Modelling of the ball burnishing process with a high-stiffness tool

This paper deals with the problem of forming a surface roughness profile of a machined surface and a definition of the optimal depth of penetration in ball burnishing which would allow minimization of surface roughness. The assumptions, which have been numerically and experimentally verified, claim that maximum surface quality, i.e., minimum surface roughness, Ra, is achieved when the depth of ball penetration into the workpiece material is approximately equal to the maximum peak height, Rp. For the purpose of numerical simulations, a surface roughness model based on milling kinematics was used. Numerical simulations and the used roughness model support the claim that penetrating with a stiff tool up to the mean line of the roughness profile yields best surface quality. The authors maintain that ball penetrations, which exceed Rp, cannot significantly improve surface quality. Furthermore, the phenomenon of profile peak deformation is substantially clarified. The analysis of internal stresses within the workpiece after ball burnishing allowed a relationship to be established between internal stress distribution along the depth of the hardened layer and ball penetration depth.