Browsing by Subject "particle size distribution"
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Item Characterization of Feedstock in the Powder Bed Fusion Process: Sources of Variation in Particle Size Distribution and the Factors that Influence Them(University of Texas at Austin, 2016) Whiting, J.; Fox, J.Substantial efforts have been placed on characterizing and modeling additive manufacturing processes. The wide scope of work already done has focused on the effects of process parameters such as laser power, hatch spacing, scan speed and strategy, and layer thickness on the final part’s properties. However, the characteristics of the actual powder should also be considered. The particles’ size, morphology, roughness, and chemical composition will affect the final part properties including surface texture, density, tensile strength, and hardness. This paper will share some of the measurement methods used at the National Institute of Standards and Technology (NIST) to better understand metal powder for additive manufacturing. These include the striation/separation in transportation and handling, sampling procedures, and the actual spreading of powder in the laser powder bed fusion process. Results are presented that illustrate variations in the particle size distribution as a function of location on the build platform, substrate/part surface condition, and vertical position.Item Effects of Particle Size Distribution on Surface Finish of Selective Laser Melting Parts(University of Texas at Austin, 2019) Lim, J.H.; Khan, N.A.Metal parts produced by Selective Laser Melting (SLM) usually exhibit poor surface finish compared to conventional manufacturing processes. There is a growing need for parts to have good surface quality in the as-built condition to minimise post-processing costs and reduce lead time. There are many studies done on the effects of processing parameters on surface finish but very little on the influence of powder characteristics. This study aims to investigate the effects of Particle Size Distribution (PSD) on surface finish of AM parts by printing coupons with Inconel 625 powders of varying PSD. It was found that roughness of internal surfaces was mainly caused by the presence of partially sintered particles. Whilst a smaller particle mean size and wider particle size range are preferred for better surface finish, a powder that is too fine may result in poor flowability affecting its processability in terms of layering and powder bed quality.Item Effects of Powder Reuse and Spatial Location Dependency on the Powder Characteristics and Defect Structure of Additively Manufactured Ti-6Al-4V Parts(University of Texas at Austin, 2021) Soltani-Tehrani, Arash; Yasin, Mohammad Salman; Shao, Shuai; Shamsasei, NimaIn laser powder bed fusion additive manufacturing (L-PBF AM), different powder characteristics including particle size and morphology may yield different packing states and thus different defect content in the resulting parts. As the powder is spread by the recoater, the packing state may not be uniform on the powder bed, giving rise to location-dependent part performance. In addition, as the powder is reused (a common practice in AM industry), its characteristics continuously evolve, causing the defect content to change from build to build. This study aims to investigate the effects of powder reuse and part location on powder characteristics as well as the defect structure of the parts. Results indicate powder reuse in an L-PBF system may reduce the number of defects in the as-fabricated parts due to the superior packing state of reused powder. Part density was also found to be location-dependent, with more defects near the gas outlet.Item Influence of Powder Particle Size Distribution on the Printability of Pure Copper for Selective Laser Melting(University of Texas at Austin, 2019) Sinico, M.; Cogo, G.; Benettoni, M.; Calliari, I.; Pepato, A.This work investigates the use of fine Cu powder, with ~ 20 vol% smaller than 15 μm size, for the selective laser melting process. Cubes reaching > 98 % density are produced at relative low laser output (175 W) and characterized. After the selection of a proper combination of laser scan parameters, the properties of fabricated parts are briefly studied through profilometry and tensile tests. Finally, a voluminous demo component for high-energy physics is manufactured to stress-test the employed SLM machine. Even though unmolten particles and lack of fusion defects are still present in the produced specimens, the investigated approach confirms that powder selection can have a huge influence on the processability of materials with high reflectivity towards near-infrared irradiation.Item Investigation the Effect of Particle Size Distribution on Processing Parameters Optimisation in Selective Laser Melting Process(University of Texas at Austin, 2011) Liu, Bochuan; Wildman, Ricky; Tuck, Christopher; Ashcroft, Ian; Hague, RichardSelective Laser Melting is an efficient process for producing metal parts with minimal subtractive post-processing required. Analysis of the parameters controlling the part quality has been performed focusing on the energy intensity during processing and the effect of the particle size distribution on factors such as ultimate tensile strength and surface finish. It is shown that the controlling the energy intensity is key to quality and can be affected by varying, for example, laser beam diameter or the scanning rate.Item Mesoscopic Simulation of Heat Transfer and Fluid Flow in Laser Powder Bed Additive Manufacturing(University of Texas at Austin, 2015) Lee, Y.S.; Zhang, W.Laser-powder bed fusion (L-PBF) additive manufacturing involves complex physics such as heat transfer and molten metal flow, which have a significant influence on the final build quality. In this study, transport phenomena based modeling is used to provide a quantitative understanding of complex molten pool transients. In particular, a three dimensional (3D), transient numerical model is developed for L-PBF additive manufacturing by solving the governing partial differential equations of mass, momentum and energy conservation. The individual powder particles are resolved using the volume of fluid method (VOF) method with a fine mesh size of 3 μm (thus at meso-scale). The powder particle arrangement including particle size distribution and packing density are taken into account in placement of individual particles calculated using discrete element method. Moreover, the model considers Marangoni shear stress, an important driving force for molten metal flow. The numerical model is used to quantitatively study the effect of laser power, scanning speed, and powder size distribution on the bead geometry and formation of balling defect.