Comparative Study of Surface Roughness in Turning of C45 Steel under Dry, Flood, and Coconut Oil-Based MQL Conditions

This study investigates the influence of cooling–lubrication conditions on surface roughness in turning of C45 steel. Experiments were conducted on an EMCO Maxxturn 45 CNC lathe using carbide cutting tools. The cutting parameters were fixed at a cutting speed of 160 m/min, a feed rate of 0.15 mm/rev, and a depth of cut of 1.0 mm. Three machining conditions, namely dry cutting, flood cooling, and coconut oil-based minimum quantity lubrication (MQL), were compared. The results showed that dry cutting produced the highest surface roughness (2.25 µm), while flood cooling and MQL reduced the roughness to 1.26 µm and 1.31 µm, respectively. Compared with dry cutting, flood cooling and MQL decreased surface roughness by 44.0% and 41.8%, respectively. The findings indicate that coconut oil-based MQL can provide surface quality comparable to conventional flood cooling while offering a more sustainable machining approach.