Tool life when high speed ball nose end milling Inconel 718™

Following a brief introduction of high speed machining (HSM) and the machinability of Inconel 718, the paper details experimental work using TiAlN and CrN coated tungsten carbide ball end mills, operating at cutting speeds up to 150 m/min. Inconel 718 is one of a family of nickel based superalloys that are used extensively for gas turbine applications requiring high temperature strength. It is an extremely difficult material to machine, not the least, because it maintains much of its strength at elevated temperatures (∼600°C), has low thermal conductivity and is prone to work harden during cutting. A 3 factor, full factorial cutting experiment at two levels is outlined with the workpiece inclined at 45° and 60° from the horizontal. The longest tool life was obtained when operating at 90 m/min cutting speed with TiAlN coated products. The choice of tool coating was the main factor influencing tool life. The primary tool wear mechanism was adhesive wear, which affected the CrN coating to a greater extent. This was accompanied by peeling off the coating to expose the K10 carbide substrate. Irrespective of the tool coating, notches developed close to the depth of cut position. With the workpiece orientated at 60°C, greater tool deflection occurred which exacerbated notch wear and edge chipping.