Simulation And Precision Control For The Whole Forming Process Of Aluminum Alloy Automotive Body Panels

The application of lightweight materials is an important way for energy saving and emission reduction in automobile industry.Aluminum alloy has become one of the mainly used lightweight materials for its excellent performances.However,due to the low elongation and low elasticity modulus at room temperature,the aluminum alloy body panels have many deficiencies in the forming process,such as difficult to form,easy to crack,large springback and low forming accuracy,which limits the wide application of aluminum alloy sheets in automobile industry.Based on the study of the bulging and bending springback rules,we have simulated the whole forming process of the aluminum alloy ceiling and investigated the corresponding accuracy control method.The main contents of this thesis are organized as follows:(1)Based on the results of unidirectional tensile test,anisotropy test and forming limit test,the mechanical properties of 6061-T6 aluminum alloy were obtained.Comparisons were made between different yield models and forming limit models and the Barlat89 yield criterion and the fitting limit curve were finally adopted for the prediction of the mechanical properties of 6061-T6 aluminum alloy,which laid the foundation for the subsequent simulation work using finite element method.(2)The law of 6061-T6 aluminum alloy was obtained both by simulation method and experiment method.Different sheet width and punching displacement were considered,and the stress-strain state and the elastic strain energy of the specimen were analyzed before and after the bulging springback and bending springback.The results show that the elastic strain energy release was the main cause of the springback,and the springback was positively correlated with elastic strain energy.(3)As a research object,truck cab ceilings with different materials,namely steel and aluminum alloy,were simulated by finite element method,and the stiffness performances were obtained.By comparing the performances of steel ceiling and aluminum alloy ceiling,the thickness of aluminum alloy ceiling was determined to be 1.5 mm considering higher safety margin.According to the characteristics of aluminum alloy material and ceiling's structure,the process flow of ceiling forming is determined,namely: blanking?drawing?trimming?flanging/punching.Finally,a model for whole forming process was established with all the needed parameters being determined.Based on the drawing result,the local surface and blank shape of the ceiling were optimized.(4)In order to improve the accuracy of the simulation model,the influence of stress release on forming accuracy was considered during the forming process.Moreover,springback effect was considered at the end of a certain simulation step to obtain the real shape of the part,which was then set as an input parameter for the next simulation step.Orthogonal test was conducted,and the results were used to confirm the optimal combination of the process parameters.The whole forming process and springback simulation of the aluminum alloy ceiling were then completed.Polynomial fitting method was implemented to reveal the relationship between springback and the coordinate value,and the precision transfer model for whole forming process was established.The model can reveal the transfer relationship of aluminum alloy ceiling's springback in time domain.The correction method of springback based on whole process forming was described.The optimal process parameters of flanging and punching process were obtained aiming at springback,and then the springback compensation was complemented.In summary,the whole process forming simulation method was adopted in this thesis,and the precision transfer model was established.we can draw the following conclusions: the aluminum alloy ceiling was formed without crack;the thinning rate was less than 17%;the springback was less than 1mm;the weight loss was 35.51% compared with the steel ceiling.The work presented in this paper has certain scientific significance and reference value for the application of aluminum alloy in large automobile panels.