Abstract:
The invention concerns a clamping device comprising a tensioning spindle whereof one end has a first axially fixed support surface and whereof the other end has a second axially mobile support surface and mobile relative to the first support surface through a clamping element. Between the two support surfaces on the tensioning spindle are one or several elastomer adapter sleeves.

Description:
BACKGROUND 
     During the machining of hollow thin-walled parts, for example sleeves, which are machined only on their outer side but not on their inner side, there is the problem that the unmachined inner side used for clamping the part has shape errors, for example non-roundness, generally in conjunction with non-uniform wall thickness in the circumferential direction or deviations from the straight cylindrical shape, under certain circumstances likewise in conjunction with wall thickness differences in the longitudinal direction. If a conventional clamping device is used, the parts are deformed elastically when being clamped in, on account of these shape errors of their inner side. As a result, during the machining of the parts, the shape errors of the inner side are, so to speak, transferred to the outer side. Therefore, it is not possible to achieve either high shape accuracy or a very high surface quality, and in addition cylindricity can barely be maintained. Therefore, the lower the wall thickness and the greater the length of the parts, the less consideration is given to clamping such thin-walled parts at their two end faces since they then deviate more or less severely under the cutting forces. In addition, the parts then tend to oscillate, so that chatter marks are additionally produced. 
     SUMMARY OF THE INVENTION 
     The invention is based on the object of providing a clamping device with which, primarily, very thin-walled and relatively long parts can be clamped satisfactorily, largely independent of irregularities of their inner surface, and their outer side can be machined with the required accuracy and surface quality. According to a preferred embodiment of the present invention, a clamping device may have the following features: there is a clamping spindle ( 11 ) which, at least at one end, is provided with coupling elements ( 12 ) for coupling to the main spindle of a machine tool, the clamping spindle ( 11 ) has a first supporting face ( 17 ) at one end which is aligned axially and faces the other end of the clamping spindle ( 11 ) and which is arranged on the clamping spindle ( 11 ) such that it cannot be displaced in the axial direction; there is a second supporting face ( 21 ) on the clamping spindle ( 11 ) at the other end, which is aligned axially and faces the one end and which is arranged on a clamping element ( 19 ) which is guided on the clamping spindle ( 11 ) such that it can be displaced in the axial direction; there is a clamping device ( 15 ), by means of which the clamping element ( 19 ) with the second supporting face ( 21 ) can be displaced relative to the first supporting face ( 17 ) and can be fixed while applying an axial clamping force to the clamping spindle ( 11 ); there is at least one clamping sleeve ( 13 ), which is produced from an elastomer, whose inner diameter is matched to the outer diameter of the clamping spindle, whose end faces are matched to the first supporting face ( 17 ) and to the second supporting face ( 21 ); a clamping sleeve ( 13 ) has a plurality of supporting strips ( 23 ) on its outer side, which are produced from a metallic material, which are permanently connected to the clamping sleeve ( 13 ), which are arranged distributed uniformly on the circumference of the clamping sleeve ( 13 ) and whose outer side ( 29 ) forms a cylinder surface section in each case which is matched to the inner diameter of the part ( 24 ). 
     Similar problems also occur during the machining of the inner side of thin-walled parts whose outer side remains unmachined, in particular when the parts are relatively long. The invention is therefore also based on the object of providing a clamping device with which, primarily, very thin-walled and relatively long parts can be clamped satisfactorily, largely independent of irregularities of their outer surface, and their inner side can be machined with the required accuracy and surface quality. In a preferred aspect of the present invention, the clamping device ( 15 ) is formed by a longitudinal section ( 18 ) of the clamping spindle ( 11 ) that is provided with an external thread and by a clamping ring ( 19 ) matched thereto and having an internal thread. 
     The fact that, instead of rigid clamping jaws, a clamping sleeve made of an elastomer is used and is guided on a smooth cylindrical clamping spindle and is compressed axially via its two end faces means that the quasi hydraulic behavior of the material of the clamping sleeve is utilized in order to compensate to a large extent for irregularities in the clamping surface of the part. The fact that there are metallic supporting strips on the outer side of the clamping sleeve means that abrasion of the clamping sleeve is avoided when the parts are pushed on and pulled off and, as a result, a higher lifetime of the clamping device and, at the same time, constant clamping security and clamping accuracy are achieved. 
     The clamping device may be adapted more easily to different lengths of the parts. In a preferred aspect, there are a plurality of clamping sleeves ( 13 ), which are axially displaceably guided on the clamping spindle ( 11 ) and which are arranged between the first supporting face ( 17 ) on the clamping spindle ( 11 ) and the second supporting face ( 21 ) on the annular clamping element ( 19 ). 
     In another aspect, the axial frictional force which occurs when the clamping sleeves are being clamped, between the clamping sleeve and its seating surface on the clamping spindle or on the basic body, is distributed over a plurality of relatively short sections where said force is lower, individually and overall. As a result, the radial clamping force of the clamping device is also distributed, at least approximately uniformly, over the entire clamping length. The fact that the clamping sleeve is designed to be shorter than its supporting sleeve and does not project beyond the end faces of the supporting sleeve, and that the transmission of the axial clamping force is performed by interposed pressure rings prevents the compliant clamping sleeves being pressed into the initially open interspaces between the supporting sleeves and damaged in the process at the start of the clamping operation. In a preferred aspect, for each clamping sleeve ( 13 ) there is a supporting sleeve ( 14 ), which is produced from a material whose dimensional stability is greater than the dimensional stability of the clamping sleeve ( 13 ), whose inner diameter is matched to the outer diameter of the clamping spindle ( 11 ) and to whose outer diameter the inner diameter of the clamping sleeve ( 13 ) is matched; the supporting sleeves ( 14 ) may have a greater length than the clamping sleeves ( 13 ); each clamping sleeve ( 13 ) may be arranged on its supporting sleeve ( 14 ) in such a way that each of the end faces of the clamping sleeve ( 13 ) does not project in the axial direction beyond the end faces of the supporting sleeve ( 14 ); a pressure ring ( 25 ) may in each case be arranged between two successive clamping sleeves ( 13 ), whose inner diameter is matched to the outer diameter of the supporting sleeves ( 14 ) and whose outer diameter is at most equal to the inner diameter of the part ( 24 ). 
     In another aspect, when the clamping device is operated, the clamping sleeves can be compressed only by the differential amount of the length dimensions. This results in an exactly defined radial clamping force and, in addition, as a result overstressing both of the elastic clamping sleeves and of the thin-walled parts is avoided. In a preferred aspect, the sum of the axial extent of the pressure ring ( 25 ) and of the clamping sleeve ( 13 ) is greater by a predefined amount ( 26 ) than the axial extent of the supporting sleeve ( 14 ) of the latter. 
     In another aspect, the number of components of the clamping device is reduced. In a preferred aspect, each pressure ring ( 25 ) is detachably or non-detachably connected to the end of a supporting sleeve ( 14 ), preferably produced in one piece with it. 
     In another aspect, the radial diameter change of the clamping sleeve is disproportionate to the axial compression movement. The same applies to a configuration according to claim  8  and according to claim  18 , respectively, a greater transmission factor between the radial diameter change and the axial compression movement being achieved. In a preferred aspect, on the clamping spindle, the seating face for each clamping sleeve is formed as the outer surface of a truncated cone, which widens toward the first supporting face, and the inner face of the clamping sleeve is matched to its seating face. In another preferred aspect, on the supporting sleeve ( 27 ), the seating face ( 28 ) for the clamping sleeve ( 31 ) is formed as the outer surface of a truncated cone, and the inner face ( 32 ) of the clamping sleeve ( 31 ) is matched to its seating face ( 28 ) on the supporting sleeve ( 27 ). 
     In another aspect, the clamping spindle or the base body can be supported at its second end, so that it gives way elastically to a lesser extent under the cutting forces and, as a result, the machining accuracy remains constant over the entire length of the part. In a preferred aspect, at its end facing away from the coupling elements ( 12 ), the clamping spindle ( 11 ) has an outer and/or an inner accommodation face ( 55 ;  56 ) for a supporting device ( 57 ). 
     In another aspect, a clamping device which can be produced and operated relatively simply is provided. In a preferred aspect, the clamping device ( 15 ) is formed by a longitudinal section ( 18 ) of the clamping spindle ( 11 ) that is provided with an external thread and by a clamping ring ( 19 ) matched thereto and having an internal thread. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following text, the invention will be explained by using a number of exemplary embodiments illustrated in the drawings, in which: 
     FIG. 1 shows a partly sectioned view of a first embodiment of a clamping device having a plurality of clamping sleeves for the external clamping of parts; 
     FIG. 2 shows an end view of a clamping sleeve; 
     FIG. 3 shows a plan view of a clamping sleeve; 
     FIG. 4 shows an enlarged detail from FIG. 1 with two clamping sleeves; 
     FIG. 5 shows an enlarged detail similar to FIG. 4 with two modified clamping sleeves; 
     FIG. 6 shows an enlarged detail similar to FIG. 4 with two further modified clamping sleeves; 
     FIG. 7 shows a longitudinal section of a further embodiment of the clamping sleeves; 
     FIG. 8 shows a longitudinal section, shown as a detail, of a second design of the clamping device having a plurality of clamping sleeves for the external clamping of parts. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The clamping device  10  that can be seen from FIG. 1 has, as main subassemblies or main components, a clamping spindle  11  having coupling elements  12 , a plurality of clamping sleeves  13  each having a supporting sleeve  14  and a clamping device  15 . In the upper half, the clamping device  10  is illustrated in the clamped state and, in the lower half, in the unclamped state. 
     The clamping spindle  11  is an elongate, circularly cylindrical body which, at its end on the left in FIG. 1, is detachably or non-detachably connected to the coupling elements  12 , by means of which it can be coupled to the main spindle of a machine tool. At its left-hand end, the clamping spindle  11  is provided with a collar  16 , whose planar, annular end face facing away from the coupling elements  12  serves as a first axial supporting face  17  of the clamping sleeves  13 . Arranged at the other end of the clamping spindle  11  is the clamping device  15 . It is formed by a longitudinal section  18  provided with an external thread and a clamping ring  19  matched thereto and provided with an internal thread. The planar, annular end face of the clamping ring  19 , facing the first supporting face  17 , forms a second supporting face  21  for the clamping rings  13 . For reasons of simpler manufacture and for improved possible adaptation to different adjustment stipulations, it may be expedient to insert a pressure ring  22  between the second supporting face  21  of the clamping ring  18  and the nearest clamping sleeve  13 . 
     As can be seen from FIG. 2 . . . FIG. 4, the clamping sleeves have the shape of a straight annular cylinder. They are produced from an elastomer. Arranged on their outer side are a plurality of supporting strips  23  of a metallic material. These supporting strips  23  are permanently connected to the clamping sleeve  13 . They are aligned parallel to the axis and arranged distributed uniformly on the circumference of the clamping sleeve  13 . The outer side of the supporting strips  23  forms a cylinder surface section which is matched to the inner diameter of the part  24  which, in FIG.  1  and to some extent in the other figures, is indicated dash-dotted. 
     The clamping sleeves  13  can be pushed directly onto the shaft of the clamping spindle  11 . The inner diameter of the clamping sleeves  13  is then matched to the outer diameter of the clamping spindle  11 . However, it is more expedient to push each clamping sleeve  13  onto a supporting sleeve  14 . The supporting sleeves  14  are produced from a material whose dimensional stability is greater than the dimensional stability of the material of the clamping sleeve  13 . Good sliding pairing between the material of the clamping sleeves  13  and that of the supporting sleeves  14  is advantageous. A metallic material is also considered for this purpose. The inner diameter of the supporting sleeves  14  is matched to the outer diameter of the clamping spindle  11 . The outer diameter of the supporting sleeves  14  is matched to the inner diameter  13  of the clamping sleeves  13  or vice-versa. The supporting sleeves  14  have a greater length than the clamping sleeves  13 . Each clamping sleeve  13  is arranged on its supporting sleeve  14  in such a way that each of the end faces of the clamping sleeve  13  does not project in the axial direction beyond the end face of the supporting sleeve  11 . 
     FIGS. 4 and 5 reveal two different embodiments of the supporting sleeve  14 , which for the purpose of distinction are designated supporting sleeve  14 . 1  (FIG. 4) and supporting sleeve  14 . 2  (FIG.  5 ), respectively. 
     In the respective lower half of the illustrations, the clamping sleeves  13  are shown in the unclamped state and, in the upper half, in the clamped state. In the unclamped state (lower half), the outer side of the clamping sleeve  13  and, in particular, that of its supporting strips  23  has a smaller spacing from the inner face of the part  24  which, for clarity, is illustrated greater than is actually the case. In the clamped state (upper half), the outer side of the clamping sleeves  13  and that of their supporting strips  23  rest on the inner side of the part  24 . The radial clamping movement of the clamping sleeves  13  needed for this purpose is effected by means of axial compression of the clamping sleeves  13 . Conversely, the radial unclamping of the clamping sleeves  13  is effected by means of axial relieving of the load on the clamping sleeves  14 . Both are effected by the clamping device  15 . In this arrangement, the clamping sleeves  13  are clamped in between the first supporting face  17  on the clamping spindle  11  and the second supporting face  21  on the clamping ring  18  (FIG.  1 ). 
     If the clamping sleeves  13  are not seated directly on the clamping spindle but each on a clamping sleeve  14 , the clamping sleeves  13  are shorter than their supporting sleeves  14 . The axial compression force of the clamping device  15  is then transmitted from one clamping sleeve  13  to the next by means of a pressure ring  25  in each case. In the embodiment according to FIG. 5, these pressure rings  25  are independent parts, as pressure rings  25 . 2 , whose inner diameter is matched to the outer diameter of the associated supporting sleeves  14 . 2 . Their outer diameter is at most equal to the inner diameter of the part  24 . In the embodiment according to FIG. 4, the pressure rings  25 . 1  are permanently connected to the associated supporting sleeves  14 . 1 , to be specific expediently produced in one piece with them. 
     Both in the embodiment according to FIG.  4  and in the embodiment according to FIG. 5, the clamping sleeves  13 , their supporting sleeves  14  and the pressure rings  25  are expediently configured in such a way that, in the unclamped state of the clamping sleeves  13 , the sum of the axial extent of the pressure ring  25  and of the clamping sleeve  13  is greater, by a predefined axial distance  26  (FIG.  4 ), than the axial extent of their supporting sleeve  24 . 
     As a result, in the clamped state of the clamping sleeves  13 , the supporting sleeves  14  form a stop which prevents the clamping sleeves  13  being compressed axially by the clamping device  15  beyond an extent matched to the relevant part  24  and, as a result, being widened radially. 
     FIGS. 6 and 7 reveal two modified embodiments of clamping sleeves and their supporting sleeves. 
     On the supporting sleeve  27 , the seating face  28  for the clamping sleeve  31  is formed as the outer surface of a truncated cone. The inner face  32  of the clamping sleeve  31  is matched to the seating face  28 , that is to say it is formed as a hollow outer surface of a truncated cone. 
     In the embodiment according to FIG. 7, on the supporting sleeve  33  the seating face  34  for the clamping sleeve  35  is formed by a plurality of longitudinal sections  34 . 1  . . .  34 . 5  of the outer surface of a truncated cone. The inner face  36  of the clamping sleeve  35  is formed by longitudinal sections, matched thereto, of the outer surface of a hollow truncated cone. The seating-face sections  34 . 1  . . .  34 . 5  follow one another axially in the same alignment. They adjoin one another via an annular planar interface  37  in each case. 
     In the embodiment according to FIG. 7, the cone angle of the seating faces  34  and the inner face  36  is considerably greater than in the embodiment according to FIG.  6 . As a result, during a predefined axial compression travel, the radial expansion of the clamping sleeve  35  is greater than in the clamping sleeve  31 . 
     FIG. 8 reveals a clamping device  40  for the external clamping of thin-walled sleeve-like parts  41 , which are machined on their inner side. The coupling elements for coupling to a machine tool are not illustrated. 
     The clamping device  40  has a hollow base body  42  having the approximately hollow cylindrical inner space  43 . At one end of the inner space  43 , on the base body  42 , there is a first supporting face  44  which is aligned axially and faces the other end. 
     Arranged in the inner space  43  of the base body  42  are a plurality of clamping sleeves  45 , which are produced from an elastomer. The inner face  46  of the clamping sleeves  45  forms the clamping face for the part  41 . It is provided with a number of supporting strips, as is the case in the clamping face on the outside of the clamping sleeves  13  of the clamping device  10 . The clamping sleeves  45  are each seated in a supporting sleeve  47 , which is produced in one piece together with a pressure ring  48  in each case. The axial compression required for the radial clamping movement of the clamping sleeves  45  is effected by a clamping device  51 , which is formed by a longitudinal section provided with an internal thread on the inner face of the basic body  42  and by an annular clamping ring  53  screwed into the latter. 
     In the case of the clamping device  40 , the operative direction of its parts in the radial direction is opposite to that in the corresponding parts of the clamping device  10  (FIG.  1 ). Taking account of this fact, their parts largely correspond to one another in terms of construction and operating mode. To this extent, reference is made to the description of this clamping device  10 , which also includes the modifications according to FIG. 5 . . . FIG.  7 . 
     As is indicated on the right in FIG. 1, in particular in the case of parts of greater length and/or lower diameter and smaller wall thickness, and in the case of an appropriately designed clamping device, it may be expedient to clamp the clamping device not only at the end having the coupling elements for the connection to the main spindle of a machine tool but also to support it at the opposite end. This can be done in different ways, for example via a supporting face located on the outside and/or via one located on the inside. 
     Outside the clamping device  15 , the clamping spindle  11  has both the outer cylindrical supporting face  55  and, in its end face, the centering hole  56  as an inner supporting face. A co-rotating lathe center  57  acts together with said centering hole  56 . For the outer supporting face  55 , a freely co-rotating or a driven chuck can be used.