Abstract

In Selective Laser Sintering (SLS), one of several powder-based Rapid Prototyping (RP) methods, thermal transfer plays an important role in machine design. Thermal control of the processing area or “space” is crucial for accurate, repeatable part formation. In a typical SLS powder bed, significant thermal transfer occurs through mixed convection and conduction. In this paper, a polymeric powder bed subjected to in-bed convection is investigated with the goal of quantitatively determining transient thermal behavior. A numerical model describing heat transfer within a powder is presented. Convection and conduction are both numerically shown to play important roles in steady state temperature profiles. The design and construction of an experimental apparatus to measure the temperature profiles within a powder subjected to forced convection are also described. Full factorial experiments are used to calibrate and validate the numerical model, as well as to examine transient behavior. Using information gained from numerical and experimental work, suggestions are made for machine design to better control part precision and reproducibility. For example, it is shown that actively controlling the temperature of air convected through the powder bed gives fine, rapid control over the feed side cylinder thermal state.

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