AGMA 12FTM11-2012 Contemporary Gear Pre-Machining Solutions.pdf

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1、12FTM11AGMA Technical PaperContemporary GearPre-MachiningSolutionsBy C. Kobialka, Gleason-PfauterContemporary Gear Pre-Machining SolutionsDr.-Ing. Claus Kobialka, Gleason-PfauterThe statements and opinions contained herein are those of the author and should not be construed as anofficial action or o

2、pinion of the American Gear Manufacturers Association.AbstractDepending on annual productionvolumes, batchsizes and workpiece geometryseveral gearmanufacturingtechnologies are used for industrial gear production. Most applicated is the hobbing process, followed bybroaching, shaping, sintering and ro

3、lling processes. Upcoming gear manufacturing processes are powerskiving, forging, precision blanking and coldforging. Due toimprovements onthe numerical control of directdrive technology the power skiving process has become a competitive gear manufacturing process incomparison to shaping, blanking a

4、nd broaching. The potentials of the reinvented power skiving process willbeexplainedbyproductionvolumeanalyses,achievablegearqualityandgeargeometrymodifications. Alsothe economical and environmental friendly aspect of the power skiving process will be explained.Copyright 2012American Gear Manufactur

5、ers Association1001 N. Fairfax Street, Suite 500Alexandria, Virginia 22314October 2012ISBN: 978-1-61481-042-13 12FTM11Contemporary Gear Pre-Machining SolutionsDr.-Ing. Claus Kobialka, Gleason-PfauterIntroductionDependingonannualproductionvolumes,batchsizes,andworkpiecegeometry,severalgearmanufacturi

6、ngtechnologies are used for industrial gear production. The one most applicated is the hobbing process, fol-lowedbybroaching, shaping,sinteringandrollingprocesses. Upandcominggear manufacturingprocessesare power skiving, forging, precision blanking and cold forging 1. Due to improvements in the nume

7、ricalcontrol of direct drive technology, the power skiving process has become a competitive gear manufacturingprocess in comparison to shaping, blanking and broaching. The potential of the reinvented power skivingprocess will be explained by production volume analyses, achievable gear quality and ge

8、ar geometrymodifications. Theeconomicandenvironmentfriendlyaspectofthepowerskivingprocesswillbeexplained.Productivity in soft gearing processesDuetoincreasedflexibilityrequestsonindustrialserialproductiontoday,batchsizesaredecreasing2,whilethepartcomplexityandtherequestedworkpiecequalityisincreasing

9、. Formeetingbothrequeststheprocesschain has to be analyzed for shortening set up times and reducedfloor tofloor times. Onepossibility ingearhobbingwastheintegrationof chamferinganddeburringwork inthehobbingprocess. Suchprocesseshavebeen realized for horizontal and vertical workpiece orientations, as

10、 those shown in Figure 1 and Figure 2.The benefits of the integration of chamfering processes into the hobbing process are given by reducedchamfertoolinvestmentsandhigheraccuracyofthehobbedlead. Thisisthebasisforreducedstockremovalrates on the hard finishing processes, such as honing or threaded whe

11、el grinding.A secondpossibility for universalgear manufacturingis thegenerationof internalor externalgears by powerskiving. Inthismanufacturingtechnology34,atoolisplacedinacrossaxisanglerelativetotheworkpiece.Similar to the shaving process, chip building is initiated by the relative velocity between

12、 tool and workpiece(Figure 3).Finish part in one setup:Needs chamfer operation between 1stand 2ndcutFigure 1. Integrated chamfering and deburring (horizontal workpiece orientation)4 12FTM111. Pre-hobbing2. Chamfering and deburring3. Finish hobbingS No burr for followinghard finishing processS Chamfe

13、ring with simpletoolsFigure 2. Integrated chamfering and deburring (pre-hone hobbing)Modification crossaxis angleRadial feed rateRotation workpieceAxial feed rateRotationtoolCross axis angleFigure 3. What is power skiving?Comparedtothehobbingprocess,thetoollifeisreducedandchipremovalrateremainsatthe

14、thesamelevel,however,alargeramountofchipsaregenerated. Ingeneralallhobbingapplicationscanberealizedbypowerskiving, but a higher tool cost will be initiated.Regarding the shaping process a tremendous reduction in manufacturing time will be initiated by the powerskiving process (see Table 1, Table 2 a

15、nd Figure 4). This will increase the productivity, but not all shapingapplications will become substituted by that manufacturing technology.For power skiving, tools from HSS and tungsten carbide can be used. In regard to the substrate costs andgrinding costs, the PM-HSS substrate material is the pre

16、ferred solution. Only in the case of small pitch5 12FTM11applications (m 1 mm) and very abrasive workpiece materials (such as cast iron) will the tungsten carbidematerial be beneficial in comparison to the HSS solution. The tapered concept is from higher flexibility andreduced machine axis. Instead,

17、 the use of cylindrical tools is more sensitive during the setup work and anadditional NC axis for the lateral offset is necessary.Table 1. Process chain in gearing - external gearPower skiving HobbingTool Skiving tool (60 teeth) Hob 500 teethContact ratio 2 teeth in contact 4 teeth in contactUse of

18、 cutting edge of thetoolFull length of cutting edge Depending on generatingposition, partial contactTool rpm 2000 2000Number of chips per minute 120,000 48,000NOTE:Based on equal cycle times power skiving will create higher tool costs per workpiece, compared tohobbing.Table 2. Process chain in geari

19、ng - external gearPower skiving ShapingTool Skiving tool (60 teeth) Shaper cutter (60 teeth)Contact ratio 2 teeth in contact 2 teeth in contactUse of cutting edge of thetoolFull length of cutting edge Like power skivingProductivity Like hobbing Factor 3 less than hobbingprocessNumber of chips per mi

20、nute 120,000 2,000NOTE:Workpiece related tool costs of power skiving are 70% higher than shaping. However, power skiving isat least factor 3 more productive than shaping.Tapered skiving tool- Flexible for helix angles- Sensitive in profile quality byresharpeningCylindrical skiving tool- Limited in h

21、elix angle of workpiece- Low tool investment- Limited modifications in profileS Gleason has until now only used tapered cutting toolsS Most trials have been realized by wet cuttingS Most power skiving cutters are from HSS-substrate materialS There is limited experience for use of tungsten carbide to

22、olsS There is limited experience for dry processesFigure 4. Tools for power skiving6 12FTM11The tool design for a given application has to show constant load and good clearance angle conditions. Formost internal gear applications, the number of teeth will be different based on the existing tool layo

23、ut ofshaping application (Figure 5 and Figure 6).Process time calculationProcess visualizationFigure 5 Tool contact for a specific workpiece applicationFigure 6. Process layout on power skiving7 12FTM11Thechipformationfromthedifferentcutsshowsonthesameleveloftoolrelatedloadtoadifferentstructureofthe

24、chips(Figure 7). Thechipcontactontherakeangleofthetoolisveryclosetothecuttingedge. Duetothethermal impact, the most used HSS tools are those from high abrasive characters. A craterization was notidentified.Due to chip deformation during the power skiving process the shown U-form chips are on a high

25、level ofcollisionby themselves. This effectis increasingthecuttingforces, andthechipflowareais veryclosetothecutting edge. By generating only L-form or I-form chips, the level of chip flow interference is reduced. Thechip flow area on the rake face is a larger distance from the cutting edge, and due

26、 to that effect, the cuttingforces decrease. A secondary effect is an improved tool life.For tool life optimization, a modified infeed strategy is possible (Figure 8 and Figure 9). Based on anoscillatingmotionbetweentheleadingandtrailingflank percut, thewear developmentonthecuttingtoolcanbe directed

27、 in a well balanced way. The power skiving of large workpieces, where the tool life of the powerskiving cutter is limited to a small number of workpieces, is also possible.Figure 7. Chips of different cuts1stcut 3rdcut2ndcut4thcut 6thcut5thcutFigure 8. Infeed strategy for power skiving8 12FTM11- Inc

28、reased tool life by well balanced workload on leading and trailing flank- Well balanced wear development on both flanks- Constant temperature load on the entire toothFigure 9. Alternative infeed strategy for power skivingThe achievable profile quality is depending on workpiece and tool set up in com

29、bination with the tool profilequality (Figure 10). Based on an AA class cutter profile angle qualities of DIN class 7 can be achieved.Further improvements of the tool quality will increase the workpiece related profile quality.Theleadqualityofthesurfaceisfromfineandnonregularstructure(Figure 11). Th

30、ediagonalstructureofthefeedmarksensuresreducednoiseinthecontactbehaviorofthegearset. Forinternalandexternalgears,leadmodifications are possible. This is an innovation regarding the possibility of flexible crowning on internalgears.The pitch line quality is from DIN class 5 quality level (Figure 12).

31、 Future optimization of the direct drivenworkpiecespindlesandtoolswillreducethepitchlinewaviness. Thesingularpitchdeviationsareonthelevelofashapingapplication. Forfinishedmanufacturingrequests,animprovementbymodifiedNC-filtersandanincreased inertia of the tool and work spindle are mandatory.Impacted

32、 byskiving cutterdesignimprovement ifpossibleFigure 10. Gear profile quality9 12FTM11That isequivalentto finishhobbingqualityFigure 11. Gear lead qualityFigure 12. Pitch deviation on power skiving10 12FTM11SummaryMainmanufacturingtechnologiesinsoftgearingarehobbing,shaping,broaching,chamferinganddeb

33、urring.In serial and mass production of gears the directly linked use of singular processes is state of the art.In parallel, the optimization of each process can be achieved by the integration of different processes. Thisshowsahighpotentialforthereductionoftheleadtimeaswellasanincreasedlevelofworkpi

34、ecequality. Thedevelopment of high performance numerical controls offers the gearing of internal and external gears bypower skiving. Power skiving will become a preferred manufacturing technology for small and medium sizebatch production.Based on the chip thickness and the friction on the chip build

35、ing mechanism of the power skiving process, awet cutting strategy is the preferred cutting process. Further developments in tool substrate materials andmodified coating technologies will drive the capability for dry manufacturing processes.Compared to hobbing, the power skiving process will initiate

36、 higher tool costs. Compared to the shapingprocess, reduced manufacturing times and increased surface structure qualities will substitute shapingapplications up to a module range of 8 mm.The energy consumption of the power skiving process is less efficient than the hobbing process due to anincreased

37、numberofchipsonthesameleveloffrictionpercut. Today,thedrymachiningandthetemperaturechange of the workpieces during the machining can become a significant quality impacting factor.Literature1 Statistisches Bundesamt/VDMA2 Klaiber, M., Maschinen- und Anlagenbau Quo Vadis? Lehrgang Praxis der Zahnradfe

38、rtigung,Technische Akademie Esslingen, 20093 Osterried, Khlewein - “Mglichkeiten der Schneidkantenprparation bei Wlzschlrdern”, 20094 Bechle,A.,“BeitragzurprozesicherenBearbeitungbeimHochleistungsverfahrenWlzschlen”,Univ.Karlsruhe, 20065 Denkena, B., “Einfluss der Schneidkantengeometrie auf die Zerspankrfte und auf dasVerschleiverhalten”, ZWF, 2005