Machining characteristics and optimization of process parameters in die-sinking EDM of Inconel 625

Inconel 625 superalloy is a versatile austenitic nickel-based superalloy with excellent strength and good ductility. It possesses excellent mechanical properties at both extremely low and extremely high temperatures with excellent resistance to pitting, crevice corrosion, cracking and crystalline corrosion. Inconel 625 superalloy is an important and frequently used material for an automobile, aerospace industries and marine application due to its excellent mechanical, chemical and physical properties. In the present research, empirical mathematical model for surface roughness and material removal rate (MRR) has been developed to study the influence ofdie-sinking electrical discharge machining (EDM) parameters, viz. peak current, pulse on time and pulse off time on Inconel 625. Central composite design is employed to plan experimental layout, and a quadratic model is adopted for empirical mathematical modeling. ANOVA is performed to test the adequacy of the model using F-test and p-test. Optimal setting of EDM parameters is obtained using composite desirability. ANOVA analysis reveals that peak current is the most dominating factor for MRR followed by pulse on time, while surface roughness is mostly influential by pulse on time followed by pulse off time. Surface roughness increases with the increase in pulse on time. MRR firstly increases with an increase in pulse on time and start decreasing after mid value (0), i.e., 15 mu s whereas surface roughness continuously increases with an increase in pulse on time. Optimal setting of EDM parameters is obtained by composite desirability function. The goal is to minimize surface roughness and maximize MRR simultaneously. Results are validated by the confirmation experiment using the optimal set of EDM parameters. The confirmation experiments reveal that the experimental and predicted results are very close with error amounting of 2.19% and 2.58% for MRR and surface roughness respectively.