DE102009048519A1 - Hydrodynamic bearing for a spindle motor, comprises stationary bearing bushes, a shaft rotatably arranged coaxial to the bearing bushes, a bearing gap, which is filled with a bearing fluid, and a pressure plate with the shaft - Google Patents

Abstract

The hydrodynamic bearing (1) for a spindle motor, comprises stationary bearing bushes (2), a shaft (6) rotatably arranged coaxial to the bearing bushes, and a bearing gap, which is filled with a bearing fluid, where two parts of the bearing are welded together with a rotary weldseam, a pressure plate with the shaft and/or a hub with the shaft and/or the bearing bushes with a counter-pressure plate (5) and/or the bearing bushes with a base plate. The weld seam is arranged completely in a circumferential groove. The welding connection is helium-tight. The hydrodynamic bearing (1) for a spindle motor, comprises stationary bearing bushes (2), a shaft (6) rotatably arranged coaxial to the bearing bushes, and a bearing gap, which is filled with a bearing fluid, where two parts of the bearing are welded together with a rotary weldseam, a pressure plate with the shaft and/or a hub with the shaft and/or the bearing bushes with a counter-pressure plate (5) and/or the bearing bushes with a base plate. The weld seam is arranged completely in a circumferential groove. The welding connection is helium-tight and is produced with a wobble-laser-welding process in which the laser beam is moved with a wobble-frequency and wobble- amplitude, where the wobble amplitude plus the beam-width of the laser beam is smaller than the groove width. A feed rate of the laser is divided by the wobble-frequency less or equal to the wobble-amplitude plus the beam-width so that a continuous weld seam is formed. A wobble-motion is circular. The circular wobble-motion and a feed direction have opposite direction of rotation. The hub is arranged on the front surface of the part to be connected. The part to be connected has a chamfer, a radius, a section (4) or a fillet chosen through which the hub is formed. The bearing bushes are welded with a counter-pressure plate and/or with a base plate. The shaft is welded to the hub. An independent claim is included for a wobble-laser-welding process for welding parts of hydrodynamic bearings.

Description

The invention relates to a hydrodynamic bearing, in particular for a spindle motor, with a fixed bearing bush, with a coaxial arranged therein, rotatable shaft and with a bearing gap which is filled with a bearing fluid, wherein at least two parts of the bearing with a circumferential weld with each other are welded, in particular a pressure plate with the shaft and / or a hub with the shaft and / or the bearing bush with a counter-pressure plate and / or the bearing bush with a base plate.

Such a hydrodynamic bearing has, for example, a pressure plate which is non-rotatably connected to the shaft. This pressure plate is arranged at an axial end of the bearing, wherein the bearing bush has an opening for the axial insertion of this pressure plate. This opening is closed by a counter pressure plate. The counter-pressure plate is welded in the prior art, for example by a laser welding process with the bearing bush. In this case, a pulsed laser is usually used, wherein the weld is formed by many overlapping Punktschweißungen. The disadvantage here is that the weld is very irregular and there is a risk that the weld is not completely tight. The tightness of a weld is tested with helium, whereby diffusing helium is detected by the weld. In the case of a non-helium-tight bearing, air can penetrate into the bearing gap during operation and / or bearing fluid can escape, which can lead to failure of the bearing both. In addition, the pulsed laser can release metal from the weld site and throw it away, contaminating the bearing with metal particles. Furthermore, the weld has an irregular and protruding surface. Therefore, a complex and expensive reworking and cleaning of the welded parts is necessary.

Newer welding processes therefore use a continuous laser beam (CW laser) to produce a continuous weld in the so-called SHADOW welding process. A modification of this method provides for the laser beam in addition to its feed direction with a certain frequency annular or zigzag or deflect accordingly. These welding methods are described in detail in the article "Reproducible Laser Welding of Copper Materials" by U. Dürr, published in the journal Metall, Volume 62, issue 10/2008 , In these welding processes, there is a risk that due to the very high energy of the laser beam, the metal sublimes and precipitates in other places as an impurity. In addition, a melt is continuously driven by the continuous laser beam in front of the beam, which, however, can extend to the edges. As a result, the center of the continuous weld is not reliably located on the butt edge of the components to be welded, which may result in areas that are not reliably helium-tight.

The object of the invention is therefore to provide a hydrodynamic bearing that is easier and less expensive to produce and whose welded joints are helium-tight.

This object is achieved in that the weld is arranged completely in a circumferential groove and is produced by a wobble laser welding method in which the laser beam is moved with a sweep frequency and a sweep amplitude.

Since the weld is sunk within the groove, the melt is reliably generated during the welding process over the butt edge and held there, creating a helium-tight weld.

In addition, the weld does not protrude from the surface of the welded parts. The weld must therefore not be reworked, as any bumps do not interfere with the surface protrude.

In addition, the side walls of the groove prevent metal particles from being thrown off the weld and contaminating other parts of the bearing.

In particular, however, it is crucial that the welded joint is produced by the wobble welding process. In this case, a continuous laser beam is deflected annularly along the weld, as already known from the prior art. The laser beam describes exactly one circulation, without appreciable overlap.

In addition to this basic annular path, the laser beam performs a wobble motion, wherein the laser beam is moved relative to the annular path, for example, circles or oscillates. there The individual loops of the wobble movement overlap each other, so that an overall ring-shaped closed weld is formed.

The width of the weld therefore no longer depends on the diameter of the laser beam, but on the amplitude of the superimposed wobble movement. The advantage here is that the laser beam can have a smaller diameter than the desired width of the weld is. This makes it possible to use a less powerful laser. In addition, the width of the weld can be varied independently of the laser beam, so that many different welding tasks can be covered with a laser system, whereby the manufacturing costs are reduced.

In order for the weld to lie completely within the groove and for the laser beam to not exceed the groove walls, the sweep amplitude plus the beam width of the laser beam must be less than the groove width, with the amplitude measured from the beam center, respectively. In this case, the groove depth is chosen so that Aufwürfe and the roughness of the weld lie completely within the groove. The sweep motion also creates a characteristic weld that reflects the sweep motion.

To create a closed, continuous weld, the individual loops of the wobble motion must at least partially overlap. This is achieved by the feed rate of the laser divided by the wobble frequency being less than or equal to the wobble amplitude plus the beam width. The overlap guarantees that a helium-tight, continuous weld is created.

Conveniently, the groove is arranged on the end face of the parts to be joined. For this purpose, the parts to be joined each have a chamfer, a radius, a groove or a shoulder, through which the groove is formed.

Further advantageous embodiments and features of the invention will become apparent from the dependent claims and the drawings.

The invention is explained in more detail below with reference to the accompanying drawings.

It shows:

1 a cross section through a hydrodynamic bearing according to the invention,

2 a detailed view of the groove between the bearing bush and counter-pressure plate with oblique groove walls,

3 (a) - (d) different groove shapes,

4 a laser motion pattern with circular wobble motion,

5 a laser motion pattern with oscillating wobble motion and

6a a detailed view of the circling sweep motion,

6b another detail view of the circling wobble movement.

The 1 shows a whole with 1 designated inventive hydrodynamic bearing. The warehouse 1 in the example has a cylindrical bearing bush 2 with a central opening 3 on, at one axial end by a paragraph 4 is widened. The opening 3 is in the area of the paragraph 4 through a circular counter pressure plate 5 locked.

Inside the opening 3 is a wave 6 arranged. In the paragraph 4 the bearing bush 2 is a printing plate 7 arranged with the shaft 6 rotatably connected.

Between the bearing bush 2 , the wave 6 , the printing plate 7 and the counterpressure plate 5 is a storage gap 8th formed, which is filled with a bearing fluid.

The bearing bush 2 forms together with the wave 6 a hydrodynamic radial bearing 9 and with the pressure plate 7 a hydrodynamic thrust bearing 10 , Alternatively or additionally, between the pressure plate 7 and the counterpressure plate 5 a thrust bearing 10 be arranged. Camps 9 . 10 be through warehouse structures 11 defined by which upon rotation of the shaft 6 a hydrodynamic pressure arises in the bearing fluid.

At the open end of the storage gap 8th is a capillary seal 12 arranged, which prevents leakage of the bearing fluid.

The bearing bush 2 is in a base plate 13 fixed. For example, with a hard disk drive, this can be part of the drive cage.

The counterpressure plate 5 closes the bearing gap 8th of the camp 1 , So no bearing fluid from the bearing gap 8th escape and no air in the bearing gap 8th can penetrate, must the counter pressure plate 5 absolutely tight with the bearing bush 2 be connected. To test the tightness of the connection, helium is placed in the bearing gap 8th directed. Due to its low density, helium diffuses very quickly even through the smallest gaps. Diffused helium can then be outside the bearing 1 be detected. If the compound is helium-tight in this test, then it is also tight in operation against air and bearing fluid.

According to the invention, the connection between the bearing bush 2 and counter pressure plate 5 generated by a wobble welding process. The weld 5 offers sufficient mechanical strength and is helium-tight. A decisive feature of the bearing according to the invention 1 is that the weld 15 within a circumferential groove 23 is arranged, which is formed by the parts to be welded. The counterpressure plate 5 and the bearing bush 2 have at their edges to be welded 18 each a chamfer, through which a V-shaped groove 14 is formed ( 2 ). The chamfer 16 at the counterpressure plate 5 has a smaller angle in the example and is wider than the chamfer 17 at the bearing bush 2 , The dimensions and angles of the individual chamfers can be varied depending on the application.

The shape of the groove is not critical. Instead of a chamfer to form the groove, can be welded to an edge 18 also a radius 19 ( 3a ), a paragraph 20 ( 3b ), a bevel with a heel 21 ( 3c ) or a groove 22 ( 3d ) exhibit. The edge shapes of the two parts to be welded can be the same or different shaped. It is crucial that the groove 23 passing through the edges 18 is formed sufficiently deep, so that when welding as possible no particles from the groove 23 can get out. Likewise, the groove must have a minimum width, so that a sufficiently stable weld 15 finds room in it.

The bearing bush 2 can additionally with the base plate 13 be welded, in which case the weld joint by a wobble welding in a groove 23 is arranged. The bearing bush 2 and the base plate 13 have at the edges to be welded 18 one paragraph each 20 , creating a rectangular groove 24 is formed.

Here is the groove 23 of course also have a different shape.

The wobble welding method according to the invention is based on a continuous-wave laser (CW laser) with an average power of about 150 W. The laser used is, for example, a Yb: YAG laser which has a wavelength of 1075 nm in the infrared range. Alternatively, other lasers with other wavelengths in the infrared range can be used.

As with known continuous-beam welding processes, the laser beam is transmitted via a beam deflector (scanner mirror) along the edges to be welded 18 distracted. In the example, this is along the circular groove 23 , which is formed by the parts to be welded. The laser beam 25 is therefore at a feed rate V along a circular path 26 moves, as in 4 is shown. In addition, this basic movement is superimposed by a sweep motion. The laser beam performs, for example, a circular motion, wherein the center of this circular motion always on the circular basic trajectory 26 lies. The deflection is done by a deflection mirror, so that the laser can be permanently installed. Both movements can be generated via the same deflection mirror. The laser beam 25 moves accordingly on a loop path 27 around the actual basic circular path 26 around. The loop track 27 always lies within the groove 23 so that the weld 15 also completely within the groove 23 lies.

The amplitude A of the wobble movement is the radial deflection of the laser beam to the base circle path 26 ( 6a ), respectively from the center of the laser beam 25 measured. Thus the laser beam 25 the groove 23 does not exceed laterally, the amplitude A of the wobble motion plus the laser beam width Bs must be smaller than the groove width Bn.

So that a continuous, helium-tight weld 15 arises, the feed rate V may not be too large. As a limit, the feed rate V divided by the wobble frequency must be less than or equal to the wobble amplitude A plus the laser beam width Bs.

This guarantees that the individual loops 28 the loop track 27 overlap so far that the weld 15 is continuous and uninterrupted.

Due to the superimposition of the feed movement and the circular wobble movement, a resulting velocity of the laser beam V ₁ or V ₂ ( 6b ). With the same sense of rotation of feed speed and circular wobble motion results in a resulting velocity V ₁ additive and thus the maximum resulting velocity is greater than the maximum resulting velocity V ₂ , which results subtractive by an opposite sense of rotation. With the same laser power and the same feed rate and thus the same process time, therefore, more energy per time per area acts on the components to be welded with an opposite direction of rotation of feed speed and circular wobble motion. This results in a more effective "merging" of the components, the material content reaches deeper into the material.

In 5 is the train 29 shown an alternative wobble movement, the laser 25 here no circular sweeping motion performs, but radial to the base web 26 oscillates back and forth, creating a zig-zag pattern. Again, the above conditions apply in terms of wobble amplitude A and feed rate V, so that a closed weld is formed.

The advantage of this wobble welding method is that the width of the weld 15 no longer of the beam width Bs of the laser beam 25 depends. Thus, a wide weld with a relatively thin laser beam can be generated. This thin laser beam requires a much lower continuous power than a wide laser beam. Thus, the weld can be done inexpensively with a low-power laser. Or alternatively, the processing time can be shortened with a powerful laser. Both leads to a reduction in the manufacturing cost of the bearing according to the invention.

The individual parameters of the welding process are not only dependent on each other by the above conditions, but also, for example, on the dimensions of the parts to be welded. The following table shows examples of parameters that are used to weld the counterpressure plate 5 are suitable. These values refer to the in 6a illustrated circular wobble motion. Laser wavelength 1075 nm Laser power 150W Beam width (diameter) 30 μm-50 μm Wobble frequency 1 kHz Wobble amplitude 200 μm feed rate 120 mm / s process time 0.25 s Groove width <250 μm Groove (weld) -radius 4.5 mm

Other parameters may be required to weld other parts of the bearing together.

LIST OF REFERENCE NUMBERS

1

hydrodynamic bearing

2

bearing bush

3

opening

4

paragraph

5

Platen

6

wave

7

printing plate

8th

bearing gap

9

radial bearings

10

thrust

11

warehouse structures

12

capillary

13

baseplate

14

V-groove

15

Weld

16

Chamfer (counter pressure plate)

17

Chamfer (bearing bush)

18

edge

19

radius

20

paragraph

21

Heel with chamfer

22

fillet

23

groove

24

rectangular groove

25

laser beam

26

Basic railway (district)

27

loop path

28

loop

29

Zig-Zag Railway

A

Wobble amplitude

bs

Wide laser beam

Bn

Wide groove

V

feed rate

V ₁ , V ₂

Laser beam speed

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• "Reproducible Laser Welding of Copper Materials" by U. Dürr, published in the journal Metall, Volume 62, issue 10/2008 [0003]

Claims (17)

Hydrodynamic bearing, in particular for a spindle motor, with a stationary bearing bush ( 2 ), with a coaxially arranged therein, rotatable shaft ( 6 ) and with a bearing gap ( 8th ), which is filled with a bearing fluid, wherein at least two parts of the bearing ( 1 ) with a circumferential weld ( 15 ) are welded together, in particular a pressure plate with the shaft ( 6 ) and / or a hub with the shaft ( 6 ) and / or the bearing bush ( 2 ) with a counter-pressure plate ( 5 ) and / or the bearing bush ( 2 ) with a base plate ( 13 ), characterized in that the weld ( 15 ) completely in a circumferential groove ( 23 ), that the welded connection is helium-tight and is produced by a wobble laser welding method in which the laser beam ( 25 ) is moved at a sweep frequency and sweep amplitude (A). Hydrodynamic bearing according to claim 1, characterized in that the wobble amplitude (A) plus the beam width (Bs) of the laser beam is smaller than the groove width (Bn). Hydrodynamic bearing according to claim 1 or 2, characterized in that the feed rate (V) of the laser divided by the wobble frequency is less than or equal to the wobble amplitude (A) plus the beam width (Bs), so that a continuous weld ( 15 ) arises. Hydrodynamic bearing according to claim 1 to 3, characterized in that a wobble movement is circular. Hydrodynamic bearing according to claim 4, characterized in that the circular wobble movement and a feed direction have opposite directions of rotation. Hydrodynamic bearing according to one of claims 1 to 5, characterized in that the groove ( 23 ) is arranged on the end face of the parts to be joined. Hydrodynamic bearing according to one of claims 1 to 6, characterized in that the parts to be joined in each case a chamfer ( 16 . 17 ), a radius ( 19 ), a paragraph ( 20 ) or a groove ( 22 ) through which the groove ( 23 ) is formed. Hydrodynamic bearing according to one of claims 1 to 7, characterized in that the bearing bush ( 2 ) with a counter-pressure plate ( 5 ) and / or with a base plate ( 13 ) is welded. Hydrodynamic bearing according to one of claims 1 to 8, characterized in that the shaft ( 6 ) is welded to a hub. Wobble laser welding method for welding parts of hydrodynamic bearings according to one of claims 1 to 5, characterized in that the sweep amplitude (A) plus the beam width (Bs) is smaller than the groove width (Bn). A method according to claim 10, characterized in that the feed rate (V) divided by the wobble frequency is less than or equal to the wobble amplitude (A) plus the beam width (Bs), so that a continuous weld ( 15 ) arises. A method according to claim 10 or 11, characterized in that a wobble movement is circular. A method according to claim 12, characterized in that the circular wobble movement and a feed direction have opposite directions of rotation. Method according to one of claims 10 to 13, characterized in that the sweep frequency is in the range of 1 kHz. Method according to one of claims 10 to 14, characterized in that the wobble amplitude (A) is in the range of 200 microns. Method according to one of claims 10 to 15, characterized in that the beam diameter (Bs) of the laser beam is in the range between 30 microns to 50 microns. Method according to one of claims 10 to 16, characterized in that the continuous power of the laser is 150 W and the wavelength in the infrared range is around 1075 nm.

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