Modelling of the capillarity effect for cylindrical shapes in Multi Jet Fusion technology

Multi Jet Fusion is one of the most productive additive manufacturing technologies available on the market. This important characteristic, together with the almost isotropic mechanical resistance of fabricated products, attracts the interest of users and industries. Despite those significant advantages, parts can present some specific defects. In particular, one of the most characteristic markers of the Multi Jet Fusion process is the capillarity effect that affects the top planar surfaces of parts. The present paper proposes an analytical model for the prediction of the capillarity effect in the case of curved edges. The model is based on the force equilibrium that is solved for circular cylindrical shapes and provides the equation of the capillary profile. An experimental activity is carried out to obtain useful data for model validation. For this purpose, a benchmark geometry is proposed that emphasises the mentioned phenomenon. Small circular cylinders are designed and then manufactured using an HP Multi Jet Fusion 4200. The parts obtained are digitalised by three-dimensional scanning. The scanned profiles of the top surfaces are analysed through statistical parameters. A preliminary result is that the capillarity effect on small circular cylindrical shapes can be considered axisymmetric. To validate the model, measured profiles of benchmark top surfaces are compared with the calculated ones. The results obtained show that the proposed equation can predict the measured data with errors in the range of one hundredth of a millimetre.