THE DEPOSITION OF ELECTRICALLY CONDUCTIVE FILMS AS A MEASURE TO IMPROVE THE ELECTRICAL-DISCHARGE MACHINING TRUING BEHAVIOR OF METAL-BONDED C-BN GRINDING WHEELS

The deposition of electrically conductive coatings has been investigat ed as a means to improve the quality and efficacy of electrical discha rge machining (EDM) as a means to true and dress composite superabrasi ve grinding cylinders composed of a Cu Co Sn alloy in the atomic ratio of 60-30-10. The grinding cylinders contained between 6.25 and 25 vol .% monocrystalline cubic boron nitride (c-BN) particles. Using direct ion beam deposition at a beam current of 227 mA and an accelerating po tential of 1 keV, ionized Ar was used to sputter elemental Cu and Ag t argets for the synthesis of conducting films to a thickness of approxi mately 5 mum. Compared with the surfaces of grinding wheels which were EDM processed in the absence of a conductive coating, the electricall y conductive coatings were found to provide greater dimensional and mi crostructural control of the truing process and resulted in a greater degree of c-BN particle retention. Slight modification to the structur e of the c-BN particles and to the wheel was observed following EDM pr ocessing. Irregular grinding wheel surfaces, characterized by craters which are believed to have been caused by the high frequency discharge of electrical impulses, were generated through EDM truing, whether tr ued in the presence or absence of such a conductive coating.