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Laser Operating Windows Prediction in Selective Laser-Melting Processing of Metallic Powders: Development and Validation of a Computational Fluid Dynamics-Based Model
摘要： The rapidly ascending trend of additive manufacturing techniques requires a tailoring of existing solidification models and the development of new numerical tools. User-friendly numerical models can be a valid aid in order to optimize operating parameter ranges with the scope to extend the modelling tools to already existing or innovative alloys. In this paper a modelling approach is described simulating the generation of single tracks on a powder bed system in a selective laser melting process. The approach we report attains track geometry as a function of: alloy thermo-physical properties, laser speed and power, powder bed thickness. Aim of the research is to generate a numerical tool able to predict laser power and speed ranges in manufacturing porosity-free printed parts without lack of fusion and keyhole pores. The approach is based on a simplified description of the physical aspects. Main simplifications concern: the laser energy input, the formation of the pool cavity, and the powder bed thermo-physical properties. The model has been adjusted based on literature data providing the track’s geometry (width and depth) and relative density. Such data refer to different alloys. In particular, Ti6Al4V, Inconel625, Al7050, 316L and pure copper are considered. We show that the printing process presents features common to all alloys. This allows the model to predict the printing behavior of an alloy from its physical properties, avoiding the need to perform specific experimental activities.
关键词： metallic alloys,numerical model,selective laser melting,additive manufacturing,laser operating window
更新于2025-09-23 15:21:01
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Numerical model for the chemical adsorption of oxygen and reducing gas molecules in presence of humidity on the surface of semiconductor metal oxide for gas sensors applications
摘要： Charge transfer between the interacting gas molecules and the surface of the sensing layer is the main mechanism for the detection of gases in semiconductor metal oxides. In the presented work, the Wolkenstein's theory of adsorption is used instead of the conventional Langmuir isotherm for the numerical modelling of adsorption of oxygen, reducing gas (CO) molecules and water vapours. A numerical model of chemical adsorption of these gas species at the surface of tin oxide (SnO2) semiconductor gas sensor is presented in this paper. Using this model, quantitative calculation of the combined effect of environmental oxygen, reducing gas (CO) and water vapor adsorption on various electronic properties like electrical conductivity, surface potential and the work function of the metal oxide surface has been carried out. The surface coverage of the chemically adsorbed oxygen gas molecules is simulated as a function of oxygen gas pressure, the temperature of the sensor surface and bulk doping level of the n-type SnO2 semiconductor. Along with oxygen, the adsorption of CO gas is simulated as a function of CO gas pressure at constant atmospheric pressure of Oxygen gas. Furthermore, the sensor response is simulated and compared both in presence of dry Carbon Monoxide (CO) gas as well in the humid environment. It is shown that in the presence of water vapor there is an increase in the conductivity due to the decrease in the surface potential barrier at the semiconductor surface.
关键词： Numerical model,Surface potential,Chemical adsorption,Gas sensor
更新于2025-09-23 15:21:01
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Photodetector with Controlled Relocation of Carrier Density Peaks: Concept and Numerical Simulation
摘要： Modern electronics faces the degradation of metal interconnection performance in integrated circuits with nanoscale feature dimensions of transistors. The application of constructively and technologically integrated optical links instead of metal wires is a promising way of the problem solution. Previously, we proposed the advanced design of an on-chip injection laser with an AIIIBV nanoheterostructure, and a functionally integrated optical modulator. To implement the efficient laser-modulator-based optical interconnections, technologically compatible photodetectors with subpicosecond response time and sufficient sensitivity are required. In this paper, we introduce the concept of a novel high-speed photodetector with controlled relocation of carrier density peaks. The device includes a traditional p-i-n photosensitive junction and an orthogonally oriented control heterostructure. The transverse electric field displaces the peaks of electron and hole densities into the regions with low carrier mobilities and lifetimes during the back edge of an optical pulse. This relocation results in the fast decline of photocurrent that does not depend on the longitudinal transport of electrons and holes. We develop a combined numerical model based on the Schrodinger-Poisson equation system to estimate the response time of the photodetector. According to the simulation results, the steep part of the photocurrent back edge has a duration of about 0.1 ps.
关键词： combined numerical model,high-speed AIIIBV optoelectronic devices,photodetector with controlled relocation of carrier density peaks,on-chip optical interconnections,Schrodinger-Poisson equation system
更新于2025-09-23 15:19:57
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Development and calibration of a CFD-based model of the bed fusion SLM additive manufacturing process aimed at optimising laser parameters
摘要： The main concern deriving from the Selective Laser Melting technique is attaining a fully dense part out of the interconnected tracks. The right choice of process parameters is of fundamental importance to get a porosity free component. In this work a model has been developed simulating the printing process with the aim of creating a simple numerical tool for designing processing windows suitable to metal alloys of any composition. The applied simplified approach makes the model use as much practical as possible, while keeping the physical description representative. The model has been calibrated fitting experimental measures of track width, depth and cross sectional area taken from three literature sources, referring to: Ti6Al4V, Inconel 625 and Al7050. Effective liquid pool thermal conductivity, laser absorptivity and depth of application of laser energy are the fitting parameters. Laser absorptivity and depth of application of laser energy result to rise almost linearly with increasing specific energy; the slopes of the three analyzed alloys result very close to each other. The obtained results give confidence about the possibility of using the model as a predicting tool after further calibration on a wider range of metal alloys.
关键词： laser parameters,numerical model,processing window,SLM,additive manufacturing,metal alloys
更新于2025-09-19 17:13:59
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Laser Welding of Transmitting High-Performance Engineering Thermoplastics
摘要： Laser processing is a rapidly growing key technology driven by several advantages such as cost and performance. Laser welding presents numerous advantages in comparison with other welding technologies, providing high reliability and cost-effective solutions. Significant interest in this technology, combined with the increasing demand for high-strength lightweight structures has led to an increasing interest in joining high-performance engineering thermoplastics by employing laser technologies. Laser transmission welding is the base method usually employed to successfully join two polymers, a transmitting one through which the laser penetrates, and another one responsible for absorbing the laser radiation, resulting in heat and melting of the two components. In this work, the weldability of solely transmitting high-performance engineering thermoplastic is analyzed. ERTALON 6 SA, in its white version, is welded by a pulsed Nd:YAG laser. Tensile tests were performed in order to evaluate the quality of each joint by assessing its strength. A numerical model of the joint is also developed to support the theoretical approaches employed to justify the experimental observations.
关键词： pulsed Nd:YAG laser welding,numerical model,polyamide 6,ERTALON 6 SA,high-performance engineering thermoplastic,mechanical testing
更新于2025-09-19 17:13:59
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Development of infrared fiber lasers at 1555?nm and at 2800?nm based on Er-doped zinc-tellurite glass fiber
摘要： We manufactured and characterized a low-loss gain fiber based on high-purity TeO2–ZnO–La2O3–Na2O undoped glass for 100-μm cladding and TeO2–ZnO–La2O3–Na2O glass for 10-μm core doped with 0.24 mol% Er2O3. To confirm that the produced fiber is a promising active element for the infrared range, we demonstrated experimentally broadband laser amplification and CW generation at the 4I13/2 → 4I15/2 transition at 1555 nm with a single-mode diode pump at 975 nm at the 4I15/2 → 4I11/2 transition. We developed a numerical model calibrated to the experimental data for prediction and optimization of laser characteristics in schemes with different parameters. The model describes single- wavelength lasing as well as dual-wavelength cascade lasing at 1555 nm and 2800 nm. It was shown numerically that for the optimized parameters, the maximum slope efficiency at 2800 nm at the 4I11/2 → 4I13/2 transition can reach ~20%. The maximum calculated efficiency at 1555 nm exceeds 30%.
关键词： Numerical model,Infrared fiber lasers,Broadband laser amplification,CW generation,Er-doped zinc-tellurite glass fiber
更新于2025-09-19 17:13:59
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Numerical investigation on He and Ar gas convective cooling for optical fiber glass drawing at short draw towers
摘要： The inert purge gas plays an important role in mass manufacturing of optical fibers, as it is usually the mixture gas of helium and argon. The natural and forced convective effects of purge gas are numerically investigated through the process simulation of glass fiber drawing in a short draw tower furnace by employing an iterative computational scheme of neck-down prediction formulation and computational fluid dynamics simulation of purge gas flow. The furnace geometric model and process conditions are based on realistic manufacturing process. It is found that neck-down shape and draw tension are quite insensitive to change of gas flow rate and helium contents level. In contrast, the recirculatory flow pattern around preform neck-down region is observed when helium contents are low, suggesting the difficulty in flushing of contamination particles out of furnace system. The increase of helium contents combined with increased flow rate in purge gas mixture could completely remove such undesirable flow patterns.
关键词： Optical fiber manufacturing,Draw tower,Numerical model,Convection,Glass fiber drawing
更新于2025-09-16 10:30:52
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Uniform and smooth molybdenum film produced through picosecond pulsed laser deposition
摘要： An approach to achieve uniform and smooth molybdenum (Mo) ?lm on a BK7 glass plate at room temperature is proposed through picosecond pulsed laser deposition, with the pulsed laser radiating the target along a linear track. A numerical model is established to analyze the in?uence of linear scanning offsets on the thickness homogeneity of the deposited thin ?lm. Through an appropriate choice of radiation intensity and scanning parameters, a uniform and smooth layer of Mo thin ?lm is prepared with its maximum thickness variation and root-mean-square roughness better than 5% and 1.2 nm, respectively.
关键词： picosecond pulsed laser deposition,smooth,numerical model,molybdenum film,uniform
更新于2025-09-11 14:15:04
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Thermal/Mechanical Interaction in Laser Perforation Process: Numerical-Model Buildup and Parametric Study
摘要： In this paper, a generic thermal/mechanical interaction model was developed to predict the penetration rate and mechanical damage around perforation tunnels that resulted from the laser perforation of rock samples. The perforating process is driven by heat emitted by a laser beam directed at the surface of a sample. The temperature propagation, thermal expansion, and thermal/mechanical interaction were modeled by coupling heat conduction in solid media with the elastic/plastic constitutive mechanical response of rocks. The phase changes that occur during the melting and evaporating process were accounted for in the latent heat of fusion and of vaporization. The heating boundary was updated dynamically along with the evolution of perforation channels. The model was used to parametrically investigate the effects of material properties, stress ratio, and laser-beam characteristics on the penetration rate and mechanical damage.
关键词： mechanical damage,numerical model,laser perforation,rock samples,thermal/mechanical interaction,penetration rate
更新于2025-09-11 14:15:04
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[IEEE 2017 International Renewable and Sustainable Energy Conference (IRSEC) - Tangier (2017.12.4-2017.12.7)] 2017 International Renewable and Sustainable Energy Conference (IRSEC) - A Three-Dimensional Finite Element Based Dynamic Thermal Model of PV Modules with an Improved Thermal Network
摘要： This paper describes a simple and efficient way to develop, and to implement a 3-D finite element (FE) based dynamic thermal model for PV modules, without an active cooling system. The 3-D model has been developed very closely to represent an actual PV panel. This dynamic thermal model can also be used for steady-state analysis too. An improved thermal network has been proposed and implemented in this work, which provides a more realistic approach towards heat dissipation from a PV module to its surroundings. Compared to typical classical thermal networks used in the literature, the proposed network improves the prediction accuracy of the thermal model significantly. The root mean square error (RMSE) between the simulated and the experimental data was found to be only 0.69 °C for the improved thermal network and 3.12 °C for the typical classical thermal network. It was also shown that ignoring the heat dissipation from the sides of a PV panel has a negligible effect on the prediction accuracy of the thermal model.
关键词： Transient Analysis,Thermal Model,3D Finite Element,PV Panel,3D Numerical Model,Thermal Network
更新于2025-09-10 09:29:36