Analysis of MQL Effect on Forces, Friction, and Surface Roughness in Turning of AISI 4140 Steel

Minimum Quantity Lubrication or MQL is an increasingly used technique for metal cutting operations and it has become an attractive alternative for machining parts at big scale production. However, fully lubricated conditions are still in use for machining special materials so that surface finish, tool wear, and temperature distribution levels remain at optimum levels. On the other hand, dry condition machining is in use as well although with some restraint due to issues with material burr, surface roughness, and tool wear. The main purpose of this work is to analyze the effects of cutting fluid flow rate, its application mechanisms, and cutting speed on surface roughness and establish the lowest possible cutting fluid flow rate that yields to minimum surface roughness (Ra). To achieve the objective, a set of experiments was performed using a Computer Numerical Control (CNC) lathe instrumented with a Kistler 9121 dynamometer and a customized cutting fluid application system to obtain coefficients of friction and cutting forces. Finally, a previously 2D finite element analysis (FEA) simulation from Akbar et al. [1] is applied and compared to experimental results to find out if the cutting force can be predicted. A first regression model that correlates cutting force and surface roughness is posed, so that FEA simulation can be implemented to predict the final surface roughness. AISI 4140 machinery steel in annealed condition is used to carry out the simulated and experimental work.