Numerical Calculation And Experimental Study Of Microsecond/Femtosecond Laser Composite Machining Of Micro Holes

As an efficient processing tool,femtosecond laser has been used in the highprecision and high-efficiency processing of micro holes in high-end equipment in many fields,represented by the film cooling holes in high-temperature turbine blades of aeroengine.However,femtosecond laser micro-hole processing still has problems such as unclear model representation,low processing efficiency,and unstable processing quality that need to be resolved urgently.On the other hand,millisecond/femtosecond laser composite processing has broad application prospects because it combines the advantages of long-pulse laser processing and ultra-short pulse laser processing.However,related research is still not mature enough,which restricts its engineering application.Researches on the problems mentioned above are conducted.The main research contents and innovations of this paper include:1.The basic characteristics of Gaussian beams are introduced and the complex physical mechanism of femtosecond laser irradiated metal materials is analyzed.The advantages and disadvantages of two temperature model and molecular dynamics simulation on describing the femtosecond laser metal ablation process are discussed.Using the molecular dynamics simulation method combined with the two-temperature model,taking metallic copper as the research object,a simulation model of a single pulse femtosecond laser ablation of copper materials is established.The simulation study of femtosecond laser parameters such as pulse width and energy density is carried out.The temperature cloud images of the system and atomic visualization diagrams under different pulse widths and different energy densities are obtained,which reveals different mechanisms about the ablation of metals irradiated by a single femtosecond laser pulse.2.Based on the simulation model in the previous step,the laser energy density within the Gaussian laser spot range is discretized,the ablation depths of multiple points are calculated separately,and the polynomial fitting is performed to approximate the cross-sectional shape of the femtosecond laser single pulse ablation crater.Then superimpose the femtosecond laser helical trajectory to establish the whole process simulation model of femtosecond laser helical machining of micro holes.3.With metallic copper as the target,and with the pulse width of the millisecond laser,the energy distribution between the three pulses of the millisecond laser and the helical trajectory of the femtosecond laser as variables,a series of experiments about millisecond/femtosecond laser composite processing micro holes are designed and carried out.The influence of millisecond laser parameters on the hole diameter and taper of the formed base hole is explored,and it is proved that the femtosecond laser helical trajectory has a direct impact on the processing and shaping of micro holes.4.Taking metallic copper as the target,the complete processing and forming of micro holes as the goal,and the total processing time as the measurement standard,a comparative experiment of femtosecond laser helical processingmillisecond/femtosecond laser composite processing is designed.The experiment results prove that compared with simple femtosecond laser helical processing,millisecond/femtosecond laser composite processing can increase the processing efficiency of micro-holes under certain laser parameters and process parameters.The research results provide a considerable theoretical and model basis for femtosecond laser helical processing of micro holes,and provide guidance for the process optimization of millisecond/femtosecond laser composite processing of micro holes,and have a certain engineering significance.