Optimization of Electro-Discharge Machining Responses of Super Alloy Inconel 718: Use of Satisfaction Function Approach Combined with Taguchi Philosophy

Abstract

Inconel 718 is a Nickel-based super alloy which possesses high strength, high temperature resistance. This super alloy is mainly used in the applications of automobile, aerospace and defence industries. Due to the extreme toughness and work hardening characteristic of the alloy, the problem of machining Incone1 718 has become a great challenge. In this work, machinability aspects of Inconel 718 have been experimentally investigated during Electro-Discharge Machining (EDM) using Copper tool electrode. Based on five-factor-five-level L25 Orthogonal Array (OA), experiments have been conducted by varying the following controllable process parameters viz. OCV (gap voltage), peak current (IP), Pulse-on Time (Ton), Duty Factor (τ) and Flushing Pressure (Fp). Machining performance has been evaluated in terms of multiple responses such as Electrode Wear Ratio (EWR), Roughness average Ra (of the EDMed surface), Surface Crack Density (SCD) and White Layer Thickness (WLT). Aforesaid performance features have been treated as objective functions towards optimization assuming that these correspond to Lower-is-Better (LB) requirement. The goal has been to determine the best setting of controllable process parameters within selected experimental domain to achieve satisfactory machining performance. Owing to the limitation of Taguchi’s optimization philosophy i.e. it cannot solve multi-response optimization problem; the concept of satisfaction function has been attempted in this research to obtain satisfaction values of individual responses, thus, facilitating aggregation of multi-response features into an equivalent single index. A distance measure has been computed next which basically determines the separation of each experimental setting (alternative) with respect to the ideal expectation (satisfaction). Finally, this distance function has been optimized (minimized) by Taguchi method.