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Simulation of Melt Penetration and Fluid Flow Behavior during Laser Welding.

机译：激光焊接过程中熔体渗透和流体流动行为的模拟。

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摘要

The purpose of this study is to understand deep penetration laser welding and the effect of laser welding parameters on the hourglass melt pool formation. A transient thermo-fluid-structural laser welding process is numerically computed using finite element techniques, and an evolution of the melt pool is continuously monitored for the measure of the weld shape and size with increasing a time step.;Deep penetration of melt is conducted by the use of high density laser heat energy; rapid evaporation, i.e., prompt phase change from solid to gas, is expected to generate a recoil pressure in the melt pool due to the enormous heat input source. The recoil pressure is considered as an important determinant to form a deep and narrow melt pool. Assuming that atmospheric and vaporized material pressures are balanced at the front of the laser beam, the evaporation of the melt leads to significant pressure work that drills down the melt to the opposite side of a base material when the material is heated over the boiling point.;Besides the recoil pressure, the surface tension of the molten material is also highly responsible for developing and widening the melt pool. The melt surface layer is often influenced by contractive forces of the molten material to minimize its surface free energy. Consequently, minimization of the energy has a substantial effect on the melt surface to stretch out its extent towards the not-yet-melted solid region. As a liquid droplet is often pulled into a spherical shape by the contractive force, the outer layer of the melt pool decreases the melt surface area for physical stability. As a result of minimizing the surface area and the surface free energy, the melt surface tends to have a flat layered shape. A contact angle at the liquid-solid interface therefore is assumed to be negligible in the laser welding study. Marangoni convection, the rate of heat loss from the melt to the ambient air, is induced by the temperature gradient of the melt surface layer; temperature dependent surface tension is conditionally applied on the layer when temperature rises over the melting point.;In the computation of melt dynamics, energy conservation and momentum equations are used to compute the effects of melt flow and the consequent thermo-fluid heat energy transfer. 2-dimensional governing equations from the Navier-Stokes, i.e., conservation of mass, linear momentum, and energy balance in fluid, are prepared to estimate how melt flow influences the rate of heat transfer and the distribution of temperature in a 2D domain. A mechanical analysis is followed by the thermo-fluid computation using a mechanism relevant to thermal expansion, and the stress distributions are investigated by the use of Von-Mises criterion.;The simulation results are compared with a set of experimental research which laser welds are made of low carbon steel. Assuming that melt flow has dominant influence on the formation of melt pool, a use of a different material and the properties is subject to yield similar results. The shape comparison of the welds describe that parameters relevant to any changes in the melt dynamics are of great importance on the formation of hourglass shaped melt pool during laser welding.
机译：本研究的目的是了解深熔激光焊接以及激光焊接参数对沙漏熔池形成的影响。使用有限元技术对瞬态热流体-结构激光焊接过程进行了数值计算，并随着时间步长的增加，不断监测熔池的演变，以测量焊缝形状和尺寸。通过使用高密度的激光热能；快速的蒸发，即从固体到气体的快速相变，由于巨大的热输入源，预计会在熔池中产生反冲压力。反冲压力被认为是形成一个深而窄的熔池的重要决定因素。假设大气和蒸发材料的压力在激光束的前端是平衡的，则熔体的蒸发会导致显着的压力功，当材料被加热到沸点以上时，熔体会向下钻至基础材料的另一侧。 ；除了反冲压力外，熔融材料的表面张力还对熔池的扩大和扩大起着很大的作用。熔融表面层通常受熔融材料的收缩力影响，以使其表面自由能最小化。因此，能量的最小化对熔体表面具有实质性影响，以将其范围扩展至尚未熔化的固体区域。由于液滴通常被收缩力拉成球形，因此熔池的外层会减小熔体表面积，从而提高物理稳定性。作为使表面积和表面自由能最小化的结果，熔融表面趋于具有平坦的层状形状。因此，在激光焊接研究中，可以认为在液-固界面处的接触角可忽略不计。 Marangoni对流，即从熔体到周围空气的热损失率，是由熔体表面层的温度梯度引起的；当温度超过熔点时，温度相关的表面张力将有条件地施加到该层上。在熔体动力学的计算中，能量守恒和动量方程用于计算熔体流动和随之产生的热流体热能传递的影响。准备了Navier-Stokes的二维控制方程，即质量守恒，线性动量和流体中的能量平衡，以估算熔体流动如何影响2D域中的传热速率和温度分布。进行机械分析，然后使用与热膨胀相关的机制进行热流体计算，并使用Von-Mises准则研究应力分布。;将模拟结果与一组实验研究进行比较，其中激光焊接是由低碳钢制成。假定熔体流动对熔体池的形成具有主要影响，则使用不同的材料和性能会产生相似的结果。焊缝的形状比较表明，与熔体动力学的任何变化相关的参数对于在激光焊接过程中形成沙漏形熔池非常重要。

著录项

  • 作者

    Koo, Bon Seung.;

  • 作者单位

    Lehigh University.;

  • 授予单位 Lehigh University.;
  • 学科 Engineering Chemical.;Engineering Mechanical.;Physics Optics.
  • 学位 Ph.D.
  • 年度 2013
  • 页码 140 p.
  • 总页数 140
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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