Abstract
Laser powder bed fusion (LPBF) typically relies on fine and spherically atomized powders, which are expensive to produce and available from a limited number of qualified vendors. To reduce cost and enable circular use of metal scrap, this thesis develops and demonstrates a complete scrap-to-LPBF process for aluminum 4047 derived from machining chips, under the constraints of no atomization and no sieving down to conventional LPBF particle sizes and shapes. Scrap aluminum was melted and cast to ingots, machined into chips, and mechanically ground to produce a coarse, bimodal powder lot (D10 ≈ 47 μm, D90 ≈ 445 μm) with an irregular, flake-like morphology and only fair flowability. The powder was characterized using laser diffraction particle size analysis, optical microscopy, Hall flow testing, and apparent/tap density measurements to describe recoating and melting behaviors. Two commercial LPBF architectures (EOS M100 and 3D Systems ProX DMP 320) were evaluated. The EOS M100’s hopper-fed dosing roller and 170 W laser proved incompatible with the coarse powder, while the ProX DMP 320, with dual feed beds and a 500 W laser, proved to be a viable platform. A generalized recoating calibration methodology was implemented by creating an enlarged ~1.1 mm recoater gap and designing a matrix of recoater speeds and feed amounts. Image-based coverage measurements and a regression interaction model showed feed amount as the dominant factor and identified operating windows achieving ≥95% area coverage while limiting powder usage. Laser processing parameters were then optimized through a sequence of single tracks, surface sheets, and cubes. Cubes built at 400 W/300 and 450 W/500 (120 μm layer thickness, 0.11 mm hatch distance) exhibited nearly pore-free microstructures, demonstrating that near-dense LPBF parts can be produced from non-atomized, coarse recycled Al4047 when recoating and energy input are explicitly tuned to the feedstock.