Tool wear processes in low frequency vibration assisted drilling of CFRP/Ti6Al4V stacks with forced air-cooling

Abstract

Drilling CFRP/Ti6Al4V stacks in one-shot time becomes essential in the modern aerospace manufacturing sectors in order to guarantee the productivity due to the demands of riveting and fastening assembly. In the present study, a novel integrated system of low frequency vibration assisted drilling (LFVAD) coupled with the forced air-cooling was designed to investigate the tool wear issues in drilling of CFRP/Ti6Al4V stacks. The used uncoated solid tungsten carbide tools were specially designed with threaded shanks forfitting the adapter of the LFVAD tool holder. Main geometrical features of the threaded shank drills include a 6.35 mm diameter, a 140° point angle, a 30° helix angle and two cutting edges. Drilling temperatures and forces were in-situ measured for the LFVAD subjected to varying conditions, and the results were compared with the conventional drilling under the identical drilling conditions. It is found that the small titanium chip segments produced by the interrupted cut of vibration drilling can be removed efficiently via the help of the forced air-cooling. Compared with the conventional drilling, slower flank wear rates and lower cutting temperatures are identified under the LFVAD with the forced air-cooling. The adhesive wear is the main wear mode for both drilling methods; however, the chemical wear becomes more pronounced while the cutting edge chipping predominates in the LFVAD. In sum, the LFVAD with the forced air-cooling is confirmed capable of improving the machinability of the CFRP/Ti6Al4V stacks from the aspects of reducing tool wear.