Performance evaluation of high-pressure cooling by using external rotary liquid applicator in milling Ti-6Al-4V alloy

An effective cooling mode with appropriate process parameters can enhance the machinability as well as productivity. In this regard, this study focuses on evaluating the machinability of widely used Ti-6Al-4V alloy with the use of high-pressure coolant jets compared to dry milling. A novel rotary applicator was designed and developed to feed high-pressure coolant jets without any drastic change of solid end mill cutter. Four flutes solid HSS end mill cutter was selected for machining because of its some intensive properties. Biodegradable VG-68 cutting oil was chosen as cutting fluid due to its better thermo-physical properties with higher flash points. Machinability was assessed at 16-32 m/min cutting speeds and feed rates of 0.08-0.16 mm/tooth with a constant depth of cut of 1.0 mm, taking into account the average cutting temperature, resultant cutting force, mean surface roughness, and tool wear. Dry milling produced the worst results for all of the investigated responses, with excessive tool wear due to the lack of cooling and lubrication. Compared to dry milling, high-pressure cooling (HPC) lowered average cutting temperature, resultant cutting force, and mean surface roughness by 11.21-21.57%, 8.63-13.12%, and 6.09-29.6%, respectively, whereas rotary high-pressure cooling (RHPC) reduced these parameters by 15.39-27.27%, 14.05-21.18%, 16.48-41.04%. RHPC's efficient cooling and lubrication increased the machinability of the Ti-6Al-4V alloy. Dry milling showed severe flank wear with increased built-up edge (BUE) development, abrasion, and adhesion, whereas HPC and RHPC dramatically reduced the severity of tool wear. In HPC and RHPC, the tool life was consequently increased by 6.8 and 9 min, respectively.