Evaluation of tribological interactions and machinability of Ti6Al4V alloy during finish turning under different cooling conditions

Abstract

The titanium alloy Ti6Al4V has several applications and is considered a difficult-to-machine material. This study evaluates some tribological interactions in finish turning of Ti6Al4V titanium alloy, including the tool wear, and coefficient of friction in tool-chip interface. Subsequently, the machinability of Ti6Al4V titanium alloy has been investigated, considering the chip geometry, chip thickness ratio, as well as changes in the total cutting force components. The turning process was carried out over a wide range of the feed rate (f) and depths of cut (ap) using hard carbide, GC1115 grade, inserts with double-layer PVD coating. The finish turning tests were conducted under the dry, flood, and MQL (minimum quantity lubrication) cutting conditions. It was found that favorable chip shapes (arc loose) were obtained in the range ap = 0.9–1.2 mm and f = 0.25–0.4 mm/rev. Increasing the f clearly affects the formation of a serrated chip. In addition, the intensity of tool wear, as well as the variations of cutting forces and chip thickness ratios were strongly affected by the applied cooling/lubricating condition. Compared to wet conditions, the Kh values decrease by ~22% with dry machining and by ~12% with MQL. Compared to wet conditions, for dry machining the cutting forces decrease to 70% and with MQL to 8%. The cumulative wear rate under dry machining increases by 18% compared to wet conditions, and with MQL reduces by 19%.