Design Rules for Additive Manufacturing of Titanium Cellular Structures by Electron Beam Melting

International audienceAdditive Manufacturing (or Rapid Prototyping) underwent an increase of interest these past decades for the fabrication of plastic prototypes. More recently, the possibility of creating metallic parts from 3D models made possible the manufacturing of new designed metallic parts1. The Electron Beam Melting (EBM) technology can produce metallic parts by selectively melting a powder's bed layer by layer with an electron beam. Manufacturing cellular materials, which is strongly difficult by conventional methods2, become elementary by additive manufacturing. The EBM technology is indeed theoretically able to produce freeform metallic foams3. Due to the process, differences in struts sizes could be observed between CAD model and the manufactured part which leads to a lower mechanical resistance. This study is focused on the determination and improvement of parameters which tailor the geometry and surface quality of titanium foams made by EBM. Different size, shape and orientations of struts (from 50µm to 3mm of diameter, circle section or squared section and horizontally or vertically-produced) have been studied by high resolution X-Ray tomography and image analysis to access to their inner properties. Their geometry, surface roughness and pore content are analysed. The area of the real cross-section (represented as an inscribed ellipse) is compared to the desired one for the prediction of the mechanical resistance and the minimum strut size allowing the desired mechanical strength. The compressive tests on foams gives a comparison with tomography results for the adaptation of Gibson and Ashby's laws4 for the mechanical resistance prediction of cellular solids made by EBM. Due to the process, it is no more possible to link directly the young's modulus with the density, so that a correction factor is created to take into account the difference between outer size and real inner cross-section