Research On Theoretical Model Of Tool Wear In Micro USM

Hard and brittle materials such as silicon, ceramics and glass have been widely used in MEMS industry for their excellent mechanical, physical and chemical properties. Micro ultrasonic machining (USM) has the ability to machine micro holes with high aspect ratio and complex three-dimensional cavities in these materials. The material removal mechanism of micro USM is similar to the conventional USM in which materials are mainly removed from workpiece by impacting abrasive particles at an ultrasonic frequency regardless of the electrical conductivity of materials. Meanwhile, the hardness of tool can be much lower than the hardness of workpiece. There is also no thermal effect zone and residual stress on workpiece after machining.Micro USM has been successfully used for generating all kinds of micro holes and3D cavities. However, tool wear is a serious problem in USM because it will affect the machining performance such as material removal rate and accuracy. Up to now, the tool wear in micro USM was studied experimentally, focusing on the influence of the machining parameters and material properties on tool wear. However, the tool wear mechanism in micro USM is not clear. And there is no theoretical model to describe the relationship between the tool wear and its related factors. To achieve optimal machining performance of micro USM, it is necessary to predict the tool wear quantitatively.In this paper, the mechanism of tool wear has been investigated by controlling a single factor from a group of micro USM experiments. It was found that the low cycle fatigue caused by high frequency impact of abrasive particles was identified as the dominant factor causing tool wear in micro USM. And then a theoretical model is proposed to estimate the tool wear quantitatively. A set of control system is developed to carry out extensive experiments to verify the model. The functions of this program include on-line tool fabrication, micro USM processing, tool detection, data storage, etc.A number of experiments with tungsten and stainless steel316L tool materials have been tested under different conditions. Experimental results agree well with the theoretical values. The tool rotation has insignificant influence on the tool wear. It was also found that the relative error between experimental and theoretical values is sensitive to the variance of abrasive particle number in the working zone and measurement error of detecting tool wear.