Analysis of burr formation mechanisms when drilling CFRP-aluminium stacks using acoustic emission

Multimaterial composites are increasingly gaining importance in the design of aircrafts due to the demand for lightweight design in the aerospace industry. Riveting is used here as an important joining technique of individual structure components in aircrafts and requires the drilling of holes into the multimaterial composites. However, the individual layers in the stack place in part contrary demands on the optimum machining process and the design of drilling tools. To guarantee a sufficient drill hole quality, it is useful to safeguard the cutting process by monitoring the drill hole quality already during machining so that the reject rate of components may be reduced. Previous research works had shown that structure-borne sound could be used successfully for an online monitoring of drilling processes. Based on these investigations, this paper is focused on examining the burr formation mechanisms in CFRP-aluminium materials during the exit of the drill. By analysing patterns in the frequency spectra, it was shown that fundamental burr formation mechanisms could be detected by means of patterns in structure-borne sound signals. In addition, it was possible to infer the burr height produced in drilling from the analysis of the characteristic patterns in the structure-borne sound spectrum. (C) 2019 The Authors. Published by Elsevier B.V.