Analytical prediction of surface morphology and residual stress induced by milling and ultrasonic surface rolling

Shape-controlled milling and integrity-controlled ultrasonic surface rolling processing (USRP) is an effective sequential machining method that enhances the surface integrity of metallic materials by reducing surface roughness (SR), increasing compressive residual stress (CRS), and improving fatigue resistance. However, accurately predicting the surface morphology and CRS during multi-process sequence remains a challenge. This study establishes analytical predictive models for the surface morphology and CRS of TC21 titanium alloy after milling and subsequent USRP, explicitly considering the initial surface state induced by milling. A surface morphology prediction model for USRP was then developed, incorporating the initial milled surface topography, revealing that USRP effectively eliminates surface peaks but does not fill concave valleys, necessitating the consideration of initial surface conditions for accurate predictions. By integrating milling-induced initial residual stress fields (IRSF), hardness variations, and yield strength modifications, an analytical model for CRS prediction based on Hertzian contact theory and elastoplastic deformation was formulated. The accuracy of the proposed models was verified through finite element simulation and experiment measurements. The findings highlight the necessity of incorporating initial surface integrity when modeling multi-process machining and provide a foundational approach for optimizing surface integrity in titanium alloy components.