Finite Element Simulation of Machining a Nickel-based Superalloy - Inconel 718

Abstract

Inconel 718 is one of the difficult-to-machine materials and is mainly used for aerospace applications. Cutting speed in machining Inconel718 is limited by shear localization observed at cutting speed above 61 m/min. Adiabatic shear failure is considered as root cause for chip segmentation. Johnson- Cook material model is used to represent strain, strain rate, and temperature dependence of strength of Inconel 718. Recht's criterion for catastrophic thermoplastic shear failure is applied to study shear instability in machining. A commercial finite element software with 2-dimensional explicit code and Lagrangian formulation (AdvantEdge) is used for finite element simulations. A user subroutine is developed to incorporate Johnson-Cook material model and Recht's failure criterion in the main code. Finite element simulations are run for a range of cutting speeds from 30.5 to 183.5 m/min. Machining is analyzed at various rake angles (-300 to 450) and feed rates (0.25-1.0 mm/rev). Results of the simulations are compared with machining test data and are found in close confirmation. Chip formation mechanism is found to be in confirmation with experimental observations reported in the literature. Effects of machining conditions on cutting and thrust forces, shear zone and tool rake face temperatures, and equivalent plastic strain in primary and secondary shear zones are reported.