# Wear Behavior of Uncoated and Coated Tools in Milling Operations of AMPCO (Cu-Be) Alloy
## 3 Results and Discussion
### Surface Roughness Analysis  
In this section the results obtained from the surface roughness analysis of the machined part are presented. The surface roughness assessment method has been described in a previous section. In Table 6, the mean values of Ra are presented.  
These values are presented as surface graphs in Figures 4 and 5, to evaluate the surface roughness value variation regarding the machining test conditions.  
\begin{table}
\begin{tabular}{c c} \hline
**Tool Reference** & **Ra [\(\mu\)m]** \\ \hline T0L18F750 & 0.102 \(\pm\) 0.005 \\ T0L36F750 & 0.128 \(\pm\) 0.006 \\ T0L48F750 & 0.137 \(\pm\) 0.007 \\ T1L18F750 & 0.096 \(\pm\) 0.020 \\ T1L36F750 & 0.134 \(\pm\) 0.023 \\ T1L48F750 & 0.244 \(\pm\) 0.030 \\ T0L18F1500 & 0.399 \(\pm\) 0.048 \\ T0L36F1500 & 0.459 \(\pm\) 0.051 \\ T0L48F1500 & 0.595 \(\pm\) 0.012 \\ T1L18F1500 & 0.400 \(\pm\) 0.019 \\ T1L36F1500 & 0.572 \(\pm\) 0.022 \\ T1L48F1500 & 0.800 \(\pm\) 0.040 \\ \hline \end{tabular}
\end{table}
Table 6: Surface roughness values registered for each of the tested conditions.  
Figure 4: Surface graph of the machined surface roughness produced by the uncoated tools for each of the tested conditions.  
\begin{table}
\begin{tabular}{c c c} \hline
**Layer** & **Composition** & **Thickness [\(\mu\)m]** \\ \hline Z1 & CrN & 2.689 \(\pm\) 0.081 \\ Z2 & DLC & 0.271 \(\pm\) 0.020 \\ Z3 & CrN & 0.570 \(\pm\) 0.031 \\ Z4 & DLC & 0.601 \(\pm\) 0.018 \\ \hline \end{tabular}
\end{table}
Table 5: Layer composition and average measured thickness.  
As seen from the figures and table presented above, the values of the surface roughness tend to rise for higher values of feed rate and cutting length. For the condition of 1500 mm/min, the surface roughness values were the highest for both tools. Although the behavior of the surface roughness values was the same for both coated and uncoated tools, the lowest values of surface roughness were detected for the coated tools for cutting lengths up to 36 m. However, for the maximum cutting length conditions (48 m), the uncoated tools produced a better surface finish on the machined material when compared to the coated tool. A bar graph comparing the surface roughness of both of these tools for each of the tested conditions can be observed in Figure 6.  
Preliminary Study of the Surface Roughness at a Lower Feed Rate Value  
Trying to analyze the influence of feed rate on the produced machined surface quality, some additional tests were conducted. These tests were performed at a 350 mm/min feed rate and with a 48 m cutting length. Three tests were conducted for each tool, uncoated and coated, analyzing the behavior of the machined surface roughness from the beginning of the test until it reached a cutting length of 48 m. In Figure 7, the evolution of surface roughness for both coated and uncoated tools can be observed.  
Figure 5: Surface graph of the machined surface roughness of the coated tools for each of the tested conditions.  
Figure 6: Comparison of the surface roughness values of uncoated and coated tools for each of the machining conditions.  
As can be observed from Figure 7, the coated tool causes a higher level of surface roughness; however, the overall values of surface roughness obtained using this feed rate value are very satisfactory, for both the uncoated and coated tools, with these producing a surface finish quality good enough to enable the skipping of a manual polishing operation after machining. However, this could be explored in a more detailed manner by analyzing the wear mechanisms of both tools for each of the cutting length stages.