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T Debroy - One of the best experts on this subject based on the ideXlab platform.

  • an improved heat transfer and Fluid Flow Model of wire arc additive manufacturing
    International Journal of Heat and Mass Transfer, 2021
    Co-Authors: G. L. Knapp, T. Mukherjee, Yanhong Wei, T Debroy
    Abstract:

    Abstract Wire-arc additive manufacturing provides the fastest metal printing rate among all printing processes. Heat transfer and Fluid Flow Models offer a usable connection between process variables and the parameters that affect the structure and properties of parts. Here we develop a computationally efficient, three-dimensional, transient, heat transfer and Fluid Flow Model to calculate temperature and velocity fields, deposit geometry, cooling rates, and solidification parameters that affect the microstructure, properties, and defect formation. Calculations are done for multi-track depositions of a tool steel H13 and a titanium alloy Ti-6Al-4V and the computed results are tested using experimental data for different processing conditions. It is found that convective Flow and arc pressure are the two most important factors that govern the width and depth of penetration, respectively. An adaptive grid technique proposed here enhances the computational speed by as much as by 50% without affecting the accuracy of the computed results. For the same processing conditions, Ti-6Al-4V exhibits a larger fusion zone than that for H13 steel attributed to the lower density of Ti-6Al-4V. In addition, Ti-6Al-4V exhibits faster cooling rates during solidification than H13 steel because of the lower difference between the liquidus and solidus temperatures for Ti-6Al-4V. A smaller hatch spacing results in a larger pool and slower cooling rates during the solidification of both alloys.

  • residual stresses and distortion in additively manufactured compositionally graded and dissimilar joints
    Computational Materials Science, 2018
    Co-Authors: T. Mukherjee, Wei Zhang, J S Zuback, T Debroy
    Abstract:

    Abstract Additively manufactured compositionally graded joints are potentially attractive to minimize abrupt changes in residual stresses and distortion of dissimilar alloy joints. Performance of these graded joints depends on the residual stresses and distortion governed by the transient temperature field during additive manufacturing and local mechanical properties of the joint. Here we develop, validate and utilize a thermo-mechanical Model to provide a definitive way to additively manufacture sound graded joints for minimizing abrupt changes in residual stresses and distortion of the dissimilar joints. This Model calculates residual stresses and distortion from accurate temperature fields calculated using a well-tested heat transfer and Fluid Flow Model and temperature dependent alloy properties estimated by thermodynamic calculations. Both graded and dissimilar joints of 2.25Cr-1Mo steel to alloy 800H and Ti-6Al-4V to 800H, fabricated using laser-assisted powder based direct energy deposition process are examined. It is found that the sharp changes in residual stresses in dissimilar joints between Ti-6Al-4V and 800H can be effectively minimized by fabricating a graded joint between them. Although the magnitudes of residual stresses in Ti-6Al-4V to 800H joint are higher than that in 2.25Cr-1Mo steel to 800H joint, the former is less susceptible to warping, buckling and delamination due to the high room temperature yield strength of the Ti-6Al-4V substrate.

  • numerical simulation of heat transfer and Fluid Flow in gta laser hybrid welding
    Science and Technology of Welding and Joining, 2008
    Co-Authors: B Ribic, Rohit Rai, T Debroy
    Abstract:

    AbstractIn order to understand the temperature fields, cooling rates and mixing in the weld pool, a comprehensive, three-dimensional heat transfer and Fluid Flow Model is developed and tested by comparing Model predictions with two sets of experimental data. The first set of data was taken from the literature. The experiments varied the separation distance between the heat sources for three arc current levels at a constant laser power. The second set of experiments analysed the effect of varying laser power for a constant heat source separation distance. The results demonstrate that the distance between the two heat sources significantly affects the cooling rates. The calculated results showed that the hybrid weld pool was very well mixed with strong convection currents resulting from the interaction between the electromagnetic and Marangoni forces. The calculated and experimental results showed that hybrid welding increases the weld pool width and gap bridgability when compared with laser welding. The we...

  • tailoring gas tungsten arc weld geometry using a genetic algorithm and a neural network trained with convective heat Flow calculations
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2007
    Co-Authors: S Mishra, T Debroy
    Abstract:

    Weld attributes like geometry and cooling rate are strong functions of the welding process parameters such as arc current, voltage and welding speed. A specific weld pool geometry can be produced using multiple sets of these welding variables, i.e., different combinations of arc current, voltage and welding speed. At present, there is no systematic methodology that can determine, in a realistic time frame, these multiple paths based on scientific principles. Here we show that multiple combinations of welding variables necessary to achieve a target gas tungsten arc (GTA) weld geometry can be systematically computed by a real number based genetic algorithm and a neural network that has been trained with the results of a heat transfer and Fluid Flow Model. The neural network embodies the power of a numerical heat transfer and Fluid Flow Model of GTA welding, since it can predict the fusion zone geometry, peak temperature and cooling rate and its input and output variables are consistent with the equations of conservation of mass, momentum and energy. A genetic algorithm is used to determine a population of solutions by minimizing an objective function that represents the difference between the calculated and the desired values of weld pool penetration and width. The use of a neural network in place of a heat transfer and Fluid Flow Model significantly expedites the computational task. The desired weld geometry could be obtained with various combinations of welding variable sets. The computational methodology described here enables fabrication of a weld with desired geometry within the framework of phenomenological laws via alternative paths involving multiple combinations of welding variables.

  • composition change of stainless steel during microjoining with short laser pulse
    Journal of Applied Physics, 2004
    Co-Authors: T Debroy, P W Fuerschbach
    Abstract:

    Weld metal composition change in 200μm deep, 304 stainless steel microjoints fabricated using millisecond long Nd-YAG laser pulses was investigated experimentally and theoretically. The variables studied were pulse duration and power density. After welding, concentrations of iron, manganese, chromium, and nickel were determined at various locations of the microjoint using the electron microprobe analysis. The temperature field was simulated as a function of time from a well-tested three-dimensional transient heat transfer and Fluid Flow Model. Using the computed temperature fields, vaporization rates of various alloying elements resulting from both concentration and pressure driven transport of vapors and the resultant composition change of the alloy were calculated. The calculations showed that the vaporization took place mainly from a small region near the center of the beam-workpiece interaction zone, where the temperatures were very high. Furthermore, the alloying element vaporization was most pronoun...

Tarasankar Debroy - One of the best experts on this subject based on the ideXlab platform.

  • Fusion zone geometries, cooling rates and solidification parameters during wire arc additive manufacturing
    International Journal of Heat and Mass Transfer, 2018
    Co-Authors: W. Ou, T. Mukherjee, G. L. Knapp, Tarasankar Debroy
    Abstract:

    Abstract Structure, properties and serviceability of components made by wire arc additive manufacturing (WAAM) depend on the process parameters such as arc power, travel speed, wire diameter and wire feed rate. However, the selection of appropriate processing conditions to fabricate defect free and structurally sound components by trial and error is expensive and time consuming. Here we develop, test and utilize a three-dimensional heat transfer and Fluid Flow Model of WAAM to calculate temperature and velocity fields, deposit shape and size, cooling rates and solidification parameters. The calculated fusion zone geometries and cooling rates for various arc power and travel speed and thermal cycles considering convective Flow of molten metal agreed well with the corresponding experimental data for H13 tool steel deposits. It was found that convection is the main mechanism of heat transfer inside the molten pool. Faster travel speed enhanced the cooling rate but reduced the ratio of temperature gradient to solidification growth rate indicating increased instability of plane front solidification of components. Higher deposition rates could be achieved by increasing the heat input, using thicker wires and rapid wire feeding.

  • heat and Fluid Flow in additive manufacturing part i Modeling of powder bed fusion
    Computational Materials Science, 2018
    Co-Authors: Tamal Mukherjee, H L Wei, Tarasankar Debroy
    Abstract:

    Abstract Structure and properties of components made by the powder bed fusion (PBF) additive manufacturing (AM) are often optimized by trial and error. This procedure is expensive, time consuming and does not provide any assurance of optimizing product quality. A recourse is to build, test and utilize a numerical Model of the process that can estimate the most important metallurgical variables from the processing conditions and alloy properties. Here we develop and test a three-dimensional, transient, heat transfer and Fluid Flow Model to calculate temperature and velocity fields, build shape and size, cooling rates and the solidification parameters during PBF process. This Model considers temperature dependent properties of the powder bed considering powder and shielding gas properties, packing efficiency and powder size. A rapid numerical solution algorithm is developed and tested to calculate the metallurgical variables for large components fabricated with multiple layers and hatches rapidly. Part I of this article describes the Model, solution methodology, powder bed properties, and Model validation. The applications of the Model for four commonly used alloys are presented in part II.

  • An improved prediction of residual stresses and distortion in additive manufacturing
    Computational Materials Science, 2017
    Co-Authors: Tamal Mukherjee, Tarasankar Debroy
    Abstract:

    In laser assisted additive manufacturing (AM) an accurate estimation of residual stresses and distortion is necessary to achieve dimensional accuracy and prevent premature fatigue failure, delamination and buckling of components. Since many process variables affect AM, experimental measurements of residual stresses and distortion are time consuming and expensive. Numerical thermo-mechanical Models can be used for their estimation, but the quality of calculations depends critically on the accurate transient temperature field which affects both the residual stresses and distortion. In this study, a well-tested, three-dimensional, transient heat transfer and Fluid Flow Model is used to accurately calculate transient temperature field for the residual stress and distortion Modeling. The calculated residual stress distributions are compared with independent experimental results. It is shown that the residual stresses can be significantly minimized by reducing the layer thickness during AM. Inconel 718 components are found to be more susceptible to delamination than Ti-6Al-4V parts because they encounter higher residual stresses compared to their yield strength.

  • Mitigation of thermal distortion during additive manufacturing
    Scripta Materialia, 2017
    Co-Authors: Tamal Mukherjee, V. Manvatkar, A De, Tarasankar Debroy
    Abstract:

    Additively manufactured parts are often distorted because of spatially variable heating and cooling. Currently there is no practical way to select process variables based on scientific principles to alleviate distortion. Here we develop a roadmap to mitigate distortion during additive manufacturing using a strain parameter and a well-tested, three-dimensional, numerical heat transfer and Fluid Flow Model. The computed results uncover the effects of both the key process variables such as power, scanning speed, and important non-dimensional parameters such as Marangoni and Fourier numbers and non-dimensional peak temperature on thermal strain. Recommendations are provided to mitigate distortion based on the results.

  • Heat transfer and material Flow during laser assisted multi-layer additive manufacturing
    Journal of Applied Physics, 2014
    Co-Authors: V. Manvatkar, A De, Tarasankar Debroy
    Abstract:

    A three-dimensional, transient, heat transfer, and Fluid Flow Model is developed for the laser assisted multilayer additive manufacturing process with coaxially fed austenitic stainless steel powder. Heat transfer between the laser beam and the powder particles is considered both during their flight between the nozzle and the growth surface and after they deposit on the surface. The geometry of the build layer obtained from independent experiments is compared with that obtained from the Model. The spatial variation of melt geometry, cooling rate, and peak temperatures is examined in various layers. The computed cooling rates and solidification parameters are used to estimate the cell spacings and hardness in various layers of the structure. Good agreement is achieved between the computed geometry, cell spacings, and hardness with the corresponding independent experimental results.

Suck-joo Na - One of the best experts on this subject based on the ideXlab platform.

  • arc interaction and molten pool behavior in the three wire submerged arc welding process
    International Journal of Heat and Mass Transfer, 2015
    Co-Authors: Degala Venkata Kiran, Woohyun Song, Suck-joo Na
    Abstract:

    Abstract A three-dimensional numerical heat transfer and Fluid Flow Model is developed to understand the temperature distribution and molten pool behavior in a three wire submerged arc welding process. The Model solves the equations of the conservation of mass, momentum, and energy along with the volume of Fluid method. The volume of Fluid method is used to track the shape of the free surface. Further, a physical Model is developed to estimate the arc center displacement. For a given welding condition, connecting the leading electrode with direct current electrode positive polarity, the middle and trailing electrodes with trapezoidal alternating current waveform displayed deeper weld pools when compared to the sine waveforms. Within the range of welding conditions considered in the present work, weld width is significantly influenced by the leading arc whereas the penetration by the middle and trailing arcs. The computed weld width and penetration are in fair agreement with the corresponding experimental results.

  • molten pool behavior in the tandem submerged arc welding process
    Journal of Materials Processing Technology, 2014
    Co-Authors: Daewon Cho, Degala Venkata Kiran, Woohyun Song, Suck-joo Na
    Abstract:

    Abstract A three-dimensional numerical heat transfer and Fluid Flow Model is developed to examine the temperature profiles, velocity fields, weld pool shape and size in a two-wire tandem submerged arc welding process. The Model solves the equations of the conservation of mass, momentum, and energy along with the volume of Fluid method. The volume of Fluid method is used to track the shape of the free surface. Further, a novel scheme is proposed to handle the arc interaction and its influence on the molten droplet transfer direction. Using the computational Fluid dynamics simulations, it is found that the droplet movement and arc forces from the leading electrode heavily affect the molten pool Flow patterns and the resultant bead shapes, even though the same heat inputs are applied. The computed weld width and penetration are in fair agreement with the corresponding experimental results.

Degala Venkata Kiran - One of the best experts on this subject based on the ideXlab platform.

  • arc interaction and molten pool behavior in the three wire submerged arc welding process
    International Journal of Heat and Mass Transfer, 2015
    Co-Authors: Degala Venkata Kiran, Woohyun Song, Suck-joo Na
    Abstract:

    Abstract A three-dimensional numerical heat transfer and Fluid Flow Model is developed to understand the temperature distribution and molten pool behavior in a three wire submerged arc welding process. The Model solves the equations of the conservation of mass, momentum, and energy along with the volume of Fluid method. The volume of Fluid method is used to track the shape of the free surface. Further, a physical Model is developed to estimate the arc center displacement. For a given welding condition, connecting the leading electrode with direct current electrode positive polarity, the middle and trailing electrodes with trapezoidal alternating current waveform displayed deeper weld pools when compared to the sine waveforms. Within the range of welding conditions considered in the present work, weld width is significantly influenced by the leading arc whereas the penetration by the middle and trailing arcs. The computed weld width and penetration are in fair agreement with the corresponding experimental results.

  • molten pool behavior in the tandem submerged arc welding process
    Journal of Materials Processing Technology, 2014
    Co-Authors: Daewon Cho, Degala Venkata Kiran, Woohyun Song, Suck-joo Na
    Abstract:

    Abstract A three-dimensional numerical heat transfer and Fluid Flow Model is developed to examine the temperature profiles, velocity fields, weld pool shape and size in a two-wire tandem submerged arc welding process. The Model solves the equations of the conservation of mass, momentum, and energy along with the volume of Fluid method. The volume of Fluid method is used to track the shape of the free surface. Further, a novel scheme is proposed to handle the arc interaction and its influence on the molten droplet transfer direction. Using the computational Fluid dynamics simulations, it is found that the droplet movement and arc forces from the leading electrode heavily affect the molten pool Flow patterns and the resultant bead shapes, even though the same heat inputs are applied. The computed weld width and penetration are in fair agreement with the corresponding experimental results.

Wei Zhang - One of the best experts on this subject based on the ideXlab platform.

  • residual stresses and distortion in additively manufactured compositionally graded and dissimilar joints
    Computational Materials Science, 2018
    Co-Authors: T. Mukherjee, Wei Zhang, J S Zuback, T Debroy
    Abstract:

    Abstract Additively manufactured compositionally graded joints are potentially attractive to minimize abrupt changes in residual stresses and distortion of dissimilar alloy joints. Performance of these graded joints depends on the residual stresses and distortion governed by the transient temperature field during additive manufacturing and local mechanical properties of the joint. Here we develop, validate and utilize a thermo-mechanical Model to provide a definitive way to additively manufacture sound graded joints for minimizing abrupt changes in residual stresses and distortion of the dissimilar joints. This Model calculates residual stresses and distortion from accurate temperature fields calculated using a well-tested heat transfer and Fluid Flow Model and temperature dependent alloy properties estimated by thermodynamic calculations. Both graded and dissimilar joints of 2.25Cr-1Mo steel to alloy 800H and Ti-6Al-4V to 800H, fabricated using laser-assisted powder based direct energy deposition process are examined. It is found that the sharp changes in residual stresses in dissimilar joints between Ti-6Al-4V and 800H can be effectively minimized by fabricating a graded joint between them. Although the magnitudes of residual stresses in Ti-6Al-4V to 800H joint are higher than that in 2.25Cr-1Mo steel to 800H joint, the former is less susceptible to warping, buckling and delamination due to the high room temperature yield strength of the Ti-6Al-4V substrate.

  • henry granjon prize competition 2006 co winner category a joining and fabrication technology numerical Modelling of heat transfer Fluid Flow and microstructural evolution during fusion welding of alloys
    Welding in The World, 2006
    Co-Authors: Wei Zhang
    Abstract:

    The present study focuses on Modelling numerous aspects of the welding process which include predictions of molten metal convection in the weld pool, size and shape of the fusion zone (FZ) and heat-affected zone (HAZ), temperature distributions in the FZ and HAZ, solidification conditions of the FZ, and phase transformation kinetics in the HAZ. Integrated Models were developed taking into account the interactions of heat, Fluid Flow and microstructure. In particular, a three-dimensional heat transfer and Fluid Flow Model was used to understand the weld pool phenomena and provided useful insight into the physics of the weld pool. Application of the computed thermal cycles and phase transformation Models including Johnson-Mehl-Avrami equation and Monte Carlo simulation provided useful tools to understand the microstructural evolution during welding. The developed Models were used to investigate several welding processes such as gas metal arc welding (GMAW) and gas tungsten welding (GTAW) and different materials including AISI 1005 low carbon steel, 1045 mild carbon steel, Ti-6AI-4V alloy and 2025 duplex stainless steel. This paper is an extensive summary of the doctoral research work carried out by the author at the Pennsylvania State University.

  • heat and Fluid Flow in complex joints during gas metal arc welding part i numerical Model of fillet welding
    Journal of Applied Physics, 2004
    Co-Authors: Wei Zhang, Cheolhee Kim, T Debroy
    Abstract:

    Gas metal arc (GMA) fillet welding is one of the most important processes for metal joining because of its high productivity and amiability to automation. This welding process is characterized by the complicated V-shaped joint geometry, a deformable weld pool surface, and the additions of hot metal droplets. In the present work, a three-dimensional numerical heat transfer and Fluid Flow Model was developed to examine the temperature profiles, velocity fields, weld pool shape and size, and the nature of the solidified weld bead geometry during GMA fillet welding. The Model solved the equations of conservation of mass, momentum, and energy using a boundary fitted curvilinear coordinate system. Apart from the direct transport of heat from the welding arc, additional heat from the metal droplets was Modeled considering a volumetric heat source. The deformation of the weld pool surface was calculated by minimizing the total surface energy. Part I of this article is focused on the details of the numerical Model such as coordinate transformation and calculation of volumetric heat source and free surface profile. An application of the Model to GMA fillet welding of mild steel is described in an accompanying article (W. Zhang, C.-H. Kim and T. DebRoy, J. Appl Phys. 95, 5220 (2004)).

  • kinetic Modeling of phase transformations occurring in the haz of c mn steel welds based on direct observations
    Acta Materialia, 2003
    Co-Authors: J W Elmer, Wei Zhang, T A Palmer, Brandon C Wood, T Debroy
    Abstract:

    Abstract In situ Spatially Resolved X-Ray Diffraction (SRXRD) experiments were performed in the heat-affected zone (HAZ) of gas tungsten arc (GTA) welds of AISI 1005 C-Mn steel to directly observe welding induced phase transformations. These real-time observations were semi-quantified using diffraction peak profile analysis to construct a phase transformation map revealing ferrite ( α ) and austenite ( γ ) phase concentration gradients in the HAZ. Weld thermal cycles were calculated using a three-dimensional heat transfer and Fluid Flow Model and then combined with the SRXRD phase map to provide a complete description of the HAZ under actual welding conditions. Kinetic Modelling of the α → γ phase transformation during heating was performed using a Johnson–Mehl–Avrami analysis, modified to take into account non-uniform weld heating and transformation in the α+γ two-phase field. The results provide the most accurate JMA kinetic parameters to date for this alloy, n=1.45 and 1n(ko)=12.2, for an activation energy Q=117.1 kJ/mole. Using this kinetic description of the α→γ phase transformation, time temperature transformation (TTT) and continuous heating transformation (CHT) diagrams for this alloy were constructed to illustrate how the combination of SRXRD experiments and numerical Modeling from one weld can be used to predict phase transformations for a variety of welding and heat treating applications.