Heat Transfer and Fluid Flow during Electron Beam Welding of 304L Stainless Steel Alloy
Heat Transfer and Fluid Flow during Electron Beam Welding of 304L Stainless Steel Alloy
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DOI：
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发表时间：
2009
期刊：
影响因子：
2.2
通讯作者：
R. Rai;T. Palmer;J. Elmer;T. DebRoy
中科院分区：
文献类型：
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作者：
R. Rai;T. Palmer;J. Elmer;T. DebRoy
建立了锁孔型电子束焊接三维传热和流体流动的数值模型，并将其应用于304L不锈钢焊缝在固定输入功率下，通过改变焦点半径得到的不同功率密度分布。该模型首先根据锁孔壁面上的能量平衡计算出锁孔几何形状，然后求解出工件内的三维温度场和流体速度。由于锁孔壁温度会影响能量平衡，进而影响锁孔穿透，因此考虑了锁孔壁温度随深度的变化。基于Prandtl混合长度假设的修正湍流模型用于计算热导率和粘度的空间可变有效值，以考虑焊接池中湍流引起的传热传质增强。与现有的文献模型不同，本文提出的模型考虑了物理过程，如锁孔壁温度随深度的变化及其对锁孔深度和沿锁孔壁流体速度计算的影响，以及三维热量和质量传递。因此，该模型可以应用于具有一系列热物理性质的材料。利用该模型研究了熔池内的流体流动模式及其对计算焊缝几何形状的影响。计算的焊缝尺寸与实测值基本吻合。Peclet数计算表明对流换热是非常重要的。通过比较有对流和无对流情况下计算的熔池几何形状，说明了对流的影响。随着峰值功率密度的增大，锁孔内的蒸汽压和壁面温度均呈上升趋势。
A numerical model for three-dimensional heat transfer and fluid flow in keyhole mode electron beam welding was developed and applied to 304L stainless steel welds made at different power density distributions achieved by varying the focal spot radius at a fixed input power. The model first calculates keyhole geometry based on energy balance on keyhole walls and then solves the three-dimensional temperature field and fluid velocities in the workpiece. Since the energy balance and, consequently, the keyhole penetration are affected by the keyhole wall temperatures, the variation of the keyhole wall temperature with depth has been considered. A modified turbulence model based on Prandtl's mixing length hypothesis was used to calculate the spatially variable effective values of thermal conductivity and viscosity to account for enhanced heat and mass transfer due to turbulence in the weld pool. Unlike models available in literature, the model proposed in this work considers the physical processes like variations of keyhole wall temperatures with depth and the resulting influence on calculation of keyhole depth and fluid velocities along the keyhole wall, and three-dimensional heat and mass transport. Thus, the model can be applied to materials with a range of thermophysical properties. The model was used to study the fluid flow patterns in the weld pool and their effects on the calculated weld geometry. The calculated weld dimensions agreed reasonably well with the measured values. Peclet number calculation showed that convective heat transfer was very significant. The influence of convection was illustrated by comparing the calculated weld pool geometries in the presence and absence of convection. The vapor pressures and wall temperatures in the keyhole increased with increase in the peak power density.