Modelling of cutting forces in orbital drilling of titanium alloy Ti–6Al–4V

• A modelling of the chip geometry taking into account the complex tool geometry.
• A modelling of elementary cutting forces taking into account the local conditions.
• Dissociation of the role of each part of the tool on the chip and forces generated.
• Better understanding of the cutting phenomena in orbital drilling.

Orbital drilling is a highly complex machining operation. Due to the tool helical trajectory, the chip thickness is highly variable along the cutting edges and during the tool revolution. This can be made even more difficult by the cutting tool geometry, which can be also very complex. This explains why cutting forces are very difficult to model and to estimate for different cutting tool geometries. The aim of this study is to develop a cutting forces model depending on the tool geometry and cutting conditions in order to control the final quality of the machined borehole. First, the geometry of the chip is modelled taking into account the parameters defining the trajectory and the tool geometry. A cutting force model, based on the instantaneous chip thickness, is then set up. An experimental study validates the modelling through measurements of cutting forces made during orbital drilling tests. From this modelling, it is possible to optimise the cutting parameters and the geometry of the cutting tool in order to control the loading on the tool and thus the final quality of the borehole.