*3.4. Hole Quality Analysis*

In this section, the quality of the hole drilled at different feed conditions per tooth and cutting speed will be analyzed, both in the laminated material and in the material manufactured by PAW-WAAM additive material in terms of the following: diameter, roughness, and burrs at the exit of the hole.

Regarding the diameter, the nominal values measured are slightly higher than the diameter of the drill, the difference being the one observed at low cutting speeds in the drilling of WAAM material, as can be seen in Figure 13.

**Figure 13.** Effect of the cutting parameters and material manufacturing process on hole diameter.

The roughness is not affected by the set of material and conditions in the cases of rotting analyzed as can be seen in Figure 14. The observed variance is greater than the differences between the conditions, which does not allow to establish significant discrepancies between the values.

**Figure 14.** Effect of the cutting parameters and material manufacturing process on the surface roughness of the hole.

Figure 15 shows the average burr results measured at the exit of the hole for the drilling conditions tested, both in the case of the wall obtained by WAAM technology and in those obtained by conventional methods such as lamination. Cutting conditions, both cutting speed and feed per tooth, do not determine the size of the burr produced at the exit of the hole. The manufacturing process of the titanium alloy wall has a significant influence. Although the variance observed in the size of the burr is greater in the case of the WAAM wall, the hole quality in terms of average burr size is improved. The size of the burr is inversely correlated with the grain size and directly with the elongation before breakage.

The results show lower burr values in cases of drilling of material manufactured by WAAM technology owing to its higher hardness and mechanical resistance typical of the manufacturing process of the wall in which we find a heating–cooling cycle that increases the local hardness.

**Figure 15.** Effect of the cutting parameters and material manufacturing process on the burr height.
