1、11FTM02AGMA Technical PaperGenerating GearGrinding NewPossibilities in ProcessDesign and AnalysisBy J. Reimann, F. Klocke, andC. Gorgels, RWTH AachenUniversityGenerating Gear Grinding New Possibilities in ProcessDesign and AnalysisJan Reimann, Dr. Fritz Klocke, and Christof Gorgels, RWTH Aachen Univ
2、ersityThe statements and opinions contained herein are those of the author and should not be construed as anofficial action or opinion of the American Gear Manufacturers Association.AbstractOne possible process for the hard finishing of gears is the continuous generating gear grinding, which hasrepl
3、acedothergrindingprocessesinbatchproductionofsmalltomediumsizedgearsduetoitshighprocessefficiency.Despite the wide industrial application of this process only a few published scientific analyses exist. Thescience-basedanalysisofgeneratinggeargrindingneedsahighamountoftimeandeffort.Thisisduetothecomp
4、lex contact conditions between tool and gear flank, which change continuously during the grindingprocess. These complicate the application of the existing knowledge of other grinding processes ontogenerating gear grinding.Theaimofthisreportistodeterminetheexistingcuttingforcesforasamplegearintrialsf
5、orthefirsttimeandtoanalyse their connection to process parameters and the appearance of profile form deviations.Simultaneously for a sample gear the same process design will be analyzed using a manufacturingsimulation. The results of trials and simulation will be compared. This report will present n
6、ew possibilities inprocess analysis and will give the process user ideas for future process improvements.Copyright 2011American Gear Manufacturers Association1001 N. Fairfax Street, 5thFloorAlexandria, Virginia 22314October 2011ISBN: 978-1-61481-001-83 11FTM02Generating Gear Grinding New Possibiliti
7、es in Process Design and AnalysisJan Reimann, Dr. Fritz Klocke, and Christof Gorgels, RWTH Aachen UniversityIntroduction and motivationInorder toimproveloadcarryingcapacity andnoise behavior case hardenedgears usually are hardfinished1. One possible process for the hard finishing of gears is the gen
8、erating gear grinding which has replacedother grinding processes in batch production of small and middle gears due to the high process efficiency.Despitethewideindustrial applicationof this process only afew scientific analysis exist. Thescience-basedanalysisof thegeneratinggeargrindingneedsahighamo
9、unt oftimeandeffort. Onereasonarethecomplexcontactconditionsbetweentoolandgearflank,whichchangecontinuously duringthegrindingprocess. Thiscomplicates the application of the existing knowledge of other grinding processes on generating gear grind-ing. The complex contact conditions lead to a high proc
10、ess dynamic which is a challenge for the design ofmachine tools, control engineering and process design.Theknowledgeofcuttingforcesandtheirtime-dependentbehaviorisnecessarytodescribeandoptimizetheprocessdynamic. Howeverthedeterminationofthecuttingforcesduringgeneratinggeargrindingisnotread-ily possi
11、ble. Tillnow, noscientific analysis exists which systematically describes theinfluenceof theprocessparameters on the cutting forces during generating gear grinding.State of the artGenerating gear grindingOne of the most efficient processes for the hard finishing of gears in batch production of exter
12、nal gears andgear shafts is the continuous generating gear grinding. The generating gear grinding is used for the hardfinishingofgearswithamoduleofmn=0.5mmtomn=10mm2,3. Bytheapplicationofnewmachinetoolsthe process can be used for grinding of large module gears (up to da= 1.000 mm) 4.The cylindrical
13、grinding worm, whose profile equates a rack profile in a transverse section, hobs with anexternalgear,Figure 1left. Theinvoluteisgeneratedbycontinuousrollingmotionofgrindingwormandwork-piece by the profile cuts method 3, 5. Profile cuts method in the generating processes means the profileformisgener
14、atedbyafinitenumberofprofilingcuts. Duetotheclosedgrindingwormnogeneratingcutdevi-ations, known from the gear hobbing, occur in generating gear grinding.Figure 1. Generating gear grinding - principle, machine settings and contact conditions4 11FTM02In comparison with other gear grinding processes th
15、e stock removal rate in generating gear grinding is veryhigh. Inmost caseit is only limitedby thereachablegear quality 3. Ingeneratinggeargrindingalwaysmul-tiplepointsofthegrindingwormareincontact. Thenumberof contactpoints changecontinuously duringthetool rotation, Figure 1 right.Thecontactsontheri
16、ghtandonthelefttoolflankareequalbyanevennumberofcontactpoints. Thisleadstoanconsistent distributionof forces. By anunevennumber of contact points alsothedistributionof forces willbe uneven. This leads to an inconsistent distribution of the cutting forces. In theexample inFigure 1 onthelineof contact
17、 of theleft tool flanks theforces aresplit intwocontactpoints. Ontheright toolflank thecuttingforce is increased, because only one point has contact. This fact can lead to a higher stock removal at thiscontact point andtoanhigher excitation. Theconsequencecanbetheappearanceofprofileformdeviationswhi
18、chreducethereachablegear quality. Scientific publications of Meijboom 9 andTrich10 describethisrelation theoretical.Publications, e.g., in6, 7, 8, andtheexistingdoctoral thesis of Meijboom 9, Trich 10 and Stimpel 11show the influenceof several parameter onthe process results. But several technologic
19、al correlations havenot been analyzed or verified in trials yet.Current challengesDuetolimitedscientific studies thetechnology users, grinding tool suppliers andmachine tool manufacturesface two main challenges.Ontheonehandtheprocessdesignandoptimizationisbasedontheknowhowoftheprocessuser. Incases,w
20、herenosufficientexperience(e.g.,newgeargeometry,nogrindingtools)exists,cost-intensivetrialshavetobe carried out to find a favored and robust process design. For this purpose usual several iterations arenecessary. In order to reduce the number of needed iteration loops the technological connections m
21、ust beanalyzed in detail in the future.On the other hand the increasing demand of high volume of wind turbine gears leads to a higher demand oflarge module gears 12. Until today most of these gears were manufactured by profile gear grinding.However, since a few years the increasing demand of large m
22、odule gears led to the usage of the more pro-ductivegeneratinggeargrinding4,12. Thescalingofexistingprocessestolargemodulegearsisnoteasilypossible. Firstofallbythehighworkpieceweightsandthehighermassinertiatheprocessdynamicbecomesone of the greatest challenges. Therefore, knowledge of the process fo
23、rces is important for process andmachine tool design.Anapproachtomeettheseexistingchallengeswillbegivenbytheresearchactivitiesintroducedinthispaper.Research objective and approachTheglobalresearchobjectiveforthegeneratinggeargrindingattheWZListheincreaseofprocessefficiencyandprocess reliability inge
24、nerating gear grinding by description of the technological correlations andcuttingforces inaholistic process model. For this purposeseveral methods for process analysis of generatinggeargrinding have been developed and will be introduced in this report.Up to now a verification of those techniques wi
25、th generating gear grinding process is missing. Sothe aim ofthis report is todeterminetheexistingcuttingforcesfor asamplegearintrialsfor thefirst timeandtoanalyzetheirconnectiontotheprocessparametersandtheappearanceofprofileformdeviations. Simultaneouslyforthe sample gear the same process design wil
26、l beanalyzed usinga manufacturingsimulation. The results ofthegrindingtrials, theanalogy trials andthesimulationwill becompared. Withtheseresults averificationforthe sample gear will be possible. This report provides information about the technological interactions ingenerating gear grinding.5 11FTM
27、02Methods for the process analysisIn the following section the new research methods for the process analysis will be described and someexamples fortheresultsof thosemethods willbeshown. Themethods fortheinvestigationof thegeneratinggear grinding are a manufacturing simulation and an analogy trial fo
28、r the generating gear grinding.Simulation of generating gear grindingThe remarks given in the state of the art show that the process results are influenced by a multitude ofparameters. Theexactconnectionsandinteractionsarenotdescribedindetail tillnow. This complicatestheprocessoptimizationanddesigno
29、fgeneratinggeargrinding. Aninvestigationoftheprocesswithamanufac-turing simulation can be an advantage to reduce the high effort of time and workpieces for the processoptimization.For the analysis of generating gear grinding an existing, verified manufacturing simulation (SPARTApro) forgearhobbingwa
30、smodified. Gearhobbingandgeneratinggeargrindingbaseonthesamekinematics. Byanincreased number of normal sections a continuous grinding worm can be approximated, Figure 2. By acomparison between the simulated key values and analytical calculated values the necessary number ofsections can be determined
31、 for the simulation of the generating gear grinding. Among other things thisnumber is depending on the workpiece and the tool geometry. For one example the effect of the number ofnormal sections on the key values and the calculation time is shown in Figure 2.Figure 3showssomeselectedresultsofthemanu
32、facturingsimulationfor onesamplegear. Itshows twokeyvalues plotted graphically for the tool profile and two key values for the evaluation of the process dynamicplotted for the tool rotation angle.The volume of penetration VD,Sumdescribes the accumulated chip volume along the tool profile. This keyva
33、lue enables an estimation of the tool loadand wear behavior alongthe profile. Inthis examplethe loadonboth tool flanks is similar. However, thetool root flank cuts a higher chip volumethan thetool tipflank. Thisuneven wear of the tool profile can lead to profile angle deviations at the workpiece, be
34、cause of the differentlocal tool load.Thecuttingdepthhcu,maxdescribesthemaximumpenetrationatonepointonthetoolprofileduringthemanu-facturing. Theanalysisof thiskey valueshows adifferent cuttingdepthatthetooltipandtool rootflank. Thisshows the different chip formation mechanisms.Figure 2. Generating g
35、ear grinding with SPARTApro6 11FTM02Figure 3. Selected results of the penetration calculationOn the right side of Figure 3 two selectedkey values to ratethe process dynamic areshown. Usually ahighcorrelation between penetration volume and process forces can be found 2. Therefore, the penetrationvolu
36、me can provide a first indication for the process dynamic.The volume of penetration VDdescribes the accumulated volume of the penetration between tool and work-pieceplottedagainstthetoolrotationangle. Inthis examplethevolumeof penetrationis veryhomogeneous.This can be an indication for a low process
37、 dynamic and a high machinability at these parameter settings.A further indicationontheexcitationcanbeprovidedbytheanalysisof thedifferenceofthepenetrationVD.This key value describes the difference of the penetration between the left and the right tool flanks and isplotted for the tool rotation angl
38、e. The graph shows a homogenous run for this example.So far a comparison of the theoretical results of the manufacturing simulation is missing. Therefore,generating gear grinding trials will be carried out.Analogy trial generating gear grindingIngeneratinggear grindingthecontact conditions betweenth
39、egrindingworm andthegear arecomplex. Ononehandthepenetrationchanges continuously andontheotherhandthenumber ofcontact pointsbetweenthe gear and the tool is variable during one tool rotation. In order to investigate generating gear grindingwithouttheinfluenceofthesecontactconditionsageometricalandkin
40、ematicalmodel forthegeneratinggeargrinding is designed at the WZL: the analogy trial for generating gear grinding.The principle of the analogy trial for generating gear grinding is shown in Figure 4. In the analogy trial thegeometry and the kinematics have to be adapted to the situation in the gener
41、ating gear grinding process.In one point the involute can be approximated by a circle with the local radius of curvature y13. For theanalogy trials the contact conditions at the pitch circle d are approximated. The influence of the curvaturealongprofileheight canbeuntendedfor gears withahighnumber o
42、f teeth. Thediameter of the workpieceintheanalogy trialdWstAequalsthedoubleradius ofcurvatureatthepitchcircle. This diameterdepends onthenumberofteethz,themodulemn, thehelix angleandthepressureanglen. Therack profileof thegrindingworm can be approximated in the investigated contact point by a face w
43、heel with a conic working surface.7 11FTM02Figure 4. Analogy trial for generating gear grinding - principle and deduction of workpiecegeometryBesidetheworkpieceandthetoolgeometrythechipgeometryintheanalogytrialhastobecomparabletothechip geometry in generating gear grinding. Therefore the cutting len
44、gth lcuAand the chip thickness hcuAaswell as the stock removal rate QWhave to be equal.Furthermore,thekinematicofthechipformationandthevelocitiesmustbefittedtothesituationingeneratinggeargrinding. Duringchipformationthelateralslidingspeed,theaxialfeedspeedvaAandthecuttingspeedvcinterfere with each o
45、ther. The cutting speed in generating gear grinding and the analogy trial are the same.The lateral sliding speed vtAcan be calculated by the rotational speed nWstAof the workpiece and the syn-chronizationrequirement. Theaxial feedspeed vaAcanbeadjusted accordingto thegenerating gear grind-ing proces
46、s as the product of rotational speed nWstAand axial feed fa.In the analogy trials the cutting force can be determined by a dynamometer which is integrated in the flux offorces. Furthermore,thesurfacestructurechanges andtheformdeviations oftheanalogyworkpiececanbeanalyzed and can be used to determine
47、 the tool wear behaviour and performance. For further informationafull description of the analogy trial design can be found in 8.In previous investigations using the analogy trial the influence of the workpiece geometry, respectively theradius of curvature, and of the process parameters were analyze
48、d. Based on the results of the measuredcuttingforcesafirstcalculationmodelforthecuttingforcesingeneratinggeargrindingwasdeveloped. Usingabiquadraticalansatzfunctiontherunofthecuttingforcescanbecalculatedwithafewrestrictionsespeciallyin the area of exponential wear behaviour, Figure 5.A correlation b
49、etween the measured forces in the analogy trial and the cutting force in generating geargrinding is missing. To verify the analogy trials generating gear grinding trial have to be carried out. Theresults will be shown in this paper.Generating gear grinding trialsForthemeasurementofthecuttingforcesingeneratinggeargrinding,theverificationoftheanalogytrialsanda comparison between the theoretical analysis with SPARTApro generating gear grinding trial have beencarried out. The experimental design and approach as well as the results wi
