An experimental investigation of deep-hole microdrilling capability for a nickel-based superalloy

Abstract

This paper presents the results of an experimental investigation into the feasibility of deep-hole microdrilling a nickel-based superalloy. This material is very challenging to machine and current drilling methods are based on non-conventional machining technologies; the traditional view is that microdrills are too fragile to be used for drilling this high-strength aerospace alloy. The work investigated mechanical microdrilling under various cutting conditions. Mechanical microdrilling may offer the chance of improved hole quality and surface integrity. Initially a review of literature was undertaken with a view to identify the best drill geometry for the production of micro holes in nickel-based alloys. Based on this review the best available commercial micro drills were selected. A special strategy was introduced for selecting the pilot drill in order to ensure gradual loading of the twist drill and reduce the chance of drill breakage. For the cutting tests, 0.5 mm diameter twist drills were used in drilling tests to a depth of 5 mm. The effect of processing parameters such as drill feed rate, spindle speed, and peck depth were evaluated, and the tool wear mechanism was also investigated. The cutting performance was characterized by the number of holes produced before drill breakage. The results show that deep-hole mechanical microdrilling of nickel-based superalloys is technically feasible and offers good hole definition and potentially competitive lead times.