Analysis of high aspect ratio small holes in rapid electrical discharge machining of superalloys using Taguchi and TOPSIS

The main aim of this paper is to perform high aspect ratio small holes using rapid electrical discharge machining (rapid-EDM) of superalloys, namely Ti–6Al–4V and Inconel 718 with the tool materials like brass tubes and copper tubes. For employing the above-said materials, the performance characteristics such as material removal rate (MRR), tool wear rate (TWR) and overcut (OC) have been studied. In these investigations, DOE-Taguchi’s L9 orthogonal array has been utilized to build an experimental layout with the machining parameters such as current, on-time, off-time and capacitance. From the analysis, it is confirmed that there was a 40% increase in MRR, 282% decrease in TWR and 56% decrease in OC for rapid-EDM of Ti–6Al–4V material using the brass tubes than the copper tubes. Further, it is also validated that there is a 61% increase in MRR, 6% drop of TWR and 33% increase in OC for rapid-EDM of Inconel 718 material using brass tubes than the copper tubes. So, this comparative study has concluded that the machining of Ti–6Al–4V using brass tube has produced a maximum of MRR and minimum of TWR and OC. In Taguchi analysis, the individual effect of machining parameters on MRR, TWR and OC was studied. In addition, optimum combinations of machining parameters for MRR, TWR and OC were also discussed. Furthermore, multi-objective optimization was executed using TOPSIS to find good combination of machining parameters.