1、11FTM20AGMA Technical PaperCase Study InvolvingSurface Durability andImproved SurfaceFinishBy G. Blake and J. Reynolds,Rolls-RoyceCase Study Involving Surface Durability and ImprovedSurface FinishGregory Blake and Jeff Reynolds, Rolls-RoyceThe statements and opinions contained herein are those of th
2、e author and should not be construed as anofficial action or opinion of the American Gear Manufacturers Association.AbstractGear tooth wear and micropitting is a very difficult phenomenon to predict analytically. The failure mode ofmicropittingiscloselycorrelatedtothelambdaratio12. Micropittingcanbe
3、thelimitingdesignparameterfor long-term durability. Also, the failure mode of micropitting can progress to wear or macropitting, thenmanifest into more severe failure modes such as bending. The results of a gearbox test and manufacturingprocess development program will be presented to evaluate super
4、 finishing and its impact on micropittingTestingwasdesignedusinganexistingaerospacetwostagegearboxwithalowlambdaratio. Allgearswerecarburized, ground and shot peened. Two populations were then created and tested. One population wasfinish honed and the second was shot peened and isotropic super finis
5、hed.A standard qualification test was conducted for 150hrs at maximum continuous load. The honed gearsexperienced micro and macro pitting during the test. The Isotropic Super Finishing (ISF) gears were alsotestedfor150hrsunderthesameloading. TheISFgearswereabsentofanysurfacedistress. TheISFgearswere
6、 further subjected to a 2000hr endurance test. The ISF gears had less surface distress after 2000hrsthan the baseline honed gears after 150hrs.Copyright 2011American Gear Manufacturers Association1001 N. Fairfax Street, 5thFloorAlexandria, Virginia 22314October 2011ISBN: 978-1-61481-019-33 11FTM20Ca
7、se Study Involving Surface Durability and Improved Surface FinishGregory Blake and Jeff Reynolds, Rolls-RoyceIntroductionIsotropic super finishing (ISF) is a technology that public literature suggests having potential for increasedpower density 3. Three tests were conducted to test the surface durab
8、ility difference between honing andISF. Demonstration of bending fatigue strength was out of scope. Previous testing has shown ISF not toincrease bending fatigue strength 4.The testing utilized a Rolls Royce technology demonstrator gearbox assembled with a gas turbine engine.Testing was performed at
9、 Rolls Royce Corporation in Indianapolis. The gear train on test was a compoundidlerarrangementaslabeledandshowninFigure1. Twosetsofgearsfromthesamemanufacturinglotwereused for testing. A comparison of the baseline gears and ISF gears is shown in Table 1.Figure 1. Rolls Royce demonstrator gear train
10、Table 1. Finishing processes of baseline and ISF test gearsMesh Gear Baseline ISF#2 D Ground, shot peened, honed Ground, shot peened, ISFC Ground, shot peened, honed,silver platedGround, shot peened, ISF, silverplated#1 B Ground, shot peened, honed,silver platedGround, shot peened, ISF, silverplated
11、A Ground, shot peened, honed Ground, shot peened, ISF4 11FTM20The configuration of Gear Cwas silver plated. As such, the ISF test gear was alsosilver plated. A chemicalprocess was usedto preparethe surfaceprior toplating tominimize alterationof thesurface. Measurementpresented later in this paper wi
12、ll show that.Test methods and parametersThree tests, using two different sets of gears, were conducted as part of this project. A Rolls Roycetechno-logydemonstratorgearboxwasusedforallthreetests. Thefirsttwotestswereconductedfor150hourseach.The third test was conducted for 2,000 hours.Anaerospacegas
13、turbineloadcyclewasselectedforthefirsttwo150hourtests. ThegraphshowninFigure 2isthetestcycle. Theloadcyclewasrepeatedtwenty-fivetimesforthebaselineandISFgears. Alltestingwasdone with MIL-L-23699 oil.TheISFgearswerereassembledandtestedforanadditional2,000plushours. Thetestwasconductedusingfourteen di
14、fferent duty cycle profiles. A summary of the actual time spent at power is shown in Figure 3.Figure 2. Endurance test six hour cycle repeated twenty five times for baseline and ISF gearsFigure 3. 2,000 hr endurance test time at HP5 11FTM20Baseline 150 hr test resultsThe gear tooth surface condition
15、 and any failure modes were classified using ANSI/AGMA 1010-E95 6.Table 2containsasummaryofthebaselinegearspost150hrtest. Figure 4,Figure 5,Figure 6,andFigure 7are low magnification white light photos of the active profile surfaces post test.Table 2. Post 150 hr engine test evaluation of baseline ge
16、arsGear Failure mode(s) per ANSI/AGMA 1010-E95Failure mode class General failure mode Specific mode / degreeD Wear Polishing ModerateContact fatigue Macropitting InitialContact fatigue Micropitting ProgressiveScuffing Scuffing MildC Contact fatigue Micropitting ProgressiveContact fatigue Macropittin
17、g InitialB Contact fatigue Micropitting ProgressiveA Contact fatigue Micropitting ProgressiveFigure 4. Baseline gear A, mesh #1, drive side, post 150 hr testFigure 5. Baseline gear B, mesh #1, post 150 hr test6 11FTM20Figure 6. Baseline gear C, mesh #2, post 150 hr test3Figure 7. Baseline gear D, me
18、sh #2, Post 150 hr testA dimensional and metallurgical evaluation was performed on all baseline gears. Allgears werefound tobeconforming. Figure 8 is a sample post test photomicrograph showing micropitting of gear C. Figure 9,Figure 10, and Figure 11 are post test analytical inspection traces showin
19、g the change in form.Figure 8. Sample metallurgical evaluation of gear C, mesh #2, displaying micropitting7 11FTM20Figure 9. Baseline gear D, mesh #2, analytical inspection, post 150 hr testFigure 10. Baseline gear C, mesh #2, analytical inspection, post 150 hr test8 11FTM20Figure 11. Baseline gear
20、B, mesh #1, analytical inspection, post 150 hr testRoughness measurements were made of the baseline gears prior to test as shown in Table 3.As stated previously, literature states that surface durability improves with increased specific oil filmthickness. Thecompositeroughness is onevariableinspecif
21、ic oilfilm thickness. As such, thegearfinishingprocess has an impact on the specific oil film thickness.The specific oil film thickness () was calculated for three roughness values, see Table 4. The values werecalculated at max HP and max oil temperature per AGMA 925-A03. The roughness values were s
22、electedbased on expected values for typical honing, threshold of honing, and ISF. The calculated specific oil filmthickness values were usedto guideselection of a finishingprocess toimprove surfacedurability. Measure-ment data from gears processed each of these four ways is presented later in this p
23、aper.Table 3. Roughness parameters of baseline gears as measured along involute, units = minPart name Ra Rp RtGear D, mesh #2 12.005 19.034 89.541Gear C, mesh #2 +9.599 +25.0261)73.3881)Gear B, mesh #1+6.611 +16.4641)48.7211)Gear A, mesh #1 11.222 33.209 57.504NOTE:1)Measurement performed post silve
24、r plate stripping.9 11FTM20Table 4. Calculated specific oil film thickness vs. roughness for different finishing processesFinishing process Ra minMesh #1 Mesh #2Production honing 12 0.8434 0.4881Threshold of honing 8 1.2882 0.7519ISF 2 5.2601 3.1025The contact fatigue margin of safety for both gear
25、meshes was calculated and presented in Table 5.Thespecificoilfilmthicknessofmesh#1isgreaterthanmesh#2,whilethecontactfatiguemarginofsafetyisless for mesh #1 than mesh #2.Honing testHoningisahardfinishingtechnologyforimprovinggeartoothsurfaceroughness7. Atestwasconductedtodetermine the threshold surf
26、ace roughness and the geometric interactions. An aerospace spur gear, asshowninFigure 12, was usedfor thehoningtest. Thegear materialandprehoneprocessingwerecommonbetween the test gear and those in the endurance testing. The process time was incrementally increased.Roughnessandformweremeasuredateach
27、interval. ThetestprocessislistedinTable 6. Itshouldbenotedthat other hone variables, such as hone material, hone geometry, stock removal, traverse speed, and rota-tional speed can also influence surface roughness and form. The variable cycle time was chosen based onexperience.Table 5. Contact fatigu
28、e MOS at max HPMesh ScMOS#1 1.190#2 1.340Figure 12. Honing test gear, 56 tooth, 6dp, 25npa, spur gear10 11FTM20Table 6. Honing trail process, X = normal processing timeStep Description1 Select production part (post grind, pre peen)3 Shot peen per RR specification4 Inspection involute, lead, roughnes
29、s, and waviness5 Hone (1.0X) using production setup and legacy machine6 Inspection7 Hone (1.9X)8 Inspection9 Hone (4.4X)10 InspectionThe post shot peen, pre hone, condition of the honing test gear is shown in Figure 13. Figure 14 shows thehoned surface after 4.4X the normal production process time.T
30、he involute form and surface roughness were measured at each interval. Figure 15 shows the change inroughness and form involute slope error as process time increased. The roughness values are listed inTable 7. The involute traces from each interval weresuperimposed andshown inFigure 16. The form err
31、orcan be seen as localized near the end of active profile verses true slope error.Figure 13. Starting condition, post shot peen, pre hone test gearFigure 14. Post final hone step, 4.4X normal hone process time11 11FTM20Table 7. Roughness vs. hone processing time, units = minProcess time factor Ra Rv
32、 Rt0.0 33.4 92.5 205.41.0 11.6 69.8 159.31.9 6.8 22.5 98.24.4 8.5 40.2 81.6Figure 15. Honing process time vs. gear profile slope error150 hr ISF test resultsA secondset of gears was processedusing ISF. TheISF gears were assembledinto thesame gearbox andtested to the same parameters as the baseline s
33、et. Table 8 shows the surface roughness of the ISF gears.Figure 17, Figure 18, Figure 19, andFigure 20arelowmagnificationwhitelight photos of theISF gears posttest. The post test surface distress was minimal and the gear deemed acceptable for further testing.2,000 hr ISF test resultsThesamegearsused
34、inthe150hrtestwerereassembled. Testingwascontinuedatthesameparametersfor2,000 hrs. Figure 21, Figure 22, Figure 23, andFigure 24are lowmagnification whitelight photos of theISFgears post 2,000 hrs. The gears showed little surface distress.Table 8. ISF test gears, roughness parameters as measured alo
35、ng involute units = minPart name Ra Rp RtGear D, mesh #2 1.2 5.8 13.0Gear C, mesh #2 1.7 6.1 16.0Gear B, mesh #1 1.8 8.5 15.9Gear A, mesh #1 2.2 8.3 19.212 11FTM20Figure 16. Hone specimen involute comparison after each hone cycle(A=4.4X,B=1.9X,C=1.0,D=0)Figure 17. ISF gear A, mesh #1, Post 150 hr te
36、stFigure 18. ISF gear B, mesh #1, post 150 hr test13 11FTM20Figure 19. ISF gear C, mesh #2, Post 150 hr testFigure 20. ISF gear D, mesh #2, post 150 hr testFigure 21. ISF gear A, mesh #1, post 2,000 hr test14 11FTM20Figure 22. ISF gear B, mesh #1, post 2,000 hr testFigure 23. ISF gear C, mesh #2, po
37、st 2,000 hr testFigure 24. ISF gear D, mesh #2, post 2,000 hr testISF process developmentThe design requirements for the four gears were as shown in Table 9. The area that is required to be ISFfinished is the full face width including the gear faces on Gear A, Gear B, Gear C, and Gear D.Media select
38、ionSelection of the media originally was based upon a test gear for theprocess approval. The gear had amuchlarger pitch and the media was able to fully engage throughout the profile and root of the test gear. Minimalprofile change was present with the process approval test gear. Correct media select
39、ion is critical to asuccessful isotropic finishing process.15 11FTM20Figure 25showsGearBandapieceoftheinitialmediausedtoprocessthegear. Ascanbeseenthemediaistoo large to contact the full depth of the tooth.The media used is a mixture of several different sizes and shapes, as shown in Figure 26.Figur
40、e 27 shows the before ISF and post ISF involute form using the initial media.Table 9. Design requirements for ISF development units = minPart name Surface RaGear A 4Gear B 4Gear C 4Gear D 4Figure 25. ISF process development shown with gear BFigure 26. ISF process development media mix16 11FTM20Figur
41、e 27. ISF process development gear chart showing excessive tip stock removalMedia selection for 2nd lotSelectionof themediafor thesecondlot of parts involvedanewmediathatfit thegear teethpitch. Figure 28shows gear B and the smaller media fitting into the tooth space to the root. The final media mixt
42、ure used isshown in Figure 29.Dimensional change through ISFThe dimensional change through ISF was established during process development.The pre and post measurement data of roughness and basic dimensions is shown inTable 10 andTable 11.Figure 30showsthepreandpostinvoluteform. Thedegradationobserve
43、dintheinitialtrials(Figure 27)wereeliminated with the smaller media.Figure 28. Gear B with smaller ISF media17 11FTM20Figure 29. ISF process development final ISF media mixture used for test gearsTable 10. Pre ISF measurementsRa aftershot peenRootdiameterOutsidediameterFace width DOPGear A 19.2 1.68
44、3 2.009 .892 2.081Gear B 23.4 5.847 6.1753 .678 6.2635Gear C 19.7 2.787 3.2672 1.267 3.2945Gear D 20.2 4.751 5.199 1.057 5.2357Table 11. Post ISF measurementsRa after ISF RootdiameterOutsidediameterFace width DOPGear A 2.728 1.683 2.009 .892 2.081Gear B 2.547 5.847 6.1753 .677 6.2633Gear C 2.263 2.7
45、87 3.2672 1.267 3.2943Gear D 2.826 4.751 5.199 1.057 5.2355Figure 30. Pre and post ISF involute form traces18 11FTM20ConclusionsS Thecasestudydemonstratedthatsurfacedurabilityisrelatedtospecificoilfilmthicknesswhichisrelatedto surface roughness.S Decreased surface roughness is one method of increasi
46、ng specific oil film thickness.S Honing and ISF are gear finishing processes that improve surface finish.S The ISF process produced a surface with a lower roughness than honing.S Gears processedwithISF hadimprovedresistancetomicropittingandthus longersurfacedurabilitylife.AcknowledgmentsThe authors
47、would like to thank the following organizations for their contributions.S Rolls-Royce Helicopter Engine Program for technical oversight, funding, and support of this project.S Metal Improvements and REM Chemical for super finishing selected test gears.References1 Drago, R. (1988), Fundamentals of Ge
48、ar Design, Butterworth Publishers Stoneham, MA, 1988.2 Alanou, M., Evans, H., Krantz, T., Snidle, R., An Experimental Investigation of the Influence of theLubrication Viscosity and Additives on Gear Wear, Report # ARL-TR-3126, US Army Research Lab,Cleveland, OH, 2005.3 Manesh, A., Niskanen, P., Engi
49、neered and Superfinished Surfaces for Precision AerospaceApplications ITT Research Institute, Chicago, IL, PTSM 02-001, 2003.4 Blake, G., Effects of Superfinishing on Bending Fatigue, 06FTM01.5 AGMA 925-A03, Effect of Lubrication on Gear Surface Distress.6 ANSI/AGMA 1010-E95, Appearance of Gear Teeth -Terminology of Wear and Failure.7 Modern Methods of Gear Manufacturing, published by National Broach & Machine, 1972.
