Effect Of Cryogenic Cooling Media On Machinability Of Beta Solution Treated Titanium Alloy Ti6al4v
Titanium and its alloys are considered difficult-to-machine materials due to several factors such as very high cutting temperature induced at the cutting edge during machining, its high strength at elevated temperature and strong chemical reactivity with many cutting tools. The machinability of titanium alloys was considerably influenced by the heat treatment conditions and its subsequent microstructure produced. A beta solution treatment process (BSTA) produces lamellar microstructure and mainly carried out to improve the fatigue properties of Ti6Al4V. This lamellar microstructure which is coarse produces high shear stress and in consequence produces high cutting forces and cutting temperature which leads to poor machinability. Cryogenic Machining using LN2 was carried out on beta solution treated Ti6Al4V using Taguchi design of experiment approach with L8 orthogonal array, where 3 factors viz. cutting speed, feed rate and depth of cut were varied on 2 levels. During cryogenic machining, LN2 was supplied with high pressure to the cutting zone which receives an effective cooling as well as the chip breaking takes place. The machinability was measured in terms of cutting forces and surface finish of the machined work piece. The chip mechanism study was also carried out to establish a direct relationship between machinability and heat treatment process.
Index Terms- Ti6Al4V, Beta solution treatment, Cryogenic, Taguchi, Chip Microstructure, Chip Mechanism