## 2 State-of-the-Art and Related Work
### Geometric Part Deviations in FDM  
The FDM-process is controlled by numerous process parameters, influencing the geometric accuracy and consequently the total quality, such as functionality or aesthetics of 3D-printed parts [15]. Especially for non-assembly mechanisms, the dimensional accuracy of the individual parts is essential for fitting in the assembly [2]. For producing parts that meet a required dimensional accuracy, a proper selection of suitable process parameters is therefore essential. Build direction and layer height significantly influence the dimensional accuracy of the fabricated part and thus have to be considered in the design stage of mechanisms. The influence of process parameters on geometric deviations of parts manufactured via FDM has been studied extensively by many researchers in the last years. [PERSON] et al. for example examined the influence of layer thickness, deposition style, support style, deposition orientation in X- and Z-direction and the build location on their influence on the part accuracy. The results indicated that the deposition in the Z-direction was the most significant parameter affecting the dimensional accuracy [16]. [PERSON] et al. investigated the influence of layer height, build orientation, raster orientation, raster width and air gap. Regarding the results, it became obvious that layer height was the most significant parameter [17]. In general, a small layer height results in smaller geometric deviations, whereby the build time is significantly increased. [PERSON] et al. fabricated complex parts in order to investigate the influence of the part shape on geometric deviations. Hereby it was observed that a cylindrical shape results in higher geometric deviations than other shapes due to its dependence on the build direction [18]. [PERSON] et al. conducted an experimental design in order to determine the influence of process parameters in FDM and thus layer thickness and filling velocity were found to be the most significant process parameters influencing the geometric accuracy [19]. According to [PERSON] et al. the geometric accuracy of FDM parts depends upon few process parameters like build orientation, number of contours, layer height, raster width, air gap and raster angle [20]. [PERSON] et al. concluded through experiments that, for both geometric deviations and surface roughness, the chosen layer height is the most significant process parameter [21]. A Taguchi design of experiment (DoE) was used by [PERSON] et al. in order to evaluate the effect of process parameters on part deviations and tolerances of FDM parts. It was concluded that parallelism, angularity and position had the largest deviation among the geometric deviations [22]. In summary, basic relationships between significant process parameters, viz. layer height and part build orientation and geometric part deviations can be determined in coherence with the layer-wise manufacturing principle of FDM. However, the quantification of their influence on the geometric part deviations is quite difficult, since it is always case- and machine-specific. Therefore, empirical predictive models using ML algorithms can help determining the resulting deviations of printed parts, influenced by the chosen process parameters [23].