Diamond turning of granite

Polycrystalline diamond compact (PDC) cutting bits are used extensively in mining and oil-hole drilling as well as in construction and non-ferrous metal cutting. This paper describes laboratory experiments of PDC cutters machining granite on a lathe under controlled conditions. Speeds, feed rates and depths of cut are varied, and in some cases cooling is adjusted to control the PDC temperature. Cutting forces, tool temperatures, tool wear and rock removal amounts are measured. It was found that both cutting forces and PDC tool temperatures (when not controlled) increase strongly as the size of the PDC wear flat increases. An experiment, designed to separate the forces on the diamond from the forces acting on the carbide, showed that the stress on the carbide is only about 13% of the stress on the diamond. Using slider wear analysis, it was shown that the PDC radial tool wear (x) was directly proportional to the tool travel distance (L). Ratios of x/L are calculated from several test series. In general, tool wear rates increased with PDC tool temperature until the PDC tool tip temperature reached an estimated 700degreesC or 750degreesC, at which time the PDC cutter would spark and catastrophically burn up. A series of tests showed the decreases in cutting forces as the rock was heated up to 500degreesC.