Appeal 2006-2987
Application 10/661,651
dimensions of the blades causing differences in the weight of the blades and
rotational imbalances during operation (Specification ¶ 0005). The APA
discloses that, “[i]n the past, this rotation imbalance problem in gas turbine
engine blisks has been addressed by one of two methods.” (Specification ¶
0006). The APA further discloses one of the methods “is to mechanically
polish or machine the blisk to remove metal from the blades, flanges and/or
platform region between the blade roots to adjust the rotation balance of the
blisk.” (Id.). Further according to the APA, “conventional balancing
machines have been used to measure the imbalance of the blisk at a suitable
speed in terms of an imbalance force vector having a magnitude in mass and
radius, and at a measured circumferential angular position around the
circumference of the blisk relative to any suitable reference portion.”
(Specification ¶ 0007). Further according to the APA, the measured
imbalance can then be corrected by removing blisk material (e.g., from the
blade) at the angular position of the imbalance vector (Id.)
Walker describes chemical milling (chem-milling or contour etching)
for removing material from contoured or shaped metal parts (Walker, pp.
511-513). Walker states that “chem-milling may be employed to reduce the
weight of sheet metal parts, critical to aerospace vehicle performance.”
(Walker, p. 511, § 28.1.1, first paragraph). The caption under Figure 28-1
further states that “[c]hemical milling is employed to remove metal to close
tolerances.” Walker further states that “[c]hem-milling and conventional
milling are complementary processes” and “refinements in chem-milling
make it possible to remove metal to form shapes or microscopic parts that
would be difficult or impossible to do by conventional machining
techniques.” (Walker, p. 512, first full paragraph). Chemical milling also
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