Preliminary Requirements

Safety Requirements

WARNING

IT IS THE RESPONSIBILITY OF THE OPERATOR TO OBTAIN AND OBSERVE THE MANUFACTURER'S MATERIAL SAFETY DATA SHEETS FOR CONSUMABLE MATERIALS. THESE CONTAIN INFORMATION SUCH AS, HAZARDOUS INGREDIENTS, PHYSICAL/CHEMICAL CHARACTERISTICS, FIRE, EXPLOSION, REACTIVITY, HEALTH HAZARD DATA, PRECAUTIONS FOR SAFE HANDLING, USE AND CONTROL MEASURES AND ALSO TO TAKE LOCAL REGULATIONS INTO CONSIDERATION.

Procedure

1. SUBTASK 70-38-16-300-001 General

   1. Do all necessary FPI, FMPI or other NDT inspections before peening.

   2. Dry and wet peening in this task are alternative processes to one another. When glass peening, wet glass peening, dry glass peening or bead peening is specified in an Engine Manual repair or service bulletin, use either the wet or dry process in this procedure. New and revised manual repairs specify bead peening by this task.

   3. For certain applications, hand-held peening is permitted. However, all peening of blades and life-limited rotating parts in those areas with specified intensity must be done with automated equipment.

      1. Engine life-limited parts are those specified in Chapter 5 of Engine Manuals and Overhaul Manuals and those other high-energy rotating parts such as disks, spacers, seals, hubs and shafts that have life limits in sections other than Chapter 5 in older overhaul manuals.

   4. TASK 70-38-13-380-501 shotpeening with cast steel shot (conforming to the current revision of AMS 2430 and AMS 2431) or conditioned cut wire shot (conforming to the current revision of AMS 2430 and AMS 2431) is a permitted alternative to this task on all titanium, steel, and nickel parts at the same specified peening intensity.

      1. It is necessary to get IAE repair source approval to do TASK 70-38-13-380-501 shotpeening with cast steel shot (conforming to the current revision of AMS 2430 and AMS 2431) or conditioned cut wire shot (conforming to the current revision of AMS 2430 and AMS 2431) as a replacement for bead peening on source approval repairs. This alternative cannot be used as transfer approval from one approved process to another.

      2. It is permitted to increase the peening intensity tolerance range to +5N/-0 when cast shot or conditioned cut wire shot is used. Increased peening intensity range is not permitted for airfoils.

         1. EXAMPLE: Where bead peening to an intensity of 10N (+3N/-0) is specified, it is permitted to do TASK 70-38-13-380-501 shotpeening with cast steel shot (conforming to the current revision of AMS 2430 and AMS 2431) or conditioned cut wire shot (conforming to the current revision of AMS 2430 and AMS 2431), to an intensity of 10N (+5N/-0).

      3. All other intensity requirements, coverage requirements, and waivers for bead peening are applicable when shotpeening as an alternative to bead peening.

2. SUBTASK 70-38-16-300-002 Definitions

   1. BEAD PEENING: The use of a high-speed stream of small ceramic or glass beads, propelled by air pressure, that hits the part surface to cause compressive stress. The compressive stress gives increased fatigue strength and resistance to stress corrosion.

   2. BEAD PEEN INTENSITY: A measure of the energy of the bead stream indicated by the arc height of a peened Almen test strip at the saturation point on a saturation curve.

   3. COVERAGE: The percentage of the specified part surface that has been peened so that visual examination at 10X minimum magnification shows a continuous pattern of dimples that overlap and that is the same in all areas and obliterates, or removes, the initial surface finish.

   4. FULL COVERAGE: One hundred percent of the specified part surface shows a continuous pattern of dimples that overlap and that is the same in all areas and obliterates, or removes, the initial surface finish as seen by visual inspection at a minimum of 10X magnification.

   5. MULTIPLE COVERAGE: The minimum peening time to get full coverage is multiplied to get coverage greater than full coverage. For example, the time to get 125 percent coverage is 1.25 times the minimum time for full coverage, and the time to get 200 percent coverage is 2.0 times the minimum time for full coverage.

   6. SATURATION CURVE: A plot of the Almen test strip arc height in relation to the test strip peening time.

   7. SATURATION POINT: The point on the saturation curve at the minimum peening time for which the Almen test strip arc height will increase by not more than 10 percent at 2.0 times the peening time.

3. SUBTASK 70-38-16-300-003 Equipment

   1. The bead peen machine must have the features that follow:

      1. Moveable nozzle(s) that direct the bead spray streams in a controlled and repeatable manner.

      2. A machine function that lets the bead stream flow stabilize before the nozzles are aimed at the part.

      3. A rotating or traversing table that moves the part at a specified rate through the bead spray stream.

      4. A mechanism that automatically moves the bead peening media and feeds it through the machine to the nozzles.

      5. A timing device that controls the peening time.

      6. A meter to record machine operation hours.

      7. The dry-peening machine must have a separator that automatically removes broken beads during machine operation. Cabinets with such separators are available from the sources in the list that follow and are also available from other sources. Refer to the V2500 Vendor List - Organizations Technical Information Repository for the source names/addresses identified by these numbers:

         05314

         OK7M2

         62555

   2. The automated bead peen machine must have a process start-and-stop safety interlock switch that operates as follows:

      1. Keeps a constant table rotation or movement of the traversing table to prevent bead spray on one location for too much time.

      2. Shuts off the peening media stream air pressure supply to stop the bead spray when the rotation or movement of the table stops.

   3. Almen test strips, test blocks, and gages must agree with the requirements of AMS 2430.

      1. The Almen gage must have 0.0001 in. (0.0025 mm) maximum graduations. Refer to SAE J442 Surface Vehicle Standard for Test Strip, Holder, and Gage for Shot Peening.

      2. Almen test strips and Almen gages are available from the sources in the list that follows and are also available from other sources. Refer to the Tool And Equipment Source Code Index in the V2500 Vendor List - Organizations Technical Information Repository for the source names/addresses identified by these numbers:

         Almen Test Strips:	Almen Gage:
         1LUR8	0CJ83
         3W485	3W485
         92830

4. SUBTASK 70-38-16-300-004 Process Requirements

   1. The operator must be sure that after bead peening, both sides of vanes must show coverage that is the same in all areas under 10X magnification, and that vane leading and trailing edges show no signs of rollover.

   2. When no specific areas to be peened are indicated, parts must be peened on all areas other than small holes and cavities to which the beads have no access.

   3. When taper peening is specified, it is necessary to put the surface in the fringe area of the peening stream or use auxiliary nozzles that peen at one half full arc height pressure. Be careful not to hit this surface with the full intensity of the full arc height pressure peening stream. Effective zero intensity is in the outer fringes of the peening stream. The taper peen area must get full coverage.

   4. When bead peening of gear teeth and splines is specified, the total area of flank surfaces, top lands, and roots of teeth must be peened to the specified intensity; ends of teeth must be peened but the minimum peening intensity requirement will be waived.

   5. Unless given differently, the variation in boundaries of areas to be peened, when limited, must be -0.000 in. to +0.125 in. (-0.000 mm to 3.175 mm) into the area where peening is not specified.

   6. A +30 percent/-0 arc height difference from the specified intensity is permitted, but with no less than 3 Almen units or 0.003 in. (0.076 mm) arc height, unless given differently for a specific part.

      1. If the intensity specified for a part is 10N, an arc height of 0.010 in. - 0.013 in. (0.254 mm - 0.330 mm, or +30 percent/-0) is satisfactory; if the specified arc height of another part is 6N, an arc height of 0.006 in. - 0.009 in. (0.153 mm - 0.228 mm, or +50 percent/-0) is satisfactory. In each example, it is best to have the mean arc height to make sure that a small decrease or increase in shop air pressure will not put the peening intensity out of the specified limits.

         NOTE

         If it is necessary that a tolerance on peening intensity be specified other than that shown above, specify either a range of intensity or a basic intensity with a tolerance; thus, an intensity of either 12N - 15N or 12N +3N/-0 shows an arc height of 0.012 in. - 0.015 in. (0.305 mm - 0.381 mm) on the Almen "N" test strip.

   7. "Peening optional" means that peening on the areas shown is optional and can have full, partial, or no coverage.

   8. To make arc height measurements on the Almen gage, put the test strip on the gage so that the indicator pointer pushes against the test strip surface that is not peened. The arc height is read over a chordal length of 1.25 in. (31.750 mm).

   9. Almen test strips must be flat within 0.000 in. +/- 0.001 in. (0.000 mm +/- 0.025 mm) when measured on an Almen gage. When you measure the flatness of the specimen, you must make an adjustment for the effect of the gage magnet; measure the flatness from both faces of the specimen and then get an average of the results.

   10. Record the Almen test strip readings and be sure to keep these records for each part to show that the part agrees with the intensity requirements. You must keep these records for a time that agrees with regulatory and customer requirements for quality records.

5. SUBTASK 70-38-16-300-005 Prerequisite

   1. Examine equipment for:

      1. Condition.

      2. Recommended nozzle size (3/8 in. or 9.53 mm diameter) and air jet size (1/4 in. or 6.35 mm diameter).

      3. Wear of hoses.

   2. Do all necessary FPI, FMPI, or other NDT inspections before peening.

   3. Machine preventative maintenance and verification of operation parameters must be done at an interval not to exceed 14 months.

6. SUBTASK 70-38-16-300-006 Procedure

   1. Fill the bead peening machine; use either the wet or dry machine, as follows:

      1. Fill the wet machine with solution code 207.

      2. Fill the dry machine with dry glass beads CoMat 02-401 BEAD, GLASS, AMS 2431/6 AGB-25 or CoMat 02-400 BEAD, CERAMIC, AMS 2431/7.

         NOTE

         Other size beads can be used that meet the AMS 2431 specification and are used in compliance with AMS 2430 procedures.

   2. Set up the test block and test strip in the cabinet and fixture so that the position of the strip in relation to the nozzle or nozzles will be exactly the same as the position of the part to be peened. Adjust the nozzle position(s) so that the peening streams have an angle of impingement as nearly perpendicular as possible to the areas to be peened.

   3. To establish the air pressure necessary to get the arc height for the specified intensity, peen the Almen test strip for 20 seconds minimum or for an interval of time necessary to give full coverage, whichever is longer. Remove the test strip from the cabinet and measure the strip on an Almen gage.

      NOTE

      If you use more than one nozzle to get coverage, turn on all nozzles for this test; use a test strip for each nozzle. The test strip must show full coverage that is the same in all areas and specified arc height.

   4. If the arc height is not at the mean specified for the part, do as follows:

      1. Discard the test strip and put a new test strip in the test block.

      2. Increase or decrease the air pressure, as necessary.

      3. Peen the new strip at the altered air pressure.

      4. Remove the strip and measure the arc height with an Almen gage. Do this operation again until you get the necessary arc height.

   5. To calculate the correct peening time, make a saturation curve to show the peening time in relation to the arc height.

      1. Peen a minimum of four Almen test strips for different lengths of time at the same pressure and table speed.

      2. Measure the arc height of each strip on an Almen gage.

      3. Make a plot of the arc height in relation to the peening time to get a saturation curve. Refer to SAE J443 Procedures for Using Standard Shot Peening Test Strip. Peen more Almen test strips for different lengths of time if more data points are necessary.

      4. The saturation point is at the minimum peening time for which two times the peening time will increase the arc height by not more than 10 percent or 0.001 in. (0.025 mm), whichever is greater. The arc height at the saturation point is the peening intensity.

         NOTE

         Test strips peened for the saturation time or longer must show full coverage.

      5. If the peening intensity is not in the tolerance limits specified for the part, adjust the air pressure or table speed, or use a different size or type bead, and then do this saturation curve procedure again.

   6. The arc height must be determined for each test strip on the fixture at the start and at the end of each lot (same set-up, parameters, test piece fixture), the start of each work shift, and a minimum of every eight hours of machine operation. Record the arc height readings and keep these records for each part.

   7. If wet bead peening is used, do a check of the peening media content of the slurry after every four hours of machine operation. Refer to solution code 207.

   8. If dry bead peening is used, test the bead by sieve analysis every eight hours of machine operation.

      NOTE

      The dry bead peening machine must have a separator that automatically removes broken beads during operation.

      1. Use the sieve analysis procedure in AMS 2430 in compliance with ASTM E 11 and ASTM D 1214.

      2. Weighed increments must satisfy the media maintenance requirements of AMS 2430.

      3. It is not necessary to do the AMS 2430 shape test of in-process media for TASK 70-38-16-380- 501.

   9. Make sure that the specified cleaning process cleaned the part. Then, when necessary, mask areas of the part not to be peened, use either a mechanical mask or sufficient layers of one of the tapes listed in TASK 70-38-13-380-501 shotpeening with cast steel shot (conforming to the current revision of AMS 2430 and AMS 2431) or conditioned cut wire shot (conforming to the current revision of AMS 2430 and AMS 2431).

      NOTE

      Bead peen outside the repair area is optional and full coverage is not necessary, unless given differently, bead peen is not permitted on knife-edges, threads, splines, or surfaces whose finish can be harmed by the peening process.

   10. Mount the part in the fixture; the area to be peened must be in exactly the same position that the test block previously occupied.

   11. 

       CAUTION

       WHEN BEAD SLURRY PEENING OR WHEN DRY BEAD PEENING IN CABINETS THAT HAVE SEPARATORS, ALL PARTS MUST HAVE A FINISH THAT IS THE SAME IN ALL AREAS. IF ANY PARTS SHOW A DULL MATTE FINISH, RATHER THAN THE USUAL SHINY PEENED FINISH, THIS IS AN INDICATION THAT THE SEPARATOR DOES NOT OPERATE CORRECTLY.

       Peen the applicable area of the part. Use the same time, table speed, and air pressure that was necessary to get the specified intensity on the test strip.

   12. 

       CAUTION

       IF YOU DO NOT REMOVE ALL REMAINING TAPE BEADS, OR OTHER UNWANTED MATERIAL (THAT IS, FOREIGN OBJECT DEBRIS (FOD)) FROM THE PART, SEVERE ENGINE DAMAGE CAN OCCUR.

       Remove masking, if used, and clean all remaining masking material from the part by TASK 70-11-26-300-503 the procedure to locally swab or wipe clean with solvent.

   13. Blow off all beads and broken bead pieces with clean filtered air. Clean the part by TASK 70-11-03-300-503 procedure to degrease parts by aqueous cleaning. Visually examine the peening, at 10X magnification, to see that it is applied equally and with full coverage. Holes and edges of the part must be free from rolled metal and all remaining beads and pieces.

   14. 

       CAUTION

       ALL POST-PEEN OPERATIONS MUST AGREE WITH THE MATERIAL REMOVAL REQUIREMENTS OF AMS 2430. NO COMPLIANCE WITH THESE REQUIREMENTS COULD CAUSE A LOSS OF THE COMPRESSIVE RESIDUAL STRESS THAT WAS A RESULT OF THE PEENING PROCESS.

       Preserve, as necessary by TASK 70-38-05-380-501 procedure to apply corrosion inhibitor.