Abstract:
The invention relates to a hydraulic expansion chuck having an end on the tool side; and an end on the machine side. A shaft is disposed on the end on the machine side for clamping the expansion chuck in a machine tool. An expanding bushing is disposed on the end on the tool side and surrounded by a pressure chamber and can be radially deformed for clamping a tool under the action of a pressure medium received in the pressure chamber.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a hydraulic expansion chuck for clamping in a tool, in particular a drill or milling cutter. 
     2. Description of the Related 
     A chuck serves to connect a rotationally driven tool to the drive spindle of a machine tool. A chuck therefore has a pronounced chuck axis, about which the chuck and the tool which is clamped therein are rotated during operation. In the direction of this chuck axis, a chuck always has a tool-side end which is provided for receiving the tool and a machine-side end which is configured for connecting the chuck to the drive spindle of the machine tool. At the machine-side end, a chuck of this type as a rule carries a conical shaft, in particular a steep shaft, what is known as an HSC (hollow shaft cone) shaft or the like. 
     What are known as the hydraulic expansion chucks form a category known per se of chucks. In an expansion chuck of this type, the receptacle for the tool is formed by a thin-walled expansion bushing. The expansion bushing is surrounded by a pressure chamber which is filled with a pressure medium, for example an oil. The expansion bushing is configured in such a way that, if pressure is applied to the pressure medium, it is elastically deformed radially and in the process clamps in the inserted tool. A hydraulic expansion chuck has the advantage, in particular, that it damps jolts and vibrations which occur during operation. As a result, a particularly high surface quality and a long service life of the tool are achieved during machining. 
     WO 2005/097383 has disclosed a hydraulic expansion chuck of this type which can advantageously be used, in particular, in mold and die construction and has a long and narrow design which is required for this purpose. The known expansion chuck has a basic body which carries, at its tool-side end, the shaft which is provided for clamping the expansion chuck in the machine tool. An approximately bell-shaped clamping sleeve which is drawn out at the free end to form an elongate and narrow neck region is placed onto the basic body on the tool side. Here, a thin-walled and hollow-cylindrical projection of the basic body extends within the clamping sleeve as far as its free end, the pressure chamber being formed at this end between the projection of the basic body and the clamping sleeve. Here, the expansion bushing is formed in the inner region of the basic body, which inner region adjoins the pressure chamber. Here, a narrow annular gap which is concentric with respect to the chuck axis is formed between the outer circumference of the basic body and the clamping sleeve, which annular gap, as a pressure transfer channel, connects the pressure chamber to a pressure generation unit, the latter being accommodated in a widened, machine-side section of the clamping sleeve. 
     The known hydraulic expansion chuck is advantageous for producing very long, narrow chuck designs. However, the production of the expansion chuck is comparatively complicated. This relates, in particular, to the production of the thin-walled projection of the basic body and the pressure-tight soldering of the clamping sleeve to the basic body. 
     DE 100 07 074 A1 has disclosed a further expansion chuck. Said expansion chuck comprises a single piece basic body, on the machine-side end of which once again a shaft is formed, while the tool-side end of the basic body forms a clamping sleeve. Here, an inner sleeve which is separate from the basic body, and therefore also from the clamping sleeve, is inserted into the clamping sleeve, which inner sleeve contains an expansion bushing and delimits, on the inner side, a pressure chamber which surrounds it. At its tool-side end, the inner sleeve is provided with an outwardly protruding annular collar which overlaps with the clamping sleeve. Here, the annular collar extends over part of the radial width of the clamping sleeve which surrounds the annular collar on the outside. The interface which is formed between the annular collar and the clamping sleeve otherwise opens into the tool-side end face of the expansion chuck. 
     SUMMARY OF THE INVENTION 
     The invention is based on the object of specifying an improved hydraulic expansion chuck which is advantageous, in particular, for realizing long and narrow designs. 
     According to the invention, this object is achieved by the features of claim  1 . The expansion chuck according to the invention comprises a tool-side end and a machine-side end, a shaft for clamping the expansion chuck in a machine tool being arranged at the machine-side end, and an expansion bushing being arranged at the tool-side end, which expansion bushing is surrounded by a pressure chamber and can be deformed radially to clamp in a tool under the action of a pressure medium which is accommodated in the pressure chamber. The machine-side end of the expansion chuck is formed by a basic body which also carries the shaft and to which, on the tool side, a clamping sleeve which adjoins the pressure chamber on the outside is attached rigidly. 
     According to the invention, an inner sleeve is inserted into the interior of the clamping sleeve, which inner sleeve is manufactured as a separate component and is therefore not integrally connected to either the clamping sleeve or the basic body. Said inner sleeve contains the expansion bushing and delimits the pressure chamber on the inside. At its tool-side end, the inner sleeve is provided with a radially outwardly protruding annular collar, by way of which the inner sleeve overlaps with the clamping sleeve in the radial direction. The annular collar is therefore designed in such a way that it protrudes beyond the inner circumference of the clamping sleeve. 
     The substantially three part production of the expansion chuck (in the form of the basic body, the clamping sleeve and the separate inner sleeve) is substantially simplified in terms of manufacturing technology in comparison with the known solution, in which a projection which is connected integrally to the basic body is provided instead of the separate inner sleeve. The pressure-tight soldering of the expansion chuck at the machine-side edge of the pressure conducting region is also simplified substantially as a consequence of the three piece design, especially since the machine-side part of the clamping sleeve and of the inner sleeve which pushed into it is directly accessible before mounting of the basic body. At the same time, the connecting point between the clamping sleeve and the inner sleeve is protected by the annular collar, by way of which the inner sleeve overlaps the clamping sleeve at the machine-side end of the expansion chuck. In particular, damage to this connecting region as a result of friction with chips, or the like is avoided effectively. 
     In order to make the expansion chuck particularly insensitive to chip abrasion, the annular collar extends over the entire width of the clamping sleeve. Here, the annular collar terminates approximately flushly with the outer circumference of the clamping sleeve, in particular on the outside. As a result, an interface formed between the clamping sleeve and the inner sleeve on the outer side of the expansion chuck does not open axially, but rather radially at the outer circumference of the expansion chuck. As a result, the transport of chips takes place approximately perpendicularly with respect to the outer region of the interface, as a result of which the chips can exert a comparatively low force on the chuck material in the opening region of the interface. 
     In order to improve the protective effect, in one advantageous embodiment of the invention, in longitudinal section through the expansion chuck, the annular collar is provided with an at least two step contour which bears sealingly with a complementarily shaped recess against the tool-side edge of the clamping sleeve. As a consequence of this contour, an interface is therefore formed in the region of the annular collar between the clamping sleeve and the inner sleeve, which interface is kinked at least twice in longitudinal section, in particular in each case by approximately 90°, approximately in the manner of a labyrinth seal. Here, at least in a part region of the interface, the clamping sleeve is connected to the inner sleeve with a material-to-material fit, namely is preferably soldered, in particular brazed. 
     A particularly stable connection of the clamping sleeve to the inner sleeve is achieved as a consequence of the “labyrinthine” profile of the interface and as a consequence of the annular collar which protrudes beyond the clamping sleeve. This connection is stable both against the pressures which act from the inside, that is to say from the pressure chamber, and against the loads which act from the outside on the tool-side end of the expansion chuck, namely, in particular, the axial pressure which is transmitted from the tool to the inner sleeve, including the vibrations which occur during operation of the expansion chuck. In addition, the connecting face is also protected effectively against the abrasion forces as a result of chips, which abrasion forces are exerted on the tool-side end of the expansion chuck from the outside. 
     The clamping sleeve preferably has a through hole which penetrates the inner sleeve completely. The inner sleeve is preferably even lengthened in comparison with the length of said through hole and therefore protrudes beyond the machine-side end of the through hole. The inner sleeve therefore engages in a positively locking manner into the basic body which adjoins the clamping sleeve on the machine side. 
     In order to generate a pressure which deforms the expansion bushing hydraulically, the chuck expediently has a pressure generation unit which is arranged offset axially with respect to the expansion bushing and the pressure chamber which surrounds it. In order to transmit the applied pressure over the axial distance between the pressure chamber and the pressure generation unit, the expansion chuck contains a pressure conducting system which is advantageously formed by an annularly closed gap or channel which is arranged concentrically with regard to the chuck axis. 
     In comparison with a customary hole as pressure conducting system, an annular gap with a comparable cross-sectional area has a generally substantially smaller radial extent. An annular gap with a sufficient cross-sectional area for pressure transmission can therefore also be attached in a space-saving manner in the case of an extremely narrow expansion chuck. Moreover, the stresses introduced under pressure application into the material of the chuck in the region of the annular pressure conducting system are always rotationally symmetrical with regard to the chuck axis, with the result that no asymmetrical deformation of the expansion chuck can occur and therefore the true running of the expansion chuck during operation is not impaired. 
     An annular and concentric pressure conducting system is particularly simple to produce using the three part production of the expansion chuck, in which the annular gap is formed between the inner sleeve and the clamping sleeve. 
     A geometry of the expansion chuck which is advantageous with regard to saving space is achieved by the fact that the pressure generation unit is arranged in the clamping sleeve. Here, a pressure generation unit with a piston/cylinder system is advantageous both with regard to simple production and with regard to a simple handling capability of the expansion chuck. Said piston/cylinder system comprises a pressure piston which is guided in a cylinder bore or a sleeve which is optionally inserted into a bore of this type. Simple filling of the pressure chamber of the pressure conducting system and of the pressure generation unit with the pressure medium is achieved by a filling hole which is angled away from the cylinder bore and connects the cylinder bore to the pressure conducting system. In one particularly simple and effective realization, the pressure piston can be actuated by means of a clamping screw. 
     In one design of the expansion chuck according to the invention which is advantageous, in particular, for mold and die construction, the clamping sleeve is drawn out on the tool side to form an elongate, narrow neck region, the axial length of which is at least four times its external diameter. In particular, the length of the neck region is at least 100 mm. 
     In one advantageous refinement, the radial extent of the annular gap is at most 0.2 mm, preferably approximately 0.1 mm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following text, one exemplary embodiment of the invention will be described in greater detail using a drawing, in which: 
         FIG. 1  shows a perspective illustration of a hydraulic expansion chuck for clamping in a tool, 
         FIG. 2  shows a side view of the expansion chuck according to  FIG. 1 , 
         FIG. 3  shows, in a longitudinal section according to  FIG. 2 , the expansion chuck there, 
         FIG. 4  shows an enlarged illustration of a detail IV from  FIG. 3 , 
         FIG. 5  shows, in a cross section V-V according to  FIG. 2 , the expansion chuck there, and 
         FIG. 6  shows an enlarged illustration of a detail VI from  FIG. 5 . 
     
    
    
     Parts and variables which correspond to one another are always provided with identical designations in all the figures. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The (hydraulic) expansion chuck  1  shown in various illustrations in  FIGS. 1 to 6  serves to clamp in a rotationally driven tool (not shown), in particular a drill or milling cutter on the drive spindle of a machine tool (likewise not shown). The expansion chuck  1  is of substantially rotationally symmetrical configuration with regard to a chuck axis  2  which forms the rotational axis, and has a tool-side end  3  and a machine-side end  4  as viewed in the direction of said chuck axis  2 . In the vicinity of the tool-side end  3 , the expansion chuck  1  is drawn out to form an elongate and narrow neck region  5  which has a receptacle  6  for the tool on the free end side, that is to say at the tool-side end  3 ). 
     Here, the axial length L ( FIG. 2 ) of the neck region  5  is four times to five times its external diameter D ( FIG. 2 ). In a preferred size, the length L of the neck region is approximately 100 mm in the case of an external diameter of 20 mm and an internal diameter d of the receptacle  6  of 12 mm. However, an even longer and/or narrower design of the expansion chuck  1  or an even lower internal diameter d can also be realized. The machine-side end  4  is provided with a shaft, for example configured as an HSC shaft (called fastening cone  7  in the following text), for connection of the expansion chuck  1  on the drive spindle. 
     As can be seen, in particular, from the sectional illustration according to  FIG. 3 , the expansion chuck  1  is substantially configured in three pieces. It comprises a basic body  8  which forms the machine-side part of the expansion chuck  1  and on which the fastening cone  7  is also formed. Furthermore, the expansion chuck  1  is formed from an approximately bell-shaped clamping sleeve  9 . The clamping sleeve  9  is placed with a widened annular region  10  onto the tool-side end of the basic body  8 . The clamping sleeve  9  tapers in a stepped manner toward the tool-side end  3  of the expansion chuck  1  in order to form the narrow neck region  5 . In its interior, the clamping sleeve  9  has a through hole  11  which is concentric with respect to the chuck axis  2 . As third constituent part of the expansion chuck  1 , an inner sleeve  12  ( FIG. 2 ) lies in this through hole  11 , which inner sleeve  12  penetrates the through hole  11  over its entire length and projects beyond the machine-side end of said through hole  11  into an axial hole  13  of the basic body  8 . 
     At its tool-side end  3 , the inner sleeve  12  is provided with an annular collar  14  which projects radially to the outside from the outer circumference of the inner sleeve  12 . As can be seen, in particular, from  FIG. 4 , said annular collar  14  has a two step contour in longitudinal section, in the course of which the external diameter of the inner sleeve  12  first of all widens in a first step in the direction of the tool-side end  3  to a center region  15 , the outer face of which is offset parallel to the circumferential face of the inner sleeve  12 . Starting from said center region  15 , the annular collar  14  is then widened in a second step toward the tool-side end  3  to form an end section  16  which is widened again. 
     The annular collar  14  corresponds with a recess  17  at the tool-side end of the through hole  11 , which recess  17  is shaped in a complementary manner with respect to said annular collar  14 , with the result that the inner sleeve  12  and the clamping sleeve  9  bear sealingly against one another in the region of the annular collar  14  and the recess  17 . Therefore, as can be seen, in particular, from  FIG. 4 , the interface  18  which is formed in that region between the inner sleeve  12  and the clamping sleeve  9  has a profile in longitudinal section which is kinked twice by in each case an angle of approximately 90°. Here, the annular collar  14  extends in the radial direction over the entire width of the clamping sleeve  9 , with the result that the end section  16  of the annular collar  14  terminates, radially on the outside, approximately flushly with the outer circumference of the clamping sleeve  9 , and the interface  18  opens in the radially outward direction on the circumferential face of the neck region  5 . The clamping sleeve  9  and the inner sleeve  12  are brazed to one another in a pressure-tight manner in an outer part section of the interface  18 . Toward the machine-side end  4 , the clamping sleeve  9  and the inner sleeve  12  are brazed to one another in a pressure-tight manner at the machine-side edge of the through hole  11 . Here, an annular groove  20  which is made in the wall of the through hole  11  ( FIG. 3 ) serves as solder flow stop in order to limit the soldered surface. 
     In its interior, the inner sleeve  12  has a hole which is concentric with respect to the chuck axis  2  and forms the receptacle  6 . The inner sleeve  12  is of thin-walled configuration in the region of the receptacle  6 . Said thin-walled region of the inner sleeve  12  forms an expansion bushing  21  which can be deformed radially in order to clamp in the tool. The expansion bushing  21  is preferably configured integrally with the inner sleeve  12 , but as an alternative can also be formed from a separate part. An approximately hollow-cylindrical void which acts as a pressure chamber  22  is formed in the region of the expansion bushing  21  between the inner wall of the clamping sleeve  9  and the opposite outer wall of the inner sleeve  12 . Said pressure chamber  22  merges at the machine-side end of the receptacle  6  into an annular gap  23  which is likewise formed between the inner wall of the clamping sleeve  9  and the outer wall of the inner sleeve  12 . Said annular gap  23  has only an extremely small radial extent R ( FIG. 6 ) of preferably 0.1 mm (corresponding to approximately 1/10 of the wall thickness of the expansion bushing  21 ) and can therefore only be seen as such in enlarged  FIGS. 4 and 6  for reasons of the resolution. In the illustration according to  FIG. 3 , the annular gap  23  can be seen only in outline as a widened black line. 
     The annular gap  23  extends in the radial direction over a large part of the length of the clamping sleeve  9  between the pressure chamber  22  and a pressure generation unit  24  ( FIG. 5 ), which is accommodated in the widened annular region  10  at the machine-side end of the clamping sleeve  9 . Here, the annular gap  23  forms a pressure conducting system which connects the pressure chamber  22  fluidically to the pressure generation unit  24  and therefore makes pressure transmission possible via a liquid pressure medium F, in particular an oil, from the pressure generation unit  24  into the pressure chamber  22 . 
     As is apparent, in particular, from  FIG. 5 , the pressure generation unit  24  comprises a cylinder bore  25 , in which a pressure piston  26  is arranged. The pressure piston  26  is guided adjustably, either directly in the cylinder bore  25  or, as shown in  FIG. 5 , in a sleeve  27  which is inserted into the cylinder bore  25 . The pressure piston  26  can be actuated by means of a clamping screw  28 . In the embodiment shown, the pressure piston  26  and the clamping screw  28  are an integral component. Here, said component is provided with an external thread which meshes with an internal thread of the sleeve  27 . The inner end of the pressure piston  26  carries a seal  29  made from an elastic material, in particular a rubber elastomer. Furthermore, the pressure generation unit  24  comprises a filling hole  30  which extends angled away from an inner end of the cylinder bore  25  in such a way that it is approximately tangent on the annular gap  23 . The filling hole  30  is therefore connected fluidically both to the cylinder bore  25  and, via a connecting groove  31 , to the annular groove  23 . The filling hole  30  is closed in a pressure-tight manner with respect to the external world by a spherical seal  32 . 
     During assembly, the inner sleeve  12  is pushed into the clamping sleeve  9  from the tool-side end  3 . After this, the basic body  8  is attached to the assembly which is formed from the clamping sleeve  9  and the inner sleeve  12 . Subsequently, in turn, the inner sleeve  12  is brazed in a pressure-tight manner to the clamping sleeve  9  and the basic body  8 . As an alternative, the clamping sleeve  9  is shrunk onto the basic body  8 . To safeguard the connection, which is formed between the basic body  8  and the clamping sleeve  9 , against rotation, a key pin  33  ( FIG. 3 ) is additionally inserted during mounting into aligned eccentric holes of the basic body  8  and the clamping sleeve  9 . 
     Before the expansion chuck  1  is commissioned, first of all the common volume of the pressure cylinder  25 , the filling hole  30 , the annular gap  23  and the pressure chamber  22  is filled completely with the liquid pressure medium F via the open filling hole  30 . In order to avoid air bubbles in the pressure system, this takes place under vacuum. After filling, the filling hole is closed in a pressure-tight manner by the spherical seal  32 . 
     In order to clamp in a tool which is inserted into the receptacle  6 , the clamping screw  28  and therefore the pressure piston  26  in the cylinder bore  25  can then be screwed in by means of a screwdriver. As a result, the volume of the cylinder bore  25  which is filled with the pressure medium F is reduced, as a result of which in turn a hydrostatic pressure of typically up to 1000 bar can be applied to the pressure medium F. This pressure is transmitted via the annular gap  23  which acts as pressure conducting system as far as into the region of the pressure chamber  22 . Here, the hydrostatic pressure brings about a deformation of the thin-walled expansion bushing  21 , which deformation is directed radially onto the chuck axis  2  and by way of which the inserted tool is clamped in the receptacle  6 . 
     In order to remove the tool out of the expansion chuck, the pressure piston  26  is reset again by a few revolutions of the clamping screw  28 , as a result of which the pressure medium F is relieved. Here, the elastically deformed expansion bushing  21  assumes its original shape again, with the result that the tool can be removed. 
     Furthermore, the expansion chuck  1  comprises an actuating journal  34  ( FIG. 3 ) for adjusting the tool axially in the receptacle  6 . The actuating journal  34  is provided with an external thread at least in a part region of its circumferential face, which external thread meshes with an internal thread of a hole  35  at the bottom of the receptacle  6 . When the tool is removed, the actuating journal  34  can be adjusted in the axial direction by means of a screwdriver which is introduced into the receptacle  6 . Along the chuck axis  2 , the expansion chuck  1  is penetrated completely by a leadthrough which is formed by aligned holes of the inner sleeve  12 , of the actuating journal  34  and of the basic body  8 . This leadthrough which is concentric with respect to the chuck axis  2  can be used, in particular, as a coolant channel. During the operation of the expansion chuck  1 , coolant can be guided through said coolant channel from the machine tool into the region of the receptacle, and therefore into the region of the tool.