## 4 Conclusions  
The aim of this work is to provide a detailed insight into the relative effects of FFF printing parameters: infill percentage, layer thickness, printing speed, printing temperature, and surface inclination angle on build part quality (dimensional accuracy and surface roughness) and resource usage, namely, energy consumption and productivity, by modeling and optimization. To achieve this aim, a literature review was carried out and a suitable experiment-based model to assess and  
Figure 16: Effects of interaction of parameters on measured productivity.  
optimize the parameters was developed. Different sets of parameters were modeled, measurements were conducted, and the results were analyzed and compared to experimental tests.  
Considering all the parameters, dimensional accuracy is mainly influenced by layer thickness and printing speed, whereas the surface roughness depends on surface inclination angle and on layer thickness. Energy consumption and productivity are primarily affected by printing speed and layer thickness. Although interactions between printing parameters can be beneficial for the required outcome, they can also hamper the process. Generally, it is apparent that layer thickness and printing speed dominate the other parameters in their importance and usually define the outcome of the printing process. However, on the other hand, there will be a trade-off between layer thickness and printing speed to ensure part quality and resource usage, which must be resolved in order to obtain high-quality and resource-efficient built parts.  
Further investigations might include a follow-up on this work by a more detailed investigation of the effects of layer thickness regarding the dimensional accuracy in the \(Z\) direction as well as the influence of the printing temperature on productivity. Moreover, the accuracy of the regression model for surface roughness needs to be enhanced to achieve more reliable predictions.  
All in all, it is evident that there is a need for further investigations on build part quality in connection with resource usage. Further, printing parameters and output variables need to be analyzed and optimized, in order to establish the FFF process as a reliable, sustainable, and competitive manufacturing alternative. Further interesting possible responses could be production costs, amount of waste, and mechanical properties of the built parts.  
Conceptualization, A.E.; methodology, A.E., S.S., and S.G.S.; software, A.E., S.S., and S.G.S.; validation, S.S.; formal analysis, A.E. and S.S.; investigation, A.E. and S.S.; resources, S.G.S.; data curation, A.E. and S.S.; writing--original draft preparation, S.S. and A.E.; writing--review and editing, A.E. and S.G.S.; visualization, S.S. and A.E.; supervision, A.E. and S.G.S.; project administration, A.E. and S.G.S.; funding acquisition, S.G.S. All authors have read and agreed to the published version of the manuscript.  
This work was carried out with the support of the Karlsruhe Nano Micro Facility (KNMF, www.knmf.kit.edu), a Helmholtz Research Infrastructure at Karlsruhe Institute of Technology (KIT, www.kit.edu) and under the Helmholtz Research Programme STN (Science and Technology of Nanosystems) at KIT. The authors also acknowledge support by Deutsche Forschungsgemeinschaft and open access publishing fund of Karlsruhe Institute of Technology.  
The authors declare no conflict of interest.