Rotary Ultrasonic Drilling of CFRP: Effect of Process Parameters on Delamination

Drilling is an essential practice, especially for the aerospace industry. Conventional machining procedures such as twist drilling are not cost effective for hard to machine materials such as titanium, advanced ceramics, carbon fiber reinforced plastics etc. Rotary ultrasonic machining (RUM) is a nontraditional machining process for hard to machine materials. RUM utilizes a rotating, ultrasonically vibrating tool (core drill) feeds into the workpiece to remove the material. Although drilling is the most common machining process for CFRP, delamination is a major problem associated with drilling, because of its heterogeneity and anisotropy. Delamination reduces structural integrity and increases assembly tolerance which leads to rejection of a part or a component. In the air craft industry, rejections caused by delamination accounts for 60% of all rejections in final assembly. This motivates researchers to identify delamination-free techniques to reduce component rejection caused due to delamination. This paper, for the first time, investigates the effects of process parameters on the delamination of CFRP processed by RUM. These process parameters are variable feed rate, variable spindle speed and the use of backing plate.