From SOM of CF/PEKK in Fig. , it is clear that the feed rate (Ff) map has a similar distribution with thrust force and MRR, indicating a positive correlation between the design variable Ff and the two optimization objectives. The effect of feed rate on Fda is more complex, as indicated by the different color distribution in the map. It is worth noting that at lower limit and upper limit of feed rate (top right and botom left of Ff map), relatively high Fda can be induced (top right and bottom left of Fda map). For spindle speed, its map showed markly different color distribution with the thrust force, Fda and MRR maps. Even at the same level of spindle speed (i.e. the same color region on spindle speed S map), the three objective functions can vary significantly, indicating spindle speed has no significant influence on the three objectives. On the other hand, the optimizaton objective maps for thrust force and MRR have similar color distribution, this implies increasing the CF/PEKK MRR can only be achieved at the cost of increased thrust force. The trade-off between Fda and MRR is nonmonotonic, considering their significantly different color distribution. However, it is worth noting that the maximum MRR can only be achived with the highest Fda (see bottom left of MRR and Fda maps).