Numerical investigation into cleanability of support structures produced by powder bed fusion technology

Purpose Support structures used in laser powder bed fusion are often difficult to clean from unsintered powder at the end of the process. This issue can be significantly reduced through a proper design of these auxiliary structures. This paper aims to investigate preliminary the airflow within differently oriented support structures and to provide design guidelines to enhance their cleanability, especially the depowdering of them. Design/methodology/approach This study investigates the cleanability of support structures in powder bed fusion technology. Digital models of cleaning operations were designed through computer-aided engineering systems. Simulations of the airflow running into the powder entrapped within the thin walls of auxiliary supports were implemented by computational fluid dynamics. This approach was applied to a set of randomly generated geometrical configurations to determine the air turbulence intensity depending on their design. Findings The results, which are based on the assumption that a relationship exists between turbulence and powder removal effectiveness, demonstrated that the maximum cleanability is obtainable through specific relative rotations between consecutive support structures. Furthermore, it was possible to highlight the considerable influence of the auxiliary structures next to the fluid inlet. These relevant findings establish optimal design rules for the cleanability of parts manufactured by powder bed fusion processes. Originality/value This study presents a preliminary investigation into the cleanability of support structures in laser powder bed fusion, which has not been addressed by previous literature. The results allow for a better understanding of the fluid dynamics during cleaning operations. New guidelines to enhance the cleanability of support structures are provided based on the results of simulations.

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Modeling of solidification microstructure evolution in laser powder bed fusion fabricated 316L stainless steel using combined computational fluid dynamics and cellular automata

Additive Manufacturing ◽

10.1016/j.addma.2019.06.024 ◽

2019 ◽

Vol 28 ◽

pp. 750-765 ◽

Cited By ~ 4

Author(s):

Yi Zhang ◽

Jing Zhang

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Stainless Steel ◽

Cellular Automata ◽

Microstructure Evolution ◽

316L Stainless Steel ◽

Solidification Microstructure ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Powder Bed

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A printability assessment framework for fabricating low variability nickel-niobium parts using laser powder bed fusion additive manufacturing

Rapid Prototyping Journal ◽

10.1108/rpj-01-2021-0024 ◽

2021 ◽

Vol ahead-of-print (ahead-of-print) ◽

Author(s):

Bing Zhang ◽

Raiyan Seede ◽

Austin Whitt ◽

David Shoukr ◽

Xueqin Huang ◽

...

Keyword(s):

Mechanical Properties ◽

Additive Manufacturing ◽

Uncertainty Quantification ◽

Process Optimization ◽

Powder Bed Fusion ◽

Assessment Framework ◽

Laser Powder Bed Fusion ◽

Content Type ◽

Powder Bed ◽

Analytical Thermal Model

Purpose There is recent emphasis on designing new materials and alloys specifically for metal additive manufacturing (AM) processes, in contrast to AM of existing alloys that were developed for other traditional manufacturing methods involving considerably different physics. Process optimization to determine processing recipes for newly developed materials is expensive and time-consuming. The purpose of the current work is to use a systematic printability assessment framework developed by the co-authors to determine windows of processing parameters to print defect-free parts from a binary nickel-niobium alloy (NiNb5) using laser powder bed fusion (LPBF) metal AM. Design/methodology/approach The printability assessment framework integrates analytical thermal modeling, uncertainty quantification and experimental characterization to determine processing windows for NiNb5 in an accelerated fashion. Test coupons and mechanical test samples were fabricated on a ProX 200 commercial LPBF system. A series of density, microstructure and mechanical property characterization was conducted to validate the proposed framework. Findings Near fully-dense parts with more than 99% density were successfully printed using the proposed framework. Furthermore, the mechanical properties of as-printed parts showed low variability, good tensile strength of up to 662 MPa and tensile ductility 51% higher than what has been reported in the literature. Originality/value Although many literature studies investigate process optimization for metal AM, there is a lack of a systematic printability assessment framework to determine manufacturing process parameters for newly designed AM materials in an accelerated fashion. Moreover, the majority of existing process optimization approaches involve either time- and cost-intensive experimental campaigns or require the use of proprietary computational materials codes. Through the use of a readily accessible analytical thermal model coupled with statistical calibration and uncertainty quantification techniques, the proposed framework achieves both efficiency and accessibility to the user. Furthermore, this study demonstrates that following this framework results in printed parts with low degrees of variability in their mechanical properties.

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On the manufacturability of Inconel 718 thin-walled honeycomb structures by laser powder bed fusion

Rapid Prototyping Journal ◽

10.1108/rpj-04-2021-0098 ◽

2021 ◽

Vol ahead-of-print (ahead-of-print) ◽

Author(s):

José M. Zea Pérez ◽

Jorge Corona-Castuera ◽

Carlos Poblano-Salas ◽

John Henao ◽

Arturo Hernández Hernández

Keyword(s):

Mechanical Properties ◽

Inconel 718 ◽

Dimensional Accuracy ◽

Honeycomb Lattice ◽

Lattice Structures ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Content Type ◽

Powder Bed ◽

Thin Walled

Purpose The purpose of this paper is to study the effects of printing strategies and processing parameters on wall thickness, microhardness and compression strength of Inconel 718 superalloy thin-walled honeycomb lattice structures manufactured by laser powder bed fusion (L-PBF). Design/methodology/approach Two printing contour strategies were applied for producing thin-walled honeycomb lattice structures in which the laser power, contour path, scanning speed and beam offset were systematically modified. The specimens were analyzed by optical microscopy for dimensional accuracy. Vickers hardness and quasi-static uniaxial compression tests were performed on the specimens with the least difference between the design wall thickness and the as built one to evaluate their mechanical properties and compare them with the counterparts obtained by using standard print strategies. Findings The contour printing strategies and process parameters have a significant influence on reducing the fabrication time of thin-walled honeycomb lattice structures (up to 50%) and can lead to improve the manufacturability and dimensional accuracy. Also, an increase in the young modulus up to 0.8 times and improvement in the energy absorption up to 48% with respect to those produced by following a standard strategy was observed. Originality/value This study showed that printing contour strategies can be used for faster fabrication of thin-walled lattice honeycomb structures with similar mechanical properties than those obtained by using a default printing strategy.

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Camera signal dependencies within coaxial melt pool monitoring in laser powder bed fusion

Rapid Prototyping Journal ◽

10.1108/rpj-01-2019-0022 ◽

2020 ◽

Vol 26 (1) ◽

pp. 100-106 ◽

Cited By ~ 1

Author(s):

Tobias Kolb ◽

Reza Elahi ◽

Jan Seeger ◽

Mathews Soris ◽

Christian Scheitler ◽

...

Keyword(s):

Surface Roughness ◽

Layer Thickness ◽

Powder Layer ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Content Type ◽

Powder Bed ◽

Sensory Signals ◽

Melt Pool ◽

Research Activities

Purpose The purpose of this paper is to analyse the signal dependency of the camera-based coaxial monitoring system QMMeltpool 3D (Concept Laser GmbH, Lichtenfels, Germany) for laser powder bed fusion (LPBF) under the variation of process parameters, position, direction and layer thickness to determine the capability of the system. Because such and similar monitoring systems are designed and presented for quality assurance in series production, it is important to present the dominant signal influences and limitations. Design/methodology/approach Hardware of the commercially available coaxial monitoring QMMeltpool 3D is used to investigate the thermal emission of the interaction zone during LPBF. The raw images of the camera are analysed by means of image processing to bypass the software of QMMeltpool 3D and to gain a high level of signal understanding. Laser power, scan speed, laser spot diameter and powder layer thickness were varied for single-melt tracks to determine the influence of a parameter variation on the measured sensory signals. The effects of the scan direction and position were also analysed in detail. The influence of surface roughness on the detected sensory signals was simulated by a machined substrate plate. Findings Parameter variations are confirmed to be detectable. Because of strong directional and positional dependencies of the melt-pool monitoring signal a calibration algorithm is necessary. A decreasing signal is detected for increasing layer thickness. Surface roughness is identified as a dominating factor with major influence on the melt-pool monitoring signal exceeding other process flaws. Research limitations/implications This work was performed with the hardware of a commercially available QMMeltpool 3D system of an LPBF machine M2 of the company Concept Laser GmbH. The results are relevant for all melt-pool monitoring research activities connected to LPBF, as well as for end users and serial production. Originality/value Surface roughness has not yet been revealed as being one of the most important origins for signal deviations in coaxial melt-pool monitoring. To the best of the authors’ knowledge, the direct comparison of influences because of parameters and environment has not been published to this extent. The detection, evaluation and remelting of surface roughness constitute a plausible workflow for closed-loop control in LPBF.

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Realistic design of laser powder bed fusion channels

Rapid Prototyping Journal ◽

10.1108/rpj-01-2020-0010 ◽

2020 ◽

Vol 26 (10) ◽

pp. 1827-1836

Author(s):

Christopher Gottlieb Klingaa ◽

Sankhya Mohanty ◽

Jesper Henri Hattel

Keyword(s):

Surface Roughness ◽

Prediction Models ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Channel Design ◽

Conformal Cooling ◽

Content Type ◽

Powder Bed ◽

Cooling Channels ◽

Conformal Cooling Channels

Purpose Conformal cooling channels in additively manufactured molds are superior over conventional channels in terms of cooling control, part warpage and lead time. The heat transfer ability of cooling channels is determined by their geometry and surface roughness. Laser powder bed fusion manufactured channels have an inherent process-induced dross formation that may significantly alter the actual shape of nominal channels. Therefore, it is crucial to be able to predict the expected surface roughness and changes in the geometry of metal additively manufactured conformal cooling channels. The purpose of this paper is to present a new methodology for predicting the realistic design of laser powder bed fusion channels. Design/methodology/approach This study proposes a methodology for making nominal channel design more realistic by the implementation of roughness prediction models. The models are used for altering the nominal shape of a channel to its predicted shape by point cloud analysis and manipulation. Findings A straight channel is investigated as a simple case study and validated against X-ray computed tomography measurements. The modified channel geometry is reconstructed and meshed, resulting in a predicted, more realistic version of the nominal geometry. The methodology is successfully tested on a torus shape and a simple conformal cooling channel design. Finally, the methodology is validated through a cooling test experiment and comparison with simulations. Practical implications Accurate prediction of channel surface roughness and geometry would lead toward more accurate modeling of cooling performance. Originality/value A robust start to finish method for realistic geometrical prediction of metal additive manufacturing cooling channels has yet to be proposed. The current study seeks to fill the gap.

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Laser powder bed fusion additive manufacturing of copper wicking structures: fabrication and capillary characterization

Rapid Prototyping Journal ◽

10.1108/rpj-01-2021-0016 ◽

2021 ◽

Vol ahead-of-print (ahead-of-print) ◽

Author(s):

Adnen Mezghani ◽

Abdalla R. Nassar ◽

Corey J. Dickman ◽

Eduardo Valdes ◽

Raul Alvarado

Keyword(s):

Additive Manufacturing ◽

Design Methodology ◽

Heat Pipes ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Content Type ◽

Powder Bed ◽

Published Report ◽

Secondary Manufacturing ◽

Design Freedom

Purpose An integral component in heat pipes (HPs) and vapor chambers (VCs) is a porous wicking structure. Traditional methods for manufacturing wicking structures within HPs and VCs involve secondary manufacturing processes and are generally limited to simple geometries. This work aims to leverage the unprecedented level of design freedom of laser powder bed fusion (LPBF) additive manufacturing (AM) to produce integrated wicking structures for HPs and VCs. Design/methodology/approach Copper wicking structures are fabricated through LPBF via partial sintering and via the formation of square, hexagonal and rectangular arrangements of micro-pins and micro-grooves, produced in multiple build directions. Wicks are characterized by conducting capillary performance analysis through the measurement of porosity, permeability and capillary rate-of-rise. Findings Copper wicking structures were successfully fabricated with capillary performance, K/reff, ranging from 0.186–1.74 µm. The rectangular-arrangement micro-pin wick presented the highest performance. Originality/value This work represents the first published report on LPBF AM of copper wicking structures for HPs/VCs applications and represents foundational knowledge for fabricating complete assemblies of copper VCs and HPs through LPBF AM.

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Keyhole Formation by Laser Drilling in Laser Powder Bed Fusion of Ti6Al4V Biomedical Alloy: Mesoscopic Computational Fluid Dynamics Simulation versus Mathematical Modelling Using Empirical Validation

Nanomaterials ◽

10.3390/nano11123284 ◽

2021 ◽

Vol 11 (12) ◽

pp. 3284

Author(s):

Asif Ur Rehman ◽

Muhammad Arif Mahmood ◽

Fatih Pitir ◽

Metin Uymaz Salamci ◽

Andrei C. Popescu ◽

...

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Energy Density ◽

Operating Conditions ◽

Dynamics Simulation ◽

Powder Layer ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Powder Bed ◽

Melt Pool

In the laser powder bed fusion (LPBF) process, the operating conditions are essential in determining laser-induced keyhole regimes based on the thermal distribution. These regimes, classified into shallow and deep keyholes, control the probability and defects formation intensity in the LPBF process. To study and control the keyhole in the LPBF process, mathematical and computational fluid dynamics (CFD) models are presented. For CFD, the volume of fluid method with the discrete element modeling technique was used, while a mathematical model was developed by including the laser beam absorption by the powder bed voids and surface. The dynamic melt pool behavior is explored in detail. Quantitative comparisons are made among experimental, CFD simulation and analytical computing results leading to a good correspondence. In LPBF, the temperature around the laser irradiation zone rises rapidly compared to the surroundings in the powder layer due to the high thermal resistance and the air between the powder particles, resulting in a slow travel of laser transverse heat waves. In LPBF, the keyhole can be classified into shallow and deep keyhole mode, controlled by the energy density. Increasing the energy density, the shallow keyhole mode transforms into the deep keyhole mode. The energy density in a deep keyhole is higher due to the multiple reflections and concentrations of secondary reflected beams within the keyhole, causing the material to vaporize quickly. Due to an elevated temperature distribution in deep keyhole mode, the probability of pores forming is much higher than in a shallow keyhole as the liquid material is close to the vaporization temperature. When the temperature increases rapidly, the material density drops quickly, thus, raising the fluid volume due to the specific heat and fusion latent heat. In return, this lowers the surface tension and affects the melt pool uniformity.

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Design guidelines for laser powder bed fusion in Inconel 718

Journal of Laser Applications ◽

10.2351/7.0000508 ◽

2022 ◽

Vol 34 (1) ◽

pp. 012015

Author(s):

Dirk Herzog ◽

Karim Asami ◽

Christoph Scholl ◽

Christoph Ohle ◽

Claus Emmelmann ◽

...

Keyword(s):

Inconel 718 ◽

Design Guidelines ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Powder Bed

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In Situ Thermography During Laser Powder Bed Fusion of a Nickel Superalloy 625 Artifact with Various Overhangs and Supports

Journal of Research of the National Institute of Standards and Technology ◽

10.6028/jres.126.005 ◽

2021 ◽

Vol 126 ◽

Author(s):

Benjamin Molnar ◽

Jarred C. Heigel ◽

Eric Whitenton

Keyword(s):

Cooling Rate ◽

High Speed ◽

Nickel Superalloy ◽

Powder Bed Fusion ◽

Support Structures ◽

Radiance Temperature ◽

Laser Powder Bed Fusion ◽

Powder Bed ◽

Melt Pool

This document provides details on the experiment and associated measurement files available fordownload in the dataset “In Situ Thermography During Laser Powder Bed Fusion of a Nickel Superalloy 625 Artifact with Various Overhangs and Supports.” The measurements were acquired during the fabrication of a small nickel superalloy 625 (IN625) artifact using a commercial laser powder bed fusion (LPBF) system. The artifact consists of two half-arch features with increasing slopes for overhangs. These overhangs range from 5° from vertical to 85° from vertical in increments of 10°. The artifact geometry and process are controlled to ensure consistent processing along the overhang geometry. This control enables the effect of overhang geometry and support structures to be isolated from effects of inter-layer scan strategy variations. The measurements include high-speed thermography of each layer, from which radiance temperature, cooling rate, and melt pool length are calculated.

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