Numerical assessment and experimental verification of the influence of the Hartmann effect in laser beam welding processes by steady magnetic fields
Numerical assessment and experimental verification of the influence of the Hartmann effect in laser beam welding processes by steady magnetic fields
复制标题
DOI：
10.1016/j.ijthermalsci.2015.10.030
复制
发表时间：
2016-03
影响因子：
4.5
通讯作者：
M. Bachmann;V. Avilov;A. Gumenyuk;M. Rethmeier
中科院分区：
文献类型：
--
作者：
M. Bachmann;V. Avilov;A. Gumenyuk;M. Rethmeier
在使用数千瓦范围内的现代高功率激光系统的深熔激光束焊接中，控制熔池中的动态是一个非常苛刻的挑战。一种在熔体中插入制动力的方法是由于外部施加的磁场而产生的所谓哈特曼效应，该方法成功地用于大规模工业应用，如铸造。因此，本研究涉及其适应激光束焊接过程的几何尺寸和时间尺度小得多。本文采用数值模拟的方法研究了稳态磁场对铝合金部分熔透焊熔体流体动力学过程的非接触缓解作用。三维传热，流体动力学，包括相变和电磁场偏微分方程求解的基础上的温度依赖性的材料性能的蒸发温度为两个不同的穿透深度的激光束。熔池表面区域的Marangoni对流和重力作用下的自然对流是熔池中的主要驱动力。在此基础上，考虑了固-液相变潜热，采用多孔介质形态的Carman-Kozeny方程对凝固过程进行了模拟，结果表明，施加恒定磁场可以改变熔体的流动模式，其变化取决于磁感应阻力和粘性阻力的比值。因此，焊缝的几何形状显着影响的发展洛伦兹力。焊接实验与16千瓦的圆盘激光器与施加的磁通量密度为500 mT左右的支持数值计算结果显示耗散效应的焊接熔池动态。
Controlling the dynamics in the weld pool is a highly demanding challenge in deep-penetration laser beam welding with modern high power laser systems in the multi kilowatt range. An approach to insert braking forces in the melt which is successfully used in large-scaled industrial applications like casting is the so-called Hartmann effect due to externally applied magnetic fields. Therefore, this study deals with its adaptation to a laser beam welding process of much smaller geometric and time scale. In this paper, the contactless mitigation of fluid dynamic processes in the melt by steady magnetic fields was investigated by numerical simulation for partial penetration welding of aluminium. Three-dimensional heat transfer, fluid dynamics including phase transition and electromagnetic field partial differential equations were solved based on temperature-dependent material properties up to evaporation temperature for two different penetration depths of the laser beam. The Marangoni convection in the surface region of the weld pool and the natural convection due to the gravitational forces were identified as main driving forces in the weld pool. Furthermore, the latent heat of solid–liquid phase transition was taken into account and the solidification was modelled by the Carman–Kozeny equation for porous medium morphology.The results show that a characteristic change of the flow pattern in the melt can be achieved by the applied steady magnetic fields depending on the ratio of magnetic induced and viscous drag. Consequently, the weld bead geometry was significantly influenced by the developing Lorentz forces. Welding experiments with a 16 kW disc laser with an applied magnetic flux density of around 500 mT support the numerical results by showing a dissipating effect on the weld pool dynamics.