Effects of cutting parameters on dry machining Ti-6Al-4V alloy with ultra-hard tools

Polycrystalline cubic boron nitride (PCBN) and polycrystalline diamond (PCD) cutting tools were used in dry machining Ti-6Al-4V titanium alloy. Their main failure mechanisms were analyzed with a scanning electron microscope (SEM) and an energy-dispersive spectrometer (EDS). Effects of cutting parameters (cutting speed and feed rate) on tool life, cutting temperature, workpiece surface roughness, and surface microhardness were characterized with a 3-D super-depth-of-field instrument, a handheld infrared thermal imager, a surface profile measuring instrument, and a microhardness tester, respectively. The results showed that the main failure mechanisms of the PCBN tool were chipping, notch, adhesion, and crater. And, the main failure mechanisms of the PCD tool were adhesion, crater, and dissolution-diffusion. The strong diffusivity of PCD material made the performance of the PCD tool better than that of the PCBN tool. When cutting speed increased in machining with the PCD tool, decreasing cutting temperature caused by the reduction of adhered workpiece material on the tool surface resulted in a lower tool wear rate at the cutting speed of 80 m/min, and workpiece surface roughness initially increased and then decreased. The surface roughness initially increased, and after the feed rate of 0.10 mm/r, the surface roughness basically kept a constant value with feed rate increasing. High cutting speed and high feed rate increased and decreased the hardening rate of machined workpiece surface layer in machining with PCD tool, respectively.