shaping the future of metrology - Brown & Sharpe

Turbine engine overhaul operations:
Inspecting turbine engine components,
particularly blades, is an important
part of not only original equipment
manufacturing, but in overhaul operations
as well. Coordinate measuring machines
are being used more frequently to
perform a number of critical engine
component inspection routines, including
blade inspection, vane and nozzle
segment inspection, and checking dimensional
features for wear and distortion.
According to Bob Lee, Brown &
Sharpe’s Manager of Aerospace Systems
Sales, CMMs offer flexibility, speed, and
improved accuracy over traditional inspection
methods, plus they provide documented
results in a variety of formats.
Shop Floor
Inspection Flexibility
CMMs have been used for the past
two decades to inspect turbine engine
blades as they are manufactured. Dimensional
data from the inspection operation
is used to adjust process parameters before
out-of-tolerance conditions produce
non-conforming parts.
“One of the advantages of coordinate
measuring machines is that they can be
used on the shop floor to inspect components
in a production environment,” Lee
said. “For example, we have an application
where a Brown & Sharpe MicroPCR ®
is used to perform a leading and trailing
edge profile evaluation on a compressor
blade on the shop floor.”
Using a full statistics package in its
MicroMeasure ® IV software, the MicroPCR
quickly computes inspection results
for one section of the blade, while
12 mfg. Shaping the Future of Metrology
CMMs boost efficiency and accuracy
the machine collects dimensional data on
subsequent sections. Blades are held in a
generic fixture that accommodates several
different sized blades.The MicroPCR has
been programmed to identify which
blade is held in the fixture by touching
three points.The CMM also allows the operator
to select specific inspection routines
for as-forged or machined
airfoils. Data
gathering
speed is
approximately
two
points
per second,
much
faster than traditional,
surface
plate tool inspection
methods. Measurement results can be
printed out in numerical or graphic form.
Collecting Large Amounts
of Data Quickly
That flexibility for shop floor process
control measurements also makes CMMs
viable alternatives to traditional inspection
methods in turbine engine overhaul
and maintenance operations. Certain
types of CMMs have the ability to collect
large amounts of data quickly and accurately,
an important consideration in turbine
engine component inspection and a
feature of coordinate metrology that sets
it apart from other types of inspection
techniques.
Brown & Sharpe’s Chameleon
multi-sensor scanning coordinate
measuring machine is designed
especially for
applications that require
gathering
large amounts
of data, and is
particularly
useful in
inspection
routines designed
to
find damaged
edges.
“The machine
is used
to perform fan
blade inspection
using a high-speed,
Coordinate measuring machines
with scanning capability can gather
large amounts of data quickly,
making analysis of contoured airfoil
shapes fast and precise.
closed-loop scanning technique. In a
closed-loop system, the probe automatically
detects changes in surface direction
and adjusts itself to maintain contact
with the part surface,” Lee said.
In this type of inspection routine,
the CMM scans the surface and trailing
edge of the blade, looking for imperfections
that indicate damage.The CMM
performs two scans. The second scan is
about 1 ⁄ 2 mm parallel to the first scan.
Data from the two scans is used by the
measuring system software to compute
the true 3D surface shape of the blade.
During analysis, spline functions are
used to remove the mismatch between
the scanned points and the nominal
points so that deviations from the nominal
to the actual can be calculated.
Separating Bad
From Good
Using coordinate measuring machines
to inspect the dimensions of turbine
blades is significantly faster than using
fixed gaging. A benefit of quick
inspection is that it is possible to isolate
bad parts from good ones, and in some
cases determine why a particular feature
is not dimensionally correct.
In one overhaul and inspection application,
the customer is using a Brown &
Sharpe MicroVal ® PFx ® to check a lowpressure
turbine blade for bend and
twist, the shroud for form, and seals
for radial height.
“The coordinate measuring machine
is programmed to recognize
what stage blade is put into
the fixture simply by checking
a Z height or radius
height,” Lee said. “From this
measurement data, the machine
identifies the blade’s
part number and accesses
the correct inspection program
automatically.”
The MicroVal PFx first measures the
shroud, then graphically shows where
the dimensions should be and where the
dimensional errors are located.The software
then performs a best fit on the
shroud shape.Then the machine measures
the dimensions of the shroud, independent
of the rest of the blade.This
analysis determines whether the shroud
is deformed or if a twist in the airfoil is
causing the shroud to be mislocated. If
the dimensions are out-of-tolerance, the
machine operator sends the blade to the
appropriate repair operation.
“Coordinate measuring machines
give turbine engine component manufacturers
and maintenance operators a
fast, efficient, and flexible method of per-
CMMs give turbine engine builders and
overhaul and repair stations the flexibility to
inspect a wide range of airfoil configurations
without the need for custom fixtures or
gages. Measurement data can be retrieved
in a variety of formats.
forming dimensional inspection of a variety
of parts and part families,” Lee said.
“They can significantly reduce inspection
time and thus contribute to bottom line
profitability.” o
Circle 704 on the READER SERVICE CARD
mfg. The Brown & Sharpe Publication of Precision Manufacturing
13