I. Introduction
Additive manufacturing (AM) or 3D printing directly fabricates physical products from a 3D CAD model by layered manufacturing processes. Since AM adds material layer by layer to construct products, this technique theoretically enables the direct printing of products with extremely complex geometry. Geometric complexity does not affect building efficiency, and no extra effort is necessary for molding construction or fixture tooling design, making 3D printing one of the most promising manufacturing techniques [1]–[4].