Tools & Technologies

By Daren Maynard

Burnishing your way to a smoother finish

For a century, an industrial engineer's home was in production environments – machine shops were where we honed our manufacturing engineering skills. One of the most important skills we learned from this not-so-bygone era is proper tool selection. A task is easier when we have tools that make our machine processes shorter while still maintaining quality. Monaghan Tool Group has teamed up with Elliot Tool Technologies to develop an Outer Diameter (OD) Carbide-Roll Burnishing Tool to handle those tasks. 

With burnishing, hardened ferrous materials can be shined and still gain surface protection because of the cold working (plastic deformation) of the ferrous surface by the burnishing tool. The tool also works with any ductile metal, removing stray surface blemishes from previous machining operations.

With a fast but steady process speed, the tool produces a surface finish between the 4 to 8 Ra/0.1 to 0.5μm/4 to 20 microinch ranges. The highly repeatable burnishing process eliminates hand polishing, grinding and honing because it can be automated on CNC machines. This saves setup and processing time, reducing labor costs while improving machinery utilization. All this adds up to a more productive shop floor.

For example, one New Hampshire job shop needed an exceptional finish on the ID of a 6-foot diameter ring of stainless grade with an average hardness of Rc33. The shop started with a preburnished surface finish of 120 Ra microinches and ended with a single-digit surface finish in a single pass at 450SFM and 0.035 IPR. The shop president estimates that his teams are machining parts in one-tenth the time of its previous processes.

The tool can be used for both internal and outer diameter burnishing operations. The manufacturing partnership makes tools for both left-handed and right-handed individuals. The OD Carbide-Roll Burnishing Tool also comes with various shank lengths (from three-fourths of an inch to 1¼ inches) and roll radii (0.032 inches to 0.125 inches).

Shops should use water-soluble or oil coolants during the machining operations.

The tool's carbide material gives buyers the option of refurbishing or reconditioning the tools to extend their life cycle.

Burnishing is superior to sanding and grinding operations because it does not remove material from the surface. It compresses the surface of the metals, reducing the grooves of the machining microfinished surface to the smoother surface finish. The carbide tool is harder than the metal being burnished; hence it is harder than the metal's yield strength.

The deformation increases the surface density, which contributes to the increased surface, corrosion and fatigue resistances, metal life span and surface hardness.

If burnishing a hard metal (cast iron and heat-treated steel), it requires a finer machined surface before performing the operation, or else it will still have the grooves after burnishing.

More ductile metals (aluminum, annealed steel and brass) can have a rougher machined surface as the carbide burning tool would be able to smooth the imperfections on the surface.

Daren Maynard is a researcher, lecturer and project manager. He is a member of IISE’s Young Professionals group.