Evaluation of novel tool geometries in dry drilling aluminium 2024-T351/titanium Ti6Al4V stack

Three novel drill geometries, multipoint, step and double cone, were designed and experimentally evaluated to understand the effect of tool geometries on the machining performance of dry drilling Al/Ti stack. Results showed that the double cone drill achieved a better hole quality and a higher efficiency due to the smaller thrust force, broken chips, and less burrs compared to the other two drill geometries. The multipoint drill generated serrated chips in titanium alloy drilling. Significant microstructure deformation occurred in the adiabatic shear band (ASB) and the second shear band. Visible cracks propagated along the ASB from the free to back surface of the chip. Phase transformation from β phase to martensite occurred in the second shear band. The drill geometry design and experimental investigation in this paper could provide guidance for drill bit design and manufacturing for Al/Ti stack drilling.