鋸片刀具工具磨床分度工作臺的設計【M7130磨床分度工作臺】,M7130磨床分度工作臺,鋸片刀具工具磨床分度工作臺的設計【M7130磨床分度工作臺】,刀具,工具,磨床,分度,工作臺,設計,m7130 on 1. Introduction EGT are a further developmentof the single layer grinding tools technology. The main characteristic of these tools is the controlled arrangementofthe abrasivegrains undera parameterizedpattern. The suitable distribution of the grains enables improved coolant and chip space on the grinding gap, features especially desired on grinding operations with high material removal rates. This tool technology has demanded the development of design and manufacturing techniques and has been extensively explored in technical publications 16. Burkhard and Rehsteiner 3 developed a semi-automatic system for the production of grain patterns for brazed bonded tools. Pinto 7 has characterized the precision of this system. The precision on the grain positioning was evaluated as a circular region (with diameter D edge , Fig. 1) around the nominal position of the grains edge. For cBN B251 the average for the diameter D edge In the experiments pattern A (the lowest grain density tested) has collapsed on the application of the specific material removal rate of 32 mm 3 /(mm s). In the present work a numerical method is presented to evaluate the performance of the grain pattern in EGT. The method comprehends a detailed model of the tool (the model combines deterministic and stochastic variables to describe the abrasive layer), a kinematic process model, a material removal model and a grain wear model. Special attention has been given to the grain wear model, aiming to predict the tool performance with different process parameters. The model validation is discussed with the results of grinding tests. 2. Wear characterization The grain wear characteristics of the ABN800 were obtained withthedetailedobservationoftheabrasivelayeronthetesttools. this failure mechanism was correlated with the increase of the material removal rates Q w 0 (Fig. 4), achieving a relationship CIRP Annals - Manufacturing Technology 57 (2008) 353356 (EGT mater method a layer. to valida num Contents lists available at ScienceDirect CIRP Annals - Manufacturing areas. The workpiece surface becomes also smoother with the increase of the material removal rate Q w 0 . This is associated to the Test tools were produced with the method proposed by 3 to evaluate the influence of different grain patterns (A, B and C in Fig. 2) and to compare the EGT with conventional electroplated tools. The higher grains densities resulted in lower values of R a ,as showninFig.3.Thiseffectiscausedbythehighernumberofgrains participating in the grinding process, generating smaller cutting was detected on the brazed bond (pull-outs are common on electroplated bonds), indicating excellent holding forces of the grains. After the detailed observation of the abrasive layers under a microscope, the dominant grain failure characteristic observed on the test tools was the micro-break of the grains. The progress of was evaluated as 187mm. Analyzing a large number of tool segments, any grain pull-out Simulation for optimizing grain pattern F.W. Pinto*, G.E. Vargas, K. Wegener (3) Institute for Machine Tools and Manufacturing (IWF), ETH Zurich, Switzerland Submitted by W. Knapp (1), Zurich, Switzerland ARTICLE INFO Keywords: Grinding Simulation Wear ABSTRACT Engineered Grinding Tools theabrasivegrains.Thedistributi improving space for coolant operationswithhighspecific grain pattern on EGT. This material removal model and properties of the abrasive geometrical cutting condition. assumed to be proportional wear takes place. The model roughness achieved with journal homepage: http:/ees.el wear/break of the most protruded grains, enlarging the number of active grains on the tool and reducing R a . * Corresponding author. 0007-8506/$ see front matter C223 2008 CIRP. doi:10.1016/j.cirp.2008.03.069 Engineered Grinding Tools ) are characterized by a predetermined and controlled arrangement of onoftheabrasivegrainscanbeusedtoenhancethegrindingprocessby supply and for chip removal. This is especially interesting for grinding ialremoval rates.Anumericalmethod wasdevelopedtooptimizethe consists of a stochastic tool model, a kinematic process model, a grain wear model. The tool model comprehends the relevant geometric The material removal model is based on the assumption of a kinematic- The wear model is based on a grain load limit and the grains load is its cutting area. Once the cutting area of one grain exceeds the limit value, tion is presented comparing the wear behavior of EGT and workpiece erical and experimental methods. C223 2008 CIRP. Technology between the share of broken grains and the Q w 0 applied. 3. Models The kinematic-geometric simulation of the three dimensional tool models has already been applied and validated to the Fig. 1. Parameterization of the grain pattern. F.W. Pinto et al./CIRP Annals - Manufacturing Technology 57 (2008) 353356354 predictionofthesurfaceroughness4,5.Thefailuremechanismof the tool, however, has not been investigated with these models. As the test tools revealed, the wear of the grain (micro-break) has expressiveinfluenceontheprocessresultsandmustbeconsidered in the numerical evaluation of the grain pattern. 3.1. Tool model Thetoolismodeledaccordingtoitsmacroandmicrogeometrical characteristics.Themacrogeometryconsiders,beyondthenominal geometry of the tool, characteristics as form tolerances of the tool body. The micro geometry is sub-divided in two groups: the abra- sives and the grain pattern. The abrasive modeled assumes simple geometries, according to the theoretical crystal morphology of the abrasive (Fig. 5). For cBN these geometries are tetrahedrons 8. Fig. 2. Sections of the abrasive layer on the tool samples. Fig.3.R a measuredatsurfacesmachinedwithEGTandelectroplatedgrindingtools. The distribution of the grain morphology and the grain size were obtained with the observation of a large amount of cBN grain samples (ABN800 B251). The model for the pattern considers the nominalgrainedgedistribution(as showninFig.1),thedeviations of the grain edges position around its nominal position (D edge ) and the stochastic orientation of the grains on the tool surface. Grainclusterandpatternfailuresarealsoincludedinthemodel as pattern deviations. Both characteristics have been evaluated as probabilities and are evaluated on each pattern position. 3.2. Kinematic process model Different grinding kinematics have already been modeled in former publications9,10.In thisworkcylindricalexternalplunge grinding operations are analyzed. 3.3. Material removal model The material removal model is based on the kinematic analysis of the process. For this approach some simplifications of the real Fig. 4. Progressive growth of brazed grain load and grain break with Q w 0 =32mm 3 / (mm s). cutting phenomenon are considered: ideal kinematic cutting condition; adiabatic process; infinite machine and tool stiffness; perfect kinematic movements; negligible chip and coolant influence on the cutting process. Fig. 5. (1) Grains according to manufactures datasheet, (2) real and (3) modeled cBN grains. Fig. 8. Roughness evaluation of tools with pattern B by the simulation without consideration of the wear effects on the abrasive layer and by tests with tool samples. F.W. Pinto et al./CIRP Annals - Manufacturing Technology 57 (2008) 353356 355 With these simplifications the cutting phenomenon is assumed to be the geometric interaction between the grain and the workpiece. This allows a further simplification: instead of a fully three dimensional description of the grain geometry, the grain projection on the plane orthogonal to the cutting speed, a two dimensional geometry, is used. Thepositionofthegrainprofileisdeterminedbythepositionof the highest grain edge, as shown in Fig. 6. Fig. 6. Simplification of the 3D grain geometry. Fig. 7. Micro-break wear model. 3.4. Grain wear model The design strategy of the grain pattern on EGT aims at the prediction of tool performance according to the kinematic adopted. The main aspects considered in this analysis are workpiece roughness and suitability of the tool to the process. The workpiece roughness results from the geometrical interac- tion of all active grains with the workpiece. The suitability of the tool requires the adoption of a failure criterion. On EGT this criterion is the grain pattern collapse due to excessive grain load. As observed on the test tools the dominant wear characteristic observed on the ABN800 grains is the micro-break of the grain edges. For the simulation, this effect is modeled as profile alterations in the grain projections (Fig. 7). The occurrence of wear on a specific grain is parameterized according to its cutting area: wear takes place after the grains cutting area has exceeded a pre-established limit. This limit is related to process parameters as the ratio between workpiece and grinding speed and grain contact length. For the testsconductedwithABN800thislimitliesbetween0.5%and2%of the grain projection area, depending on the speed ratio between the tool and the workpiece. After the modification of the grain profile, a new rotation of the tool is simulated. This process is repeated up to the moment of either any grain achieves a critical load level (all grains have a cutting load below the critical value) or a tool failure criterion is achieved. The assumed failure criteria are: (a) contact between the tool body and the workpiece; (b) roughness parameter cannot be achieved. Besidestheworkpieceroughnessandtheloadofeachgrain,the simulation software delivers other useful outputs to the optimiza- tion of the tool performance, such as: the viability of the grain pattern production with the placing system; the position of the active grain edges and; the region of the tool where the grains are heavily loaded. 4. Results A comparison between empirical and numerical results can be done with the simulation of EGT with similar grain patterns applied on the test tools (pattern A, B, and C in Fig. 2). Onthetestedtoolsamplestheadoptionoflarger Q w 0 implicates a larger load on the single grains and lead to representative alterations of the abrasive layer topography. Due to the break characteristics of ABN800, the progressive wear of the grains lead to an alteration of the active grain edges distribution and to a reduction of the workpiece roughness. The major influence of the grains wear was confirmed with the numerical simulations. Without the consideration of the grain wear mechanism, the behavior of the workpiece roughness simulated differs from the behavior observed with the experi- ments. Especially for the higher values of Q w 0 the deviations between numerical and empirical values are larger, mainly due to the more representative alteration on the abrasive layer (Fig. 8). Withtheimplementationofthewearmodelinthesimulationit is possible, with the adoption of coherent grain wear criteria, to reproduce the same tool behavior as observed with the tool samples (Fig. 9). On the simulation method proposed, the cutting area of the grains is applied as wear criteria. The values of critical cutting area for the grains were evaluated with simulation of tools with similar characteristics as the tool samples. The value of the critical cutting areaisassumedcorrectwhentheworkpieceroughness(Fig.9)and Fig. 9. Roughness evaluation of tools with pattern B by the simulation with consideration of the wear effects on the abrasive layer and by tests with tool samples. evaluation of the grinding kinematics and on the assumption of a perfect kinematic cutting condition. The simulation results were compared with the results obtained with three different grain patterns on EGT. The alterations of the micro profile of the tool caused by the grains wear are, on empirical and numerical results, the major influence on the workpiece roughness. A good correlation concerning the share of broken grains and workpiece roughness could be achieved. The diverse outputs available with the numerical method enable the analysis of aspects, which cannot be observed in experiments with the tool samples, like the distribution of the grains cutting area or the effective share of active grains on the tool. F.W. Pinto et al./CIRP Annals - Manufacturing Technology 57 (2008) 353356356 Fig. 10. Comparison of the share of broken grains evaluated with simulated and empirical methods for pattern B. the share of broken grains (Fig. 10) of the virtual tool match the values obtained with the tool samples. The alteration of the abrasive layer topography can be also observed on the distribution of the cutting areas of the grains (Fig. 11). On the unworn abrasive layer a few grains are largely loaded and have dominant effect on the workpiece roughness. Adding the wear model, the cutting areas of the grains are limited by the value of the critical area (A lim , Fig. 11). The break of the overloaded grains generates new distribution of the cutting areas. In comparison with the unworn tool, the micro-break character- istic of the ABN800 leads to the enlargement on the number of active grains on the process, especially on those with small cutting areas, and tend to generate smoother workpiece surfaces. 5. Conclusions The numerical tool model generated is based on the description of the tools geometrical characteristics, on the Fig. 11. Cutting area distribution simulated for an EGT with pattern B, with and without grain wear model. References 1 Chattopadhyay AK, Hintermann HE (1994) On Performance of Brazed Single- Layer cBN Wheel. Annals of the CIRP 43(1):313317. 2 Sung CM (1999) Brazed Diamond Grid: A Revolutionary Design for Diamond Saws. Diamond and Related Materials 8:15401543. 3 Burkhard G, Rehsteiner F (2002) High Efficiency Abrasive Tool for Honing. Annals of the CIRP 51(1):271274. 4 KoshyP,IwasakiA,ElbestawiMA(2003)SurfaceGenerationwithEngineered Grinding Wheels: Insights from Simulation. Annals of the CIRP 52(1):271 274. 5 Aurich JC, Braun O, Warnecke G, Cronjager L (2003) Development of a Super- abrasive Grinding Wheel with Defined Grain Structure Using Kinematic Simu- lation. Annals of the CIRP 52(1):275280. 6 Ghosh A, Chattopadhyay AK (2007) Performance Enhancement of Single- Layer Miniature cBN Wheels Using CFUBMS-deposited TiN Coating. International Journal of Machine Tools and Manufacture 47(1213):1799 1806. 7 Pinto FW (2005) Grain Pattern Evaluation on Engineered Grinding Tools. LAMDAMAP 2005:412421. 8 Bailey MW, Hedges LK (1995) Crystal Morphology Identification of Diamond and ABN. Industrial Diamond Review 1(95):1114. 9 Inasaki I (1996) Grinding Process Simulation Based on the Wheel Topography Measurement. Annals of the CIRP 45(1):347350. 10 Marinescu JD, Rowe WB, Dimitrov B, Inasaki I (2004) Tribology of Abrasive Machining Processes. William Andrew Publishing. The adoption of wear criteria for the grains within the numerical simulation allows the evaluation of the suitability of an EGT for a grinding process not only with the workpiece roughness, but also to avoid the application of the tool with grinding conditions where the grains are overloaded. The adoption of the tool model and of the process simplifications allows a fast evaluation of the tool models, even with the computational power of conventional desktops. This fact promotes the application of this numerical simulation in industry. Further development of the simulation strategy should enable the prediction of the grinding forces and incorporate a library with the wear characteristics for different abrasives and workpiece materials. Acknowledgements TheauthorsliketothanktheprojectpartnersListemannAGand Zigerlig TEC GmbH for cooperation in the development of the brazed EGT and BBT of Switzerland for funding.