Sequential multistage deep rolling under varied contact conditions

Abstract

It is possible to induce compressive residual stress, strain hardening and reduce the surface roughness by applying deep rolling to metallic surfaces. The resulting enhancement of surface integrity is based on the mechanical impact during the deep rolling process (internal material loads). For a single contact as well as multiple contacts with identical contact conditions, a good approximation for the correlation between the process parameters and the resulting material modification was achieved in previous works. By regarding the equivalent stresses, based on Hertzian equations, the modifications by means of the residual stresses were assessed. This paper shows an approach to describe the resulting material modification when using multiple contact stages in a deep rolling process under varied contact conditions. AISI 4140 is processed. For the generation of linear deep rolling tracks resulting from multistage deep rolling, the maximum internal material load is held constant also when varying the ball diameter between the different contacts. Three different levels of internal material loads are applied with two ball diameters and three different total numbers of contacts per linear track. The analysis of the material modifications is based on XRD measured residual stresses and geometrical track descriptions.