Abstract: In order to enhance the micro level and precision of micro holes machined by ultrasonic machining (USM), the key technologies for machining micro holes are studied, which include high precise machine tool, USM unit, manufacturing technology of the micro tool and the choice of the geometric parameters. The dynamic stability of the tool is analyzed, which shows that the stability of compressive bar depends on not only the static pressure but also the ultrasonic amplitude. The Mathieu equation for discriminating the dynamic stability is derived. The criterion for calculating critical pressure and critical length of the tool is obtained from simplifying the Mathieu equation, which can solve the problem of the tool’s bend, breakage, and deteriorating the hole shape accuracy caused by the improper choice of tool length, static pressure and ultrasonic amplitude. The experiments of micro holes machining using micro-USM with work vibration are carried out, the experimental results show that the wear rate of the micro tool increases with the accretion of the feed rate and the amplitude. On the developed micro USM system, the micro hole with diameter of 13 μm can be machined.

Key words: Micro hole, Micromachining, Non-traditional machining, Ultrasonic machining