Abstract:
A veined cutting tool for producing holes in various materials is disclosed. The veined cutting tool includes a tungsten carbide body using a sintered abrasive particulate such as diamond (PCD) or Cubic Boron Nitrite (PCBN). The cutting tool shields a portion of the PCD or PCBN edge on the cutting side to reduce the overall length of the exposed PCD or PCBN to prevent the cutting edge from chipping and increase the service life of the cutting tool.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to cutting tools. More specifically, the present invention relates to an improvement in Polycrystalline Diamond (PCD) veined or Polycrystalline Cubic Boron Nitrite (PCBN) veined cutting tools. 
       BACKGROUND 
       [0002]    Veined cutting tools as described in U.S. Pat. Nos. 4,713,286 and 4,762,445 provide for drills, end mills, reamers and other cutting tools with multiple cutting edges fixed to a tungsten carbide body using a sintered abrasive particulate such as diamond (PCD) or CBN. These tools have proven to be advantageous in drilling, reaming, and milling various advanced composite materials and non-ferrous materials and are now well known as cutting tools. 
         [0003]    Generally, the high cost and delicate nature of these tools restrict them to use only where cutting conditions can be closely controlled by computer numerically controlled (CNC) machines to avoid impact, vibrations, and/or variable feed conditions that would destroy the cutting edges. 
         [0004]    One area where such veined PCD or PCBN tools are widely used is in drilling advanced carbon fiber reinforced plastic (CFRP) composites and stackups of these materials with aluminum or titanium on CNC equipment for advanced aircraft frames. However, many areas of these planes do not allow for the use of CNC drilling equipment making portable power feed air motors the preferred method of drilling the necessary fastener holes. 
         [0005]    Prior to this invention, the use of PCD or PCBN drills with these air motors was not considered feasible for drilling difficult materials like layers of advanced composites and titanium. Typically, these air motors use what is called a hard tooling fixture with guide bushings. PCD or PCBN drills were known to chip the sides or margins of the drill as they were guided by these bushings due to the delicate nature of the exposed PCD cutting edge. 
         [0006]    U.S. Pat. No. 5,611,251 also teaches a method of making a PCD or PCBN drill using a brazeable PCD or PCBN blank and makes reference to other variations for brazeable PCD and PCBN drill construction using commercially available blanks from Megadiamond or Debeers. 
         [0007]    Such cutting tool construction taught or referenced by U.S. Pat. No. 5,611,251 invariably uses low rake angles to strengthen the cutting edge and to compensate for the ready nature of these edges that tend to chip. Such art does not teach a way of preventing the chipping of the cutting edges. 
         [0008]    In view of the limitations of prior art PCD drill bits, reamers, and milling cutting tools, the present invention was developed to address these limitations and is an improved PCD cutting tool having a shielded PCD or PCBN cutting edge. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention relates generally to cutting tools. In the present invention, a PCD or PCBN cutting tool and method of manufacture is provided with a shielded cutting edge leaving only a small portion of the cutting edge exposed to engage the work material. 
         [0010]    Such shielding prevents the delicate edges of the PCD from being damaged by bushings or the work material while still providing for additional tool life by removing the shielding material in increments as necessary to expose fresh cutting edges. 
         [0011]    To manufacture a cutting tool with a shielded cutting edge, the vein of PCB or PCBN or any other suitable material is angled such that a shield is created for the vein by leaving a portion of the shielding material in front of the vein during the grinding processes used to form the cutting tool. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a side plan view of the end of a drill bit representative of the current state of the art; 
           [0013]      FIG. 2  is a side plan view of the end of a reamer representative of the current state of the art; 
           [0014]      FIG. 3  is a perspective of an embodiment of the end of a drill according to the present invention; 
           [0015]      FIG. 4  is an enlarged view of the drill shielding at the corner of a drill in the area specified  FIG. 3 ; 
           [0016]      FIG. 5  is a side plan view of an embodiment of the end of a reamer according to the present invention; and 
           [0017]      FIG. 6  is an enlarged view of the reamer shielding at the corner of a reamer in the area specified in  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    The embodiments of the present invention will be best understood by reference to the drawings. It will be readily understood that the components of the present invention, as generally described and illustrated in the figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the cutting tools of the present invention, as represented in  FIGS. 3 through 6 , is not intended to limit the scope of the invention, as claimed, but is merely representative of presently preferred embodiments of the invention. 
         [0019]    The apparatus and method of the present invention have been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully resolved by currently available cutting tools. The present invention has wide application in machining applications as diverse as reaming automotive engine valve guides as well as drilling stackups of CFRP and titanium airframe parts. The shielding of the delicate cutting edges will open many applications where these cutting tools in the past have not stood up to the various cutting forces. 
         [0020]      FIGS. 1 and 2  illustrate prior art of PCD or PCBN cutting tools. In these tools the PCD or PCBN is exposed along the margin of the tools to provide additional regrind life and to aid in the chip flow across the face of the PCD or PCBN and to avoid the welding of the chips to the cutting edge. 
         [0021]      FIGS. 3 and 4  illustrate a PCD or PCBN drill using a shielded cutting edge where the shielding protects the side of the tool from damage from chipping or fracturing along this edge. 
         [0022]    In  FIG. 3 , the drill  10  which has a body made of a first material such as tungsten carbide, also has a vein  12  of a suitable second material such as a sintered abrasive particulate such as Polycrystalline Diamond (PCD) or Polycrystalline Cubic Boron Nitrite (PCBN) having a cutting edge  14 . The drill  10  also has a land  16  and a lead  18  that is the leading edge of the land  16 . The vein  12  is angled such that a shield  20  is created that extends along the leads  18  in front of and adjacent to the vein  12 . This shield  20  is positioned in the area that is particularly susceptible to chipping use to prevent unwanted chipping of the vein  12 . 
         [0023]      FIG. 4  shows the shielding  20  of the PCD or PCBN edge  14  in more detail with reference numeral  22  being the distance of the exposed PCD or PCBN edge  14  of the vein  12 , such distance being a minimum of 0.002 inches and a maximum of 0.010 inches in preferred embodiments. The rake angle  26  intersects with the flute angle to create the exposed PCD or PCBN edge  14 , and the thickness of the shielding  20  in front of the PCD or PCBN vein  12  is defined by thickness  24  and preferably will be a minimum of 0.005 inches up to about 0.015 inches, but more preferably about 0.010 inches. The rake angle  26  can be varied to create different exposed edges  14  of the PCD or PCBN depending on the helix angle of the drill  10 . 
         [0024]    In one embodiment, the helix angle is preferably about 24 degrees and the rake angle  26  is preferably about 4-8 degrees positive to the central axis  28  ( FIG. 3 ) of the drill  10 , with the optimal rake angle  26  being about 6 degree positive to the central axis  28 . 
         [0025]    The shielding  20  material is fused directly to the PCD or PCBN with an extremely strong attachment or bond to avoid being peeled back by the force of material flowing across the edge and is best attached during the Ultra High Pressure sintering process used to produce veined tools as disclosed in U.S. Pat. No. 4,713,286. 
         [0026]    The material can be varied in the sintering process and can include a number of materials that can both protect the PCD or PCBN cutting edge  14  and provide other beneficial properties such as lower friction. In the simplest form, the shielding  20  material is the same tungsten carbide of the drill  10  used to hold the vein  12 . In such cases, the shielded cutting edge  14  results from leaving a portion of the original nib material in front of the vein  12  during the grinding processes. This also has the beneficial effect of lowering the manufacturing costs by avoiding contact between the cutting edge  14  and the vein  12  of PCD or PCBN. 
         [0027]      FIGS. 5 and 6  illustrate a PCD or PCBN reamer also using a shielded cutting edge. The reamer  30  of  FIG. 5  has one or more veins  32  of a suitable material such as Polycrystalline Diamond (PCD) or Polycrystalline Cubic Boron Nitrite (PCBN) having a cutting edge  34 . The reamer  30  also has multiple lands  36  and lead  38  that are the leading edges of each land  36 . At least one vein  32  is angled such that a shield  40  is created that extends along one of the leads  38  in front of and adjacent to the vein  32 . Similar to the drill  10  of  FIG. 3 , the shield  40  is positioned in the area that is particularly susceptible to chipping so as to prevent unwanted chipping of the vein  32  during use of the reamer  30 . 
         [0028]      FIG. 6  shows the shielding  40  of the PCD or PCBN edge  34  for the reamer  30 . In a similar fashion, an edge  34  of PCD or PCBN is exposed for a distance  42  near the corner of the reamer  30  of 0.005 inches, sufficient to engage the work piece but generally protected from damage by contact with the hole wall or guide bushing. The thickness of the shield  40  is defined by angle  44 . 
         [0029]    The scope of this invention is not limited to the above-described preferred embodiments. The terms and expressions used are terms of description and there is no intention of excluding any equivalents of the features shown and described, but it is recognized that various modifications, appreciable to one of ordinary skill, are possible within the scope of the invention claimed.