Appeal 2006-2987
Application 10/661,651
We affirm.
I. BACKGROUND
The invention relates to a method of chemical milling at least one
blade of a gas turbine engine bladed disk (blisk) to rotationally balance it.
These blisks include rotor blades arranged around a disk or hub
(Specification Figure 1). According to the Specification, “[a] gas turbine
engine blisk is typically manufactured from a one piece solid forging which
is conventionally machined using either mechanical machining (mechanical
milling) or electrochemical machining (ECM)” (Specification ¶ 0004). But
often after machining not all the blades of the blisk have the same
dimensions and, therefore, the blades vary in weight (Specification ¶ 0005).
The variations cause rotational imbalances during operation in the gas
turbine engine (id.). Appellants’ method uses a chemical milling method to
correct imbalances. Claim 1 is illustrative of the subject matter on appeal:
1. A method for selective chemical milling of a rotationally imbalanced
gas turbine engine blisk having a hub and a plurality of blades made of metal
spaced circumferentially around the hub and extending radially outwardly
therefrom, each of the blades of the blisk having a leading edge, a trailing
edge, a chord defined by a line extending from the leading to the trailing
edge, a convex curved surface, a concave curved surface and a thickness
defined between the convex and the concave surfaces, the method
comprising the step of selectively treating at least one blade of the blisk with
a chemical etchant of the metal that the at least one blade is made of for a
period of time sufficient to change the at least one of the chord and thickness
so that the blisk is rotationally balanced.
The Examiner rejects the claims under 35 U.S.C. § 103(a) and relies
upon the following prior art references to show unpatentability:
Fishter US 4,534,823 Aug. 13, 1985
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