Investigating the influences of coatings on the built-up layer formation during cutting of Ti-6Al-4V

Abstract

Built-up Layer (BUL), produced by accumulating workpiece on the tool rake face, has the tool protective effect and the smaller depth of overcutting during cutting of metal material. The main objective of this paper is to clarify the influences of coating characteristics on the BUL formation process during cutting of titanium alloy. Dry cuttings of Ti-6Al-4V with three different cutting tools (uncoated, PVD coated, and CVD coated carbide tools) were conducted. After the cutting tests, the cutting tools were observed through laser confocal microscopes (LCM) and scanning electron microscopy (SEM). The BUL formation conditions were examined from the viewpoint of the adhesion’s shape, surface roughness, and the amplitude variation of cutting force. From the results, as expected, it was confirmed that BUL can form on the tool rake face for different tools at the cutting speed below 50~70 m/min and it can protect the tool rake face from wear to some extent. It was also determined that the coating characteristic nearly has few effects on the BUL formation mechanism but it can change the size of BUL and affect the stability of BUL. On the other hand, the BUL formation played a great role on the fall-off of coating. Finally, the ability of BUL to decrease the tool wear was also analyzed. The results indicated that BUL can be used to decrease the tool wear formation and to extend the tool life at the cutting speed below 70 m/min during dry cutting of Ti-6Al-4V and the size of BUL plays a decisive role in the protective effect.