GB2159736A - Clamping device for tools, such as drills, milling cutters or the like - Google Patents

Abstract

The invention relates to a clamping device for clamping tools, such as drills, milling cutters, lathe tools etc. The clamping device comprises an axially slotted collet (4) for receiving the actual tool shank (6) of the tool. The collet (4) is connected to a coupling nut (5), which is fitted exclusively manually to the front section (3) of a chuck (2) as far as a predetermined stop (7'). To produce the clamping pressure as a result of elastic deformation of the slotted collet (4) against the inserted clamping shank (6) of the tool, clamping means (21) operating hydraulically, such as a clamping sleeve (21) is provided. The hydraulic clamping pressure is applied to the working piston (9) displacing the clamping sleeve (21) axially, by turning a threaded bolt (10) inwards. <IMAGE>

Description

SPECIFICATION Clamping device for tools such as drills, milling cutters or the like.

The invention relates to a clamping device for tools, such as drills, milling cutters or the like, in which a collet for receiving a tool shank can be applied by means of a coupling nut to the front part of a chuck positively but so that it can be released.

For clamping tools with a cylindrical clamping shank, such as for example drills, slot drills, lathe tools etc., mechanical clamping devices are known, in which the shank of the tool to be clamped is inserted in a collet provided with axial slots and is clamped in the latter. This takes place by means of a coupling nut belonging to the collet, which is detachabley connected to the collet and is screwed by an axial thread to the front part of the chuck.

When the coupling nut is screwed onto the chuck, the clamping force of the collet is brought about by complementary conical tapers, which are formed on the periphery of the collet and in the insertion opening of the front part of the chuck so that when the coupling nut is screwed on, radial thrust components press the slotted collet firmly against the tool shank to be clamped.

These mechanically operating collets with a coupling nut have the drawback that when the coupling nut is screwed on, the clamping force cannot be applied in an exactly defined manner. The clamping normally takes place by hand with the assistance of auxiliary mechanical means, such as for example a pin spanner, which is inserted in corresponding recesses in the coupling nut, whereby in practice in order to achieve a secure clamping fit of the coupling nut, the latter is rotated into its final clamped position additionally with hammer blows. This manual application of the collet with a coupling nut does not ensure that a predetermined, exactly defined clamping force is produced in each individual case.

Moreover, since the magnitude of the clamping force depends on the pitch of the thread and therefore a thread with the smallest possible pitch is used, the drawback also exists that the application of the clamping nut takes a relatively long time. Finally, part of the clamping force applied is lost in the screw thread of the coupling nut or as a frictional force within the conical contact surface. In known clamping devices operating hydraulically with pressure medium such as oil, grease or the like, these drawbacks do not occur. In these hydraulic clamping devices, a piston with stroke limitation is actuated by way of a manually adjustable clamping bolt, which is located in the front part of the chuck at right angles to the chuck axis.Due to this the hydraulic oil, metered in a chamber system, is pressed against a thin-walled expan sion bush consisting of special high-speed steel. This expansion bush is surrounded over its entire length by pressure medium, so that it can be compressed or expanded uniformly cylindrically and centrally with respect to the central axis of the chuck. At both ends the expansion bush is connected to the front part of the chuck securely and in a liquid-tight manner. Due to an adjustable longitudinal stop likewise provided in the front part of the chuck, the clamping length itself can be altered.The pressure relief takes place due to the fact that the clamping bolt is turned back manually, due to which as a result of the pressure drop which occurs in the hydraulic chamber system, the expansion bush is turned back to its initial position and releases the clamped tool shank and thus the tool.

However, hydraulic clamping devices of this type have the drawback that their tolerance range is extremely small. Therefore, for all current tool diameters, complete clamping devices are necessary, so that for clamping diameters of different sizes of for example 10,12,16,20,25 and 32 mm, a separate, complete clamping tool adapted exactly to these different diameters is required, the latter consisting of a chuck with the aforedescribed clamping members. The known hydraulic clamping devices with their high clamping accuracy and simple operation nevertheless require a plurality of such clamping devices, on account of their low tolerance range, which leads to considerable and cost-intensive stock keeping.It is intended that the advantages of mechanical collets with their large tolerance range and correspondingly low stock requirements in comparison with hydraulic clamping devices are maintained by the invention and that their drawbacks with regard to their generally inadequate magnitude of clamping force and their lacking capacity for accurate definition are avoided. Accordingly the invention intends to provide a clamping device which does not have the drawbacks of mechanical collets, but maintains their advantages and combines the latter with the advantages of hydraulic clamping devices, whilst avoiding the drawbacks of the latter.

The invention provides a clamping device for tools, such as drills, milling cutters or the like, in which a collet for receiving a tool shank can be applied by means of a coupling nut to a front part of a chuck positively but so that it can be released, wherein clamping means actuable by means of a pressure fluid are provided and are operable to elastically deform the collet in its clamping position.

A simple embodiment is obtained if as a development of the invention, a stop for the coupling nut of the collet is provided on the front part of the chuck, which when fitting the coupling nut exactly defines its final position and in which furthermore the coupling nut is provided exclusively for fitting by hand. This can take place for example due to the fact that the outer periphery of the coupling nut is provided solely with knurling or the like so that tightening of the coupling nut by auxiliary mechanical means, such as for example a pin spanner or by using hammer blows is precluded.

A simple construction results if at least one clamping member operated by pressure medium, preferably in the form of a clamping sleeve is provided between the slotted collet and the front part of the chuck. In this case this clamping sleeve is advantageously located between the slotted collet, in which the tool shank is inserted and the inner wall of the front part of the chuck so that the clamping sleeve is able to slide axially under the action of hydraulic or similar forces, with respect to the collet located in its end position.

When the clamping sleeve is sliding, which takes place under hydraulic force, in order to obtain a sufficiently great clamping force on the inserted tool shank, in a further embodiment the outer surface of the collet and the inner wall of the clamping sleeve have a complementary conical construction so that when the clamping sleeve slides, the collet is tensioned by radially acting force components against the inserted tool shank.

Provided for the axial displacement of the clamping sleeve itself is a hydraulic chamber system, which comprises a hydraulically operated pressure piston, which is connected hydraulically to a servo piston provided in another pressure chamber. By simple insertion of this servo piston, as a result of the reduction of the pressure chamber, the hydraulic pressure in the chamber system is increased until the exactly predetermined clamping force is set up at the pressure piston displacing the clamping sleeve.

A structurally simple arrangement is obtained if the collet and the clamping sleeve, as well as the pressure piston displacing the clamping sleeve together with the pressure chamber are arranged in a central recess in the front part of the chuck.

In this case the collet is advantageously connected for example by way of an intermediate ring to the coupling nut in a secure but detachable manner, so that by simple screw ing-on or by a suitable bayonet connection, the collet together with the coupling nut can be screwed onto or fitted to the front part of the chuck in its fixed abutment position.

In order to ensure that the operator is able to recognise in a simple manner from outside whether the necessary exact clamping pressure has been applied, according to a further feature of the invention a hydraulic connection is provided between one of the pressure chambers of the hydraulic system and a further pressure chamber. Also located in this further pressure chamber is a sliding piston, which on reaching the predetermined operating pressure, is moved into an indicating position which is preferably marked and is clearly visible from outside, under the action of the existing hydraulic pressure. The arrangement is preferably such that this piston with the visual indication and the piston which can be adjusted by hand for producing the necessary clamping pressure are arranged in a common plane, preferably radially or obliquely with respect to the axis of the chuck.

After a clamping operation, in order to bring the clamping sleeve in a simple manner into a reliable restored position, according to a further feature of the invention, a mechanically operated resetting device for the clamping sleeve is provided.

Advantageously, this resetting device may consist of a release screw mounted to move in a transverse bore in the front part of the chuck, which screw by way of an intermediate part, for example a ball, engages with an axial adjusting force component on a part, for example the edge of a recess, of the clamping sleeve.

Further features of the invention are described in detail hereafter with reference to one embodiment illustrated in the drawings, in which: Figure 1 shows a chuck according to the invention, whereof the lower part is shown in section; Figure 2 is a section on line ll-ll of Figure 1; Figure 3 is a section on line Ill-Ill of Figure 1. to an enlarged scale.

A chuck 2 of known basic construction is clamped securely in a rotating working spindle, for example a drilling or milling spindle 1, shown solely diagrammatically in Figure 1. On the side remote from the clamping point on the working spindle, the chuck 2 has a front part 3 with a receiving location for clamping a shank 6 of a working tool (not shown in detail), for example of a drill, milling tool or the like. In the embodiment the inner surface 3' of this receiving location is cylindrical. The front periphery of the part 3 is provided with an external screw thread 7, whereof the end comprises a coupling nut 5 as a radial front edge 7' for the stop. This coupling nut 5 is connected to a retaining ring 5', which in turn receives the front section of a collet 4. The collet 4 is provided in the normal manner with axial slots 4' and has a preferably cylindrical inner wall 4" adapted to the outer periphery of the tool shank 6. The outer periphery of the collet 4 has a conical construction so that it widens out in the direction of arrow 19, i.e.

towards the insertion opening of the collet.

The collet 4, retaining ring 5' and coupling nut 5 thus together form the collet part nor mally referred to as a whole, which is seated on the end section of the tool shank 6 and is easily exchanged for a collet part of another size.

The outer peripheral surface of the coupling nut 5 is free from engagement openings for a tool and comprises solely knurling or the like in order to ensure that it together with the collet 4 can be screwed by the operator solely by hand onto the thread 7 of the front part 3 of the chuck 2. In place of the axial screw thread 7 shown in the embodiment, another positive connection, for example a bayonet connection, a link or the like with a corresponding stop may be provided.

It is essential that the screwing-on of the parts 4, 5, 5' takes place solely by hand and up to the stop determined by the front edge 7'. Due to this it is ensured that the operator can screw on the collet 4 together with the coupling nut 5 solely as far as the stop 7' provided by the end of the screw thread 7, without the actual clamping force for the collet 4 and thus the clamping of the tool shank 6 being able to be applied by way of the coupling nut 5.

Located between the slotted collet 4 and the front part 3 of the chuck 2 is a clamping sleeve 21, whereof the inner wall 21 b corresponds exactly to the cone of the outer peripheral surface of the collet 4, whereas the outer periphery 21 a of the clamping sleeve 21 is constructed cylindrically to correspond to the inner periphery of the receiving location of the front part 3 of the chuck 2.

The clamping sleeve 21 is arranged to slide axially in the front part 3 with respect to the collet 4. For this purpose a bore 8 lying radially or obliquely is provided in the front part 3 of the chuck 2, in which a servo piston 9 of a hydraulic clamping system is mounted.

The servo piston 9 bears towards the outside against a threaded bolt 10, which is guided to move in a threaded insert 11 of the chuck part 3.

Located on the other side of the pressure piston 9 is a seal 12, which may consist of rubber or the like and seals the actual pressure medium chamber 13, in which the hydraulic pressure medium, for example grease, oil or the like is located, with respect to the piston 9. The pressure medium chamber 13 is connected by way of a bore 14 or the like lying axially to a pressure chamber 15, which lies centrally with respect to the axis 2' of the chuck. An axially movable pressure piston 16 is mounted to reciprocate in this pressure chamber 1 5.

The pressure piston 16 is sealed by means of a seal 18 with respect to the front part 3 of the chuck 2 and on its side lying at the front in the direction of the arrow 19, i.e. in the feed direction, comprises a peripheral section 20 whereof the front edge 20' bears against the rear edge of the clamping sleeve 21. As mentioned, this clamping sleeve comprises internally a conicity corresponding to the outer periphery of the collet 4, so that in the case of axial displacement of the pressure piston 16 and of the related displacement of the clamping sleeve 21 in the direction of arrow 19, radial pressure is exerted on the slotted collet 4, by which the clamping pressure is applied to the shank 6 of the working tool inserted in the collet 4.

For clamping a tool with a tool shank 6, the collet 4 with the coupling nut 5 is fitted on the end of the tool shank 6, inserted in the chuck 2 and attached to the latter by screwing the coupling nut 5 onto the external screw thread 7 of the front part 3 of the chuck 3. In this case the coupling nut is screwed solely by hand and without using any tool as far as the end 7' of the screw thread 7. In this end position of the coupling nut 5 limited by the stop, the tool with the shank 6 has assumed its final exact working position.The actual clamping of the tool now takes place simply due to the fact that the threaded bolt 10, which may be constructed for example as a socket head cap screw, is screwed into the threaded sleeve 11, due to which the servo piston 9 is shifted forwards, due to which a corresponding hydraulic pressure now builds up in the communicating chambers 13, 14, 15, by which the pressure piston 16 (working piston) with the collar 20 is shifted forwards in the direction of arrow 19. In this case, by way of the front edge 20' of the collar 20, the adjoining clamping sleeve 21 is likewise moved forwards. In this case, as a result of the described conicity of the mating inner surface of the clamping sleeve 21 and of the corresponding conical outer face of the slotted clamping sleeve 4, the latter is compressed radially and the tool shank 6 is clamped firmly in the chuck 2.

In a further construction of the invention, an indication device for the clamping force applied is also provided on the chuck 2. The latter preferably lies in the same radial plane as the threaded bolt 10 and the pressure piston 9 and consists of a further pressure chamber 22 connected to the pressure medium chamber 13, in which a piston 23 with a collar 23' is mounted against a spring 28, which when pressure is applied leaves the bore against the force of the spring 28, which is mounted with a screwed sleeve 29 in the front part 3 and is provided with a marking at its end, so that when a predetermined hydraulic clamping pressure is reached, as a result of the emergence of this marking on the piston 23, a reliable indication of the existing clamping pressure is provided.It is thus ensured for the operator that independently of the former setting position of the collet 4, he can be certain that the required clamping force has been applied in the system.

For the release of the tool, for example of the drill or the like, first of all the threaded bolt 10 is turned in the opposite direction, i.e.

radially outwards. The hydraulic pressure in the system is subsequently reduced, due to which the collet 4 and clamping sleeve 21 are relieved of clamping pressure. The clamping sleeve 21 may then be returned to its initial position. For this purpose a release screw 24 is provided, which is seated in a bore 17 provided with a screw thread 27 in the front part 3 and due to pushing-in presses by way of a ball 25 in an annular recess 26 of the clamping sleeve 21 and moves the latter axially in the opposite direction to that of arrow 19 so that the collet 4 is released and the shank 6 of the tool together with the collet 4, retaining ring 5' and coupling nut 5 can be exchanged as a whole.

The construction according to the invention has the advantage that the cylindrical collets operating mechanically and a simple construction together with the coupling nuts can be exchanged easily and thus the wide tolerance range desired for these mechanical collets is maintained. However, on the other hand, since the clamping force itself must no longer be applied manually by way of the coupling nut of the collet, undefined and thus inaccurate clamping forces are prevented from being applied. On the contrary, the application of the clamping force is defined exactly by way 9f the hydraulic clamping system. Due to this errors when applying the clamping force are avoided.Due to the fact that the coupling nut of the collet has no engagement means for clamping tools to be operated manually, it is ensured that when the coupling nut is screwed on, the clamping force cannot be applied manually by way of the coupling nut.

The invention thus makes it possible to use known exchangeable collets, i.e. collets with a coupling nut together. Due to the fact that it is ensured that solely a defined, exact clamping force can be applied hydraulically, which in addition can be ascertained and controlled clearly as a result of the indication device provided, it is guaranteed that the tool is always clamped with the predetermined clamping force. By way of addition, in comparison with mechanical clamping devices, the hydraulic clamping force may be many times greater. Finally, as a result of the application of the clamping force by way of hydraulic pistons and cylinders, losses in the clamping force as a result of the conicity or as a result of the transmission of the clamping force exclusively by way of the screw thread, are dispensed with, as is the case in conventional mechanical collets.Also, overall a considerable improvement in the truerunning of the clamping device in comparison with mechanical clamping devices is achieved, because in the construction according to the invention, the clamping force is initiated exclusively in the axial direction. In addition, the device according to the invention is easy to operate, since any manual operations, such as in the conventional collets with a coupling nut, and thus also any risk of injury for the operator are dispensed with.

Due to the fact that the individual collets with a coupling nut can be used and exchanged, storage in comparison to conventional clamping devices operating solely hydraulically is considerabley reduced, in which case at the same time the advantage is achieved that a substantially greater clamping range than in exclusively hydraulic clamping devices is provided. Finally, the release of the clamping device is also considerabley simplified, since for this solely a radial displacement of the threaded bolt 10 or of the release screw 24 is necessary.

With regard to operating techniques, the great advantage is provided that with the device according to the invention, the working tool, for example a milling cutter, drill or the like, maintains its exactly preset and defined working position during the clamping operation and after the clamping operation without any variations, which in mechanical collets is not possible with the accuracy now achieved, since when clamping by hand by means of the coupling nut, the collet may move axially, which once again necessitates re-adjustment of the working-tool in the accurate working position.

In contrast to this, in the construction according to the invention, after being brought into the end position by the operator in the chuck 2, the collet 4 has an irreversible position with respect to the latter, especially since the clamping force is applied exclusively by way of the clamping sleeve 21 which is able to move axially and is displaced axially by the hydraulic piston 16. Due to this, a variation of the position of the tool never occurs.

Finally, the front section of the collet 4, which projects beyond the front part 3 of the chuck 2, instead of being provided with an angular initial stage is provided with a rounded initial stage, due to which the flow of the force in this region is assisted and at the same time a compensation, for example of thread errors between the screw thread of the coupling nut and the screwing-on thread 7 is achieved.

Claims (21)

1. A clamping device for tools, such as drills, milling cutters or the like, in which a collet for receiving a tool shank can be applied by means of a coupling nut to a front part of a chuck positively but so that it can be released, wherein clamping means actuable by means of a pressure fluid are provided and are operable to elastically deform the collet in its clamping position.

2. A clamping device according to Claim 1, wherein provided on the front part of the chuck is a stop for the coupling nut of the collet.

3. A clamping device according to claim 2, wherein the coupling nut is constructed for mounting by hand, by knurling of its outer surfaces.

4. A clamping device according to any one of claims 1 to 3, wherein at least one said clamping means actuable by said pressure fluid is provided between the collet and front part of the chuck.

5. A clamping device according to claim 4, wherein the clamping means is a clamping sleeve located between the collet and an inner wall of the front part.

6. A clamping device according to claim 5, wherein the clamping sleeve is mounted to slide axially with respect to the collet which is located in the end position of such movement.

7. A clamping device according to claim 6, wherein an outer surface of the collet and an inner wall of the clamping sleeve have a complementary conical construction whereby when the clamping sleeve slides forwardly of the chuck, the collet can be clamped by thrust components acting in the radial direction.

8. A clamping device according to claim 6 or claim 7, wherein for axial displacement the clamping sleeve is in operative connection with a pressure piston in a pressure chamber and acted upon by said pressure fluid, whereof the pressure chamber is connected by said pressure fluid to a servo piston pressure chamber.

9. A clamping device according to claim 8, wherein the pressure piaton, the respective pressure chamber, collet and clamping sleeve are located in a central recess in the front part of the chuck.

10. A clamping device according to claim 8 or claim 9, wherein the servo piston with the respective pressure chamber and a threaded bolt are arranged at right angles to the axis of the chuck.

11. A clamping device according to claim 10, wherein two pressure chambers are connected by way of an axially extending bore.

12. A clamping device according to any one of claims 8 to 11, wherein the pressure piston is sealed by an annular seal with respect to the front part of the chuck.

13. A clamping device according to claim 11, wherein the pressure piston has a projecting peripheral section, whereof a front edge bears against an adjacent front edge of the clamping sleeve.

14. A clamping device according to any one of claims 8 to 13, wherein a pressure fluid connection is provided between one of the pressure chambers and a further pressure chamber, in which an indicator piston is arranged to slide so that on reaching the predetermined clamping pressure it assumes an indicating position.

15. A clamping device according to claim 14, wherein the indicator piston and the servo piston are arranged in a common plane at right angles to the axis of the chuck.

16. A clamping device according to any one of claims 5 to 15, comprising a mechanically operated recessing device for the clamping sleeve.

17. A clamping device according to claim 16, wherein the recessing device comprises a release screw mounted to slide in a transverse bore in the front part of the chuck.

18. A clamping device according to claim 17, wherein said release screw acts by way of an intermediate part with an axially directed force component on the edge of a recess in the clamping sleeve, whereby when the release screw is moved rearwardly of the chuck, the clamping sleeve is restored to its initial position.

19. A clamping device according to claim 18, wherein said intermediate part comprises a ball.

20. A clamping device according to any one of claims 1 to 19, wherein said pressure fluid is hydraulic fluid.

21. A clamping device for tools substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.