Burnishing of a non-axisymmetric curved surface with a CNC lathe

The present study proposes a novel burnishing process called non-axisymmetric curved surface (NACS)-burnishing using a lathe that can machine a non-axisymmetric curved surface, such as a cam for internal combustion engines, with high efficiency. In the present paper, the offset in the Y-direction, which is a unique machining condition for NACS-burnishing, is first described. In this machining method, since the contact point of the burnishing tool changes continuously, the apparent rake angle of the burnishing tool also changes continuously, and its sign affects the finished surface properties. Therefore, it will be shown that the rake angle can be negative in the entire machining region by setting an offset of the tool in the Y-direction based on the geometrical relationship between the tool and the workpiece, and the conditional equation of the rake angle is derived. Next, actual NACS-burnishing experiments are carried out, and the effectiveness of the method is verified in terms of surface roughness and residual stress with the availability of the offset in the Y-direction. In particular, although tearing occurs when there is no offset, it is confirmed that the torn surface can be eliminated by the offset. Thereby, a surface roughness Ra of less than 0.2 mu m and a compressive residual stress of over 200 MPa can be obtained for hardened steel with HRC60, which has sufficient surface properties.