An experimental study of the effect of machining variables on the surface integrity of Inconel 718 superalloy

The surface integrity of Inconel 718 superalloy was investigated in orthogonal metal cutting tests under various cutting conditions. Inconel 718 hot rolled sheet, Rockwell hardness R;A comprehensive analysis of surface integrity of the machined surface was made quantitatively based on the surface and subsurface residual stress, plastic deformation and microhardness and qualitatively based on the surface texture and subsurface microstructure. Accurate grids (393.7 lines/ cm) were developed through photofabrication methods for plastic strain analysis. Tool forces and chip thickness were measured and shear plane angle and temperature were calculated.;Tool forces decreased and shear angles increased both with increased cutting speeds and reduced tool-chip contact lengths. Shear stress on shear plane was independent of test conditions investigated. Continuous chips were produced under all the conditions. Surface residual strains and the depth of deformed zone decreased with increased cutting speeds and reduced depth of cut and reduced tool-chip contact length. Residual tensile stress was produced in all the cases, which increased with cutting speed up to 0.63 m/s beyond which it remained constant, decreasing slightly at 1.61 m/s. Lubrication was effective at lower cutting speeds in reducing the thermal stresses. Surface region hardness increased to R;Surface damage in the form of deep short grooves and shallow long grooves were noticed at lower cutting speeds and severely fractured surfaces were observed with dry cutting. Overall surface integrity was better with lubricant, low depths of cut, controlled contact length tools and at high cutting speeds. The extensive experimental data also helped the validation of a parallel predective study involving finite element methods in metal cutting.