Furthermore, to analyse the surface morphology and shape of the powder particles, techniques like computed tomography (CM) and Scanning Electron Microscopy (SEM) are used while particle size distribution is measured using the laser diffraction method (Slotwinski et al., 2014). Another important factor associated with the 3D printing powder is flowability and this is measured using the hall flow meter as mentioned by Slotwinski et al. Anderson et al. (1991) suggested that the manufacturing process is responsible for the inherent characteristics of the feedstock materials. As per Anderson et al., in Gas Atomization (GA) method, the atomisation of metallic alloy is achieved by a rapid flow of nitrogen and argon gas while Bourdeau (1983) claimed that in Rotary Atomisation (RA) method simply atomises metallic alloys by using a rotating disk mechanism which disintegrated the metallic
- 19 - alloy into its constituent atoms. The collection mechanism for RA comprises of Plasma Rotating Electrode Process (PREP) which collects the molten metal drops flung by the rotating disk as suggested by Champagne and Angers (1984); Ozols et al. (1999) and finally this method produces metal powder and the end of the collecting bar is melted using arc welding to collect the deposited powder particles. Another process of producing the metallic powder is Water Atomisation (WA) where the collection system consists of a high-pressure water jet which atomises the molten droplets coming out of the rotatory disk as proposed by Seki et al. (1990). The quality of the powder is important for an appropriate and uniform flow from the delivery mechanism to the area of interest, a fine and uniform quality powder ensures steady and continuous flow which eventually creates a uniform and smooth surface when a concentrated beam along with nozzle delivery mechanism is used (Tang et al., 2015). Thus, both processes of additive manufacturing, i.e. DED and PBF ideally require fine quality allow a powder with good size distribution and surface finish. The cost of manufacturing of this allow powder 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 the manufactured product should be considered before the selection of the powder for any AM process. Wire-fed AM processes are rather cheap as compared to the powder manufacturing as the wires of various alloys are manufactured by simple machining processes and very few chemical processes are required in their manufacturing. Stecker et al. (2006); Syed et al. (2006) suggested the use of wire-fed AM for filling large areas where fine details are less important because this method often results in higher deposition of material as compared to powder particle-based AM.
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- Fall '15
- Selective laser sintering, Particle size distribution, sintering, Additive manufacturing