scholarly journals Crystallographic tomography and molecular modelling of structured organic polycrystalline powders

CrystEngComm ◽  
2021 ◽  
Author(s):  
Parmesh Gajjar ◽  
Thai T. H. Nguyen ◽  
Jun Sun ◽  
Ioanna D. Styliari ◽  
Hrishikesh Bale ◽  
...  
Keyword(s):  
Molecular Modelling ◽  
Powder Bed ◽  
Powder Packing ◽  
Polycrystalline Powder

Novel combination of crystallographic tomography and molecular modelling is used to examine the powder packing behaviour and crystal interactions for an organic polycrystalline powder bed.

scholarly journals Analytical Modeling of In-Process Temperature in Powder Bed Additive Manufacturing Considering Laser Power Absorption, Latent Heat, Scanning Strategy, and Powder Packing

Materials ◽  
2019 ◽  
Vol 12 (5) ◽  
pp. 808 ◽  
Author(s):  
Jinqiang Ning ◽  
Daniel Sievers ◽  
Hamid Garmestani ◽  
Steven Liang
Keyword(s):  
Additive Manufacturing ◽  
Computational Efficiency ◽  
Molten Pool ◽  
Laser Power ◽  
Analytical Modeling ◽  
Single Track ◽  
Scanning Strategy ◽  
Powder Bed ◽  
Powder Packing ◽  
High Computational Efficiency

Temperature distribution gradient in metal powder bed additive manufacturing (MPBAM) directly controls the mechanical properties and dimensional accuracy of the build part. Experimental approach and numerical modeling approach for temperature in MPBAM are limited by the restricted accessibility and high computational cost, respectively. Analytical models were reported with high computational efficiency, but the developed models employed a moving coordinate and semi-infinite medium assumption, which neglected the part dimensions, and thus reduced their usefulness in real applications. This paper investigates the in-process temperature in MPBAM through analytical modeling using a stationary coordinate with an origin at the part boundary (absolute coordinate). Analytical solutions are developed for temperature prediction of single-track scan and multi-track scans considering scanning strategy. Inconel 625 is chosen to test the proposed model. Laser power absorption is inversely identified with the prediction of molten pool dimensions. Latent heat is considered using the heat integration method. The molten pool evolution is investigated with respect to scanning time. The stabilized temperatures in the single-track scan and bidirectional scans are predicted under various process conditions. Close agreements are observed upon validation to the experimental values in the literature. Furthermore, a positive relationship between molten pool dimensions and powder packing porosity was observed through sensitivity analysis. With benefits of the absolute coordinate, and high computational efficiency, the presented model can predict the temperature for a dimensional part during MPBAM, which can be used to further investigate residual stress and distortion in real applications.

On Characterizing Uncertainty Sources in Laser Powder Bed Fusion Additive Manufacturing Models

2019 ◽  
Author(s):  
Tesfaye Moges ◽  
Paul Witherell ◽  
Gaurav Ameta
Keyword(s):  
Additive Manufacturing ◽  
Computational Models ◽  
Input Parameter ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Powder Bed ◽  
Flow Models ◽  
Uncertainty Sources ◽  
Powder Packing ◽  
Ontology Language

Abstract Tremendous effort has been dedicated to computational models and simulations of Additive Manufacturing (AM) processes to better understand process complexities and better realize high-quality parts. However, understanding whether a model is an acceptable representation for a given scenario is a difficult proposition. With metals, the laser powder bed fusion (L-PBF) process involves complex physical phenomena such as powder packing, heat transfer, phase transformation, and fluid flow. Models based on these phenomena will possess different degrees of fidelity as they often rely on assumptions that may neglect or simplify process physics, resulting in uncertainty in their prediction accuracy. Predictive uncertainty and its characterization can vary greatly between models. This paper characterizes sources of L-PBF model uncertainty, including those due to modeling assumptions (model form uncertainty), numerical approximation (numerical uncertainty), and model input parameters (input parameter uncertainty) for low and high-fidelity models. The characterization of input uncertainty in terms of probability density function (PDF) and its propagation through L-PBF models, is discussed in detail. The systematic representation of such uncertainty sources is achieved by leveraging the Web Ontology Language (OWL) to capture relevant knowledge used for interoperability and reusability. The topology and mapping of the uncertainty sources establish fundamental requirements for measuring model fidelity and guiding the selection of a model suitable for its intended purpose.

Study of Droplet Diffusion in Hydrothermal-Assisted Transient Jet Fusion of Ceramics

2020 ◽  
Author(s):  
Fan Fei ◽  
Li He ◽  
Levi Kirby ◽  
Xuan Song
Keyword(s):  
High Performance ◽  
Functional Materials ◽  
Processing Parameters ◽  
Layer By Layer ◽  
Transient Solution ◽  
Powder Bed ◽  
Manufacturing Method ◽  
Precise Control ◽  
Powder Packing ◽  
Diffusion Profiles

Abstract Hydrothermal-assisted transient jet fusion (HTJF) is a powder-based additive manufacturing method of ceramics, which utilizes a water-mediated hydrothermal mechanism to fuse particles together, eliminating the use of organic binders in forming green bodies and thereby contributing to high green-density parts (> 90%) advantageous for fabricating functional materials with high-performance. In the HTJF process, a transient solution such as water is selectively deposited into a powder bed in a layer-by-layer fashion followed by a hydrothermal fusion process. Upon the ejection and deposition of a droplet of the transient solution on the surface of the powder bed, the diffusion behavior of the liquid significantly influences the particle fusion and the fabrication accuracy of the HTJF process. Precise control of the liquid diffusion in the powder bed is critical for the fabrication of ceramic structures with both high density and accuracy. In this paper, the dependence of transient solution diffusion on different process parameters (i.e., powder packing density, droplet size, pressure, etc.) in the HTJF process were studied. Both numerical modeling and experimental methods were used to quantify the relationships between processing parameters and diffusion profiles of transient solution droplets (e.g., diffusion width/depth). Optimum processing conditions were identified to mitigate the undesired diffusion of transient solution droplets in the powder bed.

scholarly journals DEM based investigation of powder packing in 3D printing of pharmaceutical tablets

2021 ◽  
Vol 249 ◽  
pp. 14012
Author(s):  
Koyel Sen ◽  
Tanu Mehta ◽  
Anson W.K.Ma ◽  
Bodhisattwa Chaudhuri
Keyword(s):  
3D Printing ◽  
Particle Density ◽  
Numerical Models ◽  
Dosage Forms ◽  
Raw Material ◽  
Pharmaceutical Dosage Forms ◽  
Printing Process ◽  
Powder Bed ◽  
Pharmaceutical Tablets ◽  
Powder Packing

3D printing is emerging as one of the most promising methods to manufacture Pharmaceutical dosage forms as it offers multiple advantages such as personalization of dosage forms, polypill, fabrication of complex dosage forms etc. 3D printing came into existence in 1980s but its use was extended recently to pharmaceutical industry along with the approval of first 3D printed tablet Spritam by FDA in 2015. Spritam was manufactured by Aprecia pharmaceuticals using binder jetting technology. Binder jet 3D printing involves a hopper for powder discharge and printheads for ink jetting. The properties of tablets are highly dependent upon the discharge quality of powder mixture from the hopper and jetting of the ink/binder solution from the printhead nozzle. In this study, numerical models were developed using Discrete element method (DEM) to gain better understanding of the binder jet 3D printing process. The DEM modeling of hopper discharge was performed using in-house DEM code to study the effect of raw material attributes such as powder bed packing density (i.e. particle size, particle density etc) on the printing process, especially during powder bed preparation. This DEM model was further validated experimentally, and the model demonstrated good agreement with experimental results.

Metal Binder Jetting Additive Manufacturing: A Literature Review

2020 ◽  
Vol 142 (9) ◽  
Author(s):  
Ming Li ◽  
Wenchao Du ◽  
Alaa Elwany ◽  
Zhijian Pei ◽  
Chao Ma
Keyword(s):  
Mechanical Properties ◽  
Additive Manufacturing ◽  
Related Factors ◽  
Powder Bed ◽  
Metal Binder ◽  
Powder Packing ◽  
Superior Mechanical Properties ◽  
Directed Energy ◽  
Reported Data ◽  
Binder Jetting

Abstract Binder jetting is an additive manufacturing process utilizing a liquid-based binding agent to selectively join the material in a powder bed. It is capable of manufacturing complex-shaped parts from a variety of materials including metals, ceramics, and polymers. This paper provides a comprehensive review on currently available reports on metal binder jetting from both academia and industry. Critical factors and their effects in metal binder jetting are reviewed and divided into two categories, namely material-related factors and process-related parameters. The reported data on density, dimensional and geometric accuracy, and mechanical properties achieved by metal binder jetting are summarized. With parameter optimization and a suitable sintering process, ten materials have been proven to achieve a relative density of higher than 90%. Indepth discussion is provided regarding densification as a function of various attributes of powder packing, printing, and post-processing. A few grades of stainless steel obtained equivalent or superior mechanical properties compared to cold working. Although binder jetting has gained its popularity in the past several years, it has not been sufficiently studied compared with other metal additive manufacturing (AM) processes such as powder bed fusion and directed energy deposition. Some aspects that need further research include the understanding of powder spreading process, binder-powder interaction, and part shrinkage.

Study of Droplet Diffusion in Hydrothermal-Assisted Transient Jet Fusion of Ceramics

2020 ◽  
Vol 143 (5) ◽  
Author(s):  
Fan Fei ◽  
Li He ◽  
Levi Kirby ◽  
Xuan Song
Keyword(s):  
High Performance ◽  
Functional Materials ◽  
Processing Parameters ◽  
Layer By Layer ◽  
Transient Solution ◽  
Powder Bed ◽  
Precise Control ◽  
Powder Packing ◽  
And Diffusion ◽  
Diffusion Profiles

Abstract Hydrothermal-assisted transient jet fusion (HTJF) is a powder-based additive manufacturing (AM) method of ceramics, which utilizes a water-mediated hydrothermal mechanism to fuse particles together, eliminating the use of organic binders in forming green bodies and thereby contributing to high green-density parts (>90%) advantageous for fabricating functional materials with high performance. In the HTJF process, a transient solution such as water is selectively deposited into a powder bed in a layer-by-layer fashion followed by a hydrothermal fusion process. Upon the ejection and deposition of a droplet of the transient solution on the surface of the powder bed, the diffusion behavior of the liquid significantly influences the particle fusion and the fabrication accuracy of the HTJF process. Precise control of the liquid diffusion in the powder bed is critical for the fabrication of ceramic structures with both high density and accuracy. In this paper, the dependence of transient solution diffusion on different process parameters (i.e., powder packing density, droplet size, pressure, etc.) in the HTJF process were studied. Both numerical modeling and experimental methods were used to quantify the relationships between processing parameters and diffusion profiles of transient solution droplets (e.g., diffusion width/depth). Optimum processing conditions were identified to mitigate the undesired diffusion of transient solution droplets in the powder bed.

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