CAGLAR, Halil Emre ORCID: https://orcid.org/0009-0001-4800-0064 (2024) HYBRID MULTI-LASER POWDER BED FUSION. PhD thesis, University of Sheffield.
Abstract
In Laser Powder Bed Fusion (LPBF) systems, both single fibre systems and multi-laser systems are currently at the forefront of industry and academic research. Among the multi-laser approaches, Diode Area Melting (DAM) stands out as a novel alternative to conventional single-fibre LPBF systems. DAM offers the advantage of processing metal powder feedstock with a low cooling rate, courtesy of its short-wavelength, low-power diode lasers. However, the system is challenged by its lack of precision processing capabilities. In contrast, single fibre LPBF is renowned for its ability to process metals with high precision, owing to its high-power laser and high velocity scanning capabilities. Yet, these systems suffer from a deficiency in high cooling rates and microstructure control. This thesis introduces a groundbreaking Hybrid Laser Powder Bed Fusion (HLPBF) system, which combines two distinct laser processing methods to explore their effects on microstructure control. Firstly, a HLPBF system was developed, comprising a traversing DAM laser head equipped with an array of nine 450 nm (4W each) diode lasers alongside a conventional 200W single fibre LPBF and galvo-scanning head operating at a wavelength of 1064 nm. Subsequently, single fibre LPBF and DAM systems were individually tested to establish a literature background for hybrid processing, including parameter maps (based on normalised energy density), side and top surface roughness, heat-affected zones, cross-sectional densities, and microstructure investigations. During the investigations with the 450 nm DAM, a new phenomenon termed the 'crescent effect' was identified and added to the literature. This effect explains the wide, slow-moving melt pool's impact on the solidified sample. The hybrid processing phase commenced with the processing of Ti6Al4V feedstock utilizing both laser types within a single sample for the first time. A specific scanning strategy delineated separate laser processing regions within the same sample, including an overlap where both lasers interacted to fuse the feedstock and bridge the two regions. The regions melted by the fibre laser experienced significantly higher cooling rates (~107 ℃/s) compared to DAM regions (~600 ℃/s), resulting in finer microstructures characterized by acicular α´/α phases. In contrast, DAM regions exhibited larger α+β grains with parent β grain sizes approximately 13 times larger than those in the fibre laser-melted zone. In addition to its microstructural spatial tailoring capabilities, this investigation of the hybrid laser system also illuminates variations in the laser-induced heat-affected zone, surface roughness, and mechanical properties across DAM, single fibre LPBF, and overlap regions within fabricated Ti6Al4V samples.
Metadata
Supervisors: | Mumtaz, Kamran |
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Keywords: | LPBF; Diode Area Melting; Multi-laser PBF; Ti6Al4V; Additive Manufacturing |
Awarding institution: | University of Sheffield |
Academic Units: | The University of Sheffield > Faculty of Engineering (Sheffield) > Mechanical Engineering (Sheffield) |
Depositing User: | Dr Halil Emre CAGLAR |
Date Deposited: | 21 Jun 2024 15:03 |
Last Modified: | 21 Jun 2024 15:03 |
Open Archives Initiative ID (OAI ID): | oai:etheses.whiterose.ac.uk:35092 |
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Description: PhD Thesis
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