Mechanical Properties of Reused Nylon Feedstock for Powder-bed Additive Manufacturing in Orthopedics

Powder reuse can reduce the material costs associated with additive manufacturing (AM). Powder reuse is posited to have immediate cost savings, such as for the orthopedic industry. However, process deviation in the medical device industry requires that both material and part quality be quantitatively assessed with respect to reuse. The ultimate tensile strength (UTS) and elongation at break (EaB) were measured from selective laser sintered nylon specimens printed with recovered build chamber powder reused 1, 4 and 8 times. Using a design of experiment approach, build temperature, layer thickness, laser speed and laser power were confirmed to influence UTS. Statistical analysis revealed that location in the bed influences UTS, but not EaB. UTS decreased significantly between Reuse 1 and 4, but not between Reuse 4 and 8, whereas EaB (evaluated with the non-parametric Friedman's test) was unaffected for both pairwise comparisons (p>0.05). A 50-50 blend demonstrated a diminished effect on UTS and further suggests that the use of recycled powder in sintered nylon part are 'rescued' with the addition of the virgin material. (C) 2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the scientific committee of the 46th SME North American Manufacturing Research Conference.