An experimental study on the drilling of CFRP sandwich structures with filled and unfilled aramid honeycomb cores

Lightweight carbon fibre-reinforced polymer (CFRP) sandwich structures with honeycomb cores have excellent specific bending stiffness and good dimensional stability; therefore, their future applications will extend extensively, despite their difficult-to-manufacture nature. Although the drilling of single CFRP structures has been widely investigated, the published experience of drilling honeycomb cored CFRP sandwich panels is strongly limited. Therefore, the main objective of the present paper is to experimentally analyse the machinability of CFRP sandwich panels with filled and unfilled aramid Cormaster honeycomb cores through the analysis of thrust force, drilling torque and drilling-induced burrs. A twist and a brad and spur drill were used in two sandwich structures at three feed levels for the drilling experiments. The thrust force and drilling torque were measured by a KISTLER dynamometer, and the burrs were processed through digital image processing of optically captured images. The experimental results show that the application of fillers in the honeycomb only slightly decreases the nominal specific stiffness of the CFRP/honeycomb sandwich structures and slightly increases the thrust force; however, a significant improvement is achievable by their application in the drilling-induced burr formation of the honeycomb core.