T H N LOG YTHE JOURNAL OF GEAR MANUFACTURING
JANUARY I FEBRUARY 1994
GEAR FINISHINGGRIND SMALL CONE ANGLE BEVEL GEARS ON CYLINDRICAL MACHINES
HELICAL GEAR BEARING CONTACT ANDREDUCED VIBRATION THROUGH CNC GRINDING
WHATS NEW IN CNC GEAR SHAPING?
THE HOBBING PROCESS AND MULTI-THREAD HDBS
It's a Pfauter ...in stock. and availabletoday with these outstandingfeatures ....aU standard!
!tGE FANUC Series 15 CNC, withuniversal-menu programming tofully automate setup
Ii!FANUC Digital AC servo drivesenall 5 axes, as well as FANUCmicroprocessor-controlled hobspindle drive system
[!(Worktable with two-start doubleworm and worm gear dr.ive
rtHob head with tangential slide,including hydro-mechanicalclamping/unclamping ofhob head swivel
lit'Quick-change hob arbordamping, including hydro-mechanical clamping attachmentfor outboard bearing support
[j{Small footprint design, includingattached-tank hydraulic andrecirculating lube system
!!f.ouilt and snpported by AmericanPfauter, conveniently located inRockford, Illinois U.S.A.
-. I
,.r
. ;1
....And much more!For the gear hobber you've always wanted,call (815) 282-3000
~."miliun IPIIlUIIRLimited Partnership
1351 Windsor RoadLoves Park, IL 61132·2698 U.s.A.
Phone: 815·282-3000Telelax: 815·282-3075
CIRCLE A-1 on READER REPl V CA.RD
Cutting ToolsIntroduces ...Oou-Gesti" HobsIn response to industry's demandsfor higher production and accu-racies, and as a result of (hesuccessful introduction of ourWafer concept for throw-awaytools. PMCf hal)developed theOpti-Gash'" hob.This hob. designed for a specificproduction application. optimizesthe hob design for maximumbenefits in pWductivity andgenerated gear geometry.Until now. most hobs have beendesigned with the minimumnumber of gashes to produce arequired gear tooth geometry cou-pled with the maximum numberof available resharpenings,Today's high costs of operationdemand higher production rates
of greater accuracyfewer. more expensive machines.The Opti-Gash hob has beendeveloped to meet these demand-ing and conflicting requirements.Our engineers designed this hobaround a specific chip load ..U1dcreated a tool having an optimumnumber of gashes at a diameterand length to suit the machinecapability and part requirement.The result is a hob which willproduce a high degree of formaccuracy - and a machine cuttingload generating low-spindletorques - producing as a conse-quence the highest possible leadand index accuracy.The low chip-load, high-quality1001 steel and coatings. along with
efficient cutting geometry resultin higher cutting rates and manymore pieces per sharpening thanwith conventional solid orsegmental hobs,The resulting reduction in machinechange-over time. rcshurpeningand recoatinu costs more thancompensares for the reducednumber of available sharpcnings.Accuracy'! lllt~ Opti-G<l'ih isavailable in all accuracy classes-better than AA DIN m'AGMAstandards if required, For a spe-ci fie proposal Oil an Opti-Gashhob for your appl ication, sendfull part and machine data to yourlocal representative or contactthe PMCf sales engineer foryour area.
Pfaut aagCutting•Limited Partnership
1351 Windsor Road. P.O. Box 2950. Loves Park. IL 61132·2950 USATelephone 815-877-8900 • FAX 815-877-0264
CIRCLE 11-2on REAlDER REPLY CARD
Gear dow' I YOUi .control costsAH,ord'able ,analysis
The new PC-based QC 1000 gear inspection system performs fast,repeatable and highly accurate Index, lead and profile tests on internaland external spur and helical gears and splines. And it does all this soeconomically that even a small shop now can replace several manual gearcheckers with a powerful,easy-to-use CNC gear inspection system.
,Fut 4-axis, valu'eUnlike some competitors' 3-axis systems, the
QC 1000offers real value with fu1l4-axis CNCcapability that handles work pieces up to 15" longand 9'1 in diameter.
I.ealrn more nowPhone 513/859-8273 or Fax 513/859-4452.
And find out how easily you can reduce your gearmanufacturingcosts.=- M&M PRECISION
... SYSTEMS c.;,;o~ationAN ACME-CLEVELAND COMPANYCIRCLEA-3 on IREADER REPLY CAR'O
process
COlier photo coune ;i of TheGleason Works. Rochester, NY.
CONTENTS1.\:\ll.·\RY/FEBRll,\ R\', 1 !)'J-I
FEATURES.Innovative CNC Gear ShaipingJohn Lange
American Pfauter Limited Partnership, Loves Park, Il., , 16
IGenelra1.iio,n lofHell_ilc,all GleiUS with NeW' Surfaces Topol'o,gy by'APlplilcatioln of eNe, IM,8'chiines .F. L. Litvin. N. X. Chen & C. L. Hsiao
The River ity of Illinois at Chicago
R. F .. Han dschuh
NASA Lewi Research Center ..Cleveland. OH 30
Grind,ing Be,vel Gears on Cylindrica'l Gear' Gr,indingliMachinesWenH'r Kiess
Hofler Maschinenbau GmbH, Ettlingen, Germany 34
SPE'CIAL FEATURES- --------
Gealr IFundamenta'ls, - 'The Gea!I' H!obbing ProcessDennis Gimp e rt
Koepfer America Limited Partnership, South Elgin, ]L.. 38
DEPARTMENTSPulbllisher~s p.ageRandom Thoughts for the New Year. 1'
.Advertiser Inde'x.find the products and services you need 9
CalendalrEvent of intcrest., ", ,. ,.., 10
iManagement Matters -'Cu.tting Down On Labor CostsWoodruff Imberman
Imberman & Deforest, Inc., Evanston, Il., ..111
Pe:ople on the iMove- _Promotions, moves to new companies, new company locations J5
Shop Floor -'Cutting Worm Gears w:ith Stalndard IGear HobsWilliam L. Lanninck , , , 451
Cilassiifieds,Products, services, and information you can \I e , ,. ,,. ,. 48
1I111'IlI1'r .\: SIIUIII
FLU COWBOl' ARTIFACTS
bridles -/{ buckles *" horsehair
bits ... books *' belts * bolos
chaps .. spurs '* saddles
,wPlWSAVS
9929 Venice Blvd.Lo~:Angeles, CA 90034
(31m 2~2'901O BJ APPOImrRNTPAX <aIm 2G::HlJIOwestern collectables '*
CIRCLE A.5011 READER REPLY CARD
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4· GEAR TECHNOLOGY
GEAR TECHNOLOGYEDITOR!.\I,
Publisher & Editor-in-ChiefMichael Goldste,jn
Associate Publisher & Managing EditorPeg Short
Senior Editor Nancy Bartels
Copy Editor Don Story
Technical EditorRobert Errtchelln
William L. lannlnckDon McVittie
Robert E. Smith
ART
Art Director hal'! ykes
Art Director Jenntter Goland
;\IARKETI:\,C ,
Advertising Sales Manager Pateicia Flam
Advertising Sales CoordinatorJean brie Mangan
CIRCULATION
Administrative CoordinatorDeborah Donigiao
Circulation AssistantMary Gabrys
RANDALL PUBUSIIiNG STAFF
President Michael 'Crtlldstein.
Vice President Richard 'Goldstein
Vice President/General Manager Peg Shott
Controller Patrick Nash
Accounting Laura Ktnaane
AIl· 00 ullant MIlI..rsha Goldstein
RANDALL PUBLISIIING, INC.1425 I..unt Avenue
P.O. Box 1426Elk Grove Village, .IL 60007
(708) 437-6604 Phone(708) 437-6618 Fax
VOL. 11,xo. 1GEAR TECH OLOG,\r, TI!fr Jgu.r8.-!!!1 of Gear ManuracLurlnlflSSN 07U-6'1i..5B-J is p~~li§.hl:'d bimllnl1LJy by RlIlif3U Publ;i!dllng.tne., I,'US Lum Ayenue, P.O. BOll ]42-6. Elk Oro ...e Village. lLfiOOU7. SubscriplloR nne" are: $40.00 in the U.S.: S.50~OOinCanildia~ S5S.no ill ult oltu:r ccuutries, Secund-CI.:lss PQ!it.!!-l~ piluJat Arli~glOn Heights, H", and et additiunal mailing office.
Rundall Publlshlng ll1.!Lkell every effort to ensure thai the prcceoesdescribed it! G~ar T~cJm(j/pgy oomorm 10 sound engmeering practice.'The Publi~berc.iilInoI:be held res:poo.s:ibleorluble fw.ujurio ~u..ll!li'lJlCdm'.aD,! d:iTrd or !.ttdiRn •.speciltc(Jn~ur:.ntiaJ. OI"C'liJl«dama,gesm any kind01" nature """hal~vef rf'Sulljng from foUO'il"'iD;!!'the procedtrre5 described.
Randall Publ~lihing j.<,; nOI responsible fur the eentem of. elarmsmade. or npinicns expressed in udvertlsernents or other primed rnarrerIn the pub~ icanun.
POSUtla.NlCT.Send :cukl:n:uchlioges rc GEAR TECHNOLOGY. TheJ'oumal of Gear Manur"lC'~urin•• 1425 LUllt A...enue; P.O. 8m, 1426.Elk Greve Village. J1.., 60007
CCom~lIIlSI:vpyrighl,ed by RANDALL PUB LlSHI NG, ENe .• 10'94.~rticlcs "PpcI!lIU1.J!, in GEAR TECHNOLOGY 1""41)' net be: reprodueedm whole or in PRrI wlthou! the express permlsslon of (he publlsher orthe author.
WI! en Gear Quailit,y lis
ACTIONspea'ks lou:der'thanl w,ords.:
Check our Line of: Action*
Meeting A or AA quaHty requirements is easiersaid than done. That's why each FHUSA hob isguaranteed - every tooth is in proper positionto generate the desired gear profile.
When gear qualiity is crit,ically important,Line of Actiion can assure success.
Insist on FHUSA hobs that are inspected andverified to meet your requirements ..ALLFHUSA hobs are ... and can.
Once you've checked our Line of Actionyou've taken the first step ... and best steptowards a better bottom line ... too!
IGM··.·I in~e~~~~;~;:,OH 44131I Phone (216) 642-0230
I. FAX (216) 642·0231'
CIRCLIE A.-6 on R:EA'DER REPLY CARD
iReduee 'generative geargrindingl wheel dressingl t.ime wiit.h Normae'sCNC Threadedl Wheel 'True'ing System:
This new system is based on replacing the existing diamond disc witha vitrified CBN wheel.The system includes the Normae Wheel Profi ling Center, software for calculating the :requiredform, and a special dresser unit to replace the existing dresser on the grinding machine, Theform is profiled on the CBN wheel on Ihe Profll ing Center, and is then mounted on the dressingun,it on the machine. Theentire form is dressed into the grinding wheel in one opera lion,including both flanks, fool radius, and modifications, Because the software accuratelygenerales the properform, the need for trial and error lest grinding is elimiaared, dramaticallyreducing setup lime.
CIRCLE .A-14 011 RE.ADER REPLY CARD
Call (313) 349-2644 todayfor more information or toarrange a demonstration.
INCORPORATED
PfRmRmnnCL fHP(RIiSL ~unlll~WHEN YOUI NEED INTRICATE DESIGNS AND' M:ETICUILOUIS CRAfTSMANSHIP" RELY ON FAIRLA_NE IGEA:R"II'NC.
NEW MACHINES JUST PURCHASED... KAPP CNC HARD FINISHER.. AMERICAN PFAUITER CNC HOB
WE OFFER:-Gear Noise Reduction Program- Expert Technical Assistance-Gear Cutting in a Wide Range
of Sizes, Types & Quantities• Prototype & Eme.rgencyRe-
pair / Rebuild Service
Quality gears up to AGMA 15, Mil-1-45208A, M I1.-81D-45662
SIZE R_ANGE -Smaller than aninch to 48"
TYPES:Spur - Internal & ExternalHelical- Internal & ExternallWorms, Warm GearsSerrations - ShaftsSplines - Internal & ExtermalSprockets - ClustersSegments' SpindlesRatchets - Gear Boxes
'COMMITTMENT10 OIJAUTVR'eishauer Ground GearsM& M Precision Gear CheckerKapp CBNHard Finished GearsAmerican Pfauter CNG HobCoordinate Measurement
Machine
Fully implemented SPC,and datacommunications cepabilities,
For the ultimate in quality gear.s, I
call or send inquiries to: I
~~=- =-______ I
Fai.rla-ne Gea.r,II.nc. I
16 GEAR TECHN,OLOGY
CIRCLE A·10 M RE.A'DER REPLY CARll
p, O. Box 409 APlymouth, M'I 48170
I Phone (31131459-2440II (8001837·1773
Fax (31;3)459-294 I
1Random Thoughts forthe new Year.
a nother year has passed and. :because of the short. term ups and idowns of the economy, it's still hard!
to judge whether we are in an appre- iciably different place than we were a iyear ago. The economy doesn't seem
to be worse than it was. but italsodoesn't seem to be a whole lot better.
The gear business seems to share
this oddly ambivalent condition.
According to my colleagues, a lot of
gears are being cut in this country andcutting tool sales are at record levels,
but no one is making much money.
Competitive pressures are forcing com-
panies to cut gears at little or no profit.Machine tool manufacturers face a
similar struggle: They too are under
pressure to lower prices, but they are
also faced with the added difficulty oflow overall volume. Add to that 'theclosing of nearly a dozen gear plants
ill 1993. probably orne kind of dubi-
ous record, and it's hard to be opti-
mistic. The fact is. the end of the Cold
War defense boom and the recession
have hit the gear industry hard.Yet business does seem to be get-
ting a bit better, even though the kep-
lies point out that what we may be
seeing here is similar to the blips we
experienced in 1991-1992. when
companies rushed to replace their low
inventories near the end of the year,
and once that was done. the little
boomlet petered out. It's hard to know
which interpretation of the facts is theright one.
Capitalism has always been aDarwinian affair. Only the strongest
and the fittest survive. While not try-
ing to minimize the devastating effect
of lost jobs and the breakup of long-
established organizations, the fact is
that the survivors of this shakeout areemerging stronger and more efficient
and are learning new strategies to sur-
vive in the new business environment.For ORe thing, there is a new
appreciation of the fact that our com-petitors are nat just. the people next
door, but those all over the globe, and
that in order to match them. every ele-
ment of our businesses, from plant
maintenance to product packaging.
has to be rethought.
Among the positive signs of this
rethinking is a growing awareness
that every resource in a business,
including its people. has to be used to
its fullest. In the most progressive
companies, the old "us/them" para-
digm of labor/management relations
is giving way to the understanding
that there is no "them," only a "we"
who have to work together if all are to
survive. As Benjamin Franklinput it
in a far different, but no less serious
context, "We must all hang together
now. or most assuredly we shall all
• . .'
PUBLISHER'S PAGEhang separately."
"We" in the gear industry also
includes our customers, and again,
our most progressive companies are
working hard at understanding the
needs of customers and meeting them
in creative ways. One example of this
is the aggres ive marketing strategy
on the part of some of ou:r major
machine tool builders. Believing that
if you get the price down. the buyer'
will come, these companies are offer-
ing non-option, lower-priced CNC
machines .. Many features that in the
past would have cost extra are now
J ....NUARy/FEBRU ... RV 1994 7
TITIVILLUS* STRIKES OEAR TECHNOLOGY!:An error appeared 'in the article. "The European Rack Shift Coefficient'X' for Americans" (July/August. 1,993).Equation Ion page 3S of thaiarticle should read as Follow :
Ilt = II + Zl2
inv a..'1 • illv a,tan a"
Our thanks to Mr. Ed leRall or the University of Wa.terloo, Waterloo.Ontario, for being more alert than we were. We regret any inconve-nience this error may have caused.
*Tit.ivillus is the patron demon of medieval scribes and modern copy editors. He creates distractlons.breaks our concentration and causes embarrassing CJTQrs.Appa_rently neither medieval scri bes normodem copy editors deserve patron saints.
NOWYOU HAVE A
CHOICE ...and iit's made Inl AMERICA!
AIW Sy3tems Co. announces 1J1aI rtIS na.v a manufactullrtg source d spiralgear roug'hlng and finishing cutters and bodes,
We also can remanulaclure most spiral cutter bodIeSand can manufacture new spiral bodes 111'1 diametersd 5" through 9" at present.
ANI can also supply roughing and finIShing cutters.hardware and repiaCemant piuts lor most 5"- 9"diameter bodes,
\iVhethef ~'s manufactunng or rema.nufaclUf1ng.consider us as an aJterna!h.oe source for replacementpalls and hardware as well as bodes and cutIe!s. 612 Hamsoo • Rata! Oak.. MlChtgan 48067'!bu'. be 11'1 lor a pleasanl surprISe. 1e.!ep/"1ooe (313) 5#3BS2 '.,FAX (313) 589-1690
C,IRCLE A·8 on REA'OER REPLY CARll
8 GEAR TECf!NOLOGY
part of the package, but the price is
still within the range of the smaller
job shop.This marketing strategy addres es
the peculiar paradox that developed
under the old price structure.
Previously, the only cornpanie that
could afford the newest CNC
machines were the volume users,
such as automotive manufacturers,
who u. cd the machine to make thou-
sands and thousands of identical
gears. thus bypassing one of the big
advantages of CNC machines: their
PUBLISHER'S PAGEquick-change flexibility, The compa-
nie thai could make the most of thisfeature couldn't afford them. This
aggressive pricing strategy should
put the machine intothe price range
of the companies - those that cut
small batches of many different gears
- that can use the machines to their
i i greatest advantage. This isa benefit,i not only far the machine manufactur-,I
ers, but for the job shops, who can
now begin to sell themselves in niche
markets and to eustomers who before
were simply out of their reach.
o change comes without pain,
and where the economy is going to be
in a year, given tile volatile global
economic environment, i .anybody's
guess. The one thing I do know is that
we cannot stop our struggle to change
and adapt to the newenvircnrnent. As
one pundit put it "Bu. ines is like
riding a bicycle; you have to keep
moving or you fall down."
Michael Goldstein,
Editor-in-Caief
GEARMACHINES
SALE.S&. SERVICE
Many Models andS.izesto .choose trom:II' G.ear Shapersttl' Gear' Hobbersttl' G.ear Shavers,II'Gear HonersV Gear Gr;indersV Hob SharpenersII' Inspection Equipment
CIRCLE A-9 on READER REPL V CARD
ADVERTISER INDEXPage NUILber
848[PC
947131548654
2,mC47BC466l3
Reader Service No.s
20]
9181315211065
3,191741614
122
24237
22II
AIW Systems
American Metal Treating Co.American Pfauter L. P.Basic Incorporated GroupBourn & Koch Machine Tool Co.Dessau Diamond ToolDiamond BlackEltech, Inc.Fairlane Gear, Inc.GMI-FhusaHigh NoonM & M Precision SystemsMTM KonigNational. Broach and Machine Co.Niagara Gear Corp.Normae, Inc.Parker Industries, Inc.Pfauter-Maag Cutting Tools L. P.Profile Engineering, Inc.Pro-Gear Co.Starcut Sales, locoStrathmore Machine Tool Co.Y'ieh Chen Co., Ltd.
48484
4812
JANUARY/FEBRUARY 1994 9
-
CALENDARJANUARY 10-14TWL Inc. Vibration Analysis,Alignment and Balancing Workshop,Uptime/Hane Industrial TrainingFacility, Milwaukee, WI. Workshopfor mechanic . maintenance per onneland operators, Covers diagnosi , mea-surement" and other vibration, align-ment and balancing basic. For moreinformation, contact Uptime, h1C"
(812) 234-00Ql7or fax (812) 232-3978.
JANUARY 23-.2'6American Society of MechanicalEngineer. ] 7th Annual EnergySources Technology Conference &Exhibition. Clarion Hotel, NewOrleans, LA, Papers and presentationson drilling and emerging energy tech-nologies, energy and environmentalmanagement, fossil fuel combustionhydrocarbon proce ing, internal com-bustion engines" materials and design,and more. For more information callASME Petroleum Divi ion, (214}746-490 1 or fax (214) 746-4902.
FlEBRUARY 21-24Center for Industrial Heat TreatingProcesses, University of incinnati,Heat Treating Work 1101'S, ClarionInternational at 0' Hare, hicago,.February 21-22 •.AppUed InductionHeat. Treating Workshop. coveringfundamental including electromagnet-ic induction, equipmentand powersupplies, metallurgy, coil design.quenching, quality control and trou-bleshooting, and Quenching Proc-esses, Part Distartkm and ResidualStress Analysis in Heat Treating,
10 GEAR TfCHNO!.OGY
covering importance 'Of distorion andstresse .control of distorion and stressin quenching, gas carburizing and car-boni-triding, straightening di tortedpari. and controlling di tortion,February 23-24, Applied CaC.arburizing In HeatTreatment,covering fundamentals of gas carbur-izing process, furnaces and atmos-phere control, instrumentation. pre-and post-heat treatimg, quality contrailand part distortion, and App.licdMetallurgy for Heat TreatingIndustries, which covers materialselection, characterization, measure-ment of mechanical properties, solidi-fication, corros ion and more. For moreinformation, contact. Dr. A. H. Soni(513) 556-27 ~0 or fax (5 I3) 556-3390.
l\IlARCH .3-SA'GMA 1994 Annual Meeting,Marriott Marco Island Re on, MarcoIsland, FL The theme of the meel.illgwill be "Perspective On World CiaManufacturing. " Jerry Plaherty,Group President of Caterpillar, will bethe keynote speaker, Note: This meet-ing is two months earlier than previ-ous meetings .. For more information,contact AGMA at (703) 684-0211 orfax (703) 684-0242.
MAY 9-10Penn State University National Centerfor Advanced Gear ManufacturingTechnologies Advanced 'Gear Man-ufacturing Sympo iurn, Penn StateUniversity, State College, PA.Speakers from government. academiaand industry discussing current gearmanufacturing technology andresearch. For more information con-tact Greg Johnson at (814) 865-8207.
CALL FOR PAPERSThe Gear Research In tinne is plan-ning an international conference onInduction Hardened Gear andPrecision Components W be held inIndianapolis, IN, on May 15-17, ]995,The conference will cover materials
processing, quality assurance andengineering performance of inductionhardened gears and precision compo-nears. The Institute is looking forpapers on the following topics: distor-tion control, case depth (optimizauonand control), cast factors, quenchingand quench ant • materials selection,pretreatment (microstructnre control),principles of coil design. bendingfatigue, coring, contact fatigue, influ-ence of carbon and alloy content,machinability, re idual stress, envi-ronmental impact and extreme appli-cations. For more information contactSharon Schaefers at OR!, (708) 241-0660, or fax. (708) 241-0662.
GlEARSCHOOLSANDWORKSHOP
.GMA bas announced the dates forit 1994 Training School for GearManufacturing sessions. The dates arejan. 10-14. Mar. 7-11, May 16-20,.
ept, U-16 and Nov. IlM8. All ses-sions will be held at Daley College inChicago. [L The 1994 curriculum isde igned to teach novice operators -those with Ies than one year's experi-ence - how to maximize the outputfrom the machines they operate. These sions are al 0 useful for sales engi-neer training. new employee orienta-tion and refresher courses for veteranoperator. Contact AGMA at (703)684-021. l for a registration packer Of
mare information.
The Falk Corporation, Milwaukee,WI. offers a series of four-day work-hops dedicated to the theory , opera-
tion and maintenance of speed reduc-er and flexible shaft couplings. Itcover installation, alignment, mainte-nance and failure analysis procedure .Contact Ron Nimmers at The FalkCorporation, (800) 852-3255, or byfax at (414) 937-4359 for the L994workshop schedule.
Cutting Down OnLabor Costs
"Psv-tor-Pertotmence" can cut costs and incresse productivity.Is it right for you?
hat can be done
I 'bO.ut the risingco t of labor? Mr.
-- - Robert Reich,U.S. Secretary of Labor,has already indicated theadministration's intentionof pushing the minimumwage from $4.25 to $4.50per hour and indexing it forinflation. That means thatevery jiggle in the inflationchart will push the mini-mum wage higher.
But of course, boostingthe minimum wage doesnot merely raise the wagerate at the bottom. In orderto maintain skill differen-tials, every wage levelabove the minimum wouldhave to move up also. Thisis what employees winexpect, and presumably theonly ways to avoid that out-come are to freeze wagelevels or raise productivity.The Germans have recentlychosen the first alternative;i.e., freezi ng wage ratesand benefit. Some Amer-ican companies, uch asFrigidaire, have chosen thesecond alternative - rais-ing productivity by instal-
Woodruff Imberman
ling pay-for-performancewage systems. It may be ofinterest to discuss both ofthese alternatives,
Germany's SolutionIn September, 1993,
Germany's metal fabricat-ing and heavy industriesassociation canceHed awage agreement for thefirst time in their history.According to the WallStreet Journal, "the an-nouncement by the Ges-amtmetall employers' asso-ciation caused a stir be-cau e it broke precedent."
Reachedthrough collec-tive bargaining, Gesarnt-metaU's labor agreementscover wages, training pro-grams, vacation days andthe "vacation money" paidto workers to help fundtheir hal idays. The con-tracts cover Germany'sautomotive, metal, electri-cal, electronics and mach-inery industries.
'Germany's generouswages and benefits andflagging productivity havemade German labor coststhe highest in the world -25% higher than in the U.S.
Managing a businesstoday ls hard work ..Let Mana'gement Mat-ters lend al hand, Tellus what manag,ementmatters interest you.W:riteto us:at IP.O. Box.1426.• Ellk IGrove. I'L6000,9, or calli our st.affat f70B) 437'-6604.
----
MANAGEMENT MATTERS
and about a third higherthan in Japan. In westernGermany. manufacturingworkers receive an averageof $26.89 an hom, of whichbenefits account for$12.47. Blue chip compa-nies such as Daimler-BenzAG and Thyssen A'G havebeen shedding tens ofthousands of jobs. idlingcapacity or shifting pro-duction to other countriesas higher costs cripple theirability to compete at homeand abroad. Hans PeterStibl, president of theGerman Chamber ofIndustry and Tracie, saidthat unions must realizethat unrealistic wagedemands will force compa-nies to cut even more jobs.
Dr.WoodruffImbermanis a principal i'l the nUlI!-agemeni consulting firm oflmberman and Deliorest,with offices in Evanston,It. £09 Angetes and Boston.
JANUARY/FeSRUARY 1994 11
SIX S,TAIR GEAR,(JIS '0, DlNI 4, AG_MA 12)
We speclalize to produce precision giears
'. Machine Too] Gears
• Auto & Motorcycle 'Gears
• Agricultural Tractors
• Printing & Textile MachineGear
• Pump Gears
.' Gear Reducers
• We can make strictlyaccording to eu lomer'ssamples or blueprints.
Manufactuffff & .Exporter
YIEHI CHEN 'CO., IT!D.No. 333" Un Sheng Rd., Chang Hue City.,Taiwan, A. O. C.Tel: 886·4-7627747, 7628550 Fax: 886·4·7620213P. O. Box S3B Chang Hua, Taiwan, 'A. O. C.
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It •• It •• II •• It • •
Introducing our newest column:"eople On The Move.
'eginning with this iSlue, we willbe reporting on
• Promotions
° Mova to newcompanies
• Company movesto new locations
Don't milS any of the newmova; 1ft hople On The Move.If you have a move of your ownyou'd like to report, call us at800"45.-8166 or fax us at :
1:2 GEAR TECHNOLOGV
" .. ing any more labor costs ployment front," wason U.S. employers," the Hanke's conclusion.
U.S..Experiencebl the U.S., we have een
a low bot steady ri e inlabor cost "The governmenthas made the cost moree pensive." according toRichard Vedder and LowellGallaway. pr-ofessor of eco-nomics at Ohio University."The only way to raise tilereal, wage rate is throughproductivity growth," bothprofessors maintained at aconference in Washington in.!July.1993.
"In Europe, wages arehigh. on top of which gOY-
emments have impo ed alaundry Iist of cost onemployers. Consequently,unemployment rate inEurope now average about12% and are as ,high as24% in Spain. Surely, wewant to avoid having theU.S. government irnpos-
professors aid.How has (he U.S. gov-
ernment contributed toincreased labor costs?According to Profe sorVedder and Galllaway,"By raising the minimumwage, by uch legislationa the Davis-Bacon Act(which mandates prevail-ing union wages to be paidon federal con trucrionprojects), by the Fair LaborStandards Act,the Nation-al. Labor Relation. Act. andbecause of programs sucha public a sistance andunemployment compensa-tion, which pay people tosit and wait until, they canfind jobs with .1 higher lev-el of compensation."
Japan offers an excep-tion, ays Steve Hanke, pro-
fessor of applied ecenom lesat John Hopkins Univer-sity. who spoke at the sameWashington conference."In Japan, wages are veryflexible, with about two-libirds of com pen arionfixedand a third in theform ofbonu e that can bevaried:' Hanke said. "Suchwage flexibiliey give Japana current. unemploymentrate of 2.5% and longemployee tenure."
Right. now. the UnitedStates occupies an interme-diate position, with wagesmore fixed than in Japan,but with fewer costly regu-
lation than In Europe. Ifadministration officials tryto pre erve high wage ratewhile putting new regula-tions and taxes all business,"we could be in for somebad times 011 the unem-
A Way Out?Japan's wage practices
have suggesteda course formany U.S. busine ses.About 2,200 Americanemployers have in tinneda pay -for-performan cesystem caned "gainshar-ing," which provides basicwage rates, plus bonusesfor the achievement of.lIiglrter levels of productivi-ty and quality.
Speaking recently alanindu trial sympo ium onhow [.0 achieve improve-ment in productivity andquality, David S, Hoyle,executive vice pre ident(operations) of Frigidairepointed out that lastingboosts in productivity andquali!y are not achieved byadding new equipment or
tinkering with the manu-facturing process. Accord-ing to Hoyte,
"In building a teamdedicated to total quality,problem must be viewedas buried treasure, to beunearthed by a workforcemotivated to improve theprocess and the product.Equipment cannot do it.Only workforce correc-tive action can do it, andhere we must recognizethe role of gainsbaring,which is really a pay-for-performance system. Withsuch a system, peoplebecome willing to makeproblems visible and worktoward their eliminationand improvement. Gain-sharing leads the wholeorganization to develop afundamental understand-j ng that the cooperative
ing the sights of an orga-nization and developingits confidence that excep-tionally high standardscan be achieved."
Hoyte concluded: "Thedomestic home applianceindustry is an Americansuccess story that attests tothe use of such pay-for-performance wage sys-tems. Over 84% of themajor appliances sold inAmerica are made :inAmerica. Excellence indesign and producti vityhas contributed greatly tothat success ."
Whether the currentfederal administration willsucceed in raising the min-imum wage rate to $4.50and indexing it for infla-tion remains to be seen.After all. Congress hasproven to be a rather stub-
MANAGEMENT MATTERS
With a pay-for-p,erlormance sys,-tern, Ipeop~lebecome willlingi to,
make problems vi:sible andworktoward their eliminatien and come'to understand that the cooperativeprocess. creates po.s:itiiveresults,
process creates greatresults. Such results arenot a chance occurrence;they flow only from sys-tematic efforts. We haveeen it at Frigidaire, at the
GM- Toyota joint venturein Fremont, CA, and else-where. Gainsharing hasbecome accepted as thepreferred method for rais-
born body and may balk atthis boost in labor cost.
But Congress has noth-ing to do with companiestrying pay-far-performancesystems on their own.Some 2,2'00 companiesnow use some variety ofsuch gainsharing programswith varied uccess.Gainsharing need not. be
Nowavailable fromDESSAU-Type DSA, andSPA DiamondDiscs forReishauer, andFassler DressingSystems.
Leaders inDiamond andCBN toolingsince 1841.
82 Midland AvenueSaddle BrookNew Jersey 07662201-478-7781Fax 201-478-1 175
emel.'E .A-13 on REAOER REPI.Y 'C.ARO
JANUARY/fEBRUARY 1994 13·
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·14 GEAR TECHNOLOGY
limited to productivity and.quality, It can also lead 10
improvements in on-timedeli verses, can speed upwork-in-progress, cutdown on tile accumulationof inventory. lead to sav-ings ill U e of gas/electricenergy, and so on.
Two Omditions forSuccess
Succe ful gainsharingprogram require at leasttwo programs:
.1. A careful study of acompany' wage and qual-
wage rates ill variousindustries. Andthey wincertainly be affected by anyfederal legislation.
The only salvation is towork ardently to boostinternal. productivity andquality .. thereby cutting unitcosts. Prayer alone will notdo it; nor will exhertationucceed for long. What. i .
required i a y tematiceffort to' improve workforcecooperation 0111 new waysof doing things, The payoffcan be great. and lasting,
MANAGEMENT MATTERS
IP'ay-for-pe!rfonnaDice ean Ileadto imp,roved pr,oductivity andquall,ity ,and to iimpr,ove:ments
in on-time' daliveries,werk-ln-preqress, iDivento'ry
Icont,roll, and Ilead to s,avin!g:sin!Utility ,and maiintenance bins.
ity records for the past two provided the ystematicyear. so as 1.0 provide a effort is done carefully withbenchmark to gauge cur- orne guidance .•rent improvements.
2. Careful indoctrinarioa Note: Readers interested in:of the entire workforce - gain sharing should refer tomiddle managers, supervi- the following articles:sors, engineers, technicalemployees and hourlyworkers - 3sl.o what iexpected of them undergainsharing and the re-wards they may anticipate.
here is no hailing therise ill Iabor co t, eventhough a company may benon-anion. Non-unioncompanies are not i elatedfrom the industrial world;they are affected by union
"Gains Through Gains-haring," (Area Develop-ment, May, 1990}. "Boost-ing Plant Performance withGainsharing," (BusinessHorizons, Indiana Univer-sity, NovJDec., 1992), andfinally, "All You EverWanted to Know aboutGainsharing," (TargetMagazine, Association forManufacturing Excellence,May/June, 1993).
PEO'PLE 'ON THE MOVE------ --- -
Sudace eombu tion, IDc~Maumee, DH. Surface Combus-
tion, Inc ..has announced the reas ign-ment of three taff members to con-solidateand facilitate the transmis-sion ofimformati.on between keyfunctional areas in the organization.
Richard l..oU,e is now ProductManager in the Special Heal TreatGroup with responsibility for projectdevelopment, proposal/contract exe-cution and project management.
Richard A. Huber will hold theposition of Rebuild/Retrofit ContractProposal Engineer, responsible forestiraatiug and proposal preparationand contract management.
Nicholas J. Orzechowski i now aProposal Engineer in the Non-FerrousProduct Area, e timation and devel-opment of proposals covering equip-ment and control. ystems forme non-ferrous industry.
Diamond. Black TechnologIesConover •. C. John Chapin has
joined Diamond Black Techrrologies,Inc., as the new National Sales &Marketing Manager. Mr. Chapinbrings many year' experieace inales. marketing and busine to his
new po 1.
Janee Produets, Inc.Mishawaka, IN. Kim Burch has
been named Sales Assistant withresponsibilitie for inside sale andcustomer service . Janco Products,Inc., is a manufacturer of fiberglas
reinforced plastics composites forelectrical, medical, marine and otherapplications.
DO'you have fleWS of employeepromotions, transfers or relocationsyou would like to' share? Send yournews release to Gear Technology"People on tile Move, P. O. Box 1426,Elk Grove Village, IL 60009, orfax itto our offices at (708) 437-6618.Note: Stories must be received by thetentiJ oj the mOllth two months priorto' the issue date to appear in a par-ticular issue. For example, if youw£HH your story to appear in theMarch/April issue, it must be if! ouroffices by January 10. Items reachingliS past our deadline dare will appear,i'l rile 'lex! issue.
If your company or orga_nizalion isplanning an educational or tradeshow event that you think wouldbe of interest to our readers,announce it in our TecbnicalCalendar. Notices need 10 be inour hands by the 10th of themonth Iw,o months prior to theissue date in which you wish yourannouncement to appear. Mailyour announcement to:
Technicall CalendarGear Technology11'.0',Box 1426Elk Grove, Vllllage, IllBOIlOeor #ax us at (70S) 437·6618.
DIAMON D BLA'CKTECHNOLOGIES, INC.
CIFlCI.'EA·15 on REA'DER 'FlEP,lY CARl)
JANUARY/FEBRUARY 19R' 15
Innovative CN CGear Shaping
J'ohn langeAmerican Pfa'uter Umi,ted Partnership,
Loves Park.IL.
oFig. 1 - Working principle of shaping iii spur gear.
Fig. 2 - Working principle ofshapillg iii helical gear.
baper - work table back-ofTsystem.
16GE ....FI TECHNOLOGY
IntroductionThe Shapil~g Process - A ,Quick Review
oj 11'8 Worki.ng Principle. In the shapingprocess, cutter and workpiece repre ent a drivewith parallel axe rotating in me h (generatingmotion) according to the number of teeth illboth cutter and workpiece (Fig, I). while thecutter reciprocates for the metal removalaction (cutting motion).
When shapingbel icalgears, an additionalspiral motion is introduced to the cutter by thehelical guide (Fig. 2). During the return stroke(relief stroke) the cutter is moved away fromthe workpiece to prevent flank contact orback-off monon.
These motion are ba ic functions of thehaping process. Efficient and flexible
processing of small lot size requires addiJ-tional automatically controlled functions andoperations which will be discussed later ..
SIJaping methods .. Any cutting actionwhich a machine tool performs is based on arelative motion between 1001 and work. Withgear hapers thi relative motion i always thecutter stroke motion which i ,depending onthe application and nape of the cutter,complemented by the generating motion andradial. infeed. In principle, three methods ofshaping gears from a combinatien of thesemotions can be considered.
Conventional ,,_. C CMachine Concept"Old Style" 1>'5."Mode,.,..". "Old style" pillioncutter-type gear shaping machine changedvery little from their conception ill the earlyl 900s. They were bridge-type cutter headmachines. with a table relieving system t.O
clear the curter from the workpiece on the
return. nonproductive stroke of the cutterspindle (Figs. 3-5). The "modern shapers,"introduced in 11969, went to a cutter spindlerelieving action instead ofthe table relievingmovement all the older style machines ..Furthermore, the cutter spindle (and its movinghousing) were mounted into a robu t column(Figs. 6-8) ..
Modern machines are at least two timesheavier than old style machines of equaldiameter capacity. They are also two to threetimes more productive than the old stylemachines. This increase in productivity isdirectly attributed to the following:
I .. Rigidity in the machine because ofcutter spindle rehef troking drive train, Thisis a much smaller and constant mass to movethan the larger mass of the table on the oldstyle machine. That mass also varied,depending on the size and weight of the gearbeing cut and the fixture.
2. Stroking rates in the range of 1,000 to2,000 strokes per minute made possible by acutter spindle relieving mechanism andhydrostatically mounted cutter spindlebearing and guides.
3. Larger cutting spindle diameters withproportionally increased horsepower of themain drive motor; for example, a 20"maximum diameter capacity modem machinemay have a 3.93" diameter cutter spindle anda 22 horsepower, stroke drive motor, while an
old style machine mayhave a cutter spindlediameter of 3.34" and a 5.7 horsepower motordriving the entire machine, i.e., the cutterspindle stroking and the rotary and radial feedchange gears (F:ig. 5}. Note: Maximum DPrating on this size machine went from 5 DPfor the old style machine to 3 DP for themodern machine.
4. Increase in overall weight of themachine by a factor of two to three times. Forexample, a 6" maximum diameter capacitymodern machine weighs l 7,000 lb ; the oldstyle machine, 4,900 111>8. Till extra weighthelps to absorb the higher cutting forces andreduces vibration.
"Moder.n·> Spindle Retief Type GearShapeI' with Challge Gear Drive Train "FirstGeneration", Figs .. 7 and 8 illustrate the drivetrain of a modern conventional gear shapingmachine with independent drives. i.e., AC
Spring Blocks
Table Relief Movement
Fig. 4 - "Old sty le" gear shaper - work table back-off system.
M'L'MOW-O·······Feed Change Gears - I--HI.A---=.;==----Il
Cutter SpindJe Rotary Driv .......-~.. I'
Radial Infeed Cam. - -Gear to be CUI
I Back-off CamI {Table Relief
System)
Work Table Drive Train
Cutter Spindle -Stroke Drive
Fig. 5 - "Old Style"· table IreUefmachine with numerous drive trainsnecessitated by having a single drive motor.
Wlall• Adjustment of relief amount and change of relief direction.• Relief amount selling adapted to the application .• Change in relief direction in e ternal/internal machining.
Fig. ,6-"Modern" spindle felief type gear shaper with change gear drivetrain (''first generatien") ..
main drive motor for stroke drive, AC servo ,John L,angedrive motor for rotary feed and rotary powertraverse and, finally. AC ervo drive motor forradial infeed and radial power traverse. Noticethat rotary feed and required rotational timingof the workpiece and cutter are handled by anindex change gear drive train. Up until the19808 and despite the introduction of CNCcontrols, the uniformity of the generatingmotions For rotary movement was maintained
is a product manager atAmerican PfauterLimited Partnership.He is currentlyChairman of the AGMAGear ManufacturingCommittee and is theauthor of numerouspapers and a contributorto the SAE Gear Design,Manufacturing andInspection Manual
JANUARY/FEBRUARY '994 11
Fig. 7 - Mechanical link between cutter and work on It mechanical gearshaper,
J. - Main drive motor stroke drive
2 - Drive motor, rotary feed,rotary power traverse, rangeof adjustment 1:2000
3 - Drive motor, radial feed,radial: power traverse, rangeof adjustment ,1 :3000
Fig. 8:- Three sepat'ate motors for stroke, rotary and radial movement.
Fig. 9 - Aconvcntiona~ gear shaping machine with a maximum diametercapacity 7" and 2" facewidths, stroking rates up t.o l,800 strokes perminute,
'18, GEAR TECHNOLOGY
almost solely by a mechanical drive trainproviding a positive link: between thesemovements. The transmission ratio was variedby change gears.
CNC Development. Fig. 9 shows a non-CNC modern spindle tehef gear shapingmachine. Fig. lO]s the same machine, bllt withCNC control. There is little difference in theouter appearance other than the operatorcontrols, however, the internal machinekinematics are quite different CNC refers notonly to programming of feeds and speeds, butmore important, to the elimination of index.change gear drive trains. In reality, littlebenefit CD_n be realized by using a CNC controlonly to program feeds and speeds.
CNC Shaper "Electronic Gear Box"~ A"full" CNC gear shaping machine does notcontain index change gear drive trains .. Therequired index ratio and the timing relationshipbetween the "C" axis cutter spindle and the"D" axis work table is controlled by eNC, i.e.,the so-caned electronic gear box. The samecontroller is used to. specify the X axis radialinfeed rates and the cutter spindle strokingrates per minute. Fig . 11 and 12 illustrate afive axis gear shaping machine. In addition tothe X, C and D axes, we also see the Z axis,which is a vertical positioning of a givenstroke length. HL" is a stroke length etting.
Flexibility and New MachineDesign Concept
A Flexible Slraper. A gear shaping machinewith a two-inch stroke has a very limitedvertical height position (distance above thework table) in which that two-inch stroke canoccur - normally only three inches or less.Because of this, the machine needs to beupplied with a riser block (a spacer mounted
between the bed of the machine and thecolumn) to elevate the maximum stroke heightto the same level as the tallest part to be cut.Consequently, shorter parts must be raised upin a special fixture to this predeterminedheight. Obvi .ously, riser blocks and built-upfixtures reduce the desired rigidity of themachine, and in tum, accuracy of the cut partand tool life. The cost for flxturing elementsincreases proportionately.
Quite frequently, shapers are used forcutting one gear in a duster of gears, becauseone or two elements in the cluster must be
shaped. i.e., cutter run-through clearance isrestricted. In addition to the shaped gear in thecluster, it would be advantageous to shapeanother gear in the cluster in the same setup.However. because of the different number ofteeth. the required index ratios, andthe fixedindex change gear drive trains, this was notpossible with the older style and firstgeneration spindle relief machines. Also, thelocation of the second gear on the shaft made itdifficult to reach. even with stacked cutters.i.e., two cutters mounted to the cutter spindle ..
In the ] 960s the cutting tool was not thelimiting factor in the cutting process.Lightweight "old tyle" machines withnumerous gear drive trains, slow stroking rateand general lack of rigidity made the machine.not the tool, the limiting factor. In the early1970s •. the modern first generation spindlerelief shapers using conventional M-2 toolsteels found the tool, not the machine, thelimiting factor. In the late 1970s and early1.9805,with the advent of powdered metal ASP30 and 60 titanium-nitrided coated cutters. wefound. in many cases, the machine to be thelimiting factor once again. New infeedtechniques had to be developed to realize thefull potential of these new tools ..
The "second generation" of the spindlerelief machines added a CNC controller, whicheliminated index change gear drive trains.These machine advances dealt with thepreviously mentioned lirnitations through thedesign features shown in Figs. 13 and 14.
The machine is fitted with a verticaladjustable cutter head slide (Z axis) (Fig. 13)which allows vertical positloni ng of theentire head. In most cases, riser blocks andspeciall y elevated work fixtures are notnecessary. For example, this 2.35" strokelength machine has an axial displacement of'the cutter he~d slide (stroking position) of6.7". Using NC techniques, the positioning ofthe cutter head slide is accurate to within atolerance of .0008".
The C and D axes, which required rotarymovement (index ratio) of the cutter spindleand rotary movement of the work tablerespectively, are controlled by CNC withrotary encoders. There are no index changegears in the machine. The resolution of therotary encoders is 3.6 arc seconds. This design Fig. 12 - 5-axes CNC gear shaper,
Fig. 10 - CNC gear simper .. Note the use of spring mount shoc.kabsorbers and nIt column for root taper eunfng capability.
M
Axis CutterPo itioning
I .c~tzCutter
Rotary Drive
Fig. 11- Kinematic dr.awing Df drive train for a 4·ax,es CNC shapero Theservo dTi",e mowrs (M) for X, D lind Care AC brush\ess type for lowmaintenance. They also. must have a wide speed range ratio, i.e., rotaryaxes Cand D 1:4800 and X rad.ia~axis ~.;1800ratio.
J"NUARVIFEBRUARY 1994 19
4-axes electronic control:Z A rial movement of cutter head slideX Radial movement of column slideC Rotary movement of cutter spindleD Rotary movement of work table
Fig. 13 - Cutter Head Slide CNC ShapeI'
Numerically controlledaxes:X Radial movement of work table slide
Rotary movement of cutter pindleD Rotary movement of work tableZ Stroke position settingL Stroke length setting
Fig. ]4 - Convcntional CNC Sha.perfeature makes ~t po sible to cut two or morecluster gears having differentindex ratios :in 11
single setup. Depending on the gear data of thecluster gear, it might be necessary to use stack-mounted cutters. The lead of both cutters mustbe rhe same. A CNC guide has not yet beendeveloped, but experirneneal work is beingdone in this area.
Example 1 in the appendix show twoexternal gear clusters being shaped in a singlesetup. CNC shapers are also perfectly capable ofcutting components having both internal gears(or splines) and external gears ina single setup.
Frequently. cluster gear have a timingrequirement between a tooth on a gear in thecluster in relation to another tooth on a secondgear in the cluster. The use or a CNC controlsystem makes it possible to meet. thesedemanding requirements .. This exampleillustrates uch an alignment requirement.Thi automotive tran mission componentrequires a tooth alignment accuracy betweenthe two gear .of .OOOS".The pan has been cuton a CNC shaper, a illustrated in Fig .. n.achieving an alignment. accuracy of .0004".This accuracy will be maintained in aproduct jon environment.
Down-and-up shaping of a component i
20 GEAR TECHNOLOGY
made possible with CNC. .he partconfiguration illustrated by E ample 2 in theappendix. dictates thai both the upper and thelower gear be shaped. To do this part in asingle etup, down-and-up shaping is required,The upper gear of the component has an outerdiameter larger than the root diameter of thelower gear. The teeth of the upper gear mustalso be aligned to the [ower gear. Thatalignment can be easily obtained. because thepart is cut in a single etup using keyed cutters.The relation of th.e cutter spindle backoff andcutting troke direction is controlled by theC C unit, When cutting the upper gear, t.hecutter relief occur on the upward. non-productive stroke. In the case of the lowergear, the cutter rei ief action occur in thedownward stroke.
Innovative Design - An.8-Axes FMS-Ready Mac/tine. Since the advent of CNC gearshaping machine in the early 1980s, hundredshave been sold worldwide. These machines,with their four and five axe , revolutionizedgear shaping production in job shops and smallbalch production by increasing productivity byfour to five times compared to older shapers.Even in mass production installations we haveeen an increase in productivity of two to three
times due to CNC cutting feed techniques andquick cutter changes.
However, the e machines were not. flexiblemanufacturing systems (FMS) or cell "ready."To meet this requirement, three additionall axesand auto too] and pallet fixture loaders wereneeded. This was a real challenge for thebuilders of CNC shapers and their CNCcontrol manufacturers. as the machine now haseight exes. Also, to be totally free ofconstraints. the Z axis stroke po itionmg rangehad to be a large as practically po sible toaccommodate various part configurations. Fig.15 illu trates such a machine. Note theadditional three axes:
o axis - quick return stroke; especiallyuseful for gears with large face width;
A axi- the direction of the cutter pindlerelief: internal versus external gears; and
B axi . - a column tilt for cutting roottaperedteeth,
Combining this machine capability with apallet fixture and a ]2- ration 1001 loaderresults in a CNC gear haping machine well
uited for FMSinstaUati.on. The flexibility ofthe large stroke positioning range (15.75") isequally important to special industries such asaircraft engine manufacturers and heavyconstruction equipment builders.
Feed Techniques to Ma1lchHigb Tech Machines
Ol1timizing ,the ,Gener;ating Mellwd. Fourtypes of infeed can be distinguished (X, C andD axes):
1. Radial, feed witb liotary m.otion. (Fig.16a). This is a traditional method, with radialinfeed of cutter or workpiece to final depth willirotary motion of both cutter and workpiece. A Fig. 15 - 8.axes CNC gear shap.ing machine ..
comparari vely short spiral. length pattern,depending on the selection of the approximatefeed rate (generating feed up to 1.0 mm(.'Q4")/double stroke and radial feed of .02-.04mm (.OOO8-.0016")/double stroke). results.
2. Radial feed without rotary motion,(Fi.g. ~6b,. Also a traditional. approach, thimethod is recommended for:
a. Shaping internal teeth in order to avoidreturn stroke marks by the tool. on workpieceswith difficult tooth geometry:
b. Reducing feed times; andc. Producing form cut profiles (single tooth
indexing method).Radial infeed i to final depth without rotary
motion of workpiece and tool. his II edprimari]y to prevent collision when hapinginternal gears and to save lime by applyinghigher infeed rates (approximately .05-.101 mm(.OO2-.004")ldouble troke), and meet pecialreq 11irements.
3..Splral method w.ith constant radialFeed. (Fig. lfic). This is used on. a modernmachine. but not necessarily one equippedwith CNC. The chip volume increases withincreasing cutting depth of the tool and
a)
b)
x.. -----
c)
+----+D
x -,~
d)
-I-----IoD
Fig. 16a -Radial feed with rotary motion.F~g. 16b - Radial.f;eed without rotary motion.Fig. 16c - Spir.al method ,,,1U1()on.stant radial feed.Flg. 16d - SpiraJ method with digJIcssive radialleed.
Tab[ .1 - Summary of cuttmg m ·tbod •
Method D cription T~,'pesof utters
I
GeneratingI
- Infeed without generating -di k-type cutters- Infeed with generating - hub-type cutters- Spiral infeed with either constant or variable radial feed - shank cutter
I index. generating - Like generating. but no Iul] work revolutions at coastant - culler types asI
feed (segment gears, special profiles which can be generated) - segment cutler- single tooth form cutter
Single indexing
I
- No generating motion of workpiece during stroke action - form cutter (primarily single tooth cutter)
J ....N U"'IIV/F'cB RU ...R Y 199< .21
uniform radial feed. This amounts tocontinuously increasing loads on the machineand the tools until the depth of the tooth isreached. Continuous uniform radial infeed is tofinal depth over several work revolutions. Thedesired large spiral length pattern. results fromappropriate feed rate combinations, dependingon gear parameters (generating feeds up to 10mm (.40")/double stroke and radial feeds ofapproximately.002-.030 mm (.000080-.OO12")/double stroke).
4. Spiral method with digressive radialfeed. (Fig. ]6d). This is the newest technologyand is on Iy possible with CNC. Here, adecreasing rate of radial feed keeps the chipvolume during the feeding process almostconstant. The result is improved tool life andimproved surface quality of the tooth flanks. Inthis method, travel is dependent on digressivefeedrate pattern. The high requirements forproper control can fully realized only with CNC.
Cutting Forces and Torque Based ou FeedTechniques. The controlled infeed of the piralinfeed method over as many as possible workrevolutions is primarily used. Comparisontestswith traditional infeed methods with or without
Shaping. Methods:I ~ Radial Infeed with Rotary MOtiOD2 - Radial Infeed without Rotary Motion3 - SpiralInfeed with COru;!IID[ Rad~11Infeed4 - Spirnllnfeed with Digressi ve Radial
InfeedI
-"\,,----@-----,II \
h \---~-----.~~-------1\~ .~
Gear Data:Z=21. M=2,25"NPA=17· 30'.HA=)S"RHMaterial: 34Cr4
o 0,5 1,0 1.,19 Cutting Time (Min)
Fig. 17 - Main cutting force diagram roughing by the four wofeedmethods,
Fig. 18 - Chi.p formation, spiral digressive infeed method ..
22 GEAR TECHNOLOGY
generating at equal time for roughing showthat the individual cutting edge is exposed to.substantiaUy reduced main cutting forces andtorques (Fig. 17). This occurs because of betterand more uniform chip formation, better chipflow and less chip deformation (Fig. 18). Thedesired effects are less cutter flank contact, lessdanger of rubbing 0[1 the return stroke, reducedtemperature build-up at the cutting edge andIesstendency for edge build-up.
Spiral Digressive Infeed CuttingTechnique. Applying the digressive infeedsubstantially increases the productiveefficiency of gear shaping, assures shortcutting times and provides effective toolutilization coupled with high accuracy. Theprocess is applied to roughing operations. withsubsequent shaving, fine rolling, honing orgrinding and to finish cutting operations suchas are shown in Fig. 19, where both higherfeed marks and enveloping cut forrnationaswith coupling gears, are acceptable or evendesirable because of the improved lubricationeffect (oil pockets). Key features of this infeedtechnique are:
1. Controlled Chip Removala. The spiral. type infeed pattern is
according to section,h. Cutting data, such as numbers of strokes,
generating feed. radial feed and cutting depth,are determined by computer control.
c .. The bases for determining cutting dataare the geometrical parameters of workpiece,tool, machine, material specifications andvalues obtained from trials.
2. H.igh Speed Finish Shapinga. This improves surface quality, part-
icularly the formation of enveloping cuts forthe desired subsequent operation.
b. This also yields extremely short finishingtimes as a result. of the high generating feedrate, which can be up to fifteentimes the rateof conventional finishing feeds, depending onthe gear parameters.
3. Spring Cuts Without Infeed For Impro-ving Quality
a. Typical tooth deviations (e.g., errorsreproduced as a result of inaccuracies buillinto the cutter or asa result of improper cuttermounting) are averaged! out.
b. The number of spring cuts depends on therelation of the number ofteeth between cutter
reduced cutter wear through the digressiveinfeed technique, a subsequent finishingoperation has generally better results thanroughing by conventional. shaping infeedmethods. This occurs because of reduced gearrunout and spacing errors, smaller requiredstock envelope and reduced chip volume.
These New Teclmologies Affect Cutti.ngTimes. The new feed techniques go hand inhand with the technology advancements madein the hardware, i.e., machine and cutting tools,The pendulum of the shaper cutting process no
and workpiece and 011 the required gear quality,Gears shaped by the digressive technique
are comparable to hobbed gears in both surfaceand enveloping cut patterns. The samecomparison applies to checking the gear,particularly to chan evaluations and tosubsequent finish operations.
Actual production re ults have shown thatselecting a machinable workpiece material andusing TiN-coated cutters (especially face-coated) can have a positive effect on thesurface quality of gears produced by thedigressive tech nique,
This is not to say that one must always lookfor the easiest material to cut. For example, ifan 8620 material is cut at a high rate (finishingata surface cutting speed of 300. fpm), a 200Brinell hardness would be preferable to thesofter 150-]60 Brinell, The softer materia] willtear and chip-weld to the flank of the cutting,especially if the cutter's face i not TiN coated.This tearing and chip-welding will lower theobtainable AGMA finish-cut accuracy from a1.0 toa 7 or 8.
Besides higher chip removal rates and Fig. 19 - Feed marks and enveloping cut forma.tion.
Table 2 - Past t.o present cutting time review,
Geilli DataDiametral PilchNo. of TeethPitch CirclePressure AngleHelix AngleFace Width
Typical Automotive Gear1230
2.88"20°30°.8"
3.15 2.5--
1.90% 290%100%
Typical TrucklAgrIcllltur.al. Gear530
6.92"20°30.°1.5"
.030"
Material/Hardness 8620/220 BHN 8620IBHNCutting Condition Preshave PreshaveQuality AGMA . 8/9 8/9... -...... __ ...""""'- ---......-_._- ------- -------.-- ---- . ,-- --------- -----,----- - -- --------------- ---------- -_ ..._-------------_ .._----_ ..........
Old ModernConv. Conv.2 2
335/115' 335/1.15'50011.74' 6701232'
--
II.0.1.77" .019".0177" .030"
--
.00.12" .00]2"
.000411 ,(1004"RadialInfeed/Stroke
Roughing1 --"F.:!.i.nisJJ.i!!g ~I_-----+----j__..
Cycle Time, Minutes,Without Load & UnloadPieces Per ShaIpening_Percentage
Modern_I- CN~.Conv, _r-Spiral Digression3 _ 3 Feed Changes
160/99']50/9'2' 242/150'150192~ 4801292'
----~I-----+---~·~~~~'-' ------1.68 17.13 7.98
180% 340%
*Old - Table relief type machine (See Figs. 3-5).Modern - Spindle relief type machine, but with change gears and independent drives (see Figs. 6-8).
!I' CNC - Spindle relief type machine with large speed ranges and without change gears (see Figs. 11-12).
JANUARY/FEBRUARY 1994 23
longer swings in favor of the cutting tool vs.the machine Of vice-versa .. Cutting tool andmachine are equal limiting factors.
Advancing Technology forMechanl.cal Components
Hydrostatic Gru'd,es. Gear shapingmachines require spur andlor helical (lead)guides. Helical gears require helical guidesthat introduce to the cutter spindle anadditional rotary motion during the workingstroke. These mechanical guides are stillrequired. but in almost all cases the cutterspindle and guide are mounted hydrostatically
'Guide ring and guide piece of a helical guide. (Fig. 20). This i a necessity based on the
Hydrostatics:The throttles of the spur and helical guides mounted inhydrostatic bearings are built into the guide ring and areaccordingly protected from damage when changing the guides,
Ftg. 20 - Hydrostatic lubrication of a helical or spur guide and cutterspind,le.
I
RTaper~
J?'"Concave Crowning
End Relieved Convex End Crowning
Fig. 2] - Types of longj:tudinal correction (Iead correctien) crowning,taper; etc.
Fig. 22 - Automati.c cutter damping feature, The cutter and adapt.erarehydro-mechanically damped into the cutter spindle.
Fig. 23 - Cutter adapters are automatically clamped concentric to thecutter spindle to a.1l accuracy of .000]-.001)2". Two cutters are mountedfor duster gearcutting.
24, GEAR T!ECHNOLOGY
high stroking rate capabilities of somemachines, i.e., 2.050 strokes per minute. Thiscan lead to cutting speeds for finishing up to492 surface feet per minute. Of course, workis being done on CNC guides, but none arecurrently svailable for quality production athigh stroking rates.
Another element which is not CNC on themachines is lead correction, i.e., crowningcapabi Ii ty. Involute modifications areproduced by modifying the cutter tooth form,but crowning is achieved by moving thecutter spindle as it traverses the face of thegear. Tbis movement is created bymodification of the "back-off cam," which ispart of the relieving mechanism for cutterrelief. Cutter relief is the process of movingthe cutter away from the gear so it does notcontact the gear on the non-cutting returnstroke. Of course, this applies only to"modern" pindle relief shapers.
Custer Cbanging - Manual QuickChange arid Fully A.utomatic Changes. SeeFigs 21-24 for illustrations of these features.
Worm and Worm Whee.l Design« forBacktasb Control. When the gear shapingprocess is evaluated for geometric capabilities,the following general statements can be made.
1. Lead errors are minimal with modernhydrostatic machines, i.e., AGMA 11-12 is anachievable quality. The hydrostatic mountingof guide and spindle maintains this capability.
2.. Profile results are Closely tied to sbapercutter tolerances, but are also related to cuttercoatings. cutler clearance and rake angles andsharpening errors.
3. Part pitch line runout errors can bedirectly related to cutter mounting errors
and/or fixturing errors.A Summary of the Benefits That Can Be
Realized from a CNC Shaper:~. The operator set-up i simplified because:a. Tile operator does not have to mount
index change gear.b. The operator does not have to set cutter
spindle stroke length and position;c. The operator doe not have to set infeed
cam. or micrometer switches fer depth of cut;d. The operator does not have to set speeds
and feeds. which can be loaded by punch 'tape Dr
DNC Dr recalled from the CNC controllermemory;
e. The operator doe not have to changedirection of cutter relieving for upcutting orinternal gear cutting to exteraal gear cutting;
f. With the appropriate cutter measuringequipment the operator does not have to cut atrial piece to verifyc~lTecl infeed setting for anoverpin dirnen. ion check, i.e.. cut a part to ize:
g. On orne machines tlle spindle back-offdirection doe n t need to be changed,
2. Clu ter gears CaJI be cut in a single etupbecause of the Z axis stroke posirion and theab ence of index change gears. If the OP di ffersfrom gear togear, stacked cutters are applied.
3. Cluster gears. with tooth location re-quirements can be cut in a single setup. C and Daxes are independently controlled,
4. Keyways, Ingle tooth. form or other formscan be cut by the plunge cutting technique, i.e.,no C or 0 axe rotation except for single toothindexing. The X axis radial infeed is the Oldyfeed component used with this technique.
5. An internal spline or gear and external gearmay be cut on the same blank. This requires theZ axl troke po i.tioning feature and stackedcutters with C and Daxes index ratio change,
6. Cutler change down-time is reduced. Thecutter can be electroniceljy measured off themachine and new tool offset data enteredthrough the CNC control while the machine isin production .. Axes used are Z stroke positionand X axis Ior new infeed depth stoppingposition ("final. i2e"). Of ecurse, this i done tocompensate for tool heightand diameter changedue to cuuer sharpening or mew set-up.
7. Zero set-up time is important inconnection with just-in-time inventory andflexible manufacturingcells and systems .. Asetup of only iii few minutes can be presently
I. - CNC gear shaping machine2 - Cuuer quick clamping
facility3 - Tool grip arm4 - Tool magazine (4 stations)5 - Slide for the grip arm with
horizontal, vertic!!! andswivelling motion
6 - Pan carousel automaticloading device
4
Fig. 24 - CNC gear haping machin •obtained on gear shaping machines if the guide doesnot have to be changed and additional supportequipment is purchased with the machine, i.e.,automatic fixture and curterchange equipment.
8. CNC gear shaping machines are more accuratethan conventinnal shaper . X-axis infeed, feed perstrokes and depth of cui (final size) are controlled bya linear electronic scale and AC servo drive. Theaccuracy of stopping at a preset infeed depth is plusor minus 40 microinches, Z-axis stroke lengthpositioning is also controlled by a linear electronlcscale to an accuracy of .0008". C and D axesarecentrolled individually by rotary encoders witharesolution of 3.6 arc second . The e new hapers arecapable of producing quality level AGMA l 1 underproduction circumstances and optionally. AGMA 12.
9. The installation of a CNC gear shaping machineinto a flexible manufacturing cell or system woulddictate automatic tool changing capability.
Appendix: CNC ShapingApplication. - The Real World
Example 1. Cuuing " Helical Gear Cluster witha Tooth Alignment Requirement in a Single Setup,Figs. 25 a, band c show a helical cluster gear with atooth location requirement. This is an automotivetransmission component. Gear I and gear II have
JANUARV/FEBRUARV 1994 251
,Gear/Cutting Datil
Number of TeethDP (Normal)Face WidthHelix Angle RHCUlling Tool
Number of Teeth 56Strokes per Minule
Rougb/Finish 40011000 40011000Cutting Speed/
Surface ft. per MinRough 138' 138'Finish 344' 331'
Cutting Method Generating DigressiveTotal Cutting Time 4 minutes, 5 seconds
3211.16.78"
c) 36°
Fig. 25 - Helical cluster gear with a tooth location reqllir,ement.
Gear/Cl!tting Data A 0,
18 2110 10
.70" .6["
Number of TeethDPFace WidthMaterial 8620Number of Teeth
in CuttersStrokes Per Mini
Culti ng SpeedSurface Ft. Per Min.
Roughing 7001167' 700/167'Finishing 10501249' 12501295'
Cutting Method Down Up(Generating) Digressive Digressi ve
To!al Cuulng Time 1.2 min
180-200 BHIN
62
F,ig.•,26,- Closter p'lanetary pinion cutting down-and-up sbaping in asingle setup.
26 GEAR TECHNOLOGV
II
4416,9.'78"
32" 38'
77
dissimilar helix. angles, modules (diametralpitch) and number of teeth (Z). The requiredtooth location alignment accuracy is .0008".The part is cut on a CNC gear shaping machineto a preshave condition in a single setup, It ismade of case-hardened material having ahardness at the time of cutting of about 190BHN, Total cutting time for the component is4 minutes, 5 seconds with an achievedalignment accuracy of .0004". The unu ualcondition here is tha.t wllille there are twodifferent helix angles, the lead of the cutterscan be made the same and still retain therequired helix. angles by changing the diameterof the cutters, A single guide satisfies the leadrequirement of both cutters.
Example 2 - Cluster Gear Cutting by theDown-and-Up Shaping .Method in a SingleSetup (Fig. 26). Note the back-to-backmounting of the cutters. When down-and-upcutting :in a single setup, it is necessary tochange the back-off direction, i.e .. therelieving action of the cutter spindle, This isdone automatically by the CNC controllerduring the repositioning of the cutters. Ofcourse, when up-cutting, the pull stroke is apower stroke, not simply a return stroke, aswhen down-cutting,
Example 3 - Cutting of Three GearClusters with Three Cutters in a Single Setup.Three gear members (Fig, 27) are cut in asingle setup. Two members have a toothlocation requirement.
Example 4 - Cutting Gears by the IndexGenerating Method. "Index generating"implies alternating generating action betweentoo! and workpiece at a given ratio with singleindexing of workpiece and/or tool. Thiscapability must be provided by the CNCcontrol and requires that the electronic drive(i.e., the controlled motion between cutter andworkpiece) can be temporarily opened andclosed at any time and at any position withoutmemory loss of travel increments,
Fi.gs. 28 and 29 illustrate how th:is profile isproduced, The pinion bore has straight-sidedtooth profiles preventing the use of standardinvolute cutters. The profiles were broached inthe past, but the many types of profiles resultedin exorbitant tool costs, and tool-relatedinaccuracies caused excessive pump noiselevels, Precutting is done by single indexing
3
6013.55.9"
Number or-I:eell1DPFace WidthMalenal Cast Iron200I'lHN
Number of 'feemin Culters
Strokes Per MinJSurface Ft. Per Min.Roughing 5001170' 500/170' 4001138'Flnishing L10013,74' 1100/374' 11001374'
Gear utling Method Generating DigressiveTotal Gear Cutting
Time 4.25 minutes
70 648.825.4
1.1" .47"
56 42 68
Fig. 27 - Planetary gear housing with three gearing elements being cut in D single setup (spurs).
Fig. 28 - Preshaping the special internal profile 'Of an oil plIDlP gear by the single ind.exing method.
SpecialTip Circle ji>-rome Fin! h
Gear/CUlling :Oam Roughing Shaping Sbaping
Number of 'feei,blGaps 17 17 17
Profile Dlrnen ions .12" x .59'" .137" .12" x .59"x .47" x .47"
Face Widlh 1.65"Cutting 'fool Indexable
CarbideStrokes Per Mill.1Surface Flo Per Min. 350m3' 7001377' Same
CUlling Method Indexing Indexing/GenerutingCurting Tirne 2.5 Minutes 5.1 Minutes
Fig. 29 - Finish-shaping the special. internal pr'OfLieof an 'Oilgear by index generating.
J ANUA R YIFE B RUA R Y 1994 27
Table 3- Finish Shaping Machffiing Sequence for a 17-TOQthWorkpiece With a Single Tooth Cutter
Workpiece teethI 2 3 4 5 6 7 8 9 10 II 1213 141516 17
II. •
•
••4 • •
13
••• •9
Gear/Cutting Data Roughing Finishing
Number of teeth/slots 60DPProfIle dimensions .OS" x .43"
x .41"2.36"Face Width
Cutting Tool Reversible Disc typecarbide insert
Strokes per MinuteCutting Speed!Surface Fr. per MinuteCutting MethodTotal Cutting Time
450 450
325' 325'Indexing Generating
17.5 minutes
Fig. 30 - Roughing and fullshing 3D internal gear with a disc cutter in asingle setup.
Cutting Method Generating IndexingTotal Cutting Time 6.5 Minutes
'Gear/Cutling Data External I Internal n
Number of Teeth! Gaps 26 3OF-slots 32 DP Semi-Round
•05" RadiusFace Widths 1.54" .9"Number of Teeth
ill Cutter 190 3Strokes Per Minute!
Surface Feet Per Minute:Roughing 80136'Finishing 160nS'
Fig. 31 - Cutting an external spline and internal recessed! slots with atooth location requirement in a single setup. This is an aircraft enginecomponent!
28 GEAR TECHNOLOGV
605
with an indexable carbide cutter insert ofspecial profile design.
Finish operations start by first machiningthe major diameter. The spaces are skippedby rapid traverse. The major diameter is usedfor locating and clamping the part forsubsequent machine operations. The next stepis finishing the tooth space for indexgenerating with an indexable carbide cutter.Its profile exactly represents a tooth of thepump pinion. The space is generated over110° and then indexed 16SO in rapid traverse.The machining sequence of the tooth spacesare indicated in Table 3.
Example 5 - Carbide Form Cutting,Roughing and Generating Finishing with aDisc Cutter in a Single Setup .. This internalgear is roughed with an index able carbidecutter insert and finished with a standard disctype cutter (Fig. 30).
Example 6 - Profiles in Recessed BoresThat Cannot Be Broached. Fig. 31 illustratesthe cutting of an external spline and internalrecessed slots with a tooth locationrequirement. By cutting this part in a singlesetup, the required position relationshipbetween the oil grooves and the external gearis no problem. The part, a difficult aircraftmateria], is shaped in 6.5 min.
Example 7 ~ Finish-Shaping of a Counter-shaft in a Single Setup. Fig. 32 illustrates twocutters tandemly mounted cutting four gears ina single setup. Each gear is cut in an individualmachine cycle. Of course, feeds and speeds arechanged automatically between each cuttingcycle. The parts are finish-cut. They werepreviously finished in a shaving operation.
Example 8 - Multiple Machining Oper-ations in One Cycle .. Pigs. 33 and 34demonstrate the flexibility of an 8-axes gearshaping machine. Note the deburring techniquein Fig. 34, operations 2a, 3a and 4a, •
Reference:Dr. Klaus Felton, "Effective Gear Shaping Principles,"presented at. American Pfauter Gear Process DynamicsClinic, Sept., 1987.
Acknowledgement: Reprinted with permission of theAmerican Gear Manufacturers Association. The opinions,statements and conclusions presented in this article arethose of the Author and in no wa.y represent the positionor opinion of the AMERlCAN GEAR MANUFACTURERSASSOCIATION.
Geu/O!!l.ti.ng Data U IHZo=29m=2 N umber of Teeth 12 13 17 21
DP 12.7 10.16 10.16 10.16Face Width .S6~ .35" .33" .33"Stroking Rates Per Minute
Rough 700 800 800 800Finish 1400 1400 1400 1400
Cutting Speed Surface fL Per Min.Rough 121' 1.41' 141.' 141'Finish 246' 246 246' ~6'
Cutting Method Generating DigressiveTool Cutting Time 2.46 minutes
Zo=50m=2,5
Fig. 32 - Finish-sbaping of a eeuntershaft in a single setup ..
1 External Gearm e 5, Z2" 98
CCP shapi ng with disc-type cutler
1 2Lead Correction
Quick. return stroke
2 Internal Gearm=5 Z:!=48
CCP shaping with disc-type cutler
Without quick return stroke
3 Timed Triangular Grooves.Posltlen-OrlentedIndexing method withreversible carbide-tipped tool(form tool)
4 Machining a Check Flange or Assembly DiameterWith Reversible HSS Tool
Fig, 33- Four ma.chining operations in one cycle.
11
: ,''13
~~~4 r/
1 Internal Gearwith Lead Correction to axis) ---'----
Fig. 34 - Seven machining operations in one cycle.
2;3;4li:xtertlal Ge.....With Different Numbersof Teeth and Face Widths
aAll 3 gears W"l! deburredwith tb£ shoulder-sideof the cutter ( pedal design)
For deburring,the rotary directionof the culler spindlechanges (C axis)
Positioning paths duringthe multiple machinmg operations:Center distance (X axis) approx. -31 to + 230 mmStroke position (Z axis) approx, 285 mm
JA.NUARVIFEBAU.AAY 1994 29
'Geo,eration of Helical Gearswith New Surfaces Topology byApplication of CN C Machines
F.L. liitvin. IN.X. Chen & C..L. IHsiaoThe 'Uniiversity.· of IIHnois at Chicago. Chica,go. IL
- -
R. F. HandschuhINASA Lew.is Research :Center. C'I'evel,and. OH
AbstractAnalysis of helical involute gears by tooth
contact analysis shows that such gears are verysensitive to angular misalignment leading toedge contact and the potential for highvibration. A new topology of tooth surfaces ofhelical gears that enables a favorable bearingcontact and a reduced level of vibration is
I
i. Contact Direction122.4
TOOlhTopGEAR \
H~' --...---IJ\.
Tooth Root
sg 111.0
8B'"is
-a 63.7 -:e",.
0:::.
ContactDirection
PINION
52.3tL-20 -lQ__ :0
Fig. 1. Edge contad due to ads misalignment (crossing angle, 6:y = .s arc-min],
10
0'III 5'",~ctI
~ 0
~
~-5
c::0.;:; -10Of)·s'":ee~
-20 ---
·35 -2:5 -IS -s
Angle ofRotation of
Pinion5 15 25 (in deg.)
Fig. 2. Transmission ·errors ,of involutc helical gears with axis misalignment(crossing angie, 6:y = 5 arc-mi~).
301 GEAR TECHNOLOGY
described. Methods for grinding helicalgearswith the new topology are proposed, A TeAprogram simulating the meshing and contact ofhel ical gears with the new topology has beendeveloped. Numerical examples that illustratethe proposed ideas are discussed.
IntroductionComputations by tooth contact analysis
(TCA) have shown that involute helical gears.are sensitive to errors such as the crossing ofgear axes (instead of being parallel) and leaderrors. These errors shift the bearing contact tothe edge and cause transmission errors of anundesirable shape (figs. 1 and 2). The transferof meshing of gears with such transmissionerrors is accomplished with a jerk, producing ahigh level of vibration and noise.
A new topology of tooth surfaces has beenproposed (Refs. 1-3) that provides for a morefavorable bearing contact and transmissionerror motion. even with misalignment present.The generation of the proposed gear toothsurfaces was based on the application ofexisting equipment for generation of helicalgears that provided linear relations betweenthe rotations and displacements of the tool andthe gear being generated. The modified geartooth surfaces proposed in Refs. 1 - 3 could begenerated as Formate®-cut by a tool of largedimensi.on or generated point by pointif computer-controlled. These methods ofgeneration have some difficulties formanufacturing, but they may be overcomeby the new approach.
T'his flew approach is based on the
II
application of CNC machines with five degreesof freedom that provide: (I) computer-controlled nonlinear functions that relate themotions of the tool and the gear beinggenerated. (2), a varied plunge of th - \001 alongthe shortest centerdi tance between the axe, ofthe tool and the pinion and (3) a point contactof tooth surfaces that is spread over anelliptical area of controlled dimensions. Thiapproach avoids edge contact and reduces the. en itivity of the gear to misalignment. Thegeneration of gear tooth urfaces may beaccomplished by form grinding.
The new form grinding method for helicalgears provides: (1) a stabilized bearing contact,(2) better condition of lubrication and (3) ap:redesigned parabolic function of tran mi sionerrors that is able to absorb an almost linearfunction of transmi ion error caused by gearmisalignment. It. is expected that the newtopology will eljrninate edge contact andsubstantlally reduce noise and vibrations ..
The proposed form grinding requires theapplication of a computer numerical controlled(eN) machine with five degree, of freedom.but only four require control by computer.Each tooth space is generated separately andindexing is required.
Bearing Contact and Transmi sionErrors of Misaligned
Involute Helical GearsThe author have developed a TeA
program for conventional involute helicalgear that permits the investigation of theimpact of misalignment. Figs. ] and 2 showLhat when the cros ing angle 6:'1 = -5 arc-ann,the contact is shifted to the edge,und thetransmission errors have the shape shown inFig. 2. Similar results are caused bythe leaderror l'IPI "" -5 arc-min.
The edge contact reduces the load capacityof the gears. The transmission errors of thetype hown in Fig. 2 will, inevitably causepremature failure. along Wilh increaedvibration and noise.
New Method for 'Grinding,Modi:fied Topology
Pirzio'n Form.Grilidillg. The form-grindingproce s for the pinion with the new topology isbased on the following ideas:
1. Consider initially that both tooth sides ofthe pinion are conventional screw involute
surfaces, Using the approach developed in Ref.4, it is possible to determine the surfaces of adisk-shaped grinding tool that. will generate theconventional screw involute surfaces. The toolperforms !he crew motion with re pecl to thepinion being generated.
2, The grinding wheel surface i modifiedin the axial section. The devi.ation of themodified tool urface from the conventionalone is represented at the mean contact point bya parabolic function. which can be contra nedto adapt to different applications. Both piniontooth sides can be ground simultaneously. Tilesurface of the pinion grinding wheel is asurface of revolution.
3. The modified grinding wheel mustperform two motions with respect 10 thepinion: The conventional. screw motion and anadditional. but varied tran Iational motionalongthe honest di: lance 'between the axe ofthe grinding wheel and the pinion. Thistranslational motion, being deeper at the edgesand less i.11the middle of the tooth width,prevents plunging of the grinding wheel intothe space.
4. Using the methods developed in Ref. 4, itis possible to determine analytically theequations of the pinion generated a de cribedabove. These equations are necessary for theTeA that has to be applied for simulation ofmeshing and contact of helical gears withmodified topology.
Gear Grindin:g. Consider thara con-ventional involute helical gear is in mesh withthe pinion who e tooth urface is modified asdescribed above. Such a gear train, if notmisaligned, win transform rotation withnegligible transmission errors. The bearingcontact of gear tooth surfaces is localized.since the gear tooth surfaces are in pointcontact at every instant. because of the piniontooth surface described above.
The goal is to keep the urface pointcontact, but to provide a predesiglled. parabolicfunction of transrnis ion errors. Such afunction is able to absorb a lineardisconnnuou function of transmi sion 'errorscaused by angular errors of misalignment. Thegoal above can be achieved by propermodification of the gear tooth surface based onthe following considerations:
1. Consider that an imaginary rack-cutter is
D.r. faydor L.Lltvmis Professor ufMecilmlicul Engineeringat VIC. He is theauthoruf 250 publications findthe lro/duof2Z patent».
Dr. NI. X. Chenfamed his degreejrumBeijing' University ofAeronautics &Astronautics and is (I
research associate IIIIlI
visilil1g lecturer at UIC.
IDlr. C. L H'siao'earned III,r doctoratefrom we and ispre emtya researchassociate al theUlliver it)'.
Dr; IR'obe:rt IF.,Handschuhis em aem5f}(JC!'engineer >L'ith NASALew; Research Center.HI' is II'l' author of over4() reports ill th« seal.gear mId numericalmethods areas.
JANUARY/FEBRUARY '99~ 3.1
I""'"""-------------------------~ ---- -~-
sirauiraneously in mesh with the pinion andgear provided with conventional screwinvolute tooth surfaces. The pinion and thegear perform rotational motions, and the rackperforms translational motions SI described asfollows:
N<1>2=<1>1 N;
where '1 and '2 are the pinion-gear centrodes,and Nl and N2 are the tooth numbers.
Obviously, the transmission function '1P2($I)is a linear one, and the gears will be sensitiveto angular errors of misalignment.
2. We may consider now that while the rackperforms translational motion St. the pinionrotates through the angle 4>1= !L, but the gear
r}rotates through the angle
Contact Tooth
122.4 -Direction GEAR ?O~II -..-..
EE~ 110.0-Q)u Tooth Rootc«I.iii Contact ToothisC;j 63.7 -
Direction PINION lop.. ...;
I'P«I0::
Tooth
52.3 -Tooth Root: Width
(rum)
-20 -10 0 10 20
Fig. 3. Latitudinal contad path w:itlt sltaft misaligllment (tly= -5').
122.4Contact Direction GEAR TOO:T"j
I y/E.5 110.0<..IU
Tooth RootB'" Contact0 Direction PIN[ON Tooth Top;; 63.7
~
I:.c
I0:1~
Tooth
52.3 • WidthTooth Rool (rom)
-20 -10 a 10 20
Fig ..4. LongitlJdinal contact path with shaft misalignment (tly = 2').
32 GEAR TECHNOLOGY
where
(I)
L\¢l2 ($1)= .alPT, - :: ::;:<1>1s -2L (4)J N,
is a parabolic function of the period of cycle ofmeshing determined as <1>1= ~n .
/
(2)
Obviously, the transmission function of thepinion and gear generated as de cribed aboveis determined as
N} 2<1>2(<1>1)= $) -. + a4>1
N2
where a¢lf is the predesigned parabolic
(5)
function 'Of transmission errors.3..The nonlinear transmission function
(Ref. 5) exists even in the case when the geartrain is aligned. The advantage of such afunction is the ability to absorb a linear butdiscontinuous function b$1 (0 ::;:4>1 ::;: .~~) thatis caused by gear misalignment. This is basedon the fact (Refs. l and 5) that the Slim offunctions represented as
can be transformed into the parabolic function
Parabolic functions (a4>I) and (a($i)2) havethe same slope. Transformation of function (6)into function (7) is equivalent. to coordinatetransformation when the coordinate system(4)2' ¢II) is translated keeping the orientation ofcoordinates axes.
4. We have assumed above that the piniontooth surface is a conventional involute screwsurface II' In reality, the pinion tooth surface1:i is a modified one as mentioned above.However, a synthesized function of trans-mission errors of the parabolic type exists inthe case of modification of the pinion toothsurface as well. This is based on the fact thatsurfacesEj ancl:q are in tangency at the meanpoint and only slightly deviate along the helixon 1:.1 that passes through the mean point.
5. These methods of modification of toothsurfaces 1:1 and .~ enable one to localize thebearing contact of II and ~ and provide apredesigned parabolic type of transmissionerror to absorb the undesired linear function
errors are reduced.3. The TCAp:rogram for helical gears with
the new topology has been developed. Theinfluence of crossing angle on the location ofthe path of contact and on the transmissionerrors has been inve tigeted, 1.1
ReferencesI. Litvin, P.L. et al. "Topology of Modified HelicalGears:' Surface Topology, March. 1989. pp'. 41·58.2. Litvin, F.L. et al. "Topology of Modified HelicalGears." NASA TMI02 134, April. 1989.3. Litvin, P.L. and J. Zhang. "Topology of ModifiedHelical Gear and Tooth Centact Analysis (T ·A)Program." NASA CR 4224, April. 1989.4. Litvin. F.L. Theory of Gearing, ASA ReferencePublication 1212, 1989.5. Litvin, F.L. 'Theory of Gearing and Application."Chapter I of Dudley's Gear Handbook; D.P'. Townsend"ed .• SecondEd., ew York.. McGraw-HilL 1991. pp, 1.1-1.43.
Aeknow:ledgement:: This article was originally presmredat the AIAAlSAEIASMEIASEE 29.1h Joint PropulsionCOflferellce and Exhibit. June 28·30. 1993, MOllie")!. CA.Copyrighr © AIM 1993. Reprinted with. permission.
caused by gear misalignment6. There are other methods for grinding the
modified gear tooth surface besides the form-grinding method propo ed here. The generationcan also be achieved by either a grinding planeor by I'll grinding WOnTI. However. a nonlinearfunction that relates the motions of the grindingwheel and the gear being generated is requiredfor both alternative cases.TeA. for Helical Gearswitb New Topo=ogy
A TeA computer program to simulate themeshing and contact of the gears with. the newtopology has been developed.
The computations have been performed fora drive with the following design parameters:NJ = 20, N2 = 40, Po = 0.[9685 nfut. a., = 20
0
,
IIp= 30°, and tooth face width FIN = 40..64 mm.Two types of path of contact can be pro-
vided as shown in Figs. 3 and 4. These can beobtained controlling the modification of thetopology of pinion-gear tooth surfaces in thelongitudinal and profile directions.
The influence of the crossing angle /1"{ isshown for the above data in Fig. 5.
The results of the investigation how thatthe almo t linear function of transmissionerrors caused by misalignment of conventionalinvolute helical surfaces (shownin Fig. 5) isindeed absorbed by the parabolic type oftransmission error. for the modified surface( ee Fig. 6).
The major axis of the contact ellip e, underan assumed light load, has been determined asshown in Figs. 3 and 4. The undesirabledisplacement of the path of contact to thebottom and the top of the gear tooth can becontrolled by the modification of the surface ofthe grinding wheel for the pinion generation.
ConclusionThe conclusions of this study ar,eas
foUows:l . A TCA program for simulation of
meshing and contact of conventional involutehellcal gear has been developed. Thilsprogram has shown that such gears are verysensitive to angular mi alignment, and highvibration is inevitable.
2. A new topology of helical gear toozhsurfaces has been developed. Methods forgrinding tooth surface have been developed.The bearing contact of gears with the proposedtopology is localized and the transmission Fig. 6. lnDllen eofmi aUg.nmen~.ontr-allSmissio.nerron(Al;;;-5·) ..
70
0- 50Q)
~..<.J<ec:~ 30....0J:::
UJc0.~ 10'"·s<IIa..
1-< -10
5535 75Angle of Rotation of Pinion (in deg.)
Fig. 5. InRuence of misali,gnment ,on lransmissio[l errors I(Ay = .5').
0
0-0)
'?tl -10.,2-...~
-20wt::0
'Vi.~EOIl0::o:f...
Angle of1-<Rotation of
-40 Pinion
-5 15 35 55 75 (in deg.)
JANUARY/FEBRUARV 1994 33
Of eour e, gear withouta common axiintersecting plane exist. The axes oflhese so-called hypoid gears cross each othersomewhere in. space. The name is derivedfrom the mating of two exact hyperboleids, 0
even gears with extremely small cone anglesare. by definition, bevel gears.
Gear box manufacturers (Refs. l -3)increa ing],y tum to cylindrical gear grindingmachines to grind pur and helical bevelgears withrnall cone angles. Most of the egears have cone angles of approximately ,5 =5<>.The reason for this is that there arccurrently no bevel gear grinding machines onthe market that can grind spur and helicalbevel gears. Even if there were, it would beimpossible to grind bevel gears with smallcone angles. as described above because ofthe extremely long middle cone di tance Rm(middle radius' of the crown gear, Fig. I.).Thi can reach length up to two meters andeven more. Rm ~ one of the setting axes on aconventional bevel. gear grinding machine,but such high numerical values Lieour ide theoperating range of these machines. Therefore,it is appropriate to move the grinding of suchgears to cylindrical gear grinding machines.The cone di ranee is of 110 significance onthese machines, and the grinding wheel ismoved along the cone envelope.
There are four prineipal solutions forsolving this problem (see Fig. 2):
Grinding Bevel Gearson Cylindrical GearGrinding Machines
Werner !KiessHo:fl!er Maschinelnba,u GmbH. Ettl'ingen, 'G'er:many
Power train designs which employ gearswith cone angles of approximately 2° to 5°have become quite common. It is difficult, if110t impossible. to grind these gears onconventional bevel gear grinding machines.Cylindrical gear grinding machines are bettersuited for this ta k. This article will providean overview of thi option and brieflyintroduce four grinding variation possibilities.
ID]N 868 define bevel gears as gearswhose reference surface, circular cone andaxes have a common point of intersection.Gears with a very sm~1I1cone also have acommon axial intersecting plane.
P crown gearMp crown gear centerRnl middle cone distanceTK pitch cone
o cone angle
fig. 1 - The relationship of th.econe all Ie to middl.e cone distance.
'34 GEAR TECHNOLOGV
(I) (IV)
0'J. I I,I .-, . I
'v I-f+'
(In)
(! I~! III •
III
s
v direction of the addition motionz stroke directionEK generating coneEZ generating cylinderS template
Fig:" .1; - Four possibilities forgrinciing beve~gears on: a cylindrical gear grinding machine.
I. he gear grinding machine is inclined to(he workpiece's cone angle.
II. The bevel gear axis Is inclined to itsown cone angle. When thi solution i used, akinematic error automaticallycccurs becausethe workpiece's generating motion isproduced by the machine table. However, thiserror can be calculated in advance and can beeliminated through numerically controlledmachine table correction movements.
In. A template, which corresponds to theworkpiece cone angle 0, is mounted on thegrinding lide carrier. The resulting additional,g,rinding wheel motion perpendicular to thetroke is produced bya tracing system which
translates the template form into the trokemovement, This is the arne proce s that isused to crown a cylindrical gear tooth,
IV. Numerically controlled actuator driventool slide eliminate the nece ity of thetemplate de cribed in Solution In above. Thenumeri cal control Lake over the ta k ofcoordinating the additional forward orperpendicular tool motion.
How do the e solutions differ from oneanother? When grinding cylindrical gear. thedouble troke and generating speed must 'becoordinated with the stroke lengthand othervariables. For Solutions I and Il. I.hicoordination is the same a for cylindricalgears. However, the double stroke speed must'be reduced by about. 20-40% in compari on tothe cylindrical gear ca e for Solutions In and[V. The reason for this i the additional
grinding wheel motion. perpendicular to the"normal" stroke ruction. As the cone angledecreases. the time loss in comparison tocylindrical gear grinding decrea es as well.
For this reason, Solution WVisthepreferredvariation fOF bevel gears with cone angles of li~ 50. Solution U i preferred for cone angleof more than 50. To achieve the desiredprecision, it is easier to realize a lower, ratherthan a faster motion with help of numericalcontrols. Solutions J and Uli can be consideredoutdated because of the additional necessity ofmechanical modifications.
However, one other consideration plays animportant rote in grinding bevel gears oncylindtical gear grinders: The principaldifference in how the involute is created ineach of the above described examples. InSolutions I, m and ]V, the generating pitchcylinder is used as a basis for generation. Itsdiameter remain constant throughout theface width of the gear. [1'1 connection with thegrindirrg wheel. the 'base cylinder alsoremains con tant. Consequently. bevel gearsground in this manner can 'be viewed as astack of cylindrical gears with displacedprofiles and infinitely mal] face widths. Theprofile displacement is not cunstant, butchanges infinitely along the tooth face width.That means that al! these infinitely thincylindrical gear plates use the same involuteas the tooth flank. Only the utilized sectionwanders (Fig. 3).
Involutes produced in this manner are
Or.-lnQ!. WernerKiessis tile head of the qualifyassurance department atHofler Ma~'ch;nenballGmbl], Eulingen, Ger-many. Prior 10 his workat Hofler. Dr. Kiessworked ill the gearmanufacturing depart-men/ of the MochineTool Research Center if)Chemnil;. Gem)fU!),.
JA'NUAAYIF.EBRUARV '994 351
vEZ
[[
m
base cylinder diametergenerating cylinder diameterinvolute
Fig. 3 - P:rofi.le dlsplaeement by bevel gear ;grinding.
N
M
M instantaneous axisN normal plane
Fig..4- Common surface line of mated bevel gea.:rs..
36 GEAR TECHNOLOGY
present in the transverse section because ofthe utilized generating cylinder. But whentwo bevel gears are paired, the commonsurface line is simultaneously the in-stanraneousaxis M (Fjg..4). In the plane inwhich the instantaneous axis is in a verticalposition (perpendicular plane N), no involuteflank rolls with another. At best, theinvolutes are distorted.
Contrary to this, involutes are createdwhen rolled with the generating pitch bevel inthe perpendicular plane on which theinstantaneous axis is in a vertical position.Solution II is the best suited example forbeveJ gears with cone angles 0 > 5° orgeometrically exact bevel gears .. Whencreating the involute with the generating pitchcone, the crown gear is the reference elementfor the layout as well as tile production of thetooth system.
A considerable number of spur andhelical bevel gears have been ground 01'1
Nova CNC cyHndricalgear grindmgmachines using Solution IV. The directionof the pointed end of the cone (up or down)was not important. near body geometryand/or the available mounting fixture werethe determining factors. In each case, bevelgears wi th c one angle s fro m 20 to 50achieved quality levels of (IV) and (In) illaccordance with DIN 3962 .•
References:I. Firrnenschrift der Zahnradfabrik Friedrichshafen AG.
Diesel & Gas Turbine Catalog 57 (1992).
Friedrichshafen, 1992.
2. Rothenhausler (Zahnradfabrik Frledrlchshafen AF);
"Getriebe fUr ch nelle und unkonventionelle Schiffe." TU
Harnburg-Harburg, 14. bis 16. October, 1.992.
3. Beam, A.B. "Beveloid Gearing." Machine Design.
December, 1954.
Acknowledgements:
All illustrations courtesy of Hofler, Ettlingen, G.ermQlry.
This article firs: appeared in GerlllQlI in Werkstau und
Betrieb 126 (1993) 7, pp. 409-410. II also appeared illEuropean Production Engineering, Sept, 1993.
Reproduced with permission.
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:38 GEAR TECHNO~OGY
The Gear HobbingProcess
Dennis ,GimpertK'oepfer America Limited Partnership"
South Elgin.IL
ear hobbing is a generating proces .The term generating refers to the factthat the gear tooth form cut is lIotlllcconjugate form of the cutting tool,lhe
hob. During hobbing both the hob and theworkpiece rotate ill a continuous rotational.relationship. [)uring this rotation, the hob itypically fed axiaUy withall the teeth beinggradually formed as the tool traverses the workface (see Fig. Ia).
FOIl" a spur gear being cut with a single starthob, the workpiece will advance one tooth foreach revolution of the cutter. Wilen bobbing atwenty-tooth gear" the hob will rotate twentytimes, while the workpiece will rotate once.The profile is formed by the equally spacedcutting edgesaroundthe hob, each taking sue-
cessive cuts on the workpiece, with the work-piece ,in a slightly different po ition for eachcut (see Fig. Ib). Several cutting edge of thetool will be cutting at the arne time.
The hob is basically a wonn with gashes.CUi axially across it to produce these cuttingedges. Each cutting tooth is also relievedradially to provide chip clearance behind thecutting edge. This also allowsthe hob face tobe sharpened and still maintain the originaltooth shape. The final profile of the tooth j
created by a number of flats blending togeth-er. The number of flats corresponds to thenumber of cutting gashes which pass theworkpiece tooth during a single rotation.Thus, the greater the number of gashes in thehob, thegreater the number of flats along the
18fig.l a & b
1b:
~.15J"DP
"Fine Pitch is
Length
Active Length
- ---
Filg. 2
profile which improves the "smoothness" ofthe tooth profile.
The CutterBobbing is a generating process, and the
hob win not cut the same shape as the cuttingtool form, An unmodified involute gear toothis produced by .<11 hob with straight-sided cut-ting edges. Involete gear cutting is the largestapplication of bobbing (Fig. 2). In contrast, astraight-sided spline tooth is produced by a hobwith curved cutting edges (see Fig. 3).
Cutter ModificationsIt is possible to design the shape of a cutting
tool to produce modified tooth forms. Theseare done for various reasons. The hob toothroot can be designed to cut the outside diame-ter of the gear tooth. With this "topping" hob,the tooth involute and the outside diameter ofthe blank will be hobbed in one operation (Fig.4). This may eliminate finish turning of thegear blank, reducing machine operations.
The outside diameter of the gear will beconcentric with the operating pitch diameter ofthe gear. This win provide a locating surfacefor subsequent operations and a method ofmea uring size.
Sharp corners between the tooth flank: andoutside diameter can be eliminated with a"semi-topping" or "tip chamfering" hob (seeFig. 5). With proper design such a hob mayalso correct the problem of gear tooth bendingunder load,
Gears which will be finished by a subse-quent operation, such as skiving, shaving orgrinding, may require clearance in the geartooth fillet area for the finishing tool. This canbe cut using a "protuberance" hob. which will
-
Fig. 3
Whole Depthof Cut
tTopping
Fig.4
Gear Toolh
Fig. 5
Dennis G,imp'eirtis rile pre idem ofKoepfer Amuletl LimitedPartnership ill SouthElgin, IL. He is theauthor of several articleson gearing subjects.
JANUARVIFEBRUARY1994 39
F. IIg.6 I
Shaved'
Paint ofIntersection of
Pre-ShavedProlilawlth
Undercut
Lowest Point01 Contact
./" with MatingGear
~ Greater ~\--_.....,than-
Shaving Stock(Depends
upon DiarnetralPitch)
Root Fillet AsGenerated byPre-ShavingHob
fig.7- -
Index Worm Gear (R.H.)
DifferentialChange Gears
Speed Change Gears- --
Fig. 8
Mechanical Vertical Hobblng Machine
Fig.9
40 GEAF\ TECHNOLOGY
produce undercut (see Fig. 6).. The protuber-ance hob is designed to provide a uniformstock for the finishing tool and to provide ablend between the bobbed root area and thefinished flank. Caution: On any modified cut-ter, we are changing the correct rack shape.Thus, the tool may cut only a certain range ofgear teeth numbers correctly (Fig. 7).
The Gear Hobbingl MachineA gear bobbillg machine consists of five
common elements:• A work spindle to rotate the work.• A hob spindle to rotate the hob.o A means of rotating the work spindle and
hob spindle with a constant of ratio, dependingon the number of teeth in the workpiece amithe number of threads ill the hob.
'. A means of traversing the curnag too!across the face of the work in the direction ofthe work axis for spur and helical gears.
• A means of adjusting the center distanceof the work and the hobs for different sizeworkpieces, Figs. 8- W show schematics forthree typical bobbing machines.
Hobbing FeedDuring bobbing, the cutting tool can be fed
in a manner similar to' a milling machine; bothconventional and climb bobbing are used (seeFig. 11). A general rule of thumb is that climbhobbing yields better tool life, and!convention-al hobbing yields a better finish, In all. cases,the cutting force should be directed against the
work spindle, never against the tailstock.The directions of feed on a hobbing
machine correspond to the work axis .. Thus,three feeds are possible - axial, radial andtangential (Figs. 12a, b, c).
It is also possible to combine more than oneaxis of feed sequentially or simultaneouslyduring the machine cycle, A radial feedapproach followed by axial feed across theface is very typi:calin fine pitch gear work oron a workpiece where an open axial approachis not possible (Fig. 13).
Axial and tangenti,ai feed are used imulta-neously for several purposes on very large,coarse pitch, wide-faced gears. The tangentialfeed presents a. sharp portion of the tool as theaxial feed cuts across the gear face (Fig .. 14).
Taper root splines are cut with simultaneousaxial and tangenti .al feed (Fig. I5).
A "jump" or "skip" cycle is used. to cut rnul-
Radial, Feed
DriveMotor
Axial FeedConventional
Climb Feed Conventional Feedl
~- :
t
Fig. 11
Tang.enlial Feed Used for Worm Wheel Generation
1994 41Fig.12c
t Radial Feed
Radial Feed Approach with Axiall Feed
JANUARY/FEBRUARY
Axial and Tangential Feed--
Fig. 14
Taper Root Hob Taper Root Spline
Fig. 15
Jump Cycle
Tapered Gear Crowned Gear
42Fig. 11
GEAR TECHNOLOGY
tip le gear elements o.n a single part. This maybe required for gear tooth alignment or simplecutting efficiency (See Fig. 16).
Tapered gears or crowned gears are pro-duced with simultaneous radial and axial feed(Fig. 17).
At the beginning of the hobbing machinecycle, the cutter will not. be generating the fulldepth of the gear tooth form. Only a small cutis made by each tooth in the hob graduallyfeeding into the part. This is known as the"approach" portion of the hobbi ng cycle. It ispossible to utilize a different feed rate duringthis approaeh Iength with a reduction in cycletime (Fig. 18).
During the hob bing of some gears orsplines, the cutter win not feed completelythrough the workpiece face ..This is known as a"blind" cut. To complete all of the teeth evenlyaround the circumference of the gear, "dwell"is utilized. During dwell the hob and work-piece continue to rotate ill a timed relationshipfor one or two more work revolutions, hutwithout feed (Fig. 19).
Multilple, Start HollsThe hob is a series of racks positioned
around the circumference of a cylindrical tool.Each successive rack is shifted axially to createa worm, typically a single thread. Thus, foreach revolution of a single start hob, the gearmust advance one tooth space (see Fig. 20).This is accomplished by the bobbing machinekinematic indexing system.
At this point, it is important to understandwhat causes the cutting marks on a hob bedgear. The marks axially across the face of tinegear wiH carre pond directly with the axialfeed per work: revolution of the tool. Themarks positioned across the profile of the gea.rwill correspond directly with the number ofgashes or flutes on the hob (Fig. 2 O. Normallyit is not possible to see the generating flatsalongthe profile of the material.
It is possible to increase the speed of thehobbing operation by utilizing a hob with morethan one thread. or example, if the hob hastwo threads, the gear must advance two toothspaces for each revolution of that hob. Thiswill double the speed of the work and doublethe production. an other factors being equal(Fig. 22). With four threads in the hob, fourteeth on the part will index with every revolu-
lion of the cutter. However, there are factorthat limit. or prevent the use of multiple startshob for all ca e .
The HobAs more and more threads are designed into
the tool, the lead of the thread will increase.Normally. a thread lead angle of 2-60 will beacceptable. Beyondix degrees, the :Ieft andright side of the cutting tooth will be loadedunequally, which will cause poor tool life. Tocompensate fo£, !:his pmb.lem, ,!he diameter of'the [001 can be increa ed slightly. but. with areduction in RPM to maintain the arne SFM.Alternanvely, the gash of the hob can be madehelical to position the cutting tooth perpendicu-lar to the cutting action.
To calculate the thread angle of a hob. 1.1 ethe following formula:
Tan a = Thread in HobDP x Hob Diameter
Example:
Tan a=_]_20x.2
Tan ,a = .025
a= 1° 2S' 56"
Another problem with multiple thread hobsis the number of effective gashe generatinglbe profile, Again. all factor being equal. atwo-start hob with twelve gashe will generatethe gear profile with six of the gashes ver usasingle-start hob with twelve gashe .
The Ho'bbing Macbine,As the number of threads in the tool
increa e , the work will index. faster. Thismeans that. the work pindle of the bobbingmachine must be able to rotate at higherspeed . On workpieces with high numbers ofteeth. the machine peed is not aproblem, butfor gears with a low number of teeth. the hob-bing machine mu t be designed correctly.
Several machine design solutions are used.For traditional worms and worm wheel workspmdle drives. a multiple- uart worm andworm wheel can be u ed. Four, eight and morethread worms are common. Another approachis to utilize a helical gear index system. Bothsy terns work effectively in providing a mod-
Fig. 118
fig. 19
Height ofFeed Mar1<s
1i
Feed Marks froml Hobbing
---
Fig. 21
JANUARYJFEIIRU"RY laa. 43:
on. e HO.b Re..v.oru.tion. W. A.S .M.any w.ork TeethAdvances the Work As There Areby . . . Threads on the .
• . Hob ('In This ., . Instance, .2).
CuI in Same time
Double-Start Hob Single-Start Hob
Mark of Enveloping Cut
Fig. 22
Pitch
1'-:;f1
Tooth Spacing Inspection Chart Showing Hob Errorfrom Even Ratio -
Fig. 23
Cut with .Double-StartHobEven ,Ratio
C1Jtwith Double-StartHobHunting Ratio
Fig. 24
I· , . II•• I,
Lead Inspection Chart Showing: Hob Error fromHunting Ratio
Fig. 25
GEAR TECHfoiOLOGY
em high-speed bobbing machine.Another consideration for the bobbing
machine is the cutting capacity. As multiple-start hobs are used, the metal removal rateincreases. If a subsequent finishing operation isused, such as shaving. rolling or grinding, it ispractical to use much higher feed rates than usedin finish hobbing. These feed rates can approachthe maximum cutting capacity of a machine.Although the actual horsepower used in the hob-bing operation is a small percentage of that usedto drive the machine itself, the "effective" powerof the machine must be considered. This effec-tive power includes horsepower, rigidity, fixmr-ing, maintenance. condition, etc.
l1hread Spacing IErrorsThe multi-start hob will have manufactur-
ing errors between the threads: in other words,the threads will not be in the correct position.This thread spacing error mayor may not havean influence on the gear cut
There are three possible conditions betweenthe number of teeth in the part and the numberof threads in the hob. First, an even ratio, suchas a 2-starl hob cutter and a 22-tooth gear (seeFig 20). to this case, one thread will cut theeven teeth, and one thread will cut the oddteeth. Thus, all of the thread-to-thread errorwill be seen in the tooth-to-tooth spacing. butnot in the lead inspection (see Fig. 23).
The second condition occurs when certainthreads of the hob will cut certain teeth, suchas a 4-start bob cutting the same 22-tooth gear(Fig. 24a).
The final condition occurs when all threadscut all the teeth. This is the most ideal condi-tion, as the thread-to-thread errors become dis-tributed among all the gear teeth and "cancel"each other out. This is known as a huntingratio (See Fig. 24b). This occurs when a 4-starthob cuts a 21-ttooth gea.r. Thethread-to-threadhob spacing errors are not seen in the tooth-to-tooth spacing, but will be seen in the leadinspection (Fig. 25).
It is possible to purchase cutnng 'tools withimproved thread-to-thread spacing .• 1
Acknowledgement; Reprinted with permission of IheAmerican Gear Manufacturers Association. The opinions.statements and conclusions presented in this article arethose of me Author and ill no way represent the position oropinion of the AMERiCAN GEAR MANUFACTURERSASSOCIATION.
Cutting Worm Gearswith Standard Gear Hobs
We m.akea lot IOf single-startworm and worm gear sets, and italways seems as thQugh we're buy-ing a.nQther special bob. We alsodoa lot of spur gear cutting, andthe spur gear hobs and the wormgear hobs look alike, SQ we wonderwby we cannot use the standardhobs for cutting worm gears tDO.
Can we do this?Bill Janninck replies: Yes, you
can. We will explain how in amoment, but we would suggest youfirst look into the catalog worm gear
Since the hand ofthe worm and the
hand of the hob mustbe the same, you
have a betterchance of finding a
stock hob for a right-handed application,because more right-handed stock hobs
are available.
Wililiam L. Janninc~k
hobs carried in stock and try to usethem as well as your own supply ofworm gear hobs whenever possible.
There are some di fferencesbetween worm gear hobs and spurgear hobs which must be taken intoconsideration when using a spur gearhob to cut a worm gear.
Single -start worms, as well asthose with multiple starts, can be ofright- or left-hand configuration.Since it is imperative that the hand ofthe worm and the hand of the hob bethe same, the chances of finding astock: hob are better for right-handedapplications because there are manymore right-handed standard stockhobs available than left-handed ones.
Worm gear designers traditionallyhave used standardized axialpitchdimensions for both the worm andgear, usually using fractional inches.The worm may have. for example,112" or .5000 axial pitch, and themating gear, for the typical rightangle or 900 axis angle, will have a5000 transverse circular pitch .. Thisdoes make it easier to establish gearand worm specifications, includingcenter distance, but there is no rea-
, :
: : son that the design cannot start withspecifications located in the normalplane and based on the normaldiarnetral pitch or normal circularpitch. A lODP gear hob, for example,
Address your giearing ques-tionsto our panel 0,1'experts.Wr,ite to them eare 01 ShopFloor. IG~earTechno,logy, P. O.Box 142,6, Elk IOrov,eVmage,IL 60009, or calli GUlr ,editorialstaff at (708),437-6604.
William LJanninckis a gear and tool designconsultant. He worked ingear manufacturing for 45years, 40 of them withIllinois Tools - 1rw . lnc.,and is the author offlumerous articles ongear· related topics.
J ....NUARV/FEBRU ...RV 1994 ,45
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46 GEAR TECHNOLOGY
When a stock hobis used as the basis
for your design,you must develop
worm specs basedon the hob
dimensions and com..plete the rest of the
design basedon the worm.
has a normal circular pitch of .31.416,and the design would have to bedeveloped around this normal planedatava different approach from theusual. procedure.
In a traditional design, the WOrmand gear set are fully specified withgear ratio, lead angle and worm andgear dimensions. Then a hob is pro-cured to suit the worm specifications.When an in-hand stock gear hob isusee! as the basis, you must developWorm specifications based on the hobdimensions and then complete the restof the design based on that wonn ..
A sample case might offer thebest explanajion. A standard 2-3/4"diameter gear hob would be marked:
WNDP 20NPA l-RH LA 2° f6'.2157 WD
The normal circular pitch NCP =rrJNDP = .31416. The actual outsidediameter of the hob measured is2.730. The hob pitch diameter wouldbe 2.730 - 2 x .U57 = 2.499. (.1157is the standard hob addendum for.2157 whole depth.)
2.418 + 2 x ,100 = 2.618. (JOO is thestandard addendum for .2157WD).The sine of the worm lead angle isNCPt(2.418 x rt), so the worm leadangle e 20
, 22'. The worm lead andaxial pitch are NCP/(cosine wormlead angle) = .3144. The worm nor-mal pressure angle is the same as thehob and is 20°. The worm threadthickness at the pitch lineis one halfof the normal circular pitch, minusome allowance for backlash. The
whole depth of the worm is asmarked on the hob and is .2157. Thisprovides enough data so that a wormcan be made that is suitable to theabove gear hob.
As with a regular worm gear hob,this hob can be I1Sed to cut any eurn-ber of teeth on the gear from 16 up,without causing natural undercut. Inour sample case, if we need a 40-tooth worm gear, its pitch diameter is(40 x .3144)ht = 4.003. The throatdiameter would be 4.003 + 2 x .100= 4.203. The center distance wouldbe the sum of worm and gear pitchradii - in this case, 3.210.
If tbe center distance for the setmust match some existing or presetdimension, it may be possible tospread or close the dimension andthen cut the worm gear oversize orundersize to suit, There is 110 impleformula to calculate how much toallow, but on our 40-tooth examplethe center distance could be variedapproximately ± .157 x NCP; that is,from 3.161 to 3.259.
There is some further flexibilityin the amount the center distance canbe altered, and for our 40-tooth gear,if the centers are closed by .314 xNCP, the worm gear pitch diameterwill coincide with the gear throat
The suggested hob diameter over- diameter, resulting in what the tradesize between the worm and hob,which will give about 30% gear facecontact, is 0.10' x .31416 (NCP) +,050 and is .081. Worm pitch diame-ter is then set at 2.499 - .081 = 2.4.18,and the worm outside diameter is
calls an all-recess-action worm gearset. Unless you are familiar with thisdesign of worm gearing, going to thisextreme is not recommended.
Another detail to be resolved isthat most all worm gear hobs are
made in a topping configuration sothe throat radius is swept out ormachined during the tooth bobbingoperation. Most spur gear hobs arenon-topping, meaning that they donot cut or touch the gear outsidediameter. In preparing a gear blank:then. the throat diameter and thesweep radius will have to bemachined as a turning operation.
We have had success using thisprocedure in a number of situations.One case was with the replacementof a gear set on an emergency basisfor an important section of a pro-duction machine. The steel wormwas salvageable, but the bronze gearwas completely worn away, result-lngin tooth breakage. The wormgear had a long lead time for anoriginal equipment replacement. themachine was foreign-built and thegear set was dimensioned in met-
---
SH'OP FLO'ORMost spur gear hobsdo not cut the gearoutside diameter;therefore, when
preparing a wormgear using such a
hob, the throat diam-eter and the sweepradius will have tobe machined as aturning operation.
des. A common replacement et,including both worm and gear, weremade using an available stock gearhob, meeting the required ratio andcenter distance .•
-._Jt -d ®.KODJWOrII
"THE FIRST NAME" IN GEARMACHINE & TESTING ARBORS
• PROVEN QUALITY
• SHORT DEUVERY TlME• SERVICE IN THE U. S.• DESIGN FOR ACCURACY
AND PERFORMANCE
• COMPETITIVE PRICE
I
KONIGMain-Tauber- Maschinenbau GmbH
Am StammholzD-978i1 Wertheim
GermanyPhone: 01149/93421876-14
IFax: 01149/93421876-25
Bourln & Koch 'CBN F'orlmGrinder
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SERVICE
IConto,ur InductionHardening S::pe,cialisls,
Spur, helical ,arrd beve,' gears()ur gear hardening equipmentincludes 3 NATCO submergedprocess machines and 4 AJAXeNe-controlled gea.r scanningmachines. We can aliso tool tomeet any pruductlon need.Write for a free brochure.
A_merican Metal Treatingl Company1(143:East 62nd StreetCleveland,OH 44103
(216,'4311-4492Fax; (216) 431-11508
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GEAR TOOTHGRINDIING SERVICES
'. Cost eff,ective geart'ooth grindingspecialists
• Gear manufacturers are our onlvcustomers
.' Prototype and production quantities• ' Capacity to 27.5' P.D., 3.5 D. P..' Able to match dehvery to your
requirements• All service to' AGMA standards with
Certified Gear Inspection IEquipment
PRO-GEAR COMPANY, INC.23 Dick Road Depew, NY 14043
Phone (716),684-3811Fax (716) 684-7717
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KLINGELNBERGHOB SHARPENERS
• Remanafacturing/Re building• Programmable Control Retrofits
I
• Updated Hydraulic Systems ,
•.Field Service Repairs
GEAR INSPECTION EQUIPMENT• Calibration/Certification
• Field Service Repairs ,
PRODUCTION HOB SHARPENINGELTECHlne. IQ~~'9841 York Alpha DriveN. Royallon, ON 44133Phone: (216) 582-8195Fax: (216) 582-8226
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EXPERT PRECISION "' 'New Design Updates
100% Satisfaction GuaranteedCOMPLEJE. f,IEUli S(,RVltE
Ca'librationand Certification ContractsHecorder Updates and Retrofits
Major Field Repa,irslParts and Su. . s
Gear Composite Computer AnalYSingAva·flable with Rebuilds on Fellows
Model #4FPRL Gear Redliners.- IPmfile Engineering', Inc.
-=-G IF I IOO.Riv~rStreet .
~q.;. :=ttA,ljr( Springfield, VT 05156
1'1, ,,~-.._ 1802) 885-9176..... ~( ~"" •• FAX (802) 885·.3745
To Advertise' in this section ofIGEAR TECHNOLOGY
ca II 708-437-6604.Rates: Line Classified - 537.50 per line. 8 line per inch. $300 minimum. Classified Display - per inch(3" min.): IX - $170. JX - $1.60. ,i5X- $150. Type will be set lO advertiser's rayoul. or GearTechnology will set type at no extra charge. .Paymenr: Full payment must accompany classified lid . Send check or Visa/MaslcrCuJd/AmericanExpress number and expiration date to: Gt(U Techftrl/tJ8Y. P. 0, Box.1426. Elk Grove ViIIs.ge. It 1iOOO9.Agfncy Cemmlsslom No agency cornrni sian on classifieds. bterials l1eadline:: Ads must be recei vcdby the 25lh of the month. two months prior to publication .. Aeceptances Publisher reserves the right toaccept or reject classified advertisements ot his discretion. .
48 GEAR TECHNOLOGY
• Hard broaching: gears.up to Rock-C-58-62:
• High-speed broachinqup to 1.20 t.o.m.
• Automatic broach sharpening
Str,athmore lMachineToo~ Company
176 East Main StreetWestborough, MA 01581-1706
Tel: (508)898-9490Fax: (508) 898-9495
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REPS V\rANTED
Box OTP. O. Box 1426
Gear TechnologyElk Grove Village, u, 6OO()Q
REPS WANTEDSales representatives wanted for majorgear machine 1001 (parallel axis, as well as'bevel gear) and CUlling 1.001 importer.Variou areas are open in the oiledStates, Mexico and Canada .
We are looking for professional organiza-tions or indi viduals with gear and salesexperience .. Highly motivated sales back-ground necessary.
GEAR P OPLE ONLY NEED AfPLY!!
Please apply in writing with:• CJV - resume. if individual.• Brochures and relevant information.
if company.
I-IELP WANTED'
PLAN _ IJPERENTENDE T: S50.001l. 300Hourly. _ENGIINEERING MANAGER: 60,000. EnclosedGear Boxe . Supervise 4 in Design of Helical. Spurand Parallel Gears,ALES NGI EER; $55,000. Gear Boxes'8· AUT\! E GINEER: S4U.OOO.ontact: Ann Hunsucker. Excel Associates. P. O.
Box 520 Cordova. TN 33038 or call (90 I) 757-9600 or Fux (901) 754-2896.
.ADV. --OIRIIAL
NEW PC·-BA,SED 'CNC GEAR INSPECTlONSYSTEM HAS· FULL 4-AXI,S 'CAPABILITYThe PC-based QC 1000 CNCgear inspection system
from M&M Precision Systems Corporation can do thework of several manual units by performing fast, repeat-able and highly accurate index, lead and profile tests ofinternal and external spur and helical gears and splines ..
This affordable and easily installed system is the onlyone in its pric-e range to offer full 4-axis CNC gear in-spection capability an work pieces up to 15" long and 9"in diameter, weighing up to 50 pounds.
Other significant features of the QC 1000 includeAGMA or DIN analysis, 0'-90° helix angle, up to 711 facewidth and diametral pitch of 4 to 64. It focuses on appli-cations for gear manufacturers and job shops who needthe accuracy and information of a fun 4-axis, generative,analytical gear inspection system, but whose budgetsrequire a simple, low cost alternative.
An Acme-Cleveland company, M&M sells more uni-versal CNC gear inspection systems in the UnitedStates than all its competitors combined .. Since develop-ing the workl's first CNC controlled analytical gear in-spection system in 19'75,. the company has created acomplete line of operator-friendly systems featuring fullyautomatic test routines, plus modular inspection andanalysis software programs that have made M&M sys-tems the accepted industry standard throughout the U.S.
Founded in 1951 as a die, fixture and gage manufac-turer, M&M first became nationally known as a majorsource for rotary and linear positioning systems in 1969 .Originally it was M&M's precision motion products thatled gear manufacturers to approach the company withtheir gear inspection requirements. The positioning sys-tems product line is still a major part of M&M's busi-ness today and contributes to ongoing improvements intheir gear inspection capabilities.
Other M&M products include master gears, splinegages and double-flank gear roll testers, as well as sys-tem upgrade packages for both manual and direct com-putercontrolled coordinate measuring machines .. t9'841sacquisition of Spline Gauges, Ltd. of Birmingham, UKadded functional gear and spline gage testing products.
The Soft Mic.® CMM system upgrade package is auniversal PC-based retrofit product tor manual CMMs.This DCC/DMIS product provides users of outdatedautomatic and joy-stick operated CMMs with a newDMIS-based operating software package in a 3- oroptional 4-axis servocontroller,
M&M products serve industries such as aerospace,agricultural. appliances, automotive, machine tool,military and off-highway vehicles throughout the world,aided by facilities in England, France and Germany,
QC 1.000 is an affordable gear inspection. syst.em
i ,.M&M !:,REels'c,N_ SYSTEMS CorporatIOn
"THE METROLOGY AND MOTION PWPlE'
M&M Precision Systems CorporarionWorld Headquarters300 Progress RoadWest Carrollton, OH 45449Phone: (513) 859-8273Fax: (513) 859-4452Contacts:James Helton, PresidentDouglas Beerck, Marketing ManagerMetrology .and Motion SystemsWaIter Lake, Sales ManagerGear Metrology SystemsBrian Slone, Sales ManagerFunctional Gear Testing Products
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GEARING THE WORLD FOR TOMORR,OWAn industry leader i.ng,ell.r-.making maebines and tools.
