【机械类毕业论文中英文对照文献翻译】先进陶瓷制品加工
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机械类毕业论文中英文对照文献翻译
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= U-TERWORTH Id- EINEMANN Tribology International Vol. 28. No. 6, pp. 415-420, 1995 wl&vier Science Limited. Printehin Great Britain 0301-679X(94)00009-3 Machining of advanced ceramics S. Jzhanrnir and 6. K. Ives Following a comprehensive survey of US industry, which confirmed that -he high cost of machining is a ,3rimary impediment to the wides,read use of advanced cer- amics-. a research programme on ceramic machining was initiated by the National Institute of Standards and Technology (NIST). The goal of th:s programme is to provide measnrement methods, data and mechrnistic information needed by industry to develop innovative, cost- effecnve methods for machining of advanced ceramics. To make sure that industries needs were properly addre,ssed and to take advantage of the e:pertise existing at academic institc tions, a consortium including industry, academic and government members was established as an integral part of the programme. The current members of the NIST Ceramic Machining Consortium are: Ceradyne, Inc.; Cincinnati Mil- acron Inc. ; Corning, Inc. ; Dow Chemi.cai Company; Eaton Corpor- ation; Eonic, Inc.; Ford Motor Company; General Electric Com- pany; General Motors Corporation; Georgia Institute of Technology; Norton Company; Stevens Institute of Technology; Texas A&M Uni- versity; Tower Oil and Technology Company; University of Maryland; University of Rochester; W.R. Grace “& Company; and West Advanced Ceramics, Inc. Presently, six projects are under investigation: Grinding Optimization, Machin- ability Database, Characterization of Machining Damage, Nano-Pre- cision Grinding, Chemomechanical Effects, and Grinding Mechanisms. Consc rtium members participate in these projects by providing materials, testing, advice and other in-kind contributions. Highlights of these projects are described below. NROEG Institute of Standards and Tech- nology, Gaithersburg, MD 20899, USA Grinding Optimization The goal of this project is to produce and collect data on the effects of grinding on the properties and performance of ceramics. Of pri- mary interest is how the strength and surface integrity vary with the grinding parameters, with emphasis on grinding conditions that result in high material removal rates. This project has been planned in two phases. In phase one, two types of silicon nitride, a reaction-bonded (RBSN) material and a sintered reaction-bonded (SRBSN) material, were selected to evaluate the effect of material removal rate on strength. The samples were machined by the participating con- sortium members using their experi- ence to select grinding conditions for the study. Each participant machined one set of 28 to 30 flexure test bars of each material. The flexure bars were returned to NIST where surface finish and fracture strength were evaluatedzM4. Scan- ning electron microscopy and stylus profilometry were used to charac- terize surface finish. Fracture strength was determined by four- point bend tests conducted accord- ing to the ASTM Standard C 1161*. The fracture strength data were analysed using Weibull statistics. The results, shown in Fig 1, indicate that no distinguishable change in fracture strength could be associ- ated with the different grinding conditions for the samples ground in the longitudinal direction, but the fracture strength was reduced when grinding was performed in the transverse direction, i.e. per- pendicular to the direction of maximum tensile stress in the flex- ure bar. These results suggest that *“Standard Test Method for Flexure Testing of Ceramics at Ambient Temperature, ” American Society for Testing and Materials, Philadel- phia, PA, 1990 the material removal rate in grind- ing could be increased over the rate currently used in practice, if the grinding direction is selected prop- erly with respect to the major tensile stress direction experienced by the component in the intended appli- cation. In phase two of this project, which is currently under way, an extensive series of tests is being employed to systematically analyse how surface finish and fracture strength vary with selected grinding parameters. Fractography will be used to identify the fracture initiation sites and to determine if machining damage con- tributed to the fracture process. A factorial design of experiments developed jointly with the NIST Statistical Engineering Division is being used for this study. In this second phase, grinding will be per- formed on three types of silicon nitride materials: reaction-bonded, sintered reaction-bonded and sin- tered silicon nitride. The results will be analysed to establish the optimum grinding parameters for the selected materials, i.e. those conditions which lead to high removal rates and acceptable levels of performance. Machinability Database The objective of this project is to develop a database containing evaluated machinability data for ceramics for use with personal com- puters. The Ceramic Machinability Database will provide access to data for different types of ceramics and will help users such as manufactur- ing engineers, tooling managers and machinists to develop machining plans for the cost-effective pro- duction of ceramic parts. For exam- ple, suppose the manufacturing engineer, having selected the appro- priate material for the part and the necessary machining operations, Tribology International Volume 28 Number 6 September 1995 415 0 500 1000 1500 2000 Volumetric Removal Rote (mm ymin) Fig 1 Characteristic fracture strength as a function of removal rate in grinding for two types of silicon nitride ground in two directions with respect to the tensile stress direction in the four-point bend baJ desires to know what machining parameters TV use. The database will provide this information. The search strategy and the struc- ture of the database have been developed jointly with the NIST Standard Reference Data Program. A commercial database manage- ment software was selected and has been used to develop a prototype version of the database. A typical search of the database begins with the user choosing the material of interest and the machining oper- ation. Next, the user may view all of the records corresponding to that material and machining operation, or may further narrow the search by selecting additional criteria. For example, the user may wish to look only at records where the surface roughness produced by machining is within a certain range. After all of the search criteria have been entered, the records that satisfy the search criteria are displayed. The user can change the order of these records, view them one at a time or see them all at one time. The records contain complete machining parameters and results of measure- ments of strength, surface rough- ness and machining forces. The user also can compare the search results graphically. An example search screen is shown in Fig 2. A proto- type version of the database is currently being evaluated by the consortium members, and will be revised according ,to their com- ments. Characterization of Machining Damage In general, three types of cracks can be produced in ceramics by grinding: lateral cracks (parallel to the surface), median and radial cracks (perpendicular to the surface) and small intergranular and transgranular microcracks. The objective of this project is to evalu- ate the feasibility of several non- destructive evaluation methods for detecting and characterizing the machining damage in ceramics. In a recent study5, well-defined median and lateral cracks were introduced in glass and silicon nitride by inden- tation in order to evaluate the capability of ultrasonics and thermal wave measurement methods for detecting these cracks. An optical micrograph of a pair of Vickers indents in glass showing median/ radial cracks (emanating from the corners of the indents) and lateral cracks (bright areas in the micrograph) is presented in Fig 3(a). A dimensioned outline of the upper indent is shown schematically in Fig 3(b). An ultrasonic echo- amplitude contour map of the upper indent is shown in Fig 3(c). An outline of the indent is superim- posed on the map to indicate the location of the indent. In this figure, the vertical cracks (i.e. median/ radial) with their planes parallel to the incident compressional waves are not clearly visible, but the 416 Tribology International Volume 28 Number 6 September 1995 lateral cracks are detected due to a reduction in the echo amplitude. The same indent was evaluated with a thermal wave technique using the optical beam deflection method in which a modulated laser beam is used to beat the surface. A second laser beam was used as a probe to monitor the heat given off by the sample by analysing the deflection of the probe beam due to the rarified air just above the sample surface. By separately ana- lysing the normal and the transverse components of the de it was possible to discern either the lateral cracks or the m cracks. In order to median/radial cracks emanating from the corners of the indent, the transverse component of the deflected probe beam (parallel to the sample surface) was used, since this component detects the thermal waves with preferential propagation along the surface and perpendicular to the vertical crack plane. A ther- mal image of the indent is shown in Fig 3(d). In the image, the darker areas indicate a larger signal corresponding to higher local tem- peratures in the specimen, where the heat flow has been disturbed by the existence of a defect or a crack. The Y-pattern of the vertical cracks can be clearly seen in Fig 3(d). Note that only the vertical cracks located along the probe beam are sensed by this technique; the cracks along the x direction are located in a plane parallel to the heat propagation direction, and therefore are not detected. Similar experiments, performed on silicon nitride, confirmed that the lateral cracks could be detected by using the normal component of the deflected probe beam5. Nano-Precision Grinding The objectives of this project are to identify the effects of grinding conditions and to establish the role of microstructure in obtaining dam- age-free silicon nitride surfaces. The ductile regime grinding process, in which material is removed by plastic deformation without leaving microcracks in the surface, is being evaluated jointly with the NIST Precision Machining Research Facility. In order to achieve the Eile .cf MATSNAME = RmBad .;:- 1 GRIT-SIZE 200 .: i Fig 2 .4 sample search screen from the Ceramic Machinability Database condil ens necessary for ductile regime grinding, an ultrahigh-pre- cision gririding machine equipped with an ai, bearing spindle is used. This n.ach;ne tool has the required capability of maintaining an extremely small depth of cut on the order of a nanometre. Table 1 is a summary of some recent results obtained on a hot-isostatically- pressed silicon nitride6. The streng :h values in the table were obtained in four-point bend tests. Each value is the characteristic fracture strength of 30 flexure bars using Weibull statistics. In-process electrochemical dressing of a metal- bond 2000 grit wheel permitted the simulGmeous grinding of multiple samples. For comparison, similar specimens were also ground by conventilonal means employing 400 grit and 900 grit wheels. The results show that ductile regime grinding not only can produce a high quality surface with a roughness in the nanometer range, but also can lead to fracture strength that is higher than the strength of bars ground with conventional grinding methods. Although it is believed that most ceram-c materials can be ground in the ductile regime mode, the range of applicable conditions is likely to depend strongly on properties and microstructure. Recent results obtained on several silicon nitride materials with various microstruc- tures have confirmed this point. The results are being analysed cur- rently to develop a correlation between mechanical properties, microstructure and surface finish. Chemomechanical Effects Interactions between chemical com- pounds added to cutting fluids and the workpiece surface in the cutting zone can have pronounced effects on the material removal process during abrasive machining. Th,e influence of chemical compounds is complex and may involve non- stoichiometric reactions accelerated by the mechanical energy involved in machining. Thus, the term chemomechanical effects is used to highlight the complex nature of these interactions, which can influence the friction coefficient, the wear rate of the abrasive par- ticles and the mechanical properties of the workpiece surface, with con- comitant effects on the machining rate. The goal of this project is to determine the effects of grinding fluid chemistry OR material removal rate in order to select the most promising additives for cutting fluids used with ceramics. Experiments were conducted on sapphire, polycrystalline alumina, silicon, silicon nitride, silicon car- bide and silica glass to evaluate the chemomechanical effects of several chemical compounds. The machin- ing tests were performed on a precision drill with metal-bonded diamond core-drills. Two chemical compounds, boric acid and a silicate compound, added to water have shown promising results in increas- ing the drilling rate by more than 50% compared to either pure water or several commercial cutting fluids. An example is. shown in Fig 4 for drilling polycrystalline alumina7s8, where an increase in the drilling rate is observed every time the distilled water is replaced with the boric acid solution. Similar tests on sapphire and silicon based materials showed no significant benefit for the boric acid solution. Based on the results, it was postulated that boric acid interacts with the amorphous grain boundary phase in polycrystalline alumina promoting intergranular fracture, thereby increasing the drilling rate. Tribology International Volume 28 Number 6 September 1995 417 50 100 150 200 250 350 Pfxition (urn) CC) Fig 3 (a) Optical reflection micrograph of a pair of Vickers indents in a glass specimen; (b) schematic drawing of the upper indent and the vertical cracks; (c) ultrasonic echo-emplitude contour plot of the upper indent; (d) thermal wave image of the surface using the transverse component of the deflected probe beam5 Table 1 Surface roughness and characteristic fracture strength of ground flexure bars6 Grinding method Surface roughness Fracture strength R, (p-n) iMPa) Conventional (400 grit wheel) Conventional (900 grit wheel) Ductile regime (2000 grit wheel) 0.03 930 0.018 920 0.003 1015 A second compound was found that increased the drilling rate of silicon- based ceramics. This compound, which is based on a silicate chemis- try, did not work with glass or alumina. However, it increased the drilling rate of silicon, silicon nitride and silicon carbide. Currently, tests are being conducted to evaluate the mechanisms by which the silicate compound interacts with the silicon- based ceramics during drilling. Grinding Mechanisms The objective of this project is to determine the fundamental mech- 418 Tribology International Volume 28 Number 6 September 1995 3 Distilled Water l Boric Acid Solution 3 0 i- 0 53 1 co 150 200 TIME (s) Fig 4 Drilling rate of polycrystalline alumina in a series of tests where the distilled water cutting fluid is periodically replaced with a boric acid solution7 anisms involved in material removal during ceramic grinding. An instru- mented surface grinder was used to measure the forces during grinding several types of silicon nitride. The measured forces were then used to calculate the specific grinding energy, defined as the energy used in removing a unit volume of material from the surface. It was found that the specific grinding energy varies with the grinding parameters and depends on the material type9. Experiments with differe:rt commercial grinding fluids showed that the specific grinding energy also depends on the type of cutting fluid. Therefore, the specific grinding energy not only depends on the properties. of the material, but it also is influenced by the grinding conditions. Nevertheless, the microstructure of the ceramic material has a controlling influence on the mode of grinding-induced damage, recently identified as intra- grain twinning/slip and intergranu- lar microcrackingiO. To identify the role of microstruc- ture, a series of tests was performed in which single or multiple scratches were made on several alumina cer- amics with different grain sizes to elucidate the material removal pro- cess in simulated grindingll. Three types of processes were found for material removal: (1) microfracture and chipping within the grains through crack propagation along the twin/slip boundaries; (2) intergranular fracture and grain dislodgement; and (3) formation of lateral, radial and median cracks, and removal of large segments by the propagation of lateral cracks. The influence of each of these processes depends on the load applied to the abrasive grit and the grain size of the ceramic. These experiments have provided new insights into the basic mechanisms of material removal in grinding and have identified the important role of microstructure in controlling the machinability of ceramics. In parti- cular, the results have shown that machinability of ceramics is related to the short-crack toughness of the material, as opposed to the long- crack toughness measured using conventional notched specimens. Acknowledgments The research activities of the Cer- amic Machining Consortium have been supported by the member organizations; the Ceramics Division, Office of Standard Refer- ence Data, and Office of Intelligent Processing of Materials at NIST; the Ceramic Technology Project of the US Department of Energy; the Ceramic Bearing Program of the Advanced Research Project Agency; and the Manufacturing Technology Program of the US Navy. Since the inception of this programme, several individuals, particularly T.J. Strakna, H. Liang, H.S. Ahn, L. Wei, H. Xu, T. Hwang, X. Dong, and G. Zhang, have made significant contributions to this programme. The authors are grateful to C.J. Evans, G. Quinn, G.V. Blessing, G. White, R. Kacker, R. Polvani, L. Oakely and J. Slotwinski for their important Fig 5 Subsurface grinding damage in aluminalO: (a) twinlslip bands; (b) intergranular microcracks Tribology International Volume 28 Number 6 September 1995 419 contributions and assistance during the course of this programme. References Jahanmir S., Ives L. K., Ruff A.W., and Peterson M.B. Ceramic machining: an assessment of current practice and research needs in the United States. National Institute of Standards and Tech- nology, Special Publication 834, Govern- ment Printing Office, Washington, DC, 1992 Jahanmir S., Strakna T., Quinn G.D., Liang H., Allor R. and West R. Effect of grinding on strength and surface integrity of silicon nitride: part I. in Machining of Advanced Materials. (Ed. S. Jahanmir). National Institute of Stan- da& and Technology, Special Publi- cation 847, Government P
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