The Master Sinter Curve and Its Application to Binder Jetting Additive Manufacturing

Abstract

The master sinter curve (MSC) is an empirical model used to predict the density of a part after being sintered. The model is typically applied to components that undergo isotropic shrinkage. Parts manufactured using binder jetting additive manufacturing (BJAM) are known to have nonuniform powder systems and high levels of anisotropy. This work explores the application of the master sinter curve to components made by BJAM. Cylindrical samples were manufactured with the long axis parallel (vertical), perpendicular (horizontal), and 45 deg to the printing direction. A bimodal blend of titanium powder (0–45 µm and 106–150 µm) was used to make samples with consistent green densities (ranging from 47.2% to 52.3%) between the different orientations. Samples were then sintered at heating rates of 1, 3, and 5 °C/min to a maximum of 1400 °C. After sintering, the samples showed significant variation between the different orientations, with vertical samples on average 7.6 ± 2.98% and 4.7 ± 1.20% denser than the horizontal and the 45 deg samples, respectively. The calculated apparent activation energies for sintering were within the same range for all orientations, 200–260 kJ/mol for vertical and 45 deg, and 140–260 kJ/mol for horizontal samples. Validation sinter runs showed that the density prediction errors of the master sinter curves were between 0.9% and 4.3%. This work shows that the master sinter curve can be applied to predict the sintered density of components manufactured by binder jetting additive manufacturing.

Sintering anisotropy of binder jetted 316L stainless steel: part I – sintering anisotropy

“…This tendency will be analysed more in detail by using the anisotropic factors in the next section. Previous studies [5,10,11,19,20] have shown that BJ components usually present larger final shrinkages along the building direction. However, no evidence on how this anisotropy is developed during the sintering process was presented before.…”

Effects of process parameters, debinding and sintering on the microstructure of 316L stainless steel produced by binder jetting

“…The linear shrinkage values calculated in the three directions confirm that the powder packing in the 100LT samples is lower, thus the number of voids to be filled during the sintering treatment and the J o u r n a l P r e -p r o o f resulting shrinkage is larger. In addition, it can be noticed that the shrinkage along the building direction is higher because of improper powder packing between layers [27,48,72,73].…”

Densification behaviour of pure copper processed through cold pressing and binder jetting under different atmospheres

“…Once the heating steps were completed, the samples were cooled down to room temperature with a 10°C min −1 cooling rate. This fast cooling prevented any significant amount of sintering from occurring during the ramp-down phase, allowing the shrinkage measurements on cooling to be used for calculating the coefficient of thermal expansion (CTE) (Wheat et al , 2020). The CTE value is required to correct the dilatometry data to represent only shrinkage due to sintering, eliminating the contribution of the thermal expansion/shrinkage of the copper particles, which individually behave as a pore-free volume when they are subjected to a thermal cycle.…”