Micro Machining of Nonconductive Al2O3 Ceramic on Developed TW-ECSM Setup

Introduction

Advancement in today’s materials technology need appropriate processes for machining of low machinability materials. Advanced machining processes are being successfully used in industries for production of components made of low machinability but electrically conducting materials. With the rapid technological development of engineering ceramic materials, the machining of the ceramics is an imperative for manufacturing engineers and applied researchers. But it becomes more difficult to machine non conductive ceramic materials once they are highly sintered. Hence, it is essential for developing an efficient and accurate machining method for processing advanced ceramic materials. For effective machining of non conductive ceramic materials e.g. Al₂O₃-ceramic, Traveling Wire Electro-chemical Spark Machining (TW-ECSM) setup has been developed. The developed setup has been utilized to machine Al₂O₃ ceramic materials and subsequently analyze the machining performance characteristics with respect to various parameters of TW-ECSM.

Traveling Wire Electro-chemical Spark Machining (TW-ECSM) is a hybrid non-conventional machining process. The TW-ECSM setup is made based on the combine phenomena of electrochemical machining (ECM) and the wire electro discharge machining (WEDM) processes. TW-ECSM has combined characteristics of ECM and WEDM, can be effectively used for machining of high strength electrically non-conductive materials e.g. Al₂O₃-ceramic. In the TW-ECSM process, the material removal takes place due to the combined effects of electrochemical (EC) reaction and electrical spark discharge (ESD) action. It has two electrodes dipped in an electrolyte which may be acidic or alkaline. The material to be machined is dipped in the electrolyte and placed very near to the cathode (tool). A constant DC voltage is applied between the machining-tool or tool-electrode (cathode) and the counter electrode (anode). The counter electrode is a flat plate with a much larger surface than the tool surface (about a factor 100). When the applied voltage is below a critical voltage of about 25 V, electrolysis occurs. Hydrogen gas bubbles are formed at the tool electrode (cathode) and oxygen bubbles at the counter electrode (anode). It has been observed that if the two electrodes are of different sizes then beyond a certain value of applied voltage, electric sparks appear at the electrode-electrolyte interface on the smaller electrode and the cell current drops. As voltage is increased, current density rapidly increases too. The density and the mean radius of the bubbles increase and bubbles finally coalesce into a gas film around the tool-electrode.