Energy Losses Estimation During Pulsed-Laser Seam Welding
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DUCTION
THE laser system efficiency given as a portion of its output and input power does not completely describe the welding process itself. This is a characteristic of the welding tool. When the total efficiency of individual laser welding process is being assessed, not only the laser system efficiency but also mainly the ability of material to absorb the incident beam power and material thermal characteristics must be considered. Although most contemporary research papers focus on the welding efficiency increase corresponding to the transition between conduction and deep penetration (keyhole) welding mode, only a few papers discussing the problems of welding efficiency numeration have been published.[1–4] The portion of laser power really absorbed by the material is estimated only roughly because welded components reflectivity is highly dependent on the actual surface condition, especially its roughness or possible contamination. The exact data are often unavailable. Therefore, energy losses cannot be sufficiently determined. Thermal welding simulations can provide us with needed information and help to evaluate the energy demands. Simulations of processes accompanying laser welding are common nowadays. Although most simulation software is developed for continuous heat input during the welding,[5–7] much fewer products have been introduced for pulsed welding simulations and only a few of them concern three-dimensional (3D) models.[8–10] We adapted the heat source of commercially available
HANA SEBESTOVA, Postdoc, Research Fellow, is with the Joint Laboratory of Optics of Palacky University and Institute of Physics of the Academy of Sciences of the Czech Republic, 17. listopadu 50a, 772 07 Olomouc, Czech Republic. Contact e-mail: [email protected] MARTINA HAVELKOVA and HANA CHMELICKOVA, Research and Development Specialists, are with the Joint Laboratory of Optics of Palacky University and Institute of Physics of the Academy of Sciences of the Czech Republic, Palacky University in Olomouc, Faculty of Science, RCPTM, 17. listopadu 12, 771 46 Olomouc, Czech Republic. Manuscript submitted October 14, 2013 METALLURGICAL AND MATERIALS TRANSACTIONS B
software to work as a pulsed system. Energy input was simulated so the weld dimensions and shape correspond to those prepared experimentally with known laser output power. The aim of these simulations was not to predict the weld dimensions but to calculate really absorbed energy to reach specific weld size. Finally, the welding process efficiencies were calculated combining experimental and simulated data.
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ENERGY LOSSES AND WELDING EFFICIENCY CALCULATION
The laser beam energy supplied to the material surface is always greater than the energy absorbed by the material because a substantial part of the incident beam reflects from the material surface.[11] Other energy losses are caused by heat conduction from the area attacked by the incident beam to the material volume, by heat emission to the surroundings, or by the heat flow inside the weld melting pool. However, reflection losse
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