Coaxial Powder Flow Research Articles

Large-eddy simulation of coaxial powder flow for the laser direct deposition process

We conduct a large-eddy simulation with Lagrangian particle tracking to study the coaxial powder flow for the laser direct deposition process. To our knowledge, this is the first numerical study in which the high-fidelity, eddy-resolving simulation approach is applied to this process. Via the eddy-resolving simulations, we show the instantaneous flow structures and the associated turbulent quantities in great detail during the development of the transient state. We examine the effect of the flow on the particles and the resulting distributions of particle positions on various horizontal planes. Moreover, we demonstrate how the particle velocities affect the particle temperatures. On assessing three settings of initial particle distributions, we find that the simulation assuming a parabolic distribution for particle velocities gives good predictions of particle velocities and temperatures that are consistent with experimental data. Finally, we examine the effect of a substrate by moving the bottom boundary to the point of intersection of the particle streams. We find that due to increased flow dissipation, the substrate raises the location of the interaction point by approximately 10%. Moreover, the resulting reduction in particle velocity slightly increases the particle temperature. These differences can lead to a quite different distribution of the powder stream and have a significant impact on the mass and energy balance of the cladding model depending on the spot size of the laser beam and powder stream.

Study of the microstructure and mechanical properties in multilayered structures created by Laser-PTA additive manufacturing

This paper proposes a laser-assisted plasma transfer arc (Laser-PTA) additive manufacturing (AM) technology using coaxial powder flow. The focus of this paper is the effect of laser energy on the deposited microstructure, including grain morphology, texture characteristics, etc. The research focuses on the ultimate tensile strength (UTS), elongation properties, as well as anisotropy improvement of the deposition material. The experimental results show that laser energy, not less than 300 W～400 W, significantly promotes grain refinement and weakens the grain growth texture in deposition layers. The laser energy can cause the growth of equiaxed fine grains in the interlaminar region, which completely blocks the continuous growth of columnar grains in adjacent layers. Additionally, laser energy can also increase the proportion of high angle grain boundaries within the microstructure of the deposited layers. Optimizing the microstructure has a favorable effect on the mechanical properties of the deposited material's structure. The tensile test results showed that the vertical and horizontal UTS and elongations were improved, with a significantly higher vertical direction tensile improvement than that seen in the horizontal direction. At the same time, the UTS average difference between the horizontal and vertical decreased by 73.29%, and the elongation average difference decreased by 67.61%, which indicates the material has improved anisotropic mechanical properties.

Characterization of laser-powder interaction and particle transport phenomena during laser direct deposition of W‒Cu composite

Abstract The laser direct deposition, one kind of additive manufacturing technologies, was used to produce W‒Cu composite material. To explain the formation of the deposited microstructure, the process of laser-powder interaction and particle transport phenomena during laser direct deposition were investigated through experiment and simulation works. The parameters of the coaxial powder flow (the distribution and the velocity of flying particles) and the particle motion on the melt pool were demonstrated with high-speed imaging. By using these parameters, a laser-powder flow interaction model was established to calculate the laser intensity attenuated by the powder flow and the temperatures of W and Cu particles. Based on the calculated results, a three-phase fluid dynamics model was constructed to simulate the transport phenomena of W and Cu particles on the substrate surface during laser deposition. The calculated results indicate that the temperatures of W and Cu particles were mainly in the solid state but with huge difference in temperature while arriving at the deposition area. The captured images show that these solid particles can be deposited until the substrate surface was slightly melted. The simulation results suggest that the heat of W particles is conducted to Cu particles rapidly after being deposited on the substrate surface. Coupled with the laser irradiation, Cu particles are melted and form a melt pool. Subsequently, a fallen W particle can float on the melt pool since the inertial force of the falling W particle and the surface tension between Cu and W are roughly balanced. In comparison, if a Cu particle falls on a floating W particle, the Cu particle will be melted and then flow into the melt pool in 300 μs. The combination of high-speed imaging and our simulation explained the deposited microstructure, i.e., the distribution of W particles in the deposition layer.

Development of predictive models for effective process parameter selection for single and overlapping laser clad bead geometry

PurposeThe purpose of this work is to explore predictive model approaches for selecting laser cladding process settings for a desired bead geometry/overlap strategy. Complementing the modelling challenges is the development of a framework and methodologies to minimize data collection while maximizing the goodness of fit for the predictive models. This is essential for developing a foundation for metallic additive manufacturing process planning solutions.Design/methodology/approachUsing the coaxial powder flow laser cladding method, 420 steel cladding powder is deposited on low carbon structural steel plates. A design of experiments (DOE) approach is taken using the response surface methodology (RSM) to establish the experimental configuration. The five process parameters such as laser power, travel speed, etc. are varied to explore their impact on the bead geometry. A total of three replicate experiments are performed and the collected data are assessed using a variety of methods to determine the process trends and the best modelling approaches.FindingsThere exist unpredictable, non-linear relationships between the process parameters and the bead geometry. The best fit for a predictive model is achieved with the artificial neural network (ANN) approach. Using the RSM, the experimental set is reduced by an order of magnitude; however, a model with R2 = 0.96 is generated with ANN. The predictive model goodness of fit for a single bead is similar to that for the overlapping bead geometry using ANN.Originality/valueDeveloping a bead shape to process parameters model is challenging due to the non-linear coupling between the process parameters and the bead geometry and the number of parameters to be considered. The experimental design and modelling approaches presented in this work illustrate how designed experiments can minimize the data collection and produce a robust predictive model. The output of this work will provide a solid foundation for process planning operations.

Analysis of Laser Cladding Bead Morphology for Developing Additive Manufacturing Travel Paths

Laser cladding is a method of material deposition used to envelop a substrate with a surface of material which has superior characteristics, such as corrosion or abrasion resistance. There are several process parameters to be adjusted to generate a deposited bead or a layer, and developing a model to predict a bead shape is challenging due to the highly level of coupling between the manufacturing process parameters and the bead geometry. This paper will present results for an experimental study where P420 steel cladding powder (a steel commonly used in injection molding) is deposited on low carbon structural steel plates using the coaxial powder flow laser cladding method. Five process parameters such as laser power, scanning speed and powder flow rate etc. are varied to explore their impact on the bead height, width, penetration, area, dilution area, and the bead shape. The bead shape to process parameter relationships are explored and predictive models are developed using analysis of variance, a ‘lumped parameter model, and artificial neural network (ANN) approaches. The best fit for a predictive model is achieved with the ANN approach. This work will be extended to incorporate a variety of substrate and clad materials, and layering parameters.

激光同轴送粉喷嘴流场模拟与可调式结构设计

激光同轴送粉喷嘴流场模拟与可调式结构设计

激光同轴送粉喷嘴流场模拟与可调式结构设计

激光同轴送粉喷嘴流场模拟与可调式结构设计

Parametric study on a coaxial multi-material powder flow in laser-based powder deposition process

The manner with which the composite powder particles injected into the laser formed molten pool decides the deposition quality in a typical laser-based powder deposition of composite material. Since, the morphology and physical properties of nickel (Ni) and tungsten carbide (WC) are different their powder flow characteristics such as the powder particles stream structure, maximum concentration at the converging spot, and the powder particles velocity are noticeably different. In the current study, a computational fluid dynamics (CFD) based powder flow model is established to characterize the coaxial powder flow behavior of Ni–WC composite powders. The key powder flow characteristics such as the stand-off distance, the diameter of the powder stream at the stand-off distance, and the velocity of the powder particles are measured using three different vision based techniques. Both the numerical and experimental results reveal the exact stand-off distance where the substrate needs to be placed, the diameter of the concentration spot of powder at the stand-off distance, and a combination of suitable nozzle angle, diameter, and carrier gas flow rate to obtain a maximum powder concentration at the stand-off distance with a stable composite powder flow.

Modeling of coaxial powder flow for the laser direct deposition process

The supplying powder jet conditions in a direct deposition process greatly influence the quality and property of deposition products. Coaxial powder flow provides the means of precise deposition due to its omnidirectional nature in a direct deposition process. In this paper, a comprehensive numerical model is presented to predict the whole process of coaxial powder flow, including the particle stream flow in and after the nozzle and laser–particle interaction process. By solving the coupled momentum transfer equations between the particle and gas phase while incorporating particle temperature evolution, the dynamic and thermal behavior of multi-particles in the stream is completely modeled. Calculated and measured results are well matched. The model is capable of predicting the powder stream structure and multi-particle phase change process with liquid fraction evolution throughout the entire process while considering the particle morphology and size distribution in real powder samples.

激光熔覆中同轴粉末流温度场的CCD检测

激光熔覆中同轴粉末流温度场的CCD检测

激光熔覆中同轴粉末流温度场的数值模拟

激光熔覆中同轴粉末流温度场的数值模拟

Transport phenomena during direct metal deposition

The evolution of temperature and velocity fields during direct metal deposition with coaxial powder injection was simulated using a self-consistent three-dimensional model based on the solution of the equations of mass, momentum, energy conservation, and solute transport in the liquid pool. The basic physical phenomena, including heat transfer, phase changes, mass addition, fluid flow, and interactions between the laser beam and the coaxial powder flow, were considered in the model. The level-set method was implemented to track the evolution of the liquid/gas interface. The temperature and velocity fields, liquid/gas interface, and energy distribution at liquid/gas interface at different times were simulated. For verification purposes, the cladding depth and height were compared with experimental results.

Numerical simulation of coaxial powder flow with carrying gas in laser manufacturing

Gas-solid two-phase flow theory is used to simulate the powder flow from coaxial nozzle in coaxial powder feeder system with carrying gas, which is the key technology in laser manufacturing. The concentration distributing of powder flow and powder parameters (focus distance to nozzle exit and focus radius of powder flow) varying is simulated and analyzed. The numerical simulation result is well consistent with the result of measurement by digital particle image velocimetry (DPIV). It is shown that the concentration of powder flow and powder pa- rameters is also influenced by gas flux and feeding powder amount. It can be found that the gas flux mainly affects the powder velocity and the powder concentration or focus pa- rameters hardly change with various gas fluxes and constant feeding powder amount. The powder concentration tends to increase with increasing powder feed amount. The focus dis- tance and powder stream radius at the focus point also increase and focus depth decreases with increasing the feeding powder. The powder flow simple model is also presented. The conclu- sion will benefit for coaxial nozzle designing and performance improving.

Numerical simulation of heat transfer and fluid flow in coaxial laser cladding process for direct metal deposition

The coaxial laser cladding process is the heart of direct metal deposition (DMD). Rapid materials processing, such as DMD, is steadily becoming a tool for synthesis of materials, as well as rapid manufacturing. Mathematical models to develop the fundamental understanding of the physical phenomena associated with the coaxial laser cladding process are essential to further develop the science base. A three-dimensional transient model was developed for a coaxial powder injection laser cladding process. Physical phenomena including heat transfer, melting and solidification phase changes, mass addition, and fluid flow in the melt pool, were modeled in a self-consistent manner. Interactions between the laser beam and the coaxial powder flow, including the attenuation of beam intensity and temperature rise of powder particles before reaching the melt pool were modeled with a simple heat balance equation. The level-set method was implemented to track the free surface movement of the melt pool, in a continuous laser cladding process. The governing equations were discretized using the finite volume approach. Temperature and fluid velocity were solved for in a coupled manner. Simulation results such as the melt pool width and length, and the height of solidified cladding track were compared with experimental results and found to be reasonably matched.

Laser beam analysis in direct metal deposition process

The quality of a laser beam profile and its stability play fundamental roles in laser material processing. Beam reflections may dramatically affect the beam quality under certain material processing conditions. In this study, experiments were carried out to examine the variations of the continuous wave CO2 laser beam profile during the direct metal deposition (DMD) process. A pyroelectric-camera-based new industrial laser beam analysis device was installed in the optical line near the laser output coupler. Experimental results are presented with the comparison of beam profiles under different cladding processing conditions, such as the coaxial powder flow cladding, preplaced powder cladding, the remelting process, and the dumping of the raw beam. It was observed that cladding using preplaced powder gives off more reflective energy from the cladding zone which deforms the beam profile and causes great power fluctuation. Laser beam profiles and stability during DMD processes were monitored and analyzed with various processing geometries and the identification of porosity formation. High contents of the oxidized contaminants in the reused H13 powder were found to cause dark discontinuities in single track cladding where obvious beam power fluctuations were observed. In multiple layer cladding, 7%–20% more reflected energy was detected in the first layer deposition than in the successive layers.

Attenuation of laser power of a focused Gaussian beam during interaction between a laser and powder in coaxial laser cladding

The power of a focused laser beam with a Gaussian intensity profile attenuated by powder in coaxial laser cladding is investigated experimentally and theoretically, and its resolution model is developed. With some assumptions, it is concluded that the attenuation of laser power is an exponential function and is determined by the powder feed rate, particle moving speed, spraying angles and waist positions and diameters of the laser beam and powder flow, grain diameter and run of the laser beam through the powder flow. The attenuation of laser power increases with powder feed rate or run of laser beam through the powder flow. In the experiment presented, 300 W laser power from a focused Gaussian beam is attenuated by a coaxial powder flow. The experimental results agree well with the values calculated with the developed model.