Enhancing micro-EDM using ultrasonic vibration and approaches for machining of nonconducting ceramics

Micro EDM (Electro Discharge Machining) is a known nonconventional process for the machining of hard to cut materials. Due to its ablating nature based on melting and evaporation through heat induced by electrical discharges, it can function independently of the hardness, toughness or brittleness of the workpiece. Because of these benefits, EDM is widely used in tool- and mould making; micro-EDM, with its much lower discharge energies, has been successfully applied to micromachining of high-accuracy parts. The precision manufacturing of high aspect ratio micro geometries such as deep micro bores relies on stable process conditions in the discharge gap. Its minimization - a precondition for minimal feature size and higher accuracy – limits the effectiveness of conventional flushing techniques, leading to a higher fraction of unwanted discharge states (open and short circuit), lower process speed, and geometrical errors. New hybrid technology approaches, such as ultrasonic or low frequency superposition, significantly raise the process stability and speed. Another restriction on the use of EDM, the exclusive machinability of electrically conductive materials, is overcome by the application of the assisting electrode method that enables a micro-ED-machining of nonconductive zirconium oxide ceramics. This paper presents the current status of investigation into the micro-EDM process with ultrasonic vibration assistance - directly applied to the workpiece and indirectly applied high-intensity ultrasonic to the dielectric - in metallic materials as well as in the machining of electrically nonconductive ceramic materials. Using ultrasonically aided micro-EDM, the process speed can be raised by up to 40%, enabling bores of less than 90 µm in diameter with aspect ratios >40 for metallic materials. The modified setup using the assisting electrode principle allows for machining of an aspect ratio >5 for nonconductive ceramic materials, leading to new possibilities for the design and manufacture of complex, high-accuracy micro parts in high-performance engineering materials