The effects of dub-off angle on chip evacuation in single-lip deep hole gun drilling

•The analyses of the effect of dub-off angles on chip transport and evacuation is carried out using CFD simulations with the support of experimental data. This was carried out to predict the trajectory of a typical chip for various dub-off angles of 0°, 5°, 10°, 20° and 30°.•The analyses of the predicted trajectories have indicated that the greater the dub-off angle the greater the tendency for the chip being trapped on the bottom of the hole.•The dub-off angle used in commercial single-lip gun drills is typically 20°. This research work suggests that designing single-lip gun drills with smaller dub-off angles would improve chip flow evacuation.

Without proper chip evacuation, gun drills will fail under intense thermal and mechanical loading during deep hole drilling of high temperature superalloys like Inconel 718. In gundrilling, the efficiency in evacuating chips is governed by the geometry of gun drills that defines the hydraulic boundary conditions for coolant and chip flow. In this paper, we propose a novel computational fluid dynamics (CFD) model that is capable to simulate and quantify the chip transportation behavior under high pressure coolant for drill geometry optimization. This is demonstrated through a case study on improving the shoulder dub-off design of commercial gun drills, which have a high tendency in trapping chips at the hole bottom. A more effective design criterion for the shoulder dub-off is thus proposed.