scholarly journals Investigation of the Influence of Powder Moisture on the Spreadability Using the Spreading Tester

2021 ◽  
Vol 166 (1) ◽  
pp. 14-22
Author(s):  
Marco Mitterlehner ◽  
Herbert Danninger ◽  
Christian Gierl-Mayer ◽  
Harald Gschiel
Keyword(s):  
Surface Roughness ◽  
Relative Humidity ◽  
Powder Bed Fusion ◽  
Analysis Method ◽  
Laser Powder Bed Fusion ◽  
Powder Bed ◽  
Moist Condition ◽  
Powder Particles ◽  
Superalloy Powder

AbstractMoisture is often regarded as one of the main reasons for poor processability of powders using Laser-powder bed fusion (L-PBF) processes. To determine the influence of moisture on the spreadability, a superalloy powder IN718 commonly used for L‑PBF processes has been conditioned in two different states: once in the as-received and dry condition and once in a moist condition obtained by storing the powder for four weeks in an atmosphere containing a relative humidity of 75%. Using a self-built spreading tester and a subsequent analysis method specially developed for testing the spreadability of a powder, the differently conditioned IN718 powder batches have been investigated regarding the surface roughness and flatness of the powder layers. Additionally, the formation of empty spots between the powder particles in the top layer has been studied.

scholarly journals On the Relevance of Volumetric Energy Density in the Investigation of Inconel 718 Laser Powder Bed Fusion

Materials ◽  
2020 ◽  
Vol 13 (3) ◽  
pp. 538 ◽  
Author(s):  
Fabrizia Caiazzo ◽  
Vittorio Alfieri ◽  
Giuseppe Casalino
Keyword(s):  
Surface Roughness ◽  
Energy Density ◽  
Process Parameters ◽  
Vickers Hardness ◽  
Powder Bed Fusion ◽  
Processing Conditions ◽  
Laser Powder Bed Fusion ◽  
Powder Bed ◽  
Fractional Density ◽  
Experimental Variation

Laser powder bed fusion (LPBF) can fabricate products with tailored mechanical and surface properties. In fact, surface texture, roughness, pore size, the resulting fractional density, and microhardness highly depend on the processing conditions, which are very difficult to deal with. Therefore, this paper aims at investigating the relevance of the volumetric energy density (VED) that is a concise index of some governing factors with a potential operational use. This paper proves the fact that the observed experimental variation in the surface roughness, number and size of pores, the fractional density, and Vickers hardness can be explained in terms of VED that can help the investigator in dealing with several process parameters at once.

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

2020 ◽  
Vol 26 (1) ◽  
pp. 100-106 ◽  
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.

Realistic design of laser powder bed fusion channels

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.

scholarly journals Characterization of additively manufactured AlSilOMg cubes with different porosities

2021 ◽  
Vol 121 (4) ◽  
Author(s):  
C. Taute ◽  
H. Möller ◽  
A. du Plessis ◽  
M. Tshibalanganda ◽  
M. Leary
Keyword(s):  
Surface Roughness ◽  
Additive Manufacturing ◽  
Structural Integrity ◽  
Lead Times ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Powder Bed ◽  
Sample Characteristics

SYNOPSIS Additive manufacturing can be used to produce complex and custom geometries, consolidating different parts into one, which in turn reduces the required number of assemblies and allows distributed manufacturing with short lead times. Defects, such as porosity and surface roughness, associated with parts manufactured by laser powder bed fusion, can severely limit industrial application. The effect these defects have on corrosion and hence long-term structural integrity must also be taken into consideration. The aim of this paper is to report on the characterization of porosity in samples produced by laser powder bed fusion, with the differences in porosity induced by changes in the process parameters. The alloy used in this investigation is AlSi10Mg, which is widely used in the aerospace and automotive industries. The sample characteristics, obtained by X-ray tomography, are reported. The design and production of additively manufactured parts can be improved when these defects are better understood. Keywords: additive manufacturing, L-PBF, AlSi10Mg, porosity, surface roughness, density.

A Combined Experimental-Numerical Method to Evaluate Powder Thermal Properties in Laser Powder Bed Fusion

2018 ◽  
Author(s):  
Bo Cheng ◽  
Brandon Lane ◽  
Justin Whiting ◽  
Kevin Chou
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Properties ◽  
Thermal Diffusivity ◽  
Laser Flash ◽  
Powder Layer ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Powder Bed ◽  
Powder Particles

Powder bed metal additive manufacturing (AM) utilizes a high-energy heat source scanning at the surface of a powder layer in a pre-defined area to be melted and solidified to fabricate parts layer by layer. It is known that powder bed metal AM is primarily a thermal process and further, heat conduction is the dominant heat transfer mode in the process. Hence, understanding the powder bed thermal conductivity is crucial to process temperature predictions, because powder thermal conductivity could be substantially different from its solid counterpart. On the other hand, measuring the powder thermal conductivity is a challenging task. The objective of this study is to investigate the powder thermal conductivity using a method that combines a thermal diffusivity measurement technique and a numerical heat transfer model. In the experimental aspect, disk-shaped samples, with powder inside, made by a laser powder bed fusion (LPBF) system, are measured using a laser flash system to obtain the thermal diffusivity and the normalized temperature history during testing. In parallel, a finite element model is developed to simulate the transient heat transfer of the laser flash process. The numerical model was first validated using reference material testing. Then, the model is extended to incorporate powder enclosed in an LPBF sample with thermal properties to be determined using an inverse method to approximate the simulation results to the thermal data from the experiments. In order to include the powder particles’ contribution in the measurement, an improved model geometry, which improves the contact condition between powder particles and the sample solid shell, has been tested. A multi-point optimization inverse heat transfer method is used to calculate the powder thermal conductivity. From this study, the thermal conductivity of a nickel alloy 625 powder in powder bed conditions is estimated to be 1.01 W/m·K at 500 °C.

scholarly journals Laser Powder Bed Fusion of Stainless Steel Grades: A Review

Metals ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 731 ◽  
Author(s):  
Zitelli ◽  
Folgarait ◽  
Di Schino
Keyword(s):  
Surface Roughness ◽  
Stainless Steel ◽  
Stainless Steels ◽  
Precipitation Hardening ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Steel Alloys ◽  
Powder Bed ◽  
Steel Grades ◽  
Mechanical Performances

In this paper, the capability of laser powder bed fusion (L-PBF) systems to process stainless steel alloys is reviewed. Several classes of stainless steels are analyzed (i.e., austenitic, martensitic, precipitation hardening and duplex), showing the possibility of satisfactorily processing this class of materials and suggesting an enlargement of the list of alloys that can be manufactured, targeting different applications. In particular, it is reported that stainless steel alloys can be satisfactorily processed, and their mechanical performances allow them to be put into service. Porosities inside manufactured components are extremely low, and are comparable to conventionally processed materials. Mechanical performances are even higher than standard requirements. Micro surface roughness typical of the as-built material can act as a crack initiator, reducing the strength in both quasi-static and dynamic conditions.

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