外加高频磁场下电弧快速成形过程的电磁-流体耦合数值模拟

外加电磁作用是改善电弧快速成形零件组织和性能的有效方式之一。为了揭示高频磁场对熔池传热、对流和形态的影响机理,采用有限元电磁计算和有限体积流体分析耦合的方法,建立电磁场、熔池温度场和流体流动场分析的三维模型,分析工件和熔池中高频电磁力/热的分布特征,研究高频电磁力与表面张力、电弧力以及熔滴冲击共同作用下的熔池表面动态变形,对比分析有/无外加高频磁场情况下熔池温度分布和流体流动模式上的差异,并由此预测外加高频磁场对凝固组织和熔池形态的改变。结果表明,高频电磁力驱动熔池流体在垂直焊接方向的平面内形成单漩涡旋转对流,有利于熔断枝晶细化晶粒,熔池表面形状向远离线圈一侧倾斜,熔宽增大。金相和焊道横截面测试证实了上述模拟结果。

Electromagneto-fluid Coupling Simulation of Arc Rapid Prototyping Process with External High-frequency Magnetic Field

External electromagnetic field is an effective tool to improve the microstructure and properties of the components fabricated by arc rapid prototyping. To reveal the effect mechanism of high-frequency magnetic field on the heat transfer, convection and shape of weld pool, the coupling simulation of electromagnetic calculation by finite element method and fluid analysis by finite volume method is used, 3D models are developed for the analyses of electromagnetic field, temperature field and fluid flow field. The distributions of electromagnetic force and heat in workpiece and weld pool are investigated; the dynamic deformation of weld pool surface is calculated taking into account electromagnetic force, surface tension, arc pressure and droplet impingement. The temperature and flow fields of weld pool are compared between the cases with and without external magnetic field, thereby predicting the effect of high-frequency magnetic field on the microstructure and weld pool shape. The results indicate that single-vortex rotary convection is formed in the section perpendicular to welding direction when applying high-frequency transversal magnetic field. Convection carrying high-temperature metal imposes a tangential impingement on the bottom of melt pool, which melts dendrites and leads to refined grain. The melt pool profile slopes to the far side of coil, causing larger weld bead width. The simulation results have been confirmed by metallographic examination and macrograph of bead profile.