Deep holes with a small diameter and a high aspect ratio are usually manufactured by a gun drilling process, especially for subsea oil and gas industry. In order to protect the devices against harsh environment (i.e. highly corrosive, pressure and temperature conditions), the equipment employs high yield strength and corrosion resistance alloys such as Inconel 718. Unfortunately, it is a challenging task to drill Inconel 718 due to its difficult-to-machine characteristics. Owning to the extremely high temperature at the cutting zone, the gun drilling tool often suffers premature failure and rapid degradation. When conventional geometrical design of cutting flute is utilized, computational fluidic dynamics (CFD) simulation has shown that the supplied coolant cannot effectively reach the cutting zone and lower its temperature during gun drilling of Inconel 718. Hence, a modified geometrical design of flute is necessary to enhance the cooling flow and pressure of the supplied coolant, so as to increase the tool life. A series of CFD simulation has shown that a reduced land width of the primary clearance face below the outer cutting edge is able to enhance the cooling flow and pressure. Then, an in-house developed gun drill grinding machine equipped with an in-situ tool geometry measurement system is utilized to produce gun drills with varying land width. Gun drilling experiments on Inconel 718 using these gun drills have proven that the tool life can be increased by around 20% when an optimized land width of primary clearance face is implemented.
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This research is supported by the Singapore Institute of Manufacturing Technology, A*STAR. Grant number is not applicable.