Study On Paint Removal Technology And Surface Integrity Control Of Aircraft Skin Based On Pulse Laser Cleaning Technology

With the high requirements for environmental protection in the industrial field,the traditional cleaning method has been unable to meet the industrial needs.The emergence of laser cleaning shows its unique advantages,which makes up for the shortcomings of the traditional cleaning method.It not only reduces the environmental pollution,but also improves the cleaning efficiency,and has a wide range of applications.The main advantages of laser cleaning include no pollution,no contact,low cost,high efficiency,good controllability,precise cleaning of the optional area,cleaning of the dangerous areas that are difficult to reach,which have been widely concerned in recent years.In the field of Aeronautics and Astronautics,when the aircraft metal skin has been in service for a long time,the paint layer on the surface will age,crack and fall off.In order to ensure the reliability and safety of flight,all the original paint layers must be cleaned regularly to facilitate the repainting of the surface.In this paper,pulsed fiber laser is used to clean the paint layer on the aircraft skin.2024 aluminum alloy and304 stainless steel are commonly used as experimental materials,and TB06-9 and TS70-1paint layer are used as cleaning objects.Firstly,the reliability of laser cleaning,the optimization of cleaning parameters and the influence law are studied.With the help of MATLAB software,the gray-scale image of the cleaning surface collected by the three-dimensional profilometer is transformed,and the gray-scale value is used to evaluate the cleanliness of the sample surface.Judging from the surface morphology,the cleaning effect of the samples in the gray range of 90.9-102 is better.By using XPS and XRD to analyze the surface elements in this gray range,the content of trace elements in the paint layer is greatly reduced,which verifies the reliability of the cleaning effect.On the basis of this gray range,the process parameters were optimized,and the samples of TB06-9 coating and TB06-9/TS70-1 composite coating were evaluated under different laser power,scanning speed,pulse frequency and spot diameter.It is found that the scanning speed has the least influence on the cleaning effect of the paint layer,the spot diameter has the most influence on the cleaning effect of TB06-9 paint layer,and the laser power has the most influence on the cleaning effect of the composite paint layer.Secondly,the surface modification and mechanism of laser cleaning were studied by cleaning different substrates.The laser cleaning mechanism is mainly ablation effect,vibration effect and plasma impact effect.The main cleaning mechanism under different parameters is also different,which is related to the amount of energy borne by the paint layer and the substrate on the unit area.When the energy density is high or the scanning speed is low,the absorption energy of the surface is high,and the vibration effect is not obvious.After laser cleaning,the average friction coefficient of the surface is reduced,the hardness of the material is improved,and its ability to resist elastic-plastic deformation is strengthened.With the change of energy density and scanning speed,the surface roughness of cleaning surface also changes.When the energy density is 18.86 J/cm~2,the surface roughness value is the largest,and when the scanning speed is less than 50 cm/s,the effect on the roughness is small.At last,the change of surface structure after laser cleaning was studied.After cleaning 304stainless steel surface coating,the micro nano particles with great difference from the matrix were found from the micro morphology.Through the study of the microstructure of cleaning surface under different energy density and scanning speed,it is found that when the energy density is 0.84 J/cm~2,the micron particles with irregular shape are more common,with an average size of 1-10μm.when the energy density reaches 2.12 J/cm~2,there are more submicron and nanometer particles,with an average size of 50-90 nm,these irregular particles are related to the generation and action mechanism of uniform particles.The large-size particles may be torn and splashed out due to the force of the paint layer material,resulting in different shapes and irregular surfaces.The nano-sized particles may be due to the phase transformation of the paint layer or the base material when heated,and quickly condensed into droplets during the gasification and evaporation process,forming uniform nano particles.