Coupling characteristics analysis of micro-emulsion cutting fluid for thickness on-machine measurement using ultrasonic.

Stable and reliable coupling state between piezoelectric ultrasonic transducer and tested workpiece is very important for ultrasonic measurement. Traditional coupling agents need to be smeared manually or recycled separately, which cannot meet the requirement of on-machine thickness measurement by ultrasonic. Herein, a suitable coupling agent is selected for thickness on-machine measurement in industrial application of ultrasonics. The acoustic impedance and the attenuation coefficient are adopted to characterize the coupling effect of coupling agents and appropriate coupled flow field is selected theoretically. The experimental system of ultrasonic on-machine measurement is established with external circulating jet. The coupling characteristics of machining coolant liquid is calculated and analyzed. From experimental comparison with commonly used coupling agents, it is indicated that the micro-emulsion cutting fluid with volume concentration from 8% to 10% could be selected as compatible coupling agent for ultrasonic on-machine measurement, because it can not only meet the ultrasonic measurement requirements, but also perform friendly to industrial environment.