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Main Title: Can Potential Defects in LPBF Be Healed from the Laser Exposure of Subsequent Layers? A Quantitative Study
Author(s): Ulbricht, Alexander
Mohr, Gunther
Altenburg, Simon J.
Oster, Simon
Maierhofer, Christiane
Bruno, Giovanni
Type: Article
Abstract: Additive manufacturing (AM) of metals and in particular laser powder bed fusion (LPBF) enables a degree of freedom in design unparalleled by conventional subtractive methods. To ensure that the designed precision is matched by the produced LPBF parts, a full understanding of the interaction between the laser and the feedstock powder is needed. It has been shown that the laser also melts subjacent layers of material underneath. This effect plays a key role when designing small cavities or overhanging structures, because, in these cases, the material underneath is feed-stock powder. In this study, we quantify the extension of the melt pool during laser illumination of powder layers and the defect spatial distribution in a cylindrical specimen. During the LPBF process, several layers were intentionally not exposed to the laser beam at various locations, while the build process was monitored by thermography and optical tomography. The cylinder was finally scanned by X-ray computed tomography (XCT). To correlate the positions of the unmolten layers in the part, a staircase was manufactured around the cylinder for easier registration. The results show that healing among layers occurs if a scan strategy is applied, where the orientation of the hatches is changed for each subsequent layer. They also show that small pores and surface roughness of solidified material below a thick layer of unmolten material (>200 µm) serve as seeding points for larger voids. The orientation of the first two layers fully exposed after a thick layer of unmolten powder shapes the orientation of these voids, created by a lack of fusion.
Subject(s): selective laser melting
additive manufacturing
process monitoring
infrared thermography
optical tomography
X-ray computed tomography
in situ monitoring
Issue Date: 24-Jun-2021
Date Available: 26-Jul-2021
Language Code: en
DDC Class: 620 Ingenieurwissenschaften und zugeordnete Tätigkeiten
Journal Title: Metals
Publisher: MDPI
Volume: 11
Issue: 7
Article Number: 1012
Publisher DOI: 10.3390/met11071012
EISSN: 2075-4701
TU Affiliation(s): Fak. 5 Verkehrs- und Maschinensysteme » Inst. Werkzeugmaschinen und Fabrikbetrieb » FG Verfahren und Technologien für hochbeanspruchte Schweißverbindungen
Appears in Collections:Technische Universität Berlin » Publications

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