Abstract:
A tool insert blank including first and second major surfaces and a plurality of edge surfaces defining an outer perimeter of the blank. A first layer defines the first major surface and a first portion of the plurality of edge surfaces proximate the first major surface. A second layer harder than the first layer is disposed substantially co-extensive with the second major surface and a second portion of the plurality of edge surfaces proximate the second major surface. At least one of the edge surfaces includes a projecting portion defining a first engagement plane and a recessed portion spaced inwardly of the engagement plane whereby the grinding wheel is engageable with the projecting portion without engaging the recessed portion. The second layer can be formed out of various materials including polycrystalline diamond and cubic boron nitride materials. A method of forming a tool insert blank is also disclosed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to tool inserts such as a cutting insert used in machining operations, blanks for forming such tool inserts and a method of manufacture. 
     2. Description of the Related Art 
     Machining methods such as turning or milling require the use of cutting tools made from hard materials. Cemented tungsten carbide was developed many decades ago as a much harder alternative to steel. Cemented tungsten carbide may be brazed to a steel shank but it is more commonly employed as an “insert” that is attached to tool holder by clamping or by engaging a screw with a hole in the insert. Such inserts have an appropriate thickness and are provided in a variety of different geometries. Some of the more common insert geometries are triangular, square and rhombic inserts. 
     More recently, polycrystalline cubic boron nitride (PCBN) and polycrystalline diamond (PCD) materials have been used with inserts to provide a harder and more wear resistant alternative. Typically, small sections of PCBN or PCD are cut with a laser or electrical discharge machining (EDM) process and the small sections of PCBN or PCD are then brazed into a corresponding pocket in a cemented tungsten carbide insert.  FIGS. 1-3  illustrate prior art inserts  10 ,  12  and  14  having a carbide body  16 ,  18 ,  20  and an inlayed section  22 ,  24 ,  26  formed out of either PCBN or PCD that has been secured in a pocket formed in the carbide body. The inlayed sections of PCBN or PCD form one or more cutting edges  28  on the insert.  FIG. 1A  which provides a perspective view of insert  10  with its inlayed section  22  secured to carbide body  16 . 
     The process of manufacturing an insert typically involves forming an insert blank that has the desired geometry but which is slightly larger than the desired final dimensions of the cutting insert. The insert blank is then ground, using a diamond grit wheel, to remove the excess material and form the cutting edge of the insert. While this does not present undue problems with insets having a PCBN cutting edge, the grinding time and grinding wheel consumption involved in grinding a PCD cutting edge presents a significant expense. An improved tool insert blank and manufacturing method that allows for the more cost-effective production of tool inserts is desirable. 
     SUMMARY OF THE INVENTION 
     The present invention provides tool insert blanks and methods of manufacturing tool insert blanks having a relatively hard layer, e.g., PCBN or PCD, that can be cost-effectively ground to form a tool insert. 
     The invention comprises, in one form thereof, a tool insert blank workable with a grinding wheel. The tool insert blank includes first and second major surfaces defining opposing sides of the blank and a plurality of edge surfaces defining an outer perimeter of the blank extending between the first and second major surfaces. A first layer defines the first major surface and a first portion of the plurality of edge surfaces proximate the first major surface. A second layer harder than the first layer is disposed substantially co-extensive with the second major surface and a second portion of the plurality of edge surfaces proximate the second major surface. At least one of the edge surfaces includes a projecting portion defining a first engagement plane and a recessed portion spaced inwardly of the engagement plane whereby the grinding wheel is engageable with the projecting portion without engaging the recessed portion. 
     The second layer can be formed out of various materials including polycrystalline diamond and cubic boron nitride materials. 
     The invention comprises, in another form thereof, a method of forming a tool insert blank. The method includes providing a multi-layered body having first and second major surfaces defining opposing sides of the body. The body includes a first layer defining the first major surface and a second layer. The second layer is harder than the first layer. A tool insert blank is cut from the body wherein the resulting blank has a first side defined by the first major surface, a second side defined by the second major surface and a second layer portion that is substantially co-extensive with the second side. The tool insert blank also includes a plurality of edge surfaces extending between the first and second sides of the blank. The plurality of edge surfaces define an outer perimeter of the tool blank. At least one of the edge surfaces includes a projecting portion defining a first engagement plane and a recessed portion spaced inwardly of the engagement plane whereby a grinding wheel is engageable with the projecting portion without engaging the recessed portion. 
     The step of cutting the tool insert blank from the body can be performed using a wire discharge machining process. The plurality of edge surfaces can be cut to form a substantially perpendicular angle with the first and second major surfaces or the edge surfaces can be cut to define non-perpendicular angle with the first and second major surfaces. 
     The invention comprises, in yet another form thereof, a method of forming a tool insert blank. The method includes providing a multi-layered body having first and second major surfaces defining opposing sides of the body. The body includes a first layer defining the first major surface and a second layer harder than the first layer. The method includes cutting a tool insert blank from the body wherein the resulting blank has a first side defined by the first major surface, a second side defined by the second major surface and a plurality of edge surfaces extending between the first and second sides of the blank. The plurality of edge surfaces define an outer perimeter of the tool blank and at least one of the edge surfaces includes a projecting portion defining a first engagement plane and a recessed portion spaced inwardly of the engagement plane whereby a grinding wheel is engageable with the projecting portion without engaging the recessed portion. The cutting of the recessed portion includes removing a portion of the second layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above mentioned and other features of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a top view of a prior art insert blank with a carbide body and an inlayed cutting tip. 
         FIG. 1A  is a perspective view of the prior art insert blank of  FIG. 1 . 
         FIG. 2  is a top view of another prior art insert blank with a carbide body and an inlayed cutting tip. 
         FIG. 3  is a top view of another prior art insert blank with a carbide body and an inlayed cutting tip. 
         FIG. 4  is a top view of an insert blank in accordance with the present invention. 
         FIG. 5  is a top view of another insert blank in accordance with the present invention. 
         FIG. 6  is a top view of another insert blank in accordance with the present invention. 
         FIG. 7  is a perspective view of the insert blank of  FIG. 4 . 
         FIG. 8  is a top view of a disk showing a cutting pattern for cutting insert blanks from the disk. 
         FIG. 9  is a side view of the disk. 
         FIG. 10  is a top view of an insert blank schematically depicting where the edges will be ground to form a cutting tool insert. 
         FIG. 11A  is a cross sectional view along line  11 - 11  of  FIG. 10  of an insert blank having perpendicularly oriented edge surfaces. 
         FIG. 11B  is a cross sectional view along line  11 - 11  of  FIG. 10  of an alternative insert blank having non-perpendicularly oriented edge surfaces. 
         FIG. 12  schematically depicts the cutting of an insert blank from a disk using a wire EDM process. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. Although the exemplification set out herein illustrates embodiments of the invention, in several forms, the embodiments disclosed below are not intended to be exhaustive or to be construed as limiting the scope of the invention to the precise forms disclosed. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Three slightly different configurations of insert blanks  30 ,  32 ,  34  in accordance with the present invention are illustrated in  FIGS. 4-6 . Each of the blanks  30 ,  32 ,  34  includes a base layer  36  and a relatively harder layer  38 . In the illustrated blanks,  30 ,  32 ,  34 , base layer  36  is a cemented tungsten carbide layer and harder layer  38  is formed out of a PCD material. Other suitable materials may also be used to form layers  36 ,  38 . For example, a PCBN material can be used to form the relatively harder layer  38 . The base layer  36  and hard layer  38  of insert blank  30  are best seen in  FIG. 7 . 
     Two opposing sides of insert blanks  30 ,  32 ,  34  are defined by major surfaces  40 ,  42 . In the illustrated embodiments, major surface  40  is formed by base layer  36  and major surface  42  is formed by hard layer  38  with both of the layers being oriented parallel with major surfaces  40 ,  42 . A plurality of edge surfaces  44  extend between the two opposing major surfaces  40 ,  42  and define an outer perimeter  46  of the insert blanks. 
     Edge surfaces  44  include projecting portions  48  and recessed portions  50 . When the insert blanks are ground to their final dimensions using a grinding wheel, the grinding wheel will engage the projecting portions  48  but will not engage the recessed portions  50 . This is schematically depicted in  FIGS. 4-6  which include a line  52  schematically depicting an engagement plane oriented substantially perpendicular to major surfaces  40 ,  42  and substantially parallel with the engaged edge. As can be seen in these Figures, engagement plane  52  will first encounter projecting portions  48  when the engagement plane is brought into contact with an edge surface  44  of the insert blank and recessed portion  50  will be spaced inwardly of the engagement plane. 
     Hard layer  38  provides a cutting edge after the insert blanks have been ground to their final dimensions and installed in a piece of machining equipment. As can be seen in  FIG. 7 , base layer  36  forms a first portion  37  of edge surface  44  proximate major surface  40  while hard layer  38  forms a second portion  39  of edge surface  44  proximate major surface  42 . Hard layer  38  is co-extensive with second major surface  42 , i.e., it has an extent that is substantially equivalent to outer perimeter  46 . Both the projecting portions  48  and the recessed portions  50  of edge surfaces  44  have a first portion  37  formed by base layer  36  and a second portion  39  formed by hard layer  38 . However, it is the portion  39  of hard layer  38  on projecting portions  48  that will act as a cutting edge after the grinding of the insert blank has been completed. 
     By providing a recessed portion  50  on the edge surfaces  44 , the grinding operation will only have to remove material from the projecting portions  44  of the insert blanks. This reduction in the quantity of material that must be removed from the insert blank during the grinding will reduce costs. The grinding of base layer  36  generally does not present a difficulty and it is the removal of a portion of layer  38  to form recessed portion  50  during the cutting of the insert blank that presents the greatest reduction in grinding expenses. This is cost savings is particularly beneficial with insert blanks having a layer  38  formed out of a PCD material. 
       FIG. 8  illustrates a disk  54  from which multiple insert blanks  30  are cut. Disk  54  is shown in cross section in  FIG. 9  and has a base layer  36  formed out of carbide or other suitable material with a layer  38  of harder material, e.g., PCBN or PCD, deposited on the base layer  36 .  FIG. 8  shows the outline of several insert blanks  30  that will be cut from the body of disk  54 . Insert blanks  30  can be cut from disk body  54  using various techniques including laser cutting methods and electrical discharge machining.  FIG. 12  schematically depicts the use of a wire electrical discharge machining apparatus  56  to cut insert blanks from disk  54 . A clamping device  58  holds disk  54  while a wire  60  of apparatus  56  is used in the cutting of process. 
     Laminated disks  54  having a carbide layer  36  and a PCD layer  38  are commercially available and can be obtained with layers  36 ,  38  of various dimensions. For example, disks  54  commonly have a total thickness of approximately 1.6 mm, 3.2 mm or 4.8 mm with a PCD layer  38  having an approximate thickness of 0.5 mm to 0.8 mm. Although the illustrated insert blanks  30 ,  32 ,  34  have two parallel layers which are both parallel and co-extensive with the major surfaces  40 ,  42 , other configurations, e.g., insert blanks having three or more layers, may also be employed with the present invention. 
     The wire of the apparatus  56  is shown in two alternative positions in  FIG. 12 . The solid line wire  60  indicates the relative orientation of wire  60  to disk  54  for cutting edge surfaces  44  that are disposed at a substantially perpendicular angle to major surfaces  40 ,  42  as depicted in  FIG. 11A . Dashed lines  62  in  FIG. 12  indicate an alternative orientation of the wire which results in edge surfaces  44  that are positioned at a non-perpendicular angle relative to major surfaces  40 ,  42  as depicted in  FIG. 11B . Various methods can be used to cut insert blanks from a larger body, however, the use of a wire EDM process to cut insert blanks from a larger body is particularly advantageous in the manufacture of insert blanks which include edge surfaces  44  that are oriented at a non-perpendicular angle relative to major surfaces  40 ,  42 . 
     The provision of inclined edge surfaces as depicted in  FIG. 11B  further reduces the quantity of material that must be removed during the grinding process to provide additional cost savings in the grinding process. As mentioned above, insert blanks must be finished with a grinding wheel or other suitable tool to provide a finished surface that corresponds to the desired final dimensions of a cutting insert. In  FIGS. 10 ,  11 A and  11 B, dashed lines  64  indicate the location of the finished surface corresponding to the desired final dimensions of the cutting insert that will be created using the insert blank. 
     As can be seen in  FIGS. 11A and 11B , finished surface location  64  is disposed at a non-perpendicular angle relative to major surfaces  40 ,  42 . When edge surface  44  forms a non-perpendicular angle that is more closely parallel to the desired final surface  64  than a perpendicularly oriented edge surface, the quantity of material that must be removed from insert blank  30  during the finishing operation can be reduced compared to the use of an edge surface  44  that is perpendicular to both major surfaces  40 ,  42 . Because it is the projecting portions  48  that will be subjected to finishing operations to obtain the desired finished surfaces  64 , recessed portions  50  can be formed by surfaces which are oriented at a perpendicular angle to major surfaces  40 ,  42  without affecting the quantity of material that must be removed during finishing operations. It is also noted that for some insert blanks, the desired finished surface is perpendicular to major surfaces  40 ,  42 . In such cases, an edge surface  44  that forms a perpendicular angle with major surfaces  40 ,  42  will minimize the quantity of material that must be removed during the finishing operation. 
     It is further noted that while the depicted finished surface location  64  does not require any material to be removed from edge surface  44  in recessed portions  50  alternative embodiments may employ relatively shallower recessed portions. For example, if the recessed portions  50  have a depth, relative to projecting portions  48 , that is only slightly less than the quantity of material removed from projecting portions  48  during the grinding or finishing operations, only a minimal amount of material will have to be removed from recessed portions  50 . The use of such “shallow” recessed portions  50  still reduces the quantity of material that must be removed during the grinding or finishing operation while allowing the recessed portion  50  to be cosmetically improved by the grinding/finishing operations and providing finished edge surfaces without a discontinuity or step at the transition between the projecting and recessed portions  48 ,  50 . 
     While  FIGS. 8 and 9  illustrate a disk  54  from which a plurality of insert blanks  30  can be cut, insert blanks in accordance with the present invention can also be manufactured using other starting materials. For example, used cutting tool inserts having suitable overall dimensions can be reclaimed and cut to form a new insert blank. 
     Insert blanks having projecting and recessed portions  48 ,  50  are not limited to any particular outer perimeter geometry. Although the illustrated insert blanks  30 ,  32 ,  34 , all have a substantially triangular outer perimeter  46 , alternatively shaped outer perimeters, e.g., square, diamond and other rhombic outer perimeters, can also be used. Numerous other regular and irregular polygon shaped outer perimeters are in common usage with insert blanks and may also be employed with the insert blanks of the present invention. 
     The use of insert blanks having projecting and recessed portions  48 ,  50  to replace alternative insert blank designs can be appreciated with reference to  FIGS. 1-6 . In this set of six figures,  FIGS. 1-3  illustrate prior art insert blanks wherein the hardened inlay forms three separate cutting edge patterns  28 .  FIGS. 4-6  illustrate insert blanks with projecting and recessed portions  48 ,  50  that provide cutting edge patterns that not only replicate those of  FIGS. 1-3  respectively but also provide the cutting pattern on each of the three corners of the insert blanks. It is also noted that as a result of this configuration, each of the insert blanks illustrated in  FIGS. 4-6  include three side edges  44  with each of the side edges  44  including a first projecting portion  48  at one end, a second projecting portion  48  at the opposite end of the edge  44  and a recessed portion  50  disposed between the two projecting portions  48 . 
     While this invention has been described as having an exemplary design, the present invention may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles.