| The lightweight of vehicle body has become the future trends of automobile industry,which has drew great attention of most manufacturers.Since the car body is made of a large number of components,it is necessary to choose the proper materials in accordance with the specific parts,which is the core concept of lightweight.At present,the body must be taken into account the lightweight,safety,manufacturing costs and other needs,so the hybrid thin plate structures have been the main alternatives of body materials,such as steel,aluminum alloy,magnesium alloy and other lightweight materials.However,steel and aluminum alloy has great difference in material properties such as deformation coefficient,thermal expansion coefficient and thermal conductivity,which causes difficulties for assembly quality control.Therefore,studying the deformation law and control method in the welding process of steel and aluminum sheets has a practical significance.In this paper,the test of spot welding assembly based on steel and aluminum has been done using the new welding technology-Cold Metal Transfer(CMT).First,the range of the welding parameters and the optimal combination of parameters were determined by the assembly test.Then,a finite element method was used to analyze the thermal fields,stress-strain fields and deformation regions during the whole welding process.Based on these,the response surface model was established to analyze the influence of welding parameters on the deformation quantitatively.Finally,the anti-deformation method was applied to reduce the welding deformation and proved the correctness of research in this paper.The specific contents are as follows:(1)To determine the optimal parameters of welding test for aluminum/steel sheetIn this paper,the parameter range of CMT spot welding of dissimilar metal sheet was primarily determined by the bisection method,then the welding parameters were determined to perform assembly.The pretreatment of the weldment was carried out before the test,and the clamping mode of the fixture is modified to improve the welding quality.After the assembling test,the size and deformation of welded core were observed by high power microscope and a tensile test was carried out to test the intensity of weld assembly,and the welding quality was comprehensively evaluated.The welding parameters of the optimal combination of tests were set based on the optimal standard of the welding quality parameters as the benchmark.(2)To establish the finite element simulation model of aluminum/steel sheetsAccording to the results of the assembly test,the finite element simulation using welding analysis software(SYSWELD)based on the assembly test was introduced to analyze the temperature field,the stress-strain field and the deformation-displacement field.Electro-thermal and thermo-mechanical coupling are involved in the analysis.Through the analysis of the typical cloud pattern at the typical welding time,the shape and size of the welding core were contrasted,thus the correctness of the simulation analysis was verfied.(3)To establish the response surface model of CMT spot welding deformation for aluminum/steel sheetsThe response surface model was established between the spot welding deformation and the main welding parameters of the dissimilar metal sheet of aluminum steel using the least squares method.Then the deformation test of sheet metals was carried out,by adding equal deformations opposite before welding,the deformations were reduced,which indicated that the model can effectively reduce the welding distortion.The research findings of this project can not only be applied in controlling welding deformation of aluminum and steel sheet,but also in the future be expanded to other dissimilar materials such as magnesium-aluminum,magnesium-steel,titanium-steel,which are widely used in automobile body,fuselage,manufacturing industry and so on.The project has great scientific value and broad application prospects in engineering. |
PDF Full Text Request