Mass transfer and flow in additive manufacturing of a spherical component

This paper proposes a novel and coherent analysis of mass transfer and thermal stress flow (direction) in solidification of spherical components such as acetabular shells in selective laser melting of Ti-6Al-4 V. A detailed description of different phenomena such as solidification behaviour at the solid/liquid interface, behaviour of moving interface, thermal gradient, Gibbs free energy, interfacial energy and equilibrium temperature were utilised to characterise mass and thermal stress flow. Experimental results showed that thermal stress and mass flow on outer surfaces are higher than those found on inner surfaces which are related to the geometry and shape of the printed structures. Due to the mass transfer and thermal stress flow, built-up lines including a dent in the outer surfaces and grooves in the inner surfaces were observed with heights on the order of 200 mu m. Post-processing is needed to remove the built-up lines which results in increasing dimensional deviations.