电子束环焊2 mm高纯铌熔池行为的数值研究

Numerical Study of Molten Pool Behavior for Electron Beam Girth Welding on 2 mm Nobium Palte

摘要:

纯铌环形焊缝是超导腔加工过程中最常见的结构之一,然而电子束环焊的熔池行为却鲜有研究。本文基于VOF算法建立了2 mm厚的高纯铌环焊过程的三维数学模型,在模型中考虑了金属蒸汽反冲压力、表面张力、重力等关键熔池驱动力,计算出了环型熔池的温度场和流场,对熔池中关键位置进行分析,并总结了纯铌环焊熔池的特点。模拟结果表明,在纯铌环形结构未熔透时,由于母材对熔池的支撑作用,匙孔波动情况与平焊类似；在环形结构焊透后,在Maragoni效应和重力的作用下,熔池表面液态金属加速扩展。此外,数值模拟与试验结果吻合良好,验证了数学模型的合理性。

Abstract:

Pure niobium girth weld seam is one of the most common structures in the process of superconducting cavity fabrication. However, the circumferential molten pool behaviour in electron beam welding (EBW) has been seldom studied. In this paper, a three-dimensional model, which is combined with the VOF model, is established to study the dynamic behaviour of circumferential molten pool in electron beam welding of 2 mm niobium plate. The influences of recoil pressure, surface tension and gravity are taken into account during the simulation process. The temperature field and flow field of the circumferential molten pool are calculated, the typical positions in the molten pool are analyzed, and the characteristics of the circumferential molten pool are summarized. During partial penetration EBW, the simulation results show that there is no obvious difference in keyhole evolution between flat welding and girth welding due to the supporting effect of the unfused base metal on the molten pool. After entering the full penetration stage, the tail of the molten pool extends rapidly under the influence of the Marangoni effect and gravity. In addition, the numerical result is in good agreement with the experimental data, which verifies the rationality of the mathematical model.