Abstract:
A milling cutter with tangentially mounted cutting inserts includes cutter pockets that are arranged at one end of the cutter body such that the screws for retaining the inserts generally radiate from the cutter&#39;s center. The cutter pockets are designed to secure a generally rectangular insert with eight or less cutting edges. The number of inserts and corresponding flutes vary as a function of the diameter of the cutter body. For example, four inserts with corresponding flutes are mounted on a 1.25″ diameter cutter body, and three inserts with corresponding flutes are mounted on a 1.00″ diameter cutter body. The increased number of flutes provide for increased metal removal rates and higher feed rates, as compared to an inserted ball nose mill or end mill. The cutter pockets are angled such that there is sufficient clearance under the insert cutting edges and present a “reverse lead” so the cutter assembly can produce a slightly undercut profile on the workpiece, or fixturing of almost five degrees so the radius generated on the workpiece can be nearly the same as that generated by a ball nose mill. The cutting inserts include facets for generating very good surface finishes on the workpiece.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to an indexable inserted milling tool. More particularly, this invention relates to a milling cutter with tangentially mounted indexable cutting inserts. 
   2. Description of the Related Art 
   In the process of milling turbine blades or “buckets”, one generally finds in use solid carbide end mills (SCEM), inserted carbide end mills (ICEM), and insert face mills for roughing only. Ball nose end mills (solid and inserted) are used for semi-finishing and in some case, finishing. The cutter paths programmed are typically radial or axial with regard to the blade form. In either case, there are axes of rotation on both the blade and the cutter, with additional axes used to produce large concave and convex surfaces. The paths are followed for as long as it takes to reduce either a block of material or a near-net shaped forging to its intended size and shape. The type of cutting tool used is generally dictated by the condition of the workpiece at the start of the process, and the capabilities of the machine. In both cases, the semi-finishing and finishing cuts are addressed by smaller diameter tools due to the radii of the turbine blade surfaces. 
   Axial cutter paths have been used on several types of single and multi-spindle NC and CNC machines. The path is basically one that travels across the front and back sides of the blade with cutting taking place across an edge of the blade between the cutting of two sides. The path includes the convex and concave surfaces, which change rather quickly as the progression of the tool makes its way around the blade, and slowly progresses from one end of the blade to the other. 
   Basically, radial paths travel from root or base to tenon or blade tip until the front or back of the blade is cut to depth. The path then moves along the leading or trailing edge to cut to the desired depth, and continues to the uncut front or back of the blade to finish removing material in the same manner as the opposite. This process has traditionally been accomplished with what is called a “Hydrotel” machine, which uses a dovetail-shaped cutter with round inserts. These multi-spindle machines are quickly becoming antiquated, spending on maintenance and refurbishing is drastically reduced, and the owners are opting for new CNC machines. Lately, machinists have found that the radial cutting path is more cost effective, and the ability to reduce or eliminate secondary finishing operations is obtainable with creative programming and tooling. This includes, but is not limited to, the tilting of the milling machine&#39;s spindle, or the workpiece such that a ball-nosed tool will not cut with the surfaces of the tool that have minimal effective speeds and feeds. 
   SUMMARY OF THE INVENTION 
   Briefly, according to this invention, there is provided a milling cutter tool comprising a milling cutter body having a plurality of insert receiving pockets, in combination with an indexable cutting insert tangentially mounted in the insert pocket. Each cutting insert comprises a body defined by first and second face surfaces, first and second long edge surfaces, and first and second radiused shorter edge surfaces, wherein each indexable cutting insert is tangentially mounted with a reverse lead angle. Each long edge surface defines a cutting face that includes a profile defined by a substantially flat central plateau, a first facet face, a second facet face and a third facet face. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features of the present invention, as well as the advantages derived therefrom, will become clear from the following detailed description made with reference to the drawings in which: 
       FIG. 1  shows a perspective view of a cutting insert according to the present invention; 
       FIG. 2  shows a front elevational view of the cutting insert of  FIG. 1 ; 
       FIG. 3  shows a top view of the cutting insert of  FIG. 1 ; 
       FIG. 4  shows a cross sectional view of the cutting insert taken along line  4 — 4  of  FIG. 3 ; 
       FIG. 5  shows a perspective view of a typical milling cutter having three new and improved cutting inserts of  FIG. 1  seated in their respective insert receiving pockets in accordance with the invention; 
       FIG. 6  shows a partial side elevational view of the milling cutter showing the negative axial rake angle of the cutting insert of  FIG. 1  when mounted in the milling cutter of  FIG. 5 ; 
       FIG. 7  shows another side elevational view of the milling cutter showing the “reverse lead” angle of the cutting insert of  FIG. 1  when mounted in the milling cutter of  FIG. 5 ; 
       FIG. 8  shows an end view of the cutter taken along line  8 — 8  of  FIG. 7 ; 
       FIG. 9  shows a schematic side view of three cutting inserts of  FIG. 1  seated in their respective insert receiving pockets and engaging a workpiece in accordance with the invention; and 
       FIG. 10  shows a perspective view of another typical milling cutter having four new and improved cutting inserts of  FIG. 1  seated in their respective insert receiving pockets in accordance with the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to the drawings, wherein like reference characters represent like elements, a cutting insert, shown generally at  10 , is shown according to the present invention in  FIGS. 1–4 . The cutting insert  10  is indexable about an axis of rotational symmetry, A, so that the cutting insert  10  has eight edges capable of functioning as effective cutting edges. The cutting insert  10  is capable of being used in a wide range of different cutting operations. 
   As seen in  FIG. 1 , the cutting insert  10  includes a body formed of a suitable cutting material and is defined by first and second planar face surfaces  12 ,  14  disposed in substantially parallel planes. For purposes of convenience, the first and second face surfaces  12 ,  14  will be referred to as upper and lower face surfaces  12 ,  14 , respectively. The cutting insert  10  includes a clamping screw bore  16  having a longitudinal axis coinciding with the axis of symmetry, A, and extending between the first and second planar face surfaces  12 ,  14 . The clamping screw bore  16  may include a pair of counter sinks  18  shaped as a part of a torus or a cone to receive a countersunk head screw  20  or any other fastening means, such as a pinlock or the like, to enable the screw  20  to lie slightly below the face surfaces  12 ,  14 . 
   Referring now to  FIGS. 2–4 , the cutting insert  10  is defined by first and second edge surfaces  22 ,  24 , which define cutting faces that extend between the long sides of the face surfaces  12 ,  14 . For purposes of convenience, the first and second edge surfaces  22 ,  24  will be referred to long edge surfaces  22 ,  24 . Because the cutting insert  10  is symmetric about a longitudinal axis, L, some of the discussion for the long edge surface  24  may be omitted for brevity. Each long edge surface  22 ,  24  defines a cutting face that includes a profile defined by a substantially flat central plateau  26  that is substantially parallel to a plane, P. Each long edge surface  22 ,  24  also includes a first facet face  28  having a downward angle  29  in the range of approximately 5° to 45°, for example, approximately 30° with respect to the plane, P, a second facet face  30  that is substantially parallel to the plane, P, and a third facet face  32  having an upward angle  31  in the range of approximately 5° to 45°, for example, approximately 20° with respect to the plane, P. It should be noted that the plane, P, is substantially parallel to the longitudinal axis, L, of the cutting insert  10 . 
   As shown in  FIG. 2 , the central plateau  26  may have a slightly higher elevation than the face surfaces  12 ,  14  and is generally hexagonal in shape (as viewed in  FIG. 3 ) that includes a pair of opposite sides  26   a  and two pair of angled sides  26   b  to form a pair of radiused corners  26   c . The angled sides  26   b  of the central plateau  26  form an acute angle  33  of approximately 80° with respect to each other. The facet faces  28 ,  30  and  32  provide for effective chip control. However, it will be appreciated that the invention is not limited by the number of facet faces or the angles of the facet faces, and that the invention can be practiced with any desirable number of facet faces with angles that provide effective chip control. 
   The primary cutting edge for a given index of the cutting insert  10  extends from section line  4 — 4  (or apex of the radius) to the intersection of the shorter radiused edge surface  34  and the angled sides  26   b , as shown in  FIG. 3 . The cutting edge  28   a  will cut, but is not intended for such cutting in the illustrated example of the invention. In order for the cutting edge  28   a  to cut effectively, the cutting insert design would need the chip control to extend along that portion of the cutting insert  10 . Thus, the focus of cutting edges that can effectively cut should be constrained to the radius edges for cutting to somewhat shallow depths, as is the typical process for low power CNC milling machines in certain industries, for example, the turbine blade machining industry. 
   The cutting insert  10  is also defined by first and second radiused edge surfaces  34 ,  36  that extend between the shorter sides of the face surfaces  12 ,  14 . For purposes of convenience, the first and second edge surfaces  34 ,  36  will be referred to as shorter radiused edge surfaces  34 ,  36 . A first cutting edge  38  is defined along the intersection of the long edge surface  22  with the upper face surface  12  and along the intersection of the long edge surface  22  with the shorter radiused edge surface  34 . A second cutting edge  40  is defined along the intersection of the long edge surface  22  with the lower face surface  14  and along the intersection of the long edge surface  22  with the shorter radiused edge surface  36 . Because the insert  10  is symmetric about the longitudinal axis, L, a third cutting edge  42  is defined along the intersection of the long edge surface  24  with the upper face surface  12  and along the intersection of the long edge surface  24  with the shorter radiused edge surface  34 . A fourth cutting edge  44  (shown in phantom in  FIG. 1 ) is defined along the intersection of the long edge surface  24  with the lower face surface  14  and along the intersection of the long edge surface  24  with the shorter radiused edge surface  36 . When one cutting edge becomes worn, the insert  10  may be indexed 180° about the axis, A, of the clamping screw bore  16  to bring the other cutting edge on the same face surface  12 ,  14  into active cutting position. In addition, the insert  10  can be indexed 180° about a vertical axis, V, to bring the other cutting edge on the other face surface  12 ,  14  into active cutting position. The insert  10  may include a locating dimple  39  for assisting in the positioning of the insert  10  in the cutting tool. 
   Referring now to  FIGS. 5–9 , an end milling cutter, shown generally at  50 , rotatable about a central axis  52  in the direction of the arrow  54  is adapted to receive three cutting inserts  10 . The milling cutter  50  includes a cylindrical metal body  56  having a shank  58  at its inner end and formed with three angularly spaced insert receiving pockets  60 . In one aspect of the invention, the inserts  10  are angled so as to present a negative axial rake angle  61  of approximately 5° to facilitate chip formation and removal from the workpiece, W, as shown in  FIGS. 6 and 9 . However, it will be appreciated that the invention is not limited by the magnitude of the negative axial rake angle, and that the invention can be practiced with any desirable negative axial or radial rake angle. 
   Each pocket  60  includes a platform  62  upon which the insert  10  is seated. The platform  62  is angled such that the insert  10  presents a “reverse lead” angle  63  in assembly, an (ANSI) lead angle  65 , or an (ISO) lead angle  67  on the workpiece, W ( FIG. 9 ). In the illustrated embodiment using a progressive process, the machine&#39;s spindle or workpiece is tilted approximately 5° such that the cutting insert  10  presents a zero degree (ANSI) angle  65 , or ninety degree (ISO) lead angle  67 , as shown in  FIGS. 7 and 9 . The reverse lead angle  63  ensures that a tool, such as a ball-nosed tool, does not cut with the end of the tool where the cutting speed and feed rate is essentially zero. In the illustrated embodiment, the milling cutter  50  having about a 1.00 inch diameter produces an elliptical cut having an ellipse with a 0.442 inch semi major axis and a 0.043 inch semi minor axis. It will be appreciated that the dimensions of the cutting insert  10  can vary depending on design of the tool. For example, the radius of the cutting insert  10  can be used to determine the size of the insert, the size of the cutter, the axial depth of the cut, as well as the ellipse for metal cutting productivity. 
   In addition, the reverse lead angle  63  provides for the insert  10  to present additional cutting edges to the workpiece, W. For example, when the insert  10  is mounted such that the upper face surface  12  is facing outwardly, the reverse lead angle  63  causes the first cutting edge  38  to be further defined by two cutting edges  38   a ,  38   b  defined by the intersection of the long edge surface  22  with the upper face surface  12  and the intersection of the long edge surface  22  with the short edge surfaces  34 ,  36  that are adjacent the upper face surface  12 . Similarly, when the insert  10  is mounted such that the lower face surface  14  is facing outwardly, the reverse lead angle  63  causes the second cutting edge  40  to be further defined by two cutting edges  40   a ,  40   b  defined by the intersection of the long edge surface  22  with the lower face surface  14  and the intersection of the long edge surface  22  with the short edge surfaces  34 ,  36  that are adjacent the lower face surface  14 . Likewise, the third and fourth cutting edges  42 ,  44  have additional cutting edges because the insert  10  is mounted with the reverse lead angle  63  of the invention. Thus, the insert  10  of the invention has a total of eight cutting edges, as compared to an insert with four cutting edges that is mounted with a lead angle of zero degrees. As a result, the insert  10  of the invention is more economical to use than a conventional insert that is mounted with a lead angle of zero degrees. 
   Each pocket  60  further includes two substantially flat and planar locating abutments  64 ,  66  disposed adjacent the inner and trailing sides, respectively, of the pocket  60 . Each insert  10  is mounted in the pocket  60  by threading the clamping screw  20  into the clamping screw bore  16  and into a tapped bore (not shown) in the platform  62 . 
   In operation, a portion of the cutting edges  38   a ,  38   b ,  40   a ,  40   b  that are defined by the intersection of the cuttting edge surfaces  38 ,  40  and the upper and lower surfaces  12 ,  14 , respectively, provide for a full radiused cutting edge which is relatively large at the cutting edge itself. By virtue of the full radiused cutting edge, the insert  10  with the two radiused ends may effectively span the gap between two spaced inserts of an adjacent row. The strength of the cutting edges  38   a ,  38   b ,  40   a ,  40   b  (and  42   a ,  42   b ,  44   a ,  44   b ) are increased by forming the radiused corners on these cutting edges. 
   The milling cutter  50  with three improved cutting inserts  10  of the present invention circumferentially mounted approximately 120° with respect to each other has a diameter of about 1.00 inches. However, the principles of the present invention can be implemented with any desirable milling cutter as is only limited by its diameter. For example, as shown in  FIG. 10 , the invention can be practiced with a milling cutter, shown generally at  70 , having a diameter of about 1.25 inches, rather than a diameter of about 1.00 inches. The larger diameter of the milling cutter  70  allows for four improved cutting inserts  10  to be circumferentially mounted at approximately 90° with respect to each other. The larger diameter milling cutter  70  with an approximately 5 degree “reverse lead” angle  63  and a negative axial rake angle  61  of approximately 5° provides an elliptical cut having an ellipse with a 0.545 semi major axis and a 0.054 semi minor axis. Thus, the elliptical cut produced by the cutting inserts  10  mounted on the milling cutter of the invention is a function of the radius of the cutting insert  10 . Thus, the milling cutter of the invention can produce any desired elliptical cut by varying the radius of the cutting insert  10 , and/or the axial and radial rakes. 
   In light of the foregoing, it will be apparent that the present invention bring to the art a new and improved on-edge indexable insert  10  in which a “reverse lead” angle  63  provides a milling cutter that can produce a slightly undercut profile on the workpiece if desired (i.e., at the root of a blade), while providing for twice the cutting edges when compared to conventionally mounted inserts. In addition, the indexable insert  10  of the present invention possesses cutting edges that have a greater effective length and greater strength when compared with inserts that are radiused in a conventional manner. 
   The documents, patents and patent applications referred to herein are hereby incorporated by reference. 
   While the invention has been specifically described in connection with various embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit.