ORIGINAL ARTICLE The drilling of Al 2 O 3 using a pulsed DC supply with a rotary abrasive electrode by the electrochemical discharge process Sanjay K. Chak & P. Venkateswara Rao Received: 20 July 2006 / Accepted: 1 October 2007 / Published online: 16 November 2007 # Springer-Verlag London Limited 2007 Abstract The electrochemical discharge machining (ECDM) process has the potential to machine electrically non-conductive high-strength, high-temperature-resistant (HSHTR) ceramics, such as aluminum oxide (Al 2 O 3 ). However, the conventional tool configurations and machin- ing parameters show that the volume of material removed decreases with increasing machining depth and, finally, restricts the machining after a certain depth. To overcome this problem and to increase the volume of material removed during drilling operations on Al 2 O 3 , two different types of tool configurations, i.e., a spring-fed cylindrical hollow brass tool as a stationary electrode and a spring-fed cylin- drical abrasive tool as a rotary electrode, were considered. The volume of material removed by each electrode was assessed under the influence of three parameters, namely, pulsed DC supply voltage, duty factor, and electrolyte conductivity, each at five different levels. The results revealed that the machining ability of the abrasive rotary electrode was better than the hollow stationary electrode, as it would enhance the cutting ability due to the presence of abrasive grains during machining. Keywords Electrochemical discharge machining (ECDM) . High-strength, high-temperature-resistant (HSHTR) materials . Central composite rotatable design (CCRD) . Abrasive rotary electrode 1 Introduction Aluminum oxide (Al 2 O 3 ) is an important ceramic materials that has wide applications in machine tools, aerospace, and electrical and electronic fields in view of its typical properties, such as high strength and hardness at high temperature, low thermal conductivity, density, and chem- ical inertness. The production of small through and blind holes, grooves, etc. by any conventional machining is very difficult and uneconomical. To overcome these problems, researchers have found a novel method of machining called electrochemical discharge machining (ECDM) [1, 2]. This is a hybrid process which has combined characteristics of electrochemical machining (ECM) and electrical discharge machining (EDM). This process has been successfully applied to machine electrically conductive materials with improved productivity [3, 4], and has also been proven as the most suitable process to machine electrically non- conductive materials, such as quartz, glass, composites, granite stone, etc. Unlike ECM and EDM, the electrical discharge in ECDM occurs between comparatively smaller sized tool electrode and electrolyte interface. The heat generated due to this discharge is used for machining electrically non- conductive materials, therefore, the machining efficiency of this process greatly depends on the properties of the material to be machined and on the type of parameters selected. The ECDM process shows low penetration depth on Al 2 O 3 due to its low fracture toughness, while the machining of deep holes is still difficult, as it shows susceptibility for cracking due to thermal shocks at high voltage, which is caused by the abrupt nature of discharge at greater tool depth inside the electrolyte. As a result, the radial overcut and the heat-affected zone widen and, finally, leads to microcracks on the machined surface. At low Int J Adv Manuf Technol (2008) 39:633–641 DOI 10.1007/s00170-007-1263-x S. K. Chak : P. Venkateswara Rao (*) Mechanical Engineering Department, Indian Institute of Technology (IIT), Delhi, New Delhi 110016, India e-mail: pvrao@mech.iitd.ernet.in