Modelling and optimization of the helical milling for hole-making in the Ti-6Al-4V alloy
Helical milling, Titanium alloys, Response surface methodology, Multi-objective evolutionary optimization, Ti-6Al-4V
The helical milling process has been explored in the production of holes for various industries,
standing out biomedical and aerospace. Due to the high precision required and the difficulty of
machining the titanium alloy Ti-6Al-4V, the cutting parameters need to be defined in order to obtain
acceptable levels of quality and precision for such applications. Helical milling, when compared to
conventional drilling, is recommended because it presents low levels of cutting forces and better
quality due to the kinematics of the process. In this work, the main objective was to study the helical
milling to obtain holes in the titanium alloy Ti-6Al-4V. For this purpose, a Box Behnken Design
(BBD) planning was used, enabling the obtaining of second-order regression models capable of
optimization, as a function of the cutting parameters of helical milling, being them, the axial and
tangential feeds per tooth and the cutting speed. The average roughness Ra, circularity (Ront) and
material removal rate (MRR) responses were evaluated. The models obtained for the Ra and Ront
analysis presented adjustments of 87.99% and 84.92% successively, corroborating a good
proportion of explanation of the data variability, having sufficient reliability for a greater
evaluation of the effects of the variables on the responses presented. Finally, for optimization, the
multiobjective optimization method by adaptive geometry estimation (AGE-MOEA) was used to
determine a set of Pareto optimal solutions for the finishing response and the material removal rate.
According to the optimization, to minimize roughness and circularity, it is necessary to adopt as
feeds: fza = 0.71 µm/tooth and fzt = 0.06 mm/tooth and a cutting speed: vc = 59.16 mm/min, while
for greater productivity, it is necessary: fza = 1.20 µm/tooth and fzt = 0.07 mm/tooth and a cutting
speed: vc = 59,16 mm/min. As analyzed through scanning electron microscopy (SEM) images, it
was possible to conclude that for low fza levels, combined with a low cutting speed, inferior surface
quality was observed due to the dragging and adhesion of removed material, as a consequence of
the difficulty in evacuating the chip.