The effects of tool edge radius on drill deflection and hole misalignment in deep hole gundrilling of Inconel-718

Straightness control in gundrilling of deep, thin-walled holes on Inconel-718 is challenging due to insufficiently explored phenomena governed by the tool edge radius effects. Such effects are activated by conservative drilling conditions for Inconel-718, which transforms the chip formation mode to a thrust-dominated mechanism. Critical changes in force generation are thus resulted, which affect the characteristics of drill deflection and thin wall deformation. In consequence, the drill's self-piloting capability deteriorates - leading to uncontrollable deflection and hole misalignment. A mechanistic model uniting the underlying force, drill deflection, wall deformation and process kinematics is proposed and substantiated, as well. (C) 2014 CIRP.