Experimental analysis of the BTA deep drilling and a new analytical thermomechanical model for assessment of cutting forces and BTA drill design

In this paper, the BTA deep drilling is analysed experimentally and by modelling. Drilling tests shows the significant effect of feed rate and the slight effect of cutting speed on the recorded axial force. Characterisation of the BTA drill inserts shows that the wear is relatively uniformed along cutting edges, except on the nose radius of the central insert. A new analytical thermomechanical model for assessment of cutting forces in the BTA drill and for tool design is then proposed. The friction coefficient involved in the model is adjusted to take into account the effect of lubrication and guide pads on cutting forces. The model predicts axial and radial forces, and torque applied on inserts of the BTA drill. Firstly, the model is validated with recorded axial force, obtained from drilling of a workpiece made of mild steel 18MND5, where the effect of cutting speed and feed rate is highlighted. A parametric study is conducted to highlight the effect of tool geometry (approach and rake angles of inserts) on the axial and radial forces and torque. This shows the potential of the model for further use as a tool design of BTA drills, based on optimal geometric parameters (e.g. cutting angles, cutting edges length) leading to a minimum loading acting on the BTA drill.