An overview of powder granulometry on feedstock and part performance in the selective laser melting process

Tan, Jun Hao; Wong, Wai Leong Eugene; Dalgarno, Kenneth

doi:10.1016/j.addma.2017.10.011

Cited by 194 publications

(165 citation statements)

References 135 publications

(228 reference statements)

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“…Despite the presence of condensate in the powder bed already being known, its effects on the mechanical and microstructural properties of final parts is yet to be assessed. It must be pointed out that, if a large amount of condensate is generated and eventually redeposited on the bed together with the ejected (spatter) particles, the surface properties of the powder will change and might influence the flowability of the reused feedstock material [101,135,136]. From Figure 10, it is possible to observe that condensate is in the form of nanoparticles since, during the cooling, there is a decrease in metal vapor solubility in the process chamber environment, giving rise to a supersaturated solution with high undercooling, a condition which fosters the formation of nanoparticles [39,97,98,126,137].…”

Section: Condensatementioning

confidence: 99%

Section: Condensatementioning

confidence: 99%

“…As mentioned above, when the time of flight is long enough, the surface of the spatter particles can experience strong oxidation, mostly in the case of highly reactive powders (i.e., Ti-6Al-4V) and powders with chemical composition characterized by the high presence of elements with a high oxidation potential (i.e., stainless steels). As a matter of fact, the presence of oxygen and interstitial elements in general (i.e., H, O) on the particles or within the environment of the build chamber (insufficient inert gas flow) can impact the chemical composition of the melt pool and its surface tension, causing unfavorable wetting conditions and affecting the following solidification and densification of the metal part [37,135]. Therefore, depending on the application of the part to be produced (biomedical, aeronautical, structural, or just a prototype), a different level of accuracy concerning the removal of heat-affected particles should be used.…”

mentioning

confidence: 99%

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Material Reuse in Laser Powder Bed Fusion: Side Effects of the Laser—Metal Powder Interaction

Santecchia

Spigarelli

Cabibbo

2020

Metals

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Metal additive manufacturing is changing the way in which engineers and designers model the production of three-dimensional (3D) objects, with rapid growth seen in recent years. Laser powder bed fusion (LPBF) is the most used metal additive manufacturing technique, and it is based on the efficient interaction between a high-energy laser and a metal powder feedstock. To make LPBF more cost-efficient and environmentally friendly, it is of paramount importance to recycle (reuse) the unfused powder from a build job. However, since the laser-powder interaction involves complex physics phenomena and generates by-products which might affect the integrity of the feedstock and the final build part, a better understanding of the overall process should be attained. The present review paper is focused on the clarification of the interaction between laser and metal powder, with a strong focus on its side effects. Figure 1. Schematics of the laser powder bed fusion (LPBF) equipment. Adapted from Reference [9] with permission from Elsevier.While the market and the applications of laser powder bed fusion continuously and impressively grew in recent years, there is a common view across users and researchers concerning the repeatability of the process in terms of chemical composition and mechanical properties of the final parts, which are of paramount importance when challenging environmental or testing conditions are considered [10][11][12][13][14][15][16].The most typical approach to study the microstructural and mechanical properties of parts built by LPBF is to compare them with castings of the same alloy or, rather, the corresponding alloy since the starting material is metal powder rather than a fuse. However, in some existing alloys designed for cast and wrought parts, laser additive manufacturing processing results in cracking or other microstructure deficiencies [11,12,16,17]. It is worth noting that LPBF has more similarities with laser welding rather than casting, since the two laser-based techniques have some common features (i.e., melt-pool formation, moving heat source) [18]. However, process parameters are, in general, quite different in terms of laser power and scan speed, and the laser-matter interaction is much more complicated in LPBF processes, since the powder feedstock is inherently unstable and the solidified material undergoes multiple thermal cycles corresponding to the fusion of subsequent layers during the additive process [19][20][21][22]. Furthermore, owing to the similarities with welding and to the complicated interaction between laser and metal particles, when comparing laser powder bed fusion with other metal forming processes, it is evident that the range of processable alloys is very limited and the number of high-productivity commercially available alloys is even smaller [23]. One of the reasons behind this is that the level of metal powder sensitivity to the laser action during LPBF is not yet fully understood, despite the efforts of the scientific community to uncover it [24][25][26][27], and ...

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Section: Condensatementioning

confidence: 99%

Section: Condensatementioning

confidence: 99%

mentioning

confidence: 99%

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Material Reuse in Laser Powder Bed Fusion: Side Effects of the Laser—Metal Powder Interaction

Santecchia

Spigarelli

Cabibbo

2020

Metals

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“…in the sequence from powder storage, to spreading in the machines, to melting, solidification, and post-processing. Tan et al (2017) extends this overview to more general aspects with a special focus on the influence of powder morphology and granulmetry. In the context of powder feedstock modeling, Gusarov (2008) studied the problem of laser energy absorption in powder beds based on a (homogenized) continuum model for the radiation transfer problem while Boley et al (2015) approached the same problem on the basis of a ray tracing scheme and a (discrete) powder bed model resolving individual particles.…”

Section: Introductionmentioning

confidence: 98%

Critical influences of particle size and adhesion on the powder layer uniformity in metal additive manufacturing

Meier

Weißbach

Weinberg

et al. 2019

Journal of Materials Processing Technology

217

110

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The quality of powder layers, specifically their packing density and surface uniformity, is a critical factor influencing the quality of components produced by powder bed metal additive manufacturing (AM) processes, including selective laser melting, electron beam melting and binder jetting. The present work employs a computational model to study the critical influence of powder cohesiveness on the powder recoating process in AM. The model is based on the discrete element method (DEM) with particle-to-particle and particle-to-wall interactions involving frictional contact, rolling resistance and cohesive forces. Quantitative metrics, namely the spatial mean values and standard deviations of the packing fraction and surface profile field, are defined in order to evaluate powder layer quality. Based on these metrics, the size-dependent behavior of exemplary plasma-atomized Ti-6Al-4V powders during the recoating process is studied. It is found that decreased particle size / increased cohesiveness leads to considerably decreased powder layer quality in terms of low, strongly varying packing fractions and highly non-uniform surface profiles. For relatively fine-grained powders (mean particle diameter 17µm), it is shown that cohesive forces dominate gravity forces by two orders of magnitude leading to low quality powder layers not suitable for subsequent laser melting without additional layer / surface finishing steps. Besides particle-to-particle adhesion, this contribution quantifies the influence of mechanical bulk powder material parameters, nominal layer thickness, blade velocity as well as particleto-wall adhesion. Finally, the implications of the resulting powder layer characteristics on the subsequent melting process are discussed and practical recommendations are given for the choice of powder recoating process parameters. While the present study focuses on a rigid blade recoating mechanism, the proposed simulation framework can be applied to and the general results can be transferred to systems based on alternative recoating tools such as soft blades, rakes or rotating rollers.

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“…Most of these studies intend to optimize the SLM process by relating the observed process outcomes with input parameters such as laser beam power and velocity, powder layer thickness, hatch spacing or scanning strategy. There are also some -but considerably less -contributions that have studied the influence of the powder feedstock on the process outcome [3,4,26,27,32,71,78]. However, only very few of these works have studied the actual interplay of powder particle properties (mechanical, thermal, optical and chemical properties on particle surfaces), bulk powder properties (morphology, granulometry and resulting flowability) as well as resulting powder layer characteristics (packing density, surface uniformity as well as effective thermal and mechanical properties) during the powder recoating process applied between two subsequent material layers in metal additive manufacturing.…”

Section: Introductionmentioning

confidence: 99%

Modeling and characterization of cohesion in fine metal powders with a focus on additive manufacturing process simulations

et al. 2019

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The cohesive interactions between fine metal powder particles crucially influence their flow behavior, which is in turn important to many powder-based manufacturing processes including emerging methods for powder-based metal additive manufacturing (AM). The present work proposes a novel modeling and characterization approach for micronscale metal powders, with a special focus on characteristics of importance to powder-bed AM. The model is based on the discrete element method (DEM), and the considered particle-to-particle and particle-to-wall interactions involve frictional contact, rolling resistance and cohesive forces. Special emphasis lies on the modeling of cohesion. The proposed adhesion force law is defined by the pull-off force resulting from the surface energy of powder particles in combination with a van-der-Waals force curve regularization. The model is applied to predict the angle of repose (AOR) of exemplary spherical Ti-6Al-4V powders, and the surface energy value underlying the adhesion force law is calibrated by fitting the corresponding angle of repose values from numerical and experimental funnel tests. To the best of the authors' knowledge, this is the first work providing an experimental estimate for the effective surface energy of the considered class of metal powders. By this approach, an effective surface energy of 0.1mJ/m 2 is found for the investigated Ti-6Al-4V powder. This value is considerably lower than typical experimental values for flat metal contact surfaces in the range of 30 − 50mJ/m 2 , indicating the crucial influence of factors such as surface roughness and potential chemical surface contamination / oxidation on fine metal powders. More importantly, the present study demonstrates that a neglect of the related cohesive forces leads to a drastical underestimation of the AOR and, consequently, to an insufficient representation of the bulk powder behavior.

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An overview of powder granulometry on feedstock and part performance in the selective laser melting process

Cited by 194 publications

References 135 publications

Material Reuse in Laser Powder Bed Fusion: Side Effects of the Laser—Metal Powder Interaction

Material Reuse in Laser Powder Bed Fusion: Side Effects of the Laser—Metal Powder Interaction

Critical influences of particle size and adhesion on the powder layer uniformity in metal additive manufacturing

Modeling and characterization of cohesion in fine metal powders with a focus on additive manufacturing process simulations

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