The present invention is directed to the technique of rapidly and economically producing cutting inserts particularly silicon carbide cutting inserts of the type described in co-pending U.S. patent application Ser. Nos. 167,019 and 167,196, by Dr. John M. Ohno, both filed July 9, 1980, and assigned to the assignee of the present invention, both abandoned in favor of co-pending continuation application Ser. Nos. 313,241 now U.S. Pat. No. 4,428,755 and 312,987, now U.S. Pat. No. 4,417,906 respectively, the entire disclosures of which are hereby incorporated by reference.
Disclosed in the above-mentioned co-pending applications is a straightforward technique (hereinafter referred to as the "press and treat" technique) for economically and rapidly forming a composite body for use as a cutting insert. Very briefly, the press and treat technique involves the preparation of a first or crystal dispersion of super-hard crystals such as diamond or cubic boron nitride crystals in carbon black and a second or core dispersion of carbon black, carbon fiber and filler material such as .alpha. or .beta. silicon carbide. The two dispersions are individually mixed with a small amount of temporary binder, such as paraffin, to lend a sufficient green strength to the two dispersions upon cold compaction thereof. After compacting the two dispersions together in a desired configuration, but compact is vacuum heated in the presence of silicon to burn off the paraffin and to allow the silicon to infiltrate both dispersions. Upon further heating, and without the need for the constant application of any type of pressure to the insert, the silicon reacts with the carbon black to form a .beta.-silicon carbide and silicon matrix which bonds both dispersions both internally and to each other.
The inserts produced in accordance with the press and treat technique may be provided with a wide variety of configurations in which the crystal and core portions may be disposed. For example, in the insert produced according to Ser. No. 312,987, the diamond dispersion layer is provided as a planar surface covering the core dispersion layer, while in Ser. No. 313,241, the crystal dispersion is provided exclusively about the periphery of the core dispersion, on the upper surface thereof. In co-pending U.S. patent application Ser. Nos. 286,613 now U.S. Pat. No. 4,504,284 and 226,604, now abandoned, filed July 24, 1981 and July 21, 1981, respectively, both by Dr. John M. Ohno and assigned to the assignee of the present invention, additional configurations are disclosed. In Ser. No. 286,613, the technique of providing an interface layer between the crystal and core portions is disclosed, the interface layer comprising a dispersion of super-hard crystals at a concentration less than that of the first crystal dispersion layer. By providing such an interface layer, the cutting insert eliminates drastic changes or gradients in the composition of the cutting insert leading to a more rugged construction. In Ser. No. 226,604, the second crystal dispersion is employed to form a cutting insert having a first crystal dispersion with the high percentage of crystals covering the top portion of the insert, the second dispersion, having the lower concentration of crystals surrounding the size of the insert. Also disclosed is the use of a plunger having a chamfer for forming the bottom surface of the compacted core dispersion to compensate for a warpage of the resulting composite during the sintering process.
Still another configuration is disclosed in co-pending U.S. patent application Ser. No. 331,370, now U.S. Pat. 4,497,634, by Dr. John M. Ohno, filed concurrently herewith and assigned to the assignee of the present invention, the entire disclosure of which is hereby incorporated by reference. The configuration includes the use of a prepressed center piece for the core dispersion, the use of the center piece reducing the cost of the insert and reducing warpage during sintering. In co-pending U.S. patent application Ser. No. 331,365, now abandoned, by Dr. John M. Ohno, filed concurrently herewith and assigned to the assignee of the present invention, the entire disclosure of which is hereby incorporated by reference, a triangular insert provided with a particular configuration in which the corner portions containing the crystal dispersion material are elevated with respect to the central core portion is disclosed. Similar to Ser. No. 331,365, is co-pending U.S. patent application Ser. No. 331,375, now abandoned, which describes an insert having raised corner portions, with the addition of a thin relatively soft metal layer which is attached to the relatively lower central core portion of the insert.
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