1、05FTM13Evaluation of the Scuffing Resistance of IsotropicSuperfinished Precision Gearsby: P.W. Niskanen, Alion Science and Technology, B. Hansen,Sikorsky Aircraft Corporation and L. Winkelmann,REM Chemicals, Inc.TECHNICAL PAPERAmerican Gear Manufacturers AssociationEvaluation of the Scuffing Resista
2、nce of IsotropicSuperfinished Precision GearsPaul W. Niskanen, Alion Science and Technology, Bruce Hansen, SikorskyAircraft Corporation and Lane Winkelmann, REM Chemicals, Inc.The statements and opinions contained herein are those of the author and should not be construed as anofficial action or opi
3、nion of the American Gear Manufacturers Association.AbstractThe high performance required from aerospace gears places stringent requirements upon the metallurgicalquality, geometry, and surface finish of mating parts. In an effort to meet their mission requirements,aerospace gears are often engineer
4、ed to operate near the upper bounds of their theoretical designallowables. Due to this, scuffing is a primary failure mode for aerospace gears.It was previously shown that specimens having an isotropic superfinish using chemically acceleratedvibratory finishing had an improved performance in Rolling
5、/Sliding Contact Fatigue (R/SCF) testing. Isotropicsuperfinishing improved R/SCF resistance up to nine times that of baseline test specimens. These tests alsodemonstrated the ability to successfully carry 30 percent higher loads for at least three times the life of thebaseline samples.1A study was t
6、hen conducted on actual gears having an isotropic superfinish. This study showed isotropicsuperfinishing technology increased a gears resistance to contact fatigue by a factor of three, and increasedbending fatigue resistance by at least 10 percent. 2 This increase in gear performance translates to
7、reducedoperation and sustainment costs, and also offers the potential for weight reduction in new transmissiondesigns.The present paper will discuss an additional study which is underway to determine and compare the scuffingresistance of isotropic superfinished aerospace gears to that of baseline gr
8、ound gears. Sample gears weremade from case carburized SAE 9310. These tests were conducted using a method that progressivelyincreases lubricant temperature until scuffing occurs, rather than the traditional load increasing method usedin FZG testing rigs. The results of the current testing reveals t
9、hat isotropic superfinished SAE 9310 specimensshow at least a 40 F higher lubricant temperature at the point of scuffing compared to as-ground baselinegears. Based on these results and the previous studies, it was concluded that this isotropic superfinishingtechnology should be incorporated in all f
10、uture aerospace gear designs. A later paper will report on similarscuffing testing performed on AMS 6308 gears due to run-outs achieved by both the baseline and isotropicsuperfinished samples during the current procedure.Copyright 2005American Gear Manufacturers Association500 Montgomery Street, Sui
11、te 350Alexandria, Virginia, 22314October, 2005ISBN: 1-55589-861-01Evaluation of the Scuffing Resistance of Isotropic Superfinished Precision GearsPaul W. Niskanen, Alion Science and TechnologyBruce Hansen, Sikorsky Aircraft Corporation andLane Winkelmann, REM Chemicals, Inc.IntroductionThe high perf
12、ormance required from aerospacegears places stringent requirements upon the met-allurgical quality, geometry, and surface finish ofmating parts. In an effort to meet these require-ments, mating parts are often designed to operatenear the upper bounds of their theoretical designstrength envelope. Pre
13、cision grinding after heattreatment is a standard practice used in the aero-space industry in order to obtain the necessary finaltolerances demanded by the need to provide higherpower density levels, without increasing componentsize or weight.Friction and wear between two sliding surfaces arein larg
14、e part dependent upon the finish of the sur-face. In particular, the roughness of the surface hasa strong influence on the coefficient of friction.Overcoming friction, especially in high performanceapplications, involves stringent lubrication require-ments. Examples of applications requiring excep-t
15、ional surface finish include gears and bearings. Anew surface finishing technology, known as Isotrop-ic Superfinish (ISF), has proven to be effective atreducing gear wear while at the same time reducinglubrication requirements. This revolutionarytechnology was developed for military helicopterapplic
16、ations as part of both the Instrumented Facto-ry for Gears (INFAC) and Power Transfer SystemsManufacturing (PTSM) programs, sponsored bythe US Army Aviation and Missile Command (AM-COM) at Redstone Arsenal. Initial testing per-formed by Alion Science and Technology Corpora-tion (formerly IIT Researc
17、h Institute), under theArmy MANTECH program (DAAJ09-95-C-0546),demonstrated that the isotropic superfinish processimproved performance in Rolling/Sliding ContactFatigue (R/SCF) specimens. This testing revealedthat superfinished samples yielded improvementsof up to 9 times the contact fatigue life as
18、 comparedto baseline test specimens. Isotropic superfinishedspecimens have also demonstrated the ability tosuccessfully carry 30 percent higher loads for atleast 3 times the life of the baseline samplesNO TAG.These promising INFAC results led to the compari-son testing of actual aerospace quality ge
19、ars in bothbaseline (final ground) and isotropic superfinishconditions. This second project, conducted underthe PTSM Program was titled, Engineered and Su-perfinished Surfaces for Precision Aerospace Ap-plications (Manufacturing Technology Report, Oc-tober 30, 2002, Contract No. DAAH23-00-C-R232). T
20、his project demonstrated the ability ofisotropic superfinishing to increase a gears resist-ance to contact fatigue by a factor of 3, and to in-crease bending fatigue resistance by at least 10percent. This increase in gear performance trans-lates to reduced operation and sustainment costsand offers t
21、he potential for weight reduction in newtransmission designs. However, the effect of theisotropic superfinish process on scuffing resistanceof gears remained unknown. This lack of knowl-edge was an obstacle to implementation of the pro-cess. Consequently, it was determined that data onscuffing resis
22、tance must be obtained.BackgroundThe isotropic superfinish process is a commerciallyavailable process that when applied to helicoptertransmission gears, can result in improved geartooth bending and contact fatigue resistance as wellas reduced noise, vibration, and operating tempera-tures. 3 4 The is
23、otropic superfinish process pro-vides a uniform surface finish by reducing the peakson the surface through the use of chemically accel-erated vibratory finishing.A detailed description of chemically accelerated vi-bratory finishing using high density, non-abrasivemedia has been published in the past
24、. 5 The fol-lowing is a brief summary of the technique. The iso-tropic superfinish is produced in vibratory finishingbowls or tubs. An active chemistry is used in the vi-bratory machine in conjunction with high density,2non-abrasive ceramic media. When introducedinto the machine, this active chemist
25、ry produces astable, soft conversion coating on the surface of themetal gears being processed. The rubbing motionacross the gears developed by the machine andmedia effectively wipes the conversion coating offthe “peaks” of the gears surfaces, but leaves the“valleys” untouched. No finishing occurs wh
26、ere me-dia is unable to contact or rub. The conversion coat-ing is continually re-formed and rubbed off duringthis stage producing a surface smoothing mecha-nism. This process is continued in the vibratorymachine until the surfaces of the gears are free ofasperities or until the surface attains the
27、desired lev-el of finish. At this point, the active chemistry isrinsed from the part and the gears are dipped in rustpreventive.The Army ManTech projects discussed above havealso shown that the isotropic superfinish process isrobust and suitable for production environments. Itdoes not require any un
28、usual or financially signifi-cant unique tooling, fixtures, or equipment. Thebudgetary cost for a “Turn Key” isotropic superfinishprocessing system is between $45,000 and$75,000. The gear performance benefits of this pro-cess, coupled with its suitability and affectability forshop floor use supports
29、 additional testing ofisotropic superfinish gears to help pave the way forimplementation of the technology in Army weaponsystems.As such, Sikorsky Aircraft Corporation and REMChemicals, Inc., teaming with the United StatesArmy and Navy, conducted a 200-hour endurancetest on the H-60 tail and interme
30、diate gearboxeswith the isotropic superfinish process applied to thebevel gears. Testing included documentation ofnoise and vibration levels along with determinationof the effects on gearbox temperature. Results ofthe H-60 tests are not publicly available at this time(AATD RDS-21 Program, Agreement
31、NumberDAAH10-01-2-0032). Sikorsky also ran an in-house test on an S-76C+ main gearbox final stagespur bull gear and mating two pinions that had beenisotropic superfinish processed. Results show a 3.7dB noise reduction for the 2nd Stage Bevel Gear,and a 7.0 dB noise reduction for the 3rd Stage BullGe
32、ar (at 1 x Bull gear clash frequency), and a 5 Fdrop in oil out temperature as a result.Additional testing is scheduled under the AATDRDS-21 and the Coating Enables High Power Den-sity Transmissions (NIST) programs to further dem-onstrate and document the improvements in geartooth life in bending an
33、d Hertzian contact. Geartooth root surface finish improvement has beenshown to increase the bending fatigue allowable.Isotropic superfinish for bearings will also be investi-gated under the RDS-21 program in the future.However, there was still a need for a program thatwould determine the scuffing re
34、sistance of theisotropic superfinish on gear tooth surfaces. Withimproved scuffing resistance criteria, new transmis-sion designs with isotropic superfinish gears can beoptimized for gear tooth strength and lubricationrequirements, which will improve overall powerdensity.ObjectivesThe objective of t
35、his PTSM Project was to deter-mine and compare the scuffing resistance of iso-tropic superfinished precision aerospace gears tothat of conventionally processed baseline samples.Sample gears were made from SAE 9310 gear steelfor this study. It was expected that this project wouldresult in the quantif
36、ication of the scuffing resistanceof isotropic superfinished precision gears. It wasfurther expected that the results of this projectwould lead to the implementation of the isotropic su-perfinish technology, if the scuffing resistance of thesuperfinished gears was shown to be equivalent orsuperior t
37、o those gears that were conventionallyprocessed.Research ApproachAlion Science and Technology Corporation, REMChemicals, Inc. and Sikorsky Aircraft Corporationagreed to participate in this project as a team. AlionScience and Technology Corporation was responsi-ble for project management, REM Chemica
38、ls Inc.for the isotropic superfinishing of the test gears andSikorsky Aircraft Corporation for test gear procure-ment, testing and data analysis. The original testplan was as follows:FabricationSikorsky Aircraft Corporation was responsible tofabricate a total of twenty four (24), 4-inch pitch di-ame
39、ter test gears, per the agreed upon drawing.Aero Gear Corporation of Windsor, CT was se-lected as the manufacturer to fabricate the gears forthese tests. The test gears were manufactured tothe following specifications:3Table 1. Specifications for the scuffing test gears.SpecificationSteel alloy: AMS
40、 6265 (SAE 9310H)No of teeth: 20Diametral Pitch: 5.0000Pressure Angle: 20.0000Arc Tooth Thickness (in.): 0.3091-0.3111Pitch Diameter (in.): 4.0000Outside Diameter (in.): 4.3280-4.4020Case Hardness (HRA): 81-85Core Hardness (HRC): 35-41EffectiveCaseDepth(in.): 0.015 minTotal Depth of Finished Case (i
41、n.): 0.045 maxTestingSikorsky Aircraft Corporation performed ScuffingResistance Testing to obtain twenty four (24) datapoints for scuffing resistance, with gear testing be-ing conducted at Pratt this al-lowed the two gears to skip against each other. Thestrain gage signals collected at 1500, 2000, a
42、nd2500 rpm during the set-up test showed a high(er)frequency signal due to the gears skipping againsteach other superimposed on the signal due to themeshing action. Because of this situation, only lim-ited testing was conducted at the lower speed. Theresults of these tests will be analyzed further t
43、o de-termine if future testing at low speed would provideuseful data.Test MethodologyThere are two approaches that can be followed inconducting power circulating gear scuffing tests.The one frequently cited in the literature (e.g., FZGscuffing test) is to establish lubrication conditionsand test spe
44、eds conducive to scuffing, and then toprogressively increase the load on each specimenuntil it scuffs. The result of this test is the load thatprecipitates scuffing. The other method is to estab-lish load and speed conditions where the gear runsproperly, and then to progressively increase lubri-cant
45、 temperature until scuffing occurs. The result ofthis test is the lubricant temperature that precipi-tates scuffing. The tests reported here were con-ducted following the second approach; it was se-lected for these tests for the following threereasons:71. Any given profile modification on a gearset
46、re-sults in optimum contact for a comparatively narrowload range. As load is increased progressivelyabove this range, the tip of the driven gear contactsthe start of active profile (SAP) on the drive gear at aprogressively increasing angle to the tangent to thesurface. Thus, the corner of the tip of
47、 the drivengear tries to dig into the surface of the driving gearcausing the lubricant film to break down and scuf-fing to occur. The result is partly an indication of thelubricant temperature at the point of contact wherescuffing occurs, and partly an indication of the re-sistance of the material t
48、o being gouged out undernon-conjugate contact. This situation is at variancewith what precipitates scuffing in an otherwise prop-erly designed gear mesh. The more useful piece ofdata for the gear designer is the temperature of thelubricant film at which scuffing occurs under givenload and speed cond
49、itions.The test rig used in these tests requires two sets ofspecimen gears, and conducts two tests simulta-neously. In the progressively increasing load type oftest, the specimen set that does not scuff will bedamaged by non-conjugate contact at the SAP onthe driving gear caused by being run at the overloadthat precipitated scuffing on the other gear set. Asthe next gearset on the other end of the test rig isbroken in and run at the lower load steps, this dam-age may be smoothed over by the repeated contactunder less severe conditions prej
