Tribological characteristics and drilling performance of nano-MoS2-enhanced vegetable oil-based cutting fluid using eco-friendly MQL technique in drilling of AISI 321 stainless steel

The implementation of sustainable manufacturing techniques to make machining operations more eco-friendly is a demanding issue that has gained attention from academic and industrial sectors. In some machining operations, a large quantity of machining fluids is wasted to make machining easier, especially during the machining of difficult-to-machine materials such as stainless steel. In such circumstances, many researchers are investigating eco-friendly techniques. Therefore, in this study, effects of minimum quantity lubrication (MQL) with MoS2-enhanced vegetable-oil-based cutting fluid on the drilling characteristics of AISI 321 stainless steel are investigated. The main aim of this study is to analyse the machining performance of various coolant-lubricant strategies, namely dry, flood, pure MQL, and three nanofluid MQL (NFMQL) with regard to thrust force and torque, surface roughness, friction coefficient, chip morphology and tool wear mechanism in drilling of stainless steel (AISI 321). Research findings indicated that NFMQL drilling conditions have given excellent drilling performance by improving drilling characteristics than pure MQL, dry and flood drilling. Among the NFMQL drilling conditions, 1.5 wt.% nano-MoS2 in sunflower oil-based MQL condition provided better cooling-lubrication effect and improved the drilling characteristics followed by 1.0 wt.% and 0.5 wt.% nano-MoS2 in sunflower oil-based MQL conditions. The 1.5 wt.% nano-MoS2 in sunflower oil-based MQL drilling had resulted in 43.2%, 68.9%, 56.8% and 41.6% reduced values of thrust force, torque, surface roughness and COF, respectively, at the 30th hole in comparison with flood drilling. Moreover, noticeable improvement in the chip morphology and tool wear rate has been achieved while drilling under NFMQL environments. The better drilling performance of nanofluid MQL may be attributed to the fact that nanoparticles (MoS2) in sunflower oil offer excellent cooling-lubrication features and provide strength to the oil film at the tool-workpiece interface. In addition, nano-MoS2 particles have high surface activity and are easily adsorbed onto the contacting surfaces, thereby maintaining the lubrication effect.