Forming Law For Cryogenic Deep Drawing Of 2219 Aluminum Alloy Spherical Shell

With the development of new generation aerospace equipment to lightweight and high reliability,there is an urgent need for a kind of aluminum alloy spherical shell with large size and ultra-thin wall thickness.It is very easy to have the defects of wrinkling and cracking when forming this kind of spherical shell at room temperature.Aiming at this problem,this paper puts forward the cryogenic drawing technology of aluminum alloy.The aluminum alloy sheet is cooled to the critical temperature with double increasing effect by cryogenic medium,and the thin-walled shell is formed by die.It has a series of technical advantages,such as high forming limit and easy control of microstructure and properties.Taking 2219 aluminum alloy spherical shell as the object,through numerical simulation and process experiment methods,this paper studies the deep drawing deformation behavior and defect form of aluminum alloy under different temperature distribution,obtains the cryogenic forming process window of spherical shell,and provides theoretical guidance and technical support for the integral forming of large-size thin-walled shell.The drawing performance of 2219-w sheet in cryogenic temperature field is obtained through the limit drawing ratio experiment of flat bottom cylindrical parts.The drawing performance of the plate is significantly improved in the cryogenic temperature field,and the limit drawing ratio is increased from 1.8 to 2.2.Through numerical simulation,the influence of thickness diameter ratio on the wrinkling trend and deformation capacity of spherical shell is obtained.The smaller the thickness diameter ratio of spherical shell,the smaller the critical wrinkling stress and the greater the wrinkling trend.At the same time,the smaller the thickness diameter ratio of spherical shell,the greater the deformation and the greater the cracking trend.The wrinkling mechanism and uniform deformation coordination mechanism of cryogenic deep drawing are revealed.In cryogenic deep drawing,the strength of flange area is affected by temperature.The lower the strength of the flange area of the specimen,the greater the wrinkling trend of the suspended area,the smaller the deformation and the more uniform the wall thickness distribution.The influence of blank holder force on the wrinkling behavior and deformation capacity of spherical shell is obtained.The wrinkling in the suspended area of spherical shell is related to the circumferential compressive stress.Increasing the blank holder force can reduce the circumferential compressive stress and inhibit the wrinkling in the suspended area of the specimen.However,the larger the blank holder force,the greater the deformation of the specimen and the greater the cracking trend.Therefore,the appropriate temperature distribution should be selected according to the thickness diameter ratio of the component.When forming spherical shells with large thickness diameter ratio,the defects are mainly cracking,and the temperature distribution with low strength in the corresponding flange area should be adopted;When forming a spherical shell with small thickness diameter ratio,the wrinkling trend is large.To ensure that the wrinkling can be controlled under the deformation conditions,the temperature distribution with high strength in the corresponding flange area should be adopted.Through the cryogenic deep drawing test,the evolution law of cryogenic forming defects is clarified,and cryogenic drawing process window is established.The lower the strength of the flange area of the cryogenic specimen,the greater the wrinkling trend of the suspended area;The lower the elongation of the flange area,the greater the cracking trend of the suspended area of the specimen.With the decrease of temperature,the strength and elongation of the material first decrease and then increase.The normal temperature in the flange area and the ultra-low temperature temperature field with the temperature lower than-160 ℃ in the flange area are the best process(temperature)window for forming spherical shells with small thickness diameter ratio.