Avrampos Panagiotis, Vosniakos George-Christopher
Manufacturing Technology Laboratory, School of Mechanical Engineering, National Technical University of Athens, Heroon Polytehniou 9, 15773 Athens, Greece.
Materials (Basel). 2024 Jul 9;17(14):3382. doi: 10.3390/ma17143382.
Powder deposition of even and homogeneous layers is a major aspect of every powder bed fusion process. Powder sieving is commonly performed to powder batches outside of the PBF machine, prior to the part manufacturing stage. In this work, sieving is examined as a method of powder deposition rather than a method to solely filter out agglomerates and oversized particles. Initially, a DEM powder model that has been validated experimentally is implemented, and the sieving process is modelled. The sieving process is optimized in order to maximize mass flow, duration of its linear stage and total mass sieved during linearity. For this, a Taguchi design of experiments with subsequent analysis of variance is deployed, proving that the larger the initial powder loaded in the sieve, the larger the sieve stimulation necessary, both in terms of oscillating frequency and amplitude. The sieve's aperture shape is also evaluated, proving that the more sides the canonical polygon has, the less the mass flow per aperture for the same maximum passing particle size. Then, the quality of the layer produced via controlled sieving is examined via certain layer quality criteria, such as the surface roughness, layer thickness deviation, surface coverage ratio and packing density. The findings prove that controlled sieving can outperform powder deposition via a non-vibrated doctor blade recoater, both in terms of layer surface quality and duration of layer deposition, as proven by surface skewness and kurtosis evaluation.
均匀层的粉末沉积是每个粉末床熔融工艺的一个主要方面。在零件制造阶段之前，通常会在粉末床熔融（PBF）机器外部对粉末批次进行筛分。在这项工作中，筛分被视为一种粉末沉积方法，而不仅仅是一种滤除团聚物和超大颗粒的方法。首先，实施了一个已通过实验验证的离散单元法（DEM）粉末模型，并对筛分过程进行了建模。为了使质量流量、线性阶段持续时间以及线性阶段筛分的总质量最大化，对筛分过程进行了优化。为此，采用了田口实验设计并随后进行方差分析，结果表明，筛网中初始装载的粉末越多，就需要越大的筛网激励，这在振荡频率和振幅方面均是如此。还对筛网的孔径形状进行了评估，结果表明，对于相同的最大通过粒径，正多边形的边数越多，每个孔径的质量流量就越少。然后，通过某些层质量标准，如表面粗糙度、层厚偏差、表面覆盖率和堆积密度，来检验通过控制筛分产生的层的质量。研究结果证明，通过表面偏度和峰度评估可知，在层表面质量和层沉积持续时间方面，控制筛分均优于通过非振动刮刀再涂器进行的粉末沉积。
