High-Efficiency Machining of Titanium Alloy Using Combined Machining Method of Driven Rotary Tool and Hale Machining

Titanium alloys are widely used as aerospace materials, especially for turbine blades, due to their excellent mechanical properties. In the high-efficiency machining of titanium alloy turbine blades, the feed rate for ball-end milling is limited to 1000 mm/min due to the low thermal conductivity and chemical reactivity of the titanium alloy. These characteristics result in tool damage and an increase in the cutting temperature, significantly reducing the machined surface accuracy. A new processing method is thus needed for achieving a high accuracy and high efficiency in titanium alloy machining. It has been reported that driven rotary machining of hardened steel improves the machined surface and increases the processing efficiency, suggesting that high-efficiency machining can be realized by employing hale machining with a rotary tool. In this study, hale machining was performed using a driven rotary tool and the effects of different cutting conditions and cutting environment on the machining characteristics were investigated. The results showed that the tool life was longest at a feed rate of 9000 mm/min among the three feed conditions because the number of times of adhesion and detachment decreased with the decreasing friction distance of the cutting edge. Furthermore, it was clarified that adhesion formation at the cutting edge was suppressed by lubrication with an oil mist in a minimum quantity lubrication environment. This lubrication effect reduced the tool damage and adherence at the cutting edge, significantly extending the tool life and improving the machined surface quality compared to the results obtained in a wet environment.