Density and shrinkage evaluation of AISI 316L parts printed via FDM process

Metal FDM process is a valid alternative to costly, energy consuming and less accessible metal Additive Manufacturing technologies. Metal parts were fabricated by means of a low-cost FDM machine with a filament composed of 316 L stainless steel particles and polymeric binder mixture, followed by debinding and sintering treatments. The objective of the study is to investigate the possible influence of some relevant FDM printing parameters on dimensional shrinkage and bulk density of the metal samples. The experimental analysis was conducted by means of a statistical method (ANOVA). Besides, a porosity evaluation was carried out to identify the real density values and the amount of opened and closed porosities of samples characterized with highest and lowest bulk density. Lines infill pattern, extrusion speed set to 20 mm/s and 0.1 mm as layer thickness was the combination of process parameters that ensured the highest nominal density (i.e. 95% of the monolithic 316 L nominal density). The statistical analysis did not show any effects due to the nozzle temperature on the bulk density. X and Y shrinkages settled around 16%, while shrinkages along Z-axis showed a greater variability. The samples with the worst bulk density showed a higher percentage of opened porosity, while the percentage of opened porosity for samples with the best combination of process parameters resulted less than 3%.