Research On Seam Welding Deformation Of Al/steel Mixed Assembled Sheet Based On CMT

With the rise of environment protection awareness,the strict emission regulation and fierce competition of car manufacturers have promoted the technology more energy-saving.As an important measure to save the energy,car body lightweight has been paid great attention of main car manufacturers.The mixed structure of dissimilar material joining is a crucial means to realize body lightweight in the future.The car body is assembled by the mixed materials sheet like metal,aluminium and magnesium.This kind of car body can not only reduce the weight of car,but also absorb more crash energy,thus improve the safety performance.However,the multi-material structure brings new challenges for joint technology.There is great difference in material properties between steel and aluminum alloy,such as thermal expansion and deformation coefficient and thermal conductivity.It makes assembly quality control quite complicated.Therefore,it is of great significance to study the welding deformation of the joint of steel and aluminum sheet.The paper applied the new welding method called Cold Metal Transfer(CMT)and studied the Al/steel sheet welding deformation systematically.In the beginning,the welding parameters were determined through a group of welding tests.Then,the process of Al/steel sheet welding was simulated with the finite element software SYSWELD.The temperature field,stress and strain field were analyzed.The thermal temperature curve and the evolution of the welding stress could be gotten.On the above basis,the BP network was constructed,it can be used to predict the deformation of welding.Finally,the welding deformation was reduced with the anti-deformation method.And the result proved the effectiveness of welding control.The detailed contents are as follows:(1)To initialize the optimal parameters of aluminum/steel sheet weldingThe parameters were determined by a host of tests.The test bed and fixture have been designed before the test.The weldment was pre-processed.Through the test,it was observed that the impact of welding parameters on the welding bead and deformation.The welding parameters were set according to the optimal standard.In order to evaluate the strength of the Al/steel welding joint,a tensile test was carried out.(2)To establish the model of Al/steel sheet welding with finite element methodBased on the result of assembly test,the welding process is analyzed by SYSWELD.The double ellipsoid heat source model was chosen to complete the simulation.The temperature field,stress and strain field and deformation field were analyzed.Through the analysis of typical moments of welding process,the feature of the Al/steel sheet welding could be found out.(3)To construct the response surface model for Al/steel sheet welding deformationBP neural network was applied to predict the deformation of Al/sheet.The deformation test of sheet metal was carried out,by adding equal amount of deformation in the opposite direction,the deformation could be reduced.It implied that the model is effective to control the welding deformation.The conclusions of this project can not only be applied in the improvement of welding quality of aluminum and steel sheet,but also be valuable to other new dissimilar materials.The prospect of this project is rather broad in the engineering field.