Numerical Modelling of Processes Governing Selective Laser Sintering
Numerical Modelling of Processes Governing Selective Laser Sintering
复制标题
选择性激光烧结过程的数值模拟
DOI：
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
R. Dayal
中科院分区：
文献类型：
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作者：
R. Dayal
本研究的重点是数值研究的传热，熔化，凝固和聚结的金属颗粒所调用的激光加热应用于选择性激光烧结。选择性激光烧结是一种很有前途的增材制造技术，适用于各种需要高度定制的材料和产品。除了具有传统制造的潜在优势外，逐层合成还带来了机械性能、可重复性、材料选择有限、生产速度慢等方面的挑战。这是由于缺乏对工艺变量和基础物理学的了解。
金属粉末通过来自移动激光源的恒定或脉冲照射进行局部加热。由于在保留未熔化的固体核的颗粒的部分熔化期间的液-液接触生长，粉末被烧结。颗粒间的接触是由接触附近的高曲率梯度驱动的熔体毛细流动形成的。致密化过程伴随着固体核的相互靠近、颗粒间液颈尺寸的增大以及最终的颗粒冷却和熔体凝固。
该过程涉及粉末床中的传热、相变、质量和动量传输的多种模式，因此非常复杂。
开发了单独的热模型来描述不同长度尺度下的热传递。考虑介质的离散性，基于非连续介质理论，建立了辐射吸收及其在粉体层中传输的热模型。另一方面，颗粒尺度模型描述了温度场的演化和颗粒内的相变，同时假设周围的颗粒粉末为均匀介质。模型预测进行了比较与商业烧结系统Eosint M270上进行的实验。
最后，一个有代表性的情况下，两个颗粒接触被认为是耦合的热和流体动力学分析。采用边界元法求解液态熔体传热和流动的控制方程。耦合模型考虑了激光加热过程中的传热、相变以及由于表面张力引起的熔体流动。详细研究了工艺参数对颗粒温度演化、接触生长和致密化速率的影响。
This study is focused on numerical investigation of heat transfer, melting, solidification and coalescence of metallic particles invoked by laser heating in application to selective laser sintering. The selective laser sintering is a promising additive manufacturing technology, applicable to a wide range of materials and products demanding a high degree of customization. Besides having potential advantages over conventional manufacturing, layer-by-layer synthesis poses challenges concerning mechanical properties, repeatability, limited choice of materials, slow production rate etc. This is due to the lack of understanding of the process variables and underlying physics.
The metal powder is subjected to local heating by constant or pulsed irradiation from a moving laser source. The powder is sintered due to liquid-liquid contact growth during partial melting of particles retaining an unmelted solid core. The interparticle contacts are developed by capillary flow of the melt driven by high curvature gradients in the vicinity of the contact. The densification is accompanied by mutual approaching of solid cores, growing size of liquid neck between the particles and finally by particle cooling and melt solidification.
The process involves multiple modes of heat transfer, phase change, mass and momentum transport in powder bed and is therefore very complex.
Separate thermal models are developed to describe heat transfer at different length scales. The thermal model for radiation absorption and its transport in powder bed is based on non-continuum approach considering the discrete nature of medium. On the other hand, particle scale model describes evolution of the temperature field and phase change in a particle, while assuming surrounding granular powder as homogeneous medium. Model predictions are compared with experiments conducted on a commercial sintering system Eosint M270.
Finally a representative case of two particles in contact is considered for coupled thermal and hydrodynamic analysis. The governing equations for heat transfer and flow of liquid melt are solved using boundary element method. The coupled model accounts for heat transfer, phase change during laser heating cycle and resulting melt flow due to surface tension forces simultaneously. Detailed study of the effect of process parameters on particle temperature evolution, contact growth and densification rate is conducted and discussed.