Chemically accelerated vibratory finishing
enhances the performance of components
that are subjected to metal-to-metal contact
or bending fatigue. When the resultant
surface has an Ra of approximately 3.0 µin.
or less and a non-directional surface pattern,
it will be referred to here as an Isotropic
Superfinish (ISF). Such surfaces are unique
in their remarkable ability to reduce friction1,
2, 3, 4, wear1, 2, 3, 4, noise5, as well as contact3,
6, 7, and dynamic fatigue8 when compared to
similar surface finishes produced by other
techniques. There has been increasing
interest in applying this process to gears
since industry is being driven to produce
higher cycle life gears at increased power
densities.
ISF is produced in vibratory finishing bowls
or tubs. A proprietary active chemistry is
used in the vibratory machine in conjunction
with high-density, non-abrasive ceramic
media9. When introduced into the machine,
this active chemistry produces a stable, soft
conversion coating on the surface of the
metal part(s) being processed. The rubbing
motion across the part(s) developed by the
machine and media effectively wipes the
conversion coating off the peaks of the
parts surfaces, but leaves the valleys
untouched. (No finishing occurs where
media is unable to contact or rub.) The
conversion coating is continually re-formed
and rubbed off during this stage producing a
surface smoothing mechanism. This process
is continued in the vibratory machine until
the surfaces of the part(s) are free of
asperities. At this point, the active chemistry
is rinsed from the machine with a neutral
soap. The conversion coating is rubbed off
the part(s) one final time to produce the ISF
surface. In this final step, commonly referred
to as burnishing, no metal is removed.
The ISF process removes more metal from
the region of a part where higher media
contact occurs. Therefore, more stock will
be removed from the addendum than from
the root fillet of a gear. Naturally, gear
engineers and designers question whether
the ISF process will negatively affect gear
geometry especially for AGMA Q11 and
higher. This paper presents before and after
(ISF processed) metrology data that is
representative of the 11 AGMA Q13 spiral
bevel gears and pinions examined during
this study. It was concluded that the ISF
processed gears and pinions maintained
their Q13 rating.