Page 24 - MetalForming May 2012

Use Steel Media to
Burnish, Deburr
Clean
Parts-finishing experts weigh in on the growing trend toward vibratory finishing with steel media, and the adoption by stampers of continuous- flow finishing equipment to eliminate secondary operations and reduce costs.
BY BRAD F. KUVIN, EDITOR
and
As described on the website of Advanced Finishing Technolo- gies, Grand Rapids, MI, mass fin- ishing is commonly used to deburr, burnish, clean, degrease, descale, dry and provide pre-plate or pre-paint fin- ishes. Parameters for metalformers to consider when specifying a mass-fin- ishing process: workpiece material, size and shape; media composition and compound type; finishing-equip- ment type and workload (batch or con- tinuous); and finish requirements.
during finishing, damage can result to delicate stampings from impingement and denting. Conversely, smaller media will produce smoother finishes.
Burnishing, Deburring and Deflashing
Mass finishing refines the surface texture of a part, measured (in micro-in.) as the average distance from the sur- face’s peaks to its valleys. The degree of surface texture is expressed as RMS (root mean square) or Ra (roughness average). A higher micro-finish trans- lates into a rougher surface and, con- versely, a lower number equates to a smoother surface.
Burnishing smoothes the surface peaks into the valleys, producing a highly reflective finish. The operation uses nonabrasive media, or metallic media with a viscous lubricating com- pound. Burnishing typically occurs with a dense media such as steel; small-
er-sized media provides the highest luster but not necessarily more work. Media that has been worn and is free of sharp edges or corners works best. Acidic compounds generally result in the brightest surfaces, although selection always should be determined on a case- by-case basis, say Terry
A part’s shape can restrict normal finishing media contact, particularly recessed areas and odd-shaped parts. Media must be shaped to optimize sur- face contact. And while large media generally will remove more material
Burnishing of stamped parts and assemblies
smoothes the surface peaks into the valleys, produc-
ing a highly reflective finish. Finishing the weldment shown here involved removing loose weld spatter and discoloration, accomplished during a 15-min. process using steel media with an acidic cleaner.
22 MetalForming/May 2012
www.metalformingmagazine.com