Title of Invention

HYDRAULIC EXPANDING CHUCK

Abstract

The invention relates to a hydraulic expanding chuck (1), which has a particularly advantageous long, narrow design. The tool end (3) of the expanding chuck (1) is equipped with an expanding bushing (10) that is surrounded by a pressure chamber (12), which can be radially deformed in order to clamp a tool by means of a hydraulic fluid (F) that is contained in said pressure chamber (12). A pressure generation unit (14) is situated at an axial distance from the expanding bushing (10) and a pressure conduction system (13) is provided to transfer pressure from the pressure generation unit (14) to the pressure chamber (12), said pressure conduction system being formed by an annular gap (11) that is concentric with the chuck axis (2).

Full Text

Hydraulic Expanding Chuck The invention relates to a hydraulic expanding chuck for clamping a tool, in particular a drill or milling cutter. A chuck serves for connecting a driven rotary tool with the drive spindle of a machine tool. Therefore, a chuck has a distinct chuck axis around which the chuck and the tool clamped in it are rotated during operation. In direction of this chuck axis, a chuck always has a tool end provided for receiving the tool and a machine end designed for connect-ing the chuck with the drive spindle of the machine tool. A category of chucks known per se are the so-called hydraulic expanding chucks. In such an expanding chuck, the adaptor for the tool is formed by a thin-walled expanding bushing. The expanding bushing is surrounded by a pressure chamber filled with a hydraulic fluid, e.g. an oil. The expanding chuck is designed in such a way that upon pressurization of the hydrau-lic fluid, it is elastically deformed in radial direction, thus clamping the inserted tool. A hydraulic expanding chuck offers in particular the advantage of damping vibrations and impacts occurring during operation. In this way, a particularly good surface quality and a long service life of the tool is achieved in the machining operations. Such a hydraulic expanding chuck is known from WO 03/095132 A1. In the known expanding chuck, the pressure chamber is formed between an expanding bushing integrally formed with a basic body, and a clamping ring screwed onto the basic body. By screwing the clamping ring relative to the basic body, the volume of the pressure chamber can be reduced or increased and thus, the hydraulic fluid can be pressurized or relieved. Contrary to the above-described expanding chuck, a hydraulic expanding chuck often comprises a pressure generation unit, formed e.g. as a piston/cylinder unit, which is arranged with an axial offset relative to the pressure chamber and the expanding bushing in direction of the tool end. Such a expanding chuck is known, for example, from WO 98/39123 A1. For transferring the pressure from the pressure generation device to the pressure chamber, this chuck comprises an oil-guiding system consisting of fine connecting holes formed into the chuck material. A chuck slipped onto a work shaft with an expanding bushing clamping both radially outwardly and radially inwardly is, furthermore, known from DE 743 530 C. In particular in the mould and die making industry, very long and narrow chucks are needed. Common expanding chucks, however, cannot be constructed in such long and narrow designs, or can only be constructed with considerable expenditure. For example, in a particularly narrow expanding chuck, a movable clamping ring, as is known from WO 03/095132 A1, cannot be mounted, for reasons of space. Furthermore, connecting holes, as are known from WO 98/39123 A1 for pressure transfer, cannot be realized due to the small wall thickness of a narrow chuck, or can only be realized with great expenditure. In addition, the technical expenditure for producing a correspondingly longer connecting hole increases drastically with increasing length of the chuck. Another problem is the fact that upon pressurization, strains develop in the material of the ex-panding chuck, also in the area of each connecting hole, which may lead to a sensible bending of the chuck and, therefore, to an impairment of the concentric running accuracy of the tool. The invention is based on the objective to provide a hydraulic expanding chuck which can be realized with relatively little expenditure in a long and narrow design and which is characterized by advantageous application properties. This problem is solved by the invention by means of the features of claim 1, according to which an expanding bushing for receiving and clamping a tool is provided on the tool end of the expanding chuck. To generate a pressure hydraulicaliy deforming this ex-panding bushing, the chuck includes a pressure generation unit arranged with an axial offset relative to the expanding bushing and the pressure chamber surrounding it. To transfer the pressure applied over the axial distance between the pressure chamber and the pressure generation unit, the expanding chuck includes a pressure conduction system, formed according to the invention by a closed annular gap or channel arranged ‘ concentrically with the chuck axis. In this way, the pressure chamber is axially extended through the pressure conduction system, in particular without transition, up to the pressure generation unit. As compared with an ordinary drill-hole used as a pressure conduction system, an annular gap with a comparable cross-sectional area has in general a considerably smaller radial dimension. An annular gap having a cross-sectional area which is sufficient for pressure transfer can, therefore be provided in a space-saving way even in an extremely narrow expanding chuck. Furthermore, the strains developing in the material of the chuck in the area of the annular pressure conduction system under pressurization are always rotationally symmetrical around the chuck axis, so that the expanding chuck cannot asymmetrically be deformed and, consequently, the concentric running accuracy of the expanding chuck during operation is not impaired. An annular and concentric pressure conduction system can be realized in a particularly simple way through a two-piece construction of the expanding chuck. The latter comprises in a preferred embodiment of the invention a central basic body whose tool end carrier the expanding bushing and a clamping sleeve slipped onto this basic body on the tool side. By choosing a suitable dimension of the inner diameter of the clamping sleeve and the outer diameter of the basic body, it is provided that an annular gap is formed between the basic body and the clamping sleeve constituting the pressure chamber and the axially adjacent pressure conduction system. For the sake of a simple and stable construction, it is preferably provided that the basic body and the clamping sleeve are joined to each other in a rigid and pressure-tight way, in particular by brazing. A geometry of the expanding chuck which is advantageous in view of space saving is achieved by arranging the pressure generation unit inside the clamping sleeve. A pressure generation unit with a piston/cylinder system is advantageous both in view of a simple manufacture and in view of a simple handleability of the expanding chuck. This system comprises a pressure piston guided in a cylindrical drill-hole or optionally in a sleeve inserted in such drill-hole. A simple filling of pressure chamber, pressure conduction system and pressure generation unit with the hydraulic fluid is achieved by means of a filling hole, angled from the cylindrical hole, which connects the cylindrical hole with the pressure conduction system. In a particularly simple and efficient realization, the pressure piston can be actuated by means of a clamping screw. In one design of the expanding chuck according to the invention, which is particularly advantageous for mould and die making, the clamping sleeve runs out on the tool side in a long stretched-out, thin neck portion whose axial length is at least four times its outer diameter. In particular, the length of this neck portion is at least 100 mm. A particular advantage of the expanding chuck according to the invention lies in the fact that with relatively little expenditure, a very narrow tool adaptor, given through the inner diameter of the expanding bushing, can be achieved. The inner diameter of the ex-panding bushing is preferably 12 mm, but can also be considerably smaller or larger. Conventional expanding chucks often require for chucking such thin tools a reducer for the tool, which can be inserted into the adaptor of the chuck. This may have a negative effect on the concentric running accuracy of the tool. To achieve an efficient clamping effect of the expanding chuck, it is considered as advantageous to keep the total volume of the entire pressure system, i.e. pressure chamber, pressure conduction system and pressure generation device, as small as possible. This is achieved in an advantageous development of the invention by choosing a very small radial dimension of the annular gap constituting the pressure conduction system and the pressure chamber. Suitably, the radial extension of the annular gap is maximally 0.2 mm, preferably approx. 0.1 mm. This extremely thin design of the annular gap additionally saves space and is, therefore, advantageous in view of particular slim designs of the expanding chuck. The annular design of the pressure conduction system offers space in the central area of the expanding chuck, which, consequently, can advantageously be used for other purposes. In one advantageous embodiment of the invention, the basic body is provided with a central passage, which can be used, for example, as a coolant channel. In another advantageous embodiment of the invention, an axial adjustment unit is provided for the tool, which is also preferably arranged in the central area of the expanding chuck. In a suitable embodiment, this axial adjustment device comprises a set pin, axially adjustable relative to the basic body, which serves as an axial stop for the tool to be clamped and is preferably guided in a central hole of the basic body. In an embodiment of a particularly simple construction, the set pin in the basic body is axially adjustable, like a screw. For this purpose, the set pin has an external thread cooperating with an internal thread in the central hole of the basic body. In one variant with a particularly advantageous handling, the set pin is adjustable by means of a radially accessible set screw, so that the axial adjustment can be actuated even if the tool has already been inserted. The inner end of the set screw, which is preferably guided in the basic body, is provided with a spiral thread that combs with an axial-linear toothing of the set pin. In the following, some embodiments of the invention are explained in detail with reference to the drawings, in which Fig. 1 is a perspective view of a hydraulic expanding chuck for clamping a tool, Fig. 2 is a side view of the expanding chuck according to Fig. 1, Fig. 3 is a longitudinal section Ill-Ill of the expanding chuck according to Fig. 2, Fig. 4 is a cross-section IV-IV of the expanding chuck according to Fig. 2, Fig. 5 is a longitudinal section of the expanding chuck according to Fig. 2, rotated around the chuck axis, as compared with Fig. 3, and Fig. 6 is a view of the expanding chuck according to Fig. 5 with an alternative design of the axial adjustment unit for the tool to be clamped. In all figures, corresponding components and sizes are always designated with the same reference numbers. The hydraulic expanding chuck (hereinafter referred to briefly as expanding chuck 1) shown in Figs. 1 to 4 in different representations serves for clamping a driven rotary tool (not shown), in particular a drill or a milling cutter, on the drive spindle of a machine tool (not shown either). The expanding chuck 1 is substantially rotationally symmetrical around a chuck axis 2 forming the axis of rotation and includes, viewed in direction of this chuck axis 2, a tool end 3 and a machine end 4. In the area of the tool end 3, the expanding chuck 1 is elongated into a long stretched-out and narrow neck portion 5, whose free end is provided with an adaptor 6 for a tool. The axial length L of the neck portion 5 is four to five times the outer diameter D. Preferable dimensions are a length L of 100 mm with an outer diameter of 20 mm and an inner diameter d of the adaptor 6 of 12 mm. Even longer and/or narrower designs of the expanding chuck 1 or even smaller inner diameters d can, however, also be realized. The machine end 4 is provided with a fastening cone 7, executed e.g. as an HSK shank, for connecting the expanding chuck 1 to the drive spindle. The expanding chuck 1 is substantially of a two-piece construction and comprises a central basic body 8, onto the tool area of which an approximately bell-shaped clamping sleeve 9 is slipped. The basic body 8 and the clamping sleeve 9 are joined to each other by brazing both on the tool side and on the machine side and are, therefore, joined in a rigid and pressure-tight manner. In the area of the adaptor 6, the basic body 8 is a thin-walled hollow cylinder. This thin-walled portion of the basic body 8 is called expanding bushing 10. The expanding bushing 10 is preferably formed integrally with the basic body 8, but can also be formed of a separate part. Between the inner wall of the expanding bushing 9 and the opposite outer wall of the basic body 8 in the neck portion 5, an annular gap 11 is formed. This annular gap 11 has only an extremely small radial extension R of preferably 0.1 mm (corresponding to approximately one tenth of the wall thickness of the expanding bushing 10) and can, therefore, for reasons of resolution, be recognized as such only in the enlarged Fig. 4, and here, above all, in the further enlarged detail A. In Fig. 3, the annular gap 11 is only visible sketchily as a thick black line. The annular gap 11 extends in axial direction over a large part of the length of the clamping sleeve 9 and forms in the area of the adaptor 6 a pressure chamber 12, in which a liquid hydraulic fluid F, in particular an oil, is received. The area of the annular gap 11 extending beyond the pressure chamber 12 in the direction of the machine end 4 constitutes a pressure conduction system 13, which fluidly connects the pressure chamber 12 with a pressure generation unit 14, which is axially offset relative to the pressure chamber 12, thus enabling a pressure transfer from the pressure generation unit 14 to the pressure chamber 12. In unloaded condition, the radial extension R is substantially constant over the entire length of the annular gap 11, so that the pressure chamber 12 merges into the pressure conduction system 13 without transition. As is apparent in particular from Fig. 4, the pressure generation unit 14 comprises a cylindrical hole 15 in which a pressure piston 16 is arranged. The pressure piston 16 is guided either directly in the cylindrical hole 15 or - as shown in Fig. 4 - adjustably in a sleeve 17 inserted into the cylindrical hole 15. The pressure piston 16 can be actuated by means of a clamping screw 18. The inner end of the pressure piston 16 carries a sealing 19 made of an elastic material, in particular a rubber elastomer. The pressure generation unit 14 also comprises a filling hole 20, extending from the inner end of the cylindrical hole 15 at such an angle that it approximately touches the annular gap 11. The filling hole 20 is, therefore, fluidly connected both with the cylindrical hole 15 and, through a connecting groove 21, with the annular gap 11. By means of a ball sealing 22, the filling hole 20 is sealed, pressure-tight, against the environment. Before putting the expanding chuck 1 into operation, the common volume of pressure cylinder 15, filling hole 20 and annular gap 11 is filled completely with the liquid hydraulic fluid F by means of the opened filling hole 20. To avoid air bubbles in the pressure system, this is done in a vacuum. After filling, the filling hole is sealed, pressure-tight, by means of the ball sealing 22. For clamping a tool inserted into the adaptor 6, the clamping screw 18 and, with that, the pressure piston 16 in the cylindrical hole 15 can be adjusted by means of a screw driver and, in this way, the volume of the cylindrical hole 15 filled with the hydraulic fluid F, can be reduced. By doing so, a hydrostatic pressure of typically up to 1000 bar can be applied on the hydraulic fluid F. This pressure is transferred through the annular gap 11, serving as pressure conduction system 13, up to the area of the pressure chamber 12, where the hydrostatic pressure causes a deformation of the thin-walled expanding bushing 10, directed radially inwardly towards the chuck axis 2, said deformation clamping the inserted tool in the adaptor 6. As compared to that, the wall thickness of the clamping sleeve 9, defining the outside of the pressure chamber 12, is relatively large, the pressure effect does not cause a significant deformation on the outer circumference of the expanding chuck 1. To remove the tool from the expanding chuck 1, the pressure piston 16 is reset by some revolutions of the clamping screw 18, which relieves the hydraulic fluid F. The elastically deformable expanding bushing 10 resumes its original shape, so that the tool can be removed. The expanding chuck 1 comprises, furthermore, an axial adjustment unit 23 for the tool, which can be seen particularly well in the longitudinal section according to Fig. 2, rotated as compared with Fig. 3. The axial adjustment unit 23 comprises a set pin 24, approximately in the shape of a hollow cylinder, which slides in a central hole 25 of the basic body 8, the tool end 26 of the set pin 24 protruding into the adaptor 6 and thus forming an axial stop for the tool to be inserted into the adaptor 6. To allow an axial setting of the set pin 24 and, thus, of the stop for the tool, the set pin 24 is provided near its machine end 27 with an axial-linear toothing 28. This toothing combs with a spiral thread 29, which is provided on the end-side of a set screw 30, which is substantially guided in the basic body 8 in radial direction relative to the chuck axis 2. It is an ad-vantage of this construction that the radial set screw 30 is accessible even after a tool has been inserted into the adaptor 6. In-a variant of the axial adjustment unit 23 of simplified construction, shown in Fig. 6, the set pin 24 is provided with an external thread 31 corresponding with an internal thread 32 of the hole 25. In this embodiment, the set pin 24 can be adjusted by means of a screw driver introduced into the adaptor 6. In both described embodiments of the expanding chuck 1, the hole 25 and an aligned hole 33 of the set pin 24 form a passage 34 along the chuck axis 2, said passage 34 being in particular usable as coolant channel through which coolant can be directed during operation by the machine tool into the area of the adaptor 6 and, thus, into the area of the tool. Furthermore, a balancing face 35, i.e. a milled-off surface specifically calculating the axial geometry of the basic body 8, is provided on the circumference of the basic body 8, said balancing face 35 precisely compensating an unbalance generated by the nonsymmetrical pressure generation unit 14. In this way, a very precise concentric running is achieved during operation of the expanding chuck 1, even at relatively high rotational speeds, which is particularly important in particular in view of the long, narrow design. Instead of the milled balancing face 35, a balancing screw screwed into the basic body 8, one or several balancing disks or other milled-out sections or drill-holes can be provided. List of reference numbers 1 (Hydraulic) expanding chuck 22 Ball sealing 2 Chuck axis 23 Axial adjustment unit 3 (Tool) end 24 Set pin 4 (Machine) end 25 Drill-hole 5 Neck portion 26 (Tool) end 6 Adaptor 27 (Machine) end 7 Fastening cone 28 Toothing 8 Basic body 29 Spiral thread 9 Clamping sleeve 30 Set screw 10 Expanding bushing 31 External thread 11 Annular gap 32 Internal thread 12 Pressure chamber 33 Drill-hole 13 Pressure conduction system 34 Passage 14 Pressure generation unit 35 Balancing face 15 Cylindrical hole 16 Pressure piston L Length 17 Sleeve D Outer diameter 18 Clamping screw d Inner diameter 19 Sealing R Radial extension 20 Filling hole F Hydraulic fluid 21 Connecting groove A Detail Claims 1. Hydraulic expanding chuck (1) with an expanding bushing (10) which is arranged on the tool end (3) thereof and which is surrounded by a pressure chamber (12), which can be radially deformed in order to clamp a tool by means of a hydraulic fluid (F) that is contained in said pressure chamber (12), with a pressure generation unit (14) situated at an axial distance from the expanding bushing (10), related to a chuck axis (2), and a pressure conduction system (13) to transfer pressure from the pressure generation unit (14) to the pressure chamber (12), characterized in that the pressure conduction system (13) is formed by an annular gap (11) that is concentric with the chuck axis (2). 2. Expanding chuck (1) according to claim 1, characterized by a basic body (8) which is central relative to the chuck axis (2) and carries the expanding bushing (10), and a clamping sleeve (9) concentrically surrounding said basic body (8), the pressure chamber (12) and the pressure conduction system (13) being formed between the basic body (8) and the clamping sleeve (9). 3. Expanding chuck (1) according to claim 1 or 2, characterized in that the basic body (8) and the clamping sleeve (9) are joined to each other in a rigid and pressure-tight way. 4. Expanding chuck (1) according to any of claims 1 to 3, characterized in that the pressure generation unit (14) is arranged in the clamping sleeve (9). 5. Expanding chuck (1) according to any of claims 1 to 4, characterized in that the pressure generation unit (14) comprises a cylindrical hole (15) with a pressure piston (16) adjustable in it, as well as a filling hole (20) connecting the cylindrical hole (15) with the pressure conduction system (13). 6. Expanding chuck (1) according to claim 5, characterized in that the pressure piston (16) is adjustable by means of a clamping screw (18). 7. Expanding chuck (1) according to any of claims 1 to 6, characterized in that the clamping sleeve (9) has on the tool side a long stretched-out thin neck portion (5) whose axial length (L) is at least four times its outer diameter (D). 8. Expanding chuck (1) according to claim 7, characterized in that the axial length (L) of the neck portion is at least 100 mm. 9. Expanding chuck (1) according to any of claims 1 to 8, characterized in that the radial extension (R) of the annular gap (11) is maximally 0.2 mm. 10. Expanding chuck (1) according to any of claims 1 to 9, characterized in that the basic body (8) includes a central passage (34). 11. Expanding chuck (1) according to any of claims 1 to 10, characterized by an axial adjustment unit (23) for the tool. 12. Expanding chuck (1) according to claim 11, characterized in that the axial adjustment unit (23) comprises a set pin (24) adjustable in axial direction relative to the basic body (8), forming an axial stop for the tool. 13. Expanding chuck (1) according to claim 12, characterized in that the set pin (24) is guided in a central hole (25) of the basic body (8). 14. Expanding chuck (1) according to claim 13, characterized in that the set pin (24) has an external thread (31) which cooperates with an internal thread (32) of the hole (25) for axial adjustment of the set pin (24). 15. Expanding chuck (1) according to claim 13, characterized in that the set pin (24) is provided with an axial-linear toothing (28) which cooperates with a spiral thread (29) of a set screw (30) guided in the basic body (8), substantially radially relative to the chuck axis (2), for axial adjustment of the set pin (24). 16. Expanding chuck (1) according to any of claims 1 to 15, characterized by a balancing face (35) milled into a portion of the circumference, for compensating an unbalance caused by the pressure generation unit (14).

Documents:

3650-chenp-2006 correspondence others 18-07-2011.pdf

3650-CHENP-2006 FORM-13 18-07-2011.pdf

3650-chenp-2006 power of attorney 18-07-2011.pdf

3650-CHENP-2006 AMENDED CLAIMS 22-05-2012.pdf

3650-CHENP-2006 AMENDED PAGES OF SPECIFICATION 22-05-2012.pdf

3650-CHENP-2006 CORRESPONDENCE OTHERS 19-07-2012.pdf

3650-CHENP-2006 EXAMINATION REPORT REPLY RECEIVED 22-05-2012.pdf

3650-CHENP-2006 FORM-1 22-05-2012.pdf

3650-CHENP-2006 FORM-13 22-05-2012.pdf

3650-CHENP-2006 FORM-3 22-05-2012.pdf

3650-CHENP-2006 FORM-5 22-05-2012.pdf

3650-CHENP-2006 OTHER PATENT DOCUMENT 22-05-2012.pdf

3650-CHENP-2006 POWER OF ATTORNEY 22-05-2012.pdf

3650-chenp-2006-abstract.pdf

3650-chenp-2006-claims.pdf

3650-chenp-2006-correspondnece-others.pdf

3650-chenp-2006-description(complete).pdf

3650-chenp-2006-drawings.pdf

3650-chenp-2006-form 1.pdf

3650-chenp-2006-form 26.pdf

3650-chenp-2006-form 3.pdf

3650-chenp-2006-form 5.pdf

3650-chenp-2006-pct.pdf