BURNISHING | S.C.A.M.I.® Roller Burnishing Systems
Roller Burnishing Overview
The Principle of Roller Burnishing Roller burnishing is a cold-working process that produces a fine surface finish. The planetary rotation of the hardened rolls creates pressure over a metal surface. Unlike cold rolling, which produces large sectional changes, roller burnishing involves cold-working on the surface of the workpiece to improve the surface structure. All machined surfaces consist of a series of peaks and valleys, all having irregular height and spacing. The plastic deformation created by roller burnishing is a displacement of the material in the peaks. When under pressure, the material in the peaks flows into the valleys. During the process, tool marks and irregularities are rolled out, resulting in a mirror-like finish with a tough, work-hardened surface that is also wear and corrosion resistant.
BURNISHING SPECIALS • The stresses formed on the material during the compression decrease toward the center. These stresses reach approximately 1mm below the surface. This increases the surface hardness. The Process • The first contact with the machined surface occurs in Section A. • Plastic deformation occurs in Section B as the yield point of the surface is exceeded. • Section D is the pressurized depth. • Once the material endures the maximum compressive strain (Section C), it starts relieving elastically (Section E) through the finishing zone. • This leaves a smooth surface and a compressive residual stress of significant peak value. Advantages of Roller Burnishing: Metallurgical Properties • Grain structure is condensed and refined. • The compacted surface is smoother, harder, and more wear resistant than ground or honed surfaces. • The process reduces surface porosity and also removes scratches that could hold reactive substances or contaminants. This increases the corrosion resistance . • Depending on the material, the surface hardness can be increased by as much as 10 points Rockwell C . This may eliminate the need for heat treatment. • The plastic deformation induces residual compressive stresses in the surface of the part. This increases the strength properties and fatigue life of the part because any forces on the part must overcome these residual stresses, as well as the tensile strength of the materials, before fatigue conditions occur. THREADING
Advantages of Roller Burnishing: Surface Finish • Creates a high finish to any machinable metal.
• Surfaces that are bored, reamed, or turned to 125 microinches or more can be finished to 4 microinch CLA or less in one pass (at feed rates of 125 to 300 mm/min). • Roller burnishing replaces grinding, honing, lapping, and other expensive secondary operations. • Tool marks are rolled out.
A B C
Compressive Residual Stress
Tensile Residual Stress
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