Roller burnishing is a metal finishing process that involves physical displacement of surface irregularities rather than cutting or grinding. The process involves moving a set or hardened rollers against the metal surface under pressure, thereby causing microscopic blemishes in the metal surface to flatten for a perfect, mirror surface. In addition to the fine finish achieved with roller burnishing, a metal part is also work hardened during the process, thereby leaving its surface better able to withstand wear and corrosion. High degrees of accuracy are also possible because the roller sets are adjustable. Additional advantages of roller burnishing include increased productivity and low overall costs.
Machined metal parts may appear fairly smooth to the naked eye but generally feature surfaces made up of numerous microscopic peaks and depressions which require removal prior to part release. This may be achieved by abrasive polishing, grinding, or honing a part to achieve the required mirror finish. The part may also be roller burnished which is a less aggressive, cold working process that not only delivers a perfect finish but also has several other beneficial effects. Roller burnishing involves moving sets of hardened, tapered steel rollers across the part surface under considerable pressure, thereby causing the metal surface to “flow out.” This flattens out peaks and fills depressions in the part surface and leaves a pristine mirror finish.
The roller burnishing process also has the effect of work hardening the part surface during finishing. Work hardening refines the crystalline structure of the metal surface at an atomic level, thereby removing internal pockets and fissures and increasing the surface hardness of the part by between 5 and 10%. This effect is generally effective up to depths of .001 to .030 inches (0.25 to .762 mm). This leaves the surface tough, dense, and extremely resistant to wear, metal fatigue, and corrosion and adds significantly to the overall life of the part.
Burnishing does not surrender anything in terms of part dimension control either because the rollers typically feature easy to set, precise adjustments. Another advantage of the roller burnishing process is an increase in productivity resulting from its latent simplicity. Burnishing requires less steps to complete; once the tooling is set up, thousands of parts can be produced by unskilled operators without any adjustment. Capital outlay on roller burnishing installations are typically lower than other processes due to the reduced number of tools involved. Burnishing also features far longer average tool life values than those returned by other finishing methods, thereby further adding to the cost efficient nature of the process.