An in-depth investigation into high fluence femtosecond laser percussion drilling of titanium alloy

High fluence femtosecond laser percussion drilling has a potential to produce micro holes for cooling purpose in turbine blades made of titanium alloys due to its short interaction time with the material. For an in-depth investigation, numerical simulation is carried out using 2D axi-symmetric two-temperature and heat conduction models in tandem, mimicking the laser percussion drilling. Moving mesh approach in finite element based COMSOL Multiphysics software is used to arrive at the crater geometry during the ablation process. The heat conduction model provides the value of surface temperature after each pulse. Taking temperature-dependent thermo-physical and optical properties with intraband absorption effect, the simulations are carried out on a 2 mm thick Ti6Al4V plate for 1-15 pulses with fluence in the range of 0.84 to 8.4 J cm(-2). For comparison, the simulation results based on room temperature properties are also included. Validation experiments are carried out and the crater morphology is measured using laser scanning confocal microscope. The overall average absolute deviations of the results for crater diameter and depth are within 20% and 40% respectively. The proposed simulation approach is robust and can be used to investigate multi pulses laser ablation process in any other applications.