Doctoral Dissertations

Keywords and Phrases

Discrete Element Method; Flowability; Powder Characterization; Powder Recycling; Selective Laser Melting

Abstract

"Powder-bed fusion refers to a subset of additive manufacturing (AM) methods which successively melts and solidifies selected regions within a powder bed on a layer-by-layer basis to construct components directly from computer-aided design files. Laser Powder-Bed Fusion (L-PBF) is a process among the powder-bed fusion techniques that utilizes a laser to consolidate particles into a material with little porosity. During the L-PBF process, the large energy input from the laser causes the production of ejecta in the form of laser spatter and condensate, both of which have the potential to settle in the surrounding powder bed compromising its reusability. In order to better understand the impact of ejecta on powder recyclability, samples of 304L laser spatter and condensate were characterized in terms of morphology, chemistry, and microstructure. Differences between ejecta and virgin powder were used as a basis for understanding the evolution in 304L powder properties with reuse in the L-PBF process over the course of 7 iterations, which revealed an improvement in flowability with recycling. The effects of evolving powder properties on the tensile and impact toughness properties were also assessed for capturing possible deterioration in mechanical performance. Due to the improvement in powder flowability during recycling, the effects of alterations in the particle size were further investigated using the Discrete Element Method (DEM). Through development of a mathematical definition of spreadability, differences in the particle size distribution as well as recoating velocity and layer thickness revealed changes in the powder-bed quality providing crucial knowledge of the mechanisms behind the powder spreading process"--Abstract, page iv.

Advisor(s)

Leu, M. C. (Ming-Chuan)

Committee Member(s)

Newkirk, Joseph William
Liou, Frank W.
Bristow, Douglas A.
Chen, Lianyi

Department(s)

Mechanical and Aerospace Engineering

Degree Name

Ph. D. in Mechanical Engineering

Sponsor(s)

Honeywell Federal Manufacturing and Techologies, LLC

Comments

This work has been funded by Honeywell Federal Manufacturing & Technologies under Contract No. DE-NA0002839 with the U.S. Department of Energy.

Publisher

Missouri University of Science and Technology

Publication Date

Spring 2020

Journal article titles appearing in thesis/dissertation

  • Powder characterisation techniques and effects of powder characteristics on part properties in powder-bed fusion processes
  • Characterization of laser spatter and condensate generated during the selective laser melting of 304L stainless steel powder
  • Characterization of AISI 304L stainless steel powder recycled in laser powder-bed fusion
  • Evolution of AISI 304L stainless steel part properties due to powder recycling in laser powder-bed fusion
  • Modeling powder spreadability in laser-powder-bed fusion using the discrete element method

Pagination

xxiii, pages

Note about bibliography

Includes bibliographic references.

Rights

© 2020 Austin Taylor Sutton, All rights reserved.

Document Type

Dissertation - Open Access

File Type

text

Language

English

Thesis Number

T 11693

Electronic OCLC #

1164778108

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