اندازه گيري تجربي خواص ترموفيزيكي پودر و شبيه سازي دوفازي در فرايند ذوب انتخابي پودر به كمك ليزر

چكيده انگليسي :

Experimental Measurement of Thermo Physical Properties of Powder and Two Phase Simulation of Selective Laser Melting Process Reza Shalilian r shalilian@me iut ac ir Date of Submission 2014 01 20 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiSupervisors Dr Abbas Ghaei Ghaei@cc iut ac ir Dr Mohsen Badrossamay mohsen badrossamay@cc iut ac irAbstract To reduce the amount of time required in the development of new products manufacturing industry hasadopted a group of technologies collectively known as solid freeform fabrication SFF systems One suchSFF process is known as Selective Laser Sintering SLS SLS takes powdered material as its input Before processing the powder is spread flat to form a thin layer A scanning laser beam selectively heatsand bonds the powder particles in a layer to form solid sections of a specified shape More powder isspread on top of the processed layer more laser scanning and bonding takes place Adjacent layers bondto each other through the laser s heating effect building up to form a solid part The main purpose of thisresearch was to study the thermal properties of powders in selective laser melting process Therefore threedifferent types of powders i e 314S HC stainless steels M2 Gas atomized and M2 water atomized werefirst subjected to a low power carbon dioxide laser and the temperature were experimentally measured at aspecific location using a K type thermocouple The measurements were then used to calculate the thermalconductivity and the laser energy absorptance of the powders at room temperature assuming that the totalvolume of powders was a continuum Knowing those properties is required for the simulation as well asanalytical study of the process In order to evaluate the accuracy of the calculated parameters thecalculated thermal conductivities and laser energy absorptance were used to predict the temperaturedistribution using ABAQUS commercial finite element package DFLUX user subroutine was developedusing FORTRAN programming language to model the moving laser heat source in the finite elementsimulations The finite element predictions during heating as well as cooling were then compared with theexperimentally measured temperature versus time A relatively good correlation were observed betweenthe experiment and simulation suggesting that the calculated parameters presented a reasonable estimationof the powders thermal properties In practice the phase change of powder particles from solid state to the molten state results in a dramaticchange in porosity of the material This in turn leads to a sudden change in both thermal conductivity andabsorptance So those models that do not take the phase change into account such as the one used in thefirst part of this study are not expected to accurately describe the thermal properties of powders inselective laser melting process It should emphasized that both the laser power and pulse on time waschosen to be very small to make sure that the powder did not melt In an attempt to take the meltingphenomenon into account and study its influence on the thermal properties of powders FLUENTcommercial package was used So the powder particles were individually modeled and the air betweenthem were also considered using the patch capability in FLUENT software A heat flux large enough tomelt the powder particles were imposed as the boundary condition The melt pool size was compared withthe previously published predicted and experimental data The comparison showed that the melt pool sizeprediction significantly improved when the phase change was considered in the simulation Finally theeffect of process parameters e g the laser power and scan velocity were also studied using the FLUENTmodel Keywords Powder Selective Laser Melting Thermal Properties Phase Change 1

شليليان، رضا

اندازه گيري تجربي خواص ترموفيزيكي پودر و شبيه سازي دوفازي در فرايند ذوب انتخابي پودر به كمك ليزر

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