Abstract:
In a tool system for machining, having at least one receptacle for a cutting insert which can be brought at least partly with a bearing surface of convex curvature into contact with a supporting surface of concave curvature on the receptacle, the convexity and concavity of bearing surface and supporting surface, respectively, which face one another, define lines of curvature which are different from one another and of which at least one deviates from the circular form.

Description:
CROSSREFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of international patent application PCT/EP2006/006806, filed on Jul. 7, 2006 designating the U.S., which international patent application has been published in German language as WO 2007/087835 A1 and claims priority from German patent application 10 2006 001 747.1, filed on Jan. 13, 2006. The entire contents of these priority applications are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to a tool system for machining, having at least one receptacle for a cutting insert which can be brought at least partly with a bearing surface of convex curvature into contact with a supporting surface of concave curvature on the receptacle. 
       RELATED PRIOR ART 
       [0003]    Tool systems of this type are known, cf. EP 1 591 179 A2. In such systems, the cutting insert, preferably in the form of a cutting tip, is formed with a cutting edge, projecting at a distance from the bearing surface, in such a way that it can be inserted in the receptacle. If the cutting insert is rotated after insertion in the receptacle, such that its bearing surface moves along the supporting surface on the receptacle, the cutting insert is fixed on account of eccentricity of the curvatures of the interacting surfaces. 
       SUMMARY OF THE INVENTION 
       [0004]    With regard to operational reliability and the highest accuracy during the machining operations, satisfactory fixing of the cutting insert in position in the receptacle is of prime importance. The object of the invention is therefore to provide a tool system for machining which meets the requirements with regard to the fixing of the cutting insert in position to an especially high degree. 
         [0005]    According to an aspect of the invention, this object is achieved by a tool system for machining having:
       a cutting insert and   at least one receptacle for the cutting insert which can be brought at least partly with a bearing surface of convex curvature into contact with a supporting surface of concave curvature on the receptacle,
 
wherein the convexity and concavity of bearing surface and supporting surface, respectively, which face one another, define lines of curvature which are different from one another and of which at least one deviates from the circular form, and
 
wherein the course of the line of curvature of the bearing surface mostly corresponds to a helix having a pitch intensifying the convexity and/or in that the course of the line of curvature of the supporting surface mostly corresponds to a helix having a pitch intensifying the concavity.
       
 
         [0008]    The fact that according to this aspect the bearing surface of the cutting insert and the supporting surface on the receptacle define lines of curvature which are different from one another and of which at least one deviates from the circular form with regard to the type of curvature opens up the possibility, on account of the rotary movement of the cutting insert, of realizing a desired increase of the resulting clamping force as a function of the increase in the angle of rotation. 
         [0009]    Compared with the abovementioned prior art, where a respective circular curvature course is provided for both the bearing surface and the supporting surface, the invention enables the cutting insert to be easily inserted into the receptacle in a freely accessible manner in the initial rotary position and achieves the effect that, during subsequent rotation, an increasing clamping force up to a maximum upon reaching the end position of the cutting insert is produced. 
         [0010]    In a preferred embodiment the cutting insert provided is a cutting tip having a bearing surface which follows, at least in a certain region, a line of curvature corresponding to an arc of a circle, the helical course of the line of curvature is provided on the supporting surface of the receptacle. The pitch is in this case oriented in such a way that, on the supporting surface, the curvature of the concavity increases in the direction of rotation of the cutting tip. 
         [0011]    In advantageous exemplary embodiments, the supporting surface, at one end of the receptacle, has an end section which follows a rectilinear course and is intended for contact with a counterholding surface which is provided on the cutting tip for supporting against cutting forces acting during operation. 
         [0012]    This end section not only absorbs the cutting forces produced at the cutting edge of the cutting tip during operation but also forms, in interaction with the counterholding surface of the cutting tip, a first stop for fixing the rotary end position of the cutting tip. At the same time, the helical course of the supporting surface adjoins the inner end of the straight end section, this course extending up to the end of the supporting surface. 
         [0013]    In this case, the arrangement may be made in such a way that following the end of the helical course of the supporting surface, there is a stop surface on the receptacle, said stop surface projecting toward the interior of the helix and forming a support for a further counterholding surface which is provided on the cutting tip for supporting against cutting forces and forms a further stop which defines the rotary end position of the cutting tip. 
         [0014]    In especially advantageous exemplary embodiments, the receptacle is designed like a pocket in a parent body in which a slot opening is cut out, and this slot opening cuts free an elastically flexible clamping part in the parent body, which clamping part surrounds a large part of the helical course of the supporting surface and ends in front of the stop surface. Whereas frictional clamping of the cutting tip is therefore effected in the corresponding region of the helical course, wherein the clamping force depends on the elasticity properties, i.e. on the material cross section cut free, of the clamping part, the stop surface, which is offset from the clamping part cut free, forms a positive-locking stop for the associated counterholding surface of the cutting tip. 
         [0015]    In order to ensure that the cutting tip is also satisfactorily fixed against transverse forces acting transversely to the cutting force, the supporting surface may have a V-shaped recess for laterally fixing a cutting tip which is provided with a bearing surface projecting in an inverted V shape. 
         [0016]    The tool system according to the invention is especially suitable for use in rotary tools, in particular milling tools, wherein the parent body may be a disc rotatable about a tool axis and having a plurality of receptacles, distributed over its periphery, for cutting tips. 
         [0017]    According to another aspect of the invention, a cutting insert for a tool system for machining is provided, having at least one receptacle for a cutting insert which can be brought at least partly with a bearing surface of convex curvature into contact with a supporting surface of concave curvature on the receptacle, 
         [0000]    wherein the convexity and concavity of bearing surface and supporting surface, respectively, which face one another, define lines of curvature which are different from one another and of which at least one deviates from the circular form, and
 
wherein the course of the line of curvature of the bearing surface mostly corresponds to a helix having a pitch intensifying the convexity.
 
         [0018]    According to another aspect of the invention, tool system parent body for a tool system for machining, having at least one receptacle for a cutting insert which can be brought at least partly with a bearing surface of convex curvature into contact with a supporting surface of concave curvature on the receptacle, 
         [0000]    wherein the convexity and concavity of bearing surface and supporting surface, respectively, which face one another, define lines of curvature which are different from one another and of which at least one deviates from the circular form, and
 
wherein the course of the line of curvature of the supporting surface mostly corresponds to a helix having a pitch intensifying the concavity.
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The invention is explained in more detail below with reference to an exemplary embodiment shown in the drawing, in which: 
           [0020]      FIG. 1  shows a perspective oblique view of an exemplary embodiment of the tool system according to the invention in the form of a milling cutter, wherein, of the plurality of cutting inserts to be accommodated on the parent body, only a single cutting tip is shown; 
           [0021]      FIG. 2  shows a truncated and perspective view, on a much larger scale compared with  FIG. 1 , of only the region of a cutting tip receptacle of the parent body of  FIG. 1  without inserted cutting tip; 
           [0022]      FIG. 3  shows a view corresponding to  FIG. 2 , a cutting tip being shown in the receptacle in a position assumed before the fixing; and 
           [0023]      FIG. 4  shows a view corresponding to  FIG. 3 , the cutting tip being shown in fixed end position. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0024]    The invention is shown below taking a milling cutter as an example, which is designated overall by  1  in  FIG. 1  and has a disc-like parent body  3 , which can be rotated mechanically in a known manner and has, distributed over its periphery, a number of pocket-like receptacles  5  for cutting inserts in the form of cutting tips  7 . As can be seen from  FIG. 1  and from  FIGS. 3 and 4 , the cutting tips  7  are in the form of a disc whose thickness measured between its flat side walls corresponds to the thickness of the parent body  3 . In a conventional manner, the cutting tips  7  can be fixed in the relevant receptacle  5  by a rotary movement and can be released by a rotary movement in the opposite direction.  FIG. 1  shows, as an auxiliary tool for rotating the cutting tips  7 , a polygonal wrench  9  having a polygonal driver  11  for the engagement in a corresponding polygonal opening  13  in the cutting tip  7 . 
         [0025]      FIGS. 2 to 4  show further details of the fixing of the cutting tips  7  in the receptacles  5 . Provided as a main element for this purpose on the cutting tip  7  is a bearing surface  15  of convex curvature, the start and the end of which are in each case situated at a distance from the cutting edge  17  of the cutting tip  7 . As can be seen in particular from  FIG. 3 , a straight end part  21  adjoins the start  19  of the concave curvature of the bearing surface  15 , said end part  21  forming on the cutting tip  7  a counterholding surface, which, in the fixing end position shown in  FIG. 4 , supports the cutting tip  7  against the cutting forces, acting via the cutting edge  17 , on the receptacle  5 . As  FIGS. 3 and 4  show, the bearing surface  15  and the end part  21  adjoining it are profiled, to be precise by a marginal cross sectional shape like an inverted V. Protection of the cutting tip  7  against lateral forces is obtained in interaction with a corresponding V shape of a recess  23  ( FIG. 3 ) in the receptacle  5 . Proceeding from the starting point  19 , the convex course of the bearing surface  15  extends in the shape of an arc of a circle up to the end  25  ( FIG. 3 ) situated at a distance from the cutting edge  17 , and a surface  27  running inward in a step-like manner adjoins said end  25 . This surface  27 , in addition to the end part  21 , which forms a first counterholding surface, forms a further counterholding surface for supporting relative to the cutting forces acting on the cutting edge  17 , as will be described in more detail below. 
         [0026]    As an essential component for fixing the cutting tip  7 , the receptacle  5  has a concavity-forming supporting surface  29 , which, as mentioned, forms a V-shaped recess  23 . At the end adjoining the outer periphery of the parent body  3 , the supporting surface  29  has an end section  31  which follows a rectilinear course and extends, with a length corresponding to the straight end part  21  of the cutting tip  7 , from the outer end up to a starting point  33  ( FIG. 2 ), where the curved course of the supporting surface  29  begins, said curved course extending up to the end  35  of the supporting surface  29 . In the present example, this curved course corresponds to a helix having a pitch intensifying the concavity on the receptacle  5 . In a practical example for a cutting tip  7  having a bearing surface  15  of a radius in the order of magnitude of 7 mm, a helix having a pitch of −0.27 mm, for example, is suitable, which corresponds to shortening of the radius of about 0.15 mm over an angular range of 200°, measured from the start  33  to the end  35  of the supporting surface  29 . 
         [0027]    If the cutting tip  7  is rotated clockwise from an initial position corresponding to  FIG. 3 , the helical course of the supporting surface  29  leads to an increasing clamping force between bearing surface  15  and supporting surface  29 . This clamping force acts at the parent body  3  on an elastically flexible clamping part  37 . The latter is cut free by a curved slot opening  39  in the parent body  3 , the slot opening  39  being directed in such a way that a curved body surrounds most of the helical course of the supporting surface  29 . As  FIG. 2  shows, the height of the side walls of the V-shaped recess  23  of the supporting surface  29  decreases down to the root of the V-shaped recess  23  in a region  41  situated approximately centrally in the length of the supporting surface  29 . This results in a reduction in the material cross section, i.e. a material weakening for promoting the elastic flexibility of the clamping part  37 , in the corresponding section  43  of the clamping part  37 . 
         [0028]    As  FIGS. 2 to 4  show, the parent body  3 , in front of the end  35  of the supporting surface  29  and thus in front of the corresponding end of the clamping part  37 , forms a stop surface  45  projecting toward the interior of the helix. In the fixing end position, shown in  FIG. 4 , of the cutting tip  7 , this stop surface  45  forms a support for the already mentioned surface  27  at the end  25  of the bearing surface  15  of the cutting tip  7 . The latter therefore has, in addition to the first counterholding surface formed by the end part  21  of the supporting surface  15 , a second counterholding surface, namely the surface  27 , which adjoins the end  25  of the bearing surface  15  in a step-like manner. The surface  27  of the cutting tip  7  also serves, in conjunction with the surface  45  of the parent body  3 , as a support against centrifugal forces, resulting from rotation for example. 
         [0029]    The invention is explained above with reference to the example of a milling tool. It goes without saying the invention can equally be used in non-rotating tools. Whereas the helical course is provided at the concavity, and convexity in the shape of an arc of a circle is used, it goes without saying that a circular course could also be provided on the receptacle and a helical course on the cutting tip, or a helical course could be provided on both the cutting tip and the receptacle, wherein only different pitches would have to be provided.