Research On Stress And Strain Control Method Of Thin-walled Structure Based On Arc Additive Manufacturin

Wire and arc additive manufacturing(WAAM)is a process in which an electric arc is used as a heat source to melt a metal wire and follow a set forming path on a substrate,stacking it in layers to form the part.However,the molten pool undergoes rapid heating and cooling solidification,resulting in large residual stresses in the formed part.Therefore,the method of plasma arc preheating of the substrate is proposed to prechange the stress distribution of the substrate,reduce the cooling rate and finally achieve the purpose of reducing the residual stress of the formed parts and improving the mechanical properties,providing a new method and a certain theoretical basis for the stress-strain control of thin-walled structures.COMSOL Multiphysics software was used to establish a single-channel multilayer three-dimensional thermal-force coupling model,and combined with infrared thermal imaging and VIC-3D strain measurement system to analyse the temperature field and stress-strain distribution characteristics during the arc additive manufacturing process.The distribution is characterised by a "semi-ellipsoidal" shape in the opposite direction of the arc movement and gradually spreads to the edge of the substrate.The stress distribution inside the part is symmetrical with a "multi-peak" distribution.A finite element model of the temperature field during single-pass multilayer deposition with arc preheating was developed to analyse the temperature field distribution during the additive process with different preheating spacing.The simulation results show that the temperature of the molten pool is up to 2000 K during the arc preheating process,and the temperature is transferred from the high temperature region to the low temperature region during the cooling process.Preheating prior to the add-on adds heat input to the overall system,but it was found that the preheating temperature has a small effect on the heat build-up in the weld.The results of the temperature field calculations were used as initial values to calculate the stresses during the additive manufacturing process and to analyse the stress distribution and evolution of the molten cladding layer after preheating.The residual stresses inside the formed part determine the final deformation of the part,and the analysis of the residual stresses in the formed part with and without preheating shows that the compressive stresses generated in the heat affected zone can reduce the deformation of the substrate by 44%,and the longitudinal and transverse residual stresses inside the formed part can be reduced by up to 56%.The longitudinal residual stresses are 43% higher than the transverse residual stresses in the formed part obtained by direct deposition,and the anisotropy of the part is improved after preheating.Finally,the tensile strength of the formed parts was compared and analysed,and the histomorphology and microscopic morphology of the parts were observed using optical microscopy and scanning electron microscopy to analyse the macroscopic morphology and microscopic defects of the thin-walled parts at different preheating temperatures.The data analysis method PCA-TOPSIS was used to optimise the process parameters for the optimum preheating conditions based on the geometry of the thinwalled part.