# CAD-Based Feature Recognition for Process Monitoring Planning in Assembly
## 5 Discussion  
The approach and implementation allow expert knowledge about process monitoring requirements to be stored and used efficiently. This enables a reduction in planning effort and costs, particularly in the case of multi-variant production with small batch sizes. When manually determining the monitoring requirements, the quality manager must determine these requirements in various workshops. This requires expert knowledge and various steps to manually determine the requirements in the CAD file and in the process plan. The approach presented in this article is also advantageous for larger batch sizes, since the determination of the monitoring requirements does not increase the production time and thus does not directly affect production costs. In the best case, costs for additional sensors are avoided. Monitoring requirements are initially needed for non-value-added monitoring tasks (i.e., secondary processes). They only indirectly impact costs through increased planning efforts, increased process understanding, earlier defect detection, and lower defect rates. Due to higher process and production standards in certain production areas, such as medical device production (due to MDR), higher process monitoring standards are needed. Another aspect to investigate is the initial cost of setting up this semi-automated identification of monitoring needs. Creating the requirement templates is not as time-consuming as defining the individual rules for recognizing assembly features. This aspect, in particular, requires a high level of expert knowledge and setup time.  
The results described in this paper show a relatively simple assembly example consisting of six parts to be assembled. The assembly plan, which consists of seven assembly processes, is also not too complex. The variety of assembly processes can lead to a complex initial setup of the presented system since different features have to be considered, and therefore rules have to be formulated. In addition, the complexity of the geometries can lead to missing features and monitoring requirements, which have to be added afterward by the user. In this use case, 14 different solid features were identified, consisting of planes, cylinders, screws, and holes. A total of 19 connection features were recognized, with 15 plane connections and 4 cylinder connections. Cylinder connections are, for example, the connections between the screw and hole (see Appendix E). These characteristics were then used to populate the monitoring requirements templates along with the information derived from the assembly plan. Here, geometry and process characteristics formulate monitoring requirements (R), as can be seen in Figure 5. Some missing requirements were added manually, such as the measuring force during joining, which was not present in the assembly plan.  
Depending on the process diversity, production yield, scrap rate, and batch size, the approach may be too time-consuming and costly. Once the initial stage of the approach is implemented, new processes or product variants bring more variety to the production, and, over time, the cost of building the approach is amortized. In addition, the approach and implementation should be semi-automated so that the user can intervene and improve the system at any time. The structure of the presented system allows the user to decide which individual module to choose. This gives the user the flexibility to increase or decrease the level of automation.