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Spectroscopic monitoring of laser blown powder directed energy deposition of Alloy 718
摘要： Experimental explorations of a spectrometer system used for in-process monitoring of the laser blown powder directed energy deposition of Alloy 718 is presented. Additive manufacturing of metals using this laser process experiences repeated heating and cooling cycles which will influence the final microstructure and chemical composition at every given point in the built. The spectrometer system disclosed, under certain process conditions, spectral lines that indicate vaporisation of chromium. Post process scanning electron microscope energy dispersive spectroscopy analysis of the deposited beads confirmed a reduction of chromium. Since the chromium concentration in Alloy 718 is correlated to corrosion resistance, this result encourages to further investigations including corrosion tests.
关键词： additive manufacturing,laser blown powder directed energy deposition,spectroscopic system,in-process monitoring
更新于2025-11-21 11:01:37
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Numerical modeling of coaxial powder stream in laser-powder-based Directed Energy Deposition process
摘要： Laser-powder-based Directed Energy Deposition (DED) process has been used extensively and becomes more and more popular in part manufacturing, repairing and prototype fabrication. It offers an effective way to deposit material via simultaneous delivery of the powders of desired material and laser beam. Complex physical events take place during the process and have great impacts on the success of the process, in which powder stream and its interaction with laser beam play a crucial role. In this paper, a new comprehensive numerical model for powder stream dynamics and heating process is developed to describe the coaxial powder stream and its interaction with laser beam. Reynolds Averaged Navier-stokes (RANS) approach is used for turbulent continuum gas flow while a discrete phase model (DPM) is applied to describe the dynamic behavior of the powder. Two-way coupling approach is adopted to account for the momentum transfer between gas and powder. A new thermal model is developed for powder stream, in which the interaction between powder stream and Gaussian laser beam is modelled through a novel numerical submodel. The obtained results of powder stream are compared with the experimental results from published literature and show good agreement.
关键词： Laser beam,Directed Energy Deposition,Coaxial powder stream,Numerical modeling
更新于2025-09-23 15:21:01
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Influence of Static Magnetic Field on the Microstructure of Nickel-Based Superalloy by Laser-Directed Energy Deposition
摘要： The influence of a static magnetic field on microstructure evolution during laser direct energy deposition was studied. Our results reveal that dendrite spacing increases with increasing magnetic field flux density (MFFD). Moreover, electron backscatter diffraction results reveal that the epitaxial growth was preferred with increasing MFFD. We discuss these findings in terms of the influence of a magnetic field on melt convection and propose that an applied magnetic field effectively limits Marangoni convection.
关键词： microstructure,static magnetic field,laser-directed energy deposition,dendrite spacing,Marangoni convection
更新于2025-09-23 15:21:01
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Directed energy deposition of Al 5xxx alloy using Laser Engineered Net Shaping (LENS??)
摘要： Here, we present directed energy deposition (DED) of wrought-like Al 5xxx AlMg alloy by Laser Engineered Net Shaping (LENS?). A transition from an Al 5083 gas atomized powder feedstock to Al 5754 characteristics of the as-deposited material due to selective evaporation of Mg was observed. Density values obtained by X-ray micro-computed tomography (μ-CT) were compared to those obtained by the Archimedes method. The latter indicated a relative density as high as 99.26%. Possible origins of porosity are discussed. The as-deposited material was comprised of both equiaxed and columnar grains with no preferred crystallographic orientation and mean grain size of 36 μm. The Young's modulus, yield stress, ultimate tensile strength, fracture strain, Poisson's ratio, and total ultimate strain energy (toughness) were determined by uniaxial tensile tests combined with digital image correlation (DIC). Fractography complemented the mechanical testing. A pulse-echo ultrasonic non-destructive test was used to obtain more accurate values of the Young's and shear moduli and to adjust the value of the yield strength accordingly. The measured mechanical properties meet the requirements of international standards for wrought Al 5754 in its annealed condition.
关键词： Additive manufacturing (AM),Mechanical properties,Micro-computed tomography (μ-CT),Laser Engineered Net Shaping (LENS?),Directed energy deposition (DED),Aluminum alloys
更新于2025-09-23 15:21:01
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In-process measurement of melt pool cross-sectional geometry and grain orientation in a laser directed energy deposition additive manufacturing process
摘要： Understanding the behaviour of melt pool during laser directed energy deposition (L-DED) is essential for the prediction and control of process quality. Previous effort was focused on the observation of melt pool surface characteristics. In this paper, a coaxial imaging system was employed to determine the melt pool cross sectional geometry and to predict solidified grain orientation during a high deposition rate L-DED process. The image processing procedure, deposition track cross-sectional profile prediction and the relationship between melt pool shape and melt pool dynamics, and grain growth orientation were investigated. Results show that sharp melt pool edges can be obtained so that melt pool width can be predicted with an accuracy of more than 95%. The estimation method of melt pool length has an accuracy of 90%. With the experimental melt pool width and depth data, the cross-sectional profiles of deposited track are predicted at an accuracy of 92% and a good match with experimental data is obtained. The melt pool formation is found to be able to allow the prediction of crystal growth directions during solidification.
关键词： Melt pool dimension,Laser additive manufacturing,Track geometry,Laser directed energy deposition,Grain growth
更新于2025-09-23 15:19:57
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Laser-Assisted Machining of Ti-6Al-4V Fabricated by DED Additive Manufacturing
摘要： Recently, the commercialization of hybrid machine tools that combine directed energy deposition (DED) additive manufacturing (AM) technology and subtractive manufacturing (SM) has rapidly progressed. This technology trend has been developed to meet the market demand for processing quality (precision) and productivity, and to produce products such as lightweight parts, and complex and special functional parts, as well as to facilitate mold production and part repair. Compared to SM technology, metal AM technology has limitations in terms of surface quality and shape accuracy. Therefore, post-processing is necessary for the AM output. Laser-assisted machining (LAM) is an innovative hybrid technique in which surface quality and productivity can be improved by enhancing the machinability of difficult-to-cut materials. LAM studies have mainly been performed on titanium alloys, nickel based alloys and ceramic materials. However, except for ceramics, no high-strength material studies have been conducted to analyze the LAM process machining characteristics of workpieces fabricated by AM process. Therefore, in this study, LAM is applied to post-processing of output fabricated by AM of Ti-6Al-4V. DED device was developed using metal powder feeder and a laser. The Ti-6Al-4V workpieces were successfully fabricated through many tests. The cutting depth for LAM was selected through thermal analysis for LAM of the fabricated workpiece. Compared to the case of traditional machining without preheating, machining characteristics in LAM experiments were analyzed and property testing was performed.
关键词： Machining characteristics,Additive manufacturing,Directed energy deposition,Ti-6Al-4V,Laser-assisted machining
更新于2025-09-23 15:19:57
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Laser metal deposition of copper on diverse metals using green laser sources
摘要： Green laser sources are advantageous in the processing of copper due to the increase of absorptivity compared with more commonly available infrared lasers. Laser metal deposition of copper with a green laser onto various substrate metals namely copper, aluminium, steel and titanium alloy was carried out and observed through high-speed imaging. The effects of process parameters such as laser power, cladding speed and powder feed rate, and material attributes such as absorptivity, surface conditions and thermal conductivity are tied together to explain the size and geometry of the melt pool as well as the fraction of the power used for melting material. The copper substrate has the smallest melt pool with a high angle, followed by aluminium, steel and titanium alloy. The incorporation times for powder grains in the melt pools vary based on the substrate materials. Its dependency on material properties, including surface tension forces, melting temperatures and material density, is discussed. Oxide skins present on melt pools can affect powder incorporation, most significantly on the aluminium substrate. The lower limits of the fraction of power irradiated on the surface used purely for melting were calculated to be 0.73%, 2.94%, 5.95% and 9.78% for the copper, aluminium, steel and titanium alloy substrates, respectively, showing a strong dependence on thermal conductivity of the substrate material. For a copper wall built, the fraction was 2.66%, much higher than a single clad on a copper substrate, due to reduced workpiece heating. The results of this paper can be transferred to other metals with low absorptivity such as gold.
关键词： Multi-material,DED,High-speed imaging,LMD,Copper,Green 515-nm laser,Laser metal deposition,Powder grain incorporation,Additive manufacturing,Directed energy deposition,Absorptivity
更新于2025-09-19 17:13:59
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Numerical modelling of heat transfer, mass transport and microstructure formation in a high deposition rate laser directed energy deposition process
摘要： In laser directed energy deposition (L-DED) processes, by applying a converged powder stream, relatively high laser power and larger laser spot, the powder utilisation efficiency and processing speed can be increased. There is, however, lack of mathematical models for L-DED. In this paper, a three-dimensional numerical model is established to study the mass transport and heat transfer in the melt pools in high deposition rate (HDR) L-DED of 316L stainless steel. The Volume of Fluid (VOF) method is employed to track the melt pool free surfaces, and enthalpy-porosity method is used to model the solid-liquid phase change. A discrete powder source model is developed by considering the non-uniform powder feed rate distribution. Results show that this model can well predict the deposited track dimensions (width, height and dilution depth). Different from conventional L-DED processes, the impact of higher mass addition on the melt pool fluid flow and temperature distribution is significant. In the regions where filler powder is injected, a downward mass flow is observed, and the temperature is slightly reduced. With the extracted temperature distribution and geometry at the solidification front, the solidification conditions are also calculated, as well as the primary dendrite arm spacing (PDAS) of the solidified tracks. Due to the high laser energy input, the temperature gradient is lower, and coarser microstructures are formed compared with conventional L-DED. The simulated results are in good agreement with experimental results.
关键词： Heat transfer,High deposition rate laser directed energy deposition,Mass transport,Primary dendrite arm spacing
更新于2025-09-19 17:13:59
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Beyond the Toolpath: Site-Specific Melt Pool Size Control Enables Printing of Extra-Toolpath Geometry in Laser Wire-Based Directed Energy Deposition
摘要： A variety of techniques have been utilized in metal additive manufacturing (AM) for melt pool size management, including modeling and feed-forward approaches. In a few cases, closed-loop control has been demonstrated. In this research, closed-loop melt pool size control for large-scale, laser wire-based directed energy deposition is demonstrated with a novel modification, i.e., site-specific changes to the controller setpoint were commanded at trigger points, the locations of which were generated by the projection of a secondary geometry onto the primary three-dimensional (3D) printed component geometry. The present work shows that, through this technique, it is possible to print a specific geometry that occurs beyond the actual toolpath of the print head. This is denoted as extra-toolpath geometry and is fundamentally different from other methods of generating component features in metal AM. A proof-of-principle experiment is presented in which a complex oak leaf geometry was embossed on an otherwise ordinary double-bead wall made from Ti-6Al-4V. The process is introduced and characterized primarily from a controls perspective with reports on the performance of the control system, the melt pool size response, and the resulting geometry. The implications of this capability, which extend beyond localized control of bead geometry to the potential mitigations of defects and functional grading of component properties, are discussed.
关键词： closed-loop control,lasers,metal,directed energy deposition,additive manufacturing,3D printing,titanium,site-specific,melt pool size
更新于2025-09-19 17:13:59
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A Hybrid Modeling of the Physics-Driven Evolution of Material Addition and Track Generation in Laser Powder Directed Energy Deposition
摘要： Directed Energy Deposition (DED) is one of the most promising additive manufacturing technologies for the production of large metal components and because of the possibility it offers of adding material to an existing part. Nevertheless, DED is considered premature for industrial production, because the identification of the process parameters may be a very complex task. An original hybrid analytic-numerical model, related to the physics of laser powder DED, is presented in this work in order to evaluate easily and quickly the effects of different sets of process parameters on track deposition outcomes. In the proposed model, the volume of the deposited material is modeled as a function of process parameters using a synergistic interaction between regression-based analytic models and a novel element activation strategy. The model is implemented in a Finite Element (FE) software, and the forecasting capability is assessed by comparing the numerical results with experimental data from the literature. The predicted results show a reasonable correlation with the experimental dimensions of the melt pool and demonstrate that the proposed model may be used for prediction purposes, if a specific set of process parameters that guarantees adequate adhesion of the deposited track to the substrate is introduced.
关键词： laser powder deposition,finite element model,thermal analysis,directed energy deposition,additive manufacturing
更新于2025-09-16 10:30:52