*3.6. Summary of the Analyses' Results*

In the present subsection, the summary of all the conducted analyses is performed. A comparison of the results obtained for the produced surface roughness, flank wear and registered wear mechanisms is made.

**Figure 18.** Abrasion marks detected on T4 tool's rake face, tested at 125% feed rate.

3.6.1. Surface Roughness Analysis Summary

In this section, the various measurements made using all the tool types in all the test conditions are presented. Both the Ra measurements taken in the radial and tangential directions are presented in Figures 19 and 20, and the test conditions are presented as seen in Section 2. The number after "L" indicates the cutting length used in that test, and the number that follows "F" indicates the percentage of feed rate that was used in the machining test.

**Figure 19.** Average values of Ra, measured in the radial direction, produced by T1, T2, T3 and T4 tools for all the different test conditions.

As previously noticed in the subsections dedicated to the individual tool analysis, the surface roughness tended to increase with the increase in cutting length; this was expected, as the tool wear is more intense for higher values of cutting length. This was verified in all the tested tools, and there was also a variation in surface roughness with feed variation, as this parameter is known to have high influence on the surface roughness [14,15]. Regarding the variation in surface roughness with feed rate, the predominant trend was that lower feed rates will confer a better surface finish to the machined part, except for T3, where an

increase in feed rate produced a better surface quality than at lower values of feed rate. It is worthy to note, however, that the surface roughness values produced by T3 were the best, being closely followed by T4. In fact, the surface quality produced at the 125% feed rate by the T3 and T4 tools was on par with the surface roughness quality produced by the T1 and T2 at the 75% feed rate, indicating that the four-fluted AlCrN-coated end-mill and the fourfluted TiAlSiN-coated end-mill are good choices for the conduction of finishing operations in this kind of material. The number of flutes has a great influence in the machining of this material, especially regarding the AlCrN-coated tools, as it can be observed that the two flutes' tools produced a worse surface quality than that of the four-fluted AlCrN-coated tool [44]. In Figure 21, the variation of machined surface quality for different feed rate values can be observed for the 2-m and 4-m cutting lengths (in the radial direction, as the identified trends were the same for both directions and the values were similar). It was observed that the trends were common for both 2 and 4 m of cutting length; however, the T4 tools seemed to be the least affected by the increase in cutting length, with the roughness values not increasing drastically for higher cutting length values, especially when compared to T1 and T2 tools. The T3 tools were also resistant to this variation. Furthermore, the results obtained for lower feed rate values were higher than those registered for T4.

**Figure 20.** Average values of Ra, measured in the tangential direction, produced by T1, T2, T3 and T4 tools for all the different test conditions.

It is worthy to note that the amount of registered tool wear negatively impacts the machined surface quality, with the conditions that produced the highest amount of wear producing the worst machined surface quality [14,15]. Tools that exhibited higher levels of VB tended to produce a worse machined surface quality, primarily since the substrate was exposed (adhesive wear and coating delamination/spalling), and were subject to wear mechanisms such as abrasive wear. This altered the cutting edge's geometry, inducing this higher surface roughness value. However, as previously mentioned, the machining parameters highly impacted the machined surface quality, with the T3 tool being a prime example of this fact.
