Tool breakout investigation in drilling using feed and cutting energy

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University of New Brunswick


Burr formation is a common problem in metal drilling processes leading to additional production costs in manufacturing. Since burrs cannot be prevented through process control and parameter optimization, obtaining a better understanding of the mechanism of the burr formation process and potentially paving the way for more appropriate development models that could mitigate the process is essential. Currently, the complex tool geometry and the dynamic nature of metal drilling pose challenges in the analysis of the drilling mechanics, and consequently, the burr formation process, thereby constraining researchers to approach the problems through the development of empirical models or alternative methods difficult to replicate. The objective of this work is to develop a new and novel method using energy analysis to identify unique points of process changes that characterize the breakout burr formation mechanism during the metal drilling process. The method developed identifies the onset of the burr breakout phenomenon, and also identifies critical points between the onset of the process and completion of the through-hole drilling process. Using a series of drilling experiments on Al 6061-T6 with standard twist drills, real-time thrust and cutting power data were collected and analyzed using a newly developed energy-difference approach (EDA). The resulting analysis was successfully mapped to the burr breakout phenomenon and validated using photomicrographs observation and microhardness testing at various points ahead of the drill point during burr breakout. Using an original approach through-hole drilling was separated into 3 primary sections identifiable using energy analysis. This work allowed for the third - critical zone, which is of primary interest in burr formation to be identified and isolated for analysis. Using the EDA process, 4 specific points of interest that characterize the actual burr formation mechanism were identified and observed for the first time: burr breakout initiation, deformation zone depth ahead of the drill point, ploughing initiation, and ploughing dominance. By identifying and quantifying the positions and depths of these critical points in the breakout burr formation, future work will allow for proper modeling, prediction, and minimization of breakout burrs.