【作者】 李静；

【导师】 许燕；

【作者基本信息】 新疆大学 ， 工程硕士（专业学位）， 2022， 硕士

【摘要】 电弧增材制造(Wire Arc Additive Manufacture,WAAM,MAG)属于直接能量沉积工艺,其具有工作效率高、组件的灵活性、更清洁和更环保等优势,广泛应用于航空航天、汽车及模具等领域。然而为了制造复杂的组件,通常不可避免地会沉积悬垂结构。仰焊成形制造可以减少额外支撑,并利用熔池自身受力作用,以提高成形制造过程的效率。而在仰焊沉积过程中,熔滴-熔池流场及温度场决定了沉积层的尺寸精度。基于此,本文研究了仰焊位置沉积过程中熔滴-熔池耦合数值模拟问题,预测熔滴、熔池尺寸和形状,探讨了工艺参数及焊接位置对流场及温度场的影响规律,同时,针对熔池失稳现象,建立了热-质分配模型,为实现多方向高效率、高精度增材制造奠定了基础。首先,以仰焊熔滴与熔池的磁流体动力学为基础,通过FLUENT软件结合UDF程序宏定义对熔滴与熔池进行源项添加,且分别在气体域和金属子域对熔滴与熔池受力源项进行求解,实现了金属沉积过程熔滴-熔池耦合动态模拟。然后,探究了工艺参数对熔滴过渡的影响规律。数值分析表明,在熔滴过渡过程中,电磁力是导致熔滴缩窄的主要因素,并且熔滴的流速变化很大,仰焊180 A时最大垂直流动速度可达到0.84 m/s,平焊熔滴流速可达1.08 m/s,且随着沉积电流减小,熔滴流速降低。其次,研究了熔池中的温度场、流场动态及沉积形貌演变行为,得到沉积电流与焊接位置对其影响规律。模拟结果表明,熔滴冲击使得熔池形成“凹坑”,且在熔池流动过程会有“台阶”效应,其中,熔滴冲击是决定最大速度的最重要驱动力,仰焊180 A时熔池中心速度为0.87 m/s,平焊熔池流速可达1.09 m/s,进而决定“凹坑”是熔深的主导因素。对比发现,相同工艺参数下,仰焊位置熔池流速降低,导致熔池温度下降,沉积层余高增大,熔宽减小。同时从熔滴尺寸、过渡频率和熔池形态验证了数值模型的准确性。最后,研究了沉积制造过程中熔池失稳行为,建立了热-质分配模型,实现了逐层工艺优化,提高了悬垂零件成形精度。即考虑热输入及润湿角因素确定焊缝截面轮廓,基于多层叠加模型及工艺参数与焊缝形状的二次回归模型,逐层工艺优化并进行了实验验证,验证了热-质分配模型的正确性。更多还原

【Abstract】 Wire Arc Additive Manufacture(WAAM,MAG)is a direct energy deposition process that offers high efficiency,component flexibility,cleaner and greener environment,and is widely used in aerospace,automotive and mold applications.However,in order to manufacture complex components,it is often inevitable that overhangs will be deposited.Back-up weld forming can reduce additional support and utilize the force action of the molten pool itself to improve the efficiency of the forming manufacturing process.In the process of back-weld deposition,the droplet-molten pool flow field and temperature field determine the dimensional accuracy of the deposited layer.Based on this,this paper studies the numerical simulation problem of dropletmolten pool coupling in the deposition process of the back welding position,predicts the droplet,the size and shape of the melting pool,discusses the influence law of the convection field and temperature field of the process parameters and welding position,and at the same time,establishes the thermal-mass distribution model for the instability of the melt pool,laying the foundation for multi-directional high-efficiency and highprecision additive manufacturing.Firstly,based on the magnetohydrohydrodynamics of the back welding droplet and the pool,the source terms of the droplets and the pool are added by the FLUENT software combined with the macro definition of the UDF program,and the droplets and the source terms of the pool force are solved in the gas domain and the metal subfield,respectively,and the dynamic simulation of the droplet-pool coupling of the metal deposition process is realized.Then,the influence of process parameters on the transition of droplets was explored.Numerical analysis shows that in the transition process of droplets,electromagnetic force is the main factor causing the narrowing of droplets,and the flow rate of the droplets varies greatly,the maximum vertical flow rate can reach 0.84 m/s when soldering 180 A,the flow rate of flat welding droplets can reach 1.08 m/s,and as the deposition current decreases,the droplet flow rate decreases.Secondly,the temperature field,flow field dynamics and sediment morphology evolution behavior in the molten pool were studied,and the influence of the deposition current and welding position on it was obtained.Simulation results show that the droplet impact makes the molten pool form a "Pit",and there will be a "Step" effect in the flow process of the molten pool,of which the droplet impact is the most important driving force to determine the maximum speed,the center speed of the molten pool is0.87 m/s when the back welding is 180 A,and the flow rate of the flat welding pool can reach 1.09 m/s,which determines that the "Pit" is the dominant factor in the depth of melt.In contrast,it is found that under the same process parameters,the flow rate of the molten pool in the back welding position is reduced,resulting in a decrease in the temperature of the molten pool,an increase in the residual height of the deposition layer,and a decrease in the melting width.At the same time,the accuracy of the numerical model is verified from the droplet size,transition frequency and molten pool morphology.Finally,the instability behavior of the molten pool during the deposition manufacturing process is studied,the thermal-mass distribution model is established,the layer-by-layer process optimization is realized,and the forming accuracy of the overhanging parts is improved.That is,considering the heat input and wetting angle factors to determine the weld cross-section profile,based on the multi-layer overlay model and the quadratic regression model of the process parameters and the weld shape,the layer-by-layer process optimization and experimental verification were carried out,and the correctness of the heat-mass distribution model was verified.更多还原