GB2175227A - Device for clamping tools to a tool holder of a machine-tool - Google Patents

Abstract

A cutting tool head 2 is clamped to a tool holder of a machine tool by means of an axial drawing element, such as a tension bolt 5, which extends through the tool holder 1 into engagement with the tool head 2. The tool head 2 is centered and positioned axially with respect to the tool holder 1 by interengagement between short frusto-conical surfaces 1b and 2b on the holder and tool head respectively, and simultaneous interengagement between axial stop surfaces 1a and 2a extending radially from the wider ends of the frusto-conical surfaces 1b,2b respectively. Relative rotation between the tool head 2 and the holder 1 is prevented by engagement of a tongue 4 fixed to the holder 1 and engaging in a radial groove in the tool head 2. <IMAGE>

Description

SPECIFICATION Device for clamping tools to a tool holder of a machine-tool The invention relatestoadeviceforclampingtool heads provided with at least one cutting edge for machining operations on atool holderwhich does not rotate during machining with centering surfaces formed on thetool head and tool holder as well as with stop faces for axial position indication and with an axially movable drawing elementforsecuringthe tool head on the tool holder, the tool head being secured againstturning relative to the tool holder by means of a groove and tongue connection.

Such devices forthe clamping oftool heads on a tool holder of a machinetoolareknowninadiversity of constructions.

In one ofthese known constructions there is provided on the tool holder a cylindrical centering element onto which the tool head designed with a cylindrical perforation is placed. The tool head is held against rotation by means of a tongue provided in a radial direction on the tool holder, which engages into a corresponding radial groove on the tool head.

The locking of the tool head on the tool holder is effected by means of several dowel pins arranged slantingly radially which engage into an annular groove in the engagement perforation ofthetool head and which, on being actuated bythe drawing element fitted with a conical head, effect the pressing ofthetool head againstan endfaceofthetool holder.

This known construction suffers from the drawback that, because ofthe cylindrical design ofthetang provided on the tool holder there is of necessity produced an amountofplaywhich,becauseofthe necessary difference in diameter between cylindrical tang and cylindrical holding perforation in the tool head required for the insertion and removal ofthe tool head, cannot be eliminated in anyway. As, for stability reasons, this play is kept as small as possible, there is also a small centering play, so that the known construction permits of an automatictool head change onlywhen the automaticchange device operates with a high degree of precision.Afurther decisive drawback arises from the fact that the transmission offorce is effected by fixing the tool head on the tool holder by means of dowel pins with small transmission surfaces which, thus, are not only very highly stressed but are also exposed to considerablewear, all the more so asthe play required bythe design between cylindrical tang and cylindrical holding perforation is also the cause of stress through dynamic cutting forces.

In a further known construction the connection between the tool head and the tool holder is effected by means of a serration and a collet chuck. The collet chuck has several clamping elements which grip a holding pin of the tool head.

The drawback of this known construction lies in the over-determination ofthe association ofthetool head with the tool holder as a consequence of the teeth of the serration which not only is used for relative securing of rotation between tool head and tool holder, but also has to take over at the sametimethe centering and axial position determination. A division error ofthe serration leads to a position error in axial and radial direction at the cutting edge ofthetool head. In spite of the employment of a Hirthserration which is very expensive and complicated to manufacture this known form of construction thus suffers from the drawback of limited accuracy.

The invention has for its object to construct a device of the type first defined hereinabove for clamping tool heads on a tool holder of a machine tool in such a mannerthat, while avoiding the drawbacks ofthe known constructions and reducing manufacturing costs, a play4reefitting of the tool head on the tool holder is achieved with positive centering and axial determination of position, the greatest possible centering play being available for the purposes of the automatictool head change.

The achievement of this object by means ofthe invention is characterised in that the tool head is provided with a short lateral arc of cone and the tool holder is provided with a corresponding counter-lateral arc of cone for centering, and in that, for the purposes of axial determination of position of the tool head on the tool carrier, provision is made at the end of the great diameter of the lateral arcs of cone for, in each case, an end face which, in the clamped condition, as a resultofthe axial pulling force ofthe drawing element, lies against its corresponding one free from play just as the lateral arcs do.

As a resu It of the construction according to the invention with centering surfaces formed as cone-shaped elements there is achieved a greater centering path on the fitting of the tool head on the tool holder, so that an automatic change of tool head is possible without difficulties. In spite of this great centering path there is achieved a mounting free from play ofthetool head on the tool carrier in the clamped state, a positive centering and axial determination of position being thus achieved as the centering and stop surfaces are kept separate from one another, so that over-determination is avoided. Because of the large areas of the centering and stop faces there is a negligiblysmallerwearandsmallsensitivityto soiling. In addition, the construction according to the invention is achieved economically.

According to a further feature of the invention the tool head may be provided with a tapped hole into which a tension bolt, arranged in the tool holder and acting as a drawing element, engages. By this means there is achieved a simple, rigid connection, self-clamping as a result of the screw thread, between tool head and tool carrier.

As a further embodiment of this construction it is proposed according to the invention to mountthe tension bolt slidably between two end positions in the tool carrier, and to load it by means of a spring operating inthepull-on direction ofthetool head. By matching the end positions and the spring it is achieved that on the setting-up of the tool head the tension bolt protrudes out of the tool carrier only to the extent that the conical centering faces cooperate for pre-centering and securing against rotation is made effective, while the screw thread of the tension bolt still engages right into the tapped hole of the tool head.

In an alternative embodiment of the invention an annular groove oftrapezoidal shape in cross-section is formed behind the inner conical surface in the tool head. Engaging into said groove are radially adjustable clamping elements with clamping faces corresponding tothe annular groove. They are adjustable by an axial movement of the drawing element. For a slightly greater cost of construction this design supplies a particularlysoiling4ree embodiment which makes possible veryfast clamping and removal ofthetool head.

In a preferred method of construction the drawing element is provided with an actuation screw thread forthe radial adjustment ofthe clamping elements. A rotation on an axially unmovably held nut has therefore as its consequence an axial displacement of the drawing elementfitted with a screwthread and whichforthis purpose is held in non-rotatable manner in the tool holder.

If rapid clamping and removal ofthetool head isto be effected with simple elements on the machine tool, the drawing element is loaded according to the invention forthe radial adjustment ofthe clamping element in the pull-on direction ofthe tool head in permanent manner by at least one spring, and it is displaceable in the opposite direction by aforce which can be applied from outside, produced, for example, by a cylinder impinged upon on one side.

By this means a simple automation ofthe clamping and removal process is made possible.

As a further possibility ofembodimentthe drawing elementforthe radial adjustment of the clamping elements may be actuatable by a pressure medium cylinder incorporated in the tool holder. This construction is advantageous when the tool holder is already provided with pressure medium connections.

Finally, it is proposed with the invention to form the clamping elements on a slit master gripping collet and to adjust by means of the conical head ofthe drawing element against the own spring action ofthe master gripping collet radially outwards. This construction known in various versions has the advantage that it is possible to use commercially available elements with high operation reliability.

Several examples of embodiment of the device according to the invention are shown on the drawing wherein Figure 1 is a longitudinal section through a tool head fitted on atool holderwith afirst embodiment of the drawing element at the start of the fixing process; Figure2 is a representation corresponding to Figure 1 in clamped position; Figure 3 is a longitudinal section corresponding to Figure 2 using a second embodiment ofthe drawing element; Figure 4 is a further possibility of execution forthe drawing element on the basis of a longitudinal section through a tool head clamped on the tool holder, and Figure 5is a representation corresponding to Figure 4, using an alternative solution forthe actuation ofthe drawing element.

Figures 1 and 2 show in connection with afirst embodiment a tool carrier 1 which is provided on its side carrying atool head 2with an annularendface la as a stop face forthe tool head 2 which has a corresponding annular end face 2a. End face 1a ofthe tool carrier 1 surrounds a short external conical surface 1 b protruding out of the tool carrier 1,the conical angle of which is within the range 1: 10two 1: 4. The tool head 2 can be placed on this external conical surface 1 b by means of an internal conical surface 2b which is formed in a central perforation of the tool head 2 provided with one or more small cutting plates 3.

The locking ofthetool head 2 against rotation on the tool carrier 1 is effected in the embodiments represented by means of a tongue 4fixed on the tool carrier 1 in radial direction in the area of the end face 1 a, which engages into a groove on the tool head 2.

In the first embodiment according to Figure 1 and 2 use is made as drawing elementforthe clamping of the tool head 2 on the tool carrier 1 of a tension bolt5 the threaded part of which engages into a tapped hole 2c of the tool head 2. The tension bolt 5 is inserted by means of a cylindrical annularflange 5a displaceably between two end positions in a hole 1 c ofthetool carrier 1. The rear end position is obtained bythe application ofthe annularflange 5a on a snap ring 6.

When the tool head 2 has been removed this rear end position is effected by means of a spring 7 which is disposed between the annularflange 5a and the bottom of the hole 1c in the tool carrier 1 and loadsthe tension bolt5 in the pull-on position ofthetool head 2. The other, forward end position ofthetension bolt 5 is achieved by the application of its annularflange 5a on the compressed spring 7.

In the example of embodiment of Figures 1 and 2 there is formed on the end ofthe tension bolt an outer hexagon 5b by means of which the tension bolt 5 can be rotated. The length ratios are matched to one another in such a mannerthatthetension bolt5 protrudes by its first screw thread according to Figure 1 precisely to the extent to which the first screw thread grips on the setting ofthetool head 2 with its inner conical surface 2b on the outer conical surface 1 b ofthetool carrier 1, when the tension bolt 5 is turned.By this means it is ensured that by means of the conical surfaces 1 and 2b a pre-centering is effected, and by means of the tongue 4 locking against rotation is effected, when the tool head 2 has been placed automatically or manually on the tool carrier 2 for clamping. A rotation ofthe tension bolt 5 thus effects a proper clamping ofthetool head 2, as a result ofwhich, by means ofthe conical surfaces 1 b and 2b and the application ofthe end faces 1a and 2a a play-free fit in the clamped condition is achieved.

On the loosening of the tension bolt 5 the spring 7 effectsthatthetension bolt 5 is drawn back correspondingly to the loosening process into the tool carrier 1, so thatthe tool head 2 retains its clamping position until the tension bolt 5 comes out ofthetapped hole 2c ofthetool head 2, and maybe accordingly also removed automatically from the tool carrier 1 atthe end ofthe releasing process.

In the second example of embodiment according to Figure 3 an annular groove 2d trapezoidal in cross-section is provided in the tool head 2 behind the inner conical surface 2b. Into this annulargroove 2d there engage radially adjustable clamping elements 8a with clamping surfaces corresponding to the annular groove 2d, which, in the example of embodiment, are formed on a master gripping collet 8. These clamping elements 8a are moved bythe conical head 9a of a drawing element9 in a radial direction contrary to the own spring action of the master gripping collet8, if the drawing element 9 is moved in axial direction relativetothetool holder 1.

In the embodiment represented in Figure 3the radial displacement of the drawing element 9 is effected with the aid of an actuation thread which is constructed at the end of the drawing element 9 as an external screwthread, and at the front end of a nut 10 provided with a spanner-application area 1 ova.

Whereas the nut 10 is rotatably mounted in the tool carrier 1,the drawing element 9 is held non-rotatably by a grub screw 11, sothatturning the nut 10 results in an axial movementofthe drawing element 9.

The clamping and removing ofthetool head 2 is effected in the embodiment according to Figure 3 in the same way as with the first example of embodiment according to Figures 1 and 2, the clamping elements 8a being moved inwardly in radial direction due to their own springing by the head 9a moved out forward ofthe drawing element9 -forthe fitting and removal of the tool head 2-to such an extent that the tool head 2 can be inserted or removed without any difficulty.

The third example of embodiment according to Figure 4 differs from that of Figure 3 in the manner of actuation ofthe drawing element 9 acting on the clamping elements 8a ofthe master gripping collet 8.

With this embodiment the drawing element is, by means of annularflange 9b screwed onto the rear end, ledslidablyin a hole lcofthetool carrier 1 and loaded in the pull-on direction ofthetool head 2 by theforce of a spring which, in the example of embodiment, is exerted by a plurality of disc springs 12. As a result of this the clamping elements are constantly in clamping position through the force of the disc springs 12.If a tool head 2 is to be taken out and a newtool head 2 isto be put on, it is necessaryto push the drawing element 9 by a force applied from the outside and overcoming the disc springs 12 in the direction of the arrow drawn in Figure 4, sothatthe clamping elements 8a, on the basis oftheir own elasticity move radially inwards, to make a removal or insertion of tool head 2 possible. As soon as this externallyapplied force is removedthediscsprings 12 push the drawing element 9 in the pull-on direction ofthetool head 2, as a resultofwhichthe head 9a of the drawing element 9 expand the clamping elements 8a ofthe master gripping collet 8 and clamps the inserted tool head 2 overthe annular groove 2d on the tool holder 1.

lnthefourthexampleofembodimentaccordingto Figure the deviation from the construction consists purely in the manner of adjustment of the drawing element 9. In this em bodimentthe drawing element 9 carries a piston 9cwhich is led slidably in a cylinder chamber 1d in the tool carrier 1. The cylinder chamber 1 d is sealed relative to the other parts ofthe tool carrier 1 by means of of cover 1 e and provided with pressure-medium connections 1 fso that the piston is slidable in both directions by pressure-medium impingement. By an appropriate control of the supply and delivery of pressure medium it is thus possible to effect clamping and removal oftheclamping elements 8a from the master gripping collet8, so that the tool head 2 may be clamped on the tool holder 1, or removed therefrom in the above-described manner.

Claims (9)

1. A device for clamping tool heads provided with at least one cutting edge for machining operations onto a tool holder of a machine tool which does not rotate during machining, with centering surfaces formed on the tool head and tool holder, as well as with stop faces for axial position determination, and with an axially movable drawing element for securing the tool head on the tool holder, the tool head being secured againstturning relative to thetoql holder by means of a tongue and groove connection, characterised inthatthetool head (2) isdesignedwith a shortfrusto-conical surface (2b) and the tool holder (1) is provided with a corresponding counter4rusto-conical surface (1 b) for centering, and in that, for the purpose of axial determination of position of the tool head (2) on the tool carrier (1 ) provision is made atthe end of the great diameter of the conical surfaces (1 b, 2b) for, in each case, an end face (1 a, 2a) which, in the clamped condition, as a result of the axial pulling force of the drawing element (5, 9), lies free from play against its corresponding one, just as the conical surfaces (1 b, 2b).

2. A device according to Claim 1, characterised in thatthetool head (2) is provided with a tapped hole (2c) into which a tension bolt (5), arranged in the tool carrier (1 ) and acting as a drawing element, directly engages.

3. A device according to Claims 1 and 2, characterised in that the tension bolt(5) is slidably mounted between two end positions in the tool holder (1 ) and is loaded by a spring (7) operating in the pull-on direction ofthetool head (2).

4. A device according to Claim 1, characterised in that behind the inner conical surface (2b) in the tool head (2) an annular groove (2d) oftrapezoidal shape in cross-section is formed, into which radially adjustable clamping elements (8a) with clamping surfaces corresponding to the annular groove (2d) engage, and which are adjustable by means of an axial movement ofthe drawing element (9).

5. A device according to Claim 4, characterised in that the drawing element (9) is provided with an actuation screwforthe radial adjustment ofthe clamping elements (8a).

6. A device according to Claim 4, characterised in that the drawing element (9), for the radial adjustment of the clamping elements (8a) in the pull-on direction ofthe tool head (2) is permanently loaded by at least one spring (12) and is slidable in the opposite direction by a force which can be applied from the outside.

7. A device according to Claim 8, characterised in that the drawing element (9) for the radial adjustment of the clamping elements (8a) can be actuated by a pressure-medium cylinder (1d,9c,1e)incorporated in the tool carrier(1).

8. A device according to at least one of claims 1 to 7, characterised inthatthe clamping elements (8a) are provided on a slit master gripping collet (8) and are adjustable, by means of the conical head (9a) of the drawing element (9) radially outwards gainstthe own spring action ofthe master gripping collet(8).

9. A device according to claim 1, substantially as described with reference to Figures 1 and 2, Figure 3, Figure 4, or Figure 5 ofthe accompanying drawings.