shot peening residual stress - Metal Improvement Company

C H A P T E R T W E L V E
C ONTROLL ING THE PROCESS
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PEENSCAN ® (Coverage Verification): Determination of shot peening coverage can be fairly easy when
softer materials have been peened as the dimples are quite visible. A 10-power (10x) magnifying glass is
more than adequate for these conditions. In many applications determination of coverage is more
difficult. Internal bores, tight radii, extremely hard materials, and large surface areas present additional
challenges in determining coverage.
Metal Improvement Company has developed the PEENSCAN ® process using DYESCAN ® fluorescent tracer
dyes for this reason. PEENSCAN ® is ideal for measuring uniformity and extent of coverage for difficult
conditions. The whitish-green dye is not visible under normal lighting conditions and must be viewed under
a UV (black) light.
The coating can be applied by dipping,
brushing, or spraying the part under analysis.
As the coated surface is impacted with peening
media, the impacts remove the fluorescent,
elastic coating at a rate proportional to the
actual coverage rate. When the part is viewed
again under black light non-uniform coverage is
visibly evident. The shot peening process
parameters can then be adjusted until the
PEENSCAN ® procedure verifies complete
obliteration of the area of concern.
Figure 12-9A through 12-9C demonstrate the
PEENSCAN ® concept. The figures are computer
simulations of a turbine blade with the green
representing the whitish-green dye (under black
light conditions). As the (green) dye is removed
from peening impacts, the (blue) base material
is exposed indicating complete coverage.
Figure 12-9a
PEENSCAN ®
Coating Prior
to Shot
Peening
The PEENSCAN ® inspection process has been found to be clearly superior to using a 10-power glass.
A U TOMATED S H OT P E E N I N G E Q UIPMENT
Throughout the world, MIC service centers are equipped with similar types of automated shot peening
equipment. When required, this network allows for efficient, economic, and reliable transfer or duplication
of shot peen processing from one location to another.
MIC also offers computer monitored shot peening (CMSP). CMSP is for components that require
additional documentation above our standard Certificate of Shot Peening as proof of shot peening
specifications (AMS-S-13165, MIL-S-13165C, AMS 2430, etc…). Parts that are designed with the intent to
employ the fatigue benefits of shot peening should use the computer controlled processes of AMS 2432.
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Figure 12-9b
Partial
Removal of
PEENSCAN ®
Indicating
Incomplete
Coverage
Figure 12-9c
Complete
Removal of
PEENSCAN ®
Indicating
Complete
Coverage