Analysis of Cutting Direction When High Speed Ball Nose End Milling a Nickel Based Superalloy

When ball nose end milling at high rotational speeds, orientation of the cutter with respect to the workpiece, together with the direction of cutting, defined as β angles, has been found by several authors to significantly affect tool life/performance. The paper details experimental work to determine the effect of cutting orientation on tool life, cutting forces, vibration and workpiece surface roughness when high speed ball nose end milling Inconel 718TM. Dry cutting was performed using 8 mm diameter solid carbide cutters, coated with TiAlN & CrN with the workpiece orientated at 45° to the cutter axis. In terms of tool life, a horizontal downwards (−βfN) cutting orientation proved to be preferable, with cut lengths >50% longer than for all other directions (+βfN, +βf and −βf). Evaluation of cutting forces and associated spectrum analysis of results, suggests that the horizontal downwards direction induced the least vibration. As a consequence, the incidence of tool chipping was significantly reduced. The low vibration also contributed to improved workpiece surface roughness, with typical values between 0.19–0.38 µm Ra, as opposed to 0.74–1.18 µm when machining in the vertical downwards (−βf) direction.