Date of Award
2023-12-01
Degree Name
Master of Science
Department
Mechanical Engineering
Advisor(s)
Ryan B. Wicker
Abstract
Laser powder bed fusion (LPBF) is a form of metal additive manufacturing that enables the development of complex parts that cannot readily be made with traditional manufacturing methods. The process utilizes a tightly focused laser beam to selectively melt and fuse layers of powdered metal to create a 3-D part.LPBF is a promising technology, but there are barriers to its adoption in most industries. Mainly, it is difficult to qualify these parts for use, since they are prone to processing defects and part-to-part variation. One source of this is part position on the building plane, especially for multi-part builds where center-built part properties often differ from a part built at a non-centered location. To shed light on the issue, a two-part experiment was conducted to examine the effects of laser beam properties on melting quality at both the center and extents of the LPBF working envelope. This included detailed characterization of the beam profile at several positions across the build plate and a single line scan experiment at the same positions. An evaluation of several LPBF beam measurement tools revealed a common limitation-- they lack the ability to measure the beam at an incident angle. This restricts beam characterization to a single position, leaving the remaining LPBF working plane uncharacterized. This is a limitation in LPBF, as many standards require beam characterization across the full LPBF working envelope. In response, a novel beam measurement tool, the 3-D Beam Mapper, was developed. This tool enabled the creation of the first known beam profile map of an LPBF build plane. The novel beam map is the first known direct observation and measurement of an LPBF beam at multiple positions and provides insight into how power delivery varies across the build plane. The 3-D Beam Mapper was validated against beam measurements using other commercially-available beam characterization tools. A single line scan experiment consisted of lasing a series of vectors on Ti64 plates at the same locations at which the beam was measured. Two vector orientations relative to inert gas flow in the build chamber were examined: scans pointing to the flow (TO) and scans running transverse to the flow (TV). The variation in scan depth as a function of position was assessed for both scanning orientations, revealing a general decrease in depth with increasing distance from the center. However, two positions in the TO-flow direction exhibited an exception to this trend. The variation in depth between the center and extent positions was statistically significant. In all but one case, TO- and TV-flow depths were also statistically different at each position. It was found that the angle between scan vector to laser beam affects the melting quality. When the beam is leaning away from the scan direction, or trailing, it is prone to form the so-called humping defect, a result of melt pool instabilities that form a discontinuous and wavy track and can lead to part-level defects such as surface roughness or porosity. The beam map data and single scan parameters were related by examining melt pool geometries as a function of absorbed energy density, Î?H. Beam-normalized melt pool depths correlate extremely well with Î?H. Additionally, a dimensionless melt pool area, a*, was introduced and shown to improve correlation to Î?H. This demonstrates a simple relationship between melt pool geometry and elliptical beam profiles. The research presented in this thesis sheds light on the position-dependent variation of beam power delivery and its impact on melt pool formation and quality. These findings can potentially be leveraged to improve process consistency across the LPBF build plane to reduce part-to-part variation.
Language
en
Provenance
Recieved from ProQuest
Copyright Date
2023-12
File Size
176 p.
File Format
application/pdf
Rights Holder
Alexandra Hernandez
Recommended Citation
Hernandez, Alexandra, "Design and Implementation of Laser Beam Measurements at the Extents of the Build Platform: Impact of Beam Location on Melt Pool Geometry" (2023). Open Access Theses & Dissertations. 3981.
https://scholarworks.utep.edu/open_etd/3981