| In the field of aircraft skin manufacturing has a wide range of TC4 titanium alloy,the surface of the protective paint layer due to damage and other reasons need to be removed,laser cleaning technology because of efficient and convenient,green,easy to achieve the advantages of automation control,it has been widely concerned.Laser cleaning technology for different cleaning objects and different laser cleaning equipment,with different cleaning process requirements,so the laser cleaning process research is necessary.In this paper,the temperature field of the cleaning process was simulated for the lacquer layer on the surface of TC4titanium alloy,and the laser cleaning test and process parameter optimization study ware carried out using nanosecond pulsed flat-top laser.The main research work is as follows:(1)By analyzing the material absorption principle and heat conduction process of laser,the temperature field simulation model of laser cleaning titanium alloy surface paint layer was established to study the influence of process parameters on the temperature field distribution of the paint layer surface.Through the analysis of the results of temperature field distribution cloud maps by controlling the single factor variable method,it was obtained that the scanning speed was influenced by the spot lap rate and the number of times the same area is subjected to pulsed laser action to influence the distribution of the surface temperature field of the paint layer,and the maximum surface temperature of the paint layer increases with the decrease of the scanning speed.The maximum surface temperature of the paint layer and substrate increases linearly with the increase of energy density.(2)The effect of energy density,cleaning speed and scanning speed on the paint removal effect was studied by single-factor test,and the effect of each process parameter on the two-dimensional shape,three-dimensional shape,surface roughness and paint removal rate of the laser cleaned specimen surface was analyzed.The results show that the effect of paint removal with the increase of energy density,cleaning speed,scanning speed,respectively,but too large energy density and too small scanning speed will reduce the quality of paint removal.Laser cleaning process mainly exists ablation cavitation effect and vibration impact effect.Before and after the cleaning of the surface of the specimen and the titanium alloy surface Vickers hardness detection and analysis,the comparative analysis method to explore the removal of the surface layer of paint and laser paint removal technology on the titanium alloy substrate surface properties of the impact.It was found that the average Vickers hardness of the laser cleaned titanium alloy substrate surface was increased from 343.48 HV to 368.74 HV,about 7.35%.(3)The significance of the effect of each process parameter on the paint removal effect was investigated by orthogonal tests,and the mathematical model between the paint removal rate and surface roughness and the process parameters was established based on the regression analysis method,and the multi-objective optimization study of the paint removal rate and surface roughness was carried out by combining the NSGA-II algorithm.The results showed that the influence of the process parameters on the paint removal effect was from large to small in terms of energy density,cleaning speed and scanning speed.The optimized parameter combinations were 3.97 J/cm~2energy density,2.58 mm/s cleaning speed and 5000 mm/s scanning speed,and the optimized results were verified experimentally.The surface morphology and physical composition of the cleaned surface were analyzed,and the measured paint removal rate and surface roughness were compared with those before optimization.Finally,the optimized combination of process parameters was obtained with better paint removal quality. |
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