Optimization of Minimum Quantity Lubricant Conditions in Hard Turning of 9CrSi Steel - An Application of Taguchi Method

Minimum Quantity Lubrication (MQL) is an advanced cooling and lubrication method that replaces traditional cooling and lubrication methods in metal cutting processes, offering several advantages. In this study, the parameters of MQL conditions were optimized during hard turning of the 9CrSi steel to achieve the minimum surface roughness. The Taguchi method was applied due to its numerous benefits, especially its high efficiency and low implementation cost. The three parameters of MQL conditions are nozzle-to-workpiece distance, fluid flow, and compressed air pressure. Each factor was investigated at three levels. Thus, the L9 array was employed for experimental design. Using Analysis of Variance (ANOVA), the research findings revealed that the compressed air pressure has the most significant impact on surface roughness compared to the other two factors, which are fluid flow and nozzle-to-workpiece distance. The compressed air pressure factor contributed over 47% of the total influence. The remaining factors, including fluid flow and nozzle-to-workpiece distance, contributed 31.07% and 9.24% respectively to the total influence on surface roughness. Furthermore, the optimal MQL conditions for achieving the best surface roughness were determined to be a nozzle-to-workpiece distance of 10 mm, a fluid flow of 50 ml/h, and a compressed air pressure supplied to the nozzle of 5 kg/cm2. A first-order regression equation was developed to predict surface roughness based on the three input parameters, yielding a determination coefficient (R-squared) of 88.08%. The research outcomes serve as a valuable reference for further studies in metal cutting processes with MQL applications.