Optimization of Electro-Discharge Coating Process using Harmony Search

Abstract

Electro-discharge machining (EDM) is a non-traditional machining process widely used in the machining of difficult to machine materials. The EDM process is extensively used in aerospace, biomedical, die and mold making industries. In some cases, the corrosion resistance and hardness of the work piece materials are required to be improved for their applications in different environmental conditions. Coating is sometimes used to enhance the resistance property of hard materials. Coating is an extended process in EDM by the utilization of tool electrode prepared by powder metallurgy (PM) route. To meet the required applications, the electro-discharge coating (EDC) specimen must be prepared with high accuracy and excellent surface finish. In this work, the electro-discharge coating (EDC) process is performed taking AISI 1040 stainless steel as work piece and copper-tungsten prepared by powder metallurgy (PM) route as electrode. The copper-tungsten tool electrodes are prepared by varying PM process parameters like compaction pressure and sintering temperature. The EDC is performed varying different PM process parameters like compaction pressure and sintering temperature along with EDC parameters like discharge current (Ip), duty cycle (τ) and pulse-on-time (Ton). The surface roughness parameters like average roughness (Ra), maximum height of the profile (Rt) and average height of the profile (Rz) are measured by the use of surface roughness measurement machine. To reduce the number of experiments, design of experiment (DOE) approach like Taguchi L18 orthogonal array has been used. The surface properties of the EDC specimen are optimized by Taguchi based VIKOR method combined with Harmony search algorithm and the best parametric setting is reported for the EDC process. Interaction of sintering temperature and compaction pressure is found to be the significant term followed by compaction pressure. With the increase in compaction pressure, specimens with superior surface quality are produced in EDC process.