Tests with a Walter Prototyp carbide milling cutter have shown Airbus that it can transform its titanium machining capabilities, doubling cutting volumes during roughing operations on one workpiece.

Applied to the Ti6Al4V alloy, a 25 mm diameter Prototyp Ti40 solid carbide end mill removed 160-200 cm3/min of material at feed rates of 50-60 m/min. This compares with 80 cm3/min at 25 m/min using a 32 mm HSS tool – cutting data that has characterised the Airbus workpiece since the mid-90s!

Machining of Ti6Al4V is inherently problematic, says Walter GB. The material, widely used for aerospace applications, has extremely poor thermal conductivity (Ti6Al4V is 7.56 W/mK while Ck45 steel is 51.9 W/mK), a low elastic modulus (110 kN/mm2 compared to Ck45's 210 kN/mm2) and a distinct tendency to 'gum', with the machining heat being largely dissipated by the tool's cutting edge rather than by the swarf, as is the case with steel.

However, Walter's development of titanium-compatible carbide substrates has resulted, for example, in the Prototyp Ti40 solid carbide end mill. This is an extremely tough and relatively vibration-immune carbide and, certainly in the Airbus project, it has proved its worth.

Further Walter trials – in this instance with Ti5553 (Ti-5Al-5V-5Mo-3Cr), a near-beta alloy with higher temperature resistance than Ti6Al4V and a Brinell hardness of 430 – have also proved successful when using the Ti40 at reduced cutting speeds and feeds.

Walter's ongoing developments in titanium machining also include larger diameter tools which necessitate the use of PVD Tiger.tec inserts - WSM35 with high wear resistance for good machining conditions and WSP45 with increased toughness for difficult conditions. Indeed, Walter's G77 insert geometry (with large rake angle of 20deg) has been optimised for titanium alloys and is now available for shoulder mills and porcupine cutters (type ADGT) and round insert cutters (RO.X).