Surface integrity after internal load oriented multistage contact deep rolling

Abstract

Mechanical treatment by deep rolling generates an improvement of the surface integrity by inducing compressive residual stress, strain hardening as well as a reduction of the surface roughness. The resulting material modification is based on the plastic deformation of surface and subsurface layers caused by the movement of a deep rolling tool across the workpiece surface under defined conditions in terms of rolling force, ball diameter and number of contacts. A correlation between the process parameters and the surface integrity to predict the modification in the workpiece is of limited validity. It is more useful to consider the internal load during the mechanical treatment in form of stress fields occurring during the process. This paper shows an approach to describe the internal load based on the hertzian stress in combination with the elastic model considering the multiple contacts in a deep rolling process. A defined variation of process parameters regarding the internal loads and the number of contacts was performed. It is shown that the correlation between internal loads and material modification (process signature) offers a good approximation to describe the surface integrity of workpieces after multistage contact in deep rolling processes. The description of material modification based on equivalent stress depth profiles enables the prediction of maximum of compressive residual stress after multistage deep rolling.