Laser shock peening quality assurance by acoustic analysis

Details Laser shock peening quality assurance by acoustic analysis Laser shock peening quality assurance by acoustic analysis

2001-10-03

2003-10-07

Williams, Hezron (Department: 2856)

Measuring and testing

Vibration

By mechanical waves

C073S011020, C073S620000, C073S643000, C356S318000

Reexamination Certificate

active

06629464

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to quality assurance methods used for quality assurance for laser shock peening and, more particularly, for acoustic monitoring and statistical analysis method for quality assurance of a production laser shock peening process.
2. Discussion of the Background 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 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. Other techniques to confine and redirect the shock waves that do not use water have also been developed.
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. Nos. 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. These applications, as well as others, are in need of efficient quality assurance testing during production runs using laser shock peening.
LSP is a deep treatment of the material and it is desirable to have a quality assurance test that is indicative of a volumetric LSP effect. It is also desirable to have a QA method that is compatible with a dual sided or simultaneous dual sided LSP process wherein substantially equal compressive residual stresses are imparted to both sides of a workpiece, i.e. along the leading edge of a gas turbine engine fan blade.
One laser shock peening quality assurance technique previously used is high cycle fatigue (HCF) testing of blades having leading edges which are LSP'd and notched in the LSP'd area before testing. This method is destructive of the test piece, fairly expensive and time consuming to carry out, and significantly slows production and the process of qualifying LSP'd components. An improved quality assurance method of measurement and control of LSP that is a non-destructive evaluation (NDE), inexpensive, accurate, quick, and easy to set up is highly desirable. It is also desirable to have a real time NDE quality assurance method that is relatively inexpensive and sufficiently economical to be used on each workpiece instead of a sampling of workpieces. LSP is a process that, as any production technique, involves machinery and is time consuming and expensive. It is desirable to have a real time NDE method so that process deviations can be discovered during a production run. Therefore, any real time techniques that can reduce the amount or complexity of production machinery and/or production time are highly desirable.
Interferometric profilometry method and apparatus to obtain volumetric data of a single laser shock peened test dimple created with a single firing of a laser used in the laser shock peening process is disclosed in U.S. Pat. No. 5,948,293 “Laser shock peening quality assurance by volumetric analysis of laser shock peened dimple”. Other QA methods are disclosed in U.S. Pat. No. 5,987,991 “Determination of Rayleigh wave critical angle”; U.S. Pat. No. 5,974,889 “Ultrasonic multi-transducer rotatable scanning apparatus and method of use thereof”; and U.S. Pat. No. 5,951,790 “Method of monitoring and controlling laser shock peening using an in plane deflection test coupon”. U.S. Pat. No. 6,254,703,entitled “Quality Control Plasma Monitor for Laser Shock Processing” discloses a method and apparatus for quality control of laser shock processing by measuring emissions and characteristics of a workpiece when subjected to a pulse of coherent energy from a laser. These empirically measured emissions and characteristics of the workpiece are correlated to theoretical shock pressure, residual stress profile, or fatigue life of the workpiece. Apparatus disclose includes a radiometer or acoustic detection device for measuring these characteristics.
SUMMARY OF THE INVENTION
A method for quality control testing or monitoring of the laser shock peening process of production workpieces includes the following steps. Step (a) includes laser shock peening a surface of the production workpiece by firing a plurality of laser beam pulses from a laser shock peening apparatus on the surface of the production workpiece and forming a plurality of corresponding plasmas. Each one of the plasmas for each one of the pulses has a duration in which the plasma causes a region to form beneath the surface. The region has deep compressive residual stresses imparted by the laser shock peening process. Step (b) includes measuring acoustic signal for each of the laser beam pulses during a period of time during the duration of each corresponding one of the plasmas. Step (c) includes calculating an acoustic energy parameter value for each of the acoustic signals for each of the corresponding laser pulses or plasmas. Step (d) includes calculating a statistical function value of the workpiece based on the acoustic energy parameter values. The statistical function value may be an average of the acoustic energy parameter values for the plurality of the laser beam pulses. In step (e) the statistical function value is compared to a pass or fail criteria for quality assurance of the laser shock peening process for accepting or rejecting the workpiece. Besides using the averages of the acoustic energy parameter values to determine the statistical function values other types of statistical functions and analysis may be used, i.e. analysis and functions using regression or standard deviations.
The pass or fail criteria may be based on a pre-determined correlation of test piece statistical function data. More particular embodiments use high cycle fatigue failure based on high cycle fatigue tests of test pieces. The test pieces may have a failure precipitating flaw within a laser shock peened area of the test piece that was laser shock peened in the same or similar laser shock peening apparatus.
Two exemplary types of acoustic signal monitoring devices are disclosed. The first type is an acoustic transducer mounted to the workpiece, which detects acoustic signals though the workpiece. The second type is a microphone located away from the workpiece, which detects airborne acoustic signals. The acoustic signals may be used to calculate various types of acoustic energy parameters of the laser p

Affiliated with

Also associated with

Rating

Laser shock peening quality assurance by acoustic analysis does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Laser shock peening quality assurance by acoustic analysis, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Laser shock peening quality assurance by acoustic analysis will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3113157