Abstract
This paper presents a comparison between simulation and experimental results of the melting process of metallic material by a pulsed laser source Nd–YAG. The simulations of temperature and velocity fields of melted material were done by solving the transient heat transfer and fluid-flow equations. Variations of the thermophysical properties were considered. Furthermore, the model included the effects of the surface-tension gradient on the fluid surface and the buoyancy force. The simulation was useful in improving our understanding of the phenomena occurring in the treated material. Using a laser triangulation sensor, an experimental study was also conducted on the surface profile of the melted zones to seek a relationship between the so-called keyhole effect and the laser triangulation measurements. The keyhole effect induced strong surface deformations and often formed cavities, which were undesirable in the surface treatment process. The laser power, energy density, and treatment duration could be optimized to prevent the keyhole effect. The predicted laser melted zone (LMZ) morphology was in good agreement with the corresponding experimental measurements for various irradiation conditions, as long as the keyhole effect did not occur.
Highlights
The role of heat-transfer phenomena in welding and surface treatment is crucial for obtaining high quality surfaces by eliminating defects, such as undercutting, non-uniform surface profile, and cavities, which are attributed to changes in fluid flow and heat transfer [1]
In an arc weld pool, flow driven by both surface tension and electromagnetic fields play an important role
At the melted bath surface, the surface tension variation with temperature must be balanced by the fluid shear stress since the surface must be continuous
Summary
The role of heat-transfer phenomena in welding and surface treatment is crucial for obtaining high quality surfaces by eliminating defects, such as undercutting, non-uniform surface profile, and cavities, which are attributed to changes in fluid flow and heat transfer [1]. Numerical and analytical models to simulate heat transfer and fluid flow during steady and transient fusion welding were developed during the last two decades. The understanding of the laser irradiation of materials involves numerous phenomena namely heat transfer, absorption, Marangoni convection, distortion, variation of the thermophysical properties, and phase transformation. Over the last two decades, several analytical [6,10] and numerical models [11] were developed to predict the temperature and velocity fields in the melting bath during laser treatments. A numerical model was developed to solve a transient heat transfer problem, for which variations of its thermophysical properties are well known This analysis improved our understanding of the effects of the irradiation conditions on the size of the melted zone during irradiation.
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