Study On The Mechanism And Technology Of Paint Laser Cleaning On Aluminum Substrate

Paint laser cleaning technology is a surface cleaning technology with efficiently and environmentally friendly,good accessibility and high controllability.Aluminum alloy is the main structural material in the field of aircraft and rail vehicles,which the surface paint needs to be cleaned regularly.Due to aircraft and rail vehicles often withstand large dynamic loads during service,the process of cleaning the paint should ensure that the fatigue property of aluminum alloy is not reduced.Therefore,the damage of substrate must be avoided during paint laser cleaning.In order to obtain the best paint removal process,it is great significance to study the laser paint removal mechanism,substrate damage behavior and the relationship between them.In this paper,the mechanism of paint laser cleaning and the damage behavior of substrate are studied by means of High-speed Camera,Scanning Electron Microscope(SEM)and MATLAB software.The relationship between the damage behavior of the substrate and the paint cleaning mechanism is established.The advantages and disadvantages of different cleaning mechanisms of the paint are analyzed.The process of paint laser cleaning is optimized,and the rationality of the process is verified through experiments.The results show that the laser cleaning mechanism of fluorocarbon paint(FP)mainly includes thermal stress,decomposition and combustion,splash.The laser cleaning mechanism of fluorocarbon aluminum paint(FAP)mainly includes thermal stress,evaporation and boiling,splash.The laser energy density threshold of the splash cleaning mechanism is significantly higher than other cleaning mechanisms.The increase of the paint surface roughness in the process of paint laser cleaning is inevitable.The increase of the paint roughness will enhance the absorption rate of the paint to the laser.The smaller the laser spot size the greater the laser energy density,the paint will form overheated liquid easier in the viscous flow state and appear to be cleaning by splashing.The main destruction forms of the oxide film formed by the pretreatment on the aluminum alloy surface are burning and cracking.And the main damage forms of the aluminum alloy substrate are surface melting and pits.The damage of the oxide film or the aluminum alloy substrate are caused by the laser directly acting on the surface.The heat generated in process of the paint laser cleaning has no effect on damage of substrate or oxide film,but the paint can increase the absorption of the oxide film or aluminum alloy substrate to laser to reduce the laser energy density threshold of damage them.The laser energy density threshold of oxide film destruction is approximately equal to the aluminum alloy substrate melting,which is smaller than the laser energy density threshold of aluminum alloy substrate pit damage.The minimum laser energy density of pit damage on the aluminum alloy substrate is2.534J/cm~2,and the paint is mainly cleaned by splashing at this time.The minimum laser energy density of the oxide film damage and the aluminum alloy substrate melting damage is b approximately equal to 0.46J/cm~2,under this condition,the FP is cleaned via decomposition-combustion,and the FAP is cleaned via evaporation-boiling.The decomposition-combustion removal process is relatively stable,and the surface roughness will not change significantly.The boiling cleaning process is unstable,and the surface roughness will change greatly,which will have a certain effect on the local heat accumulation of the substrate surface.The process that FP can be cleaned mainly by decomposition and combustion,and FAP can be cleaned by evaporation is designed.Through the process experiment,it is verified that the above paint laser cleaning process can realize that the paint is cleaned without damage to the substrate.