Toolbit Mounted Thin Film Zinc Oxide Sensors for Process Control in Lathe and Milling Machine Applications

Thin films (1.8 microns thick) of ZnO have been deposited on tungsten carbide tool inserts by rf diode sputtering. The goal is to use ZnO film as a sensor to monitor acoustic emission generated during cutting or t ool fracture. The sensor has detected resonances in the machine structure in the 100 Hz to 20 KHz range as well as acoustic emission signals originating at the cutting site in the 100- 500 KHz range. During forced tool fracture, distinctive signals were observed from the sensor which could be used for cutting operation shut-down. The measured ZnO stress sensitivity averaged about 0.022 v-m/N which is about 35% of the s ingle crystal value. The highest observed was about 0.04 v-m/N. The sensor was still operational at the end of the useful cutting lifetime of the i nsert.