# Systemic Evaluation of PSS in the Early Concept Phase Using Graph-Based Reasoning
## 5 Validation
### GEAR Method--Step 1: Preparation  
In step 1, the scale and scope of the evaluation in terms of considered EVC, as well as the PSS concept in terms of architecture and functional structure, are determined as reference points for the evaluation. This assists domain experts in eliciting their a priori knowledge regarding influencing factors relevant for achieving the EVCs. In the use case, the PSS for powder recycling is evaluated regarding its anticipated operational performance, that is, its ability to recycle a maximum amount of metal powder. Metal powder is recycled in two ways according to the concept. It is recycled internally by technical systems installed at the industrial company's manufacturing plant. In addition, it can be recycled externally via a service provider through a process called re-atomization if the powder's level of contamination is too high for internal recycling or if the powder has already been fused into a solid part. All powder that cannot be recycled either internally or externally has to be disposed of as scrap, which is the default way of handling used metal powder without a PSS. To assess the performance, three EVCs with corresponding metrics were provided:  
* \(EVC_{\text{intern}}\): Amount of recyclable powder processed by on-site recycling systems [kg];
* \(EVC_{\text{extem}}\): Amount of recyclable powder processed by an external service partner [kg];
* \(EVC_{\text{scrap}}\): Amount of powder that becomes scrap at the customer site and is disposed of by the service provider [kg]. Since the company aims to internally recycle as much powder as possible and minimize the amount disposed of as scrap, powder recycled internally has the highest value to the company. Recycling through an external service provider is considered only half as attractive as internal recycling. Powder disposed of as scrap has only 10% of the value of externally recycled powder. Based on these considerations, an evaluation function was provided to reflect this prioritization of the EVCs: \(\text{Evaluation}=20\cdot EVC_{\text{intern}}+10\cdot EVC_{\text{extern}}+1\cdot EVC_{\text{scrap}}\). This function reflects the importance of internal recycling, with external recycling being less desirable and scrap disposal being the least preferred. Figure 13: AM process with examples of the technical systems used in the PSS to enable powder recycling (based on [76]). In order to assess the three defined EVCsm the core value delivery processes of the PSS during the middle-of-life (MOL) phase is anticipated. Before stating the involved PSS elements, it has to be noted that the steps of the GEAR method were conducted iteratively, as suggested in the description. The considered PSS elements presented in the below are, therefore, a result of iterations during which PSS experts refined their understanding of the PSS process and prioritized the most relevant PSS elements. Therefore, the presented hierarchical architecture of the PSS reflects a more mature state of understanding in terms of PSS elements relevant for the EVCs compared to conducting step 1 for the first time. Since it reflect the latest understanding, the presented PSS elements are all considered in the graph model. The PSS elements considered for EVC evaluation, together with their variations, are shown in Figure 14 and explained in brief as follows:  
_Technical Systems_:  
* Recycling Systems: Systems necessary to capture and internally recycle metal powder. * Production System: The additive manufacturing machine responsible for the vast majority of powder that requires recycling. It is considered part of the PSS because the industrial company has control over these machines and could, in theory, change them. _Services_:  
* Service Partners: The companies that collect powder from the industrial company to recycle or dispose of it. For scrap disposal provider, no variations are depicted because scrap disposal is the default option and is not considered as a variable part in the PSS concept.