We report on an experimental investigation of the incubation effect during irradiation stainless steel with bursts ultrashort laser pulses.A series birefringent crystals was used to split pristine 650-fs pulses into up 32 sub-pulses time separations 1.5 ps and 3 ps, respectively.The number selected varied between 50 1600.The threshold fluence measured in case Burst Mode (BM) processing depending burst features, i.e. their separation time, bursts.We found as many values combinations...

In this study, laser metal fusion with feedstock wire is addressed. We investigated how various process parameters affect the fraction of beam energy that absorbed by and workpiece transfer from to melt pool. To perform research, a thermo-fluid dynamic model tracking free surface deformation was developed include feeding solid predict its melting. The modeled as function local curvature temperature, accounting for multiple Fresnel reflections absorptions. applied Titanium alloy (Ti-6Al-4V)...

A computational fluid dynamics approach is used to analyse the influence of beam shaping in fusion welding on melt thermal flow. Three shapes are studied at several travel speeds: a reference Gaussian profile and its elliptic elongations along transverse direction. It found that these change not only intensity direction thermocapillary flow but also pattern. For instance, contrary other profiles, shape elongated generates front vortices assist metal pre-heating. can result deeper...

This study explores the possibility of tailoring fusion zone in conduction mode laser welding using a deformable mirror for beam shaping multi-kilowatt continuous wave sources. Three power density distributions were shaped and used bead on plate Ti64 plates at three travel speeds. The effect melt pool free surface geometry, cross section, microstructure hardness profiles was measured studied. It is shown that geometry can be modified mirror. A narrower longer or wider, shorter shallower one...

A recent review pointed out that the existing models for gas tungsten arc coupling electrode (a cathode) and plasma are not yet complete enough. Their strength is to predict with good accuracy either electric potential or temperature field in region delimited by workpiece. weakness their poor ability these two fields at once. However, both of important since they govern heat flux workpiece through current density gradient. New developments have been made then. They mainly concern approaches...

Abstract We have considered four different approaches for modelling the electromagnetic fields of high-intensity electric arcs: (i) three-dimensional, (ii) two-dimensional axi-symmetric, (iii) potential formulation and (iv) magnetic field formulation. The underlying assumptions differences between these models are described in detail. Models to reduce same limit an axi-symmetric configuration with negligible radial current density, contrary model (iv). were retained implemented open source...

Various models coupling the refractory cathode, cathode sheath and arc at atmospheric pressure exist. They assume a homogeneous with uniform physical state, differ by layer plasma model. However even most advanced of these still fail in predicting extent attachment when applied to short high-intensity arcs such as gas tungsten arcs. Cathodes operating conditions present non-uniform state. A model taking into account first level this non-homogeneity is proposed based on criteria. Calculations...

Comprehensive models of heat transfer require specification the total amount received by workpiece. The objective this work was to critically examine use a water-cooled stationary anode calorimeter obtain both arc efficiency and input into For simplicity clarity, last quantity is called gross input. effects current, material type water flow rate on performance were determined experimentally. Some measures for reducing errors in calorimetry evaluated. Improvements made reduce losses from top...

The present work concerns the electromagnetic force models in computational fluid dynamics simulations of melt pools produced with electric arcs. These are commonly applied to gas metal arcs transfer, welding and additive manufacturing. Metal drop impact on pool is thus included this study. literature use either numerical solutions Poisson equations or one two analytical developed by Kou Sun, Tsao Wu. rely assumptions for which effect predictions remains be understood. thoroughly...

Partially ionized plasmas corresponding to different ionization degrees are derived and connected one with each other by the diffusion approximation methodology. These following electrical discharges: a thermal arc discharge, glow discharges in local thermodynamic equilibrium -LTE- non-LTE, non-LTE discharge interacting an electron beam (or flow).

A new approach is proposed to model and simulate numerically surface chemistry within the frame of rarefied gas flows. It developed satisfy all together following points: (i) describe phase at microscopic scale, as required in flows, (ii) wall macroscopic avoid prohibitive computational costs not only consider crystalline but also amorphous surfaces, (iii) reproduce on average laws correlated with experimental results, (iv) derive analytic models a systematic exact way. The problem stated...

A thermal plasma is studied accounting for both impact ionization, and an electromagnetic field. This problem modeled based on a system of Boltzmann type transport equations. Electron-neutral collisions are assumed to be much more frequently elastic than inelastic, complete previous investigations [4]-[6]. viscous hydrodynamic/diffusion limit derived in two stages doing Hilbert expansion using the Chapman-Enskog method. The resultant fluid model characterized by temperatures, non equilibrium...

Abstract Fluid dynamics models for laser material processing with metal fusion in conduction mode generally assume a constant absorptivity. This parameter is known to govern the process. However, it used be pre-set by extrapolating absorptance measurements made at different conditions or adjusted reproduce experimental bead shapes. In this study new approach developed. It consists predicting as function of local surface conditions, including temperature. The proposed model applied alloy...

Abstract Energy-transport models taking into account impact ionization are derived from a kinetic framework by formal asymptotic methods. The derivation is based on system of Boltzmann transport equations governing the distribution functions conduction electrons and holes in semiconductor. charge carriers assumed to obey degenerate gas statistics. energy exchanged during collisions between carrier phonon supposed be weak. Ionization elastic retained at leading order carry out rigorous...