## 5 Conclusions and Discussion
Figure 11: Samples printed by the optimal parameter settings for the overall manufacturing performance. (a) ASTM D638; (b) ASTM D695; (c) ASTM D3039. The manufacturing performance measures of each experiment are displayed in Figure 12. Since all the performance measures are desired to be minimized, a data point can be optimal as it becomes closer to the right lower corner of the performance space in Figure 12. The data points in red indicate the manufacturing performance measures of the optimal parameter settings from the multiple response optimization. They show that all three designs can properly achieve the overall manufacturing performance at the same parameter settings; universal parameter settings across designs to optimize the overall manufacturing performance can exist for the FFF process using CFR-PEEK. The optimal parameter settings for the overall manufacturing performance are obtained under the equal importance assumption among the performance measurements. Thus, the optimal settings can be varied if each performance measure has different importance. It indicates the necessity of an appropriate decision-making framework that enables the decision maker to reflect relative importance among performance measurements in finding optimal parameter settings for the overall performance improvement. The primary contribution of this study is to establish a basis for additive manufacturing capabilities for CFR-PEEK applications from manufacturing performance perspectives. The findings from this study will provide useful information about the optimal parameter settings to enhance the manufacturing performance of fabricated products using CFR-PEEK. The approach of this study attempts a transition of prevailing mechanical performance viewpoints to manufacturing performance viewpoints. Thus, the approach will open potential research opportunities in understanding the complex dynamics among the different manufacturing performance measures and in addressing effective operational methods for additive manufacturing to improve the overall manufacturing performance. Nonetheless,  
Figure 12: Optimal parameter settings (in red) for the overall manufacturing performance. (**a**) ASTM D638; (**b**) ASTM D695; (**c**) ASTM D3039. the current study should be extended by considering several issues in future work. First of all, additional designs should be analyzed to generalize the findings of the optimal parameter settings since the current research compares three simple designs. Second, additional FFF process parameters and manufacturing performance measures that are critical for CFR-PEEK applications should be considered along with other advanced composite polymers to fully address the relationships between the process parameters and the manufacturing performance measures. Lastly, both the mechanical performance and manufacturing performance should be investigated together to identify the possible trade-offs between them depending on process parameters. Then, the determination of the optimal parameter settings will be formulated as a more complex decision-making problem in which various trade-offs exist between the mechanical and manufacturing performance. Conceptualization, K.P. and G.E.O.K. ; methodology, K.P., G.K. and H.N. ; formal analysis, K.P., G.K., H.N. and H.W.J. ; investigation, K.P., G.K. and H.N. ; writing--original draft preparation, K.P., G.K., H.N. ; writing--review and editing, G.E.O.K. and H.W.J. All authors have read and agreed to the published version of the manuscript. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MIST) (No. 2018R1C1B5040256) for [PERSON]. This work was also supported by Research Assistance Program (2020) in the Incheon National University for [PERSON]. The authors declare no conflict of interest.