Metal additive manufacturing (AM) enables the production of non-trivial geometries and intricate internal structures. Directed energy deposition (DED) is one such AM process that has the inherent advantage of producing multi-material components on complex pre-existing geometries. Significant recent interest in DED processes has been driven by the need for inexpensive powders and potential material recycling. In this work, we explore the possibility of using non-standard arbitrary shaped metal powders within the DED process. A standard numerical model, comprising a three-dimensional viscous, compressible, turbulent solver with two-way discrete phase coupling is employed to understand the mechanics of gas-driven non-spherical powder flow. Spatial distributions of non-spherical powder on a set of pre-existing geometric features (e.g., corners, curved surfaces) are evaluateds and compared with standard spherical powders. The effect of particle collisions on the substrate is evaluated and corresponding density distributions are quantified. Non-spherical particles are generally found to exhibit higher velocities, and greater deposition track width, compared to spherical particles. Our simulations also reveal the effect of particle shape on their flow properties and final powder density. Using a custom-built DED configuration, we present preliminary experimental results of single-track depositions using both spherical and non-spherical powder particles. Based on our findings, we make a case for the use of non-spherical powders for DED applications.
Commercial metal powders used as feedstock for additive manufacturing (AM) applications are primarily produced via gas or water atomization techniques. These are highly capital-intensive and inflexible, making the resulting powders as much as 3–10 times more expensive than corresponding cast ingots. Recently, we have demonstrated a potential alternative route for making metal powders — using surface grinding. The resulting powders have shown promise for use as stock in metal directed energy deposition (DED) processes. This work explores the applicability of these alternatively produced powders for laser sintering and related applications. Spherical metal powder particles (AISI 52100, SS 304) in the range of 5–100 microns were first produced using surface grinding. These powders were post-processed and segregated into monodisperse and polydisperse batches, representing high quality-low yield and low-quality-high yield stock, respectively. A high-power fiber laser source of 50 microns spot diameter was used to sinter these two stock powders, with nitrogen as a shielding gas, and their performance was evaluated using a range of ex situ analysis techniques. The latter included metallography, SEM/EDS and XRD analysis and was used to evaluate sintering quality in both cases, including melt pool and heat-affected zone characterization. Based on these results, we present recommendations for the use of mono- and polydisperse metallic powders and demonstrate the potential utility of using grinding as an alternative technique for the production of metal powders for laser sintering applications.
The curious occurrence of perfectly spherical particles when a steel substrate is slid against a hard abrasive was first observed and documented by Robert Hooke in the 17 th century. Similar particles have subsequently been observed in numerous other abrasion-type processes, ranging from grinding of steels to sliding rock faults. The prevalent hypothesis, originally proposed by Hooke, is that these particles are formed due to high local temperatures between the abrasive and the substrate, resulting in melting, droplet ejection and subsequent resolidification-the melting-resolidification hypothesis. In this work, we revisit this phenomenon using in situ analysis of a model steel-abrasive contact geometry, complemented by analytical calculations. It is found that the temperature within the contact zone, for typical contact conditions used, is far from the melting point and that spherical particles do not form in the absence of oxygen. We thereby propose a modification of the melting-resolidification hypothesis, involving an intermediate exothermic oxidation stage, and provide quantitative evidence for each step of the process. Our results have implications for a wide class of abrasive systems that involve the formation and utilization of spherical metallic particles.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.