External sensors (as shown in Fig. ), on the other hand, require additional installation and mainly include measurements of force, torque, acoustic emission (AE) and temperature . monitoring is also crucial in CFRP machining, as temperature increases in the cutting zone can influence the tribological behaviour at the cutting tool-CFRP interface, impacting tool wear. . The two commonly deployed sensors for temperature monitoring are thermocouple and Infrared (IR) thermal camera . Thermocouples provide precise point-specific temperature measurements at high frequencies (up to 100,000 Hz), while IR thermal cameras can capture temperature distributions over larger areas. Transform or Hilbert-Huang transform. Since signal feature extraction is not the primary focus of this review, readers are referred to a topical review for more detailed insights on this subject.