1、11FTM01AGMA Technical PaperA New Way of Face GearManufacturingBy H.J. Stadtfeld, The GleasonWorksA New Way of Face Gear ManufacturingDr. Hermann J. Stadtfeld, The Gleason WorksThe statements and opinions contained herein are those of the author and should not be construed as anofficial action or opi
2、nion of the American Gear Manufacturers Association.AbstractFace gears have been discussed for many years. Almost every industry tried to find and realizeapplicationsfor face gears. There are two major intentions to apply face gears in power transmissions:- The advantage to be able to use a cylindri
3、cal gear as a pinion member.- Particular design solutions which require a plurality of cylindrical driving members e.g., in a propulsionsystem.While the automotive and truck industry conducted substantial research in the application of face gearsystemsintheirdrivetrains,theresultsdidnotfavorfacegear
4、sversusbevelandhypoidgears.Inmanycases,thefacegearsystemwasfoundthelesseconomicalsolution.Although,atfirstitseemstheopposite,sincethedrivingpinioninafacegearunitcanbeproducedmorecosteffectivethenabevelpinion,themanufacturingofthefacegearitselfwasexpensive.Machinetoolsrequireaspecialdesignandarenotre
5、adilyavailableandthecutting tools have to be designed specifically for the particular face gear design.Theobstacleswhichpreventedmanufacturersinthepasttoapplyfacegearswereremovedentirely,whentheBevel Gear Technology Group at The Gleason Works invented a new way of forming the profile of face geartee
6、th,usingstandardbevelgearcuttingandgrindingmachinesaswellasstandardcutterheads.Theideaisbased on the tools used in straight bevel gear cutting and grinding according to the CONIFLEX method,however, using a generating gear which is not flat like it is for straight bevel gears but cylindrical, resembl
7、ingthe mating cylindrical pinion for the particular face gear design.The complexity of modified cylindrical hobbing and shaping machines and job dependent custom toolingdisappears completely with the new CONIFACEtcutting and grinding process.Inthemeantimeanumberofsuccessfulfacegeardevelopmentsfrompo
8、wertooltransmissionviaautomotiveapplications to aircraft components have been manufactured and being tested. The breakthrough of theCONIFACE system is based not only on the standard equipment for manufacturing but based to the sameextend on the availability of software tools for tooth contact analys
9、is flank form optimization, coordinatemeasurementandclosedloopcorrections.Alsosummariesforsharpeningofthecuttingbladesandthesetupof cutting and grinding machines are available and tested.Copyright 2011American Gear Manufacturers Association1001 N. Fairfax Street, 5thFloorAlexandria, Virginia 22314Oc
10、tober 2011ISBN: 1-978-61481-000-13 11FTM01A New Way of Face Gear ManufacturingDr. Hermann J. Stadtfeld, The Gleason WorksIntroductionFace gears are plane ring gears (face angle = 90) which mate with spur or helical pinions. Such a face gearpair transmits motion and torque between two shafts which in
11、tersect at an angle of 90 (Figure 1, left). Theaxes of pinion and gear intersect in the most common cases in the crossing point or they dont intersect buthave a certain distance (offset) between them.The expanded definition of face gears , commonly used today covers all angular transmissions, where
12、a“special ring gear” meshes with a cylindrical pinion in a non-parallel axis arrangement. Figure 2 for exampleshowsatthebottomafacegearwitha15faceangleinmesh witha cylindricalpinion. The shaftangle ofthisarrangement is 165.The broader definition of face gears covers also the conical gear in Figure 2
13、 but it presents the separation tobevelgearsontheonehandandtobeveledcylindricalgearsontheotherhand. Althoughatfirstitappearsananachronism, it has to be pointed out that in fact in every angular transmission which consists of a truecylindricalpinionandagearwhichresultsfromtherollconditionswiththatpin
14、iontheinitialconjugategearhasa very typical flank form with a surface characteristic which is influenced only by the pinion and the shaftangle. 1Common manufacturing methodsThe generating gear of each face gear is always the mating cylindrical pinion. Cylindrical pinions aregenerated with a simple g
15、enerating rack. The flank profiles of the resulting pinions are involutes. Thecomplexity of manufacturing face gears is based solely on the fact that no simple generating gear can befound. First the trapezoidal rack generates the more complex involute(on thepinion teeth),then theinvolutegenerates th
16、e even more complex profile function on theface gearteeth, whicheven changesalong thefacewidth. A pinion with only one more tooth or a slightly changed addendum modification can not roll correctlywiththesamefacegear. Thisleadstofacegearmanufacturingmethodswhicharebasedontheprincipleofagenerating cyl
17、indrical pinion. The special tool geometries of those methods are derived from the individualspur or helical pinion, which should mate with the manufactured face gear.RpoRgoRpmRgmRRgiRpoRgo=RpmRgm=RRgi=RaFigure 1. Face gear and cylindrical pinion (left) compared to bevel gear set (right)4 11FTM01Fig
18、ure 2. Face gear with 15 face angle and cylindrical pinionFigure 3 shows a modified cylindrical gear hobbing machine which employs a special hob for face gears(shown enlarged in Figure 2 on the right side). One hob start winds about two times around the disk shapedcutter body, where the cutter body
19、is curved in width-wise direction (in the axial plane). The individual hobbladeswhichhaveaninvoluteprofile,aregroupedliketheteethofthecorrespondingcylindricalpinionaroundthe pinions root cylinder. The disk cutter for face gears attempts to represent the corresponding cylindricalpinion, similar to th
20、e way a regular hob represents a generating rack. There are process related distortionssome of which can be corrected. The cutter disk moves during the cutting process in the “Feed Direction”across the face width. Such a cutter disk can only be used for one particular face gear design, which makesst
21、andardization of the cutting tools impossible 2.A very elegant and geometrically sound cutting method for face gears uses a shaper cutter as shown inFigure 4. The blade profile of the shaper cutter is equal to the corresponding pinion profile, where backlashandrootclearancehavebeenconsideredinthedes
22、ignofthetool. Alsohere,thetoolisacustomdesign,butiscalculated and manufactured like a regular shaper cutter.Figure 3. Machine and disk shaped hob for face gear hobbing5 11FTM01Figure 4. Shaper cutter and face gear on 90 angle work headHard finishing by continuous grinding with a threaded grinding wh
23、eel as shown in Figure 5 is very fast yet itrequires the same corrections as already mentioned for the hobbing disk cutter. Dressing of the threadedgrinding wheel is complicated because it requires a spatially inclined involute path and it presents undercutconditions on the two sides of the threaded
24、 grinding disk.Figure 5. Continuous generating grinding of a face gear 36 11FTM01The single indexinggenerating grindingas shownin Figure 6delivers veryprecise flankforms. The profileoftheperipheralgrindingwheelresemblesthenormaltoothprofileofthecorrespondingcylindricalpinion,wherebacklash and root c
25、learance has been considered. It is required that the grinding wheel traverses in eachgenerating roll position along the entire face width. The discrete generating positions have to be chosen inincrements fine enough since there is no automatic process to supportrounding ofthe generatingflats. Bothf
26、lanks of one slot can be ground simultaneously which is advantageous regarding grinding time and grindingquality. The generating motion is a swing rotation of the grinding wheel around the virtual axis of the corres-ponding cylindrical pinion, as indicated in Figure 5. In spite of the simultaneous m
27、achining of both flanks ofone slot, single index grinding is the slowest of the methods discussed so far 4.The new CONIFACE methodOne question raised from the discussions in the last paragraphs is: “Is there a universal tool which can beappliedonanexistinggearcuttingorgrindingmachinedesigninordertos
28、imulatetheinvoluteshapedtoothofthecorrespondingcylindricalpinionduringthemachiningprocess?” Asimulation ofthe piniontooth alongtheentire face within any roll position would be of great advantage because this could eliminate the timeconsuming traversing motion and at the same time would provide a rou
29、nding between the generating flats.AlltheabovementionedcriteriaarefulfilledfromCONIFLEXcuttersandfromCONIFLEXgrindingwheels5,however, the bladeprofile ofthe CONIFLEX cutter is required to have an involuteprofile. Figure 7showsto the right such a modification on a CONIFLEX grinding wheel. In order to
30、 come to a standard tool it is alsopossible to modify the cutter disk swing rotation during the roll motions such that also a blade with a straightcutting edge will generate a correct face gear flank. This can be achieved with the Gleason standard feature“Modified Roll”.Thecontactlinesbetweenthecutt
31、erdiskandtheflankofthecorrespondingcylindricalpinionaredrawnintheleft part of Figure 7. These contact linesextend alongthe entireface widthbut theyare differentto theactualgenerating lines, which are identical to the contact lines between cylindrical pinion and face gear. Animportantaspectisthefacew
32、idthorientationofthecontactlinesbetweenfacegearflanksandenvelopedtoolsurface, because it presents the possibility to eliminate any traversing feed motion.Figure 6. Single indexing generating grinding of a face gear7 11FTM01Figure 7. Line contact and involute profile on a CONIFLEX toolFigure 8 elabor
33、ates on the interaction between tool and face gear. In spite of the similarity with Figure 6, therelationships are fundamentally different. The tool disk in Figure 7 is tilted to match the pressure angle of thecorresponding cylindrical pinion. The generating roll is indicated in Figure 8 beginning a
34、t the topland in aclockwisedirection. Inafirstapproximationtheuniversaltooldiskrepresentsaplanewhichcarriesthegener-atingprofile(involuteontangentialplane). Thisisthereasonwhyonlyonefaceof thetool diskcan beutilizedat one time to simulate one flank of the generating gear (corresponding cylindrical p
35、inion) in order to form aface gear flank. This leads subsequently to a “Two Cut Process” which further underlines the analogy to theCONIFLEX process.Figure 8. Interaction between tool disk and face gear8 11FTM01Basic settings for face gear manufacturingThe required freedoms for the manufacturing of
36、a face gear are present in every modern PhoenixtII bevelgear cutting or grinding machine. In view of the similarity between face gears and straight CONIFLEX bevelgears, the application of bevel gear machines seems to be a useful combination between process andmachine tool. Bevel gear machines common
37、ly use basic data for the part program calculation performed bythe control computer. This led to the task to derive basic settings for the manufacturing of face gears, whichare based to some extenton thesimilarity tothe CONIFLEXstraight bevelgear manufacturingprocess. Thebasic data defines the relat
38、ionship between the tool and the generating axis as well as the relationshipbetween this generating axis and the work axis.Figure 9 shows in the top section the cutter disk as a straight line with its axis which is tilted to the pressureangleofthecorrespondingcylindricalpinion. Thecutterdiskinthelow
39、ersectionofFigure 9(topviewofupperdrawing), represented as a circular section was placed such that the root line of the face gear is tangent to it.After the known position of the work relative to the cutter disk, the location of the generating axis has to bedetermined in a next step. This axis is pe
40、rpendicular to the axes X and Z in Figure 8. Its location in theX-Z-planeisfoundbysmoothingthepitchcircleofthecorrespondingcylindricalpiniononto thenominalpitchplaneofthefacegear. Foracompletesetofbasicsettings,thegeneratingratiobetweengeneratinggearandworkisstillmissing. Itiscalculatedlikeinthecase
41、ofpinionswhichmatewithFORMATEgearsasthequotientbetween number of generating gear teeth (corresponding cylindrical pinion) and number of work gear teeth(face gear).The resulting basic data are:S. Radial distance between cutter and generating axisi. Cutter tiltj. Tilt orientationq0. Center of roll ang
42、le (angle of s-vector around generating axis)Xb Distance between cutter center and generating axis in Z-directionXp Axial work locationRa. Ratio of rollSurface generation and analysisNotonlyisthemanufacturingofafacegear possiblewith thedata derivedin thelast section,but atheoreticalgeneration of sur
43、face points and tooth contact analysis canalso beconducted previousto themanufacturingin order to optimize the face gear transmission properties.CONIFACESoftwareusesthegeometricaldataofthecylindricalpinionwhichshouldmatewiththefacegear.Optimization of the principle roll conditions e.g., by optimizat
44、ion of the radial location of the face gear toothwidtharepossible andshould happenin thefirst step. Thesuccess ofthis optimizationcan beverified ontheshape and location of the undercut lines. Figure 10 shows the undercut lines of an initial face gear (leftgraphic)andtheoptimizedversionintherightgrap
45、hicofFigure 10. Theactiveloadtransmittingflanksurfacearea (above the undercut line) was enlarged by more than 20% as result of the optimization. Ease-Off, toothcontact pattern and motion error are optimized in a second step. Results of a tooth contact optimization arediscussed in the following secti
46、on.The surface points are also available for coordinate measurements of the face gear flank surfaces. Thismathematical foundation enables the calculation of corrections for the cutting or grinding machine after the3-D-measurement which allows the correction of errors in spiral angle, pressure angle,
47、 tooth thickness andtooth depth in the same way as known for spiral bevel gears.Method specific propertiesLength crowning can also be applied to face gear flanks by creating an internal cone of the cutter disk, like inthecaseofCONIFLEXstraightbevelgears. Profilemodificationsarepossiblebyasecondorder
48、modification9 11FTM01of the ratio of roll or simply by using blades with profile curvatures. A geometrical characteristic of the CONI-FACEprocessisthecurvedrootlinewhichiscreatedbytheperipheralcutter. Figure 11showsprojectionsofthe cutter outline in different roll positions.Figure 9. Vector diagram
49、for basic setting calculation10 11FTM01Figure 10. Undercut lines, left before, right after optimizationFigure 11. Projections of the blade tip circleIt is evident in Figure 11 that in different roll positions, different curved cutter paths areeffective ingeneratingthe flank and forming the root line. This circumstance causes a non linear distortion of the involute bladeprofile as it generates the face gear flank. This has an influence to the contactgeometry asthe twoEase-Offplots in Figure 12 show. Figure 12 is the result of a tooth contact analysis calculation b
