El-Hachemi Amara - Academia.edu (original) (raw)

Papers by El-Hachemi Amara

Research paper thumbnail of Numerical approach for hydrodynamic behavior in the kerf with a quasi-complete model of the laser cutting process

Journal of the Optical Society of America A, 2020

The fundamental physical phenomena occurring during the process of laser cutting are still only s... more The fundamental physical phenomena occurring during the process of laser cutting are still only slightly understood, and thus the need to develop mathematical and numerical models to optimize the process parameters has become unavoidable for obtaining products with superior quality and for better use. It is in this context that we propose a new approach by building a model to study the laser cutting process, by including several physical mechanisms which interact during the cutting process, such as the laser–metal interaction (wavelength effect, energy absorption, …), the phase change (solidification/fusion), the heat transfers, the fluid flows with influence of the free surface, the turbulent gas jets, and the kerf formation. In view of the complexity of the phenomena put into action, the fundamental mechanisms related to the cutting process are very difficult to understand and then to model. It is indeed necessary to take into account all of the aforementioned interactions, avoidi...

Research paper thumbnail of Fundamentals of Optical Instrumentation for Spectroscopic and Imaging Applications

WORLD SCIENTIFIC eBooks, Feb 1, 2023

Research paper thumbnail of Experimental investigations on fiber laser color marking of steels

Applied Surface Science, Oct 1, 2015

We develop an experimental approach with the aim to bring a contribution to the comprehension of ... more We develop an experimental approach with the aim to bring a contribution to the comprehension of the occurring phenomena during laser color marking of steels. A home-made marking device using a pulsed fiber laser has been used to treat steel samples under different laser beam operating parameters, for different compositions of the processed steel, and at normal atmospheric conditions. The treated samples were analyzed either by optical and scanning electronic microscopy, as well as by energy dispersion spectroscopy. The results show the influence of the operating parameters on the obtained colors.

Research paper thumbnail of Simulation of multiple injection flow in free stream of keyhole cavity during laser welding

XV International Symposium on Gas Flow, Chemical Lasers, and High-Power Lasers, Mar 23, 2005

In the present study, we develop a simple mathematical model of the vapour jets flow inside a cav... more In the present study, we develop a simple mathematical model of the vapour jets flow inside a cavity, in order to provide some understanding of the physics of the flow and to obtain qualitative data relative to the vapour flow properties. We consider a fluid as an ideal gas (air) at high pressure and temperature injected from orifices located perpendicularly

Research paper thumbnail of Laser Ablation: Effect on Ambient Pressure on Titanium Plume Expansion Dynamics

Bulletin of the American Physical Society, Oct 5, 2010

Research paper thumbnail of Numerical Simulation of Transient 3D Temperature and Kerf Formation in Laser Fusion Cutting

World Academy of Science, Engineering and Technology, International Journal of Materials and Metallurgical Engineering, Nov 28, 2014

Research paper thumbnail of Effect of the Convective Losses During Selective Laser Melting Process

Research paper thumbnail of Effects of the Velocity and the Nature of the Inert Gas onthe Stainless Steel Laser Cut Quality

The effects of inert assisting gas nature and velocity on laser cut qual- ity are investigated. A... more The effects of inert assisting gas nature and velocity on laser cut qual- ity are investigated. A pure fusion cutting process just above melting point is con- sidered, where the molten steel velocity is given as a function of the two acting forces represented by the pressure gradient and the frictional forces applied by the laminar gas flow. In the case of nitrogen assisting gas, the stainless steel melt film exhibits a visible separation point. The point where the melt flow is separated out from the solid wall depends strongly on the gas velocity. It is pushed down the cut surface when the gas velocity is increased. Furthermore, we have investgated the use of different inert gases (nitrogen, argon and helium) to blow the molten material out of the kerf, and it was noted that the argon and the nitrogen gases evacuate more easily the molten metallic film, compared to the helium gas from their cooling rates point of view. It is concluded that the two first gases are more efficient in ...

Research paper thumbnail of Evolution of the solidification isothermaccording to the geometry of the heat source during deep penetration laser welding

Research paper thumbnail of Ultrafast modification of copper properties under femtosecond laser excitation

Optica Advanced Photonics Congress 2022

Optical and thermal properties of copper films under femtosecond laser excitation has been dynami... more Optical and thermal properties of copper films under femtosecond laser excitation has been dynamically calculated as a function of time using a two-temperature model coupled with Drude model. Ultrafast changes have been observed when the material is still cold.

Research paper thumbnail of Wavelength effect on striation formation during metal laser cutting

We develop a study on laser cutting of metals withassist gas jet, the aim is to investigate the e... more We develop a study on laser cutting of metals withassist gas jet, the aim is to investigate the effect of the beam wavelength on striation formation. The finite volume method is used to discretize the differential governing conservation equations, which are numerically solved. The interfaces are tracked by implementation of the VOF method, whereas an enthalpic approach allows to take into account the melting and re-solidification phenomena. The results show that the used wavelength may play a role in striation formation.We develop a study on laser cutting of metals withassist gas jet, the aim is to investigate the effect of the beam wavelength on striation formation. The finite volume method is used to discretize the differential governing conservation equations, which are numerically solved. The interfaces are tracked by implementation of the VOF method, whereas an enthalpic approach allows to take into account the melting and re-solidification phenomena. The results show that the ...

Research paper thumbnail of On the Vortex Formation Effect During the Application of a Nitrogen-Gas Assisted Laser-Fusion Cutting Technique to Stainless Steel

This paper focuses on the vortex formation effect during the application of a laser-fusion cuttin... more This paper focuses on the vortex formation effect during the application of a laser-fusion cutting technique. This industrial technique is typically associated with the ejection of a film of molten stainless steel blown off by a subsonic laminar jet of nitrogen gas used to assist the process. Without taking into account the transverse movement of the workpiece, we consider a 4 mm thick stainless steel plate. The resulting molten metal flow is assumed to be laminar, steady, viscous and incompressible. The numerical results reveal vortex structures adjacent to the walls at the entrance of the kerf, and a pair of eddies outside the kerf. Remarkably, these vortex structures can produce a separation point in the molten film, and thereby they can affect the surface quality of the processed material. The problem is investigated in the framework of a numerical technique available in the Fluent software, based on a volume of fluid (VOF) surface-tracking strategy and the enthalpy method to ac...

Research paper thumbnail of Effect of Laser Cutting Parameters on the Heat Affected Zone and on the Boundary Layer in Steel Laser Processing

Defect and Diffusion Forum, 2020

This paper investigates the effect of the laser cutting parameters on the heat-affected zone, and... more This paper investigates the effect of the laser cutting parameters on the heat-affected zone, and on the boundary layer of stainless steel processing. A new analytical resolution based on the boundary layer theory is used to deduce the interaction effects of the cutting parameters on the above zones. The results revealed that, the laminar nitrogen assist gas has a negligible effect on the HAZ depth but it has a remarkable effect on the molten boundary layer. It is also noticed that the pressure gradient remains very small compared to the interface shearing and the conductive heat losses from the cutting zone towards the substrate is dominant compared to the convective heat losses towards the gas.

Research paper thumbnail of Simulation by temperature gradient adaption of wavelength effect in metal laser cutting

Journal of Laser Applications, 2017

Laser cutting of thick metal workpieces requires the use of low operating speeds which, however, ... more Laser cutting of thick metal workpieces requires the use of low operating speeds which, however, will have an influence on the cut quality following the used laser wavelength. In this study, we develop a model which takes into account the Fresnel coefficients in order to determine the local laser absorbed energy as a function of the beam incidence angle on the surface workpiece. The deposited laser energy occurs on the metal/air interface which evolution is tracked by the volume-of-fluid multiphase model. In the simulation, in order to find the difference between the patterns obtained on the kerf walls when different laser wavelengths are used, an important number of cells must be used at the regions of interest, which are characterized by high gradients, but a larger number of cells will have the consequence to complete the calculation with much less computer time consumption. Therefore, a gradient adaption method was implemented in order to control the number of cells, by multiply...

Research paper thumbnail of Characterization of Titanium Oxide Layers Formation Produced by Nanosecond Laser Coloration

Metallurgical and Materials Transactions B, 2017

Laser marking technique is used to produce colors on titanium while scanning a metallic sample un... more Laser marking technique is used to produce colors on titanium while scanning a metallic sample under normal atmospheric conditions. To proceed with different operating conditions related to the laser beam, the parameters of a Q-switched diode-pumped Nd:YAG (k = 532 nm) laser, with a pulse duration of s = 5 ns, are varied. The effect on the resulting mark quality is the aim of the present study which is developed to determine the influence of the operating parameters (i.e., pulse frequency, beam scanning speed, and pumping intensity) and furthermore their combination, such as the accumulated fluences and the overlapping rate of laser impacts. From the obtained experimental results, it is noted that the accumulated fluences and the scanning speed are the most influential operating parameters during laser marking, since they have a strong effect on the surface roughness and reflectance, and the occurrence of many oxide phases such as TiO, Ti 2 O 3 , TiO 2 (c-phase, anatase, and rutile).

Research paper thumbnail of Surface laser marking optimization using an experimental design approach

Research paper thumbnail of Two temperature approach to femtosecond laser oxidation of molybdenum and morphological study

Applied Surface Science, 2017

Highlights  Computation of the molybdenum lattice temperature.  Molybdenum oxide nanorods forme... more Highlights  Computation of the molybdenum lattice temperature.  Molybdenum oxide nanorods formed after laser treatment.  Strain in the molybdenum film due to laser treatment.  Cross section SEM showing layer different layers.

Research paper thumbnail of Dynamics of photo-ablated carbon plasma in an inert gas atmosphere

Laser and Particle Beams, 1998

Time and space-resolved emission spectroscopy measurements were performed to investigate plasma d... more Time and space-resolved emission spectroscopy measurements were performed to investigate plasma dynamics during laser evaporation of a graphite target in an ambient inert atmosphere. Intense molecular emission is found to occur behind a front separating the plasma from the foreign gas. Two stages of expansion are found and are well described, using a viscous drag force model for the first one and a delayed ideal blast wave model for the second. The vibrational temperature estimated using the Swan band in helium at different pressures is presented.

Research paper thumbnail of Effect of the radiative losses during selective laser melting process

Materials Today: Proceedings, 2021

Research paper thumbnail of The Marangoni Convection Effect on Melt Pool Formation during Selective Laser Melting Process

Defect and Diffusion Forum, 2021

In order to predict the effect of the Marangoni convection and the morphology of melted stainless... more In order to predict the effect of the Marangoni convection and the morphology of melted stainless steel powder, during the selective laser melting (SLM) process, a transient three-dimensional numerical model is developed at the mesoscale. The evolution of the temperature and velocity fields’ is then studied. The initial powder bed distribution is obtained by the discrete element method (DEM) calculation, and the temperature distribution and the molten pool shape deformation are calculated and analyzed by the Ansys-Fluent commercial code. The molten pool shape is obtained by considering the influence of Marangoni convection on the internal flow behavior. The recoil force was not considered in our calculation. As main results, a slight deviation between the position of the maximum temperature of the molten pool and the center of the laser spot is observed. The direction of the heat diffusion is more likely to be horizontal and the flow centrifugal, which causes the melt track to be wi...

Research paper thumbnail of Numerical approach for hydrodynamic behavior in the kerf with a quasi-complete model of the laser cutting process

Journal of the Optical Society of America A, 2020

The fundamental physical phenomena occurring during the process of laser cutting are still only s... more The fundamental physical phenomena occurring during the process of laser cutting are still only slightly understood, and thus the need to develop mathematical and numerical models to optimize the process parameters has become unavoidable for obtaining products with superior quality and for better use. It is in this context that we propose a new approach by building a model to study the laser cutting process, by including several physical mechanisms which interact during the cutting process, such as the laser–metal interaction (wavelength effect, energy absorption, …), the phase change (solidification/fusion), the heat transfers, the fluid flows with influence of the free surface, the turbulent gas jets, and the kerf formation. In view of the complexity of the phenomena put into action, the fundamental mechanisms related to the cutting process are very difficult to understand and then to model. It is indeed necessary to take into account all of the aforementioned interactions, avoidi...

Research paper thumbnail of Fundamentals of Optical Instrumentation for Spectroscopic and Imaging Applications

WORLD SCIENTIFIC eBooks, Feb 1, 2023

Research paper thumbnail of Experimental investigations on fiber laser color marking of steels

Applied Surface Science, Oct 1, 2015

We develop an experimental approach with the aim to bring a contribution to the comprehension of ... more We develop an experimental approach with the aim to bring a contribution to the comprehension of the occurring phenomena during laser color marking of steels. A home-made marking device using a pulsed fiber laser has been used to treat steel samples under different laser beam operating parameters, for different compositions of the processed steel, and at normal atmospheric conditions. The treated samples were analyzed either by optical and scanning electronic microscopy, as well as by energy dispersion spectroscopy. The results show the influence of the operating parameters on the obtained colors.

Research paper thumbnail of Simulation of multiple injection flow in free stream of keyhole cavity during laser welding

XV International Symposium on Gas Flow, Chemical Lasers, and High-Power Lasers, Mar 23, 2005

In the present study, we develop a simple mathematical model of the vapour jets flow inside a cav... more In the present study, we develop a simple mathematical model of the vapour jets flow inside a cavity, in order to provide some understanding of the physics of the flow and to obtain qualitative data relative to the vapour flow properties. We consider a fluid as an ideal gas (air) at high pressure and temperature injected from orifices located perpendicularly

Research paper thumbnail of Laser Ablation: Effect on Ambient Pressure on Titanium Plume Expansion Dynamics

Bulletin of the American Physical Society, Oct 5, 2010

Research paper thumbnail of Numerical Simulation of Transient 3D Temperature and Kerf Formation in Laser Fusion Cutting

World Academy of Science, Engineering and Technology, International Journal of Materials and Metallurgical Engineering, Nov 28, 2014

Research paper thumbnail of Effect of the Convective Losses During Selective Laser Melting Process

Research paper thumbnail of Effects of the Velocity and the Nature of the Inert Gas onthe Stainless Steel Laser Cut Quality

The effects of inert assisting gas nature and velocity on laser cut qual- ity are investigated. A... more The effects of inert assisting gas nature and velocity on laser cut qual- ity are investigated. A pure fusion cutting process just above melting point is con- sidered, where the molten steel velocity is given as a function of the two acting forces represented by the pressure gradient and the frictional forces applied by the laminar gas flow. In the case of nitrogen assisting gas, the stainless steel melt film exhibits a visible separation point. The point where the melt flow is separated out from the solid wall depends strongly on the gas velocity. It is pushed down the cut surface when the gas velocity is increased. Furthermore, we have investgated the use of different inert gases (nitrogen, argon and helium) to blow the molten material out of the kerf, and it was noted that the argon and the nitrogen gases evacuate more easily the molten metallic film, compared to the helium gas from their cooling rates point of view. It is concluded that the two first gases are more efficient in ...

Research paper thumbnail of Evolution of the solidification isothermaccording to the geometry of the heat source during deep penetration laser welding

Research paper thumbnail of Ultrafast modification of copper properties under femtosecond laser excitation

Optica Advanced Photonics Congress 2022

Optical and thermal properties of copper films under femtosecond laser excitation has been dynami... more Optical and thermal properties of copper films under femtosecond laser excitation has been dynamically calculated as a function of time using a two-temperature model coupled with Drude model. Ultrafast changes have been observed when the material is still cold.

Research paper thumbnail of Wavelength effect on striation formation during metal laser cutting

We develop a study on laser cutting of metals withassist gas jet, the aim is to investigate the e... more We develop a study on laser cutting of metals withassist gas jet, the aim is to investigate the effect of the beam wavelength on striation formation. The finite volume method is used to discretize the differential governing conservation equations, which are numerically solved. The interfaces are tracked by implementation of the VOF method, whereas an enthalpic approach allows to take into account the melting and re-solidification phenomena. The results show that the used wavelength may play a role in striation formation.We develop a study on laser cutting of metals withassist gas jet, the aim is to investigate the effect of the beam wavelength on striation formation. The finite volume method is used to discretize the differential governing conservation equations, which are numerically solved. The interfaces are tracked by implementation of the VOF method, whereas an enthalpic approach allows to take into account the melting and re-solidification phenomena. The results show that the ...

Research paper thumbnail of On the Vortex Formation Effect During the Application of a Nitrogen-Gas Assisted Laser-Fusion Cutting Technique to Stainless Steel

This paper focuses on the vortex formation effect during the application of a laser-fusion cuttin... more This paper focuses on the vortex formation effect during the application of a laser-fusion cutting technique. This industrial technique is typically associated with the ejection of a film of molten stainless steel blown off by a subsonic laminar jet of nitrogen gas used to assist the process. Without taking into account the transverse movement of the workpiece, we consider a 4 mm thick stainless steel plate. The resulting molten metal flow is assumed to be laminar, steady, viscous and incompressible. The numerical results reveal vortex structures adjacent to the walls at the entrance of the kerf, and a pair of eddies outside the kerf. Remarkably, these vortex structures can produce a separation point in the molten film, and thereby they can affect the surface quality of the processed material. The problem is investigated in the framework of a numerical technique available in the Fluent software, based on a volume of fluid (VOF) surface-tracking strategy and the enthalpy method to ac...

Research paper thumbnail of Effect of Laser Cutting Parameters on the Heat Affected Zone and on the Boundary Layer in Steel Laser Processing

Defect and Diffusion Forum, 2020

This paper investigates the effect of the laser cutting parameters on the heat-affected zone, and... more This paper investigates the effect of the laser cutting parameters on the heat-affected zone, and on the boundary layer of stainless steel processing. A new analytical resolution based on the boundary layer theory is used to deduce the interaction effects of the cutting parameters on the above zones. The results revealed that, the laminar nitrogen assist gas has a negligible effect on the HAZ depth but it has a remarkable effect on the molten boundary layer. It is also noticed that the pressure gradient remains very small compared to the interface shearing and the conductive heat losses from the cutting zone towards the substrate is dominant compared to the convective heat losses towards the gas.

Research paper thumbnail of Simulation by temperature gradient adaption of wavelength effect in metal laser cutting

Journal of Laser Applications, 2017

Laser cutting of thick metal workpieces requires the use of low operating speeds which, however, ... more Laser cutting of thick metal workpieces requires the use of low operating speeds which, however, will have an influence on the cut quality following the used laser wavelength. In this study, we develop a model which takes into account the Fresnel coefficients in order to determine the local laser absorbed energy as a function of the beam incidence angle on the surface workpiece. The deposited laser energy occurs on the metal/air interface which evolution is tracked by the volume-of-fluid multiphase model. In the simulation, in order to find the difference between the patterns obtained on the kerf walls when different laser wavelengths are used, an important number of cells must be used at the regions of interest, which are characterized by high gradients, but a larger number of cells will have the consequence to complete the calculation with much less computer time consumption. Therefore, a gradient adaption method was implemented in order to control the number of cells, by multiply...

Research paper thumbnail of Characterization of Titanium Oxide Layers Formation Produced by Nanosecond Laser Coloration

Metallurgical and Materials Transactions B, 2017

Laser marking technique is used to produce colors on titanium while scanning a metallic sample un... more Laser marking technique is used to produce colors on titanium while scanning a metallic sample under normal atmospheric conditions. To proceed with different operating conditions related to the laser beam, the parameters of a Q-switched diode-pumped Nd:YAG (k = 532 nm) laser, with a pulse duration of s = 5 ns, are varied. The effect on the resulting mark quality is the aim of the present study which is developed to determine the influence of the operating parameters (i.e., pulse frequency, beam scanning speed, and pumping intensity) and furthermore their combination, such as the accumulated fluences and the overlapping rate of laser impacts. From the obtained experimental results, it is noted that the accumulated fluences and the scanning speed are the most influential operating parameters during laser marking, since they have a strong effect on the surface roughness and reflectance, and the occurrence of many oxide phases such as TiO, Ti 2 O 3 , TiO 2 (c-phase, anatase, and rutile).

Research paper thumbnail of Surface laser marking optimization using an experimental design approach

Research paper thumbnail of Two temperature approach to femtosecond laser oxidation of molybdenum and morphological study

Applied Surface Science, 2017

Highlights  Computation of the molybdenum lattice temperature.  Molybdenum oxide nanorods forme... more Highlights  Computation of the molybdenum lattice temperature.  Molybdenum oxide nanorods formed after laser treatment.  Strain in the molybdenum film due to laser treatment.  Cross section SEM showing layer different layers.

Research paper thumbnail of Dynamics of photo-ablated carbon plasma in an inert gas atmosphere

Laser and Particle Beams, 1998

Time and space-resolved emission spectroscopy measurements were performed to investigate plasma d... more Time and space-resolved emission spectroscopy measurements were performed to investigate plasma dynamics during laser evaporation of a graphite target in an ambient inert atmosphere. Intense molecular emission is found to occur behind a front separating the plasma from the foreign gas. Two stages of expansion are found and are well described, using a viscous drag force model for the first one and a delayed ideal blast wave model for the second. The vibrational temperature estimated using the Swan band in helium at different pressures is presented.

Research paper thumbnail of Effect of the radiative losses during selective laser melting process

Materials Today: Proceedings, 2021

Research paper thumbnail of The Marangoni Convection Effect on Melt Pool Formation during Selective Laser Melting Process

Defect and Diffusion Forum, 2021

In order to predict the effect of the Marangoni convection and the morphology of melted stainless... more In order to predict the effect of the Marangoni convection and the morphology of melted stainless steel powder, during the selective laser melting (SLM) process, a transient three-dimensional numerical model is developed at the mesoscale. The evolution of the temperature and velocity fields’ is then studied. The initial powder bed distribution is obtained by the discrete element method (DEM) calculation, and the temperature distribution and the molten pool shape deformation are calculated and analyzed by the Ansys-Fluent commercial code. The molten pool shape is obtained by considering the influence of Marangoni convection on the internal flow behavior. The recoil force was not considered in our calculation. As main results, a slight deviation between the position of the maximum temperature of the molten pool and the center of the laser spot is observed. The direction of the heat diffusion is more likely to be horizontal and the flow centrifugal, which causes the melt track to be wi...