Assessment of jojoba as a pure and nano-fluid base oil in minimum quantity lubrication (MQL) hard-turning of Ti-6Al-4V: A step towards sustainable machining

The article presents a feasibility study on jojoba - a vegetable oil - as a candidate base oil mixed with and without molybdenum disulfide nano-particles (nMoS2) in hard-machining with minimum quantity lubrication (MQL). The jojoba oil is benchmarked against commercially available mineral oil (LRT 30) for machining of Ti–6Al–4V alloy. The machining performance in terms of cutting force, tool wear, and surface roughness is assessed under five cutting environments, namely, dry turning, MQL (jojoba oil and LRT 30), nanofluid MQL (jojoba oil + nMoS2 and LRT 30 + nMoS2) is evaluated applied with different concentrations of nanoparticles (0.1, 0.5, and 0.9% by weight). The results show that jojoba oil, in pure and nano-fluidic condition as well, presents itself as a strong and sustainable replacement for commercially available mineral oil for MQL turning. The improvement in performance with jojoba oil is attributed to long chain fatty acidic structure (monoesters), excellent thermal oxidative stability, high viscosity index, and lamellar structure of nMoS2. The MQL turning with jojoba oil + nMoS2(0.1%) is found to have a reduction in cutting force, surface roughness, and tool wear in the range 35–47%. The overall results show that jojoba oil, as well as jojoba oil with an optimum concentration of MoS2 nanoparticles, emerged as a sustainable machining alternative.