Laser shock peened gas turbine engine seal teeth

Stock material or miscellaneous articles – All metal or with adjacent metals – Having variation in thickness

Reexamination Certificate

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C428S610000, C219S121640, C148S565000, C148S900000, C415S174500

Reexamination Certificate

active

06200689

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to gas turbine engine rotor seals with teeth such as labyrinth seal teeth and, more particularly, to such teeth having localized compressive residual stresses imparted by laser shock peening and repaired seals with teeth rebuilt by welding.
2. Description of Related Art
A variety of stationary and rotating seals, often referred to as the labyrinth type, are used in various parts of a gas turbine engine. During manufacture, operation, maintenance, etc., such seals, which include one or more projections or teeth connected with a support structure, can be worn or damaged.
It has become common practice to repair in a relatively cost effective manner certain types of such seal teeth or projections by first removing the damaged portion of the tooth. The same material of the tooth then is reapplied as by welding, with excess added material being removed, such as by machining, to regenerate the tooth. Methods and apparatus for conducting such repair is described in U.S. Pat. No. 4,657,171 by Bertrand G. Robins, issued Apr. 14, 1987. As is described in this and other patents referenced therein, a filler material in wire form is moved in a reciprocating manner into and out of a weld pool created by a heating source such as an electric arc to build up the teeth.
Poor weldability, including poor weld flow characteristics and crack sensitivity of the metal from which the projection or tooth is made, characterizes seal teeth repaired in this manner and often prevents repairs in a practical manner or limits the useful operating life of the components thus repaired. Accordingly, when damaged, the costly member may be replaced rather than repaired. The weldment repairs forms a heat affected zone which is that portion of the base metal which was metallurgically altered due to the welding heat. The heat affected zone also is very crack sensitive and, therefore, reduces the useful operational life of the repaired part. Therefore, it is highly desirable to improve the crack sensitivity of the heat affected zone as well as that of the part itself. The present invention incorporates laser shock peening to accomplish this and provide an improved weld repair and article therewith.
Laser shock peening or laser shock processing, as it is also referred to, is a process for producing a region of deep compressive residual stresses imparted by laser shock peening a surface area of a workpiece. Laser shock peening typically uses multiple radiation pulses from high power pulsed lasers to produce shock waves on the surface of a workpiece similar to methods disclosed in U.S. Pat. No. 3,850,698, entitled “Altering Material Properties”; U.S. Pat. No. 4,401,477, entitled “Laser Shock Processing”; and U.S. Pat. No. 5,131,957, entitled “Material Properties”. Laser shock peening, as understood in the art and as used herein, means utilizing a laser beam from a laser beam source to produce a strong localized compressive force on a portion of a surface by producing an explosive force by instantaneous ablation or vaporization of a painted or coated or uncoated surface. Laser peening has been utilized to create a compressively stressed protection layer at the outer surface of a workpiece which is known to considerably increase the resistance of the workpiece to fatigue failure as disclosed in U.S. Pat. No. 4,937,421, entitled “Laser Peening System and Method”. These methods typically employ a curtain of water flowed over the workpiece or some other method to provide a confining medium to confine and redirect the process generated shock waves into the bulk of the material of a component being LSP'D to create the beneficial compressive residual stresses.
Laser shock peening is being developed for many applications in the gas turbine engine field, some of which are disclosed in the following U.S. Pat. No. 5,525,429, entitled “Laser shock peening surface enhancement for gas turbine engine high strength rotor alloy repair”; U.S. Pat. No. 5,675,892, entitled “Laser shock peening for gas turbine engine vane repair”; U.S. Pat. No. 5,591,009, entitled “Laser shock peened gas turbine engine fan blade edges”; U.S. Pat. No. 5,492,447, entitled “Laser shock peened rotor components for turbomachinery”; and U.S. Pat. No. 5,674,329, entitled “Adhesive tape covered laser shock peening” as well as others.
SUMMARY OF THE INVENTION
The present invention includes a method of repairing an annular metallic article and the article which has an axially extending annular support and a projection extending generally radially therefrom. The projection has an associated operating radial height as measured from a radially facing annular first surface of the support and an associated shape. The method includes removing at least a worn upper portion of the projection forming a stub extending away from the first surface and a bonding surface at a stub end spaced apart from the first surface and metallurgically bonding a sufficient amount of metallic material to the bonding surface so to allow restoration of the projection to the associated operating height and shape. An annular heat affected zone is formed in a portion of the stub bounded by the bonding surface during the metallurgical bonding. Next, a first portion of the metallic material is removed to restore the projection to the operating height and shape. A first outer surface portion of the tooth extending over at least a portion of the heat affected zone is laser shock peened preferably after the removing of the first portion of the metallic material. A tip of the stub formed by the removing of the first portion of the metallic material may also be laser shock peened and a non-heat affected zone portion of the stub extending at least a partial length of a distance from the heat affected zone to the first surface may also be laser shock peened.
The restored projection may include opposite forward and aft facing annular surfaces, the forward facing annular surface each having the first outer surface portion of the tooth and the aft facing annular surface having a second outer surface portion of the tooth. The laser shock peening may be performed on the first and second outer surface portions, preferably simultaneously. The laser shock peening includes firing at least one laser beam with sufficient power to vaporize ablative material on the outer surface portions and impart deep compressive residual stresses extending into the heat affected zone from the outer surface portions. The laser beams may be fired normal to the surface portions at an inclined angle with respect to a radial plane that is perpendicular to an axial centerline about which the annular support is circumscribed or at an oblique angle to the surface portions. The ablative material vaporized on the outer surface portion may be a metal of the heat affected zone of the stub, an ablative paint coating, or an ablative tape coating.
The repaired annular metallic article of the present invention includes an axially extending annular support having a radially facing annular first surface and a projection generally radially extending therefrom. The projection has an associated operating radial height as measured from the radially facing annular first surface and an associated shape. The projection includes a stub formed by removing a worn upper portion of the projection, a bonding surface at a stub end spaced apart from the annular first surface, and a tip. The tip is formed by metallurgically bonding a sufficient amount of metallic material to the bonding surface and removing a first portion of the metallic material to restore the projection to the operating height and shape. An annular heat affected zone formed in a portion of the stub bounded by the bonding surface during the metallurgical bonding includes a laser shock peened region having deep compressive residual stresses imparted by laser shock peening extending into the heat affected zone from an annular first outer surface portion of the heat affected zone. The restored projection may have opposite g

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