# Towards an Automated Design Evaluation Method for Wire Arc Additive Manufacturing
## 2 State of the Art
### Current Methods for Manufacturability Evaluation
#### 2.1.2 Evaluation Methods for Additive Manufacturing  
In the realm of manufacturability analysis for additive manufacturing, several methods are proposed in the literature. First of all, the 3D-MAT as described before can be applied to analyze the geometry in a broader view not related to a specific manufacturing method [18; 26]. [PERSON] et al. propose an algorithm for computing the local thickness and the related medial surface representation [26]. To ensure accurate thickness estimation, a heuristic for surface sampling is provided: the element size \(s\) should be chosen to be smaller than the radius of 90% of the surface elements. [PERSON] et al. extend this approach by adding angle measurement to the computation of the 3D-MAT. Furthermore, they present a method for the classification of surface elements in wall and corner regions based on their corresponding position on the medial surface: The medial surface is separated into inner planes and stub planes, whereby stub planes are planes that touch the geometry's surface while inner planes are only connected to other stub or inner planes. Surface elements that belong to stub planes are then considered to be corner regions, and all other elements are wall regions [18]. A conceptual method tailored to laser beam melting is proposed by [PERSON] et al. [19]. This method also applies the 3D-MAT to measure distances and angles. In addition, it incorporates overhang detection based on the comparison of neighboring surface normals and a routine to compute cross-sectional areas by slicing the geometry with cutting planes. Most notable is their proposition for feature classification: They propose to distinguish curvature and thickness measurement by the angle between the two normal vectors related to an inscribed sphere. However, they fail to define limit values for a proper distinction. An alternative method to check for manufacturability with selective laser melting and sintering is demonstrated by [PERSON] and [PERSON] [20]. Their method classifies surface elements into straight, convex, and concave environments by comparing the angles between neighboring normal vectors. Afterward, wall thicknesses and gap sizes are determined by measuring the distance of straight elements to the opposite elements, whereas convex and concave opposing pairs of elements are used to calculate cylinder and bore hole diameters,  
Figure 1: Example for Heuvers’ circles with different diameters \(D\) and \(d\). respectively. However, this method is restricted to the defined set of features and is not capable of evaluating edge sizes or free-form shapes. Further methods for design evaluation are usage of the heat kernel signature, which recognizes features based on their heat transfer characteristics [27], a voxel-based representation [28], shape diameter functions [29], or machine learning approaches [30; 31]. Moreover, an approach specifically tailored to WAAM using feature-based modeling and CAD macros is contributed by [PERSON] et al. [21]. Nevertheless, due to its dependence on feature-based modeling, this method restricts the design process to a specific CAD system and a limited set of features. In addition, some works suggest the use of a database [19] or a manufacturability ontology [32; 33] to relate manufacturability determining factors such as machinery, material, or process parameters to corresponding design constraints considered by the design evaluation tool. Thus, a comprehensive and flexible manufacturability evaluation system can be created, that supports manufacturability optimization in the design process by incorporating all relevant knowledge. Lastly, it has to be noted that an alternative approach to foresee manufacturability in the design process is to conduct multiscale finite-element simulations of the whole process chain [17]. However, we focus in this work on pure geometric manufacturability analysis to provide immediate feedback to the designer.