Transient Model for Keyhole During Laser Welding

A novel approach to simulating the dominant dynamic processes present during concentrated energy beam welding of metals is presented. A model for transient behavior of the front keyhole wall is developed. It is assumed that keyhole propagation is dominated by evaporation recoil-driven melt expulsion from the beam interaction zone. Results from the model show keyhole instabilities consistent with experimental observations of metal welding, metal cutting and ice welding

Measurement and calculation of recoil pressure produced during CO{sub 2} laser interaction with ice

Evaporation is a classical physics problem which, because of its significant importance for many engineering applications, has drawn considerable attention by previous researchers. Classical theoretical models [Ta. I. Frenkel, Kinetic Theory of Liquids, Clarendon Press, Oxford, 1946] represent evaporation in a simplistic way as the escape of atoms with highest velocities from a potential well with the depth determined by the atomic binding energy. The processes taking place in the gas phase above the rapidly evaporating surface have also been studied in great detail [S.I.Anisimov and V. A. Khokhlov, Instabilities in Lasser-Matter Interaction, CRC Press, Boca Raton, 1995]. The description of evaporation utilizing these models is known to adequately characterize drilling with high beam intensity, e.g., >10{sup 7} W/cm{sup 2}. However, the interaction regimes when beam intensity is relatively low, such as during welding or cutting, lack both theoretical and experimental consideration of the evaporation. It was shown recently that if the evaporation is treated in accordance with Anisimov et.al.'s approach, then predicted evaporation recoil should be a substantial factor influencing melt flow and related heat transfer during laser beam welding and cutting. To verify the applicability of this model for low beam intensity interaction, the authors compared the results of measurements and calculations of recoil pressure generated during laser beam irradiation of a target. The target material used was water ice at {minus}10 C. The displacement of a target supported in a nearly frictionless air bearing under irradiation by a defocused laser beam from a 14 kW CO{sub 2} laser was recorded and Newton's laws of motion used to derive the recoil pressure

Photo-thermoinduced changes of transmission spectra of As₄₀-xSbxS₆₀ amorphous layers

The results of investigation of the As₄₀-xSbxS₆₀ (x = 0-10) thin films transmission spectra depending on exposure and heat treatment conditions are given. It was established that illumination and annealing of films leads to the absorption edge shift into the longwave spectral region. The values of pseudogap width Eg are determined. Optical characteristic changes of films are caused by photo-thermostructural transformations taking place in them under irradiation and annealing

Modeling of laser keyhole welding: Part I. Mathematical modeling, numerical methodology, role of recoil pressure, multiple reflections, and free surface evolution

A three-dimensional laser-keyhole welding model is developed, featuring the self-consistent evolution of the liquid/vapor (L/V) interface together with full simulation of fluid flow and heat transfer. Important interfacial phenomena, such as free surface evolution, evaporation, kinetic Knudsen layer, homogeneous boiling, and multiple reflections, are considered and applied to the model. The level set approach is adopted to incorporate the L/V interface boundary conditions in the Navier-Stokes equation and energy equation. Both thermocapillary force and recoil pressure, which are the major driving forces for the melt flow, are incorporated in the formulation. For melting and solidification processes at the solid/liquid (S/L) interface, the mixture continuum model has been employed. The article consists of two parts. This article (Part I) presents the model formulation and discusses the effects of evaporation, free surface evolution, and multiple reflections on a steady molten pool to demonstrate the relevance of these interfacial phenomena. The results of the full keyhole simulation and the experimental verification will be provided in the companion article (Part II).close698