Study of Micro Ultrasonic Machining of CFRP/Ti Stacks

Carbon fiber reinforced plastic (CFRP) composite is one of the most sought after material owing to its superior physical and mechanical properties such as high-durability and high strength-to-weight ratio. CFRP composites are often used by stacking up with titanium (Ti) to form multi-layered material stacks for applications involving extreme mechanical loads. However, machining of CFRP/Ti multi-stacks is quite complex and challenging task since both materials are difficult-to-machine materials and show completely different machinability properties. The challenge is further escalated when there is a need to machine CFRP/Ti stacks at micron level. Several problems arise during the machining process due to the non-homogeneous structure, anisotropic and abrasive properties of composite. Traditional methods of micromachining the CFRP/Ti stacks results in several issues including high cutting force and torque and high tool wear, composite delamination, large groove depth in composite, and poor surface quality. Ultrasonic machining (USM) process has been successfully used to machine titanium, CFRP and CFRP/Ti stack at macro scale. Micro Ultrasonic machining is a downsized version of macro ultrasonic machining process that is developed to machine hard and brittle materials. This research explores the possibility of using Micro USM process to conduct micromachining of CFRP/Ti multi stacks. The effect of various process parameters including abrasive grit size, tool material and type on the material removal process is studied. The study found that micro ultrasonic machining process is capable of successfully micromachining CFRP/Ti stacks with zero CFRP delamination, minimal variation in CFRP and Ti hole sizes and longer tool life. Further, a three-dimensional finite element simulation study is performed on micro ultrasonic machining of CFRP/Ti stacks. The simulation results revealed that the workpiece is not subject to any significant normal stresses during the machining process, while variations in shear stresses is seen on the inside surfaces of the machined cavities.