Tool Wear Analyses in Low Frequency Vibration Assisted Drilling of CFRP/Ti6Al4V Stack Material

Drilling of fiber-metal compound materials is one of the most challenging machining operations. Besides frequently occurring damages of the borehole surface tool wear is a major concern when drilling compound stacks. The significantly divergent cutting conditions of fiber reinforced plastics and metallic alloys require compromises in the tool geometry as well as the cutting materials and coatings. Excessive cutting edge rounding due to the brittle and abrasive fibers leads to increasing cutting forces and temperatures in the metallic alloy. This usually results in a catastrophic failure of the tools. In the present study low frequency vibration assisted drilling (LFVAD) of CFRP/Ti6Al4 V [10/10 mm] was investigated in terms of tool wear and compared to conventional drilling. Solid carbide drills with a diameter of 4.8 mm and different CVD and PVD coatings have been tested. The flank wear as well as the adhesions at the cutting edges have found to be significantly lower when using LFVAD. The tool life could be increased by more than 300% compared to conventional drilling. This is based on considerably lower process temperatures and an improvement of the process stability which could be proved by cutting force measurements. Additionally the chip extraction was found to be more efficient due to the generation of small chip segments which is a consequence of the interrupted cut. Best results in terms of tool wear and borehole quality have been achieved with an AlCrN coating.