Tool insert

Abstract: A tool insert comprises an abrasive compact layer (10) having a working surface (12) and an opposite surface (14) bonded to a cemented carbide substrate (16) along an interface. At least one cemented carbide projection (18) extends through the compact layer (10) from the compact/substrate interface to the working surface (12) in which it presents a matching surface (20). The total area of the carbide matching surface (20) is less than that of the compact working surface (12). The cemented carbide projection may take the form of one or more islands (62), or the form of a skeleton (76, 78) enclosing within it a plurality of discrete abrasive compact zones or sections (80, 88).

Description: BACKGROUND OF THE INVENTION This invention relates to a tool insert. Abrasive compacts are used extensively in cutting, milling, grinding, drilling and other abrasive operations. The abrasive compacts consist of a mass of diamond or cubic boron nitride particles bonded into a coherent, polycrystalline hard conglomerate. The abrasive particle content of abrasive compacts is high and there is an extensive amount of direct particle-to-particle bonding. Abrasive compacts are made under elevated temperature and pressure conditions at which the abrasive particle, be it diamond or cubic boron nitride, is crystallographically stable. Abrasive compacts tend to be brittle and in use they are frequently supported by being bonded to a cemented carbide substrate. Such supported abrasive compacts are known in the art as composite abrasive compacts. The composite abrasive compact may be used as such in the working surface of an abrasive tool. Composite diamond abrasive compacts are generally manufactured by placing a layer of diamond particles on a cemented carbide body to form an unbonded assembly and then subjecting that unbonded assembly to elevated temperature and pressure conditions at which diamond is crystallographically stable. Cobalt from the carbide substrate infiltrates the diamond mass during the compact manufacture. In so doing, the carbide substrate in the region of the compact/substrate interface is depleted of cobalt giving rise to stresses in the substrate. These stresses can lead to failure of the composite compact during use. United States Patent No. 4,592,433 describes a cutting blank comprising a substrate formed of cemented carbide and including a cutting surface. A plurality of shallow grooves are formed in the cutting surface and strips of diamond compact are disposed in the grooves. The strips may be arranged in various patterns. In use, the carbide material wears away exposing the diamond strips which cut through a substrate in a rake or claw-like manner. The relatively soft carbide material dominates in the cutting surface so that the harder diamond strips can be exposed, in use. United States Patent No. 5,154,245 discloses rock bit buttons of cemented carbide containing a plurality of polycrystalline diamond bodies, each of which is completely surrounded by cemented carbide. Thus, there are a plurality of polycrystalline diamond islands in a cemented carbide working surface. United States Patent No. 4,997,049 discloses a tool insert comprising an abrasive compact layer having a working surface which is flat and provides a continuous cutting edge extending around the entire periphery thereof and an opposite surface bonded to a cemented carbide substrate along an interface. The tool insert has a recess with curved sides formed therein and in which the abrasive compact is located. In another embodiment the recess is an annulus located in one of the carbide end surfaces. SUMMARY OF THE INVENTION According to the present invention, a tool insert comprises an abrasive compact, particularly a diamond abrasive compact, layer having a working surface which is flat and provides a continuous cutting edge extending around the entire periphery thereof and an opposite surface bonded to a cemented carbide substrate along an interface, and at least one cemented carbide projection which extends through the compact layer from the compact/substrate interface to the working surface in which it presents a matching surface which defines an island in the compact working surface, the total area of carbide matching surface being less than 20 percent that of the compact working surface. DESCRIPTION OF THE DRAWINGS Figure 1 illustrates a plan view of an embodiment of a tool insert of the invention; Figure 2 is a section along the line 2-2 of Figure 1. Figure 3 is a plan view of an unbonded assembly for use in producing the tool insert of Figure 1; Figure 4 is a section along the line 4-4 of Figure 3. DESCRIPTION OF EMBODIMENTS The working surface of the abrasive compact layer is flat, and provides a continuous cutting edge extending around the entire periphery thereof. The total area of carbide matching surface is less than 20 percent that of the compact working surface. The carbide surface or surfaces in the compact working surface, are matching in the sense that they form a continuous profile with the compact working surface. The or each carbide matching surface in the compact working surface defines, in effect, an island. Thus, the carbide matching surfaces, in this form of the invention, define discrete, separate entities. The cemented carbide projection or projections may be bonded to the substrate, or may form an integral part of the substrate. The cemented carbide projection and substrate may be made of the same cemented carbide or of different cemented carbide. Any cemented carbide known in the art such as cemented tungsten carbide, cemented tantalum carbide, cemented titanium carbide, cemented molybdenum carbide and mixtures thereof may be used. As is known in the art, cemented carbides contain a binder phase, generally present in an amount of 3 to 15 percent by mass. The binder is typically a transition metal such as cobalt, nickel or iron or an alloy thereof. The cemented carbide projection may contain a minor amount, i.e. less than 10 percent by volume, of diamond or cubic boron nitride particles. The abrasive compact may be any known in the art, but will generally be a cubic boron nitride or diamond compact. The abrasive compact is preferably a diamond compact. Diamond compacts have a diamond content of at least 70 percent by volume and are polycrystalline in nature. They will contain a second phase containing a diamond catalyst which is typically nickel, cobalt or iron. An embodiment of the invention will now be described with reference to Figures 1 and 2. Referring to these figures, a tool insert comprises an abrasive compact 10 having flat surfaces 12 and 14 on opposite sides thereof. The surface 12 provides the working surface for the tool insert, while the surface 14 is bonded to a cemented carbide substrate 16. This cemented carbide substrate may be any known in the art. The cemented carbide substrate 16 has a projection 18 which extends through the compact 10 from the surface 14 to the working surface 12 of the compact. The projection 18 provides an island 20 of carbide in the working surface 12 of the compact. The carbide island 20 lies in the same plane as that of the working surface 12 of the compact. Peripheral edge 22 of the abrasive compact provides a continuous cutting edge which consists entirely of abrasive compact. The projection 18 reduces the stresses which are created in the carbide substrate 16 during manufacture of the tool insert thereby reducing failure of the tool insert in use. The tool insert of Figures 1 and 2 may be produced from an unbonded assembly illustrated by Figures 3 and 4. Referring to these figures, the assembly comprises a cemented carbide body 30 having a recess 32 formed in the upper surface 34 thereof. A bonded mass 36 of carbide particles is placed centrally in the recess 32. A bonded mass 38 of diamond particles is located in the recess 32 around the carbide mass 36. The masses 36, 38 will typically comprise the particles uniformly dispersed in a suitable organic binder. The unbonded assembly is heated to volatilise most of the organic binder. Some binder remains to retain the bonding in the masses 36, 38. Thereafter, the unbonded assembly is placed in a reaction capsule which itself is placed in the reaction zone of a high temperature/high pressure apparatus. The contents of the reaction capsule are subjected to diamond synthesis conditions, e.g. a temperature of the order of 1400 - 1600°C and a pressure of the order of 50 to 60 kilobars, and these conditions are maintained for a period of 10 to 15 minutes. Binder such as cobalt from the carbide body 30 infiltrates both the diamond and carbide masses. A diamond compact (10 in Figures 1 and 2) is produced from the diamond mass 38, while a cemented carbide insert or projection (20 in Figures 1 and 2) is produced from the carbide mass 36. Both the diamond compact and the cemented carbide projection are firmly bonded to the carbide substrate 30 and to each other. To produce a tool insert of the type illustrated by Figure 1, the sides of the substrate 30 are removed by grinding or other suitable means back to the dotted lines shown in Figure 4.

Claims: A tool insert comprising an abrasive compact layer (10) having a working surface (12) which is flat and provides a continuous cutting edge (22) extending around the entire periphery thereof and an opposite surface (14) bonded to a cemented carbide substrate (16) along an interface, at least one cemented carbide projection (18) extending through the compact layer (10) from the compact/substrate interface to the working surface (12) in which it presents a matching surface (20) which defines an island in the compact working surface (12), the total area of the carbide matching surface (20) being less than 20 percent that of the compact working surface. A tool insert according to Claim 1 wherein the abrasive compact (10) is a diamond compact. Use of a tool insert according to Claim 1 or Claim 2 as a drill bit insert. A drill bit comprising an insert according to Claim 1 or Claim 2.

Inventors: LLOYD ANDREW IAN GIFFORD, TANK KLAUS, LLOYD, ANDREW IAN GIFFORD, TANK, KLAUS
Applicants: DE BEERS IND DIAMOND, DE BEERS INDUSTRIAL DIAMOND DIVISION (PROPRIETARY) LIMITED
Application year: 1993
Main classification: E21B10
IPC codes: B25J9, B25J19, B23B51, B24D3, B23B27, E21B10, B23C5, B24D99