Quantification of drilling quality and mechanisms in CFRP composites

Abstract

Drilling on fibre reinforced composites is a crucial process in fabrication of airframes in aircraft industry. In this research, an extensive experimental investigation on drilling and machining CFRP laminates using different tools is carried out to analyse effects of processing parameters on drilling performance. Drilling performance and quality of circular holes on a commercial aircraft CFRP laminate are investigated, using drill bit with three different configurations made of solid carbide, namely GT50 dagger drill, GT15 reamer drill, and twist drill. Back support of different geometry, as full support, partial support and no support, is employed during drilling at spindle speeds of 500, 1000, and 2000 rpm, and feed rate of 50 mm/min. Thrust force and torque, are measured. Quantification of the quality and holes integrity is accomplished by evaluating surface roughness, heat distribution, drilled hole roundness or circularity, chip size, and damage factor. The second major study is an energy-based analysis based on the energy balance model established by William’s on cutting polymers is presented by addressing Mode I fracture as a key mechanism in different cutting directions in a unidirectional CFRP laminate, induced by orthogonal cutting. Then, tool wear and tool life of dagger and reamer drill bits are investigated, evaluating blunting and wear of the tools. With that, assessment on tool wear and tool life are made by addressing their significant influence on thrust force and torque during drilling, delamination factor in the CFRP laminates, fibre peel-up and push-down mechanisms, surface roughness and temperature increase. Lastly, finite element analysis is added to explore and predict the drilling mechanism and chip removal mechanism as a function of failure criteria. With all that has been addressed above, this study plays a critical role for selection of the optimal drilling conditions for minimising production cost and maximising productivity.