## 5 Discussion  
The proposed methodology presents an approach for ensuring the functionality of FDM-printed non-assembly mechanisms taking into account comparatively large joint clearance and geometric part deviations depending on the choice of process parameters. The results of the statistical tolerance analysis using sampling technique of the presented case study indicate that the joint clearance has a major influence on the motion behaviour and thus has to be considered (1.75 mm maximum deviation). The same applies to the geometric deviations of the linkages resulting from the FDM process as they also mainly influence the motion behaviour of the mechanism which can be seen in the higher deviation of the FKC (2.21 mm and 2.58 mm deviation). Furthermore, it can be stated that the choice of process parameters has an impact on the motion accuracy as parameter set 1 results in a smaller deviation of the coupling curve (see Table 5).  
The joint clearance was considered in the tolerance analysis in terms of MBS. Hereby gravity and friction within the joints were neglected in the first approach due to the high computational effort. For a further enhancement of the MBS, gravity affecting the journal and friction between journal and bearing can additionally be considered and subsequently evaluated on their influence. Through the implementation of predictive models using ML techniques, the geometric deviations resulting from the choice of process parameters were precisely predicted in terms of tolerances and resulting joint clearances. The trained models indicate good forecast quality regarding the CoP and the RMSE values in Table 3. The integration of these empirical predictive models in the statistical tolerance analysis eliminates a major drawback as there is currently no applicable guideline for tolerancing in FDM and tolerance values have to be estimated. In order to predict geometric deviations of printed parts considering other process parameters, further experiments need to be conducted. Hereby the usage of a different printers is purposeful as parameters like e.g., extrusion temperature and velocity can be varied and thus be considered. Since this contribution proposes a general methodology for ensuring the functionality of additively manufactured non-assembly mechanisms, with some process-specific adaptions, it can be applied to other AM technologies, such as SLA and SLM as well. Furthermore, for a realistic representation of the joint clearance affected by form deviations like e.g., the staircase effect resulting from the AM process, the surface of bearing and journal could be considered in terms of Skin Model Shapes or Statistical Shape Analysis for the integration in tolerance analysis [45].  
\begin{table}
\begin{tabular}{l c c} \hline \hline  & **Parameter Set 1** & **Parameter Set 2** \\ \hline Predicted tolerance & 0.36 mm & 0.47 mm \\ Predicted deviation of clearance c & 0.04 mm & 0.14 mm \\ Deviation FKC & 2.21 mm & 2.58 mm \\ \hline \hline \end{tabular}
\end{table}
Table 5: Deviation of the desired motion behaviour for the functional key characteristic (FKC), using a 95% quantile for the different parameter sets.  
Hereby, the influence of the seam style could also be evaluated more precisely as it may cause clattering motion within the joint.