Research On Integrated Process Of Hot Rapid Gas Forming Of 2A12 Aluminum Alloy Sheet

In order to meet the demand of lightweight in automobile field,aluminum alloy and other lightweight alloys have been widely used in automobile.The hot gas forming of metal sheet has been developed greatly to solve these problems that aluminum alloy has poor forming performance and is easy to crack during forming at room temperature.However,because the die is filled with high pressure and room temperature gas,the temperature distribution of metal sheet is not uneven and the forming pressure of metal sheet is unstable,which can't meet the requirements of dimensional accuracy for complex parts.Therefore,on the basis of this integrated process,a hot rapid gas forming technique of metal sheet is put forward.The principle of this technique is to fill the upper and lower cavity of the hot die and sheet with gas with equal pressure,and the gas in the lower mold cavity is released rapidly to form instantaneous high pressure,and then the sheet forming is completed under the high pressure.The process can avoid the problems of uneven temperature and unstable gas pressure when sheet is forming,and can greatly improve the pressure rate of sheet forming,so that the sheet deformation is more uniform.In this paper,2A12 aluminum alloy sheet is taken as the research object,Through the method of simulation and experiment,the advantages and disadvantages of traditional sheet hot gas forming and sheet hot rapid gas forming are compared,and the forming regulation of the sheet hot rapid gas forming is explored,which is to provide theoretical guidance and technical support for the practical application of the hot rapid gas forming integrated process.Firstly,the influence of temperature and strain rate on the high temperature mechanical properties of 2A12-O aluminum alloy sheet was studied by high temperature uniaxial tensile test.The stress-strain relationship of 2A12-O aluminum alloy sheet with temperature in the range of 375?⁴25?and strain rate in the range of 0.001s^-10.1s^-1 was determined.and the high temperature constitutive equation was established.It is found that with strain rate increasing,the limit stress and strain hardening index n value of the material will increase.With the temperature increasing,the limit stress and n value of the material will decrease,but the strain rate sensitivity index m value will increase.Besides,based on the mechanics analysis of free bugling and die filled process,it is established that equivalent stress and strain of the center of free bugling part are related to bugling height and wall thickness,and the relationship is founded between gas pressure and limit filling fillet during die filled.Secondly,through the numerical simulation of free bugling,the effects of pressure rate and temperature on the stress,strain and wall thickness distribution of the bugling parts are obtained.With the pressure increasing at the same dome height,the overall equivalent stress will increase,the equivalent strain in the dome apex will decrease,and the wall thickness distribution is more uniform.With temperature improving,the overall equivalent stress and the equivalent strain in the dome apex will decrease,and the wall thickness distribution is more uniform.Through the numerical simulation of die filled,we obtain not only the influence of pressure rate and temperature on the wall thickness distribution of the part but also the influence of forming pressure and temperature on the capacity of a sheet filling the die during rapid gas forming.Increasing the pressure rate and the temperature is beneficial to improve the uniformity of the wall thickness distribution of the forming parts.With the forming pressure and temperature increasing during rapid gas forming,the capacity of filling the die instantaneously is improved.When the temperature is 475?,the forming pressure is12.0MPa,and the die depth is 10 mm and 20 mm respectively,the degree of sheet instantaneous filling die is as high as 86%and 90%.Finally,a special device for the sheet hot rapid gas forming has been established,which can meet the research of the forming regulation of the process.The heating and controllable temperature of the device can reach 550?.The controlled pressure of the gas pressure control system can reach 16MPa and the control precision is±0.1MPa.The gas can be sealed and input reliably.The cooling device can effectively prevent the heat transfer of the die to the press.The die can guarantee the air pressure seal to meet the requirements of different depth forming experiments.Through the experimental study of die filled,the ability of instantaneous filling die of sheet with different forming pressures and temperatures is obtained.The difference between the numerical simulation results and the experimental results is within 5%,and the numerical simulation results are very close to the experimental results.The experimental results show that the higher the forming pressure in the die and the temperature are,the stronger the ability of the instantaneous filling die of sheet is.When the temperature is 475?,the forming pressure is 12.0MPa,and the depth of the die is 10mm,the degree of instantaneous filling die has reached 91%.