THE EFFECT OF THE GAS OUTLET ON THE GAS VELOCITY FIELD IN MASS-PRODUCTION OF HFCVD DIAMOND-COATED DRILLS

In the present study, the finite volume method (FVM) is adopted to investigate the effect of gas outlet on the fluid field generated by a hot filament chemical vapor deposition (HFCVD) setup that is designed for the mass-production of diamond coated drills. The temperature field is calculated simultaneously such that its effect on the gas flow can be included in the resulted gas velocity field. First, the effect of outlet radius (Rout) is investigated using a 2-outlets arrangement. The results show that the gas field obtained with Rout = 10 mm is superior to Rout = 5 mm or 15 mm, which not only can produce higher gas velocity, but also a more uniform gas field in filament plane. To further refine the uniformity of gas field outside the filament area, four 4-outlets arrangements with different combinations of the distance between gas outlets and worktable and gas inlets coverage are proposed and a comparative study on their effect on the gas field is conducted. The simulation results show that allocating two additional outlets near the worktable is beneficial for enhancing the uniformity of gas velocity field outside the filaments but slightly worsen it near the filaments. Finally, actual deposition experiments are conducted to justify the simulation results and the results suggest that the gas velocity in the drill region plays critical role on the growth rate of diamond film and the 4-outlets arrangement could provide more uniform growth environment than the 2-outlets arrangement.