Coupled rotation-vibration micro-EDM enabled by passive conversion of electrode runout into axial vibration with improved debris removal

The fabrication of deep micro-holes using micro-electrical discharge machining (micro-EDM) is severely constrained by tool electrode runout and inefficient debris evacuation, particularly when electrode diameters are reduced to a few tens of micrometres. Existing solutions commonly rely on additional actuators, which not only increase the structural complexity and assembly difficulty of the spindle system but also introduce limitations in dynamic stability and miniaturization due to increased system mass and reduced structural stiffness. To address these challenges, this study proposes a novel method that passively converts the inherent radial runout of a rotating micro-electrode into controlled axial vibration by incorporating a flexible V-block clamp beneath the upper rotational clamp, thereby simultaneously eliminating radial runout at the electrode tip and generating vibration without requiring external driving units. A mathematical model was established to link vibration amplitude to runout magnitude, clamp spacing, and spindle speed. Based on this principle, a compact spindle integrating rotation, inchworm feed, and the runout-to-vibration conversion was designed and fabricated. Multiphase flow simulations employing the mixture model combined with a dynamic mesh method reveal that the coupled rotation-vibration motion induces periodic pressure fluctuations within the discharge gap, thereby inducing complex and intense flow structures that promote bubble dynamics and accelerating debris evacuation. Micro-hole drilling and groove scanning experiments further validate the effectiveness of the proposed approach. Under large-amplitude vibration conditions, the groove depth increased by 109% compared with rotation-only machining, while the surface roughness Ra decreased from 0.26 μm to 0.23 μm. Moreover, micro-holes with a diameter of ~170 μm and an aspect ratio of ~100 were successfully fabricated. This study advances micro-EDM technology by simultaneously achieving structural simplification, high rotational accuracy, and enhanced debris removal capability, enabling a practical and scalable strategy for the development of ultra-precision systems for high-aspect-ratio microstructure fabrication.