Abstract:
An indexable milling insert has a trigon shape and includes a mounting hole placed centrally in the milling insert, an upper side and a lower side, which sides are parallel with each other and act as an alternating first support surface and second support surface. The milling insert is furthermore provided with major cutting edges, which are oriented perpendicularly to the axis of the mounting hole as well as arranged in such a way that a turning of the milling insert around the center of the mounting hole into an alternative cutting position alternatively a flipping of the milling insert into an alternative cutting position provides an identical position of the major cutting edges in relation to a workpiece. The major cutting edges of the milling insert are furthermore placed in the milling insert, when the same is tangentially mounted in a cutting body, so that the shortest distance of the major cutting edges to the axis of the hole in top view is smaller than the distance of a third support surface to the axis of the hole. A milling cutter tool having such a milling insert mounted is also disclosed.

Description:
BACKGROUND AND SUMMARY 
     The present invention relates to the field of chip removing machining and particularly to a milling insert and a milling cutter tool in which the milling insert is mounted. The milling insert is shaped as a trigon shape having a number of cutting edges and is adapted to be mounted in a milling cutter body of the milling cutter tool. 
     Previously known trigon-shaped milling inserts are shaped to be mounted substantially radially in a milling cutter body, the axis of a centrally placed mounting hole being directed tangentially in relation to the milling cutter body. Such a mounting requires a considerable recess in the milling cutter body so that mounting of a milling insert could be accomplished, which in turn means that the milling cutter body at a certain radius only can receive a certain a number of milling inserts. Furthermore, radial mounting means that the strength of the milling insert to a certain extent depends on the extension thereof in the axial direction of the mounting hole. 
     Tangentially mounted milling inserts can be seen in, for instance, WO 2005/075135, U.S. Pat. No. 6,872,034 and U.S. Pat. No. 7,014,396. 
     It is desirable to provide an improved trigon-shaped milling insert, which can be mounted tangentially in the milling cutter body of a tool and which furthermore is provided with dedicated support surfaces for an improved abutment against a pocket of the milling cutter body. 
     It is also desirable that the support surfaces are placed on the milling insert as well as in the milling cutter body in such a way that the cutting forces in a milling operation contributes to an increased abutment against the pocket as well as to minimizing the torque to turn the milling insert radially out of the pocket. 
     It is also desirable to provide a milling cutter tool for such a milling insert. 
     An aspect of the invention relates to an indexable milling insert having a trigon shape, which milling insert comprises a mounting hole placed centrally in the milling insert, an upper side and a lower side, which sides are parallel with each other and act as an alternating first and second support surface. The milling insert is provided with major cutting edges, which are oriented perpendicularly to the axis of the mounting hole as well as arranged in such a way that a turning of the milling insert around the center of the mounting hole alternatively a flipping of the milling insert into an alternative cutting position provides an identical position of the major cutting edges in relation to a workpiece. In this connection, the major cutting edges of the milling insert are placed in the milling insert, when the same is tangentially mounted in a cutting body, in such a way that, in the shown top view, the shortest distance of the major cutting edges to the axis of the hole is smaller than the distance of a third support surface to the axis of the hole. 
     Furthermore, milling inserts may be shaped so that the distance in top view between each major cutting edge and an adjacent third support surface grows in the direction from an associated nose edge. 
     Furthermore, the milling insert may comprise three major cutting edges placed on the edge of the respective lower/upper side near a cutting corner. 
     The milling insert may be provided with third support surfaces placed along the sides of the milling insert at a right angle in relation to the imaginary extension of the first support surface. 
     The milling insert may be provided with additional third support surfaces placed along the sides of the milling insert at a right angle in relation to the imaginary extension of the second support surface. 
     The third support surfaces may be pair-wise arranged in direct connection with and on both sides of a cutting corner of the milling insert. 
     The milling insert may be provided with clearance surfaces placed in direct connection with the first support surface and the second support surface in the extension of the respective major cutting edges along the edge of the respective first and second support surface so that the clearance surfaces form an acute edge angle with the imaginary extension of the support surfaces. 
     The milling insert may be provided with corner surfaces placed at an angle to and in direct connection with the third support surfaces and at a right edge angle in relation to the imaginary extension of the first and the second support surface. 
     The milling insert may furthermore be shaped so that each corner surface and adjacent third support surface connect to each other under an angle β, where 10°&lt;β&lt;20°, preferably is 13°&lt;β&lt;17°. Furthermore, a milling insert may be shaped so that each major cutting edge forms an angle φ with the appurtenant third support surface, which angle φ is of the same size as the angle β±2°. 
     All support surfaces of the milling insert may be completely planar. 
     The major cutting edge of the milling insert may also transform directly into a nose edge. 
     The milling insert may furthermore comprise six minor cutting edges, each one having an extension from the first support surface toward the second support surface at a substantially parallel orientation with the symmetry axis of the mounting hole. 
     The milling insert may also be shaped so that each minor cutting edge is of the same size as the third support surface in a direction parallel with the axis of the hole. Each minor cutting edge may also connect directly to a nose edge. 
     Furthermore, all cutting edges connected to each other may be situated in the same plane. 
     An aspect of the invention also relates to a milling cutter tool comprising a milling cutter body having a plurality of insert pockets. Each insert pocket is intended to receive a milling insert shaped according to anyone of the above-mentioned milling inserts. 
     The insert pockets of the milling cutter tool may comprise a main support surface against which the milling insert is arranged to abut by the first/second support surface thereof. 
     The insert pocket of the milling cutter tool may also comprise a wedge-shaped support pocket having primary support surfaces arranged, in which support pocket the milling insert is mounted with abutment of the pair-wise arranged third support surfaces thereof against the primary support surfaces in order to, by means of arising cutting forces in a milling operation, provide an increased abutment force of the milling insert against the support pocket. 
     The support pocket of the milling cutter tool may furthermore be provided with a secondary support surface against which another one of the third support surfaces of the milling insert is arranged to abut. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described closer by means of embodiment examples, reference being made to the accompanying drawings, where 
         FIG. 1  shows a milling insert according to the present invention in top view, 
         FIG. 2  shows the milling insert in perspective view, 
         FIG. 3  shows a side view of the milling insert, 
         FIG. 4  shows a cross section of the milling insert according to line B-B in  FIG. 1  and  FIG. 3 , 
         FIG. 5  shows a perspective view of a milling cutter body according to the present invention without any milling inserts mounted, 
         FIG. 6  shows a side view of the milling cutter body having mounted milling inserts in engagement with a workpiece. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIGS. 1-4 , there are shown a double-sided or indexable milling insert according to the present invention, which has a trigon-shaped or hexagonal basic shape as well as is manufactured from directly pressed cemented carbide. With “cemented carbide”, reference is here made to WC, TiC, TaC, NbC, etc., in sintered combination with a binder metal such as, for instance, Co or Ni. The milling insert is preferably at least partly coated with layers of, e.g., Al2O3, TiN and/or TiCN. In certain cases, it may be justified that the cutting edges consist of or comprise soldered superhard materials such as CBN or PCD. 
       FIG. 1  shows a trigon-shaped milling insert  10 , by which is meant that the milling insert, in top view, is substantially triangular but that each side of the triangle is broken outward from the center of the triangle in order to form two sides of each one of the sides of the triangle, which means that the milling insert has obtained six corners, the tip angles of the triangle having been made more obtuse. The two sides form an angle between themselves in the interval of 25°-35°, preferably 28°-31°. Another way of describing a trigon-shaped milling insert is that an imaginary circle inscribed in the milling insert touches the periphery of the milling insert in six points. However, the present milling insert has every second of the six corners chamfered in order to form corner surfaces that are seen more clearly below. Thus, the milling insert comprises six sides S 1 , S 2 , S 3 , S 4  S 5 , S 6 , each one of which comprises a major cutting edge, H 1 , H 2 , H 3 , H 4 , H 5 , H 6 , three major cutting edges H 2 , H 4 , H 6  of which are shown in  FIG. 1  in direct connection with an upper side constituting an upper first support surface  11 , while the other three major cutting edges H 1 , H 3 , H 5  are found on the lower side of the milling insert. For the mounting of the milling insert  10  in an insert pocket, a mounting hole  12 , including the axis  70  thereof, is provided centrally in the milling insert  10 . In direct connection with the upper support surface  11  of the milling insert, three clearance surfaces  21 ,  23 ,  25  are provided at the sides S 1 , S 3 , S 5 , which clearance surfaces form the angle α with the upper support surface  11 . Correspondingly, in direct connection with the opposite lower second support surface  13  of the milling insert, three additional clearance surfaces  22 ,  24 ,  26  (not visible in  FIG. 1 ) are provided at the sides S 2 , S 4 , S 6 , which additional clearance surfaces also form the angle α with the second support surface  13 . The first support surface  11  and the second support surface  13  have substantially the shape of an equilateral triangle. 
       FIG. 2  shows in a perspective view the upper first support surface  11  of the milling insert, the first major cutting edge H 1  of the milling insert, the second major cutting edge H 2  of the milling insert, the third major cutting edge H 3  of the milling insert, the fourth major cutting edge H 4  of the milling insert, and the sixth major cutting edge H 6  of the milling insert. Furthermore, the figure shows that each major cutting edge H 1 -H 6  transforms into a nose cutting edge N 1 -N 6 , the first N 1 , the second N 2 , the third N 3 , the fourth N 4  and the sixth N 6  one of which nose cutting edges are shown in the figure. Furthermore, it is shown in the figure that each nose cutting edge N 1 -N 6  connects directly to a minor cutting edge B 1 -B 6 , the first B 1 , the second B 2 , the third B 3 , the fourth B 4  and the sixth B 6  one of which minor cutting edges are shown in the figure. The minor cutting edges form the three cutting corners SH of the milling insert. All edges are situated in the same plane. To each major cutting edge H 1 -H 6  and minor cutting edge B 1 -B 6 , a chip breaking countersunk recess U 1 -U 6  connects, the first U 1 , the second U 2 , the third U 3  and the sixth U 6  one of which recesses are shown in the figure. These in relation to the edges countersunk recesses, give the edges a positive rake angle so as to cut easily in a workpiece. The first  21  and the third one of the clearance surfaces  21 - 26  are also shown in the figure. 
     Furthermore, corner surfaces  31 - 36  are provided in direct connection with the respective clearance surfaces  21 - 26  and placed as additional sides of the milling insert so that the first  31  and the sixth  36  one of the corner surfaces are placed between the sides S 1  and S 6 . Correspondingly, the second  32  and the third  33  one of the corner surfaces are placed between the sides S 2  and S 3 , and the fourth  34  and the fifth  35  one of the corner surfaces are placed between the sides S 4  and S 5 , compare with  FIG. 1 . 
     Furthermore,  FIGS. 1 and 2  show third support surfaces  41 - 46 , which are situated on the six sides of the milling insert with an axial extension that is smaller or equal to half the thickness of the milling insert so that the first  41  one of the third support surfaces is situated on the first side S 1  of the milling insert, the second  42  one of the third support surfaces is situated on the second side S 2  of the milling insert, the third  43  one of the third support surfaces is situated on the third side S 3  of the milling insert, the fourth  44  one of the third support surfaces is situated on the fourth side S 4  of the milling insert, the fifth  45  one of the third support surfaces is situated on the fifth side S 5  of the milling insert, and the sixth  46  one of the third support surfaces is situated on the sixth side S 6  of the milling insert. All the third support surfaces may be planar and intended to absorb tangential forces on the milling insert. Also the clearance surfaces  21 - 26  may be planar. 
     The first  21  one of the clearance surfaces, the first  31  one of the corner surfaces and the first  41  one of the third support surfaces form a first group G 1  of surfaces, which, via the first  21  one of the clearance surfaces, connect to the upper first support surface  11 . As is seen in  FIG. 1  and  FIG. 2 , the corresponding groups G 3  and G 5  connect to the upper first support surface, and the groups G 2 , G 4  and G 6  to the opposite lower second support surface  13 . 
     The corner surfaces  31 - 36  and the third  41 - 46  support surfaces are perpendicular in relation to both the upper first  11  and the lower second  13  support surface, which means that the upper  11  and the lower  13  support surface are parallel with each other. However, the corner surfaces  31 - 36  and the third  41 - 46  support surfaces within each group connect to each other under an angle β, where 10°&lt;β&lt;20° and preferably is 13°&lt;β&lt;17°, see  FIG. 1 . Thus, the corner surfaces and the third support surfaces, respectively, form the angle 90°+α with the clearance surface within each group G 1 -G 6 . 
     Furthermore, in  FIG. 1 , an angle φ is indicated, which shows the angle between a major cutting edge H 1 -H 6  and an appurtenant third  41 - 46  support surface, which angle φ is of the same size as the angle β±2°. 
       FIG. 3  shows a side view of the milling insert where the upper support surface  11  is parallel with the lower support surface  13 . The figure also shows the first major cutting edge H 1  with the appurtenant first nose cutting edge N 1  and first minor cutting edge B 1 , as well as the sixth major cutting edge H 6  with the appurtenant sixth nose cutting edge N 6  and sixth minor cutting edge B 6 . Furthermore, the figure shows the first chip-breaking recess U 1  as well as the sixth chip-breaking recess U 6  diagonally situated in relation to the first chip-breaking recess U 1  in the shown view. The figure also shows the diametrical position of the group G 1  including the clearance surface  21 , the corner surface  31  and the support surface  41  in relation to the group G 6  including the surfaces  26 ,  36 ,  46 . The other two side views of the milling insert are arranged in a corresponding way as shown in  FIG. 3  when the milling insert is rotated one third of a revolution at a time around the axis  70  of the mounting hole. The figure also shows that the two corner surfaces  31 ,  36  are connected to each other by a waist  51 , which contributes to a distribution of possible stresses over the corner surfaces  31 ,  36 . In a corresponding way, also other corner surfaces are pair-wise connected to each other by a corresponding waist. 
     It should also be noted that all clearance surfaces  21 , . . . ,  26  end at a distance from the nose cutting edges in order to contribute to a strengthening of the milling insert in this portion. Compare also  FIGS. 1 and 2 . 
       FIG. 4  shows a section B-B according to  FIG. 3  and according to the dashed line in  FIG. 1  through the mounting hole  12  but beside the axis  70 , the projection of which in the mounting hole  12  has been indicated by the numeral  71 . The figure shows the clearance surfaces  21 ,  23  and  26 , which all form the angle α with the upper and lower support surface  11 ,  13 , respectively, where 20°&lt;α&lt;45° preferably that 25°&lt;α&lt;40°. The third clearance surface  23  transforms into the third  43  one of the third support surfaces. The figure also shows the third chip-breaking recess U 3  and the third major cutting edge H 3 . 
       FIG. 5  shows a milling cutter body  81 , without any milling inserts mounted, for a milling cutter tool according to the invention. The milling cutter body is provided with a plurality of identically shaped insert pockets  82 , each one of which is provided with a main support surface  83  against which a milling insert is arranged to be mounted by a screw  84 , see  FIG. 6 , being screwed-in through the mounting hole of the milling insert into a threaded fastening hole  85  in the insert pocket of the milling cutter body  81 . The insert pocket  82  is provided with two primary support surfaces  86 ,  87  as well as with a secondary support surface  88 . Together, the primary support surfaces form a wedge-shaped support pocket  93 , against which the third support surfaces of the milling insert abut after an assembly, and against which the milling insert is pressed by the tangential cutting forces when the milling cutter tool machines a workpiece. The secondary support surface  88  does also contribute to a force absorption of cutting forces on the milling insert, but has above all the purpose of facilitating mounting of the milling insert in the insert pocket  82 . 
       FIG. 6  shows a milling cutter tool  91 , in the form of a cutting body  81  having a number of mounted milling inserts  10 , during machining of a workpiece  92 . The direction of rotation of the milling cutter tool  91  is shown by the arrow, the translation motion of the milling cutter tool upon milling being into the plane of the paper. In this connection, the milling insert  10  is mounted with one of the cutting corners SH thereof placed for abutment by the support surfaces thereof in the corresponding primary support surfaces  86 ,  87  of the wedge-shaped support pocket  93  of the insert pocket. Between the abutment surfaces  86 ,  87 ,  88  of the insert pocket  82 , clearances  94 ,  95  are provided to eliminate stresses between the surfaces as well as to eliminate point loads from the corner surfaces of the milling insert. 
     Thus, the present invention relates to an economically advantageous milling insert for milling, which allows a stable location of the milling insert in the milling cutter body for a milling cutter tool, as well as to a milling cutter tool for such a milling insert. 
     The milling cutter tool is intended to be used for end milling or for face milling. 
     The invention is not limited to the embodiment described above but may be varied within the scope of the subsequent claims. 
     The disclosures in Swedish patent application No. 0601388-2, from which this application claims priority, are incorporated herein by reference.