Laser assisted machining of Inconel 718 super alloy

This research work assesses the effect of Laser Assisted Machining (LAM) on the machinability of Inconel 718 using a triple layer coated carbide and a sialon ceramic tool. This study was motivated by issues related to poor machinability of IN718 under conventional machining operations. In this work a focused Nd:YAG laser beam was used as a localized heat source to thermally soften the workpiece prior to material removal. Finishing operations were assumed throughout the experiments. Optimization screening tests were performed over a wide range of cutting speeds (ranging from 100 to 500 m/min) and feeds (ranging from 0.125 to 0.5 mm/rev). Results showed a significant drop in all three components of cutting force when thermal softening caused by the laser power was in effect. These tests yielded the optimum cutting speed and feed to be 200 m/min and 0.25 mm/rev for the coated carbide and 300 m/min and 0.4 mm/rev for the ceramic tool. Under these optimum conditions tool life tests were carried out. Drastic increase in terms of the material removal rate (MRR) was demonstrated under LAM conditions as compared to conventional machining. A nearly %300 increase in MRR was established for the coated carbide tool while slightly reducing tool life, mainly because the coatings offering thermal and wear protection could not withstand the high temperatures associated with LAM. Nearly %800 increase in MRR for the ceramic tool was achieved while improving tool life (about %50). In all cases, improvements in surface finish and surface integrity were observed. The dominant mode of tool failure was observed to be average flank wear for all tools tested. However, the coated carbide tool exhibited signs of chipping and flaking in the coatings. The morphology of the chips produced was analyzed and it was shown that temperature and increased chip thickness were the main causes of transition from steady state to shear localized chip structure. Shear localized or sawtooth chips tended to form at high temperatures when maximum undeformed chip thickness reached 140 microm.