Metal Jet Research Articles

From impact to solidification in drop-on-demand metal additive manufacturing using MetalJet

Drop-on-demand metal jetting is a promising additive manufacturing (AM) technology that is gaining interest due to its capability to directly print complex single and multi-material components at high resolutions. It also has key advantages over other metal AM techniques, such as avoiding powder handling and extensive post-processing. In this method, parts are built via spatially controlled deposition of individual molten droplets onto a substrate. Therefore, the success of the process entirely depends on the behaviour of these single droplets from deposition to solidification including their interactions with the substrate, which is scarcely investigated to date. To fill this research gap, the in-house MetalJet platform was used to investigate the spreading and solidification of metallic micro-droplets at low Weber numbers. This was undertaken onto various substrates using a range of jetting and substrate temperatures through an integrated experimental, analytical, and computational approach. This study reports that increasing the substrate temperature enhanced the diffusion between the droplet and substrate, hence improving the bonding. Moreover, ripples forming on a droplet’s periphery during solidification disappeared at elevated substrate temperatures, resulting in improved inter-droplet bonding. Furthermore, the significant role of the substrate wettability and thermal properties, which control the droplet’s dynamics and solidification behaviour, respectively, is elucidated. This highlights the importance of substrate material selection using this technology. The results presented in this article underpin the optimal process conditions under which the 3D structures produced with this technology can exhibit reliable integrity and consistency. This represents a step forward in the direct metal printing of high resolution functional multi-material components.

In-process monitoring and prediction of droplet quality in droplet-on-demand liquid metal jetting additive manufacturing using machine learning

In droplet-on-demand liquid metal jetting (DoD-LMJ) additive manufacturing, complex physical interactions govern the droplet characteristics, such as size, velocity, and shape. These droplet characteristics, in turn, determine the functional quality of the printed parts. Hence, to ensure repeatable and reliable part quality it is necessary to monitor and control the droplet characteristics. Existing approaches for in-situ monitoring of droplet behavior in DoD-LMJ rely on high-speed imaging sensors. The resulting high volume of droplet images acquired is computationally demanding to analyze and hinders real-time control of the process. To overcome this challenge, the objective of this work is to use time series data acquired from an in-process millimeter-wave sensor for predicting the size, velocity, and shape characteristics of droplets in DoD-LMJ process. As opposed to high-speed imaging, this sensor produces data-efficient time series signatures that allows rapid, real-time process monitoring. We devise machine learning models that use the millimeter-wave sensor data to predict the droplet characteristics. Specifically, we developed multilayer perceptron-based non-linear autoregressive models to predict the size and velocity of droplets. Likewise, a supervised machine learning model was trained to classify the droplet shape using the frequency spectrum information contained in the millimeter-wave sensor signatures. High-speed imaging data served as ground truth for model training and validation. These models captured the droplet characteristics with a statistical fidelity exceeding 90%, and vastly outperformed conventional statistical modeling approaches. Thus, this work achieves a practically viable sensing approach for real-time quality monitoring of the DoD-LMJ process, in lieu of the existing data-intensive image-based techniques.

Soft X-ray radiography for measurements of a dense metal plasma created by intense relativistic electron beam on a tantalum target

A radiographic diagnostic has been developed to quantify the plume of erosion products after the interaction between a target and a relativistic electron beam. The diagnostic is based on a point Z-pinch (PZ-pinch) with a metallic plasma jet. It creates an X-ray source with a typical size of 10 μm, a photon energy of up to 3 keV and a flash duration of 3 ns. The X-ray visualization system is based on a thin scintillator and a CCD camera. The spatial resolution of the diagnostic was evaluated experimentally. The spatial frequency limit was found to be about 1.5 line pairs per millimeter. The diagnostic was tested in an experiment performed using an LIA-5 linear induction accelerator. An electron beam with a current of 400 A, an energy of 3.5 MeV and a pulse duration of 80 ns was focused on a plane tantalum target 1 mm in thickness. The FWHM of the focal spot was ∼ 2 mm. Radiographs of the plume were taken with different delays after different accelerator pulses. According to our data, the plume most commonly propagates toward the beam. After 70 μs its length was about 70 mm, i.e. the plume expansion rate was about 1 km/s. The area density of the semi-transparent regions of the plume was estimated as lying in the range 3 · 10-16–2 · 1017 cm-2.

Electromagnetic pulse welding on a magnesium–aluminum joint: role of angle of welding

ABSTRACT Electromagnetic pulse welding technology shows a wide range of applications in welding dissimilar metals. In this work, the effect of the angle between the magnesium sheet rolling route and welding direction on the magnesium–aluminum joint has been studied. An electromagnetic pulse welding equipment WD-28 was used to weld the magnesium sheet and aluminum sheet. The angle was set to 0º, 45º, and 90º, and the discharge energy was set from 10.08 kJ to 17.92 kJ. The mechanical property of the magnesium–aluminum joints was compared. Scanning electron microscope and energy dispersive spectrometer were used to observe the microscopic morphology and element distribution of the bonding interface. Results show that the tensile strength of the joint is the highest when the angle is 0º under the same conditions. The tensile strength of the magnesium sheet, the movement of the collision point, and the metal jet during the electromagnetic pulse welding process were affected by the angle, causing the difference in the thickness of the diffusion layer, the morphology of the wavy interface, and the length of the welded zone. Moreover, the quality of the joints with different angles can be improved by increasing discharge energy.

Numerical Simulation of Conical and Linear-Shaped Charges Using an Eulerian Elasto-Plastic Multi-Material Multi-Phase Flow Model with Detonation.

This study developed a hydrocode to numerically simulate both conical and linear-shaped charges using an Eulerian multi-material and multi-phase flow model. Elasto-plastic solids and the detonation of a high explosive charge were modeled using a Johnson–Cook material model and the programmed burn model, respectively. Further, the plasticity of the solids was calculated using a radial return mapping algorithm. The model was solved using a high-resolution computational fluid dynamics (CFD) technique on Cartesian grids. Material interfaces were tracked using the level-set method, and the boundary conditions were imposed using the ghost fluid method. The developed hydrocode was validated using high-speed impact problems. Consequently, the developed hydrocode was used to successfully simulate the evolution and penetration of metal jets in shaped charges after a detonation.

Crack Formation in Chill Block Melt Spinning Solidification Process: A Comparative Analysis Using OpenFOAM®

The application of FeSiB family magnetic materials in the electrical or electronic industry has significantly increased owing to the development of amorphous and nanocrystalline metallic glasses using melt spinning and chill block melt spinning technology, which involves a rotating metal wheel with a high rotation speed. With this technique, a thin ribbon is obtained owing to the jet of liquid metal expelled from a casting nozzle at high pressure and temperature over the outer surface of the wheel. The cooling rates that can be achieved lead to disorder in the crystalline lattice of the metal, which is dependent on the chemical composition. As soon as the material jet is expelled by the nozzle, turbulence can occur in the solidification puddles. This generates defects and cracks in the solidification profile. In this study, numerically simulated ad hoc events in OPENFOAM® are comparatively examined using a real process.

Simulation and Experimental Study on Forming Process of Wavy Interface in Electromagnetic Pulse Welding Based on Metallic Jet

Simulation and Experimental Study on Forming Process of Wavy Interface in Electromagnetic Pulse Welding Based on Metallic Jet

Study of a Negatively Buoyant Jet of Liquid Metal in a Density-Stratified Ambient

Study of a Negatively Buoyant Jet of Liquid Metal in a Density-Stratified Ambient

Metallic Melt Jet Fragmentation in a Water Pool: Experiments and Numerical Simulations

Metallic Melt Jet Fragmentation in a Water Pool: Experiments and Numerical Simulations

DEPLOYMENT OF THE ANALYTIC HIERARCHICAL PROCESS FOR COMPARATIVE ANALYSIS OF ADDITIVE MANUFACTURING TECHNOLOGIES IN THE MANUFACTURE OF INJECTION MOULDS

he current environment of changing market trends drives the manufacturing industry to strive for efficient manufacturing technologies. A mould manufacturer was using traditional manufacturing approaches to fabricate injection moulds. The traditional approach compromised the competitiveness of the organisation, resulting in a lower production rate and high operational costs owing to lengthy changeover times. Given several alternatives, the aim of this study was to determine the best suitable additive manufacturing technology for the manufacture of moulds. The analytic hierarchical process was deployed as the method to compare and select the best 3D printing technology from among recent additive manufacturing (AM) technologies that would meet surface finish, dimensional accuracy, cost, and manufacturing lead time requirements. Four AM options were multilevel concurrent printing, MELD technology, a Metal Jet 3D printer, and VELO3D. The final results indicated that the VELO3D was better than the other additive manufacturing technologies for the manufacture of moulds. Keywords Analytic hierarchical process; Additive manufacturing; Injection moulding

Physics-Based Inversion of a Millimeter-Wave Diagnostic for Liquid Metal Additive Manufacturing

This article presents a physics-based inversion technique for reliable characterization of droplets deposited by a liquid metal jetting additive manufacturing system, using an in-situ millimeter wave diagnostic. The overall approach is demonstrated in a custom droplet-on-demand liquid metal jetting system with effective droplet diameters ranging from 0.8 to 1.7 mm. The inversion results demonstrate that this approach can provide information about the droplet size and lift-off distance between the droplet and the diagnostic by monitoring the amplitude and phase of the reflection coefficient at the input port.

Quantitative Risk Assessment for Aerospace Facility According to Windrose

Wind direction and speed are the most important factors that determine the degree of damage caused by a jet fire. In this study, the metal hose used to extract/supply fuel was identified as the component with the highest risk for a jet fire occurring at an aerospace facility. A risk assessment was performed to evaluate the individual risk of a jet fire from the metal hose according to the wind direction and speed. HSE failure data was applied for calculating the jet fire probability including metal hose failure, ignition frequency, and jet fire frequency. Which was 3.0 × 10−4. The individual risk of different fatality probabilities was calculated according to the wind rose data for the aerospace facility. The individual risk from jet fire in the aerospace facility was calculated with a maximum risk of 3.35 × 10−5 and a minimum risk of 1.49 × 10−6. The individual risk satisfied HSE ALARP criteria. In addition, firewalls, extinguishing systems, and an emergency shut off system were enhanced, and it was thought that the risk from jet fire could satisfy acceptable criteria.

Insights into drop-on-demand metal additive manufacturing through an integrated experimental and computational study

Drop-on-demand metal jetting is a recent additive manufacturing technology opening new opportunities for the fabrication of complex single and multi-metal components. MetalJet, the Océ developed technique used in this study, has the capacity to produce molten micro-droplets (60–80 µm) at temperatures up to 2000 °C to form single and multi-material objects. Applications for this technology include flexible circuits, advanced electronic components and biotechnologies. However, full exploitation of this technology is impeded by a lack of understanding of various aspects of the process, including droplet bonding and interface formation, residual stress development and the evolution of microstructure. This paper uses an integrated numerical and experimental approach to provide insights into these research questions. Thermal models were used to investigate droplet-to-substrate adhesion and explain the experimentally-observed morphology of droplets. Thermo-mechanical modelling was used to investigate residual stress development and its role in the observed droplet warping and delamination. The knowledge obtained from this study can be used to underpin the development of functional multi-material printing.

Experiments of melt jet-breakup for agglomerated debris formation using a metallic melt

In severe accidents in a light water reactor, the relocated molten core (so-called corium or melt) can form a debris bed. The debris bed coolability is a critical issue for prevention and mitigation of the molten core–concrete interactions. Agglomeration has a serious impact on assessment of debris bed coolability if agglomeration forms massive debris (so-called agglomerated debris) by merging of melt particles with others when the melt particles accumulate on a floor. This paper presents the results of melt jet-breakup experiments for agglomerated debris formation using a simulant metallic melt. The experiments injected a melt jet of a low-melting point metal through a circular nozzle into a test section filled with coolant water. The particles were generated due to the melt jet-breakup accumulated on to a catcher, which is a flat plate made of stainless steel, installed in the test section. A high-speed video camera imaged particle formation and accumulation on the catcher plate. Agglomerated debris was confirmed by morphological investigation of the recovered debris. The experimental results revealed the effects of the melt jet injection conditions (melt temperature, coolant temperature, and coolant depth) on the mass fraction of agglomerated debris. On the basis of the experimental results, we proposed a simple correlation to estimate the mass fraction. The simple correlation successfully reproduced the mass fraction of agglomerated debris obtained in the DEFOR-A test [Kudinov et al., Nucl. Eng. Des., 301 (2013), 284–295]. The experimental data base presented in this paper makes further contributions to the modeling and validation of mechanistic models or simulation tools for agglomerated debris formation.

Measurement of velocity in swirling flows of liquid metals in the presence of a magnetic field

Studies of the dynamics of a round submerged jet of liquid metal in a transverse magnetic field. The experiments were performed in the range of Reynolds numbers up to 1000 and Hartmann numbers up to 1300 using a probe technique for measuring velocity using potential sensors. Detailed three-dimensional flow structures are visualized using a direct numerical simulation method independent of the experiment. The paper presents data on the averaged velocity field and statistical characteristics of the flow, reproducing the complex nature of a substantially unsteady flow, in which zones of reverse fluid flows are detected and a significant heterogeneity of the velocity field is observed.

Modelling the complex evaporated gas flow and its impact on particle spattering during laser powder bed fusion

The additive manufacturing (AM) of metals is becoming an increasingly important production process with the potential to replace traditional techniques such as casting. Laser Powder Bed Fusion (LPBF) is used in many applications to print metal parts from powder. The metal powder is heated locally with sufficient laser radiation that the liquid melt easily reaches its boiling temperature, which leads to a metallic vapour jet that can entrain both powder bed particles and molten droplets. The small size of laser-matter interaction site makes a detailed experimental analysis of the process challenging. Synchrotron X-ray imaging experiments are one of the few methods which can capture the dynamic melting and solidification processes. Comparing such experiments with computer simulations of the process is an important approach in order to better understand the manufacturing process and to analyse the influence of process parameters on the evaporated gas jet and the subsequent impact on particle ejection, leading to potentially reduced AM component quality. The melting and solidification of the metal powder is simulated using an Eulerian multiphase approach based on a control volume discretization of powder bed and substrate and a volume of liquid separation from melt and gas phase. The gas phase modelled as an ideal gas reaches velocities up to 100 m/s. Lagrangian particle tracking in the simulation demonstrates that the velocity fields calculated by the Eulerian multi-phase approach in combination with a standard drag-force model lead to particle accelerations in good agreement with those measured experimentally. In order to avoid numerical laborious Lagrangian calculations, a direct method to compare an Eulerian multiphase simulation with synchrotron X-ray experiments was introduced and validated . This approach is used to analyse the influence of process parameters including laser power and laser speed on the maximal acceleration of particles from the melt pool area. While the particle acceleration increases linearly with line energy in the conduction mode, a linear decrease of the acceleration with increasing line energy can be found in the transition mode before the acceleration increases again with line energy in the keyhole mode.

Numerical simulation of the shear stress produced by the hot metal jet on the blast furnace runner

During steel casting process a jet of molten metal runs out of the blast furnace hearth and strikes the runner. The continuous impact of hot fluids causes significant damage to its surface, which is made of refractory concrete. In particular, the initial impact on the dry runner is expected to be critical. This work deals with the analysis of the mechanical impact on the runner through the numerical simulation of the process. We propose an incompressible turbulent isothermal Navier-Stokes model, where turbulence is modelled considering two k−ω models (standard and SST). The interface dynamics is described by applying the Volume of Fluid (VOF) method, while the surface tension vector is provided by the Continuum Surface model (CSF). Their numerical results are performed in 2D. A comparative analysis of the most suitable transient turbulent multiphase model is presented by simulating benchmark physical experiments. The shear stress arising from the impact of the jet on the runner is also analyzed. An improvement of the classical analytical expression given in [1] is proposed. Both, the chosen turbulence model, and the formulas to compute the shear stress are validated using two benchmark laboratory tests and three numerical experiments. Numerical results are given for the impact of the jet on the dry runner of the blast furnace.

Four dimensional wave propagation simulation in liquid metal with realistic thermal fluctuation

In this paper, we performed a four-dimensional numerical simulation to calculate wave propagation in a thermal fluctuating liquid metal in order to obtain detailed knowledge on a wave propagation in coolant material of a Sodium-cooled Fast reactor (SFR). The wave and the medium are described in three spatial and one temporal dimensions. We made use of a massive data set to describe the fluctuating situation of the medium. This data set was provided by Computational Fluid Dynamics (CFD) with a Large-Eddy Simulation (LES) model, which calculated the temperature field with a higher spatial resolution than Reynolds-Averaged Navier–Stokes turbulence models (RANS). This data set was furthermore obtained from other studies on a numerical and physical experiment called PLAJEST that created mixing jets of liquid metal in order to simulate the status of running SFRs. Because of the limitation of computational resources, previous acoustic studies applied to such a medium could only use the spatial–temporally averaged fluctuating heterogeneity of a medium calculated by RANS turbulence model. This limitation may overlook wave fluctuation because of the difference of the resolution between computational fluid dynamics and acoustic wave length. Our numerical effort allowed us to study the most realistic acoustic wave propagation in liquid metal than in any former studies. A new important result was obtained in this work as we demonstrated that ultrasonic measurements could follow thermal-hydraulic fluctuations in an opaque liquid with high sensitivity. This result was obtained through the definition of descriptors to analyze medium fluctuations along the wave path. We defined a very new measurement index, called hereafter Cumulated Temperature Fluctuation Intensity (CTFI), to correlate the variations in the thermal-hydraulic conditions to the wave variations. We demonstrated a good correlation between the second derivative of this index and the second derivative of several acoustic measurements, then we discussed the easiest measurements to be used in practice in an industrial setup.

Flat liquid metal jet affected by a transverse magnetic field

A liquid metal flat jet immersed in a square duct under the influence of a transverse magnetic field is studied experimentally. Two cases are considered: when the applied magnetic field is oriented parallel (coplanar field) or perpendicularly (transverse field) to the initial plane of the jet. The main goal of the study is to investigate the mean flow characteristics and the stages of the jet's transformation. Signals of streamwise velocity at different locations are measured, which allows us to determine average velocity profiles and spatial-temporal characteristics of the velocity field. The two considered configurations are directly compared under the same flow regimes, with the same equipment. Figs 8, Refs 11.

Study on melt jet breakup behavior with nonorthogonal central-moment MRT color-gradient lattice Boltzmann method

In this paper, the melt jet breakup behavior are numerically studied in 3D with nonorthogonal central-moment MRT color-gradient lattice Boltzmann method, which could significantly enhance the numerical stability and accuracy when applied to flows with very high Reynolds number. Firstly, the methodology to simulate immiscible two-phase flow is validated by conducting droplet oscillation tests. Then the ability of this model to accurately predict melt jet breakup in water is validated by simulating molten Wood's metal jet breakup experiments. Meanwhile, the breakup mechanisms are clarified. For the leading edge, the breakup of the side part is due to large eddies, the main part of the leading edge starts breakup owning to Rayleigh-Taylor instability. For the jet column, small droplets and filaments are stripping due to Kelvin-Helmholtz instability, segment breakup of the jet column is owning to Rayleigh-Taylor instability. Finally, the model is employed to simulate molten corium jet breakup in water. The hydrodynamic characteristics such as jet penetration depth, jet breakup length and fragment size are analyzed in detail. It is found that the simulation results are basically consistent with the dimensionless jet breakup length predicted by Epstein et al.‘s correlation when E0=0.1, but relatively shorter. RTI theory significantly overestimates mass median diameter while critical Weber number and KHI theories underestimate it.