Modelling of the multi-jet fusion capillarity effect on close facing edges


Purpose
The purpose of this paper is to develop a physical model able to predict the shape of the capillarity effect in multi-jet fusion when two facing edges mutually affect each other. The work also aims at testing the consistency of such a model with experimental observations.


Design/methodology/approach
An analytical model of the phenomenon is developed considering the surface tension of the polymer melt adhering to the unfused powder. The general equilibrium equations are solved by imposing the boundary conditions corresponding to the case of two close facing edges, in which the shapes of the menisci are mutually influenced. The analytical model is validated through an experimental activity. Specifically, a set of parallelepipeds with variable width was manufactured using an HP Multi Jet Fusion 4200. The morphologies of capillarities were captured via three-dimensional scanning and compared with those predicted by the model.


Findings
The results of this study demonstrate that the average error to the experimental capillarity profile is lower than that obtained by existing methods. Particularly, considerable improvements are achieved as far as the maximum capillarity height is concerned. The manufactured specimens exhibit a change in slope near the edges, which is arguably attributable to coating powder and other effects not included in the analytical model.


Originality/value
The model presented in this study differs in hypotheses from previous methods in literature by assuming a null derivative of the capillarity shape in the central point of the meniscus. This allows for a more accurate prediction of the defect morphology in the case of close facing edges.
