Ultrasonically Assisted Drilling of Carbon Fibre Reinforced Plastics

Carbon fibre-reinforced plastics (CFRPs) gained substantial acclaim in recent decades and are used in aerospace, automotive and structural applications due to their high strength-to-weight ratio, high stiffness, high fatigue and corrosion resistance. CFRPs are manufactured near to net shape but some machining processes such as drilling cannot be avoided. Drilling induces damage (delamination, matrix cracking, matrix burning, lamina cracking and fibre pull out) in CFRP because of high axial thrust forces and a temperature rise. In this research an attempt is made to use ultrasonically assisted drilling (UAD) to reduce the axial thrust forces. In UAD high frequency (~ 20 kHz) vibrations are superimposed on a drill bit, preferably in axial direction, to reduce the thrust forces. In this study, experiments are conducted in two stages. At the first stage an initial setup with an existing UAD transducer is used to compare UAD with conventional drilling (CD) of CFRP. A reduced thrust force is experienced in case of UAD when compared to CD. At the second stage, drilling dynamics, i.e. feed speed, is changed along with the improvement of the transducer, and an enormous amount of force reduction (>80%) is observed in case of UAD (as compared to CD).