Denis Carron

2D longitudinal modeling of heat transfer and fluid flow during multilayered direct laser metal deposition process

Derived from laser cladding, the direct laser metal deposition (DLMD) process is based upon a laser beam–powder–melt pool interaction and enables the manufacturing of complex 3D shapes much faster than conventional processes. However, the surface finish remains critical, and DLMD parts usually necessitate postmachining steps. Within this context, the focus of our work is to improve the understanding of the phenomena responsible for deleterious surface finish by using numerical simulation. Mass, momentum, and energy conservation equations are solved using comsol multiphysics® in a 2D transient model including filler material with surface tension and thermocapillary effects at the free surface. The dynamic shape of the molten zone is explicitly described by a moving mesh based on an arbitrary Lagrangian–Eulerian method (ALE). This model is used to analyze the influence of the process parameters, such as laser power, scanning speed, and powder feed rate on the melt pool behavior. The simulations of a single layer and multilayer claddings are presented. The numerical results are compared with experimental data, in terms of layer height, melt pool length, and depth of penetration, obtained from high speed camera. The experiments are carried out on a widely used aeronautical alloy (Ti–6Al–4u2009V) using a Nd:YAG laser. The results show that the dilution ratio increases with increasing the laser power and the scanning velocity or with decreasing the powder feed rate. The final surface finish is then improved.

Residual Stress Analysis in AA7449 As-Quenched Thick Plates Using Neutrons and Fe Modelling

In the current trend toward thicker aluminium plates, a major concern is the generation of high internal stresses during quenching, which can cause distortions during machining and pose serious safety concerns. Although the material is stretched after quench, substantially reducing residual stresses, they are not fully suppressed. In addition, the cooling rate is not large enough at the core of such thick plates to prevent any precipitation. This has a great impact on the efficiency of ageing. In this work, residual stress distributions in a heat-treatable aluminium alloy AA7449 thick plate in the as-quenched state measured by neutron diffraction are presented. A comparison between single (311) diffraction peak and multiple peaks analysis using Pawley algorithm is shown. The variation of the stress free reference value through the plate thickness is discussed and measured stresses are compared with residual stresses predicted by a thermomechanical finite element model of quenching.

Surface Finish Issues after Direct Metal Deposition

Derived from laser cladding, the Direct Metal Deposition (DMD) laser process, is based upon a laser beam – projected powder interaction, and allows manufacturing complex 3D shapes much faster than conventional processes. However, the surface finish remains critical, and DMD parts usually necessitate post-machining steps. In this context, the focus of our work was: (1) to understand the physical mechanisms responsible for deleterious surface finishes, (2) to propose different experimental solutions for improving surface finish. Our experimental approach is based upon: (1) adequate modifications of the DMD conditions (gas shielding, laser conditions, coaxial or off-axis nozzles), (2) a characterization of laser-powder-melt-pool interactions using fast camera analysis, (3) a precise check of surface aspects using 3D profilometry, SEM, (4) preliminary thermo-convective simulations to understand melt-pool hydrodynamics. Most of the experimental tests were carried out on a Ti6Al4V titanium alloy, widely investigated already. Results confirm that surface degradation depends on two aspects: the sticking of non-melted or partially melted particles on the free surfaces, and the formation of menisci with more or less pronounced curvature radii. Among other aspects, a reduction of layer thickness and an increase of melt-pool volumes to favor re-melting processes are shown to have a beneficial effect on roughness parameters.

Measurements and Modeling of Stress in Precipitation-Hardened Aluminum Alloy AA2618 during Gleeble Interrupted Quenching and Constrained Cooling

Solutionizing and quenching are the key steps in the fabrication of heat-treatable aluminum parts such as AA2618 compressor impellers for turbochargers as they highly impact the mechanical characteristics of the product. In particular, quenching induces residual stresses that can cause unacceptable distortions during machining and unfavorable stresses in service. Predicting and controlling stress generation during quenching of large AA2618 forgings are therefore of particular interest. Since possible precipitation during quenching may affect the local yield strength of the material and thus impact the level of macroscale residual stresses, consideration of this phenomenon is required. A material model accounting for precipitation in a simple but realistic way is presented. Instead of modeling precipitation that occurs during quenching, the model parameters are identified using a limited number of tensile tests achieved after representative interrupted cooling paths in a Gleeble machine. This material model is presented, calibrated, and validated against constrained coolings in a Gleeble blocked-jaws configuration. Applications of this model are FE computations of stress generation during quenching of large AA2618 forgings for compressor impellers.

Monitoring precipitation kinetics in heat treatable aluminium alloys using in-situ resistivity in Gleeble thermomechanical simulator

A conventional way to determine precipitation kinetics in heat treatable aluminium alloys is to monitor the associated solute loss by in-situ resistivity. A Gleeble machine is used to perform so called isothermal quenching (IQ) resistivity measurements. IQ consists in quenching the alloy down to a given temperature and holding it at this temperature. The results are validated against measurements performed with a classical four-points method using continuous current on the same alloy.

Numerical Simulation of Electron Beam Welding and Instrumental Technique

In the present work, thermal cycles measured with thermocouples embedded in specimens are employed to validate a numerical thermometallurgical model of an Electron Beam welding process. The implemented instrumentation techniques aim at reducing the perturbations induced by the sensors in place. The numerical model is based on the definition of a heat source term linked to the keyhole geometry predicted by a model of pressure balance using the FEMLAB code. The heat source term is used by the thermometallurigal simulation carried out with the finite element code SYSWELD. Kinetics parameters are extracted from dilatometric experiments achieved in welding austenitization conditions at constant cooling rates.

2D finite element modeling of heat transfer and fluid flow during multilayered DMD laser process

Derived from laser cladding, the Direct Metal Deposition (DMD) laser process is based upon a laser beam – powder – melt pool interaction, and enables the manufacturing of complex 3D shapes much faster than conventional processes. However, the surface finish remains critical, and DMD parts usually necessitate post-machining steps. Within this context, the focus of our work is to improve the understanding of the phenomenon responsible for deleterious surface finish by using numerical simulation. Mass, momentum, and energy conservation equations are solved using COMSOL Multiphysics® in a 2D transient model including filler material with surface tension and thermocapillary effects at the free surface. The dynamic shape of the molten zone is explicitly described by a moving mesh based on an Arbitrary Lagrangian Eulerian method (ALE). This model is used to analyze the influence of the process parameters, such as laser power, scanning speed, and powder feed rate, on the melt pool behavior. The simulations of a single layer and multilayer claddings are presented. The numerical results are compared with experimental data, in terms of layer height, melt pool length, and depth of penetration, obtained from high speed camera. The experiments are carried out on a widely-used aeronautical alloy (Ti-6Al-4V) using a Nd:YAG laser.Derived from laser cladding, the Direct Metal Deposition (DMD) laser process is based upon a laser beam – powder – melt pool interaction, and enables the manufacturing of complex 3D shapes much faster than conventional processes. However, the surface finish remains critical, and DMD parts usually necessitate post-machining steps. Within this context, the focus of our work is to improve the understanding of the phenomenon responsible for deleterious surface finish by using numerical simulation. Mass, momentum, and energy conservation equations are solved using COMSOL Multiphysics® in a 2D transient model including filler material with surface tension and thermocapillary effects at the free surface. The dynamic shape of the molten zone is explicitly described by a moving mesh based on an Arbitrary Lagrangian Eulerian method (ALE). This model is used to analyze the influence of the process parameters, such as laser power, scanning speed, and powder feed rate, on the melt pool behavior. The simulations of a s...