Parametric optimization of powder mixed electrical discharge machining for nickel-based superalloy inconel-800 using response surface methodology

Abstract

Background: Electrical Discharge Machining (EDM) is a well-established non-conventional machining process for the machining of electrically conductive and difficult-to-machine materials. But its applications are limited because of the slow machining rate and poor surface finish. Powder mixed EDM (PMEDM) is unitary of the recent progresses in the EDM process in which powder particles mixed in the dielectric fluid results in higher machining rate and better surface quality. In the past, limited work has been found on PMEDM of Inconel-800 material. Researchers have reported about machining with different powder particles like aluminum powder, silicon carbide, graphite etc. in the dielectric fluid of EDM, but the effect of powder particles, i.e. Tungsten carbide, cobalt and boron carbide along with tool material i.e. copper, copper-chromium and graphite on Inconel-800 material has not been explored. The purpose of the present work is to look into the issue of tool material (Cu, copper-chromium, and graphite) along with powder particles (tungsten carbide, cobalt and boron carbide) suspended in EDM oil on Inconel-800 material. Methods: The present work includes optimization of Material Removal Rate (MRR) and Tool Wear Rate (TWR) for the machining of Inconel-800 material using Powder Mixed Elctric Discharge Machining (PMEDM). Different input parameters such as peak current, pulse on-time, pulse off-time, tool and powder materials along with effect of three micro powder particles, i.e. tungsten carbide, cobalt and boron carbide and three electrodes i.e. copper, copper-chromium, and graphite have been considered for the experimentation. The box-Behnken method of Response Surface Methodology (RSM) has been used for designing the experiments along with the Desirability Approach for multiple response parameters optimization. The adequacy of the proposed mathematical models have also been tested using analysis of variance (ANOVA). Microstructure analysis and transfer of different factors on the machined surface has also been investigated using Scanning Electron Microscope (SEM), Energy Dispersive Spectrometer (EDS) and X -Ray Diffraction (XRD). Results: The results showed that peak current, pulse on-time, and tool material significantly affects the Material Removal Rate (MRR) while peak current, pulse on-time, tool material and powder materials affected the Tool Wear Rate (TWR). Pulse off-time has a trifling effect on both MRR and TWR, while powder particles on MRR. From desirability approach, the optimal combination of parameters found to be current 1 amp, pulse on-time 0.98 μs, pulse off-time 0.03 μs, tool material 0.31 and the powder (suspended particles) 0.64. Conclusion: The analysis of the experimental observations highlights that the current, pulse on-time and tool material have found to be the most decisive factors for MRR, while current, pulse on-time, tool material and powder particles for TWR.