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Session Chairperson: Prof. Enrique J. Lavernia, Department of Chemical Engineering and Materials Science, University of California, Irvine, CA 92717; Dr. Prabir K. Chaudhury, Concurrent Technologies Corporation, 1450 Scalp Avenue, Johnstown, PA, 15904
8:30 am KEYNOTE
THERMO-FLUID ISSUES IN SPRAY FORMING: Michael M. Chen, University of Michigan, Ann Arbor, MI, 48109-2125; Dawn White Ford Scientific Laboratories, Dearborn, MI, Chuan Li, University of Michigan, Ann Arbor, MI, 48109-2125
A critical review on the heat transfer and fluid mechanical issues of spray forming will be presented. The paper will focus on those thermo-fluid issues which have important influence on the spray and solidification processes as well as the properties of the product, combining the perspectives of materials and manufacturing scientists and specialists in heat transfer and fluid mechanics. Among the topics to be considered are atomization, dynamics of sprays, including oversprays, droplet solidification, splat formation due to impact of liquid droplets and partially solidified particles with the substrate, heat transfer and solidification in the formed part, and residual stress formation. Emphases will be placed on current levels of understanding of the physics from a first principles point of view, semi-quantitative estimates of the length and time scales of interest, and current capabilities for accurate modeling and prediction. Recommendations for future research and development will also be made, based on results of the survey.
9:00 am INVITED
NUMERICAL INVESTIGATION OF MULTI-PHASE FLOW INDUCED POROSITY FORMATION IN SPRAY DEPOSITED MATERIALS: J.-P. Delplanque, E.J. Lavernia, R.H. Rangel, Department of Chemical Engineering and Materials Science, University of California, Irvine, Irvine, CA 92697-2575
Several mechanisms have been recently identified as responsible for porosity formation in spray deposited materials. These mechanisms may be categorized according to their underlying fundamental nature; chemical (e.g., porosity generated by a foaming agent), physical (e.g, solidification shrinkage porosity), or dynamical (e.g., liquid-jet overflow). This investigation focuses on the latter category: pore formation mechanisms related to liquid metal flow and interactions between the flowing liquid metal and the irregular solid formed by the previously deposited droplets. These mechanisms are investigated using a combination of analytical models and detailed numerical simulations. The numerical model is based on a Navier-Stokes solver combined with the Volume Of Fluid method to track free surfaces. A multi directional algorithm is used to simulate the solidification process. The model case considered is that of liquid metal flooding of a random dense particle packing made of solidified droplets. Particular attention is devoted to cases where there is insufficient liquid to fill all the interstices and to capillary effects.
CALCULATION OF POWDER SIZE IN CENTRIFUGAL ATOMISATION AND SPRAY FORMING: Huiping Li, P. Tsakiropoulos, Department of Materials Science and Engineering, University of Surrey, Guildford, Surrey GU2 5XH, England, UK
A model of the flow of melts on rotating disks has been combined with models based on wave theory to predict the size of powder particles in centrifugal atomisation/spray forming. The analysis considers the role of process parameters and materials properties on powder size. The dependence of powder particle size on disk diameter and rotating speed as well as type of melt are calculated and compared to experimental results.
NUMERICAL SIMULATION OF GAS ATOMIZATION IN SPRAY FORMING PROCESS: Huimin Liu, Concurrent Technologies Corporation, 1450 Scalp Avenue, Johnstown, PA 15904
The spray forming process is emerging as a cost-effective manufacturing route for net and near-net shape preforms in a wide range of materials. In the past, numerical simulations have been made to model the melt delivery, the spray deposition, and the consolidation stages in the spray forming process. However, the atomization stage, particularly gas flow in the nozzle-close region and melt break-up kinetics, have not been adequately simulated. Atomization is a key stage in the spray forming process because it determines the size, size distribution, and initial conditions of the particles, hence, influences particle velocity, temperature, cooling rate, microstructure, and thus the mechanical properties of the spray-formed preforms. This work uses numerical tools to model atomization mechanisms. The full compressible Navier-Stokes equations are solved to simulate the gas flow in the nozzle-close region. The melt flow and heat transfer are modeled on the basis of the boundary layer theory and the modified van Driest and Cebeci mixing-length turbulence model. The information on the flow and temperature fields obtained from the numerical simulation is then used to investigate melt break-up and droplet formation during atomization.
10:00 am BREAK
MODELING OF OSPREY SPRAY METAL FORMING PROCESS: T.R. Govindan, The Pennsylvania State University, Applied Research Laboratory, P.O. Box 30, North Atherton Street, State College, PA 16804-0030
A detailed computational model of the spray metal forming process is being developed. The model provides process figures of merit, identify process control parameters, and help process design in support of the process development activity. The core of the model is an Eulerian-Lagrangian flow solver in which the gas phase is treated in an Eulerian framework involving the Reynolds Averaged Navier-Stokes equations and the droplets are treated as a discrete phase involving single particle dynamics. Statistics are generated from the discrete phase by computing a large sample of particle "trajectories" in the force field due to the gas phase. In turn, particle statistics generate forces in the gas phase equations. Models are used in the discrete phase for particle drag, heat transfer, and solidification. The computer code is capable of handling complex three-dimensional geometries. Results will be presented showing details of the two-phase flow in a typical Osprey spray chamber; gas flow velocity and temperature distributions, gas flow and droplet interactions, droplet cooling curves and deposition profiles. Computed results will be compared with available experimental data.
INVESTIGATION OF THE PROCESS PARAMETERS CONTROLLING THE MICROSTRUCTURAL CHARACTERISTICS AND THE POROSITY OF SPRAY DEPOSITED TANTALUM ALLOYS: J.-P. Delplanque, W.D. Cai, R.H. Rangel, E.J. Lavernia, Department of Chemical Engineering and Materials Science, University of California, Irvine, California 92697-2575
An induction skull melting (ISM) spray forming process was used to investigate the spray atomization and deposition of tantalum alloys. Several systems were considered in order to tackle the scientific issues inherent to the spray forming of refractory metals in a gradual manner. Optical microscopy, X-ray diffraction and scanning electron microscopy were used to characterize the spray formed materials and oversprayed powders. A theoretical and numerical analysis of the deposition and solidification of tantalum alloy droplets was conducted concurrently. This approach is based on a multi-directional solidification model combined with a Navier Stokes solver for flows with interfaces. Various droplet size and impact velocities consistent with the experiments were considered. The simulation results and the experimental data were compared and analyzed in order to identify the critical process parameters controlling the microstructure and porosity of as-deposited tantalum alloys.
DROPLET ENTHALPY MEASUREMENT BY CALORIMETRY FOR CONTROLLED SPRAY FORMING: C. Tuffile, A. DiVenuti, Department of Mechanical Engineering, Tufts University, Medford, MA 01255; T. Ando, Department of Mechanical, Industrial and Manufacturing Engineering, Northeastern University, Boston, MA 02115; J.H. Chun, Laboratory for Manufacturing and Productivity, Massachusetts Institute of Technology, Cambridge, MA 02139
A non-adiabatic calorimetric method was developed and used to determine the enthalpy of droplets in a spray as a function of flight distance with the purpose of providing critical information for the controlled spray forming using uniform-droplet sprays (UDS). A UDS consists of droplets that are uniform in size and thermal history and can be used to produce a variety of novel deposit microstructures in a controlled manner. Such controlled spray forming, however, requires thorough characterization of the thermal state of the uniform droplets. The calorimetric method developed accounts for the heat loss that occurs while collecting the droplets in the calorimeter, and uses a data acquisition system for in-situ determination of droplet enthalpy. Comparison of measured droplet enthalpy values and those predicted by model calculations shows a very good agreement.
SIMULATION OF THE SPRAY FORMING PROCESS USING A WIRE-FED LASER TECHNIQUE: T. Seefeld, E. Schubert, G. Sepold, Universitat Bremen, Verfahrenstechnik/FB4, Postfach 330440, D-28334 Bremen, Germany
The spray forming process offers advantages for both material properties and process technology. A deeper understanding of the spray forming process, with particular concern to the complex disintegration phase and the formation of the deposit. The present work introduces an experimental set-up to investigate the in-flight behavior of sprayed droplets. In a chamber with controlled atmosphere, a spray cone is wire. This process allows to skip the complete melting unit of a spraying facility and facilitates maintaining a spraying experiment for a desired period of time (a couple of minutes generally) and changing the set of parameters for the next experiment within minutes in order to save time diameter and feed rate, laser beam power and intensity, and atomizing gas flow. During spraying of mild steel with nitrogen, the nitrogen content of droplets sampled at various locations within the spray cone is investigated. The results of the in-flight interaction of the sprayed dropletes with the ambient atmosphere are discussed.
THE ROLE OF ALUMINA PARTICULATE IN MICROSTRUCTURAL AND FORGING PROPERTIES OF SPRAY ATOMIZED AND DEPOSITED Fe-Al ORDERED INTERMETALLIC COMPOUNDS: L. Martinoz, M. Amaya, O. Flores, Instituto de Fisica, UNAM, A.P. 48-3, 62251, Cuernavaca, Morelos, Mexico; D. Lawrynowics, R.J. Lavernia, Department of Chemical Engineering & Materials Science, University of California, Irvine, CA 92697-2575
Spray atomization and deposition, hot isostatic pressing, and forging at high temperatures were used for processing FeAl intermetallic compounds alloyed with Boron and fine alumina particulates. Extensive optical microscopy, SEM, and TEM studies, as well as mechanical properties characterization are described. The alumina particulate play a role in refining and stabilizing the material microstructure and improves forgeability. The advantages of spray atomization and deposition are discussed. Work supported by CONACYT grant 3878A.
MODELLING DROPLET BEHAVIOUR DURING SPRAY FORMING USING FLUENT: P.S. Grant, R.P. Underhill, B. Cantor, Oxford Centre for Advanced Materials & Composites, Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH; D.J. Bryant, Rolls-Royce plc, Elton Road, P.O. Box 31, Derby DE24 8BJ, UK
A finite difference based fluid dynamics software program, FLUENT, has been used to model the 2-dimensional dynamic and thermal behaviour of Udimet 720 droplets during gas atomisation and spray forming. The effect of atomising gas pressure pressure, spray distance and melt mass flow rate (MFR) on the equilibrated droplet spray temperature has been examined and the predictions compared with measured maximum deposit temperatures from spray forming experiments performed under the same process conditions. The predicted spray temperatures at the substrate were always higher than the measured deposit temperatures under all conditions, and were found to increase with (I) decreasing gas pressure, (ii) decreasing spray distance, and (iii) increasing MFR. Mean droplet temperatures and velocities were found to be strongly dependent on droplet size with mean droplet temperature decreasing, and mean droplet axial velocities increasing, with decreasing droplet size.
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