The Effects of Tool Degradation on Hole Straightness in Deep Hole Gundrilling of Inconel-718

摘要

Straightness control in deep hole gundrilling of Inconel-718 is challenging. In this study, the drills are found to degrade rapidly on the cutting edges, bearing pads and side margins, largely due to the extreme heat resistivity of the high temperature superalloys. Severe adhesive wear developed on the rake and flank faces deteriorates cutting efficiencies of the cutting edges while diffusive wear on the bearing pads and side margins deteriorates self-piloting efficacies of the drill. Coupled with highly irregular wear rates on the inner and outer cutting edges, the drills are forced against the hole at high rotational speeds – leading to escalations in frictional contact, heating and thermal damage on the bearing pads and side margins. As a consequence, the drills are deflected from the designated drilling course and resulted in straightness deviation on the part of hole drilled. Through the accumulation of partial straightness deviation over the course of high aspect ratio drilling, the final hole produced is deflected in a constant trend as governed by the rate and behaviour of tool degradation.