2.2.3. Machining Tests

The tests were performed using a milling center—HAAS VF-2 CNC machining center (HAAS Automation, Oxnard, CA, USA)—with a maximum speed of 10,000 rpm and a maximum power of 20 kW. Because the workpiece material was supplied as a round bar with a 158 mm diameter, a strategy was selected in which the tool would machine the material's surface in a spiral motion. The initial bar had a considerable height (of about 1 m); as such, it was necessary to cut this bar into sections so as to enable a stiffer machining process. The bar was cut using a bandsaw, creating sections with a height of 32 mm. These sections were then face-milled, guaranteeing a constant height of 30 mm (due to possible deviations in height created by the bar's cutting process).

Further, regarding the machining strategy, it was concluded that the best solution would be for the tool to perform an initial plunge at the round bar's center, then machining from the center to the bar's periphery. By adopting this strategy, the selected radial depth of the cut would be kept constant from the beginning of the test to its end, thus preventing undesired wear phenomena related to the change in this parameter throughout the test.

The machining tests were performed using cutting fluid (water-miscible) that was projected externally (5% oil in water) relative to the tool. The machining parameters were selected based on the tool's substrate manufacturer (INOVATOOLS). The choice was made based on the optimal parameters for optimal surface roughness production. The machining tests were designed using a full factorial experiment design. The final selected machining parameters can be observed in Table 4. In this table, the values for the cutting speed (Vc), feed per tooth (fz), cutting length (Cut. Length), axial depth of cut (ap), and radial depth of cut (ae), as well as the respective tool reference for each tested condition are shown. A total of three tools per test condition were used to improve the quality of the obtained results regarding the performance and wear sustained by the tested tools.

Two cutting lengths were selected to observe how the tool wear would progress throughout the machining of the workpiece, which were 5 and 15 m. Two cutting speeds were also selected, 100 and 125 m/min, to evaluate the influence of this parameter on tool wear and production quality (machined surface roughness). Regarding feed per tooth, this parameter is also known to have an influence on tool wear and production quality; therefore, three values were tested, with the center value (100%) being 0.0700 mm/tooth. As observed in Table 4, the values for ap and ae were kept constant, with the selected ae value being 75% of the tool's cutting diameter (tool diameter was 6 mm).


**Table 4.** Selected machining parameters for the conducted tests.
