Dimensional Instability Studies in Machining of Inconel 718 Nickel Based Superalloys as Applied to Aerogas Turbine Components

Inconel 718 alloy is used extensively in aerogas turbines and this alloy is most difficult to machine and highly prone to dimensional instability after machining. Such detrimental phenomenon poses enormous problem in engine assembly and affect structural integrity. This paper highlights the systematic research work undertaken to study the plastic deformation characteristics of Inconel 718, effect of process variables on machined surface, subsurface and dimensional instability. Also illustrated the technique developed for simultaneous optimization of several process variables such as cutting speed, feed, depth of cut, rake angle and tool nose radius, to control the residual stresses and dimensional instability, within the acceptable tolerance band of the component. Prediction equations were developed for residual stress, dimensional instability, tool life, surface finish and material removal rate. Predicted data were validated experimentally. This paper also presents the qualitative and quantitative data on dimensional instability with specific case studies of jet engine components and clearly illustrates the approach followed to develop technique to control such detrimental effect.