Study On Welding Deformation And Optimization Of Fixture Scheme For Large Scale Thin-walled Structures

Large scale thin-walled structures are widely used in the skeleton of aerospace products due to their high strength and light weight,such as rocket storage tank.In the manufacturing assembly process,the joints of the parts are usually welded.Due to the large flexibility and geometric nonlinearity of the thin-walled structure,different clamping constraints have great influence on its overall stiffness of the structure,which further affect the welding deformation.When the size of structure increases,the influence of the fixture constraint on the stiffness of the structure increases nonlinearly,which makes the relationship between the clamping constraint and the welding deformation more complicated.At present,the selection of clamping constraint lacks the theory,mainly depends on experience and repeated repair after welding to ensure accuracy.Therefore,revealing the relationship between the clamping constraint and welding deformation and realizing the optimization of the clamping scheme are of great significance to improve the welding efficiency and assembly quality of aerospace products.In this paper,by considering the edge effect of the weld zone and the constraint of the elastic zone,the accurate welding calculation model of large scale thin-walled structure under different clamping constraints is established based on the three-dimensional stress mapping method.The model is used to study the influence of clamping constraints on structural stiffness and welding deformation.Optimization of clamping scheme for structures with various configurations is conducted using FEM method and the BPSO algorithm,which provides theoretical guidance for the selection of the clamping constraints of rocket tank during the actual welding assembly process.It is very important for improving the welding quality.The main research contents are as follows:(1)Welding model of large-scale thin-walled structure considering the influence of clamping constraintsAccording to the assembly process and the typical clamping scheme,the stiffness distribution of the thin plate structure is derived based on the theory of elastic mechanics,and the influence of the clamping position and size parameters of the structure on the stiffness of the thin plate are analyzed.The stress partition mapping method is proposed to establish an accurate model on the prediction of welding deformation.Different clamping schemes are applied to local model,and the mapping relationship of stress components between the local model and the global structure is established.Finally,the welding deformation after releasing clamping is obtained.(2)Analysis of welding deformation of large-scale thin plate under different clamping schemesBased on the theory of stress partition mapping method,finite element model of large scale thin-walled structure is established,and ABAQUS software is used for numerical simulation.The effects of clamping constraints,welding parameters and part dimension on the welding deformation of large thin-walled structures are investigated by numerical simulation.The influence of constraints in different schemes on welding deformation is different.The impact of different size parameters on deformation is different.(3)Optimization design of clamping scheme for large thin-wall structure of rocket storage tankCombined with the characteristics of welding and clamping,based on the "N-2-1" positioning principle,the minimum strain energy of a single part in the state of being clamped is optimal target function.Combined with ABAQUS finite element technology and binary particle swarm optimization,the optimization model of key parts for rocket tank is established.The finite element is used to calculate the overall strain energy of a single part,and the BPSO is programmed by MATLAB to optimize the fixture constraint position of large scale thin-walled structures with different geometries.The welding deformations under clamping restraints before and after optimization for the different geometries of rocket tank are compared to verify the feasibility of the optimization scheme.