【机械类毕业论文中英文对照文献翻译】滚齿机上硬质合金刀具疲劳性断裂调查
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机械类毕业论文中英文对照文献翻译
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【机械类毕业论文中英文对照文献翻译】滚齿机上硬质合金刀具疲劳性断裂调查,机械类毕业论文中英文对照文献翻译,机械类,毕业论文,中英文,对照,文献,翻译,滚齿机上,硬质,合金刀具,疲劳,断裂,调查
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A. AntoniadisProfessor,Technological Educational Institute of Crete,Chania, Greecee-mail: antoniadischania.teiher.grN. VidakisTeaching Fellow,Technological Educational Institute of Crete,Heraclion, Greecee-mail: vidakisebeh.grN. BilalisAssociate Professor,Technical University of Crete,Chania, Greecee-mail: bilalisdpem.tuc.grFatigue Fracture Investigation ofCemented Carbide Tools in GearHobbing, Part 1: FEM Modeling ofFly Hobbing and ComputationalInterpretation of ExperimentalResultsGear hobbing is a highly utilized flexible manufacturing process for massive production ofexternal gears. However, the complex geometry of cutting hobs is responsible for thealmost exclusive utilization of high-speed steel (HSS) as cutting tool material. The limitedcutting performance of HSS, even coated HSS, restricts the application of high cuttingspeeds and restricts the full exploitation of modern CNC hobbing machine tools. Theapplication of cemented carbide tools was considered as a potential alternative to modernproduction requirements. In former investigations an experimental variation of gear hob-bing, the so-called fly hobbing was applied, in order to specify the cutting performance ofcemented carbide tools in gear production. These thorough experiments indicated thatcracks, which were not expected, might occur in specific cutting cases, leading to theearly failure of the entire cutting tool. In order to interpret computationally the reasonsfor these failures, an FEM simulation of the cutting process was developed, supported byadvanced software tools able to determine the chip formation and the cutting forcesduring gear hobbing. The computational results explain sufficiently the failure mecha-nisms and they are quite in line with the experimental findings. The first part of this paperapplies the verified parametric FEM model for various cutting cases, indicating the mostrisky cutting teeth with respect to their fatigue danger. In a step forward, the second partof the paper illustrates the effect of various technological and geometric parameters tothe expected tool life. Therefore, the optimization of the cutting process is enabled,through the proper selection of cutting parameters, which can eliminate the failure dangerof cemented carbide cutting tools, thus achieving satisfactory cost effectiveness.1IntroductionThe application of High Speed Cutting HSC! was proved to bethe most powerful manufacturing strategy, considering the in-crease in productivity and the achievement of the desired costefficiency. However, in spite of the evolution of highly sophisti-cated CNC hobbing machining tools, the claim for HSC in gearmanufacturing has not yet been attained. The main reason for thisis the almost exclusive utilization of High Speed Steel HSS! asthe hobbing cutting tool material, as a consequence of its complexgeometry. The application of the coating technology in HSS hobsimproved significantly the cutting performance of the tool. Nev-ertheless, the upper cutting speed limit of HSS, even coated, is upto 100150 m/min, which is low for modern production require-ments. In addition, dry cutting is not applicable for coated oruncoated HSS tools, which is not in agreement with the currentworld wide environmental trends. Even in cases, where dry cut-ting with coated HSS tools is applied, the selection of the permit-ted cutting parameters restricts the efficiency, the exploitation andthe cutting possibilities of the hobbing machine tools.The most promising alternative material for cutting hobs comesfrom the evolution of cemented carbides, which are widely usedin massively produced cutting inserts. Despite the complex geom-etry of hobbing tools, their construction by cemented carbides isnowadays possible. The increased cost of cemented carbides toolsis quite amortized by the doubtless wear superiority when com-pared to HSS. However the brittleness of hardmetals may causefatigue failures in an early stage, due to the discontinuous chipproduction occurring in gear hobbing. Such phenomena were thor-oughly detected in special cutting experiments 1,2#. These fail-ures yield to a poor exploitation of the wear performance of ce-mented carbide tools, since their appearance makes the entirehobbing tool out of order. Brittle fatigue failures are normallycaused by high stress levels occurring at various cutting toolsand usually are consequences of wrong selection of cuttingparameters.This paper illustrates a quantitative analysis of the stressescourse in hobbing tools, aiming at interpreting the early tool fa-tigue failures computationally. In order to accomplish this task,special well-proved software tools were used, which render thechip formation mechanisms and calculate accurately the cuttingforce components. Finally, the development of a parametric FEMsimulation of the cutting teeth yields the description of the toolsstress field, for various cutting cases and technological param-eters. The stress results are compared to existing mechanical prop-erties of the tool materials, explaining in this way quantitativelytheir fatigue expectations. As it will be presented, the computa-tional results are in line with the experimental ones, proving thevalidity of the utilized analytical and FEM models. Furthermore, aContributed by the Manufacturing Engineering Division for publication in theJOURNAL OFMANUFACTURINGSCIENCE ANDENGINEERING. Manuscript receivedMay 2000. Associate Editor: M. Elbestawi.784 Vol. 124, NOVEMBER 2002parametric analysis presented in the second part of this paper il-lustrates the effect of various cutting parameters on the predictionof the tool life, allowing the optimization of nearly every specificcutting case.2Chip Geometry and Cutting Force Components inGear HobbingThe principles of gear hobbing are presented in Fig. 1. Thisgear manufacturing method, where each gear tooth is produced bysuccessive penetrations of the tool teeth in the individual Gener-ating Positions GP!, is of complicated kinematics, and it is diffi-cult to be modeled. In addition, based on the tool position duringeach penetration into a gear gap, a number of revolving positionsare used to describe the corresponding generating position. A de-cisive factor that determines the tool behavior is the chip forma-tion mechanism, which is also complicated, due to the complexcutting kinematics. Therefore, each chip type is responsible forcertain cutting force components that contribute to the overallcutting loads. This behavior is described by the chip forms that areinserted in the bottom part of the same figure for various gener-ating positions.Mathematical models that quantify the chip formation for eachindividual generating position are nowadays well established andwidely used 310#. These models are further used to predict thecourse of the cutting force components that exhibit a remarkableinfluence to the tool lifetime. The simulation of gear hobbing,with the aid of the FRSWEAR model, yields the chip dimensionsfor each revolution of every generating position, considering themanufacturing, geometrical and technological specification of thecutting tool, the workpiece and the cutting kinematics 1113#. Inthis paper a new module for the FEM Simulation of gear hobbinghas been added to FRSWEAR model. The structure of this newmodule FRSFEM is presented in Fig. 2. The above mentioneddata are interactively inserted using a modern software environ-ment, enabling the mathematical description of gear hobbing ki-nematics for specific cutting cases. The unreformed chip crosssections over the development of the cutting edge are then deter-mined for every generating position. The cutting force compo-nents can be determined at this stage, as they depend on the un-deformed chip dimensions and on experimentally determinedconstants 1417#. Using these cutting forces, the critical stressesoccurring in gear hobbing tools can be determined. Besides theseoutputs, the FRSWEAR model is able to predict the progress ofthe tool wear and to propose proper hob tangential feed amounts,in order to achieve an even wear progress over the successivecutting teeth 18#. The whole software has an open and modularstructure, offering a user-friendly graphical interface with interac-tive communication for data input and results output.Typical outputs of the FRSFEM model for a specific generatingposition of a certain manufacturing case are presented in Fig 3. Onthe left part of this figure the entire penetration of the specificcutting tooth into the examined generating position is shown. Themodel assumes special coordinate systems for the tool, which isrotating and moving following the tool paths, as shown in thefigure. The discretization of this generating position in variousrevolving positions is evident in this graph. The diagram in themiddle of the same figure illustrates the unreformed chip distribu-tion over the development of the cutting edge for the successiverevolving positions. The number of the revolving positions is alsoa variable parameter, depending on the required computationalaccuracy. The cutting force components calculated in the tool co-ordinate system are also presented in the right part of Fig. 3.These loads are overall values and they are composed of the el-ementary forces produced by the chip dimensions along the cut-ting edge. All these results are stored in proper files for everygenerating position that is required to form a gear gap.Despite the fact that the complicated hobbing kinematics can betreated analytically with the aid of the FRSFEM model, the ex-perimental procedure is laborious. The reason is that each cuttingtooth cuts a certain generating position and penetrates to everyworkpiece teeth for each workpiece revolution and subsequently,owing to the axial feedrate repeats the same procedure. Therefore,some of the cutting teeth cut generating positions with increasedchip dimensions and they are subjected to high cutting loads andwear. Due to this reason, besides the problem of poor tool utiliza-tion, the experimental study of this cutting process becomes evenFig. 1Chip formation and typical chips at various tool-generating positions in gear hobbingJournal of Manufacturing Science and EngineeringNOVEMBER 2002, Vol. 124 785more difficult. On the other hand, the complexity of tools withcomplete geometry makes their dismounting from the machinetool spindle and the subsequent evaluation of the experimentalstatus difficult.For those reasons, in order to increase the experimental effi-ciency and to facilitate the evaluation of the test results, advancedexperiments with one cutting tooth, the so-called fly hobbing,were used. In this manufacturing technique, the cutting tool isreplaced with a cylindrical holder, on which one cutting tooth caneasily be mounted and dismounted. The tooth geometry corre-sponds strictly to the DIN 3972 regulations 19#. This approachaccurately simulates gear hobbing with tool having one origin. Avariation of this method with two cutting teeth simulates completetools with two origins. The aim of this procedure is the separationof each generating position from the others and the ability to studycomprehensively their effect on the tool wear failure initiation andprogress. Consequently, each tool cuts every generating positionand this is taken into account in the present analysis, as it will befurther explained.3FEM Modeling and Mechanical Properties of theCutting TeethIn order to determine the stress field occurring in gear fabrica-tion using gear hobbing, modern CAE calculations were per-formed. The reason for selecting FEM software to compute thestresses and strains is the complicated tool geometry and processkinematics, as well as the highly variable cutting force compo-nents. Taking into account the volume of the involved parameters,a parametric approach was used, in order to produce a flexible andreproducible model. The cutting teeth modeling strategy is pre-sented in Fig. 4. The model was built in parametric terms, byFig. 2The flow chart diagram to the developed FRSFEM programFig. 3Determination of the cutting force components at individual generating position in gearhobbing786 Vol. 124, NOVEMBER 2002Transactions of the ASMEmeans of the APDL Ansys Parametric Design Language! moduleof the ANSYS FEA code. The entire geometry of the cuttingtool is standardized by DIN 3792 norm, as a function of its mod-ule and diameter. Therefore, the modeling routine was written interms of such parameters, considering also the tool clearanceangles and thickness. Owing to the complex teeth geometry, abottom up modeling strategy was utilized, as it is presented in themiddle diagram of the same figure. Hereby keypoints, lines, areasand volumes were determined sequentially, forming in this way a3-D solid model.This model consists of six volumes, in order to perform a finermeshing near the tool-workpiece contact areas and a coarser netaway from these regions. This way, the available computer re-sources are properly allocated, thus increasing the accuracy of theFEM calculations. The nodes density was also set as a variableparameter for optimization purposes. The optimized model con-sists of 23105eight-noded brick elements, performing in thisway a mapped meshing see the right part of Fig. 4!. More ele-ments in a denser mesh did not manage to increase the computa-tional accuracy, whereas the CPU solution time was unacceptablyincreased. The cutting force components explained in Fig. 3 areproperly distributed to the rake nodes, using a special APDL rou-tine that takes into account the chip compression ratio, besides thegeometric location of each node 20#. The model is pure elastic, sothat it requires only the tool elasticity modulus and Poissonsconstant.The above-mentioned mechanical properties of the finite ele-ments are also variables, allowing the applicability of the modelfor HSS and cemented carbide tools. In the present analysis themechanical properties of ISO-P 40 cemented carbide were used inthe model. Figure 5 summarizes the static and fatigue propertiesof this material. The left diagram of this figure exhibits the bulkhardness of cemented carbides versus their cobalt content 21#.Further calculations of the present analysis correspond to experi-mental data performed by using fine-grained P 40 cemented car-bide. For this reason, the Vickers hardness for this material wasfound from this diagram to be 1430 HV. This value, besides theresistance of this material to plastic deformation, may be used todetermine its static stress limit, considering that this value forbrittle materials equals to the one third of their pyramid hardness22,23#. On the other hand, the right diagram of the same figureillustrates the fatigue limits for cemented carbides, also as func-tion of their cobalt content 21#. For fine-grained P 40 hardmetalthe value for continuous endurance, i.e., 108loading cycles,equals to 83 N/mm2.The static and the fatigue stress limits can be used to elaboratethe Woehler diagram for the specific material, as it is illustrated inthe diagram in the middle of Fig. 5 24#. Considering the purposeof the present analysis, the abscissa of this diagram was reason-ably transformed from loading cycles to number of successivecuts. When the level of the occurring stresses is known, this dia-gram can be used to determine the number of loading cycles, i.e.,the number of successive cuts, which a certain tool made of P 40hardmetal is expected to develop a fatigue failure mechanism.This is also a great tool to examine the FEM model sufficiency.When the number of cuts required to cause tool failures in aFig. 4FEM modeling of hob teeth developed by FRSFEM programFig. 5Static and fatigue properties of cemented carbide tool materialJournal of Manufacturing Science and EngineeringNOVEMBER 2002, Vol. 124 787specific cutting case, is experimentally determined, the stress levelthat yields from the Woehler diagram must be in agreement to theFEM calculations.Initially the model was used to calculate the cutting stresses forevery generating position in cutting cases where experimental re-sults were available. Taking into account that every generatingposition is subdivided in successive revolving positions, it wasreasonable to solve the revolving position holding the bigger chipdimensions and consequently higher cutting loads. Figure 6 illus-trates such a calculation for a certain generating position of aspecific cutting case with climb and equi-directional hobbing, us-ing a cutting tool with two starts. The upper left diagram showsthe calculated revolving position of the examined generating po-sition. The corresponding cutting forces on the tool rake face areapplied in the model, and they are shown in the middle part of thesame figure. It is obvious that the cutting force components are inagreement to the formation of the produced chip. The solution ofthe specific cutting case offers the deformation of the cutting toothand it is shown in the bottom left part of the same figure. Finally,the von Mises stress distribution at the entire tool is presented inthe right part of Fig. 6. As it was expected, the most fatigue riskyregion is the cutting tooth head, which fits to the experimentalobservations, as it will be explained. It is also obvious that thestress contours follow the distribution of the chip thickness andconsequently the development of the cutting force components.4Correlation of Computational and Experimental Re-sultsThe FEM model was further used to calculate the course of thecutting stresses in every generating position of the cutting casepresented before. The computational results are summarized in theleft diagram of Fig. 7, which presents the maximum von Misesstresses in three endangered rake regions versus the successivegenerating positions. These regions are the transient regions be-tween the leading and the trailing flanks to the tool head respec-tively and the middle of the tool head. The stress results indicateas the most hazardous region the trailing flank of the cutting tool.The variation of the stress course at this region is a result of theuneven chip dimensions per generation position and the collisionbetween the chips produced at the flanks and the tool head respec-tively, a behavior which is experimentally and computationallydetected 1#. As it was previously described, the experimental pro-cedure was examined with the aid of fly hobbing with continuousaxial feed. Therefore, the cutting tooth cuts in every generatingposition, and it is subjected successively every stress of the dia-gram. To evaluate the experimental results, a representativeequivalent stress must be calculated, with respect to the fatiguetheory for collective loads 24#. This stress level for the currentcutting case corresponds to the horizontal line of the same dia-gram and equals to the 3100 N/mm2.The experimental behavior of cemented carbide tools of thiscutting case are presented in the diagram at the right part of Fig. 7,which present the determination of the flank wear at the transientregions of leading and the trailing flanks versus the overall cuttingwidth OCL! of the work gear 1#. The experiment was terminatedafter the early failure of the cutting edge at the transient region,between the middle of head and the trailing flank, as it is illus-trated by the micrograph of Fig. 7. The OCL can easily be turnedinto a number of successive cuts considering the transmission ra-tio, the cutting speed and the applied axial feed. For this case theOCL equals 85 mm that corresponds to 4050 successive cuts. Thecomputational and experimental results are finally compared inthe middle part of the same figure, using the Woehler diagram ofthe specific tool material. This diagram states that the achievednumber of cuts corresponds to a representative equivalent stress of2960 N/mm2, whereas the computational one is about 4% higher.This difference is absolutely reasonable, considering expected ar-ithmetical errors and other imponderable factors that cannot beincluded to the FEM model.Similar results are presented in Fig. 8, which present the deter-mination of the flank wear at the transient regions of hob versusthe overall cutting width OCL! of the work gear in a counterdirectional hobbing case 1#. For this case the OCL equals 710mm that corresponds to 31950 successive cuts. The comparisonbetween the computational and experimental results states that theachieved number of cuts corresponds to a representative equiva-lent stress of 2450 N/mm2, whereas the computational one isabout 6% higher.The method was further applied for other cutting cases, whichwere also experimentally examined. Hereby, Fig. 9 illustratestypical chips for two variations of the same cutting case of climbhobbing, i.e., the equi- and the counter-directional one. Each partof this figure illustrates chip developments for two different rep-resentative generating positions, per cutting case. For each ofthese chip diagrams a smaller adjacent diagram illustrates the re-gions of the tool rake that is subjected to cutting load components,Fig. 6Cutting forces and Mises stress distribution at hob tooth in climb and equi-directionalhobbing788 Vol. 124, NOVEMBER 2002Transactions of the ASMEfor specific revolving positions. The relationship between thesediagrams is obvious. For example in the upper left pair of dia-grams, the examined revolving position produces a chip that startsfrom the upper part of the trailing flank, passes the tool head andterminates at the one third of the length of the leading flank.Consequently, the model is subjected to cutting load componentsat the same regions.The FEM simulation of the cutting tools, which corresponds tothe aforementioned cutting cases, yielded results that are insertedin the diagrams of Fig. 10. The left diagram illustrates the vonMises stress distribution for equi-directional climb hobbing versusthe successive generating positions. The critical regions are thesame presented in Fig. 7. The experimental procedure indicatedthe generating position from 217 to 29, which correspond to theshaded region of the same diagram, as the most endangered ones.The level of the computational stresses explains quantitatively thisstatement, since their level more or less leads to a poor fatigueexpectation. Identical results are presented for the case of counterdirectional climb hobbing in the right part of the same figure. Forthis cutting case the most endangered generating positions arefrom 6 to 15, which also fit to the experimental results 1#.The comparison between the experimental and the computa-tional results presented, indicated that the developed model pro-duced an adequate simulation of the hob cutting teeth. The evalu-ation of the calculated stress field managed to interpret the earlyfatigue failures of cemented carbide hob teeth computationally.The adequacy of the FEM modeling strategy was proved also byexperimental results. The validation of the simulation, allows us toexpand the calculations in further cutting cases without the needfor additional laborious experimental work. In this way the toollifetime can be predicted for every possible variation of tool-workpiece combinations, cutting materials and cutting conditions.For this purpose the second part of this paper presents a paramet-ric analysis of such interactions, which may contribute to the op-Fig. 7Maximum Mises stresses at individual generating positions in fly climb and equi-directional hobbing and fatigue prediction of cutting toothFig. 8Fatigue prediction of cutting tooth in fly climb and counter-directional hobbingJournal of Manufacturing Science and EngineeringNOVEMBER 2002, Vol. 124 789timization of every cutting condition. In this way, the doubtlesswear performance of cemented carbide tools can be exploited, byavoiding cutting conditions that lead to unexpected early tool fa-tigue failures.5ConclusionThe experimentally detected early fatigue failures of cementedcarbide hobs were examined in this work, with the aid of analyti-cal and numerical software tools. The application of the FRSFEMmodel enabled the determination of chips and cutting force com-ponents for every generating position per cutting case. The FEMsimulation of the hob tooth geometry produced a reliable solidmodel, able to calculate precisely the stress strain field occurringin gear hobbing with hardmetal tools. The model was used tointerpret experimental results of such tools. Therefore, through thecalculated stresses and the mechanical properties of the tool ma-Fig. 9Chips and cutting forces distribution at equi- and counter directional climb hobbingFig. 10Critical generating positions for cutting tool cracks in climb and equi-directionalhobbing790 Vol. 124, NOVEMBER 2002Transactions of the ASMEterial, we can estimate the expected tool life and the cutting con-ditions which will avoid the early fracture. The model allows us tocreate a database of optimal cutting conditions for a wide varietyof tool-workpiece combinations.NomenclatureGP 5 Generating PositionRP 5 Revolving PositionHV 5 Vickers Pyramid Hardness daN/mm2#TRS 5 Traverse Rapture StrengthFEM 5 Finite Elements MethodTF 5 Cutting tooth Trailing FlankLF 5 Cutting tooth Leading FlankH 5 Cutting tooth HeadOCL 5 Overall Cutting Length mm#sA5 Axial feed mm/rev#t 5 Cutting depth mm#v5 Cutting speed m/min#m 5 Work gear and hob tool module mm#ni5 Number of hob columnsz15 Number of hob originsz25 Number of work gear teethd25 External work gear diameter mm#b25 Gear helix angle #Fij5 Force component at direction i of coordinate system jN#SEQV5 Von Mises Equivalent Stress N/mm2#Sy5 Yield Strength N/mm2#References1# Sulzer, G., 1971, Leistungssteigerung bei der Zylinderradherstellung durchgenaue Erfassung der Zerspankinematik, Ph.d. thesis, TH Aachen.2# Venohr, G., 1985, Beitrag zum Einsatz von hartmetall Werkzeugen beimWaelzfraesen, Ph.d. thesis, TH Aachen.3# Bouzakis, K., and Koenig, W., 1981, Process Models for the Incorporation ofGears Hobbing into an Information Center for Machining Data, CIRP Ann.,30, pp. 7782.4# Bouzakis, K. D., 1979, Ermittlung des zeitlichen Verlaufs der Zerspankraft-komponenten beim Waelzfraesen Teil 1: Digitalrechnerprogramm FRDYN,VDI-Ber., 12119!, pp. 943950.5# Bouzakis, K. D., 1979, Ermittlung des zeitlichen Verlaufs der Zerspankraft-komponenten beim Waelzfraesen Teil 2: Einfluesse technologischer Parameterder Werkzeuggeometrie und der Werkradgeometrie, VDI-Ber., 12120!, pp.10161026.6# Antoniadis, A., 1989, Determination of the Impact Tool Stresses During GearHobbing and Determination of Cutting Forces During Hobbing of HardenedGears, Ph.d. thesis, Aristoteles University of Thessaloniki.7# Bouzakis, K. D., and Antoniadis, A., 1993, Berechnung der mechanischenWerkzeug spannungen beim Hartmetall-Waelzfraesen, VDI-Ber., 135, pp.8388.8# Joppa, K., 1977, Leistungssteigerung beim Waelzfraesen mit Schnellarbeitss-tahl durch Analyze, Beurteilung und Beinflussung des Zerspanprozesses,Ph.d. thesis, TH Aachen.9# Tondorf, J., 1978, Erhoehung der Fertigungsgenauigkeit beim Waelzfraesendurch systematische Vermeidung von Aufbauschneiden, Ph.d. the
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