Analytical prediction and experimental verification of surface roughness during the burnishing process

Burnishing is a superficial plastic deformation process used as a surface smoothing and surface enhancement finishing treatment after some machining processes to generate a compact and wear-resistant surface for longer and efficient component life.In this study, the smoothing mechanism of burnishing is established, in which the geometries of burnishing tool and workpiece, the microscopic topography of the machined surface and the mechanical properties of workpiece are taken into consideration. The elasto-plastic deformation law of the cross-section of a stripy asperity is established by the solutions to the Boussinesq–Flamant problem and then by the slip-line field theory. The expressions describing the relation between surface roughness and burnishing force are derived using the Winkler foundation assumption where the shear between adjacent cross-sections is ignored.The expressions reveal that the decrease of surface roughness is proportional to burnishing force to the 2/3 power in roller burnishing and to the 1/2 power in ball burnishing. The proportional constants are only determined by the yield stress of workpiece with geometrical parameters held constant, and have nothing to do with the elastic constants such as Young's modulus and Poisson's ratio used in Hertz theory. The lowest surface roughness and the optimum burnishing force can be obtained. The lowest surface roughness is proportional to the initial surface roughness, and burnishing can decrease the surface roughness of workpiece up to about 75% to 87.5% which depends only on the semi-angle of asperity. The above adopted assumptions, the conclusions worked out and the predicted results are verificated by the experiments and related literatures.