Burnishing (metal)

Burnishing is a metalworking process used to smooth and polish a metal surface through plastic deformation. It involves rubbing a hardened tool, often made of steel or tungsten carbide, against the workpiece with significant pressure. This action flattens the surface asperities (microscopic peaks and valleys), reducing surface roughness and increasing reflectivity.

Unlike abrasive processes like grinding or polishing, burnishing does not remove any material from the workpiece. Instead, it redistributes the existing surface material. This makes it a cold working process that can also increase surface hardness and improve fatigue resistance due to the introduction of compressive residual stresses.

Burnishing is commonly used for:

• Improving the surface finish of machined parts.
• Sealing porous materials.
• Hardening surfaces to increase wear resistance.
• Improving the fit between mating parts, such as bearings and shafts.
• Applying decorative finishes.

The effectiveness of burnishing depends on factors such as the material being worked, the tool material and geometry, the applied pressure, the speed of the process, and the use of lubricants. Different burnishing techniques exist, including roller burnishing, ball burnishing, and slide burnishing, each suited to specific applications and workpiece geometries.