Assessing the Effect of Nonelectrical Process Parameters During the Sted of Holes on Inconel 718 Alloy

Abstract

Drilling of high aspect ratio holes on Inconel 718 is difficult owing to its high hot hardness and corrosion resistance, and low thermal conductivity. Shaped tube electrolytic drilling (STED) is a variant of the electrochemical machining process, wherein a tubular tool is used as the cathode supplying electrolyte through it to the machining zone. Given the nature of underlying material removal phenomenon, the performance of the STED process is influenced by a wide range of process parameters. These parameters can broadly be categorized into two categories: the electrical and nonelectrical parameters. This research work aims to assess the effect of nonelectrical process parameters like electrolyte type, tool insulation conditions, and tool feed rate on the performance characteristics such as average diametral overcut and material removal rate. The experimental results revealed that the material removal rate (MRR) was maximum in the case of aqueous NaCl solution, while the average diametral overcut (ADOC) was minimum in the case of aqueous NaNO3 solution. The STED in the mixed NaCl + NaNO3 406solution resulted higher MRR and lower ADOC compared to the constituents aqueous NaNO3 and aqueous NaCl solutions, respectively. A tool electrode, fully insulated around side face, rendered lower and uniform ADOC than that with the tool electrode having an exposed length of 1 mm, for all types of electrolyte solutions. Moreover, MRR increased with an increase in the tool feed rate, irrespective of the type of electrolyte solutions and tool insulation conditions. The FESEM micrographs of the hole surfaces used to study the surface morphology also highlighted the benefits of using fully insulated tool.