The invention relates to a lance unit for fitting into a spindle of a machine tool and to a spindle comprising such a lance unit.
Two channel minimal quantity lubrication (MQL) devices are known, in which in the vicinity of the point of contact between a tool such as a drill bit and a workpiece a mixture of air and lubricant is produced, which contains a very low proportion of lubricant. Such an MQL device may be inferred for example from DE 196 55 334 B4.
In this known MQL device the lance unit rotates with the spindle, thereby necessitating a high-precision and costly rotary coupling at the rear end of the lance unit because spindles in modern machining centres rotate at up to 20,000 rpm and fluids are to be handled at pressures of 8 bar and more.
The object of the present invention is therefore to develop a lance unit according to the preamble of claim 1 in such a way that it is possible to dispense with a costly rotary coupling at the rear end of the lance.
This object is achieved according to the invention by a lance unit having the features indicated in claim 1 and/or a spindle having the features outlined in claim 20.
In the lance unit and/or spindle according to the invention the liquid pipe carrying the liquid lubricant is connected in a rotationally fixed manner to the base part. The free end of the liquid pipe together with the adjacent rotating parts of the spindle itself form a kind of rotary coupling, which however need not be machined to a high degree of precision because a good fluidic seal is obtained by means of the gas stream that under operating conditions flows paraxially over the outside of the liquid pipe. The quantities of lubricant that are discharged from the end of the liquid pipe are moreover so small that a pressure-tight liquid seal is not necessary here. The corresponding small liquid volumes, as they are discharged from the end of the liquid pipe, are carried away by the air stream sweeping over the lance end.
With the lance unit according to the invention even in the case of a large length it is nevertheless ensured that the lance unit in the spindle is well able to withstand the mechanical loads, to which it is subject there during operation, in particular the transverse accelerations that arise when the spindle is traversing from one working point to another.
The pivot bearings provided according to the invention are used to support the liquid pipe, which for reasons of space or material cannot be of an absolutely rigid construction, radially against preset points and hence prevent bending of the liquid pipe, which might lead to undesirable contact with a rotating part of the spindle, which may rapidly lead to damage of the liquid pipe on account of the high rotational speeds of the spindle.
This support is effected either directly against a spindle bore or against a bore of a part connected to the spindle, such as a collet chuck actuating rod. These bores are to he understood below collectively by bearing bore, i.e. a bore, against which the liquid feed pipe of is the lance unit is transversely supported.
Advantageous developments of the invention are indicated in sub-claims.
In the case of liquid pipes that are not too long and have good rigidity, it is often sufficient to support the liquid pipe against a single point spaced apart from the foot of the pipe.
In the case of longer liquid pipes, if a plurality of spaced-apart pivot bearings are provided in accordance with claim 2, it is possible to dispense with increasing the wall thickness of the liquid pipe, a measure that is occasionally not possible for reasons of space. The locations of the pivot bearings are, roughly speaking, so selected that they are situated at the places where the operation-related excursions from the spindle axis are at their greatest. Typically, these are regions that are situated at excursion- or oscillation antinodes.
The development of the invention according to claim 3 makes it possible to provide the pivot bearings at a defined distance from one another but to fit pivot bearings and liquid pipe as a preassembled unit into the spindle. There is therefore also no need to provide a stop shoulder or the like on the bearing bore that receives the lance unit. A further advantage is that between the pivot bearings and either the bearing bore or the outer surface of the liquid pipe it is possible to allow axial relative movements, such as are required if the lance unit is disposed in the interior of a hollow tie rod, which is provided in many spindles for actuating a collet chuck, by means of which tool carriers carrying the tools are detachably braceable with the spindle.
Preferred locations, at which pivot bearings are provided, are described in claims 4 and 5. These locations correspond to oscillation antinodes.
In a lance unit according to claim 6 the entire arrangement of liquid pipe and pivot bearings is preassembled in a cartridge that may easily be mounted in a bearing bore. The provision of such a finished sub-unit is of particular interest because the lance unit are of a very compact construction in radial direction and represent a precision-engineered precision unit that remains the preserve of experts.
Claim 7 indicates various possible ways, in which a pivot bearing may be concretely configured. Here, in particular the choice depends on how large the bearing is in radial direction, the rotational speeds that the bearing endures, the extent to which air may flow through the pivot bearing, and the radial forces that have to be taken up by the pivot bearing.
Particularly preferred in this case are the plain bearings indicated in claim 8, which are notable for high speed resistance and particularly low friction combined with a mechanically simple construction. Such bearings may also easily be configured in such a way that air may flow through them in axial direction.
Sliding layers of the type proposed in accordance with claim 8 do admittedly have good sliding properties but are often brittle and are frequently impossible to produce in situ on a liquid pipe. The development according to claim 9 makes it possible to manufacture corresponding bearing sleeves as separate parts that are then mounted with a finished sliding layer onto the liquid pipe.
By virtue of the development of the invention according to claim 10, the annular space that remains between the outer surface of the liquid pipe and the inner surface of a bearing bore that receives the lance unit may be used to transport gas, which is used to feed the lubricant in small portions to the point of contact between tool cutting edge and material of the workpiece.
By virtue of the development of the invention according to claim 12 it is possible to reduce the swirl that is imparted to the gases flowing through the bearings by the passages of the pivot bearings.
The development of the invention according to claim 13 is advantageous in view of the fact that the radial supporting forces that are needed at various points of the liquid pipe are different. However, if a bearing, given the same installation space, needs to produce only a lower supporting force, it may be optimized in respect of other parameters, for example service life or air permeability.
The development of the invention according to claim 14 makes it possible to displace the entire lance unit by a small amount in axial direction. This allows the entire lance unit to follow the adjusting movement of a tie rod, which is used to actuate a tool carrier collet chuck disposed in the end of the spindle. There is therefore no need to provide any axial relative mobility between the cuter race of the pivot bearing and the receiving bore of the spindle for the lance unit.
In a lance unit according to claim 15 the gas pipe, which provides the gas that carries the small liquid volumes to the working point, is also fixed in direction of rotation. Just like the liquid pipe, the gas pipe may also be already connected to the base part in the works. The lance unit therefore comprises the entire liquid feed so and gas feed of the minimal quantity lubrication.
In a lance unit according to claim 16, the air pipe and the liquid pipe are mechanically connected to one another by one or more air-permeable distance parts and therefore form an extremely stable, rigid shell structure.
In this case then according to claim 17 the same advantages are obtained, namely usability in a spindle with tie rod for actuating a collet chuck, as has already been described above with reference to claim 14.
In a lance unit according to claim 18 the liquid pipe is able to tilt slightly at the bearing points. This prevents localized high flexural torques that otherwise act at the bearing points upon the wall of the liquid pipe. Such loads might lead during continuous operation to fatigue fractures.
The effect achieved by the development of the invention according to claim 19 is that the pivot bearing provided with the connection part is movable under spring action relative to a bearing bore that receives it, is tiltable relative to the axis of this bearing bore, and is displaceable in axial direction along the bearing bore.
These advantages are obtained according to claim 20 in a manner, in which the clear cross section of the bore that receives the bearing arrangement is not significantly impaired in the region lying between the bearings.
The development of the invention according to claim 21 is advantageous in view of good axial displaceability of the pivot bearing relative to the bearing bore, wherein at the same time good torque transmission through the connecting part to the bearing bore is obtained.
The development of the invention according to claim 22 is advantageous in view of the symmetry of the bearing point. If there are two more closely adjacent pivot bearings, this is advantageous also in terms of failure safety because, in the event of wear or failure of one of the bearings, its function may be taken over by the other bearing.
In the development of the invention according to claim 23 it is guaranteed that the various pivot bearings operate with low friction and exhibit only low wear also over a prolonged service period.
In a spindle according to claim 24, the gas that feeds tiny droplets of lubricant to the work point is directed through the spindle itself. As a result, on the one hand an additional cooling of the spindle is achieved and on the other hand there is slightly more room in the spindle bore that receives the lance unit. This makes it possible for example to design the tie rod, which is used to actuate the collet chuck, with a slightly thicker wall so that the collet chuck may be operated with very high actuating forces and nevertheless have a long service life.
The effect achieved by the development of the invention according to claim 25 is that the machining of the spindle that is necessary to provide the gas channel is particularly easy.
The alternative according to claim 26 is used preferably when the spindle bore as such provides enough room to transport the gas and a bypass has to be provided only at the pivot bearings because these are not gas-permeable or are gas-permeable to a limited extent. This bypass may then be realized simply by cutting inwardly open grooves into the inner wall of the spindle bore. The outer race of the pivot bearings is then defined by the inner end faces of the ribs left between the grooves.
By virtue of the development of the invention according to claim 27 it is possible for the actuation of the tool carrier collet chuck and the feed of lubricant and gas to be accommodated in a compact manner in the interior of the spindle.
The effect achieved by the development of the invention according to claim 28 is that between the lumen of the tie rod and the exterior thereof it is possible to establish a flow connection, which as a whole has a good cross section of passage, but in peripheral direction extensively retains the load-bearing material of the axially loaded tie rod.
There now follows a detailed description of embodiments of the invention with reference to the drawings. These show:
In
In the spindle housing a spindle 12 is supported by means of bearings 14, 16. The spindle 10 in its middle portion carries a rotor 18, which together with a stator 20 forms a spindle motor 22.
Provided on the, in
The clamping arms 30 are pressed into their position, in s which they lock the tool carrier 26, by means of an actuating sleeve 36 that is screwed onto the end of a hollow tie rod 38 guided slidingly in a spindle bore 29. The fie rod 38 is preloaded, in the drawing to the right, by means of a cup-spring assembly 40 and may be moved, in is the drawing to the left, by means of a clamping cylinder 42 lying axially outside of the spindle, with the result that the lugs of the clamping arms 30 move clear of the retaining shoulder 32.
The clamping cylinder 42 comprises a cylinder 44, as well as a piston 46 that is movable therein and connected to the right end of the tie rod 38.
Pressure medium channels that are not reproduced in the drawing are used to feed pressurized hydraulic fluid to the respective required working chamber of the clamping cylinder 42.
Extending centrally in a longitudinal bore, denoted by 48, of the tie rod 28 is an oil pipe 50, which is fixed in direction of rotation and is supported via pivot bearings 52-1, 52-2 and 52-3 at three axially spaced-apart points radially against the bore 48 of the tie rod 38. The pivot bearings 52 are in each case a plain bearing comprising a central hub portion 54, from which three ribs 56 run radially outwards.
The plain bearing sleeves are manufactured from a carbon material that runs with a low coefficient of friction along the outer surface of the oil pipe 50, which is manufactured from high-grade steel. The ribs 56 are seated in an interference fit on the inner surface of the bore 48 and the hub part 54 cooperates in the sliding play with the outer surface of the oil pipe 50.
There are typically three ribs 56 distributed in peripheral direction, the thickness of which is selected such that they are able to withstand the radial loads of the pivot bearing that are to be expected during operation, but to the extent that is compatible with stability care is taken to ensure that the grooves 58 left between the ribs 56 are as large as possible so that the pivot bearing as a whole has good permeability to air in axial direction.
As is evident from
The oil pipe 52, the clamping cylinder 42 and the base part 60 form together with the pivot bearings 52 a lance unit 66 that is capable of providing a lubricant/air mixture with a low lubricant content at the end situated on the left in the drawing. For this purpose, the interior of the bore 48 is loaded with compressed air via the base part 60, while the interior of the oil pipe 50 is loaded with lubricating oil from the base part 60.
Integrated into the base part 60 is a dosing valve, which under the control of a control unit (not represented) opens for short time intervals so that in a corresponding manner in each case a small volume of liquid is pushed out of the front end—situated on the left in the drawing—of the oil pipe 50. This small oil volume, which on separating from the end of the oil pipe 50 is split into smaller fractions, is then carried to the left in the drawing by the air flowing towards it along the outer surface of the oil pipe 50.
The oil/air mixture thus obtained is taken over by a mixture channel 68, which is formed in a channel sleeve 70 screwed into a connection socket 72 that is connected to the tool carrier 26. The mixture then passes to the tool receiver—to be imagined on the left in the drawing—of the tool carrier and, from there, into the lubricant channels of the tool (not represented).
As is evident from the drawing, the mixture channel 68 surrounds the free end of the oil pipe 50 with slight radial clearance and has a narrowing 74 downstream of the end of the oil pipe 50.
A lip seal 76 seals off the outer surface of the connection socket 72 in the direction of the tie rod 38.
In the spindle described above, the oil pipe 50 is able to move in axial direction relative to the tie rod. 38 because the plain pivot bearings 52 realize a pivot bearing arrangement as well as an axial bearing arrangement.
In the embodiment according to
In this variant, therefore, the oil pipe 50 moves together with the tie rod 38 in axial direction when a tool carrier is to be released or tightly clamped.
In the spindle according to
A similar but simpler bypass is provided for the pivot bearing 52-3.
In the embodiment according to
In a corresponding manner an axial displaceability of the end of the oil pipe 50 is provided in the base part 60.
An oil-pipe anti-rotation element comprises two ribs 92, which are welded onto the outside of the end of the oil pipe 50 and cooperate with a guide groove 94, which are provided in a bearing chamber 96 of the base part. The bearing chamber 96 is vented through a channel 98 in the direction of the environment.
The feed of lubricating oil to the oil pipe 50 is effected through a bore 100 or an oblong hole in the wall of the oil pipe 50 as well as through a channel 102 of the base part 60 that is in communication with the lubricating oil connection 62.
In the embodiment according to
The unit formed by oil pipe 50 and air pipe 104 is then radially supported likewise via a pivot bearing 52 against the spindle bore 29. Given the relatively small axial dimension of the oil pipe/air pipe unit it is sufficient to provide only a single pivot bearing. This pivot bearing has in particular the same construction as described with reference to
In a modification, rolling-contact bearings are also eminently usable in this embodiment because the annular space between spindle bore and outer surface of the air pipe 104 is not needed to transport a fluid.
The construction of a plain pivot bearing is represented once more in detail in
This again shows the hub portion 54 of the pivot bearing 52 as well as the three ribs 56, which extend radially outwards from the hub portion 54 and situated between which are the wide grooves 58 that provide for a flow of air through the pivot bearing without extreme throttling.
The external hearing sleeve 116 is firmly embedded in a carrying sleeve 118, which again comprises a hub portion 120 and three ribs 122 uniformly distributed in peripheral direction. The outer surfaces of the ribs 122 are connected in a fixed manner to the inner surface of a bearing bore (spindle bore or tie rod bore), the inner surface of the hub portion 120 carries the external bearing sleeve 116 in a fixed manner.
The magnetic pivot bearing shown in
End wails 130, 132 of the bearing drum 124 run with greater sliding play in front of the inner surface of the spindle- or tie rod bore, thereby forming between the end walls 130, 132 a compressed-air-filled pocket that guarantees an air cushion bearing arrangement.
In the case of the pivot bearing according to
The nozzle bores 134 are arranged radially in rings, and a plurality of such nozzle rings are provided spaced axially apart in the bearing sleeve.
The pivot bearing according to
The connection arms 144 may be resilient.
The bearing sleeve 142 in the axial region, in which the ball hearing is disposed, has a widening 148 with truncated-cone-shaped transition portions.
By virtue of the arrangement shown in
The running surfaces of the pivot bearings used in the various embodiments described above may additionally themselves be lubricated. This may be effected either by means of an oil-mist stream or by a direct feed of lubricant to the running surfaces.
In
Alternatively, a plain bearing surface that is adjacent to the oil pipe 50 may easily be lubricated by providing very fine lubricating openings 154 in the corresponding region in the oil pipe 50, as indicated in
The inner races of the two ball bearings are connected in a fixed manner to the oil pipe 50, the outer races are connected by three lamellae 158 made of spring steel that are uniformly distributed in peripheral direction and welded to the outer races. As is evident from the drawing, the lamellae 158 have a convexly curved geometry, and the outside diameter of the outer races of the ball hearings 52-a, 52-b is smaller than the inside diameter of the bearing bore 48.
The curvature of the lamellae 158 is so selected that the cage formed by the lamellae 158 and the outer races of the ball bearings is insertable with an interference fit into the bearing bore 48.
The cross section of the lamellae 158 is preferably a sharp-cornered rectangle as in a leaf spring, so that the lamellae 158 are seated in peripheral direction tightly in the bearing bore 48.
As a result, at the bearing point shown in
A further result is the pivot bearing arrangement that is realized by means of the ball bearings 52-a, 52-b.
The ball bearings are moreover axially displaceable relative to the bearing bore, this being assisted by means of the gently curved outer surface of the lamellae 158. The bearing point shown in
Finally, the bearing point, apart from the ball bearings themselves, also has a practically unchanged cross section of passage for the air.
In the embodiment according to
This facilitates the mounting of the lance unit in a spindle.
As is indicated by dashes in
In
In an axially extended region, the length of which in the embodiment in question is approximately one and a half times the diameter of the bore 48, there are cut into the wall of the tie rod 38 slots 78, which have a narrow width, for example 0.2 to 0.5 mm, and are uniformly distributed in peripheral direction. Because of their length this slots, despite their narrow width, have a good total average surface area for air. As the material of the tie rod is reduced only slightly in peripheral direction, the tie rod 38 is able to transmit high loads also in the region of the slots 78.
The air that exits from the tie rod through the slots 78 is guided through a hollow-turned portion 164 of the spindle bore 29, which extends as far as the next point of air passage, to the next point of air passage where it is fed back into the interior of the tie rod through an arrangement corresponding in a horizontally mirror-inverted manner to the arrangement of
Components already described above in a comparable function once more bear the same reference characters and are not described in detail again.
The pivot bearing 15 formed by a ball bearing is now seated in a bearing part 142, which comprises an annular portion 166 that overlaps the outer race 52A, but not the inner race 52I, of the ball bearing.
Moulded onto the annular portion 166 are three axial retaining arms 168 that are distributed in peripheral direction and positively encompass the lateral surface of the outer race 52-A. The retaining arms 168 carry on their ends locking tongues 170, which extend radially inwards and engage over the end face of the outer race 52A.
Rectangular carrying lamellae 172 are cut out of the wide retaining arms 168 and bent outwards so as to form with the peripheral surface of the holder arms 168 an angle of 45 degrees.
In the unloaded state the radially outer axial edges of the carrying lamellae 170 lie on a circle, the diameter of which is greater than the diameter of the bore 48. The carrying lamellae 170, inserted into the bore 48, are therefore deformed and under initial tension.
When loaded in the direction of rotation, their outermost edges cut in and the result is good self-boosting locking. The carrying part 142 may be twisted counter to the direction of rotation by the application of force. The carrying part may moreover be displaced axially by the application of force, wherein the outermost edges of the carrying lamellae 170 operate like the blades of an ice skate.
The entire carrying part is a stamped and bent component made of spring steel sheet. By expanding the cage formed by the retaining arms 168, the carrying part 142 may easily he clipped (in
Number | Date | Country | Kind |
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10 2009 011 336.3 | Mar 2009 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2010/001379 | 3/5/2010 | WO | 00 | 12/2/2011 |