Single Track Research Articles

A holistic approach for evaluation of Gaussian versus ring beam processing on structure and properties in laser powder bed fusion

In this study, a holistic evaluation strategy employing a complex test artifact, coupled with single line scan tracks, was employed to examine the influence of different laser beam energy profiles on various features of laser-based powder bed fusion of metals (PBF-LB/M). Using IN718, results revealed a significant influence of the laser beam on bead geometry. Specifically, the conventional Gaussian beam produced deeper, concave-shaped melt pools, while the ring beam resulted in wider and shallower beads. In terms of productivity, the artifacts (two each) fabricated using the Gaussian beam required 6 h and 6 min of build time, while those built using ring beam required only 3 h and 49 min (37% build time reduction) but a defocused Gaussian beam (not included in this study) can match the productivity of the ring beam. However, the holistic approach using the complex test artifact highlighted drawbacks associated with the ring beam, including increased lack of fusion porosity, compromised resolution for features below 0.5 mm, and less than 10% elongation to break in both as built and heat-treated conditions. While acknowledging the potential for improvement through further process optimization, the study concludes that the shallower melt pools produced by the ring beam may cause limitations as layer thicknesses increase. Microstructural analysis revealed distinct grain characteristics, with the Gaussian beam producing more equiaxed grains and the ring beam favouring columnar grains positioned along the build direction. The work primarily highlights the need for and benefits from a holistic analysis in PBF-LB/M technology, ensuring data driven outcomes.

The Effects of Particle LET and Fluence on the Complexity and Frequency of Clustered DNA Damage.

Clustered DNA-lesions are predominantly induced by ionizing radiation, particularly by high-LET particles, and considered as lethal damage. Quantification of this specific type of damage as a function of radiation parameters such as LET, dose rate, dose, and particle type can be informative for the prediction of biological outcome in radiobiological studies. This study investigated the induction and complexity of clustered DNA damage for three different types of particles at an LET range of 0.5-250 keV/μm. Nanometric volumes (36.0 nm3) of 15 base-pair DNA with its hydration shell was modeled. Electron, proton, and alpha particles at various energies were simulated to irradiate the nanometric volumes. The number of ionization events, low-energy electron spectra, and chemical yields for the formation of °OH, H°, , and H2O2 were calculated for each particle as a function of LET. Single- and double-strand breaks (SSB and DSB), base release, and clustered DNA-lesions were computed from the Monte-Carlo based quantification of the reactive species and measured yields of the species responsible for the DNA lesion formation. The total amount of DNA damage depends on particle type and LET. The number of ionization events underestimates the quantity of DNA damage at LETs higher than 10 keV/μm. Minimum LETs of 9.4 and 11.5 keV/μm are required to induce clustered damage by a single track of proton and alpha particles, respectively. For a given radiation dose, an increase in LET reduces the number of particle tracks, leading to more complex clustered DNA damage, but a smaller number of separated clustered damage sites. The dependency of the number and the complexity of clustered DNA damage on LET and fluence suggests that the quantification of this damage can be a useful method for the estimation of the biological effectiveness of radiation. These results also suggest that medium-LET particles are more appropriate for the treatment of bulk targets, whereas high-LET particles can be more effective for small targets.

Design and analysis of three-dimensional braiding machine with track change interlocking

When performing three-dimensional braiding, the carrier base of a conventional braiding machine can only be move on a single track, but cannot be switched between tracks. In this study, a three-dimensional braiding machine with orbital change interlocking is designed to realize the carrier track change. Aiming at the crucial components in track change interlocking mechanism, the track change process is separated into seven periods, and the driving function of slider and electric rotary are obtained. The kinematics model of track change interlocking mechanism is established, the velocity, position and trajectory of carrier base are analyzed on ADAMS simulation software. The results show that the carrier base maximum velocity is −226.51 mm/s, the carrier base maximum position is 68.30 mm, and the carrier base maximum vibration is 0.14 to 1.08 mm in track change process, prototype test indicate that three-dimensional braiding machine with track change interlocking is feasible, provides reference for the future design of three-dimensional braiding machine.

Generating brick-like melt pools for Laser-Based Powder Bed Fusion using flexible beam shaping: a proof of concept on bead-on-plate single tracks

Despite the highest industrial maturity among additive manufacturing processes, laser-based powder bed fusion of metals (PBF-LB/M) lacks the productivity to further establish as an industrial manufacturing process. One approach for adjusting the melt pool shape to increase productivity in PBF-LB/M is spatial beam shaping. The freedom of beam shaping is almost unlimited, owing to modern optical concepts. The key is a beam shape optimized for a specific target. In this publication, the target is a brick-like melt pool cross-section. The publication demonstrates how the corresponding laser beam shape is designed using numerical optimization. The computed beam shape is reproduced using reflective spatial light phase modulators. The calculation is validated based on single-track experiments. Applying the optimized beam shape results in a melt pool shape similar to the optimization target. The width and depth of the melt track produced deviate by a maximum of 7 % from the specified target values.

Tornar-se sujeito de uma profissão: contornos de si gestados entre os fragmentos de um currículo de formação em Educação Física

Abstract This article problematizes professional subjectivations produced in a physical education undergraduate curriculum that tried to house broad work expectations in a single formative track, which included both acting in K-12 education and non-school contexts. Moved by post-structuralist assumptions, this problematization conceives the curriculum as a device, a weave-image composed of truths, power relations, and subject fabrication processes, whose analytical construction is made possible through a methodological gesture of a cartographic nature. From the narratives of graduates who followed the curriculum in question, two figures or characters emerged who, when described, have been delineated and recognized within Physical Education. These figures put us in front of distinct and dissonant ways of obliging oneself with professional truths, dissolving the plenitude of certain unifying pretensions that echo in this training field.

Multiphysical simulation of hot cracking in Laser-Based Powder Bed Fusion

This study extends an existing comprehensive computational framework to gain insight on hot cracking in the simulation of laser-based additive manufacturing via powder bed fusion. A novel approach to predict hot crack susceptibility based on vapor cavitation, building on a conceptual model akin to the Rappaz-Drezet-Gremaud criterion is introduced. Unlike conventional practices involving ex-situ evaluation of a criterion, the proposed model emerges implicitly from the underlying multiphysical modeling framework. The model exhibits sensitivity to variations in both material attributes (e.g., alloy composition) and processing conditions (e.g., laser beam shape or scanning strategy). Furthermore, non-equilibrium solidification is incorporated in the underlying Mass-of-Fluid framework, and a model for multi-layer printing is introduced to extend the length and time scale, enabling the derivation of detailed thermal histories on near-part-scale level. Consequently, the framework proves pivotal in optimizing process parameters, transcending the limitations inherent in conventional single melt track computational experiments.

Fast spatial laser beam modulation for improved process control in Laser Powder Bed Fusion

We report on the implementation of a high frequency beam oscillation (wobbling) strategy for improving process control during laser powder bed fusion of single weld tracks on Inconel 625. Oscillation frequencies ranging from ~ 600 Hz to 7000 Hz, and different oscillation trajectories (circular, parallel or perpendicular to the direction of scanning) were explored. Highspeed imaging was used to elucidate the dynamics of the melt pool induced by the wobble beams, along with in situ absorptivity measurements to substantiate our hypothesis that the dynamic nature of wobble beams reduces absorptive losses due to laser-vapor interactions and results in improved coupling at the melt pool. Operando X-ray radiography was carried out to visualize sub-surface melt flow dynamics, correlate to spatter mechanisms and optimize the window for improving process stability. Our observations indicate that wobble beams increase the aspect ratio of the melt pool by up to 4×, depending on the oscillation frequency and energy input. Highspeed imaging and X-ray radiography reveal an optimized process parameter window for reducing spatter, improving absorptivity and creating a stable melt pool at high (several kHz) oscillation frequencies.

Mesoscale Simulation of Laser Powder Bed Fusion with an Increased Layer Thickness for AlSi10Mg Alloy

Low performance is considered one of the main drawbacks of laser powder bed fusion (LPBF) technology. In the present work, the effect of the AlSi10Mg powder layer thickness on the laser melting process was investigated to improve the LPBF building rate. A high-fidelity simulation of the melt pool formation was performed for different thicknesses of the powder bed using the Kintech Simulation Software for Additive Manufacturing (KiSSAM, version cd8e01d) developed by the authors. The powder bed after the recoating operation was obtained by the discrete element method. The laser energy deposition on the powder particles and the substrate was simulated by ray tracing. For the validation of the model, an experimental analysis of single tracks was performed on two types of substrates. The first substrate was manufactured directly with LPBF technology, while the second was cast. The simulation was carried out for various combinations of process parameters, predominantly with a high energy input, which provided a sufficient remelting depth. The calculations revealed the unstable keyhole mode appearance associated with the low absorptivity of the aluminum alloy at a scanning speed of 300 mm/s for all levels of the laser power (325–375 W). The results allowed formulating the criteria for the lack of fusion emerging during LPBF with an increased layer thickness. This work is expected to provide a scientific basis for the analysis of the maximum layer thickness via simulation to increase the performance of the technology.

Compiling Method of Single Track Heavy Haul Railway Operating Diagram in Group Tracking Mode

Compiling Method of Single Track Heavy Haul Railway Operating Diagram in Group Tracking Mode

Development of crystallographic misorientation in laser powder bed fusion 316L stainless steel

This study examines the development of crystallographic misorientation and its relations to the solidification microstructure in Laser Powder Bed Fusion (LPBF) alloys. We performed a single laser track experiment on an SS316L single-crystal substrate to characterize the correlation between solidification features and misorientation evolution within a single LPBF melt pool and found that the sources of misorientations inside the melt pool can be attributed to both rapid solidification (misorientation aligning precisely with the cell walls & colony boundaries) and residual stress-induced plastic deformation (misorientation independent of solidification morphology), while the residual stress-induced plastic deformation acts as the sole mechanism to extend this misorientation outside of the melt pool boundary. The misorientation development both inside and outside of the melt pool always occurs through a crystal rotation around one of the {111} axes without any obvious correlation with the sample orientations. Additionally, we conducted a comprehensive literature overview of mechanisms in the solidification process and critically assessed the current understanding of misorientation formation and the causes of the loss of epitaxial grain growth.

Development of a rapid solidification model for additive manufacturing process and application to Al-Si alloy

Accurate prediction of the solidification microstructure produced by additive manufacturing (AM) process is indispensable for the precise manufacturing process control. In the present study, a simple solidification model that can be applied to the powder bed fusion – laser beam (PBF-LB) process has been developed by integrating conventional and rapid solidification theories in literature. Based on the solidification parameters calculated by Rosenthal equation, the present solidification model can predict the primary dendrite arm spacing (PDAS), primary cell fraction, and solute profile using solute trapping, dendrite tip undercooling, and eutectic undercooling. Single track experiments for Al-12Si binary alloy were also performed to validate the accuracy of the model.

Обеспечение формирования функциональной грамотности на уроках иностранного языка

Functional literacy is an important skill that can be developed in a second language classroom at secondary and high school. This article introduces a functional literacy program of advanced training for teachers of foreign languages. The author used axiological, personal-activity, and interdisciplinary approaches with non-participant observation methods and pedagogical modeling to analyze legal norms, school standards, and foreign and domestic publications. The program offers a single school-university track represented as a course of professional training for teachers of foreign languages at the Siberian Institute of Management, Novosibirsk. Teachers of foreign languages donated their teaching and learning experience in preparing students for state exams in foreign languages and functional literacy development. The study revealed some gaps in the academic standardization, advanced training for teachers, and methodological support for Second Language at school. The author identified vectors of prospective development in the field of functional literacy as school, as well as the reasons behind the passive attitude of most school teachers to functional literacy development. Advanced training in this sphere should be compulsory and interdisciplinary. The connection between functional literacy, state exam diagnostics, and teachers’ competences is of exceptional importance in Russian education and requires more continuity.

Prediction of Ni-based alloy microstructure in wire arc additive manufacturing from cellular automata model

Wire Arc Additive manufacturing (WAAM) process is a class of directed energy deposition processes with wire feedstock. The process enables a higher build rate than the powder-based additive process and integrates multiple custom wire feedstock to induce spatial variation of microstructure and composition. The lower speed employed in WAAM reduces the cooling rate and resultant residual stress compared to the powder bed fusion process. The systematic epitaxy across the layer creates a directional/columnar microstructure for Ni-superalloy. Here, we report cellular automata model development to predict the microstructure evolution with surface and bulk nuclei for single track and multiple layers. The cellular automata model was developed to account for secondary element addition, predict segregation, local melting, and latent heat release, as well as predict crystallographic texture/Euler angles from orientation information. We experimentally validated the layer-level microstructure and texture from SEM and EBSD, respectively, and found agreement with the CA model developed.

Monitoring of Single-Track Melting States Based on Photodiode Signal during Laser Powder Bed Fusion.

Single track is the basis for the melt pool modeling and physics work in laser powder bed fusion (LPBF). The melting state of a single track is closely related to defects such as porosity, lack of fusion, and balling, which have a significant impact on the mechanical properties of an LPBF-created part. To ensure the reliability of part quality and repeatability, process monitoring and feedback control are emerging to improve the melting states, which is becoming a hot topic in both the industrial and academic communities. In this research, a simple and low-cost off-axial photodiode signal monitoring system was established to monitor the melting pools of single tracks. Nine groups of single-track experiments with different process parameter combinations were carried out four times and then thirty-six LPBF tracks were obtained. The melting states were classified into three classes according to the morphologies of the tracks. A convolutional neural network (CNN) model was developed to extract the characteristics and identify the melting states. The raw one-dimensional photodiode signal data were converted into two-dimensional grayscale images. The average identification accuracy reached 95.81% and the computation time was 15 ms for each sample, which was promising for engineering applications. Compared with some classic deep learning models, the proposed CNN could distinguish the melting states with higher classification accuracy and efficiency. This work contributes to real-time multiple-sensor monitoring and feedback control.

Process Parameter Optimization for Laser Powder Bed Fusion of Fe-Si Alloy Considering Surface Morphology and Track Width of Single Scan Track.

A laser power bed fusion (L-PBF) manufacturing process was optimized by analyzing the surface morphology and track width w of single scan tracks (SSTs) on Fe-3.4wt.%Si. An SST was evaluated under process conditions of laser power P, scan speed V, and energy density E = P/V. The SST surface shape was mainly affected by E; desirable thin and regular tracks were obtained at E = 0.3 and 0.4 J/mm. An L-PBF process window was proposed considering the optimal w of SST, and the appropriate range of E for the alloy was identified to be 0.24 J/mm to 0.49 J/mm. w showed a strong relationship with E and V, and an analytic model was suggested. To verify the process window derived from the appropriate w of SST, cubic samples were manufactured with the estimated optimal process conditions. Most samples produced had a high density with a porosity of <1%, and the process window derived from SST w data had high reliability. This study presents a comprehensive approach to enhancing additive manufacturing for Fe-3.4Si alloy, offering valuable insights for achieving high-quality samples without the need for time-intensive procedures.

The effect of molten pool evolution on the formation of surface structures during laser polishing

As a novel surface treatment technology, in-situ laser polishing aims to improve surface finish of 3D printed parts, while laying the foundation for the integrated processing of 3D printing and laser polishing. However, the polishing process will introduce a few new surface structures (undercuts, step structures, ripples, etc.), which will affect the surface roughness. In this work, the surface roughness and surface structure after high power and low power polishing were compared respectively through experiments. In addition, a 2D transient numerical model was developed to explore the forming mechanism of different structures. The evolution of temperature field, velocity field and freedom surface of melting pool under different parameters were analyzed by the model. The results showed that the solidification induced surface structure with large roughness was generated after high power polishing. During its formation, the thermocapillary force was dominant and drove the tangential flow of fluid. While, low power polishing resulted in ripple structure with small roughness. The emergence of this structure was primarily due to the capillary force as the leading force in the melting pool flow process, which drove the normal flow of the melt, thus eliminating the large surface curvature. Furthermore, the width of the melting pool in the simulation was compared with the width of the single scanning track, and they were in good agreement. Finally, by adjusting the test strategy, it was found that the surface roughness could reach the lowest (0.88 ± 0.06 μm) only when the two structures coexisted.

Studies on fabrication of protruded multi-shaped micro-feature array on AA 6063 by laser micromachining

Miniaturization of parts of devices is the driving force for fabrication of micro-features. In this study fabrication of protruded multi-shaped micro-feature array on AA 6063 is attempted by laser micromachining. For fabricating the protruded microfeatures, the process parameters such as laser power, scanning speed and frequency of the laser beam have been optimized by considering track depth, width, and surface roughness as the output parameters. Three different cross sections in the tracks such as pileup section, W-section, and Gaussian groove section are observed. It is found that shape of the tracks vary with the scanning speed for the same power and frequency of the laser beam. The tracks of pileup section, W-section, and Gaussian groove section were produced for a laser scanning speed of 100 mm/s, 200mm/s, and 300 mm/s, respectively. Further, a laser-thermal ablative model is developed for predicting the depth of the single track and simulated using COMSOL® Multiphysics. The predicted track depths obtained from the simulations have good agreement with experimental results. In order to produce the protruded microfeatures of different shapes, multiple track analysis is done by fabricating the single tracks adjacent to one another by overlapping them, and the overlapping distance is optimized. The protruded microfeatures are then fabricated by removing the surrounding material for different scanning strategies and it is found that the contour strategy produced the features with minimal form error. Finally, it is demonstrated that an array of protruded micro-features of polygon (square, hexagon), and circular cross sections can be fabricated using the optimized process parameters for various applications.

The effect of aluminium concentration on the resistance of Si3N4 to ion track formation

The role of Al impurities on the structural response of polycrystalline silicon nitride to swift Xe and Bi ions at single ion track and overlapped ion track fluences is investigated. Si3N4 with Al impurity concentrations of 3 at.%, 1 at.% and 0.1. at.% were examined by means of high resolution scanning transmission electron microscopy. The threshold electronic energy loss (Set) required to form amorphous tracks was found to decrease with increasing Al fraction from above 33 keV/nm (0.1 at.% Al) to below 22 keV/nm for specimens containing about 3 at.% Al. All specimens were partially amorphized at overlapping ion fluence and the amorphous fraction monotonically increased with increasing Al content at the same ion fluence.

Development and application of a simplified thermo-evaporative multi-track laser powder bed fusion model for Ti6Al4V

Often the parametric analyses of the laser powder bed fusion (LPBF) process are concerned with laser power or scan speed, and other parameters such as scan spacing are paid lesser attention, particularly due to the huge computational power required for their investigation. Hence, in this study a simple and efficient thermo-evaporative model is developed for multi-track LPBF that excluded the solution of melt pool flow dynamics and thus enabled faster and economic simulation of the problem. Material evaporation was added to control the temperature rise up to reasonable levels, which acted only as a heat loss flux on the top boundary. The model has been first validated against the single track results and then applied to multi-track modeling for several different values of scan spacing while other parameters are kept constant. The study showed the potential of the developed thermo-evaporative model in simulating the multi-track problem and conducting a parametric analysis concerning the variation of scan spacing. The results were verified against the experimental results at a higher scan spacing where the computed and experimental porosities were compared qualitatively, and it was observed that the proposed model predicted the lack of melting porosity very well. The temperature field and other thermal characteristics such as thermal gradients and heating/cooling rates were calculated and discussed as well.

The columnar to equiaxed transition of CoCrNi medium-entropy alloy fabricated by laser directed energy deposition

Understanding and revealing the evolution mechanism of the columnar to equiaxed transition (CET) that occurred in the medium-entropy alloys (MEAs) fabricated by laser directed energy deposition (LDED) is crucial for achieving the tunable microstructure and mechanical properties. In the present work, a CET map was established to explain the effect of the laser energy density (LED) on the CET of the LDED fabricated single tracks of the CoCrNi MEA. The results show that the CET observed in single tracks is related to the morphological transformation of cellular substructure, which is governed by constitutional undercooling. With the increase of LED, the maximum value of the constitutional undercooling exceeds the critical nucleation undercooling earlier, which facilitates the heterogeneous nucleation and inhibits the epitaxial growth of rod-like cells, and finally causes a promoted CET. The correlation among the average cell size, geometrically necessary dislocation density, and average hardness of single tracks was also discussed. The present work not only uncovers the mechanism of the CET and grain growth in the LDED-fabricated CoCrNi MEA but also provides theoretical guidance for fabricating other MEAs with ideal microstructure and performance.