Date of Award
Master of Science in Aeronautical Engineering
Department of Aeronautics and Astronautics
Ryan O'Hara, PhD
The manufacture of components in Additive Manufacturing processes is limited by the range of materials available. Qualification of materials for Additive Manufacturing is time intensive, and is often specific to a single type of machine. In this study, an approach to selecting power, speed, and hatch spacing values for a newly powderized material, AF9628 weapons steel, is described that results in highly dense (>99.9%) parts on an MLab 200R Cusing. Initial power and speed values used in a weld track study were selected based on a survey of parameters used on similar materials, with a focus on the energy density value known as laser fluence. Shape and penetration depth of the weld tracks were used to select the most promising parameters for generation of solid parts. Solid cylinders were printed with hatch spacing values of 90%, 80%, and 70% of the weld track widths and evaluated for porosity using sectioning and microscopy and CT scanning. Several parameter combinations resulted in parts with >99.9% density, with these parts occurring at a fluence value of between 200 and 300 J/mm3, and a volumetric energy density (EV ) value of between 80 and 90 J/mm3. Initial material characterization of the as-built material was conducted, with strength and hardness values that met or exceeded values taken from the original material patent. Weld track studies at various laser focal diameters were then conducted on the larger, more powerful M2 Cusing by sweeping along a 250 J/mm3 line of fluence, and solid parts were successfully generated using hatch spacing values based on 80% of the weld track width. Additionally, the gas atomized AF9628 powder morphology and chemistry were evaluated in both the virgin and used-sieved conditions, with no change in print quality directly attributed to powder recycling.
DTIC Accession Number
Hager, Erin M., "Process Parameter Development of Additively Manufactured AF9628 Weapons Steel" (2019). Theses and Dissertations. 2220.