Abstract:
A cutting insert includes a body that forms top and bottom surfaces, and a center hole intersecting at least the top surface (e.g., a through-hole). A portion of the top surface which extends around the center hole includes an array of projections radiating laterally outwardly around the center hole. A distal end of each projection disposed farthest from the center hole defines a tip of the projection. The projections form at least six tips spaced circumferentially apart. Each tip has a planar top face. A clamp has flat contact surfaces which press downwardly against the planar top faces of respective projections simultaneously as the clamp pulls the insert against an upstanding support surface.

Description:
This application is a Continuation of International Application Serial No. PCT/SE03/01749 filed on Nov. 12, 2003, and which published as WO 2004/058437 on Jul. 15, 2004. 

   BACKGROUND 
   The present invention relates to plate-like cutting inserts, intended for chip removing machining of metallic materials, the inserts having a central hole for receiving part of a clamp. Such indexable inserts normally have cutting tip angles below 80° and are usually intended for different types of copying. On the market, there is now a plurality of different types of insert holders, which are especially adapted for such indexable inserts, such as rhombic, rhomboid or isosceles triangular indexable inserts. The material used to make such indexable inserts is normally sintered cemented carbide or ceramics. 
   A frequently used type of indexable insert is provided with a so-called wiper geometry outside in each active cutting corner. The meaning of this is a radius-modified corner geometry, with the corner radius in the cutting corner being composed of a plurality of small radii adjacent each other, with each radius portion adjoining the next radius portion having another radius size. With this type of geometry, it has become possible to increase the feeding of the cutting insert significantly at the same time as a desired good surface finish of the machined workpiece can be attained. Upon the use of such cutting inserts having a wiper geometry, the cutting insert is not clamped by the usual lever holders, e.g., of the type shown and disclosed in U.S. Pat. No. 3,314,126. Upon use of a wiper insert, it is now desirable to employ a holder system, which upon clamping of the cutting insert, applies not only an inward-drawing force but simultaneously also a downward-pressing force. This represents in itself a certain limitation as for the choice of geometries for the upper chip side of the cutting insert. 
   OBJECTS AND SUMMARY OF THE INVENTION 
   Against this background, it is an object of the present invention to provide a new insert design, which on the one hand, is adapted for an efficient locking by means of the above-mentioned type of insert holder having inward-directed as well as downward-directed tensile forces, and which on the other hand leaves a sufficiently large margin on the top side of the cutting insert in order to, e.g., enable desired corner marking or other geometric marking or which enables insertion of more advanced chip breaker geometries directly pressed into the upper chip surface. 
   The present invention relates to a cutting insert which comprises a body that forms top and bottom surfaces, and a center hole intersecting at least the top surface (e.g., a through-hole). A portion of the top surface which extends around the center hole includes an array of projections radiating laterally outwardly around the center hole. A distal end of each projection disposed farthest from the center hole defines a tip of the projection. The projections form at least six tips spaced circumferentially apart. Each tip has a planar top face. 
   The invention also relates to a cutting tool employing such a cutting insert in combination with a holder and a screwed-in clamp. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described closer in detail in connection with preferred embodiments of the invention shown in the drawings: 
       FIG. 1  shows a side view of an insert holder and an indexable cutting insert according to a first embodiment of the invention, 
       FIG. 2  shows a top plan view of an insert holder in cooperation with an indexable insert according to  FIG. 1 , 
       FIG. 3  shows bottom view of a clamp shown in  FIGS. 1–2 , 
       FIG. 4  shows a top plan view of an indexable insert according to  FIGS. 1–2 , 
       FIG. 4   a  is a fragmentary view of the insert showing one type of projection in an array of projections, 
       FIG. 4   b  is a fragmentary view of another part of the insert showing another projection in the array, 
       FIGS. 5   a – 5   c  show the clamp and the indexable insert in three respective cutting positions, 
       FIG. 6  shows a top perspective view of an alternative insert shape according to the invention, and 
       FIG. 7  shows a top perspective view of an additional insert shape according to the invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   The indexable insert  10  shown in  FIGS. 1–2  is shown in cooperation with a holder clamp  11 . The indexable insert has, in this shown embodiment, a rhombic base shape and cutting tip angles δ below 80°. The planar top and bottom surfaces  12  and  13  of the indexable insert, which are mutually parallel, form a right angle to the edge surfaces uniting them. The indexable insert  11  has a central through hole  14 , the center axis of which is oriented perpendicularly to the flat surfaces  12  and  13  of the cutting insert. The seating in which the indexable insert  10  is received comprises a bottom support surface  15  and two side support surfaces  16  and  17  upstanding perpendicularly from the surface  15 . The bottom support surface  15  may be formed either by an insert holder  18 , as in the shown embodiment, or by a separate conventional shim plate (not shown) mounted by means of a suitable fastening means (not shown). 
   So as to enable clamping of the indexable insert  10  in the seat of the insert holder, the clamp  11  is maneuverable by means of a tightening screw  21  extending through an elongate recess  19  of the clamp and threadedly connected in a threaded boring  20  in the holder  18 . The center axis C 1  of the boring  20  is oriented parallel to the center axis C 2  of the insert hole  14 . The clamp  11  includes an arm  2 , the front end of which has a downwardly-inwardly directed projection  22  extending into the insert&#39;s center hole  14  and having a surface  4  facing the boring  20  and oriented at an oblique angle α in relation to the center axis C 2  of the hole  14 . The projection  22  is arranged to be brought to engagement with a rear portion of the wall of the hole  14  i.e., a portion of that wall that is closest to the screw  21 . The engagement occurs at a contact point  23  a distance down in the insert hole. Simultaneously, contact surfaces of the bottom side  6  of the clamp arm  2  engage the top surface  12  of the cutting insert at locations  24  near the rear side of the center hole  14 . 
   The opposite rear end of the clamp arm  2  comprises a second projection  25  which is received in a recess  26  in the insert holder  18 , the end surface  27  of the projection  25  being convexly formed and arranged to be brought into surface contact with a corresponding planar stop face  28  of the recess  26 , which stop face is formed at an oblique angle to the center axis C 1  of the tightening screw. Alternatively, the end surface  27  may be flatly formed for surface contact with the planar stop face  28 . The size of the oblique angle a should be substantially the same as, or somewhat less than, the acute angle of inclination β at which the rear contact surface  28  in the holder is oriented. 
   According to the invention, the portion of the upper surface of the cutting insert extending around the central hole  14  includes an array of projections which radiate laterally outwardly around the center hole and which can be raised or recessed with respect to the adjacent portions of the insert&#39;s top surface. For example, in  FIGS. 1–5   c  there is an array  29 . of projections  40  which radiate around the center hole  14  in a laterally outward direction, i.e., laterally relative to the axis C 2  of the center hole  14 . Each projection has a planar (flat) top face  42  which is spaced from adjacent portions of the insert&#39;s top surface, e.g., the projections are recessed with respect to those adjacent surface portions, but they could instead be raised. The distal ends  30  of the projections, i.e., the ends of the projections spaced farthest from the center hole, could be in the form of one or more tips, which could be sharp, rounded or blunt. 
   For example, in the embodiment shown in  FIGS. 1–5   c , there are six projections  40   a – 40   f  which are joined together to create a generally star-shaped projection array as viewed in  FIG. 4 . Each of the projections  40   a  and  40   d  has a distal end comprised of two sharp tips  30   a ,  30   b  (e.g., see  FIG. 4   a ), whereas each of the remaining projections has a distal end comprised of three sharp tips  30   c ,  30   d ,  30   e  (e.g., see  FIG. 4   b ). 
   In a polygonally shaped insert having a pair of oppositely disposed corners which are bisected by a common imaginary bisector that passes through the center of the center hole, the projection array is preferably configured symmetrically about that bisector. 
   For example, in the rhombic-shaped insert shown in  FIGS. 1 through 5   c , a bisector B bisects two opposing acutely-angled corners G, G′ of the insert  10  and passes through the center of the hole  14 . The projections  40   a ,  40   d  (each of whose distal end comprises two tips  30   a ,  30   b ) are arranged symmetrically with respect to the bisector B such that the tips  30   a ,  30   b  are symmetrically disposed on opposite sides of the bisector. 
   The substantially star-shaped array  29  is intended to be in surface contact (in contrast to point contact or line contact) with contact surfaces of the clamp arm  2  at locations situated near the central insert hole  14 , namely a pair of spaced-apart flat (planar) contact surfaces  32   a  and  32   b . A laterally inner edge of the array  29  coincides with the hole  14 . 
   The contact surfaces  32   a ,  32   b  are shown as being arc-shaped, having a tapering width. Alternatively, other shapes are possible, such as triangular as shown at  33   a  and  33   b  in  FIG. 4 . 
   In  FIGS. 5   a ,  5   b  and  5   c  is shown how the indexable insert  10  can enable exposure of the acute-angled cutting corner, designated  34  in  FIG. 5   a , as well as the obtuse-angled cutting corner, designated  35 , for chip forming machining with one and the same type of clamp. 
   In  FIG. 6 , an alternative insert  10 ′ having a projection array  29 ′ is shown, having six spaced-apart heart-shaped projections  36   a ,  36   b ,  36   c ,  36   d ,  36   e  and  36   f  radiating laterally outwardly around the center hole. The distal end of each projection comprises two convexly rounded tips  50   a ,  50   b . Planar top faces of the projections are parallel with the surrounding flat surface portions  12  as well as being raised relative thereto, i.e., elevated a distance in relation to the surface portions  12 . The laterally inner limiting edge  38  of each heart-shaped projection is concavely curved with radius substantially equal to the radius of curvature of the central hole  14 . Each edge  38  is spaced laterally (radially) outwards by a small distance from the hole  14 . 
   In  FIG. 7 , another insert embodiment  10 ″ is shown, with the radiating projection array  29 ″ radiating around the insert hole  14  being in the form of six projections  37   a – 37   f  spaced-apart from each other in circumferential directions, the distal end of each projection being in the form of two blunt tips  60   a ,  60   b . The inner limiting edge of each projection is, as in the case of  FIG. 6 , concavely circularly curved with a radius of curvature substantially equal to the radius of curvature of the central hole  14 . Each such surface segment is, furthermore, terminated a small distance from the hole  14 . 
   In accordance with the present invention, there is provided a cutting insert whose top surface can be engaged by a clamp to be effectively clamped in two directions, and which leaves sufficient area on the top surface in order to, e.g., enable desired corner marking or other geometric marking or which enable insertion of more advanced chip breaker geometries directly pressed into the upper chip surface. 
   Although the present invention has been described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without departing from the spirit and scope of the invention as defined in the appended claims.