Micro ultrasonic machining hemispherical mold for MEMS resonator gyroscope using a novel ultraprecise ceramic entire-ball tool

Abstract

The manufacture of inertial-grade and tactical-grade diamond micro electro mechanical systems (MEMS) hemispherical resonator gyroscopes is limited by the manufacturing accuracy of the monocrystalline silicon hemispherical concave mold, on which the gyroscope shell is formed. To solve this problem, this paper presents a new method for micro-ultrasonic machining of microhemispherical molds for resonator gyroscopes using an ultraprecise ceramic entire-ball tool (UCET). To study the wear mechanism of the UCET and the influence of tool wear on the surface integrity and form accuracy of the microhemispherical mold, a mathematical model for the tool wear of micro-ultrasonic machining of microhemispherical molds with UCET is established and verified by experiments. The micro-ultrasonic amplitude, the abrasive material and the abrasive size is found to have significant influences on the tool wear of the UCET. The wear rates of tungsten carbide and silicon nitride ceramic tools are 2.22% and 3.64%, respectively, which are far less than the wear rate of 8.03% of bearing steel. The wear condition agrees with the theoretical model. The machining experiment shows that the radius change, ΔR, is 6.47 µm of the microhemispherical mold processed by UCET, which is much better than 32 µm of the micromold processed by micro-electro discharge machining at one time. After 10 continuous machining runs, the deviation rate of the form accuracy of the micromold is 1.71%, 3.71% and 24.21%, due to the wear of tungsten carbide, silicon nitride and bearing steel, respectively. It can be seen that micro-ultrasonic machining of microhemispherical molds using UCET has the characteristics of a high initial form accuracy, low wear rate, high integrity and form accuracy. This is a potentially effective method to obtain micromolds with high accuracy and surface integrity.