Numerical Simulation And Experimental Study Of Surface Micro-Nano Structure Prepared By Femtosecond Laser

Femtosecond laser processing has obtained important applications in precision processing due to its unique advantages.During processing,the material absorbs very high energy in a short time,and then many complex changes occur.Including electroacoustic coupling,dielectric breakdown and plasma formation.The interaction process between femtosecond laser and material is a non-linear change process.Many scholars have explored this.At the same time,femtosecond laser experiments are also being carried out extensively.In this paper,the following researches on the mechanism of femtosecond laser and stainless steel interaction are carried out.the study:(1)Based on the typical theory of dual temperature model,the mechanism of femtosecond laser ablation of stainless steel is studied.The finite difference method is used to solve the dual-temperature model.Based on the consideration of electronic heat conduction and energy convection,the single-pulse ablation process of 304 stainless steel is first numerically simulated.The effects of laser energy density,pulse width and delay time on electron temperature,lattice temperature and ablation depth are studied.(2)On the basis of theoretical research,the expression of the single pulse light source term in the classic model was improved,and a theoretical model of stainless steel multipulse ablation was established.The improved theoretical model was used to simulate and analyze the evolution process of electron and lattice temperature with time and ablation depth,as well as the surface response law,and summarize the influence of different pulse numbers,pulse widths and energy densities on the ablation process.It is found that the pulse width is very important for femtosecond laser micro-nano processing of metal materials.Choosing an appropriate pulse width can be used for femtosecond laser micronano processing.(3)A finite element model of stainless steel femtosecond laser micro-nano processing was established.This model covers the temperature distribution and energy accumulation effects during processing,including the following aspects: The heat transfer model considers the effects of energy transfer,heat convection,and heat radiation,The thermophysical parameters of materials change with temperature,and the timely removal of metal materials caused by thermal evaporation is considered.This model provides a technical basis for studying the energy deposition process of femtosecond pulsed laser processing mechanism using finite element method.(4)The composition and working principle of the femtosecond laser micromachining system are briefly introduced,and the basic operating specifications and advantages of the laser confocal microscope are introduced.Then,a preliminary experimental study on 304 stainless steel was carried out using the processing system,and a higher-quality pore and microgroove structure was obtained.The microstructure and surface roughness values of the hole and microgroove structure were obtained by using a microscope,and the reasons for the roughness profile,wave profile and crosssectional profile were analyzed.Through the method of numerical simulation and experimental verification,the fit between the model and the experiment is verified to promote the development of femtosecond laser precision machining.