Impact of Number of Flutes and Helix Angle on Tool Performance and Hole Quality in Drilling Composite/Titanium Stacks 2011-01-2744

The main difficulties in machining composites and titanium are the excessive abrasive nature of the composite material and the poor thermal conductivity of titanium. When composites are combined with titanium in stacks, drilling them becomes even more difficult. Burrs and chips, which are produced when drilling the titanium, damage the composite layers and produce holes outside the required hole size accuracy. Although material stack-ups such as Carbon Fibre Reinforced Plastic/Titanium (CFRP/Ti) or CFRP/Al have been in industry for at least 20 years, more research is required regarding the influence of different drill geometry features on tool performance and hole quality while drilling these materials. The experiments reported in the literature have shown that drilling in CFRP/Ti stacks is a difficult task, as each of the materials requires a different approach, requiring extremely different types of drill geometry and cutting conditions. It is also suggested that titanium causes the biggest problems when machining CFRP/Ti stacks.

This paper presents results from drilling experiments where four different drill designs were used differing in number of flutes and helix angle. Investigation and comparison was made in terms of cutting forces, temperature and hole quality. Even a small change in drill point geometry might cause differences in the performance of a drill. This research shows that the number of flutes in the drill and the helix angle influences tool performance and a definite relationship exists between these two factors. It was found that a two-flute drill with a high helix angle shows promise to lower temperature in the cutting zone and reduce the cutting forces when drilling CFRP/Titanium stacks.