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Title: In situ measurements of layer roughness during laser powder bed fusion additive manufacturing using low coherence scanning interferometry

Here, layer-to-layer height measurements of additively manufactured 316L stainless steel using high speed spectral-domain optical coherence tomography (SD-OCT) are presented. Layers are built up using an open architecture laser powder bed fusion machine while height measurements are made in-line along the process laser path following each layer print. Printed cubes, with and without an internal ‘overhang’ channel, were built to investigate the effect of scanning parameters on surface structure. Layer-to-layer scan rotation strategy significantly impacts surface roughness between layers which in turn can influence porosity. Spatter particles, which have been correlated with numerous defect modalities, generate high points in the powder bed and can persist on a melted surface for many layers. Laser power significantly affects overhang morphology, as measured by SD-OCT. Large dross occurs in the high energy density regime, while balling and a capillary-driven coalescence of unstable melt pools perpendicular to the scanning direction occurs in the low energy density regime. High fidelity powder-scale simulations of deep powder layers were used to further elucidate the underlying physics revealed by SD-OCT measurements and high speed imaging, yielding insight to defect formation mechanisms which can lead to improved process parameters.
Authors:
 [1] ;  [2] ;  [1] ;  [1] ;  [2] ;  [2] ; ORCiD logo [1]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Physical and Life Sciences Directorate
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Engineering Directorate
Publication Date:
Report Number(s):
LLNL-JRNL-747073
Journal ID: ISSN 0264-1275; 930945
Grant/Contract Number:
AC52-07NA27344; 15-ERD-037; 18-SI-003
Type:
Published Article
Journal Name:
Materials & Design
Additional Journal Information:
Journal Volume: 154; Journal Issue: C; Journal ID: ISSN 0264-1275
Publisher:
Elsevier
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA); USDOE Laboratory Directed Research and Development (LDRD) Program
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; 47 OTHER INSTRUMENTATION; Additive manufacturing; Laser powder bed fusion; Selective laser melting; In situ process monitoring; Optical coherence tomography; Interferometry
OSTI Identifier:
1438941
Alternate Identifier(s):
OSTI ID: 1459125

DePond, Philip J., Guss, Gabe, Ly, Sonny, Calta, Nicholas P., Deane, Dave, Khairallah, Saad, and Matthews, Manyalibo J.. In situ measurements of layer roughness during laser powder bed fusion additive manufacturing using low coherence scanning interferometry. United States: N. p., Web. doi:10.1016/j.matdes.2018.05.050.
DePond, Philip J., Guss, Gabe, Ly, Sonny, Calta, Nicholas P., Deane, Dave, Khairallah, Saad, & Matthews, Manyalibo J.. In situ measurements of layer roughness during laser powder bed fusion additive manufacturing using low coherence scanning interferometry. United States. doi:10.1016/j.matdes.2018.05.050.
DePond, Philip J., Guss, Gabe, Ly, Sonny, Calta, Nicholas P., Deane, Dave, Khairallah, Saad, and Matthews, Manyalibo J.. 2018. "In situ measurements of layer roughness during laser powder bed fusion additive manufacturing using low coherence scanning interferometry". United States. doi:10.1016/j.matdes.2018.05.050.
@article{osti_1438941,
title = {In situ measurements of layer roughness during laser powder bed fusion additive manufacturing using low coherence scanning interferometry},
author = {DePond, Philip J. and Guss, Gabe and Ly, Sonny and Calta, Nicholas P. and Deane, Dave and Khairallah, Saad and Matthews, Manyalibo J.},
abstractNote = {Here, layer-to-layer height measurements of additively manufactured 316L stainless steel using high speed spectral-domain optical coherence tomography (SD-OCT) are presented. Layers are built up using an open architecture laser powder bed fusion machine while height measurements are made in-line along the process laser path following each layer print. Printed cubes, with and without an internal ‘overhang’ channel, were built to investigate the effect of scanning parameters on surface structure. Layer-to-layer scan rotation strategy significantly impacts surface roughness between layers which in turn can influence porosity. Spatter particles, which have been correlated with numerous defect modalities, generate high points in the powder bed and can persist on a melted surface for many layers. Laser power significantly affects overhang morphology, as measured by SD-OCT. Large dross occurs in the high energy density regime, while balling and a capillary-driven coalescence of unstable melt pools perpendicular to the scanning direction occurs in the low energy density regime. High fidelity powder-scale simulations of deep powder layers were used to further elucidate the underlying physics revealed by SD-OCT measurements and high speed imaging, yielding insight to defect formation mechanisms which can lead to improved process parameters.},
doi = {10.1016/j.matdes.2018.05.050},
journal = {Materials & Design},
number = C,
volume = 154,
place = {United States},
year = {2018},
month = {5}
}