Masters Theses

Keywords and Phrases

Additive manufacturing; Laser powder bed fusion (LPBF); Selective laser melting (SLM); Solidification; Undercooling; X-ray imaging

Abstract

"Fusion-based metal additive manufacturing (AM) has garnered much interest in recent decades. Despite the popularity of fusion-based AM technologies such as selective laser melting (SLM), there are still fundamental questions and uncertainties that need to be addressed. In this work, we focus on the understanding of the undercooling in the SLM process and the uncertainties induced by the laser beam size, power, and scan speed. First, we report the estimation of undercooling in the SLM process from the solidification rate measured by in-situ high-speed synchrotron x-ray imaging, based on the dendrite growth velocity model. The undercooling changes as a function of location and time as the solidification front proceeds to the surface of the melt pool. A general increasing trend is observed for AlSi10Mg, while a general decreasing trend is observed for Ti6Al4V. The opposite overall evolution trend of the undercooling for the two AM materials is attributed to the ratio of the latent heat to heat capacity and the thermal diffusivity. The temporal and spatial variation of the undercooling and the dependence of undercooling evolution trend on material properties revealed here are important for understanding microstructure evolution in fusion-based metal AM. Second, the uncertainties in the SLM process due to variations of laser beam size, power, and scan speed from the optimized values are identified by in-situ x-ray imaging and the leading cause of uncertainty is revealed. A small ( < 5%) variation in the laser beam size, power, and scan speed results in linear variations in the depression zone, melt pool, and spatter behavior. The variation in the SLM dynamics identified in this work is important for understanding the sensitivity of the SLM process to the laser processing parameters"--Abstract, page iv.

Advisor(s)

Chen, Lianyi

Committee Member(s)

Gu, Yijia
Liou, Frank W.

Department(s)

Mechanical and Aerospace Engineering

Degree Name

M.S. in Manufacturing Engineering

Sponsor(s)

National Science Foundation (U.S.)
Boeing Company
Missouri University of Science and Technology. Center for Aerospace Manufacturing Technologies (CAMT)

Comments

This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. This work is funded by the National Science Foundation. This work also received funding from the Boeing Company through the Center for Aerospace Manufacturing Technology (CAMT) at Missouri University of Science and Technology.

Publisher

Missouri University of Science and Technology

Publication Date

Spring 2020

Journal article titles appearing in thesis/dissertation

  • Undercooling in laser powder bed fusion metal additive manufacturing
  • Sources of uncertainty induced by laser processing parameters in selective laser melting of Ti6Al4V

Pagination

xi, 73 pages

Note about bibliography

Includes bibliographic references.

Rights

© 2020 Meelap Michael Coday, All rights reserved.

Document Type

Thesis - Open Access

File Type

text

Language

English

Thesis Number

T 11670

Electronic OCLC #

1164095591

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