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Bekir Sami Yilbas - One of the best experts on this subject based on the ideXlab platform.
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Flow and heat transfer characteristics of assisting gas impingining onto an alumina coated hole in relation to Laser Drilling
Optics & Laser Technology, 2014Co-Authors: Shahzada Zaman Shuja, Bekir Sami YilbasAbstract:Abstract Flow and heat transfer characteristics of the assisting gas impinging onto the coated holes are investigated in relation to the Laser Drilling Process. The alumina coating with thickness of 250 μm is considered at the surface of the carbon steel substrate. Three cases are considered by incorporating different locations of the coating on the carbon steel. These cases include coating at the top of the workpiece, coating at the bottom of the workpiece, and coating both at the top and at the bottom of the workpiece. A no-coating situation of the hole is also presented for the comparison reason. To resemble the Laser Drilling Process, the wall temperature of the coating and the carbon steel substrate is kept at the melting temperatures during the simulations. A numerical scheme incorporating the control volume approach is introduced and the Reynolds stress turbulence model is used to account for the turbulence effect of the impinging assisting gas. An experiment is carried out in line with the simulation conditions to examine the morphological changes at the coating-carbon steel interface. It is found that the assisting gas temperature exceeds the melting temperature of the steel substrate along the coating thickness and as the assisting gas progresses further into the hole, heat transfer from the assisting gas to the hole wall takes place. This, in turn, increases thermal erosion at the hole wall in the vicinity of the coating-steel substrate interface. The Nusselt number and the skin friction attain large values along the coating thickness in the hole.
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Thermal Analysis of Laser Drilling Process
Laser Drilling, 2012Co-Authors: Bekir Sami YilbasAbstract:In Laser Drilling Process, the material removal involves with evaporation at the surface, liquid ejection, and solid heating. However, liquid ejection vanishes for the Lasers with the pulse length within the rage and higher than the nanoseconds. However, in Drilling applications mass removal by liquid ejection is desirable because the rate of material removed becomes high. Analytical modeling the Laser heating Process in relation to Drilling is difficult, since Process involves with the phase change and fluid flow due to the evaporation at the surface. However, numerical modeling is feasible with some useful assumptions.
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Laser Drilling and Plasma Formation at the Surface
Laser Drilling, 2012Co-Authors: Bekir Sami YilbasAbstract:In Laser Drilling Process, plasma, consisting of charged ions, electrons, and neutral atoms is formed above the surface. Drilling Process is effect by the size and transient nature of the surface plasma, since the plasma partially absorbs the incident radiation and acts like a heat source contributing to the Drilling Process. However, formation of the excess plasma modifies the hole geometry at inlet and lowers the drilled hole quality. In order to reduce the difficulty of a theoretical investigation of Laser beam plasma interactions a framework is described which resolves the interaction into zones, each of which may be considered separately.
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parametric study to improve Laser hole Drilling Process
Journal of Materials Processing Technology, 1997Co-Authors: Bekir Sami YilbasAbstract:In the Laser Drilling Process, the quality of the drilled holes is the main task. A method of studying the influence on the quality of the main Process variables needs to be developed, which seeks to improve the quality and explains the Drilling mechanism. In the present study, the effect of the Laser parameters and the material properties on the hole quality when Drilling is examined. A statistical approach, referred to as factorial design, is employed to test the significance level of the factors that affect the hole quality. Three materials, stainless steel, nickel and titanium, are considered. The experimental study yields tables of significance of each factor on the aspects that determine the quality of the holes. The hole geometry is evaluated by assigning marks for each geometric feature, the marking scheme being conducted relevant to the importance of the hole feature.
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Liquid ejection and possible nucleate boiling mechanisms in relation to the Laser Drilling Process
Journal of Physics D: Applied Physics, 1997Co-Authors: Bekir Sami Yilbas, M. SamiAbstract:The Laser Drilling Process is a complex phenomenon. This is especially true after the evaporation Process starts. It is experimentally evident that liquid ejection occurs due to drag forces developed around the solid cavity and/or explosion resulting from nucleation of vapour bubbles in the liquid zone. Therefore, study into the ejection of liquid due to vapour bubble formation is necessary. Consequently, the present study examines the liquid ejection mechanism experimentally and possible saturated nucleate boiling is treated theoretically. In the experimental study, streak photography is introduced while a kinetic theory is adopted for the heat transfer model. This enables us to obtain the surface and internal temperature rise due to the Laser heating pulse. It is found that the time measured for the liquid expulsion from the heated zone is identical with the time computed corresponding to possible saturated nucleate boiling.
Y Hahn - One of the best experts on this subject based on the ideXlab platform.
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a generalized thermal modeling for Laser Drilling Process i mathematical modeling and numerical methodology
International Journal of Heat and Mass Transfer, 1997Co-Authors: R K Ganesh, Amir Faghri, Y HahnAbstract:Abstract Conduction and advection heat transfer in the solid and liquid metal, respectively, the free surface flow of the liquid melt and its expulsion, the tracking of the solid-liquid and liquid-vapor interfaces with different thermo-physical properties in the two phases and the evolution of latent heat of fusion over a temperature range are mathematically modeled for the two-dimensional axisymmetric case in the transient development of a Laser drilled hole where the impressed pressure and temperature on the melt surface is provided by a one-dimensional gas dynamics model. Significant improvement made to our earlier melting and solidification submodel is discussed that comprises a temperature transforming model on a fixed grid system. The resulting advection-diffusion equation's compatibility with the present fluid flow simulation model is described. The mathematical formulation of the submodels and the numerical methodology is presented.
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a generalized thermal modeling for Laser Drilling Process ii numerical simulation and results
International Journal of Heat and Mass Transfer, 1997Co-Authors: R K Ganesh, Amir Faghri, Y HahnAbstract:Abstract Once the fluid configuration and the associated velocity field are obtained in a given time step using the VOF method which tracks the free surface, the energy equation is solved as an advection-diffusion equation using the control volume finite difference method. The energy equation rigorously models the phase-change both ways and tracks down the phase front as well. This paper discusses the verification of the phase-change model in cylindrical coordinates with the available results in the literature for a two-region freezing problem and its subsequent incorporation into the Laser Drilling model making the phase-change submodel robust in many respects. Numerical material removal rates are compared with experimental ones and found to be in good agreement. Contour plots of solid, fluid, pressure and temperature are provided at different times during the Drilling Process.
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A generalized thermal modeling for Laser Drilling Process—II. Numerical simulation and results
International Journal of Heat and Mass Transfer, 1997Co-Authors: R K Ganesh, Amir Faghri, Y HahnAbstract:Abstract Once the fluid configuration and the associated velocity field are obtained in a given time step using the VOF method which tracks the free surface, the energy equation is solved as an advection-diffusion equation using the control volume finite difference method. The energy equation rigorously models the phase-change both ways and tracks down the phase front as well. This paper discusses the verification of the phase-change model in cylindrical coordinates with the available results in the literature for a two-region freezing problem and its subsequent incorporation into the Laser Drilling model making the phase-change submodel robust in many respects. Numerical material removal rates are compared with experimental ones and found to be in good agreement. Contour plots of solid, fluid, pressure and temperature are provided at different times during the Drilling Process.
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A generalized thermal modeling for Laser Drilling Process—I. Mathematical modeling and numerical methodology
International Journal of Heat and Mass Transfer, 1997Co-Authors: R K Ganesh, Amir Faghri, Y HahnAbstract:Abstract Conduction and advection heat transfer in the solid and liquid metal, respectively, the free surface flow of the liquid melt and its expulsion, the tracking of the solid-liquid and liquid-vapor interfaces with different thermo-physical properties in the two phases and the evolution of latent heat of fusion over a temperature range are mathematically modeled for the two-dimensional axisymmetric case in the transient development of a Laser drilled hole where the impressed pressure and temperature on the melt surface is provided by a one-dimensional gas dynamics model. Significant improvement made to our earlier melting and solidification submodel is discussed that comprises a temperature transforming model on a fixed grid system. The resulting advection-diffusion equation's compatibility with the present fluid flow simulation model is described. The mathematical formulation of the submodels and the numerical methodology is presented.
Amir Faghri - One of the best experts on this subject based on the ideXlab platform.
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vaporization melting and heat conduction in the Laser Drilling Process
International Journal of Heat and Mass Transfer, 1999Co-Authors: Yuwen Zhang, Amir FaghriAbstract:Abstract Melting and vaporization phenomena during the Laser Drilling Process are investigated in this paper. The locations of the solid–liquid and liquid–vapor interfaces were obtained by solving energy conservation equations at the interfaces. The dependence of saturation temperature on the back pressure is taken into account by using the Clausius/Clapeyron equation. The conduction heat loss to the solid is also included in the model and is solved by using an integral approximate method. The results show that the fraction of the heat lost through conduction to the solid is very small and its effect on the vaporization Process is not significant. On the other hand, the conduction heat loss significantly reduces the thickness of the liquid layer, which becomes the recast layer after Drilling.
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a generalized thermal modeling for Laser Drilling Process i mathematical modeling and numerical methodology
International Journal of Heat and Mass Transfer, 1997Co-Authors: R K Ganesh, Amir Faghri, Y HahnAbstract:Abstract Conduction and advection heat transfer in the solid and liquid metal, respectively, the free surface flow of the liquid melt and its expulsion, the tracking of the solid-liquid and liquid-vapor interfaces with different thermo-physical properties in the two phases and the evolution of latent heat of fusion over a temperature range are mathematically modeled for the two-dimensional axisymmetric case in the transient development of a Laser drilled hole where the impressed pressure and temperature on the melt surface is provided by a one-dimensional gas dynamics model. Significant improvement made to our earlier melting and solidification submodel is discussed that comprises a temperature transforming model on a fixed grid system. The resulting advection-diffusion equation's compatibility with the present fluid flow simulation model is described. The mathematical formulation of the submodels and the numerical methodology is presented.
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a generalized thermal modeling for Laser Drilling Process ii numerical simulation and results
International Journal of Heat and Mass Transfer, 1997Co-Authors: R K Ganesh, Amir Faghri, Y HahnAbstract:Abstract Once the fluid configuration and the associated velocity field are obtained in a given time step using the VOF method which tracks the free surface, the energy equation is solved as an advection-diffusion equation using the control volume finite difference method. The energy equation rigorously models the phase-change both ways and tracks down the phase front as well. This paper discusses the verification of the phase-change model in cylindrical coordinates with the available results in the literature for a two-region freezing problem and its subsequent incorporation into the Laser Drilling model making the phase-change submodel robust in many respects. Numerical material removal rates are compared with experimental ones and found to be in good agreement. Contour plots of solid, fluid, pressure and temperature are provided at different times during the Drilling Process.
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A generalized thermal modeling for Laser Drilling Process—II. Numerical simulation and results
International Journal of Heat and Mass Transfer, 1997Co-Authors: R K Ganesh, Amir Faghri, Y HahnAbstract:Abstract Once the fluid configuration and the associated velocity field are obtained in a given time step using the VOF method which tracks the free surface, the energy equation is solved as an advection-diffusion equation using the control volume finite difference method. The energy equation rigorously models the phase-change both ways and tracks down the phase front as well. This paper discusses the verification of the phase-change model in cylindrical coordinates with the available results in the literature for a two-region freezing problem and its subsequent incorporation into the Laser Drilling model making the phase-change submodel robust in many respects. Numerical material removal rates are compared with experimental ones and found to be in good agreement. Contour plots of solid, fluid, pressure and temperature are provided at different times during the Drilling Process.
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A generalized thermal modeling for Laser Drilling Process—I. Mathematical modeling and numerical methodology
International Journal of Heat and Mass Transfer, 1997Co-Authors: R K Ganesh, Amir Faghri, Y HahnAbstract:Abstract Conduction and advection heat transfer in the solid and liquid metal, respectively, the free surface flow of the liquid melt and its expulsion, the tracking of the solid-liquid and liquid-vapor interfaces with different thermo-physical properties in the two phases and the evolution of latent heat of fusion over a temperature range are mathematically modeled for the two-dimensional axisymmetric case in the transient development of a Laser drilled hole where the impressed pressure and temperature on the melt surface is provided by a one-dimensional gas dynamics model. Significant improvement made to our earlier melting and solidification submodel is discussed that comprises a temperature transforming model on a fixed grid system. The resulting advection-diffusion equation's compatibility with the present fluid flow simulation model is described. The mathematical formulation of the submodels and the numerical methodology is presented.
V. Favier - One of the best experts on this subject based on the ideXlab platform.
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Investigation of delamination mechanisms during a Laser Drilling on a cobalt-base superalloy
Journal of Materials Processing Technology, 2013Co-Authors: Jérémie Girardot, Matthieu Schneider, Laurent Berthe, V. FavierAbstract:Temperatures in the high pressure chamber of aircraft engines are continuously increasing to improve the engine efficiency. As a result, constitutive materials such as cobalt and nickel-base superalloys need to be thermally protected. The first protection is a ceramic thermal barrier coating (TBC) cast on all the hot gas-exposed structure. The second protection is provided by a cool air layer realized by the use of a thousand of drills on the parts where a cool air is flowing through. The Laser Drilling Process is used to realize these holes at acute angles. It has been shown on coated single crystal nickel-base superalloy that the Laser Drilling Process causes an interfacial cracking (also called delamination), detected by a cross section observation. The present work aims at characterizing interfacial cracking induced by Laser Drilling on coated cobalt-base super alloy. On the one hand, this work attempted to quantify the crack by several microscopic observations with regards to the most significant Process parameters related as the angle beam. On the other hand, we studied the difference of the Laser/ceramic and the Laser/substrate interaction with real time observation by using a fast movie camera.
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Simulation of the Laser Drilling Process with the Constraint Natural Element Method
2012Co-Authors: Jérémie Girardot, Matthieu Schneider, Lounès Illoul, Laurent Berthe, Nathan Ranc, Philippe Lorong, V. FavierAbstract:These works present a numerical alternative to the simulation of the Laser Drilling Process. The use of the finite element method to modeling the hole creation during a Laser pulse shows difficulties in front of a moving boundary problem. This moving boundary is induced by a fast phase transformation and also by high thermal gradient. The C-NEM (Constraint Natural Element Method) was tested in order to solve these numerical difficulties and to use the high potential of this original method. The physical interaction of the Laser Drilling will be reminded and the chosen mathematical model will be specified. A simulation was made with the data for pure iron in order to validate the numerical choice.
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Simulation of the Laser Drilling Process with the Constraint Natural Element Method
International Congress on Applications of Lasers & Electro-Optics, 2012Co-Authors: Jérémie Girardot, Matthieu Schneider, Lounès Illoul, Laurent Berthe, Nathan Ranc, Philippe Lorong, V. FavierAbstract:These works present a numerical alternative to the simulation of the Laser Drilling Process. The use of the finite element method to modeling the hole creation during a Laser pulse shows difficulties in front of a moving boundary problem. This moving boundary is induced by a fast phase transformation and also by high thermal gradient. The C-NEM (Constraint Natural Element Method) was tested in order to solve these numerical difficulties and to use the high potential of this original method. The physical interaction of the Laser Drilling will be reminded and the chosen mathematical model will be specified. A simulation was made with the data for pure iron in order to validate the numerical choice.These works present a numerical alternative to the simulation of the Laser Drilling Process. The use of the finite element method to modeling the hole creation during a Laser pulse shows difficulties in front of a moving boundary problem. This moving boundary is induced by a fast phase transformation and also by high thermal gradient. The C-NEM (Constraint Natural Element Method) was tested in order to solve these numerical difficulties and to use the high potential of this original method. The physical interaction of the Laser Drilling will be reminded and the chosen mathematical model will be specified. A simulation was made with the data for pure iron in order to validate the numerical choice.
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Simulation of the Laser Drilling Process with the Constraint Natural Element Method
International Congress on Applications of Lasers & Electro-Optics, 2012Co-Authors: Jérémie Girardot, Matthieu Schneider, Lounès Illoul, Laurent Berthe, Nathan Ranc, Philippe Lorong, V. FavierAbstract:These works present a numerical alternative to the simulation of the Laser Drilling Process. The use of the finite element method to modeling the hole creation during a Laser pulse shows difficulties in front of a moving boundary problem. This moving boundary is induced by a fast phase transformation and also by high thermal gradient. The C-NEM (Constraint Natural Element Method) was tested in order to solve these numerical difficulties and to use the high potential of this original method. The physical interaction of the Laser Drilling will be reminded and the chosen mathematical model will be specified. A simulation was made with the data for pure iron in order to validate the numerical choice.These works present a numerical alternative to the simulation of the Laser Drilling Process. The use of the finite element method to modeling the hole creation during a Laser pulse shows difficulties in front of a moving boundary problem. This moving boundary is induced by a fast phase transformation and also by high thermal gradient. The C-NEM (Constraint Natural Element Method) was tested in order to solve these numerical difficulties and to use the high potential of this original method. The physical interaction of the Laser Drilling will be reminded and the chosen mathematical model will be specified. A simulation was made with the data for pure iron in order to validate the numerical choice.
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Delamination induced by Laser Drilling on a base cobalt superalloy
International Congress on Applications of Lasers & Electro-Optics, 2012Co-Authors: Jérémie Girardot, Matthieu Schneider, Laurent Berthe, V. FavierAbstract:Temperatures in the high pressure chamber of aircraft engines are continuously increasing to improve the engine efficiency and constitutive materials need to be thermally protected. The first protection is a ceramic thermal barrier coating (TBC) cast on all the hot gas-exposed structure. The second protection is provided by a cool air layer realized by the use of a thousand of drills on the parts where a cool air is flowing through. The Laser Drilling Process is used to realize these holes at acute angles on this coated mutlimaterial. The present work aims at characterizing interfacial cracking induced by Laser Drilling on coated cobalt base super alloy. This work attached to quantify the crack by several microscopic observations with regards to the most significant Process parameters related as the angle beam. The difference between the Laser/ceramic and the Laser/substrate interaction is also studied with real time observation by using a fast movie camera.Temperatures in the high pressure chamber of aircraft engines are continuously increasing to improve the engine efficiency and constitutive materials need to be thermally protected. The first protection is a ceramic thermal barrier coating (TBC) cast on all the hot gas-exposed structure. The second protection is provided by a cool air layer realized by the use of a thousand of drills on the parts where a cool air is flowing through. The Laser Drilling Process is used to realize these holes at acute angles on this coated mutlimaterial. The present work aims at characterizing interfacial cracking induced by Laser Drilling on coated cobalt base super alloy. This work attached to quantify the crack by several microscopic observations with regards to the most significant Process parameters related as the angle beam. The difference between the Laser/ceramic and the Laser/substrate interaction is also studied with real time observation by using a fast movie camera.
George Chryssolouris - One of the best experts on this subject based on the ideXlab platform.
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optical emissions for monitoring of the percussion Laser Drilling Process
The International Journal of Advanced Manufacturing Technology, 2010Co-Authors: Aristidis Stournaras, Konstantinos Salonitis, George ChryssolourisAbstract:In percussion Laser Drilling, a sufficiently powerful Laser beam is used for the formation of a hole on the workpiece. In this study, the investigation of utilizing optical signals, acquired by means of photodiodes and emitted from the Processing zone for real-time monitoring, is presented. The correlation between the sensor output and the geometry of the hole, determined by the depth and upper diameter, is investigated, and the results are presented. In general, the results indicate that there is a strong correlation between the optical signal output and the diameter of the hole.
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on acoustic emissions in percussion Laser Drilling
The International Journal of Advanced Manufacturing Technology, 2010Co-Authors: Aristidis Stournaras, George ChryssolourisAbstract:Laser Drilling is a well established sheet metal Processing method. The development of a monitoring system capable of assessing the dimensions of holes is the subject of this work. This paper investigates the applicability of an acoustic-based monitoring system for the percussion Laser Drilling Process. Correlation between the sensor output and the hole's geometry, determined by its depth and upper diameter, is investigated and the results are presented. In general, the results indicate that a correlation exists between the acoustic signal output and the depth of the hole.
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Acoustic and optical sensing for monitoring of blind Laser Drilling geometrical features
International Congress on Applications of Lasers & Electro-Optics, 2009Co-Authors: Aristidis Stournaras, Konstantinos Salonitis, George ChryssolourisAbstract:The scope of this study is to investigate the utilization of optical and acoustic emissions, originating from the Processing zone, for monitoring of the percussion Laser Drilling Process. For that purpose, an acoustic microphone and photodiodes were off-axially arranged, relatively to the Laser beam, and for both types the correlation between the sensor output and the geometry of the hole was theoretically investigated. The results have been compared with the experimental data.The scope of this study is to investigate the utilization of optical and acoustic emissions, originating from the Processing zone, for monitoring of the percussion Laser Drilling Process. For that purpose, an acoustic microphone and photodiodes were off-axially arranged, relatively to the Laser beam, and for both types the correlation between the sensor output and the geometry of the hole was theoretically investigated. The results have been compared with the experimental data.
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a theoretical and experimental investigation on limitations of pulsed Laser Drilling
Journal of Materials Processing Technology, 2007Co-Authors: Konstantinos Salonitis, Aristidis Stournaras, George Tsoukantas, Panagiotis Stavropoulos, George ChryssolourisAbstract:Abstract A theoretical and experimental investigation of the limitations of the pulsed Laser Drilling Process is presented in this study. A theoretical model has been developed for simulating the Process of Drilling with medium irradiance Laser beams. It takes into account the required time for reaching melting temperature as well as the melting and the subsequent removal of a volume of material during each Laser pulse. The model estimates for a specific Laser beam power, a maximum drill depth. The pulsing frequency of the Laser beam has no effect on the maximum drill depth. A 1.8 kW CO 2 Laser has been used for the experimental verification of the theoretical predictions and the fine tuning of the model.
