CASE sm Processing

New York Shot peening Chemically Assisted Surface Engineering, or CASE sm, is a two-stage process developed by Metal Improvement Company to extend a component’s surface fatigue life beyond that provided by shot peening alone. CASE consists of shot peening followed by isotropic finishing. The isotropic finishing step of the CASE process improves traditional vibratory honing techniques by the addition of mild chemicals, which removes the asperities left from shot peening and retains shallow micro-indentations for lubricant retention.

CASE is ideal for surfaces that require both excellent fatigue strength and surface finish due to contact loading. CASE has proven effective in improving resistance to pitting and micro pitting of gear teeth flanks, failure mechanisms that limit the performance of many gear designs. For example, transmission gears utilized in aerospace, automotive racing and off-highway applications are required to run for many years under high root bending loads and tooth flank contact loads. CASE has proven successful for use in all these industries.

Surface finishes of 10 micro-inches (Ra) or better are attainable with CASE on carburized gears. The figure below shows a typical roughness profile of a carburized gear after shot peening and also after the isotropic finishing portion of CASE.

Shot Peening California
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The “peak to valley” of the shot peened finish is ~ 2.9 microns. After isotropic finishing, performed as part of CASE, this improves to ~ 0.6 microns.