neobjavljeni prilog sa skupa
Price of material in selective laser sintering (SLS) of polymer products is not the most important factor, but it does play a significant role when analyzing overall i.e. the final price of the product and therefore recycling of material is becoming an increasingly important factor, as well as ratio of the shares in combining original and already used material.
Properties of the final product (roughness, dimensions, mechanical properties and water absorption) are also affected by the orientation in the working area of the machine. One of the most used materials in SLS is polyamide, which is known for being affected by conditioning. This is especially important when we want to apply a product made by selective laser sintering in conditions of high humidity or outdoor application when it is raining. All of this will be reflected in the change in mass and deformation. In the paper an analysis of the impact of three different types of product orientation in the machine working area and three different ratios of the used polyamide material (100% original, combined in 50:50 ratio of original and recycled and 100% recycled material after the third cycle of usage) on water absorption of the polyamide product made by selective laser sintering has been performed. Test specimens are made by SLS procedure with processing parameters: energy density 0.0564 J/mm2, power 21 W, laser speed 2500 mm/s, hatch distance 0.25 mm. As water absorption depends on the thickness of the test specimen, fluid in which it is placed and environment (e.g. temperature) in this experiment test specimens had thickness of 4 mm, and the testing was conducted at room temperature and in distilled water. Test specimens are used for the testing of flexural and tensile properties according to standard ISO 178 and ISO 527. After seven days test specimens in two orientations in xy axis (one lying down and one standing up) and of original and mixed material sank, i.e. their density after water absorption became higher than the density of water. Test specimens with orientation in the z axis sank after 21 days. Test specimens of recycled material with xy axis lying down orientation sank only after 14 days, whereas xy standing up orientation and z orientation remained floating even after 28
days of testing. With water absorption materials change their mass. In polyamide which is used in SLS procedure up to the fourth day the mass increases linearly, up to seventh day the maximum value is reached. Orientation xy axis lying down in original material has the highest mass after 28 days. Depending on the type of material the test specimens made of recycled material have the lowest mass during the entire absorption period, but they also absorb the highest amounts of water (original material have water absorption ≈ 1.28%, mixed material has water absorption ≈ 1.75% and recycled material have water absorption ≈ 1.93%). Also, most water is absorbed by z orientation (in recycled material water absorption is ≈ 2%).
additive manufacturing; orientation; polyamide PA 12; recycled material; selective laser sintering; water absorption
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