation of the inner diameter of the thrust plate blank 50 during coining. However, this force cannot be simultaneously applied to the entire circumference at the initial stage of deformation, but one end is always caused. Wake up. As a result, the core metal 70 may tilt during coining, and the perpendicularity between the core metal 70 and the thrust plate blank 50 may be deteriorated.

Therefore, in this embodiment, in order to avoid such a situation, the distance L from the lower end face of the thrust plate blank 50 to the end face on the base end side of the metal core 70 and the outer diameter of the thrust plate blank 50 The relationship with the dimension (2R) is L ≧ 2R. Referring to FIG. 4 in detail, when the clearance between the inner diameter of the lower die 90 and the metal core 70 is s, and the squareness δ between the metal core 70 and the thrust plate blank 50 is required, the geometrical requirement is as follows. , 2R, L≫δ, s, 2R
S / L ≦ δ. In the case of this embodiment, 2R, L
Was on the order of several mm, and the clearance s was φ3 μm or less to allow the core metal 70 to move in the axial direction during coining, and the allowable value of the squareness δ was 3 μm or less. Therefore, the above geometrical requirements can be used, and when the values of s and δ are substituted, L ≧ 2R.

In order to improve the transferability of the groove patterns of the upper and lower dies 80 and 90, it is necessary to increase the surface pressure during coining to equalize the internal stress generated in the thrust plate (during molding). . It was confirmed that when the surface pressure was at least three times the yield stress of the thrust plate material, the internal hydrostatic pressure state was uniformly distributed and the transferability was improved. Therefore, the surface pressure at the time of coining is set to 3 to 5 of the yield stress of the thrust plate material in consideration of the life of the upper and lower dies 80 and 90.
It is preferable that the setting be made twice.

Then, the coining device having the above-described configuration is connected to a press machine, and the pair of upper and lower dies 80 and 90 are relatively moved in the axial direction so that both end surfaces and the entire inner and outer peripheral surfaces of the thrust plate blank 50 are sealed. By pressing, the groove patterns of the upper and lower dies 80 and 90 are transferred to both end surfaces of the thrust plate blank 50, and grooves for generating dynamic pressure are carved. Thus, the above-described thrust plate 30 is obtained.

Here, the depth of the groove for generating the dynamic pressure formed in the thrust plate 30 is set to 15 in order to minimize the collapse of the cross-sectional shape of the groove and to reduce the variation in the groove depth.
It has been confirmed that the thickness is preferably not more than 12 μm, in order to further reduce the variation in the groove depth. After coining, the thrust plate in which the dynamic pressure generating grooves are engraved by pressing is pressed by the core metal 7 by plastic deformation.
0 and the outer cylinder 100, the core metal 70 and the outer cylinder 10
Depending on the manner in which the thrust plate is removed, an excessive deformation force may act on the thin and rigid rigid thrust plate, which may adversely affect the flatness of the thrust plate.

Therefore, in this embodiment, while the thrust plate is sandwiched between the upper die 80 and the lower die 90, the core metal 7
0, and then remove the outer cylinder 100 or the upper die 8
0 and the lower die 90 while sandwiching the thrust plate.
Or the outer cylinder 100 is removed simultaneously, or the outer cylinder 100 is removed first, and then the core metal 70 is removed while sandwiching the thrust plate between the upper mold 80 and the lower mold 90. Thus, in any case, the thrust plate could be ejected from the metal core 70 and the outer cylinder 100 without deteriorating the flatness of the thrust plate.

In order to further improve the roughness of the bearing surface of the thrust plate, after the thrust plate is ejected from the metal core 70 and the outer cylinder 100, the bearing surface is pressed by a press machine using a flat mold. Spanking). As a spanking mold, a cemented carbide with no hole at the center and a mirror-wrapped surface is used. The inner and outer diameters of the thrust plate are not restricted, and the load is 1-2 times the yield stress of the thrust plate material. The pressure was set to double. Under the above conditions, a thrust plate having a flatness of 1 μm or less and excellent surface roughness could be obtained.

As is clear from the above description, in this embodiment, the upper and lower dies 80 and
The groove pattern of 90 is transferred to both end surfaces of the thrust plate by plastic working to form a dynamic pressure generating groove, and the inner diameter portion of the thrust plate is finished with high precision by the molded portion 72 of the metal core 70, so that the through hole is formed. Thrust plates having excellent dimensional accuracy of the holes 31 can be efficiently mass-produced at low cost.

Also, during coining, both ends and the entire inner and outer peripheral surfaces of the thrust plate blank 50 are pressed in a sealed state, so that plastic flow of the material in the radial direction can be reduced. As a result, the upper and lower dies 80 and 90 are free of burrs and the like, so that the cleaning process of the upper and lower dies can be omitted, and the processing cycle can be increased.

The structure of the coining device used in the above embodiment can be changed as appropriate without departing from the purpose of processing. For example, a pair of upper and lower dies preferably have a symmetrical design, but are not necessarily symmetrical. There is no. Next, referring to FIG. 6, thrust plate blank 5 during coining.
The effect of the force exerted on the upper and lower end surfaces on the product flatness will be described.

As shown in FIG. 6, when a load is applied to the thrust plate blank 50 from above the shaft, the upper and lower dies 8
The thrust plate blank 50 sandwiched between 0 and 90 is
The thrust plate blank 50 receives the frictional force in the axial direction from the outer cylinder 100 and the metal core 70 by sinking downward in the axial direction due to the compression. Assuming that the force applied to the upper end face of the thrust plate blank 50 at this time is F ', the force applied to the lower end face is F, and the frictional force is R, F' = F + R → F 'from the condition of the balance.
ΔF, and the force applied to the upper and lower end surfaces of the thrust plate blank 50 becomes asymmetric. As a result, if the difference between the forces applied to the upper and lower ends is large, the flatness of the thrust plate as a product (specifications are satisfied at 1 μm or less) is adversely affected.

Therefore, in order to make the forces applied to the upper and lower end surfaces of the thrust plate blank 50 during coining symmetric,
It is conceivable to perform coining by moving the outer cylinder 100 and the core metal 70 at a speed half that of the relative speed of the upper and lower dies 80, 90 in the axial direction, and facing the upper and lower dies 80, 90 at a constant speed. In order to perform such coining, the core metal 70 is lightly pressed into the thrust plate blank 50 and set so that the base end surface of the core metal 70 does not stick to the base 101 surface. Can be moved up and down the axis.

As a result, the symmetry of the force applied to the upper and lower end surfaces of the thrust plate blank 50 is improved as compared with the state in which the base end surface of the metal core 70 cannot move with respect to the base 101 as in the above embodiment. As a result, the flatness of the product thrust plate was improved. In addition, in FIG.
O-ring or rubber 1 between the lower end surface of
02 and the like are inserted so that the outer cylinder 100 can move in the axial direction. However, a clearance may be simply provided between the lower end surface of the outer cylinder 100 and the base 101 so that the outer cylinder 100 can move in the axial direction. Good.

[0037]

As is clear from the above description, according to the present invention, the dynamic pressure generating grooves are formed by transferring the upper and lower die groove patterns, which are most difficult to secure in processing, to both end surfaces of the thrust plate by plastic working. Since the thrust plate is engraved and the inner diameter portion of the thrust plate is finished with high accuracy by the metal core, the effect of efficiently mass-producing the thrust plate with excellent dimensional accuracy of the through hole at low cost can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory view for explaining a method of manufacturing a thrust plate for a hydrodynamic bearing device as an example of an embodiment of the present invention, showing a state in which a thrust plate blank is inserted into a cored bar.

FIG. 2 is an explanatory view for explaining a method of manufacturing a thrust plate for a hydrodynamic bearing device, which is an example of an embodiment of the present invention, and is a diagram showing a molding state of a thrust plate blank.

FIG. 3 is an enlarged view of a cored bar.

FIG. 4 is an explanatory diagram for explaining the relationship between the outer diameter dimension 2R of the thrust plate blank and the insertion length L of the base end portion of the core metal into the lower mold.

FIG. 5 is an explanatory diagram for explaining a method of manufacturing a thrust plate for a hydrodynamic bearing device according to another embodiment of the present invention.

FIG. 6 is an explanatory cross-sectional view for explaining a hydrodynamic bearing device provided with a thrust plate obtained by the manufacturing method of the present invention.

FIG. 7 is an explanatory sectional view for explaining a conventional hydrodynamic bearing device.

[Explanation of symbols]

 Reference Signs List 30 thrust plate 31 through hole 50 thrust plate blank 51 through hole 70 core bar 80 upper die 90 lower die 100 outer cylinder

Continued on the front page (72) Inventor Katsuhiko Tanaka 1-5-50 Kumeinuma Shinmei, Fujisawa-shi, Kanagawa F-term in NSK Ltd. (reference) 3J011 AA04 BA06 CA02 DA02 KA04 MA03

Claims (1)

[Claims] 1. A method of manufacturing a thrust plate for a hydrodynamic bearing device having a through hole at a center portion and grooves for generating dynamic pressure at both end surfaces, wherein a core fitted into a through hole of a thrust plate blank. A pair of upper and lower dies each having a groove pattern for generating a dynamic pressure formed on both sides of the core bar so as to sandwich the thrust plate blank and opposing both end surfaces of the thrust plate blank. And an outer cylinder fitted to the outer peripheral surfaces of the thrust plate blank and the upper and lower molds to guide the axial movement of the thrust plate blank and the upper and lower molds. The thrust plate blank is moved and pressed in a state in which both end surfaces and the entire inner and outer peripheral surfaces of the thrust plate blank are sealed, so that the groove pattern is formed on both end surfaces of the thrust plate blank. Method for producing a thrust plate for a fluid bearing apparatus characterized by engraving grooves for generating dynamic pressure in accordance with the over down.