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Experimental Study and Simulation of Ultrasonic Vibration Effect on Powder Spreading in Selective Laser Sintering Process

Ghovvati, Sadegh | 2019

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 52010 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Movahhedi, Mohamadreza
  7. Abstract:
  8. Selective laser sintering is an additive manufacturing technique based on fusion of powder bed, wherein after spreading a powder layer, a focused laser beam directs onto selected points of powder bed to fuse powder particles together. This process is repeated layer by layer until the final part is created. Although utilization of blade as a conventional powder spreading (CPS) mechanism has a good compression ability, the fixed contact line between blade and powder bed surface results in improper powder flowability and increasing shear forces applied on underneath layer. In this study, in order to obtain the basis for conducting practical experiments, discrete element simulation of powder spreading process with blade performed while geometry and speed of blade were changed. The results of simulation indicate that increasing the blade speed leads to a decrease in flow of powder under blade and subsequently to increase porosity and surface roughness. For solving powder flowability problem, an ultrasonic assisted powder spreading (UAPS) mechanism which applying vibration to blade in the direction of its motion direction is designed and fabricated. Surface roughness and deposited powder mass are compared between UAPS and CPS processes at 3 blade speed and for 2 blade geometry (flat blade and blade with curvature). The results show that ultrasonic vibrations at a speed of 2.5 cm / s lead to an 84% increase in surface smoothness compared to CPS, but at higher speeds and for flat blade, this effect is diminished. The blade vibration at the ultrasonic frequency has caused, independent of the blade geometry, the amount of deposited powder increases and the excess powder transferred by the blade decreases; so that the percentage of deposited powder amount for the curved blade in UAPS has increased from 29.8% to 46% on average. Also, applying ultrasonic vibrations to flat blade has increased the percentage of the amount of deposited powder, on average, from 17.9% to 29%; but as the speed increased, the positive effect of ultrasonic vibrations has been reduced
  9. Keywords:
  10. Ultrasonic Spreading ; Additive Manufacturing ; Powder Flowability ; Selective Laser Sintering (SLS)Method ; Discrete Element Method

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