Use of Electric Discharge Sintering for Elaboration of Diamond Tools

A number of installations for electric discharge sintering of powder materials is developed. There are installations in which energy is delivered by following currents: 1) superposition of the direct and alternating (with frequency up 7900 Hz) currents, 2) alternating current (50 Hz). The sintering is carried out in conductive (graphite) moulds. The sintering is often done in thermal and electric insulator moulds (for example, ceramic on Si3N4 base, asbestos cement). At sintering of metal-diamond composition in insulator moulds metallic electrodespunches (steel) are used. Such a variant of sintering allows one its duration to short from ~900 s down to ~60–150 s. This ensures complete safety of dimensions and operating characteristics of diamond grains. The technologies of various diamond elements for tools for treatment of glasses and soft stones (stone saws, tools in forms of tablets, rings). The preliminary pressure which is applied to powder sample simultaneously with current was equal to ~10 MPa (~100 kg/cm2). The end pressure was equal to ~100 MPa (~1000 kg/cm2). The current density was equal to ~700– 1200 A/cm2. Tests of diamond tablets (diamond 20/14 mkm, binder 80 % Cu+20 % Sn) at grinding of glass had shown: the abrasivity of tablets with common diamonds is equal to ~50 g/(cm2 min), and abrasivity in case with diamonds annealed in hydrogen is equal to ~70 g/(cm2 min).