Abstract:
The invention relates to a hydraulic expansion chuck with a basic body, with an expansion bush which is received in the basic body and defines a reception space for a tool to be chucked, and with a pressure chamber which is delimited between the expansion bush and the basic body, at least one solder region being provided, in which the expansion bush is soldered to the basic body, wherein, between the pressure chamber and the solder region, a seal is provided which is formed by an at least essentially fluid-tight bearing contact of the expansion bush against the basic body.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a hydraulic expansion chuck. 
         [0002]    Hydraulic expansion chucks usually have a basic body, an expansion bush which is received in the basic body and defines a reception space for a tool to be chucked, and a pressure chamber which is delimited between the expansion bush and basic body, at least one solder region being provided, in which the expansion bush is soldered to the basic body. 
         [0003]    A shank of a tool to be chucked can be inserted into the reception space of such an expansion chuck. The pressure chamber is then put under pressure, the expansion bush being loaded against the shank of the tool. The shank of the tool is then held frictionally in the reception space. 
         [0004]    When the tool received in the expansion chuck is used for roughing work, high torques have to be transmitted between the expansion chuck and the tool. So that high torques can be transmitted reliably, the pressure chamber is loaded with high pressure. This leads to high stress upon the solder region, by means of which the expansion bush is connected firmly to the basic body. 
         [0005]    The object of the invention is to provide an expansion chuck which is distinguished by a high load-bearing capacity and which has a solder region with high fatigue strength. 
       SUMMARY OF THE INVENTION 
       [0006]    To achieve this object, the invention provides an expansion chuck which has a basic body and an expansion bush which is received in the basic body and defines a reception space for a tool to be chucked. Furthermore, a pressure chamber is provided, which is delimited between the expansion bush and the basic body. To connect the expansion bush and basic body, at least one solder region is provided, in which the expansion bush is soldered to the basic body. Between the pressure chamber and the solder region, a seal is provided, which is formed by an at least essentially fluid-tight bearing contact of the expansion bush against the basic body. The seal ensures that the pressure which is generated in the pressure chamber for the purpose of chucking the tool is not present directly at the solder region. This prevents the pressure from attempting to press the two surfaces soldered to one another apart. Such load would act perpendicularly to the plane in which the solder material is located and will consequently act in a direction in which the load-bearing capacity of the solder region is comparatively low. Particularly in the case of a large number of load alternations, such as result from vibrations during milling which lead to pressure fluctuations in the pressure chamber, there is the risk that the soldered joint is damaged over the course of time. On account of the seal, according to the invention, such load upon the solder region is prevented, thus leading to a marked increase in the service life and in the load-bearing capacity of the soldered joint between the expansion bush and basic body. In this case, there is no need for any elastomeric seals or other additional components susceptible to wear; the seal according to the invention may be formed solely by the suitable interaction of surfaces of the basic body and of the expansion bush. 
         [0007]    According to a refinement to the invention, there is provision whereby the seal is formed by a press fit between the expansion bush and the basic body. Such a press fit can be achieved at low outlay. It ensures permanent prestress between the expansion bush and the basic body, so that the solder region is no longer exposed to the hydraulic fluid by which the pressure chamber is put under pressure. A further advantage which arises from the use of a press fit is that the position of the expansion bush in relation to the basic body is maintained exactly, even in the nonsoldered state, once this position has been set correctly during the mounting of the expansion bush. The expansion bush is therefore maintained in its position in relation to the basic body during soldering, without separate fixing being necessary for this purpose. 
         [0008]    According to a preferred embodiment of the invention, there is provision whereby the press fit is formed by means of a press portion which differs in diameter from the diameter of the solder region lying next to it. This ensures that the stresses necessary for the press fit are concentrated onto the press region and do not encroach upon the solder region lying next to it. Furthermore, on account of the difference in diameter, the gap which is present in the solder region between the expansion bush and the basic body and leads to an optimal soldered joint can be set with high accuracy. 
         [0009]    Preferably, in this case, there is provision whereby the press portion is formed by a portion of the expansion bush which is thickened in diameter and on one side of which the solder region lies and on the other side of which the pressure chamber lies. This configuration has advantages in terms of production, since the receptacle which is located inside the basic body and into which the expansion bush is inserted can be made with a constant diameter in the region of the press fit and the solder region, while the thickened portion of the expansion bush can be produced by lathe turning at low outlay. 
         [0010]    According to a preferred refinement of the invention, the provision whereby the seal is formed by a bearing portion which projects axially with respect to the solder region lying next to it. The bearing region has a double function here: on the one hand, it forms the seal which prevents the solder region lying behind the bearing portion from being exposed directly to the hydraulic fluid. On the other hand, the bearing portion ensures that an exactly defined gap between the expansion bush and basic body is formed in the solder region. 
         [0011]    Preferably, there is provision whereby the bearing portion is formed on the expansion bush. This, too, is advantageous in terms of the overall production costs, since the various surfaces of the expansion bush which are to be machined are more easily accessible than the surfaces in the basic body of the expansion chuck which lie inside the receptacle for the expansion bush. 
         [0012]    According to a refinement of the invention, there is provision whereby the bearing portion extends in a plane which is oriented perpendicularly to the mid-axis of the reception space. In this refinement, the bearing portion serves as an axially active stop for the expansion bush, by means of which stop the correct position of the expansion bush inside the receptacle in the basic body can be ensured. 
         [0013]    According to a further refinement of the invention, there is provision whereby the seal is formed by a bearing portion which is arranged on the basic body and which engages into a groove provided on the expansion bush, so that said bearing portion is offset in the axial direction with respect to the solder region. In this refinement, the bearing portion acts in a similar way to a labyrinth seal, and in this case the sealing-off action can be improved in that the bearing portion engages with certain pressure into the groove in the basic body. 
         [0014]    Preferably, there is provision whereby the expansion bush has a press portion at its end lying inside the basic body and a bearing portion at its end lying outside. In this refinement, the expansion bush can be pushed into the receptacle in the basic body, said receptacle having been previously equipped with solder rings. The bearing portion serves in this case for positioning the expansion bush in the axial direction, while the press portion ensures that the expansion bush does not move, during soldering, out of the position set during preliminary mounting. 
         [0015]    According to a refinement to the invention, there is provision whereby the expansion bush is provided with a thread, by means of which said expansion bush is screwed into the basic body, and whereby the solder region extends into the thread. The thread constitutes an additional mechanical connection between the expansion bush and the basic body, thus giving rise to higher radial rigidity of the expansion chuck. Particularly in combination with a press fit inside the basic body between the latter and the expansion bush, the chucking of a tool in the expansion chuck becomes, overall, especially rigid. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The invention is described below by means of various embodiments illustrated in the accompanying drawings in which: 
           [0017]      FIG. 1   a  shows an expansion chuck in a side view; 
           [0018]      FIG. 1   b  shows the expansion chuck in a front view; 
           [0019]      FIG. 1   c  shows the expansion chuck in a sectional view; 
           [0020]      FIG. 2  shows a section through that part of an expansion chuck which is provided with the expansion bush, according to a first embodiment of the invention; 
           [0021]      FIG. 3  shows a section through that part of an expansion chuck which is provided with the expansion bush, according to a second embodiment of the invention; and 
           [0022]      FIG. 4  shows a section through that part of an expansion chuck which is provided with the expansion bush, according to a third embodiment of the invention 
       
    
    
     DETAILED DESCRIPTION 
       [0023]      FIGS. 1   a  to  1   c  show an expansion chuck  10  which has a machine tool-side end  12  and a tool receptacle-side end  14 . The expansion chuck  10  has a basic body  16  composed of metal and an expansion bush  18  likewise composed of metal. Inside the expansion bush  18 , a reception space  20  is formed, which issues on the tool receptacle-side end face of the expansion chuck. Between the outer surface of the expansion bush  18  and the inner surface of a receptacle  22  in the basic body  16 , into which receptacle the expansion bush  18  is inserted, a pressure chamber  24  is formed. This can be supplied with a hydraulic fluid via ducts, not shown, so that a high pressure builds up in the pressure chamber  24 . As a result of this pressure, the expansion bush  18  is partially loaded inward elastically, so that a tool arranged in the reception space  20  can be firmly chucked. 
         [0024]    With reference to  FIG. 2 , then, a first embodiment of the invention is explained. The expansion bush  18  is connected at its inner end, that is to say on the side facing away from the tool receptacle-side end  14  of the expansion chuck, to the basic body  16  by means of a solder region  30 . The solder region  30  is formed by a cylindrical gap between the outer surface of the expansion bush  18  and the wall of the receptacle  22  in the basic body  16 . The gap is filled with solder material which comes from a solder ring  32  which is inserted into the receptacle  22  during the mounting of the expansion bush  18  in the basic body  16 . 
         [0025]    Between the solder region  30  and the pressure chamber  24 , a seal  34  is provided, which is formed by a press fit between the expansion bush  18  and the basic body  16 . For this purpose, the expansion bush  18  is provided with a press portion  36 , the outside diameter of which is slightly larger than the outside diameter of the expansion bush  18  in the area of the solder region  30 . That inside diameter of the receptacle  22  which is assigned to the press portion  36  is selected such that the desired press fit is obtained when the expansion bush  18  is pushed into the receptacle  22  in the basic body  16 . 
         [0026]    The press fit ensures, on the one hand, that the hydraulic fluid by which the pressure chamber  24  is loaded cannot act directly upon the solder region  30 , in particular it is not present on that side of the solder region  30  which faces the pressure chamber  24 . This prevents the hydraulic fluid from acting directly upon the solder region  30  and from attempting to press the two surfaces soldered to one another apart. Furthermore, the press portion  36  acts in the same way as a stable mount, by means of which the inner end of the expansion bush  18  is supported in the basic body  16  in a highly stable manner in the radial direction. 
         [0027]    The expansion bush is provided on the outer side with a thickened flange  40  which is likewise soldered to the basic body  16 . The solder region is composed here of two offset regions, to be precise a radially oriented solder region  41 , which is arranged between the inwardly directed end face of the flange  40  of the expansion bush  18  and the basic body  16 , and a cylindrical solder region  42 , which is provided between the outer circumference of the flange  40  and the basic body  16 . A solder ring  44  is arranged, during mounting, between these two solder regions  41 ,  42 . 
         [0028]    A seal  46  between the solder region  41 ,  42  and the pressure chamber  24  is also present on the outer side of the expansion bush  18 . The seal  46  is formed here via a projecting bearing portion  48  on the inwardly directed end face of the flange  40  of the expansion bush, which bearing portion projects in the axial direction, as seen from outside, with respect to that surface on the flange  40  of the expansion bush  18  which is part of the solder region  41 . The bearing portion  48  in this case forms for the expansion bush  18  an axial stop which defines how far the expansion bush  18  can be pushed into the receptacle  22  in the basic body  16 . 
         [0029]    During the mounting of the expansion chuck  10 , the expansion bush  18 , together with the solder rings  32 ,  44 , is pushed into the basic body  16 . During the last pushing-in phase, the press portion  36  is pushed into the reception portion, assigned to it, in the basic body  16 . On account of the dimensioning of the press portion  36  and of the assigned reception portion, the desired press fit is established. The expansion bush  18  can be pushed in until the bearing portion  48  bears sealingly against the wall, assigned to it, in the receptacle  22  in the basic body  16 . The resulting contact force can be influenced by how firmly the expansion bush  18  is pushed into the basic body  16 ; the press fit forming the seal  34  maintains the bearing force in the region of the bearing portion  48 , even when external pressing-in forces no longer act. 
         [0030]    The basic body  16  and the expansion bush  18  are subsequently heated so that the two parts are soldered to one another. In this case, a temperature/time profile may be used, by means of which the expansion chuck is at the same time also cured in the desired way. 
         [0031]    After the conclusion of curing, the expansion bush  18  is connected firmly to the basic body  16 . The press portion  36  acting in the manner of a mount ensures very high radial rigidity on the inside. High rigidity is likewise obtained on the outside, since the flange  40  of the expansion bush is connected firmly to the basic body  16  by means of the two solder regions  41 ,  42  which are oriented in different directions. All the solder regions  30 ,  41 ,  42  are in each case protected against direct loading with hydraulic fluid by a seal (formed at the inner end by the press fit of the press portion  36  and at the outer end by the firm bearing of the bearing portion  48  against the basic body  16 ). In this case, it is unimportant for the action of the seal if a small quantity of hydraulic fluid can overcome the seal and reach the corresponding solder region. On account of the damping action of the seal, pressure fluctuations in the pressure chamber  24  even in this case have markedly lesser effect upon the fatigue strength of the soldered joints than would be the case without a seal. 
         [0032]      FIG. 3  shows an expansion chuck according to a second embodiment. The same reference numerals are used for the features known from the first embodiment and to that extent reference is made to the above explanations. 
         [0033]    The inner side of the expansion bush  18  is designed in the same way as in the first embodiment. 
         [0034]    The connection between the expansion bush  18  and basic body  16  on the outer side differs from the first embodiment in that a thread  50  is provided on the circumferential surface of the flange  40  and is screwed into a corresponding counter thread in the basic body  16 . The axial prestress between the bearing portion  48  and the basic body  16  can thus be set with high accuracy by means of the torque with which the expansion bush  18  is screwed into the basic body  16 . During soldering, the solder material of the solder ring  44  is also drawn into the region of the thread  50 , so that a very firm mechanical connection between the expansion bush  18  and the basic body  16  is obtained there. 
         [0035]    A third embodiment is shown in  FIG. 4 . The same reference symbols are used for the features known from the preceding embodiments and to that extent reference is made to the above explanations. 
         [0036]    In the third embodiment, too, a seal  34  in the form of a press fit is used on the inner side and is arranged between the pressure chamber  24  and the solder region  30 . On the outer side, two offset solder regions  41 ,  42  are used in a similar way to the first embodiment. The difference from the first embodiment is that, in the third embodiment, a seal  60  is used which is designed in a similar way to a labyrinth seal. For this purpose, the basic body  16  is provided with a cylindrical bearing portion  62  which projects toward the outside and which engages into a groove  64  on the expansion bush  18 . The groove  64  is formed on that end wall of the flange  40  which is directed toward the inside, and in this case the dimensions of the bearing portion  62  may be designed in relation to the groove  64  such that the bearing portion  62  engages with certain pressure into the groove, in particular on the outer side; on the radially inner side, part of the pressure chamber  24  may be contiguous to the bearing portion  62 . 
         [0037]    In this refinement, two surface pairings arranged perpendicularly to one another, to be precise the outwardly directed end face of the bearing portion  62  and its annular circumferential surface, together with the surfaces of the flange  40  which are assigned to them, separate the pressure chamber  24  from the solder regions  41 ,  42 . The bearing portion  62  serves, furthermore, as a mechanical bearing for the expansion bush  18 , so that, overall, a highly stable construction is obtained in the radial direction. Moreover, the end face of the bearing portion  62  acts as a stop during the mounting of the expansion bush  18  in the receptacle  20  in the basic body  16 .