| Description |
Manufacture of a component typically involves a long sequence of manufacturing processes. At the end of that sequence is the finishing process, which defines the surface state of a component. It is well known that the surface of a manufactured component has an effect on its structural integrity, hence the term surface integrity. This research systematically investigates surface integrity with a focus on the metal cutting process. Specifically, this research investigates the effects of the wiper tool nose radius on the surface integrity of the 2024-T351 aluminum alloy with facing and turning machining processes. The research is broken into two phases. Phase 1 involves a detailed investigation of the surface state through examination of metal chips, surface texture, residual stress, and machining forces. Phase 2 involves constant amplitude fatigue loading of surfaces equivalent to those from Phase 1. Phase 1 of the study showed that the wiper tools yielded a generally lower surface roughness than standard geometry cutting tools. However, the surface profiles yielded by the wiper tools showed additional plastic deformation that was not predicted by geometrical models for the surface profiles. This was attributed to a chip side flow phenomenon that was found to be unique to the chips yielded by the wiper tools. As part of the surface texture study, a normalized kurtosis parameter was developed to describe the deviation from theoretical, geometry-derived surface profiles. Residual stresses measured as part of Phase 1 showed a tensile residual stress profile for 2024-T351 aluminum for all studied cutting tool, cutting fluid, and machining conditions. However, the wiper tool generally yielded less tensile surface residual stresses than a standard cutting tool. It was also found that varying the cutting fluid conditions had no significant effect on the residual stress profile yielded by the cutting process. Phase 2 of this study was marred by undesirable fretting failures at the fatigue specimen grip interface, so relevant fatigue lifetimes of the surface states in Phase 1 were not captured. Potential solutions to this issue have been provided along with the details necessary to perform Phase 2 as part of a future study. In response to the lack of Phase 2 fatigue data, much of this thesis is devoted to providing detailed frameworks and guidance to aid in the future study of metal cutting and other finishing processes as they relate to surface integrity. |
