| MIG-WAAM(wire arc additive manufacturing)is a net near forming technology based on the principle of discrete stacking,which is widely used in aerospace,oil and gas pipelines,medical devices and other fields because of its advantages of high material utilization,low cost and short R & D cycle.At present,the research on MIGWAAM technology mainly focuses on morphology control and process research.Because it is difficult to obtain the accurate real-time temperature field history and residual stress distribution rules through the experimental method,it is difficult to obtain the relationship between the process parameters and the temperature field history and performance.Therefore,with the rapid development of computer technology,finite element simulation technology is gradually applied to the research of MIG-WAAM process and can effectively solve these problems.In this thesis,the MIG-WAAM process of 316 L stainless steel is studied by combining experiment and simulation.Through the single-layer single-channel experiment,the influence of additive current and additive speed on the layer width,layer height and morphology of additive parts was analyzed.The finite element simulation models of single-layer single channel and multi-layer single channel are established by using the additive current,additive speed,corresponding layer width and layer height in the single-layer single channel foundation experiment.In this paper,the Visual Enviroment module is used to fit the double ellipsoid heat source model most suitable for MIG-WAAM simulation,and SYSWELD is used for calculation.Based on the thermoelastic plasticity method,the temperature field,stress field and deformation of single layer single channel and multi-layer single channel are simulated,and the effects of additive current,additive speed,additive direction and interlayer cooling time on the whole thermal process,stress field and deformation are analyzed based on the thermoelastic plasticity method,the temperature field,stress field and deformation of single layer single channel and multi-layer single channel are simulated,and the effects of additive current,additive speed,additive direction and interlayer cooling time on the whole thermal process,stress field and deformation are analyzed.Adjusting the additive direction and increasing the interlayer cooling time will increase the residual stress in some areas;when adding materials in the same direction,the heat at the end of the arc is much greater than that at the end of the arc,resulting in serious deformation of the end of the arc;When the interlayer cooling time is long enough,increasing the interlayer cooling time has little effect on the deformation.Finally,the accuracy of finite element simulation calculation is verified by measuring the experimental temperature process by thermocouple and measuring the residual stress by X-ray diffraction method.In the process of MIG-WAAM,the microstructure and mechanical properties of additive parts will change due to the thermal interaction between the front layer and the rear layer.Therefore,this paper analyzes the microstructure and mechanical properties of single-layer single-pass and multi-layer single-pass additive parts.It is found that the solidification mode of 316 L stainless steel WAAM is FA,and the microstructure is mainly γ austenite and a very small amount of δ Ferrite.he cooling rate is higher in the area close to the substrate,the grains are fine,and the hardness is higher.The heat accumulation of the interlayer structure is serious,the grains are coarse,and the hardness is reduced.Increasing the cooling time between the layers can refine the grains and improve the hardness.Increasing the cooling time between the layers can refine the grains and improve the hardness.Increasing the interlayer cooling time has little effect on the tensile strength,but with the increase of the interlayer cooling time,the tensile strength and elongation in the vertical direction both increase continuously. |
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