Experimental Investigation and Parametric Optimization during Magnetic Field-Assisted Electric Discharge Machining of Nimonic 90

The inherent challenges encountered in the conventional machining of Nimonic-90, such as the formation of built-up edges and the localization of shear stress, arise because of its low thermal conductivity and high melting point. In the current study, a novel approach combining electric discharge machining (EDM) with a magnetic field environment, known as magnetic field-assisted EDM (MFEDM), is introduced to address the challenges encountered during conventional machining. The experiments were performed by varying the input parameters, such as the peak current (Ip), pulse-on time (TON), and pulse-off time (TOFF). A comparative analysis of EDM and MFEDM processes was conducted by measuring the material removal rate (MRR), radial overcut (ROC), and surface roughness (SR). The experimental results revealed that the magnetic field exerted a beneficial effect, leading to a higher MRR, lower ROC, and improved surface roughness. Furthermore, topographical analyses were conducted to examine the surface defects, recast layer, and crater formation, whereas scanning electron microscopy (SEM) analysis confirmed the superior surface quality achieved with MFEDM. The SEM micrographs demonstrated a reduction in the recast layer, micropores, crack formation, and globule formation on the machined surface when MFEDM was employed. The XRD analysis indicated the presence of various phases, including a small number of impurities. Additionally, the non-dominated sorting genetic algorithm II (NSGA-II) coupled with TOPSIS was employed for multi-objective optimization of the input parameters.