Vibration Assisted Drilling of Carbon Fiber Reinforced Polymer and Titanium Alloy for Aerospace Application

Abstract

The physical and mechanical characteristics of carbon fiber reinforced polymers (CFRP) and Ti6Al4V make them widely used in the aerospace industry. The hybrid structure of CFRP/ Ti6Al4V material has been used in the new generation of aircraft manufacturing. The drilling process of these materials is often associated with unfavorable machining defects such as delamination, burr formation, reduced surface integrity, and tensile residual stresses. These machining defects are attributed to high thermal load, continuous chip morphology, and poor chips evacuation efficiency. Vibration-assisted drilling (VAD) uses an intermittent cutting process to control the uncut chip thickness and chip morphology. VAD has potential advantages include low thermal load, high chips evacuation effectiveness, and longer tool life. This thesis presents an experimental investigation into the effect of VAD machining parameters on the cutting energy, CFRP delamination, surface integrity, geometrical geometry, Ti6Al4V burr formation, induced residual stresses, and tool wear during the drilling process of CFRP, Ti6Al4V, and CFRP/Ti6Al4V stacked materials. Moreover, a kinematics model is developed to link the observed results to the independent machining parameters (i.e., cutting speed, feed rate, modulation amplitude, and modulation frequency). The experimental work covers a wide range of machining parameters using four levels of frequencies (83.3, 125, 1500, and 2150 Hz). The VAD results show up to 56 % reduction in the cutting temperature with a significant enhancement in the CFRP entry and exit delamination, geometrical accuracy, surface integrity, and burr formation. The use of VAD also generates compressive stresses, hence improving the part fatigue life.