A radiographic technique for measuring the powder packing density in the cavities of trabecular bone (dosimetry)

AbstractAdditive manufacturing of polymer powders is nowadays an industrial production technology. Complex thermal phenomena occur during processing, mainly related to the interaction dynamics among laser, powder, and heating system, and also to the subsequent cool-down phase from the melt to the parts. Thermal conductivity of the powder is a key property for material processing, since an inhomogeneous temperature field in the powder cake leads to uneven part properties and can strongly limit productivity because only a smaller portion of the build chamber can be used. Nevertheless, little is known about the relationship between thermal conductivity, packing density, and presence of fillers, which are used to enhance specific properties such as high temperature resistance or stiffness. The development and consequent validation of a device capable of measuring thermal conductivity as a function of powder packing density are then extremely important, providing an additional tool to characterize powders during the development process of new materials for PBF of polymers. The results showed a positive correlation between packing density and thermal conductivity for some commercially available materials, with an increase of the latter of about 10 to 40% with an increase of the packing density from 0 to 100%. Problems arose in trying to replicate the compaction state of the powder, since the same amount of taps led to a different packing density, but this is a known problem of measuring free-flowing powders such as the ones used for additive manufacturing. Regarding fillers, an increase of about 40 to 70% of thermal conductivity when inorganic fillers such as carbon fibers are added to the neat polymer was observed, and the expected behavior following the rule of mixture was only partially observed.

Download Full-text

Evaluation of Binary and Ternary Models in Powder Packing Density for Additive Manufacturing Applications

American Journal of Engineering and Applied Sciences ◽

10.3844/ajeassp.2021.314.322 ◽

2021 ◽

Vol 14 (2) ◽

pp. 314-322

Author(s):

Taher M. Abu-Lebdeh ◽

Oluwatobiloba Adetokunbo Kalejaiye

Keyword(s):

Additive Manufacturing ◽

Packing Density ◽

Powder Packing ◽

Manufacturing Applications

Download Full-text

Experimental and Numerical Study on the Packing Densification of Metal Powder with Gaussian Distribution

Metals ◽

10.3390/met10111401 ◽

2020 ◽

Vol 10 (11) ◽

pp. 1401

Author(s):

Huadong Yang ◽

Shiguang Li ◽

Zhen Li ◽

Fengchao Ji

Keyword(s):

Numerical Simulation ◽

Packing Density ◽

Simulation Analysis ◽

Numerical Study ◽

Three Dimensional ◽

Packed Bed ◽

Element Model ◽

Powder Particle Size ◽

Metal Powders ◽

Powder Packing

In the additive manufacturing of metal materials, powder bed fusion 3D laser printing is the most widely used processing method. The density of the packed bed is another important parameter that can affect the part quality; however, it is the least understood parameter and needs further study. Aiming at addressing the problem of the powder packing density in the powder tank before powder spreading, which is neglected in the existing research, a combination of numerical simulation and experimental research was used to analyze the powder particle size distribution, powder stiffness coefficient, and vibration condition. Considering the van der Waals forces between the powders, a discrete element model suitable for fine metal powders for 3D printing is proposed. At the same time, a mathematical model that takes into account the vibration state is proposed, and the factors affecting the density of the powder were analyzed. A self-designed and manufactured three-dimensional vibration test rig was used to conduct physical experiments on spherical metal powders with approximately Gaussian distributions to obtain the maximum densities. The results obtained by the numerical simulation analysis method proposed in this paper are in good agreement with the experimental results. The influence of the amplitude and vibration frequency on the powder packing density is the same; that is, it increases with an increase in amplitude or frequency, and then decreases with a further increase in amplitude or frequency after reaching the maximum. It is unreasonable to discuss the packing densification only relying on the vibration intensity. Therefore, it is necessary to combine the amplitude and frequency to analyze the factors that affect the packing density of powders.

Download Full-text

Discrete-Element Simulation of Powder Spreading Process in Binder Jetting, and the Effects of Powder Size

Volume 1: Additive Manufacturing; Advanced Materials Manufacturing; Biomanufacturing; Life Cycle Engineering; Manufacturing Equipment and Automation ◽

10.1115/msec2021-63351 ◽

2021 ◽

Author(s):

Ana Paula Clares ◽

Guha Manogharan

Keyword(s):

Size Distribution ◽

Packing Density ◽

Discrete Element ◽

Bimodal Distribution ◽

Powder Size ◽

Spreading Process ◽

Powder Packing ◽

Element Simulation ◽

Wide Range ◽

Binder Jetting

Abstract Binder Jetting has gained particular interest amongst Additive Manufacturing (AM) techniques because of its wide range of applications, broader feasible material systems, and absence of rapid melting-solidification issues present in other AM processes. Understanding and optimizing printing parameters during the powder spreading process is essential to improve the quality of the final part. In this study, a Discrete Element Method (DEM) simulation is employed to evaluate the powder packing density, flowability, and porosity during powder spreading process utilizing three different powder groups. Two groups are formed with monoidal size distributions (75–84 μm and 100–109 μm), and the third one consisting of a bimodal distribution (50 μm + 100 μm). A thorough investigation into the effects of powder size distribution during the powder spreading step in a binder jetting process is conducted using ceramic foundry sand. It was observed that coarser particles result in higher flowability (62% decrease in repose angle) than finer ones due to the cohesion effect present in the latter. A bimodal size distribution yields the highest packing density (8% increase) and lowest porosity (∼12% reduction) in the powder bed, as the finer particles fill in the voids created between the coarser ones. Findings from this study are directly applicable to binder-jetting AM process, and also offer new insights for AM powder manufacturers.

Download Full-text

Effect of Fineness of Fly Ash on Powder Packing Density and Paste Performance

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.701.296 ◽

2013 ◽

Vol 701 ◽

pp. 296-301

Author(s):

Wen Yang ◽

Na Qian Feng ◽

Ch’ng Guan Bee ◽

Xiao Deng

Keyword(s):

Compressive Strength ◽

Fly Ash ◽

Packing Density ◽

Composite Powder ◽

Dense Packing ◽

Powder Packing

This paper discusses the effect of fineness of fly ash on powder packing density, compacting voidage, paste fluidity and compressive strength. The results showed that when the content of fly ash is between 0%~40%, the compacting voidage of the composite powder is reduced by adding the fly ash with D50 1.0μm and 3.0μm, not by the fly ash with D50 12.0μm. The results of pressured entities voidage are consistent with the calculated values by Aim-Goff model. The optimal content of fly ash with D50 1.0μm and 3.0μm are 30% and 25% respectively, which is more helpful to improve the dense packing density of composite powder. There are good corresponding relationships between compacting voidage, dense packing density and fluidity in composite powder or paste by adding the fly ash with D50 1.0μm and 3.0μm, the fly ash can reduce the dense packing voidage of composite powder, and improve the fluidity of fresh paste.

Download Full-text