Assessment of positional error and hole quality during vibration-based drilling of aerospace alloy

Abstract

Modulation assisted drilling (MAD) superimposes low frequency (< 1000 Hz) and high amplitude (< 150 µm) vibrations to the cutting tool, more specifically to the drill bit in the feed direction during drilling. The present work investigates the effect of low-frequency vibrations on the drilled holes quality during MAD for nickel-based superalloy, Inconel-718 as work material. The vibrations were superimposed on the drill bit using a specialized tool holder (TriboMAM, a piezoelectric driven patented device). Quality comparison of conventionally and modulated-assisted drilled holes was done on the basis of positional error by a novel approach. As per the discrete chip production model during MAD, a rotational speed of 2200, the modulation frequency of 220 Hz, amplitude of 0.008 mm, and feed rate of 0.031 mm/rev led to a reduction in positional error, thrust force and torque by 52 %, 11 %, and 32 %, respectively, in comparison with the CD. MAD due to its intermittent cutting nature, results in a better lubricant flow during the operation, and production of finer chips; both factors help to reduce frictional heat, tool wear and thrust force. These attributes, in turn help to achieve less positional error. Moreover, the cyclic drilling force also contributes to reduce thrust force as well as positional error due to hammering action. Thus, the results of the study indicate that MAD is a better contender for quality-oriented machining of the given superalloy within the chosen parametric domain following the discrete cutting model.