Experimental investigation on dry EDM using helium gas dielectric

A dry EDM process uses a gaseous dielectric, as a possible substitute for liquid dielectric for precision machining. Due to fluctuations in temperature and oxidation on the dry EDMed surface, critical issues regarding this process are: 1) presence of micro-cracks on dry EDMed surface; 2) surface damage due to arcing; 3) reattachment of work material on the tool; 4) large dimensional oversize in the dry EDMed holes. This work proposes use of helium gas dielectric to effectively cool machined surfaces so as to reduce damage and improve machining accuracy. In this regard, a systematic experimentation using Taguchi L8 orthogonal array has been performed to understand the influence of processing parameters and helium gas dielectric on MRR, TWR, oversize and depth achieved. It is observed that the use of helium gas significantly reduces thermal damage on machined surfaces, and helps lower work material deposition on the tool, and the oversize in dry ED machined holes. The analysis of results show that speed (N) and current (I) are the dominant factors that influence MRR and oversize, whereas dielectric gas pressure (P) is the most significant in influencing TWR.