Binder-powder interactions in binder jetting: Binder drying, layer shifting, and inter-layer binding

Abstract

Binder jet additive manufacturing shows significant potential for cost-effective massive production of complex-shaped parts. However, defects like layer shifting degrade the part quality, hindering its widespread adoption. In this work, a resolved computational fluid dynamics and discrete element method coupling model is developed to investigate the detailed physics in the binder jetting process, including binder drying, layer shifting, and inter-layer binding. Non-uniform temperature distribution of the primitive is caused by the uneven powder layer thickness and inherent heating path from the top to the bottom. The primitive is displaced downwards and forwards under the action of normal and shear forces resulting from the motion of the roller and powder particles above it. Longer drying time enables the binder to be stiffer and further withstand shearing during the spreading of new powder layer. Inter-layer binding is reproduced by simulating two-layer binder jetting process, where the weak binding case shows disconnected binders. The simulation results align well with experimental observations and analytical predictions, accurately capturing powder spattering, liquid spreading behaviour, layer shifting, and droplet penetration dynamics. This study offers comprehensive insight into the fundamental mechanisms of the binding process, and provides guidance for defect mitigation to address current challenges in binder jetting technology.