r is higher due to the cost of the fabrication process and a low yield of the

R is higher due to the cost of the fabrication

This preview shows page 19 - 22 out of 167 pages.

r is higher due to the cost of the fabrication process and a low yield of the atomisation process, to solve this issue as suggested by Tang et al., PBF processes often reuse solidified powder at the cost of shape irregularities and poor surface finish in the manufactured product. These are the reasons the 3D printing powder selection is critical, and cost and quality requirements of t he manufactured product should be considered before the selection of the powder for any AM
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process. Wire-fed AM processes are rather cheap as compared to the powder manufacturing a s the wires of various alloys are manufactured by simple machining processes and very few c hemical processes are required in their manufacturing. Stecker et al. (2006); Syed et al. (200 6) suggested the use of wire-fed AM for filling large areas where fine details are less importa nt because this method often results in higher deposition of material as compared to powder p article-based AM. To measure the size distribution for determining the quality of alloy powder, various t echniques, including image analysis, dry sieving and laser diffraction are used (Pieri et al., 20 06). The selection of method is associated with the shape of the powder particles while most of the techniques assume that the particles are somewhat spherical and the particle size distrib ution is graphically represented by showing particle diameter on x-axis while frequency or pe rcentage occurrence is shown on y-axis the greater the opening of this curve, the more distrib uted the particle sizes are within the powder (Ganiga and Cyriac, 2016). Ideally, all the particl es should have a similar diameter which will ensure uniform flow and surface finish in the ma nufactured product. As per Chen et al. (2006), powders with the difference in size distribution behave diff erently in manufacturing processes and packing structure within the manufactured part is dire ctly affected. A wide size distribution of the particles may create a good quality product as sm all particles have the tendency to fit the inter-particle gaps of the large particles thus ensuring good surface finish and a high density of packing, although, high density will also result in a high surface contact area which results in higher friction (Chen et al., 2006). Furthermore, bro ad size distribution powder also requires a low beam intensity laser during the manufacturing process. Narrow particle distribution powder offers higher flowability which accelerates the p rocess of manufacturing. To measure the particle size distribution, various researchers includi ng Ouchiyama and Tanaka (1989); Yu and Standish (1991) used numerical computational met
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hods to predict the diameters of the granular mixture of particles containing a mixture of diffe rent spherical shaped particles. Kim et al. (2001) further improved the model proposed by Ou chiyama and Tanaka to measure the impact of PSD on the top layer density of manufactured parts during the AM process.
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  • Fall '15
  • Selective laser sintering, Particle size distribution, Additive manufacturing

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