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yourAccurate-gear inspection depends on tepa.

data evaluation. Profit depends on speed. Mug CNC gear_iiithree" tin the lab and on the shop Ooor.• Maag mechanical machines combine the speed and automatic chccking of CNCthe reliability of a base circle disc design for profile and lead gear inspection.• Only Maag multi-axis electronic machines measure internal and external spur, helicaland cluster gears with up to 1'5sets of teeth, all in a single setup, with accuracy of.000040io ..• Maag's unique easy-to-usemenu programming, and software automatically bring thestylus to the tooth surface,If you'd like to know bow to spot your bad apples quicker, contact Americ~n Pfauter,925, !EstesAve.. Elk Grove Village, IL 60007. Phone (3,12)640-7500.

one-time entry 01 partprint and tolerancedata. 'Mo!!se' .er-mlts use ,of CJ)techniques.

Plotter deUversmunH:olor 'hardlCORY01 graphicSand lesl: data.

CNCslalus,monitor provldustatus and !)Osl·lionaJldlspla.y ofmechanleal systemand! ONe controlfunctions,

Operator ControlP,anell'lor part load.ingl and mad"llnll,set up.

Our Modell 3000 CC Gealr Anal:yzer is a thlrd generation eNC gear inspection system in-corporating aU,ofUIS' comprenenstce analytical tests and 'evaluation ,eapabiUties ,ofp.reviolJs M & M systems. such as our Model 2000,. but with these added capabilities:• Dramat,ically lmproved speed and accuracy through new mechanical system ,design,

and advanced eNe ,eontro:1techn'O'I'ogy. -• Computer hardware and appllcatlons software are modular to allow the user to buy

only Ole required capaibility,.,This makes the 3000 OCadaptab'I'e to, laboratory testingl'Orproduction-Une iinspection.

• Integrated StatisUcal Process Control w:ith local data base capability is an ,'O,ptlonalfeature'.

'. INetworking with MAPS oompatlbility is avaUa.ble'.• IRobotic interfacinglfor totally automatic load/test/unload 'Operation 'can be

incorporated.For more lintormatlon or applications asslstanee, wl'ite or calil: M &. M Precislon Systems"300, Progress Rd., West Oarrollton, OHI 45449, 5113/e59~a273,TWX ,El1 0/450-2626, See,us a.IFAX S13/859-4452. Booth # 213

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thel bardest .slecl istIJ ~I easIest clIolce ... CI'AIl REX?6

!For hobs, shaper cutters and other gear cuttingtools that are more than a cut above the rest, specifyCrucible CPM8 REX.8 76. With 33% total alloy con-tent and an attainable hardness of HRC 68-70, thishigh speed steel provides the highest availableoomaination of red hardness, wear -reSistance andtoughness,either coated or uncoated.

A Big-Thlree US. auto ma'Ker recently r;eaUz·eda300% improvement in gear cutting tool HIe byswitchingl from M3 IHSS to CPMi FlEX ]16. Withgreater tool lite and excellent gr.indability, CPM REX76, means less downtime because resharpeninq iseasier and tess trequent

CPM REX 7'6 is just one of 10 high speed steelsproduced Iby the Crucible Particle Metallurgy pro-cess ..Wlith the !industry's widest material selection,Crucibl'e can meet your specific needs at any pro-ductiv.ity level. You 'can selectively upgrade to thebest CPM rnatenal tor the right application.

On your next order specify a h:igh speed steelthat's hard to beat... CPM REX 76 or anothermember of the CPM FlEXfamily. To learn more, con-tact your nearest Crucible Service Center,. or writeCrucible Service Centers, 5639' West GeneseeStreet" Camillus, NY 13031.

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6 Gear Technol'ocv

AGMA'S "BABY" GROWS UP

From tiny beginnings. the AGMAGear Expo is growing into a fine, strap-ping show. This year's effort, GearExpo '89, "The Cutting Edge," will bebigger and better than 'ever. Whatstarted as a few tabletop exhibits inChicago fOUf years ago has now grownto a full-size, international exhibitionat the David Lawrence ConventionCenter in Pittsburgh. With over 160exhibitors, including major gearmanufacturers and suppliers fromaround the world, this year's showpromises to be a great success as well.

AGMA ha provided the nearlyperfect forum to I'ook for andlor sellgear rnachinerv, supplies and auxiliary'equipment. At Gear Expo '89, you canconcentrate on gear machines andrelated products without wanderingthrough a maze of other machineryandequipment. By scheduling the FallTechnical Conference on overlappingdates at the same location, AGMA hasprovided attendees with a financially'efficient opportunity to keep abreast ofthe latest in gear research. For virtuallythe same price, you can view both thelatest products and the latest research.Presidents, managers, engineers andop raters can alii come away withvaluable knowledge. This is a double-barrelled opportunity that serious

provide the most efficient way to keepup with both the latest lin products andresearch. For many, the, hanc tothe cutting edge of the gear productmarket does not even require an over-night stay.

Gear Expo '89' and the l chni alConferenc continue to need yoursupport in order to remain successfuland useful. More important, yourattendance at these events wi'll helpkeep your company cornp titive andbetter able to take advantage of thiswindow of opportunity.

competitors in the gear market shouldnot overlook.

The last two years have been goodfor both gear customers and manufac-turers. The economy has been growingalong with capital expenditures. Theneed for new equipment and thewherewithal to buy it are more inbalancethan they have been for sometime. But as we should have I, arnedfrom recent past history, the goodtimes don't last forever. Currenteconomic indicators have levelled off,although business remains strong allover the Northern Hemisphere. Wehave a window of opportunity nowthat will not stay open indefinitely.There may never be a bettertime toinvest in new equipment and trainingfor you and your company.

Gear Expo '89 is the perfect place tostart Pittsburgh, with its lower costsand central location, and the combina-tion show and technical conference

Michal Goldstein,Editor/Publisher

Nigh! view of Pittsburgh skyline.

September/Oc~ober 1969 7

.. JlJ,A. ., H...nJ.'..~ ,e~·~. ·.MJ,Uwf.. S ., -u,_.J'P' 1~.MuAM1~e~ .M~

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KAorSince 1927 Telephone (313) 474-8200- . II. ~ ST'ARCUT SALES INC Telex 23-0411w- 23461 IndustrialParkDrive~F:rmi~gt~/Hill:,Michi:a:~:o(~~3) 474-9518

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EDITORIAL STAFFPUBUSHER & EDIrOR·IN·CIUEFMicha.el GoldsteinASSOCIATE PVBUSHER &MANA.GENGEDITORPeg ShortASSOCIATE EDITORNancy BartelsEDITORIAL ASSISTANTMJeheJle ShortART DIRECTORKimberly ZarleyDESIGNERIPRODUCrION ARTISTJennifer ShortADVERTISING SALES MANAGERPatricia. FlamSALES COORDINATORMary MichelsonCIRCULATIONPam Nolan

RANDAlL PllBUSIDNG STAFFPRESIDENTMichael GoldsteinVICE PRESIDENTRichard GoldsteinVICE PRESIDENT/GEN. MGR.Peg ShortACCOUNTINGRuth J. KussinART CONSULTAm'Marsha Goldstein

RANDALL PUBUSHING CO•• ]NC.1401 Lunt Avenue

P.O. Box ]426Elk Grove, ]L 60007

(312) 437 .f5604

OUR COVERAn early GouJd rotaJy cutting machine,

probably for .spur gears, circa 1850. Thismachine was donated to AGMA. and hasbeen re;tored by Paul S. Morales ofChicago Gear/D.O.. James Corp., Chicago,lL. In .the 18405 Gould produced .approx·imately two machines a year; this machineis numbered 13. At some time, one of thelegs of this .ttliJ.chinewas patched by meansof a cold hammer weld. The repair is over100 years old now and stiJ1 holding.

S.TEC~NOf!GJfRTheJournal olGearManufacturing

CONTENTS PA.GENO.

IFEATURES

HARn F.INISHING .AND FINE FINISHING - PART I 10Dr .. Ing, H. Schriefer, Carl Hurth GmbH &: Co, Munich, West Germany

WHIT.E ETCHING A~REAS ON CASE·HARJ)ENED GEARSProf. Dr. -Ing, Hans Winter, Dr. -Ing Gerhard Knauer,Technical University of MunichJohn J. Gamel, Solar Turbines, Inc., San Diego, CA

I

IIDEPARTMENTS

GEAR EXPO '89

EDITORIAL 7

ADVERTISERS' INDEX 41

TECHNICALCALENUAR 43

BACK TO BASICS •••GEAR GRINUING

Yogi Sharma, P.E., Philadelphia Gear Corporation,King of Prussia, PA

26

CLASSIFIEDS 4:6

September/October, 1989 Vol. 6, No.5

CEAR 1"ECHNOWGY, "the Jou'''al·"f Gea r M"""(acl,,.lnil (lSSN 0743·68581 is published btmcruhly b~ Randall Pubh"hinRCo .• Inc .. 1425 Lunt Avenue, P. O. Box. 1426, Elk Grove Village. II~60007. GEAR T:E:CIiNOLOGY. The Journal of Cear Manufac·turing. Subscription rates are: $40.00 in the United States. 550.00 in Canada, $55.00 in all other foreign countrie s. Second- las..posta!!o paid at Arlinglnn H.il!hts. It. and at additional mailing office.

Postmaster: Send address '''."goo to GEAR TECHNOLOGY. The Journal of Cear Manufacturing. 1425 IAml 1\\,"""", I'. O.8,,>< 1426. Elk Grove Village. IL 60007.

©Conlenls copyrighted by RANDALL PUBLISHING CO., INC. 1989. Articles appearing in CEAIl TECUNOLOCY may· not hereproduced in whole or in part without the express permission of the publisher or the author.

MANUSCRlPTS= We are requesting technical papers with an educational empheals fUf ilnyunc ha'lli ng an)rthinA: In dD with th edesign. manufacture, testinll or processing of gears. Sub~t.s 5Du!lht are solutions to specific problems ••• "1"""1]" ns of"...,.. 00 h""lnl!)l.techniques, designs. processes, and alternative manufacturing methods, TIlcse C~I"! range from the" HuV!,'to ... " u( ge-.arru(tmg[BACK TD BASICS) to the most advanced technolol!J.'. All manuscripts submitted will be "".fully considered. However, the Publishe,assumes no respcnsibillty for the saf.~ orreturn of man uscripts, M.nus<:ripts must be accompanied by a ..,If'adJ'''''''' .... ..,If·.t.om",,'"I:lYil0!'i'7_~~ sent to GEAR TECHNOLOGY, The Journal cf Gear Manufacturin/l ..... 0. Box 1426, Elk Crove, II. GOQ09.

September/October 1;989 9

nd Fine Finishingrt1

. -Ing, H. Sc:hrielerMunich, West Germany

Dr. -ING. HERBERT SCHRIEfER is with Hurth Company,Munich, where he is technical manager for the Division of Machines and'Systems. He studied' at the Technische Unrvmitiit in Berlin and'worked'at the Laboratory for Machine Tools (WZL) at the TechnischeHochschule Aachen where he developed the geometry and kinematicpart of a program sequence for bevel and hypoid' gears, This programsystem represents the most extensive and universal computer analysisof the running and stress conditions of complex gear drives today.

IntroductionProfitable hard machining of tooth flanks in mass production

has now become possible thanks to a number of newlydeveloped production methods. As used so far. the advantagesof hard machining over green shaving or rolling are that elabo-rately modified tooth flanks are produced witha. scatter of dosemanufacturing tolerances. Apart from an. increase of load

I cap.acity, the chief aim. is to solve the complex problem of reduc-I ingthe noise generation by load-conditioned kinematic

modiJications of the tooth mesh.'us,o) In Part Il, we shan dealwith operating sequences and machining results and with gearnoise problems.

Geometry of Gear FlanksNoise generation of teeth i.nmesh has two causes. The first.

a modulation of gear mesh rigidity, (3.5.6) is mainly influenced bythe implemented geometry, such as the helix and pressure angleschosen, theaddendum/dedendum modification on high toothdesign, etc.. and, thus .•depends only to a small extent on theprecision geometry of flanks via contact rigidity. (~) The secondcause is meshing errors, (8-9) which, however, are due directly tothe precision geometry of flanks asa function of the load. Fig.1shows influences on the geometry precision of flanks determin-ed by the load and by manufacturing, and from the qualitat:iveviewpoint. the relative tooth contact and generatingbehavior. (1.8.9)

The left column lists the reasons for various tooth modifica-tions. The second column shows the topological modificati.on offlanks, while the third column illustrates the tooth contact

without load and under load. The fourth column is a qualitativerepresentation of the single flank displacement error withoutload and loaded on account of the modifications of individualfJanks.

Suitably designing modifications require that the generatedimpact and torsional vibrations produced by the single flankdisplacement errors are kept within dose tolerances over thetotal load range of the gear unit. In practice, such modificationsare determined by means of the measurement analysis of thenoise emission under operating conditions. The result is a flankseomt'!ry havmg severaJ superimposed modilications as shownin the lower part of the illustration. Since the modifications arewithin a range of a few micrometers, their kinematic effec-tiveness requires a production method with the least possiblescatter of tolerances.

As an empirical value, tooth quality grade 5 - 6 ace. DIN 3962is sufficient for the finished flank. The possible ranges of scatteredtolerances could then be absorbed by the modification bandwidth (such as aownings) of the gear flanks without producingharmful sinsIe flank displacement errors.

Fig. 2 shows the reduction of tolerance from precut toothquality grade 9 to finish tooth quality grade 5-6, and also thepercentage to which the influences of the systems' componentson the result should be evaluated.

It wiD be noted here that the column "machine + tool" has thehighest influence altogether. The reason is that deviations of thetool or of machine kinematics will show directly, while otherdeviations, such as those of fixtures, will only have an indirectinfluence. This means that, in case of profile error, the machinetogether with the tool may have profile errors of ± 31'1T1.TheinfluencE 01only O.5pm for redamping and measuring will bepossible only if the toothing deviations are referred to the sameposition as for machining. This would require a theoreticaldefinition of the tooth gearing axis. This is feasible by a com-puterited alignment 01 the topographies of several flanks that aredistributed over the work gear periphery.

With conventional measuring instruments the influence by

_01~,,,,,1Is,~,-, _.1IiIlImo!

1"'-'-'

01""_"01~'Mil. :u.n4Iol"!old. ~tter 0'pn>(I_U!:!ion-,TopolD!IlCllnyoptimized 'l\a:nk,-My

of supenmpowdJ

of flanks for noise

reclamping and measuring should be assumed to be higher.With such demands on precision. the border line for metal cut-

ting processes inmass production has been reached. A solutionwill only be possible with processes featuring a minimum ofkinematic settings and where the tool flank geometry is either anaccurate conjugated mating gear or a conjugated linear sectionwith reference to the flank geometry required.

Kinematics of Hard Finishing and fine FinIsJUngSince the work gear flank geometry is composed of linear

elements, the linear contact also applies to the gear mesh whenmachining with a conjugated tool. {Sl The three settingparameters which have precedence for generating a conjugatedtool flank geometry from a preset cylindrical gear flankgeometry are

a. crossed-axes angleb. externally or internally toolc. center line distance of crossed axes.Fig. 3 shows the tool used for the crossed-axes angle range

'c.•"" q"'iliity 'II I (DINHe,lIlafter'III "milling

,,..- I_I piltGtlI ........-. IIH~ IMp 'p, !IzD,

!.~.. ~ .tn~ i'ri~ !BiII!!'!!wwm

l·u_ I~~

!I~ 1Ni1l!!:"" !l'ii"!1'1

V J 1fig. 2 - Reduction of tolerance from premachining to finislting of tooth lI.nks.

. 3 - Relative position wren the tool and work gear

September/October 1989 "

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CNC Thread Grinders from Matrix candrastically reduce your production time.Programmable control of infeedl andauto.grind cycle, plunge grinding cyclesand dressing, combined with the largestfamily of thread grinders in the world,make' Matrix the logical choice to so'iveyour grinding problems regardless etmaterial! or application,

Appropriate to a multitude of applica-tions, Matrix CNC Thread Grinders areideal for ball screw production, internaland external A. P. L grinding, worm grin-ding, micrometer and surgical screwproduction, 'gnindingl the tra.cks in recir-culating !ball nuts, and many more.These Matrix machines can handlealmost any aspect of precision grinding.

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Maximum ground diameter 8" 12.5" 12.5" 10" 10"Grinding wheel diameter ! 14' I - 20" 1" to 5" 20"HP 01 wheelhead: drive I 5 and 7% 11110, 200t 25 10, 20 or 25 5 10, 20 or 25Heli>: of wtleel, LH& RH I 2[J" I 45° 45° 10" 24°Workhea.d! thrUi !bore· I 1.5" Iii 3.97" 3.'917" N/A 6'tJ"

Internal or externall threads of vinuallyany form, singl'e or multi-start, right orleft hend, parallel or tapered: 'call beeasily ,ground with or without relief. litonly takes the right Mallrix CNC ThreadGrinder for the Job.

Choices of wheel dressingl units areavailable in convsntlonalltemplata ordresser arm style, diamond roll, crushroll plus a versatile CNG Dress Unit

Several of the more popular Matriixthread grinding models are shown in thetable at lefl. Details on otner modelsavailable can be ,obtained by wrmng orcalling Matrb" ..Churchill Corporation,5903 Harper Road, Solon, Ohio 441139or 21'6/248-7950. FAX 216-248-7981.

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OO<h/~45o.(4) A conjugated crossed helical gearing is produc-ed. Theefleetlve cutting velocity is the vector sum of the slidingvelocity along the profile VH and along the lead Vl = Vu

.sin,),Ims{31' Assuming 'the peripheral velocity Vu of the tooland the helix a.ngle 131 of the work gear to, be constant, thelongitudinal velocity VL depends sinusoidally on 'Y.

Assuming further that the external tool diameter is constant,an increasing v will result in a lower number of tool teeth, since'Y "'" 130 + 131,

Chip Forming Mechanisms DuringHaril Finishing and fine Finishing

Fig.4!. shows a tooth of a work gear in conjugated meshwith a tooth of the abrasive tool. Chip removal occurs at everypoint of the momentary contact line only in the direction ofviel = vi: + v.H .

The momenta:ry kinematic condition of a cutting edge whencutting into the material could be described as a rolling andsliding of the rolling circles .to and t1 in the direction of vieJ. Thedirection of vRe]depends mainly on -y. If 'Y = 0, vR'e!will beoriented exclusively from addendum to dedendum, If 'Y movestowards (90" + (31), viel will he increasingly parallel to the leaddirection.

Accordingly, the relative conditions of curvature diverge con-siderably from each other. If the circles of curvature are small,as shown in Fig. 4, the cutting grain will penetrate very steeplyinto the material and will leave the cutting path after a short con-tact length. The condition for the next cutting grain to have suf-ficient material for actual penetration and not be shovedelasticaUy away win be decisive for the structure of the cuttingsurface yo, UI

With smalleffective circles of curvature and high rollingvelocities, the cutting structure requires a higher density of cut-ting edges than for large circles of curvature and low roUingvelocities, That means, with an increasing 'Y, 'the structure of thetool must he more open.

This short survey of metal cutting mechanisms is intended toillustrate that in gear finishing, the geometric and kinematic pro-cess parameters dependent on the tool and the work gear willsubstantially affect the choice of a suitable cutting and bondingmaterial. as well as optimal structure of 'cutting surface .

Drive System For Hard Finishingand fine finishlng

Another essential mark of distinction between these twomodes of finishing is the type of drive system used. Fig. 5 shows

fig. 4 - Operating condit ions of a cutting grain during relative sliding and rollingof the momentary equivalent circles of curvature,

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September/October 1989' 1.3

the various modes of current drive systems.The left side of the picture shows the radial load connection

with a two-flank contact. (4) The work gear is in free mesh withthe too] without controlling the drive gear. This hard finishingprocess is similar to the green shaving process and producessimilar quality grades, but before heat treatment. The two~f1ankmethod is not discussed in this paper.

The drive mode shown in the middle of the illustration canonly be used to improve the microstructure of the flanks, forflank modifications, and for removing defectsfrom gears. Dueto the braking force, there is only a one-flank contact, so that thevarious divergences of right-hand and left-hand flanks have noinfluence.

Both drive modes shown are not able to specifically generatea definite flank geometry, since the tool follows the pitchgeometry produced by premachinmg.

From rig. 2 we see that in order to produce a specific definiteflank geometry based on a usual premachining.a stock removalof about 50 to 1oo,/Lmper flank is required. To this effect the tooland the work gear must be in constrained mesh, as is shown sym-bolically on the right side of the illustration.

The left part of Pig. 6 shows a mechanicalIyconstrained meshusing helical toothed conical gears. (4) The relatively simple andsafe mechanically constrained mesh meets the requirements forhigh torsion rigidity and dynamic transmission. The tool - aCBN-coated cutter - and the work gear are coaxially mountedon the spindles of the helical toothed gearing, work being donewith single-flank contact. The stock is removed by a relativetangential displacement.

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'4 Gear lechnol'og-y

Relative tangential displacement is achieved by obtaining acontact of flanks of both gearings beyond the nominal center linedistance. When the gearings approach radially lip to theirnominal center line distance, they must make way for each otherwhile rotating, this is achieved by making one flank of the toolpenetrate into the flanks of the work gear during rotation.

By knowing accurately the relative tangential displacementson a change of the center line distance, one will be able to main-tain accurate backlash tolerances.

T 0015 For Hard Finishing and Fine FinishillgAs was said initially, the main problems with hard finishing

processes are encountered in the high accuracy required in massproduction, because the result of the machining must bereach-ed with staristical reliability, Deviations from the tool Hankgeometry are reproduced on approximately a 1:1scale as devia-tions of the work gear Hank geometry. From the' overalltolerances for the work gear profile, for instance, a separate tooltolerance of ± 3ILm wi1Jhave to be kept for the machine and thetool (Fig. 2).

Fig. 7 shows various possibilities of production for hardfinishing and fine finishing tools.

D__

,o

Fig. 5 - Drive modes fOT hard machining processes with a non-defined geometryof the cu ttin& edge.

The method for tool production shown on the left of the figureconsists of producing a coarse positive replica of the tool by atechnique like hobbing. From this gear a negative mold is made.A mixture of synthetic resin and abrasive grains is cast into thjsmold, which 'then sets to form the tool gear with an approximateshape of flanks.

The accurate flank profile of the tool is obtained by means ofa diamond dresser. In its coated condition, this wheel has pre-ciselythe flank profile of the work gear flank desired. The syn-'thetic resin bonded tool is used predominantly with drive modeswithout a constrained mesh. It is most suitable for improvingsurface finish and for removing damages.

The production of the vitrified bonded tool is shown in thecentral past of the illustration. The disk type gear is given apreliminary profile by a fonngrinding wheel, while 'the accurateflank profile is again obtained by means of a diamond dresser.This tool. version is mainly used for drive modes with con-strained mesh. The chip removal here is proportionately higherthan for the synthetic-resin bonded tool version.

On the right side of the illustration is the dIawing of a toolcoated with abrasive material. The flank geometry, including allnecessary modifications of flanks, is ground. After coating itmay be possible Ito either dress the tool with a diamonddressePl or 'to use it directly for hard finishing ..

The close admissible tolerances within a range of a fewmicrometers for the tool emphasizes the problem of tool wear.It may be solved either by dressing the tool in the machine witha diamond dresser or by using wear-resistant cutting materialswhich will be removed from the basic tool aft·er the end of theservice llle ..In this case, the basic tool could be reeoated severaltimes.

Computer AssistanceSince geometrical and kinematical correlations with regard to

the production of basic hard alloy coated tools are quite com-plex, they requifle an extensive assistance by computers ..Its aimwould be to produce aU manufacturing dataand machine set-

Fig. '7 - Basic possibilities of producing gear-like tools.

tings automatically on the basis of the data of the desired toolflank geometry.

Fig. 8 shows at detail of the manufacturing drawing for haId

..-,.......".~-

Fig. 8- Detail.ofa workshop drawing~~ng coated hard finishing tools.

* Compact ~sJ9n: Ideal for cell enVlfonment5.

* Durable. Designed 10 meet production del'11ilnds

* Fast set "lP and operi!tkln: Most set ups maoe In less II1i!n I mlJ1Ute WI\hI)'plCal cycle urnes of I rnmere or less

* Portable: Wllh Opt!ONI cart II can be moved 'rom work Staoon 10WOfK Station

* Fast chucking: QUickly chucks most parts WlthDllt costly ana [uTI!!!consuming special lOOllng

* Vernier Scales: Vernier scale~ on me adjustment axes allow quICk andconsisrent repeat setups.

* Modular Deslgn: onnoos Install and remove In seconds* Vel'QtiI'e System: With !he opt!onal equipment pracllC Ily any type or

gear and edge finish can readily be achieved.

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alloy coated tools. The upper part of the illustration showstopological deviations with regard to the enveloped involute sur-faces, Such deviations are strongly affected by the crossed-axesangle and by the axial position of the gearing with reference tothe crossingofaxes ..The lower part of the illustration shows themeshing conditions of the tool in the axial section. The requiredflank limiting geometries of the tool can be gathered from thesedrawings.

Machinery for Hard Fmishmgand HneFinishingMachinery for hard finishing and for fine finishing have

similar designs. Essential differences, due to different aims, con-cern the drive system and the controls.

The "fine finishing" mode aims at removing damage-and at im-proving the microstructure of flanks. The process is character-ized by the unconstrained mesh of the tool and the work gear.

The "hard finishing" mode aims at producing gears ready forassembly, starting from the work gear that has been hardenedbefore finishing. It is characterized by the constrained mesh ofthe tool and the work gear. On the one hand, this finishing modeshould have a metaJ removing capacity of 10 to lOO/Lfll pe:r flank,while at the same time, the microstructure of flanks should makefurther finishing unnecessary .

Editor's Note: Part II of this article will discuss Operating Se-quences and Machining Results and Gear Noise With HardFinished and Fine Finished Gears.

References:1. GOE13BELET, J. 'Tooth Contact Test of Cylindri.cal Gears,"

Dissertation, TH-Aachen. 1980, (In German.)

2, KLOECKER, M. "Noise Reductions of Machine Tools." Disser-tation. TH-Aachen, 1982. (In Cerman.)

3. LACHENMAlER, S. "Design of Special Cylindrical Gear Teethfor Vibration and Noise-Reduced Running." Dissertation, TH-Aachen, 1983. (In German.)

4, BAUSCH, T. e! a!. Gear Production Methods. Expert-Verlag,Sindelfingen, 1986. (In Cerman.)

5. NEUPERT, B.."Computation of the Tooth Forces, Contact andRoot Stresses of Cylindrical, Bevel and Hypoid Gears." Disser-tation, TH-Aadlen, 1983. (In German.)

6, WECK, M. - "Improvement in the Field of Gear Technics,"Indusfrie-Anzeiger, 109 (1987) 90 ..(In German.)

7. SCHLEICH, H. "SharpeningofCBN GrindingWheels." Disser-tation, Tl-l-Aachen, 1982. (In German,)

8. SCHRIEFER. H. "Computation of the Flank Ceometry, Contact,and Running Conditions of Bevel and Hypoid Gears." Disserta-tion, TH-Aadlen, 1983. (In German.)

9. ST ADTFELD, H. "Practical Computerized Design of Bevel andHypoid Gears," Dissertation, TH-Aa.chen, 1987, (In German.)

10. STEFFENS, K. "Ihermomechanics of Grinding." Dissertation,TH-Aarnen, 1983. (In German).

11. WECK, M, Machine Tools, Automatic and Control System5.VDI-Verlag, Dusseldorf, 1982, (In German.)

12, WERNER, G .."Kinematics and Mechanics of Grinding Processes."Dissertation, TH-Aachen, 1971. (In German.)

13. KONIG, W., ST~FFENS, K., WERNER, A. "Computer Simula-tions of Grinding Processes." Industrie-Anzeiger, 1'09 (1987) 68.(In German). -

Acknowledgement: Reprinted courtesy o.f Society of ManufacturingEngineers. Presented at the 1987 Gear Processing and M_anufa.cturingClinic, Nov. 17-19. 1987, Southfield, Ml.

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16 Gear Technology

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White ltching AreaCase-Hardened Cea

AUTHORS:

PROFESSOR DR. -ING. HANS WLNTERis the head of t~leLaboratory of Gear Researchand Gear Design at the Technical U,liversity ofMunich. He has held positioP1S in tile Gemra'lgear industry since 1956 working for Zahnrad-fabrik Fn'edn'chshafen and DEMAG Duisberg inInarlufacturing. development. desigrt andresearch. He received his doctorate from theTechm'cal Universi.ty of Municl1 and studied asan associate of Prof. Dt.-lng h.e. GustavNiemann'.

DR. -lNG. GERHARD KNAUER isa grad-uate engineer of FZG and is an engineer atZa}ml'ad!abrik Friedrichshajen.

MR. JOHN J. GAMEL is a senior designengineer with SO/Dr Turbines. Inc.. San Diego,CA. Prior to coming there. he worked at theNaval Ship Systems Engi11eerillg Station inPhiladelphia. PA. He smdied at FlG during1986.

Abstract:The phenomenon of white layers, which

arises from high stress, can be observed undera microscope after the white layers have beentreated with a weak nitric acid solution. Theiroccurrences in zones of high shear stress canprovide qualitatively valuable indications ofthe size and direction of the stress, and they canpoint out possible starting points for flankdamage. An investigation of this phenomenonis described.

IntroductionIt is known that on the surface and just

under the surface of rolling elements ofhardened steels, so called ~white layers" canbe observed, This phenomerton.also called

Professor Dr.-Ing. Hans Winter,Dr .-Ing ..Gerhard Knauer

Technical University of MunichJohn J. Gamel

Solar Turbines, Inc., San Diego, CA

"white etching areas (\NEA)," arises fromhigh stress. These white etching areas arestructured zones which are affected whenetched with diluted nitric acid and whichthen forma light contrast with the matrixwhen observed with a microscope.

In References 1, 2, 6, 7, 10, 12 and 13,the different forms of appearances havebeen described and their appearances inconnection with the actual stress have beenanalyzed. In the same way, the structure ofthese structured zones can be regarded asknown to a large degree. The conditionsfor the appearance of WEA on the surfaceare high friction and/or impact stress;whereas, WEA were observed beneath thefunctioning surface only inelements whi.chwere at the same time exposed to stronghydrostatic pressu re and a shear stress. r La)

In 'the cited reference, the origin of WEAbeneath the surface resulted because thepresence of a mechanical thermodynamicstate induced such high tensions, that in theareas, the shear resistance 'Of the material,had been exceeded. The flanks of the crackwhich run in the direction of the greatestshear stress are heated to the meltingtemperature in an extremely short timebecause of the plastic deformation of thestructure. In this process the carbidesdissolve and the carbon enters the gamma-matrix. After self-cooling, because of thesurrounding structures with considerablylower termperamres, we get a highly over-saturated martensite.

Untll new the investigations of WEAphenomena have been carried out largelywith rolling element bearings ..It is knownthat rolli element bearings are exposed tosubstantially higher Hertzian pressure thangears under similar conditions. This isprobably why the 'Occurrence of whiteetching areas on gears has 5.0 far beennoticed in 'On)y a few cases, and it is still notclear whether WEA can be regarded acause of flank damage. This article willdescribe, further some fonns of occurrencesof \IVEA. on the highly stressed flanks ofcase-hard ned gears. In addition, we willdiscuss w ether there is a connection withfatigue fa ilu

This research is based on a number ofoperating tests with case-hardened gearsforthe investigations of pit t ing resisrance.which h ve also been subsequently ana-lyzed through metallographic investiga-tions". It is, therefore, not the purpose ofthis article to analyze the microstructureand triggering mechanism of WEA (Werefer here rather to the abundance of ex-isting literature), but we will investigate theoccurrence of \IVEA. in connection with thestress .of the tooth flanks and the conse-quences of it.

•All operating tests and metaliOlfilphic investiga-tions were performed at the Gear ResearchLaboratory (FZd of the Technicat University ofMunich. West' Germany

White Etching Areas in theArea of the Tooth Flank.

Material Fatigue on Non-metallic.Inclusions Beneath the Surface

The sliding-rolling motion under highHertzian stress in the contact of two matingtooth flanks leads to a three-axis-pressure-stress state, which is superimposed by ashear stress resulting from the friction load.The main shear stress, which can beregarded as the cause of the .crack(6.111has,with ideal geometrical bodies, a path to thedepth, as shown in Fig. 1.

According to investigations of Refer-ences 4 and 5, micro-Hertaian fields of ten-sion are formed on machined surfaces dueto previous damage as well as scratchesand roughness. These fields of tension leadto paths of tension that are different fromthose that should be taken in an idealgeometrical body. In Fig. 1, the path of themain shear tension fora. rectangular notchwith a depth of 0.1 ~ and a length of 0.2~ has been added. According to this, themain shear stress directly beneath the sur-face is considerably greater than the max-imum, which follows the currenthypothesis about the endurance. Whenreaching a depth of 0.5 bH the influence ofthe surface roughness has decreased. Afterthat depth, the path of the tension followsthe pattern of the Hertzian pressuredistribution on the ideally smooth surface.In this area Ithemain shear stress is directedagainst the surface just under 450

• Inaddi-tion to this, in the area of non-metallic in-clusions peaks of tension occur, as pointedout in Fig. 2, which can lead to localized 'ex-ceeding of the allowable shear. (SeeReferences 3 and 4\. )

The calculation derived from Fig.. 2 isconfirmed by Fig. 3. An oxidation inclu-sion, whose E-modulus is about two timesas large as for steel, lies in the area of the in-ner point of single contact, about 0.14 mmbelow the surface of the flank in the area ofhigh main shear stress. (See Fig. 1.) In anundisturbed structure, the main shear ten-sion did not reach a value which would becritical for a case-hardened steel. However,the approximate 2.5-fold increase in ten-sion due to the inclusion (compare Fig. 2)led to the occurrence of cracks and WEA,which, in accordance with the path of mainshear stress, are approximately 450 withrespect to the surface, The gear data andthe operating conditions for this experi-ment are listed in.Table 1.

In different publications. for example,References 6 and 10, an increase of VVEAinconnection with a greater number ofrevolutions has been noticed. This leads tothe conclusion that also with non-metallicinclusions. WEA do not appearimmediately after the first stress cycle.They only occur after a certain period ofstress due to plastic deformation whichcauses change in the state of the residualstress. Possibly the crack expands veryquickly once a critical state of deformationis reached, and the crack travels in its en-vironment to temperature regions whichare above melting temperature. (SeeReference 10,) The high impact stress thatoccurs with roller element bearings canap-parently also be reached locally with gears.In Reference 6, it is noted that a minimumimpact stress of T45 = 725 n/mm2(105,2001b/in2), at the inner ring of aroller element bearing, leads to the occur-rence of WEA. Also, with case-hardenedgears, the main impact stress of this dimen-sion can occur in the area of inclusions.

The cracks which occur on non-metallicinclusions below the surface of case-hardened gear flanks generally extend verylittle. So far, it has not been provenwhether they extend to the surface andcause damage at the flank.

The strictly local limitation of WEA tonon-metallic inclusions and the connectionwith the relation (E inclusion I I:: steel)become apparent in the example of sulfurcontent in case-hardened gears made of(continued on page 22)

Table 1Gear Data and Operating Conditions

Module (Diametral Pitch)m = Smm (S.08Iin.)Number of teeth (1 = Pinion/

2 = gear)zl/zz = 17118Face widthb = 16mm (0.63 in.)Center distancea = 91.Smm (3.60 in.)TorqueM = 360Nm (265 ft-lb)K - factorK = U.l Nzmrrr' (16S0psi)Hertzian Pressure at rolling point CPc = 1440 N/mmRevolutions of the driving pinionn= 3000 min-1

NEe:-,

:z..5 600..'"~;; 400...c.."'"...." 200CI.~

1·1000

800

o0.1 0.2 0,3 o.~ A,S

Distance from surfgCI in IMI •

Fig. 1- The path of the main shear stress into thdepth with over laying of the Hertzian pressure andfriction stress on a tooth flank. (See Table 1.)

o

4

1~ 2.,:I:

\:;."Ii~

o 0,5 1,0 1,5 2,0

EllncLu5ionl/EtsteellF;ig, 2- The increase in tension in the surroundingso( non-metallic inclusions in the process of over-running bearing steel 100 Cr 6. Reference 3: FLndingsfrom optical tension. model tests in simulating thestress dlstribution on a con lac! line of a ball bearinginner ring 6309 for Fr - 19200 N radial load.

Fiig. 3 - WEA starting from an oxide inclusionbeneath the flank surface of a case-hardened gear of16 Mn CrS.

September/October 1989 19

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WHITE ETCIDNG AREAS ... (continued from pag,e 19)

16MnCrS (See Table Z), with globularlyformed sulfide inclusions in which a greatnumber of very small WEA can be noticedin the area of high impact stress. TheseWEA result exclusively from inclusions;whereas, such occurrences cannot befound with long strips of manganesesulfide. Globular sulfides are harder thanmanganese sulfides due to combinationwith the sulfide influencing elements. Thecracks that have been examined are neverlonger than some I'm and never have con-nection to the surface. (See Fig, 4.) The in-dusions themselves are spread out veryfinely,

The Stress of the Gear Flankat tile Begjnn.ing of Contact

It is a fact that WEA frequently occur insurface areas which are exposed to strongshock stress, In highly stressed gear pairs,

Table 2Material and Heat Treatment

~ig, 4 - White etching areas at globular form sulfideinclusions beneath the flank surface.

22 Gear Technology

the gear teeth that are in contact aredeformed, so that the followLng gear toothtip strikes against the flank of the drivingpinion in the area of the gear tooth root tooearly. (See Reference 8.) This leads to anLmpact shock. Shown in Fig. 5 is the toothstretching signal of the driving pinionunder the conditions described inTable 1,which shows a very steep increase at thebeginning of contact which points out 3.

very high shock-type stressat the begin-ning of contact,

Metallograph:icalexamina.tions showthat the greatest number of and the mostprominent WEA could be found in thisarea. (See Fig. 6.)

Fig, 7 shows WEA at the surface whichhave occurred due to high stress caused byth impact shock, Their extension in depthis between 30 and 5QJlm, Beneath the SUT-

face, the WEA are limited by a crack whichruns almost parallel to the surface, Due tothe contact shock, there occurs localJy highpressureas well as strong friction forces,because of which the flank surface is ex-posed to an extreme shear stress in thisarea, Shown in Fig, 8 is the path and thedirection of Ithemain shear stress relative tothe local pressure on the flank for two fric-tion values as a function of depth from thesurface.

Only with increasing depth does thedirection of the main shear stress comecloser to an angle of 45° relative to the sur-

---.20pm

1

S'S c·c· DO' r E

Path of contact _

A,'B,C.D.E Attuall)Qlh of contactA·,B',CP,E' Theordical path 01 ,(onlaU

rag. 5 - Tooth stretching signal in root of the pinienover the length of gearcontact, (See Table 1.)

fig. 6 - Position of the white etching areas in the areaor the ~nning .or contact on the f1alll of the driv-ing pinion.

fig_ 7 - Whi te etching areas in the area of the begi nning of contact on the surface of a case-hardened pin-ion made of 16 Mn Cr 5.

1---4'

20llm

Fig. 8 - The path and the direct jon ·of the main impactstress for two different friction values.

Fig. 9 - White etching area in the area of the surfacein the direction of the main shearstress,

Fig.10-location of the maximum impact stress withPH=1440 N/mm2 bH~0.20mm in relation to thefriction value.

face. Correspondingly, the angles of theWEA change as is pointed out in Fig. 9.

The position of the main shear stressminimum depends on the magnitude of thecoefficient of friction. As shown in Fig. 10from /L = 0.40 onwards, the maximummain shear stress lies at the surface. As frio-tion stress increases, the point at which thedirection of the main shear stress reachesthe 45° limit can be found as it travelsdeeper.

This connection, again, is valid only forideal geometrical bodies. Since tooth flankscan be considered as t,eclmicalsurfaces, wehave to take also Intoaccount the tension-increasing effect of the notches directly inthe area of the impact shock beneath thesurfaceaccording to RefereneeS. (See Fig.1.) Also favoring the formation of VVEAisthe local flash temperature, which again islargely dependent on friction value.

Caused by the effects of running-in, the[cantinued OM page 36)

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gears where teeth have been cut beforeheat treatment, but through-hardenedgears are also ground for higher ac-curacies. In the case of fine pitch gears,many times teeth are ground in at finishedblank without any previous teeth cuttingoperation.

Gear Grinding PreparationFollowing are some of the items which

should be considered carefully indetail forsuccessful gear grinding.

Preparation of the Gear Blank. Thecommon statement, "A good gear blank is

Gear Grinding fundamentalsYogi Sharma, P.E.,

Philadelphia Cear CorporationKin,g of Prussia, PA

AUTHOR:

yocm SHAruv1A is employed in gearmanufartun·ng.and design at Philadelphia GearCorp. He holds an M.S. degree ill mechanicalengineering from Villanova University and onein industria/engil1eering from Penn State. Mr.Sharma is a .licensed mechanical engineer in thestate of Pennsylvania ,and a senior member ofSME

IntroducdonThis article deals with certain items to

be taken i.ntooonsideration for gear grind-ing, common problems that arise in gear

26 Gear Techno'iogy

grinding and their solutions. The discus-sion will be limited to jobbing or low-batch production environments, whereexperimental setup and testing is notpossible for economic and other reasons,

Gear grindi.ng is basically performedeither to finish hardened gears or toenhance the accuracy of gears or both.The accuracy from gear grinding includesdesired lead and profile modifications,lower spacing and runouterrors, and highsurface finish. Most of the time, geargrinding is associated with case-hardened

Fig. 1- Double hel ical pinion shaftshowing groovefor grinding wheel clearance.

a must fo.r a good gear," is very true Ior asuccessful. gear grinding operation. Asgear grinding is quite often the last opera-tion in gear manufacturing, any com-promise in gear blank design, processing,or manufacturing can cause unnecessarydelays, poor quality, or rejected parts.

The following items should be con-sidered for gear blank preparation.

Grinding Wheel Runout Clearance atTooth Grinding. Gear blanks with eon-straints on one or both ends must bechecked for proper grinding wheel

clearance. These include double helicalgears, pinion shafts with teeth running outin diameters higher than root diameter,etc.

The grind.ing wheel runout clearance isa function of many factors, such as grind-ing wheel diameter, helix angle, DPN,etc., but the grinding wheel diameter is themost influential item. One of the simplesolution approaches is to providedesigners a 'chart for runout clearancebased on DPN, helix, and grinding wheeldiameters onavailable machines, along

with a machine capacity chart. This willallow designers to have a preliminarydesign with a reasonable accuracy, whichmust be verified by an appropriate personin manufacturing, Runout clearancevalues can also be included in gear designprograms and provided to the designerwith gear data. In cases of crlticalappli-cation. runout clearancecan befine tunedwith dummy blanks on grindingmachines ..

fig. 1 shows a double helical pinion;Fig. 2 shows a pinion shaft with runout

fig. 2 =Double helical pinion shaft showing runout(or grinding wheel clearance.

Sepfember IOctober 1989 27

CIRCLE A-li90N REAIDERREPLY CARD

clearance for a grinding wheel, and Fig, 3shows suggested vaJues for double helicalgear groove widths.,

S lection ,ofProper Blank Tolerances.The tolerances of the blank, such as TIR ofmounting or locating bore, squareness oftheborewithmountingswface, etc., mustbe decided based onall related factors, in-cluding quality requirements. Fig. 4 showssome of these values on a simpler gearblank ..

Pfreparation of Any Sub-Assembly Be-roJ'1@ ':ooth Grinding,. Fig,S shows a sub-assembly ,of 3. gea.r with a shaft . As in anyfinal machining operation, prior sub-assembly work is quite helpful in achiev-ing higher accuracies.

As shown in 'this sketch, if the teeth areground after sub-assembly, the runoutand squareness problems, are minimized,These two problems arise becausetolerances add up if the gear and shaft aresub-assembled after gear grinding.

PliOper [ndicating Proot Surfaces orBands on Gear Blanks,. Proof surfaces, acritical item mgear grinding, must not beoverlooked. A gear reaching the' toothgrinding stage without proper indicatingsurfaces can cause unsatisfactory qualityand long delays. Fig. 6 shows an. exampleof a gear with proof surfaces.

Blank Inspection Before Tooth Grind-ing. In certain critlcalapplicatiens, gearblanks must be checked for requiredvalues of runout and squareness of moun-Ilingsurfaces 'to avoid poor quality and ex-cessive delays. Random checks mast bedone on aU work prior to tooth grinding.

Sel etion of Proper Quality Number.

Standard InvoluteSpecial Forms,

Splinel ,& SeflrstionMultipl'e' Thf'ieadl

ShankTYrpe

AGMA standard 390.03 is the most com-mon gear quality reference guide in use inthe U.S. Th selection of proper qualityclass number is quite critical. as a lowernumber will not meet the d sign re-quirements, while a higher number will in-crease the cost. The selection of properquality number should be made based onpast experience, application, limitationsof grinding machines, and many otherfactors.

Wherever possible, desired lead andprchlecharts should be defined dearly toavoid any conhrsionat gear grinding. The

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cost of tooth grinding increases at a muchfaster rate at.higher quality levels than atlower levels. in other words, the cost ofchanging the quality number 10 to 11 islower than changing 12 to D, Cost is notthe only factor to be considered, Asquality number rises, the number of toothgrinding machines available 110 achieve thehigher quality decreases, causing manyother problems.

The matched sets approach is quite ad-vantageous in high precision gears. Inmat-ched sets, the gear and pinion profiles andleads are matched in such a way thatmismatchina set does not exceed thetolerance on lead or profile for the ap-plicable quality number. In matched setsconditions, one member. most frequently

a gear with a higher number of teeth, isground first and checked. The lead andprofile charts are studiedcarefuUy, andmodifications to achieve the desired matchMe made in the tooth grinding of thematching member. One disadvantage ofmatched sets is that any replacement in thefuture has to be made in sets, but on theother hand, in any critical application,replacement of one member is not desiredanyhow. Also, in the case of matched sets,dear detailed advanced agreementsbe-tween user and supplier can eliminate un-necessary misunderstandings and delays,

In some special cases, certain tolerancerelief can be allowed inspecific gear qualityelements, which mayreduce corrections attooth grinding. Some examples are lead-in

drives with eccentric cartridges and profileand lead-in hardened pinions over 55 Rcrunning with through-hardened gearlessthan 40 Rc.

Grinding .A1lowanoe and Heat Treat-ment. In. simple words, grinding allowancein tooth grinding is extra material I.eft ontooth flanks (and fillet. i.ncases where thefillet is to be ground). lit is required to grindthe tooth surfaces to proper profile. leadand other quality elements within. specifiedtooth sizes. Exoessive grind allowancecauses many problems, such as longergrind time, loss of case depth, etc. Onthother hand, insufficient grind allowancewill result in undersize tooth thickness. Im-proper grind allowance (excessive or insuf-ficient) will cause many problems, such as

IntrDducing ....

SINGLE FLANKCHAMFERING FORGEARS AND PINIONS

II Mal &II ........ , TnIIIJ

higher costs, longer delays, and rejectedparts in extreme cases or criticalapplications.

Following are some factors influencinggrinding allowance.

Heat Treatment Method. The heat treat-ment method is very iIlfIuential in selectingtheamount of gear grinding allowance.Below are the commonly used heat treat-ment methods for gear teeth.

1. Case carburizing and hardening2. Induction hardening (tooth-to-

tooth and coil)3. Case nitriding4. Through-hardeningThe distortions innitriding are very low;

whereas, they are quite predictable in theinduction hardening process. Case car-

burizing and hardening distortions arequite complicated and magnify with sizeand shape. Many factors, such as design,material machining before heat treatment,shape of part, fix turing in carburizing,quenching, and machining after heat treat-ment,influence what a gear grinder will seewhen he makes a touch on a grindingmachine ..

Any compromise in one or more fac-tors, affects the final outcome. Most of thefactors are so interrelated and intercon-nected that many times the investigationand corrections are carried out at thewrong point, One Df the most effectivemethods is to start with a completely openmind and record the results after everyoperation.

Machining of gears after heat treatmen]and before tooth grinding is very criticaland must not be overlooked or neglected.A gear can be checked :for runout in theplane of rotation on a turning or grindingmachine with a roller in teeth, hut there isno. easy means of checking teeth in an ax-ial plane, Quite often, overcorrections aremade in one plane, causLngextra problemsin the other plane. One effective approachis to indicate proof surfaces created inmachining before cutting and used in cut-ting in both planes. Another very eHectivemethod is to tumor grind proof surfacesafter hardening and check the gear forrunout and lead. finish machine the gearbore and faces or shaft journals after mak-ing corrections based on runout and lead

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charts, relative to proof surfaces createdafter hardening and used for setting on gearchecking machines. The above method iseffective, but needs two extra operationsand a longer cyde ..Also it is Lneffect:ivewhen a gear has irregular distortions, suchas taper along length or oval shape ofdiameter.

Gear Blank Configuration. A well pro-portioned configuration oJ gear or pinionshalt will have fewer distortions in heattreatment . On the other hand, poor designwill cause excessive distortions. Sometimesapplication or weight limitations make ablank unsuitable for case-carburizing andhardening. (See fig. 6.) The above situa-tion can be handled in a number of ways:either leave extramateria1 all around or usequench press in final! quenching. The use ofquench presses with univeral dies in a job-bing enviroment needs much marie plan-ningand estimation than in mass or highproduction environments. In high produc-tion, customized dies are prepared andtested on sample pieces with dilierentad-justments on quench press, and setups arecompletely optimized for production. Onthe other hand, a jobbing environmentdoes not allow detailed testing or custom-ized tooling. VVhenever there is more thanone piece in a.batch, the first piece shouldbe die quenched and measured beforequenching the rest of the pieces, allowingthe 'tool modificat:ionand setup ad-justments for better results, Anotherrecommended approach in quenching is tostart with a lower damp and expandpressures rather than. high values, whichmay Cause excessive growth, resulting invarious problems at tooth grinding. (SeeFig. 7.)

Tooth Size. DPN or module, helix angle,outsidediameter, face width, etc.. all affect

Fig.. '1- Quenching a cylindrical gearwith specialconfiguration. (Courtesy Klingilnberg Corporation. I

the amount of grinding allowance r'f-quired. For example, the working depth ona 2 DPN is twice that on a 4: DPN tooth ..

Gear ApplicaHon. Certain applicationsneed much tighter control. on tooththickness than others ..In the case of an ap-plication with tighter tooth thickenss re-quirernents, higher grind allowances canavoid tooth thickness problems at toothgrinding.

Some other factors affecting grindallowance are gear cutting operation andequipment, gear grinding equipment, gearquality requirements, etc.

Selection of Proper Cutting Tools. High

production allows the use of customizedtools with optimized grinding allowanceand protuberance. while low quantity PI'O-duction imposes the use of universal tool-ing as much as possible. The foUowingsteps are suggested to maximize Itheuse ofpre-grind tools with best possible condi-tions at gea.r grinding.a. Standardize fillets for aU new designs

and use them wherever possible. Fig. 8shows a comparison of standard filletsand full fillets.

b. Select and standardize grinding allow-anee on the basis of various factorsdiscussed previously.

8, -,

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Fig..8 - Standard fillet vs full fillet.

Fig. 9 - Undercut produces by a pre-grind hob anda protuberance type hob,

IIJ ~_ .. _. __ t .- ..... ---"' __ of" __ ~

101 -.....---.. -....--_ .... --A - .......-- .......11) ., .......

.-.- ---,---ft ........- ~III .--. _ __ IIoft,~- ..--- _--

Fig. 10 - Representation of the gear grinding process.(Courtesy of BHS Hofler. Ettlingen. West Germany.)

34 'Gear Technology

c. Select protuberance on the basis ofDPN. Excessive protuberance on gearcutting tools can cause unclean profileabove TrF (SAP) at tooth grinding,while insufficient protuberance cancause grinding step problems. Fig. 9shows undercut produced by a pre-grind hob and a protuberance type hob.

d. Adjust the thickness ofaH pre-grindtools on the basis of grindingallowance.

The universal tool selection alwayscauses certain shortcomings at tooth grin-ding, and constant monitoring must bedone to avoid major problems.

The importance and necessity ofcustomized tooling for all critical andspecial applications cannot be overem-phasized.In such cases, an optimized toolalways avoids many problems at toothgrinding.

Grindin,g ProcessTooth grinding of gears can be classified

into two main processes: generating grind-ing and form grinding. Ingenerating grind-ing, the teeth are ground as the gear mils inrelation to the reciprocating grindingwheel. The process is similar to gearmeshing with a straight sided rack. Thethree most common methods or machinesare:

Conical Wheel Machines ..As shown inFig. 10, both flanks an! ground in-dependently, After each tooth is com-pleted, the machine indexes to the nexttooth until the gear is ground, Desired leadand profile and modifications are made onthe machine. The profile is modified bygrinding wheel dressing, and leadmodifications are obtained through the useof cams,

Saucer V'lheel Machines. In this method,the gear being ground has oscillatingrolling-generating motion, while twogrinding wheels sweep out the involuteprofiles by the relative motion, The twomost common methods are 0° grindingmethod and 15° 120° grinding method.

The two most common types of thesemachines available are the horizontal typeand vertical type, each suitable for differentsizes, etc.

Threaded Wheel Machines. Threadedwheel machines operate on the same prin-ciple as gear hobbing machines. Threadedwheel machines are quite productive, buthave limitations in pitch and overall size.

Form Crinding ..This process uses a form

grinding wheel to grind both flanks, whilethe work piece is maintained in a fixedradial position. Form grinding is quiteuseful in many applications, and both ex-ternal and internal gears can be ground bythis method.

Grinding WJ1eeJ Selection. Selection ofthe grinding wheel is quite important ingear grinding. Following are some of thevariables to consider when choosing agrindlng wheel. (Fig. 11).

Abrasiv,es ..The four main abrasives inuse are

a. Aluminum oxide (AL203

b. Silicon carbide (SC)c. Cubic Boron Nitride (CBN)d. Diamond

The use of "cubic boron nitride" is increas-ing every day. It is stili mainly limited toform grinding in gears but much researchinto its use in grinding is being done. Dia-mond is rarely used in gear grinding.

The other variables in grinding wheelselection are gri,t size, grade or hardness,and structure, A properly selected wheelshould maintain its form for a reasonableperiod and produce the required surfacefinish without burning the tooth surface.Gri.t that is too hard and fine will maintainits edge and give good surface finish, butmaterial. removal is slow and chance ofburning is too high. On the other hand,soft and coarse grit win remove metal fastwithout burning, but the edge wear will behigh. The consumption of the soft wheel isalso high.

One simple rule of selecting grade orhardness is "the harder the material, thesofter the grind wheel and vice versa". Toget satisfying results from grinding wheels,the following are suggested.a. Monitor the performance of the grind-

ing wheel constantly,b. Maintain good records.c. Work with a limited number of

suppliers.d. Sel.ectthe grinding wheel based on heat

treatment, pitch, surface finish,andother factors.

e. Continue some kind of program toupgrade the grinding wheels .. Besidesgrinding whee.1s, tit dressers and dress-ing equipment must be maintainedproperly.

Coolant for Wet 'Grinding. The impor-tance of the proper selection of coolant inwet gear grinding must not beunderestimated. The use of coolant reducesthe grinding wheel loading, lowers(continued on page 37)

Abrasives Standard Marking System

ThIS chart presents symbols found In a typical gnnclmg wheel speclficabon - they repreII80t the vanabIecomponents of a grinding wheel The markmg sequence conforms 10 the standard system used throughoutthe grinding wheellncluslry.

9A 46 K 5 VABRASIVE TYPE GRIT SIZE GRADE STRUCTURE BOHDTYPE

Rov "'""'" 0....CO&ME ~ - B-OQINOIO

'0 C 0 ,~u ..s.-::~Oll'" 2A 11 0 MI\I(TAI.Sc-:. ~ 010. JI\ ,. E R...-R

Sooc: A,b,i'" OIJlllo 51! 18 F vlllt •• o~AlumO:a:.m .... 2!l G

1< "SiPK. Alum. 0101 ..500<:_0. ... "" -- 1sc-.;: jIJum 0•.- ..... XI -- 8

:J!i J •__ 0.... ... ... • 10_"'""'0 .... 274 !>oI L 11T__ O-

RA eo ... ~_B.II

touaI' "'"'" 0.<10 Til ~ 12.. 0 KCICILJ'OAE WtEEUIAog so eo.- c 10 p lJo.->&< c.n.o. rc 110 '.'~PIou $I c..- )C 90 - to

111> 0,~_s.oc.OG '20 18

ComI>nohon .. CIt 1:C

_N.Alum Dull 1M 180.... 51 IA<bodo u-- v~ w

2«l2lIQ:l2Oooc.!OO!Ill

fig. 11 - Standard marking system for abrasives.(Courtesy Bay State Abrasives Division, Abrasive In-dustries. lnc.)

Can you do effective case dieiPthstudiesiin 2 minutes?

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WHITE ETCHING AREAS ... (continued from page 23)stress in the area of the beginning of contact ...-----------------:11decreases with an increasing number ofstress cycles. It can therefore be expectedthat the WEA would occur at this spotfollowing a comparatively short amount oftime.

Specific Characteristics of theExamined White Etching Areas

Structure and the composition of WEAhave been met.alIogr-aphically examined ona broad basis in various research tests. Thefindings with case-hardened gears arelargely in agreement with the aforemen-tioned research. According to ourmeasurements on our sample, the micro-hardness of the WEA at the surface isbasedon an average of 1200HV11 dearly higherthan that of the surrounding matrix withabout 850HV1.

The WEA at the surface examined on thelight electron microscope show a partlyporous structure which points to a temper-ing process. (See Fig. 11.) Also, with thelight microscope, regions of a darker colorcan be seen within theWEA .. It is stillunclear whether within the surface near theWEA" as shown in Fig. 12" such hightemperatures can occur that can temper the

I

wiflank 5urfn:- II

- Ii

I

I1

P~rp'ndrcul(lrcut I----:1.1

I

Fig. 11- Porous structure in the surface area of a gearflank.

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'" Universal, multiparameter rolling flank 'geartester with computer and recorder.

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36 Gear Technology

Fig.]2- Partly tempered WEA at the flank surface.

:Fig. 13a - Crack near the surface (unetched slide).

Fig. 13b- View magnification. of the crack shown in.Fig. 13a that is bordered with white etching area.(Etched with HN03 .•)

(continued on page 39)

GEAR GRINDING tUNDAMENTAl.S .... (continued from page 35)operating temperatures, maeasesgrinding :r---....-.;--:;......::;......--=====;-;::===:::::;-----------,wheel life. and gives better swface finish onteeth flanks. The following considerationsshould be noted when selecting and usinga gear grinding coolant.a. The quality of gear grinding coolant

must not be sacrificed in the name ofcoolant standardization.

b. Gear gTinding coolant must be con-stantly monitored for contaminationand dilution.

c. Samples from every machine or systemshould be taken out. periodicallychecked, and results recorded.

d. Wind deflectors should be used wherenecessary.The surface speed of a grinding wheel isquite high, causing an envelope of high-speed air to form around it.Consequently, the velocity of coolantmust be high enough to penetrate the airlayer. The use ofa wind deflector isvery helpful in this situation.

e. Sparking must be eliminated as soon asit occurs, Sparks during wet grindingusually indicate that coolant is not:reaching the required spot in sufficientquantity. It indicates intermittentheating. which is highly undesirable. asit can lead to surface tempering or

Standard _---_End'DresSlngRailer

A sllarp Slep IS producedwhen gnodl ng ,"adequatelyund rcul gear w,ln regula,dressed wheel

A R,dlUssed wheel pro-ducn a srnoem IranSll\Onbel_n looth flank and rootunder same condlhons

cracking or both.

Fig. 12 - End dresser options for saucer wheel grind- ing machines,

Gear Grinding Pwblemsand Sgggest dSclutlons ApPl'oath

Gear Grinding Steps. Grinding steps intooth fillets have various causes and arevery detrimental. They act as stress risersand also reduce the critical case depth intooth fillets. Any subsequent work per-formed to remove the steps raises the costand can cause various other problems.Here ace some suggested approaches toeliminate orreduoe the steps in tooth fillets.a. Always use at hob with proper pro-

tuberance, thickness, blend angle, fillet

radius. etc.b, Use the correct amount of grinding

allowance on tooth thickness at cutting.c. Grind the tooth flank to proper depth.

Define and use the point of maximumundercut in grinding setup.

d. Continuously train and educatepersonnel.

e. Monitor and resolve problems by im-mediate attention.

Sometimes it will be quite difficult toavoid steps completely, because of ex-cessive distortion at heat 'treatment use ofimproper tools. excessive grinding allow-ance. etc. In such cases. use of a grinding

CAN YOU IMAGINE: THAT WE ONLY MANUFACTURE INISERTEID BLADE HOBS?

CAN YOU IMAG,IINE: THAT OUR STAND'ARD MATERIIAL IS M35,?

CAN YOU IMAGINE: THAT OUR STAND'ARD QUALITY IS CLASS "A"?

CAN YOU IMAGINE: THAT WE CAN GRIND YOUR: HOB WITH A CONTIINUOUS PROFILE FOFf

ULTIMATE ACCURACY OVER THE ENTIRE TOOTH LENGT.H?

CAN YOU IMAGINE: THAT A HOB WHICH MAY BE MOIRE iEXPENSIVE ACTUALLY LO'WERS,

YOUR, COST PER WORKPIECE?

CAN YOU IMAGINE: INDUSTRY HAS SUPPORTIED' THIIS NO COMPROMIS,E APPROACH FOR OVIER,40 YIEARS?

CAN YOU IMAGINE: IEXPLAINING TO PURCHASING THAT A TOOL WHICH MAY BE MORE EXPENSIVE

ACTUALLY COS,TS TIHE COMPANY LESS?

CAN YOU IMAGINE: WHAT !HAPPENS WHEN YOU IDON'T !HAVE THE RI(3HT TOOL FOR THE JOB AND YOUR

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wheel with tip radius can avoid sharp cor-ners in grinding steps. The amount ofradius can be selected on the basis of DPN,grinding machine, and all other factors.The same approach can be used in conicalwheel machines. (See Fig. 12.)

GeM Grinding Cracks. Gear grindingcracks or grinding checks usually indicatetha.t there is process control problem, eitherin heat treatment or in gear grinding orboth.

Heat Treatment. The correct amount ofcase carbon content is very critical, as aninsuffident amount can cause low hardnessproblems; whereas, excessive case carboncontent can cause the presence of retainedaustenite. The grinding process generatespressure and heat, which causes transfor-mation. Retained austenite transformationat grinding isconsidered a source of surfacetempering or cracks or both.

free carbides or carbide networks in casestructures is another side ·effectof excessivecase carbon content ..Excessive hardness ofthe material (fr~ carbides) can causelocalized overheating. Overheating duringthe grinding operation results in surfacetempering 'or cracks or both.

Heat treatment operations usually resultin some film on the surface of heat treatedparts. This scale must be removed beforegrinding, as it tends to. load the grindingwheel. Surface oxidation in heat treatmentprcduces a thin layer of decarburized andsoft material on teeth flanks. This materialleads up the grinding wheel, causingoverheating, leading to. surface temperingor cracks or beth.

Excessive distortions in an irregular pat-tern make it difficult for machine operatorsto locate the highest point on the gear toothsurface. If the grinding cut is not started atthis point, excessive amounts of materialwill be removed during the cut from highpoints. Excessive cuts will generateoverheating and can lead to. cracking orsurface tempering or both. This problemcan be handled easily by the machlneoperator on a machine with threadedwheels and continuous indexing.

Gear Grinding. The variables in geargri-"ding operations are the gear grindingmachine, Ithegrinding wheel, the grindingcoolant in the case of wet grinding, andgrinding machine setup.

Any problem. with one or morevariables can lead to. various problems, in-dudingcracks on teeth. As discussedbefore, overheating or eecessive heating at

38 Gear lechnology

any point in the grinding operation canlead to surface tempering or grindingcracks or both. This overheating can becaused by a combination of factors, such asmalfunction of the gear grinding machine,use of an improper grinding wheel, un-suitable coolant or improper positioning ofcoolant nozzle, and an excessiveamount ofcut or material removal.

Gear Grinding Cost In a jobbing or lowbatch production, gear grinding cost is animportant matter. The estimation is nor-mally based on many factors in grinding,such as number of teeth, DPN,. helix angle,face, material, grinding allowance. quality,method, machine, etc., and the final.number is corrected on the basis of past ex-perience. Somehow, the estimation usuallyfalls short of actual time. In the currentcompetitive world, the gear grinding costhas to. be maintained at a reasonable level.Below are some suggested approaches.a. Setup preparation cannot be overem-

phasized in a low production atmo-sphere. It is a good practice to havemore than one item ready for thegrin-ding machine. Incase something goeswrong at the last minute with the firstitem on line, the next on line can bestarted without excessive idle time.

b. Heat treatment distortions or metallur-gical characteristics and inadequatemanufacturing process control. willdeliver gears with high inaccuracies to.gear grinding, which will increase grind-ing time. Therefore, a good control. atheal treatment and manufacturing pro-cess will not only cut grinding times, butwill also reduce scrappage and enhancequality ..

c. A good preventative maintenance ofgear grinding machines will keep down-time minimum.

d. Training and education of personnel isquite critical and must not beoverlooked ..

e. Useaf skiving hobs can be very helpfulin many ways, such as removing mostof the distortions and delivering a gearto grmding with limited grindallowance, reducing grinding time,removing any heat treatment scale ordecarburized and soft layers of materialfrom teeth flanks, reducing the possibil-ity of the surface tempering or grindingcracks or beth.

MiscellaneousStress Relieving After Tooth Grinding.

A stress relieving operation after tooth

grinding is highly desirable in allcritical ap-plications. This stress relieving minimizesthe possibility of latent grinding cracks. la-tent grinding cracks are the cracks thatdevelop in the storageor early period ofuse. The typical stress .relieving for case-carburized and hardened parts is around32-00 F for four hours, which can be furtherrefined for every application. This stressrelieving must be carried out as soon aspossible after tooth gr:i~ding, as anyex-cessively delayed stress relieving may beteo late.

GrindLng Allowance at Tooth CutHng.As discussed earlier, excessive grindingaJlowallcecauses many problems. Toavoid excessive material left at teeth cut-ting, all cutting personnel should betrained, parts must be checked, and sizesrecorded after teeth cutting. In cases whereQ.c. personnel are not available, thesesteps can be 'taken by shop supervisors.

Use of <II Quench Press. The use of aquench press with proper setup can keepdistortions well in control. Many com-plicated parts can be pre-machined to suitquench press use.

Prequenching and Tempering. Pre-quenching and tempering of rough-tumedgear blanks can be advantageous instabilizing and estimating growth of a gearin final heat treatment.

Checking. All ground parts must bechecked for cracks after grinding. It is alsovery important to do frequent ma.gnaf1uxinspection during the grinding operation,particularly in case of a large batch or biggears, to catch. any problem at an. earlystage.

Handling of GeMS With GrLndingCracks, Any part with sever grindingcracks or surface tempering cannot besalvaged. The suggested approach for partswith minor problems include: stress relief,regrinding to remove cracks, magnafluxinspection for cracks, checking final toothsizes, and reporting all Hndings to. theengineering department for disposition.Gears With. Close Tooth Thickness Toler-ances. Many applications need dose toothtolerances. A practical approach is to keepan approved master in the same environ-ment as gears being ground and comparesizes. For the most part, the first piece of ahatch can be used as a master after com-plete inspection.Acknowledgement: Reprinted courtesy of the Societyof Manufacturing Etrgin2ers, from its Gear Process.ingand Mtlnufactun'rrg Clink. NOI}. 1,3, 1988. lrrdit:ma-polis. IN.

WH.ITE ETCHING .AREA5 ... (continued from page 36)

WEA structureYOIAsa condition for the formation of

WEA under high stress, we must also con-sider the initial structure and the heat treat-ment of the steel which influences thedistribution of the carbides.i!" The moreeven the carbides are spread out, the bet-ter conditionsare for the formation ofWEA. Table 21ists the heat-treatment datafDr the examined gears.

Possible Connection Between WhiteEltching Areas and Rank Damage

Fig. 13a.showsa crack beneath the sur-face of a tooth flank on an unetched slide.Fig. 13b shows the crack at the HNOJ -

etched slide in an area magnification.The fact tna.! the crack is bounded with

WEA, in accordance with the theorydescribed in Reference 10, points to a veryhigh crack propagation. The questionwhether the crack has a connection to thesurface cannot be answered by just a singleplane of a cut; however.we have to assumethat such cracks can lead to pitting. Figs. 141and 15show slides of tooth flanks of a driv-ing pinion with white etching areas near thebeginning of contact and a frontal view ofthe damaged flank.

On both pictures, the lower part of theflank is characterized by strong fatiguescratches and pores due to the high stress ofthe impact shock. Starting in this zone, pit-ting stretches out in the negative slippagearea which caused the failure of the pinion.

TheVIIEA that are shown as a.light elec-tron microscopical picture I:iedirectly onthe surface. (See fig. 16.) In the right halfof the picture the strongly fatigued toothflank around the WEA can be discerned ..

Based on the 'theory in Reference 10about the fonnation of WEA. there is thefollowing connection between WEA. andflank damage in case-hardened gears.

At hard, non-metallic inclusions, highshear stresses that lead to the formation ofIimlted cracks can occur locally ..If the in-clusions lie deeply, the crack does not ex-tend to the surface, but it can favor an out-break of pit.ting by growing together witha crack 'originating at the surface. It cannot,however, be regarded as the cause .of thepitting ..Inclusions below the surface cer-tainly do not primarily have an influenceon flank damage.

Inzones of high stress, fer example at 'thebeginning of contact, WEA occur at thesurface due to strong friction and high flashtemperature. Simultaneously, high shear

stresses lead to the formation of cracksfrom which pores and, later on, pittingmay arise. In this case WEA cannot defi-nitely be seen as the cause of the large pit-tings. Rather, WEA are an indicator for theoccurrence of high shear stress. Thus, as anexample, they allow for the conclusion ofhigh friction values at the beginning ofcontact.

Obviously, the material compositionand the state of the structure are the criteriafor the formation of WEA. A case-hard-ened outer layer with fine carbide distribu-tion, as could be found in the examinedgears, seems to favor the formation ofwhite etching areas.

CondusionIn this essay the phenomenon of white

etching areas on the flanks of highlystressed case-hardened gears has beendescribed. It can. be assumed that WEAarenot the cause of fatigue damage on 'toothflanks. Their occurrences in zones of highshear stresses, however,can providequalitatively valuable indications ,of the(continued on page 45)

fig.14-flank damage on a pinion. WEA at the sur-face In the area of initialpitting (Pc = 1600 N/mm2).

Rg.15 - Flank damage on 'the pinion 'WEA at the SW'-

faa? in the area of initial pitting. (Pc-I560N/mm2l.

Perpendicular cut Flanksul'face

SeJ:),tember/Octoberl989 39

40 Gear Technology

A'GMA GEAR EXP'O '89David Lawrence Convention Center

Pittsburgh, PennsylvaniaNovember 6-8, 19'89

FE

DOCK

Food Service Area

D,3

139 238

i 137 236

20x30

12500N

121 220 W119 218 -1

(f)

<t

20,,20

20x50

101

r-:'=IT"

MAIN ENTRANCE

247-346

20x20

243

239-338 II237 336J

235 334J

122:"" 120x)0

221

20x30

213

20,,50

Booths are lO'.xlO'unless otherwise noted.

3250 00 0en '\tw 321 420 W..J 319 418 ..J(f) (f)

<t <t 20,,20

20x30415

1311--- -

20,,40

20x30

343

EXlt~

339' 438

434I

333 432!

20)(30

4471546

20,,20.547

545

543443

40,,50

I

I 431

401 - sao

ADVERTISERS'INDEXThe advertiserslisted below will have booths at Gear Expo '89 ..

Booth No. 1341-36-38AGMA1500 King Street, H201Alexandria, VA 22314(703) 684-0'211

Booth No. 30'1AMERICAN PFAUTER CORP.925 Estes AvenueElk Grove Village, IL 60007(312) 640'-7500

Booth No. 125CIMA U.s.A.50'1 S. Lake Blvd.Richmond, VA 232-35(80'4) 794-9777

Booth No. 343FAYSCOTT225 Spring StreetDexter, ME 04930(207) 924-7331

Booth No. 507*FUKUYAMA & ASSOC.3340' San Marcos Dr.Brookfield, WI 53005(414) 781-4245

Booth No. 335GMI MUTSCHLERP.O. Box 193Clarendon HiHs, IL 60514(312) 986-0'756

Booth No ..420'GEAR TECHNOLOGYP.O'. Box 14261425 Lunt AvenueElk Grove Village, It60007(312) 437-660'4

Booth No. 236GUEHRING AUTOMATION, INC.P.O. Box 125W227N6193 Sussex RoadSussex, WI 530'89(414) 246-4994

Booth No. 432-34HOffMAN ALTER CORP.22795 Heslip DriveNovi, Ml 480'50(3D) 348-7955•& Seen III Pre-Show Issue.

Booth No. 120ITW ILLINOIS TOOL WORKS360'1 W. T ouhy Ave.lincolnwood, IL 60645(312) 675-2100

Booth No. 319INDUSTRIAL ELECTRIC HEATINGP.O. Box 991Warren, OH 44482(216) 372-8506

Booth No.l39I.R.M. INTERNATIONAL5633 East State StreetRockford, It 61108(815) 397-8515

Booth No. 234JAMES ENGINEERING11707 McBean Dr.EI Monte, CA 91732(818) 442-2898

Booth No. 101KUNGELNBERG AMERICA CORP.P.O. Box 3692615200 Foltz Industrial Pkwy.Strongsville. OH 44::1.36(216) 572-2100

Booth No. 239-338KOEPFER AMERIlCA, INC.555 Tollgate Road, Suite CElgin, IL 60123(312) 931-4121

Booth No. 213M & M PRECISION SYSTEMS300 Progress RoadWest Carrollton, OH 45449(513) 859-8273

Booth No. 311MITSUBISHI HEAVYINDUSTRIES LTD.873 Supreme DriveBensenville, It 60106(312) 860-4220

Booth No. 237"MULTI-ARC SOENTIFICCOATINGS200 Roundhill DriveRockaway, NJ 07866(201) 625-3400

Booth No. 54.3-45-47NORMAe r INC.P.O.80x69Airport Road Ind. ParkArden, NC 20704(704) 684-1002

Booth No. 114-116*OERLlKON-BOHRLE LTD.Birchstrasse 1558050 - Zurich, SwitzerlandPhone 011316 2211

Booth No. 301PFAUTER-MAAG CUTTING TOOLSP.O. Box 29501351 Windsor RoadLoves Park, It 61132(815) 877-0'264

Booth No. 102PROCIEDYNE CORP.221 Somerset StreetNew Brunswick, NJ 08901(201) 249-8347

Booth No. 243RElSHAUER COR~ORATION1525 Holmes RoadElgin, It 60121-7458(3I2) 888-3828

Booth No. 201STARCUTSALES, INC.P.O. Box 37623461 Industrial Park Dr.Farmington Hills. MJ 48332-0376(313) 474-8200

Booth No. 236TRE-STATEMOTOR. TRANSIT 'CO.P.O. Box 113Joplin, MO 64802(800) 641-7582

Booth No. 505VALMET100 Production CourtNew Brjtain, CT 0605](203) 223-6784

Booth No. 143WMW570 BradJey Hill Rd.Blauvelt, NY 10913(914)358-3330

September /Octoberl989 41

ULTRAI_ICA,SE™IHi'gh s,P,e',e"d iinductio,nl gear' hlalr'd!enlinlg'

cutSCOS,ts, IB'n,d eili!miinates cariburiiziinlgl

• EUmilna,tes carburiiz,ing.,• Is easlily integrat.edlint.o your gear

manufacturing eell. .• Eliminates dimensional distortion problems.• Reduces ove,rall imalnufacturingl C'DStS.

• P,rocesses a wide variety of 'g:ears.• UUUzes,pro,ven ihiigh performan;cetech,nology;The new IEH 50' 1KHz sollid state ULTAA~CASESystem offers you surface hardened g.ears atproduction Ilinespeeds. ULTRA-CASIE enables you10 harden g.ears twice as fast as any othercomparable induction system with less equipmentandlat lower cost

_ See us at Booth #31.

ANI AJA.X MAGNETHERMIC G,ROUP COMPANYCIRCLE A-28 ON !READER REPLY CARD

UnHk,ecurrently avaaabte systems, UtTRA~CASErequires no pre-heat cycle which often affects corehardness. U!LTIRA-CASE50' KHz alsceltmtnatesthe use of outmoded RF sets.Let Industriall Electnc Heating put ULTiRA·CASE towork for you. Send us a sample part or let us makea production run. We can svsn handlle some ofyour heat treatinq jobs in our plant For moreinformation, write to:Industriall Electric Heating. 3949 Lyman IDrive,HiUiard, Ohio 430'26; Phone (614) 876-0456, orP.O. 80x991, Warren, Ohio 44482; or call(216) 37.2-8574, telex 982482, fax (216) 372-8644.

-- ----------------------------------------

TECHNICAL CALENDARSEPffl'i,iIBER12-14, 1989'. 'Short Course onGear Noise ..Ohio State University, Colum-bus, OH.. This course will cover generalnoise measurement and analysis, causes ofgear noise, noise reduction techniques,dynamic modeling, gear noise signalanalysis, and modal anaJysis. of gear boxes ..Fer more lnformation contact: OSu.Engineering Short Courses, 2070 NeilAvenue, Columbus, OH4321O-U75. Ph:(614) 292-8143. Fax: (614) 292-3163.

SEPTEMBER U~20,. 1989. EuropeanMadtine Tool Show, Hannover, West Ger-many ..Exhibil:s from. 36 countries w:iII showcutting and fanning equipment, machinetools, CAD/CAM, robotics, etc. For morewonnation, contact: Hannover Fairs,USA, Inc., 103 Carnegie Center, Princeton,NJ, 08S40. (609) 987:':1202.

OCTOBER 3-5,1989. st\I1E Gear Process-ing aad Manu£a~g Cllnic, HyattRegency, Dearbom, M1.- Three-dayclinic

,!::";~I..;"~ b ~r.l.;"~ .J':L • L__.l__on lJ.Jj"""""IO, ro ..........'& ~wnng, 1l<U"'t:U-

ing, hobbing, and other gear related sub-jects. Tabletop exhibits on Wednesdaynight. For more infonnation, call: DominicJ. Aheamat 5MB Headquarters, (313)271-1500 x 384 .. fax: (313) 271-2861.

NOVf.li.,ffiER6-S" 1989. AGMA Gear Ex-po ~89', David la.wrence ConventionCenter, Pittsburgh,. PA. Exhibition of gearmachine tools, supplies, accessories andgear products, For more infonnallon, con-tad: Wendy Peidl, AGMA, 1500 KingStreet, Suire 200,. Alexandria, VA, 22314.(703) 684-0211.

NOvavmER 7-9,. 1989~AGMA fa!] Tech-nieal Meeting,. Pittsburgh,PA. Seminars ona variety of gearing subjects held in con-junction with Gear Expo '89..

NOVf1dBER 29 - DECEMBER 1. fW'l-damentals of Gear Design. Seminar,University of Wisconsm.;MiIwaukee. Thiscourse will cover basic design considera-tions in the development of a properlyfundioning gear system. It is planned withthe designer, user and beginning geartechnologjstin mind. For more informa-tion, contact: Richard G.Al~, Center forContinuing &.gineering Education, Univer-sityof Wisconsin-Milwaukee, 929 North6th Street, Milwaukee, WI, 53203. Ph:(414) 227-3125.

CIRClJE A-29 ON READER REPLY CAIROSeptem'berjOctober 198943

3,~'weekdelivery of Pfauter- Maag:PDQ special-form hobsl

C.h.eck the chart for hob siz:eswitb guaranteedPfauter-Maag cuttingtoo~ quaIUy ....tailoredtoyour tooth form requiremen.ts .••delivered PDQ~!

We stock machined PDQ hob blanks, ready for finishgrinding., to cover the DP range of 3,to 100.

Workilng from your tooth form reference, we'U CAD-design your cutting toot form the grinding wheel andship your quality tools in just 3 weeks! Allow one extraweek for TiNite coating.·

Telephone us toll-free with your tooth form details,(800-435-4176). Or send us your tooth form byFAX.(815-877-0264).,

This PDQ program covers gear hobs. involute splinehobs, straight-sided serration hobs, and parallel-keyplin hob. Not covered are shanks. tapered bores or

periph ry, or dutch keyways.

CUffi ToolsLimited Partner.shlp

Purchaser of Sarber-Colman Gear Tools Division

135' Windsor Road', P.O. Sox 2950. t..OV8S Par/{. It 6H32-2950 USATelephone 815.877-8900' I. fAX 815-B77-0264

CIRClE A~30 ON REAOER IRlfLV CARD

TypicalDP Range Diameler lenglh Bore. Mal.rial

-

35-100 .750 .500 .315 M423().80 1.125 1.125 .500 M42

't---- ~-16-35 1.875 1.875 .750

I M42

8-20 3.000 3.000 1.250 M3

4-10 4.000 4.000 1.250 1 M3 .-3-6 5.000 5000 1.500 MS

See LIS at Sooth #3011

WHETE. ETCHING AREAS ...{continued from page 39)

size and direction of the stress, and theycan point out possible starting points forflank damage.

In order to come to a quantitative con-clusion about the definite connection be-tween calculated paths of tension and theformation and direction of WEA on thetooth flanks, ,3 further .ana]ysis must ex-amine the influence of residual stress,which, especiallyat the surface, must notbe negleded.

It isa1so unclear whether the tempera-tures that locally occur at the flanks cancause a tempering process, and, thereby,the decay of the WEA structure over alonger time.

Ref~l'ences

1. BORG£SE, S.A., A 5t11dy o/the GrowthMechanism 0/ LmticuIar Carbides inCyclically Stressed 52100 Steel. ResearchLabor.atory, SKF Industries, Inc., 1968.

2. EYRE, T.S. and BAXTER, A. 'The For-mations of While Layers at Rubbing SIH'-faces." Metals and Materials, 1972,,,p.142-146.

3. KENGERER, F. WCAS, G. and uu-JEKVIST, B,. "Development of Roller Ele-ment Steel and Its Matnufacture." HeatTreating Technical R~port 3D, 1975, 2,pages 91·98. Un German)

4. JOACHIM, F.J. .Investigation of Pitting inHeat Treated and Normalized Gears.Dissertation, TU Munch n, 1984. ([nGerman)

5 ..KASER, W. Can tn'buting Factors to Pit-ting on Case-Hardened' Gears. Influenceof Case Depth and .Lubrication on theFlank l.oad Carryil1,g Capacity. Disserta-Ilion, TU Milnchen, 1989. (ln German)

6. MARTIN, J.A., 130RGESE:,B.A. andEBERHARD, A.D. "MicrostructuralAlterations ,of Rollil\g~Bea:ring SteelUnde:rgoing Cyclic Stressing:' Trans.Amer. Soc. Mech,. Eng .. 59, 1966, pp,555-567. ..

'I. MARTIN, I,A., BORCESE, S.A.. andEBERHARD', A.D. Third SummaryRepo.rt on Structural Studies of .BearingSteel Undergoing Cyclic Stressing.Research laboratory, S](f Industries,lnc., 1967.

S. NIEMANN. G. and WINTER, H.Machine Elemenfs, Volume 2, Springer-Verlag, 1983. (In German) .-

9. OSTER, P. The Stress 011 Gear Flanks inElastic-Hydrodynamic Terms. Disserta-tion, TU Miinch n, 1982. Un Gelman)

10. SCHLICHT. H. "Regarding th Forma-lion of White Etching Areas (WEAl inRolling Elements." Heat TreatingTeclmicalRep0r128 (1973) 2. pp, 112-123.(In German)

11. STAHu, G. "Possibilities and Limitationsof Rapid Surface Hardening on Steel,"Heat Treating Technical Ri?por134 (1979)2. PI'. SS-6J. (In German)

12. SWAHN, H., BE.CKER, P.c. andVINGSBO, O. "Martensite Decay Durin~Rolling Contact Fatigue in BaLIBearings."

MIior gut' mll\utlCtuNl'l In thelUto-motive IIKI Mlion Industry rely on the'quality 01 HoHmann IPreliur. F)lerSysttml lor IheIr eonvenlionallnd CBN'grinding appIicIflonJ.The comblllltion of h.igl'l ~ fIHratIon:,,coolant lemperalUlI' stablllD&n MdmJlt cOUtclIon ' urea manulacturtng atprecISIon gem.

MetalIrlrgical Tra,ISQctio'I5 A, Vol. 7A,1976, S. 1099-1110.

13. VOSKAMP, AP., et al., "GradualChanges in Residual Siress and Micro-structure During Contact Faligu in BallBearings." Metals Teclmology, 1980, S.14-21.

Acknowledgement: Reprinted willi permission of fhl.'

A merican Gear Manufacturers Assoaation. The opi·nions. statements and (onc/usiafl I1reserlti1d ,"lhispaper are those of the Authors ,m" ill· no way repre-sellt the positiol1 or opinion of tile AMERICA.NGEAR MANUFACTURERS ASSOCIATION.

THE L'EA'DE'RINI GEAR

'GRINIDINGIF:ILTRATION

Hottmann PrftuRe Fit.. otItr ft\II\yldY.n ..... uchlS:.' Incrutedlcooflnt IOd ~ IHI• Improved producI quality.lIgnlflcanl reckJctIon '" opemtng COlli

SEE US AT &,BOOTH #432-484 W

I IOFFMA'N\J FILTER CORPOR_ATIION22847 IHESLIP DRIV,E •P,HOINE ,(313) 348-7855

NOVII, M.IICHliQAN 48050• FAX (3,13) 348-7901

CIRCLE A~31 ,ON REAIDER R1PLV CARD'

September/October 1989 45

-- - I .

iI

WE'VE GROWN.GEAR' T'OOTH

'GRINDINGI SERVICES'EXPANDED CAPACITY AND SERVICE,• Pro-Gear has acquired the'

faciJi,Ues and equipment ofAllegheny Gear. ..

• Gear Tooth Gr1inding Capacity to27.5 inch pitch diam-eters. .

• Inspection capacity to 45 inches.• AUservioes to,AGMA standards.

IPRO-GEAlR COMPANY, INC.23IDick Road

Depew, NY 14043Phone ,(7116)684-3811

Fax (716) 684-7717

CIRCtE A-32 ON! READER REPLYCARD

GEAR ESTIMATINGPROCESS PIANNINGOPERAnON SHEEtSFree Information, on the

World~Best SelJi~gSystem

GEA:R TESTliNGI ,AND'DESIGN FACILITIES

MANUfACTURERS TECHNOLOGIES,INC.59 INlERSTATE DRIVE

WEST SPRINGREtD, MA 010091(413) 73:H972

FAX (413) 739-9250

• GEAR :DESIGN (NOI'SE - STRENGTHI) I• ROTATIING GEAR (TORQUE - SPEED

CONTAOL) TEST MACHINES.• SINGL'E TOOTHi B'ENDING FATIGUE

TESTING.'. STATISTICAL PLANNING - ANALYSIS.• WROUGHT STEelS. SINTE.AED

METALS, NON·METALLIC MATLS .• CAD' IFACIUTIES FOR LOW COST

SET-UP.• CUSTOM TEST MACHINE DESIGN• EXP,ERIENCED PERSONNEL.11-------------1

'II PACKER' EN(UNEERiING3121355·5722, ext, 214

BOX 353, NAPERVIL.LE, IL 60566~------------------~ICIRCLE A-33 ON READER ,REPLYCARD CIRCLE A-34 ON! READER REPLYCA'RO

- - - - - -- --------------- ---

SHOP'SUP,ERI'NTENDENTAIRCRAFT 'GEAR IFAOILITYAn aggressive aircraft arid preCisionparts-manufacturer (Gearboxes, GearShafts, :Housings): is seeking an: ex-perienced shop superintendenl withthe ability to supervise a 200 parsonshop. The candidate, must l1av8 handson machining experience and know-ledge of pr,ecisiol'l parts, tools, fixtures,processing and manufacturing. In re-turn we offer an attactivs salary, ex-cellent benefits and a future-directedenvironment. Pl'ease submit. yourresume wi,th salary history to:

ACR; INDU5TR,IES, INC.15375 Twenty Three Mile Rd.Mt. Clemens, MI 48044-9680eQUAL OPPORTUNITY EMPLOYER

Rates: Classified Displa.y-per inch(minimum 3l,1!X-$1130, 3X-$120, 6X-$110.T~pe willi be set to adveniser's layout or Gesrr:echnofogy will set type at no extra charge'.Wordl Coun.: 35 characters per line, 7 linesper lncn,

46, Gear Technology

PROCESS ENGINEERSG!EAFUNG,

A world leader in Quality Gears andTransmissions has immediate open-ings in :itsEngineering Department atIts Newton, N.C.! manufacturinglocation.

Applicants should have C N C andgearing experience and M.E. iDegr,ee.

These entry level positions offeroompelitive salaries and a solid benefitpackage.

Send resume and salary require-mentto:

R..G. Patrick - Personnel DirectorGetrag Gears of North America

1848 Getrag; ParkwayNewton, North Carolina 28658

EEO - MfF/HN

Chief Engineers/ManufacturingProcessing IEngineers

$45,QOO.$65,000,Gear Processlng/Design/Quoles,

Ann Hunsucker, Excel Auoclate.P.O. Box. 520, Cordiova, IN 38018

(901)757,,19600 or Fax: (901) 754-.2896

Payment: Full payment must accompanyclassified ads. Mail copy to Gearr:ec/tnology, P:O. Box 1426, Elk Grove,Village, III. 60009. Agency Commission: Noagency commission on classifieds.

!Manager IM'echanical EngineerlngiOur company. a leading manufacturer-of machine tooland related products. currently has an open[ngfor aMgr.lMechanlc:aJ EngIneering" The ideal candidate willhave the following baokground and ,qualifications: 8-10

• yrs. of mechanicaJ engineering experience In gear pro-. duction eQuipment and gear cutters, 3-5 yrs.ln a super-

'II vIsory capacity'. strong ~ersnip Q.ua1i1ies and a ~E.

IStarting salary In 5DK range. plus bonus plan partlclpa-II.'on. Sen.cI resufIle.to: Box HM', cIa of Gear Technology.P.O. Box 1426, IElkGrove Vmage, IL 6OOIJ:7

1Mterlal Deadline: Ads must be Ireceived bythe .251h of the month!, two months, Iprlor topubllCSltion.Acceptance: Publisherreserves the' right to accept or rejectclassified adveJ1isemelltsat his dJscretion.

370' ,COMMERCE DR1FT.'W.ASH1NGTON IPA.19D34 U:S.A •.

1,~BOo.S23.251G. F.AX: 1.8D0.635-6273

CIRCLJE A-3S ON IREADER REPL¥ CARD

SOPHISTICAliED &EAR IHARDENING,

FUlLL.SElMGE IHEAl TREAmIS :SPEElAUZIlIG IN• lnduclllll andI, me' Hardentng

- lntema] & External Naito Ge ,Hardening- CoU Lnduclion Hardeni_ng- Gear, S/1.aft &, ,Roll Flame HarrJerung

• Aerospace Spec Car1lunzmg & HardenilllJ- Gleason ,Press QuenChing- Large 48x72l1ll6 ln egJaI Quench Furnaces- HOI Oil DJenchmg- De!p' 126 in, Pit Furnace

• SuI!Zero Trea!ment • AUDnum• Military.Specmcations • SlarIEss.' Me . rgM;aJ CoI1suIting

- - The Cincinnati Steel Treatirlll Co.

1

_, IIILPI 5701 Marle~nt Avenue., II Cincinna " QIio 45227The Symbol 01 (513) 271·3173

llJafay" SerVIce Fax (513) 271·3510

CIROLE A-36 ON READER REPlV CARD

september/October 1989 47

red Tet' ~ eet Your TlotalIe Plrocessing

n'ts~

Only Abar Ipsen offers you thewidest Irange of heat treatingand surface' treatmentequipment for gear and geartool manufaclur:ing.Rugged, FlexibleAtmosphere Carburlzl:ng •••The 110 line is ,automated forJIT manufactunngand isA38dily adaptable-to nit.emperand other carbul'izlng andnitriding processes.IEnhanced Wear I FatlgueIAeslsta'nce for PrecisionAerospace Gearlngl •••!Plasma carburizing andnitriding systems provideuniform case depths forIprooisionsur1ace hardening.

MaXilmumTool SteelHardening •.• You can selectfrom any of three "IHighPressure Quench"''' vacuumfurnaces for high hardness,distortion control, and qualityprocessing of even the mostgeometnically complex gearcuttingl tools.Increased C'lfuilng ToollUfe, ,. TiNI Sputter IonPlating System gives you:superior hardness, increasedlubricity and the ability to cutharder materials ..Call us today and tell us aboutyour application requirements.Chances are we've gal thethermal' processing systemthat's right for you.

lRibar 113 ;E!n IIndustries

905 Pennsylvania Blvd.Feasterville, PA 19047(215)-355-4900Telex: 4761058Fax: 216-357-4134

P.O. Box 6266Rockford. n, 611'25(8,15)-332-4941Telex: '6871503Fax: 81&;332-4995

CU~CLE A-37 ON REA'DER REPLYCARD48 'Gear Technology

Just For FunGear Nomendature

Gear - Equipment used for recreational acti-vity (e.g., fishing gear or hunting gear)

Pinion - What everyone has. (Some are notworth much.)

Rack - fa arrange billiard balls befor a game.

Worm - Used with fishing. gear.

leelJl1 - Hard bones in jaw. (Or in glass nexHobed.l

Pitch - To throw.

Pressure Angle - To fish in a toum m nt,

Base CirCle - Croup of unsavory friends.

Pitch lLine- Space between home plate andpitchers mound.

Base Pi1.ch - A throw to first.

NOl111al Plane - One with wings.

Hand - An appendage with four fingers andathumb. (Some are a (;II thurnbs.I

Lead - Element number 82 on the PeriodicTable.

MOllnting Distance - Space between rearend and saddle.

B.acklash - Q.C:s reaction to an engineeringprint change.

Tip, - Sage advice from a gear expert.

Tip, Relief - When gear expert finally stopsgiving advice.

Hllet - Boneless strip of meat.

Tolerance - Numberof cups ofcoffee that anengi neer can dri nk wilhout relief.

IRunoul - When there isn't any more.

Mating Gears - Where other gears comefrom.

Tight Mesh - What mating gears need.

Addendum - When you take 2 ....2 and get 4,you have add -ndum up.

ShaH - What we all get now and th· n.

Hearing Surface - Thai part not cov red by abikini.

Key Way - The best rout 10 the coffeemachine.

Scrap - An argument with the foreman beforeparts are sorted.

Sort - What overtime is used for.

Engineering - (Railroad I rm) Train gettingclose, watch il!

Q.C - Something we do before gears areshipped away.

'Gear Blan'k - The look on a person's facewhen gears ,ar m -nlioned.Courtesy of CIMA USA

ASTE •.IFOR

EA·SY TO INSTAL!L- Because of Its small size and weight, the FORMASTER does not reoqutre major machine modiHcaUons and 'can be Installed on nearly any glrinder. In,sta:illationcanusualily be accomplished in tess thana. day. -EASY TO OIPERATIE - Two, axls design simpllUles programming and operation. You cancnoose betweentour popular controls thatfeature menu and G·eode programmingl, graph,icsimulation" automatic corner roundl,ng,automatic diamond tbtckness compensanon, andmore

ACCURATE - Te wi,thin ± .'0001 If of programmed dlmensiion, with repeat accuracy to within.00006", Extr,a precisi,on roller Ibeariingl ways, pre-loaded roller screws and optical tlnearencoders, as well'llas supenor desig:n and!construcncn, give the !FOR'MASTE:Rthe ablliity to,holdInspection '9la.geaccuracy.P'R,OD'UCTIVE - No templates or special diamond rolls are needed, so lsad times, and tool-ingllnventorles are reduced, Most fOlrms, can be programmed and dressed In, ready to grind In30 to 45 minutes. Refreshing tne form Ibetween grindiingl passes iisaccompllshed mseccnds.VE.RS.ATIILE - Can be usedl withl single polnt diamonds or wiitih ,oiPUona'llrotairy ,diamondwheel attachment, Nearly ,any form can be dressed QuicKly.,'easily and! accurately.DURABLIE - Hard seals are closely fitted andl are air purgled to totailly 'exclude contemina-Uon. sealed servo motors, automatic lubrlicatlon and total!ly enclosed encoders mlnlmlze downttrne and 'ensure lon'9 service life.

MADiE liN U.S.A.

Patent No. 4,559,919

Ip .0. Bo.x 691

Arden, IN,'C:28704(704) 684~1002

Booth, #545

IMPROVIES .ACCUIRACY

REIDUCES WHEELDRESSIINIG TIIM'E

IP.,0,•Box 2,07Nonhiviille, 1M II48,1167

'(313) 349'·2644,

CIRCUE A-AO ONREADERREPLV CARD

'S,HAVE IOFF TlHAT EXP,EN'S,EI FRO'M YOUR PRODUCTION cosr

TH A MITS,UBISH .,Mitsubishi's CNC gear shaving machine assures you high productivity withsetup time reduced to 1/8 of the conventional type shavers. Positioning of work-piece and cutter, diagonal angle setting are all controlled automatically fromthe CNC.Cutting conditions are stored in memory for ease of operation. Sturdy construc-tion and thermally balanced structure maintains high accuracy,For more details please contact our sales engineer at our Bensenville office,

DIASH!AVE

IFA30CNC ---eSee us at Booth #311.

J.. !!!T.'DIu'S'R'!.H!.5-1.Marunouch, 2-ch~ Chl)'Oda-ku, JoIo.".:>. Japan

Cable Add' .... HISHIJU TOKYO

Mia.ubl.hl Hu"y Ilnd:ustrl •• Am.r:le., Inc..873 Supreme On"", B""" .....,.~ .. Il 60160 Phone (312) 860-4220

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