| Under the background of low carbon and energy saving,the forming of domestic sheet parts is developing towards light weight integration and energy consumption reduction in recent years.Aluminum alloy materials have been widely used in automobile,photovoltaic energy storage,rail transit and other industrial fields with the advantages of high specific strength,good corrosion resistance,and excellent formed surface quality,among which light aluminum alloy has become one of the most ideal materials in the lightweight technology of industrial equipment.However,due to the low plasticity and poor forming of light aluminum sheet,the soft die medium forming method is usually used.However,due to the use of rigid blank holder,on the one hand,when the shape difference between the blank holder area and the deformation area is large and the sheet flow resistance is increased,wrinkling and cracking defects are easy to occur,which is not conducive to improving the sheet formability.On the other hand,materials such as gas,liquid,solid particle or viscous medium are used as the force transfer medium in the soft die medium forming.The forming die structure is complex,and the sealing part is easy to be polluted.In view of the above problems,based on the forming process method of solid medium,a new forming method of sheet metal without blank holder is proposed by taking advantage of the heat sensitive characteristics of Sn Bi alloy medium,controlling its rheological behavior through temperature,changing the flow state of the blank holder area,and realizing the blank holder free forming of sheet metal.The main work contents and conclusions are as follows:(1)Taking 5052 aluminum alloy curved surface parts as the target structural parts,using low melting point alloys as the force transfer medium,the formability of lightweight aluminum plates under pressure forming with low melting point alloys was studied.The sheet forming processes under different media thicknesses,stamping rates,rheological strength,and friction were compared,and a constitutive model of the material at room temperature was established.(2)Aiming at the problems caused by mesh distortion of Lagrangian grid in the simulation,the Euler(CEL)coupling analysis method is adopted.After the test and simulation calculation,it is found that the CEL coupling method is more suitable for the test data.In addition to accurately simulating the dynamic changes of the continuous sheet metal forming process,it can also pass the simulation calculation before the test without the test,reducing the number of tests.(3)The influence of low melting point alloy assisted forming on sheet formability under different test parameters was discussed.During the pressure forming process of SnBi alloy medium,the equivalent strain near the middle of the plate is larger,the inner diameter of the upper plate increases,the contact area between Sn-Bi alloy medium and the upper part of the plate decreases,and its tangential stress also decreases;The thickness of Sn-Bi alloy medium(H)directly changes the radial stress state of the plate.The maximum stress area of the plate at H=10mm begins to increase,and the maximum stress area of the plate at H=12mm is obviously sparse.By comparing and analyzing the thickness distribution of the simulated and test pieces,it can be seen that when the plate is transiting from the support area to the medium flow area,it will be transiently thinned and cracked due to the influence of the two-way tensile stress and the tangential stress.When H=12mm and D=30mm,the thinning rate is 8%,which reduces the tangential stress of the low melting point alloy medium on the plate,thus inhibiting the fracture. |
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