Numerical Simulation And Experimental Study Of Aluminum Alloy Paint Layer Cleaned By Nanosecond Laser

With the increasing application of laser cleaning technology in the aerospace industry,the research on its mechanism and process has a great demand in industrial cleaning field.In this paper,theoretical analysis,numerical simulation and experiment are combined to solve the problem of efficient removal of aircraft coating.Numerical simulation and experimental study on the acrylic polyurethane coating of 2024aluminum alloy surface cleaned by nanosecond pulsed laser were carried out.The finite element model of moving nanosecond pulsed laser cleaning was established to explore the influence of different laser parameters on the temperature field of laser cleaning and the surface morphology of substrate after cleaning.The main research work is as follows:(1)Based on the interaction mechanism of laser and material,the heat conduction model of laser energy in material was studied and analyzed,and the theoretical model of laser energy density required for pulsed laser cleaning of paint layers with different thickness was further obtained.Based on laser ablation theory,the interaction mechanism between laser and paint layer was studied assisted by thermal shock and vibration,plasma shock wave and other physical processes.The theoretical removal model of laser cleaning area was established to lay a theoretical foundation for exploring the coordinated regulation of laser parameters and scanning parameters and the multi-parameter optimization model.(2)A finite element model of moving nanosecond pulsed laser cleaning of acrylic polyurethane coating on 2024 aluminum alloy surface was established by COMSOL Multiphysics software.The temperature field and displacement field of the cleaning process were visualized and analyzed to simulate the dynamic distribution of the temperature field and the morphology of micro-pits,and the influence of different laser parameters(scanning speed,spot overlap rate,laser energy density)on the temperature field distribution of laser cleaning and the width,depth and depth-width ratio of micro-pits on the substrate surface after cleaning were investigated and provide guidance for parameter selection of experiments.(3)Based on the simulation analysis results,nanosecond pulsed laser cleaning related experiments were carried out to explore the influence mechanism of different laser parameters on the 3d morphology,surface roughness and surface micro-morphology of the cleaned surface,and the following conclusions were obtained.When the surface paint layer is removed completely by pulse laser,the cleaned surface exhibited the morphology with micro-pits or groove.When the laser energy density was15~25 J/cm~2,scanning speed is 2500 mm/s,repetition frequency is 100 kHz,overlapping rate was 50%,the PVH(peak valley height)of surface is 35.534~50.234?m.After repainting,the adhesion of the paint film on the substrate surface reaches 22MPa or more with this the parameter rang,which can obtain a good surface quality conform to the requirements of the coating process.