compounded by the process of precipitation. Particles that are normally acquired through cryogenic milling are inappropriate in most of the circumstances and normally fail for the processing of Selective Laser Sintering (Velu and Singamneni, 2014). Powders those are cryogenic milled end in fragile, less condensed parts of Selective Laser Sintering with poor properties and low density. For Selective Laser Sintering powders, a particular PSD (particle size distribution) is needed to be able processed on equipment of Selective Laser Sintering. The particle size distribution is generally measured by the systems of laser diffraction. Nevertheless, in fact, with such measurement the portion of trivial particles is abandoned on frequent basis. The increased cohesiveness between the particles decreases free flowing behavior of powder and prevents the processing of Selective Laser Sintering. As particularly the powder which is cryogenic milled often represents a high number of fine particles. 2.2.5 Experimental Procedure A sintered construction is developed by series of layers which are predefined. Such layers are fundamentally made up of sintered lines which are partially superimposed or flanked one on the other. Thermal models are introduced to provide an evaluation of cross-sectional profile of sintered line. Sintered width reflects the effect of laser radiation and restricts the series of disparity of scan spacing between the adjacent lines and then it is joined to scanning lines in order to construct a layer and thus to process the time. An experimental machine of Selective Laser Sintering is used to develop sintered
lines for changing levels of ED (Energy Density). Specific thermal and heat conductivity are derived with the help of experiments (Yadroitsev, Bertrand and Smurov, 2007). Nylon powder is normally chosen due to the thermal properties (diffusivity and thermal conductivity) which reflect the range of thermoplastics that are used for prototyping. Furthermore, average size distribution and spherical shape are uniform permitting the analysis of process of agglomeration. Nylon powder is placed in a container by a hopper that automatically gets charged which flattens the polymer bed and provides guarantee of flatness of surface. The temperature of bed was at 20°C i.e. room temperatu re (Song and Koeing, 1997). Sintered lines are stuck to supporting fragments of container with the help of acrylic resin. As the last step, non-sintered particles, which affect the process of measurement, are detached by putting the container on a device that vibrates. As a result, particles associated with the arrangement through hygrometric conditions or through friction can be eliminated upholding the reliability of structure. 2.2.6 Models for Sintering There are different methods for modelling the sintering, including numerical, analytical and empirical methods, which are considered on the previous studies. On this section, these models have been classified and introduced briefly.
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- Fall '19