Browsing by Subject "thermal behavior"
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Item Forced Convection in a Polymeric Powders(1996) Norrell, Jeffery L.; Wood, Kristin L.; Crawford, Richard H.; Bergman, Theodore L.In a Selective Laser Sintering (SLS) powder bed, thermal transfer occurs through multiple modes. Forced convection through the powder, or downdraft, has recently been implemented in SLS machines in an effort to enhance thermal transfer within the powder bed. In this paper, forced convection is analytically shown to be a significant thermal transfer mode for low porosities, such as seen in SLS powder beds. A polymeric powder bed subjected to downdraft is investigated with the goal of quantitatively determining thermal behavior. A numerical model describing heat transfer within a powder is presented. The design and construction of an experimental apparatus to measure the temperature profiles within a powder subjected to forced convection is described. Using the information gained in these experiments, it may be possible to better control the thermal environment of SLS powder beds, reducing growth and internal stress build-up.Item Simulation of the Thermal Behavior and Analysis of Solidification Process During Selective Laser Melting of Alumina(University of Texas at Austin, 2018) Zhang, Kai; Liu, Tingting; Liao, Wenhe; Zhang, Changdong; Zheng, Yi; Shao, HuangSelective laser melting (SLM) has rapidly developed in the past decade. High precision-complex ceramics parts can be directly fabricated using this technology. To study the thermal behavior of molten pools in the selective laser melting of alumina (Al2O3), we established a three-dimensional model based on ANSYS. Then, combined with simulation results, the physical phenomena during the rapid solidification process were discussed. The simulation results showed that the laser power and scanning speed exerts a marked influence on the maximum temperature, liquid lifetime, dimensions, and temperature gradient of the molten pool. Owing to the different temperature gradients in the molten pool, the thermal capillary force on the free surface varies. As a result, a slight difference exists between the stripy solidification structures. Different orientations of columnar crystals can be obtained. The underlying mechanism controls the direction of the temperature gradient with suitable processing routes, such as decreasing the scanning speed.