Ultrasonic machining (USM) of natural quartz is investigated in relation to aystal orientation. The rate of cutting was measured along directions perpendicular to carried out on lateral surfaces achieved by USM. It is shown that cutting rate and surface roughness are dependent on aystal orientation. These dependencies are preliminary discussed in relation to indentation fiacture mechanics and fiacture toughness anisotropy of natural quartz. Scanning electron microscopy analysis shows that brittle microcracking is the main wear mechanism involved with material removal. X-, Y-, Z-and AT-cut planes. Surface profilometry was
l. INTRODUCTIONSince the 1940% a-quartz has been the material of choice in the majority of fiequency control devices. Due to its piezoelectric and elastic properties, quartz crystals have been used in the production of electromechanical devices such as resonatm, filtas and sensors [1,2]. Virtually, all devices fabricated today use cultured quartz. These crystals exhibits greater uniformity than natural quartz and are fiequently avaiable fiee fiom inclusions, twins and with low amounts of impurities. One of the remaining uses of natural electronic-grade material is in the manufacture of resonators used as pressure sensors m deep wells. Besides aystal quality, of the primary importance m fiequency control devices is the manufacturing technology employed to fabricate these units. The metrological accuracy required for high-Q resonators depends on both surfhce finish and accuracy of plate geometry [l]. Because quartz is a brittle, hard and nonconductive material, ultrasonic machining (VSM) appears as one of the few types of manufactlaing processes showing the ability to machine electromechanical devices with camplex shapes. For instance, the edge shape and the bridges of BVA resonators and the monolithic strucutre of pressure sensors have been achieved by USM [3].From the tribological point of view, USM can be classified as a tbree-body abrasive wear mode [4]. USM is M impact ginding process where abrasive particles are hammered against the surface of the workpiece. A cutting tool attached to a t r a n s d u c e r h o r n combination is vibrated longitudinally at a resonant fiequency. A slurry with abrasive grains is flushed through the gap between tool and the work surface. The tool progressively reproduces its shape into the workpiece, as long as machining takes place. 0-7803-5400-11991 S 10.00 0 1999 IEEE Similar as in grinding, lapping or polishing, research on USM presents certain difficulties due to the large number of operating conditions [5,6]. Material removal rate, surface h i s h and machining accuracy are influenced by various process parameters such as amplitude and fkquency of ultrasonic oscillations, hardness and size of abrasive particles, static load and properties of the workpiece mataial. The influence of these parameters on surface finish and metrological accuracy of resonator's components was not systematically investigated. Until now, just the effect of abrasive grain size on th...
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