Date of Award
2025-08-01
Degree Name
Doctor of Philosophy
Department
Mechanical Engineering
Advisor(s)
Yirong Lin
Abstract
The adoption of Laser Powder Bed Fusion (LPBF) for aerospace hardware requires qualification strategies that ensure repeatable, reliable, and certifiable performance. This dissertation focuses on a qualification effort for an aerospace titanium bracket to be used for a serial production aircraft, following a fixed-process, sample-centric methodology. The work was performed following industry expectations for mechanical performance, dimensional tolerance, and process control, and culminated in the successful qualification of the bracket for flight hardware installation.
The qualification effort was divided into four primary objectives. Machine and parameter qualification was first to establish a baseline LPBF process on an SLM 280 HL system using Ti-6Al-4V powder feedstock. Results across repeated builds revealed spatial variations in mechanical performance, particularly in areas with insufficient gas flow. These findings led to a redesign of the gas flow system in collaboration with the OEM, which significantly improved build uniformity. Second, material, process, and supplier qualification were conducted using an extensive test matrix, which included tensile, shear, fatigue, fracture toughness, metallography, and chemistry assessments, all done at NADCAP-certified laboratories. All results met or exceeded aerospace OEM requirements, and the process was frozen for production use.
Third, part qualification confirmed that the LPBF bracket satisfied all functional, dimensional, and material criteria. The first article underwent CMM-based dimensional inspection, tensile testing, and X-ray computed tomography, all of which passed the necessary quality metrics. Additional blue-light scanning during development revealed as-built distortion, informing optimization of build orientation and support strategy. Lessons learned included the impact of hot isostatic pressing on final geometry and the need to lock orientation early to avoid requalification. Fourth, recurring production testing monitored quality over time. Statistical process control tools (Cp, Cpk, Pp, Ppk) revealed that oxygen contamination (due to inconsistent purge practices) led to chemistry drift and degradation in ductility. A change was implemented to ensure purging reached a verified oxygen threshold before each build. Additionally, a comparative fatigue study demonstrated the feasibility of ultrasonic fatigue testing as a rapid, cost-effective screening tool. Equivalent results were achieved between traditional uniaxial fatigue (20 Hz) and ultrasonic testing (20 kHz), with a reduction in test time from almost six days to under ten minutes for 10 million cycles. This finding supports the integration of high-throughput fatigue methods into future qualification protocols. The dissertation concludes with a forward-looking proposal to evolve from a sample-centric to a subsystem-centric qualification model. Rather than relying solely on sample testing, this approach emphasizes the performance of core machine subsystems (mainly gas flow and atmosphere control). Additional recommendations include subsystem benchmarking, beam profiling, powder reuse management, and advanced fatigue characterization.
In summary, this work not only qualifies a functional aerospace component but also contributes a robust case study in the maturation of LPBF process control and lays the groundwork for scalable, repeatable qualification methodologies that will support the broader industrialization of metal AM in aerospace.
Language
en
Provenance
Received from ProQuest
Copyright Date
2025-08
File Size
133 p.
File Format
application/pdf
Rights Holder
Jorge Mireles
Recommended Citation
Mireles, Jorge, "Establishing And Advancing Qualification Strategies For Aerospace Components Produced Using LPBF" (2025). Open Access Theses & Dissertations. 4414.
https://scholarworks.utep.edu/open_etd/4414