A study of the effect of palm oil as MQL lubricant on high speed drilling of titanium alloys

The main objective was to study the potency of MQL palm oil (MQLPO) as a lubricant in the high speed drilling of Ti–6Al–4V. For the comparison, MQL synthetic ester (MQLSE), air blow and flood conditions were selected. Uniform flank wear, micro-chipping, thermal cracking and flaking were the dominant tool failure modes. It was found that MQLSE and MQLPO gave comparable performance with the flood conditions. In addition, MQLPO outperformed MQLSE on the cutting forces, temperature, power and specific cutting energy. This shows that palm oil can be used as a viable alternative to synthetic ester for MQL lubricant.

Research Highlights
► The dry condition produced a poor result in terms of tool life, high cutting forces and machining temperature. However, the MQLSE (synthetic ester), MQLPO (palm oil) and flood conditions exhibited comparable performance in tool life.
► Uniform flank wear, micro-chipping, thermal cracking and flaking were the dominant tool failure modes under high speed drilling of Ti–6Al–4V at all coolant–lubricant conditions.
► Adhesion, attrition and abrasion were the distinct tool wear mechanisms responsible for the formation of failure modes in all coolant–lubricant conditions. In addition, both MQLSE and MQLPO improved the intensity of the workpiece adherence on the cutting tool compared to the dry condition.
► This research shows that the flood condition can be replaced by the MQL condition, thus alleviating pollution and improving health and safety. At the same time, the introduction of MQLPO is not only beneficial to its biodegradability but also could enhance the cooling and lubricating ability compared to MQLSE.