06FTM02

Isotropic Superfinishing of S--76C+Main Transmission Gears

by: B. Hansen, Sikorsky Aircraft Corporation, M. Salernoand L. Winkelmann, REM Chemicals, Inc.

TECHNICAL PAPER

American Gear Manufacturers Association

Isotropic Superfinishing of S--76C+ MainTransmission Gears

Bruce Hansen, Sikorsky Aircraft Corporation, Mike Salerno and LaneWinkelmann, REM Chemicals, Inc.

[The statements and opinions contained herein are those of the author and should not be construed as anofficial action or opinion of the American Gear Manufacturers Association.]

AbstractIsotropic Superfinishing is a chemically accelerated vibratory finishing process that is capable of generatingsurface finishes with an Arithmetic MeanRoughness (Ra) < 3 min. This process was applied to the third stagespur bull gear and mating pinions along with the second stage bevel gears of a Sikorsky S--76C+ maingearbox. Thegearbox completed thestandardAcceptanceTestProcedure (ATP) anda200--hour endurancetest. During these tests noise, vibration, and operating temperatures were shown to be significantly reduceddue to the lower friction. This technology has since been flight certified and integrated into the S--76C+ withseveral aircraft in commercial service. A description of the tests, performance data and a general descriptionof the process will be presented.

Copyright © 2006

American Gear Manufacturers Association500 Montgomery Street, Suite 350Alexandria, Virginia, 22314

October, 2006

ISBN: 1--55589--884--X

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Isotropic Superfinishing of S--76C+ Main Transmission Gears

Bruce Hansen, Sikorsky Aircraft CorporationMike Salerno and Lane Winkelmann, REM Chemicals, Inc.

Introduction

Noise and vibration control is a primary concern forthe transmission design engineer, and particularlyso in the design of a helicopter main transmission.Excessive vibrations generated by transmissionstypically result in undesirable noise levels inhelicop-ter cockpits and/or cabins, which cause operatorand/or passenger aural discomfort and/or damageto sensitive on--board instrumentation. Cabin and/or cockpit noise/vibration abatement is of particularconcern in helicopters wherein the final stage of re-duction gearing of themain transmission comprisesone or more bull pinions interacting with a centralbull gear.

For example, Sikorsky helicopters of the S--76 se-ries, e.g., S--76A, S--76B, S--76C, have a maintransmission that includes three stages of reductiongearing: a first stage for eachengine output consist-ing of helical gearing, an intermediate stageconsist-ing of spiral bevel gearing, and a final reductionstage comprising a central bull gear that inter-meshes with right and left hand bull pinions (to com-bine the inputs of the two engines that provide themotive power for the helicopter). Research hasshown that the cockpit and/or cabin noise levels ofS--76 helicopters are primarily the result of vibra-tions originating in the main transmission.

Narrow band Fast Fourier Transform (FFT) analy-ses, A--weightedoctave levels, andoverall DBA lev-els recorded in the cockpits and/or cabins of S--76A,S--76B, and S--76C helicopters indicate that interiornoise levels are predominately the result of vibra-tions occurring at the bull gearing meshing frequen-cy of 778 Hz, as illustrated in Figure 1. The vibra-tions produced by the first and second reductionstages of S--76 main transmission gearboxes, i.e.,the noise levels generated by the helical and spiral

bevel gearing as illustrated in Figure 1, occur athigher frequencies and typically are not significantrelative to the dominant noise levels produced bythe fundamental and first few harmonics of the bullgearing meshing vibrations.

The gearbox vibrations resulting from bull gearmeshing are transmitted to the helicopter airframevia the transmission housing. The resultant air-frame vibrations generate noise in the helicoptercockpit and/or cabin. Abatement of such noise byacoustic treatment of the cockpit and/or cabin interi-or is generally inefficient, and therefore, effectivenoise control solutions must be implemented at thenoise source, i.e., the main transmission.

To effectively abate such noise, it is necessary toidentify the primary causal factor(s) of bull gearingvibrations. The vibrations generated by the helicop-ter main transmissionmay be aggravated bymesh-ingbetweenmisalignedbull gearing, i.e., the centralbull gear and bull pinion(s). Previous efforts to re-duce the noise levels generated by intermeshingbetweenmisaligned bull pinions and the central bullgear includedmodifications to provide effective bullgear tip relief. While suchmodifications resulted in amodest reduction in bull gearing vibrations, the re-sultant reduced interior noise levels of S--76 heli-copterswere judged to still present anunacceptablelevel of aural discomfort.[1]

As a result, several avenues were explored tomorefully identify the design and operating parametersthat cause noise induced by the intermeshing gearsof a drive train. One such avenuewas the investiga-tion of Superfinishing usingChemically AcceleratedVibratory Finishing. This process generates a verysmooth surface on the flanks of gears and has prov-en its ability to reduce the coefficient of friction[2],and in laboratory testing, the frictional component ofnoise known as Vibro--Acoustic Noise.[3]

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Figure 1: Chart showing that the predominant cabin noise is produced by the gearing meshingvibrations of the first few harmonics of the bull gear. Note that the highest cabin noise level ispredominately the result of vibrations occurring at the first harmonic bull gearing meshing fre-

quency of 778 Hz.

Vibro--acoustic noise

The gear meshing cycle consists of a large amountof sliding between the teeth making contact. At thepitch point, the gears experience pure rolling, how-ever, the areas before andafter thepitch point expe-rience much more sliding motion. At this interface,the teeth experience high contact stresses whichcan result in low oil film thickness. When this hap-pens, the result can be mixed or boundary lubrica-tion conditions which lead to an increased coeffi-cient of friction. At this point, the coefficient offriction is controlled either by the choice of lubricantor the surface finish of the teeth. This sliding and/orshearing of intermeshing teeth has been theorizedas a significant contributor to the total noise signa-ture of a gearbox and in the last few years, thistheory has been proven in laboratory testsNO TAG.As such, it will be appreciated that by Superfinish-ing, the friction coefficient on the gear teeth will bedramatically reduced, and so too, is the component

of noise produced by the sliding action of the inter-meshing gear teeth.

Superfinishing using chemicallyaccelerated vibratory finishing

Chemically accelerated vibratory finishing incorpo-rating highdensity non--abrasive ceramicmedia en-hances the performance of components that aresubjected to metal--to--metal contact or bending fa-tigue. The isotropic surface generated is uniquewhen compared to even the finest honing and lap-ping in that it has no directionality and is capable ofproducing a final surface roughness of < 4 min. (0.1mm) Ra. It has a texture which consists of only ran-dom scratches and shallow dents. When the result-ant surface has an Ra of approximately 4.0 min. (0.1mm) or less and a non--directional surface pattern, itis referred to as an Isotropic Superfinish (ISF®),however, for this document Superfinish will be usedto denote this process and surface topography.Figure 2 shows anSEM image at 1000X of a typical

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ground surface with an Ra of approximately 10 min.(0.25 mm) ((top image) and a Superfinished surfacewith anRa< 2 min. (0.05 mm) (bottom image) for ref-erence. Note the directional asperities on theground surface and the lack of directional asperitieson the Superfinished surface. Only light scratchesand tiny dents are visible amongst smooth, pla-teaued areas of the Superfinished surface. It istheorized that these tiny dents facilitate lubricantretention during operation.[4] Such surfaces are

unique in their remarkable ability to reduce fric-tion[2], wear[5], operating temperature[6], andnoise[3], as well as contact[7] and dynamic fatigue[8]

when compared to similar surface finishes pro-duced by other techniques. There has been in-creasing interest over the years in applying this pro-cess to aerospace gears since the industry is beingdriven to produce higher cycle life gears at in-creased power densities while still allowing for largesafety margins.

Figure 2: Scanning Electron Micrograph (SEM) at 1000X of a typical ground surface with an Raapproximately 10 min. (0.25 mm) (top) and a Superfinished surface with an Ra < 2 min. (0.05 mm)(bottom). Note the isotropic (non--directional) surface texture on the Superfinished surface ver-

sus the directional asperities on the ground surface.

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The Superfinish process is discussed in detail else-where[7], but the following is a brief summary of theprocess. Superfinish is produced in vibratory finish-ing bowls or tubs. A proprietary active chemistry isused in the vibratory machine in conjunction withhigh--density, non--abrasive ceramic media. Whenintroduced into the machine, this active chemistryproduces a stable, soft conversion coating on thesurfaceof thegear(s) beingprocessed. The rubbingmotion across the gear(s) developed by the ma-chine and media effectively wipes the conversioncoating off the “peaks” of the gear’s surfaces, butleaves the “valleys” untouched. (No finishingoccurswhere media is unable to contact or rub.) The con-version coating is continually re--formed and rubbedoff during this stage producing a surface smoothingmechanism. This process is continued in the vibra-tory machine until the surfaces of the gear(s) arefree of asperities. At this point, the active chemistryis rinsed from the machine with a neutral soap. Theconversion coating is rubbed off the gear(s) one fi-nal time to produce the Superfinished surface. Inthis final step, commonly referred to as burnishing,no metal is removed.

The Superfinish process is a mass finishing opera-tion whereby tens or hundreds of gears can be si-multaneously processed in the samemachine. If allof the raw gears placed in the vibratory machine areidentical at the start, then they are all identically fin-ishedat the endof theprocess. Every gear toothwillhave the same surface finish and geometry sincethe parts continually and randomly move throughthe vibratory machine and statistically experiencethe same chemical and media exposure. If onetooth on a gear has its tooth thickness reduced by0.0003 inches (0.0076 mm), then every tooth onthat gear andevery gear in the finishingmachinewillhave its tooth thickness reduced by the sameamount. Therefore, there is no need for costly finalinspection of each and every gear as must be doneafter grinding or honing.

In addition, the simplicity of the Superfinish processyields a very robustmanufacturingmethod. Vibrato-ry machines are run for years without any mainte-nance except for minor lubrication. The media isnon--abrasive so it retains its shapeandsize for long

periods of time. The important parameters that con-trol the surface finishingoperation are thenumberofgears in the finishing machine, the concentration ofthe active chemistry, the flow rate of active chemis-try, and theprocessing time. All of theseparametersare easily controlled. The process lends itself to au-tomation, and has been commercially used over thepast 19 years.

S--76C+ Main Transmission Testing

Origin of the test gears

Sikorsky Aircraft Corporation supplied off the shelfS--76C+ main transmission gears to REM Chemi-cals, Inc. for Superfinishing. This process was ap-plied to the third stage spur bull gear andmatingpin-ions along with the second stage bevel gears. SeeFigure 3 for a schematic of the S--76C+ drive trainand the gears processed. These gears weremanufactured from AMS 6308 steel, carburized toexistingSikorskyAircraft Corporationspecificationsand precision ground. The goal was to Superfinishthese production gears to a Ra < 4 min. (0.1 mm)across the active profile area of the teeth.

Starting condition of the test gears

The five gears were accepted production gears andwere in typical aerospace precision ground condi-tion. The surface roughness of the gears wasmeasured by REM Chemicals, Inc. upon receiptand prior to processing using a Hommel T1000profilometer fitted with a 5 micron radius stylus andfollowing the ISO 4288 specification for themeasurement of surface roughness. For easycomparison to the finished surface, a TracingLength (Lt) of 1.5 mm and a Wavelength Cut--off(Lc) of 0.25 mm was used in the measurement ofthe as--received gears since this is the specificationfor a non--periodic surface pattern and Ra between0.8 min (0.02 mm) and 4.0 min (0.1 mm). The surfaceroughness results of the as--received, or startingcondition, gears prior to Superfinishing is listed inTable 1. A typical surface roughness profile anddata printout for an as--received gear is shown inFigure 4. This printout is from a third stage spurpinion gear.

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Figure 3: Schematic of an S--76C+ drivetrain which highlights the gears Superfinished during theproject.

Table 1: Surface roughness measurements of the S--76C+ main transmission gears as--receivedprior to Superfinishing.

Measurement pa-rameter

Second stage bevelpinions and gears (min.)

Third stagespur pinion (min.)

Third stage bull gear(min.)

Ra 13 to 18 16 to 17 13 to 17Rz 80 to 115 97 to 101 83 to 113Rmax 109 to 167 119 to 129 133 to 141* All measurements taken at Lt = 1.5 mm and Lc = 0.25 mm using a 5 micron radius stylus tip.

Figure 4: A typical surface roughness measurement for an as--received (un--Superfinished)S--76C+ main transmission gear. The trace was taken along the profile and within the active pro-file region of the tooth flank on a third stage spur pinion. This measurement is typical of all as--received gears used in the project. The scale to the right of the profile indicates that each verti-

cal segment represents 5 mm and each horizontal segment represents 100 mm.

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Superfinish process

The Superfinishing process consisted of the follow-ing steps:

1. Critical areas of the five gears such as bearingjournals, threads and bolt holes were masked inorder to prevent stock removal during theSuper-finish process.

2. Theexposed sections of thegears were cleanedof grease, oil and contaminants in order to en-sure a uniform reaction with the active chemis-try.

3. Superfinish (stock removal phase) using com-mercially available active chemistry.

4. Burnish (cleaning) using commercially availableburnishing compound.

5. Unmask critical areas.

6. Rust prevent using commercially available rustpreventative.

Final condition of the test gears after Superfin-ishing

After processing, the gears were photographedandfinal surface roughness measurements were takenof each gear. Visual inspection of the gears showedthat the directional asperities had been removedleaving a smooth and flat contact surface in itsplace. The appearance of the gears was bright andhighly reflective, indicative of a highly polished sur-face. Figure 5 shows a section of teeth from thethird stage bull gear after Superfinishing. Note thereflections of the other teeth across each flank.

Figure 5: An image of a section of teeth fromthe third stage bull gear after Superfinishing.Note the reflections of the other teeth across

each flank.

The final surface roughness of thegears wereagainmeasured by REM Chemicals, Inc. after Superfin-ishing using a Hommel T1000 profilometer fittedwith a 5 micron radius stylus and following the ISO4288 specification for the measurement of surfaceroughness. A Tracing Length (Lt) of 1.5 mm and aWavelength Cut--off (Lc) of 0.25 mm are specifiedfor a non--periodic surface pattern and Ra between0.8min. (0.02mm)and4.0min. (0.1mm). Thesurfaceroughness results of the Superfinished gears islisted in Table 2. A typical surface roughness profileand data printout for a Superfinished gear is shownin Figure 6. This printout is from a third stage spurpinion gear.

Table 2: Surface roughness measurements of the S--76C+ main transmission gears aftersuperfinishing.

Measurementparameter

Second stage bevel pin-ions and gears (min.)

Third stage spurpinion (min.)

Third stagebull gear (min.)

Ra 3.5 to 3.9 2.4 to 3.1 1.6 to 3.5Rz 21 to 28 21 to 23 10 to 34Rmax 30 to 40 29 to 34 15 to 76* All measurements taken at Lt = 1.5 mm and Lc = 0.25 mm using a 5 micron radius stylus tip.

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Figure 6: A typical surface roughness measurement for a Superfinished S--76C+ maintransmission gear. The trace was taken along the profile and within the active profile region of

the tooth flank on a third stage spur pinion. This measurement is typical of all gearsSuperfinished during the project. The scale to the right of the profile indicates that each vertical

segment represents 5 mm and each horizontal segment represents 100 mm

Gear Testing

Test stand

After Superfinishing, the gears were returned to Si-korsky Aircraft for final inspection, assembly andtesting. Once assembled, the S--76C+ main trans-

mission was fitted with accelerometers in variouslocations to best measure amount of vibration gen-erated by the Superfinished gears during the Ac-ceptance Test Procedure (ATP) and ultimately the200 hour endurance test. Figure 7 shows an imageof the assembled S--76C+ main transmission.

Figure 7: S--76C+ main transmission after assembly.

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The transmission was then mounted on the teststand. Oncemounted, several thermocoupleswereattached. The placement locations of the thermo-couples are dictated by the ATP specification. Twothermocouples of great interest are located at theoil--into transmission (out of the oil cooler) and theoil--out of the transmission (into the oil cooler). An

imageof themounted transmissionand test stand isshown inFigures 8and 9. TheS--76C+ helicopter isa dual engine aircraft, so themain transmission hastwo power input points. The test stand consists oftwo electric motors supplying the input power intothe transmission and a water brake attached to therotor shaft to supply the resistance and load.

Figure 8: Rear view of the S--76C+ main transmission mounted on the test stand ready to beginthe Acceptance Test Procedure (ATP) and 200--hour endurance test.

Figure 9: Front view of the S--76C+ main transmission mounted on the test stand ready to beginthe ATP and 200--hour endurance test.

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Acceptance Test Procedure (ATP)

The ATP is a mandatory test that all productiontransmissionsmust satisfactorily complete to beac-cepted as flight worthy. This test simulates typicaltorque loadings experienced by the transmissionduring normal operation. To be accepted, the trans-mission must meet specifications for several pa-rameters, but theparametersmost important duringthis test were visual inspection for scuffing, vibrationlevels and oil temperature. The specification statesthat input temperature of the lubricant must bemaintained at 75° +/-- 2° C throughout the testing.The minimum main shaft thrust load throughout alltesting is to be 11,000 lbs. with the tail take--off loadset at 155 ft--lbs. Failure criteria are scuffing on thebevel pinions or gears, a vibration signature of nomore than 35 G’s acceleration at specified frequen-cies and a maximum oil--out of transmission (intocooler) temperature of 115° C.

The testing started with the transmission being ser-vicedwith DOD--L--85734 lubricating oil to the topofthe sight glass. The first stage of the ATP was a 2hour break--in cycle, after which the bevel pinionsand gears are visually inspected for scuffing. Nonewas seen. This was done while the transmissionwas still mounted on the stand. The second stagewas a 6 hour break--in cycle. The bevel pinions andgears were inspected twice during this period forscuffing just as before during the 2 hour break--incycle. None was seen during either inspection. Af-ter the break--in cycle was completed, the 2 hour“bench test” was conducted. This consisted ofseven test conditions at varying lengths of time thattotaled one hour. The sequence is repeated at theendof the seventh test condition to give twohoursoftest time. This was the actual ATP test and the peri-od at which all measurements for oil temperatureand vibrations were recorded.

200--Hour Endurance Test

Following the initial ATP test, the main transmissionwas subjected to 200 hours of endurance testing.This testing was conducted on the same test standwith the same data collection system in place. Thetest was conducted using a load spectrum consist-ing of 21 stepswhich total 10 hours of test time. Theload spectrum was repeated twenty times to total200 hours of torque loadings which simulate normaloperation. Thebevel pinions andgearswere visual-

ly inspected several times throughout the test. Theseals were visually inspected for oil leakage every 5hours. The testing conditions and durations arelisted in Table 3.

Table 3: 200--hour endurance test loadconditions and durations.

Step # Condition Duration(minutes)

1 Idle Power 52 60% Max Continuous

Power60

3 80% Max ContinuousPower

60

4 Idle Power 55 90% Max Continuous

Power60

6 Idle Power 57* Max Continuous Power 1808 Idle Power 59 Takeoff Power 510 OEI--2.5 minute Power

(L/H)2.5

11 Idle Power 512 OEI--2.5 minute Power

(L/H)2.5

13 OEI--30 minute Power(R/H)

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14 Idle Power 515 Takeoff Power 516 OEI--2.5 minute Power

(R/H)2.5

17 Idle Power 518 OEI--2.5 minute Power

(R/H)2.5

19 OEI--30 minute Power(R/H)

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20 Idle Power 521 Max Continuous Power 120* 658 ft--lbs. Input torque per engine input = 100%transmission torque.

Results

The Superfinished S--76C+ transmission com-pleted both the 2--hour ATP and the 200--hour en-durance test with flying colors. The visual inspec-tions of the bevel pinions andgears throughout bothtests indicated that no scuffing occurred during ei-ther test. In fact, it was noted that the gears ap-peared as if they had never been “run--in” at all. Af-ter all testing, the gears did not have any wear orcontact pattern formation on the contacting areas ofthe teeth.

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During the ATP, both vibration and temperaturewere measured during the run. Since this is a stan-dard test that all production main transmissionsmust complete, there was a wealth of baseline datato compare with the Superfinished transmission.The first surprising result was that the vibration lev-els of the third stage bull gear 1xmesh (776Hz) andthe second stagebevel pinion1 xmeshwere signifi-cantly reduced. When compared to the baselinedata, this indicates a 7 decibel reduction at the thirdstage bull gear 1x mesh and a 3.7 decibel reductionat the second stage bevel pinion and gear 1xmesh.As discussed earlier, it is these two frequencies thatcause the most aural discomfort in the cabin and/orcockpit of a helicopter. Theseare also themost diffi-cult to abate due to their vibro--acoustic nature, thatis, these frictional excitations are carried throughthe shafts to the housings where are then trans-ferred to the airframe, thus creating noise inside thecabin and /or cockpit. Figure 10 shows the mea-sured ATP vibration levels of the S--76C+ main

transmission, baseline versus Superfinished.

The second surprising result was that the oil--outtemperature (oil into the cooler) was approximately5° C lower than baseline S--76C+ main transmis-sions. Figure 11 compares the oil--out temperatureas measured by the thermocouple with three pro-duction S--76C+ main transmissions that had alsorecently completed the ATP. It should be noted thatthe temperature reduction was not at only onetorque loading, but was consistently lower through-out the entire torque band. Figure 11 shows base-line data being collected at 450, 500, 550, 600 and650 ft--lbs of torque. The Superfinished trend lineshows one point at 329 ft--lbs of torque and thenthree points at each of the following loads, 526 and592 ft--lbs. The reason for the multiple points is thatthe Superfinished main transmission was runthrough the ATP test several times in order to verifythe results and establish a trend line to use as acomparison.

125

130

135

140

145

150

155

Decibel

1x Bull 2x Bull 3x Bull Bevel

Gear Mesh and Harmonic

Baseline SuperfinishFigure 10: Measured ATP vibration levels for S--76C+ main transmissions, baseline versus Super-finished. Note the 7 decibel reduction at the third stage bull gear 1x mesh and the 3.7 decibel

reduction at the second stage bevel pinion and gear 1x mesh.

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S--76C+ VIP LOW NOISE TRANSMISSION

Main Gearbox Oil Temperature

Oil Out Temp vs. Torque

72.5

75

77.5

80

82.5

85

87.5

90

280 320 360 400 440 480 520 560 600 640 680

Torque (One input, ft--lbs)

Temperature

(F)

A231--00269 A231--00268 A231--00267 A231--00086 Superfinished

Figure 11: Oil--out temperature of S--76C+ main transmission. Plotted are three production trans-missions as the baseline (top trend line) and one Superfinished transmission run through the

ATP test three times to verify the results and establish a trend line (bottom line).

Conclusions

The Superfinish Process is a viable method to sig-nificantly reduce the in cabin and/or cockpit noiseand vibrations which occur at the lower and mostnoticeable frequencies. It does this by reducing thefriction between the meshing gears by lowering thesurface roughness through a controlled processthat removes the surface irregularities (asperities)causedbymachining, grindingand/or shot peening.This produces a very unique surface texture that isdescribedas isotropic (non--directional) and is char-acterized by an Ra < 4 min. (0.1 mm) The data pre-sented in this paper indicates that SuperfinishedS--76C+ main transmission gears have the follow-ing qualities:

1. Lower friction.

2. Lower vibro--acoustic noise.

-- Third stage bull gear 1x mesh reduced by 7decibels.

-- Second stagebevel pinion andgear 1xmeshreduced by 3.7 decibels.

3. Lower operating temperatures.

-- 5° C temperature reduction when comparedto baseline main transmissions during theATP.

References

1. Vinayak, H, et al., US Patent 6,918,181 B2,“Gear Tooth Topological Modification forReducing Noise and Vibration in TransmissionSystems”.

2. Nebiolo W. P., “Isotropic Finishing of Helicopter& Turboprop Gearbox Components”, AESF2001 Aerospace/Airline Plating & MetalFinishing Forum, Portland, Oregon, March27--29, 2001.

3. Houser D. R., Vaishya M., Sorenson J.,“Vibro--Acoustic Effects of Friction in Gears: AnExperimental Investigation”, 2001 SAE Noiseand Vibration Conference, Traverse City, MI,2001--01--1516, April 2001.

4. Niskanen, P., Hansen, B., Winkelmann, L., “TheEvaluation of the ScuffingResistance of Isotrop-ic Superfinished Precision Gears”, 2005 AGMAFall Technical Meeting, October, 2005, PaperNumber 05FTM13.

5. Niskanen, P., A. Manesh, R. Morgan. “ReducingWear with Superfinishing Technology,” TheAMPTIACQuarterly, Vol. 7, No.1, 2003, pp. 3–9.

6. Winkelmann, L., Holland, J., Nanning, R., “Su-perfinishing Motor Vehicle Ring and PinionGears”, 2004 AGMA Fall Technical Meeting,October, 2004, Paper Number 04FTM13.

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7. Winkelmann, L., Michaud M., Sroka G., SwigloA., Mahan D., “Chemically AcceleratedVibratory Finishing for the Virtual Elimination ofWear and Pitting for Steel Gears”, AGMA FallTechnical Meeting, Detroit, Michigan, 01FTM7,October, 2001.

8. Winkelmann, L., Michaud M., Sroka G., SwigloA., “Impact of Isotropic Superfinishing on Con-tact and Bending Fatigue of Carburized Steel”,SAE Off--Highway Congress, Las Vegas, Neva-da, 2002--01--1391, March, 2002.