INVESTIGATING THE MICRO-EDM MACHINABILITY OF BULK METALLIC GLASS IN MICRO-EDM DRILLING

Bulk Metallic Glass (BMG) is a solid metallic material with disordered atomic structure, that has the characteristics of high elasticity, hardness, fracture toughness, and superior corrosion resistance. High aspect ratio micro-through holes on BMG has prospective applications in space, nuclear reactor, thermodynamics engineering, biomedical, and electronics industries. In this study, the micro-EDM machinability of BMG (Vit 1b: Zr67Cu10.6Ni9.8Ti8.8Be3.8 (wt%)) is evaluated. The micro-EDM machinability of BMG has been assessed based on the volume of material removal rate (MRR), tool wear rate (TWR), micro-hole surface quality, and dimensional accuracy. The effect of various electrical and non-electrical parameters is studied. It is found that micro-EDM is capable producing high aspect ratio micro-holes on difficult-to-machine BMG. The deposition of resolidified debris around the edge of the micro-holes, both at the entrance and exit side, are found to be a common phenomenon in micro-EDM of BMG. The reduction of capacitance was found to be the effective way for reducing the resolidified debris around the edges. Capacitance was found to be have more pronounced effect, with gap voltage having little effect on the quality of micro-holes. The electrode rotational speed had insignificant effect on the quality of micro-holes. In terms of dimensional accuracy, which was measured by overcut and taper angle, both the gap voltage and electrode rotational speed had little effect. The lower electrode rpm was found to reduce the taperness of the micro-holes, although the material removal rate decreases and tool wear rate increases. Finally, analysis of the composition of tool electrode before and after machining indicates the migration of materials from the dielectric and workpiece to the tool electrode and vice versa.