Tool insert

Abstract: A tool insert comprises an abrasive compact layer (56) having a curved working surface (60), at least a portion of which provides a cutting surface, and an opposite surface bonded to a cemented carbide substrate (50) along an interface, at least one cemented carbide projection (58) extending through the compact layer (56) from the compact/substrate interface to the working surface (60) in which it presents a matching surface (62) which defines an island in the compact working surface (60), the total area of the carbide matching surface (62) being less than that of the compact working surface (60).

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. 5,030,250 discloses a method of making tool inserts in accordance with the preamble of claim 1. 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 cemented carbide tool insert having a recess with sloping sides formed therein and in which an abrasive compact is located. In one 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 layer having a curved working surface, at least a portion of which provides a cutting surface, and an opposite surface bonded to a cemented carbide substrate along an interface, characterized by at least one cemented carbide projection extending 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 the carbide matching surface being less than 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; and Figure 2 is a section along the line 2-2 of Figure 1. DESCRIPTION OF EMBODIMENTS The working surface of the abrasive compact layer is curved and that surface, or at least a portion of that surface, provides a cutting surface. An example of a curved surface is a hemispherical surface. The total area of carbide matching surface will generally be substantially less than, e.g. 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 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, there is shown a tool insert comprising an elongate cemented carbide substrate 50 which is generally right-circular, cylindrical in shape. The substrate 50 has one end 52 adapted to be mounted in the working surface of a tool and an opposite working end 54. The working end 54 of the substrate is hemispherical. An abrasive compact layer 56 is provided in the working end 54. This abrasive compact layer has six evenly spaced cemented carbide projections 58 extending through it. The projections 58 extend through the compact layer 56 and terminate at the hemispherical surface 60 of the layer 56. As can be seen clearly from Figure 1, the top surfaces 62 of the projections 58 provide a plurality of cemented carbide islands in the compact working surface 60. Further, the surfaces 62 follow the hemispherical contour of the compact working surface 60. In use, the end 52 of the insert will be mounted in the working surface of a tool such as a drill bit. The hemispherical surface 60 will provide the cutting or abrading surface for the insert. The compact layer 56 will be harder than the cemented carbide projections 58 which will tend to wear away quicker. This wearing away will create sharp cutting edges within the surface 60, improving the cutting action of the tool insert. Further, the projections 58 reduce stress formation in the carbide substrate 50. The sides 64 of projections 58 may slope towards or away from each other, or these sides may be parallel to each other. The tool insert of Figures 1 and 2 may be produced using generally the method described in United States Patent No. 5,030,250. In this method, the substrate will be suitably shaped with an end surface providing the desired projections. The slurry, or similar form, of the components, in particulate form, necessary to make the compact layer will be pressed or squeezed between adjacent projections on insertion of the substrate into the container.

Claims: A tool insert comprising an abrasive compact layer (56) having a curved working surface (60), at least a portion of which provides a cutting surface, and an opposite surface bonded to a cemented carbide substrate (50) along an interface, characterized by at least one cemented carbide projection (58) extending through the compact layer (56) from the compact/substrate interface to the working surface (60) in which it presents a matching surface (62) which defines an island in the compact working surface (60), the total area of the carbide matching surface (62) being less than that of the compact working surface (60). A tool insert according to claim 1 wherein the total area of carbide matching surface (62) is substantially less than that of the compact working surface (60). A tool insert according to claim 1 or claim 2 wherein the total area of the carbide matching surface (62) is less than 20 percent that of the compact working surface (60). A tool insert according to any one of the preceding claims wherein the curved working surface (60) is a hemispherical surface. A tool insert according to any one of the preceding claims wherein the abrasive compact (56) is a diamond compact. Use of a tool insert according to any one of the preceding claims as a drill bit insert. A drill bit comprising an insert according to any one of claims 1 to 5.

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: E21B10, B24D99