Femtosecond laser drilling 100 μm diameter micro holes with aspect ratios > 20 in a Nickel based superalloy

Micro holes with high aspect ratios are essential for the cooling performance of aero-engines. Challenges persist in deep hole drilling due to the escalating stringent requirements in terms of hole diameters, aspect ratios, and 3D profiles. In this study, we propose a two-step femtosecond laser drilling method to produce cylindrical micro holes with diameters of ∼100 μm, aspect ratios >20, and near-zero taper angle in Inconel 718 plates. In the first drilling period, the laser polarization trepanning method is used, yielding through-holes with aspect ratios >20 but undesired tapers and irregular shapes at the hole exit. A new method called laser spinning is then introduced in the second drilling period, proficiently decreasing taper angles to be < 0.05° and improving the irregular exit profiles into circular contours. Employing a rotating inclined laser beam, the laser spinning method facilitates deep hole drilling by enhancing laser penetration, solely resulting augmented hole diameters at the exit without compromising hole aspect ratios. The efficacy of this drilling approach is achieved through modifying the incident laser reflection on internal hole walls. Overall, the presented results and analyses hold great promise for high-quality deep hole drilling in opaque materials, particularly for products regarding aero-engines.