Micro ultrasonic machining and its applications in MEMS

A combined machining method, micro ultrasonic machining (micro-USM), is proposed here for the fabrication of three-dimensional (3D) microstructures with high aspect ratios. Wire electro-discharge grinding (WEDG) and electro-discharge machining (EDM) are combined onto the USM machine to provide a capability of making co-axial microtools for USM and, thereafter, microholes as small as 15 mu m in diameter and a variety of high-aspect-ratio microstructures on brittle materials have been achieved for the first time by optimizing the ultrasonic machining processes. The combination of WEDG, EDM and USM on a micro-USM machine also makes possible the construction of complete 3D micromachines within one total manufacturing process. With this method, a 3D micro center-pin bearing air turbine has been successfully developed. The design, fabrication and testing issues are described in this paper.