Study On Threshold Of Continuous-Nanosecond Combination Laser Layered Paint Removal

Laser cleaning technology is a relatively new cleaning technology developed rapidly in recent years.It can be applied to the removal of various surface pollutants.Compared with the traditional chemical cleaning method,laser cleaning does not require cleaning medium,and only produces a small amount of dust in the cleaning process.Therefore,it is almost non-polluting to the environment,and laser cleaning does not damage the substrate.With its many advantages,laser cleaning technology is gradually replacing the traditional cleaning technology in many fields.Laser cleaning technology not only opens up a new development of laser technology in the industrial field,but also shows a broader application prospect in many fields with its advantages of non-destructive,environmental protection and high efficiency.Therefore,researchers in China and abroad have carried out a lot of research on laser cleaning technology.At present,in the research at home and abroad,the laser used for laser cleaning is mostly continuous laser and nanosecond pulse laser,and the cleaning technology is more mature.In recent years,the emerging combined laser has more advantages in laser efficiency and effect,which brings new ideas to laser cleaning technology.Especially in the laser paint removal of high-speed rail,automobile and other car bodies,the paint layer is generally multi-layer structure.The physical and chemical properties of each paint layer are different,the thickness is different,and the distribution is not uniform.In the laser paint removal,it is difficult to achieve the ideal paint removal effect by using a single laser system,and the combined laser can be more easily realized by controlling the laser parameters,improving the efficiency of paint removal and improving the paint removal effect.Therefore,it is of great reference value and practical significance to study the threshold value of continuous-nanosecond laser delamination paint removal.The research results will provide theoretical basis for the development of laser cleaning.In this paper,continuous laser and continuous-nanosecond combined laser were used to study the cleaning threshold of the paint layer on the surface of the car body.Taking different types and thicknesses of paint layers on the surface of 7075 aluminum alloy substrate as cleaning objects,the temperature variation law,the removal depth variation law,the cleaning threshold and the mechanism of laser de-painting were studied.Through the research in this paper,the theoretical model of combined laser layered paint removal was established.By combining simulation and experiment,the temperature change,removal depth change and laser paint removal effect of continuous laser and continuous-nanosecond combined laser in the process of laser paint removal were analyzed,and the laser cleaning thresholds of different systems were given.According to the change characteristics of cleaning thresholds,the differences in the mechanism of laser paint removal were analyzed.The research results of this paper will provide important theoretical basis for laser cleaning in practical application in laser system and parameter selection.Firstly,the corresponding temperature rise and ablation vibration models are established by analyzing the physical process of laser-coating interaction.A two-dimensional axisymmetric geometric model was established according to the matrix and the parameters of each paint layer.The numerical simulation was carried out by using the finite element simulation software.The temperature change and removal depth change of laser paint removal were obtained by simulation calculation.Through the simulation of the laser paint removal process,the laser parameters such as the cleaning threshold of each paint layer and the matrix damage threshold were obtained.Secondly,the paint removal experiments of continuous laser and continuous-nanosecond combined laser were carried out respectively.A comparative study was carried out on the target materials of alkyd paint,epoxy varnish and epoxy primer on 7075aluminum alloy substrates.The effects of continuous laser,combined laser total energy injection and other factors on the temperature,removal depth and removal effect of different coatings were mainly analyzed.The experimental results showed that the optimal cleaning threshold for single-layer paint target removal by continuous laser was 177.74W/mm~2,the optimal cleaning threshold for double-layer paint target removal was 192.90W/mm~2,and the optimal cleaning threshold for three-layer paint target removal was 147.44W/mm~2.The optimal cleaning threshold for the removal of single-layer paint target by combined laser was determined to be 74.92 J/mm~2,the optimal cleaning threshold for the removal of double-layer structure target was 104.69 J/mm~2,and the optimal cleaning threshold for the removal of three-layer paint target was 60.07 J/mm~2.In the experiment,it was found for the first time that the optimal cleaning threshold of the thick three-layer coating was lower than that of the thin double-layer coating target,and the mechanism of laser paint removal was analyzed.Finally,the paint removal thresholds of continuous laser and continuous-nanosecond combined laser were compared,and the difference of laser cleaning thresholds was analyzed.Combined with the simulation and experimental results,the mechanism of laser paint removal was revealed.