Chatter control in end-milling process using time-delay variation driven by workpiece excitation

This study investigates regenerative chatter suppression using workpiece excitation to induce controlled time-delay variation. Numerical simulations and milling experiments were performed with a designed active workpiece holder capable of exciting the workpiece in two orthogonal directions. Unlike conventional spindle speed variation, which adversely affects the spindle life and reliability when large variation amplitudes and frequencies are applied, the proposed approach introduces time-delay variation by modulating the relative velocity between the cutting edge and the workpiece at the cutting point, allowing higher excitation frequencies and amplitudes. Stability analysis based on high-precision time-delay variations obtained through numerical calculation showed that increasing excitation frequency and amplitude significantly increased the critical axial depth of cut at the onset of chatter, even at high spindle speeds. The analysis also revealed that approximated time-delay models can cause non-negligible prediction errors under high spindle speed, excitation frequency, and amplitude conditions. The suppression effect strongly depended on the excitation frequency, showing limited impact at half-integer multiples of the tooth-passing frequency, while a pronounced increase in the critical depth of cut and vibration reduction was achieved as the excitation frequency approached an integer multiple of the tooth-passing frequency. Although increasing excitation amplitude enhanced chatter suppression, excessively large amplitudes reduced its effectiveness, indicating the existence of an optimal excitation amplitude. Milling experiments validated the numerical predictions, confirming reduced chatter vibration and improved surface roughness. The results demonstrate the feasibility and effectiveness of workpiece excitation as an alternative chatter suppression strategy, offering a contribution to high-speed and high-precision machining processes.