Friction characteristics in green drilling titanium alloy Ti6Al4V

Titanium alloy Ti6Al4V, as difficult-to-cut material, has poor machinability. Conventional cutting fluid serves as a coolant and lubricant. In green drilling, water vapor is recognized as an effective coolant; however, its lubrication properties are not well known in drilling. This paper investigates the friction characteristics between chip and tool in green drilling Ti6Al4V, compared with that in sliding and turning process. A friction evaluation model is developed based on the equivalent model of drilling, then is used to calculate the effective friction coefficient. Results indicate that the friction coefficient on the tool-chip interface is considerably reduced in drilling by water vapor, so the drilling forces decrease, too. The friction coefficient decreases as velocity increases in drilling, which is different from the law of sliding tests; the friction coefficient increases when the distance to chisel edge increases.