Burnishing is a non-subtractive manufacturing process in which pressure is applied to the surface of a workpiece by burnishing tools in the form of rollers, balls, etc. The strengthening or hardening of the surface layer of the workpiece is achieved by the mechanical changes caused by the burnishing process.
During burnishing, the surface layer of the workpiece is plasticised. At the point of contact, the burnishing force induces contact stresses in the surface layer of the material. When the value of these stresses exceeds the yield point, the material near the surface begins to flow. The elastically deformed part of the surface layer then interacts with the plastically deformed part of the layer, causing compression and displacement.
With regard to the nature of the action of the burnishing tools on the surface, the burnishing process is divided into:
static – the burnishing forces are invariable and act on the workpiece through the burnishing tools, which are in continuous contact with the workpiece. Static burnishing techniques include:
- sliding burnishing – a smooth burnishing tool (usually a diamond) is pressed against the surface of the workpiece with an appropriate force and moves along its surface, causing sliding friction and plastic deformation of surface irregularities in the burnishing zone.
- rolling burnishing – during the process, the burnishing tools (discs, balls, rollers) roll along the workpiece surface under the load of statically acting thrust forces.
dynamic – the burnishing forces change periodically and the burnishing tools are not in continuous contact with the workpiece. Among the dynamic burnishing techniques, the following can be distinguished:
- concentrated impact burnishing – this process involves the cyclical concentrated impact of rotating burnishing tools in the form of balls (also discs or mandrels) on the surface of the workpiece.
- dispersed impact burnishing – this process involves the impact on the surface of the workpiece with a stream of balls moving at high speed, delivered by a rotor ejector or compressed air.
