Gamma titanium is brittle and prone to cracking at room temperature, making finish machining very challenging. Machining near net parts is a key project activity and translates to finishing parts from other near-net processes and with other materials. Different aspects of machining were therefore investigated within MMTECH.
FIDIA modified their G996 machine tool to make it suitable for milling gamma titanium. The machine tool needs to be rigid and subsystems include an electro-spindle, toolholder cone and tool locking system and a tool lubrication and cooling system. Accessories include a filtration system for liquid and air and a novel vibration monitoring system. CNC options include ViMill and an automatic software cycle.
When cutting gamma titanium, it is important consider whether the cutting process is continuous (turning, drilling) of interrupted (milling). When machining Gamma TiAl in continuous cutting temperature may rise and tool wear can be promoted easily. Cutting speed will depend as well on feed rate and depth of cut (turning) or diameter( drilling), but in general values close to 20-50m/min are recommended. In the case of interrupted cutting, tool has time to cool down, and thus higher cutting speeds can be employed. For finishing conditions cutting speed up to 150mm/min could be employed providing tool lives longer than 60 minutes. On the whole, coatings such as AlCrSiN, AlTiN or AlSiTiN families are highly recommended in cutting tools to avoid rapid tool wear. Either MQL lubrication (best tool-wear although anti-wear coatings are required) or dry milling (best roughness) should be used. The optimum cutting parameters were also determined.