## 2 Materials and Methods
### KB System
#### 2.1.2 Knowledge Processing Phase
Regarding the second section of the knowledge processing phase, classification of the material requires the definition of two clusters according to Ashby [34] classification, which is (i) material class (e.g., carbon steel, stainless steel, aluminum alloy) and (ii) material type (e.g., AISI 304, 34 NiCrMo16). These two groups allow for the allocation of a given DFW rule to a generic class (e.g., stainless steel) or a specific type (e.g., AISI 304) of materials. The identification of these two clusters allows for the classification of DFW rules that are valid for any material (N.A. ; not applicable), for a given material class (e.g., stainless steel), or for a given material type (e.g., AISI 304). It is worth noting that the material in the case of welding processes refers to the material of the base plates (that can be two or more different materials based on the type and the number of the base plates) and the material of the filler material (if applicable). Regarding the third and last section of the knowledge processing phase, the classification of geometrical parameters and thresholds deals with 3D CAD features to recognize in relation to a given DFW rule. Authors defined four clusters, namely, (i) 3D CAD features (e.g., plates orientation); (ii) product manufacturing information (PMI) (e.g., roughness, tolerances); (iii) dimension/geometry (e.g., plate thickness, plate length, plate width); and (iv) rule/s to verify (e.g., thickness variation less than 1.5 times). Feature recognition systems may extract, from a 3D virtual model, CAD features and the related data used for the computational phase. The 3D CAD feature recognition procedure is described in detail in the following Section 2.2. It is worth mentioning that the current study refers to \"assembly feature\" to be recognized (i.e., the relative position of plates/component) and related parameters (i.e., the thickness of first plate/component vs. thickness of second plate/component) that can be read by the analysis of a 3D model (B-rep representation). In addition to these clusters, another item of the classification (label) characterizes the rule--the rule type. This attribute may assume the following values: (i) information, (ii) warning, and (iii) critical. \"Information\" is a type of recommendation that would be desirable. However, it does not affect the processing of the component, nor its cost. A \"warning\" is an important aspect to address since it saves wasting manufacturing time and cost. Still, it does not prevent component manufacturability. \"Critical\" is the most significant rule, actually stopping the component manufacturability. An example may facilitate the understanding of the type of information to insert for each section. The DFW rule reported in the table is the W025, and it is defined as the following: \"Avoid weld beads crossing.\" For the first cluster of information, in this specific case, the rule is valid for all the arc welding processes (technology type-level I), independently from the specific type process (technology type-level II). For the second cluster of information, again the rule is applicable in general for all materials (material class) independently from the specific type (material type). For the third cluster of information, CAD features to recognize from the CAD models are (i) the weld beads and (ii) the position of the weld beads. No information is required regarding the PMI, while for parameters, it is required to assess the distance between the weld beads (D) in all the directions (x, y, z) and the dimension of the weld beads (if more dimensions are available, the largest one is recorded). Thus, the rule that discerns validated and non-validated rules is D \(\geq\) 2,5 Z. When D is less than 2,5 Z the rule is non-validated (the weld beads are crossing other beads of the heat-affected zone); otherwise, the rule is always validated.