Abstract:
The present invention relates to a drill having an aggressive drill point geometry. The point geometry allows greater stability and feed rates, while decreasing the heat generated at drill point. The present invention is provided by a drill comprising drill body having at least two helical flutes, a pair of cutting surfaces on an end of the drill body, a web formed between the two cutting edges, and a web thinning notch formed on either side of the web. Each notch forms a notch cutting edge having a positive rake angle.

Description:
TECHNICAL FIELD  
         [0001]    The invention relates generally to a drill having a specialized drill point for boring holes into metals. More specifically the invention relates to a drill having a web-thinning V-notch and aggressive geometry allowing improved centering, faster penetration of the work piece, faster cutting speeds, and improved chip forming geometry.  
         BACKGROUND OF THE INVENTION  
         [0002]    A wide variety of drill point styles are known and particularly adapted for specific drilling tasks. For example, the 118 degree general purpose drill bit is the most commonly used drill point and gives satisfactory results in a wide variety of materials. Another type is the “Racon”, or radiused conventional point which forms a relatively large arc with its curved lips and has a rounded lip corner reducing corner wear and eliminating burrs at exit. Split point, or crankshaft drill points are known in the art for being self-centering and requiring less torque and thrust during drilling. The Double Angle point is used in drilling of abrasive materials. The double angle on this point acts as a chamber concentrating tool wear along the entire cutting lip and reducing corner wear. A helical drill point has a “S” shaped chisel making the point self-centering and requiring less torque and thrust.  
           [0003]    Regardless of the shape of the chisel or lip curvature, the life of the drill point depends on how well the point dissipates heat. If the point does not adequately conduct heat away from its cutting edges, the temperature buildup will “burn” the point and diminish the life of the drill bit. The heat generated at the lip of the drill point is directly related to the load and stresses the lip is subjected to. The more efficiently load stresses are dissipated, the less heat is built up at the cutting edge of the drill point. The Racon point mentioned above attempts to minimize stress by curving the cutting lip. Although this point does offer an improvement, heat dissipation and wear are still critical concerns in the art.  
           [0004]    A problem with these drills is that the center of the drill point at the intersection of the two cutting surfaces forms a chisel. The chisel edges resemble the center ridge of a roof, and cannot be made sharp in the sense that the cutting edges of the drill can be made sharp. The chisel edge is also the most slowly moving part of the drill, being nearest to the center. This combination of inherent dullness and slow speed means that the chisel edges do not so much cut a chip as they plow up or extrude a chip ahead of them. This extruded workpiece material tends to build up in front of the chisel edge, wearing it more quickly than the faster moving and sharper main cutting edges. In order to minimize the effect of the chisel, prior art drill points have been formed with a web thinning gash or notch which reduces the length of the chisel point. However, these notches formed a negative or neutral cutting angle adjacent to the main cutting edge. While generally an improvement, a portion of the main cutting edge was lost and replaced with a longer, but less effective cutting edge. Therefore, there remains a need in the art for a drill having a shorter chisel without an accompanying loss of effective cutting edge surface.  
         SUMMARY OF THE INVENTION  
         [0005]    An object of the present invention to provide an aggressive drill point geometry for a drill. These and other advantages are provided by a drill comprising a drill body having at least two helical flutes, a pair of cutting surfaces on an end of the drill body, each cutting surface having an associated land formed thereon, a web formed between the two cutting edges, and a web thinning notch formed on either side of the web, wherein each notch forms a notch cutting edge having a positive rake angle. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    The invention and developments thereof are described in more detail in the following by way of embodiments with reference to the drawings, in which:  
         [0007]    [0007]FIG. 1 is a side elevational view of the drill with aggressive point geometry of the present invention;  
         [0008]    [0008]FIG. 2 is a perspective view of the drill point of the drill of the present invention as shown in FIG. 1;  
         [0009]    [0009]FIG. 3 is a rotated side elevational view taken along the leading edge of the cutting edge of the drill of the present invention as shown in FIG. 1;  
         [0010]    [0010]FIG. 4 is a detailed plan view of the drill of the present invention as shown in FIG. 1; and  
         [0011]    [0011]FIGS. 5 and 6 are perspective views of the V-notch portion of the drill of the present invention as shown in FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]    Turning now to a preferred embodiment of the invention, FIG. 1 illustrates a drill  10  in accordance with the present invention. It is contemplated that the drill  10  is made of a sintered metallic hard material such as solid carbide. However, the drill may be comprised of high speed steel or any other suitable material and is not limited as such. The drill  10  comprises a first end, or shank  12 , opposite a second end, or point  14 , having a body  16  therebetween, and a rotational axis  19  through the center of the drill  10 . The shank  12  is gripped by a rotating device (not shown) to drive the drill  10 . The body  16  comprises at least two spiral grooves, or flutes  18  in the form of a helix along opposite sides of body  16  which provides chip evacuation during rotation similar to an auger action. Although the flute helix angle shown is  30  degrees, the invention is not limited to a  30  degree helix angle. In between the flutes  18  are lands  20  which are reduced in diameter except at the leading edge called the margin  22 . The reduction in diameter reduces friction between the workpiece and the drill  10 . The margin  22 , forms a full diameter to aid in supporting and guiding the drill  10 . The lands  20  terminate at the point  14  of the drill  10 . The point  14  of the drill  10  is generally cone-shaped and is formed at a cone angle or included angle θ.  
         [0013]    Referring now to FIG. 2, the point  14  comprises two lips or cutting edges  30  formed at the interface of the clearance  32  and the flutes  18 . The cutting edges  30  are formed as a curved or helical lip which helps reduce stress during operation similar to the Racon drill point. The cutting edges  30  form a positive rake angle (not shown) due to the interface of the helical flutes  18  and the cone-shaped point  14  which is best shown in FIG. 3 which depicts the axial rake angle a and FIG. 4 which shows the radial rake angle β.  
         [0014]    Referring again to FIG. 2, the point further comprises a primary clearance surface  32  behind each cutting edge  30  which is formed at a primary clearance angle (not shown) such that only the cutting edges  30  are in contact with the material to be cut. A secondary clearance surface  52  may also be formed adjacent the primary clearance surface  32  at a steeper angle (not shown) to provide additional clearance behind the cutting edges  30 . The clearance surfaces  32 ,  52  prevent additional friction during the cutting operation and provide additional room for facilitating the removal of chips cut from the material. The drill  10  may also include flush channels  34  typically formed through the entire length of the drill  10  and terminating at the clearance surfaces  32 ,  52  of the point  14 . The flush channels  34  carry coolant fluid to help cool the drill  10  and to flush and transport chips out of the hole through the flutes  18 .  
         [0015]    The point  14  of drill  10  further comprises the area between the flutes  18  which is generally referred to as the web  36 . The intersection of the clearance  40  and the cone produces a straight line chisel  38  and forms a negative rake angle with the conical surface. As previously mentioned, the negative rake angle chisel  38  does not cut efficiently. In order to minimize the effect of the chisel  38 , the present invention utilizes a web-thinning, V shaped notch, or gash  40  which reduces the length of the chisel  38 . The V shaped notch  40 , referred hereafter as the V-notch  40 , is generally shaped like a “V” and will be discussed in further detail below.  
         [0016]    In one embodiment of the present invention, the point  14  comprises cutting edges  32  having a Land  60  on at least a portion of the cutting edge  32  in order to further improve the cutting performance of the tool  10 . A land  60  is a straight or tapered edge prep of the relief wall and rake face as it is frequently desirable to provide a chamfer along the cutting edge  30  of a cutting tool  10  in order to reduce stress concentration encountered during use, thereby preventing edge chipping and increasing tool life. Although a K-land  60  is shown, the present invention is not limited to a particular type of edge preparation or land. The edge prep, or land  60 , is defined by the angle it makes with the rake face of the cutting tool, and its width, i.e., the distance in the plane of the tool&#39;s rake face from the beginning of the land portion thereon to the edge generated by the intersection of the land portion and the clearance surface  32  of the tool. Similarly, a corner break  61  may be provided at the interface of the margin  22  and the point  14 . The corner break  61  as shown is a chamfer or clip, but may also be formed as a radius. The corner break  61  helps prevent corner edge chipping and premature wear, thereby increasing the life of the tool  10 . The corner break  61  also helps reduce heat concentrations that are associated with a sharp edge.  
         [0017]    Referring now to FIG. 4, another feature of the cutting edges  30  is that in addition to the lip formed as a positive rake angle in the direction normal to the point surface  14 , a radial outward portion of the cutting edge  30  is formed as a positive rake angle β in a radial direction. The positive radial rake angle β results in chip formation and chip movement radially inward as opposed to typical drill point geometries which are designed to move the chips radially outward.  
         [0018]    The V-notch  40 , is shaped like a “V” having a radiused trough  42  at the bottom of the V-notch  40  and a first generally planar side  44  on a leading side of trough  42  and a second generally planar side  46  on the opposite side, or trailing side of the trough  42  as also shown in FIG. 5. The first side  44  and second side  46  are at an angle φ with respect to each other. Like the prior art web-thinning techniques, the V-notch also reduces the length of the cutting edges  30  as the leading side  44  of the V-notch  40  is cut into a portion of the cutting edge  30  such a reduction also reduces the width of the chips making it easier to evacuate the chips, as best shown in FIG. 4. However, the V-notch  40  of the present invention is formed such that the trough  42  of the V-notch  40  is at a compound angle with respect to axis  19  such that the leading edge  44  of the V-notch  40  forms a positive rake angle. As shown in FIGS. 1 and 6, trough  42  is formed longitudinally as a compound curve at a skew angle λ between the centerline B of trough  42  and a line A perpendicular to the axis  19  of the drill  10 . The trough  42  is also formed at a tilt angle  8  with respect to axis  19  normal to the skew angle λ as shown in FIG. 6. The resulting formation of the positive rake angle on the V-notch  40  actually extends the effective positive rake angle cutting edge length of drill  10 . The multiple cutting edges  30 ,  44 , aggressively bite into the material to be drilled as the drill  10  rotates. Additionally, the positive rake angle cutting edge  44  results in enhanced self-centering of the drill tool  10  by providing an aggressive geometry which bites into the material adjacent the chisel. The negative or neutral prior art web thinning techniques allowed the drill point to “walk” along the surface of the material to be cut, thus moving the drill away from the desired location, or resulted in bell-mouthing of the drill hole entrance.  
         [0019]    The trailing side  46  of the V-notch  40  is generally cut into either the primary clearance surface  32  (when the drill is formed with only one clearance surface) or in the secondary clearance  52  as shown in the figures of the present invention. The trailing side  46  forms an additional clearance surface, shown adjacent the secondary clearance surface  52  at a tertiary clearance angle (not shown) and helps improve chip removal from the drill  10 . Accordingly, the flush channels  34  work in conjunction with the drill point geometry to efficiently remove chips from the hole. The drill point geometry pushes the chips radially inward toward the flutes  18  while the flush liquid flows along the clearance surfaces  32 ,  52 , through the V-notch  40  and into the flutes  18  and out of the hole. The V-notch  40  location and shape help in chip formation and removal. Leading edge  44  of the V-notch  40  cuts the material, the chips are curled as they hit the trailing side  46  of the V-notch  40 .  
         [0020]    As previously mentioned, the cutting edges  30  have a positive axial rake angle α, a positive radial rake angle β, and are curved as the edges  30  move radially inward. The V-notch also has a positive rake angle and a shape conducive to curling and breaking the chips. These curl up the chips formed in front of the cutting edges  30 ,  44 , and help break them up and send them down the flutes and ultimately out of the hole. The process is aided by coolant holes  34 , one formed through the clearance surfaces  32 ,  52 , just ahead of the V-notch. Pressurized coolant pumped down the holes  34  flushes the chips off the cutting edges  30 ,  44 , and out of the hole. In the point geometry configuration of the present invention, the chisel edge  38  lies totally behind the cutting edge  30  that precedes it, next to the V-notch  40 . This configuration provides an easy exit path for the material plowed up ahead of the chisel edge  38 , which can flow down the clearances surfaces  32 ,  52 , behind the cutting edge  30  and into the adjacent V-notch  40 .  
         [0021]    Although the present invention has been described above in detail, the same is by way of illustration and example only and is not to be taken as a limitation on the present invention. Accordingly, the scope and content of the present invention are to be defined only by the terms of the appended claims.