| Wire Arc Additive Manufacturing（WAAM）technology,with many advantages,such as low equipment cost,high material utilization,suitable for forming large-size components and so on,is widely used in aerospace and other technology fields.However,in the WAAM process,excessive heat accumulation will be produced for the complex thermal process,with the formation of large temperature gradient and the increase of high-temperature oxidation area,it is easy to lead to the emergence of molding defects,which restricts the further development of the technology.Therefore,it is of great significance to study the process scheme to reduce heat accumulation and prevent high-temperature oxidation in the WAAM process.In this paper,taking Ti-6Al-4V titanium alloy as the filling material and WAAM technology based on Gas Tungsten Arc Welding（GTAW）as an example,the distribution of shielding gas in WAAM process is simulated,the influence of shielding gas on heat dissipation of thin-walled parts is analyzed,and the heat dissipation value is optimized;Then the finite element model is constructed and the distribution law of temperature field is analyzed.The process schemes of reducing heat accumulation and preventing high-temperature oxidation are put forward respectively.The specific research contents are as follows:（1）The Fluent software is used to simulate the distribution of shielding gas in the WAAM process.It is found that with the increase of shielding gas flow rate,the coverage range and concentration of shielding gas around the thin wall also increase.When using the same gas flow rate,extending the sidewall of the shielding gas cover downward can effectively increase the range and concentration of shielding gas.In this study.Aiming at the shortcomings of the traditional protection device of the shielding gas cover in protecting parts from high-temperature oxidation,the solution of extending the shielding gas cover sidewall downward is proposed to improve the protective effect of the drag hood on the thin wall and reduce the influence of high-temperature oxidation on the thin wall.（2）By analyzing the simulation results of shielding gas distribution,to confirm the heat dissipation scheme in the WAAM process.The heat thin-wall dissipation in the shielding gas cover part should be treated by natural convection,and the thin-wall heat dissipation at the nozzle should be treated by forced convection according to the thermal convection coefficient of 21.2824 W/（m~2·K）.Using the optimized heat dissipation parameters to simulate the temperature field in the manufacturing process is beneficial to improving the computational accuracy of the model.（3）By using the validated finite element model,numerical simulations were carried out on the swing deposition process of the filling material and the interlayer dwelling method,to analyze the influence of different factors on the temperature field and optimize the shielding gas parameters through temperature data.The results show that the swing process and the interlayer temperature at 200°C can effectively reduce the heat accumulation.Besides,the swing process can improve the surface planeness of the parts and reduce the post gas flow duration.The simulation results have guiding significance for the adjustment of process parameters to reduce material heat accumulation and prevent high-temperature oxidation in the actual WAAM process,and provide a beneficial reference for the process of manufacturing high-quality components by arc additive manufacturing. |
