Engine Titanium Consortium - Center for Nondestructive Evaluation ...

Surface Finish Studies
The plans for the surface finish study have been refined during this reporting period with
significant input by the three OEMs. GE has primary responsibility for this activity and will
initiate the execution of the plan. While the plan is not quite finalized, the sequence of events
is as follows –
(1) GE has FBHs placed in the pancake, performs UT characterizing of the holes, applies the
1 st set of machining passes, acquires profiles of the machining grooves, and performs UT
with specified transducers,
(2) P&W performs UT inspection of the 1 st machined surface, applies the 2 nd set of machining
passes, and performs UT inspection of the 2 nd machined surface,
(3) GE acquires profiles of the 2 nd machined surface, and performs UT inspection of the 2 nd
machined surface,
(4) Honeywell performs UT inspection of the 2 nd surface, applies the 3 rd set of machining
grooves, and performs UT inspection of the 3 rd surface,
(5) GE performs UT inspection of the 3 rd surface finish, and acquires profiles of the 3 rd
machined surface,
(6) Data is analyzed by the team to relate surface finish conditions to near surface resolution
and to signal to noise ratio. Hopefully, a relationship can also be established between
feedrate and front surface signal ringdown.
Some of the details that are yet to be worked out include identification of the transducers to be
used, which feedrates to use, what is the minimum UT data that should be collected at each
site, and how should the machinists requirements be controlled/recorded.
Beam Properties
A goal of subtask 1.3.2 is to design an inspection scheme that achieves #1/2 FBH sensitivity in Ti
forgings. When designing a zoning scheme and choosing transducers, one of the key steps is to
define the requirements of the ultrasonic pulse volume. It has been shown theoretically and verified
experimentally that the signal-to-noise (S/N) ratio is approximately inversely proportional to the
square root of the pulse volume. Thus, to meet the subtask goal, one needs to define the
restrictions on the pulse volume that provide acceptable S/N ratios for a #1/2 FBH inspection.
During the previous and current quarters such data was acquired at GE-QTC. Signal-to-peak-noise
ratios were measured using several transducers with different focal characteristics to achieve a
wide range of pulse-volume values. The measurements were performed on the highest noise
“property” coupons from each OEM’s Ti 6-4 forging. Two of the three coupons had arrays of #1
FBH drilled into them, and one of the holes in the PW coupon served as a reference against which
peak noise values were measured. The data acquired using an F6 transducer with the beam
focused on the FBHs is shown at Figure 3. The gain was selected such that the response from
#1/2 FBH would be at 80% Full Screen Height (FSH). The peak noise was measured for each of
Quarterly Report – January 1, 2002 –March 31, 2002
print date/time: 6/6/2002 - 8:39 AM – Page 60