Feasibility of producing optimal surface integrity by process design in hard turning

There is a growing demand in hard turning industry to produce favorable surface integrity (surface finish, microstructure, microhardness, and residual stress) for improving component performance. Suitable process parameters will produce certain favorable surface integrity or at least avoid detrimental phase transformations to component performance. It is not clear if surface integrity is controllable using a set of selected process parameters. This research is to study the feasibility of obtaining four distinct types of surface integrity, which may have potential dramatic effects on fatigue life of hard-machined components. This study identifies surface integrity first and follows with the necessary conditions possible to create it in hard turning. Favorable surface integrity for optimal fatigue life can be produced using small feeds and sharp cutting tools. From the process point of view, tool wear is the dominant factor to promote white layer formation and yields a large variance of surface roughness, which may significantly deteriorate component life. A white layer could be more than 30% harder and a dark layer about 60% softer than the bulk material.