碳纤维复合材料飞机蒙皮表面漆层激光清洗工艺研究

Research on Laser Cleaning Process of Paint Layer on Carbon Fiber Composite Aircraft Skin

激光清洗碳纤维增强树脂基复合材料(CFRP)表面涂层一直面临着形貌破坏与基体过热的风险。为了明晰工艺参数对激光清洗CFRP飞机蒙皮表面油漆的影响规律,探究CFRP表面油漆的激光清洗机理,进行了红外纳秒激光清洗CFRP表面油漆的实验。首先利用田口正交阵列开展了不同参数下的清洗实验。随后采用信噪比(S/N)与方差分析(ANOVA)探讨了激光功率、扫描速度、搭接率与重复频率等工艺参数对油漆清洗深度、表面粗糙度和清洗温度的影响。最后借助红外热成像与高速摄像技术,对激光清洗过程中的温度响应、羽流形成与消逝及漆层动态行为进行了观测。研究结果表明:搭接率是影响清洗深度、表面粗糙度和清洗温度的最主要参数,扫描速度与激光功率的影响同样显著,而重复频率的影响不显著。CFRP表面油漆的激光去除机制主要以激光热效应造成的热烧蚀、气化为主。

Objective Resin-based composite material(CFRP)surface coatings have always faced the risk of morphological damage and substrate overheating during laser cleaning.The key for solving these problems lies in the need for sufficient process experiments to establish a reliable relationship between the cleaning parameters and characteristics.Cleaning depth(H),surface roughness(S_(a)),and cleaning temperature(T)are the three most important cleaning indicators.H represents cleaning efficiency and effectiveness,S_(a) is related to the quality of re-coating,and T reflects the trend of thermal damage.Therefore,this study uses an infrared nanosecond laser to remove paint from a CFRP surface and uses laser power(P),scanning speed(V),overlap rate(η),and repetition frequency(f)as variables to study and statistically analyze the H,S_(a),and T of the samples.Infrared thermography and high-speed imaging techniques are used to observe the temperature response of the samples,the state of the plume,and the dynamic behavior of the paint layer to determine the cleaning mechanism of the paint layer.This study is expected to provide a basic reference for improving the efficiency of laser paint removal and the quality of respraying and reducing thermal damage to CFRP substrates.Methods Four controllable parameters are used:laser power,scanning speed,repetition frequency,and overlap rate.Five levels are designed under each group of parameters to form an L25 orthogonal matrix.Then,a laser cleaning experiment is conducted to obtain 25 sets of samples ranging from No.1 to No.25.After the cleaning procedure is completed,the macroscopic and microscopic morphologies of the cleaned samples are observed.At the same time,the paint cleaning depth and sample surface roughness are measured via a laser confocal microscope.Finally,the obtained experimental data are analyzed using the analysis of the variance(ANOVA)and signal to noise ratio(S/N)methods.In addition,an infrared thermographic camera is used to record the temperature response of the experimental samples during the cleaning process,and a high-speed camera is used to capture the dynamic behavior of the samples.Results and Discussions A signal-to-noise ratio analysis is performed on the cleaning depth,surface roughness,and cleaning temperature using the expected large,large,and small characteristics,respectively.The analysis results(Table 4)indicate that for the cleaning depth,the influencing factors are ranked from high to low by weight,namely,lap rate,laser power,scanning speed,and repetition frequency.For surface roughness and cleaning temperature,the influencing factors are ranked from high to low by weight,namely,lap rate,scanning speed,laser power,and repetition frequency.The ANOVA results(Table 5)indicate that for cleaning depth,roughness,and cleaning temperature,the critical probability(P′)values of the overlap rate,scanning speed,and laser power are all less than 0.05.Therefore,at a 95%confidence level,the overlap rate,scanning speed,and laser power have statistically significant effects on cleaning depth,roughness,and cleaning temperature.In contrast,the contribution rate of repetition frequency is relatively low,with a P′value greater than 0.05,making it a less important process parameter.The detection results(Fig.8)by the infrared thermal imager indicate that the laser cleaning process causes two high-temperature areas.The first is where the laser acts on the substrate.The minimum cleaning temperature in this area is 244℃,and the maximum cleaning temperature is 590.4℃.The other high-temperature region is the high-temperature plume region above the sample.The high-speed camera monitoring results(Fig.11)indicate that the paint layer undergoes drastic changes due to the action of the laser,the most obvious being the generation of bright plasma and the formation of a plume perpendicular to the sample.A large number of turbid particles are observed inside the plume.Conclusions This study focuses on the influence of process parameters on the laser cleaning of paint layer on the CFRP aircraft skin.For the cleaning depth,surface roughness,and cleaning temperature,the overlap rate is the most significant influencing parameter,with contribution rates of 50.51%,59.07%,and 69.09%,respectively.A lower overlap rate is not conducive to the uniform removal of paint,and an increase in the overlap rate will significantly increase the temperature of the substrate.Laser power and scanning speed also have a significant influence on cleaning depth,surface roughness,and cleaning temperature,whereas repetition frequency has no significant effect.The removal of paint is mainly based on the thermal erosion mechanism.During the cleaning process,the surface temperature of the paint layer rapidly increases to the decomposition temperature and the paint transforms into small particles and gases,forming a high-temperature plume above the sample.The above results will provide a reference for improving laser paint removal efficiency and respraying quality and reducing substrate thermal damage.