| With the rapid development of China’s industry,the aerospace industry has developed rapidly.Skin parts are a key part of the aircraft and their service life and performance are directly determined by the quality of the skin.In the aerospace industry,the processing technology of aircraft skins usually adopts the method of stretch forming,which has the advantages of simple production and manufacturing,and small amount of springback of formed parts.However,during the stretch forming process,the skin tends to have problems such as wrinkles.,cracks,slip lines.,and rebound.Therefore,the research on the stretch forming of aircraft skin is of great significance to consolidate and enhance China’s aviation manufacturing industry.This article is from a civil aircraft project,the main content and conclusions are as follows:1.The establishment of a finite element model The skin of this paper is made of 2024 aluminum alloy,and the mold and clamp are rigid bodies.Firstly,the mold,skin and clamp CATIA model are built according to the size,and then imported into the ABAQUS software.The finite element model of the skin stretch forming is established by applying material properties,constraints,contact,friction and boundary conditions.2.Stretch trajectory design.The stretching trajectory depends on the mold,and the principle of the stretching trajectory is designed according to the shape of the mold.In order to ensure the perfect fit of the skin and the mold,the mold is applied at the imximum cladding angle to obtain the trajectory of the clamp,and the finite element simulation is performed.3.Stretch trajectory optimization.In this paper,the tension trajectory is optimized,and conpared with the three aspects of stress,equivalent plastic strain and thinning rate before optimization:the amplitude of stress change in the forming zone after optimization is basically unchanged,but the range of stress variation becomes smaller;The maximum equivalent plastic equivalent plastic strain of the shaped zone is reduced by 21.6%,the minimum equivalent plastic equivalent plastic strain is reduced by 8.7%,and the equivalent plastic strain is reduced by 47.1%.The maximum thinning rate of the shaped zone after optimization Decrease,the thickness variation is reduced by 45.8%.Therefore,after the optimization of the stretching trajectory,the skin is more uniform and the forming quality is better.4.Parameter optimization for stretch forming.It is mainly explored from skin size,friction and temperature.The skin sizes selected in this paper are 1900mm,2100mm,2300mm,2500mm.Studies have shown that as the skin size increases,the maximum tensile stress does not change,but the more uniform the stress distribution in the forming zone;the maximum equivalent plastic strain decreases and The uniformity of the equivalent plastic strain distribution in the forming zone is uniform;the smaller the maximum thinning rate,the more uniiform the thickness distribution of the forming zone.The friction coefficients selected in this paper are 0.3,0.2,0.1,and 0.05.Studies have shown that proper reduction of friction coefficient will improve the forming quality,but when the friction coefficient is 0.05,the forming quality will deteriorate,so choose the appropriate friction.The coefficient is such that it does not cause cracking or wrinkling.When the influence of temperature on tensile forming is studied,the selected temperature is 20°,135°,160°,180°.The results show that the mximum tensile stress decreases with the increase of temperature,and the maximum tensile stress in the forming zone decreases.Small,the magnitude of stress change is also reduced;the maximum equivalent plastic strain is reduced,and the maximum equivalent plastic strain in the forming zone is reduced,and the variation of equivalent plastic strain is also decreasing;the maximum thinning rate is decreasing,and forming The minimum thickness of the zone is increasing and the thickness variation is decreasing.Therefore,low temperature thermoforming can improve the forming quality of the skin. |
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