Micro-Drilling of Sapphire Using Electro Chemical Discharge Machining

Abstract

Electrochemical discharge machining (ECDM) refers to a non-traditional machining method for performing effective material removal on non-conductive hard and brittle materials. To increase the ECDM machining efficiency, traditionally, the method of increasing the machining voltage or increasing the electrolyte concentration is used. These methods can also cause overcut reaming of the drilled holes and a rough surface on the heat affected area. In this study, an innovative combinational machining assisted method was proposed and a self-developed coaxial-jet nozzle was used in order to combine two assisted machining methods, tool electrode rotation and coaxial-jet, simultaneously. Accordingly, the electrolyte of the machining area was maintained at the low liquid level and the electrolyte was renewed at the same time, thereby allowing the spark discharge to be concentrated at the contact surface between the front end of the tool electrode and the machined material. In addition, prior to the machining and micro-drilling, the output of the machining energy assisted mechanism was further controlled and reduced. For the study disclosed in this paper, experiments were conducted to use different voltage parameters to machine sapphire specimens of a 640 μm thickness in KOH electrolyte at a concentration of 5 M.

Effect of Machining Limiting Factors on Drilling Progress during Spark Assisted Chemical Engraving (SACE): General Trends

“…These include modifying the tool shape, including using flat sidewall-flat front tool [7], side-insulated tool [8], drill bit [9], helical tool with high-speed rotation [10], internally structured tube electrode [11] and spherical tip tool [12]. Other attempts include using pulsed voltage [13,14], modifying the electrolyte constituents [15,16], adding tool motion such as rotation [17] and orbital motion [18], adding tool vibration [19], vibrating electrolyte [20] and doing magnetic assisted field machining [21,22]. It was also shown that deeper holes could be established through adding pressurized electrolyte flow [23] and by applying counter-resistant feeding through reducing the magnitude of contact force between the tool and substrate as drilling progresses [24].…”