400 W. 13th St., Rolla, MO 65409

Tunay Turk, a doctoral candidate in mechanical engineering, will defend their dissertation titled “Sensor Embedding and Thermal Monitoring Strategies for Laser-Foil-Printing Additive Manufacturing.” Their advisor, Dr. Ming Leu, is Curators Distinguished Professor of Mechanical Engineering. Their co-advisor, Dr. Jonghyun Park, is professor in the mechanical and aerospace engineering department. The dissertation abstract is provided below.

This dissertation investigates Laser Foil Printing (LFP), a novel metal additive manufacturing (AM) process that fabricates parts layer-by-layer using metal foils as feedstock. To enhance LFP productivity, four process steps were optimized: spot welding, pattern welding, contour cutting, and edge polishing. Through empirical optimization, a significant reduction in processing duration (88.1%) was achieved. A unique aspect of this study was the introduction of laser polishing as an edge polishing technique within the LFP process. This innovative approach, employing an overlapping spiral pattern, leverages selective laser remelting and erosion to effectively suppress elevated edges. To stabilize the molten melt pool and facilitate the secure embedding of sensors into LFP-fabricated metal parts, a discrete spot scanning strategy was implemented. This strategy ensured uniform cooling rates and consistent solidification. The fabricated parts were subjected to detailed analysis, including melt pool dimension evaluation using scanning electron microscopy (SEM) and residual stress assessment using X-ray diffraction (XRD). Compared to line-raster scanning, discrete spot scanning resulted in a 18.6% reduction in residual stresses. Grain size analysis, conducted using electron backscatter diffraction (EBSD), revealed a potential correlation with the observed reduction in residual stresses. Additionally, the successful embedding of temperature sensors within the parts using the discrete scanning strategy demonstrates its potential for in situ monitoring applications. To gain further insights into the melt pool dynamics and thermal behavior, numerical simulations and infrared (IR) thermography were conducted for both continuous line and discrete spot scanning strategies. The simulation model accurately predicted melt pool dimensions, achieving an accuracy range of 81.1% to 96.8%. IR measurements revealed that continuous line scanning produced larger melt pools with varying cooling rates along the path, while discrete spot scanning offered a more uniform surface thermal gradient and consistent cooling rates.

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