Research On Mechanism And Experiment Analysis Of Laser Polishing TC4 Alloy

Laser polishing as a modern polishing technology,which has some advantages,like high precision,no contact friction,it is regarded as a potential polishing method.Now,the research work lacks of systematic research on the numerical simulation of pulsed laser polishing and the process parameters optimization.For this status quo,a simulation model for pulse laser polishing TC4 alloy was established,study effect of different process parameters on the polishing effect.At the same time,the prediction model of process parameters and post-polishing performance index was established,used multi-objective intelligent optimization algorithm to optimize the prediction model,and the appropriate combination of process parameters was obtained.The specific research results and conclusions are as follows:(1)A two-dimensional axisymmetric transient model was established for simulating pulsed laser polishing TC4 alloy.According to the true linear morphology data,established geometric model,which contains three physical fields that solid heat transfer,laminar flow and moving mesh,Marangoni effect and non-isothermal flow was also coupled,heat source is a pulse moving Gaussian heat source,which can well simulate the melting flow effect and temperature change well in laser polishing process.(2)Analyzed temperature field,velocity field and surface morphology change of simulation model.It was found that the surface topography change process can be divided into two stages: in the early stage,when the peak of the melted surface fills the concave valley,the capillary is the dominant force,and the surface becomes flat.In the next stage,the secondary morphology changes of some surfaces make some redundant protrusions,the thermocapillary is the dominant force.For the influence of parameters,drew the conclusions: Both energy density and spot overlap rate have V-shaped relationship with the polished roughness,and are positively correlated with the molten pool depth.Finally,the numerical variation of capillary and thermocapillary was analyzed,and it is proved that capillary is the main stress of surface morphology change.(3)Designed single factor experiments of focal offset of distance,laser power,repetition frequency,scanning speed,scanning way,process times.Selected suitable range of the first four parameters,fixed the two parameters in subsequent experiments.At the same time,the simulation results are compared with the actual experiments,and it was found that the overall change trend is basically the same.After that,the hardness changes after polishing were explored based on the selected process parameter range.From changes of surface elements were analyzed by EDS spectrum,it was found that carbon elements generally decreased after polished,indicating softening in some areas of the material.(4)According to the relevant application scenarios,the roughness and microhardness are proposed to evaluate the laser polishing effect comprehensively.Response surface quadratic polynomial,BP neural network and RBF neural network were used to establish the prediction model between the process parameters(focal offset distance,power,speed and frequency)and the roughness and microhardness after polished,and the prediction accuracy was compared.After that,NSGA-II algorithm and multi-objective particle swarm optimization algorithm were respectively used to optimize the model with the highest prediction accuracy.The Pareto solution set obtained was then screened and compared to obtain the final result.The results show that the roughness decreases by 61.53% and the microhardness only decreases by 12.09%,which could satisfied the expected application demand of TC4 alloy.