**1. 3D CAD slicing**

AM requires an input computer-aided design (CAD) model of the part which may be de‐ signed in a CAD system, or obtained from reverse engineering such as 3D scanners. Once the CAD model is completed, it is converted to the standard STL format, which is most common‐ ly used to represent 3D CAD models in additive manufacturing. A section of an STL file and its 3D model are shown in **Figure 1**. In an ASCII STL file, the CAD model is represented using

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triangular facets, which is described by the x-, y-, and z-coordinates of the three vertices and a unit vector to indicate the normal direction that point outside of the facet [1]. Redundant informationforindicatingmodelname,facetnormal,andvertexisalsoincluded.Inthefollowing sections, unidirection slicing and multidirection slicing of STL models are described.


**Figure 1.** Example of an STL file format and its model.
