Tool wear and hole quality investigation in dry helical milling of Ti-6Al-4V alloy

This paper focused on combined study on the evolution of tool wear and its influence on borehole quality in dry helical milling of Ti-6Al-4V. The carbide tools with TiAlN coating were used in this experimental investigation. The tool wear characteristics both at front and periphery cutting edges were investigated using an optical microscope and SEM-EDS techniques. The experimental results demonstrate that the combined effects of chipping/fracture, diffusion, and oxidation have significant bearings on front cutting edge failure, while the flank wear was predominant at the periphery cutting edges. The cutting speed was correlated with tool failure mechanizes, and the different wear rates at front and periphery cutting edge caused different variation trends of cutting force in thrust and horizontal direction during hole-making process. The quality of machined holes was evaluated in terms of geometry accuracy, burr formation, and surface roughness. The exit-burrs of machined hole were closely correlated with front cutting edge wear. However, high hole quality was observed even the near end of tool life from the point of view of diameters, roundness error, and surface finish due to the smooth wear pattern at periphery cutting edges. Severe tool wear at front cutting edges will cause excessive exit-burrs, but it has no obvious effect on geometry and surface roughness in helical milling of Ti-6Al-4V.