| At present,aircraft skin depainting mainly uses chemical cleaning and manual grinding methods,but there are drawbacks that are difficult to avoid,such as the use of a large number of chemical paint removers that cause environmental pollution and endanger health,manual grinding labor intensity and quality stability is difficult to ensure.Laser paint removal has become a very green,efficient and intelligent advantage of automatic cleaning technology.In foreign countries,aircraft skin laser paint removal technology has been recognized by the Federal Aviation Administration(FAA)and has been applied on a large scale.Although China has made a series of achievements in theoretical research,the key technologies are insufficiently mastered,and it will take time to realize industrialization and engineering application.The complex laser multi-parameter coupling mechanism,the difficulty of ensuring the accuracy of the path planning of the intelligent laser paint removal system,and the limited adaptability of the contour of the cleaning workpiece limit its engineering application.Among them,the geometric contour of the paint removal object and the stability of the system's conformal movement will affect the paint removal effect.Aircraft skin laser depainting involves freeform or geometric mutation areas such as slot type and rivet neighbor,which may lead to laser incidence angle and defocus constantly changing in time and space dimensions,and the energy distribution of the spot is distorted,different types of laser beams,such as gaussian and flat-top beams,will affect the effect and efficiency of paint removal.Spot energy distribution has an important impact on the material mechanism,paint removal effect and efficiency,and establishing the correlation between the microscopic damage form and the macroscopic removal effect of the material has become one of the research priorities and hotspots.Aiming at the problem that aircraft skin laser descaling involves distortion of the energy distribution of the spot caused by freeform surface,the thesis first studied the single pulse damage characteristics of the Gaussian beam.The influence of laser incidence angle and defocus amount on material damage threshold,damage crater size and microscopic morphology was studied by control variable method,and the influence law of focus-workpiece position relationship on damage characteristics was obtained,and the laser-material mechanism was revealed.Based on the single-pulse damage characteristics of the material,the energy distribution of single-pulse and multi-pulse spot was further studied.A dot-line energy distribution model was established,the correlation between the damage characteristics of the material and the simulation results was verified,and the optimal process parameter group for aircraft skin laser paint removal was obtained.With reference to the spot energy distribution model and the research results of single pulse damage characteristics,the effect and efficiency of paint removal were studied.By characterizing the microscopic morphology,removal depth,surface roughness and paint removal area calculation method per unit time,the effectiveness of the spot energy distribution simulation method was verified,and the influence of laser incidence angle and defocus amount on the paint removal effect and efficiency was obtained.The results showed that the changes in the laser angle of incidence and defocus will affect the material damage threshold,the diameter of the damage crater and the depth of action,among which the experimental values of the crater diameter and depth of action had a good correlation with the theoretical values.The influence of the focal point-workpiece position relationship in the spatial dimension on the mechanism of action of the two was elaborated,the laser paint removal process guided by the simulation results can completely remove the paint on the surface of the aluminum aloy without damaging the matrix,and the surface roughness was slightly increased.Compared with the conventional laser incidence(angle of incidence 90°,defocus amount of 0mm),reducing the laser incidence angle to 45° and increasing the defocus amount to +4 mm can improve the paint removal efficiency,which was increased by 1.7 times and 3.1 times,respectively.Aiming at the problems of spot energy distribution and different laser-material mechanisms caused by different beam types,the single pulse damage characteristics and spot energy distribution of Gaussian beams and flat-top beams were studied.The influence of beam type on the morphology,size and spot energy distribution of paint damage craters was explored by controlling variable method,the laser-material mechanism of the two beams was clarified,the dot-line spot energy distribution model of the two beams was established,and the paint removal process parameter group of Gaussian and flat-top beams was obtained.Based on the process parameter group of two beams,the laser paint removal experiment was carried out to study the influence of beam type on paint removal effect and efficiency,and the influence law of beam type on paint removal effect and efficiency was obtained.The results showed that the experimental results and simulation results of the damage crater size of the Gaussian beam and the flat-top beam were related,and the influence of the beam type on the laser-material mechanism was elaborated.When the same energy density,the diameter of the damage crater by the flat-top beam was about 15 times that of the Gaussian beam,indicating that the use of the flat-top beam can effectively increase the laser action area.The Gaussian and flat-top beams had achieved complete removal of the paint on the surface of the aluminum aloy,and the paint removal efficiency of the flat-top beam was about 37.6 times that of the Gaussian beam.The research results can provide a technical reference for the application scenario of aircraft skin laser descaling involving freeform surfaces. |
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