Performance of Carbide Tools in Green Machining of Ti-6242S

Abstract

The performance of the off-center ball end mill carbide tools: alloyed uncoated (W-Ti/ Ta/ b)C-Co (tool A) and multiplayer, PVD-<oated (WC-Co) (TiCN/TiAlN/TiN) (tool B) with nominal diameter of 16 mm when end milling titanium alloy Ti-6%Al-2%Sn-4%Zr2% Mo-O.08%Si (Ti-6242S) under green machining condition is reported in this paper. Results from the machining trials show that localised flank wear (VB») is the dominant failure mode for both tools due to the concentration of coupled thermo-mechanical load at the tool leading edge. After machining for approximately 20 minutes, tools A and B start to reach VB) ~ 0.3 mm when used at a cutting speed of 100 m/min and a feed of 0.15 mm/tooth. Further examination using SEM/EDAX shows that flank wear, rake wear, plastic deformation and brittle fracture are other failure modes suffered by the tools because of adhesion (attrition) and dissolution diffusion wear mechanisms. In conclusion, tools A and B can be recommended for green milling of Ti-6242S with the best compromise between cutting speed and tool life being given by end milling at cutting speeds of 100-125 m/min. At cutting speeds and feeds of 0.15-0.2 mm/tooth, axial depth-of-cut 2-2.5 mm and radial depth-of-cut of 8.8 mm, tool life of tools A and B can be represented by mathematical models T V°.30 /,0.89 a 0.84 = 74.851 and T V020 /,0.22 a.o.Jo ~ 137.710, respectively.