Roughness of composite materials: Characterization of hole quality in drilling of Al/CFRP stacks

Composite materials are increasingly used in the aeronautical field thanks to their high specific mechanical properties. To simplify assembly operations and reduce associated costs, the current trend in the industrial field is to optimise drilling processes since composite materials, due to their structure, are difficult to machine. The present work aims at studying the correlation between the arithmetic average roughness of the internal surface of holes made on carbon fibre reinforced composite material stacks with the parameters that characterise the drilling process and the tool geometry. Roughness is a rarely used quality parameter for composite materials due to the presence of multiple layers and fibres that can compromise the results; the obtained roughness measurements were assessed on the basis of the results obtained through image-processing techniques applied to acquired pictures of the internal hole surface.