Tool life and tool wear in taper turning of a nickel-based superalloy

Due to their high ductility and strain hardening coefficient, high mechanical strength and hardness even in high temperatures, chemical affinity with almost every tool material, and low thermal conductivity, nickel-based superalloys are known to present very low machinability. Some researchers point out that taper turning may prolong tool life as ramping may distribute tool wear along tool edge, avoiding the presence of notch wear in the end of the depth of cut, which usually occurs in the tools used in turning of these alloys. In this work, tool life, tool wear, and resulting surface roughness of Inconel 625 were evaluated for taper turning in comparison with straight turning. In taper turning, double feed was tested to compensate metal removal rate reduction (since in this operation, the feed length is doubled), and in order to avoid roughness increase caused by the higher feed, a wiper tool was used. Results show that taper turning was not successful in terms of tool life, although the furrowing mechanism of the tool coating caused by the hard burr formed, that leads to notch wear, was avoided. This mechanism was replaced by strong adhesion that promoted rapid and wide flank wear. Feed increase has also produced microchipping due to the extra load on the tool edge. Although wiper tool had provided better finishing when high feed was employed, conventional tool seems to be more suitable for tapering considering tool life.