Abstract:
The invention relates to a broaching tool, in particular a keyway broaching tool, comprising a holder which defines a longitudinal axis and has a shank, extending in the longitudinal direction, as support for a cutting body which can be fixed in a seat of the shank by means of a clamping device. The seat has a passage which is at a distance from the free end of the shank and extends transversely to the longitudinal axis and the inside of which forms guide surfaces for bearing surfaces of the cutting body, which can be inserted into the passage in an insertion direction. An end-position limit for the inserted cutting body is formed on guide surfaces and on associated bearing surfaces. The clamping device produces a force component on the cutting body which presses the latter against the end-position limit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a Continuation application of International patent application PCT/IB 2008/001076, filed Feb. 13, 2008, which claims the priority of German patent application DE 10 2007 008 081 filed Feb. 17, 2007. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Brief Summary of the Invention 
         [0003]    The invention relates to a broaching tool, in particular a keyway broaching tool, comprising a holder which defines a longitudinal axis and has a shank, extending in the longitudinal direction, as support for a cutting body which can be fixed in a seat of the shank by means of a clamping device. 
         [0004]    2. Related Prior Art 
         [0005]    If such broaching tools are used for machining operations in which the highest accuracy and high surface quality are required, two main requirements have to be met. Firstly, it must be ensured through high strength of the shank that forces and moments, in particular bending moments, which are introduced into the seat via the cutting body are absorbed by the shank in an absolutely reliable manner without changes in the geometry occurring. 
         [0006]    Secondly, the positional fixing of the cutting body itself in the seat of the shank must be designed to be absolutely secure. 
         [0007]    Both of these requirements cannot be easily met, in particular if the broaching tool, in particular during use as a keyway broaching tool, is intended for internal machining in a bore of a workpiece or in a hollow body. In order to achieve an adequate working depth in these cases, for example in order to achieve inner longitudinal keyways in a bore with sufficient keyway length, it is necessary for the shank to have a corresponding length. If the machining is to be carried out in bores having a relatively small diameter, this inevitably results in a slim, elongated design for the shank, a factor which is detrimental to the structural strength. In addition to this problem there is also the fact that the design of the seat for the cutting body results in a local reduction in the load-bearing material cross section of the shank, a factor which likewise impairs the structural strength. 
       SUMMARY OF THE INVENTION 
       [0008]    In view of these problems, the object of the invention is to provide a broaching tool, in particular a keyway broaching tool, in which an especially torsion-proof and deflectionresistant working position of the cutting body even in a comparatively slim design of the shank is ensured. Further, it is an object to provide a corresponding cutting body. 
         [0009]    According to the invention, this object is achieved in a first aspect by a broaching tool comprising a cutting body, a holder which defines a longitudinal axis and has a shank, extending in the longitudinal direction, as support for the cutting body, a clamping device for fixing the cutting body in a seat of the shank; wherein the seat has a passage which is at a distance from the free end of the shank and extends transversely to the longitudinal axis and the inside of which forms guide surfaces, for bearing surfaces of the cutting body, which can be inserted into the passage in an insertion direction, wherein an end-position limit for the inserted cutting body is formed on guide surfaces and on associated bearing surfaces, and wherein the clamping device produces a force component on the cutting body which presses the latter against the end-position limit. 
         [0010]    Owing to the fact that, according to the invention, the seat of the cutting tool is formed by a passage in the shank, said passage forming a guide for the cutting body to be inserted into the passage, wherein guide surfaces of the passage bear against bearing surfaces of the cutting body, the cutting body is accommodated in the passage in a matching, enclosed manner and thereby forms a reinforcing body which compensates, as it were, for the reduction, caused by the forming of the passage, in the material cross section of the shank. Owing to the fact that, according to the invention, an end-position limit is also provided for the inserted cutting body and the clamping device is designed in such a way that it produces a force component on the cutting body which presses the latter against the end-position limit, optimum positional fixing of the cutting body is obtained by the bearing surfaces thereof bearing against the guide surfaces of the passage in which the cutting body is enclosed. 
         [0011]    With regard to the design of the end-position limit, the arrangement can be made in such a way that at least one surface part projecting from a bearing surface is provided on the cutting body, said surface part forming a stop surface which, when the cutting body is inserted, comes to bear against a step, forming a counter-stop, of a guide surface of the passage. 
         [0012]    In alternative exemplary embodiments, however, the arrangement can also be made in such a way that at least one surface part of the guide surface of the passage forms a sloping surface which is inclined relative to the insertion direction and against which a slope, forming part of the bearing surface, of the cutting body bears when the latter is inserted into the desired end position. 
         [0013]    Irrespective of the design of the end-position limit, it is ensured that the positional setting and fixing of the cutting body is effected with the greatest accuracy owing to the fact that the clamping device, when clamping the cutting body in place, produces a force component on the cutting body which presses the latter against the end-position limit. 
         [0014]    In advantageous exemplary embodiments, the cutting body has a parent member in the form of a plate which is to be accommodated in the passage of the shank and whose wide sides opposite one another form bearing surfaces for the guide surfaces of the passage. Due to such bearing against the inside of the passage over a large area, the parent member of the cutting body especially helps to reinforce the structure of the shank. 
         [0015]    In such exemplary embodiments, the clamping device can advantageously have a clamping screw which passes through a hole in the parent member of the cutting body, said hole running perpendicularly to the wide sides, defining parallel planes, of said parent member, wherein, for the clamping screw, a tapped hole is provided on the shank in one of the guide surfaces of the passage. This configuration opens up the advantageous possibility of realizing on the cutting body, in a simple manner in terms of design, the desired force component for bearing against the end-position limit by the relative positional arrangements of the hole in the parent member of the cutting body, of the tapped hole in the passage of the shank and of the end-position limit for the cutting body being selected in such a way that the tightening of the clamping screw produces both a clamping force and the force component which acts in the insertion direction and presses the projecting surface part of the cutting body against the counter-stop of the passage in the desired manner or presses the slope of the cutting body against the sloping surface of the passage of the shank. 
         [0016]    The cutting body preferably has at least one cutting edge on an extension, extending radially relative to the longitudinal axis, of the parent member. 
         [0017]    In especially advantageous exemplary embodiments which permit especially efficient and economical production of longitudinal keyways in bores, two extensions opposed to one another are provided on the parent member in order to form two cutting edges which extend in a radially projecting manner, diametrically relative to one another, from the shank and work with a pushing action in working directions opposed to one another. 
         [0018]    In this case, the arrangement can be made in such a way that the extensions are designed to be axially symmetrical to one another, preferably symmetrical to the axis of the hole which is provided in the parent member for the clamping screw. 
         [0019]    The object is also achieved according to another aspect of the invention by a cutting body for use in a broaching tool according to the invention, wherein the cutting body comprises a plate-like parent member which has at least one extension forming a cutting edge, and comprising a hump projecting on a wide side of the plate-like parent member and having a step which forms a stop surface for a counter-stop in the seat of the tool holder. 
         [0020]    According to still another aspect the invention relates to a cutting body for a broaching tool according to the present invention, comprising a plate-like parent member which has at least one extension forming a cutting edge and has a sloping surface on a narrow side, which sloping surface, for the end-position limit, can be brought to bear against a sloping surface formed in the seat of the tool holder. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The invention is explained in detail below with reference to exemplary embodiments shown in the drawing, in which: 
           [0022]      FIG. 1  shows a perspective oblique view of an exemplary embodiment of the broaching tool according to the invention, shown virtually twice full size compared with a practical embodiment; 
           [0023]      FIG. 2  shows a perspective oblique view, depicted at an even larger scale, of a cutting body for the exemplary embodiment in  FIG. 1 ; 
           [0024]      FIG. 3  shows a side view, depicted approximately at the scale of  FIG. 1 , of the exemplary embodiment; 
           [0025]      FIG. 4  shows a longitudinal section along section line IV-IV in  FIG. 3 ; 
           [0026]      FIG. 5  shows a longitudinal section, corresponding to  FIG. 4 , of a second exemplary embodiment of the broaching tool, only the front part of the shank being shown in a truncated illustration; 
           [0027]      FIG. 6  shows a side view, similar to  FIG. 3 , of both the first and the second exemplary embodiments, but rotated by 90 degrees relative to  FIG. 3  and the shank being located inside the bore, to be machined, of a schematically indicated workpiece; 
           [0028]      FIG. 7  shows a section along section line VII-VII approximately 1.5 times enlarged compared with  FIG. 6 , the workpiece not being shown; 
           [0029]      FIGS. 8 and 9  show a front view and a side view, respectively, of the cutting body, shown in perspective in  FIG. 2 , of the first exemplary embodiment, approximately 3.5 times enlarged compared with a practical embodiment; 
           [0030]      FIG. 10  shows a front view, corresponding to  FIG. 8 , of the cutting body for the second exemplary embodiment of the broaching tool, and 
           [0031]      FIG. 11  shows a plan view, approximately 8 times enlarged compared with a practical embodiment, of the cutting body of the first exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0032]    The holder  1 , designated by  1  overall in  FIGS. 1 and 3 , has a rear clamping part  3  with which the broaching tool can be clamped in place in a machine tool (not shown), by means of which the tool can be moved in the direction of the tool longitudinal axis  4  ( FIGS. 3 and 6 ) for a reciprocating broaching operation in the forward direction and rearward direction. Adjoining the clamping part  3  is a shank  5 , which is narrowed relative to the clamping part  3  and the front shank end of which is designated by  7 . Whereas the clamping part  3  is by and large of circular-cylindrical shape, the outer surface of the shank  5  has contouring with flat surface regions  9  and  11 , see in particular  FIG. 1 . At a small distance from the front end  7 , the shank  5  has a passage  13 , the inside of which forms guide surfaces for a cutting body which can be inserted in an insertion direction and is depicted overall by  15  in the figures. Further details of the cutting body  15  are illustrated in particular in  FIGS. 8 to 11 . The passage  13  has inner guide surfaces  17  in planes parallel to one another and to the longitudinal axis  4  and guide surfaces  19  in planes running transversely to the longitudinal axis  4 . In interaction with bearing surfaces of the cutting body  15  to be pushed in, these guide surfaces  17  and  19  form a matching guide, into which the cutting body  15  can be pushed in an insertion direction, to be precise from an entry end of the passage  13 , said end being shown in  FIGS. 1 ,  3  and  4  and  5  as that end of the passage  13  which lies at the top, where the passage is widened via sloping surfaces  21  and  23 . The cutting body  15  can be inserted from the insertion end right into an end position which is defined by an end-position limit and in which the guide surfaces  17  and  19  bear in a matching manner against the associated bearing surfaces of the cutting body  15 . 
         [0033]    As mentioned,  FIGS. 8 to 11  show further details of the cutting body  15 , where  FIGS. 8 ,  9  and  11  show a cutting body  15  for a first exemplary embodiment and  FIG. 10  shows a cutting body  15  for a second exemplary embodiment. In both exemplary embodiments, the cutting body  15  has a plate-like parent member  25 , the wide sides  27  of which run in planes parallel to one another. These wide sides  27  form, with surface regions, the bearing surfaces for the guide surfaces  17  of the passage  13 . The by and large rectangular parent member  25  forms, with its planar narrow sides  29  parallel to one another, the bearing surfaces for the guide surfaces  19  in the passage  13 . 
         [0034]    The cutting bodies  15  of both exemplary embodiments have extensions  31  on two diametrically opposite corner regions of the parent member  25 , said extensions  31  being formed axially symmetrically to one another and forming a respective cutting edge  33 . As can be seen most clearly from  FIG. 8 , the extensions  31  are symmetrical to the axis of a through-hole  35  which is located in the center of the wide sides  27  of the parent member  25  and has a tapered widening  37  at one hole end. 
         [0035]    As already mentioned, the cutting body  15  can be inserted from the insertion end of the passage  13  in an insertion direction into the guide, in which guide surfaces  17 ,  19  are guided on the bearing surfaces formed by the wide sides  27  and the narrow sides  29  of the cutting body, to be precise right up to an end-position limit. The first and the second exemplary embodiments to be described here differ merely with regard to the design of the end-position limit. As shown in  FIG. 7 , a widening  38  is provided for this purpose in the passage  13  in the first exemplary embodiment, a step  39  being formed on the guide surface  17  by this widening  38 . This step  39  forms a counter-stop for a stop surface which is formed on the parent member  25  of the cutting body  15 . The configuration on the parent member  25  in this respect can best be seen from  FIGS. 4 ,  8  and in particular  11 . As shown there, a hump  41  rises from the one wide side  27  of the parent member  25 , and this hump  41  forms a plateau defined on three sides by bevels  43  and having a stop surface  45  which is perpendicular thereto and is located on the fourth side and which, when the cutting body  15  is in the end position in the passage  13 , interacts with the step  39 , forming the counter-stop, in the passage  13 . 
         [0036]    As already mentioned, the parent member  25  of the cutting body has a central hole  35  with a conical widening  37  at the end. A clamping screw  47  passes through this hole  35 , as a component of the clamping device, and can be screwed into a tapped hole  49  opening out at the guide surface  17  of the passage  13 . Like a countersunk head screw, the clamping screw  47  has a screw head  51  widening conically from the screw shank. As can best be seen from  FIG. 7 , in which the cutting body  15  is shown in its end position, the tapped hole  49  and the through-hole  35  in the parent member  25  of the cutting body  15  are eccentric to one another in such a way that, when the clamping screw  47  is tightened, the conical head  51  in interaction with the conical end widening  37  of the hole  35  produces a force component on the cutting body  15  which thrusts the latter downward in the direction of view according to  FIG. 7 . This means not only that the clamping screw  47  clamps the cutting body  15  in place, by the wide side  27  of the parent member  25  being pressed against the guide surface  17  of the passage  13 , but that the stop surface  45  formed on the hump  41  of the cutting body  15  is pressed, for a defined end-position limit, against the step  39  in the passage  13 . 
         [0037]    As shown by the comparison of  FIGS. 8 and 10 , the cutting body  15  of the second exemplary embodiment does not have a hump  41  on the parent member  25 . Instead, in order to form the end-position limit, that narrow side  29  of the parent member  25  which lies at the bottom in  FIG. 10  has an inclination relative to the other narrow side  29 , this inclination being in the order of magnitude of about 11 angular degrees in the exemplary embodiment shown. In a corresponding manner, as shown in  FIG. 5 , the associated guide surface  19  of the passage  13  has a corresponding inclination. Whereas in the first exemplary embodiment the passage  13 , at that guide surface  17  which is provided with the aperture  53  for the clamping screw  47 , has a widening  38 , forming the step  39 , as counter-stop for the hump  41  of the cutting body, this guide surface  17  in the second exemplary embodiment is continuous except for the aperture  53 . In the same way as in the first exemplary embodiment, however, the tapped hole  49  and the hole  35  in the parent member  25  of the cutting body  15  in the second exemplary embodiment are also eccentric in such a way that, when the clamping screw  47  is tightened, the conical surface on the head  51  in interaction with the conical end widening  37  of the hole  35  produces a force component on the cutting body  15  along the guide surfaces  17  in such a way that the sloping narrow side  29  of the parent member  25  and the sloping guide surface  19  of the passage  13  bear against one another in the end position, as a result of which a push-in movement is limited by the resulting constriction of the guide in the end position. 
         [0038]    Owing to the fact that, in both exemplary embodiments, extensions  31  which are symmetrical to one another and have cutting edges  33  are provided on the parent member  25  of the cutting body  15 , the tool according to the invention is especially suitable for forming a plurality of longitudinal keyways  55  in the bore  57  of a workpiece  59  in a, as it were, “continuous” machining operation, said workpiece  59  merely being indicated schematically in  FIG. 6 . Due to the symmetrical arrangement of the extensions  31  having the cutting edges  3 , the tool works with a pushing action in both directions of the reciprocating working movement, such that, during a working cycle in which a reciprocating relative movement is produced between holder  1  and workpiece  59 , for example by the holder being driven longitudinally, two keyways  55  opposite one another can be machined. In the process, the radial infeed movement can be effected either by feed movements imparted to the workpiece  59  or by infeed of the holder  1 . In order to produce keyways  55  distributed over the inner circumference of the relevant bore  57 , the workpiece  59  can be rotated relative to the holder  1  or the latter can be rotated relative to the workpiece  59 .