Abstract:
A related cutting insert includes a cutting insert body comprising sintering a layer of a superhard material, machining a hole through said sintered layer, brazing said machined layer onto a preformed cemented carbide substrate, and grinding a brazed product to form a cutting insert of predetermined shape.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to cutting inserts having cutting edges formed from a superhard abrasive material, and methods of making the same.  
       BACKGROUND OF THE INVENTION  
       [0002]     In the description of the background of the present invention that follows reference is made to certain structures and methods, however, such references should not necessarily be construed as an admission that these structures and methods qualify as prior art under the applicable statutory provisions. Applicants reserve the right to demonstrate that any of the referenced subject matter does not constitute prior art with regard to the present invention.  
         [0003]     Indexable cutting inserts using a superhand material for cutting typically have a polygonal shape with the superhard material disposed at the corners of the polygon. The superhard material, often a cubic boron nitride or polycrystalline diamond material, aids in the cutting of hard workpiece materials such as metals. These cutting inserts are typically mounted in a fixed position to a cutting tool so as to present one of the corners or areas containing superhard material to the surface of a workpiece. After being used for a period of time, the area of superhard material becomes worn. The cutting insert can then be unfastened from the cutting tool and rotated so as to present a new fresh corner or area of superhard material to the surface of the workpiece.  
         [0004]     There are two predominant ways of making such inserts. According to one technique, a stacked structure is formed comprising a first layer of hard backing material and a layer of superhard cutting material superimposed onto the backing layer. Cutting tips are then cut from this stacked structure and brazed to a cutting insert body, typically at a corner thereof. U.S. Pat. No. 5,183,362 to Kuroyama et al., the disclosure of which is incorporated herein by reference, in its entirety, describes such a technique.  
         [0005]     However, several problems are associated with such techniques. The braze joint connecting the cutting tips to the body of the cutting insert creates an inherent weak point in the structure. This is particularly true due to the high temperatures that tend to exist during use of such cutting inserts, these high temperatures being in close proximity to the braze joint. Another problem posed by such techniques is that the extent of superhard material presented to the workpiece and available for wear is limited, thus limiting the useful operating period for that particular cutting edge.  
         [0006]     A second technique for forming indexable cutting inserts involves providing a blank or substrate having pockets formed therein which are filled with superhard material, then subjecting the blank to a sintering operation which bonds the superhard material to the substrate. The blank is then subsequently machined to give the cutting insert its final shape, i.e.—a generally polygonal body with superhard material disposed at the corners thereof. U.S. Pat. No. 5,676,496, the disclosure of which is incorporated herein by reference, in its entirety, describes such a technique.  
         [0007]     Such techniques also present certain difficulties. The process by which the superhard material is bonded to the blank or substrate is difficult and costly. In this regard, the cost of the superhard and substrate raw materials are relatively minor when compared with the costs associated with the process cycle necessary to join them. Thus, from a production efficiency point of view it would seem preferable to form an indexable insert with many corners containing superhard material. That way, the number of costly joining process cycles could be minimized while producing inserts that had many cutting corners. However, customers of such cutting inserts seem to strongly favor cutting inserts having relatively few cutting corners, which are more costly to make on a per unit basis using this technique. Most cutting inserts sold have only 24 cutting corners.  
         [0008]     Another disadvantage associated with this second technique is that if a single pocket of superhard material is defective, the entire insert cannot be sold and may have to be scrapped. Yet another disadvantage or inefficiency is that only a single cutting insert is produced from each costly and difficult process cycle.  
         [0009]     In general, such superhard material-containing inserts have been held in place by an external (e.g., top) clamp. See, for example,  FIG. 25  of U.S. Pat. No. 5,183,362 which shows a top clamp with a preformed, separate chip breaker. Another type of clamping used with other types of cutting inserts involves the use of a screw which passes through a hole in the insert, often in the center of the insert. Such holes may be straight or involve an offset portion to assist in seaming the insert. See, for example, U.S. Pat. No. 5,147,158 which discloses in cross-section a “trumpet” style of central hole for securing purposes. Laser cutting or EDM (electro-discharge machining is used to cut the superhard material and it can be appreciated that machining of a “trumpet” style hole in the superhard material is quite difficult and expensive to do. In addition, the accuracy of such cuts is problematic.  
         [0010]     Thus, a need exists in the art to address the problems discussed above and others.  
       SUMMARY OF THE INVENTION  
       [0011]     The present invention provides devices and methods that address the above-mentioned problems, and others.  
         [0012]     The present invention provides improved indexable cutting inserts and improved methods of producing the same.  
         [0013]     According to one aspect, the present invention provides a method making a cutting insert comprising forming a layer of superhard material, forming a hole in said layer, attaching said layer onto a commented carbide substrate also having a hole corresponding to the hole in said superhard layer, and attaching a preformed annular body within said holes.  
         [0014]     According to further aspect, the present invention provides a cutting insert a cutting insert comprising a base portion of a commented carbide, a layer of superhard material attached to said base and a hole through both said base portion and layer, said hole extending generally corrically from said layer through said base. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES  
       [0015]      FIG. 1  is a top view of a blank or preform constructed according to the principles of the present invention.  
         [0016]      FIG. 2  is a side view of the blank of  FIG. 1 .  
         [0017]      FIG. 3  is a top view of another embodiment according to the principles of the present invention.  
         [0018]      FIG. 4  is a side view of the blank of  FIG. 5 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]     Exemplary arrangements and techniques according to the present invention will now be described by reference to the drawing figures.  
         [0020]     According to the present invention, a blank is formed from a superhard cutting material. The blank can also be formed from a hard material and a superhard cutting material. An illustrative embodiment of such a blank is shown in  FIGS. 1 and 2 . As shown therein, the blank  10  comprises a top layer or portion  11  of a superhard material and a bottom layer or portion  12  of a hard material. While the blank  10  is illustrated as having a polygonal-like shape, other geometries are clearly possible, such as a disk.  
         [0021]     Generally, the superhard cutting material and the hard material are sintered together using conventional pressing and sintering techniques to form a solid shape. A central hole  13  may be formed during the pressing and sintering but is preferably machined after sintering. The hole  13  is designed so as to receive an appropriate mounting means, e.g., a screw, when the finally prepared insert is to be mounted in an appropriate holder.  
         [0022]     In the embodiment of  FIGS. 1 and 2 , the shape of the central hole is defined by a preformed cemented carbide insert  14  which is brazed into place in the central hole  13 . It will be appreciated that this cemented carbide insert  14  can be preformed into any particular shape necessary for the ultimate mounting. By performing the cemented carbide body  14  by pressing and sintering, various shapes of the central hole can be accurately and relatively easily made. Preferably, the cemented carbide of insert  14  is the same as that of layer  12 . If desired, a chip breaking geometry may be formed (e.g., by EDM) on the appropriate surfaces of the superhard layer.  
         [0023]     As shown in  FIG. 2 , the insert  14  is preferably preformed into a shape in which the inner walls  15  converge in a generally conical manner from the top of the superhard layer  11  towards the bottom of the hard material  12 . Such a design assists in securing the screw (not shown) firmly within the central hole when attaching the insert to the holder.  
         [0024]     In  FIG. 1 , there is indicated in dotted lines  14  a circle in which round inserts can be formed, if desired, of the superhard material and cemented carbide.  
         [0025]      FIGS. 3 and 4  depicts another embodiment of the invention. In this aspect, the superhard cutting material  31  is first made with a shape such as described in Provisional Patent Application No. 60/474,956, herein incorporated by reference in its entirety, and cut into the particular shape as shown. The cemented carbide is either made in one piece or made as two pieces  32  and  34  as shown brazed together along braze lines  36  and  37 . Again, the central hole  33  may be shaped by the perform  34  to the desired shape for ultimate mounting. In  FIG. 4 , line  38  depicts the final shape of a cutting insert to be formed from perform  32 . Although the description has indicated that the center hole  13  is cut to a size sufficient to allow the cemented carbide insert  14  to be brazed into that hole, it should be understood, particularly if the initial blank is of sufficient size, that the material removed from the blank to form the center hole  13  may itself serve as a blank for the preparation of another, albeit smaller, cutting insert.  
         [0026]     The substrate  12  is formed from any suitable hard material. Examples of suitable materials include cemented carbides, cermets, and hard metal alloys. One suitable composition is a WC-Co cemented carbide having 10 to 20 weight % Co, and preferably having 15 to 17 weight % Co. The superhard material  11  can comprise any suitable material chosen for its cutting characteristics.  
         [0027]     The superhard material  11  can comprise a boron nitride, such as cubic boron nitride (CBN), or a diamond material such as polycrystalline diamond (PCD). The CBN or PCD material may have additions of other materials, such as carbides, nitrides, carbonitrides, oxides, and/or borides of metals chosen from groups IVa to Vla of the periodic table. The superhard material  16  can be in the form of a composite of CBN or PCD particles forming a first phase, and at least a second phase of a semiconductor (e.g.—Si), metal (e.g.—Cu, Ti, Al), metalloid, or alloys thereof.  
         [0028]     The sintering type treatment can be performed at elevated temperatures and pressures as described, for example, in U.S. Pat. No. 5,676,496. Examples of suitable processes are described, for example, in U.S. Pat. Nos. 4,991,467 and 5,115,697, the disclosures of which are incorporated herein by reference, in their entirety.  
         [0029]     The cutting tips  31  can be formed from a disk by any suitable cutting or material removal/separation procedure. Once such procedure is wire cutting, such as EDM wire cutting.  
         [0030]     The cutting tips can be provided with any suitable geometry. According to one advantageous aspect of the present invention, the cutting tips  31  are provided with a geometry that will provide a mechanical retention or lock when placed within the body of an indexable cutting insert in addition to the brazed joints, as will be described in more detail. Acording to the illustrated embodiment of  FIG. 3 , a cutting tip  31  which is removed from the blank  10  has a geometry or shape that can generally be characterized as a dovetail shape or geometry.  
         [0031]     A specific illustrative example of this type of cutting tip geometry comprehended by the present invention is illustrated in  FIG. 3 . The geometry or shape of the cutting tip  31  illustrated in  FIG. 3  can be described as follows. A pair of converging forward surfaces  42   a  and  42   b  meet at a forward nose  44 , which is preferably rounded. The nose  44  is presented to the workpiece during use of the cutting tip. As illustrated in  FIG. 3 , a portion of the surfaces  42   a  and  42   b , and the nose  44  comprise superhard cutting material  31 . The extent of superhard cutting material  31  extending from the apex of the nose  44  and back along surfaces  42   a  and  42   b  corresponds to dimension “L”, and can be termed the leg length. According to one embodiment of the present invention, the dimension L is at least 2 mm. According to another embodiment, the dimension L can be at least 3 mm.  
         [0032]     Moving in the direction away from the forward nose  44 , subsequent to the converging surfaces  42   a  and  42   b  is an area of reduced width or a waisted section  45 . The waisted section is defined by a first pair of angled surfaces  46   a  and  46   b , as well as a second set of surfaces  48   a  and  48   b . Surfaces  46   a  and  48   a , as well as  46   b  and  48   b  meet at the area of reduced width and define a trough-like formation. The cutting tip may also comprise a planar rear surface  49 .  
         [0033]     Numerous modifications to the above-described geometry are contemplated, so long as the insert geometry provides a self-locating, self-retention property when placed in a cutting insert body.  
         [0034]     Additional advantages will be evident to those of ordinary skill in the art.  
         [0035]     The described embodiments of the present invention are intended to be illustrative rather than restrictive, and are not intended to represent every possible embodiment of the present invention. Various modifications can be made to the disclosed embodiments without departing form the spirit or scope of the invention as set forth in the following claims, both literally and in equivalents recognized by law.