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This paper investigates the influence of carrier gas flow on the external flow field of coaxial powder feeding nozzle. FLUENT software was adopted to establish gas-solid two-phase flow. The simulation of powder stream field under different carrier gas flow was also carried out. Results show that the larger the flow of carrier gas is, the higher the...
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A 3D full size numerical model of a ring-type coaxial nozzle was established to obtain particle space trajectory and convergence character. The realizable k-ε model was applied in the gas flow phase. The powder flow was coupled with the gas flow by using Euler–Lagrange approach as a discrete phase model. Different powder material and particle sizes...
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... Pulsed laser cladding is a surface-strengthening technology with many advantages. This process is an additive fabrication procedure based on material deposition, which overturns the traditional mechanical processing "material reduction" feature and has a high-cost performance in the manufacturing of key components in the fields of aerospace and defense industry [1]. The contour size, accuracy, and performance as well as the cladding layer depend to a considerable extent on the flow state of the powder "waist beam" formed under the nozzle. ...
During the pulsed laser cladding process, complex thermal accumulation occurs between powder and beam due to the pulsed laser periodic change. The selection of process parameters affects the cladding layer quality, and the correlation between the parameters is high. It is of great significance to obtain high quality cladding layer to determine the influence of the powder-carrying gas nitrogen velocity, powder feeding port diameter, and powder feeding angle on the powder flow, as well as the optimal powder shading rate and the mechanism of powder interaction with pulsed laser beam. In this paper, a gas–solid coupling model during the pulsed laser cladding process of three-beam coaxial powder feeder was established, and the rotating Gaussian heat source function of pulsed laser was written to calculate the temperature, flow velocity, and concentration distribution considering the interaction between laser and powder. The orthogonal test method was used to optimize the process parameters in order to reduce the shading rate of powder and improve the laser energy utilization. On this basis, a full cycle three-dimensional multi-field coupling numerical model for pulsed laser cladding process was established, and the temperature, flow, stress fields, and multi-component heat and mass transfer behaviors were calculated under different powder shading rates. The flow temperature of powder was collected by infrared thermometer and compared with the numerical results, the reliability of the model was verified. This study provides a significant theoretical basis for the full-cycle optimization of process parameters and the improvement of cladding layer quality during pulsed laser cladding.
... A series of related studies have been carried out based on numerical modeling. Guo et al. [8] studied the influence of powder carrier gas flow rate on powder convergences, and the results showed a negative correlation between the mass concentration of the powder and the flow rate of the powder carrier gas. Liu et al. [9] determined the powder mass concentration distribution at different locations and analyzed the influence of powder jet velocity and particle size on the powder mass concentration distribution using the weight measurement method. ...
Laser direct metal deposition (DMD) can supply a new method in the fields of surface modification and near-net forming. The powder flow behavior and its convergence characteristics play a crucial role in the deposition quality during the DMD process. In this research, the k-ε turbulence model based on the computational fluid dynamics (CFD) modeling method was innovatively employed to establish the numerical model of the gas-powder flow. Then, the dense discrete phase model (DDPM) was utilized in this gas-powder coupling model to accurately calculate the collision between particles as well as between particles and inner wall of the nozzle. Afterward, the response surface method (RSM) was carried out to design the numerical simulation scheme, analyze a series of simulation results, explore the correlation between the process parameters and the responses, and establish the prediction model of powder convergence characteristics. Furthermore, the process parameters were optimized by considering the influence of defocusing amount, with smaller powder spot diameter and higher maximum powder mass concentration as optimization objectives. It was found that the prediction model of powder convergence characteristics demonstrated a high degree of accuracy and reliability. The single-deposition track exhibited better deposition quality fabricated with the optimized process parameters. The research method and results mentioned in the present study were expected to provide significant theoretical guidance for the selection and application of process parameters during the laser direct metal deposition process.
... A series of related studies have been carried out based on numerical modeling. Guo et al. [8] studied the influence of powder carrier gas flow rate on powder convergences, and the results showed a negative correlation between the mass concentration of the powder and the flow rate of the powder carrier gas. Liu et al. [9] determined the powder mass concentration distribution at different locations and analyzed the influence of powder jet velocity and particle size on the powder mass concentration distribution using the weight measurement method. ...
Laser direct metal deposition (DMD) can supply a new method in the fields of surface modification and near-net forming. The powder flow behavior and its convergence characteristics play a crucial role in the deposition quality during the DMD process. In this research, the k - ε turbulence model based on the Computational Fluid Dynamics (CFD) modeling method was innovatively employed to establish the numerical model of the gas-powder flow. Then, the Dense Discrete Phase Model (DDPM) was utilized in this gas-powder coupling model to accurately calculate the collision between particles and between particle and inner wall of the nozzle. Afterward, the Response Surface Method (RSM) was carried out to design the numerical simulation scheme, analyze a series of simulation results, explore the correlation between the process parameters and the responses, and establish the prediction model of powder convergence characteristics. Furthermore, the process parameters were optimized by considering the influence of defocusing amount, with smaller powder spot diameter and higher maximum powder mass concentration as optimization objectives. It was found that the prediction model of responses demonstrated a high degree of accuracy and reliability. The single deposition track exhibited better deposition quality fabricated with the optimized process parameters. The research method and results mentioned in the present study were expected to provide significant theoretical guidance for the selection and application of process parameters during the laser direct metal deposition process.
... Laser cladding technology is an integral part of metal 3D printing, which is capable of repairing the surface dimensions of workpieces and extending their service life through the simultaneous action of laser irradiation on alloy powder and metal surfaces to form metallurgically bonded cladding layers [1]. At present, laser cladding is primarily utilized in industrial fields such as aerospace, defense and automotive ships [2]. The working modes of laser energy sources in laser cladding can be categorized into two types: continuous wave (CW) and pulsed wave (PW). ...
Continuous wave (CW) and pulsed wave (PW) are the two principal modes of working to control the laser heat source. Different laser heat source working modes have an essential impact on the rapid cooling and heating temperature change rate during the cladding, which directly determines the cladding layer quality. The laser cladding process is meaningful to quantitatively reveal the mechanism of single-channel multilayer cladding and forming under different laser heat source working modes. In this paper, a multi-field coupled 3D numerical model of the single-channel multilayer cladding process under diverse laser working modes is proposed, and the thermal physical parameters of the cladding material are computed on the basis of CALPHAD method. The mechanism of the impact of distinct working modes on the multi-field coupled ephemeral evolution process of laser cladding is investigated by using the solid/liquid interface tracking technique, which comprehensively considers the light-powder interaction between the powder waist beam and the laser beam in diverse working modes. The temperature, flow and stress fields are computationally solved for a single-channel multilayer cladding process. On the foundation of this study, the mechanism of the impact of pulse duty cycle and pulse frequency on the cladding behavior of single-channel and multi-layers during pulsed laser cladding was dissected. The macroscopic morphology and microstructure of the cladding layer were observed by KEYENCE VH-Z100R ultra-deep field electron microscope, and the feasibility of the model was confirmed. This study provides an important theoretical rationale for enhancing the cladding quality under different laser working modes.
... Liu et al. [18] used numerical simulations to study the effect of the powder supply rate on the concentration of nickel alloy powder particles between the coaxial nozzle and the substrate and found that the powder concentration had a positive correlation with the powder supply rate. Guo et al. [19] established a coaxial nozzle model to study the influence of powder flow with different carrier gas flows on the external flow field of the nozzle. It was found that the larger the carrier gas flow was, the higher the flow field velocity at the nozzle outlet was. ...
Laser direct metal deposition (LDMD) enables not only the preparation of high-performance coatings on the surfaces of low-property materials but also the three-dimensional direct manufacturing and re-manufacturing of parts. In the LDMD process, the spatial coupling characteristics of the powder flow and the laser beam are the key factors affecting the forming quality of the cladding layer. Based on the gas–solid two-phase flow theory, a numerical model of coaxial powder feeding was established by CFD. The powder flow characteristics of the lower part of the nozzle, the powder particle motion trajectory, and the optical-powder spatial coupling morphology and law were studied, and the relationship between the powder flow morphology, laser beam, and powder utilization was explored. On this basis, the law between the optical-powder coupling characteristics and the geometric characteristics of the cladding layer is discussed in conjunction with LDMD experiments. The results show that the powder concentration scalar located in the focal plane of the laser beam can be used to visualize the optical-powder coupling morphology. When the powder feeding speed exceeds the loading capacity of the carrier gas flow, the powder concentration in the center of the spot and the powder utilization rate decrease. When the carrier gas flow rate is 4.0 L/min and the powder feeding rate is 4.0 g/min, the best utilization rate achieved is 81.4%. In addition, the H (height) of the cladding layer is more sensitive to changes in the powder concentration than the W (width). These findings provide new ideas for nozzle structure design and the optimization of LDMD parameters.
... At the same time, there are problems in the transportation of great amounts of powder with high particle concentration in a jet. Previously, most experimental and theoretical works [4][5][6][7][8][9][10][11][12][13][14][15][16][17] considered only low powder flow rates, normally about 10-40 g/min. Despite that such articles are present, they do not pay special attention to the study of two-way coupling effect between gas and powder flows. ...
... For example, in [6], the comparison of the images obtained from a CCD and high-speed camera shows a good agreement between the calculations and experiment. In [9][10][11], the gaspowder two-way coupling is considered, but only for low powder flow rates and collisions between particles. The authors of [9] explain this approximation by the low probability of the collisions because of the low powder volume fraction. ...
Direct material deposition (DMD) is the technology of producing new parts and making coating depositions, where much powder should be transported with high accuracy. At high powder flow rates (50–100 g/min), the interaction between a gas and powder flow (two-way coupling), as well as collisions between particles, impose a significant influence on the powder jet focusing. In the light of these effects, the paper presents the numerical analysis of the structure of gas-dispersed flows formed by continuous coaxial nozzles. Considerable variations in the gas-dynamic flow are shown in the focus area when the powder volume fraction is above 0.5 %. The obtained results are in a good agreement with the experimental ones and show the importance of the two-way coupling of both phases. The efficiency of a triple coaxial nozzle with a non-parallel arrangement of channels for carrier and shaping gases is analyzed for different powder particle sizes.
The efficiency of powder-based a directed energy deposition (DED) nozzle is dependent on its ability to direct the pneumatically conveyed powder into the meltpool. Computational fluid dynamics (CFD) with discrete phase modeling (DPM) has been used to investigate the optimization of DED nozzle geometry and DED parameter selection, however the effect of material choice for nozzle fabrication has not been fully investigated. To explore the effects of the nozzle material on powder efficiency a CFD DPM model was created and analyzed in Ansys FLUENT. Various nozzle materials were simulated using statistical models for the coefficient of restitution (COR) between the powder and nozzle wall from literature. The results of the CFD DPM model aligned well with experimental data for a 316L stainless steel prototype nozzle. CFD DPM results indicated that using a material with a lower mean COR value improved the powder efficiency of the nozzle. Powder efficiency improved because the component of powder velocity normal to the direction of gas flow was reduced in nozzles made from materials with lower COR values, which in turn led to fewer impacts between the particles and the nozzle walls.
In blown powder directed energy deposition (DED) additive manufacturing powdered metal feedstock is pneumatically conveyed to the meltpool via a nozzle. DED nozzles have been the subject to a growing number of research efforts using computational fluid dynamics (CFD) with multiphase flows to study and optimize powder flow. However, many research papers published to date contain powder – nozzle impact dynamics behavior that is not realistic or not derived from experiments that resemble the powder conveyance process in the DED nozzle being studied. To provide a set of data representative of DED powder flow through a nozzle particle image velocimetry (PIV) experiments were conducted using 316L stainless steel metal powder and flat targets with varying surface roughness made of oxygen free copper, mild steel, P20 tool steel, 316L stainless steel, Inconel 718, and Ti-Al6-V4. Normal coefficients of restitution (COR) were calculated and compared to several analytical and empirical models in literature.
