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Metal additive manufacturing is increasingly used as a complementary manufacturing technique in industrial settings and slowly moving from pure prototyping applications toward full production. In parallel, there is an emergence of Industry 4.0, where the applicability of concepts such as digital twins of manufacturing machines and components are being investigated. Compared to conventionally manufactured parts, typical quality metrics of metal additively manufactured components such as dimensions, roughness, porosity, and hardness are underperforming in an as-built state. As a mitigation strategy, the build chamber variables are often measured and logged by the metal additive manufacturing system to maintain a stable production environment. Thus, proper insight into the expected responses in part quality from changes in those build chamber variables is important in the pursuit of digital twins and process improvement. This sheds more light on the influence of the gas flow variables, namely gas flow speed, relative pressure, and oxygen content on the metal additive manufacturing quality metrics, specifically channel roughness, bulk porosity, average diameter, the equivalent diameter of the unobstructed cross-sectional area, and hardness of the bulk. A Design of Experiments was implemented on two laser powder bed fusion systems, namely an SLM 280 processing 316L stainless steel and an SLM 500 processing Ti6Al4V. The current work found that surface oxidation of 316L and Ti6Al4V components may be classified based on simple red, green, and blue (RGB) color constituent analysis. The influence of gas flow variables was found to be different in the two investigated SLM systems, suggesting a high dependency on the processed material. Oxygen content in the build chamber had the highest standalone effect on the selected quality metrics, while the gas flow speed had the lowest standalone effect. The second-order effects were found to be, in general, more significant than the main effects. The findings of the current work is a step towards an improved understanding of the interaction effects of gas flow conditions on typical quality metrics of metal additive manufactured components. By the creation of simple but computationally fast response surface models, in-line assessments may be carried out and the effect of process variability on component quality may be evaluated in-situ while being one step away from the full feedback control implementation in the digital twin. Following the methodology of the current work for other laser powder bed fusion systems enables the generation of 3D point cloud visualizations for decision making under uncertainty.

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.

Conformal cooling channels, made by the laser powder bed fusion process, are a promising design strategy for optimising cooling and process control of manufacturing tools and injections moulds. The...

Crystallization fouling presents a significant challenge in a wide range of industries. Accurate understanding of crystal formation is crucial for planning preventative measures and maximizing the effectiveness of maintenance interventions. In this study, we demonstrate that understanding net deposition rates depends on the knowledge of the detachment mechanisms and deposition distribution characteristics. We quantify deposition in a once-through flow set-up and visualize crystal formation through high-resolution X-ray micro-computed tomography scanning. Additionally, we quantify the height distribution of deposited crystals through computed surface texture parameters. Finally, we use computational fluid dynamics, implementing large-eddy simulations turbulence modelling and Eulerian transport of chemical species, to describe bulk and wall reactions and quantify energy and mass transport in turbulent eddies. Results show that attachment and detachment processes depend on fluid hydrodynamics; the influx of material determines the overall deposition to the surface, while the deposition pattern is governed by the surface morphology of the initial surface morphology. Our findings provide a foundation for understanding fouling mechanisms and present a template for developing more accurate prediction models., Chemical Engineering Journal, 430 (2), ISSN:0300-9467, ISSN:1385-8947, ISSN:1873-3212, ISSN:0923-0467

Residual stresses and deflections are two major issues in laser-based powder bed fusion (L-PBF) parts. One of the most efficient and reliable ways for predicting residual stresses and final distortions is via a calibrated numerical model. In this work, a part-scale finite element thermo-mechanical model for Ti6Al4V is developed in the commercial software Abaqus/CAE 2018. The flash heating (FH) method is used as the initial multi-scaling law to avoid time-consuming meso-scale simulations. The model has been verified by doing a mesh-independency analysis. To check the validity of the model, dedicated experiments involving samples with specific scanning strategies were performed. Experimental measurements were made by optical 3D scanning with the fringe projection technique. An in-house made Python script was written for the stripe-wise and layer-wise partitioning of the numerical model, along with material and boundary condition attributions. As expected, the results show that layer-wise FH is insensitive to the scanning pattern and will lead to an isotropic stress field. It is shown that the FH method overestimates the minimum deflection magnitude compared to the experiments by 46.2 %. Sequential FH (SFH) is then proposed to resolve this problem. Results show that by refining the stripe widths in SFH from 15 mm to 1.5 mm, the deviation between the predicted and measured deflection reduces from 35.7 % to 1.19 %. However, the required computational time increases from 9.3 h to 65 h.

Metal additive manufacturing is highly suited to enhance the performance of engineering applications with sophisticated internal features and passageways. Laser Powder Bed Fusion (LPBF) is commonly used or considered for fabrication in these applications, although the resulting channels can show significant form and surface deviations, particularly due to dross-formation at overhang-areas. Binder Jetting (BJ), another additive manufacturing method that can process metals does not employ a heat source to fuse powder particles during build-up and therefore has the potential to overcome these limitations. In this study, additively manufactured circular channels with a nominal diameter of two millimeters are made by LPBF and BJ in seven different directions and are extensively analyzed depending on their orientation. The test-artifacts are made by four different state-of-the-art LPBF and BJ system manufacturers with standard parameters in 17−4PH stainless steel and with similar layer thicknesses. A novel type of X-ray Computed Tomography (CT) image analysis method for additively manufactured channels is applied in combination with commercial image analysis software. Form deviations and surface texture are characterized in accordance with ISO1101 and ISO 4287:1997. Results show a high level of precision, independently of build direction for channels made by BJ when compared to LPBF. The accuracy of BJ-channels is strongly dependent on the appropriate scaling before printing. Parallel to the build direction, LPBF-channels exhibit superior characteristics. The channels investigated in this work are categorized into ISO tolerance grades IT13−17 for LPBF and IT13−15 for BJ following ISO268−2. Based on the findings, design considerations and characteristic attributes of each process to manufacture channels are discussed within a broader context.

The increasingly complex shapes and geometries being produced using additive manufacturing necessitate new characterization techniques that can address the corresponding challenges. Standard techniques for roughness and texture measurements are inept at characterizing the internal surfaces in freeform geometries. Hence, this work presents a new methodology for extracting and quantitatively characterizing the roughness on internal surfaces. The methodology links X-ray CT with complete roughness characterization of channels manufactured by laser powder bed fusion through a novel image analysis approach of X-ray CT data. Global and local orientation parameters are defined to enable a full 360° description of the roughness inside additively manufactured channels. X-ray CT data is analyzed to generate 3D deviation data – based on which multiple local roughness profiles are extracted and analyzed in accordance with the ISO 4287:1997 standard. To demonstrate the proposed methodology, seven circular 17-4 PH stainless steel channels produced at different inclinations and with a diameter of 2 mm are investigated as a case study. Qualitative and quantitative characterization of the roughness is obtained through the use of the proposed methodology. A strong dependence of the local roughness on the corresponding α and β orientations is found. A simple regression model is subsequently extracted from the calculated roughness values and allows prediction of Ra-values in the channels for the ranges between 0° ≤ α ≤ 90° and 80° ≤ β ≤ 280°. In addition to decreasing the effective hydraulic diameter of a cooling channel, the surface roughness also influences the local Nusselt number, which is quantified using the extracted regression model.

In this paper we describe metal additive manufacturing (AM) processes in general, and laser bed fusion processes in particular. The process characteristics are described, and the various modelling approaches demonstrated. The open AM architecture developed at DTU Mechanical Engineering is introduced, as well as an alternative process chain based on AM and subsequent injection moulding.