【正文】 g a plex tool to achieve maximum performance pared to more basic tools.Fig. 2.[7].An alternative approach is to use a simple “pencil” tool and contour machine the plex shape with a CNC programme, see2652. A few CNC controlled path rotary USM systems are available mercially such as the SoneX 300 from Extrude Hone Limited (France)。Carbon fibre posite acceleration lever, holes and outline profile machined by USM1415and their good chemical stability and high temperature performance offers the possibility of greater thermodynamic efficiency in gas turbine applications5354. Sintered alumina, silicon carbide and silicon nitride products generally have a hardness 1500Ωcm26,and24,andμm deep with microcracking5[36]and surface finishes of Ra –[37].USM data on graphite, silicon carbide and a range of ceramic materials from work by Gilmore[33]is summarised inandmm ? ToolMRR(mm3/min) 10500SiC/B4C3950Aluminium Oxide1000SiC/B4CZirconia1100B4CSialon1500B4CSilicon Carbide2400B4C2. Basic elements of an ultrasonic machine tool. The ultrasonic generator and ultrasonic transducerWith a conventional generator system, the horn and tool are set up and mechanically tuned by adjusting their dimensions to achieve resonance. Recently, however, resonance following generators have bee available which automatically adjust the output high frequency to match the exact resonant frequency of the horn/tool assembly[33]. The power supplied depends on the size of the transducer17,and12,4057or a piezoelectric deviceandkHz for a 20[58]. It also allows greater horn design flexibility and can acmodate tool wear. In addition, the horn can also be redesigned/machined several times without critical loss of amplitude3046. The major drawback of magnetostrictive transducers are their high electrical losses (. eddy current loss) and low energy efficiencies (≈55%)5960. A typical piezoelectric transducer42,and[62]with a thickness usually less than 10% of the total ultrasonic transducer length18,2859. They are not liable to heat damage and appear to be more easily adaptable for rotary operationsFig. 4. The oscillation amplitude at the face of the transducer is too small (–23,and2660. Optimum tuning is specific for each horn material1,20,64,6667.Fig. 4.[69].The tool should be so designed to provide the maximum amplitude of vibration at the free end (antinode) at a given frequency16,and[68].Tools can be attached to the horn by either soldering or brazing, screw/taper fitting. Alternatively, the actual tool configuration can be machined on to the end of the horn4,66,and[72]. When deep hole drilling with a trepanning tool, the ability to feed the abrasive through the centre of the horn and tool is a great advantage thus reducing side friction16,27,4073. For optimum results, the system should maintain a uniform working force while machining and be sufficiently sensitive to overe the resistance due to the cutting action1640. The applied force must be chosen carefully since too low a setting will not yield the maximum cutting rate whereas too high a setting will cause jamming between the tool and abrasiveandN are typically used. The force is particularly critical when drilling small holes less than Fig. 513,28,and2,and1627. The most mon abrasive materials used are aluminium oxide, silicon carbide, boron carbide, etc.12,27,76,and3,andMethods of slurry delivery16,4074.3. Material removal mechanismsExtensive work on the mechanism of material removal has been done by Shaw[80], Rozenberg et al.22,4360. These mechanisms are detailed inand prise:?Mechanical abrasion by direct hammering of the abrasive particles against the workpiece surface28,35,40,60,and?Micro chipping by impact of the free moving abrasive particles35,50,and?Cavitation effects from the abrasive slurry27,48,and?Chemical action associated with the fluid employedandUSM material removal mechanisms13,and[13]and displacement of material at the surface, without removal, by plastic deformation1336which will occur simultaneously at the transient surface.With porous materials like graphite as opposed to hardened steels and ceramics, cavitation erosion is a significant contributor to material removal23,35,and2735considered that cavitation erosion and chemical effects were of secondary significance with the majority of workpiece materials acting essentially to weaken the workpiece surface, assist the circulation of the abrasive and the removal of debris. In RUM, Komaraiah et al.[84]found that the theoretical static load required for the formation of Hertzian cracks in brittle materials was less than that for sliding indentation.. Effect of various operating parameters on material removal rate (MRR)The amplitude,[10], an eddy current probeand[86]or laser speckle pattern interferometer2739. Ideally, the amplitude should be equal to the mean diameter of the abrasive grit used in order to optimise the cutting rate4,10,24,and[35]showed that MRR ∝77,andξ, and yet others13,27,74,8889have suggested that MRR ∝at constant frequency and static load. In general, MRR increases as the amplitude of tool vibration increases (everything else remaining constant)andFig. 7.Fig. 7.[74].Some authors2775have suggested that at constant amplitude, MRR ∝up to a frequency,Hz. At higher frequencies, up to 5375. Rozenberg et al.[22]have shown that, in practice, an increase in static load from zero, with other parameters constant, yields an approximately linear relationship between MRR and static load. Above an optimum value, the MRR decreases owing to a reduction in the size of the abrasive grains reaching the tool/workpiece interface and insufficient slurry circulation16,43,75,andFig. 8, the amplitude and mean grit size23,7091. KopsPenetration rate vs. static load for various areas23,43,7488.The abrasive material should be hard