scholarly journals A Coupled DEM/SPH Computational Model to Simulate Microstructure Evolution in Ti-6Al-4V Laser Powder Bed Fusion Processes

Metals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 858
Author(s):  
Sharen Cummins ◽  
Paul W. Cleary ◽  
Gary Delaney ◽  
Arden Phua ◽  
Matthew Sinnott ◽  
...  
Keyword(s):  
Computational Model ◽  
Microstructure Evolution ◽  
Flow Simulation ◽  
Single Layer ◽  
Laser Fusion ◽  
Powder Bed Fusion ◽  
Powder Morphology ◽  
Spherical Powder ◽  
Powder Bed ◽  
Scan Pattern

A new multi-stage three-dimensional transient computational model to simulate powder bed fusion (L-PBF) additive manufacturing (AM) processes is presented. The model uses the discrete element method (DEM) for powder flow simulation, an extended smoothed particle hydrodynamics (SPH) for melt pool dynamics and a semi-empirical microstructure evolution strategy to simulate the evolving temperature and microstructure of non-spherical Ti-6Al-4V powder grains undergoing L-PBF. The highly novel use of both DEM and SPH means that varied physics such as collisions between non-spherical powder grains during the coating process and heat transfer, melting, solidification and microstructure evolution during the laser fusion process can be simulated. The new capability is demonstrated by applying a complex representative laser scan pattern to a single-layer Ti-6Al-4V powder bed. It is found that the fast cooling rate primarily leads to a transition between the β and α martensitic phases. A minimal production of the α Widmanstatten phase at the outer edge of the laser is also noted due to an in situ heat treatment effect of the martensitic grains near the laser. This work demonstrates the potential of the coupled DEM/SPH computational model as a realistic tool to investigate the effect of process parameters such as powder morphology, laser scan speed and power characteristics on the Ti-6Al-4V powder bed microstructure.

scholarly journals The use of non-spherical powder particles in Laser Powder Bed Fusion

2021 ◽  
Vol 1135 (1) ◽  
pp. 012018
Author(s):  
Tatiana Fedina ◽  
Jesper Sundqvist ◽  
Alexander F. H. Kaplan
Keyword(s):  
High Speed ◽  
Process Zone ◽  
Analytical Calculation ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
High Speed Imaging ◽  
Powder Morphology ◽  
Spherical Powder ◽  
Powder Bed ◽  
Computed Microtomography

Abstract Laser powder bed fusion (LPBF) generally involves the use of near-spherical powders due to their smooth morphology and enhanced flowability that allow for easier powder layering and laser processing. Non-spherical powders, on the other hand, are more cost-efficient to manufacture, however, the underlying mechanisms of their movement and interparticle interaction on the powder bed are still unclear. Thus, this study reports on the use of irregular iron-based powder material in LPBF, with a specific focus on particle motion and interaction behavior on the powder bed. The powder morphology, sphericity and particle size were analysed using X-ray computed microtomography and scanning electron microscopy. Based on the acquired data and by using a simplified analytical calculation, the influence of the particle shape/size on the particle movement in LPBF was established. High-speed imaging was employed to investigate the particle flow dynamics in the process zone, as well as the powder entrainment phenomenon. Particle entrainment and entrainment distances along the scanning direction were measured for near-spherical and non-spherical powders. The obtained results were compared between the powders, revealing a dissimilar particle transfer behavior. Non-spherical powder had a shorter entrainment distance partly attributed to the weaker drag force acting on these particles.

scholarly journals A novel physics-based and data-supported microstructure model for part-scale simulation of laser powder bed fusion of Ti-6Al-4V

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Jonas Nitzler ◽  
Christoph Meier ◽  
Kei W. Müller ◽  
Wolfgang A. Wall ◽  
N. E. Hodge
Keyword(s):  
Selective Laser Melting ◽  
Microstructure Evolution ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Laser Melting ◽  
Cooling Rates ◽  
Powder Bed ◽  
Proposed Model ◽  
Microstructure Model ◽  
Transformation Diagrams

AbstractThe elasto-plastic material behavior, material strength and failure modes of metals fabricated by additive manufacturing technologies are significantly determined by the underlying process-specific microstructure evolution. In this work a novel physics-based and data-supported phenomenological microstructure model for Ti-6Al-4V is proposed that is suitable for the part-scale simulation of laser powder bed fusion processes. The model predicts spatially homogenized phase fractions of the most relevant microstructural species, namely the stable $$\beta $$ β -phase, the stable $$\alpha _{\text {s}}$$ α s -phase as well as the metastable Martensite $$\alpha _{\text {m}}$$ α m -phase, in a physically consistent manner. In particular, the modeled microstructure evolution, in form of diffusion-based and non-diffusional transformations, is a pure consequence of energy and mobility competitions among the different species, without the need for heuristic transformation criteria as often applied in existing models. The mathematically consistent formulation of the evolution equations in rate form renders the model suitable for the practically relevant scenario of temperature- or time-dependent diffusion coefficients, arbitrary temperature profiles, and multiple coexisting phases. Due to its physically motivated foundation, the proposed model requires only a minimal number of free parameters, which are determined in an inverse identification process considering a broad experimental data basis in form of time-temperature transformation diagrams. Subsequently, the predictive ability of the model is demonstrated by means of continuous cooling transformation diagrams, showing that experimentally observed characteristics such as critical cooling rates emerge naturally from the proposed microstructure model, instead of being enforced as heuristic transformation criteria. Eventually, the proposed model is exploited to predict the microstructure evolution for a realistic selective laser melting application scenario and for the cooling/quenching process of a Ti-6Al-4V cube of practically relevant size. Numerical results confirm experimental observations that Martensite is the dominating microstructure species in regimes of high cooling rates, e.g., due to highly localized heat sources or in near-surface domains, while a proper manipulation of the temperature field, e.g., by preheating the base-plate in selective laser melting, can suppress the formation of this metastable phase.

The role of texturing and microstructure evolution on the tensile behavior of heat-treated Inconel 625 produced via laser powder bed fusion

2020 ◽  
Vol 769 ◽  
pp. 138500 ◽  
Author(s):  
Giulio Marchese ◽  
Simone Parizia ◽  
Masoud Rashidi ◽  
Abdollah Saboori ◽  
Diego Manfredi ◽  
...  
Keyword(s):  
Microstructure Evolution ◽  
Tensile Behavior ◽  
Inconel 625 ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Powder Bed ◽  
Heat Treated

On Characterizing Uncertainty Sources in Laser Powder Bed Fusion Additive Manufacturing Models

2021 ◽  
Author(s):  
Tesfaye Moges ◽  
Kevontrez Jones ◽  
Shaw Feng ◽  
Paul Witherell ◽  
Gaurav Ameta
Keyword(s):  
Additive Manufacturing ◽  
Computational Models ◽  
Predictive Accuracy ◽  
Powder Bed Fusion ◽  
Metal Powders ◽  
Laser Powder Bed Fusion ◽  
Powder Morphology ◽  
Powder Bed ◽  
Uncertainty Sources ◽  
Ontology Language

Abstract Tremendous efforts have been made to use computational models of, and simulation models of, Additive Manufacturing (AM) processes. The goals of these efforts are to better understand process complexities and to realize better, high-quality parts. However, understanding whether any model is a correct representation for a given scenario is a difficult proposition. For example, when using metal powders, the laser powder bed fusion (L-PBF) process involves complex physical phenomena such as powder morphology, heat transfer, phase transformation, and fluid flow. Models based on these phenomena will possess different degrees of fidelity since they often rely on assumptions that may neglect or simplify process physics, resulting in uncertainties in their prediction accuracy. Predictive accuracy and its characterization can vary greatly between models due to their uncertainties. This paper characterizes several sources of L-PBF model uncertainty for low, medium, and high-fidelity thermal models including modeling assumptions (model-form uncertainty), numerical approximations (numerical uncertainty), and input parameters (parameter uncertainty). This paper focuses on the input uncertainty sources, which we model in terms of a probability density function (PDF), and its propagation through all other L-PBF models. We represent uncertainty sources using the Web Ontology Language (OWL), which allows us to capture the relevant knowledge used for interoperability and reusability. The topology and mapping of the uncertainty sources establish fundamental requirements for measuring model fidelity and for guiding the selection of a model suitable for its intended purpose.

Microstructure evolution of Inconel 738 fabricated by pulsed laser powder bed fusion

2018 ◽  
Vol 4 (2) ◽  
pp. 97-107 ◽  
Author(s):  
Jose Alberto Muñiz-Lerma ◽  
Yuan Tian ◽  
Xianglong Wang ◽  
Raynald Gauvin ◽  
Mathieu Brochu
Keyword(s):  
Microstructure Evolution ◽  
Pulsed Laser ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Powder Bed
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