Residual stress profiles induced by abrasive flow machining (AFM) in 15-5PH stainless steel internal channel surfaces

Abstract

Surface integrity is an important factor to select finish process of a part’s surface and evaluate its quality. In particular, residual stress is one among important parameters to affect its fatigue life. Abrasive flow machining (AFM) has long been considered to be an effective surface finish process of external surfaces with complicated geometries or conformal cooling channels. Surface topography and surface roughness produced by AFM were shown to be comparable to those by grinding. However, more research on residual stress induced by AFM needs to be done. Different surface topographies after AFM with abrasive media having different abrasive size and concentration have been reported. Three different wear mechanisms, such as rubbing, ploughing, and cutting, have been known to be responsible for creating those surface topographies and their material removal. Therefore, in this study, 15-5PH stainless steel internal channel surfaces were created by boring. Then, their surfaces were finished by AFM with different abrasive size and concentration. Their material removal and surface topographies showed a big difference. Surface topography analysis reveals their possible wear mechanisms and movements, which can result in residual stress profiles in both directions – parallel and perpendicular to AFM flow. Big abrasive grains (54 grit size) left frequent pile-ups and curved flow lines on the workpiece surface, indicating that significant ploughing mechanism and rolling movement occurred during AFM. As a result, its compressive residual stress in the direction perpendicular to AFM flow gradually decreased with respect to the workpiece depth. On the other hand, clear abrasion and straight flow line were observed on the workpiece surface after AFM with MV65%-150 having medium grit size and highest concentration, suggesting significant cutting mechanism during AFM and the least plastic deformation among AFM finished surfaces in this study. Consequently, its compressive residual stresses in the both directions decreased sharply as the workpiece depth increased. AFM is characterized by its low material removal rate, however, it can induce compressive residual stress on the finished surface because its process temperature rise is not significant compared to other finish processes, such as grinding and turning.