# Towards an Automated Design Evaluation Method for Wire Arc Additive Manufacturing
## 3 Methods
### Application of WAAM Design Rules to 3D-MAT Geometry Indicators  
The defined set of geometry indicators will be utilized to evaluate the manufacturing fitness of a part according to the design rules stated in Section 2.2. While the geometry indicators are computed over the complete geometry, the design rules usually apply only to certain features (like corners, walls, gaps, etc.) or regions (e.g., cross-sectional changes) of the geometry. Moreover, these features mentioned in manufacturability guidelines are often somewhat vague, and no exact geometric definitions of the features are stated. Therefore, a method has to be developed to classify elements of the discretized surface (that are triangles of the surface mesh) into regions that belong to a specified feature. In the literature, two approaches to the classification of 3D-MAT results have been developed by [PERSON] et al. (2018) and [PERSON] et al. (2019) (see Section 2.1.2). Whereas the method proposed by [PERSON] et al. gives a clear distinction between wall and corner regions, the additional computation needed to segment the medial surface is rather complex. Therefore, we chose to expand the simpler method proposed by [PERSON] et al. to classify surface elements based on the angle information, thus reusing the geometry indicators. Consequently, for every assessed feature, a geometry indicator, a manufacturability constraint derived from the design guidelines, and a classification filter to restrict the design rule to the relevant region are needed. The features considered by our approach are wall thickness, clearance, edge radius, bead angle, and thickness gradient (see Figure 4). In addition, the minimal and maximal part size could be checked by comparing the bounding box of the geometry to the specified limits. The other more general criteria, such as symmetry, surface-to-volume ratio, and overall complexity, are not considered by our approach. A summary of the considered design rules, their limit values, and their classification filters is given in Table 2.  
The design guidelines for WAAM only specify a minimum wall thickness induced by machinery and process parameters. A part's maximum thickness is until now not specified. Hence, a lower limit of \(s\geq 2\,\mathrm{mm}\) is defined for wall thickness, measured by the secant's length \(s_{i}\) of the inside 3D-MAT. This rule is applied to opposing facets as classified by the wall angle. There is a degree of freedom up to which angle a feature should be considered a thin tapered wall and from which angle it should be classified as a corner. Figure 5 shows various angles that can be classified as either a tapered wall or a corner. We set the limit to an angle of \(0\leq\alpha\leq 65^{\circ}\) for, in this region, the two facets can still reasonably be called facing each other, and experimental tests show a good differentiation of the two features with this choice. Nevertheless, the separation limit is only a matter of classification since thin elements would be detected as regions of a small corner radius if the limit was chosen differentiy. Likewise, a lower limit of \(s_{\mathrm{o}}\geq 2\,\mathrm{mm}\) is applied for clearance with the only difference that the secant length of the outside 3D-MAT is used. Classification is defined by the outer angle, analogously to the wall thickness. Note that the choice of \(2\,\mathrm{mm}\) as the minimum limit is a conservative estimate since in the literature a value of \(0.9w_{\mathrm{min}}\) (minimum wall thickness) is stated, albeit only for Al5A06 [36]. Towards the corner and edge radii, the literature gives no more quantitative recommendation than to choose them \"generous\" to allow for post-machining and to avoid stress