Surface integrity when machining age hardened Inconel 718 with coated carbide cutting tools

Considerable attention has been given to the use of ceramic cutting tools for improving productivity in the machining of heat resistant super alloys (HRSA). However, because of their negative influence on the surface integrity, ceramic tools are generally avoided particularly for finishing applications. As a result the main high end manufacturers are more or less dependent on carbide cutting tools for finishing operations. Still the improper use of carbide cutting tools can also result in poor surface integrity. The objective of this investigation is to develop a set of guidelines, which will assist the selection of the appropriate cutting tools and conditions for generating favorable compressive residual stresses. This paper specifically deals with residual stresses and surface finish components of surface integrity when machining (facing) age hardened Inconel 718 using two grades of coated carbide cutting tools specifically developed for machining HRSAs. The cutting conditions were obtained from investigations based on optimum tool performance. The effect of insert shape, cutting edge preparation, type and nose radius on both residual stresses and surface finish was studied at this optimum cutting condition. This investigation, suggested that coated carbide cutting tool inserts of round shape, chamfered cutting edge preparation, negative type and small nose radius (0.8 mm) and coolant will generate primarily compressive residual stresses.