Laser Peening Airfoils with Weld Repairs

LSP Technologies (LSPT) gained a patent in 1999 during a time that the aerospace industry was experiencing patterns in damages in aircraft gas turbine engine airfoils: Method using laser shock peening to process airfoil weld repairs pertaining to blade cut and weld techniques.  It is “A method… for repairing damage to an airfoil… [that] provides for the removal of a section of the airfoil….  A replacement piece larger than the residual void is provided….  A joining operation welds or otherwise joins the replacement piece to the airfoil at the cut-away surface… [and] a portion of the seam is processed by laser shock peening to induce compressive residual stresses therein.”

At the time, the Air Force was having issues with the B1 Bomber.  LSPT and GE successfully created a solution to allow repaired aircraft blades to perform as if they were new.  The ability to provide a repair process to treat used, fielded blades and return them to service was only one among the many original reasons for pursuing laser shock peening of gas fired turbine engine blades.

Damage to the B1 bomber blades predominately occurred during take-offs and landings.  The engine ingested particles and debris (dust, sand, rock, or ice) that nicked and dented the leading edge of the fan blades. The leading edge is one of the most stressed portions of the blade, and high stress at the bottom of a dent or nick causes premature fatigue failures.  Every time there is a new engine cycle with dents in blades that remain unrepaired, the dent propagates, ultimately leading to a separation. Laser Peening imparts compressive residual stresses around the damaged area which prevents the dent from propagating.   These compressive stresses act to ‘push the materials together.’

This patent speaks to a repair process which involved cutting out the damaged areas, welding replacement pieces to fill the cracks and then smoothing the surface to reduce tensile stresses in the area, and then laser peening the area to apply compressive residual stresses.  Of the many benefits of laser peening, reduced maintenance expenses and increased time-on-wing represent the largest cost savings and key benefits.  Damage in critical, failure prone, components is mitigated with laser peening, allowing engines to run longer between maintenance cycles.  There isn’t a need to tear down and inspect an engine as frequently.  The value proposition is the savings, because general wear and tear will not degrade the performance of the engine; its damage tolerance is significantly increased.

Laser peening is currently used on new gas fired turbine engine blades in the aerospace and power generation industries, among other aerospace structural components and on applications in other industries.  Laser peening prevents the damage that these typically experience during normal operating conditions, increasing their damage tolerance, fatigue life and strength, and resistance to stress corrosion cracking, fretting fatigue, and other wear conditions.

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