Effects of particle elongation on the binary coalescence dynamics of powder grains for Laser Sintering applications
Effects of particle elongation on the binary coalescence dynamics of powder grains for Laser Sintering applications
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DOI：
10.1016/j.powtec.2019.12.025
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发表时间：
2020-03
影响因子：
5.2
通讯作者：
S. Haeri;L. Benedetti;O. Ghita
中科院分区：
文献类型：
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作者：
S. Haeri;L. Benedetti;O. Ghita
本文研究了激光烧结（LS）过程中粒子形状和粘弹性对PEK HP3粒子二元聚并速率的影响。对PEK HP3粉末进行了表征，并用热段显微镜（HSM）测定了烧结速率。平均而言，与理论相比，颈部生长速度表现出较慢的动态。此外，在一些试验中，观察到颈部大小的初始生长延迟和/或收缩。为了理解这种行为，在类似的条件下研究了单个非球形颗粒的动力学。在表面张力的作用下，颗粒的周长逐渐缩小，最终达到球形状态，表明单个聚结单元的形状影响烧结速率。此外，利用现有的理论方法研究了粘弹性对烧结速度的影响，结果表明粘弹性可以改变结结速度，但即使在很大的底波拉数下，颈生长速度也呈严格增加的趋势。为了研究形状效应，进行了长条形椭球颗粒头部接触时的流体体积（VoF）模拟，并确定了颈部生长速率。这些分析表明，颈部尺寸的收缩可以完全由几何效应和聚结粒子的局部表面曲率引起。此外，存在一个临界纵横比，超过这个纵横比，聚并就不会完成，收缩会继续，直到聚并粒子对最终分离形成两个独立的球体。为了解释这一现象，计算了聚结颗粒表面的局部曲率，结果表明，在颈部与颗粒主体形式接触点处曲率的局部最小值被认为是导致分离的原因。
In this paper, the effects of particle shape and viscoelasticity on the binary coalescence rates of a pair of PEK HP3 particles in the Laser Sintering (LS) process are investigated in detail. PEK HP3 powder was characterised and the sintering rates were determined using Hot Stage Microscopy (HSM). On average, the neck growth rate shows a slower dynamic compared to the theory. Furthermore, in some of the trials an initial delay in growth and/or a contraction in the neck size were observed. To understand this behaviour, the dynamics of individual non-spherical particles were studied under similar conditions. The overall perimeter of the particles shrank and they gradually attained a final spherical state under the effect of surface tension forces, which indicates that the shape of individual coalescing units influences the sintering rates. In addition, the effects of viscoelasticity on the sintering rate were investigated using the available theoretical approaches and results show that viscoelasticity can change the rate of coalescence but the neck growth rate shows a strictly increasing trend even for very large Deborah numbers. To investigate the shape effects, volume-of-fluid (VoF) simulations of elongated ellipsoidal particles in head-to-head contact were performed and the neck growth rates were determined. These analyses show that the contraction of the neck size can occur purely due to geometrical effects and local surface curvatures of the coalescing particles. In addition, a critical aspect ratio exists beyond which the coalescence does not complete and the contraction continues until the pair of coalescing particles eventually separate forming two independent spheres. To explain this phenomenon, the local curvatures along the surface of coalescing particles were calculated and the results show that local minima in the curvature at the neck's contact points with the particles' main body form which is believed to drive the separation.