Isotropic Finishing (Superfinishing)

CASE sm, is a two-stage process developed by Metal Improvement Company (MIC) to extend a component's surface fatigue life beyond that provided by shot peening alone. CASE sm consists of shot peening followed by isotropic finishing. The isotropic finishing improves traditional vibratory honing techniques which remove the asperities left from shot peening and machining but retains shallow micro-indentations for lubricant retention.

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

Surface finishes of better than 0,25 microns (Ra) are attainable with CASE sm on carburized, nitrided and induction hardened gears.

Controlled Shot Peening is the bombardment of a surface with small high quality spherical media called shot. Each piece of shot striking the metal acts as a tiny peening hammer imparting a small indentation or dimple on the surface.  The action of impinging the surface yields the material in tension but further movement is restrained by the core and a surface residual compressive stress results. The magnitude of the compressive stress is directly related to the base materials yield strength and is approximately equal to 80% of that value in compression.

Secondary processing by Shot Peening (Dual Peening) at a lower intensity and modified shot size will have the effect of reducing roughness, increasing the surface stress and increasing the cold work of the near surface area will give additional benefit.

Key Features

  • Surface reduction to mirror like finishes
  • Optimum surface roughness and stress characteristics
  • Reduced contact/surface fatigue
  • Increased lubrication retention, heat transfer and reduced noise
  • Good rounding ability to sharp edges for ease of handling and assembly
  • Reduced manufacturing times and production costs

Potential Applications

Isotropic Finishing (Superfinishing)Isotropic Finishing (Superfinishing)