1、 AEROSPACE MATERIAL SPECIFICATION Laser Peening AMS 2546Issued 1. SCOPE 1.1 Purpose: This specification covers the requirements for computer controlled laser peening of metal part surfaces to induce residual compressive stresses at and beneath the surface. 1.2 Application: Laser peening is utilized
2、to induce compressive residual stresses at and beneath the surface of metal parts to depths of 0.040” to 0.080” (1 to 2 mm) depending on the metal properties and the laser peening processing parameters. These residual stresses can provide improved fatigue life and stress corrosion resistance, althou
3、gh usage is not limited to such applications. 1.3 Safety a standardized technique for laser peening of the coupon; and a standardized device and method for measuring the coupon before and after laser peening. 3.3.1.1 The metal coupon to use for process verification of laser peening shall be an SAE 1
4、070 spring steel Almen C test strip and shall be processed on one side only. All test strips used for intensity verification shall conform to SAE J442 except thickness and flatness tolerance shall be 0.0005 inch (0.013 mm). A method of compensating for initial out of flatness may be used, if approve
5、d by the cognizant engineering organization. However, mechanically deforming strips to meet the flatness requirement is not permitted. Hardness shall be 45 to 48 HRC and measured in accordance with ASTM E 18 at approximately 1/2 inch (12.7 mm) from either end on the longitudinal center line of a fla
6、t side using Rockwell “C” scale, or equivalent (see 8.9). To avoid hardness tester impressions on strips, a sampling plan for hardness, ANSI Z1.4, AQL of 0.01 may be used. Reuse of Almen C test strips is not permitted. SAE - 4 - AMS 2546 AMS 25463.3.1.2 Almen Strip Holding Fixture: Either a scrap pa
7、rt or a representative nonadjustable fixture shall be fitted with a test strip support block that conforms to SAE J442. The fixture shall be oriented in the laser peening workstation such that the Almen C test strip is at the same processing orientation as the part will see during production laser p
8、eening. This setup shall be used for all subsequent verifications as indicated in the processors work instructions for each part. 3.3.1.3 The laser shall be set to the identical processing conditions utilized for production laser peening of the parts, including beam energy density and pulse width. T
9、he same opaque overlay and transparent overlay materials shall be used for the coupon as the parts. 3.3.1.4 The Almen C test strip shall be indexed to generate a laser spot pattern. Alternatively, the Almen C strip can be held stationary and the laser beam spot can be moved to generate an equivalent
10、 laser spot pattern. The Almen test strip shall be laser peened with a pattern representative of that which is utilized during production processing in accordance with the dimensions and areas defined by the engineering drawing (see 8.2.2). 3.3.1.5 The method for measuring the arc height deflection
11、of the Almen test strips shall be in accordance with the procedures in SAE J442. The gages used for measuring the flatness and arc height of Almen test strips shall conform to the requirements of SAE J442, except that the gages shall have digital readout and have an accuracy of 0.0001 inch (0.0025 m
12、m). Almen gages shall be zeroed, at a minimum, once daily using a flat gage block. 3.3.1.6 When Almen strips are used for process verification, the arc height (deflection) shall fall within the range required by the engineering drawing. 3.3.1.7 An alternative method of verifying the setup of the las
13、er peening conditions which utilizes different parameters from those specified in 3.3.1.1, 3.3.1.2, 3.3.1.3, 3.3.1.4, 3.3.1.5, and 3.3.1.6 may be used if approved by the cognizant engineering organization. 3.3.2 Beam Spot Size and Shape: The size and geometric shape of the individual laser spots, th
14、e sequence and pattern of their application within the specified zone, and the number of distinct laser peening passes (or layers) shall be approved by the cognizant engineering organization and contained within the processors work instructions. 3.3.2.1 The method of verifying the appropriate laser
15、peening coverage (see 8.7) of the designated zone on the part (such as a visual inspection of the surface) shall be approved by the cognizant engineering organization and contained within the processors work instructions. 3.3.3 Peening Intensity: The laser beam operating parameters needed to achieve
16、 a specific laser peening intensity shall include a numeric value of the energy density (Joules/cm2) or power density (GW/cm2) and pulse width (nanoseconds) of the laser beam for each laser spot area. 3.3.3.1 The energy density (fluence) shall be determined by dividing the measurement of the pulse e
17、nergy (Joules) by the measured area (cm2) per 3.3.3.4. SAE - 5 - AMS 2546 AMS 25463.3.3.2 The power density (irradiance) shall be determined by dividing the energy density by the pulse width. 3.3.3.3 The laser pulse energy shall be measured with an energy meter or calorimeter and verified at not gre
18、ater than an annual basis. 3.3.3.4 The laser spot area shall be measured by a method that is acceptable to the cognizant engineering organization. 3.3.3.5 The pulse width shall be measured at the Full Width Half Maximum (“FWHM”) of the laser beams temporal profile. The laser pulse width shall be mea
19、sured with an appropriate fast detector and recorder traceable to national standards and verified on an annual basis. 3.3.4 Allowable Process Variation: 3.3.4.1 During production laser peening, the average laser beam energy output (in Joules) shall be within 10% of the specified energy value in the
20、processors work instructions (or an otherwise demonstrated range that is acceptable to the cognizant engineering organization.) 3.3.4.2 During production laser peening, the average laser beam pulse width (in nanoseconds) shall be within 3 nanoseconds of the specified pulse width in the processors wo
21、rk instructions (or an otherwise demonstrated range that is acceptable to the cognizant engineering organization.) 3.4 Preparation of Parts for Laser Peening: 3.4.1 Except as otherwise specified, the parts shall be within dimensional and surface finish requirements, free of grease, dirt, oil, corros
22、ion, and corrosion-preventive coatings such as anodic coating, plating, and paint prior to laser peening in the zone to be processed and in any adjacent areas to be masked. If cleaning by the processor is required, the method of cleaning shall be acceptable to the cognizant engineering organization
23、and included within the processors work instructions. 3.4.1.1 The opaque overlays required for laser peening shall be applied by the processor. 3.4.2 Except as otherwise specified, all machining of areas to be laser peened shall be completed, all fillets shall be properly formed, and all burrs and s
24、harp edges shall be removed prior to laser peening. 3.4.3 All heat treatments to meet requirements for mechanical properties shall be completed prior to laser peening. 3.4.4 When magnetic particle, fluorescent penetrant, eddy current or ultrasonic surface wave inspection is required, parts shall rec
25、eive such inspection prior to laser peening. SAE - 6 - AMS 2546 AMS 25463.4.5 Parts which exhibit corrosion or mechanical damage shall not be peened unless the noted condition is acceptable to the cognizant engineering organization. 3.4.6 Cleaning, prior to laser peening, shall be accomplished by me
26、thods that ensure the removal of contaminants such as oil, grease, or paint. 3.4.6.1 Titanium alloys shall be cleaned using solvents containing less than 30 ppm halogenated compounds. 3.5 Laser Peening of Parts: 3.5.1 After machine setup and process verification, parts shall be suitably mounted and
27、laser peened in accordance with the part-specific work instructions. 3.5.2 Almen C strips or other process verification gauges employed in the establishment of laser peening conditions shall be used for periodic verification of processing conditions in accordance with 4.3. 3.5.3 During the processin
28、g of each component, processing trends for laser beam energy and the pulse width shall be monitored. The laser peen process shall be interrupted whenever the running average laser beam energy or the running average laser beam pulse width deviates outside of their allowable variations (3.3.4). The nu
29、mber of data points to be used in the running average may be based on a statistical sampling program to be approved by the cognizant engineering organization. 3.5.4 A record shall be kept of the position of any laser peen spots on production parts where the laser beam energy and/or the laser beam pu
30、lse falls outside their allowable variation limits. Rectification procedures for reprocessing these laser peen spots shall be approved by the cognizant engineering organization, and the procedures shall be in the processors work instructions. 3.5.5 Distortion of the part due to imposition of the com
31、pressive residual stresses shall not be cause for rejection, unless such distortion was not present on the pre-production samples (see 4.4.1) or is not permitted by the cognizant engineering organization. 3.6 Post Treatment: 3.6.1 After laser peening, all opaque overlays and other processing materia
32、ls shall be removed from the surfaces of the parts with methods that will not erode, abrade, scratch or etch these surfaces. The method of cleaning shall be acceptable to the cognizant engineering organization and shall be included in the processors work instructions. 3.6.2 Mechanical straightening
33、after laser peening is not permitted, unless specifically authorized by the cognizant engineering organization. SAE - 7 - AMS 2546 AMS 25463.7 Tolerance: Laser peening of the specified zone: Laser peening coverage within the specified zone shall be a minimum of 100%. Unless otherwise specified, the
34、dimensions of the transition zone where laser peening coverage is optional shall be -0.000 to +0.250 inches (-0.0 to +6.0 mm) into the area on the part where laser peening is not required (see 8.2). 3.8 Post-Process Inspection: 3.8.1 When processing conditions permit, visual inspection of the part s
35、urface shall be conducted to verify evidence of processing after removal of the process overlays. For situations where processing conditions or material properties do not provide evidence of processing on the surface (8.8), visual inspection of the processing overlay shall be conducted to verify evi
36、dence of processing. 3.8.2 Prior to shipment additional visual inspection of the parts shall be conducted for evidence of cleanliness, the complete removal of all traces of the processing overlays, and for any dings, nicks or scratches. 4. QUALITY ASSURANCE PROVISIONS: 4.1 Responsibility for Inspect
37、ion and Process Control: The processor shall be responsible for the performance of all inspections specified. When parts are to be tested, they shall be supplied by purchaser. Purchaser reserves the right to sample and perform any testing deemed necessary to ensure that the laser peen processing con
38、forms to the specified requirements. 4.2 Classification of Tests: 4.2.1 Acceptance Tests: All process verification tests (3.3.1) are acceptance tests and shall be performed on each production lot (See 4.3.1.1). 4.2.2 Periodic Tests: Beam spot size and shape (3.3.2), peening intensity (3.3.3), covera
39、ge (3.3.2.1) and allowable process variations (3.3.4) are periodic tests and shall be performed at a frequency selected by the processor unless a frequency of test is selected by purchaser. 4.2.3 Preproduction Tests: All tests are preproduction tests and shall be performed for each part or lot prior
40、 to initial production in each laser peening machine. SAE - 8 - AMS 2546 AMS 25464.3 Sampling and Testing: 4.3.1 At the beginning and the end of processing each lot and at periodic intervals not to exceed eight hours, at least one process verification test sample shall be tested in accordance with 3
41、.3 for each laser peening condition, or at other periodic intervals as approved by the cognizant engineering organization. The information for each Almen strip or process verification sample shall be recorded as in 4.3.2. 4.3.1.1 A lot is defined as a group of parts of the same part number that are
42、laser peened in one setup of the laser peening machine (See 3.3) and reference the testing results from Almen strips or other process verification gauges from the beginning, end or most recent periodic testing intervals of the production run. 4.3.2 Intensity Verification: Laser peening parameters fo
43、r each laser peened part shall be available for review by the purchaser. The following information shall be recorded for each Almen C strip or process verification coupon: - Part number and, when applicable, serial number - Date and time of laser peening each lot number - Laser peening machine cell
44、number - Overlay materials - Specified laser peening energy density or power density and pulse width - As-measured average energy density or power density and pulse width - Almen strip or process verification gauge results. 4.4 Preproduction Approval: 4.4.1 The process control factors and/or a prepr
45、oduction part shall be approved by the cognizant engineering organization before production parts are supplied. 4.4.2 There shall be no change in the procedures, processing parameters, or criteria from those on the approved work instructions without the approval of the cognizant engineering organiza
46、tion. A change is defined as one which could adversely affect the induced residual compressive stresses or coverage; or which the cognizant engineering organization indicates could affect the performance properties of the part or repeatability of the process. 4.4.3 Process control factors for laser
47、peening of parts shall include, but are not limited to, the following. Processers procedures shall identify tolerances, ranges, and/or control limits, as applicable to ensure process repeatability. - Laser type and part specific operating program - Robot type and part specific operating program - Op
48、aque overlay layer and its method of application and removal - Transparent overlay method of application SAE - 9 - AMS 2546 AMS 25464.4.3 (Continued): - Number of laser beams - Single or dual sided peening - Laser beam power density (GW/cm2) - Laser beam pulse width (nanoseconds at FWHM) - Laser spo
49、t size and shape, sequence, and pattern and number of layers - Specific zones on the part to be processed - Any special equipment such as jigs or fixtures - Sampling requirements for process control - Pre and postcleaning procedures, if used - Method of verifying laser beam coverage - Post peening inspection, treatment, and protection. 4.4.4 Any of the process control factors for which parameters are considered proprietary by the processor may be assigned a code designation. Each variation in such parameters shall be assigned a modified code designation. Details of the proce
