MACHINING OF THROUGH HOLES IN NON-CONDUCTIVE ALUMINUM NITRIDE CERAMIC USING ELECTRICAL DISCHARGE MACHINING PROCESS

摘要

Ceramic materials are known for their high hardness and strength-to-weight ratio, resistance to wear, and chemical inertness. These materials can be deployed at elevated temperature even to the limit where super alloys cannot be used. The distinctive properties of ceramics make them difficult to machine by conventional processes because of their brittle ness. Electrical discharge machining (EDM) is a non-contact machining process that can machine any workpiece irrespective of its hardness, as long as the material is electrically conductive. Therefore, the challenge that comes with the EDM of ceramics is the electrical non-conductivity. In this study, an innovative method (modified assisted-electrode method) has been proposed, which can be used to successfully machine through holes in pure and non-conductive ceramic materials using the EDM process. The effect of machining parameters and conductive coating has been studied. In addition, the possible material removal method has been investigated using the scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) analysis. It is found that multi-layer coating with conductive copper tape sandwiched with graphene and carbon nanotubes in between the tape worked as a successful assistive electrode method. The SEM and EDS analysis indicates melting and thermal spoiling as possible material removal mechanisms during EDM of electrically non-conductive Aluminum nitride (AlN) ceramics. The deposition of carbon at the edge of the holes indicate generation of conductive carbon layer favoring continuous sparking during the machining process, and this makes the EDMof non-conductive AlN possible. The walls of the drilled holes become conductive and allow the machining to go through even beyond the conductive layer range. The performance characteristics depends on both the electrical parameters and assistive electrode method.