Research On Technology And Mechnism Of Laser Composite Cleaning Paint Coating From Aluminum Alloy Surface

The aircraft needs to be overhauled regularly during the service process.The paint coating on the fuselage surface needs to be removed and the fuselage needs to be repainted in the overhaul.Laser paint removal has been widely concerned in this field in recent years due to its advantages of environmental friendly and high efficiency.The laser cleaning of paint coating with different wavelengths and pulse widths has different characteristics.In this paper,millisecond pulse CO₂ laser and nanosecond fiber laser are studied.The characteristics and mechanism of two kinds of single laser sources paint removal are discussed.A multi-source laser cleaning method suitable for the removal of composite coating on the surface of aircraft skin is proposed.The specific research contents are as follows:Firstly,the characteristics and mechanism of paint removal by millisecond pulse CO₂ laser and nanosecond pulse fiber laser are studied.Paint removal experiments with two kinds of single laser source were carried out.The dynamic behavior and temperature field in the cleaning process were observed by high-speed camera and infrared thermal imager.The micro and macro morphology of the cleaned sample surface were analyzed.Using COMSOL finite element software,two-dimensional physical models of paint coating removal by two kinds of single laser sources are established.The temperature field and stress field in the cleaning process are simulated.According to experimental phenomena and numerical simulation results,Ablation effect plays a major role during millisecond pulse CO₂ laser paint removal.The heat input is large during the cleaning process,and there is combustion product residue after cleaning.The process of nanosecond pulse laser paint removal includes multiple mechanisms such as ablation effect,thermoelastic expansion effect and reverse bremsstrahlung effect.Laser energy can be precisely controlled to avoid damage to the substrate,but the effect of composite coating removal is poor.Secondly,this paper presents a multi-source laser cleaning method for removing the thick composite coating.The millisecond pulse CO₂ laser was at the front to thin paint coating through ablation effect.Then the nanosecond pulse laser remove the coating layer close to the substrate.The optimal laser parameters are: CO₂ laser average power 200 W,pulse width 1ms,pulse frequency 500 Hz,nanosecond laser power 200 W,pulse width 60 ns,pulse frequency 10 k Hz.Finally,a method for evaluating the effect of multi-source laser cleaning paint coating is proposed.The cleaning effect is evaluated by visual inspection,micro morphology analysis,image processing,surface element composition analysis and other methods.When the coating residual rate is less than 3%,and the substrate surface does not melt,the cleaning effects is qualified.According to the evaluation method,the samples cleaned under the above optimal parameters are analyzed,and The coating residual rate of the sample surface was analyzed was 0.965%,and the substrate surface did not melt.