Abstract:
A tool retraction receiving element includes a receiving section ( 3 ) for receiving a tool ( 15 ) and a clamping section ( 9 ) for clamping the tool retraction receiving element ( 1 ) in a tool receiving carrier. The receiving section ( 3 ) for the tool ( 15 ) and the clamping section ( 9 ) of the tool retraction receiving element ( 1 ) overlap in the longitudinal direction. An adapter positions one such tool retraction receiving element.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a tool retraction receiving element with a receiving section for retracting a tool and a clamping section for clamping the tool retraction receiving element in a tool receiving carrier. The present invention also relates to an adapter for positioning of the tool retraction receiving element. 
   BACKGROUND OF THE INVENTION 
   In conventional shrink-fit tool holders, the holding section for shrinking fitting the tool is configured on one end of the shrink-fit tool holder. The clamping section for clamping the shrink-fit tool holder in a tool holder support is configured in the longitudinal direction spaced away from the holding section for the tool on the opposite end of the tool holder. When shrink-fitted tools are being used on a machine tool, for example, a milling machine, lathe, or drilling machine, the surface of the workpiece, which in particular has been machined by cutting, often does not have the desired quality. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a shrink-fit tool holder for an adapter for accommodating a shrink-fit tool holder by which the disadvantages of the prior art can be overcome, especially by which better surface qualities of the machined workpieces can be achieved. 
   In a shrink-fit tool holder with a holding section for shrink-fitting of a tool and a clamping section for clamping the shrink-fit tool holder in a tool holder support, the object of the present invention is achieved by the receiving or holding section for the tool and the clamping section of the shrink-fit tool holder overlapping in the longitudinal direction, i.e., the receiving section and clamping section having a common axial location. By superposition of the holding section for the tool with the clamping section in the axial direction, short, compact shrink-fit tool holders can be formed which have very high stiffness, especially in the radial direction. This stiffness in turn leads to better surface quality of the machined workpieces. Moreover, the service life of the tools can be increased by the short structural length of the shrink-fit tool holder. 
   One preferred embodiment of the shrink-fit tool holder of the present invention is characterized in that the overlapping is more than 50% of the total length of the shrink-fit tool holder. For many applications, it is sufficient if the overlapping is more than 30%. In this way deflection of the shrink-fit tool holder in the radial direction is avoided in operation. 
   Another preferred embodiment of the shrink-fit tool holder of the present invention is characterized in that the overlapping extends essentially over the entire length of the clamping section for clamping the shrink-fit tool holder in a tool holder support. At least one partial section with an extension which is approximately 5% of the total length of the shrink-fit tool holder can be configured without overlapping. 
   Another preferred embodiment of the shrink-fit tool holder of the present invention is characterized in that the holding section for shrinking fitting of the tool is formed by a through hole extending over the entire length of the shrink-fit tool holder. The through hole preferably has a circular cross section, but can also have a polygonal cross section. 
   Another preferred embodiment of the shrink-fit tool holder of the present invention is characterized in that the through hole on its end opposite the clamping section has a centering section with a widened inside diameter. The centering section is used to hold and center, before shrink fitting, one end of the tool which is to be shrink-fitted. 
   Another preferred embodiment of the shrink-fit tool holder of the present invention is characterized in that following the clamping section, a circumferential groove is formed having a rectangular cross section. The circumferential groove interacts with a cam configured on a clamping nut and used to release the tool holder after machining. 
   Another preferred embodiment of the shrink-fit tool holder of the present invention is characterized in that on the end of the shrink-fit tool holder, opposite the clamping section and following the circumferential groove, a conical section is formed which widens toward the circumferential groove. The conical section facilitates placement of a tensioning nut. 
   Another preferred embodiment of the shrink-fit tool holder of the present invention is characterized in that the clamping section has the shape of a cone. The dimensions of the cone are preferably standardized, for example, according to DIN 6499. 
   Another preferred embodiment of the shrink-fit tool holder of the present invention is characterized in that the clamping section has the shape of a circular cylinder. The configuration of the clamping section is matched to the shape of the tool holder support. 
   An adapter of the present invention for use with the above described shrink-fit tool holder is characterized by a depression with dimensions matched to the end of the clamping section of the shrink-fit tool holder. The depression can be configured as a conical or cylindrical depression, and ensures that almost the entire outer circumferential surface of the shrink-fit tool holder is accessible from the outside to deliver heat to the shrink-fit tool holder. The depth of the depression is chosen such that tilting of the tool holder in place is reliably prevented. With inductive heating and an electrically conductive, especially metallic adapter, the vertical dimension of the depression is comparatively small, for example, 1 to 5 mm, especially approximately 2 mm. 
   One preferred embodiment of the adapter of the present invention is characterized in that the adapter tapers toward the shrink-fit tool holder. Tapering simplifies the placement of the heating element on the adapter. 
   Another preferred embodiment of the adapter of the present invention is characterized in that the adapter is configured with at least two parts and comprises a base adapter and an adapter insert on which the depression and/or the tapering is/are configured. This arrangement facilitates use of the base adapter for shrink-fit tool holders of different sizes. The different shrink-fit tool holders together with the pertinent adapter inserts can be used with one and the same base adapter. The base adapter in turn is matched to the heating device to be used. 
   Another preferred embodiment of the adapter of the present invention is characterized by a central threaded hole in which a threaded bolt is held with a turning capacity. A free end of the bolt forms a stop for the tool when the shrink-fit tool holder is positioned on the adapter. By turning the threaded bolt the shrink-fitting depth of the tool can be continuously adjusted. 
   Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring to the drawings which form a part of this disclosure: 
       FIG. 1  is a side elevational view in section of a shrink-fit tool holder according to a first embodiment of the present invention; 
       FIG. 2  is a perspective view of the shrink-fit tool holder of  FIG. 1 , before a tool is shrink-fitted; 
       FIG. 3  is a perspective view of the shrink-fit tool holder of  FIG. 1 , when the tool is being centered; 
       FIG. 4  is a perspective view of the shrink-fit tool holder of  FIG. 1 , with the tool shrink-fitted; 
       FIG. 5  is a side elevational view in section of an adapter insert according to an embodiment of the present invention for positioning of the shrink-fit tool holder of  FIG. 1 ; 
       FIG. 6  is a side elevational view in partial section of a base adapter according to an embodiment of the present invention for use with the adapter insert of  FIG. 5 ; 
       FIG. 7  is an enlarged, side elevational view in section of detail VII of the base adapter of  FIG. 6 ; 
       FIG. 8  is a side elevational view in partial section of the base adapter of  FIG. 6 , with the adapter insert of  FIG. 5  in place; 
       FIG. 9  is a side elevational view in partial section of the adapter of  FIG. 8 , with the adapter insert of  FIG. 5  and the shrink-fit tool holder of  FIG. 1  in place; 
       FIG. 10  is a side elevational view in section of a shrink-fit tool holder according to a second embodiment of the present invention; 
       FIG. 11  is a perspective view of the tool holder of  FIG. 10 ; 
       FIG. 12  is a side elevational view in section of a shrink-fit tool holder according to a third embodiment of the present invention; 
       FIG. 13  is a perspective view of the tool holder of  FIG. 12 ; and 
       FIG. 14  is a side elevational view in section of an adapter according to another embodiment of the present invention with the shrink-fit tool holder inserted. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows a shrink-fit tool holder  1  having a through hole  3  for holding the tool shaft  16  of a tool  15  (see  FIGS. 2 to 4 ). The through hole  3  has a section  5  with a constant inside diameter. On one end the section  5  undergoes transition into a centering section  6  with a slightly widened inside diameter. On the other end, the section  5  undergoes transition into a section  7  with a likewise slightly widened inside diameter. 
   The shrink-fit tool holder  1  is configured as a rotationally symmetrical holder body. On its outer circumference the tool holder has a conical clamping section  9  tapering toward the free end. The wider end of the clamping section  9  is adjoined by a circumferential groove  10  used to hold the cam of a clamping screw (not shown). The circumferential groove  10  in the axial direction is followed by a conical section  12  tapering away from the circumferential groove  10 . The conical section  12  is used to ensure simple positioning or sliding over of the clamping nut with the cam. For this purpose, the largest outside diameter of the conical section  12  is larger than the pertinent inside diameter of the clamping nut with the cam. 
     FIG. 2  shows the tool  15 , for example, a drill, shortly before shrink-fitting into the shrink-fit tool holder. In  FIG. 3 , the free end of the tool shaft  16  for its centering is inserted into the centering section  6  of the shrink-fit tool holder  1 . In  FIG. 4  the shaft  16  of the tool  15  is shrink-fitted into the through hole  3 . 
     FIG. 5  shows an adapter insert  20  in a longitudinal section. The adapter insert  20  is configured rotationally symmetrical, and comprises a depression  22  used to hold the free end of the clamping section of the shrink-fit tool holder shown in  FIG. 1 . The depression  22  can be a cylindrical depression. In  FIG. 5  the depression  22  is made slightly conical to facilitate the placement of the shrink-fit tool holder. 
   The adapter insert  20  is equipped with a through hole  23 . The hole  23  comprises one hole section  24  and another hole section  25 , the hole section  24  having a larger inside diameter than the hole section  25 . In the hole section  25 , the hole  23  is penetrated by a through hole  26  which extends perpendicular to the through hole  23 . The hole  26  is used to hold a pretensioned ball which is used in turn to fix the adapter insert  20  in a base adapter  35  (see  FIG. 6 ). The through hole  23  extends centrally through the adapter insert  20 , and at the same time forms the longitudinal axis of this rotationally symmetrical component. 
   On its outer circumference the adapter insert  20  comprises four sections  29 ,  30 ,  31 , and  32 . The section  29  is located in the area of the depression  22 , and is slightly conical, the section  29  tapering toward its free end. The section  30  follows the conical section  29 , and has a constant outside diameter. The section  31  adjoins the section  30  and widens from the section  30  in a conical shape. The section  32  follows the section  31  and has a somewhat smaller outside diameter than the section  30 . 
     FIG. 6  shows the base adapter  35  in a longitudinal section which is likewise configured rotationally symmetrical. The base adapter  35  is equipped with a central holding hole  37  with an inside diameter matched to the outside diameter of the section  32  of the adapter insert  20 . In this way insertion of the adapter insert  20  with the section  32  into the holding hole  37  of the base adapter  35  is facilitated. 
   A circumferential groove  38  with a triangular cross section is formed in the holding hole  37 . As shown in the enlarged sectional view in  FIG. 7 , the groove flanks of the triangular groove  38  are configured at an angle  39  to one another. 
   As is shown in  FIG. 6 , the holding hole  37  is part of a central through hole  40  defining the longitudinal axis or axis of rotation of the base adapter  35 . The through hole  40  comprises three additional sections  41 ,  42 , and  43  with different inside diameters, proceeding from the holding hole  37 . The hole section  41  has the smallest and the hole section  43  has the largest inside diameter. In addition, an inside thread is formed in the hole section  41 . The outside the base adapter  35  has a section  44  with a widened outside diameter. 
     FIG. 8  shows the base adapter  35  from  FIG. 6  with the adapter insert  20  from  FIG. 5  in place. As is to be seen, the section  32  of the adapter insert  20  is held in the holding hole  37  of the base adapter  35 . A threaded bolt  50  is screwed into the section  41  with the inside thread of the base adapter  35 . One free end of bolt  50  projects into the section  42  of the through hole  40 . The other free end  51  of bolt  50  projects into the hole section  24  of the adapter insert  20 . Moreover, in the through hole  26  of the adapter insert  20 , a ball  52  is pretensioned using a spring  53 . The ball  52  is partially pressed out of the through hole  26  by the spring  53 . The part of the ball  52  projecting out of the through hole  26 , when the adapter insert  20  is in place in base adapter  35 , is held in the groove  38  of the base adapter  35 . In this way unwanted loosening of the adapter insert  20  from the base adapter  35  is prevented. 
     FIG. 9  shows how the shrink-fit tool holder  1  shown in  FIG. 1  is positioned with the free end of the clamping section  9  on the depression  22  of the adapter insert  20 . The section  43  of the through hole  40  is used to connect the base adapter  35  to a conventional heater (not shown). 
   By heating the shrink-fit tool holder of the present invention and by the resulting widening of the through hole  3 , the tool shaft  16  of a tool  15  can be reversibly or releasably connected securely to the shrink-fit tool holder  1 . The through hole  3  of the shrink-fit tool holder  1  relative to the cylindrical tool shaft  16  is configured smaller by at least approximately 0.01 mm, especially by at least approximately 0.02 mm, than the clamping diameter of the cutting tool  15 . The overlap of the inside diameter of the through hole  3  and the outside diameter of the tool shaft  16  is influenced among other factors by the material used. As a result of the change in the volume of solids, which is proportional to the temperature when heated, the inside diameter of the through hole  3  of the shrink-fit tool holder  1  is enlarged. The widening by heating is carried out in the elastic range of the material. Thus, the clamping process can be repeated as often as desired, that is, the process is reversible. 
   Heating of the tool holder, when the tool shaft is being shrink-fitted into the through hole of the shrink-fit tool holder, takes place in the temperature range from +100 to +380° C., especially +250 to +330° C. In the heated state of the shrink-fit tool holder  1 , the optionally supercooled tool shaft  16  can be inserted into the through hole  3 . Upon subsequent cooling of the shrink-fit tool holder  1  with the tool shaft  16  inserted to temperatures in the range from −20 to +110° C., the shrink-fit tool holder  1  tries to reach its initial state again. In the process, a clamping pressure is produced on the cylindrical tool shaft  16  in the radial direction by cooling of the shrink-fit tool holder  1 . The level of the clamping pressure is determined primarily by the overlap of the outside diameter of the tool shaft  16  with the inside diameter of the through hole  3  of the shrink-fit tool holder  1 . Little overlapping results in a low clamping pressure. Extensive overlapping results in a high clamping pressure. The clamping process is reversible and can be repeated any number of times as long as the deformation takes place in the elastic area of the material used. 
   In the conventional processes, the shrinkage area lies outside the clamping insert. This arrangement has the disadvantage that for each cutting tool clamping shaft diameter, a correspondingly complex and expensive tool holder is needed. The long structural shape moreover has the disadvantage that the radial load of the machining spindle rises significantly. This loading then leads to a loss of stiffness and radial deflection of the machining spindle. 
   The shrink-clamping system of the present invention does not require expensive, special tool holders, but can be installed in conventional universal draw-in collet chucks or machining spindles with collet chuck holders due to its mating outer configuration. By superposition of the shrinkage area with the clamping area, the shortest cutting tool chucking mechanisms can be accomplished. One major advantage is the maximum radial stiffness of the machining tools. This stiffness in turn results in extremely high surface qualities of the machined workpieces. 
   The shrinking-clamping process of the present invention takes place directly in the clamping cone. In this way, extremely short clamping of the cutting tools is possible. The clamp insert hole, also designated as the through hole  1 , is superimposed by the clamping cone also designated as the clamping section  9 . The shrink-fit clamping insert, which is also designated as the shrink-fit tool holder  1 , is very inexpensive to produce and can be inserted into any commercial standard collet holder. The shrink-fit tool holder  1  of the present invention compared to conventional clamping techniques permits two to four times higher torque transmission with simultaneously higher radial stiffness. 
   The shrinking-clamping system of the present invention enables short shrinking-in and shrinking-out times. A tool can be changed in seconds by inductive heating of the shrink-fit tool holder with high energy density. In this way, true running accuracies of the cutting tools of less than 3 μm can be implemented with maximum clamping force and radial stiffness. 
   The shrink-fitting of a tool shaft into a shrink-fit holder using an adapter of the present invention is described in what follows. First, the base adapter  35  must be connected to a suitable adapter insert  20  which is dependent on the shape and dimensions of the shrink-fit tool holder  1 . Then, the adapter which has been preassembled in this way is inserted into the base holder of a shrinking device (not shown). Then, the shrink-fit tool holder  1  is slipped onto the adapter insert  20 . An induction coil (not shown) is then centered and fixed over the shrink-fit tool holder  1 . After that the tool shaft  16  is inserted into the centering section  6  of the through hole  3 , and the shrinkage device is activated. 
   The through hole  3  of the shrink-fit tool holder  1  is enlarged by the change in volume which is proportional to temperature. As soon as widening of the through hole  3  of the shrink-fit tool holder  1  is greater than the outside diameter of the tool shaft  16 , the tool  15  by its own weight falls into the through hole  3 . The free end  51  of the threaded spindle  50  forms a stop for the free end of the tool shaft  16 . Then, the heat source can be turned off. Due to the cooling which now follows, the shrink-fit tool holder  1  tries to attain its original shape. This reshaping however is prevented by the tool shaft  16 . The resulting stress provides for the tool shaft  16  to be held positively and nonpositively in the shrink-fit tool holder  1 . 
   To accelerate the cooling process, the shrink-fit tool holder  1  with the tool shaft  16  located in it can be cooled in a cooling station (not shown). 
     FIG. 10  shows a second embodiment of a shrink-fit tool holder  101  of the present invention in a longitudinal section.  FIG. 11  shows the pertinent perspective view. The receiving or holding section  103  is formed by an opening which extends in the longitudinal direction of the shrink-fit tool holder, in this embodiment by a through hole which extends over the entire length. The end of the opening which is the left end in  FIG. 10  and which holds the tool is radially widened. In particular, a radius  161  is molded on this end, as especially shown in the enlargement of the corresponding extract of  FIG. 10 . The radius  161  is generally less than half the diameter of the holding section  103 , especially less than 20% of it, and preferably in the range of one mm or less. In this way, the tool can be easily and precisely inserted into the shrink-fit tool holder  101  without tilting. 
   On its end facing the clamping section  109 , the shrink-fit tool holder  101  has an opening which extends in the longitudinal direction of the shrink-fit tool holder and which forms another section  107 . Section  107  has a diameter greater than that of the holding section  103 . The opening as in the embodiment shown can be a section of a through hole. It could also be made as a blind hole. The opening is preferably cylindrical in the longitudinal direction, especially circular-cylindrical. 
   Due to the greater diameter, the wall thickness of the clamping section  109  is reduced in this further section  107 , for example, down to a few mm or only 1 mm on the free end. This ensures advantageous energy-storing, and thus, elastic deformation of the clamping section  109 . This arrangement is furthermore improved if one or more slots  162   a ,  162   b ,  162   c  are made in the further section  107  which have at least in sections an extension in the axial direction. In this embodiment, three slots  162   a ,  162   b ,  162   c  in the axial direction are uniformly distributed in the circumferential direction. The slots  162   a ,  162   b ,  162   c  can also extend obliquely to the axial direction. Except for the slots  162   a ,  162   b ,  162   c , the shrink-fit tool holder  101  is rotationally symmetrical relative to its longitudinal axis. 
   The wall thickness provided in the further section  107  is especially dependent on the materials, the tool dimensions, and the workpiece to be machined. Due to the reduced wall thickness, small differences of the cone angle can also be compensated by elastic deformation of the shrink-fit tool holder  101 , and a higher true running accuracy of the overall system is achieved. 
     FIG. 12  shows a third embodiment of a shrink-fit tool holder  201  of the present invention in a longitudinal section.  FIG. 13  shows the pertinent perspective view. In the third embodiment, the holding section  205  is offset from the middle to the end which holds the tool, and is overlapped only to a lesser degree by the clamping area  263  comprising the clamping section  209 , the groove  210 , and the conical section  212 . On the end which holds the tool, the holding section  205  can have a centering section as in the first embodiment. Moreover this end has a radius  261  of, for example, 0.1 to 5 mm, especially 0.2 to 3 mm, and preferably 0.4 to 2 mm, for simplified insertion of the tool. The overlap of the holding section  205  with the clamping area  263  is, for example, up to twice the clamping diameter. 
   On its end facing the clamping section  209 , the shrink-fit tool holder  201  has an opening which forms the section  207  and which is part of the through hole. From the end, slots  262   a ,  262   c  are configured axially analogously to the second embodiment. A section of the opening set back from the end has an internal thread  264 , into which a stop for the tool to be inserted can be precisely positioned. The axial extension of the further section  207  is, for example, twice the magnitude of the diameter of the further section  207 . A transition section between the inside thread  264  and the holding section  203  is preferably free of threads. 
   Especially under unfavorable spatial conditions in the working space between the workpiece clamping area and the cutting tool, this embodiment offers advantages especially for small milling tools, also because the elastically deformable region of the clamping area  263  is larger. 
     FIG. 14  shows a second embodiment of an adapter of the present invention with the inserted shrink-fit tool holder, in a longitudinal section. The second embodiment has a base body  135  and an adapter insert  120 . The adapter insert  120  can be assembled from two parts  120   a ,  120   b , the interface running at a right angle to the plane of the drawings of  FIG. 14  and parallel to the longitudinal axis of the configuration. Preferably, they are identical parts  120   a ,  120   b . The adapter insert  120  is made of an electrically insulating material, preferably of a fiber-reinforced ceramic, especially of a ceramic reinforced with glass fibers. 
   The two parts  120   a ,  120   b  can be clamped to one another by a preferably closed ring  165 . The ring  165  can be made of metal or of a temperature-resistant plastic. The base body  135  on its end facing the adapter insert  120  has a connecting piece with a groove  138  formed on its inside into which the ring  165  can fit. 
   An adjustment pin which extends through the adapter insert  120  can be inserted or preferably screwed into the base body, preferably centrally. The axial position of the tool can be inserted into the shrink-fit tool holder  1  can be adjusted with precision by the adjustment pin. 
   The depression  122  which faces the shrink-fit tool holder  1  and holds it extends in the axial direction so far that the clamping section  9  of the shrink-fit tool holder  1  is essentially overlapped. In this way, the clamping section  9  is covered during heating and a change of the surface, for example, by oxidation is thus advantageously prevented. To this end, the conical shape of the depression  122  can be matched to the conical shape of the shrink-fit tool holder  1  such that air is essentially excluded. Moreover, the shrink-fit tool holder  1  is reliably fixed in the adapter insert  120 . Furthermore, the shrink-fit tool holder  1  can be easily removed after shrink-fitting by the multipart adapter insert  120 . With inductive heating in the electrically insulating adapter insert  120 , no current is induced and heat forms in spite of the overlapping of the adapter insert  120  in the shrink-fit tool holder  1 . 
   While various embodiments have been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims.