# Systemic Evaluation of PSS in the Early Concept Phase Using Graph-Based Reasoning
## 5 Validation
### GEAR Method--Step 2: Elicitation of the Evaluation Logic
The specific knowledge gaps with an impact on the EVCs are listed as follows:  
* _Influences such as turbulence in the AM machine causing powder to remain in filter_: Different AM machines leave different amounts of powder in the filter. The amount depends on effects related to the amount of energy inserted into the powder bed determined by printing patterns, as well a as the general machine design. There are no data or experience present describing these relationships. * _Influences of climatic conditions on the printing process and resulting powder scrape_: Climate is a driving factor for printing results, as complex physical phenomena occur. However, no sufficiently detailed studies or long-term data collection have been conducted yet. * _The service provider's willingness to pay for recyclable powder_: The price for which the industrial company can sell used metal powder to the third-party service provider has to cross the threshold of profitability. If this threshold is not passed, no powder is sold to the external provider, as it would not be economically feasible. So far, no concrete inquiries or negotiations have been conducted to address this knowledge gap. * _The influence of powder specifications impacting the amount of recycled that is reusable powder_: As defined in the guideline and described in step 1 of the GEAR method, it remains unclear to what extent a reduction in specification requirements for powder quality is tolerable such that the build quality remains high. It is also uncertain exactly how much more powder would become available for reuse under a less strict guideline. * _The amount of separated coarse powder_: This refers to the unclear amount of oversize material during internal recycling depending on the specific degradation characteristics of the metal powder from the industrial company, for which no data or experience exist. An index node was added to the KGL for all knowledge gaps, with best-/worst-case scenarios modeled in opposing probabilistic assignments to capture extreme scenarios. The combinability of the PSS elements was defined in the CVL. The variations of the PSS elements, which were introduced in step 1 of the GEAR method, are listed as follows:  
* PSS concept variation with both internal and external recycling: For internal recycling, a corresponding deterministic assignment was used to specify that all internal recycling systems must be installed together. Individual recycling systems (e.g., only a sieving station) may not be installed, as all systems are required simultaneously for internal recycling. External recycling is also part of this variation. * PSS concept variation with only internal recycling (no external recycling): Characteristics for the external service provider must be fixed as _no external recycling_. Internal recycling systems are considered. * PSS concept variation with only external recycling (no internal recycling): In contrast to the previous case, the values of the recycling systems must be set to _not available_, but external recycling is available. * PSS concept variation with neither internal nor external recycling: The values of the recycling systems must be set to _not available_, and the values for the external service provider must be fixed as _no external recycling_. The entire powder flow is disposed of as scrap, as no recycling can take place. For the modeling of the probabilistic graphical model and reasoning analysis, open-source tool GenNie was used. Within GenNie, the distinction of layers according to the PSS abstraction framework can only be represented via the manual layout. Figure 17 shows the graph structure with nodes (see Appendix A Table A1): offset nodes at the top form the PSS concept variation layer, and nodes below represent the evaluation logic layer, with dark blue nodes for evaluation criteria and a black decision-making node. Nodes indicating knowledge gaps appear at the bottom. Figure 16: Causal map providing an overview of the elicited causal relationships within the PSS concept relevant for the EVCs.