Y38滾齒機(jī)差動機(jī)構(gòu)、分度軸及走刀掛輪架設(shè)計

Y38滾齒機(jī)差動機(jī)構(gòu)、分度軸及走刀掛輪架設(shè)計,Y38滾齒機(jī)差動機(jī)構(gòu)、分度軸及走刀掛輪架設(shè)計,y38,滾齒機(jī),差動,機(jī)構(gòu),分度,走刀掛,輪架,設(shè)計 hobbing for these failures, an FEM simulation of the cutting process was developed, supported by advanced software tools able to determine the chip formation and the cutting forces during 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 paper applies the verified parametric FEM model for various cutting cases, indicating the most risky cutting teeth with respect to their fatigue danger. In a step forward, the second part of the paper illustrates the effect of various technological and geometric parameters to the expected tool life. Therefore, the optimization of the cutting process is enabled, through the proper selection of cutting parameters, which can eliminate the failure danger of cemented carbide cutting tools, thus achieving satisfactory cost effectiveness. 1 Introduction The application of High Speed Cutting HSC! was proved to be the most powerful manufacturing strategy, considering the in- crease in productivity and the achievement of the desired cost efficiency. However, in spite of the evolution of highly sophisti- cated CNC hobbing machining tools, the claim for HSC in gear manufacturing has not yet been attained. The main reason for this is the almost exclusive utilization of High Speed Steel HSS! as the hobbing cutting tool material, as a consequence of its complex geometry. The application of the coating technology in HSS hobs improved significantly the cutting performance of the tool. Nev- ertheless, the upper cutting speed limit of HSS, even coated, is up to 100150 m/min, which is low for modern production require- ments. In addition, dry cutting is not applicable for coated or uncoated HSS tools, which is not in agreement with the current world 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 and the cutting possibilities of the hobbing machine tools. The most promising alternative material for cutting hobs comes from the evolution of cemented carbides, which are widely used in massively produced cutting inserts. Despite the complex geom- etry of hobbing tools, their construction by cemented carbides is nowadays possible. The increased cost of cemented carbides tools is quite amortized by the doubtless wear superiority when com- pared to HSS. However the brittleness of hardmetals may cause fatigue failures in an early stage, due to the discontinuous chip production 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 entire hobbing tool out of order. Brittle fatigue failures are normally caused by high stress levels occurring at various cutting tools and usually are consequences of wrong selection of cutting parameters. This paper illustrates a quantitative analysis of the stresses course 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 the chip formation mechanisms and calculate accurately the cutting force components. Finally, the development of a parametric FEM simulation of the cutting teeth yields the description of the tools stress 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 quantitatively their fatigue expectations. As it will be presented, the computa- tional results are in line with the experimental ones, proving the validity of the utilized analytical and FEM models. Furthermore, a Contributed by the Manufacturing Engineering Division for publication in the JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING. Manuscript received May 2000. Associate Editor: M. Elbestawi. 784 Vol. 124, NOVEMBER 2002 A. Antoniadis Professor, Technological Educational Institute of Crete, Chania, Greece e-mail: antoniadischania.teiher.gr N. Vidakis Teaching Fellow, Technological Educational Institute of Crete, Heraclion, Greece e-mail: vidakisebeh.gr N. Bilalis Associate Professor, Technical University of Crete, Chania, Greece e-mail: bilalisdpem.tuc.gr Fatigue Fracture Cemented Hobbing, Fly Hobbing Interpretation Results Gear hobbing is a highly external gears. However almost exclusive utilization cutting performance of speeds and restricts the application of cemented production requirements. bing, the so-called fly cemented carbide tools cracks, which were not early failure of the entir Investigation of Carbide Tools in Gear Part 1: FEM Modeling of and Computational of Experimental utilized flexible manufacturing process for massive production of , the complex geometry of cutting hobs is responsible for the of high-speed steel (HSS) as cutting tool material. The limited HSS, even coated HSS, restricts the application of high cutting full exploitation of modern CNC hobbing machine tools. The carbide tools was considered as a potential alternative to modern In former investigations an experimental variation of gear hob- was applied, in order to specify the cutting performance of in gear production. These thorough experiments indicated that expected, might occur in specific cutting cases, leading to the e cutting tool. In order to interpret computationally the reasons ating Positions GP!, is of complicated kinematics, and it is diffi- cult to be modeled. each penetration are used to describe cisive factor that tion mechanism, cutting kinematics. certain cutting force cutting loads. This inserted in the bottom ating positions. Mathematical individual generating widely used 31 course of the cutting influence to the with the aid of the for each revolution manufacturing, geometrical cutting tool, the workpiece this paper a new has been added module FRSFEM data are interactively ment, enabling the nematics for specific sections over the mined for every position of a certain manufacturing case are presented in Fig 3. On of the specific is shown. The tool, which is shown in the in various diagram in the chip distribu- the successive positions is also computational in the tool co- part of Fig. 3. of the el- along the cut- files for every gap. can be model, the ex- each cutting to every subsequently, Therefore, with increased loads and tool utiliza- becomes even Journal of Manufacturing ol. 124 785 In addition, based on the tool position during into a gear gap, a number of revolving positions the corresponding generating position. A de- determines the tool behavior is the chip forma- which is also complicated, due to the complex Therefore, each chip type is responsible for components that contribute to the overall behavior is described by the chip forms that are part of the same figure for various gener- models that quantify the chip formation for each position are nowadays well established and 0#. These models are further used to predict the force components that exhibit a remarkable tool lifetime. The simulation of gear hobbing, FRSWEAR model, yields the chip dimensions of every generating position, considering the and technological specification of the and the cutting kinematics 1113#.In module for the FEM Simulation of gear hobbing to FRSWEAR model. The structure of this new is presented in Fig. 2. The above mentioned inserted using a modern software environ- mathematical description of gear hobbing ki- cutting cases. The unreformed chip cross development of the cutting edge are then deter- generating position. The cutting force compo- the left part of this figure the entire penetration cutting tooth into the examined generating position model assumes special coordinate systems for the rotating and moving following the tool paths, as figure. The discretization of this generating position revolving positions is evident in this graph. The middle of the same figure illustrates the unreformed tion over the development of the cutting edge for revolving positions. The number of the revolving a variable parameter, depending on the required accuracy. The cutting force components calculated ordinate system are also presented in the right These loads are overall values and they are composed ementary forces produced by the chip dimensions ting edge. All these results are stored in proper generating position that is required to form a gear Despite the fact that the complicated hobbing kinematics treated analytically with the aid of the FRSFEM perimental procedure is laborious. The reason is that tooth cuts a certain generating position and penetrates workpiece teeth for each workpiece revolution and owing to the axial feedrate repeats the same procedure. some of the cutting teeth cut generating positions chip dimensions and they are subjected to high cutting wear. Due to this reason, besides the problem of poor tion, the experimental study of this cutting process Science and Engineering NOVEMBER 2002, V parametric analysis presented in the second part of this paper il- lustrates the effect of various cutting parameters on the prediction of the tool life, allowing the optimization of nearly every specific cutting case. 2 Chip Geometry and Cutting Force Components in Gear Hobbing The principles of gear hobbing are presented in Fig. 1. This gear manufacturing method, where each gear tooth is produced by successive penetrations of the tool teeth in the individual Gener- Fig. 1 Chip formation and typical chips at various nents can be determined at this stage, as they depend on the un- deformed chip dimensions and on experimentally determined constants 1417#. Using these cutting forces, the critical stresses occurring in gear hobbing tools can be determined. Besides these outputs, the FRSWEAR model is able to predict the progress of the tool wear and to propose proper hob tangential feed amounts, in order to achieve an even wear progress over the successive cutting teeth 18#. The whole software has an open and modular structure, 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 generating tool-generating positions in gear hobbing of each generating position from the others and the ability to study comprehensively reproducible model. The cutting teeth modeling strategy is pre- terms, by 786 Vol. 124, of the ASME their effect on the tool wear failure initiation and sented in Fig. 4. The model was built in parametric Fig. 3 Determination of the cutting force components at individual generating position in gear hobbing NOVEMBER 2002 Transactions more difficult. On the other hand, the complexity of tools with complete geometry makes their dismounting from the machine tool spindle and the subsequent evaluation of the experimental status difficult. For those reasons, in order to increase the experimental effi- ciency and to facilitate the evaluation of the test results, advanced experiments with one cutting tooth, the so-called fly hobbing, were used. In this manufacturing technique, the cutting tool is replaced with a cylindrical holder, on which one cutting tooth can easily be mounted and dismounted. The tooth geometry corre- sponds strictly to the DIN 3972 regulations 19#. This approach accurately simulates gear hobbing with tool having one origin. A variation of this method with two cutting teeth simulates complete tools with two origins. The aim of this procedure is the separation Fig. 2 The flow chart diagram to progress. Consequently, each tool cuts every generating position and this is taken into account in the present analysis, as it will be further explained. 3 FEM Modeling and Mechanical Properties of the Cutting Teeth In 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 the stresses and strains is the complicated tool geometry and process kinematics, 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 and the developed FRSFEM program means of the APDL of the ANSYS FEA tool is standardized ule and diameter. Therefore, the modeling routine was written in analysis the were used in properties of this material. The left diagram of this figure exhibits the bulk Journal of Manufacturing ol. 124 787 Fig. 5 Static and fatigue properties of cemented carbide tool material Science and Engineering NOVEMBER 2002, V terms of such parameters, considering also the tool clearance angles and thickness. Owing to the complex teeth geometry, a bottom up modeling strategy was utilized, as it is presented in the middle diagram of the same figure. Hereby keypoints, lines, areas and volumes were determined sequentially, forming in this way a 3-D solid model. This model consists of six volumes, in order to perform a finer meshing near the tool-workpiece contact areas and a coarser net away from these regions. This way, the available computer re- sources are properly allocated, thus increasing the accuracy of the FEM calculations. The nodes density was also set as a variable parameter for optimization purposes. The optimized model con- sists of 2310 5 eight-noded brick elements, performing in this way 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 unacceptably increased. The cutting force components explained in Fig. 3 are properly distributed to the rake nodes, using a special APDL rou- tine that takes into account the chip compression ratio, besides the geometric location of each node 20#. The model is pure elastic, so that it requires only the tool elasticity modulus and Poissons constant. The above-mentioned mechanical properties of the finite ele- ments are also variables, allowing the applicability of the model hardness 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 was found from this diagram to be 1430 HV. This value, besides the resistance of this material to plastic deformation, may be used to determine its static stress limit, considering that this value for brittle materials equals to the one third of their pyramid hardness 22,23#. On the other hand, the right diagram of the same figure illustrates the fatigue limits for cemented carbides, also as func- tion of their cobalt content 21#. For fine-grained P 40 hardmetal the value for continuous endurance, i.e., 10 8 loading cycles, equals to 83 N/mm 2 . The static and the fatigue stress limits can be used to elaborate the Woehler diagram for the specific material, as it is illustrated in the diagram in the middle of Fig. 5 24#. Considering the purpose of the present analysis, the abscissa of this diagram was reason- ably transformed from loading cycles to number of successive cuts. 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 40 hardmetal 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 a Ansys Parametric Design Language! module code. The entire geometry of the cutting by DIN 3792 norm, as a function of its mod- for HSS and cemented carbide tools. In the present mechanical properties of ISO-P 40 cemented carbide the model. Figure 5 summarizes the static and fatigue Fig. 4 FEM modeling of hob teeth developed by FRSFEM program region is the cutting tooth head, which fits to the experimental observations, as stress contours follow consequently the 4 Correlation sults The FEM model cutting stresses presented before. left diagram of stresses in three generating positions. tween the leading tively and the middle as the most hazardous The variation of uneven chip dimensions between the chips tively, a behavior detected 1#. As i cedure was examined number of cuts corresponds to a representative equivalent stress of 4% higher. expected ar- that cannot be the deter- of hob versus in a counter equals 710 comparison states that the equiva- one is cases, which 9 illustrates case of climb one. Each part different rep- For each of the re- components, 788 Vol. 124, of the ASME it will be explained. It is also obvious that the the distribution of the chip thickness and development of the cutting force components. of Computational and Experimental Re- was further used to calculate the course of the in every generating position of the cutting case The computational results are summarized in the Fig. 7, which presents the maximum von Mises endangered rake regions versus the successive These regions are the transient regions be- and the trailing flanks to the tool head respec- of the tool head. The stress results indicate region the trailing flank of the cutting tool. the stress course at this region is a result of the per generation position and the collision produced at the flanks and the tool head respec- which is experimentally and computationally t was previously described, the experimental pro- with the aid of fly hobbing with continuous 2960 N/mm 2 , whereas the computational one is about This difference is absolutely reasonable, considering ithmetical errors and other imponderable factors included to the FEM model. Similar results are presented in Fig. 8, which present mination of the flank wear at the transient regions the overall cutting width OCL! of the work gear directional hobbing case 1#. For this case the OCL mm that corresponds to 31950 successive cuts. The between the computational and experimental results achieved number of cuts corresponds to a representative lent stress of 2450 N/mm 2 , whereas the computational about 6% higher. The method was further applied for other cutting were also experimentally examined. Hereby, Fig. typical chips for two variations of the same cutting hobbing, i.e., the equi- and the counter-directional of this figure illustrates chip developments for two resentative generating positions, per cutting case. these chip diagrams a smaller adjacent diagram illustrates gions of the tool rake that is subjected to cutting load NOVEMBER 2002 Transactions specific cutting case, is experimentally determined, the stress level that yields from the Woehler diagram must be in agreement to the FEM calculations. Initially the model was used to calculate the cutting stresses for every generating position in cutting cases where experimental re- sults were available. Taking into account that every generating position is subdivided in successive revolving positions, it was reasonable to solve the revolving position holding the bigger chip dimensions and consequently higher cutting loads. Figure 6 illus- trates such a calculation for a certain generating position of a specific cutting case with climb and equi-directional hobbing, us- ing a cutting tool with two starts. The upper left diagram shows the calculated revolving position of the examined generating po- sition. The corresponding cutting forces on the tool rake face are applied in the model, and they are shown in the middle part of the same figure. It is obvious that the cutting force components are in agreement to the formation of the produced chip. The solution of the specific cutting case offers the deformation of the cutting tooth and it is shown in the bottom left part of the same