A Novel Approach to the Design of Self-Piloting Drills With External Chip Removal, Part 2: Bottom Clearance Topology and Experimental ResultsOn the Experimental Optimization of Tool Geometry for Uniform Pressure Distribution in Single Edge Gundrilling

Abstract

An investigation into the effect of gundrill geometry on the coolant flow, in gundrilling, is carried out. This investigation deals mainly with the loss of coolant pressure occurring in a limited space between the flank of the gundrill and the bottom of the predrilled hole. This space is named as “bottom clearance.” The pressure loss in the bottom clearance is classified into, (a) pressure loss due to flow interaction with the bottom of the drilled hole (impact pressure loss), and (b) pressure loss due to hydraulic resistance of the annular groove connecting the bottom clearance and the chip removal passage. The study indicates that a significant part of the pressure loss occurs due to flow deflection at the bottom of the hole. The reduction of pressure loss can be achieved either by reducing the coolant velocity at the orifice exit, or, by increasing the coolant pressure in the bottom clearance. In this study, the shoulder dub-off angle of the gundrill is experimentally optimized to increase the coolant pressure in the bottom clearance, thereby achieving uniform coolant pressure distribution. This uniform pressure distribution resulted in increased gundrill life without compromising the quality of the machined hole.