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Modeling and Analysis of the Powder Deposition Mechanisms of Selective Laser Sintering Process

Shakiba, Abdorreza | 2018

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50757 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Movahedi, Mohamad Reza
  7. Abstract:
  8. Selective laser sintering is a technique which uses a laser as the power source to sintering some selected points at a bed of powder in order to create a solid structure. In this research the SLS mechanisms of powder deposition is simulated and surface smoothness and layer density created by each mechanism is computed. For this purpose roller, blade and hopper mechanisms are simulated. For this simulation, polyamide 12 (PA2200) which is a common material is used. In this simulation at first powder specifications are extracted according to the references and for particle shape instead of using the spherical particle shape we use a certain shape that is more close to reality which created by GID software. The geometry of the blade, roller, hopper and also the tank are modelled in PFC2D software. Simulation of the process is done by the same software. This software work according to the discrete element method. In order to Simulation conditions be close to each other, the produced powder by software is equal in different conditions and the powder diffusion mechanism changes in each examination. The test performed for the blade mechanism, performed for all conditions. But for roller mechanism tests are selected according to the Taguchi offer. Results show that in the edge of blade mechanism, the powder accumulates in the curvature of edge and in high speed (about 50 mm/sec) cannot provide required flow in layering and surface smoothness exceed 48 micron But in lower speed (about 10mm/sec) results of blade with curvature is a little better than blade without curvature and it is about 24 micron. In roller mechanism, increasing the linear velocity causes the horizontal displacement of the powders on previous layers and decrease the surface smoothness but increasing rotational speed reduces the weight of the blade front powder on the previous layers. Surface smoothness for the best roller mechanism condition calculated about 29 micron. The hopper mechanism is performed at five linear speed. In very low speeds pressure of the powders inside the tank on the previous layers increases and affects the quality of the previous layers. On the other hand increasing too much speed makes the powder inside the tank unable to provide the required flow of layering. For checking out the density of layers, Compression ratio of layers is calculated. Generally the density of the layers created by the roller mechanism is higher than other methods
  9. Keywords:
  10. Additive Manufacturing ; Selective Laser Sintering (SLS)Method ; Discrete Element Method ; Powder Mechanics ; Powder Deposition

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