Tool wear in turning titanium alloys

Sammanfattning: In this master thesis, performed at AB Sandvik Coromant, wear and tool life of uncoated WC/Co grades have been investigated during longitudinal turning of the titanium alloy Ti-6Al-4V. Due to titanium’s poor thermal conductivity and high chemical reactivity towards most metals, high temperature is achieved between the tool and workpiece material, resulting in high tool wear rates. The high temperature initiates crater wear, which rapidly degrades the tool and shortens the tool life. It was found in this work that new WC/Co tools can perform better in this application area than today’s used grade for turning titanium alloys, H13A. An increase in tool life by 45% respectively 50% was obtained compared to the reference grade H13A at cutting speeds of 70 and 115 m/min. It was also shown that increase of coolant pressure did not enhance the tool life, while usage of a high pressure tool holder instead of a conventional tool holder gave an improved tool life.Characterization of the wear was performed using LOM and SEM. The wear mechanisms acting on the tools were found to be adhesive, chemical and abrasive wear giving rise to mainly flank and crater wear, regardless of cutting speed, coolant pressure and choice of tool holder.By further analysis of the crater wear using electron microprobe analysis it was found that diffusion of carbon between the tool and workpiece material occurred during the machining. A carbon depleted area was observed in the subsurface for the reference grade but not for the new grades showing improved performances in the turning tests.