Stone working – Miscellaneous
Patent
1984-04-13
1985-12-10
Whitehead, Harold D.
Stone working
Miscellaneous
51283R, 51308, 409131, 501 97, B28D 100
Patent
active
045572445
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to the use of densified silicon nitride powder as a cutting tool for a low density silicon metal body.
BACKGROUND OF THE INVENTION AND PRIOR ART STATEMENT
Densified silicon nitride has been developed as a structural material for high tempratuare applications and only recently has been discovered to be particularly useful for cutting cast iron, provided the composition is modified by certain second phases (see U.S. Pat. No. 4,323,323). One attempt by the prior art to machine a metal other than cast iron (namely, aluminum) with a spinel modified Si.sub.3 N.sub.4 tool, demonstrated relatively poor results (see Japanese patent No. 49-113803). It has thus become evident that silicon nitride modified to cut one fully dense metal is not universally suitable for cutting various other fully dense metals or materials.
Concurrent with the above development in the prior art, a need has arisen in the ceramic processing arts for efficiently cutting low density metal compacts from which the ceramic is made (see U.S. application Ser. No. 444,901, entitled "Method of Forming Dense Ceramic Bodies", also assigned to assignee hereof). The prior art typically uses tungsten carbide or high speed tool steels to cut low density metal compacts such as silicon. Because of the abrasive nature of silicon particles, these tools have a relatively short cutting life.
This invention deals with the use of a ceramic cutting tool to meet the need in the ceramic processing arts for cutting a low density metal compact to be subsequently converted to a ceramic. The prior art has also attempted to use a dense ceramic (Al.sub.2 O.sub.3) cutting tool to cut a lower density specimen of generally the same ceramic. Such attempt was at relatively low speeds, of limited success, and thus demonstrated the narrow and unpredictable cutting characteristics of ceramics (see "Ceramic Cutting Tools for Machining Unsintered Compacts of Oxide Ceramics" by Holcomb and Rey, Ceramic Bulletin, Vol. 61, No. 12, 1982.
SUMMARY OF THE INVENTION
The invention is a method of machine cutting a semidense silicon comprising particulate body by relatively moving a substantially fully dense silicon nitride cutting tool against the body to shear off portions of the body along a predetermined path.
Preferably the machine cutting of the body is carried out to shear a path having a cross-sectional area of at least 0.01 square inch. The shearing preferably separates the silicon from the body as a powder or chips. Advantageously, the relative cutting movement is carried out by using th tool to cut deep grooves in the silicon comprising particulate body to define sub-bodies, leaving only enough ungrooved material between the sub-bodies to define hinges therebetween. The deep grooves may be cut in a grid pattern penetrating to a depth of about 90-95% of the body.
The silicon nitride tool employed preferably has a density in the range of 3.2-3.29 gm/cm.sup.3 and a hardness in the range of 86-92 on the Rockwell 45-N hardness scale. The tool can be advantageously shaped as a milling tool, a turning tool, or as a grooving tool. It is advantageous if the difference in density between the silicon nitride tool and the semidense silicon comprising object is at least 1.0 gm/cm.sup.3.
The semidense silicon comprising particulate body preferably has a density in the rangae of 1.0-1.9 gm/cm.sup.3. The body is preferably comprised of a nonreacted heat agglomeration of silicon powder and oxygen carrying powder agents, the oxygen carrying agents being present in an amount so that the agglomeration, when nitrided, will consist substantially of silicon nitride and oxynitrides. To this end, the oxygen carrying agents preferably comprise about 4-12% Y.sub.2 O.sub.3 and about 0.5-5% Al.sub.2 O.sub.3. The oxygen carrying agents, when reacted, form a silicon nitride object with about 2-14% oxynitrides. Advantageously, the silicon comprising particulate body is shaped as a disc having a thickness of about 0.3-0.8 inch and opposed faces with a diameter of about
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Ford Motor Company
Malleck Joseph W.
May Roger L.
Whitehead Harold D.
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