Abstract:
The present disclosure relates to cutting tools and cutting inserts in general, and more particularly to the specific shapes of cutting edges on cutting tools and cutting inserts. In an embodiment, a cutting tool with a cutting edge formed as a sinusoidal curve is provided. In an embodiment, a rotary drill bit including a cutting insert comprising a sinusoidal curve is provided.

Description:
FIELD OF THE DISCLOSURE 
       [0001]    The present disclosure generally relates to cutting tools, and more particularly, to drills, drill bits, and cutting inserts. 
       BACKGROUND 
       [0002]    Rotary cutting tools are used to machine on workpieces. In particular, rotary cutting tools may be used to remove material from a workpiece, so as to form a workpiece to a desired size or shape or create particular features on the face of a workpiece. Generally, a rotary cutting tool is turned around its longitudinal axis while one or more cutting edges on the cutting tool are brought into contact with a workpiece so as to remove material from the workpiece. Rotary cutting tools include mill cutters such as end mill cutters and ball nose cutters, which are used in milling machines to form features such as slots, keyways, and pockets on a workpiece. Other types of cutting tools include drills, which may be used to form cylindrical holes in a workpiece, as well as mill drills, which may be used similarly to a milling machine. 
         [0003]    The performance of a cutting tool is dependent upon the quality of its one or more cutting edges. Over time and as a result of prolonged use, the one or more cutting edges of a cutting tool may become dull as a result of prolonged physical contact between the cutting tool and workpieces. Cutting tools generally remove material from a workpiece through abrasion; the friction caused by this repeated rough contact may slowly wear away or dull the cutting tool. 
         [0004]    As a result, cutting tools typically last for limited amounts of time before requiring replacement. The operational life of a cutting tool may be extended by employing replaceable cutting edges (for example, in the form of replaceable cutting inserts or drill bits), which allow the life of the cutting tool itself to be prolonged by using new cutting edges. 
         [0005]    Replaceable drill bit inserts or cutting inserts are well known in the art. By way of example, U.S. Pat. No. 9,085,947 to George et al. discloses a rotary drill bit for engaging an earth strata material featuring a removable cutting insert. Similarly, U.S. Pat. No. 7,311,480 to Heule et al. discloses a drilling tool cutting insert adapted to be clamped in a rotatably driven drilling tool base body. U.S. Patent Publication No. 2007/0036622 provides a removable spade drill insert. The contents of these references are incorporated herein by reference in their entireties. 
         [0006]    However, the one or more cutting edges on the drill bit or cutting insert wear down over time, requiring that the drill bit or cutting insert be replaced. This necessitates ongoing costs associated with purchasing and storing replacement parts as well as the logistical overhead required to manage the replacement parts. Further, time is lost each time a cutting tool needs to be shut down, either to replace the tool itself or merely the cutting edges which have degraded. 
         [0007]    Accordingly, there is still a need for improved cutting tools in general, and more particularly for improved cutting edges, drill bits, and cutting inserts, that overcome the disadvantages, limitations, and shortcomings of known devices. For example, it is desirable to provide an improved cutting tool that provides a longer useful life. It is also desirable to provide an improved cutting tool that is less susceptible to catastrophic failure and has improved performance characteristics, including, for example, an increased penetration rate. 
       SUMMARY 
       [0008]    An embodiment of the present invention provides a drill insert comprising: a pair of cutting webs inclined relative to each other; a pair of transversely opposed cutting portions, each cutting portion partially defining a side portion of a corresponding cutting web, each cutting portion comprising: an outer cutting edge; an inner cutting edge connected to the outer cutting edge at a transition point; and wherein the inner cutting edge of each cutting portion converge at a point region and each inner cutting edge is sinusoidal in shape. 
         [0009]    Another embodiment provides a chisel portion for a drill comprising: a centrally disposed point region centered; a pair of cutting edges transversely opposed relative to the point region, each cutting edge comprising an inner cutting edge adjacent to the point region and an outer cutting edge connected to the inner cutting edge; wherein each inner cutting edge is sinusoidal in shape. 
         [0010]    Another embodiment provides a drill bit comprising: a drill body having a rotational axis running longitudinally through a forward end and a rear end; a pair of cutting webs located at the forward end inclined relative to each other; a pair of transversely opposed cutting portions, each cutting portion partially defining a side portion of a corresponding cutting web, each cutting portion comprising: an outer cutting edge; an inner cutting edge connected to the outer cutting edge at a transition point; and a notch having a first face, a curved second face and a curved valley, the curved valley connecting the first face and the second face, the first face bound by the curved valley and the inner cutting edge; and a chisel defined by the first face, the valley, the second face and the inner cutting edge of each cutting portion and the cutting webs converging to a point region; wherein each inner cutting edge is sinusoidal in shape. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The following disclosure as a whole may be best understood by reference to the provided detailed description when read in conjunction with the accompanying drawings, drawing descriptions, abstract, background, field of the disclosure, and associated headings. Identical reference numerals, when found on different figures, identify the same elements or functionally equivalent elements. The elements listed in the abstract are not referenced but nevertheless refer by association to the elements of the detailed description and associated disclosure. 
           [0012]      FIG. 1 a    is a top elevation view of a cutting insert in accordance with an embodiment of the present disclosure; 
           [0013]      FIG. 1 b    is a side elevation view of the cutting insert of  FIG. 1   a;    
           [0014]      FIG. 2 a    is a top elevation view of a cutting tool in accordance with an embodiment of the present disclosure; 
           [0015]      FIG. 2 b    is a side elevation view of the cutting tool of  FIG. 2   a;    
           [0016]      FIG. 3 a    is a top elevation view of a cutting insert featuring a gradual constant-radius curve on the secondary cutting lips; 
           [0017]      FIG. 3 b    is a top elevation view of a cutting insert featuring a sharp constant-radius curve on the secondary cutting lips; 
           [0018]      FIG. 3 c    is a top elevation view of a cutting insert featuring linear secondary cutting lips; 
           [0019]      FIG. 3 d    is a side elevation view of the cutting insert of  FIG. 3   c;    
           [0020]      FIG. 4 a    is a top elevation view of a cutting tool featuring a constant-radius curve on the secondary cutting lips; 
           [0021]      FIG. 4 b    is a top elevation view of a cutting tool featuring linear secondary cutting lips; 
           [0022]      FIG. 4 c    is a top elevation view of a cutting tool featuring a constant, convex radius curve on the secondary cutting lips; 
           [0023]      FIG. 4 d    is a side elevation view of the cutting insert of  FIG. 4   b;    
           [0024]      FIG. 5  depicts several types of curves that may be applied to a cutting edge; 
           [0025]      FIG. 6 a    depicts a cutting insert with a sinusoidal secondary cutting lip overlaid with a combined radii secondary cutting lip; 
           [0026]      FIG. 6 b    depicts a cutting insert with a sinusoidal secondary cutting lip overlaid with a single-radius secondary cutting lip; 
           [0027]      FIG. 6 c    depicts a cutting insert with a sinusoidal secondary cutting lip overlaid with a linear secondary cutting lip; 
           [0028]      FIG. 7 a    depicts a cutting insert with a sinusoidal secondary cutting lip overlaid with a convex single-radius secondary cutting lip; 
           [0029]      FIG. 7 b    depicts a cutting insert with a sinusoidal secondary cutting lip overlaid with a concave single-radius secondary cutting lip; 
           [0030]      FIG. 7 c    depicts a cutting insert with a sinusoidal secondary cutting lip overlaid with a linear secondary cutting lip; and 
           [0031]      FIG. 8  is a top elevation view of a cutting insert in accordance with an embodiment of the present disclosure including lines illustrating the cutting force along a secondary cutting lip. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    The present disclosure is not limited to the particular details of the apparatus depicted, and other modifications and applications may be contemplated. Further changes may be made in the apparatus, device, or methods without departing from the true spirit and scope of the disclosure herein involved. It is intended, therefore, that the subject matter in this disclosure should be interpreted as illustrative, not in a limiting sense. 
         [0033]    As shown in  FIGS. 1 a    and  1   b,  in an exemplary embodiment of the present disclosure, a cutting insert  100  includes a pair of cutting webs  102  that are inclined relative to one another. A cutting portion  104  of each cutting web  102  includes an outer cutting edge  106  and an inner cutting edge  108 . The cutting portions  104  are transversely opposed to each other. Each cutting portion  104  includes a notch  110  which has a first face  112  and a second face  114  that meet at a joiner line  116  (also referred to as a valley). The first face  112 , the second face  114 , and/or the valley  116  may include curvature so that when the inner cutting edge  108  is cutting a material, the cut material can traverse down the first face  112 , then through the joiner line  116 , and curl up along the second face  114 . In an embodiment, the first face  112  abuts the inner cutting edge  108  which is formed by a sinusoidal curve. In an alternative embodiment, the inner cutting edge is described one by one of the following curves: an involute curve; a cycloid curve; a trochoid curve; or a curve based on the Archimedean spiral. These curves are discussed in greater detail below in reference to  FIG. 5 . In an embodiment, the second face  114  is described by a radial curve. In another embodiment, the valley  116  is described by a radial curve. In an embodiment, the second face  114  and the valley  116  are described by curves of different radii. In an embodiment, the joiner line  116  has no width and is merely the intersection between the first face  112  and the second face  114 . In an alternative embodiment, the valley  116  has a defined width and forms a separate face between the first face  112  and the second face  114 . 
         [0034]    In an embodiment, the cutting portions  104  are substantially symmetrical to one another. 
         [0035]    As shown, in an embodiment, the notch  110  is formed with a smaller radius at the bottom of the notch  110  along the second face  114  than along the first face  112  (which is adjacent to the inner cutting edge  108 ). The rake angle, or the angle of a cutting tool with respect to the cutting direction, determines the ease or efficiency with which a cutting edge bites into or cuts a material. Using conventional designs, the rake angle formed along the cutting portion  104  is positive or neutral, preventing the cutting portion  104  from efficiently cutting through a workpiece and causing the workpiece to be deformed rather than cut. In contrast, the design of the notch  110  creates a positive rake along the inner cutting edge  104  of the notch  110 , which cuts a workpiece efficiently, forming one or more chips and causes the inner cutting edge  108  to bite into a workpiece aggressively. This reduces the friction between the cutting insert  100 , thereby also reducing the amount of heat created during use and assisting in prolonging the life of the cutting insert  100 . Similarly, the outer cutting edge  106  may be formed so as to have a positive rake angle, thereby increasing the efficiency of the cutting insert. 
         [0036]    A chisel  118  of the cutting insert  100  is defined by convergence of the cutting web  102  and the notch  110  to a point region  118   a.  Each cutting web  102  may include a first web surface  120  and a second web surface  122  that are connected by a web line  124 . The first web surface  120  and the second web surface  122  are inclined relative to each other such that the web line  124  defines a peak relative to the first web surface  120  and the second web surface  122 . The web surfaces  120  and  124  converge to the point region  118   a  to form a part of the chisel  118 . Accordingly, the chisel  118  is formed by the first web surface  120  and the second web surface  122  of each cutting web  12 , and first face  112 , the second face  114  and the joinder line  116  of the notch  110 . 
         [0037]    The outer cutting edges  106  are also referred to as the primary cutting lips, while the inner cutting edges  106  are also referred to as the secondary cutting lips. 
         [0038]    In an embodiment, the cutting insert  100  includes a pair of openings  126  configured to enable the insert to be secured to a cutting tool (not shown). In an embodiment, the cutting insert  100  is configured to be held within a front end of a cylindrical drill body, while the rear end of the drill body is secured to the remainder of the cutting tool or drilling machine. The cutting insert  100  may be secured, for example, in a slot in the drill body using the pair of openings  126 . 
         [0039]    In an embodiment, the cutting insert  100  has a diameter D. In an embodiment, the inner cutting edge  110  has a length from the point region to the transition point  128  that is less than half of the diameter D. In an embodiment, the inner cutting edge  110  has a length that is 0.49 times the diameter D. 
         [0040]    In an embodiment, the curve on the inner cutting edge  110  may be defined by the expression y=sin(2*π*πx+π), with x describing an x coordinate on an x axis, y describing a y coordinate on a y axis that is perpendicular to the x axis, the point (0,0) defined as center of the point region  206 , and the point (1,0) defined as the transition point  128  between the inner cutting edge  110  and the outer cutting edge  108 . In an embodiment, the slope of the inner cutting edge  110  is equivalent to the slope of the outer cutting edge at the transition point  128 . In other words, the inner cutting edge  110  smoothly joins the outer cutting edge  108  without any discontinuity. In an embodiment, the amplitude of the inner cutting edge  110  may be no more than 0.5 millimeters. In an embodiment, the amplitude of the inner cutting edge  110  is 0.5 millimeters. 
         [0041]    As shown in  FIGS. 2 a  and 2 b   , in an exemplary embodiment of the present disclosure, a cutting tool  200  includes a substantially cylindrical main body  202  having a rear portion  204  at one end and a point region  206  at an opposite end. The rear portion  204  is configured to be held by a drilling machine while the point region is configured to cut a workpiece. 
         [0042]    The cutting tool  200  is similar in many respects to the cutting insert  100 . Accordingly, the same parts are referred to herein with the same reference numbers or terms. The cutting tool  200  is configured to rotate about a longitudinal axis  208  which runs through the shank portion  204  and the point region  206 . The cutting tool  200  includes an outer cutting edge  210  and an inner cutting edge  212 . As with the cutting insert  100  of  FIG. 1 , the outer cutting edge  210  and the inner cutting edge  212  may be formed so as to have a positive rake angle, for example through the use of a notch  110  adjacent to the inner cutting edge  212 . 
         [0043]    Conventionally, the secondary cutting lips of a cutting insert are made in the form of either substantially straight lines or curves of a constant radius. Referring to  FIGS. 3 a   - 3   d,  cutting inserts in accordance with embodiments of the present disclosure are depicted with conventional curves applied to the secondary cutting lips. As shown in  FIG. 3 a   , a cutting insert  300   a  may feature secondary cutting lips  302   a  with a sharp constant-radius curve. Alternatively, as shown in  FIG. 3 b   , a cutting insert  300   b  may feature secondary cutting lips  302   b  with a gradual constant-radius curve. As shown in  FIG. 300 c   , a cutting insert  300   c  may instead feature secondary cutting lips  302   c  that are substantially linear (e.g., are straight without significant curvature).  FIG. 3 d    depicts a side elevation view of a cutting insert  300   c  with linear secondary cutting lips  302   c.    
         [0044]    Similarly, the secondary cutting lips of a conventional cutting tool are often made in the form of either substantially straight lines or curves of a constant radius. Referring to  FIGS. 4 a   - 4   d,  cutting tools in accordance with embodiments of the present disclosure are depicted with conventional curves applied to the secondary cutting lips. As shown in  FIG. 4 a   , a cutting tool  400   a  may feature secondary cutting lips  402   a  with a constant-radius curve. Alternatively, as shown in  FIG. 4 b   , a cutting tool  400   b  may feature secondary cutting lips  402   b  which are substantially linear (e.g., are straight without significant curvature). As shown in  FIG. 4 c   , a cutting tool  400   c  may feature secondary cutting lips  402   c  which feature a constant convex radius.  FIG. 4 d    depicts a side elevation view of a cutting tool  400   b  with linear secondary cutting lips  402   b.    
         [0045]    Unlike curves used in conventional designs, referring to  FIG. 5 , in embodiments of the present disclosure, various types of curves may be applied to the inner cutting edge  108 ,  212  and the outer cutting edge  106 ,  210 , including: sinusoid curves  502 ; involute curves  504 ; cycloid curves  506 ; trochoid curves  508 ; and curves based on the Archimedean spiral  510 . As discussed in greater detail below, in a preferred embodiment, a sinusoidal curve is used for the secondary cutting lips on a cutting insert or cutting tool. 
         [0046]    Referring to  FIGS. 6 a -6 c    and  FIGS. 7 a   - 7   c,  the different shapes of various curves applied to the secondary cutting lips of cutting inserts and cutting tools, respectively, are illustrated by overlays of the sinusoidal curve  602 ,  702  of a preferred embodiment with other types of curves. 
         [0047]      FIG. 6 a    depicts a sinusoidal secondary cutting lip  602  overlaid with a combined radii secondary cutting lip  604  on a cutting insert  602   a.  As shown, the combined radii secondary cutting lip  604  is formed by combining two curves together, wherein each curve is taken from the circumference of a circle with a different radius. In sharp contrast thereto, the sinusoidal secondary cutting lip  602  is described by a sinusoidal equation, such as y=sin(2*π*π+π).  FIG. 6 b    depicts a sinusoidal secondary cutting lip  602  overlaid with a single-radius secondary cutting lip  606  on a cutting insert  602   b.  As shown, the single-radius secondary cutting lip  606  is formed by one curve taken from the circumference of a circle (e.g., a curve with a constant radius).  FIG. 6 c    depicts a sinusoidal secondary cutting lip  602  overlaid with a linear secondary cutting lip  608  on a cutting insert  602   c.    
         [0048]      FIG. 7 a    depicts a sinusoidal secondary cutting lip  702  overlaid with a convex single-radius secondary cutting lip  704  on a cutting tool  702   a.  As shown, the convex radius secondary cutting lip  704  is formed by taking a portion of the circumference of a circle and placing it so as to form a convex curve. In sharp contrast thereto, the sinusoidal secondary cutting lip  702  is described by a sinusoidal equation, such as y=sin(2*π*π+n).  FIG. 7 b    depicts a sinusoidal secondary cutting lip  702  overlaid with a single-radius secondary cutting lip  706  on a cutting tool  702   b.  As shown, the single-radius secondary cutting lip  706  is formed by one curve taken from the circumference of a circle (e.g., a curve with a constant radius), placed so as to form a concave curve.  FIG. 7 c    depicts a sinusoidal secondary cutting lip  702  overlaid with a linear (also known as straight edge or split point) secondary cutting lip  708  on a cutting tool  702   c.    
         [0049]    Multiple advantages exist to utilizing variable-radius curves generally, and sinusoidal curves in particular, for the secondary cutting lips. For example, applying a sinusoidal curve to the secondary cutting lips provides for smoother cutting. The cutting force is dispersed perpendicular to the secondary cutting lips at each point along the secondary cutting lips. For a conventional design employing straight or linear secondary cutting lips, the entirety of the cutting force is directed in the same direction. For a conventional design employing a single radius curve, the cutting force seemingly originates at the center point for the circle which would be formed by completing the radial curve. In contrast, with reference to  FIG. 8 , forming a secondary cutting lip  802  using a sinusoidal curve causes the applied cutting forces  804  (shown as arrows that are each perpendicular to the secondary cutting lip  802  at a different point) to be dispersed in different directions, dividing the force and enabling the secondary cutting lip to make smoother cuts. 
         [0050]    Further, utilizing a sinusoidal curve for the secondary cutting lips causes material removed from a workpiece to be divided into smaller portions than those formed by secondary cutting lips using either straight or radial curves. In other words, the sinusoidal shape combined with the positive rake angle of the secondary cutting lips causes “chip splitting,” which efficiently removes material from a workpiece with a minimal amount of friction or wasted energy in the form of heat. 
         [0051]    Additionally, forming the secondary cutting lip  802  using a sinusoidal curve increases the overall length of the secondary cutting lips, as compared with conventional designs using a radial curve or a straight edge. Cutting edges wear faster when higher forces (termed cutting loads) are applied along the cutting edge. By lengthening the cutting edge, the cutting load experienced at each point along the cutting edge is reduced for a given cut, thereby lengthening the service life of the cutting edge. 
         [0052]    As an added benefit, the use of a sinusoidal curve for the secondary cutting lips enables the secondary cutting lips to smoothly join the primary cutting lips. With reference again to  FIGS. 4 a   - 4   d,  conventional designs result in abrupt discontinuities at the transition point  406  between the secondary cutting lips  402  and the primary cutting lips  404 . These discontinuities cause the transition points to extrude away from the primary cutting lips  404  and secondary cutting lips  402  and as a result the transition points  406  experience significantly greater force than any other point on the cutting lips, causing significantly increased wear over time and leading to the degradation of both the secondary cutting lips  402  and the primary cutting lips  404  as the transition point  406  wears down. In sharp contrast thereto, as shown in  FIG. 2 a   , the transition point  214  between the secondary cutting lips  212  and the primary cutting lips  210  is smooth when the secondary cutting lips  212  are shaped as a sinusoidal curve. This eliminates the increased wear at the transition point  214 , as the transition point experiences the same or similar amount of force as the remainder of the cutting lips. 
         [0053]    These advantages are supported by testing comparing conventional designs featuring straight and radial curves to the presently disclosed sinusoidal curve for the secondary cutting lips. In repeated experiments cutting metal using all three designs, the sinusoidal curve exhibited significantly less wear after drilling 100 holes than either the straight line or multiple radius designs. 
         [0054]    One of skill in the art will recognize that all the various components identified in this disclosure may be made from any material or combination of materials suitable for the expected structural load and environment for drilling and cutting including, without limitation, metals, composites, engineered plastics, natural or synthetic materials, etc. Furthermore, such components may be formed in any conventional manner, such as by molding, casting, machining, cold or hot forming, forging, etc. Still further, such components may be finished in any conventional manner, such as painting, powder coating, plating, etc., or may be unfinished. 
         [0055]    Furthermore, while the particular preferred embodiments have been shown and described, it is obvious to those skilled in the art that changes and modifications may be made without departing from the teaching of the disclosure. The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as limitation. The actual scope of the disclosure is intended to be defined in the following claims when viewed in their proper perspective, based on the related art.