Characterising ionised air metalworking fluid application during titanium alloy shoulder milling

As manufacturers seek to improve cutting process sustainability, alternative metalworking fluid (MWF) strategies are increasingly being explored. For the first time, this study characterises tool wear when shoulder milling both Grade 5 titanium (Ti-6Al-4V) and Grade 2 commercially pure titanium (CP-Ti) with a novel through-spindle Aurion Machining Technologies ionised air (IA) MWF setup. Preliminary results show that during CP-Ti milling trials, the IA strategy led to a tool life of between 85% and 91% of that which was achieved with soluble oil emulsion MWF, whilst during Ti-6Al-4V milling the observed tool life with IA was between 158% and 278% greater than with emulsion coolant at analogous cutting conditions (2.58 and 3.78 times respectively). In addition, IA generated a 26.2% reduction in surface roughness after Ti-6Al-4V milling, potentially indicating a change in tool–surface interaction behaviour. These benefits are compounded as IA returns to its original condition rapidly after utilisation, meaning low environmental and health impact with no waste MWF liquids/gases/mist, clean metal cuttings and low delivery power. Beyond these promising results, cooled and dried but non-ionised air was also shown to perform strongly (regarding tool wear in Ti-6Al-4V milling), relative to emulsion MWF, such that at 190 m/min cutting speed it generated 90% of the tool life which was achieved by the IA strategy. Whilst these preliminary findings require confirmation through repeat testing, IA remains of clear interest for further experimental investigation across a range of subtractive processes. Moreover, this work highlights the potential benefits, niches and configurations for air-based MWFs in general, with further mechanistic and tribological exploration warranted.