Abstract:
A cutting insert includes a body comprising a superhard material or a superhard material and a cemented carbide, a hole through said body, and a preformed hole inlay in said hole to allow securing of the insert to a holder. The method of making same is also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     The present application is a continuation-in-part of pending application Ser. No. 10/857,922 filed Jun. 2, 2004. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to cutting inserts having cutting edges formed from a superhard abrasive material, and methods of making the same.  
         [0003]     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.  
         [0004]     Indexable cutting inserts using a superhard 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.  
         [0005]     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.  
         [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]     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 securing the insert. See, for example, U.S. Pat. No. 5,147,158 which discloses in cross-section a “trumpet” style of clamping 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.  
         [0008]     In U.S. Pat. No. 6,120,570, there is a disclosed a method of making a cutting insert of a superhard material which is sintered onto a cemented carbide base by high pressure and temperature. A hole is simultaneously formed in the insert through the use of a plug, preferably made of the same cemented carbide as the base, which is not bonded to the insert but is removed after sintering. In  FIG. 3  of U.S. Pat. No. 6,120,570, the hole is shown to be tapered towards the bottom of the insert.  
         [0009]     U.S. Pat. No. 5,536,119 shows a conventional cutting insert in which a through hole has an upper part which is substantially cylindrical while the remaining part tapers downwardly in the form of a convexly vaulted surface.  
         [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 of the present invention there is provided a cutting insert comprising a base portion of a superhard material or a superhard material attached to a cemented carbide with a hole for clamping said insert wherein said hole is formed in an inlay attached to said base portion.  
         [0014]     In another embodiment, there is provided a method of making a cutting insert comprising:  
         [0015]     forming a layer of superhard material;  
         [0016]     attaching said layer onto a superhard material or a cemented carbide substrate;  
         [0017]     forming a hole through said layers; and 
        attaching a preformed hole inlay within said hole.       
 
     
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES  
       [0019]      FIG. 1A  is a top view of a blank and  FIG. 1B  a finished cutting insert constructed according to the principles of the present invention.  
         [0020]      FIG. 2A  is a side view of the blank and  FIG. 2B  of the finished cutting insert of  FIG. 1 .  
         [0021]      FIGS. 3A-3F  are top views of other embodiments according to the principles of the present invention.  
         [0022]      FIGS. 4A and 4B  are side views of another embodiment according to the principles of the present invention.  
         [0023]     FIGS.  5 A-D are side views of another embodiment according to the principles of the present invention.  
         [0024]      FIGS. 6A and 6B  are side views of still another embodiment according to the principles of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]     Exemplary arrangements and techniques according to the present invention will now be described by reference to the drawing figures.  
         [0026]     According to the present invention, a blank is formed from a superhard cutting material. The blank can also be formed from at least one hard material and at least one superhard cutting material. An illustrative embodiment of such a latter blank is shown in  FIGS. 1A, 1B ,  2 A and  2 B. 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 circular.  
         [0027]     Generally, the superhard cutting material and the hard material are sintered together using conventional high-pressure and high-temperature techniques to form a solid body in disc form. Such techniques are conventional and are disclosed, for example, in U.S. Pat. No. 5,676,496. When made only of a superhard material, the body can be formed in one step. Examples of other suitable processes are described, for example, in U.S. Pat. Nos. 4,991,467 and 5,115,697, the disclosures of which are herein incorporated by reference in their entirety. The particular form of the blank can then be cut, e.g., by electro-discharge machining (EDM) from the disc. At least one blank hole  13  may be formed during the pressing and sintering but is preferably machined after processing. The inner wall of the blank hole in the top portion and bottom portion of the blank form an interface  17 .  
         [0028]     In the embodiment of  FIGS. 1B and 2B , the shape of the blank hole is defined by a preformed hole inlay  14  which is mounted, preferably attached and most preferably brazed, into place in the blank hole  13  within the interface in the insert. It will be appreciated that this hole inlay  14  can be preformed into any particular shape necessary for the ultimate mounting. By preforming the hole inlay  14  by any appropriate technique for the chosen material, for example, by pressing a sintering a cemented carbide, various shapes can be accurately and relatively easily made. The hole inlay  14  may be made of any suitable material such as steel, a powder metallurgically formed steel, etc., but is preferably made of a cemented carbide. Most preferably, the cemented carbide of hole inlay  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.  
         [0029]     It will be appreciated that the blank hole  13  should extend through the entire body but the hole inlay  14  does not necessarily extend through the entire body so long as the hole inlay  14  provides the required mounting support for the mounting means (not shown) when the insert is mounted in the tool holder. For example, when the cutting insert is double sided (e.g., as in  FIG. 9 ), two hole inlays may be used to form the appropriate mounting supports. In addition, there may be multiple hole inlays, some of which do not extend all the way through the body.  
         [0030]     As shown in  FIG. 2 , the hole inlay  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 clamping hole when attaching the insert to the holder. It will be appreciated that the clamping hole has a design appropriate for also other clamping systems, for example, a cylindrical clamping hole.  
         [0031]      FIG. 3  shows other variants in which the shape of the hole inlay is other than round as in  FIGS. 1A and 2A . These variations are shown as  FIGS. 3A-3F . In  FIGS. 3A-3F , the cutting inserts are shown from the top with the top layer of superhard material  11  and hole inlay  14  visible. It will be understood by the skilled artisan that other shapes may also be utilized, if desired. In all shown cases, the clamping hole  16  is round and generally conical but other shapes are possible.  
         [0032]      FIGS. 4A and 4B  show other embodiments of the invention in which the hole inlay  14  has a length such that it extends below from the bottom plane of the insert. In this case, the insert is a single-sided insert. As shown, this bottom portion  15  has a form, preferably a non-circular form, which corresponds to a cavity in the tool holder (not shown) and serves to secure the insert more firmly in the tool holder. Although not shown, it will be understood that the clamping hole can extend through the bottom portion  15 .  FIG. 4A  illustrates an embodiment where the superhard layer  11  is present only in an upper portion of the insert where  14  represents the inlay while  FIG. 4B  illustrates an insert in which the super hard layer extends from the top to the bottom of the insert.  
         [0033]      FIGS. 5A and 5B  illustrate a double-sided insert in which in the length of the hole inlay  14  is such it extends beyond the top and bottom planes of the insert ( FIG. 5B ) or is formed in the top and bottom planes ( FIG. 5A ).  FIG. 5C  shows an insert in which the axis x-x of the blank hole  13  is not perpendicular to the plane axis y-y of the cutting insert  20 . If desired, the axis x-x of the blank hole  13  may not be parallel to the axis z-z of the clamping hole inlay  14  ( FIG. 5D ). The cavity in the hole inlay should correspond to the protruding part of the tool holder ( FIG. 5A ) and vice versa ( FIG. 5B ) and may, if desired, be formed from at least two preformed sections (not shown).  
         [0034]      FIG. 6  shows an embodiment of the present invention in which the outer walls of the hole inlay  14  is formed preferably in a conical shape with corresponding conical-shaped walls in the blank hole or through the whole body In  FIG. 6A , the walls of the hole inlay  14  and the blank hole are flush. In  FIG. 6B , the walls of the hole inlay  14  and the blank hole have different conocity whereby either one or both of the walls can be cylindrical.  
         [0035]     The hard material of  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 6 to 20 weight % Co. Various preferred embodiments may contain 9 to 11 weight % Co or 15 to 17 weight % Co.  
         [0036]     The superhard material of  11  can comprise any suitable material chosen for its cutting characteristics. For example, it may comprise a polycrystalline cubic boron nitride (PCBN), a polycrystalline diamond material (PCD) or a ceramic based on silicon nitride and/or alumina. The superhard material may also have additions of other materials, such as carbides, nitrides, carbonitrides, oxides, and/or borides of metals chosen from groups IVa to VIa of the periodic table.  
         [0037]     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.