Influence of pre-machining on the surface integrity after processing by mechanical surface treatment

The functional performance of workpieces is strongly influenced by the surface and subsurface properties which are affected and can be adjusted by manufacturing processes. The finishing process determines the final form and the surface roughness of a machined component. Nonetheless, the final surface integrity is a result of the total material modification along the whole process chain. Previous manufacturing processes affect the initial residual stress state and the work hardening in the subsurface layers. Furthermore, the resulting material modifications may vary depending on the initial or pre-machined material state. In this paper, the influence of pre-machining processes on the resulting surface integrity after mechanical finishing processes is analyzed. As finishing processes, deep rolling and so called “grind-strengthening” with varied process parameters are chosen. The initial material state is generated by heat treatment followed by pre-machining using three different processes: turning, grinding and electrochemical etching leading to strong variations in the surface-near properties. For the analysis of the influence of initial material state residual stresses as well as the shear stress were considered. Both processes, deep rolling and grind-strengthening, achieve comparable compressive stresses at the surface, whereby the residual stress states can deviate for constant parameters under variation of pre-machining. The residual stress depth profiles show a significant influence of the initial state for the grinding process but minor influence for deep rolling. The investigations contribute to a better understanding of mechanisms causing material modification during mechanical surface treatment and along the process chain.