Abstract:
The present invention relates to a V-notched web formed on a drill insert of a drill tool assembly. The V-notched web allows greater stability and feed rates, while decreasing the heat generated at the insert tip. The present invention is provided by a drill insert comprising a drill insert body having at least two cutting edges, a web between the two cutting edges, and a web thinning notch formed on either side of the web. Each web thinning notch forms a notch cutting edge having a positive rake angle.

Description:
TECHNICAL FIELD  
         [0001]    The invention relates generally to a cutting insert to be placed into a tool holder for boring holes into metals. More specifically, the invention relates to a cutting tool insert having a specialized geometry at the web of the insert, allowing increased stability at various feed rates.  
         BACKGROUND OF THE INVENTION  
         [0002]    Drilling systems are frequently used to provide cylindrical holes in metallic workpieces. The cutting or boring action of the drill system may be carried out by an elongated, substantially cylindrical drilling tool, such as a combination of a tool holder and a drill insert, which is selectively attached thereto. Such an arrangement may then be used in an application wherein one end of the tool holder is securely mounted in a driving apparatus, which rotates the holder about its longitudinal axis. At the opposite end of the elongated tool holder, the cutting insert engages the material to be cut. Alternatively, the workpiece may be made to rotate relative to the holder and cutting insert, such as in positioning the holder in the tail stock of a lathe or the like. Further, the tool and workpiece may be made to rotate relative to one another. The use of cutting inserts allows for quick changing of the insert upon wear of the cutting surfaces instead of the entire tool, and allows for one tool to be used for a variety of different boring applications by simply changing the insert and not the entire drill assembly.  
           [0003]    One problem with prior art cutting tools is that the point or tip of the insert does not efficiently cut into the workpiece. This is due to negative or neutral rake angles formed by web thinning techniques near the chisel of the insert. This results in deformation of the workpiece rather than cutting, which increases the heat produced at the drill insert point. Furthermore, the prior art insert geometry could result in instability, which can cause deviations in the dimensions of the hole being bored, also known as runout and/or bellmouthing which is undesirable. Additionally, prior art drill systems and inserts were configured such that chips from the drilling process were not formed efficiently, causing deterioration of the cutting surfaces. The configuration of the cutting surfaces also did not allow for producing positive rakes in association with chip removal flutes to facilitate chip formation.  
         SUMMARY OF THE INVENTION  
         [0004]    The present invention provides a novel drill insert having a V-notched web. The V-notched web allows greater stability and feed rates, while decreasing the heat generated at the insert tip. The stability of the V-notch can further enhance the self-centering capability of existing self-centering configurations of drill inserts. These and other objects of the invention are provided by a drill insert comprising a drill insert body having at least two cutting edges, a web between the two cutting edges, and a web thinning notch formed on either side of the web. Each web thinning notch forms a notch cutting edge having a positive rake angle. These and other objects of the invention are also provided by a drilling tool assembly comprising a holder having a body portion and a head portion, the head portion having a recess formed on one end thereof and a drill insert body securedly insertable within the recess of the holder. The drill insert body has at least two cutting edges, a web between the two cutting edges, and a web thinning notch formed on either side of the web. Each web thinning notch forms a notch cutting edge having a positive rake angle. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    The invention and developments thereof are described in more detail in the following by way of embodiments with reference to the drawings, in which:  
         [0006]    [0006]FIG. 1 is an exploded assembly view of the drill tool assembly according to a preferred embodiment;  
         [0007]    [0007]FIG. 2 is a partial perspective view of the holder associated with the assembly;  
         [0008]    FIGS.  3 A- 3 E are a variety of different views of an insert according to a first embodiment of the present invention having a flat chisel;  
         [0009]    FIGS.  4 A- 4 E are a variety of different views of an insert according to a second embodiment of the present invention having a multifaceted chisel; and  
         [0010]    FIGS.  5 A- 5 E are a variety of different views of an insert according to a third embodiment of the present invention having a multifaceted chisel and reduced clearance cut. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0011]    Turning now to a preferred embodiment of the invention, FIG. 1 illustrates a drill tool assembly  10  generally indicated. Drill tool assembly  10  comprises a holder  12 , which has a body  14  and head portion  16  associated therewith. In the preferred embodiment, holder  12  has, in general, a cylindrical shape with a first end  20  and second end  22 . As shown in FIG. 2, the first end  20  of holder  12  has a clamping or holder slot  30 , which may extend across the entire diameter of the head portion  16  or, at least, over a center portion thereof at the general location of the rotational axis  18  of holder  12 . The holder slot  30  has a bottom wall  32  positioned in substantially perpendicular orientation relative to the rotational axis  18  of the holder  12 . In the preferred embodiment, the assembly  10  may further include a locating boss or dowel pin  24 , which is positioned precisely with respect to the axis  18  and extends from the bottom wall  32  of the holder slot  30 . The pin  24  may be positioned within a hole  26  extending downwardly from the bottom wall  32  of slot  30  along the axis  18  of the holder body in a press fit relationship to position pin  24 . Alternatively, the locating boss, which, in the preferred embodiment, comprises pin  24 , may be configured in another manner to achieve the corresponding functionality of pin  24 , such as an integral member extending from bottom wall  32 . Within the holder slot  30 , a drill insert  35  is precisely positioned with respect to the holder  12  to perform the desired drilling function in conjunction therewith. As will be hereinafter described in more detail, the insert  35  has a point geometry comprising a plurality of cutting surfaces, which are precisely positioned with respect to the axis  18  of the holder  12  to minimize errors in a resulting drilling operation using assembly  10 .  
         [0012]    More particularly, the preferred embodiment of holder  12  is shown in FIG. 2, and may be configured to include at its first end  20  a pair of clamping arms  34 , which extend about holder slot  30 . The clamping arms  34  preferably include apertures  36 , which accommodate screws  38  (see FIG. 1) to secure the drill insert  35  in its position within the holder slot  30 . In the preferred configuration, the holes  36  are threaded to engage screws  38 , and mate with screw holes formed in the drill insert  35  in a predetermined manner to precisely locate the drill insert in a predetermined location within holder slot  30 , as will be described in more detail. Each of the clamp arms  34  may also include a lubrication vent  28 , which allows the application and flow of lubrication adjacent the cutting surfaces of the drill insert to facilitate the drilling operation. The clamp arms  34  may also include angled or curved surfaces, which facilitate chip removal via chip evacuating grooves  37  on each side of the holder  12 . The seating surface  32  is also shown to be designed as a planar surface, which corresponds to the planar bottom portion of the preferred drill insert  35 , although another configuration of bottom surface  32  may be employed and is contemplated herein.  
         [0013]    Turning to FIG. 3A, a first embodiment of the drill insert  35  is shown. The drill insert  35  may form a spade drill blade, with side edges  60  of the blade being generally parallel with the rotational axis  18  of the holder  12  once the insert  35  is positioned and secured with holder  12 . When secured with holder  12 , drill insert  35  will also have a rotational axis, which desirably is coaxial with axis  18  of holder  12 . The drill insert  35  will also have a width  61 , which, upon being rotated with holder  12 , forms an outside diameter of the assembled tool. The drill insert  35  further includes cutting edges  64  on its upper surface in the form of an obtuse V-shape, with cutting edges  64  on each side of the axial center  62 , also known as the dead center. The cutting edges  64  may include a plurality of cutting components, which cooperate together to provide the desired cutting surface  64  for the material and/or drilling application. In general, the insert  35  is designed to cut when rotationally driven in conjunction with holder  12  in a predetermined direction, and is not reversible, although such drilling blade configurations are known to those skilled in the art and could be used in conjunction with the present invention if desired. The drill insert  35  further preferably includes apertures  70 , which cooperate with the apertures  36  in clamp arms  34  to secure insert  35  within holder slot  30  and seated against seating surface  32 . Additionally, each of the apertures  36  and  70  are preferably formed with countersunk portions formed as a bearing surface adapted to be engaged by a corresponding tapered or like surface on the screws or other fastening mechanism  38 . The enlarged clamping head of the screws  38  may be of any convenient shape, such as conical, ball-shaped, or in another form to correspond with the similar surfaces in the tool holder  12  and insert  35 . In a typical fashion, by offsetting the axes of the apertures  36  and  70 , upon securing insert  35  within slot  30  by means of screws  38 , the insert  35  will be forced downwardly against the seating surface  32 . Insert  35  may include a locating slot  65 , which allows positioning of the locating pin  24  therein. This connection is further described in co-owned U.S. Pat. No. 5,957,635, which is herein incorporated by reference.  
         [0014]    Insert  35  also includes a V-notch feature  66  as best shown in FIGS.  3 B- 3 E. A V-notch  66  is located on either side of the chisel  68 , which is formed across the insert web and extends through axial center  62 . A negative feature of drill inserts and twist drills, in general, is that the chisel must act as a cutting edge. The chisel  68  has a negative rake angle, which does not cut efficiently but rather deforms the metal. This results in high thrust forces being required and excessive heat being developed at the point  62 . The V-notch  66  forms a type of flute on either side of insert  35 , which reduces the web and length of chisel  68 . Prior art notches typically were formed as a full radius. The prior art notches provide a neutral cutting edge, which still does not efficiently cut but rather extrudes or deforms the metal. The V-notch  66  is formed having a small radius R at the bottom of the notch, which extends outward from the radius center along linear legs forming the sides of the V-notch  66 . This creates a positive rake along the cutting edge of the V-notch  66 , which cuts the material by forming a chip and minimizes extrusion or deforming of the metal during cutting operations. The positive rake of the V-notch  66  allows the insert cutting surfaces to bite into the workpiece in a more aggressive fashion, which results in higher feed rates and increased stability while, at the same time, creating less heat generated at the tip of the insert  35 . In drills having a flat chisel (such as in FIGS.  3 A- 3 E), there is a tendency for the drill to walk around the chisel during drilling operations resulting in runout and wander of the drilled hole. The V-notch  66  helps improve the self-centering capability of the drill insert  35 .  
         [0015]    That the notch  66  can also be used with an insert having a self-centering configuration, as shown in FIGS.  4 - 5 . In FIGS.  4 A- 4 E, a multi-faceted chisel point  68 ′ is shown on a drill insert  35 ′. Chisel  68 ′ is created by a clearance cut  72  along a longitudinal center line of insert  35 ′, which is parallel to the cutting edges  64 . The multi-faceted chisel point  68 ′ is not as apt to wander as a flat chisel  68  which results in a self-centering characteristic of the chisel  68 ′.  
         [0016]    In FIGS.  5 A- 5 E, a second configuration of a multi-faceted chisel point  68 ″ is shown on insert  35 ″. Chisel  68 ″ is created by a diagonal clearance cut  72 ′ extending through the center point  62  of chisel  68 ″ from each trailing edge corner. The diagonal clearance cut  72 ′ increases the strength of the insert  35  by removing less metal than as shown in the previous clearance cut  72 , while retaining the multi-faceted chisel point  68 ″. As with the previous embodiment, the multi-faceted chisel point  68 ″ is not as apt to wander as a flat chisel  68  which results in a self-centering characteristic of the chisel  68 ″.  
         [0017]    To increase stability of the drill insert, the angle of the chisel can be optimized to allow a longer or shorter chisel. The chisel angle optimization is a function of the location and depth of the V-notch  66  as well as the clearance angles. It is contemplated that the drill insert is made of a sintered metallic hard material such as carbide, cermet, ceramic, monocrystalline and polycrystalline diamond, or boron nitride. However, the drill insert may also be comprised of high speed steel.  
         [0018]    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.