Fundamental 3D simulation of the femtosecond laser ablation for cooling hole drilling on Ni and Fe based aero-engine components

Femtosecond laser ablation is widely applied in the drilling of film cooling holes of turbine blades and vanes. A deep understanding of the interaction between the femtosecond laser and the target material is crucial for processing parameter optimization. In this work, numerical simulations are performed on the basis of a traditional two-temperature model, and laser irradiation on the surface of Ni-based and Fe-based superalloys is investigated. The evolution of electron and lattice temperature is calculated, and the crater morphology and recast layer thickness are thus determined with respect to the vaporization and melting temperatures. The depth and diameter of the crater and melting front are not greatly changed by advancing the single-pulse energy from 20 μJ to 120 μJ and 720 μJ, which is contrary to the opinion that machining efficiency is strongly determined by the applied pulse energy. However, Fe seems to be more easily ablated than Ni, resulting in a larger crater depth. By setting different values of pulse width, single-pulse energy and electron–phonon coupling strength, the evolution of electron and lattice climax temperature is investigated, and the underlying nature of energy coupling is clarified. The two temperature model is further extended to simulate the multiple-pulse laser percussion process. The crater maintains a rotating parabolic shape while deepening. Interestingly, the material removal rate is the highest at a certain depth for different single-pulse energies and target materials. The physical presence of a first increasing then decreasing trend is analysed in detail. In the end, the relationship between crater depth and pulse number indicates that the focal spot should shift downward by a feeding rate to realize high-efficiency laser ablation.