Lensed fiber-assisted laser–electrochemical hybrid machining for high-precision micro-hole drilling

Laser–electrochemical machining (LECM) combines the high material removal capability of laser processing with the superior surface integrity of electrochemical machining, making it a promising technique for precision drilling of difficult-to-machine materials. However, conventional LECM systems often suffer from unstable laser coupling and limited control of laser energy distribution within the machining zone. To address these challenges, a lensed fiber-assisted LECM process was developed for machining Inconel X-750. The proposed approach employs a coaxial lensed fiber to deliver and focus the laser beam directly through a capillary tool electrode, enabling localized laser heating at the machining front while electrochemical dissolution removes the thermally affected material. Optical simulations revealed that the lensed fiber reduced the laser spot diameter by 51.3% and increased the peak laser intensity by 351.7% compared with the conventional flat-end fiber configuration. The effects of voltage, feed rate, laser power, and spherical end–workpiece gap on machining performance were systematically investigated in terms of side gap (Δs), front gap (Δb), and material removal rate (MRR). Orthogonal analysis demonstrated that laser power was the dominant factor affecting dimensional accuracy, whereas feed rate had the greatest influence on MRR. The optimal parameter combination was identified as 22 V voltage, 2.0 mm/min feed rate, and 15 W laser power. Under optimized conditions, the process achieved a maximum MRR of approximately 9.87 mg/min, while maintaining controlled dimensional characteristics with side-gap and front-gap values of 86.11 μm and 215.34 μm, respectively. The fabricated holes exhibited excellent circularity, smooth sidewalls, and negligible thermal damage, with no observable recast layer, microcracks, or severe surface defects. Surface characterization confirmed that electrochemical dissolution effectively removed the laser-induced heat-affected layer while preserving the alloy's overall chemical integrity. Furthermore, laser coupling through the capillary tool electrode using lensed fiber focusing was experimentally validated. The coupling efficiency increased from approximately 62.5% at 14 A to a maximum of 81.8% at 18 A, confirming efficient laser transmission and energy utilization within the machining zone. The results demonstrate that lensed fiber-assisted LECM provides an effective strategy for high-efficiency, low-damage machining of nickel-based superalloys and offers significant potential for precision hole fabrication in aerospace, energy, and advanced manufacturing applications.