Electric heating – Metal heating – By arc
Reexamination Certificate
1999-08-30
2001-12-25
Elve, M. Alexandra (Department: 1725)
Electric heating
Metal heating
By arc
C219S121730, C219S121850
Reexamination Certificate
active
06333488
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to laser shock peening (LSP) and, more particularly, to a method for setting up and controlling the flow of water or other confinement media over the laser shocked area of the work piece during a laser shock peening process.
2. Description of Related Art
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 work piece. Laser shock peening typically uses one or more radiation pulses from high power pulsed lasers to produce an intense shock wave at the surface of a work piece 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 pulsed 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 at the impingement point of the laser beam by the instantaneous ablation or vaporization of a thin layer of that surface or of a coating (such as tape or paint) on that surface.
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. 5,756,965 entitled “On The Fly Laser Shock Peening”; U.S. Pat. No. 5,591,009 entitled “Laser shock peened gas turbine engine fan blade edges”; U.S. Pat. No. 5,569,018 entitled “Technique to prevent or divert cracks”; U.S. Pat. No. 5,531,570 entitled “Distortion control for laser shock peened gas turbine engine compressor blade edges”; U.S. Pat. No. 5,492,447 entitled “Laser shock peened rotor components for turbomachinery”; U.S. Pat. No. 5,674,329 entitled “Adhesive tape covered laser shock peening”; and U. S. Pat. No. 5,674,328 entitled “Dry tape covered laser shock peening”, all of which are assigned to the present Assignee.
Laser peening has been utilized to create a compressively stressed protective layer at the outer surface of a work piece, which is known to considerably increase the resistance of the work piece 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 work piece or some other method to provide a plasma confining medium. This medium enables the plasma to rapidly achieve shockwave pressures that produce the plastic deformation and associated residual stress patterns that constitute the LSP effect. The curtain of water provides 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. This confining medium also serves as a carrier to remove process generated debris and any unused laser beam energy. Water is an ideal confining medium since it is transparent to the ND:YAG beam wavelength and is easy to implement in production. The water curtain should be kept in continuous contact with the surface of the work piece or part being LSP'd and at a minimum predetermined thickness or in a range of thicknesses. The water curtain often must be kept at a depth of about 0.02 inches.
The current state of the art is to constantly monitor the confinement media via video monitor. This requires full attention of the operator and provides no thickness measurement data.
SUMMARY OF THE INVENTION
A method for setting up a transparent confinement media nozzle for flowing the confinement media during laser shock peening of a work piece includes the following steps for at least one point on a correlation surface of a test piece related to one patch of work piece to be laser shock peened: Step A) flowing a confinement media and setting a flow rate of the confinement media through a confinement media flow nozzle; Step B) positioning the nozzle to flow the confinement media through the nozzle and onto the correlation surface; and Step C) measuring a confinement media layer thickness on the correlation surface using an ultrasonic transducer attached to a side of the test piece opposite that of the correlation surface. The ultrasonic transducer is attached to a side of the test piece opposite that of the correlation surface. One embodiment of the invention employs the work piece as the test piece and the correlation surface is a first laser shock peening surface on a first side of the work piece. A preferred embodiment of the invention further includes Step D) comparing the measured and recorded confinement media layer thickness from Step C) against a predetermined value or range of values for confinement media layer thickness, and Step E) determining whether to reset the confinement media flow rate and/or nozzle position or proceeding with the laser shock peening of the work piece with the confinement media flow rate and nozzle position set in Step A) based on the comparison in Step D). If called for then Step F) resetting at least one of the confinement media flow rate and nozzle position and repeating Steps C), D), and E) is used.
One embodiment of the invention calls for performing Steps B) and C) for a plurality of points on the patch of the work piece to be laser shock peened and in Step D) comparing the measured and recorded confinement media layer thickness for each of the points from Step C) against the predetermined value or range of values for confinement media layer thickness. Then performing Step E) to determine whether to reset the confinement media flow rate and/or nozzle position or proceed with the laser shock peening of the work piece with the confinement media flow rate and nozzle position set in Step A) based on the comparison in Step D). Then, if called for, performing a Step F) resetting the confinement media flow rate and/or nozzle position and repeating Steps C), D), and E).
The method is preferably performed in a laser shock peening system having at least one fixed laser beam source for laser shock peening and a controllable first manipulator holding the work piece. Between Steps A) and B) a work piece attitude and/or a work piece position is adjusted by the first manipulator to match the work piece attitude and the work piece position during laser shock peening of the work piece. The setting and resetting of the nozzle position is done using a controllable second manipulator holding the nozzle.
For dual sided laser shock peening, the Steps A) through E) are a first set of steps and the method further includes performing a second set of the Steps A) through E) on a second laser shock peening surface of the work piece on a second side of the work piece opposite the first laser shock peening surface of the first side after Steps A) through E) are performed on the first laser shock peening surface. One particular embodiment provides for performing the method on a gas turbine engine component having an airfoil such as a turbine, compressor, or fan blade with leading edge and a trailing edge. The sides are convex suction and concave pressure sides of the airfoil and the patch is located along one of the edges. In one embodiment of the invention, an epoxy acoustic coupling material is placed between the ultrasonic transducer and the airfoil.
In yet another embodiment of the invention, the method is used to calculate a schedule of nozzle attitude and nozzle position settings for each of the points to provide a predetermined confinement media thickness over each of the points and then laser shock peening the work piece by firing a laser beam pulse from a laser shock peening apparatus on each of the points while flowing the confinement media over the points. The nozzle attitude and the nozzle position are set according to the schedule for each of the points during the laser shock peening prior to each firing for which the schedule calls for a change in the nozzle a
Klaassen Richard E.
Lawrence Wayne L.
Elve M. Alexandra
General Electric Company
Hess Andrew C.
Ramaswamy V.
LandOfFree
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