JP2001200399A - Surface working method for fluid dynamic pressure bearing member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute surface finishing prior to dynamic pressure groove working of a fluid dynamic pressure bearing member at a low cost. SOLUTION: In a surface working method prior to dynamic pressure groove working of the fluid dynamic pressure bearing member, the surface 1A of a workpiece 1 is first roughly worked by cutting and thereafter the required surface machining quantity ΔS for working the workpiece 1 to a desired size is calculated and the workpiece 1 is disposed to face a smooth circumferential surface 23A of an electrode 23 for working via an electrolyte 21. Pulse current is passed between the workpiece 1 and the electrode 23 for working, by which the surface 1A of the workpiece 1 is worked by electrolytic etching by as much as the required surface machining quantity ΔS and a required surface state is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for machining a surface of a fluid dynamic bearing member such as a shaft and a sleeve of a fluid dynamic bearing before machining a groove.

[0002]

2. Description of the Related Art A fluid dynamic pressure bearing using lubricating oil or the like needs to form minute dynamic pressure grooves for generating dynamic pressure. For this reason, conventionally, when processing a fluid dynamic bearing member such as a shaft or a sleeve, methods such as rolling, chemical etching, and electrolytic etching utilizing plastic deformation of metal have been adopted.

[0003] Among them, a method of forming a micro-groove using electrolytic etching is particularly capable of forming a groove at a high speed, capable of forming a high-quality processing with a smooth processing surface, and ensuring that the etching solution is safe for the human body. In recent years, it has attracted particular attention because it can use a neutral salt and is excellent in safety.

For example, Japanese Unexamined Patent Application Publication No. 9-192932 discloses a process in which a predetermined micro-groove shape is electrolytically processed and an electrode exposure of a micro-groove shape corresponding to the micro-groove shape to be processed in the workpiece. And an electrode tool having a portion are disposed close to each other and opposed to each other, and the workpiece and the electrode tool are respectively connected to the negative electrode and the positive electrode of an electrode processing power source, and a predetermined distance is provided between the electrode tool and the workpiece. In the case where the workpiece is eluted in accordance with the shape of the micro-groove by applying an electric current while flowing the electrolytic solution to perform electro-machining of the micro-groove, the electrode tool and the workpiece are relatively separated with a predetermined processing gap. And a pulsed voltage is output from the power source for electrode processing at predetermined time intervals to control the total amount of electricity supplied from the power source for electrolytic processing. That controls the electrolytic processing amount of the fine groove shape, thereby, a method of performing electrolysis microgrooves machining is disclosed.

In machining a shaft, a sleeve, and the like of a fluid dynamic pressure bearing, since the dynamic pressure groove itself is minute, the groove depth and the like are very small. For this reason, conventionally, when the surface of the workpiece is finished before the dynamic pressure groove processing, the finished surface has a sufficient surface roughness as compared with the processing depth for the groove processing performed thereafter. It is common to finish the surface by machining.

[0006]

However, according to the conventional processing method described above, cutting, grinding, and, in some cases, a polishing step are required in order to achieve a predetermined finished surface accuracy, so that processing time is required. At the same time, there is a problem that machining defects increase, resulting in an increase in machining cost.

An object of the present invention is to provide a method of processing a surface of a fluid dynamic bearing member before processing a dynamic pressure groove, which can solve the above-mentioned problems in the prior art.

[0008]

According to the present invention, there is provided a method of machining a surface of a fluid dynamic bearing member before machining a dynamic pressure groove, the method comprising first cutting a given workpiece. After roughing in the, the required amount of processing for calculating the target material to the target dimensions is calculated, the workpiece is opposed to the smooth surface of the processing electrode via the electrolyte, and the workpiece and A method is proposed in which a pulse current is passed between the processing electrode and the workpiece so that the surface of the workpiece is processed by electrolytic etching by the required surface processing amount and the surface is brought into a required surface roughness state. .

The difference between the actually measured dimension of the workpiece obtained by the rough machining and the target dimension is calculated, and the processing corresponding to the difference is performed by electrolytic etching using an electrolytic solution. In addition to being able to work to the required dimensional value well, the surface roughness of the workpiece can also be set to the required value at the same time. As described above, since the finishing dimension and the finished surface roughness of the bearing member such as the shaft and the sleeve can be processed while being simultaneously controlled, the bearing member can be stably processed with high quality.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a process diagram showing a part of the working process for explaining a working process of a shaft of a fluid dynamic bearing according to the present invention.

As shown in FIG. 1A, a columnar workpiece 1 made of stainless steel to be processed as a shaft is prepared. The outer diameter dimension S1 of the workpiece 1 is sufficiently larger than the target outer diameter dimension S0, and the surface roughness of the surface 1A can be, for example, about 10 μm to 100 μm.

Next, as shown in FIG. 1B, the surface 1A of the workpiece 1 is cut using a cutting device 11 so as to have a predetermined coaxiality and concentricity. Roughing is performed so that the diameter dimension is about 5 to 10 μm larger than the target outer diameter dimension S0. The surface roughness of the workpiece 1 obtained by this roughing is set to about 2.5 μm between the peaks and valleys. That is, it is necessary that the surface roughness at this time does not become larger than the cutting allowance for the target outer diameter dimension S0.

As described above, the workpiece 1 as a raw material is cut by the steps shown in FIGS. 1A and 1B so that the outer diameter dimension is close to the final target dimension value. S2 is a slightly larger value, and a workpiece 1 for a shaft having a surface roughness of the order of several μm is obtained.

Thereafter, as shown in FIG. 1C, the surface 1A of the workpiece 1 is sufficiently washed, and a stylus type outer diameter measuring device 12 is used as shown in FIG. 1D. The outer diameter S2 of the workpiece 1 after the roughing is measured. And the work material 1
Calculates the surface processing amount S2-S0 (= ΔS) of the surface 1A necessary to make the target outer diameter dimension S0. here,
As the outer diameter measuring device 12, besides the stylus type, a laser type, a capacitance type, and the like can be used. In addition, it is preferable that a plurality of points along the axial direction of the workpiece 1 can be measured at the same time, instead of one measurement point.

FIG. 2 shows that the surface 1A of the workpiece 1 after the rough processing obtained as described above is processed by a surface processing amount ΔS by electric field etching, and its outer diameter is set to the target outer diameter S.
A finishing device for finishing the surface roughness of the surface 1A to a predetermined value while setting the surface roughness to 0 is shown.

The finishing apparatus 20 has a processing tank 22 filled with an electrolytic solution 21.
The workpiece 1 is set in a cylindrical machining electrode 23 provided in the workpiece 2. The processing electrode 23 is the inner peripheral surface 2
3A is a cylindrical surface, the surface 1A of the workpiece 1 is surrounded by the inner peripheral surface 23A of the processing electrode 23, and the gap of the processing gap G formed between the surface 1A and the inner peripheral surface 23A. Width W
The workpiece 1 is coaxially arranged in the processing electrode 23 by using a fixing jig (not shown) so that is uniform over the entire circumference.

The workpiece 1 and the processing electrode 23 are made of an electrolyte 2
1 so that the electrolytic solution 21
Is satisfied by

A DC power supply 24 is electrically connected through a switch 25 as shown in FIG. 2 to apply a processing pulse voltage required for processing to the processing gap G. That is, the negative electrode of the DC power supply 24 is directly connected to the processing electrode 23, and the positive electrode of the DC power supply 24 is connected to the workpiece 1 via the switch 25.

An on / off controller 26 is provided for periodically turning on and off the switch 25, and the switch 25 is turned on / off in response to an on / off control signal S from the on / off controller 26. Is repeated, whereby the machining pulse voltage is repeatedly applied to the machining gap G. Here, the switch 25 can be a semiconductor switching element such as a transistor, for example.

Reference numeral 27 denotes the processing tank 22.
This is an electrolytic solution reprocessing device for purifying the electrolytic solution 21 therein and returning the purified electrolytic solution to the inside of the processing tank 22 again. The electrolyte reprocessing device 27 includes a drain pipe 27A.
This is a regenerating processing apparatus for an electrolytic solution having a known configuration in which the electrolytic solution 21 in the processing tank is taken in through the processing tank and the regenerated electrolytic solution is returned into the processing tank 22 through the supply pipe 27B. The description of is omitted.

Reference numeral 28 indicates that the electrolytic solution 21 is pressurized and sent into the machining gap G, thereby
This is an electrolytic solution jetting device for creating a flow of the electrolytic solution 21 therein to improve the processing speed and the processing stability. The electrolytic solution jetting device 28 takes in the electrolytic solution 21 in the processing tank 22 through an intake pipe 28A, pressurizes the electrolytic solution 21 by a pressurizing pump (not shown), and pressurizes the electrolytic solution 21 from an injection nozzle 28B. It has a well-known configuration in which it is fed toward the processing gap G. The delivery pressure of the electrolytic solution 21 can be adjusted by a flow control valve 28D attached to the delivery pipe 28C, and the delivery pressure can be known by the pressure gauge 28E.

FIG. 2 shows a configuration in which only one injection nozzle 28B is provided. However, a plurality of injection nozzles 28B are provided along the processing gap G and On the other hand, the electrolytic solution 21 can be evenly sent out into the processing gap G.

Next, a specific processing example by the electrolytic processing apparatus 20 will be described. In the present embodiment, an aqueous solution of NaCl is used as the electrolytic solution 21. The surface 1A of the workpiece 1 is processed by applying a current to the processing gap G for a predetermined time by applying a processing pulse voltage.

At this time, the voltage value and the application time are determined depending on the gap width W, the concentration and temperature of the electrolytic solution 21, the depth of the processing groove, and the processing area.

For example, a 35% NaCl aqueous solution at 30 ° C. is used as the electrolyte 21 and the value of the gap width W is set to 500 μm.
When a pulse voltage with a duty of 1/5 was applied at 2V × 1A, the work material 1 which was a stainless steel material
Was processed at a speed of about 2 μm per second.

Also in this example, the processing time was about 5 seconds or less. Further, the difference from the target processing dimension of the workpiece 1 after the processing was within ± 0.3 μm. Furthermore, the surface roughness, which was initially about 2.5 μm between the peaks and valleys, became about 0.1 μm, and an effect as a polishing process was obtained.

While an example of processing a shaft has been described with reference to FIGS. 1 and 2, processing of a sleeve and processing of a disk-shaped member such as a thrust plate can be performed in the same manner. it can. In any case, the following advantages can be obtained.

The bearing member is roughly machined to a substantially desired size and surface roughness before machining the groove by mechanical machining such as cutting, and the subsequent finishing is performed by machining the smooth surface machining electrode and the workpiece. The surface is processed by passing a pulse current for a predetermined period of time with an electrolyte interposed in the gap between the material and the gap, thereby achieving the target processing dimensions and target surface roughness of the workpiece before groove processing. The surface processing before groove processing of the hydrodynamic bearing member is performed in a short time and with high precision compared to the conventional method in which all processes are performed by mechanical cutting, polishing, etc. At the same time, the surface of the workpiece, which is the processing surface, can be processed uniformly and smoothly, so that it is possible to provide a dynamic pressure bearing with stable quality.

[0030]

According to the present invention, the bearing member is roughly machined to a substantially desired size and surface roughness before machining the groove by mechanical machining such as cutting, and the subsequent finishing is performed smoothly. The surface processing electrode and the material to be processed are opposed to each other, and the surface is processed by flowing a pulse current for a predetermined time with an electrolyte interposed therebetween, thereby performing the surface processing of the material before the groove processing. Since the target processing dimensions and target surface roughness are realized at the same time, compared to the conventional method in which all processes are performed by mechanical cutting, polishing, etc., the surface processing before groove processing of the dynamic pressure bearing member is shorter. And at the same time, it is possible to provide a dynamic pressure bearing with stable quality, because the surface of the material to be processed can be processed uniformly and smoothly.

[Brief description of the drawings]

FIG. 1 is a process chart for explaining a part of a shaft machining process according to a method of the present invention.

FIG. 2 is a schematic cross-sectional view showing a part of an example of a finishing apparatus used in a step of finishing a shaft obtained by the step shown in FIG. 1 by electrolytic etching.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Workpiece material 1A Surface 11 Cutting device 12 Outer diameter measuring device 20 Finishing device 21 Electrolyte 23 Processing electrode 23A Inner peripheral surface 24 DC power supply 26 On / off controller 27 Electrolyte solution reprocessing device 28 Electrolyte jet device S0 Target outer diameter S1 Outer diameter S2 Outer diameter

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) F16C 33/14 F16C 33/14 Z

Claims (2)

[Claims] 1. A surface machining method for a fluid dynamic pressure bearing member before machining a dynamic pressure groove, wherein a surface of a given workpiece is first roughened by cutting, and then the workpiece is set to a target dimension. Calculate the required surface processing amount for, facing the workpiece to the smooth surface of the processing electrode via the electrolyte, passing a pulse current between the workpiece and the processing electrode, thereby A surface processing method for a fluid dynamic bearing member, wherein the surface of the workpiece is processed by electrolytic etching by the required surface processing amount and the surface is brought into a required surface roughness state. 2. A method for processing a surface of a fluid dynamic bearing member, wherein the workpiece is a shaft constituting a fluid dynamic bearing.