Precision deflection control of thin-walled plates in pressure-assisted milling: Synergistic thresholds and multi-objective optimization

This study proposes an optimization method based on synergistic threshold adjustment to address the deflection control challenges in the pressure-assisted milling process of Al7075-T6 thin-walled plates. A synergistic threshold system was established, integrating critical deflection ($D_{\text{cr}}$ = 0.25–0.4 mm) and critical pressure ($P_{\text{cr}}$ = 0.25–0.3 MPa), to simultaneously suppress elastoplastic instability and enhance machining efficiency. The strategy was further optimized using the Non-dominated Sorting Genetic Algorithm (NSGA-II) for multi-objective parameter selection. Experimental results demonstrate that the pressure-assisted (P) significantly improves structural rigidity, reducing the thin-walled plates maximum deflection by 80 % (from >1.0 mm to 0.2 mm). The $D_{\text{cr}}$ threshold effectively prevents plastic deflection by confining equivalent strain below the material yield limit, ensuring machining integrity. The $P_{\text{cr}}$ threshold optimizes contact stress distribution, achieving dynamic equilibrium between instability suppression and energy consumption control; exceeding this range diminishes deflection inhibition efficiency. Under particularly aggressive machining parameters (axial depth of cut a_p > 0.5 mm, feed per tooth $f_z$ >0.25 mm/tooth), the material removal rate (MRR) achieved a 100 % increase when pressure-assisted was applied (P = 0.2 MPa) compared to conventional machining without pressure assistance (P = 0 MPa). Pareto-optimal parameter sets derived from NSGA-II achieved simultaneous deflection reduction and MRR improvement, surpassing the limitations of conventional processes in both machining accuracy and efficiency. This deflection control method, enabled by parameter synergy, provides theoretical and practical guidance for high-efficiency precision machining of thin-walled plates.