Experimental Investigation of Cutting Parameter Effects on Tool Wear in Surface Defect Machining of Hardened AISI 4340 Steel Using CBN Cutting Tools

Surface integrity and tool life are critical concerns when machining hardened steels. Hard turning using Cubic Boron Nitride (CBN) tools has become an effective alternative to conventional grinding due to its improved productivity and operational flexibility. However, excessive tool wear during machining of hardened materials remains a major challenge. In this work, an experimental investigation was carried out to study the influence of cutting parameters on tool wear during Surface Defect Machining (SDM) of hardened AISI 4340 steel. Artificial surface defects were generated on the workpiece using Electrical Discharge Machining (EDM) in order to create controlled intermittent cutting conditions. Turning experiments were performed on a CNC lathe under dry machining conditions while varying cutting speed and feed rate. Flank wear of the cutting tool was evaluated using scanning electron microscopy (SEM), and Response Surface Methodology (RSM) was employed to develop a predictive model. The experimental findings indicate that both cutting speed and feed rate significantly influence tool wear progression. Increased cutting speed and feed rate resulted in higher tool wear due to elevated cutting temperature and mechanical loading at the cutting interface. The developed cubic regression model showed high predictive accuracy with a coefficient of determination of 0.9991. The results demonstrate that the SDM approach can improve machining performance by reducing continuous tool–workpiece interaction and enhancing chip breakability.