Spectrogram Analysis of Acoustic Emissions in Skin Milling of Thin Aluminum Sheets

Excessive vibration and noise in thin aluminum sheet milling reduce machining stability, tool life, and surface quality; however, systematic studies remain limited. To address this gap, this study investigated acoustic emissions during skin milling using spectrogram analysis and finite-element model analysis performed with Ansys. Experiments were conducted on 2 mm aluminum sheets, with acoustic signals continuously recorded under varying spindle speeds. At 2500 rpm, forced vibration and self-excited chatter dominated the response. At 5000 rpm, excitation frequencies approached the natural modes, producing resonance and position- dependent variations in vibration intensity. At higher speeds (7500-8000 rpm), harmonic components of forced vibration prevailed, reflecting the increasing influence of tool rotation on dynamic behavior. The results confirm that vibration characteristics are governed by spindle speed, machining position, and structural stiffness, and they can be effectively and reliably utilized for real-time monitoring to enhance process stability, extend tool life, and improve surface quality.