The Influence of Post-SLS-Build Annealing on Nylon 11 Material Properties

Functional energy storage and return prosthetic and orthotic devices have been manufactured out of Nylon 11 using selective laser sintering due to its high ductility and energy return properties. However, there is concern that material voids caused by incomplete sintering may compromise material properties and lead to premature fracture. Post-build annealing has the potential to eliminate voids caused by incomplete sintering and increase part ductility and strength. The purpose of this study was to post-build anneal Nylon 11 tensile specimens at 1) slightly below their melting temperature, 2) their recrystallization temperature, and 3) their glass transition temperature for two different time durations (12 and 24 hours) to assess the effectiveness of annealing in improving ductility and strength. Specimens annealed at their glass transition temperature had significantly greater percent elongations and lower Young’s moduli than specimens annealed close to their melting or recrystallization temperatures. At each temperature, specimens annealed for shorter durations demonstrated a greater increase in percent elongations and a greater decrease in Young’s moduli. Annealing at the glass transition temperature for 12 hours resulted in the highest percent elongation, although it was not significantly different from the control (unannealed) specimens. However, at these annealing conditions Young’s modulus significantly decreased from the control specimens. Across all annealing conditions, Young’s modulus and percent elongation were found to be negatively correlated. Future work should focus on annealing specimens for additional combinations of temperature and duration to further improve ductility while minimizing the negative effects on part strength.