Surface roughness response to drilling of Ti-5Al-5Mo-5V-3Cr using Ti-Al-N PVD coated and uncoated WC/Co tools

The surface response to drilling of the high performance titanium alloy Ti-5Al-5Mo-5V-3Cr (Ti-5553) with WC/Co tools cannot be assumed to similar to that of Ti-6Al-4V (Ti-64). Comparison of surface roughness for holes drilled in Ti-5553 with Ti-Al-N PVD coated and uncoated WC/Co tools at low and high cutting feed and speed was investigated. Cutting surface speed was shown to have more of an impact on surface roughness than that of feed, with high cutting speeds causing higher and more varied Ra value. In addition using coated tools at lower cutting speeds resulted in a lower average Ra. In most cases, the coated tools achieved lower Ra values compared to the uncoated tools. This is thought to be due to a difference in cutting edge radius and better stability associated with the coated tools. High variance in RMax was observed for all tested conditions and tools, in some cases RMax was above 10 µm. Alicona and SEM imaging identified re-adhered material pickup as the probable cause. A correlation between torque and surface roughness was identified for the drilling of Ti-5553 and further investigation is proposed for using torque measurement as an alternate way of quantifying surface roughness without probe measurement or image analysis.