A Study On Processing And Tools For Superplastic Forming Of Aluminum Alloy Automobile Body Panels

It has been a significant tendency due to the requirement of saving automobile weight, that aluminum alloy sheet instead of steel sheet is used for material of automobile body panels. More efforts are putting into superplastic forming of aluminum alloy automobile body panels, which can overcome some shortages, such as lower elongation and higher springback which appears during the cool stamping. At present, the aluminum alloy used for superplastic forming of automobile body panels is a special 5083 aluminum sheet for SPF which has fine grain, better superplastic behaviors and higher strength of superplastically formed part. However only few companies in the world can produce the special sheet, so there are some difficulties in its wide industrial application. AA5182 and 6016 are two commercial aluminum alloy sheets used in cool stamping of automobile body panels at present. A study on processing and tools for superplastic forming of AA5182 and 6016 aluminum alloy automobile body panels is presented in this paper. The study will help to impulse application of aluminum alloy in automobile industry. The main contents of the study are as follows.1. The superplastic tension test of AA5182 and 6016 aluminum alloy was carried out under different temperature and strain rate, u is found out that under the conditions of initial strain rate 0.0016/s and 0.016/s, 375C and 500 C, the elongation of AA51S2 is 210% and 225% respectively, the m value is 0.25 and 0.35 respectively. As to 6016, at 500C the elongation was less than 150%. The test results show that superplasticity of AA5182 is better than that of6016.2. The material microstructure of both aluminum alloys AA5182 and 6016 before and after tension test is observed in order to investigate theirmicrostructure evolution due to tension test. The results show that the grain of AA5182 keeps equiaxed before and after deformation, while that of 6016 was elongated due to tension deformation. Based on the microscopic mechanism, the deformation of AA5182 is mainly controlled by grain boundary sliding, and deformation of 601-6 is controlled by dislocation creep. This is why superplasticity of AA5182 is better than that of 6016.3. The free bulging experiments of both alloys AA5182 and 6016 are carried out in order to estimate the deformation capability under the condition of bidirectional tension. The experimental results point out that the critical thickness without fracture is 0.3mm at 375C for AA5182 aluminum alloy sheet with initial thickness 1mm, that means the thinning limit without fracture of AA5182 is 70%. The critical thickness without fracture is 0.25mm at 500C for 6016 aluminum alloy sheet with initial thickness 1mm, and the thinning limit without fracture of 6016 is 75% at 500C.4. A front fender of car is selected as the forming object. Based on the shape characters of the fender and superplastic experimental results, AA5182 aluminum sheet is selected as the blank of superplastic forming of the fender. The superplastic bulging is selected as forming processing, where forming temperature is 375C, and a plane binder is designed.5. The dies, heater and temperature controller system for superplastic bulging process of the fender are designed and manufactured by CAD/CAM. The back of the die is hollowed out and the wall thickness is made as uniform as possible. The heater includes three part: inner heater placed into die, the outer annular heater, around the die and the upper heater plate. The heater offers enough heat energy to heat the die uniformly and to prevent the fracture caused by thermal stress. The die temperature is controlled by relay of the temperature controller through a set of thermocouple in the die.6. The numerical simulation of the free bulging test is carried out. A comparison of experimental and simulated results is to validate the reliabilityof the FEM numerical simulation of superplastic bulging processing. The comparison shows that the simulated results are in agreement with the exper...