Pénétration de liant dans un lit de poudre en impression 3D par jets de liant

Binder jet printing is a versatile, efficient, and scalable method of additive manufacturing, particularly for metals and ceramics. A significant challenge in the development of binder jetting systems is the formulation of binder fluids. The interaction between a binder and a powder system is complex, and while models do exist to predict the general dynamics of printing, they have not been widely tested in binder jetting. If printing behaviour can be predicted, the development of binders can be accelerated, thus improving yields, mechanical properties, and speed of binder jetting. In this study, existing capillary models of binder jetting will be reviewed, with emphasis on their applications in binder jetting processes. An experimental validation, using a design of experiments approach, of these models with respect to the printing of polymeric binders is presented. The effect of key properties, such as viscosity, surface tension, and contact angle, is tested, along with polymer-specific properties such as molecular weight, chemistry, and entanglement state (onset of chain entanglement in solution between individual polymer molecules). An additional study on the effect of temperature is presented, given the importance of heating the powder bed in production processes. The results show that binder absorption times generally follow the predictions of capillary models. However, highly concentrated solutions deviate significantly from the expected trends. The role of entanglement, heating, and evaporation of solvent is considered to explain these deviations. It is demonstrated that concentrated solutions close to the onset of entanglement will absorb much more slowly than predicted. Additional data is provided to show limitations of a common model, the effect of printing properties on final part quality, and the relationship between mechanical properties of green bodies and the properties of binders. It is concluded that future models of binder jet printing must account for the changing properties of the binder due to evaporation throughout the absorption process, with additional considerations for entanglement in polymer systems. Improved models will provide a more accurate understanding of the flow and solidification of binder in the powder, allowing faster development of new binders for improved performance in printing, enabling improved efficiency and new applications.