1、08FTM10AGMA Technical PaperThe Effect ofSuperfinishing on GearMicropitting, Part IIBy L. Winkelmann, O. El-Saeedand M. Bell, REM Chemicals, Inc.The Effect of Superfinishing on Gear Micropitting, Part IILane Winkelmann, Omer El-Saeed and Matthew Bell, REM Chemicals, Inc.The statements and opinions co
2、ntained herein are those of the author and should not be construed as anofficial action or opinion of the American Gear Manufacturers Association.AbstractOne of the most common failure mechanism of highly stressed case carburized gears is micropitting (graystaining). 1,2,3 The standard FZG gear test
3、 (FVA Work Sheet 54) is generally used to determine themicropitting load capacity of gear lubricants. In recent years, FZG gear testing has also demonstrated itsusefulness for evaluating the effect of superfinishing on increasing the micropitting load capacity of gears.Suchstudies,however,canonlybea
4、ffordedbymajorcorporationsorresearchconsortiumswherebythedatais typically kept confidential. Results from the Technical University of Munich were previously presented inPart 1 of this paper.4 Part II will present the results of Ruhr University Bochum. Both research groupsconcluded that superfinishin
5、g is one of the most powerful technologies for significantly increasing the loadcarrying capacity of gear flanks.Copyright 2008American Gear Manufacturers Association500 Montgomery Street, Suite 350Alexandria, Virginia, 22314October, 2008ISBN: 978-1-55589-940-03The Effect of Superfinishing on Gear M
6、icropitting Part IILane Winkelmann, Omer El-Saeed and Matt Bell, REM Chemicals, Inc.IntroductionIt shouldbenotedfrom theoutset that the datapre-sented in Part I and Part II of this paper was gener-atedbyindependentlaboratories. Superfinishingofthegearswastheauthorssolecontributiontothesestudies. The
7、authorsprovidednoinputontheselec-tion of the testing facilities, procedures or parame-ters. Theconclusions listedat theendof this paperwere solely those of the testing laboratory.Part I of this paper discussed the FZG Brief Test ofGray Staining (BTGS), which was designed toquickly induce micropittin
8、g. It is an economical testin terms of cost and time to determine how lubri-cants, lubricant temperature, coatings and surfacefinishes influence micropitting. The BTGS, showedthat superfinishing significantly reduces micropit-tingincomparisontobaselinegears.4 Thisfindingstresses the importance of su
9、rface finish for resist-ing the formation of micropitting.Part II of this paper discusses the results of a moreintensive micropitting testing performed accordingto FVA-Information-sheet 54/I-IV. The mineral oilused for lubrication was an ISO viscosity class 200which contains a special additive (the
10、nature of theadditiveisunknowntotheauthors)toreducethemi-cropitting carrying capacity. Baseline tests with anon-modified standard-FZG-C-gear were carriedouttodemonstratethemicropittingpropertiesoftheoil. The test gears were standard-FZG-C-gearswhichhadthesurfacemodifiedby superfinishingtoa low Rough
11、ness Average (Ra). The pitch line ve-locityduringalltestingwassetto8.3m/sandthelu-bricant was injected at 60C.A brief summary of the test procedure taken fromFVA-Information-sheet 54/I-IV is given below:The micropitting test may be used to determinequantitatively the influence of lubricants (especia
12、llyadditives), the lubricant temperature and other in-fluential factors on micropitting. The micropittingtest differentiates between oils and thus facilitatesthe choice of a lubricant with sufficient micropittingload capacity.The operating conditions (circumferential speedandlubricanttemperature)may
13、besuitablyadaptedfor testing lubricants for a large variety of applica-tions in the micropitting test. To differentiatebetween the various test options, which are carriedout according to the same test sequence, but withdifferent test conditions, they are designatedsimilarly to the FZG-scuffing test
14、by test gear type/circumferential speed/and lubricant (inlet tempera-tureinaccordancewith theselected test conditions(e.g., standard test: GT-Cl8.3190; GT =micropitting test).The micropitting test consists of two parts. It com-prises a load stage test followed by an endurancetest. In the load stage
15、test, the ability of the gear-lubricant tribological system to resist micropitting isdetermined under specified operating conditions(lubricant temperature. circumferential speed) intheform of a failureload stage. The endurancetestprovidesinformationontheprogressofthedamageafter higher numbers of loa
16、d cycles.(FVA 54.1-IVTest procedure for the investigation of the micropit-ting capacity of gear lubricants).5ExperimentalGear designThe gears used were the standard FZG-C typegearsformicropittingtesting. Table1givesthegen-eral data for these gears.Baseline GearsBaseline gears were unmodified from th
17、especifications given in the FVA Information Sheet54.Superfinished gearsAsetofgearsconformingtothespecificationsgivenin FVA Information sheet 54 were finished usingchemically accelerated vibratory finishing asdescribed in detail elsewhere.6, 7,This processutilizes high density non-abrasive media toe
18、nhance the performance of components that aresubjected to metal-to-metal contact or bendingfatigue. The Isotropic Superfinish (ISF) processgeneratesauniquesurfacewhencomparedtoeventhe finest honing and lapping in that it has no direc-tionality with a final surface roughness of 0.25 mmRaor less. This
19、 ISFsurface will be referred to assuperfinished throughout this paper.4Table 1. Specifications are given for FZG C-type gears for use in micropitting testing ac-cording to FVA Information Sheet 54 5Material 16 MnCr5 (DIN 17210)HeattreatmentS Case carburized to 750 HV1in the area of the tooth flankS
20、Case depth: 0.8 1.0 mm(after grinding)S Core strength: 1000 1250N/mm2S The zone close to the sur-face has no residual auste-nite content visible in the mi-croscope (7.5 mm6 945.1 167 1093.9 168 1244.9 169 1395.4 1610 1547.3 16Endurance test8 1244.9 80ffm20 mm10 1547.3 8010 1547.3 8010 1547.3 8010 15
21、47.3 8010 1547.3 80After each16-hour stageof the loadstage test andevery 80-hour cycle of the endurance test, the fol-lowing inspection and measurements were madeon the pinion:1. ffm, average profile form deviation, in mm,2. GF, micropitting area of gear flank, in %, and3. W, weight loss of gear, in
22、 mg.Failurewasdefinedby theaverageprofiledeviation(ffm). For the load stage test failure occurred whenffmexceeded7.5mm. Fortheendurancetestfailureoccurred when ffmexceeded 20 mm(seeTable3).Experimental dataTest run 1Theresultsofffm,GFandWaregiveninFigures2a,2band2c,forthebaselineandsuperfinishedgear
23、s,respectively. For the baseline gears, failure oc-curred at load stage 8, since ffmwas approximately8.5 mm. By the end of load stage 8, approximately30% of the gear tooth flank was covered withmicropitting, which increased to 60% by thecompletion of test run 1 (Load Stage 10), with W at54 mg.Thesup
24、erfinishedgears however,showednomea-surable variation for ffm, or GF at the end of loadstage10. Meanwhile,therewasonlyapproximately8 mg of weight loss on the pinion.Figures 3 and 4 show the presence of micropittingfor the baseline pinion and their absence on thesuperfinished pinion.6Figure 2. Measur
25、ements of test run 1 (load stage test) (a) ffm, (b) GF, (c) W on the baseline andsuperfinished pinionsTest run 2Test run2consistedof aloadstagetest followedbyan endurance test.Theresultsofffm,GF,andWaregiveninFigures5a,5band5c,forthebaselineandsuperfinishedgears,respectively. For the baseline gears,
26、 failure againoccurred at load stage 8, since ffmwasapproximately 8.5 mm. By the end of load stage 8,approximately 28%of thegear toothflank was cov-ered with micropitting, which increased to 60% bythe end of the load stage test with W at 57 mg.Intheendurancetestthebaselinepinionexceededthe 20-mm fai
27、lure limit during the third 80-hourcycle at load stage 10 with a ffmof approximately20.2mm.Bytheconclusionoftesting,ffm,GFandWreached 28 mm, 80%, and 128 mg, respectively.7Figure 3. Pictures of three teeth on thebaseline pinion after the completion of loadstage 10 of test run 1 show micropitting ona
28、pproximately 60% of the tooth flankFigure 4. Images showing the lack ofmicropitting on the superfinished pinionfollowing the completion of load stage 10 oftest run 1 showing no micropitting on thetooth flanks8Figure 5. Measurements of test run 1 (load stage test) (a) ffm, (b) GF, (c) W on the baseli
29、ne andsuperfinished pinionsThe superfinished gears, showed no measurablechangeforffmorGFattheendoftheloadstagetest.There was only approximately 6 mg of weight losson the pinion.Insharpcontrasttothebaselinegears,thesuperfin-ishedgearsshowedanegligibleffmof0.5mm,nomi-cropitting (GF of 0%), and a mere
30、13 mg W by theconclusion of Test Run 2.Figure 6 and Figure 7 show the presence of micro-pitting for the baseline pinion and their absence onthe superfinished pinion.9Figure 6. Three teeth on the baseline pinionafter test run 2 showing 79% of the tooth flankcovered in micropitting, with the band of t
31、hedensest micropitting specifiedThe thin (0.5mm) gray mark on the superfinishedpinion was attributed to the lack of tip relief on themating gear and was not a manifestation of micro-pitting. A better view of the gray mark is shown inFigure 8 where it was investigated under a micro-scope.Conclusions1
32、. The baseline gears had a lower resistance tomicropitting.a. Profile form deviation was 28 mm by the endof the endurance test.b. Micropitting coverage at the end of the loadstage test was 60% and 79% by the end ofthe endurance test.c. Weight loss was 38 mg after the load stagetest,and129mgbytheendo
33、ftheendurancetest.Figure 7. Picture of 3 teeth on thesuperfinished pinion after test run 2 (loadstage test and endurance test) showing a thingray mark that was attributed to the gears nothaving any tip relief. The gears show nomicropitting2. Thesuperfinishedgearsnevershowedmicropit-ting nor reached
34、any of the specified failurecriteria.a. Profile form deviation was 0 mm at the endthe load stage test and only 0.5 mmatthecompletion of the endurance test.b. Micropitting coverage at the end of both theloadstagetestandendurancetestwasnon-existent (0 %).c. Weight loss was 6 mg after the load stagetes
35、t, and 13 mg by the endof theendurancetest.3. The superfinishing results are remarkable de-spite the use of unfavorable oil which showeddamage at load stage 8 on the baseline gears.10Figure 8. Microscope image of the thin graymark of the dedendum circled on two flanksof the superfinished pinion. An
36、investigationdetermined that this mark was notmicropittingAcknowledgementsThe authors would liketo thank Dipl.-Ing. G Ltzig,and Prof. Dr.-Ing. W. Predki with the University ofBochum for performing the testing along with Win-ergy for their part in making this information avail-able.References1. Snidl
37、e, R.W., Evans, H.P., Alanou, M.P.,Holmes, M.J.A., Understanding Scuffing andMicropitting of Gears, RTO-AVT SpecialistsMeeting. Willimsburg, USA, 7-9 June 2003.RTO-MP-AVT-109.2. Astrene, T.T., 20 Minutes with Walt Musial,Tribology & Lubrication Technology. May 2004,p. 26-34.3. Barnett, D., Elderkin,
38、 J.P., and Bennett, W. AnAnalytical Approach to the Prediction of Micro-pitting on Case Carburized Gears, Gear Indus-try Journal. 4thQuarter 2006. p.32-46.4. Winkelmann, L., Bell, M. and King, B., TheEffect of Superfinishing on Gear Micropitting,Part I,63rdAnnual STLE Meeting, Cleveland,Ohio, USA, M
39、ay 21, 2008.5. Forschungsvereinigung Antriebstechnik, E.V,FVA Information Sheet, Research Projects Nr.54/I-IV, 1993.6. Arvin, J., Manesh, A., Michaud, M., Sroka, G.,and Winkelmann, L., The Effect of ChemicallyAccelerated Vibratory Finishing on GearMetrology, 02FTM01, AGMA Fall TechnicalMeeting, St.
40、Louis, MO, October 2002.7. Winkelmann, L., Bell, M., and El Saeed, O.,TheCapacity of Superfinished VehicleCompo-nents to Increase Fuel Economy, ASME 2007International Design Engineering TechnicalConferences & Computers and Information inEngineering Conference, September 4-7,2007, Las Vegas, Nevada, USA,DETC2007-34860.
