Precision fabrication of high-aspect-ratio micro-holes in 40 mm-thick TC4 alloy by coaxial electrolyte-enveloped laser-electrochemical hybrid machining

Fabricating high-aspect-ratio micro-holes in thick-walled titanium alloys presents a persistent challenge due to the conflicting requirements of high machining efficiency and superior surface integrity. In this study, a coaxial electrolyte-enveloped laser-electrochemical hybrid tool is proposed to achieve high-efficiency and precision micro-holes fabrication in 40 mm-thick TC4 alloy. This novel configuration delivers laser energy through a multimode fiber waveguide (MFW) while independently supplying electrolyte through an annular channel, ensuring the synchronous coupling of laser irradiation, electrochemical reaction and electrolyte transport. A time-resolved multiphysics model was established to explicitly bridge the temporal gap between nanosecond laser pulses and microsecond electrochemical pulses. Simulations reveal that independent and coaxial delivery significantly improves laser coupling efficiency to 94.2% while enhancing flow uniformity. Experimental results demonstrate that the hybrid process increases the volumetric removal rate by approximately 28.6% compared to electrochemical machining (ECM). Ultimately, a micro-hole with a depth-to-diameter ratio of ∼30.9 and an average surface roughness of Ra ∼2.34 μm was successfully fabricated. These findings validate the feasibility of the proposed hybrid tool for producing high-integrity, recast-layer-free deep micro-holes in difficult-to-cut aerospace materials.