飞机蒙皮纳秒脉冲激光除漆工艺与机理研究

Technology and Mechanism of Nanosecond Pulse Laser Paint Removal of Aircraft Skin

目的寻求2024航空铝合金基体表面环氧漆层纳秒脉冲激光去除的最佳工艺参数。方法运用正交试验方法,通过改变激光功率、脉冲频率和扫描速度等参数,结合三维轮廓仪和扫描电子显微镜分析试样表面除漆后的微观形貌和残漆率。同时,为了研究激光除漆机理,采用能谱仪和拉曼光谱仪分析除漆前后环氧漆层成分的变化情况。结果工艺参数对试样除漆后残漆率的影响的主次顺序为扫描速度、激光功率、脉冲频率。当扫描速度较小时,随着激光功率的提高,激光烧蚀效应占据主导地位。在增加脉冲频率时,单脉冲激光能量密度随之减小,激光烧蚀效应减弱,除漆效果变差。实验以残漆率为优化指标,获得的最佳除漆工艺参数组合为扫描速度60 mm/s、激光功率7 W、脉冲频率20 kHz。使用此工艺参数测得试样表面的残漆率平均值为0.02。结论通过选择合适的工艺参数,采用纳秒脉冲激光可以有效去除铝合金基体表面的环氧漆层,并且不会损伤基体。除漆机理以激光烧蚀效应和热振动效应为主,漆层被激光烧蚀后形成碳化物,经过二次激光清洗,碳化物受到热振动效应作用可被基本去除,该研究可为今后飞机蒙皮除漆工艺参数的确定提供参考。

Researches on laser paint removal mainly focus on the influence of laser energy density,scanning speed,pulse frequency and scanning times on paint removal effect and substrate performance.Although the best paint removal parameters are finally determined,there are some contingencies in the selection of paint removal research parameters.Orthogonal test method is a design method to study multi-factor and multi-level.It selects some representative level combinations from the comprehensive experiment according to Galois theory,and analyzes the results to find out the optimal level combination.In this study,a fiber pulse laser with a wavelength of 1064 nm was used to remove about 35μm thick epoxy paint on the surface of 2024 aluminum alloy substrate,which is commonly used in aircraft skin.The optimum process parameters of nanosecond pulse laser removal of epoxy paint on 2024 aviation aluminum alloy substrate were scientifically analyzed and found by orthogonal test.The micro morphology and residual paint rate of the sample surface after paint removal were analyzed by changing the parameters such as laser power,pulse frequency and scanning speed,combined with three-dimensional profilometer and scanning electron microscope.At the same time,in order to study the mechanism of laser paint removal,the composition changes of epoxy paint layer before and after paint removal were analyzed by energy spectrometer and Raman spectrometer.It is found that the main order of the influence of laser paint removal process parameters on the residual paint rate after paint removal is:scanning speed,laser power and then pulse frequency.The effect of scanning speed on the residual paint rate is obvious.When the scanning speed is low,the energy accumulation effect of pulsed laser is more obvious,the temperature of paint layer increases rapidly under the action of laser,and the high-temperature ablation effect of paint layer due to laser absorption increases gradually.When the scanning speed is high,the ablation effect is weakened,but due to the different coefficient of thermal expansion between the paint layer and the substrate,thermal stress is generated between them,resulting in the paint layer bouncing off the substrate due to thermal vibration.Taking the residual paint rate as the optimization index,the best combination of paint removal process parameters is obtained as follows:scanning speed of 60 mm/s,laser power of 7 W and pulse frequency of 20 kHz.The average value of residual paint rate on the surface of the sample is 0.02.By selecting appropriate process parameters,nanosecond pulse laser can effectively remove the epoxy coating on the surface of aluminum alloy matrix without damaging the matrix.The paint removal mechanism is mainly laser ablation effect and thermal vibration effect.By comparing the Raman spectra before and after paint removal,it is found that the Raman characteristic peaks of most functional groups in the components of epoxy paint disappear,and there are only weak carbide characteristic peaks.After laser ablation,a large number of carbides are formed in the epoxy paint layer on the sample surface.After the secondary carbon removal treatment,the carbides are basically removed by the effect of laser thermal vibration.This study can provide a reference for the determination of paint removal process parameters of aircraft skin in the future.