Coaxial Nozzle Research Articles

Production of hollow germanium alloy quasi-spheres through a coaxial nozzle

Hollow germanium alloy quasi-spheres of diameters 1–2 mm have been produced based on hollow jet instability. The germanium was first melted at around 1273 K and then extruded from a coaxial nozzle into an inert atmosphere by argon supplied to the inner nozzle. The falling spheres were cooled by water spray and collected in a bucket. The spheres had relatively smooth inner and outer surfaces, but were somewhat aspherical. The ex-post characterization of germanium sphere revealed Ge, Fe, Cr and Ni at atomic percentages of 64.04%, 16.21%, 8.55% and 10.30% respectively.

Laser Cladding Ti Coated CBN/CuSnTi Alloy on Steel for Grinding Tools of Ocean Ship

ABSTRACT Zhao, X.; Yu, T.; Zhao, Y.; Zhang, Y.; Yang, L.; Jiang, S., and Wang, W., 2018. Laser cladding Ti coated CBN/CuSnTi alloy on steel for grinding tools of ocean ship. In: Liu, Z.L. and Mi, C. (eds.), Advances in Sustainable Port and Ocean Engineering. Journal of Coastal Research, Special Issue No. 83, pp. 571–578. Coconut Creek (Florida), ISSN 0749-0208. In this study, laser cladding CBN/CuSnTi alloy mixed powder on the AISI 1045 steel substrate for grinding tools of ocean ship was investigated. Various laser cladding processing parameters were conducted to find the appropriate laser cladding parameters to fabricate grinding tools of ocean ship in the continuous fiber laser beam with coaxial powder nozzle. The morphology of the laser cladding layer was analyzed by laser scanning confocal microscopy (LSCM) and the CBN grits with specific laser process parameters was observed by scanning electron microscopy (SEM). The interface conditions among the CBN grit/alloy matrix/substrate were detected by SEM...

DETERMINATION OF TECHNOLOGICAL PARAMETERS OF THE AEROSOL TYPE RAIL LUBRICATORS

The article presents the results of experimental studies of technological parameters of a pilot sample of aerosol type lubricant. As a lubricant, the industrial I-12A oil was added with the addition of graphite powder to it, which provides the implementation of a two-layered coating of the working surface of the rail. The test piece is a closed type oiling unit, which feeds on compressed air and allows the regulation of air and oil supply to the working nozzle. For drawing of a lubricant on a working surface the coaxial nozzle with the external formation of an aerosol - a mixture of oils and air is used.Studies were conducted in laboratory conditions. At the first stage, the geometric dimensions of the stain of the oil applied to the vertical surface were measured, depending on the distance between the nozzle and the surface. Such data makes it possible to adjust the settings of the injector placement relative to the rail, taking into account the permissible dimension of the approach, which is essential for the introduction of rail pads under operating conditions. Subsequently, depending on the width of the stain of the oil and the thickness of the lubricating layer from the supply of oil and air, were installed. Also, the dependencies of the cutting time of oil and air are set. The obtained data are necessary for determining the oil consumption in the operation of similar rail lubricants in real conditions. In addition, these data allow you to adjust the control system of the rail lubricant by the criterion of the limit time of cutting the oil and minimizing the cost of lubricant.According to the results of laboratory studies, an estimation of the effectiveness of the aerosol type air-lubricant was performed on the criterion of the total consumption of the lubricant for the predicted resource of the rails in the curved sections of the track. It was obtained the dependence of the number of inclusions of the lubricant and the lubricant flow rate on the number of load cycles for the rails for the projected resource. For one load cycle, a single passage of the wheelset of rolling stock along the rail was taken.

Powder catchment in laser metal deposition

Laser metal deposition (LMD) of Inconel 718 using a coaxial nozzle is investigated by high-speed imaging. The interaction of individual powder grains with the laser induced melt pool surface and, finally, their catchment in the LMD track is observed. Powder catchment trends are explained by interpreting physical phenomena, such as the melt flow and surface tension. Distinct zones for powder catchment are categorized depending on the position of initial interaction between powder grains and the melt pool. Particles are introduced outside the melt pool ricochet and do not attach to the clad. Particles arriving outside the laser spot, onto the solidifying skin of the melt pool, are caught, and may incorporate. Some particles may remain on the clad surface as surface roughness on the built part. Particles interacting with the laser-irradiated region of the melt pool tend to move toward its center and readily incorporate into the melt. Quantitative analyses of high-speed videos are carried out to measure incorporation time of powder grains in the melt pool, their velocity, and distance traveled.

A 3D cell printed muscle construct with tissue-derived bioink for the treatment of volumetric muscle loss

Volumetric muscle loss (VML) is an irrecoverable injury associated with muscle loss greater than 20%. Although hydrogel-based 3D engineered muscles and the decellularized extracellular matrix (dECM) have been considered for VML treatment, they have shown limited efficacy. We established a novel VML treatment with dECM bioink using 3D cell printing technology. Volumetric muscle constructs composed of cell-laden dECM bioinks were generated with a granule-based printing reservoir. The 3D cell printed muscle constructs exhibited high cell viability without generating hypoxia and enhanced de novo muscle formation in a VML rat model. To improve functional recovery, prevascularized muscle constructs that mimic the hierarchical architecture of vascularized muscles were fabricated through coaxial nozzle printing with muscle and vascular dECM bioinks. Spatially printing tissue-specific dECM bioinks offers organized microenvironmental cues for the differentiation of each cell and improves vascularization, innervation, and functional recovery. Our present results suggest that a 3D cell printing and tissue-derived bioink-based approach could effectively generate biomimetic engineered muscles to improve the treatment of VML injuries.

Experimental and computational study of tones occurring with a coaxial nozzle

The source of audible tones occurring with a coaxial nozzle is explored experimentally as well as computationally. The hardware is comprised of an inner and an outer nozzle, without a center-body, that are held together by a set of four struts. With increasing jet Mach number ( Mj), first a tone occurred at about 2550 Hz around Mj = 0.06. At higher Mj, a tone at 5200 Hz dominated the noise spectra. The corresponding non-dimensional frequency, based on the effective thickness of the inner nozzle lip and jet exit velocity, turned out to be about 0.2, a value characteristic of Karman vortex shedding. Thus, vortex shedding from the inner nozzle lip could be linked to the tones. From a comparison of acoustic wavelengths and nozzle dimensions, as well as locations of the pressure nodes and anti-nodes from the computational results, it was inferred that the vortex shedding excited one-quarter-wave resonances within the divergent sections of the nozzle. Such resonances in the inner and the outer nozzles produced the higher and the lower frequency tones, respectively.

Modeling of the effect of powder parameters on laser cladding using coaxial nozzle

Results of a mathematical modeling of metal substrate melting and formation of a solid cladding layer by injection of powder particles through a coaxial nozzle during laser cladding are presented. The powder flow is assumed to be a mixture of a metal material (copper) and a gas (argon). The gas-powder flow from the coaxial nozzle is simulated as a mixture of two interpenetrating fluids, taking into account turbulences in the form of a standard k-ε model. Phase transition is simulated by means of a phase field method. Microstructure of metal crystals during solidification has been modeled. The modeling in macro-scale was carried out for different values of average density of the powder material, resulting in influence of the density on the results of the laser cladding, such as width of the heat-affected zone, width of the cladding layer, height of the cladding layer, height and width of non-melted powder. Modeling of a high-precision laser cladding has been carried out with low gas-powder flowrates. Influence of the powder size distribution and its mean density on the cladding shape is revealed. Effect of rotation of the metal flow inside the cladding is observed. For low flowrates (5 mm/s) of the carrier gas a concave shape of the layer of the non-melted powder is obtained. Influence of technological parameters (laser power, velocity and powder feed rate) on the geometry of a single-track laser clad and heat affected zone (HAZ) has been revealed. Simulations have been performed in 2D and 3D showing a good applicability of the 2D approach to describe thermal-fluid processes for the slow-moving cladding head and low gas-powder velocities that are typically used for the precise laser cladding.

Design optimization and experimental study of coaxial powder-feeding nozzle in the laser cladding process

To improve the powder convergence and cladding layer quality, the three-dimensional axisymmetrical powder flow through a coaxial feeding nozzle was simulated by the Eulerian-Eulerian two-fluid model. With the composite design via the response surface method, the significance between the main geometric dimensions of nozzle and fluidization characteristics of powder flow was analyzed and regression-fitted. Moreover, a mathematical model was constructed to optimize the nozzle structure, and the optimal nozzle was used in laser cladding experiments. The results show that appropriate powder flow can be obtained in the condition of the carrier gas more than 9 l/min, and the powder sending rate less than 7.5 g/min. The structural parameters of the optimized nozzle are as follows: nozzle angle of 62.94°, outlet width of 1.0mm, exit radius of 5.83mm, and flow separation angle of 3.00°. With the optimized nozzle, the waist diameter and focus depth of the original powder flow decreased by 39.4 and 46.4%, respectively, and the discrepancy between the experimental and simulation results was less than 9%. With the appropriate technological parameters, a layer with good geometry morphology and appropriate dilution rate can be prepared in the laser cladding process with a coaxial feeding nozzle.

Особенности горения круглой микроструи водорода в спутной струе смеси воздуха и нанопорошка

Results of the experimental studies of a round hydrogen microjet combustion in a coaxinal jet of air and SiO2 nanopouder mixture efflux from a slot-hole (multinozzle) coaxial nozzle at subsonic and supersonic efflux velocity are presented. It is shown that scenarios of a hydrogen microjet combustion in a coaxinal jet of air and nanopouder mixture are similar to scenarios of diffusion combustion of a hydrogen microjet at subsonic and supersonic efflux velocity. Existence of “bottleneck flame region” is revealed at subsonic and a flame separation from a nozzle exit at supersonic efflux velocity. It is found that with efflux velocity growth of jets it is possible to observe intensification of the luminescence of the flame at the boundary between the jet of hydrogen and air / nanopowder mixture and existence of «bottleneck flame region» as in a laminar coaxial jet and in a flame of a hydrogen microjet combustion. On the other hand, it is possible to observe actually disappearance of the «bottleneck flame region» at approach to transonic efflux velocity.

Взаимодействие круглой микроструи воздуха с коаксиальной (спутной) струей воздуха на сверхзвуковой скорости их истечения

Results of experimental studies of the round hydrogen microjet interaction with a coaxial air for supersonic speed jets efflux are presented in this work. It is shown that interaction of round and coaxial air jets at their supersonic efflux leads to appearance of a train small/large-scale and, on the contrary, large/small-scale supersonic cells on a resultant jet with growth and reduction of speed of its efflux, respectively. It is found that the result of the round and coaxial air jets interaction at their supersonic efflux does not depend on geometrical parameters of a round and coaxial exit nozzle.

Effects of the Nozzle Tip Clogging and the Scanning Direction on the Deposition Process During Laser Metal Deposition of Alloy 718 Using a Four-Stream Discrete Nozzle

Depending on the configuration of the LMD system, the nozzle tilting is necessary to be able to manufacture parts with complex geometry. In these cases, the use of discrete coaxial nozzles is recommended. With this type of nozzle, the powder can clog the internal tips of the nozzle streams due to an inappropriate shape, size distribution, humidity or temperature conditions of the powder particles during the deposition process. This undesired effect can be an opportunity depending on the combination of the activated powder tips for coating complex surfaces when the geometry of the substrate acts as a barrier for the powder stream.This work presents for first time the effect of the scanning direction and the stream clogging on the deposition process in terms of powder efficiency, Material Deposition Rate (MDR) and clad geometry and dimensions, when Alloy 718 is deposited by LMD using a four-stream discrete coaxial nozzle.

LES–RANS of Installed Ultra-High-Bypass-Ratio Coaxial Jet Aeroacoustics with Flight Stream

Using large-eddy simulation–Reynolds-averaged Navier–Stokes (LES–RANS), this paper studies a round coaxial nozzle with an ultra-high bypass ratio of 15, with and without a wing-flap geometry. Depending on engine placement, the nozzle can become extremely close to the wing-flap geometry, introducing strong installation effects. Two different flap deflections of 8 and 14 deg are contrasted with an isolated round nozzle. A flight stream is applied and an Ffowcs Williams-Hawkings (FWH) surface placement procedure for installed jets is proposed. Impressive agreement with available experimental data is economically achieved for far-field overall sound pressure level and spectra as well as near-field spectra. The LES provides a wider range of polar and azimuthal angles at 1 deg increments, providing one of the most detailed acoustics data sets to date. The installed cases generate up to 20 dB more noise at mid-low frequencies due to large flap trailing edge sources. Additional sources are introduced by the interaction of the flight stream with the lifting surfaces. Second-order space-time correlations reveal length and time scales in the flow. Fourth-order space-time correlations indicate increasing magnitudes of the dominant noise source components with increasing flap angle. The three-dimensional unsteady data set produced should lead to improved acoustics models.

A validated analytical-numerical modelling strategy to predict residual stresses in single-track laser deposited IN718

Direct Energy Deposition (DED) is being increasingly used to repair high value components that have been damaged in-service. The uptake of DED and laser cladding operations for repair is inhibited by accurate modelling techniques. Often the repair process required is unique, therefore modelling techniques are necessary to determine the process inputs for the specific application. The DED process subjects the component to high thermal gradients resulting in high magnitude residual stresses and component distortion. Prediction of these parameters would reduce the need for costly experimental trials to quantify the repair strategy. Here, a single-track deposition of IN718, utilising a Nd:YAG laser source and coaxial nozzle, was modelled using a semi analytical-numerical approach. The track profile, temperature fields, melt pool geometry and stress evolutions were simulated for a constant set of process parameters. A corresponding experimental trial was conducted to validate the proposed model, through the use of focus variation microscopy, in-situ temperature measurements, optical micrographs and neutron diffraction measurements. A good correlation between the experimental and numerical data sets were apparent. The track profile was predicted with a maximum error of 1.98% and 0.43% for the width and height respectively. The maximum error for the peak temperature and residual stress was 3.1% and 18% respectively. Overall, the modelling strategy presented encompasses the key process variables, allowing accurate predictions of the thermal and mechanical effects of the process.

Computer simulation of aerosol nanoparticles focusing and deposition process for functional microstructure fabrication

The possibility is shown of using computer simulation to predict the size of the structures formed by the dry aerosol jet printing method. Computer modeling consisted in determining the model parameters and solving the system of equations to determine the trajectories of Ag nanoparticles of size up to 45 nm in the process of focusing and deposition through a coaxial nozzle with an outlet diameter of about 100 μm on the substrate surface located 0.5 mm away from the nozzle. As a result of the comparative analysis, a satisfactory agreement between the model and the experiment is established.

OPTIMIZATION OF THE EFFICIENCY OF THE LASER METAL DEPOSITION PROCESS APPLIED TO HIGH HARDNESS COATINGS BY THE ANALYSIS OF DIFFERENT TYPES OF COAXIAL NOZZLES

Laser Metal Deposition (LMD) or laser cladding is a technology capable of coating, repairing and manufacturing components by injecting molten metal powder on a substrate. Some of the advantages of this technology are: wide range of materials available in powder, reduced thermal distortion, coatings and repaired parts of high quality. However, the biggest advantage can be its relative ease of implementation in a multiprocess machine tool and subsequent automatization. The supply of hybrid machines in the world market that implements the LMD process is increasing (IBARMIA, DMG MORI, MAZAK, OKUMA, etc...), making the production more flexible in a single machine and introducing this process in more applications and industrial sectors. However, hybridization also presents problems that are difficult to solve. Some of the most noteworthy are those associated with the use of powdered metallic material both from the point of view of the safety and hygiene of the operators and also of the waste management and integrity of the machine itself, being its most serious effects at lower efficiency of the process. In this article, the study of the efficiency of different LMD nozzles is addressed for the coating of a hardened steel using for it the hybrid multiprocess machine IBARMIA ZVH45 /1600 Add + process, with the aim of finding the most efficient and, therefore (the one that generates less waste) and which, in turn, offers good productivity. Keywords: Laser cladding, hybrid manufacturing, LMD, coatings, hardened steel, wear resistance, coaxial nozzle.

Study of metallic powder flow in discrete coaxial nozzles

Additive technologies are gradually introducing into modern manufacturing, complementing or dislodging conventional material processing technologies. This is because of they have a unique advantage in the manufacture of products. Currently, among the popular additive laser technologies the most promising and productive technology is the direct laser deposition (DLD). The distribution of powder particles in a gas-powder flow is an important parameter that determines the powder capture coefficient (PCC) and, as a consequence, the efficiency of the DLD process. The powder flow distribution depends on the shape of the particles, the stability and the parameters of supply of the carrier gas and powder. When above conditions are fulfilled, gas-powder flow becomes stationary, which allows to determine PCC. The measurements of the PCC for different amounts and cases of nozzle positions were conducted. Having analysed the experimental and calculated results we can conclude that the model of the powder stream satisfactory describes one tube nozzle.

The influence of pulsed CO2-laser radiation on the transport of powder during laser cladding of metal

The problem of measurement of the in-flight velocity and temperature of particles in the light field of a pulsedperiodic laser was solved using contactless detection methods. The solution of the problem is based on using a spectrometer and a complex of laser and optical means. The diagnostic technique combines two independent methods for measuring the in-flight particle velocity: a passive one, based on the registration of the natural radiation emitted by the heated particles in the gas flow, and an active one, using the effect due to laser-beam scattering. Histograms of the statistical distributions of particle velocities for two operating modes of a coaxial nozzle were presented. There is no laser radiation in the first mode. There is pulsed laser radiation in the second mode. In the experiments, various powders (Al2O3, Mo, Ni, Al) with particle size distributions typical of laser deposition technology and various working gases (air, nitrogen, argon) were used. СО2-laser works in pulse-periodic mode with a mean power up to 2 kW. Pulsed power reaches several ten/hundred kilowatts. It is shown that in the field of laser radiation, powder particles acquire additional acceleration due to the evaporation and the appearance of a reactive force due to the recoil pressure of the vapors emitted from the irradiated part of the particle surface. It is shown that laser radiation can significantly affect the velocity and temperature of powder particles being transported by a gas jet. At the maximum carrier-gas velocity of up to 30 m/s, the velocities of single particles due to the laser-induced acceleration can reach the values of the order of 120 m/s.

Fiber-Based Mini Tissue with Morphology-Controllable GelMA Microfibers.

The use of microscale fibers could facilitate nutrient diffusion in fiber-based tissue engineering and improve cell survival. However, in order to build a functional mini tissue such as muscle fibers, nerve conduits, and blood vessels, hydrogel microfibers should not only mimic the structural features of native tissues but also offer a cell-favorable environment and sufficient strength for tissue functionalization. Therefore, an important goal is to fabricate morphology-controllable microfibers with appropriate hydrogel materials to mimic the structural and functional complexity of native tissues. Here, gelatin methacrylate (GelMA) is used as the fiber material due to its excellent biological performance, and a novel coaxial bioprinting method is developed to fabricate morphology-controllable GelMA microfibers encapsulated in calcium alginate. By adjusting the flow rates, GelMA microfibers with straight, wavy, and helical morphologies could be obtained. By varying the coaxial nozzle design, more complex GelMA microfibers such as Janus, multilayered, and double helix structures could be fabricated. Using these microfibers, mini tissues containing human umbilical cord vein endothelial cells are built, in which cells gradually migrate and connect to form lumen resembling blood vessels. The merits of cytocompatibility, structural diversity, and mechanical tunability of the versatile microfibers may open more avenues for further biomedical research.

Bioprinting of coaxial multicellular structures for a 3D co-culture model

With three dimensional (3D) bioprinting technology, it is feasible to fabricate various types of tissue models, in which multiple kinds of cells can be co-cultured. In this study, a novel 3D coaxial co-culture model in vitro was established by direct bioprinting. Using a four-layer coaxial nozzle, novel coaxial multicellular structures were fabricated, which contained two layers of alginate hydrogel as shell and two layers of hollow channels for cell perfusion. Sodium alginate (Na-Alg) was crosslinked by calcium cation with the contact of coaxial flows, forming a tubular coaxial structure of hydrogel. Human umbilical vein endothelial cells (HUVECs) and human umbilical vein smooth muscle cells (HUVSMCs) were used for a typical vascular co-culture model. Collagen solutions loaded with HUVECs and HUVSMCs were perfused into the layers of hollow channels and gelled at 37 ℃. The forming effect was favorable with good integrity. Pertinent process parameters of the bioprinting were investigated. Mechanical properties of four-layer coaxial structures were evaluated, indicating the higher mechanical strength than monolayer hydrogel structure. Cell viability assay after cell perfusion showed that the process of cell perfusion was feasible. In 7-day culture, cells maintained a steady proliferation. The immunohistochemical expression of HUVECs and HUVSMCs was detected in the structure. Cell work showed good biological functions of this 3D coaxial co-culture model.

Analysis of the Process Parameter Influence in Laser Cladding of 316L Stainless Steel

Laser Cladding is one of the leading processes within Additive Manufacturing technologies, which has concentrated a considerable amount of effort on its development. In regard to the latter, the current study aims to summarize the influence of the most relevant process parameters in the laser cladding processing of single and compound volumes (solid forms) made from AISI 316L stainless steel powders and using a coaxial nozzle for their deposition. Process speed, applied laser power and powder flow are considered to be the main variables affecting the laser cladding in single clads, whereas overlap percentage and overlapping strategy also become relevant when dealing with multiple clads. By setting appropriate values for each process parameter, the main goal of this paper is to develop a processing window in which a good metallurgical bond between the delivered powder and the substrate is obtained, trying simultaneously to maintain processing times at their lowest value possible. Conventional metallography techniques were performed on the cross sections of the laser tracks to measure the effective dimensions of clads, height and width, as well as the resulting dilution value. Besides the influence of the overlap between contiguous clads and layers, physical defects such as porosity and cracks were also evaluated. Optimum process parameters to maximize productivity were defined as 13 mm/s, 2500 W, 30% of overlap and a 25 g/min powder feed rate.