Abstract:
A cutting insert rotated about an axis may be utilized during a metal working operation and applied against the rotating workpiece to enhance tool performance. Coolant may be provided through the central bore of the cutting insert utilizing bypass ports around the threaded hold-down bolts. Additionally, the cutting insert may be held within the toolholder pocket utilizing hoop walls which follow a serpentine path to provide flexibility. Finally, relative rotation of the cutting insert with respect to the toolholder body may be prevented utilizing a pair of protrusions within the toolholder pocket which engage a pair of recesses within a side of the cutting insert.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is directed to metal working operations and, more particularly, to an assembly for rotating a cutting insert about a central axis during a metal working operation. The subject invention is also directed to the cutting insert itself, the toolholder for cutting the insert, and a design to provide coolant to the cutting insert. 
     2. Description of Related Art 
     During a metal working operation, such as a turning operation, where a stationary insert is urged against a rotating workpiece, the insert cutting edge acting upon the workpiece is heated by the workpiece until the operation is complete or until the cutting edge begins to break down through a failure mechanism, such as creater wear or plastic deformation. To avoid these modes of failure, and to permit more efficient operation of the cutting insert, in the past, circular cutting inserts have been mounted upon toolholders, such that the cutting inserts were freely rotatable about the insert central axis. A particular cutting insert was then presented to the workpiece and oriented in such a fashion that the rotary motion of the workpiece on, for example, a lathe, imparted to the cutting insert a force acting in a direction tangential to the insert. The motion of the workpiece acted against the cutting insert not only to machine the workpiece but, furthermore, to rotate the circular cutting insert such that the cutting edge of the insert was continuously refreshed. As a result, under ideal conditions, no single segment of the cutting edge experienced prolonged exposure to the workpiece. Furthermore, the cutting edge operated at a lower temperature, thereby allowing greater cutting forces and improved efficiency of the metal working operation. 
     This type of spinning insert may exhibit extraordinarily long tool life and remarkable speeds. However, this same spinning insert may fail in an equally dramatic fashion when the cutting conditions change slightly, or when the cartridge bearings, used by the cutting insert for rotating, begin to deteriorate. 
     A method and assembly are needed capable of rotating the cutting insert about its own axis during a metal working operation, whereby the speed and direction of rotation is not determined by the rotation of the workpiece itself, but is determined by independent forces acting upon the cutting insert. In conjunction with this, a design is needed which may efficiently introduce coolant to the cutting insert. 
     SUMMARY OF THE INVENTION 
     In one embodiment of the subject invention, a cutting insert is comprised of a circular body having a central axis extending therethrough. The insert is intended to machine a workpiece. The body has a top surface and a bottom surface with a central bore having a diameter and extending through the body between the top surface and the bottom surface. At least one side extends around the body between the top surface and the bottom surface. A cutting edge extends along the intersection of the at least one side and the top surface. A central plateau extends about the central bore from the top surface of the body. The plateau includes radial horizontal slots across the top and along the width of the plateau to provide a path for coolant from the central bore of the body. 
     Another embodiment of the subject invention is directed to a toolholder for holding a circular cutting insert. The insert is intended to machine a workpiece by rotation of the insert about the central axis. The toolholder is comprised of a body having central axis extending therethrough. The body is comprised of a pocket extending within the top of the toolholder for accepting the circular insert. The pocket is surrounded by a hoop defining a pocket floor, an inner hoop wall, and an outer hoop wall. A threaded holding bore extends downwardly through the pocket floor to a central coolant bore. The threaded holding bore is adapted to receive a threaded hold-down bolt. At least two bypass ports are offset from the threaded holding bore but fluidly connect the central coolant bore and the pocket floor, thereby capable of providing coolant between the central coolant bore and the pocket when a hold-down bolt obstructs the threaded holding bore. 
     Another embodiment of the subject invention is directed to a toolholder system comprised of a toolholder body and a circular cutting insert mounted within the toolholder body. The toolholder body has a bore along a central axis extending therethrough and a pocket extending within the top of the toolholder for accepting the circular insert. The pocket is surrounded by a hoop defining a pocket floor, an inner hoop wall, and an outer hoop wall. A threaded holding bore extends downwardly through the pocket floor to a central coolant bore. The threaded holding bore is adapted to receive a threaded hold-down bolt. At least two bypass ports are offset from the threaded holding bore but fluidly connect the central coolant bore and the pocket floor, thereby capable of providing coolant between the central coolant bore and the pocket when a hold-down bolt obstructs the threaded holding bore. The circular cutting insert has a circular body with a central axis extending therethrough, a top surface and a bottom surface. A central bore has a diameter and extends through the body between the top surface and the bottom surface. At least one side extends around the body between the top surface and the bottom surface. A cutting edge extends along the intersection of the at least one side and the top surface. A central plateau extends about the central bore from the top surface of the body. The plateau includes radial horizontal slots across the top and along the width of the plateau to provide a path for coolant from the central bore of the body. A hold-down bolt has a head and a shank, wherein a portion of the shank is threadedly engaged with the threaded holding bore and the head retains the cutting insert within the pocket. The shank diameter in the region of the cutting insert bore is sufficiently less than the diameter of the central bore such that there is a gap therebetween fluidly connecting the at least two bypass ports with the radial horizontal slots of the cutting insert. 
     Yet another embodiment of the subject invention is directed to a cutting insert having a circular body with a central axis extending therethrough. The body has a top surface and a bottom surface with a central bore having a diameter and extending through the body between the top surface and the bottom surface. A side extends around the body between the top surface and the bottom surface. There are only two diametrically opposed indentations within the side adapted to engage protrusions within the inner wall of a pocket within a toolholder body to prevent relative rotation of the insert relative to the toolholder body. A cutting edge extends along the intersection of the at least one side and the top surface. 
     Yet another embodiment of the subject invention is directed to a toolholder for holding a circular cutting insert. The toolholder is comprised of a body having a central axis extending therethrough. The body is comprised of a pocket extending within the top of the toolholder for accepting the circular insert. The pocket is surrounded by a hoop defining a pocket floor, an inner hoop wall, and an outer hoop wall. The hoop is generally circular with a hoop diameter but follows an oscillating serpentine path about a radius defining the cylinder to provide flexibility for radial expansion of the hoop. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the toolholder with a rotatable insert operating upon a rotating workpiece in accordance with the subject invention; 
         FIG. 2  is a perspective view of the toolholder system illustrated in  FIG. 1  in accordance with the subject invention; 
         FIG. 3  is an exploded perspective view of the arrangement illustrated in  FIG. 2 ; 
         FIG. 4A  is a bottom view of a cutting insert that may be used with a toolholder discussed herein; 
         FIG. 4B  is a side view of the cutting insert illustrated in along lines “ 4 B- 4 B” in  FIG. 4A ; 
         FIG. 4C  is a top view of the cutting insert illustrated in  FIG. 4A ; 
         FIG. 5A  is a cross sectional view of the toolholder in accordance with the subject invention; 
         FIG. 5B  is cross sectional view along arrows “ 5 B- 5 B” in  FIG. 5A ; 
       FIG.  5 B′ is an enlarged version of  FIG. 5B ; 
         FIG. 5C  is a top view of the toolholder illustrated in  FIG. 5A ; 
         FIG. 6  is a cross sectional view of the toolholder similar to that illustrated in  FIG. 5A , however, including a cutting insert within the pocket of the toolholder secured therein with a hold-down bolt; 
         FIG. 7  is an exploded perspective view of the arrangement illustrated in  FIG. 6 ; 
         FIG. 8  is an assembled perspective view of the arrangement illustrated in  FIG. 6 ; and 
         FIG. 9  is a cross sectional view of the assembly illustrated in  FIG. 8  highlighting the flow path of coolant fluid. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a workpiece  10  rotating about the centerline  15  in a direction indicated by arrow  20  wherein, for example, the workpiece  10  is mounted upon a lathe. A toolholder  50  has mounted thereupon a cutting insert  100 . The cutting insert  100  has a central axis  105 . The insert  100  is secured to the toolholder  50  in a non-rotatable fashion such that rotation of the toolholder  50  is translated directly to the rotation of the cutting insert  100 . As one example, the insert  100  and the toolholder  50  may rotate in a direction illustrated by arrow  110 . The toolholder  50  may be secured within an adapter  75 , which is mounted to a spindle, and which then would be mounted to a machine tool capable of rotating the adapter  75  in the desired direction and at the desired predetermined rotational speed. The toolholder  50  may be secured within the adapter using any number of techniques known to those skilled in the art of rotary tools. However, as illustrated in  FIG. 1 , the adapter  75  has an internal bore  76  therein which accepts the toolholder  50  and secures the toolholder  50  within the adapter  75  utilizing, for example, a locking nut  80  which is threadably secured to the body of the adapter  75  and urges the toolholder  50  therein. The mechanism for securing the toolholder  50  within the adapter  75  may be one of many different mechanisms including a collet or a lock screw and such mechanisms are well know to those skilled in the art of rotating tools. 
     A toolholder assembly is comprised in part of the cutting insert  100  illustrated in detail in  FIGS. 2 ,  3 , and  4 A- 4 C. The cutting insert  100  is comprised of a circular body  102  having a central axis  105  extending therethrough. The insert body  102  has a top surface  107  and a bottom surface  109 . A central bore  112  having a diameter D 1  extends through the body  102  between the top surface  107  and the bottom surface  109 . A side  114  extends downwardly from the top surface  107  and is angled at a clearance angle A of between 5-30 degrees. A shoulder  116  extends radially inwardly from the side  114  to a generally vertical wall  118 . The wall extends downwardly to a chamfer  119  that intersects with the bottom surface  109 . The chamfer  119  may have an angle Y between 0 and 30 degrees to ease insertion of the insert  100  into a toolholder pocket. 
     A cutting edge  115  extends along the intersection of the side  114  and the top surface  107 . 
     The generally vertical wall  118  may be completely vertical or may taper inwardly as the wall  118  extends downwardly to mate with a toolholder pocket having a cylindrical shape or a taper inwardly as the pocket deepens. 
     Of particular interest, a central plateau  120  extends about the central bore  112  from the top surface  107  of the body  102 . The plateau  120  includes radial horizontal slots  122  across the top surface  107  and along the width W 1  of the plateau  120 . As will be explained, these slots  122  provide a path for coolant fluid supplied through the central bore  112  of the body  102 . 
     Returning to  FIG. 3 , the cutting insert  100  may further include a hold-down bolt  130  with a shank  132  having a threaded portion  134 . As illustrated in  FIG. 3  and as furthermore illustrated in  FIG. 6 , the hold-down bolt  130  fits within the central bore  112  and has a head  136 . The shank  132  has a diameter D 2  which is sufficiently smaller than the diameter D 1  of the central bore  112  to define a coolant gap  140  between the shank  132  and the wall  113  of the central bore  112  along the length of the central bore  112 . As illustrated in  FIG. 6 , the portion  142  of the bolt  130  along the length of the central bore  112  may be unthreaded. 
     As furthermore illustrated in  FIG. 6 , the bolt head  136  has an underside  144  that is generally planar and contacts the top  121  of the central plateau  120  to provide a flush fit. As furthermore illustrated in  FIGS. 3 and 6 , the top  121  of the central plateau  120 , with the exception of the radial horizontal slot  122 , may be planar. Additionally, the insert bore  112 , in the direction of the bottom surface  109  to the top surface  107 , may diverge in the region of the central plateau  120 . 
       FIGS. 3 through 6  illustrate the toolholder  50  comprised of a body  150  having a central axis  152  extending therethrough and co-axial with the cutting insert central axis  105 . The body  150  has a pocket  155  extending within the top of the toolholder body  150  for accepting the cutting insert  100 . The pocket  155  is surrounded by a hoop  157  defining a pocket floor  159 , an inner hoop wall  161 , and an outer hoop wall  163 . As illustrated in  FIGS. 5A and 6 , a threaded holding bore  165  is adapted to receive the threaded hold-down bolt  130 . 
     Typically, coolant traveling through a toolholder travels the entire length of a central bore and is ejected at the end of the toolholder. However, in the present design, the hold-down bolt  130  acts as an obstruction to the toolholder central bore  167 . To overcome this obstruction, directing attention to  FIGS. 7 and 8 , bypass ports  169   a ,  169   b  are offset from the threaded holding bore  165  but fluidly connected to the central coolant bore  167  of the toolholder body  150  to provide coolant between the central coolant bore  167  and the pocket  155  when a hold-down bolt  130  obstructs the threaded holding bore  165 . 
     As illustrated in  FIG. 5C , each of the bypass ports  169   a ,  169   b  may be a cylindrical bore through the toolholder body  150  adjacent to the threaded holding bore  165 . As illustrated in  FIG. 8 , each bypass port  169   a ,  169   b  has a centerline  170   a ,  170   b  that is offset from the central axis  152  of the toolholder central bore  167 . 
     Because the bypass ports  169   a ,  169   b  deliver coolant to the pocket  155  only at particular locations within the pocket  155 , the toolholder  150  may further include a manifold  172  ( FIGS. 5A and 6 ) within the pocket floor  159  adjacent to the threaded coolant bore  167  to accept and distribute coolant around the central bore  112  of the cutting insert  100 . The manifold  172  may be a conically shaped recess. Additionally, as illustrated in  FIG. 5C , the bypass ports  169   a ,  169   b  do not fully intersect with the manifold  172 . To permit unobstructed flow from the bypass ports  169   a ,  169   b , grooves  171   a ,  171   b  cut across the pocket floor  159  to fully connect the bypass ports  169   a ,  169   b  with the manifold  172 . 
     Because the toolholder body  50  with the insert  100  therein may be used for high speed rotating applications, the bypass ports  169   a ,  169   b  may be similar in size and radially symmetric about the body central axis  152 . 
       FIG. 9  illustrates a path line  174  showing the path of the coolant from the toolholder central bore  167  through the bypass ports  169   a ,  169   b  into the manifold  172  through the gap  140  and then through the radial horizontal slots  122  where it is expelled. 
     In one embodiment of the subject invention, the wall  118  of the cutting insert  110  is cylindrical and the inner hoop wall  161  of the pocket  155  is cylindrical and there is an interference fit between the cutting insert wall  118  and the inner hoop wall  161  of the pocket  155 . 
     Returning to  FIG. 8 , it is apparent that, as the result of the hold-down bolt  130 , the central coolant bore of the toolholder body may extend only as far as the threaded holding bore  165 . As furthermore illustrated in  FIG. 8 , the bypass ports  169   a ,  169   b  have centerlines  170   a ,  170   b  that are offset from central axis  152  of the toolholder body  150 . The bottom surface  109  of the cutting insert  100  is flush with the planar floor  159  of the pocket  155  to axially locate the insert  100  and to provide a fluid seal therebetween. However, it is also possible for the shoulder  116  to abut with the end  153  ( FIG. 3  and  FIG. 8 ) of the toolholder body  150  to axially locate the cutting insert  100  within the pocket  155  and to provide a fluid seal therebetween. 
     What has so far been described is a design for providing coolant to the cutting region of a rotating cutting insert when the rotating cutting insert is secured to a rotating toolholder body using a centrally located hold-down bolt. 
     In another embodiment of the subject invention, to secure the cutting insert  100  within the toolholder body  150 , another design feature complements and/or replaces the hold-down bolt  130 . 
     Directing attention to FIGS.  3  and  5 A- 5 C, the hoop  157  of the toolholder body  150  is generally circular having a hoop diameter D 3  but follows an oscillating serpentine path  176  about a radius R 3  following the hoop diameter D 3  to provide flexibility for radial expansion of the hoop  157 . This radial flexibility provides some leeway and reduces the need for tight tolerances to mate the cutting insert  100  with the toolholder  50 . Directing attention to FIGS.  5 B and  5 B′, the serpentine path  176  is comprised of interior slices  178  taken from the inner hoop wall  161  and exterior slices  180  taken from the outer hoop wall  163 . The internal slices  178  and the external slices  180  may form an arc  181  about the respective inner hoop wall  161  and outer hoop wall  163  having an arc angle A 1 , A 2 , respectively. The purpose of the internal slices  178  and the external slices  180  is to provide flexibility for radial expansion of the hoop  157 . The size and locations of the curved slices  178 ,  180  may vary. While the shape of the slices  178 ,  180  is illustrated as curved, they may have any number of shapes including rectangles, C-shaped, or U-shaped. However, it is important that any surface that would form an inwardly facing sharp edge or corner would be rounded to reduce any stress concentrations caused by such a sharp edge or corner. Additionally, depending upon the thickness between the inner hoop wall  161  and the outer hoop wall  163 , the slices  178 ,  180  may have a circular shape, whereby only a portion of the circle is not penetrating the thickness. The inner hoop wall  161  has an inner hoop diameter D 4  and the outer hoop wall  163  has an outer hoop diameter D 5 , wherein the hoop walls  161 ,  163  between the curved slices  178 ,  180  maintain their respective diameters. As illustrated in  FIG. 5B , the interior curved slices  178  alternate with the exterior curved slices  180  about the circumference of the hoop  157 . 
     Directing attention to  FIGS. 3 and 5C , the interior curved slice  178  comprises a cylindrical hole  182  extending into the pocket floor  159 , wherein the cylindrical hole centerline  184  is spaced from the inner hoop wall  161  such that the projection of the cylindrical hole  182  onto the inner hoop wall  161  is an arc  181 , as previously discussed. 
     Directing attention to FIGS.  4 A and  5 A- 5 C, the toolholder body  150  further includes at least two protrusions  186   a ,  186   b  extending radially inwardly from the pocket  155 , wherein the protrusions  186   a ,  186   b  are adapted to engage two matching indentations  195   a ,  195   b  ( FIG. 4A ) within the wall  118  of the cutting insert  100  mounted within the pocket  155 . Directing attention to  FIGS. 4A-4C , the wall  118  of the cutting insert body  102  includes at least two diametrically opposed indentations  195   a ,  195   b  within the wall  118  adapted to engage the protrusions  186   a ,  186   b  within the inner hoop wall  161  of the pocket  155  of the toolholder body  150  to prevent relative rotation of the cutting insert  100  relative to the toolholder body  150 . It is necessary to have only two indentations  195   a ,  195   b  to engage the two protrusions  186   a ,  186   b  of the cutting insert  100 . However,  FIG. 3  illustrates a cutting insert  100  with indentations around its entire perimeter. This provides additional strength and rigidity to the insert body  102  since less material is removed from the body  102 . As illustrated in  FIG. 4B , the indentations  195   a ,  195   b  extend from the bottom surface  109  partially up the side  114  of the insert body  102 . In another embodiment, posts (not shown) could be inserted within the holes  179  created by the interior slice  178  and these posts would engage the indentations  195   a ,  195   b  within the wall  116  of the insert  100 . These posts would replace the currently illustrated protrusions  186   a ,  186   b.    
     Directing attention again to  FIG. 5A , the protrusions  186   a ,  186   b  are located adjacent to the pocket floor  159 , and may be located at the intersection of the inner hoop wall  161  with the pocket floor  159 . Directing attention to  FIG. 5B , the protrusions  186   a ,  186   b  may extend upward along the entire length of the inner hoop wall  161 . As shown in  FIG. 9 , the wall  118  of the insert body  102  mates with the inner hoop wall  161  to preferably form an interference fit. The serpentine path  176  of the hoop  157  should provide sufficient radial flexibility so that insertion of the cutting insert  100  into the toolholder  50  is relatively easy. However, to assist, a chamfer  119  may be introduced adjacent to the wall  118 . As an example, for a toolholder having an end with a 14 mm nominal diameter, the interference may be between 0-0.05 mm. As a result of the flexible hoop  57  design, the forces the head  136  of the hold-down bolt  130  impart to the cutting insert body  102  to urge it into the pocket may be less since the insert body  102  is retained within the pocket  155  by the flexible hoop  157 . Additionally, as illustrated in  FIG. 6 , the bottom surface  109 , of the insert body  102  abuts against the floor  159  of the pocket  155  to axially locate the cutting insert body  102  within the toolholder body  150 . As previously mentioned, it is also possible for the shoulder  116  of the insert  100  to abut with the end  153  of the toolholder body  150  to axially locate the cutting insert body  102  within the toolholder body  150 . 
     While the toolholder  50  has been discussed with respect to rotary applications, it should be appreciated that the toolholder  50  or another toolholder having a similar pocket configuration may be effective for non-rotating applications also and use of the subject invention is by no means limited to only rotating applications. 
     While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. The presently preferred embodiments described herein are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.