Surface defect and chatter monitoring in robotic drilling CFRP composites using acoustic emission technique

Robotic machining is feasible for cutting composites in the field of aviation manufacturing with the benefit of high flexibility and applicability. Riveting is widely used as an important joining technique of aircraft structures requiring hole making on CFRP composites. However, due to the inhomogeneous and anisotropy characteristics of CFRP composites and the weak rigidity of robot, surface damage, and chatter are prone to occur during robotic drilling process, which significantly affect geometrical accuracy of assembled structure. In this work, robotic drilling trials on CFRP composites with different parameters (spindle speed: 3000–15000 rpm, feed rate: 0.01–0.10 mm/rev) were conducted to understand the formation mechanisms of surface damage, as well as the relationship between acoustic emission (AE) signals and defect characteristics. The root mean square (RMS), fast Fourier transform and short-time Fourier transform were successfully used for processing AE signals. The occurrence of entry burr and exit burr were investigated based on different fiber cutting angle and corresponding fiber fracture mechanisms. Drilling status and detailed mechanisms of indentation during robotic drilling were identified/monitored by processing AE signals in the time domain, frequency domain, and time-frequency domain analysis. Matrix cracking, delamination and fiber failure during robotic drilling process was highly related with AE frequency of 0–129, 133–203 and 221–346 kHz, respectively.