Evaluating the Effect of Deposition Strategy on Mechanical Characteristics of 316L Parts Produced by Laser Powder Directed Energy Deposition Process

The production of large components, the possibility to repair damaged parts and the ability to produce components of multi-graded or functional-graded materials are the main drivers of the research and the application of the Laser Powder Directed Energy Deposition (LP-DED) process. However, the knowledge of the process and of the relationships among the process parameters and the characteristics of the produced part is currently not completely understood. The aim of this paper is to fill the current gap in the scientific literature related to the effect of the deposition strategy on the part quality. Therefore, the influence of two of the most important parameters, namely the deposition path and the idle time, on the residual stresses and porosity is evaluated on 316L samples produced by the LP-DED process. The obtained results show that both parameters have a high influence on the porosity level and the residual stresses. In particular, it can be seen that a high value of idle time worsens both porosity and residual stresses. Then, it is also observed that the raster deposition path leads to a lower value of stresses

Simulating the sintering of powder particles during the preheating step of Electron Beam Melting process: Review, challenges and a proposal

The powder bed preheating before melting is a distinctive manufacturing step of the Electron Beam Melting (EBM) process. During preheating slight sintering occurs and small necks are formed between neighbouring particles. The necks improve the heat transfer and the powder bed strength allowing a reduction of supports structures and the neutralisation of the so-called smoke. However, preheating may represent over 50% of the total production time. This work investigates the major strategies in literature for preheating phase optimisation and proposes a numerical simulation approach to evaluate the neck growth and the corresponding sintering level

A multiscale framework for the evaluation of thermal conductivity of sintered powder at the powder bed fusion with electron beam conditions

The thermal conductivity of the powder bed during the electron beam powder bed fusion (PBF-EB) process strongly influences the process conduction and the quality of the components produced. The evaluation of this property is challenging. The models currently available in the literature cannot provide values of the thermal conductivity that consider the temperature evolution typical of the preheating step. This work presents a novel computational framework to evaluate the thermal conductivity of a powder bed for the PBF-EB process. The framework combines the thermal conditions of the PBF-EB process with information on the geometrical features of the powder bed and an analytic method to calculate the thermal conductivity and its variation with temperature and time. The proposed numerical framework is applied to the body centred structure (BCC), a typical arrangement that can emulate the PBF-EB conditions. The numerical framework is multiscale by nature, providing information about the whole powder bed starting from geometrical information about the neck among the powder particles

Effect of the Sintering Conditions on the Neck Growth during the Powder Bed Fusion with Electron Beam (PBF-EB) Process

A distinctive characteristic of the powder bed fusion with electron beam (PBF-EB) process is the sintering of the powder particles. For certain metallic materials, this is crucial for the success of the subsequent step, the melting, and, generally, the whole process. Despite the sintering mechanisms that occur during the PBF-EB process being similar to well-known powder metallurgy, the neck growth rates are significantly different. Therefore, specific analyses are needed to understand the influence of the PBF-EB process conditions on neck growth and neck growth rate. Additionally, some aspects, such as the rigid body motion of the particles during the sintering process, are still challenging to analyze. This work systematically investigated the effects of different particle diameters and particle diameter ratios. Additionally, the impact of the rigid body motion of the particles in the sintering was analyzed. This work demonstrated that the sintering results significantly depended on the EB-PBF process conditions

Build orientation effect on Ti6Al4V thin-wall topography by electron beam powder bed fusion

Additive Manufacturing is a key enabling technology for Industry 4.0 and the Green Deal, allowing more efficient resources exploitation while providing innovative design to critical components. Electron Beam Powder Bed Fusion (EB-PBF) is an edge technology for many sectors, i.e. aerospace, medical, and automotive. The control of the surface finish by surface topography measurements is essential to engineer surface functional properties, whose specifications are application specific. This works investigates the effect of thin-wall orientation and surface inclination on the topography, described by areal field and feature parameters, to provide designers with a useful tool in the early stage of product development and tolerance specification and verificatio

On the Telegraph Process Driven by Geometric Counting Process with Poisson-Based Resetting

We investigate the effects of the resetting mechanism to the origin for a random motion on the real line characterized by two alternating velocities v1 and v2 . We assume that the sequences of random times concerning the motions along each velocity follow two independent geometric counting processes of intensity λ , and that the resetting times are Poissonian with rate ξ> 0 . Under these assumptions we obtain the probability laws of the modified telegraph process describing the position and the velocity of the running particle. Our approach is based on the Markov property of the resetting times and on the knowledge of the distribution of the intertimes between consecutive velocity changes. We obtain also the asymptotic distribution of the particle position when (i) λ tends to infinity, and (ii) the time goes to infinity. In the latter case the asymptotic distribution arises properly as an effect of the resetting mechanism. A quite different behavior is observed in the two cases when v2< 0 < v1 and 0 < v2< v1 . Furthermore, we focus on the determination of the moment-generating function and on the main moments of the process describing the particle position under reset. Finally, we analyse the mean-square distance between the process subject to resets and the same process in absence of resets. Quite surprisingly, the lowest mean-square distance can be found for ξ= 0 , for a positive ξ , or for ξ→ + ∞ depending on the choice of the other parameters

Renewable Resources for Enantiodiscrimination: Chiral Solvating Agents for NMR Spectroscopy from Isomannide and Isosorbide

A new family of chiral selectors was synthesized in a single synthetic step with yields up to 84% starting from isomannide and isosorbide. Mono- or disubstituted carbamate derivatives were obtained by reacting the isohexides with electron-donating arylisocyanate (3,5-dimethylphenyl- or 3,5-dimethoxyphenyl-) and electron-withdrawing arylisocyanate (3,5-bis(trifluoromethyl)phenyl-) groups to test opposite electronic effects on enantiodifferentiation. Deeper chiral pockets and derivatives with more acidic protons were obtained by derivatization with 1-naphthylisocyanate and p-toluenesulfonylisocyanate, respectively. All compounds were tested as chiral solvating agents (CSAs) in H-1 NMR experiments with rac-N-3,5-dinitrobenzoylphenylglycine methyl ester in order to determine the influence of different structural features on the enantiodiscrimination capabilities. Some selected compounds were tested with other racemic analytes, still leading to enantiodiscrimination. The enantiodiscrimination conditions were then optimized for the best CSA/analyte couple. Finally, a 2D- and 1D-NMR study was performed employing the best performing CSA with the two enantiomers of the selected analyte, aiming to determine the enantiodiscrimination mechanism, the stoichiometry of interaction, and the complexation constant

Accuracy of complex internal channels produced by laser powder bed fusion process

Additive manufacturing (AM) technology has great potential in manufacturing complex internal channels for several applications such as satellite-communication microwave systems. These systems can have complex shapes and make traditional finishing processes a challenge for additive parts. Therefore, it is desirable that the internal surfaces are as close as possible to the tolerance of the field of application. In this study, a complex component, a unique waveguide device with bending, twisting and filtering functionalities, has been designed and manufactured in AlSi10Mg alloy through laser powder bed fusion (L-PBF) process. Three different prototypes with three different curvature (R of 50 mm, 40 mm and 30 mm), operating in Ku/K band, have been manufactured and tested showing a very good agreement with the desired performances. Using 3D scan data, the internal deviations from the CAD model have been evaluated showing an average deviation of the internal areas of about 0.08 mm, 0.046 mm and 0.023 mm from the CAD model for the R of 50 mm, 40 mm and 30 mm respectively The surface roughness measured in the internal channel is about Ra (arithmetic average roughness) of 8 μm ± 1.3 μm and Rz (average maximum height of the roughness profile) of 62.3 μm ± 0.34 μm