Mechanism, characteristics and modeling of micro ultrasonic machining

The ever-increasing demand for miniaturized products has motivated the micromanufacturing industry to continuously develop or enhance processes that are able to fabricate micro components made of various materials. There exists a large space for the process improvement to enable an economic micromachining of a wide variety of electrically nonconductive and chemically inert, hard and brittle materials used in electronic, medical and automotive industries. As a niche micromachining process developed near about decade ago, micro ultrasonic machining (Micro USM) is capable of machining high aspect-ratio features on these materials without significantly changing metallurgical, chemical, or physical properties of workpiece material because of its non-thermal, non-chemical and non-electrical nature. Moreover, Micro USM is a process with low requirement on equipment and machining cost. The limited understanding of process mechanism and some technical barriers such as fast tool wear, however, restricts its industrial application and necessitates an in-depth investigation. The research of this thesis contributes to the establishment of a fundamental knowledge base for Micro USM through experimental and analytical investigations aimed at an understanding of the mechanism of material removal, the range of machinable feature sizes, effect of machining parameters on the productivity and surface of the machined feature. A mechanistic model for calculating material removal rate is proposed. Furthermore, the phenomenon of decreased material removal rate at an increased static load is explained from a new perspective substantiated with a semi-quantitative analysis. The experimental data presented in this thesis also contributes to build a data base for material removal rates, tool wear rates, and surface quality