Investigation of sidewall formation mechanisms in micro-milling of high-aspect-ratio slots: Modeling, experiments, and process strategy

High-aspect-ratio slow-wave structures, widely employed in vacuum electronic devices for aerospace long-range communication and radar systems, impose stringent sidewall-verticality requirements due to their strong influence on electron–wave coupling performance. To elucidate the mechanism governing sidewall deviation during micro-milling of high-aspect-ratio blind slots, the tool–sidewall interaction was analyzed, and a mathematical model incorporating attachment error, tool wear, and cutting forces was developed to support subsequent experimental investigations. Short-path machining experiments of high-aspect-ratio slots reveal that the sidewall verticality is primarily affected by tool deflection, which arises from cutting-force amplification induced by progressive tool wear, and is accompanied by a deterioration in surface quality. Incorporating the measured attachment errors and cutting parameters into the proposed model, the deviation between the predicted and experimentally measured sidewall verticality remains within 0.4°. Long-path machining results further demonstrate that severe tool wear during processing leads to substantial tool-diameter loss and elevated cutting forces, causing the new tool to perform even worse than the worn tool with respect to sidewall verticality. By mechanistically evaluating the respective contributions of tool wear, cutting forces, and runout to sidewall formation, a roughing–finishing strategy was formulated to mitigate tool deflection, down-milling material accumulation, and feature inconsistency in long-path micro-milling. This strategy significantly improves sidewall verticality and surface integrity, enabling a 255 μm-deep slot to maintain sidewall angles above 89°. The outcomes provide mechanistic insight and process-planning guidance for achieving high geometric accuracy in precision micro-milling of high-aspect-ratio features.