The ASTM International Committee F42 on AM technologies defines AM as the “process of joining materials to make objects from three-dimensional (3D) model data, usually layer by layer, as opposed to subtractive manufacturing methodologies (ASTM F2792–10 Standard Terminology for Additive Manufacturing, 2009,). Generally, AM technologies involve the use of a computer, 3D modelling software (CAD), machine equipment and specific materials. Once a CAD model is produced, the model data, usually converted in stereolithography (STL) format, are first decomposed into a series of 2D, finitely thick cross sections, which are then fed into an AM machine that lays downs or adds successive layers of liquid, powder, sheet material or other, in a layer-upon-layer fashion to fabricate a 3D object metals, ceramics, polymers, composites, or biological materials.
