1、AGMAINFORMATIONSHEET(This Information Sheet is NOT an AGMA Standard)AGMA938-A05AGMA 938-A05AMERICAN GEAR MANUFACTURERS ASSOCIATIONShot Peening of GearsiiShot Peening of GearsAGMA 938-A05CAUTION NOTICE: AGMA technical publications are subject to constant improvement,revision or withdrawal as dictated
2、 by experience. Any person who refers to any AGMAtechnicalpublicationshouldbesurethatthepublicationisthelatestavailablefromtheAs-sociation on the subject matter.Tablesorotherself-supportingsectionsmaybereferenced. Citationsshouldread: SeeAGMA938-A05,ShotPeeningofGears,publishedbytheAmericanGearManuf
3、acturersAssociation, 500 Montgomery Street, Suite 350, Alexandria, Virginia 22314,http:/www.agma.org.Approved May 3, 2005ABSTRACTThisinformationsheetprovidesatoolforgeardesignersinterestedintheresidualcompressivestressproper-tiesproduced byshot peening and itsrelationship to gearing. It also discuss
4、es shot media materials, deliverymethods, and process controls.Published byAmerican Gear Manufacturers Association500 Montgomery Street, Suite 350, Alexandria, Virginia 22314Copyright 2005 by American Gear Manufacturers AssociationAll rights reserved.No part of this publication may be reproduced in
5、any form, in an electronicretrieval system or otherwise, without prior written permission of the publisher.Printed in the United States of AmericaISBN: 1-55589-847-5AmericanGearManufacturersAssociationAGMA 938-A05AMERICAN GEAR MANUFACTURERS ASSOCIATIONiii AGMA 2005 - All rights reservedContentsPageF
6、oreword iv.1 Scope 1.2 Normative references 1.3 Theory of shot peening 14 Effects of shot peening 25 Shot delivery methods 5.6 Shot media 67 Shot peening process controls 68 Recommendations for specifying shot peening parameters 10Bibliography 14.AnnexesA Graphs and figures expressed in U.S. customa
7、ry units 12Figures1 Bending fatigue improvements from shot peening 2.2 Typical residual stress curve from shot peening 3.3 Approximate depth of compressive layer in steel versus Almen intensity 44 Extrapolation of depth of shot peened compressive layer when surfacehas residual compressive stress pri
8、or to shot peening 4.5 Relative changes from various shot peening intensities using the sameshot size 5.6 Spiral separator for removing broken shot media 77 Shot intensity measurement using Almen strip 88 Comparable intensity values between N, A, and C scales 89 Examples of Almen block mounting on a
9、n actual gear part and on arepresentative geometry 9.10 Saturation curve 9Tables1 Shot size versus intensity range 5AGMA 938-A05 AMERICAN GEAR MANUFACTURERS ASSOCIATIONiv AGMA 2005 - All rights reservedForewordThe foreword, footnotes and annexes, if any, in this document are provided forinformationa
10、l purposes only and are not to be construed as a part of AGMA InformationSheet 938-A05, Shot Peening of Gears.Thepurposeofthisinformationsheetistoprovideacentralizedreferenceforshotpeeninginformation for other AGMA documents. Previously, multiple AGMA documents hadvarying descriptions of the shot pe
11、ening process. This information sheet provides athorough process description to assist the gear designer in understanding andimplementing the shot peening process.ThefirstdraftofAGMA938-A05wasmadeinAugust2003. ItwasapprovedbytheAGMATechnical Division Executive Committee in May 2005.Suggestionsforimp
12、rovementofthisdocumentwillbewelcome. TheyshouldbesenttotheAmericanGearManufacturersAssociation,500MontgomeryStreet,Suite350,Alexandria,Virginia 22314.AGMA 938-A05AMERICAN GEAR MANUFACTURERS ASSOCIATIONv AGMA 2005 - All rights reservedPERSONNEL of the AGMA Metallurgy and Materials CommitteeChairman:
13、Phil Terry Lufkin Industries, Inc.Vice Chairman: Dale J. Weires Boeing Defense therefore, this docu-ment is classified as an information sheet and not astandard. This document intentionally avoids anyreference to quantifying potential increases in gearratingsthroughtheuseofshotpeening. Anyratingsinc
14、reaseattributedtoshotpeeningshouldbeagreedupon between the gear manufacturer and purchas-er, and preferably verified through testing.This document is intended for use by those experi-encedingearmaterialsanddesign. Itisnotintendedfor use by the engineering public at large.Annex A provides figures and
15、 tables in U.S.customary units.2 Normative referencesThe following documents contain provisions which,throughreferenceinthistext,constituteprovisionsofthisinformationsheet. Atthetimeofpublication,theeditions were valid. All publications are subject torevision, and the users of this information sheet
16、 areencouraged to investigate thepossibility ofapplyingthe most recent editions of the publications listed.ANSI/AGMA1012-G05,GearNomenclature,Defi-nitions of Terms with Symbols.AMS-S-13165, Shot Peening of Metal Parts (for-merly MIL-S-13165).3 Theory of shot peeningThe primary purpose for shot peeni
17、ng is to inducebeneficial residual compressive stresses in thesubsurfacelayerofapart. Thisoccursbybombard-ing a metals surface with small, round particlescalled shot. Each impact of the shot media has theeffect of leaving a small hemisphere of residualcompressivestressthatoccursfrom localizedyield-i
18、ng of the base material at the point of shot impact.The materials surface attempts to restore itself, butis restrained by adjacent material, resulting in aresidual compressive stress. Through repeatedimpacts that create overlapping dimples, a uniformlayer of residual compressive stress can be ex-pec
19、ted, provided the shot peening process andmedia are carefully controlled.Duringservice,agearrootfilletissubjecttorepeatedbendingloads. Theseloadsgenerateappliedtensilestresses which are highest in the materials subsur-facelayer. Withtheadditionofshotpeening,appliedbendingstressesareopposedbyresidual
20、compres-sive stresses that have the effect of resisting fatiguecrack initiation and growth throughout the compres-sive layer. For bending fatigue improvement, shotpeening should extend, as a minimum, from thebottom of the root fillet past the tangent pointbetween the root and flank.The beneficial ch
21、aracteristics of residual compres-sive surface stresses are associated with theireffects on fatigue crack initiation behavior. Netstress is the summation of applied and residualstress. When the magnitude of the residual com-pressive stress is greater than the magnitude of theapplied tensile stress,
22、a net compressive stress iscreated. In theory, fatigue cracks will notinitiate inanet compressive stress zone. In addition, fatiguecracksdonotpropagateasreadilyinacompressivestress zone.Residualcompressivesurfacestressesareeffectivein improving bending fatigue life in the elasticmaterial behavior (h
23、igh cycle fatigue) regime.Loading in the plastic material behavior (low cycle)regimeeliminateslifeimprovementeffectsofresidu-al compressive stresses. Failures in the elasticmaterial regime generally initiate at the surface,making surface compressive stresses effective.AGMA 938-A05 AMERICAN GEAR MANU
24、FACTURERS ASSOCIATION2 AGMA 2005 - All rights reservedResidual compressive stress can fractionally in-creasetheelasticendurancestrengthorsignificant-ly increase high cycle fatigue life. Endurancestrengthimprovementswithcompressivestressarenot a direct correlation and only applicable in theelastic be
25、havior regime. For example, introductionof 700 MPa of residual compressive stress doesnottranslate to a 700 MPa improvement in endurancestrength. The bending fatigue improvement trendswith shot peening are shown in figure 1.Gear designs typically experience bending fatigueenhancement when properly s
26、hot peened. Sincegear manufacturing techniques and applicationsdiffer dramatically, it is difficult to predict specificbending fatigue increases.Shotpeeningmaybeusedtomitigateconditionsthatreducehighcyclefatiguebehaviorsuchasgeometri-cal stress risers, machining stresses, grinding dam-age, or interg
27、ranular oxidation. When using shotpeening to mitigate stress riser effects, the depth ofthe compressive layer must exceed the stress riserdepth.The response of surface microstructures to shotpeening is highly dependent on the amount ofretainedaustenite. Shotpeeningwillinducesub-mi-croscopic dislocat
28、ions, strain induced phase trans-formations, or both. The retained austenitetransformation may improve residual compressivestresseffectsduetothevolumeincreasethatoccurswith martensite transformation.4 Effects of shot peeningThe shape of a typical residual stress curve fromshotpeeningisshowninfigure2
29、andisafunctionofthe hardness and strength of the material at thesurface. Heat treatmentand surfacemicrostructurehave significant effects on the residual stressresulting from shot peening.The important features of this curve are discussedbelow.4.1 Maximum compressive stressMaximum compressive stress
30、is proportional to thehardnessandstrengthofthegearmaterialssurfacebeing shot peened. For steel gears, a user canapproximate this value by multiplying the ultimatetensile strength by a factor of 55%. For example, agear surface with a hardness of 55 HRC (2000 MPatensile strength) will produce a maximu
31、m compres-sive stress of about 1100 MPa.From figure 2, it should be noted that:- Themaximum compressivestress remainsrela-tively unchanged regardless of peeningparameters, as it is primarily a function of thematerials surface hardness and strength;- The maximum compressive stress usuallyoccurs sligh
32、tly subsurface;801001201401601802002201.E+04 1.E+05 1.E+06 1.E+07Not shot peened Shot peenedBendingfatiguestrengthNumber of cycles (log scale)IncreasedendurancestrengthIncreasedfatigue lifeFigure 1 - Bending fatigue improvements from shot peeningAGMA 938-A05AMERICAN GEAR MANUFACTURERS ASSOCIATION3 A
33、GMA 2005 - All rights reserved- When the gear material is harder than the shotpeeningmedia,theresultingmaximumcompres-sivestressisreduced. Inaddition,surfacefinishis less affected when using shot media that issofter than the base material.4.2 Depth of compressive layerThe depth of the compressive la
34、yer from shotpeeningisafunctionofthepeeningparametersandmaterial properties, primarily surface hardness.Larger shot mediaand highershot velocityincreasetheimpactenergyandalsothedepthofcompressivelayer. Hardergearmaterialsrespondwithshallowerdepths of compression. The depth of compressivelayerversusA
35、lmenintensitycanbeapproximatedasshowninfigure3,assumingshotmediaisashardorharder than the surface being shot peened. See7.3.1 for discussion on Almen intensity.Itisimportanttorememberthatwhilethesurfacehasa residual compressive stress condition, there is adepth at which the stress field goes through
36、 theneutral axis and then becomes tensile.Gear heat treatments thatinduce residualcompres-sivestress(e.g.,carburization,inductionhardening)will produce a residual stress curve after shotpeeningthatdoesnotcrosstheneutralaxisnearthesurface. The depth of the compressive layer isdefined as the depth whe
37、re the positively slopingportion would cross the neutral axis if it wereextended as shown with the dotted line in figure 4.4.3 Surface residual compressive stressThe following statements and figure 5 generallyapply to the surface compressive stress:- The surface compressive stress is usually lesscom
38、pressive than the maximum compressivestress.- As shot velocity is increased for a selected shotsize to achieve a deeper depth of compression,the magnitude of surface compressive stressgenerally decreases. This tradeoff should beconsidered when selecting shot peening param-eters.- Alargershotsizeatth
39、esameshotpeenintensityas a smaller shot size will generally result in animproved surface finish and more surface com-pressive stress relative to the maximum com-pressive stress. Compressive depth propertiesshould be similar provided both shot sizes areused at the same intensity. The larger shot size
40、hasmoremassandwouldrequirealowerveloc-itythanthesmallershotsizetoachievethesameintensity. Thelargershotsizespreadstheimpactlocation over a greater surface area resulting inless dimpling.- Aroughersurfacefinishisgenerallyindicativeofa more aggressive shot peen with more pro-nounced “peaks and valleys
41、”.- A finer surface finish is generally indicative of aless aggressive shot peen with less pronounced“peaks and valleys”.0400.000 0.016Depth (below the surface)Surface0Maximum compressive stressSurface compressive stressDepth of compressive layerIncreasingresidualtensilestressIncreasingresidualcompr
42、essivestressFigure 2 - Typical residual stress curve from shot peeningAGMA 938-A05 AMERICAN GEAR MANUFACTURERS ASSOCIATION4 AGMA 2005 - All rights reservedNOTE:1) See 7.3.1 for explanation of intensity values.2) See annex A for English equivalent.Depthofcompressivelayer,mmAlmen intensityFigure 3 - A
43、pproximate depth of compressive layer in steel versus Almen intensity-160-120- 80- 4000.002 0.004 0.006 0.008 0.0100Depth of compressive layerSurface compressive stressMaximum compressive stressResidualcompressivestressDepth (from surface)Figure 4 - Extrapolation of depth of shot peened compressive
44、layer when surface has residualcompressive stress prior to shot peeningAGMA 938-A05AMERICAN GEAR MANUFACTURERS ASSOCIATION5 AGMA 2005 - All rights reserved-180-140-100- 60- 20200.000 0.004 0.008 0.012 0.016DepthLower intensity Higher Intensity00ResidualcompressivestressFigure 5 - Relative changes fr
45、om various shot peening intensities using the same shot size- Using the proper shot intensity range for a givenshotsizeisimportant. Usingveryhighintensitiesfor a given shot size in an attempt to achievedeep compressivelayer propertiesis notrecom-mended because of the potential of reducing thecompres
46、sivesurfaceproperties. Refertotable1forguidelinesonappropriateintensityrangesforvarious shot sizes.- Should the designer wish to maximize compres-sivedepthandsurfacecompressiveproperties,adualshotpeenisrecommended. Thisconsistsoftwo shot peen operations. The first shot peen isusuallyperformedwithala
47、rgermediaatahigherintensity to achieve compressive depth proper-ties. Asecondshotpeenoperationisusuallyper-formed with a smaller shot size at a lowerintensitytoimprovethesurfacefinishandresult-ing surface compressive stress.5 Shot delivery methodsAccelerationoftheshotmediaisgeneratedbyoneofthe follo
48、wing methods.5.1 Air pressure/nozzleThis method uses a compressed air system todelivertheshotthroughanozzle(s). Shotvelocityisadjusted primarily by modifications in air pressuresettingsandnozzleorificesize. Thisisthepreferredmethod of shot peening gears as the nozzle(s) canbe directed at specific lo
49、cations, such as the gearroot.5.2 Centrifugal wheelThis method uses a paddle wheel configurationwhere shot is fed into the center of a rotating wheel.Therotationofthewheelacceleratestheshot. Shotvelocity is adjusted primarily by modifications inwheel speed settings. The primary advantage of acentrifugalwheelisthatlargevolumesofshotcanbedelivered in short time periods.Table 1 - Shot size versus intensity rangeCast steelshot sizeRecommended intensityrange, mmMinimum Maximum70 0.20 N 0.18 A110 0.10 A 0.25 A170 0
