Research On Deep Drawing Of 2195 Aluminum Lithium Alloy Spherical Bottom Component At Cryogenic Temperatures

In order to meet the high reliability,long life and lightweight requirements of the new generation of carrier rockets and aircraft carrier equipment,there is an urgent need for an overall structure to replace the split tailored welded structure,and an aluminum-lithium alloy with lighter weight and higher strength to replace conventional aluminum alloys.For this reason,a kind of aluminum-lithium alloy thin-walled curved components with an overall structure appeared.The formability of aluminum-lithium alloys at room temperature is poor,and the thin-walled curved components are prone to wrinkles when integrally formed.The coexistence of wrinkles and cracks in the integral forming of such thin-walled curved components of aluminum-lithium alloys has always been an international problem that plagues the industry.In recent years,it has been discovered that aluminum-lithium alloys have a double-increasing effect that greatly increases elongation and hardening index at the same time under cryogenic temperature conditions,which is very conducive to forming such aluminum-lithium alloy thin-wall curved components.For this reason,this article takes 2195aluminum-lithium alloy sphere-bottom specimens as the research object.Through numerical simulation and process experiments,the drawing deformation law of aluminum-lithium alloy sheets under different cryogenic temperature distributions and blank holder conditions is studied,so as to formulate reasonable forming process of 2195 aluminum-lithium alloys spherical bottom component,which provides theoretical guidance and technical support for the manufacture of large and complex thin-walled aluminum-lithium alloy components in a new generation of spacecraft.Through the numerical simulation of the axisymmetric model,the drawing deformation of the spherical bottom component under different cryogenic temperature distribution and blank holder conditions was studied.Under the uniform temperature field,the cryogenic temperature deep-drawing spherical bottom component had more uniform deformation and a smaller wall thickness reduction rate than the normal-temperature deep-drawn spherical bottom component.When the unit blank holder force is 1.5MPa,the minimum wall thickness of the formed specimen at 25? is about 1.80 mm,and the minimum wall thickness of the components formed at-180? and-196? was 1.85mm;Under the condition of normal temperature in the flange area and the gradient temperature of-196? in the cavity area,the flange area had a low degree of hardening at room temperature,it was easier to flow,and the wall thickness distribution was more uniform.Under the unit blank holder force of 1.5MPa,the minimum wall thickness of the ball bottom is about 1.86 mm,which is further improved compared to the condition of-196?.Under the unit blank holder force of 1.5MPa,the minimum wall thickness of the spherical bottom component was about 1.86 mm,which was further improved compared to the condition of-196?;In a uniform low temperature field and a gradient temperature field,the specimen can withstand a larger blank holder force and has a greater tendency to resist concentrated deformation.Under a unit blank holder force of 9.5 MPa,the minimum wall thickness of the deep-formed spherical bottom part at room temperature is 1.68 mm,1.78 mm at-180?,1.79 mm at-196?,1.80 mm under gradient temperature conditions.Through the numerical simulation of a quarter of the three-dimensional model,the influence of blank holder conditions on the wrinkle behavior of the spherical bottom component under the condition of cryogenic gradient temperature was studied.Increasing the blank holder force can suppress the wrinkling behavior of the spherical bottom component.When the unit blank holder force is 1.5MPa and 3.5MPa,the components all wrinkled.When the unit blank holder force increased to 5.5MPa,there was no wrinkling at spherical bottom component,the minimum wall thickness was 0.88 mm,and the wall thickness reduction rate was 12%;The drawing bead structure can suppress wrinkling under a small blank holder force.Under the condition of the semi-circular groove drawing beads and the unit blank holder force of 2.5MPa,no wrinkling occurred,and the minimum wall thickness was 0.87 mm,square groove drawbead with smaller deformation resistance,and the unit blank holder force of2.5Mpa can also suppress wrinkles,while the degree of wall thickness reduction was further reduced,and the minimum wall thickness was 0.89 mm.An cryogenic temperature deep drawing process experimental device was established,including a cooling unit,a double-action press,a low-temperature mold,and a control and data acquisition unit.The cooling unit supplies the cooling medium for the low-temperature mold and the plate,and was regulated by the control and data acquisition unit according to the temperature signal in real time.It used mold cooling and liquid nitrogen soaking to realize the componentition cooling of the plate.When the plate meets the test temperature condition,the double action press realized edge pressing and deep drawing.Among them,the table size of the double-action press is 3500×800mm2,the maximum blanking force is 1150 KN,and the maximum drawing force is 2000 KN.The cooling unit can achieve rapid cooling of the plate and mold within 5-10 minutes,and adjust the temperature distribution of the plate according to the needs of the experiment.Through the deep drawing process experiment under normal temperature uniform temperature field and low temperature gradient temperature field,the deep drawing performance of 2195 aluminum-lithium alloy spherical bottom components under different temperature fields was obtained.Through variable blank holder force and variable drawbead structure The deep drawing comparison test revealed the suppression mechanism of the blanking conditions on the wrinkle defects.The spherical bottom component with a thickness-to-diameter ratio of 5‰ is deep-drawn at room temperature,due to poor plasticity,the limit depth is only 54.3mm;Under normal temperature of the flange area and the gradient temperature condition of-196? in the die area,the spherical bottom component formed under the square groove drawing bead and 10 t blank holder force had wrinkling phenomenon,the depth of the semi-circular groove deep drawing bead and the spherical bottom part formed under 7.5t blank holder force was 110 mm.There was no wrinkle defect during the deep drawing process.The depth was increased by 102.6% relative to normal temperature.The minimum wall thickness was 0.879 mm,the thinning rate was 12.1%;The formation mechanism of ultra-low temperature deep drawing defects of aluminum-lithium alloy sheet was revealed,and the cryogenic temperature deep drawing process window with a thickness-to-diameter ratio of 5‰ was formed.