Design and manufacturing engineers are not fully aware of the different possibilities that PolyJet ä technology offers. The goal of this article is to provide the design and manufacturing engineers with greater knowledge about the final properties of parts printed with PolyJet rapid prototyping technology. This knowledge includes the effect of printing orientation and post-processing on the mechanical and surface properties of printed parts. Eighteen different samples considered all the possible printing orientations and the surface finishing treatments recommended by the manufacturer. These finishing properties include part printing using the matte/glossy option and removal of the support material using water pressure and/or a caustic soda bath. Tensile tests and surface roughness measurements were analysed for the printed samples using the statistical design of experiments in order to determinate the influence of the printing orientation and finishing properties on the results. These tests showed that the part orientation has a significant effect on elastic modulus and fracture stress while there is no statistical significance on ultimate tensile strength. With regard to the finish, none of the tensile test outputs showed significant differences. In terms of roughness, the analysis of variance indicated that position and finish presented statistically significant differences between the means of the three roughness directions. From all these experiences, it is possible to conclude that the glossy finish and the xy printing direction worked very well regarding roughness, whereas the critical load direction of the part should be placed along the x-axis when printing.

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SUMMARYTo perform the mechanical design of a machine through computer-aided techniques, at least three main di erent products should be used: a CAD software, to model the parts of the machine; a MBS program, to analyse the kinematics and dynamics of the whole system; and a FEA code, to determine the level of stress and strain su ered by each component. If it is true that CAD software is usually well connected with the two other tools, the same does not happen in what respects to FEA-MBS interfaces. Moreover, since both the large-amplitude motion and the elastic deformation are coupled, they cannot be solved separately, and the usual practice consisting of ÿrst analysing the machine motion assuming rigid bodies, and then calculating stresses under the loads previously generated, is just an approximation. In order to provide mechanical designers with a tool which makes easier and shorter the design-cycle, this paper presents a comparison between the two options that are currently available to address the mentioned problem: a dynamic MBS formulation which simultaneously solves motion and performs stress analysis by considering exible bodies; and a non-linear module of a FEA code, which takes into account large displacements and ÿnite rotations. The comparison is carried out in terms of accuracy and e ciency through four examples. The results lead to the conclusion that, for similar accuracy, the ÿrst method is largely more e cient. Therefore, the interest of developing MBS commercial codes which integrate motion calculation and stress analysis through the mentioned approach is envisioned, as long as they would provide faster solutions.

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