High-quality drilling method for CFRP blind holes guided by acoustic emission signals

Carbon fiber reinforced plastic (CFRP) has been widely used to produce aircraft wings, aircraft engines, and wind turbine blades. It is inevitable that defects such as pits, cracks, delamination, and scratches will appear on the surface of CFRP after long-term operation under extreme conditions. Cutting specific-sized blind holes on the surface of CFRP is crucial in precisely removing damaged material and preparing for subsequent component repairs. In this paper, a rotating isometric parallel line (RIPL) scanning method under the guidance of AE signal is proposed to achieve high-quality and efficient cutting of blind holes. The machining mechanism coupled with thermal ablation and mechanical denudation at different scanning intervals has been described. A cosine similarity (CS) algorithm for extracting acoustic emission (AE) signals has been proposed. The interface between adjacent pre-impregnated materials with different arrangement directions was accurately identified by determining the mutation point of cosine similarity (CS) values, and the scanning trajectory has been adjusted online to be perpendicular to the carbon fiber under the guidance of CS values. Compared with the traditional isometric concentric circle (ICC) and isometric parallel lines (IPL) scanning methods, RIPL can effectively avoid defects such as pits, and improve the cutting efficiency by 27.1 % (0.587 mm³/s to 0.746 mm³/s) and 33.9 % (0.557 mm³/s to 0.746 mm³/s), respectively.