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 an enormous problem in engine assembly and affects structural integrity. This paper highlights the systematic research work undertaken to study the plastic deformation characteristics of Inconel 718, and the effect of process variables on machined surface, subsurface, and dimensional instability. Also illustrated is 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 it clearly illustrates the approach followed to develop a technique to control such detrimental effect. [S0742-4795(00)00901-7]

Aero gas turbine components made of Inconel 718 superalloy revealed significant dimensional instability after machining. The dimensional instability is a manifestation of alterations in residual stresses and microstructure, which are influenced by machining parameters. This paper presents a simultaneous optimization technique used to control the dimensional instability in turning operation. Empirical equations are established for predicting surface residual stresses, surface finish, dimensional instability and tool life using response surface methodology. Experimental results show a strong correlation between residual stresses and dimensional instability. A desirability function approach is used to optimize the multiple responses and machining parameters are derived for practical applications. Inconel 718 test specimen and jet engine components machined with optimal cutting parameters show dimensional instability within the acceptable tolerance band. [S1087-1357(00)01704-4]

Machining of aero-gas turbine components made of titanium alloys, using different combination of tools, cutting fluids and machining parameters revealed two important characteristics namely, chemical reactivity and dimensional growth. The former is pronounced when machined with carbide tools using Sulphur based cutting oils. The reactivity was not noticeable when machined either with CBN or ceremet tools, contrary to the reports in the literature. This mechanism of chemical reaction has been studied including the development of microcracks at 400°F. The other phenomenon of dimensional growth is also anlysed in detail and machining parameters to reduce this growth are arrived at. The heat treatment is also envisaged to help in depriving of this detrimental dimensional growth by relieving the machining stresses. Also the scope for further research in this area is clearly defined.

This paper highlights an attempt at evolving a computer aided manufacturing system on a personal computer. A case study of an advanced technology jet engine component is included to illustrate various outputs from the system. The proposed system could be an alternate solution to sophisticated and expensive CADICAM workstations.

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.