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Licensed Unlicensed Requires Authentication Published by De Gruyter Oldenbourg 2018

2 Deep hole gun drilling of nickel-based superalloys

Keng Soon Woon, Guan Leong Tnay and Swee Hock Yeo


Miniature deep holes with length to diameter ratios above 100 are commonly produced with mechanical gun drilling because of the efficiency of this process in meeting stringent straightness and finishing requirements. However, such superiority diminishes while drilling nickel-based superalloys such as Inconel 718. This chapter addresses the fundamental cause arising from a critical change in the generation of cutting force that induces adverse impacts on deflection of drills, burnishing along the hole and the eventual deterioration in straightness accuracy. The unique tool wear and failure modes are discussed in detail to provide insights into the underlying challenges, especially on the severe thermal-mechanical loading conditions. To improve tool life during the process, an effective methodology that increases coolant efficiency through strategic optimization of drill designs is presented. Besides this, a new approach in designing pilot holes for gun drilling based on pilot hole and gun drill design compatibility is described, as effective tool-work engagement enhances drilling stability that benefits tool life as well as straightness accuracy. Finally, exploratory solutions to the adverse impacts of re-sharpening gun drills with primitive manual grinding apparatus - a long-standing challenge in multiple-pass gun drilling are also duly addressed.

© 2018 Walter de Gruyter GmbH, Berlin/Munich/Boston
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