Research On Welding Deformation Of Sheet Metal Based On Thermal,Electric And Mechanical Coupling

Since last century,many researches have been done on the assembly variation of automobile body parts.So far most of the assembly variation analysis models proposed only consider the manufacturing variation of parts and locating variation of fixtures as the only variation sources which will effect on assembly variation.Variation of welding process has always been ignored.However,during the assembling,welding is a complex process with high energy input and a large amount of heat release,which causes the deformation of sheet metal parts.Welding deformation may directly influence the subsequent assembling.Even more serious is its impact on product‘s quality.Hence,research on the impact of welding deformation on the global assembly variation is essential to a much more practical assembly variation analysis model.In this paper,finite element software has been used to simulate the deformation of sheet metal parts after welding.According to the FEM,this paper reached the result of the deformation caused by pre-pressing stress,temperature distribution at different moment during welding process and the residual stress and deformation after welding.On the basis of single-spot welding analysis,this paper established a multi-spot FEA model and analyzed the deformation of sheet metal parts after welding.Then,according to the data of FEA models,a local-deformation response surface model has been built.And it has been validated through spot-welding test.Finally,a global assembly variation analysis model considering local-deformation variation has been established on the basis of influence coefficient method.An assembly case has been proposed to verify the global assembly variation analysis model.Major research works are listed below:(1)Single-spot welding deformation analysis of sheet metal partsThis paper adopted sequential coupling method to simulate the complex process of welding process including thermoelectric coupling,thermal-mechanical coupling.The temperature field,stress field and displacement filed after welding have been reached through FEA.In addition,the distortion rule of sheet metal parts under different welding parameters has been concluded,which laid the foundation of multi-spot welding deformation FEA model.(2)Multi-spot welding deformation analysis of sheet metal partThermo-elastic-plastic method has been common used in simple welding structure.However it takes large amount of calculation and time to operating,which makes it not suitable for complicated welding structure.Inherent strain method can often been seen in seam-welding analysis because of its simple calculation.So,this paper used inherent strain method to analyze multi-spot welding structure on the basis of the stress and strain data concluded from single-spot welding analysis.Furthermore,deformation of multi-spot structure under different spot-arrangement form and welding sequence has been analyzed.(3)Establishment of local-deformation model of sheet metal partsWelding is a complex process with no qualitative mathematical formula to describe so far.This paper used Design Expert to fit the response surface equation of local-deformation.This equation reflects the implicit relation between local-deformation and welding parameters.Welding tests have been done to verify the equation proposed.(4)Establishment of global assembly variation analysis model So far,most of the researches on assembly variation model ignore the variation of thermal function.This paper introduced influence coefficient method and established the variation model of welding process.Finally,a global assembly variation analysis model based on common variation sources and local-deformation variation has been built.An assembly cased has been proposed to verify the model.The findings of this paper can not only be used in complicated structure welding analysis,but also optimize the existing car body assembly variation analysis model in order to control the product dimensional quality of car body.In addition,the assembly variation model proposed in this paper can be used in aircraft,ship and other sheet metal manufacture industry,which has a strong practical value and bright prospect of engineering application.