Experimental study on micromachining of CFRP/Ti stacks using micro ultrasonic machining process

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 such as in aerospace and automotive industries. However, the 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 the CFRP/Ti stacks at micron level. Several problems arise during the machining process due to the non-homogeneous structure and anisotropic and abrasive properties of composites. Traditional methods of micromachining the CFRP/Ti stacks result in several issues including high cutting force and high tool wear, composite delamination, large groove depth in composites, and poor surface quality. Ultrasonic machining (USM) process has been successfully used to machine titanium, CFRP, and CFRP/Ti stacks at macro scale. Micro ultrasonic machining is a downsized version of macro USM process that is developed to machine hard and brittle materials such as quartz, glass, and ceramics at micron scale. This research explores the possibility of using the micro USM process to conduct micromachining of CFRP/Ti multi stacks. The effects of various process parameters including abrasive grit size, tool material and type on the material removal rate and surface quality are studied. The study found that micro ultrasonic machining process is capable of successfully micromachining CFRP/Ti stacks. In comparison with conventional processes, micromachining of CFRP/Ti stacks using micro ultrasonic machining process resulted almost zero CFRP delamination, minimal variation in CFRP and Ti hole sizes, and longer tool life.