Research On Cryogenic Temperature Deep Forming Process Of 2024 Aluminum Alloy Thin Wall Parts For Aircraft Doors

Thin-wall components of cabin categories are important components of aircraft boarding doors and service doors.They need to be opened and closed frequently when personnel or cargo pass through the aircraft operation process.Therefore,they have high requirements for airtightness,rigidity,reliability and interchangeability.The thin-wall member of the cabin category has a high overall drawing height and a stepped structure,and it is easy to crack and wrinkle in the bottom fillet and local features during forming at room temperature,making the overall forming difficult.In order to solve the above problems,a new idea of forming 2024 aluminum alloy cabin door thin-walled parts at ultra-low temperature was proposed by taking advantage of the advantages of ultralow temperature deformation to enhance the work hardening ability of aluminum alloy materials and improve the uniformity of deformation and formability of materials.The main research work and achievements are as follows:(1)The forming properties and microstructure evolution of 2024 aluminum alloy under ultra-low temperature and complex stress conditions were studied.The mechanism of plastic enhancement under ultra-low temperature and the variation of strain,thickness and hardness of dilated specimen at different temperatures were obtained.The results show that the strength and toughness of the deformed materials increase significantly at ultra-low temperature(-196℃),the maximum thinning rate of the samples decreases,and the hardness increases to some extent.In addition,the ultralow temperature deformed samples show a stronger <111>orientation along the rolling direction,and a stronger <100> orientation at room temperature.Moreover,the proportion of small Angle grain boundary of the ultralow temperature deformed samples is higher,and the grain structure of the samples after heat treatment is finer.(2)The numerical model of 2024 aluminum alloy cabin door thinwalled parts deep drawing was established,and the numerical simulation of ultra-low temperature drawing process was carried out.The influence of different process parameters on the quality of components was studied,and the cracking and springback conditions of components were predicted at different temperatures.The optimum process parameters of ultra-low temperature deep drawing for thin wall parts of hatch doors were obtained.The results show that the process parameters,such as temperature and blank holder force,have important effects on the forming quality of components.With the decrease of temperature,the component thinning rate gradually decreases,and the cracking does not occur when the temperature is below-150℃.In addition,the wrinkling of the member decreases with the increase of the blank holder force,but the thinning rate of the member increases when the blank holder force is too large.The optimal parameters of numerical simulation are as follows: round corner R10 of die,temperature-196℃,friction coefficient between blank and die,blank holder ring and punch are 0.15 and 0.1,and the pressure per unit area of flange area of member is between 0.467Mpa-0.510Mpa(corresponding to the size of blank holder force 55-60 k N).(3)Design and manufacture of ultra-low temperature deep drawing die tooling and ultra-low temperature refrigeration system for thin-walled cabin door parts,and carry out the ultra-low temperature deep drawing process experiment of 2024 aluminum alloy cabin door thin-walled parts,find out the cause of wrinkling,cracking and other defects in the forming process and control means,and achieve high-performance overall forming of thin-walled cabin door parts.It provides a new idea for highperformance manufacturing of thin wall parts of hatch category.The test results show that the 2024 aluminum alloy door thin-wall forming can be realized at-196℃,and the maximum thinning rate and hardness of some parts at-196℃ increase by 12.33% and 15.53%,respectively,compared with room temperature.The thickness distribution of ultra-low temperature forming components is more uniform,and the thinning rate of components basically stays below 13.5%,which meets the requirements of component production.