Coolant flow in drilling titanium considering two phase boiling

Abstract

In drilling titanium alloys, significant heat build-up on drill cutting edges due to insufficient heat dissipation raises tool temperature, leading to its rapid wear. Researchers have experimented with a variety of cooling methods to reduce temperature as well as tool damage. The in-situ monitoring of temperature of cutting edges presence of fluids in the drilling is difficult. Therefore, computational fluid dynamics (CFD) based model is proposed to investigate the temperature distribution along the drill cutting edges, and the flow characteristics of the cutting fluids such as water, mist and liquid nitrogen around the cutting edges. The boiling of cutting fluids near the cutting edges of the drill was considered by using Volume of Fluid (VOF) multiphase model in the analysis. The mist cooling was handled using a discrete phase model, and the Euler–Lagrangian technique was employed to deal with interactions between air and droplets. The highest vapour volume fraction of coolants was detected along the chisel edge of the drill cutting edge in flood and cryogenic cooling conditions. Whereas, for mist cooling, maximum vapour volume fraction of coolants was detected end of cutting edges. As the liquid nitrogen has an unusually low boiling point, it undergoes a quick phase change during the initial stages of drilling. Coolant velocities around the cutting edges in flood, cryogenic, and thick-thin mist cooling were 0.03–0.12 m/s, 0.7–0.9 m/s, 4–9 m/s, and 6–13 m/s, respectively. The maximum temperature of the drill drops by 45–48%, 32–38%, 29–36%, and 24–32% in cryogenic, thick mist, thin mist and flood conditions, respectively, over the dry condition. The numerically predicted temperature lies within an error of ∼4–18% of that of the average experimental temperature.