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Title: Reducing residual stress by selective large-area diode surface heating during laser powder bed fusion additive manufacturing

Abstract

High residual stresses are typical in additively manufactured metals and can reach levels as high as the yield strength, leading to distortions and even cracks. Here, an in situ method for controlling residual stress during laser powder bed fusion additive manufacturing was demonstrated. By illuminating the surface of a build with homogeneously intense, shaped light from a set of laser diodes, the thermal history was controlled thereby reducing the residual stress in as-built parts. 316L stainless steel bridge-shaped parts were built to characterize the effect of in situ annealing on the residual stress. A reduction in the overall residual stress value of up to 90% was realized without altering the as-built grain structure (no grain growth). Some annealing effects on the cellular-dendritic solidification structure (patterns of higher solute content) occurred in areas that experienced prolonged exposure to elevated temperature. A comparison of the in situ process to conventional post-build annealing demonstrated equivalent stress reduction compared to rule-of-thumb thermal treatments. Use of this method could reduce or remove the need for post processing to remove residual stresses.

Authors:
 [1];  [2];  [1];  [1];  [3];  [1];  [4];  [1]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Materials Science Division
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Materials Engineering Division
  3. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Laser Systems Engineering Operations
  4. Univ. of California, Davis, CA (United States). Mechanical Engineering Dept.
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE; LLNL Laboratory Directed Research and Development (LDRD) Program
OSTI Identifier:
1524749
Report Number(s):
LLNL-JRNL-766658
Journal ID: ISSN 2214-8604; 956145
Grant/Contract Number:  
AC52-07NA27344
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Additive Manufacturing
Additional Journal Information:
Journal Volume: 28; Journal ID: ISSN 2214-8604
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 42 ENGINEERING; residual stress; microstructure; annealing; in situ

Citation Formats

Roehling, John D., Smith, William L., Roehling, Tien T., Vrancken, Bey, Guss, Gabriel M., McKeown, Joseph T., Hill, Michael R., and Matthews, Manyalibo J. Reducing residual stress by selective large-area diode surface heating during laser powder bed fusion additive manufacturing. United States: N. p., 2019. Web. doi:10.1016/j.addma.2019.05.009.
Roehling, John D., Smith, William L., Roehling, Tien T., Vrancken, Bey, Guss, Gabriel M., McKeown, Joseph T., Hill, Michael R., & Matthews, Manyalibo J. Reducing residual stress by selective large-area diode surface heating during laser powder bed fusion additive manufacturing. United States. doi:10.1016/j.addma.2019.05.009.
Roehling, John D., Smith, William L., Roehling, Tien T., Vrancken, Bey, Guss, Gabriel M., McKeown, Joseph T., Hill, Michael R., and Matthews, Manyalibo J. Mon . "Reducing residual stress by selective large-area diode surface heating during laser powder bed fusion additive manufacturing". United States. doi:10.1016/j.addma.2019.05.009. https://www.osti.gov/servlets/purl/1524749.
@article{osti_1524749,
title = {Reducing residual stress by selective large-area diode surface heating during laser powder bed fusion additive manufacturing},
author = {Roehling, John D. and Smith, William L. and Roehling, Tien T. and Vrancken, Bey and Guss, Gabriel M. and McKeown, Joseph T. and Hill, Michael R. and Matthews, Manyalibo J.},
abstractNote = {High residual stresses are typical in additively manufactured metals and can reach levels as high as the yield strength, leading to distortions and even cracks. Here, an in situ method for controlling residual stress during laser powder bed fusion additive manufacturing was demonstrated. By illuminating the surface of a build with homogeneously intense, shaped light from a set of laser diodes, the thermal history was controlled thereby reducing the residual stress in as-built parts. 316L stainless steel bridge-shaped parts were built to characterize the effect of in situ annealing on the residual stress. A reduction in the overall residual stress value of up to 90% was realized without altering the as-built grain structure (no grain growth). Some annealing effects on the cellular-dendritic solidification structure (patterns of higher solute content) occurred in areas that experienced prolonged exposure to elevated temperature. A comparison of the in situ process to conventional post-build annealing demonstrated equivalent stress reduction compared to rule-of-thumb thermal treatments. Use of this method could reduce or remove the need for post processing to remove residual stresses.},
doi = {10.1016/j.addma.2019.05.009},
journal = {Additive Manufacturing},
issn = {2214-8604},
number = ,
volume = 28,
place = {United States},
year = {2019},
month = {5}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record

Figures / Tables:

Figure 1 Figure 1: a) Schematic of the diode annealing system. b) Detailed line drawing of the dotted line in a), showing the laser scanner and dichroic mirror in proximity to the build plate. c) Image of the bridges attached to 1 inch build plates that were built for the study, superimposedmore » with the two mask shapes that were used. d) Diagram showing the diode-annealing process in time and the ramp down of diode power.« less

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Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.