## 3 Machinability Analysis
### Power and Energy Consumption  
In Figure 5, the results obtained in the active electric power (\(P\)) and the energy consumption (\(E\)) in the turning process can be observed.  
The \(P\) evolution recorded during the turning operations revealed a clear dependence on the cutting parameters, particularly on \(v_{c}\). In all tested configurations, an increase in \(v_{c}\) resulted in a noticeable rise in \(P\). This behavior is in good agreement with the higher spindle speeds required, which lead to a greater electrical demand. Moreover, higher \(v_{c}\) intensifies friction, requiring more power in the spindle rotation to withstand the mechanical resistance generated during the cutting process.  
Although cutting forces decrease with diameter (Figure 4), the increase in power consumption is mainly due to the higher spindle speeds required to maintain constant \(v_{c}\). Given that cutting forces in PLA-CF are much lower than in metals, their increase at higher cutting parameters is not sufficient to explain the rise in power demand.  
The \(f\) influence on \(P\) is more moderate and less systematic. In some cases, increasing \(f\) led to a slight increase in power, while in others, the values remained relatively constant or even decreased. This irregularity can be associated with the combined effect of reduced cutting time and more efficient material removal at higher \(f\), which partially offsets the rise in instantaneous mechanical load. As \(f\) increases, the contact time between tool and material per unit length decreases, which reduces frictional losses and thermal buildup, contributing to a more efficient process.  
Regarding the influence of \(D\), a tendency toward increased power demand was observed as the diameter decreased, particularly under high-speed conditions. Although the reduction in cutting forces might suggest a decrease in mechanical resistance, the higher spindle speeds required to maintain a constant \(v_{c}\) at smaller diameters result in increased rotational energy and, hence, higher power draw from the spindle drive.  
\begin{table}
\begin{tabular}{c c c} \hline \(D\) **(mm)** & **Rxy (N)** & **\(\sigma\) (MPa)** \\ \hline
18 & 46.30 & 0.182 \\
16 & 39.84 & 0.198 \\
14 & 36.51 & 0.237 \\ \hline \end{tabular}
\end{table}
Table 4: _Rxy_ resultant and shear stress values in the interlayer FFF sample during turning operation.  
Figure 5: Electric measurements in the cutting process: (**a**) active power; (**b**) energy consumption.  
The analysis of \(E\) reveals that, independently of P, cutting parameters with longer machining times (low \(v_{c}\) and low \(f\)) result in higher total energy consumption \(P\). This is because the reduction in material removal rate at low values of \(v_{c}\) and \(f\) extends the operation and leads to higher cumulative energy consumption.  
Conversely, increasing the feed rate significantly reduced the energy required to complete each machining pass. This reduction is not only due to shorter processing times, but also due to the improved cutting efficiency achieved at higher feeds, where material is removed more aggressively and the tool-material interaction time per unit length is reduced. These conditions favor a more efficient use of electrical energy, especially when combined with moderate spindle speeds.  
These results reflect the complex interplay between kinematic and energetic aspects of the turning process and underline the importance of considering both tool-material interaction and machine dynamics when analyzing power consumption in the post-processing of FFF-manufactured PLA-CF components. The observed trends also suggest that minimizing cutting speed and optimizing feed rate could be effective strategies for reducing energy consumption during machining, without compromising surface quality or process stability.