Abstract:
A tool holder has a first holder part for inserting into a receptacle in the machine tool and a second holder part for holding a tool. The tool holder has a conduit for directing a coolant and/or lubricant to the tool from a coolant and/or lubricant source. The tool has a conduit section for the coolant and/or lubricant for directing the latter to a machining point, and wherein, in the fitted state of the tool in the tool holder, the conduit is in contact with the conduit section at a coupling point. Provision is made for there to be an air feed line which directs compressed air from a compressed-air source into the region of the coupling point in such a way that the compressed air acts on the outer circumferential surface of the conduit and of the conduit section. Furthermore, methods for operating such a tool holder are described.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of and priority to German Patent Application No. 10 2010 037 453.9, filed Sep. 10, 2010, and German Patent Application No. 10 2010 037 822.4, filed Sep. 28, 2010, the contents of each of which are hereby incorporated by reference in their entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. The Field of the Invention 
         [0003]    The invention relates to a tool holder for holding a tool and for rotationally coupling the tool to a machine tool, wherein the tool holder has a conduit for directing a coolant and/or lubricant through to the tool from a coolant and/or lubricant source, wherein the tool has a conduit section for directing the coolant and/or lubricant to a machining point, and wherein, in the fitted state of the tool in the tool holder, the conduit of the tool holder is in contact with the conduit section of the tool at a coupling point, such that coolant and/or lubricant flows or can flow from the conduit of the tool holder into the conduit section of the tool. Furthermore, the invention relates to a method for operating such a tool holder. 
         [0004]    2. The Relevant Technology 
         [0005]    A tool holder of this type is known from DE 296 24 433 U1. Here, a spindle device for a machine tool is described in which two feed path systems for separately directing air and liquid into a spindle are provided. Furthermore, a mist-generating device is provided which mixes air and liquid fed through this feed path system and discharges a mist-like mixture in order to lubricate or cool the tool at its machining point. It has proved successful, with such “minimum quantity lubrication”, to use said oil mist for cooling or lubricating the tool in order to ensure effective machining by the tool with an adequate tool life. 
         [0006]    In a design of the type mentioned at the beginning, the conduit is placed against the conduit section in an axially abutting manner in order to be able to supply the machining point with coolant and/or lubricant even in an interchangeable tool. In this case, it has been recognized as a disadvantage that segregation of the oil mist can take place in the event of leakages at the coupling point between conduit and conduit section, i.e. the oil can separate from the oil mist and lead to contamination of the tool holder. To the same degree, the oil in the cooling lubricant is of course reduced in this case, which has corresponding negative effects on the cutting process. 
         [0007]    A tapping chuck for a tap with minimum quantity lubrication is known from DE 198 21 186 C1, which tapping chuck has an axially central lubricant passage with an axially displaceable coolant tube for a lubricant aerosol and a machine-side minimum quantity lubrication source, from which the lubricant aerosol is directed to the longitudinal bore of the tap. The coolant tube is pressed into its engagement position against the longitudinal bore of the tap by the aerosol pressure acting on its inner end faces, irrespective of the axial position of the tap, and is preloaded outwards by a spring. As a result, the sealing effect at the coupling point between coolant tube and tap is improved. 
         [0008]    DE 10 2005 050 754 B4 discloses a tool holder for minimum quantity lubrication in which a coolant and/or lubricant tube for an aerosol provided as coolant and/or lubricant bears against a sealing ring inserted in the tool for sealing said coolant and/or lubricant tube at the end face thereof. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    The object of the present invention, then, is to configure a tool holder of the type mentioned at the beginning in such a way that it becomes possible to seal the coupling point between conduit and conduit section in a simple and efficient manner, such that in particular an escape of coolant and/or lubricant at the coupling point can be at least largely avoided. Furthermore, a corresponding method for operating a tool holder is to be proposed. 
         [0010]    The achievement of this object by the invention is characterized according to claim  1  in that there is a gas feed line, in particular an air feed line, which directs compressed gas, in particular compressed air, from a compressed gas source, in particular a compressed air source, into the region of the coupling point in such a way that the compressed gas, in particular the compressed air, acts there on the outer surfaces (or outer circumferential surfaces) of the conduit of the tool holder and on the outer surfaces (or outer circumferential surfaces) of the conduit section of the tool and prevents an escape of coolant and/or lubricant at the coupling point. 
         [0011]    This air acts from outside as sealing air on the conduit and on the conduit section at the coupling point, and therefore it is ensured in this way that no coolant and/or lubricant escapes from the conduit or from the conduit section. 
         [0012]    The coolant and/or lubricant is in particular an oil mist or an oil aerosol, as used in particular in minimum quantity lubrication. 
         [0013]    Advantages configurations and developments follow from the dependent claims. 
         [0014]    According to the invention, in the method for operating such a tool holder as proposed in claim  7 , a coolant and/or lubricant is directed at least from time to time from the coolant and/or lubricant source to the tool via the conduit, wherein, at least during the feeding of the coolant and/or lubricant, air under pressure is fed in via the air feed line and delivered to the coupling point between the conduit and the conduit section. 
         [0015]    In this case, provision is preferably made for the pressure of the air delivered to the coupling point to be at least as high at the coupling point as the pressure in the interior of the conduit or of the conduit section in the region of the coupling point in order to achieve optimum sealing. 
         [0016]    The effect achieved with this configuration or this procedure is that a sealing air shield builds up around the outer circumference of the conduit and of the conduit section in the region of the coupling point, and so it is not possible for oil mist to escape at the coupling point or for oil to escape from the oil mist and for this to lead to contamination or to the oil mist losing oil. 
         [0017]    Accordingly sealing of the coupling point is achieved in a simple manner, and this sealing works efficiently and can be realized in a simple manner. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    Exemplary embodiments of the invention are shown in the drawing, in which: 
           [0019]      FIG. 1  shows, in a sectional illustration, a tool holder with tool according to a first embodiment of the invention, 
           [0020]      FIG. 2  shows the detail “W” according to  FIG. 1 , 
           [0021]      FIG. 3  shows the detail “X” according to  FIG. 1 , 
           [0022]      FIG. 4  shows a sleeve element with coolant tube in section IV-IV according to  FIG. 1 , and 
           [0023]      FIG. 5  shows an alternative embodiment of a sleeve element with coolant tube in a section. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]    A first exemplary embodiment of the tool holder  1  proposed according to the invention is shown in  FIGS. 1 to 4 . The tool holder  1  is coupled on a spindle side  20  to a drive spindle (not shown) of a machine tool (not shown) and holds a tool  4  on a tool side  21  and couples said tool  4  in a rotational coupling to the drive spindle of the machine tool, such that the tool can be or is rotationally driven about a rotation axis a by the drive spindle via the tool holder  1 . The tool  4  is preferably a tap and the tool holder  1  is preferably a tapping chuck, but the tool  4  can also be a cold-forming tap, thread milling cutter or also any other rotating tool working with a cutting or non-cutting action. 
         [0025]    In the embodiment shown, the tool holder  1  is of substantially two-piece design and comprises a first holder part  2 , which has the spindle side  20  and is designed for coupling to the drive spindle of the machine tool, and also a second holder part  3 , which has the tool side  21  and is designed for holding the tool  4  and which is rotationally coupled to the first holder part  2  and permits, in a manner known per se, certain axial length compensation by means of limited axial mobility relative to the first holder part  2 , while at the same time being coupled for conjoint rotation, and by means of a length compensation spring  51  which acts towards the tool  4 . However, a one-piece embodiment of the tool holder  1  and/or an embodiment without length compensation is also possible. 
         [0026]    In the exemplary embodiment shown, the tool  4  is clamped in place in a collet  34 , which is clamped in place or compressed from outside by a clamping sleeve or insert sleeve  31  in a manner known per se via, for example, tapered clamping surfaces by means of a clamping nut  33  screwed onto the insert sleeve  31 . The insert sleeve  31  is in turn coupled in a manner known per se to the first holder part  2  for conjoint rotation. The insert sleeve  31 , collet  34  and clamping nut  33  belong to the second holder part  3 . 
         [0027]    After the tool  4  has been fitted into the tool holder  1  and the tool holder  1  has in turn been inserted into the machine tool, the spindle (not shown) of the machine tool rotates the tool holder  1  together with tool  4  about the rotation axis a. By corresponding axial feed with respect to the rotation axis a, the machining side  7  of the tool  4  is brought into contact with the workpiece to be machined, e.g. in order to cut a thread. 
         [0028]    It is important that the machining point  7  of the tool  4  is adequately supplied with coolant and/or lubricant KS, for which purpose there is a coolant and/or lubricant supply line which comprises a conduit  5  which extends in the tool holder  1  coaxially to the rotation axis a and a conduit section  6 , connected in series with the conduit  5 , in the tool  4 . 
         [0029]    The conduit  5  of the tool holder  1  and the conduit section  6  of the tool  4  are fluidically connected to one another at a coupling point  8 , and the outlet opening  57  of the conduit  5  opens into the conduit section  6  or is connected to the latter. In particular, the conduit  5  of the tool holder  1  and the conduit section  6  of the tool  4  abut against one another at the end faces at the coupling point  8 , i.e. the end face  54  of the conduit  5  and the end face  45  of the tool  4  around the conduit section  6  bear against one another over a surface area, for example via complementary bearing surfaces, which, for example, can be of conical design, such that a certain degree of sealing is achieved. 
         [0030]    Coolant and/or lubricant KS which is fed under pressure into the conduit  5  at the inlet opening  50  thereof in the upper region therefore reaches the machining point  7  via the conduit  5  and then via the conduit section  6 . 
         [0031]    The conduit  5  is designed in particular as an elongated tube (coolant tube) and runs from the tool  4  through the interior space of the insert sleeve  31  and the interior space of the first holder part  2  up to a guide sleeve  15 , in which it is axially displaceable in a sealed manner via a seal  55  and has the inlet opening  50  for the coolant and/or lubricant KS. The length compensation spring  51  rests on a spring bearing ring  56  on the outer side of the conduit  5 . 
         [0032]    On the outlet side, the end of the conduit  5  plunges into a recess in the collet  34  and rests there with the end face  54  on the end face  45  of the tool  4 . The recess in the collet  34  forms a surrounding space  98  for the coupling point  8 . The surrounding space  98  is sealed in a pressure-proof manner by the clamped tool  4  and opens into an interior space  95  of the insert sleeve  31 , which interior space  95  is adjacent to the surrounding space  98 , is located above the collet  34  and is larger in diameter. The interior space  95  is closed off at the top, or on the side facing away from the surrounding space  98 , by a sleeve element  10  which surrounds the conduit  5 . The sleeve element  10  has a central leadthrough (or bore)  11 , running axially with respect to the rotation axis a, for the conduit  5  and is sealed all around on the conduit  5  via a seal  12 . 
         [0033]    Following the sleeve element  10  or above the sleeve element  10 , the conduit  5  runs inside a further cavity of the insert sleeve  31 , said cavity accommodating the second sub-passage  92 B of a second passage  92  and the spring bearing ring  56  of the conduit  5 . A first sub-passage  92 A of the second passage  92 , which first sub-passage  92 A follows at the top or follows the second sub-passage  92 B, runs around the conduit  5  inside the first holder part  2  and the retaining sleeve  16 , in which the guide sleeve  15  for the conduit  5  is arranged, and accommodates most of the length compensation spring  51 . 
         [0034]    In particular an oil mist or an oil aerosol, i.e. oil to which air is added, said oil being present in the form of tiny droplets in the air, is now used as coolant and/or lubricant KS. 
         [0035]    In particular on account of the segregation of the oil and the air inside the conduit  5  and in particular at the coupling point  8  to the conduit section  6 , the coolant and/or lubricant KS can escape at the coupling point  8 , despite the end faces  54  and  45  which bear against one another, and oil can collect in the surrounding space  98  and also in the interior space  95  and can also escape from the tool holder  1 . 
         [0036]    So that none of the oil mist of the coolant and/or lubricant KS can escape at the coupling point  8 , compressed air DL is admitted according to the invention to the surrounding space  98  around the coupling point  8 , said compressed air DL acting from outside on the outer surfaces of the conduit  5  and on the outer surfaces of the conduit section  6  of the tool  4 . The compressed air DL prevents the coolant and/or lubricant KS from escaping at the coupling point  8 . To this end, the pressure p 2  of the compressed air DL is preferably set at least as high as the pressure p 1  of the coolant and/or lubricant KS prevailing in the interior of the conduit  5  and of the conduit section  6  at the coupling point  8 . 
         [0037]    The pressure p 1  of the coolant and/or lubricant KS is typically between 4 bar and 6 bar, and so the pressure p 2  of the compressed air DL should be set correspondingly high or higher. However, an approximately equal pressure p 2 =p 1  is already sufficient, and therefore the compressed-air source used for producing the oil mist of the coolant and/or lubricant KS can also be used for sealing at the coupling point  8 . The compressed air DL is applied, as it were, as sealing air to the outer circumference or the outer surface of conduit  5  and conduit section  6  at the coupling point  8 , such that no oil mist can escape from the conduit  5  or from the conduit section  6 . 
         [0038]    To feed the compressed air DL, a compressed-air feed line  9 , which comprises various sections or sub-passages  91 ,  92 ,  93 ,  95  and  98 , is now provided in the tool holder  1 . 
         [0039]    In the exemplary embodiments shown, the compressed air DL provided as sealing air is directed forwards to the coupling point  8  in the compressed-air feed line  9  parallel to the coolant and/or lubricant KS and thus outside the conduit  5 . 
         [0040]    First of all, as shown in  FIGS. 1 and 2 , the compressed air DL is injected from a compressed-air source (not shown) through an inlet opening  90  into a first passage  91 , running parallel to the conduit  5  and eccentrically to the rotation axis a, in or on the wall of the guide sleeve  15  or between guide sleeve  15  and retaining sleeve  16  and flows through this first passage  91  into the second passage  92  and then through the second passage  92 , that is to say first through the first sub-passage  92 A and then through the second sub-passage  92 B, up to the sleeve element  10 . 
         [0041]    According to  FIGS. 1 and 3 , a third passage  93  is now formed in the sleeve element  10 , and this third passage  93  runs in the sleeve element  10  from the side adjoining the second sub-passage  92 B parallel to the rotation axis a and eccentrically to the leadthrough  11  for the conduit  5  and opens with an outlet opening  94  into the interior space  95  in the insert sleeve  31 . Finally, the compressed air DL passes from the interior space  95  into the surrounding space  98  at the coupling point  8 . 
         [0042]    Since the interior space  95  and the surrounding space  98 , except for the third passage  93 , at which the compressed air DL is applied at the pressure p 2 , are otherwise closed in a pressure-proof manner, the pressure p 2  of the compressed air DL substantially prevails in the surrounding space  98  and in the interior space  95 , said pressure p 2  being opposed to the internal pressure pl in the entire region of the coupling point  8 . 
         [0043]    A configuration of the compressed-air leadthrough on the sleeve element  10  as an alternative to the configuration in  FIG. 3  can be seen in  FIG. 5 . The leadthrough  11  for the conduit  5  in the sleeve element  10  is now designed to be larger in diameter than the outside diameter of the conduit  5  and is not sealed by a sealing ring  12  as in  FIG. 3 . As a result, according to  FIG. 5 , there is formed between sleeve element  10  and conduit  5  an annular gap or air passage gap  14  which opens into the interior space  95  and through which the compressed air DL flows or can flow from the second sub-passage  92 B into the interior space  95 , instead of through the third passage  93  in  FIG. 3 . 
         [0044]    The tool holder  1  shown is otherwise of a known design, and therefore further explanation in this respect can be dispensed with, especially since the scope of the present invention primarily concerns the sealing of the coupling point by means of sealing air. 
         [0045]    In addition to the purely axial feeding of the compressed air, the compressed air can also be directed, for example, laterally to the tool holder  1 . 
       LIST OF DESIGNATIONS 
       [0000]    
       
         
           
               1  Tool holder 
               2  First holder part 
               3  Second holder part 
               4  Tool 
               5  Conduit 
               6  Conduit section 
               7  Machining point 
               8  Coupling point 
               9  Air feed line 
               10  Sleeve element 
               11  Bore 
               12  Sealing element (O-ring) 
               13  Through bore 
               14  Air passage gap 
               15  Guide sleeve 
               16  Retaining sleeve 
               20  Spindle side 
               21  Tool side 
               31  Insert sleeve 
               33  Clamping nut 
               34  Collet 
               50  Inlet opening 
               51  Length compensation spring 
               55  Sealing ring 
               56  Spring bearing ring 
               57  Outlet opening 
               90  Inlet opening 
               91  First passage 
               92  Second passage 
               93  Third passage 
               94  Outlet opening 
               95  Interior space 
               98  Surrounding space 
             a Rotation axis 
             DL Compressed air 
             KS Coolant and/or lubricant 
             p Pressure