Cutting parameters and tool geometry selection for plunge milling - Analysis of cutting forces at the bottom of deep titanium workpieces

Plunge milling is a machining process recognized to be efficient for roughing deep workpieces. This is due to the distribution of cutting forces on the tool. Important axial forces and reduced radial forces lead to more rigidity, and eventually productivity. It is commonly used in the case of machining hard to cut materials, like titanium alloys. However, plunge milling process can exhibit a problem at the end of plunging phase, which is the increase of cutting forces. Within this paper, the study considers the case of wet plunge milling process applied to Ti6Al-4 V alloy, that is the most generally used titanium alloy and applied in a wide range of applications. The authors investigate the effects of the geometrical parameters and the cutting parameters on the amplification of the cutting forces at the bottom of deep pockets. The study shows that the augmentation of the chip cross-section is the cause of the increase of the cutting forces, and a geometrical model is set up so as to predict the enlargement of the chip cross-section depending of several parameters. The results indicate that the entering angle and the nose radius of the insert are the main influential geometrical parameters. Furthermore, is was found that for cutting parameters, the principal influential parameter is the radial offset. Thus, proper cutting parameters and type of insert should be carefully chosen in order to avoid high levels of cutting forces at the bottom of deep titanium workpieces in plunge milling operations.