Controlled Shot Peening has long been recognized as a very effective process to prolong the fatigue life of all types of
gears. Three recent innovations have extended the state of the art: 1) by a process that provides a smooth surface after
peening to increase the resistance to surface fatigue; 2)by a coupon system that makes possible actual X-Ray diffraction
curves to monitor production shot peening; and 3)by a computer program that permits a reasonable prediction of residual
stress curves.
CA.S.E.sm is an acronym for Chemically Assisted Surface Engineering. Frequently, when the bending fatigue life of
very high cycle gears has been increased by shot peening the tooth roots, the next mode of failure is surface fatigue or
piting of the contact faces. There has been a need, particularly for automotive and aircraft transmissions, to extend the
surface fatigue life beyond that provided by shot peening alone and smoothing the surface after peening has been found to
be very effective.